Coal grinding pulverizing mill system is suitable for various application, widely used in power plants, cement plant, metallurgy, building materials to grind coal into fine powder for combustion purpose.
Our TONGLI coal mill is an efficient, compact and versatile equipment that can process almost all types of coal, including bituminous coal, anthracite, lignite and petroleum coke. We offer a variety of coal mills to meet different process requirements, such as ball mills, vertical coal mills, medium speed coal mills and air-swept coal mills. The vertical coal mill efficiently grinds raw coal into extremely fine particles through the compression and shear forces generated between the large rollers and the rotating table, without the need for additional crushing equipment, and has a drying system that can handle materials with high moisture content. Especially when used with a variable speed motor, the TONGLI coal mill can grind petroleum coke and anthracite to a fineness of less than 5% + 90 microns, ensuring excellent performance and application flexibility. The finished products are widely used in boilers or combustion systems of major power plants and cement plants.

Coal Grinding Pulverizer Plant Equipment List

"Boost your efficiency with our Coal Grinding Vertical Roller Mill, designed for high-quality coal pulverization in power, metallurgy, and chemical industries. Consistent, reliable performance."

"Achieve precision with our Roll Wheel Medium-Speed Coal Pulverizer. Perfect for various coal types, reducing energy use and increasing output. Discover how it can enhance your production"

"Optimize your coal grinding with our MPS Coal Pulverizer Grinding Machine. Low maintenance, high-quality pulverization for any coal type."

"Improve your process with our Coal Pulverizing Air Swept Ball Mill. High-efficiency, uniform pulverization even for challenging coals. Maximize your coal quality"
Coal Grinding Plant ADVANTAGES
Tongli coal mill can process almost any type of raw coal, and can handle abrasive and sticky materials with moisture content below 1% and up to 25%.
Extremely durable and operates a minimum of 3,000 hours between internal inspections. The tire roller bushings can be used on both ends, ensuring that every surface is utilized.
High separation efficiency is ensured by reducing bypass discharge. Low specific power consumption of the mill motor, low vibration, energy savings due to minimal pressure loss and optimized airflow.
Maintenance is simple and convenient. All parts of the coal mill are equipped with doors for easy maintenance, and the rollers are equipped with hydraulic maintenance devices.
Safety, depending on the explosion potential of the type of coal you are using, our coal mills are supplied with nitrogen firefighting systems and are equipped with CO and O2 online monitoring systems
Flexibility, the liner segments are double-sided and interchangeable, and can be reversed after edge wear to utilize the entire liner surface.
Uniform feeding, star-shaped feeder ensures uniform feed flow into the coal mill, resulting in optimal mill operation, including minimizing power consumption. And equipped with heating device to prevent sticking.
Automatic return, the classifier is located above the grinding rollers and draws air-entrained material from the mill into the rotor. The rotor rejects coarse particles and returns them to the grinding table for further grinding
COAL PULVERIZER MILL GRINDING PROCESS

Raw Coal Crushing
First, the raw coal is processed by the crusher and the particle size is reduced to a range suitable for grinding. The crushed coal is sent to the central coal drop pipe of the pulverizer through the conveying equipment and fed evenly into the grinding ring area by the feeding device. In order to improve the process efficiency, the system uses an independent induced draft fan to provide hot air, which enters through the hot air port at the bottom of the pulverizer, not only providing a drying function for the grinding process, but also providing power for coal powder transportation.
Quantitative Feeding
In the vertical pulverizer, the raw coal falls from the central coal drop pipe onto the rotating grinding ring, and moves to the periphery of the grinding ring under the action of centrifugal force and enters the grinding area. Under the action of the hydraulic loading device, the grinding roller exerts a strong pressure on the coal on the grinding ring, so that it is ground into fine powder while forming a coal bed.
Material Drying & Grinding
During the grinding process, hot air blows up lighter and smaller coal powder particles through the grinding ring and fully dries them, while providing power for subsequent separation and transportation. Larger coal powder particles fall back to the grinding ring at a lower air flow velocity for re-grinding, while heavy debris passes through the air flow, enters the hot air chamber and is discharged to the stone coal box by the slag removal device.
Coal Ball Mill Grinding
In the ball mill, the raw coal enters the rotating cylinder through the feeding device, and impacts, squeezes and rubs with the steel balls in the cylinder, thereby being crushed into coal powder. The airflow plays an important role in the ball mill, which can not only dry the coal powder, but also bring the fine powder out of the cylinder. The coal powder particles that do not meet the fineness requirements are returned to the cylinder through the return device for further grinding to ensure the uniformity and quality of the final product.
Powder Classification
The ground air-powder mixture is sent from the vertical coal mill or ball mill to the powder selection system for further separation and treatment. The powder selector achieves accurate classification of coal powder particles through the interaction of the moving blades and the stationary blades. Qualified fine coal powder is sent to the coal powder bin or directly into the furnace through the powder outlet, and the coarse particles are returned to the grinding ring or cylinder through the inner cone for further grinding. The speed of the moving blades of the powder selector can be adjusted according to demand, so as to control the fineness of the exported coal powder and meet the process requirements. Heavy impurities fall into the hot air chamber after being separated by the air flow of the wind ring, and are discharged from the system by the slag cleaning device to ensure the stable operation of the equipment.
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WHY CHOOSE US
"We have been using this ball mill for more than two years and the stability is excellent. The equipment has strong adaptability when processing high-moisture coal. The equipment is easy to maintain and has low operating costs."

CFO
"The coal grinding efficiency of the Tongli vertical roller mill is very high. Compared with our previous ball mill, the energy consumption is reduced by about 30%. It occupies a small area, and the installation and commissioning process was also very smooth. The installers were also very professional and responsible."

CEO
"We chose tongli EPC service. The project team was very professional and the construction period was strictly controlled. The final equipment performance and production efficiency fully met the contract requirements. We are very satisfied!"

CEO
"The entire coal grinding system is excellent in terms of equipment performance and automation. Both the ball mill and the vertical roller mill are easy to operate and have high coal grinding efficiency, which is very important for a large power plant like ours. The supplier's after-sales service is also timely and in place."

CEO
FAQ
The wind-swept coal mill (or wind-swept coal mill) is a device used for coal powder processing. It combines the working principles of wind power and mechanical grinding to crush raw coal into fine coal powder for use in power plants, industrial boilers or other facilities that need to burn pulverized coal.
1. Wind-swept system: The wind-swept coal mill uses air flow to carry away the ground coal powder by introducing high-temperature air or flue gas flow. The air flow moves rapidly in the mill, carrying the pulverized coal powder out of the mill, which can avoid coal powder accumulation and ensure effective grinding.
2. Crushing process: The material enters from the top of the mill and is distributed to the grinding disc by gravity. The grinding roller presses the coal block from above for grinding. The grinding process uses the rotation of the grinding disc and the pressure of the grinding roller. The ground coal powder is discharged through the wind-swept system.
3. Recycling: Most of the fine coal is recycled into the mill through the separator for further grinding, and the unground coal blocks are returned for re-crushing to ensure that the fineness of the coal powder meets the use requirements.
The advantages of wind-swept coal mill are: High efficiency: wind-swept coal mill ball mill can efficiently crush coal blocks, making the coal powder particle fineness adjustable to meet different combustion requirements. Energy saving: the wind-swept system takes away the coal powder, which can reduce heat loss, improve grinding efficiency and reduce energy consumption. Flexibility: it can handle raw coal of various hardness and humidity and adapt to different types of coal. Automatic control: equipped with an automatic control system, it can monitor the grinding process in real time and adjust parameters to maintain stable production efficiency.
First, the raw coal is processed by the crusher and the particle size is reduced to a range suitable for grinding. The crushed coal is sent to the central coal drop pipe of the pulverizer through the conveying equipment and fed evenly into the grinding ring area by the feeding device. In order to improve the process efficiency, the system uses an independent induced draft fan to provide hot air, which enters through the hot air port at the bottom of the pulverizer, not only providing a drying function for the grinding process, but also providing power for coal powder transportation.
In the vertical pulverizer, the raw coal falls from the central coal drop pipe onto the rotating grinding ring, and moves to the periphery of the grinding ring under the action of centrifugal force and enters the grinding area. Under the action of the hydraulic loading device, the grinding roller exerts a strong pressure on the coal on the grinding ring, so that it is ground into fine powder while forming a coal bed.
During the grinding process, hot air blows up lighter and smaller coal powder particles through the grinding ring and fully dries them, while providing power for subsequent separation and transportation. Larger coal powder particles fall back to the grinding ring at a lower air flow velocity for re-grinding, while heavy debris passes through the air flow, enters the hot air chamber and is discharged to the stone coal box by the slag removal device.
In the ball mill, the raw coal enters the rotating cylinder through the feeding device, and impacts, squeezes and rubs with the steel balls in the cylinder, thereby being crushed into coal powder. The airflow plays an important role in the ball mill, which can not only dry the coal powder, but also bring the fine powder out of the cylinder. The coal powder particles that do not meet the fineness requirements are returned to the cylinder through the return device for further grinding to ensure the uniformity and quality of the final product.
The ground air-powder mixture is sent from the vertical coal mill or ball mill to the powder selection system for further separation and treatment. The powder selector achieves accurate classification of coal powder particles through the interaction of the moving blades and the stationary blades. Qualified fine coal powder is sent to the coal powder bin or directly into the furnace through the powder outlet, and the coarse particles are returned to the grinding ring or cylinder through the inner cone for further grinding. The speed of the moving blades of the powder selector can be adjusted according to demand, so as to control the fineness of the exported coal powder and meet the process requirements. Heavy impurities fall into the hot air chamber after being separated by the air flow of the wind ring, and are discharged from the system by the slag cleaning device to ensure the stable operation of the equipment.
1. Pfeiffer MPS type vertical roller mill
MPS type vertical coal mill is a technology developed by Pfeiffer Company in West Germany, also known as extraordinary mill. (The heavy MLS type mill developed and manufactured based on Pfeffer's technology also belongs to this category). The mill uses a drum-shaped grinding roller and a bowl-shaped grinding disc with arc grooves. It has a high grinding efficiency. There are three grinding rollers, which are installed tilted relative to the grinding disc and arranged at 120 degrees to each other. The roller skin is assembled and combined.
The tensioning force transmitted by three hydraulic tensioning rods is transmitted to the three grinding rollers through the pressure frame, and then transmitted to the material layer between the grinding rollers and the grinding disc. The hydraulic tensioning rod cannot lift the grinding roller and the pressure frame at the same time when starting the mill, so an auxiliary transmission device is provided.
When starting, open the auxiliary transmission first, and then open the main transmission after a certain period of time. The powder selection device consists of static blades arranged at a set inclination angle, which guide the airflow to rotate and enhance the function of separating materials. The dynamic cage rotor located in the middle of the powder selection device is driven to rotate by the top transmission device, and stepless speed regulation can be conveniently achieved. It has the function of strengthening the rotating wind speed in the middle of the powder selection device, enhancing the powder selection efficiency and conveniently adjusting the fineness of the finished product by adjusting the speed (the higher the speed, the finer the fineness).
The guide blades of the nozzle ring are installed at a fixed inclination, which is conducive to guiding the incoming air to form a spiral upward trend, so that part of the coarse particles can be separated from the rising air flow and return to the grinding disc before entering the powder selection device. Before operation, you can enter the mill and block the cross-section of the nozzle ring to change the ventilation area of the wind ring, thereby changing the wind speed (the smaller the total area, the greater the wind speed) to meet the wind speed requirements of materials with different specific gravities.
During maintenance, the hydraulic tensioning rod can only lift the pressure frame connected to the roller, but the connecting plate between the pressure frame and the grinding roller bracket should be removed first. And fix the grinding roller with special loading and unloading tools. The air locking device at the feeding port adopts three hydraulically controlled gates, which has both the function of locking the air and controlling the feeding amount. The air lock at the slag discharge port is controlled by two gravity flap valves.
2. F.L.Smidth ATOX vertical coal roller mill:
This mill is designed and manufactured by F.L.Smidth of Denmark. It uses cylindrical grinding rollers and flat track grinding discs. The roller skins are assembled and combined, which is convenient for replacing the roller skins. There are generally three grinding rollers, which are distributed at 120° to each other and installed vertically relative to the grinding disc.
The three grinding rollers are connected to the roller shaft flanges by three flanges on the center frame. Then three hydraulic stretching rods are connected to the other ends of the three roller shafts respectively to transmit the hydraulic pressure to the grinding disc and the material layer. The hydraulic stretching rods can lift the grinding rollers and the center frame as a whole. Therefore, there is no auxiliary transmission, and the main transmission system is directly started when starting.
The powder selection device has replaced the original static inertial separator with the SEPAX powder selection machine. SEPAX is also a high-efficiency powder selection machine developed in Denmark. Its structure is also divided into a circle of static guide blades and a dynamic cage rotor composed of narrow blades in the middle. Its mechanism and function are roughly similar to the powder selection device used by MPS. However, a horizontal separation ring component is added to the cage rotor, which is conducive to the horizontal rotation of the rotating airflow in layers, clear airflow movement, and little interference between airflow layers, making the powder selection and classification function more efficient.
The static blade can be pre-set with an inclination angle to assist in adjusting the fineness of the product. During operation, the blade angle can also be adjusted by adjusting the external adjustment bolts on the top of the machine. The nozzle ring is similar to the MPS type. The air lock device at the feed port adopts a mechanically driven rotary impeller structure, which can both lock the air and control the feed amount. The bottom of the feed chute is a sandwich structure for hot air, which has an anti-blocking effect. The slag discharge port adopts a closed electromagnetic vibrating feeder to discharge the material, which has a material sealing function.
3. Polysius RM type vertical roller mill
This mill is manufactured by Polysius Company in West Germany. Since it started production in 1965, it has been mainly sold in Europe. The RM mill has undergone three generations of technological transformation, and its current structure and function are quite different from other types of vertical mills. It is mainly characterized by two groups of assembled grinding rollers. Each group of rollers is assembled by two narrow rollers. There are four grinding rollers in two groups. These two rollers adjust their speeds corresponding to the grinding disc. It is beneficial to reduce the speed difference between the inner and outer tracks of the grinding disc and the rollers, thereby reducing the wear caused by friction, extending the service life of the roller skin, and reducing the slippage of materials between the rollers and the disc.
Each grinding roller is also tire-shaped, and the grinding disc corresponds to two circles of grooved tracks. The cross-section of the grinding disc is a bowl-shaped structure. The two grooved tracks on the grinding disc increase the number and time of material grinding, which is beneficial to improve the grinding efficiency. Each group of grinding rollers has a roller frame, and each roller frame has a hook at both ends. Each hook is connected by a hydraulic pull rod, a total of 4. The pull rod transmits pressure to the grinding roller and the material bed through the hook and the roller frame, crushing the material. The crushing force is continuously adjustable to suit the operating requirements.
The hydraulic tensioning system allows each set of double rollers to move freely in three planes, such as vertical rise and fall and relative roller axis axial deflection and a small amount of horizontal movement along the roller radial direction. If the inner roller near the center of the grinding plate is lifted by the coarse material, the pressure of the outer roller on the material will increase, and vice versa. This interactive function of each narrow roller in each set of grinding rollers also leads to efficient grinding.
The shape of the grinding track and the roller surface can affect the offset of the hook after wear and deformation. It can be compensated by measuring its wear and adjusting the hook hanging position accordingly. This helps to balance the pressure provided to the double rollers and maintain the grinding effect.
The roller surface of the double roller group can also be turned 180o as a whole for installation after uneven wear. The nozzle ring outlet area is designed to be adjustable from the outside of the casing. The adjustment device is 8 positioning pin baffles. The nozzle ring area can be changed by pushing and pulling out a certain amount of permission and positioning with a pin, thereby changing the rising speed of the airflow in the mill (the smaller the area, the higher the air speed) to meet the needs of different production. The nozzle ring guide vanes are installed vertically, which is conducive to reducing ventilation resistance.
The powder selection device uses the SEPOL type high-efficiency powder selection machine. The difference from the SEPAX type used by the Smith ATOX type is that there is no horizontal spacer ring on the cage rotor, but the inclination angle of the static blades on the periphery is adjustable, and the adjustment mechanism is located at the top of the casing. The blade inclination can also be changed by manually turning the adjustment mechanism when the mill is running, which is conducive to assisting the dynamic blades to adjust the product fineness as needed. A diverter plate is set at the outlet of the coarse powder funnel to make the coarse powder fall to two areas with lower dust concentration. The coarse powder cone bucket of the powder selection device of the RMK vertical mill used for coal grinding is also designed as a split combination type, which is conducive to separating the two halves of the cone bucket around the pin axis to both sides when repairing the powder selection device, which is convenient for maintenance operations.
Each vertical mill is jointly responsible for lifting the external circulating materials discharged from the slag outlet by two external hoists, and then feeding them into the two return material inlets on the top of the casing, entering the scattering plate of the powder selection device or directly entering the vertical mill for external recirculation grinding.
The air-locking feeding device at the feed inlet is used to feed materials evenly by the impeller-type mechanical transmission feeding valve, which can both adjust the feeding amount and minimize the leakage air volume. It is designed to heat the center of the coarse material feeding valve with hot air and pass the hot air into the chute interlayer for heating, which is conducive to preventing the materials with high moisture from sticking and clogging in the feeding valve and the chute. The slag outlet is equipped with a gravity air-locking valve. An auxiliary transmission is set in the transmission device because the grinding roller cannot be lifted by the hydraulic tie rod.
4. Loesche LM type vertical roller mill
This mill is manufactured by Loesche Company in West Germany with technology. There are two types of Loesche mills introduced and used in China: one is the Ube-Loesche mill manufactured by UBE Company of Japan and Loesche Company of West Germany through technical cooperation, that is, the LM type series manufactured by UBE Company; the other is the Loesche mill manufactured by Fuller Company of the United States under a contract with Loesche Company of West Germany, which is the LM type series manufactured by Fuller Company. Their main structures are basically the same.
Large Loesche mills are 4-roller type (models with output below 150t/h have two rollers). It is a cone-shaped grinding roller and a flat track grinding disc, without a roller frame. The pressure between the grinding roller and the grinding disc is provided by a hydraulic stretching device with a corresponding number of rollers. When working, the rocker arm is used as a lever to transfer the tension generated by the oil cylinder on the stretching rod to the grinding roller for grinding. The biggest feature is that the hydraulic stretching rod can reduce the starting torque required for the drag motor to the minimum value by controlling the lifting of the grinding roller. Therefore, ordinary motors with 70% or 80% starting torque can be used without auxiliary transmission. A hydraulic roller turning device is also provided to simplify maintenance work.
During maintenance, the roller can be turned out of the casing by connecting to the hydraulic device, and the roller skin can be replaced within one day. The hydraulic control lever is outside the mill and does not require air sealing, but when the roller is in the grinding position, the roller air seal must maintain a negative pressure of 500mmH2O inside the mill to prevent excessive dust-laden gas from penetrating into the bearing.
5. Babcock & Wilcox (B&W) E/EL Ball-and-Race Type Coal Pulverizers
The B&W E/EL series ball-and-race coal pulverizers are advanced, robust grinding systems designed specifically for pulverizing coal into fine particles for combustion in power plants. These pulverizers are widely recognized for their durability, efficient performance, and adaptability to various coal types, making them a popular choice in industries where consistent fuel preparation is critical.
The E/EL pulverizers employ a ball-and-race grinding mechanism, where steel balls rotate in a race (a circular track) inside the pulverizer. Coal is fed into the center of the race and crushed under the rolling action of the balls. The rotating grinding race and pressure from the rollers ensure efficient pulverization of coal into fine particles.
Airflow is integrated into the design to simultaneously dry and convey pulverized coal out of the grinding chamber. This feature helps maintain optimal combustion conditions and minimizes unburned carbon in fly ash.
As a key equipment, the correct operation of coal mill is crucial. Incorrect operation methods may lead to serious hidden dangers or even equipment failure. The following are common situations of incorrect operation and the problems they may cause:
Too much coal overflow: This situation will cause coal to block the stone coal discharge channel, and coal will accumulate in the side body, greatly increasing the risk of coal mill fire.
Continuous operation when the outlet temperature is lower than the specified value: If the outlet temperature is too low, the coal cannot be fully dried and is easy to adhere to the inside of the coal mill and the coal powder pipe, causing the coal powder pipe to be blocked and may cause fire.
Operation with an outlet temperature higher than the specified value: Excessive outlet temperature will cause volatiles in the coal to escape quickly, thereby increasing the risk of fuel ignition. Once the temperature exceeds the specified value of 11°C, the control system should immediately close the hot air shut-off door to avoid danger.
Operation with a ventilation volume lower than the specified value: Insufficient ventilation will cause coal powder to deposit in the coal powder pipeline, causing blockage and may cause fire.
Operation with ventilation volume higher than the specified value: Although this situation is not as dangerous as the above situation, excessive ventilation volume will accelerate the wear of the equipment and may cause the coal powder fineness to decrease, affecting the combustion effect.
Operation with the coal discharge gate closed: Closing the discharge gate will hinder the discharge of debris, causing debris to accumulate in the machine body. If it is operated for a long time, it will affect the discharge system and increase the risk of failure.
1. When starting for the first time, first connect the power supply of coal mill motor, and start the coal mill after ensuring that all starting conditions are met and completing comprehensive inspection before operation. Connect the sealing air of grinding roller device, gear box and grinding bowl hub gas seal device, open the hot air stop gate, and adjust the cold and hot air dampers through the control system to provide appropriate ventilation volume and inlet air temperature. Before feeding coal, warm grinding should be carried out for at least 15 minutes according to the specified outlet temperature. By adjusting the hot and cold air control dampers, the coal mill reaches the normal outlet temperature (65℃~82℃), ensuring that the coal can be dried immediately after entering the coal mill, reducing the risk of coal powder pipe blockage and promoting stable ignition of coal.
After completing warm grinding and ignition preparation, manually control the coal feeder to feed coal at 25% rated output, and gradually increase the coal feeding amount after the outlet temperature returns to the set value. If the coal mill vibrates at low load rate, the coal feeding amount can be appropriately increased to eliminate vibration. After reaching the correct outlet temperature, gradually increase the coal feed rate as the unit load increases. When the load reaches 80% during operation, the second and subsequent coal mills can be put into operation. After reaching the required coal feed rate, switch the coal feeder to automatic control.
2. During normal shutdown, the coal mill needs to be cooled to a temperature lower than the normal operating temperature before clearing the stored coal. The recommended cooling temperature is 50°C. Gradually reduce the load to the minimum coal feeder speed, and reduce the coal feed rate by 10% each time under manual operation to ensure that the outlet temperature remains within the set value and the ventilation volume is maintained under automatic control. After reaching the minimum coal feed rate, close the hot air stop gate to reduce the outlet temperature, and at the same time, fully open the cold air damper. Stop feeding coal after the coal mill cools to about 50°C, continue to run the coal mill for more than 10 minutes to clear the stored coal, and turn off the motor after the low motor current shows that the grinding has stopped. When shutting down the lubrication system in cold weather, drain the cooling water to prevent ice in the pipe, and check whether the pipeline is damaged or the lubricating oil is contaminated before restarting.
3. In case of emergency shutdown, if the furnace is out of flame or the fuel supply needs to be stopped urgently, the coal mill motor should be stopped immediately, the coal feeder should be cut off and the hot air stop gate should be closed. To prevent the residual coal from spontaneous combustion, it is recommended to use inert medium (such as steam) for protection. When cleaning the coal mill, pay attention to safety to prevent the combustible gas in the coal powder from causing accidents. After checking the closure of the relevant valves, cut off the power supply according to the safety measures of the power plant and mark the warning. Be careful when cleaning, take good protection, and check whether the coal mill has cooled to the ambient temperature.
After the emergency shutdown, if you need to restart, ensure that the coal mill has cooled to the ambient temperature and follow the normal startup steps. Blow out the residual coal before starting, start only one coal mill at a time and run it for at least 10 minutes, and then gradually restore the normal load after all coal mills are put back into operation.
4. When the coal mill catches fire, it may be caused by excessive temperature, accumulation of foreign debris, deposition of stone coal or abnormal operation. Common signs are rapid increase in outlet temperature or peeling of paint on the coal powder pipeline. When dealing with a fire, the coal mill cannot be shut down, and the inspection door must not be opened before all fire conditions are cleared and cooled to ambient temperature. The fire extinguishing steps include closing the hot air stop gate, fully opening the cold air damper, and feeding coal to the coal mill at an appropriate coal feeding rate. If necessary, water is injected to cool the coal mill, and a series of protective measures are taken to ensure safety.
5. In addition, the operation and maintenance of the coal mill requires regular inspection of the wear and lubrication conditions of various parts of the equipment, especially the grinding roller, grinding bowl and transmission gearbox. The lubricating oil should be replaced on time to keep the oil clean and prevent particle contamination from causing premature wear of the equipment. At the same time, monitor the vibration and promptly investigate the cause when abnormal, such as the damage of the grinding roller or liner, which needs to be repaired in time. By optimizing the parameters of the coal mill (such as pressure difference, air volume, etc.), the operating efficiency can be improved, and the energy consumption and maintenance costs can be reduced.
The following items need to be checked before the equipment is started:
Whether the motor and control system are normal.
Whether the pressure of the sealing air system meets the requirements.
Whether the coal feeder can run smoothly without jamming.
Whether the air volume, pressure and damper position of the ventilation system are within a reasonable range.
Whether the oil level of the lubrication system is normal and the circulation is smooth.
Whether the stone coal discharge port is unobstructed to prevent the accumulation of stone coal from affecting the operation.
Under special operating conditions, such as starting in a low temperature environment or temporarily increasing or decreasing the load, the coal mill parameters should be adjusted according to the operation manual to ensure the stability of the coal mill system and the boiler combustion system.
1 Platform foundation: includes reducer base platform, motor base platform, anchor bolt box, tie rod seat and turntable platform. After each platform is adjusted and fixed, it is buried in the foundation during the secondary grouting. The motor platform, reducer platform and tie rod seat are fixed in the foundation with anchor bolts, the turntable platform is fixed by ground anchors and expansion bolts, and the high-pressure oil station is fixed to the foundation with expansion bolts.
2 Motor: It is a high starting torque asynchronous motor, model YMKQ500-6-6, rated power 450kW, rated voltage 6000V, 988 rpm, protection level IP54, insulation level F. The direction of rotation needs to be checked before starting the coal mill. For details, see "YMKQ500-6-6 450kW High Starting Torque Asynchronous Motor Instructions".
3 Coupling: Used to transfer power between the motor and the reducer. The direction of rotation needs to be checked before starting the coal mill.
4 Reducer: It is a SXJ140 vertical bevel gear planetary reducer, which not only transmits the grinding disc torque, but also bears the roller loading force and the impact force generated by the vibration of the coal mill. For details, see "SXJ140 Reducer Operation and Maintenance Instructions".
5 Machine base: It mainly bears the weight of large components such as the upper casing and separator of the coal mill, as well as the horizontal torsional load transmitted to the casing through the casing guide device during the operation of the coal mill. The lower part of it accommodates the reducer, the upper part is equipped with a machine base sealing device, and the small opening on the side is used to install the slag box.
6 Slag box: It includes a hydraulic slide slag door, a slag box body and a slag collecting bucket. The hydraulic slide slag door is installed at the bottom of the machine base and the slag box to control the stone coal discharge port between the primary air chamber and the slag box and isolate the slag box from the outside world. The high-pressure oil of the high-pressure oil station performs the switch action through the hydraulic cylinder on the slag door frame. The spring on the slag door maintains the sealing. The connecting rod between the door plate and the hydraulic cylinder is sealed with a graphite packing coal powder stuffing box, and is equipped with an open and closed position indicator. There is a manual slag discharge door on the slag discharge box, which is sealed with silicate refractory fiber rope. During operation, the opening and closing of the hydraulic slide slag discharge door and the manual slag discharge door must strictly follow the operating procedures to prevent the high-temperature hot air from spraying out and ensure safe operation.
7 Machine base sealing device: It consists of a sealing ring housing, a carbon sealing ring and a spring. The entire device is installed on the top plate of the machine base through the sealing ring housing. The sealing ring housing, the carbon sealing ring and the transmission disc form a sealed air chamber, and the air is supplied inward from the sealed air inlet. The two circles of graphite sealing rings inside the carbon sealing ring are divided into 18 fan-shaped segments, which are tightened on the transmission disc by springs to form a floating seal to prevent eccentric damage to the shaft. The graphite sealing ring has good sealing effect and wear resistance, which is conducive to on-site maintenance and replacement, and has an automatic compensation for wear. When the coal mill is running at positive pressure, it is necessary to ensure that the sealing air pressure in the sealed air chamber is higher than the primary air pressure in the primary air chamber △P≥2kPa, and the pressure difference value is monitored. Most of the sealed air is blown into the primary air chamber through the upper gap of the sealed shell, and a very small part leaks into the atmosphere, preventing the primary air and dust in the primary air chamber from leaking outward, and improving the surrounding environment of the coal mill.
8 Transmission disc and scraper device: The transmission disc is rigidly connected to the reducer to transmit torque, installed on the output transmission flange of the reducer, fastened by 16 M48 bolts, and equipped with a grinding disc on the top. During operation, the output torque of the reducer is transmitted to the transmission disc through the friction force of the contact surface between the output transmission flange and the transmission disc. The transmission disc drives the grinding disc to rotate through the three transmission pins on the top, and also bears the upper loading force and component weight, and transmits force to the reducer body and coal mill foundation through the thrust pad of the reducer. Two scraper devices are symmetrically installed on the transmission disc, which rotate with the transmission disc. The normal gap between the scraper and the bottom of the primary air chamber is 6 to 10 mm, which can be adjusted by fastening bolts after wear.
9 Grinding ring and nozzle ring: It consists of a rotating part and a stationary part. The rotating part includes a grinding ring tray, a liner (12 pieces), a conical cover, etc. It rotates under the drive of the transmission disc. The nozzle blade is bolted to the grinding ring tray and rotates with the grinding disc. The stationary part is fixed on the casing. The gap between the rotating part and the stationary part is 5-12mm. The liner is embedded in the grinding ring tray and fastened with wedge bolts. The joint surface between the liner and the grinding ring tray and all the bolt thread parts should be coated with MoS₂. The conical cover plate evenly distributes the coal dropped from the coal drop pipe onto the grinding disc and prevents water and coal from leaking into the space under the transmission disc.
10 Grinding roller device: It consists of a roller frame, a roller shaft, a roller sleeve, a roller core, a bearing, an oil seal, etc. The grinding roller is located between the grinding disc and the press frame, tilted 15°, and positioned by the press frame. The roller sleeve is worn on one side and can be turned over for use when the wear reaches a certain depth. The rollers run at high temperatures, and the inner oil temperature can reach 110℃. High-viscosity, high-viscosity index, and high-temperature stability synthetic hydrocarbon SHC high-temperature bearing gear oil is used. Each roller is filled with 22 liters of oil. The oil seal is completed by two oil seals. The first oil seal seals the external environment, and the second oil seal seals the internal lubricating oil. The lip of the first oil seal is lubricated with high-temperature resistant grease between the two oil seals. There are two types of bearings, large and small, in the rollers. The large bearing is a cylindrical roller bearing, and the small bearing is a double-row radial spherical roller bearing, which bear radial force and axial force respectively. The roller frame transmits the loading force to the rollers, and is connected to the movable pipeline connected to the sealing air system. The sealing air flows through the inner cavity of the roller frame to the outside of the roller oil seal and the air sealing ring between the roller frames, forming a clean annular seal to prevent coal powder from entering and damaging the oil seal, and has the effect of cooling the temperature of the rollers. A respirator is installed at the end of the roller shaft at the roller frame to connect the sealing air and the internal oil chamber, eliminate adverse effects, ensure normal air pressure and a good environment in the oil chamber, and there is a hole for measuring the oil level on the roller shaft, which is screwed with a screw plug after use.
11 Pressing frame device: It is an equilateral triangle structure with a guide block. The hydraulic loading system applies the loading force to the three corners of the pressing frame through the pull rod loading device. There is a hinge shaft seat at the bottom of the pressing frame. The hinge shaft connects the roller frame and the pressing frame, and transmits the hydraulic loading force to the grinding roller, so that the grinding roller can swing freely around the hinge axis within a certain range, realize the extrusion and grinding movement, and improve the grinding efficiency. The pressing frame can also be lifted by the hydraulic system to realize the lifting function of the grinding roller. There is a guide positioning structure on the pressing frame, which is convenient for positioning and transmitting tangential force during work. The gap adjustment at the guide block is based on the alignment of the three pull rod axes and the center of the pull rod seat.
12 Casing: It consists of a casing, an anti-wear protection plate, a guide device, a hot air outlet, a pull rod seal, a manhole door, various inspection doors and explosion-proof steam pipelines. The lower part of the casing is welded to the base, and the upper part is connected with bolts and separators. The inner surface of the casing is equipped with anti-wear guard plates to prevent coal powder from scouring the inner wall. The lower part, the top plate of the base, the transmission plate, and the rotating nozzle ring form a primary air chamber. The three protruding parts on the upper part of the casing are equipped with pressure frame guide devices, which are used to guide the pressure frame vertically, limit the rotation of the pressure frame with the grinding roller, and control the geometric center of the intersection of the three grinding roller axes. There are manhole doors, three grinding roller inspection doors (for grinding roller oiling and placement of detection elements) and two primary air chamber inspection doors (for inspection of scraper assemblies and accident slag removal) on the casing. There is a tie rod sealing device at the place where the pull rod passes through the casing to ensure that the coal powder does not leak out and the pull rod can move up and down freely; the primary air inlet is connected to the primary air furnace, which is the primary air inlet for coal powder drying and transportation. There is an explosion-proof steam inlet on the primary air inlet. When the coal mill is started and stopped normally or stopped in an emergency, fire steam must be sprayed into the coal mill through the explosion-proof steam pipeline to prevent coal powder from spontaneous combustion or explosion.
13 Tie rod loading device: It consists of tie rod, thrust spherical bearing, proximity switch, measuring scale and tie rod connecting sleeve. The upper part of the tie rod is connected to the press frame through the thrust spherical bearing, and is led out of the casing through the tie rod seal. The lower part is connected to the loading cylinder through the connecting sleeve. There is a measuring device on the tie rod to display the coal seam depth and wear condition of the wear-resistant parts of the coal mill. The situation can be understood from the outside during the operation of the coal mill. The proximity switch indicates the lifting and lowering of the grinding roller.
14 Loading cylinder: The coal mill has 3 loading cylinders, which are evenly distributed at 120 degrees. Each cylinder body is equipped with an accumulator. The upper part of the cylinder is connected to the tie rod, and the lower part is equipped with a spherical bearing, which is fixed on the tie rod seat of the foundation. The diameter of the cylinder is 160mm, the diameter of the piston rod is 100mm, the piston stroke is 300mm, and the rated pressure is 21MPa.
15 Separator: The explosion-proof capacity of the coal mill is 3.5 bar. The centrifugal separator has a spherical head, which is mainly composed of a separator shell, a folding door, an inner cone, a powder return baffle, a folding door operator, a powder outlet, a coal drop pipe, etc. Its function is to separate the coarse particles in the gas-powder mixture sent from the grinding area, return them to the grinding area through the powder return baffle, and the coal powder that meets the combustion requirements is sent to the boiler through the powder outlet. The fineness of the coal powder is achieved by operating the folding door operator to adjust the opening of the folding door. The opening of the folding door is generally 25° - 80°, and the normal working angle is about 45°. The optimal working angle needs to be determined by the coal mill test.
16 Separator railing: It is convenient for maintenance personnel to climb to the top of the separator from the machine base platform through a ladder to perform operation tests, maintenance and repair work.
17 Sealing pipeline system: The sealing air is divided into three routes to reach the roller seal, tie rod seal and machine base seal. Install butterfly valves on the machine base seal and tie rod seal pipelines to distribute the air volume. Adjust the butterfly valve scale without affecting the differential pressure between the sealing air and the primary air during the initial operation of the mill. Make corresponding adjustments when the differential pressure changes in the later stage of wear. The sealing air to the mill roller enters the coal mill through the annular air duct inside the separator, and then enters the roller frame through three vertical air ducts equipped with joint ball bearings. One end of the vertical pipe is fixed to the roller frame, and the other end is connected to the separator sealing air duct with a joint bearing to avoid the impact of grinding vibration. The bronze sleeve matched with the joint ball bearing is easy to wear and needs to be checked and maintained frequently and replaced when necessary.
18 Explosion-proof steam system: Enter the mill from the primary air chamber and separator respectively, used for explosion-proof during the start and stop of the coal mill. The steam inlet user should prepare a steam trap to prevent water from entering and damaging the roller sleeve and lining.
19 High-pressure oil pipeline system: connect the high-pressure oil station with the loading cylinder, including the oil inlet pipeline and the oil return pipeline.
20 High-pressure oil station: Provides operating power for the loading cylinder, implements roller loading, and lifts and lowers the roller when starting and stopping. For details, see the "High-pressure oil system use and maintenance instructions".
21 Thin oil station: Specially used for circulating cooling lubricating oil for reducer, including the oil inlet and return lines connecting the thin oil station and the reducer. For details, see the "XYZ200 - L type thin oil station use and maintenance instructions".
22 Machine base platform: Convenient for maintenance staff to climb up from the zero-meter floor through a ladder to perform operation inspection, maintenance and inspection.
23 Sealed fan: Includes main fan, inlet filter, outlet flexible joint, outlet muffler and check valve. For fan use, please refer to the relevant fan manual.
24 Special tools: The manufacturer provides special tools required for the installation, measurement and maintenance of coal mill equipment, such as special tools for rollers, special tools for wear-resistant linings, special tools for transmission discs, and special tools for reducers.
1 Tongli Coal Mill Overview
Today, airflow vertical roller mills have become the standard solution for coal grinding equipment, among which the compact Tongli is the leading airflow vertical roller mill. It has high reliability, low installation cost and a variety of sizes. It can grind and dry various types of coal and has excellent unit energy consumption economy.
2 Multifunctional system characteristics
Suitable for a variety of installation types: Suitable for inert or non-inert, direct or indirect combustion systems. Inert systems are designed for indirect combustion and are a common solution for cement plants.
Efficient separator: Equipped with an efficient ZJTL dynamic separator, it can grind coal to the required fineness. When equipped with a variable speed mill motor, it can grind petroleum coke and anthracite to a fineness of less than 5% +90μm, and can withstand harsh outdoor conditions.
3 Built-in economy
Flexible component size: The size of the separator and nozzle ring is independent of the mill itself and can be selected according to the amount of gas required for drying, conveying and separating materials to avoid overinvestment.
One-time processing of high-water coal: It can grind and dry coal with a moisture content of more than 20% in one time.
Cost advantage: The possibility of customer-provided parts and the low civil engineering cost brought by compact mill installation improve economic efficiency.
4 Working principle process
The raw coal enters the mill through the rotating gate and feed chute and is unloaded to the rotating grinding disc. The rotation of the grinding disc causes the material to flow to the grinding rail. The coal is ground between the grinding disc and three rollers. After passing through the baffle ring, it is entrained in the hot dry gas. The gas brings the coarse particles back to the grinding disc, and the fine particles are swept to the separator. The separator allows the final product to enter the mill outlet. The coarse particles return to the grinding disc for further grinding. The final product leaves the mill from the top and enters the filter or cyclone separator with the gas for collection.
5 Tailor-made layout points
Consider heat source and safety: The layout needs to consider the heat source of drying raw coal and the fire and explosion hazards of coal and coal dust. The mill should be impact-resistant and equipped with multiple explosion-proof valves.
Equipment shock resistance: Feed is extracted from raw coal silos and conveyed in closed equipment. The mill, separator and feeding equipment are shock resistant up to 4.0 bar
6 Non-inert and inert operation modes
Non-inert operation: Non-inert operation is possible when grinding low-explosive to medium-explosive coals. Excess air from clinker coolers or heat generators can be used for dry conveying. No circulating air or water injection is required. The atmosphere can maintain the flow without explosion risk.
Inert operation: Cement plants can operate under inert conditions using kiln preheater exhaust gas, and can recover clean gas from the grinding technology system filter to maintain the flow. There is a water injection system to compensate for the low water content of raw coal. For different types of coal, the grinding system has different arrangements to control the oxygen content.
7 Features of wear-resistant grinding segments
Segmented design: The grinding table and rollers are equipped with segmented wear parts, which can use hard wear-resistant materials without the risk of thermal cracks.
High material utilization: The cylindrical shape of the rollers makes the segments reversible, improves material utilization, and the use of wear-resistant materials ensures long life.
8 Anti-fatigue design
The hydraulic cylinder fixed base generates grinding force for the roller, and the hydraulic force is transmitted to the end of the roller shaft through the tie rod. The tie rod joint is a prestressed bolt flange with high fatigue resistance. The roller assembly is concentric with the workbench through the horizontal torque rod and connected to the buffer chamber. The roller is lifted before starting the mill motor, and the mill fan is running to feed and lower the roller.
9 Effective lubrication system
The oil circulation system effectively lubricates the roller bearings. Each roller is supplied with regulating oil separately from the public supply station, and the separate circulation system provides filtration and temperature regulation.
10 Sturdy ZJTL rotary air separator
Structure and drive: The top of the mill housing is connected by a flange, and the rotor shaft is driven by a variable speed AC motor through a gear set and runs in the guide vane ring.
Working process: The entrained material enters the rotor through the guide vane, the rotor separates the coarse particles and returns to the grinding table, and the air and finished material leave through the outlet pipe. The product fineness can be adjusted by changing the rotor speed. The separator has strong wear resistance, and the discharge cone and shutters are made of wear-resistant materials.
11 High-performance gear sets
The standard main gear sets are solid helical gears or more compact helical planetary gears, designed for high dynamic loads, with high service factors, and the axial thrust bearings are segmented, the thrust pads are immersed in an oil bath, and the lubricant is regulated and filtered in a separate pump station.
12 Wear segment replacement methods
The roller and table segments can be easily replaced inside the large mill using a small crane, and the roller wear segments of small mills can be replaced externally. Tongli 30 and smaller mills can pull the entire roller assembly to a special cart for maintenance on the platform in front of the mill.
The MPS series coal mill is an external force roller-disc coal mill with three fixed grinding roller assemblies. The three grinding roller assemblies are evenly arranged on the grinding disc. The grinding pressure is provided by the hydraulic cylinder. The loading force acts on the three grinding roller assemblies and the grinding disc through the loading frame, and finally acts on the foundation. During operation, the coal that falls into the middle of the rotating grinding disc is thrown onto the surface of the grinding disc tile under the action of centrifugal force and is crushed by the grinding roller. The drying and grinding of the material are carried out simultaneously. The primary air is ejected from the nozzle ring around the grinding disc, which plays the role of drying and blowing the crushed material on the grinding disc into the partial separator on the middle frame body, and the coarse and fine powders are separated in the separator. The coal powder that meets the requirements is blown away, and the coal powder that does not meet the requirements will fall back to the grinding disc for re-grinding. Foreign impurities and large pieces of material cannot be blown away by the primary wind because of their heavy weight. They will fall through the nozzle ring into the primary air chamber at the bottom of the middle frame, and then be scraped into the slag box by the scraper mechanism for discharge. The MPS coal mill is driven by a squirrel cage motor. Planetary bevel gear reduction coal mill working principle diagram The machine not only transmits torque and decelerates, but also bears the vertical and horizontal forces generated by the weight and loading force of the coal mill. The rear output shaft of the main motor can be connected to a turning device for coal mill maintenance.
1. Lower frame
The lower frame surrounds the reducer and supports the middle frame, and the lower frame is connected to the foundation through anchor bolts. A slag discharge box is set next to the lower frame, and a hydraulic gate valve is set on the upper part of the slag discharge box.
Middle frame, wear-resistant lining, inspection door, tie rod sealing deviceThe circular middle frame with a static nozzle ring is welded to the lower frame and surrounds the grinding parts. The wear-resistant plate is installed on the nozzle ring and the inner wall of the middle frame. An inspection door is provided on the cylinder wall of the middle frame. The middle frame bears the tangential load of the loading frame and provides a sealed air interface for the three tie rods. The tie rod passes through the sealed air duct on the middle frame, and an expansion joint is set at the connection with the middle frame to compensate for the movement of the tie rod and seal the tie rod. The middle frame provides an interface for inert steam for the lower part: the grinding area and the primary air inlet.
2. Grinding disc and scraper mechanism
The grinding disc is installed with grinding disc tiles, and the grinding roller runs on it. The grinding disc transmits the torque provided by the planetary bevel gear reducer. The two scrapers are bolted to the grinding disc, and the grinding disc is bolted to the output flange of the reducer.
3. Rotating nozzle ring
The nozzle ring surrounds the grinding disc and consists of two parts: the dynamic nozzle ring (fixed on the grinding disc) and the static nozzle ring (fixed on the middle frame).
4. Grinding disc tile
The grinding disc tile is cast from a high-chromium alloy material with high wear resistance. The grinding disc tile is fixed by clamping bolts. There is a center cover in the middle of the grinding disc to separate the coal and prevent dust, water, etc. from entering the lower space.
5. Grinding roller with bearing and grinding roller bracket
The reaction force generated by the weight of the equipment, grinding pressure, and rotation is borne by the grinding roller bearing. Since the lubrication condition affects the life of the bearing, special attention should be paid to the lubrication condition. The lubricating oil grade and lubricating oil quantity are given in the lubricant list. The lubricating oil level should not be lower than the minimum oil level to ensure that the sealing ring of the grinding roller is immersed in the oil pool. In order to avoid oil leakage or impurities entering the bearing, special attention should be paid to a good sealing effect. Two sealing rings made of high temperature resistant materials are sleeved on the shaft, and the gaps of the sealing rings are filled with grease to increase the service life. The hollow roller bracket is connected to the sealing air system pipeline, and the sealing air enters the front end of the shaft through the annular cavity inside the roller bracket. In order to compensate for the influence of pressure caused by temperature changes, a breather is provided on the roller shaft sealing air channel. There is an oil level detection hole at the end of the shaft. The oil level is measured by inserting the oil dipstick into the inside of the grinding roller. This hole will be blocked with a screw plug. The roller sleeve is cast from a high-chromium alloy material with high wear resistance. The roller sleeve is installed in the bearing seat and fixed on the side with a clamping ring.
6. Loading frame, loading ring and swing adjustment device
The loading frame prevents torsion through the three corners of the middle frame body. There are limit plates made of special cast iron on the loading frame and the middle frame body to withstand the torsion pressure and support the loading frame. The loading frame bracket is used to connect the grinding roller and the loading frame. The grinding roller is connected to the loading frame through two separate radially swingable sleeves and support rings, so that the grinding roller can swing horizontally along the surface of the grinding disc. If necessary, the inclination angle of the grinding roller can be adjusted by this component. Whether it is rising or falling, the grinding roller is always adjusted by the adjustment mechanism to maintain a certain inclination so that it can maintain the correct position with the grinding disc tile. Tie rod fixing and indicating device One side of the tie rod is connected to the loading frame, and the other side is connected to the hydraulic cylinder piston rod through a connecting piece. The hydraulic cylinder is connected to the tie rod anchor plate on the foundation through a spherical bearing. The heads of the three hydraulic cylinders of each coal mill are equipped with limit switches. When the sensor bracket on the connecting piece enters the action area of the limit switch, the limit switch is triggered and the grinding piece is in the operating position.
7. Lower frame sealing ring
The coal mill is a pressurized equipment. In order to prevent the hot air inside from leaking, a labyrinth sealing ring is installed on the lower frame. The sealing ring is a flange ring with sealing air passing through it. The sealing ring is installed on the upper surface of the lower frame through a support ring and a gasket. The lower frame sealing ring has three sealing points: support ring I, support ring II and gasket are used to separate the contact between primary air, coal powder and the outside world (between the sealing ring and support ring I, and between support ring I and support ring II). The labyrinth seal at the bottom of the sealing ring serves to prevent ambient air from entering the coal mill. The number of labyrinth seals at the top of the sealing ring is less than that at the bottom, so that there is continuous sealing air entering the coal mill to ensure that the primary air inside cannot leak out. The pressure difference between the sealing air and the primary air is monitored, and when their pressure difference is reduced to the minimum, the coal mill will shut down.
8. SLK separator and its internal sealing air duct
The SLK separator is a static baffle separator, which is installed on the middle frame and becomes part of the coal mill. The air-powder mixture is blown from the grinding disc to the separator by the rotating primary air, where the coarse powder is separated and falls back to the grinding disc for re-grinding, and the coal powder that meets the requirements is blown to the burner for combustion. The direction of airflow rotation can be adjusted manually. Under the condition that the primary air volume and coal quality are constant, the fineness of the coal powder changes with the change of the opening of the separator blade. Each grinding roller has a sealed air duct connected to the annular duct on the separator. One end of the duct is connected to the roller bracket, and the other end is connected to the annular duct on the separator through a spherical bearing, so that the displacement of the grinding roller during grinding can be compensated. An inert steam pipeline insertion point is provided at the outlet of the separator.
9. Planetary bevel gear reducer KMP360
The reducer consists of two-stage transmission, one is a bevel gear set, and the other is a planetary gear set. The input shaft is installed horizontally, and the bevel gear, planetary gear and output flange are installed vertically. The bevel gear set and the planetary gear set are connected by a gear coupling. In order to withstand the static and dynamic pressure from the coal mill, a set of thrust bearings is provided at the upper housing. The housing with ribs evenly bears the pressure on the thrust bearing. In addition, the reducer housing can be used as an oil tank, and the bevel gear is placed on the oil surface. The lower part of the housing is designed to install the bevel gear set. The upper part of the housing is designed to install the inner ring and thrust bearing, and an oil drain valve is provided in the thrust bearing chamber. The vertical dynamic and static loads are transmitted to the surrounding of the housing through the thrust bearing and then to the foundation. The housing has a sealing effect on oil and dust.
10. Transmission gear system
The bevel gear adopts the Klingelnberg spiral bevel gear system, and the planetary gear adopts the involute spur gear system. The sun gear and planetary gear are surface hardened, and the inner ring is quenched and tempered and finely machined.
11. Bearings
All shafts are equipped with long-life bearings, and the planetary gear bracket and output flange bear radial and axial thrust. Thrust bearings are used to generate continuous dynamic pressure lubrication. The thrust bearings are mounted on reinforced metal blocks and can rotate freely in all directions. The metal blocks are placed on unquenched metal discs and bear the load. This factor should be recorded and considered when the roller is loaded for the first time. Semi-sliding friction will occur during the deceleration and operation of the coal mill. When the grinding roller is rotated with a turntable, it is necessary to lift the grinding roller to reduce the load to avoid unnecessary wear.
12. Lubrication
Lubrication and cooling of the gear system, bearings and thrust bearings of the reducer are provided by independent lubrication stations, and different pipelines are set inside and outside the reducer. The amount of lubricating oil at different lubrication points is determined by the manufacturer. The thrust bearing is arranged in an annular housing, and the gas and oil are sealed by a labyrinth seal filled with grease. The lubrication surface of the thrust bearing is lower than the surface of the oil pool where the lubricating oil flows continuously.
13. Lubrication system
The reducer has a separate lubrication system. The oil pump sucks oil from the lubricating oil pool at the bottom of the reducer, transmits it and delivers it to the lubrication points of the reducer through the heater, filter and cooler. The lubrication system lubrication station is installed on the foundation. In order to load and drain the lubricating oil in the reducer, stop valves are installed at the inlet and outlet of the oil pump respectively. The pressure and temperature of the oil can be read by the local display instrument, and the flow of the lubricating oil is indirectly measured by the temperature and pressure detection device in the coal mill automatic control system (such as the temperature of the oil pool at the bottom of the reducer and the temperature of the thrust bearing).
1. Sequence for starting the coal mill
Before starting the coal mill, start the lubricating oil system first. When the oil temperature of the reducer oil pool is lower than 25℃, start the low-speed pump first, and the electric heater starts working at the same time. When the oil temperature of the reducer oil pool is higher than 28℃, the oil pump switches from low speed to high speed; when the oil temperature of the oil pool is higher than 30℃, cut off the heater. When the oil supply pressure is greater than 0.13MPa, the reducer oil temperature reaches 28℃, and the thrust bearing oil pool oil temperature is lower than 50℃, it indicates that the lubrication system program has completed the start-up conditions (lubrication conditions are available), and this process is automatically completed by the oil system program control cabinet.
2. Before starting the sealed fan, the following conditions must be met: the primary air door of the coal mill inlet is closed; the cold air door of the coal mill is closed; the sealed air damper door of the coal feeder is opened; the raw coal hopper gate is opened; the coal powder isolation door of the coal mill outlet is opened; the primary fan is started and the primary air pressure is established; the turning device is disengaged; the hydraulic shut-off door is opened; the thermal protection system is normal.
Then start the sealed fan to make the difference between the sealed air pressure and the primary air pressure reach the required value, and the differential pressure value ΔP ≥ 2kPa for the conditions of starting the mill. Then start the high-pressure oil station, start the loading oil pump and adjust the pressure value of the proportional relief valve. Because there is coal accumulation on the mill plate, in order to prevent coal powder explosion, explosion-proof fire-fighting steam should be added for 6-10 minutes before the primary air is added. Adjust the separator outlet temperature control to the start control, and then add the primary air to purge the mill. After the purge, adjust the primary air volume to a value slightly higher than the minimum value for coal powder to extinguish or the minimum air volume required by the mill. Adjust the coal feeder to the minimum coal feed and start. After the mill is started, load it to normal operation, and the proportional relief valve of the hydraulic oil station receives the 4-20mA signal synchronized with the coal feed to implement variable loading on the grinding roller. Finally, adjust the mill output according to the boiler load. Within a certain range, there is a linear relationship between the mill output and the primary air volume. The standard air curve can be adjusted according to different types of coal. It is required to perform each step according to the automatic procedure to complete the whole process of "pulverizer start-up". Manual operation can also be performed in special circumstances. After confirming each step of the control procedure according to the "pulverizer start-stop protection logic diagram", press the manual button until the last step, press the pulverizer start button (motor closing).
Normal pulverizer stop Before stopping the mill, adjust the coal feed to the minimum coal feed, and at the same time reduce the separator outlet temperature. Complete the stop procedure according to the "normal pulverizer stop" in the "pulverizer start-stop protection logic diagram". Then the cold air door is "opened" and the primary air door is "closed". When the separator outlet temperature drops to ≤60℃, stop feeding coal, and the pulverizer idles for 60 seconds - 120 seconds before stopping the mill.
3. Quick stop of coal mill
Quick stop of coal mill is adopted in the following cases: coal feeder is out of coal or less than the minimum coal feed; coal mill vibrates suddenly; lubrication system fails; pressure difference between sealing air and primary air ≤1.5kPa; primary air volume is less than the minimum air volume; separator outlet temperature: t2≤60℃ or t2≥110℃; roller oil temperature ≥110℃; reducer inlet oil pressure ≤1.0kPa; plane thrust bearing oil pool temperature ≥70℃; coal mill motor coil temperature ≥130℃.
4. Emergency stop of coal mill
Emergency stop of coal mill is adopted in the following cases: boiler safety protection action; primary air volume is less than 85% of the minimum air volume; separator outlet temperature: t2≤55℃ or t2≥120℃; roller oil temperature ≥120℃; motor stops rotating.
When the mill is shut down in an emergency, the following equipment operations must be performed simultaneously: emergency shutdown of the hot air isolation door at the inlet of the coal mill; shutdown of the primary hot air door and the primary cold air door; cut off the power supply of the coal feeder; and supply explosion-proof steam.
If the fault cannot be eliminated and the operation of the coal mill cannot be restored after the emergency shutdown for 1 hour, the following operations should be performed in time: the coal mill is started empty and the large amount of accumulated coal on the grinding plate is discharged to avoid spontaneous combustion of the accumulated coal; the sealing fan, lubricating oil station, and high-pressure oil station can be closed.
If the fault has been eliminated after the emergency shutdown and the coal mill can be restarted, the following preparations should be performed: check the coal mill and auxiliary equipment; discharge slag. Then start the coal mill according to the "normal start" procedure.
Technical data of coal mill operation, interlocking protection and alarm
Technical data of coal mill startup (reference): pressure difference between sealing air and primary air ≥2kPa; roller oil temperature ≤100℃; primary air volume under standard working condition 25.14kg/s; separator outlet temperature 70 - 100℃; reducer oil temperature ≥28℃; reducer plane thrust bearing ≤50℃; reducer inlet oil pressure ≥0.13MPa.
Technical data of coal mill rapid stop (reference): roller oil temperature ≥110℃; coal feeder coal feed ≤20%; reducer inlet oil pressure ≤0.10MPa; separator outlet temperature ≥100℃; separator outlet temperature ≤60℃; reducer plane thrust bearing ≥70℃; motor bearing temperature ≥90℃; motor coil temperature ≥130℃.
Coal mill emergency shutdown technical data (reference): separator outlet temperature ≥120℃; separator outlet temperature ≤55℃; grinding roller oil temperature ≥120℃; primary air volume is less than 85% of the minimum air volume.
The change of coal powder fineness in the pulverizer is directly related to the boiler combustion efficiency and the economic efficiency of the power plant operation. The main factors affecting coal powder fineness include separator impeller speed, primary air volume, coal feed rate and hydraulic loading pressure. Based on the field test data of MPS medium-speed coal mill, this paper analyzes in detail the influence of these factors on the fineness of coal powder of different types of coal (lean coal and bituminous coal mixed with lean coal).
1. Influence of separator impeller speed and primary air volume
The experiments show that the changes of separator impeller speed and primary air volume significantly affect the coal powder fineness. When the speed of the dynamic separator impeller gradually increases, the fineness of the coal powder is significantly improved and the powder particles tend to be finer; while at the same impeller speed, with the increase of the primary air volume, the coal powder gradually becomes coarser. This is because the increase in primary air volume enhances the airflow carrying effect, allowing some of the coarser coal powder that has not been fully ground to be directly transported out. Compared with static separators, dynamic separators can classify and refine coal powder more efficiently. Further analysis showed that when grinding lean coal, the R90 value of coal powder fineness was lower on average than that of bituminous coal mixed with lean coal. For example, when the impeller speed is 80 r/min, the R
When the impeller speed reaches 140 r/min, the difference still exists, the lean coal value is 10% and the mixed coal value is 13%. The main reason why the mixed coal powder is coarser is related to the higher moisture content of bituminous coal. Higher moisture content will reduce the dryness of bituminous coal and weaken its brittleness, resulting in larger coal powder particle size.
2. The influence of coal feed rate and primary air volume on coal mill
Under the conditions of fixed separator speed and separator outlet temperature, changes in coal feed rate and primary air volume will also affect the coal powder fineness. When the coal feed rate increases, the air-coal mass ratio decreases, making the coal powder finer. The test shows that when the coal feed rate reaches 47 t/h, the coal powder fineness is significantly improved, because the appropriate air-coal mass ratio helps to optimize the grinding and separation efficiency. However, at a smaller coal feed rate (such as 33 t/h), since the primary air volume cannot be too small (to avoid sedimentation in the powder conveying pipeline), the air-coal mass is relatively large, resulting in coarser coal powder particle size. In the test of lean coal and bituminous coal mixed with lean coal, the coal powder fineness of lean coal is slightly better than that of mixed coal under the same conditions, but the difference between the two remains at about 3%. At the same time, when the primary air volume increases to a certain extent, the increase in the mass concentration of coal powder will improve the separation efficiency of the separator, making the coal powder particle size further refined.
3. Effect of hydraulic loading pressure
Hydraulic loading pressure is one of the key parameters affecting coal powder fineness. Under the premise of fixed separator speed and outlet temperature, the hydraulic loading pressure gradually increased from 5 MPa to 8 MPa, and the coal powder fineness showed a trend of gradually becoming finer. This is because the higher loading pressure enhances the extrusion and grinding effect of the grinding roller on the coal seam, reducing the particle size of the coal powder. However, when the coal feed rate reaches 47 t/h and the loading pressure reaches 8 MPa, part of the coal powder becomes coarser. This is because there is too much coal in the grinding disc and the gap between the grinding roller and the grinding disc is too small, resulting in some coal powder not being fully ground and being carried away by the hot air. For bituminous coal, the effect of hydraulic loading pressure on coal powder fineness is more obvious, and the increase in pressure can effectively refine the coal powder particles.
4. Comprehensive analysis shows that the dynamic separator impeller speed, primary air volume, coal feed rate and hydraulic loading pressure are the key factors affecting the fineness of coal powder. Reasonable adjustment of these parameters can effectively optimize the fineness of coal powder. For example, appropriately increasing the impeller speed, controlling the primary air volume, optimizing the air-coal mass ratio and loading pressure can achieve precise control of coal powder fineness, thereby improving boiler combustion efficiency and the economy of power plant operation. At the same time, the coal powder characteristics of different types of coal also require targeted adjustment of the pulverizer parameters to ensure that the coal powder fineness meets the process requirements.
1 The influence of coal characteristics on coal mill output
The physical and chemical properties of coal have a direct impact on the output of coal mill, including coal hardness (compressive strength), volatile matter, moisture content and particle size distribution. For example:
Coal hardness: Higher hardness will increase the difficulty of coal mill grinding and reduce output. Lean coal (anthracite) is usually hard and requires stronger grinding force, while bituminous coal is relatively easy to grind due to its soft texture.
Moisture content: The total moisture in coal puts forward requirements for the drying capacity of coal mill. Higher moisture content will not only increase grinding resistance, but also cause coal powder to adhere to the surface of grinding rollers and grinding discs, reduce the effective grinding area, and ultimately lead to a decrease in output.
Coal particle size: The larger the particle size of the raw coal, the longer the time required for grinding, resulting in a decrease in the amount of powder per unit time. Therefore, the pre-crushing process of coal is an important link in improving the output of coal mill.
2. Separator performance and speed adjustment
Separator performance plays a decisive role in the balance between coal mill output and coal powder fineness.
Separator impeller speed: A higher speed will make the coal powder finer, but it will cause some coarse particles to be separated back to the grinding disc, increase the circulation load, and indirectly affect the pulverizer's pulverizing efficiency. Conversely, a lower speed will reduce the coal powder fineness requirements and increase the coal powder output.
Separation efficiency: The design performance and operating status of the separator (such as blade wear or blockage) will directly affect the pulverized coal sorting effect. If the separator efficiency is low, a large amount of pulverized coal may not meet the fineness requirements and need to be re-grinded, increasing the equipment load and reducing the output.
3. Balance between primary air volume and air-coal ratio
The primary air system not only determines the smoothness of coal powder transportation, but also directly affects the output and quality of coal powder.
Air-coal ratio: The matching of air volume and coal feed is the key. If the air-coal ratio is too large, the coal powder will become coarser and the grinding effect will decrease; if the air-coal ratio is too small, it may cause the powder delivery pipeline to deposit or even block, seriously affecting the operating stability and output of the pulverizer.
Primary air volume adjustment: In the direct-blowing system of the medium-speed pulverizer, low air volume restrictions may lead to a decrease in output when running at low load. Therefore, optimizing the operating parameters of the primary air system is a necessary measure to improve the efficiency of the coal mill.
4. The influence of hydraulic loading pressure
The hydraulic loading pressure of the grinding roller determines the size of the grinding force, which in turn affects the fineness and output of the coal powder.
Changes in loading pressure: When the pressure is higher, the grinding effect is stronger, but if the coal supply is insufficient or the coal seam thickness is too large, the coal powder may not be fully separated, but the output will decrease.
Adaptability of coal types: When grinding bituminous coal with high moisture content, a higher loading pressure can improve the powder discharge efficiency; when grinding lean coal, the increase in loading pressure needs to be moderate, otherwise it is easy to increase the grinding resistance.
5. Coal mill operating parameters and equipment conditions
The design performance and actual operating conditions of the coal mill have a direct and obvious impact on the output.
Wear of the grinding disc and grinding roller: Wear of the grinding disc and grinding roller surface will lead to a decrease in grinding effect, coarsening of coal powder particle size, and more energy is required for grinding, and the output will also decrease. Regular maintenance and replacement of grinding rollers are important means to ensure efficient operation of equipment.
Equipment vibration and operation stability: The operation vibration of the coal mill may be caused by factors such as bearing failure, unbalanced load or uneven material distribution. Large vibration will not only reduce the grinding efficiency, but also may cause unplanned equipment shutdown, seriously affecting the output.
Type of coal mill: Different types of coal mills (such as ball mills, medium-speed mills, and vertical mills) have differences in design output and adaptability. For example, medium-speed mills are more suitable for direct-blowing boiler systems, while ball mills are more suitable for indirect blowing systems.
6. Separator outlet temperature and system drying capacity
The control of separator outlet temperature is crucial for the drying and separation of coal powder.
Temperature difference between lean coal and bituminous coal: When grinding lean coal, the separator outlet temperature can reach more than 110°C, while when grinding bituminous coal, it is usually controlled below 90°C to avoid the risk of coal powder spontaneous combustion. Higher outlet temperature will increase the dryness of coal powder, which is conducive to reducing coal powder adhesion and thus increasing output.
Drying system capacity: The output of coal mill is limited to a certain extent by the drying capacity, especially for high-moisture coal. When running at low temperature or with insufficient air volume, the dryness of coal powder is not enough, which will lead to unstable operation of equipment and ultimately affect the output.
7. Stability of coal feeding system
The uniformity of coal feeding directly determines the grinding efficiency and output of coal mill.
Coal feeder performance: Large fluctuations in coal feeding will lead to uneven distribution of materials on the grinding disc, affecting the grinding effect.
Matching of coal feeding: Under high load conditions, too low coal feeding will lead to fine coal powder particle size, while too high coal feeding may lead to insufficient grinding, which will affect the sorting effect of the separator.
8. Coordination of system auxiliary equipment
The improvement of coal mill output depends not only on the main equipment, but also on the efficient operation of related auxiliary systems.
Conveying system resistance: The design and operation status of the powder feeding pipeline (such as whether there is blockage or powder accumulation) will directly affect the conveying efficiency of coal powder.
Desulfurization system and boiler requirements: When the boiler operation requires a higher coal powder fineness, the output of the coal mill may be constrained, especially when the coal quality is poor.
First, the types and textures of coal vary greatly, and different boilers have different requirements for coal powder particle size. Generally speaking, coal powder needs to meet the standard of about 90% of the 200-mesh screening rate and have the characteristic of adjustable fineness. Whether it is a ball mill or a vertical mill, it needs to meet this high-precision requirement to ensure stable coal powder quality and excellent combustion performance.
Secondly, coal usually contains a high moisture content. The moisture content of ordinary coal is about 15% or more, while the moisture content of lignite is as high as 45%. This means that the coal grinding equipment must have drying capabilities and be able to effectively remove moisture during the grinding process. The vertical mill is particularly outstanding in this regard. Its unique air-swept design does not require a separate drying equipment. It achieves synchronous grinding and drying through high-temperature airflow, which greatly reduces the process flow and equipment investment.
In addition, the high volatile content in coal is a flammable substance. In addition, the flammability of coal itself puts forward strict flame retardant and explosion-proof requirements for coal grinding equipment. The vertical mill is designed with multiple safety measures such as explosion-proof valves and inert gas protection to ensure higher production safety. Due to its traditional structure, the ball mill usually needs to be equipped with additional explosion-proof facilities, which increases the complexity of the system.
At the same time, coal often contains hard impurities, and the presence of these impurities makes the grinding process face higher wear resistance requirements. In contrast, the vertical mill can handle these hard particles more efficiently through the direct extrusion and shearing action of the grinding roller and the grinding disc, while reducing the wear rate and extending the service life of the equipment.
From the performance point of view, the vertical mill has significant advantages. Compared with the ball mill of the same scale, the grinding power consumption of the vertical mill can be reduced by 20% to 40%. Especially when the moisture content of the raw coal is high, the vertical mill can grind and dry coal with a moisture content of up to 10% by adjusting the temperature and air volume of the inlet air, without the need for additional auxiliary equipment. In addition, the vertical mill integrates the five functions of crushing, grinding, drying, powder selection and conveying, with a compact layout and an area of only 60%-70% of the ball mill system, which significantly improves the space utilization and process efficiency.
From the perspective of product quality, the vertical mill is equipped with a high-efficiency dynamic powder selector, which has high powder selection efficiency and large adjustment room. Its powder fineness can be controlled below 3% of the 0.08 mm sieve residue, which can meet the grinding needs of most cement production lines for inferior coal or anthracite, with better combustion performance and higher thermal efficiency.
In contrast, although the air-swept ball mill also has a certain drying capacity, its hot exhaust gas utilization efficiency is low and the circulating load is large, resulting in a slightly lower grinding efficiency than the vertical mill. Moreover, when processing coal with a large amount of moisture, the ball mill system often needs to add pre-drying equipment, which increases the overall energy consumption, and the unit power consumption is also 10%-12% higher than that of the vertical mill.
Comprehensive analysis shows that vertical mill is more suitable for coal powder preparation due to its environmental protection and energy saving, integrated drying and grinding, and efficient powder selection, especially when dealing with high-moisture and flammable coal. Although ball mill still has room for application in certain specific processes, its overall performance and economy are not as good as vertical mill. Therefore, for users who pursue high efficiency and low energy consumption, vertical mill is a better choice.
The cost of building a coal milling line varies depending on many factors, including equipment selection (vertical mill or ball mill), output requirements, scope of supply, and configuration of auxiliary facilities.
1. Impact of supply scope
The cost of a coal grinding production line is closely related to the scope of supply. A complete coal grinding production line usually includes main equipment, auxiliary equipment and supporting systems:
Main equipment: such as vertical coal mill or ball mill, is the core equipment of the entire production line, and its price accounts for about 50% to 60% of the total investment.
Auxiliary equipment: such as powder selector, hot air furnace, dust removal system, conveying equipment, etc., accounting for about 20% to 30% of the cost.
Electrical and automation systems: including electric control cabinets, PLC control systems and monitoring devices, accounting for 10% to 15% of the investment.
Civil engineering and installation: includes the cost of infrastructure construction, equipment installation and commissioning, accounting for 10% to 20% of the total investment.
2. Equipment selection: comparison between vertical mill and ball mill
Equipment selection is a key factor affecting investment costs, and there are significant differences between vertical mills and ball mills in terms of price and operating costs.
Vertical coal mill: Vertical coal mill integrates crushing, grinding, drying, powder selection and transportation, with simple process flow and small footprint. Taking a vertical coal mill with an annual output of 100,000 tons of coal powder as an example, the equipment purchase cost is approximately RMB 5 million to 8 million. At the same time, the power consumption of the vertical mill during operation is 20% to 40% lower than that of the ball mill, which can significantly reduce long-term operating costs.
Ball mill: The initial investment of a ball mill is relatively low. The purchase cost of a ball mill with an annual output of 100,000 tons of coal powder is approximately RMB 3 million to 5 million. However, the ball mill system requires additional auxiliary equipment such as dryers and powder classifiers. The overall system is complex and the unit power consumption is high, 10% to 15% higher than that of the vertical mill. In addition, ball mills have higher operating and maintenance costs, and the long-term costs may exceed those of vertical mills.
3. Impact of Production Capacity on Cost
The design capacity of a coal grinding production line directly determines the specifications and investment scale of the equipment. For example:
A production line with an annual capacity of 50,000 tons: Suitable for small to medium-sized boiler users, the investment for a vertical mill system is approximately 600,000 to 900,000 RMB (about 85,000 to 128,000 USD), while for a ball mill system, the investment ranges from 500,000 to 700,000 RMB (about 70,000 to 97,000 USD).
A production line with an annual capacity of 100,000 tons: A common medium-scale size, the investment for a vertical mill system ranges from 1,000,000 to 1,300,000 RMB (about 140,000 to 180,000 USD), and for a ball mill system, it ranges from 800,000 to 1,100,000 RMB (about 112,000 to 155,000 USD).
A production line with an annual capacity of 200,000 tons or more: Mainly servicing large power plants or cement companies, the investment for a vertical mill system ranges from 1,500,000 to 2,000,000 RMB (about 211,000 to 283,000 USD), and for a ball mill system, it ranges from 1,200,000 to 1,600,000 RMB (about 170,000 to 226,000 USD).
4. Total Investment Estimate
Based on the supply range, equipment selection, and production capacity, the total investment for a coal grinding production line can be estimated as follows:
Small-scale production line (annual capacity of 50,000 tons): 800,000 to 1,200,000 RMB (about 112,000 to 169,000 USD).
Medium-scale production line (annual capacity of 100,000 tons): 1,200,000 to 1,800,000 RMB (about 169,000 to 253,000 USD).
Large-scale production line (annual capacity of 200,000 tons): 2,000,000 to 3,000,000 RMB (about 283,000 to 425,000 USD).
5. Other Cost-Influencing Factors
Raw coal moisture and particle size: High raw coal moisture or large particle size may require stronger drying capabilities or pre-crushing equipment, thus increasing investment costs.
Environmental requirements: Strict environmental regulations may require high-efficiency dust removal systems, explosion-proof devices, and low noise equipment, which could increase costs by 15% to 20%.
Regional factors: Labor costs, logistics expenses, and civil construction costs in the project location can affect the total investment.
1. Application of coal mill in pulverized coal boiler:
After the transformation of modern boiler systems, the use of coal mills has significantly improved combustion efficiency, reduced pollutant emissions, and desulfurization, denitrification and dust removal devices can be installed. These measures not only helped achieve the national energy conservation and emission reduction standards, but also improved the economic benefits of enterprises. For example, a typical pulverized coal boiler can save 10% of its annual fuel costs and reduce sulfur dioxide emissions by more than 60% by using a coal pulverizer.
2. Blast furnace pulverized coal injection system:
The system is widely used in the power, steel and metallurgical industries. In the entire system, the quality of coal powder preparation directly determines the operating efficiency of the entire system. Due to the high requirements for coal powder and large output, traditional coal mills cannot meet these requirements. More and more customers are choosing advanced coal mills, such as vertical roller mills, which can achieve a 200-mesh screen residue rate of more than 85%, ensuring efficient and high-yield coal powder production. These systems can operate stably at 80% of their designed output, while conventional equipment can only achieve 60% output.
3. Preparation of coal powder for coal chemical industry:
Coal chemical industry converts coal into gas, liquid and solid products through processes such as gasification, liquefaction, distillation and tar processing. The preparation of coal powder is an indispensable part of the process. Advanced coal mills are key as they need to handle high ash and high moisture coal feedstock. Taking some models of vertical mills as an example, they can grind coal powder to a 3% sieve residue below 0.08 mm particle size, ensuring efficient production of chemical products. By reducing grinding costs and energy consumption, these advanced equipment make the coal chemical process more economically viable.
4. Lime kiln (rotary kiln) coal powder preparation:
In the lime kiln, the quality of coal powder directly affects the quality of quicklime and its use in metallurgy, chemical industry, building materials and other industries. Modern lime kilns have an increasing demand for coal powder, which puts forward more stringent requirements on coal powder processing equipment. For example, using advanced coal mills, coal powder with a particle size of less than 90 microns (200 mesh) can be produced, improving the efficiency of quicklime and reducing fuel costs. Using a vertical roller mill, coal powder can be ground to a specific surface area of 3000 cm²/g, which optimizes the energy use in the rotary kiln and makes the entire production process more energy-efficient.
1. Type of coal
Hardness and volatility: Different types of coal (such as anthracite, bituminous coal, lignite, etc.) have different hardness, volatility, abrasiveness and calorific value. These factors directly affect the selection of coal mill. For example:
Anthracite (Vsr<9%): The hardness is high, and the coal mill needs to withstand greater pressure, so it is more appropriate to choose a medium-speed coal mill (such as the HLM series).
Bituminous coal (Var-19%~27%): It has high volatility and moderate abrasiveness, which is suitable for medium-speed coal mill direct-blowing system.
Lignite (Ke≤3.5): It has a low erosion wear index and is suitable for fan coal mill or high-speed coal mill system.
2. Output capacity
Production capacity requirements: The size of the coal mill is selected according to the output requirements of the coal powder. For working conditions with high output requirements, it is recommended to choose a large-scale medium-speed coal mill (such as the HLM series) to improve production efficiency and reduce downtime and maintenance time.
Tonnage demand: For example, if a production line needs to process 100 tons of coal per hour, a coal mill of corresponding size is required to meet this demand.
3. Moisture
Coal moisture content: The moisture content of coal will affect the selection and operation of the coal mill. For high-moisture coal (such as lignite), a coal mill that can effectively dry the coal needs to be selected, such as a medium-speed coal mill equipped with a drying device or a fan coal mill.
External moisture MP: For coal powder with an external moisture of ≤15%, it is more appropriate to use a medium-speed coal mill direct-blowing system. For high-moisture coal powder, special drying systems and equipment need to be considered to avoid blockage and damage.
4. Types of coal mills
Combustion characteristics: The selection of coal mills also needs to consider the combustion characteristics of coal powder, including explosiveness, volatile matter, ash content, etc. Different coal mill models (such as steel ball coal mills, fan coal mills, medium-speed coal mills) are suitable for coals with different combustion characteristics.
Boiler load and burner structure: The selection of coal mill should match the requirements of boiler load and burner to ensure that the quality and particle size of coal powder can meet the operation requirements of boiler.
Equipment inspection and maintenance: When selecting coal mill, it is also necessary to consider the equipment inspection cycle, maintenance cost and supply of spare parts to ensure the long-term stable operation of the equipment.
4.1Low-speed coal mill: ball mill
The typical representative of low-speed coal mill is ball mill. Its working principle is: a high-power motor drives a heavy cylinder to rotate through a gearbox. The steel balls in the cylinder fall freely after rotating to a certain height. The coal blocks are crushed by the impact of the steel balls and the pressure grinding between the steel balls and between the steel balls and the guard plates. The over-coarse coal powder is screened out by the separator and returned to the cylinder for re-grinding. Hot air is not only used to transport coal powder, but also plays the role of drying coal, so hot air is also called desiccant. In the pulverizing system, the ball mill has the following characteristics:
Long continuous operation time, easy maintenance, stable output and fineness, large storage capacity, quick response, large operating flexibility, low air-coal ratio, saving spare coal machine, and a wide range of coal types. It is mainly used for hard and medium-hard coal types, especially for coal with high volatile matter and strong abrasiveness. Nevertheless, this low-speed ball mill is bulky, consumes a lot of metal, occupies a lot of space, has a high initial investment, and is suitable for full-load operation.
4.2 Medium-speed coal mill: vertical coal mill
The characteristic of the medium-speed coal mill is that the grinding parts are composed of two sets of relatively moving grinding bodies, and the coal blocks are squeezed, ground and crushed between these two sets of grinding bodies. At the same time, the hot air introduced into the coal mill dries the coal and sends the coal powder to the separator for classification. Qualified coal powder is carried out of the mill with the air flow, and the coarse particles return to continue grinding. The medium-speed coal mill has the following advantages:
The equipment is compact, occupies a small area, consumes less electricity (about 50%~75% of the steel ball mill), has low noise, and is relatively light and sensitive in operation and control. It is mainly suitable for the preparation of medium- and high-volatile bituminous coal (Vanr-27%~40%), coal with high moisture content ≤15%, and coal powder with strong abrasiveness. In addition, the medium-speed coal mill is not suitable for processing harder coal.
4.3 High-speed coal mill
The speed of the high-speed coal mill is between 500~1500 r/min, mainly including fan mill and hammer mill. Its working principle is that the coal blocks are impacted by high-speed impact and collide with the mill shell, and the coal blocks collide with each other. The high-speed coal mill and the coal powder separator form an integral whole, with a simple and compact structure and low initial investment. It is particularly suitable for high-moisture lignite and bituminous coal with high volatile content and easy to grind. Although it has strong adaptability, the impact plate is directly affected by the air flow and is severely worn, so its service life is short, generally around 1000 hours, and it is frequently replaced. It is suitable for direct-blowing boilers in power plants, but not for blast furnace injection workshops.
4.4Basis for selecting coal mill models
When selecting the model of coal mill, the following factors need to be considered comprehensively:
Combustion characteristics, abrasiveness, and explosion characteristics of coal types: such as volatile matter, ash content, moisture, etc.
Coal mill pulverizing characteristics and coal powder fineness requirements: Different coal mills have different adaptability.
Type of pulverizing system: According to the pulverizing system, choose a direct-blowing or storage (intermediate storage) system. The direct-blowing system is suitable for pulverized coal with high grinding fineness requirements, while the storage system is suitable for the storage and re-transportation of pulverized coal.
Boiler furnace structure and burner structure: Ensure the matching of coal mill and boiler furnace to achieve the best combustion efficiency and emission standards.
For example, the intermediate storage hot air powder delivery system of the ball mill is suitable for anthracite (Vsr<9%) and coal with strong abrasiveness, and the exhaust gas powder delivery system of the ball mill is mainly used for bituminous coal with high volatile content. The medium speed coal mill direct blowing system is suitable for grinding coal powder with medium to high volatility and low moisture content. The fan coal mill is suitable for grinding lignite and providing coal powder for direct blowing boilers in power plants.
1. Coal pulverizer fire
Problem: Coal pulverizer fire may be caused by spontaneous combustion of accumulated coal powder or other fire sources.
Possible causes: Common causes include leakage of coal powder pipeline, blockage of coal powder nozzle causing coal powder to accumulate inside the mill, and introduction of fire source due to negligence of operators.
Corrective measures: First refer to the fire extinguishing steps for emergency treatment to ensure safety. Next, check the coal powder nozzle of the coal pulverizer to ensure that it is unobstructed, check whether the coal powder pipeline is leaking or accumulating, and make necessary repairs. Ensure that the operator strictly implements the safety operating procedures to avoid the introduction of fire sources.
2. Failure of hot air damper
Problem: Failure of hot air damper may cause hot air to fail to enter the coal pulverizer normally, thereby affecting the combustion state of coal powder.
Possible causes: Mechanical failure of hot air damper, failure of control system or damage of electric actuator.
Corrective measures: Close the hot air door, stop the operation of the coal pulverizer immediately, and make necessary repairs. Depending on the specific fault situation, it may be necessary to replace the damaged electric actuator or repair the control system. Open the cold air damper, ensure safety and then resume normal operation of the coal mill.
3. Failure of cold air damper
Problem: Failure of cold air damper will prevent cold air from entering the coal mill, affecting the cooling effect.
Possible causes: Mechanical failure of cold air damper or failure of electric actuator.
Corrective measures: Manually open the cold air damper, shut down the coal mill and perform maintenance. According to the actual situation, replace the damaged electric actuator or repair the control system to ensure that cold air can enter the coal mill normally for cooling.
4. High outlet temperature of coal mill
Problem: Abnormal increase in outlet temperature of coal mill may be due to uneven coal feeding, too fine coal powder or insufficient hot air volume.
Possible causes: Failure of coal feeder and blockage of coal feeding pipe, resulting in insufficient or uneven supply of coal powder. Failure of outlet thermocouple and inability to accurately detect temperature.
Corrective measures: The coal mill should be stopped immediately for cleaning, and the coal feeding pipe should be checked and cleaned to ensure smooth supply of coal powder. Verify the calibration of coal feeder, check the hardness change and humidity of coal, and repair or replace as required. Check the outlet thermocouple to ensure that it is working properly, and calibrate or replace it as required.
5. Low outlet temperature of coal mill
Problem: Too low outlet temperature of coal mill will affect the combustion effect of coal powder.
Possible reasons: Too low coal feeding rate, high humidity of coal powder, insufficient hot air volume, etc.
Corrective measures: Reduce the coal feeding rate, check the calibration of coal feeder and the change of coal hardness. Increase the hot air volume, optimize the primary air temperature, and ensure that the coal powder is fully dried. Check the overload of coal mill. If the opening of hot air door has reached 100%, the coal feeding rate needs to be reduced. Ensure that the fineness of coal powder is moderate to avoid too coarse or too fine powder affecting the combustion effect.
6. Failure of cold air damper
Problem: Failure of cold air damper may cause cold air to fail to enter coal mill normally, thus affecting the cooling effect.
Possible reasons: Mechanical failure or failure of electric actuator.
Corrective measures: Manually open the cold air damper, shut down the coal mill, and perform maintenance. Check and repair the control system or replace the electric actuator to ensure that the cold air can enter the coal mill normally for cooling.
7. Coal mill overload
Problem: Coal mill overload may be caused by excessive coal feeding or too wet coal.
Possible causes: Coal powder is too fine, coal type changes, improper installation or commissioning of the coal mill, etc.
Corrective measures: If the hot air door opening has reached 100%, the coal feeding rate needs to be reduced. Check the calibration of the coal feeder, the hardness and humidity of the coal. Adjust the separator speed or adjust the opening of the folding door to ensure that the fineness of the coal powder is moderate to avoid excessive coarseness or excessive fineness affecting the load of the mill.
8. Coal powder is too fine
Problem: Coal powder is too fine, which will cause the coal mill to overload or incomplete combustion.
Possible causes: The separator speed is too low, the folding door opening is improper, the coal type changes, etc.
Corrective measures: Reduce the separator speed, adjust the folding door opening, and ensure that the fineness of the coal powder is within a reasonable range. Check the motor and reducer to ensure that they are working properly, and repair or replace them if necessary.
9. Coal powder is too coarse
Problem: Coal powder that is too coarse will affect the operating efficiency of the pulverizer and the combustion effect of the pulverized coal.
Possible reasons: The separator speed is too high, the opening of the folding door is too large, the coal type has changed, etc.
Corrective measures: Increase the separator speed, adjust the opening of the folding door, and ensure that the fineness of the pulverized coal meets the requirements. Check the hardness and humidity of the coal type to ensure that it adapts to the working conditions of the pulverizer.
10. High pressure difference in the grinding bowl
Problem: High pressure difference in the grinding bowl may be caused by blockage of the pressure joint, failure of the pressure sensor, or narrow air passage of the pulverizer.
Possible reasons: Poor airflow caused by blockage or pollution.
Corrective measures: Clean the pressure joint of the grinding bowl to ensure that it is unobstructed. Recalibrate or replace the pressure sensor. Remove the air throttle ring to increase the air flow. Check the ventilation control system to ensure that the channel area around the mill is sufficient and improve air distribution.
11. Blockage of coal powder pipeline
Problem: Blockage of coal powder pipeline will affect the supply of coal powder and cause unstable operation of the pulverizer.
Possible causes: accumulation of coal powder particles, poor air circulation or improper operation.
Corrective measures: Clean the coal powder pipeline to ensure normal ventilation and wind speed. Recalibrate the coal feeder, check the cause of the blockage and eliminate it. Adjust the coal powder fineness to ensure that it meets the operating requirements of the coal mill.
12. Incorrect coal powder fineness
Problem: Incorrect coal powder fineness will affect the operating stability of the coal mill and the combustion effect of coal powder.
Possible causes: improper separator position or speed, inaccurate sampling.
Corrective measures: Check the separator position and speed to ensure that they meet the requirements. Check the sampling device, position and procedure to ensure its accuracy. Replace the parts of the coal mill, check the gap between the grinding roller and the grinding bowl liner, and ensure that the operating status of the mill is normal.
13. Change of coal type
Problem: Change of coal type may cause unstable operation of the coal mill or the coal mill configuration is not suitable for the new coal type.
Possible causes: Changes in coal hardness, humidity, particle size and volatile matter.
Corrective measures: Check the hardness, humidity and volatility of the coal, adjust the coal feed and the operating parameters of the coal mill. Check the gap between the grinding roller and the grinding bowl liner to ensure that it meets the requirements of the new coal type. Adjust the separator speed and the opening of the folding door to ensure that the coal powder fineness is within a reasonable range.
1. Explosion-proof device of coal mill:
Nitrogen fire-fighting system: In coal mill, nitrogen fire-fighting system is usually used to prevent explosion. The system displaces oxygen by providing an inert nitrogen gas curtain, thereby preventing coal powder from forming an explosive mixture with oxygen. During normal operation and maintenance, the nitrogen fire-fighting system can effectively reduce the risk of explosion.
Carbon monoxide/oxygen online detection system: Coal mill is equipped with a real-time carbon monoxide and oxygen monitoring system, which is essential for real-time monitoring of gas concentration. High concentrations of carbon monoxide may indicate incomplete combustion or the presence of explosive gases, and it is very important to take timely measures. If the oxygen concentration is too high, it may cause coal powder to explode, requiring rapid intervention.
2. Explosion-proof valve design:
Explosion-proof valve design of mill body: In order to prevent the explosion from spreading inside the mill, explosion-proof valves are usually installed at key parts of the mill, such as coal powder inlet and outlet, under the grinding roller, etc. These valves are designed to quickly release pressure to prevent the explosion from spreading to the entire equipment, thereby reducing the risk of fire and explosion.
Explosion-proof valve design for dust collector: Explosion-proof valves are also installed in the dust collector of the coal mill. These valves are used to isolate and prevent the spread of explosions. The setting of these valves is designed to prevent the explosion from spreading through the system, thereby reducing the scope of the explosion and protecting the safety of the entire plant.
3. Explosion-proof design of electrical control:
Explosion-proof electrical enclosures: The control system of the coal mill is designed with explosion-proof electrical enclosures to protect the electrical components from coal dust and potential sparks. These enclosures can ensure that the internal electrical equipment is sealed and will not be affected by dust, thereby preventing sparks from triggering explosions.
Sealed electrical connections: The explosion-proof design of the electrical control system also includes sealed cable connectors and enclosures to ensure that there are no gaps or openings for dust to enter, thereby avoiding sparks caused by electrical faults.
Dedicated power distribution panels: The power distribution system of the coal mill usually includes dedicated explosion-proof panels that isolate the electrical components and prevent electrical faults from spreading throughout the plant. This isolation measure helps prevent the spread of explosions.
3.1 Basic types of explosion-proof electrical equipment
Explosion-proof electrical equipment is mainly divided into flameproof type, increased safety type, intrinsic safety type, positive pressure type and oil-immersed type. In the coal mill system, the commonly used explosion-proof electrical equipment mainly includes flameproof electrical equipment, explosion-proof control devices and overload protection devices. These devices play an important role in different links of the coal mill system to ensure the safe production.
3.2 Application of explosion-proof electrical equipment in coal mill system
In the coal mill system, the application of explosion-proof electrical equipment is mainly reflected in the following aspects:
3.2.1Isolation spark device: The isolation spark device is set at the inlet and outlet of the coal mill, which can effectively prevent the sparks generated by the high-speed movement of coal powder from causing explosion. At the same time, the isolation spark device can also reduce the wear of coal powder on the equipment and extend the service life of the equipment.
3.2.2Explosion-proof control device: The explosion-proof control device is the core part of the coal mill system. It can realize remote control of the coal mill and avoid safety hazards when the operator is operating on site. The explosion-proof control device also has functions such as overload protection and short-circuit protection, which can cut off the power supply in time when the equipment fails to prevent the accident from expanding.
3.2.3Overload protection device: The overload protection device is one of the important safety devices in the coal mill system. It can cut off the power supply in time when the equipment is overloaded, avoiding equipment damage or fire and other safety accidents caused by overload.
4 The importance of safety devices
The installation of safety devices for explosion-proof electrical equipment in the coal mill system is crucial to ensure production safety. These safety devices can cut off the power supply in time and prevent sparks when the equipment fails or abnormal conditions occur, thereby avoiding accidents. Therefore, in the design and operation of the coal mill system, the setting and maintenance of safety devices should be fully considered to ensure the safe and stable operation of the equipment.
COAL GRINDING MACHINE PULVERIZER TECHNICAL DATA
Item | Verified Coal |
Pulverizer Model | ZJTL2520HP-II |
Reducer | KMP360 Planetary Bevel Gear Reducer |
Separator | Static Separator SLK410 with Manual Adjustable Baffle |
Grinding Force | Hydraulic Variable Loading |
Nozzle Ring | Rotating Nozzle Ring |
Slag Discharge | Pneumatic Gate Valve, Manual Slag Box |
Motor Power | 800kw |
Sealing Fan | Central Supply, One Running, One Standby |
Turning Gear | Yes |
Explosion Pressure | 3.5bar |
Rotational Speed | 30.95rpm |
Grinding Disc Shape | Disc Type |
Grinding Disc Tiles (Quantity) | 11pcs |
Grinding Disc Tile Material | GX260CrMoNi2021 |
Grinding Disc Tile Hardness | 730x30HV |
Roller Diameter | 1750mm |
Roller Sleeve Material | GX260CrMoNi2021 |
Roller Sleeve Hardness | 730x30HV |
Middle Frame Material | Standard Steel |
Design Pressure Standard | 3.5bar |
Total Weight | ~166007kg |
Total Height | 10485mm |
Coal Pipe Diameter | φ670 (Outer Diameter)mm |
Maintenance Door | 1 Door |
Roller Bearing Lubrication | Splash Lubrication |
Separator Type | Static Baffle Type |
Separator Model | SLK410 |
Separator Blade Adjustment | Manual |
Hydraulic System | |
Grinding Pressure Oil Pump Flow | 16L/min |
Max Force | 160bar |
Max Reaction Force | 50bar |
100TPH POWER PLANT COAL PULVERIZER DATA SHEET
Item | Unit | Design Capacity: | Verified Capacity: | |
1 | Pulverizer Output | |||
Maximum Output | t/h | 93.9 | 88.1 | |
Calculated Output (BMCR) | t/h | 76.85 | 72.4 | |
Guaranteed Output | t/h | 84.5 | 79.64 | |
Minimum Output | t/h | 23.48 | 22.03 | |
2 | Pulverizer Load Rate | |||
Maximum Load Rate | % | 100 | 100 | |
Minimum Load Rate | % | 25 | 25 | |
3 | Pulverizer Ventilation Volume | |||
Maximum Ventilation Volume | t/h | 162.67 | 154.1 | |
Calculated Ventilation Volume (BMCR) | t/h | 152.8 | 144.9 | |
Ventilation Volume at Guaranteed Output | t/h | 157.25 | 149.1 | |
Minimum Ventilation Volume | t/h | 122 | 122 | |
4 | Inlet Drying Medium Temperature | °C | 360.8 | 366.7 |
5 | Pulverizer Speed | r/min | 30.94 | 30.94 |
6 | Pulverizer Ventilation Resistance | |||
Maximum Ventilation Resistance | Pa | 7205 | 7205 | |
Ventilation Resistance at Guaranteed Output | Pa | 6789 | 6803 | |
Calculated Ventilation Resistance | Pa | 6451 | 6464 | |
7 | Pulverizer Seal Air System | |||
Seal Air Volume (per unit) | kg/s | 1.07 | 1.07 | |
Seal Air Pressure (or difference with primary air pressure) | Pa | 2000 | 2000 | |
Exit Volumetric Flow (including seal air and water vapor, BMCR) | m³/s | 47.7 | 45.5 | |
Exit Airflow (including seal air, BMCR) | kg/s | 47.83 | 45.53 | |
Exit Powder Port Diameter | mm | 690 | 690 | |
Exit Powder Port Velocity | m/s | 25.5 | 24.32 | |
Seal Air Leakage | kg/s | 0.32 | 0.32 | |
8 | Pulverizer Exit Temperature | °C | 65 | 65 |
9 | Pulverizer Exit Coal Powder Moisture | % | 13 | 13 |
10 | Pulverizer Power Consumption (BMCR) | kW.h/t | 6.793 | 7.222 |
Power Consumption at Guaranteed Output | kW.h/t | 6.53 | 6.95 | |
11 | Pulverizer Wear Rate | g/t | 4–6 | 4–6 |
12 | Stone Coal Volume (BMCR) | t/h | 0.0384 | 0.0362 |
Stone Coal Volume at Guaranteed Output | t/h | 0.0423 | 0.0398 | |
13 | Main Component Lifespan | |||
Roller Sleeve | h | 12000 | 12000 | |
Grinding Bowl Liner Plate | h | 15000 | 15000 | |
Roller Bearing Seal | h | 20000 | 20000 | |
Stone Coal Scraper | h | 12000 | 12000 | |
14 | Pulverizer Weight | t | 169 | |
Dimensions (Diameter/Height) | m | 5.7/10.6 | ||
Max Lifting Weight During Installation | t/component | 28.5 (Separator) | ||
Max Lifting Weight During Maintenance | t/component | 10.35 (Roller) | ||
Max Lifting Height During Maintenance | m | 10 |