As a kind of industrial solid waste generated after coal combustion, ash and slag are usually sent to the slag silo for storage through a slag discharger and a crusher. Since the slag silo has a generally small capacity, it can only be used as a transfer silo and does not have long-term storage capacity. Therefore, the ash and slag can generally only be transported to the ash and slag field for landfill in the form of automobiles in bulk. Ash fields not only occupy a lot of land resources, but also cause harm to soil and ecological environment.

Therefore, by transporting the ash from the slag silo to the dry slag grinding system, after crushing and grinding, the finished ash is produced, and then comprehensively utilized, which has become an effective and environmentally friendly treatment method.

1 Dry slag grinding process system

The dry slag grinding process system includes feeding and crushing part, grinding part, and grinding tail conveying part.

1.1 Dry slag feeding and crushing part

A hole is opened on the side of the cone bucket of the slag silo to reclaim the material, and a manual double-layer bar gate, a pneumatic gate valve, and a weighing belt scale are arranged under the reclaiming port. The belt scale measures the dry slag and sends it to the dry slag compound crusher , the particle size of the crushed dry slag is less than 5mm, and it falls directly into the inlet of the mill.

1.2 Grinding part

Using a tubular ball mill, the dry slag entering the mill is crushed and ground in the mill to produce finished ash with a fineness of more than grade 3 ash.

A pulse bag filter is installed at the end of the grinding mill to extract the dust-laden humid and hot gas in time, and at the same time, the ventilation inside the mill is strengthened to improve the grinding efficiency. The exhaust gas is directly discharged into the atmosphere after purification, and the emission concentration can meet the national environmental protection requirements. The fine ash collected by the dust collector falls into the mill tail air chute. A manual butterfly valve is set on the exhaust pipe of the dust collector to adjust the air volume.

1.3 Grinding tail conveying part

A speed-regulated air lock feeder, an air chute and a steel wire belt elevator are set under the discharge port of the grinding tail to transport the ground product ash to the newly built intermediate warehouse.

A set of positive pressure dense phase conveying silo pump is set under the middle silo to pneumatically convey the finished ash to the designated location.

2 Common problems and preventive measures of dry slag grinding engineering

2.1 Common problems and preventive measures of the mill body

1) The dry slag grinding system adopts a tubular ball mill, and the grinding body in the rear chamber of the mill is a steel section grinding body. During the casting process, the grinding body of the steel section may be doped with some scrap materials. Due to the irregular shape, unqualified hardness and generally small size of the scrap scrap, after wear, it will enter the grinding machine along the discharge grate along with the finely ground finished ash. Tail conveyor system. The existence of corner material will cause the rear feeder to jam, resulting in poor transportation and affecting the stability of the system.

Prevention and control measures: strictly control the product quality during the casting process of the steel section grinding body to reduce the doping of the scrap; screen the steel section grinding body before it is assembled to separate out the unqualified scrap; Regularly clean up the leftover scraps on the discharge grate.

2) The shape of the sieve holes of the discharge grate plate of the mill is mostly diamond or rectangle, and the size of the sieve hole is too large. Too large sieve hole will cause the grinding body of the steel section to enter along the discharge grate plate along with the finished ash after the loss is reduced. The grinding tail conveying system causes the rear feeder to jam, which affects the stability of the system.

Prevention and control measures: Check the size of the sieve hole of the discharge grate plate of the mill before installing the discharge device of the mill body. If the size is too large, replace the discharge grate plate with a smaller sieve hole size; Cylindrical shape, which will be proportionally reduced after wear, so it is recommended that the mesh shape be square.

3) The grinding body in the front chamber of the dry slag grinding fine-tube ball mill is a steel ball grinding body. During the rotation of the mill, the steel ball grinding bodies collide with each other, and the noise is large.

Prevention and control measures: Since the ash will radiate a lot of heat during the grinding process, it is impossible to set a soundproof cover for the mill. Therefore, a closed grinding workshop can be built, and targeted noise reduction measures can be taken to ensure that the noise level outside the workshop meets the environmental protection requirements, and at the same time, the necessary noise reduction equipment can be provided for regular inspection personnel.

2.2 Common problems and preventive measures of auxiliary systems

1) The ash and slag fall down through the slag drop pipe, and then are quantitatively sent to the dry slag crusher for crushing after being measured by the weighing belt scale. Due to the large change in the coal quality of the burning coal, the size and shape of the ash and slag have large deviations. When large pieces of ash and slag fall into the belt scale, the center of gravity of the belt may be shifted, resulting in a deviation phenomenon, resulting in the chain jump of the mill. .

Preventive measures: Belt scales add a deviation correction device to automatically correct its trajectory when the belt deviates; the control system adds deviation signals to monitor the belt in real time, and take timely measures when a slight deviation occurs to avoid the mill from jumping.

2) The dry slag grinding crusher crushes the ash and slag through the high-speed rotating hammer, and the particle size after crushing is less than 5mm. Due to the fast rotation speed, the rotary disc and hammer head inside the crusher are subjected to a large impact force when they collide with the slag, resulting in serious wear and tear.

Prevention and control measures: replace the material of the hammer head of the crusher with high-manganese alloy steel; the surface of the turntable is treated with wear-resistant and anti-corrosion ceramic patches.

3) The speed of the crusher is fast during operation, and the recoil force received when it collides with the ash and slag is large, resulting in strong vibration during the operation of the equipment. At the same time, due to the uneven wear of the hammer head, its rotation axis may be offset, which will also increase its vibration.

Preventive measures: Reinforce the support platform of the crusher; use a soft connection for the connection between the crusher and the front and rear equipment pipes to avoid other equipment being affected by vibration; the control system adds vibration detection signals to monitor its vibration value in real time to ensure the safe operation of the system.

4) The grinding body of the steel section of the mill will inevitably enter the grinding tail conveying system along the discharge grate along with the finished ash. Once it enters, it will cause a jam to the rear feeder and affect the stability of the system.

Prevention and control measures: Change the electric feeder of the grinding tail discharge device to a flap valve; add an iron removal device to the grinding tail to capture the unqualified grinding bodies and discharge them through the slag discharge port.

The implementation of the dry slag grinding project can solve the problems of slow sale of ash and slag, large area of ​​slag yard, huge environmental pollution risk, etc. It can realize zero discharge of ash and slag, and has the characteristics of comprehensive utilization of resources and environmental protection. At present, the performance of dry slag grinding projects is still relatively small. Therefore, during the implementation of the project, we must strictly control the quality of construction, installation, and equipment, and summarize the experience of migrating similar projects to ensure the stable and reliable operation of the system.