Pingwei Power Generation Co. Ltd. coal transport system in the design and construction, due to dust control measures in domestic coal handling system is being explored, no mature experience to draw on. Although the dust management problem is considered, the equipment selection is not suitable and the expected effect cannot be achieved. After that, a three-step plan for comprehensive dust control was proposed, namely water washing, dust suppression and dust collection. After the initial treatment, the first step of ground water washing has been completed, and the effect is good. The latter two steps cannot be continued for various reasons. Due to the failure to comprehensively complete the comprehensive treatment of the coal handling system, the system dust concentration is still exceeding the standard, especially the outlet of the coal crusher and the dust at the tail of the belt conveyor are seriously exceeding the standard. The highest dust concentration is 64.1mg/m3, and the exit velocity of the tail guide groove is 7 ～10m/s, the flow rate is 10 584—15120m3/h. When the outlet of the guide trough is running, a large amount of powder is sprayed outwards. The particles are 1-3mm. After running, the ground can be obviously dusty, polluting the environment and endangering the health of the employees. .
2. Analysis of the causes of dust
2.1 The original coal is broken and the particles become smaller, which is the internal cause of dust generation.
After the raw coal is crushed by the coal crusher, the particles are basically below 6mm. As the raw coal particles become smaller, the surface area will increase, the particle gap will increase, the density will decrease, and the surface moisture will decrease. This is the internal cause of dust generation, which is also the following for the coal crusher. The reason why the grade belt conveyor dust is larger than the upstream belt conveyor.
2.2 Induced wind generated by the blasting effect of the coal crusher rotor
When the coal crusher rotates, the ring hammer and the ring hammer arm on the rotor are equivalent to the fan blades, which induces induced wind. The coal crusher selected by the plant is TKK48X103 type, and the blast effect is theoretically small. Later, because the coal crusher is easy to block coal, the sifter of the coal pulverizer is cut off. Although the problem of coal plugging is solved, the sieve plate loses the diversion effect, and the induced wind generated by the coal pulverizer flows. In the trough, the wind pressure and flow rate of the guide trough increase, and the powder at the outlet of the guide trough is intensified.
2.3 induced wind falling from the falling coal pipe
The coal mine to the tail tribe coal pipe drop is about 14m. When such a large drop passes through the coal flow, the high-speed falling coal flow compresses the air in the falling coal pipe, thereby generating airflow, which intensifies the dust discharge at the outlet of the guide trough. .
2.4 The feeder outlet (the coal crusher inlet) is not tight, and the induced wind of the coal crusher is provided. The internal cause of the induced wind is caused by the coal crusher rotor shredder, and the feeder outlet is not tightly sealed. The machine produces an external cause of induced wind. Because the feeder outlet is not tightly sealed, the feeder å‘» å‘» è¿›å£ è¿›å£ è¿›å£ è½ è½ è½ è½ è½ è½ è½ è½ è½ å‡ºå£ å‡ºå£ å‡ºå£ å‡ºå£ å‡ºå£ å‡ºå£ å‡ºå£ å‡ºå£ å‡ºå£ å‡ºå£ å‡ºå£ å‡ºå£ å½¢æˆ å½¢æˆ å½¢æˆ å½¢æˆ å½¢æˆ å½¢æˆ å½¢æˆ å½¢æˆ å½¢æˆ å½¢æˆ å½¢æˆ å½¢æˆ å½¢æˆ å½¢æˆ å½¢æˆ å½¢æˆ å½¢æˆ ç»™The machine exits and is driven by the coal crusher rotor to eject from the outlet of the guide trough.
2.5 Dust generated by coal accumulation at the end of the drum
The original empty section cleaner before the tail roller was damaged and removed, so that the pulverized coal adhered to the tape could not be removed, and it was brought into the tail roller, and became fine powder to form dust under the rolling of the tail roller.
2.6 Dust generated by belt jitter
The belt comb-shaped idler wears unevenly, which causes the belt to shake more, thereby generating dust.
2.7 The powder of the tail buffer roller is not good.
The belt buffering roller of the belt conveyor was originally a flexible bracket type cushioning roller. The buffering principle was to use the elastic deformation of the bracket to buffer the impact of the coal flow on the coal conveying tape. When the coal flow impacts, the buffer roller bracket is deformed, the belt and the buffer roller are displaced downward, and a gap is formed between the guide groove and the belt, and the dust is ejected from the air gap.
2.8 The original guide trough is flat top, and the single-layer curtain is sealed in the front section. The buffer volume is small, the back section is easy to form micro-positive pressure, the outlet air volume is large, the wind speed is high, and the top is easy to accumulate dust.
3. Governance plan
The main reason for the dust generated at the coal pulverizer outlet is the induced wind generated by the blasting effect of the coal pulverizer rotor and the induced wind caused by the drop of the falling coal pipe, followed by the air gap generated by the tail buffering roller buffer deformation guiding groove. The induced wind generated by the machine and coal flow causes the guide trough to be positively pressurized. If the guide groove is simply blocked, the positive pressure of the guide groove will be further increased, and finally it will be ejected from a weak link. If only the water spray is added at the outlet of the guide trough, the dust of the fine particles can be suppressed, but the larger particles that induce wind entrainment cannot be eliminated. Therefore, when considering the dust control plan, we must carry out all-round comprehensive management in accordance with the principle of taking advantage of the situation and carrying out various plans.
3.1 Closing the feeder to reduce the air intake of the coal crusher
3.1.1 The buffer coal hopper has a certain seal bottom coal to prevent the wind between the feeder and the buffer coal hopper.
3.1.2 Feeding machine trough sealing canvas should be inspected regularly and found to be damaged and replaced in time.
3.1.3 The joint of the feeder chute outlet and the coal crusher inlet shall be completely sealed with canvas or tape.
3.1.4 Feeder observation The hole door is made into a sealed door.
3.1.5 The coal crusher enters and exits the coal pipe and its flange joint surface for comprehensive repair and sealing.
3.2 Reforming the guide trough
3.2.1 Remove the flat cover plate of the original guide trough, change it into an arc-shaped arch cover, increase the volume of the guide trough, relieve the positive pressure of the guide trough, and reduce the dust on the top of the guide trough.
3.2.2 Extend the length of the guide trough to increase the airflow stroke, and use the natural attenuation of wind pressure and wind speed to achieve the effect of natural dust deposition. The original guide belt of the belt conveyor is 8m long and is now 14m. From the perspective of governance practices, this method works best.
3.2.3 Install the multi-stage dust curtain in the guide trough. The detachable dust curtain is installed every 2m at the top of the guide trough. The material uses a vulcanized rubber sheet with a nylon core. The ordinary rubber sheet is easy to tear and is not wear-resistant. The thickness of the rubber sheet is about 3mm. The rubber sheet is too thick, the rigidity is not large, and it is easy to be elastically deformed; if it is too thin, it is inelastic and easily rushed away by the airflow. In this transformation, the guide trough is installed with 13-level dust curtains. After the transformation, the airflow passes through the friction of the dust curtains. The exit wind speed is attenuated from the original 7-10m/s to almost zero, and the outlet of the guide trough is basically windless. There is no obvious granular dust on the exit ground. From the perspective of governance practice, this program is the preferred solution for dust reduction.
3.3 Add water spray to further reduce dust
3.3.1 Guide groove installation 5 models are PCL-4-120° nozzles (bore aperture 4mm, fog angle 120°), controlled by solenoid valve type 075-DV. Practice has proved that after the water spray, a layer of moist protective film is formed on the surface of the coal to suppress dust leakage.
3.3.2 Add 3 models of PCL-4-120° nozzles to the feeder slot. The feeder chute is wider, where the coal seam is thinner, and the spray is added here, and the moisture in the coal is easily controlled evenly. Due to the increase of moisture in the coal, the dust caused by the vibration of the feeder can be reduced, and the dust generated during the crushing process of the coal crusher can also be reduced.
3.4 Replace the belt buffer roller at the tail of the belt conveyor, and install the cleaner on the comb roller
3.4.1 Replace the original spring plate cushioning roller with the cushioning roller of the fixed bracket.
3.4.2 Replace the comb-shaped stick with severe wear to reduce the belt shake.
3.4.3 Install a reverse belt cleaner before the roll.
3.5 Guide bag is equipped with bag filter, reducing the positive pressure of the guide groove. Install one LZZ-35 bag filter in the middle of the guide groove of each belt conveyor. The air volume of the dust collector is 8,000-10,000 m3/h.
4. Summary of experience
The dust concentration at the exit of the coal crusher is greatly reduced. The dust concentration in the area is reduced from 64.1mg/m3 before treatment to 2.2mg/m3, which is lower than the national standard of 10mg/m3. Greatly improved. Through the actual operation, there are 3 points of experience.
4.1 For dust generated due to large drop and induced wind, it is advisable to use a guide trough expansion and a dust curtain treatment plan. The solution has low cost and obvious effect. The disadvantage is that the dust curtain wears quickly, the replacement cycle is short, and the maintenance amount is large.
4.2 For dust generated due to low surface moisture and fine coal particles, a water spray dust suppression scheme should be adopted. The shortcoming of this scheme is that the amount of water spray is not suitable for control, which often results in a large water content of coal. Winter water pipes are easy to freeze, freeze and crack, and there are seasonal problems.
4.3 When selecting the bag filter, the air volume should be greater than 1.25 times the dust volume. If the air volume of the precipitator is chosen to be small, the negative pressure is difficult to form. The bag filter has a good effect in the initial stage of use. After a period of use, the bag is easy to be knotted, the ventilation is reduced, the efficiency is lowered, and the bag is difficult to clean.
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