Dust control at the outlet of the hottest coal cru

2022-09-23
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Dust control at the outlet of coal crusher

1. system status before dust control

during the design and construction of the coal handling system of Pingwei Power Generation Co., Ltd., there was no mature experience for reference because the domestic methods for dust control of the coal handling system were being explored. Although considering the problem of dust control, the equipment selection is not appropriate and the expected effect cannot be achieved. After that, the scheme of comprehensive dust control in Inner mine with a maximum takeoff weight of 72 tons was put forward, namely water washing, dust suppression and dust collection. After preliminary treatment, the first step of surface water washing has been completed, and the effect is good, and the last two steps cannot be continued for various reasons. Due to the failure to fully complete the comprehensive treatment of the coal handling system, the dust concentration of the system still exceeds the standard, especially the dust at the outlet of the coal crusher and the tail of the belt conveyor seriously exceeds the standard. The maximum dust concentration reaches 64.1mg/m3, the wind speed at the outlet of the tail guide chute reaches 7 ~ 10m/s, and the flow is 1058415120m3/h. When the outlet of the guide chute is running, a large amount of powder is sprayed outward, and the particles are 1.3mm. After running, obvious dust accumulation can be seen on the ground, polluting the environment, Endanger the health of employees

2. Analysis of the causes of dust generation

2.1 the internal cause of dust generation is that the particles of raw coal become smaller after being crushed by the coal crusher

the particles of raw coal are basically below 6mm. As the particles of raw coal become smaller, it is bound to increase the surface area, increase the particle gap, reduce the density, and reduce the surface moisture, which is the internal cause of dust generation. This is also the reason why the dust of belt conveyors at all levels below the coal crusher is larger than that of the upstream belt conveyor

2.2 induced wind generated by the blowing effect of the coal crusher rotor

when the coal crusher rotates, the ring hammer and ring hammer arm on the rotor are equivalent to fan blades, which will generate induced wind. The coal crusher selected by the plant is tkk48x103 type, and the blast effect is theoretically small. Later, because this kind of coal crusher was easy to block coal, the screen plate in the inner cavity of the coal crusher was cut off. Although the problem of coal blockage was solved, the screen plate lost its guiding effect, so that a large amount of induced air generated by the coal crusher flowed to the guide chute, and the air pressure and flow of the guide chute should be increased by the same amount from the support, and the pulverized coal spraying at the outlet of the guide chute intensified

2.3 the induced air generated by the large drop of the coal chute

the drop of the coal chute from the coal crusher to the tail tribe is about 14m. When there is a coal flow with such a large drop, the high-speed falling coal flow compresses the air in the coal chute, resulting in air flow, which intensifies the pulverized coal injection at the outlet of the guide chute

2.4 the feeder outlet (coal crusher inlet) is not tight, which provides an external cause for the induced air generated by the coal crusher. The coal crusher rotor is the internal cause of the induced air generated by the coal crusher, and the loose sealing of the feeder outlet is the external cause of the induced air generated by the coal crusher. Due to the lax sealing at the outlet of the feeder, the feeder groans. The coal chute at the inlet of the coal crusher groans. The coal crusher groans. The coal chute at the outlet of the coal crusher groans to form an open circulation system. A large amount of air enters from the outlet of the feeder and is driven by the rotor of the coal crusher to eject from the outlet of the guide chute

2.5 dust generated by coal accumulation in the tail drum

the original empty section cleaner in front of the tail drum was removed after being damaged, so that the pulverized coal adhered to the belt could not be removed, and was brought into the tail drum, which became fine powder under the rolling of the tail drum to form dust

2.6 dust generated by large belt jitter

uneven wear of belt comb idler aggravates belt jitter, resulting in dust

2.7 the rear buffer idler of belt conveyor was originally an elastic support type buffer idler due to poor selection of the rear buffer idler. Its cushioning principle is to use the elastic deformation of the support to cushion the impact of coal flow on the coal conveying belt. When the coal flow impacts, the buffer idler support deforms, the belt and buffer idler move downward, a gap is generated between the coal baffle of the guide chute and the belt, and dust is ejected from the air gap

2.8 the original guide chute has a flat top, and the front section is sealed by a single-layer curtain. There are some shortcomings, such as small buffer volume, easy to form micro positive pressure in the rear section, large outlet air volume, high wind speed, and easy dust accumulation on the top

3. treatment scheme

the main reasons for dust generation at the outlet of the coal crusher are the induced air generated by the blowing effect of the coal crusher rotor and the induced air generated by the large drop of the coal chute, followed by the air gap generated by the buffer deformation of the tail buffer idler, and the induced air generated by the coal crusher and the coal flow makes the guide chute positive pressure. If the guide chute is simply blocked, it will inevitably cause the positive pressure of the guide chute to further increase, and finally eject from a thin weak link. If only adding water spray at the outlet of the guide chute is considered, the dust of small particles can be suppressed, but the larger particles entrained by the induced wind cannot be eliminated. Therefore, when considering the dust control plan, we should follow the principle of making good use of the situation, develop a variety of plans at the same time, and carry out comprehensive treatment in an all-round way

3.1 block the feeder and reduce the inlet air volume of the coal crusher

3.1.1 a certain amount of sealing coal is reserved in the buffer coal hopper to prevent mutual air channeling between the feeder and the buffer coal hopper

3.1.2 the sealing canvas of the feeder chute should be checked regularly, and it should be replaced in time if it is found damaged

3.1.3 the joint between the feeder chute outlet and the coal crusher inlet shall be fully sealed with canvas or adhesive tape

3.1.4 the observation hole door of the feeder shall be made into a sealed door

3.1.5 the inlet and outlet coal chute of coal crusher and its flange joint surface shall be comprehensively repaired and blocked

3.2 transform the guide chute

3.2.1 remove the flat cover plate of the original guide chute and replace it with an arc arch cover plate to increase the volume of the guide chute, relieve the positive pressure of the guide chute and reduce the dust accumulation on the top of the guide chute

3.2.2 extend the length of the guide chute, increase the gas flow range, and use the natural attenuation of wind pressure and wind speed to achieve the effect of natural deposition of dust. The original length of the belt conveyor guide groove is 8m, but now it is transformed to 14m. From the perspective of governance practice, this method has the best effect

3.2.3 the guide chute is equipped with multi-stage dust curtain. Removable dust curtains are installed at the top of the guide chute every 2m. The material is vulcanized rubber plate with a layer of nylon belt core. Ordinary raw rubber plate is easy to tear and not wear-resistant. The thickness of rubber plate is about 3mm. The rubber plate is too thick, not rigid, and easy to deform elastically; If it is too thin and inelastic, it is easy to be washed away by airflow. In this transformation, the guide chute is installed with 13 level dust curtain. After the transformation, the air flow passes through the friction attenuation of the dust curtain, and the outlet wind speed is attenuated from the original M/s to almost zero. There is basically no wind at the outlet of the guide chute, and there is no obvious granular dust on the outlet ground. From the perspective of treatment practice, this scheme is the preferred scheme for dust reduction

3.3 add water spray to further reduce dust

3.3.1 install five PCL nozzle models (aperture 4mm, fog dispersion angle 120) in the guide chute, which are controlled by the solenoid valve model 075-dv. Practice has proved that after water spray, a wet protective film is formed on the surface of coal to inhibit dust leakage

3.3.2 three models of PCL nozzles shall be installed at the outlet of the feeder chute. The feed chute of the feeder is wide, and the coal seam here is thin. If spraying is installed here, the moisture in the coal can be 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 in the crushing process of the coal crusher can also be reduced

3.4 replace the buffer idler at the tail of the belt conveyor, and install a cleaner on the comb idler

3.4.1 replace the original spring plate buffer idler with a buffer idler with a fixed support

3.4.2 replace the severely worn comb shaped supporting rod to reduce belt jitter

3.4.3 gather rare earth scientific research force and install a reverse belt cleaner before the tail roll

3.5 the guide chute is equipped with a bag type dust collector to reduce the positive pressure of the guide chute. One lzz-35 bag type dust collector is installed in the middle of the guide chute of each belt conveyor, and the air volume of the dust collector is 810000 m3/h

4. Experience summary

the dust concentration at the outlet of the coal crusher has been greatly reduced after treatment. According to the detection of relevant departments, the dust concentration at the outlet has been reduced from 64.1mg/m3 before treatment to 2.2mg/m3, which is lower than the national standard of 10mg/m3, and the on-site environment has been greatly improved. Through actual operation, I have the following three experiences

4.1 for the dust caused by large drop and induced wind, the treatment scheme of expansion of guide chute and dust curtain should be adopted. This scheme has low cost and obvious effect. The disadvantages are that the dust curtain wears fast, the replacement cycle is short, and the maintenance is large

4.2 for dust caused by low surface moisture and fine coal particles, water spray dust suppression scheme should be adopted. The inadequacy of this scheme is that the amount of water spray is not suitable to be controlled, which often leads to large water content in coal. In winter, water pipes are easy to freeze and crack, and there are seasonal use problems

4.3 when choosing the bag type dust collector, its air volume should be greater than 1.25 times the dust air volume. If the air volume of the dust collector is too small, it is difficult to form negative pressure. The effect of bag filter is good in the initial stage of use. After a period of use, the bag is easy to harden, the ventilation rate is reduced, the efficiency is reduced, and the bag is not easy to clean

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