The terminal ash storage of coal-fired power plants is one of the main sources of dust pollution in the plant area, and the dust phenomenon in the dry ash bulk process is the main cause of fly ash pollution in the reservoir area. Dust pollution in dry ash bulk is not only one of the ills that affect the safe and civilized production of the whole plant, but also the hardest-hit area that causes dust damage in occupational health. Through an in-depth analysis of the working process and principle of the dry ash bulk machine, the various causes of the dust phenomenon are discussed from the aspects of the design, equipment, and operation of the bulk machine.
The design reasons are as follows: the capacity of the matched dust collector or the dust blower Small, insufficient gas treatment capacity, does not match the maximum ash drop of the unloader; the radial clearance between the bulk feed tube and the dust collection sleeve is unreasonable; the axial arrangement of the ash drop tube of the bulk machine is unreasonable; bulk joint The outer cone design is unreasonable. The reasons for the equipment are: the actual air volume of the dust collector does not meet the design requirements; the gap between the bulk feeding tube and the dust collecting tube cannot be effectively maintained; the gray material level measurement and control system failure. The reasons for operation include: the amount of ash falling in the bulk machine is out of reasonable range; the responsibility of the operator is not strong; the maintenance of the equipment is not timely.
The pollution of fly ash in the coal-fired power plant area will not only affect the environment of the plant, but also affect the safe and stable operation of on-site electrical switches, rotating machinery and other equipment, or the hardest hit area caused by dust pollution in occupational health. One of the main sources of dust pollution in the plant area is the terminal ash silo. There are three common dust pollution phenomena in the ash storage area: one is the ash phenomenon caused by the damage of the filter bag of the top filter, the second is the ash phenomenon caused by the leakage of pipelines and valves in the reservoir area, and the third is the dust phenomenon during the dry ash bulk process. . Among the three types of dust pollution, the damage of the filter bag and the leakage of pipes and valves are low and easy to handle. The phenomenon of dry ash bulk dust not only occurs frequently in the daily production process but also difficult to control and control, which is the main cause of fly ash pollution in the reservoir area.
1. Dry ash bulk machine working process and principle
Dry ash bulk refers to the process of using the dry ash bulk machine to pack the fly ash collected by the terminal ash warehouse into the fly ash tanker. The dry ash bulk machine is mainly composed of a lifting mechanism, an ash drop pipe, a dust collecting sleeve, a bulkhead, and a dust remover (dust exhaust fan). When the dry ash is in bulk operation, the fly ash tanker is first driven into the working area, so that the storage tank inlet is located directly below the bulkhead, and the bulk ash tube and the dust collecting sleeve under the bulkhead are retractable hoses. The lifting mechanism can complete the lowering and rising movement of the bulkhead to adapt to the loading and unloading work of different heights.
Bulk machines generally have an automatic control function, which can be used to complete the unloading operation according to a preset program. First, the lifting device is activated, and the bulkhead is dropped above the feed inlet of the storage tank, and then the bag filter and the unloader are activated. The fly ash in the ash silo falls into the fly ash tank body through the plug-in valve, the unloader, and the feed pipe in the order of self-weight (as indicated by the thick arrow in the figure), and the dust generated by the unloading process passes through the falling The passage between the gray pipe and the dust collecting sleeve enters the bag filter and is removed (as indicated by the thin arrow in the figure). The clean air after the treatment is discharged from the air outlet of the dust collector, and the collected dust finally falls into the tanker. When the tank level reaches the specified position, the level detecting device feeds back the electric signal of the control system, immediately stops the unloader, delays the dust collector (dust exhaust fan), and opens the hoisting motor to lift the bulkhead. When the bulkhead approaches the predetermined position, the hoisting motor is turned off, thereby completing the bulk operation of the dry ash.
2. Analysis of the causes of dust in dry ash
2.1 Design reasons
(1) The capacity of the matched dust collector or dust extraction fan is too small, and the gas treatment capacity is insufficient, which does not match the maximum ash loss of the unloader. When the ash tanker enters the ash quickly, the airflow overflowing from the tank body cannot enter the bag filter in full time, and the positive pressure airflow envelops a large amount of dust to dissipate outward and causes serious dusting.
(2) The radial clearance between the bulk feeding tube and the dust collecting sleeve is unreasonable. The gap between the ash pipe and the outer casing is too small, which will cause the cross-section of the inlet duct of the dust collector to be too small, which will affect the air volume of the dust collector.
(3) The axial arrangement of the ash pipe of the bulk machine is unreasonable. The size of the ash collecting nozzle extends out of the conical dust-collecting cover. The ash-flow falling from the ash outlet and the airflow that is sucked into the dust collecting hood during the bulk process may affect the dust removal effect, resulting in a more complicated loading process. Big dust phenomenon.
(4) The outer tapered surface of the bulk joint is not designed properly. The conical bulk joints increase the positioning accuracy of the tanker, and it is difficult to ensure a tight seam between the bulk joint cone and the car can. If there is a gap between the two, it will increase the air leakage of the dust collector and affect the establishment of the negative pressure environment in the ash area, thus affecting the dust collection effect of the dust collector.
2.2 Reasons for equipment
(1) The actual air volume of the dust collector does not meet the design requirements.
If the dust collector has an inlet duct blockage, a filter bag paste bag, and a negative pressure fan head is small and affects the air volume of the dust collector, the dusty airflow overflowing when the gray tanker is filled with ash cannot enter the bag filter completely and in time, and the bulk process is carried out. Will cause dust.
(2) The gap between the bulk feed tube and the dust collector cannot be effectively maintained.
Due to the poor rigidity and the sparse spacing of the dust collecting pipe of the partial bulkhead, the flexible pipe wall is sucked instantaneously when the dust suction fan is working, so that the pipe wall is closely attached to the outer wall of the falling ash pipe, and the dust collector and the ash tank are closed. During the air passage, the air in the gray tank can not enter the dust collector smoothly, and dust will form.
(3) Gray level measurement and control system failure.
When the dry ash in the tanker is full, the level measurement and control system fails to issue a signal to stop the feed in time, causing the dry ash in the ash tank to overflow.
3. Countermeasure for dry dust in bulk dust
Through the specific analysis of the causes of dust ash in dry ash, the most important measure to prevent dust is to keep the negative pressure in the gray tank body and ensure that the dust-laden air generated in the bulk process can all enter the dust collector. Around this core, it is recommended to take measures to prevent the occurrence of dust from the following aspects.
3.1 Design measures
(1) The dust collector (dust exhaust fan) should handle the air volume to meet the requirements. There are four main considerations for the treatment of air volume: one is to consider the volume of air that the dry ash is discharged from the tank; the second is to consider the system leakage; the third is to consider the air volume caused by the thermal expansion of the air to increase sharply; the fourth is to consider enough margin to It can compensate for the decrease of the flow rate caused by the decrease of the gas permeability of the filter bag of the dust collector, the clogging of the inlet air passage, and the like.
(2) A reliable sealing device should be designed for possible leakage of bulkheads, dust collecting interfaces, etc., to prevent dust from spilling out. It is recommended to use a hemispherical joint on the lower part of the bulkhead to improve the adaptability of the bulkhead to the gray tank opening, or to design a gas rise seal to ensure that the joint is tight.
(3) There must be sufficient radial clearance between the dusting pipe of the bulk machine and the dust collecting casing to ensure the smooth flow of the air duct between the dust collector and the gray tank. It is recommended that the radial clearance be not less than 150 mm, and the cross-sectional area at the narrowest point of the annular passage is not less than the cross-sectional area of the inlet pipe of the precipitator.
(4) The ash collecting nozzle should be properly extended out of the conical dust collecting hood to ensure clear boundary between the gas path and the ash road during the bulk process, and reduce the hedging disturbance of the upward effluent to the falling ash flow, thereby reducing dust. According to the actual operating experience of the site, it is recommended that the length of the ash pipe extending out of the cone cover is not less than 80-100mm.
3.2 Equipment measures
(1) Properly reduce the spacing of the dust collecting sleeve clamping hoop to prevent the flexible pipe wall from sucking and attaching to the outer wall of the falling gray pipe when the dust suction fan is working. It is also possible to transform the dust collecting hose into rigid dust removing sleeve that can be moved and retracted, which not only ensures dust removal effect but also greatly improves the life of the dust removing sleeve.
(2) Replacing the original textile hose with a conical steel tube to replace the original textile hose to make the ash pipe, can ensure the expansion and contraction requirements of the bulkhead, and also reduce the wear of the pipe body and improve the life of the ash pipe.
(3) The lower part of the bulkhead adopts a spherical design instead of the tapered structure so that the bulkhead can be engaged with the circular feed inlet of the tanker at any angle without any gap. At the same time, the requirements for positioning accuracy of fly ash tankers have been relaxed, and the difficulty of the operator's bulkhead alignment has also been reduced.
(4) In the measurement and control device, the diaphragm pressure switch is used instead of the material level switch. Since the pressure switch can resist static electricity and can be dusty and dusty, it can ensure the accuracy of the gray material level measurement and improve the reliability of the control system.
3.3 Operational measures
(1) Parking should be accurate when unloading operation, and the bulkhead and the gray car inlet should be accurately docked without gaps. Make full use of the auxiliary sealing facilities such as the rubber pad on the bulkhead and the gas rising seal to ensure that the joint is tight.
(2) Control the speed of falling ash in a reasonable range. At the beginning of the bulk machine start-up, it is necessary to gradually load the loader load or slowly open the flapper valve to prevent the dust from being caused by the rapid expansion of the air inside the tanker; the fly-off speed should be controlled in advance to prevent the occurrence of dust. Tanker ash and dust.
(3) Strengthen the maintenance of bulk machines, timely deal with the defects of dust collectors such as blockage of dust collectors, failure of pulse injection, timely replacement of damaged telescopic hoses of bulk machines, replacement of heavily worn fan impellers, etc., to ensure the normal operation of the dust removal system.
Eliminating the dust pollution of the terminal ash storage of coal-fired power plants is of great significance to ensure the stable operation of equipment in the reservoir area, promote safe and civilized production on-site, and reduce the occupational hazards of employees. By optimizing the design, perfecting the equipment, and standardizing the operation, it is possible to eliminate the dust pollution phenomenon in the dry ash bulk process.
(1) Optimize the design.
The dust volume of the dust collector should be matched with the ash drop amount of the unloader, and a reliable sealing device should be designed in the possible leaking parts such as the bulkhead and the dust collecting interface. The axial distance and radial direction between the ash pipe and the dust collecting sleeve of the bulk machine The gap should meet the dust collection requirements.
(2) Improve the equipment.
Replace the textile hose with a tapered steel tube superimposed with a telescopic tube structure, replace the cone-shaped bulkhead with a spherical bulkhead, and replace the material level switch with a diaphragm pressure switch to improve the reliability of the bulk machine and reduce the chance of dust.
(3) Standard operation.
When the ash discharge operation is performed, the bulkhead and the ash car inlet must be docked accurately. During the start and stop of the bulk machine, the ashing speed should be properly controlled, and the equipment problems should be eliminated in time.
Contact: Ms. Jane
Phone: +86 136 0202 1569
Tel: +86-22-2944 4813
Add: Room 608 KG Building No.256 East Road Dongli District, Tianjin, China