The electric bag composite dust remover is a new generation of high-efficiency dust removal equipment that combines electric dust removal and bag filter in a box. The electric bag composite dust removal technology combines the advantages of electric dust removal and bag dust removal. The mechanism is “charged dust collection†and “intercepting filtrationâ€. In the electric field, 80% of the coarse particle dust is removed with a small energy consumption to reduce the dust load of the filter bag; the electrocoagulation between the charged dust particles improves the characteristics of the dust layer and generates a new charge. Mechanism of dust filtration characteristics: heterogeneous charge particles coagulate and form large particle dust, improve the fine particle collection rate; the same charge repels each other and rapidly spreads to form a uniform distribution of gas gel suspension, so that the dust arrangement rules on the surface of the filter bag are Order, fluffy, good gas permeability, high porosity of the dust layer, good exfoliation. Therefore, using a lower cleaning pressure (0.25 MPa), the desired cleaning effect can be achieved, thereby prolonging the cleaning cycle of the filter bag and the service life of the filter bag.
In the electric power conversion bag project, the shell structure of the original precipitator, the inlet horn, the ash discharge device, the air distribution device, and the first electric field (or the first two electric fields are retained according to actual conditions and user requirements) are generally retained or updated. Transformation. The latter electric fields will be transformed into bag dust removal areas. After the completion of the transformation, the main structural components of the electric bag composite dust collector can be roughly divided into: the dust removal part of the electric area, the dust removal part of the bag area, the outlet flue, the bypass system, the water spray cooling system of the grate cooler and other parts.
The electric-to-electricity bag project needs to consider the characteristics and functions of the major components of the entire precipitator, as well as the interaction and influence of each part, and also consider the modification of the induced draft fan directly related to the precipitator. The following mainly describes the design points of the dust removal part of the electric area, the dust removal part of the bag area, the bypass system, and the water spray cooling system of the grate cooler.
First look at the dust removal part of the electrical area. The electric dust removal part is located at the front part of the electric bag composite dust remover. Its function is to perform dust removal on the flue gas entering the dust remover, remove most of the coarse particles in the flue gas and a considerable amount of medium and small particle dust, and greatly reduce the dust entering the bag. Part of the smoke dust concentration and charge the dust particles. In the bag dust removal part, the charge force between the dust particles makes the dust layer formed on the surface of the filter bag relatively loose when the filter bag is filtered, and the filtration resistance is greatly reduced compared with the pure bag filter.
In the retrofit design of the electric zone, it is generally necessary to ensure that the dust removal efficiency of an electric field is above 80%. To achieve this requirement, the following conditions must be met: sufficient dust collection area to meet efficiency; uniformity of airflow distribution into the electric field. ; to ensure the restoration of the normal operation of the original equipment electrical area, including the adjustment of the pole spacing, the replacement of the vibrating hammer and the vibrating anvil.
The transformation of the electrical area is generally based on recovery and overhaul. For the original equipment to be used for a long period of time and the internal damage of the electrical area is relatively serious, all internal parts will be replaced to ensure the normal operation of the electrical area.
The dust removal part of the bag area includes the design of the filter bag, the blowing system, and the cleaning method. The filter bag is the core component of the dust collector. It is necessary to select the appropriate fiber material according to the composition and temperature of the flue gas. Then, according to the discharge requirements and the life of the filter bag, combined with the economy, different filter material structures are selected. Cement rotary kiln kiln bag filter can be selected from P84 (polyimide) filter material, glass fiber membrane filter material, P84 glass fiber composite felt film filter material; yoke head can be selected with Nomex or glass fiber Film filter material.
The design of the air bag adopts the principle of air bag, which can ensure the pressure loss of the air bag during injection is relatively small, but it is not suitable for the air bag from the perspective of manufacturing, installation and economy. Therefore, each air bag can be mutually The connection ensures that the instantaneous replenishment of the pressure loss during blowing reduces the volume of the air bag.
At present, the main cleaning method of the bag filter is pulse injection technology, which is mainly composed of a pulse valve, a gas bag, a blowing pipe and a pulse blowing control system. The blowing control system uses a matrix circuit to control the pulse valve by triggering the rows and columns. The advantage of this is that it saves the number of PLC output points, reduces the number of cables, and reduces the investment cost. The cleaning control mode adopts online timing cleaning, online fixed resistance cleaning, offline cleaning, online and offline combined with cleaning, and these methods are independent but coexist at the same time, and can be manually controlled and automatically controlled to switch.
Bypass system. When the system has high temperature flue gas, especially when the cement kiln head waste heat boiler is not working, it is necessary to set a bypass device on the gas path to allow most of the flue gas to pass through the bypass to protect the filter bag. Providing a bypass device on the airway requires the valve to have good airtightness, otherwise a short circuit of the smoke (as long as one thousandth of the leakage) will cause the dust collector to fail to meet the discharge standard. To achieve the "zero leakage" and maintenance-free requirements for bypass closure, an ideal way is to use a two-layer steel bypass valve with a double-deck flapper valve at a certain distance from the bypass valve baffle. The corresponding valve seat is used to achieve a double-layer rigid seal, and the valve plate and the valve seat are integrally formed during processing.
Cooling machine water spray cooling system. The kiln head electric precipitator is changed to the bag filter or the electric bag filter. The operating temperature is relatively high when there is no waste heat boiler or the waste heat boiler is stopped. In order to avoid high temperature flue gas damage to the filter bag, a water spray cooling device can be installed. A set of nozzles is arranged between the top waste heat boiler pipe and the dust collector inlet pipe on the grate cooler, and the cooling water enters the variable frequency pump through the shut-off valve of the water tank, and is sprayed from the nozzle mouth through the water inlet of the check valve, the shut-off valve, the pipe and the nozzle. Into the chiller, the amount of water injected into the nozzle can be adjusted by adjusting the speed of the pump. To prevent the nozzle from being clogged with dust when the nozzle is not sprayed with cooling water, the nozzle can be purged with compressed air on the bypass. The control of the water spray cooling device is carried out by a PLC controller according to the temperature signal on the grate cooler, and the normal temperature of the flue gas entering the dust collector is <160 °C. When the temperature rises to 180 °C, the controller should close the compressed air valve on the bypass to start the water pump. When the temperature rises to 190 °C, the shut-off valve at the outlet end of the pump is opened, and the water is sprayed from the pipe and the nozzle into the grate cooler.
Practical engineering application case
Qinghai Qilianshan 5000t/d cement kiln electric precipitator single chamber four electric field transformation before the electric precipitator inlet flue gas parameters are as follows: air volume: 730000m3 / h; gas temperature: 200 ~ 250 ° C (max400 ° C); inlet dust concentration: ≤ 30g/Nm3. After the transformation, the performance requirements of the dust collector: export discharge concentration: ≤ 20mg / Nm3; equipment running resistance: ≤ 1200Pa.
Transformation plan and implementation
1) Retain and repair an electric field internal component of the original electrostatic precipitator, repair and correct an electric field anode plate, adjust the pole spacing, and perform gas-tight repair welding on the air leakage point of the casing.
2) Remove the remaining three electric field internal components to arrange the bag filter bag, retain the original dust collector top beam, and place the air bag in the top beam, and arrange the bypass at the top of the electric field.
3) The clean air chamber adopts a large clean air chamber of 3.75 meters high, which is convenient for indoor bag change.
4) The flue is stepped. The CFD airflow simulation technology is used to determine the reasonable flue step section and the poppet valve port size. Two poppet valves are installed in each chamber to realize on-line maintenance and off-line cleaning.
5) Install a pressure transmitter in each inlet and outlet. Each pressure chamber is equipped with a differential pressure transmitter. The pressure differential pressure signal is sent to the central control display screen to monitor the operating pressure and differential pressure of the equipment in real time.
6) For the high temperature flue gas of the kiln head, the double filter bag protection device of the bypass valve system and the grate cooler water spray cooling system is added during the transformation. The start and stop of the bypass valve and the grate cooler water jet pump are controlled by the temperature control signal.
After the completion of the electric precipitator renovation project, the main engine is running well. After the transformation, the outlet concentration of the electric bag composite dust collector reached 14.98mg/Nm3, the equipment running resistance was 600~700Pa, and the pulse valve and the poppet valve operated normally.
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