When selecting the filtering wind speed for a bag filter, if using a bag filter with a counter blowing air for dust cleaning or a bag filter with offline pulse dust cleaning, the filtering wind speed should be the net filtering wind speed, which should be noted. As a widely used dust removal equipment in industrial dust removal, bag filter has played a significant role in dust collection and treatment in boiler plants. It is an important equipment for controlling industrial dust. The start-up operation of bag filter has a direct impact on the operation status and dust removal effect of the equipment. Only by correctly operating the equipment and ensuring stable operation can a good dust removal effect be achieved.
The structure of a bag filter consists of upper, middle, and lower boxes, an ash discharge device, and a spray cleaning system. It mainly includes a dust removal and cleaning air box, a dust removal box, an ash hopper, an inlet air flow device, a filtration unit, a spray cleaning system, an ash unloading system, a bracket, a ladder, a guardrail, a lighting system, an over temperature display, a fault alarm system, and a PLC microcomputer control system.
The control system of bag filter is mainly designed in seven aspects:
1、 Differential pressure detection: The differential pressure transmitter is used to detect the pressure difference between the inlet and outlet of the bag filter, and sends a standard 4-20mA signal to the PLC analog input module for pulse valve selection of injection program and monitoring of the operating resistance of the bag filter.
2、 Selection of pulse valve spraying program: The bag filter has 4 bag bundles, totaling 4 pulse valves. There are two modes of injection for the four pulse valves: timing injection mode and differential pressure injection mode. When the rotary switch on the control cabinet door selects the "differential pressure" mode, the pulse valve automatically selects the blowing program based on the pressure difference detected by the differential pressure transmitter.
3、 Main control equipment: 2 inlet and outlet baffle valves, 4 rotating motors, 4 large-diameter pulse valves, 2 Roots blowers (1 in use and 1 backup), and 6 silo wall vibrators. 1 pressure transmitter, 1 differential pressure transmitter and other testing equipment.
4、 Control of entrance and exit baffle doors: The opening and closing of the baffle doors are driven by an electric head. The electric head configured for this project is an integral structure, which has the advantages of low failure rate and fewer peripheral circuits.
5、 Control of warehouse wall vibrator: The warehouse wall vibrator has two control modes: "nearby" and "remote". The nearby mode is completed on the machine side operation box and is offline manual. The remote mode is controlled by PLC, and the status signal is sent to PLC for display on the upper computer.
6、 Control of Roots blowers: Each dust removal unit is equipped with two Roots blowers, one for backup and one for use, providing air source for the blowing system. The Roots blower occupies a very important position in the entire bag dust removal equipment. To prevent unauthorized operation by non staff, the control of the Roots blower is divided into two control modes: manual control and remote automatic control. An emergency stop button box is installed next to the machine.
7、 Control of rotary motor: Rotary blowing is a process in which a rotary motor drives a reducer to slowly rotate a rotating rod. The rotating rod has four rotating arms that form a 90 degree angle with each other at the same level near the end of the flower board. Each rotating arm has a different number of nozzles for blowing clean air.
The bag filter should be started using the following methods:
1、 Power on the ash hopper heater 24 hours before starting.
2、 Bring the boiler online (using normal boiler start-up procedures).
3、 When the exhaust temperature of the dust collector reaches 120 ℃, start opening the subsequent compartments until all compartments are open.
4、 Set the dust collector's cleaning mode to automatic offline cleaning mode.
5、 Drive all inlet and outlet lift valves and butterfly valves, leaving them in the open position.
6、 Close the bypass lift valve.
7、 Close the inlet and outlet lift valves of the first four compartments.
8、 Turn off the automatic dust cleaning mode. At this point, as much ash as possible should be left on the filter bag.
The upper box of the bag filter includes a liftable top cover and an air outlet. There are flower boards and filter bag components inside the middle box. The lower box has an ash hopper, air inlet, and maintenance door. The dust discharge device of the bag filter is a rotary discharge valve. The spray cleaning system consists of a pulse controller, an electromagnetic valve, a spray pipe, and an air bag.