Plenum Pulse Jet Bag filter is divided into several chambers, there are 32,64,96,128etc, bags in each chamber,and on each outlet pipe of the chamber is equipped with a lifting valve driven by cylinder connected to the outlet air pipe. When the bag filter processes the dusty gas for a while (or the resistance reaches the preset value), the dust cleaning controller gives a signal,the lifting valve of the first chamber will shut down to cut off the airflow, then the pulse valve of this chamber starts working, and the compressed air( above 0.5MPa )pulses into the clean gas chamber to clean the dust on the filter bags. The whole process takes 5-15 seconds , after that the lifting valve reopens, the chamber will start over to collect the dusty gas. All chambers works in the same way one by one. Due to its high efficiency of dust cleaning, plenum bag filter can be used to process high concentrated dusty gas as high as 1000g/m3.

4.1 Introduction on Pulverized Coal

The high concentrated pulverized coal is flammable and combustible in process of transporting and dust collection.The main reason for its combustion are spontaneous combustion and foreign fire source. The spontaneous combustion is caused due to following factors: environment, the concentration & fineness of the coal dust, Oxygen content in the coal dust and static electric fire. The coal dust in cement factory has following characteristics:

High Inlet Concentration. At step of secondary dust collection, the inlet concentration of coal dust collection system is always controlled below 60g/Nm3, but at the first step of duct collection, the concentration could be as high as above 1000g/Nm3, which is covered in the range of flammable and explosive.(the flammable and explosive range is 40 ~2000g/Nm3,according to international standard)

High Volatility & Granularity. Coal dust of the following characteristics Vdaf >20%,Granularity<0.1mm is quite easy for combustion and explosion,and the cement factory mostly adopts soft coal, its Vdaf is between 25~33%, 80% of the coal dust Granularity<0.08mm,it belongs to explosive dust powder.
High Moisture Content. If it’s dry mill system, the exhaust gas must contains moisture, the dew point is between 50~55℃,very easy for dew formation.
The heat source for dry mill is generally from kiln head after-wind or air heater, these heat source may cause combustion due to open fir it may contain.
4.2 special design for anti-explosion and anti combustion
Due to flammable and explosive of raw coal and the tender’s technical data requirement, we specially design the coal dust collection system.
Special Design on Filter body
In order to avoid the coal dust accumulation inside the bag filter. All beams and separation boards are designed with dust shield with its angle >70℃. The wide angle avoids the dust accumulation. In order to avoid the improper operation and dew formation caused by high humidity, the heat preservation and moisture preservation should be done at the same time.
Anti-static filtering materials.
The high concentrated dusty gas may cause static electricity due to friction with filter bags.the accumulation of statics may cause open fire and combustion.the anti-static filter bags material avoid the above mentioned phenomenon, meanwhile,the bag filter body should contact with ground, ground resistance <4Q.
Anti-explosion Safety Door.
There’s a safety door in each chamber, before explosion the door could automatically open to relief pressure, the volume could be adjusted to ensure the safe working of the whole equipment.
High efficiency dust cleaning system.
As per our ten years experience, we are very clear that the normal reverse-blowing dust cleaning system can not work efficiently for high concentrated dusty gas. Due to the high concentration, the dusty gas is very easy to accumulate on the outside surface of the filter bags, in order to reduce the time its staying on the bags,we need to shorten the dust cleaning period, enlarge the cleaning strength, hence we adopts high pressure air pulse cleaning(high pressure sir 5-7kg/cm3) to clean the bags one by one, at the same time,the venturis on each bag enlarges the air flow volume, which helps to clean the filter bags effectively in short time.
Good Leakproof-ness,Minimum Air Leakage Rate.
Because the dust collection system works under negative pressure, the leakproof-ness directly influences the Oxygen content in the equipment, hence the requested air leakage rate<3% to avoid the explosion.
Safety Inspection and Warning.
A. Over temperature warning system
It designed with temperature measure thermistor, when the inlet duct or hopper’s temperature reached the limited value, the control system will give warning signals, and automatically the equipment stops working, fire extinguishing or cooling measures will be taken.
Equipped with CO2 or N2 fire extinguishment system
When the internal temperature exceeds the normal value,or its CO content passes 300ppm, the fire extinguishment system will start automatically to lower down the equipment internal temperature for equipment protection. But if it’s pulverized coal combustion caused temperature rise and CO content enrich,there will be an alarm, the CO2 or N2 fire extinguishment system will start automatically to stop explosion.