The main points of explosion-proof design of dust collector

1.1 pulverized coal temperature

Different coal types have different ignition temperatures, but for finer coal powder, due to the increased specific surface area, the explosion temperature is much lower than its ignition point. Usually the ignition temperature is below 40 ℃.

1.2 Volatile matter of pulverized coal

The combustible gas produced by the heating of pulverized coal is burned before the coke. Under the same conditions, the higher the volatile content, the more violent the explosion of pulverized coal. Usually measured by the pulverized coal explosion index Ur, when U`>20%, the explosiveness of pulverized coal increases greatly.

1.3 Concentration of pulverized coal

Only when the concentration of pulverized coal in the air reaches a certain level, an explosion will occur. The lower limit concentration of pulverized coal-air mixture explosion is 20-309/m³, and the upper limit is 2000-70009/m³. There is no explosion hazard at concentrations outside the two limits.

1.4 Particle size of pulverized coal

The finer the pulverized coal, the easier it is to spontaneously ignite and explode. According to the data, when the fineness of the pulverized coal is greater than 0.1mm, almost no explosion will occur.

1.5 Ash and water content of pulverized coal

The higher the ash content in pulverized coal, the weaker the explosiveness; the greater the moisture content, the less likely it is to explode.

1.6 Fire source

1.6.1 Spontaneous combustion after pulverized coal accumulation

In the pulverized coal preparation system (including pipelines and equipment), due to unreasonable structural design and improper process layout, pulverized coal is slowly accumulated and spontaneous combustion occurs.

1.6.2 Entrainment of Mars in the system

Like Mars entrained in hot air.

1.6.3 Static electricity produces sparks

In the system, the pulverized coal particles collide with the pipe wall and the box, resulting in electrostatic sparks.

Among the preventive measures, it can be divided into positive measures and negative measures; positive measures include the use of inert gas, explosion-proof structure design and correct operation and maintenance; negative measures are mainly to set explosion-proof valves and fire extinguishing devices.

2.1 The “inert” gas coal mill system is generally arranged at the end of the rotary kiln, and adopts open-circuit negative pressure operation, and uses the exhaust gas discharged from the rotary kiln as the drying medium. This gas has a low oxygen content (can be regarded as an inert gas), which can play an explosion-proof role; if the temperature of the exhaust gas is insufficient, which affects the drying of the coal in the coal mill, the exhaust gas can be properly heated to increase the temperature in the mill.

2.2 Adopt explosion-proof structure design The structure design must meet the explosion-proof requirements.
Specific measures include:

(1) No dust accumulation plane is allowed inside the dust collector. When designing, the inclination angle of each place is greater than 70, and the pulverized coal will not deposit and cause spontaneous combustion;

(2) The ash hopper adopts a large-angle elongated structure. The amount of ash stored in the ash hopper is very small, and the ash discharge valve uses a flap to discharge ash to reduce the possibility of coal powder fire caused by friction and heat;

(3) Choose antistatic filter material. The filter bag is connected to the dust collector shell through the skeleton, and the static electricity generated on the filter bag is introduced into the ground through the metal wire in the filter material, which effectively prevents the possibility of sparks from static electricity;

(4) Set up a pressure relief device. A pressure relief device is added to the dust collector. Once the pressure rises to a certain limit, the pressure relief device is activated to release the pressure. Usually the pressure of explosion-proof valve is 1kg/cm²;

(5) Equipped with advanced microcomputer control system. In the control system, multi-point detection is adopted for the key parameters of operation such as pressure and temperature, and the alarm is indicated in time.

2.3 Reasonable operating procedures

Operation management is also an important part of explosion-proof measures, and a reasonable operation system can minimize the possibility of explosion.

(1) After the dust collector is put into operation, the normal operating temperature and pressure should be determined. Generally, the temperature is controlled between 50 and 60 °C, and the pressure is controlled between 700 and 800 Pa;

(2) Select the best cleaning cycle and cleaning time according to the resistance change to reduce the system resistance, improve the dust collection efficiency and prolong the life of the filter bag;

(3) Excessive ash accumulation is not allowed in the ash hopper of the dust collector, and the number of times of cleaning and unloading should be consistent;

(4) During normal operation, the inspection door cannot be opened to prevent the dust-containing gas in the dust collector from exploding in the air;

(5) The explosion-proof valve is an important part of the dust collector. The material and structure of the explosion-proof valve should not be changed at will, and the explosion-proof diaphragm should be checked regularly.