Industrial production is the main cause of dust generation. When the dust reaches a sufficient concentration within a certain range, it will cause an explosion if it encounters a fire source, and the consequences are unimaginable.
In order to avoid the occurrence of such problems, reasonable and feasible explosion-proof measures must be taken to improve the safety of dust explosion hazardous areas, and fundamentally reduce or even eliminate the occurrence of dust explosion.
1.What is an explosion-proof dust collector?
Explosion proof dust collector is a kind of dust removal equipment specially designed for explosive environment. Its main function is to control the dust generated in the process of industrial production and clean production sites.
Explosion proof dust collector can prevent industrial dust explosion from causing damage and control the impact caused by dust explosion within a controllable range. In general, explosion-proof dust collectors are used after dust explosion, but there are also some things that are used before dust explosion, that is, within a few microseconds before the dust explosion is detected, the dust collectors are quickly reinforced or the sparks are extinguished. This is called explosion-proof dust collectors.
The explosion-proof dust collector is different from the conventional dust removal function in structure, function and operation. It adopts a variety of explosion-proof design and safety measures to ensure safe and effective operation in potentially explosive environment. For example, the use of explosion-proof motors, explosion-proof appliances, explosion-proof valves, etc., can effectively prevent dust and harmful gases from entering the electrical load, thus preventing the occurrence of explosion hazards. Equipped with efficient filter materials and filtration technology.
2. Design principle of explosion proof dust collector
（1）Pressure relief device design
The original intention of explosion-proof design is to extinguish the combustible explosion in the initial stage and avoid the occurrence of explosion. In case of explosion, the pressure relief device in the dust collector can also effectively deal with it. During the design of the pressure relief device, the explosion relief pressure should be set at half of the design pressure of the bag chamber of the dust collector, that is, 5-7.5kpa. When the pressure reaches 10KPA, the staff need to open the pressure relief device for pressure relief.
A certain tilt angle shall be designed on the side of the dust remover to prevent air from entering. During the pressure relief process of the device, due to a certain tilt angle on the side, the device can automatically reset by its own gravity. In addition, in order to enable the dust collector to quickly relieve pressure, enough space should be reserved in the design process, and the position of the pressure relief port should be carefully considered, such as connecting the exhaust port with the outdoor safety pressure relief device by pipeline.
（2）Explosion venting device
The explosion relief device is designed to ensure the safe production of the system. The device mainly includes explosion-proof safety valve, explosion-proof diaphragm, heavy hammer safety valve and shrapnel type explosion relief device. In addition, it is also necessary to set up platforms and railings under the pressure relief device, in which the platform can only be used during maintenance, so the staff can use chains to block the platform at ordinary times, and set warning signs to prohibit the staff from passing freely.
（3） Determination of air volume, air pressure and wind speed
The air inlet device of the dust remover is composed of the lower air duct, the air volume control valve and the rectangular air inlet pipe. In the process of designing the air inlet pipe, the design design needs to comprehensively consider the negative pressure resistance of the air duct wall plate, and the air volume control valve can be used as a factory pass. Generally, the thickness of the valve plate of the dust arrester is controlled at about 5mm, and the wind speed of the main pipe should be able to effectively reduce the dust concentration in the pipe and avoid accumulation. Generally speaking, the wind speed of the wood dust main pipe is not less than 20m/s, and the wind speed of the magnesium aluminum dust main pipe is not less than 23m/s. The wind speed at the hood shall be determined according to the specific materials and operation mode.
（4） Adoption of inerting device
When the dust collector uses inert gas as the medium, the control of the internal oxygen content of the dust collector should be strengthened. The flow of powder filled in the central dust removal system shall not be greater than 50% of the lower explosion limit. After the inerting device is added to the dust remover, an explosion-proof device with monitoring function shall be added, which can automatically alarm in case of abnormal operation.
（5）Automation design and detection alarm interlocking function
The automatic design and detection alarm interlock function is an indispensable function in the dust explosion-proof system. When the system finds that there is a potential danger nearby, this function will send the alarm information to the mobile fracture through the central control system, and prevent the occurrence of dust explosion.
3.Precautions for dust collector in inflammable and explosive places
In the process of using the dust collector, many dusts are flammable and explosive. In addition to improving the fire and explosion prevention measures in the workshop of the production enterprise, it is also necessary to carry out special treatment on the dust collector to increase the explosion-proof capacity of the dust collector, so as to ensure the normal operation of the dust collector and ensure the safety of production.
Dust containing a large amount of CO and H2 is inflammable and explosive. We all know that in addition to these, most of the dust produced by all combustible materials are inflammable and explosive dust, such as flour, pulverized coal, sawdust, cotton staple fiber, etc., and even some metal powders are prone to explosion under specific conditions, such as aluminum powder, etc.
In the dust removal process of these inflammable and explosive dusts, the reliable airtightness of the dust removal equipment must be achieved to prevent air inhalation or gas leakage, so as to ensure the safe operation of the system in a stable environment.
In addition, the dust collector itself should also follow certain principles in design to achieve its own explosion-proof. The main safety measures are as follows:
(1)Safety and explosion-proof measures for dust collector
- In terms of dust collector structure: the bag type dust collector used to process combustible gas is usually designed as a circular type to increase the smoothness of dust flow and avoid excessive accumulation of dust.
- The dust collector adopts fire-proof and explosion-proof dust collection bag, and the pressure relief device is added.
- The dust collector shall ensure continuous dust removal and avoid dust deposition.
(2)Pipeline safety valve of dust removal equipment
- The flue gas pipeline shall avoid dead corners as far as possible to ensure that the pipeline is unblocked; And increase the air velocity to prevent gas retention.
- A safety valve is set on the front pipe of the fan so that the pressure can be released in case of gas explosion.
- The upper safety valve is often located at the top of the flue. During normal production, the gland shall be buckled down and sealed with a water seal with a height of 250mm; in case of fierce combustion in the flue and the pressure is greater than the weight of the gland, the gland shall be rushed open in an emergency to relieve the pressure.
- The lower safety valve is set in front of the machine. During normal production, the gland closes the pressure relief hole under the action of the hammer. The pressure relief hole is welded with a thin copper plate. In case of explosion, the gas will break through the copper plate and open the gland for pressure relief.
4.What are the explosion control measures for dust removal system?
During the daily operation of the dust removal equipment, some safety problems will be encountered, especially in places with inflammable and explosive dust such as woodworking factories. Therefore, the dust removal system needs to be equipped with explosion-proof and explosion control equipment. The explosion control measures of the dust removal system mainly include:
1. The filter bag material shall be selected according to the nature of the dust gas. When dealing with the dust gas, if the high temperature gas is encountered, the dust removal filter bag with high temperature resistance, corrosion resistance and low flammability shall be used. If inflammable and explosive dust is encountered, the material of the filter bag should be high temperature resistant and non combustible.
2. In case of combustion or sparks splashing, a combustion chamber or spark spreader can be set in front of the dust remover to completely burn the incompletely burned dust and gas.
3. When using dust remover for dust removal, explosion-proof motor equipment should be installed on the dust remover, and alarm equipment must be installed for combustible gas treatment.
4. Explosion proof pressure relief openings shall be set at the necessary places of the dust removal system to avoid explosion due to excessive pressure. Lightning protection measures shall be taken and lightning rods shall be installed outdoors.
5. To avoid sparks caused by debris in the air flow impacting the impeller and casing, the fan should be installed behind the dust removal equipment.
6. Pay attention to the hygiene and tidiness of the workshop to avoid dust spontaneous combustion or explosion due to the accumulation of dust in the workshop and dust inside the dust collector.
5、 How to improve the explosion-proof ability of dust removal equipment?
Many dusts are flammable and explosive. Therefore, to increase the explosion-proof ability of dust removal equipment, the following aspects should be taken into account:
1. In the process of dust removal, the dust removal equipment should have reliable airtightness to prevent air inhalation or gas leakage, so as to ensure the safe operation of the system in a stable environment.
2. In terms of the structure of the dust removal equipment, it is recommended to design the bag type dust collector for handling combustible gases into a circular type to increase the smoothness of dust flow and avoid excessive dust accumulation.
3. Fire proof and explosion-proof dust removal bag is adopted, and pressure relief device is added.
4. Ensure continuous dust removal and avoid dust deposition.
5. The flue gas pipeline shall avoid dead corners as far as possible to ensure that the pipeline is unblocked; And increase the gas flow speed to prevent gas retention. A safety valve is set on the front pipe of the fan so that the pressure can be released in case of explosion. The upper safety valve is often set at the top of the flue and the lower safety valve is set in front of the fan.
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