1. What is an Explosion-Proof Dust Collector?
An explosion-proof dust collector is specialized equipment designed for use in explosive environments. Its primary function is to control dust generated during industrial processes and clean production areas.
Explosion-proof dust collectors prevent harm caused by industrial dust explosions by containing the effects within a controllable range. Typically, these collectors act after a dust explosion has initiated; however, some act before an explosion occurs—detecting an imminent explosion within microseconds and rapidly reinforcing the collector or extinguishing sparks. These are also classified as explosion-proof dust collectors.
Explosion-proof dust collectors differ from conventional dust collectors in structure, function, and operation. They incorporate various explosion-proof designs and safety measures to ensure safe and effective operation in potentially explosive environments. For example, the use of explosion-proof motors, explosion-proof electrical equipment, and explosion-proof valves effectively prevents dust and hazardous gases from entering electrical components, thereby avoiding explosion risks. They are also equipped with high-efficiency filter media and filtration technologies.
2. Design Principles of Explosion-Proof Dust Collectors
(1) Pressure Relief Device Design
The primary goal of explosion-proof design is to suppress combustible material explosions in their initial stages, preventing the explosion from occurring. If an explosion does happen, the pressure relief device in the dust collector can handle it effectively.
During the design of the pressure relief device, the burst pressure should be set to half the design pressure of the dust collector baghouse, i.e., 5-7.5 KPa. When the pressure reaches 10 KPa, personnel need to activate the pressure relief device to release the pressure.
The sides of the dust collector should be designed with a certain incline. This design prevents air ingress. During pressure relief, due to the inclined sides, the device can automatically reset using its own gravity. Additionally, to enable rapid pressure relief, sufficient space must be reserved in the design, and the location of the pressure relief port must be carefully considered—for example, connecting the exhaust port to an outdoor safety pressure relief device via piping.
(2) Explosion Venting Device
The purpose of the explosion venting device is to ensure safe production within the system. This device mainly includes explosion-proof safety valves, explosion-proof diaphragms, weight-type safety valves, and spring-type explosion venting devices. Furthermore, a platform and railing should be installed below the pressure relief device. The platform is only used during maintenance, so it should normally be blocked off with chains and warning signs to prohibit unauthorized access.
(3) Determination of Air Volume, Pressure, and Velocity
The air intake device of the dust collector consists of a lower air duct, an air volume regulating valve, and a rectangular intake duct. When designing the intake duct, the designer must comprehensively consider the negative pressure resistance of the duct wall panels. The air volume regulating valve can be a standard factory component. Typically, the valve plate thickness for dust explosion protectors is about 5 mm. The main duct air velocity should effectively reduce the dust concentration inside the pipeline to prevent accumulation. Generally, for wood dust, the main duct air velocity should not be less than 20 m/s, and for magnesium/aluminum dust, it should not be less than 23 m/s. The hood face velocity should be determined based on the specific material and operation method.
(4) Use of Inerting Devices
When the dust collector uses inert gas as a medium, control over the internal oxygen content should be strengthened. The flow rate of powder injected into a central dust collection system should not exceed 50% of the lower explosion limit. After installing an inerting device in the dust collector, an explosion-proof device with monitoring functionality should be added. This device can automatically sound an alarm if abnormal operation is detected.
(5) Automated Design and Detection-Alarm Interlock Function
The automated design and detection-alarm interlock function are indispensable in dust explosion-proof systems. When the system detects potential hazards nearby, this function sends alarm information to a mobile terminal via the central control system and helps prevent dust explosions.
3. Precautions for Dust Collectors in Flammable and Explosive Environments
During the use of dust collectors, many types of dust possess flammable and explosive characteristics. Apart from production workshops enhancing fire and explosion prevention measures, the dust collectors themselves require special treatment to increase their explosion-proof capability, ensuring normal operation and production safety.
It is well-known that dust containing large amounts of CO and H₂ is flammable and explosive. Beyond these, dust generated from most combustible materials is generally flammable and explosive, such as flour, coal dust, wood chips, and textile fibers. Certain metal powders, like aluminum powder, can also explode under specific conditions.
During the dust collection process for these flammable and explosive dusts, reliable airtightness of the dust collection equipment is essential to prevent air ingress or gas leakage, ensuring the system operates safely under stable conditions.
Additionally, the dust collector’s design should adhere to certain principles to achieve inherent explosion-proofing. The main safety measures are as follows:
I. Safety and Explosion-Proof Measures for Dust Collectors
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Dust Collector Structure: Baghouse dust collectors handling combustible gases are often cylindrical to improve dust flow and prevent excessive accumulation.
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Use fire-resistant and explosion-proof filter bags and install pressure relief devices.
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Ensure continuous dust cleaning to prevent dust deposition.
II. Safety Valves in Dust Collection System Ductwork
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Avoid dead angles in flue ducts to ensure smooth flow; increase air velocity to prevent gas stagnation.
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Install safety valves on the ductwork before the fan for emergency pressure relief in case of a gas explosion.
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Upper safety valves are typically located on the top of the flue. During normal operation, a cover is sealed with a water seal (250 mm high). In case of intense combustion inside the flue, pressure exceeding the cover’s weight forces it open for pressure relief.
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Lower safety valves are installed before the fan. During normal operation, a cover closes the relief port under the force of a counterweight. The port is welded with a thin copper plate. In an explosion, the gas ruptures the copper plate and opens the cover for pressure relief.
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4. What are the Explosion Control Measures for Dust Collection Systems?
During daily operation, dust collection equipment can face safety issues, especially in places like woodworking factories where flammable and explosive dust is present. Therefore, dust collection systems need explosion-proof and explosion control equipment. The main explosion control measures for dust collection systems include:
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Select filter bag materials based on the dust/gas properties. For high-temperature gases, use filter bags resistant to high temperatures, corrosion, and with low flammability. For flammable/explosive dust, choose materials that are high-temperature resistant and non-combustible.
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Install a combustion chamber or spark trap before the dust collector to allow complete combustion of incompletely burned dust and gases when encountering combustion or sparking.
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Use explosion-proof motor equipment on the dust collector. Install alarm systems when handling combustible gases.
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Install explosion-proof pressure relief vents at necessary points in the system to prevent explosions from overpressure. If installed outdoors, implement lightning protection measures like lightning rods.
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Install the fan after the dust collection equipment to prevent sparks generated by debris impacting the impeller or casing within the airflow.
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Maintain workshop cleanliness and tidiness to prevent dust accumulation in the workshop and inside the dust collector, which could lead to spontaneous combustion or explosion.
5. How to Improve the Explosion-Proof Capability of Dust Collection Equipment?
Since many types of dust are flammable and explosive, enhancing the explosion-proof capability of dust collection equipment primarily involves the following aspects:
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Ensure reliable airtightness of the dust collection equipment during operation to prevent air ingress or gas leakage, ensuring safe operation in a stable environment.
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Regarding equipment structure, design baghouse dust collectors handling combustible gases in a cylindrical shape to improve dust flow and prevent excessive accumulation.
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Use fire-resistant and explosion-proof filter bags and install pressure relief devices.
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Ensure continuous dust cleaning to prevent dust deposition.
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Avoid dead angles in flue ducts to ensure smooth flow; increase air velocity to prevent gas stagnation. Install safety valves on the ductwork before the fan for emergency pressure relief in case of an explosion. Upper safety valves are typically on the flue top, and lower safety valves are before the fan.
