Dust explosions occur when dust particles suspended in the air come into contact with oxygen and undergo a rapid oxidation reaction under specific conditions. This reaction releases a large amount of heat, resulting in high temperatures and pressures, which can be extremely dangerous.
Conditions for Dust Explosion
Four key conditions must be met for a dust explosion to occur:
1.Combustible Particles: The dust particles must be small enough and distributed in a cloud-like state at a sufficient concentration.
2.Oxidizing Agent: There must be enough oxygen to support combustion.
3.Ignition Source: There must be a sufficient energy ignition source.
4.Enclosed Space: A closed space must exist to support the explosion.
Anti-Explosion Measures
The goal of anti-explosion measures is to extinguish combustible materials within the equipment at the initial stage. This action prevents excessive explosion pressures. A successful suppression system can activate when the explosion pressure reaches 10 kPa, ensuring that the maximum pressure inside the equipment remains below 100 kPa. If an explosion occurs, explosion venting is the most reliable and economical method to protect bag filters. The most common form of explosion venting is through explosion venting devices.
1. Explosion Prevention Measures
Effective measures to prevent dust explosions primarily involve using a good dust collection system to control and prevent dust accumulation. Specific measures include:
- Preventing Dust Accumulation in Pipes: Ensure that there is no dust buildup in the pipes.
- Strictly Controlling Ignition Sources: Avoid open flames, hot surfaces, welding, cutting, and electrical sparks.
- Using Inert Gases: Reduce oxygen concentration to prevent explosions. Although effective, this method may be difficult to implement in some situations and requires significant investment.
2. Structural Design Measures
Special structural designs can help prevent combustible dust accumulation inside the dust collector. All beams and partitions should have dust covers. The cover angle should be less than 70°, and the hopper's slope should be greater than 70°. To eliminate dust accumulation due to small angles between hopper walls, adjacent side panels should be welded with material slides. Additionally, designers should consider adding heating elements to prevent blockages caused by improper operation or high humidity. Each hopper should also have wall vibrators or air cannons to prevent dust buildup.
Dust collectors can have anywhere from 1 to 12 hoppers, which may lead to uneven airflow. To address airflow distribution issues, consider the following solutions:
1.Add baffles to the airflow duct.
2.Use adjustable valves between the lifting valve rod and valve plate to accommodate changes in the working environment.
3.Install airflow regulation valves in the inlet branch to adjust airflow in each chamber, keeping the difference within 5%.
3. Equipment Grounding and Explosion-Proof Components
Due to safety requirements, explosion-proof dust collectors often operate outdoors. Grounding and lightning protection become essential measures. However, dust collectors typically do not have lightning rods.
Choosing explosion-proof components is crucial in explosion prevention. Dust entering electrical load components can induce explosion risks. During operation, electrical load components may generate electric sparks due to current transmission. This can easily trigger an explosion in the presence of dust. Therefore, all electrical load components must be explosion-proof. This measure eliminates potential explosion risks and ensures safe operation. For instance, the pulse valves and lifting valves of pulse dust collectors must be explosion-proof.
4. Static Electricity Protection Measures
Within the dust collector, high concentrations of dust can generate static electricity through friction. This static charge can lead to sparks and potential fires. To mitigate static hazards, use conductive materials in filter bags. For example, embed conductive metal wires or carbon fibers in polyester needle felt to discharge accumulated static.
5. Detection and Fire Prevention Measures
To prevent incidents before they occur, implement necessary fire prevention measures in the dust collection system:
- Firefighting Facilities: Common options include water, CO2, and inert extinguishing agents. Cement plants typically use CO2, while steel mills may employ nitrogen.
- Temperature Detection: Install thermometers at the inlet of the dust collector to monitor temperature changes. If the temperature rises abnormally, the system should trigger an alarm.
- CO Detection: In large dust collection systems, it may be challenging to monitor temperature changes across all locations. Therefore, install a CO detection device at the dust collector outlet or hoppers to monitor for combustion signs.
6. Explosion Venting Devices
Use explosion venting membranes, rupture discs, and vent doors to ensure timely pressure release during an explosion. This action prevents air from entering and fueling further combustion.
Calculation of Explosion Venting Area
Calculating the explosion venting area is crucial. For dust collectors handling high concentrations of explosive dust, an insufficient venting area will not meet requirements, while an excessive area can lead to waste. Typically, the ratio of venting area to dust collector volume should remain between 1:5 and 1:50, depending on the dust's explosion index.
In design, set the venting pressure to half of the bag chamber design pressure, typically between 5 and 7.5 kPa, with a maximum of 10 kPa. When the internal pressure of the dust collector reaches this value, the venting device should activate to release pressure.
Moreover, to ensure rapid pressure release, ample space is necessary. Position the venting outlet appropriately and use pipes to direct exhaust to the outdoors for safe venting.
Selection of Accessories
1. Selection of Anti-Static Filter Materials
During operation, filter bags can generate and accumulate static electricity. This accumulation can attract dust, leading to a layer of dust that may reach 0.5 to 2 mm thick. The discharge of static electricity can create sparks, posing a risk of dust explosions. Thus, to mitigate static hazards, ensure the filter material can release static charges through the grounded dust collector body. Incorporate conductive fibers into the filter material to enhance conductivity. These fibers can be metallic or modified synthetic fibers.
Stainless steel metal fibers (4-20 mm) offer excellent conductivity and can easily blend with other fibers. They exhibit good flexibility, mechanical strength, chemical resistance, and high-temperature tolerance, making them suitable for anti-static filter materials.
2. Explosion-Proof Pulse Valves
For pulse bag dust collectors in explosive environments, select explosion-proof pulse valves. There are two main types: one enhances the sealing of the solenoid valve, and the other integrates the solenoid pilot valve within an explosion-proof solenoid valve assembly, connecting it with air tubes.
3. Fire Extinguishing Devices
Dust collectors should include temperature warning systems and automatic fire extinguishing devices. When CO2 concentration in the air reaches 30%-40%, it can suffocate combustible materials. At 40%-50%, it can suppress gasoline vapors and other gas explosions. The CO2 automatic extinguishing device should have a fixed CO2 supply source, releasing CO2 extinguishing agents through connected pipes with nozzles.
Each hopper should also have a nitrogen protection device to prevent smoldering. This device consists of a resistance thermometer, control system, solenoid valve, and nitrogen injection pipe (1.5 in/DN32). When the temperature in the hopper exceeds the set alarm temperature (adjustable between 100-200°C), the solenoid valve opens automatically to inject nitrogen. The injection time can be adjusted from 0 to 30 minutes, controlled by a PLC.
By implementing the above preventive and safety measures, we can effectively reduce the risk of dust explosions and protect both equipment and personnel. Proper dust management in industrial operations contributes to a safer working environment.
For more information or to learn about our products, please nous contacter. Darko is committed to providing high-quality explosion-proof dust collection solutions to ensure your industrial safety.
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