Bag filter fire causes and response methods

2020-08-06

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The birth of gunpowder has accelerated the escalation of warfare from the cold-weapon era to the modern warfare with guns and bullets, which has increased the destructive power but also marked the progress of human technology!

In industrial dust removal, if the dust is not handled properly, it is equally prone to dangerous accidents with the same destructive power as gunpowder. Industrial dust has many flammable and explosive properties: dust containing large amounts of CO and H2 flammable and explosive; all combustible materials produced by the dust are flammable and explosive (flour, coal dust, wood chips, cotton staple fiber, etc.) characteristics; even individual metal powder in specific conditions are also prone to explosion, such as aluminum powder. In addition to the production plant to improve the fire and explosion-proof measures, but also need to special treatment of dust collectors, dust collectors to increase the explosion-proof capacity, not only to ensure the normal operation of dust collectors, but also to ensure the safety of the entire production. Today, Yi Xiaobian will talk to you about the causes and solutions of the bag filter fire.

It is not uncommon for a bag filter to catch fire in operation. In the process of dust collector operation, there are many dusts which are flammable and explosive, and the dusts not only pass through the dust collector system but also may stagnate or accumulate in various parts of the system; some dusts are spontaneously combustible or electrically charged, meanwhile, most of the filter bag materials are flammable, under such operating conditions, there is a risk of combustion and explosion accidents, and the consequences of such accidents is very serious.

First of all, we should understand the working conditions of the dust collector, and if necessary, the nature of the dust and gas should be identified by laboratory tests to determine whether the handling of dust and gas is combustible and explosive. And take the following fire and explosion-proof measures:

1. use anti-static and non-combustible materials for the filter media;

2. the arrangement of combustion chamber or spark eliminator in front of the dust collector in order to make the incomplete combustion of dust and gas complete or to sink the brought in sparks;

3. a reasonable design of the system piping and the body of the dust collector equipment to keep the system open and avoid the deposition of dust;

4. the installation of explosion-proof pressure relief devices in the necessary parts of the system;

5. the dust removal system and dust removal equipment are provided with lightning protection and grounding measures;

6. measures are taken to prevent the accumulation of static electricity, and each part is grounded with conductive materials;

7. the adoption of explosion-proof electrical equipment;

8. removal of residual accumulation of dust;

9. the dust removal system is designed as a negative pressure system to avoid sparks from the dust in the airflow hitting the impeller or casing of the fan.

We must achieve reliable dust collector containment in the process of handling these flammable and explosive dusts to prevent air inhalation or leakage of flammable gases in the process to ensure safe operation of the system in a stable environment. The dust collectors themselves all follow certain principles in their design to achieve their own explosion-proof, with the following main safety measures:

First, the bag dust collector for handling combustible gas is usually designed into a round shape to increase the smoothness of dust flow and avoid excessive dust accumulation; use fireproof and explosion-proof dust bags and increase the pressure relief device; the dust collector ensures continuous dust cleaning to avoid dust deposition.

Second, dust removal equipment pipeline safety valve: flue gas pipeline as far as possible to avoid dead ends, to ensure smooth pipeline; and improve the airflow speed to prevent the occurrence of gas stagnation; set up a safety valve in front of the fan pipeline in case of gas explosion can be emergency pressure relief; upper safety valve is often located at the top of the flue. Normal production gland buckle down to keep sealed with a water seal, water seal height of 250mm; in case of intense combustion in the flue, the pressure is greater than the weight of the gland, that is, the emergency flush open the gland to relieve pressure. The lower safety valve is located in front of the machine, under normal conditions, the gland closes the pressure relief hole, the pressure relief hole is welded with a thin copper plate. In case of an explosion, the gas breaks through the copper plate and opens the gland to relieve pressure.

If the flue gas contains oily particles, will be attached to the surface of the filter bag, when attached to a certain extent will not only affect the effect of dust removal, high-temperature flue gas through the filter bag may also ignite, if this is the case can consider the use of "pre-dusting" process to reduce the ability to attach oily particles, but also to reduce the probability of fire.

There is a special example is the shot blasting machine. Shot blasting machine group use process bag dust collector is easy to catch fire, will cause large economic losses, the main causes of fire are the following: 1:

1. rust dust is a secondary flammable solid, its ignition point and ignition energy are low. If the average particle size of rust dust is 100-150mm, the ignition temperature range is 240-439℃, which is much lower than its melting temperature. The combustibility of dust is related to its particle size, composition, concentration, heat of combustion and combustion speed, etc. The smaller the particle size, the larger the specific surface area, the easier it is to ignite. The dust produced by shot blasting is very fine, the main components are iron powder, iron oxide and dust, take the rust dust for ignition test, a little that is on, such as in the fan airflow of combustion, burning speed is very fast, while the cartridge dust collector filter material is generally paper or polyester fiber, the latter is the majority, these two materials are flammable. There are several possible situations where flammable rust dust is set on fire. The source of combustion is usually caused by incandescent particulate matter, impact and friction sparks, electrostatic sparks, etc.

2. External incendiary material is inhaled into the dust collector. Resulting in fire external hot particles are inhaled into the dust collector, igniting the internal rust dust, resulting in flammable cartridge fire combustion, welding and gas cutting sparks spark temperature are up to several hundred degrees, igniting the rust dust is easy. Shot blasting machine used in the impeller rotation speed for the general n = 2250fmin, the projection speed is greater than 80m / s, high-speed steel shot hitting the steel plate may also produce hot particles or sparks are inhaled into the dust collector to start a fire.

3. High temperature inside the blast machine canister. Resulting in a natural fire into the shot blasting machine within the processing of steel plate temperature should generally be controlled within 80 ℃, a single shot blasting machine total power up to generally in tens to hundreds of kilowatts, most of the mechanical energy will be converted into heat, in the production process, the temperature of the system will gradually rise, while the material is transformed into dust, the specific surface area increases, increasing the activity of the material, in the presence of combustible conditions, combustible dust oxidation The speed of exothermic reaction exceeds its heat dissipation capacity and eventually transforms into combustion called dust spontaneous combustion, and the finer the dust, the easier it is to spontaneously combust. Fe, FeO, Fe20, Fe0 in the rust dust will accelerate the oxidation in the oxygen-rich environment at higher temperature to produce a large amount of oxidation heat, a large amount of dust accumulation in the dust collector, heat gathering may make the rust dust reach the self-combustion temperature, thus self-combustion occurs.

4. Static electricity leads to fire. Rust dust generates static electricity in the high speed airflow. Friction between dust grains or between dust and objects due to natural radiation, ions or electron attachment usually causes the dust grains to become electrically charged. When the rust dust flows in the pipeline, it rubs itself against each other, and the friction between the dust particles and the inner wall of the pipeline and equipment can generate thousands of volts of electrostatic potential, while such dust electrostatic has the characteristics of dispersion and suspension, dispersion increases the friction area, suspension makes the rust particles contact but not continuous, which leads to higher and higher electrostatic potential. When the accumulated potential increases to the breakdown field strength between the dust, electrostatic sparks will be generated, and when the discharge energy reaches or exceeds the minimum ignition energy of the rust dust, a fire accident will occur. Tests show that the chemical fiber filter media is usually the most concentrated place to generate static electricity, the dust piled up on the filter cartridge so that the electric field strength of space increases, when the accumulation of dust between the breakdown field strength, electrostatic spark discharge will occur, the discharge energy is sufficient to ignite the rust dust.

5. Another possible reason is that the shot blasting machine itself is not reasonable dust collector design, and this is no way to solve the problem, can only find manufacturers to let them re-produce a dust collector and their own model of shot blasting machine to match.

Speaking of which, you gentlemen, the bag dust collector fire causes and solutions, should have a certain understanding, welcome to leave a message with Yi Xiaobian exchange experience, said the wrong place, welcome to point out.

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