How to design explosion - proof dust removal system

Dust explosion characteristics:

Dust explosion occurred three conditions:

(1)The air reaches a certain concentration of dust,in the upper and lower limits of the explosion,the general lower limit of the most people concerned about the explosion;

(2)An ignition source with sufficient energy;

(3)Adequate air or oxygen mixed contact.

What dust is easy to explode?

At present,the industry has the danger of dust explosion:

(1)Metal industry (magnesium, titanium, aluminum powder, etc.)

(2)Coal industry (activated carbon, coal dust, etc.)

(3)Synthetic materials industry (plastics, dyes, etc.)

(4)Textile industry (cotton dust, dust, paper dust, wood dust, etc.)

(5)Chemical fiber industry (polyester dust, polypropylene dust, etc.)

(6)Military, fireworks industry (gunpowder, explosives, etc.)

(7)Food industry (flour, starch, etc.)

(8)Agricultural and sideline products processing industry (cotton dust, tobacco dust, sugar, etc.)

(9)Feed industry (blood meal, fish meal, etc.)

Explosion - proof technology:

Explosion-proof technology can be divided into preventive technical measures and design measures.

Preventive measures refer to the fact that the concentration of dust is lower than the lower limit of the explosion and the accumulation of dust and the elimination of effective ignition sources. The design measures refer to measures to prevent the explosion from occurring when the measures to prevent the explosion are ineffective. Which includes anti-blast, explosion suppression, explosion, explosion and so on.

Anti-explosion, that is the structure itself can withstand the explosion pressure, the structure itself does not burst. Anti-explosive structure is resistant to explosion pressure and explosion-resistant shock pressure, explosion-resistant pressure design should comply with pressure vessel design and manufacturing specifications, and resistance to explosion shock pressure can be properly relaxed. In general: resistance to explosion shock pressure of 1.5 times the resistance to explosion pressure.

In order to avoid excessive explosion pressure, a successful explosion suppression system can operate at an explosion pressure of 1 * 104 Pa, and the maximum pressure in the device after the suppression is less than 1 * 105 Pa. Anti-explosive is divided into two kinds, one for the passive, such as water bags and flame retardant powder device, such devices is the explosion pressure rose to a certain extent, automatic rupture throwing water or flame retardant powder; one for the active, Explosion sensor, control unit and high-pressure driven high-speed spray (HRD) suppression device consisting of intelligent suppression device.

Flameproof is to prevent the explosion in a container from occurring along the connecting pipe to the subsequent container, which causes the system to explode and cause greater damage. However, the biggest explosion in practice is because the explosion-proof device can not work or is not designed.

Explosion, dust explosion will produce up to 0.7-1 MPa pressure, and the explosion-proof measures can be increased pressure constraints in the component material strength can withstand the range, detonation to reduce the explosion hazards have an important role.

Explosion protection of bag filter:

1.Control the amount of dust accumulated in the bag filter.

Industrial combustible dust dangerous concentration is generally: 20-6000 g/m³. Usually the bag filter is the last part of the process system, dust-laden gas through the pipeline into the bag filter was trapped to form a dust layer, and through the pulse backlash ash fell into the hopper. In these processes, the concentration of dust in the bag filter is likely to be within the above hazardous concentration range. Therefore, to strengthen the system ventilation, especially in order to timely cleaning, so that bag dust and dust in the pipeline concentration is lower than the lower limit of the danger range. The timely removal of the dust of the funnel, the safe operation of the bag filter is essential.

The use of continuous discharge valve, you can ensure timely ash, to prevent dust in the dust collector box accumulation.

2.Clear the ignition source.

In the bag filter is the main source of ignition: the main ignition source, impact or friction generated cremation, static cremation and shell temperature.

(1)Ordinary ignition source is mainly brought by the fire directly from the outside, especially the gas cutting flame and welding sparks, because the bag filter are generally welded parts, for the gas cutting flame and welding sparks are mainly produced when the repair equipment. So you can strengthen management, improve workers awareness of explosion-proof and other aspects of control, in the repair of the equipment should also remove the repair parts around the dust.

(2)The impact or friction generated by the spark is usually a nut or iron and other metal objects inhaled bag filter caused by the collision of the spark, the elimination method is mainly: in the dust cover set the appropriate metal mesh, electromagnetic iron device,to prevent the metal into the dust collection pipe and bag filter, the maintenance should be promptly removed into the pipeline metal material. Secondly, the ventilator is best arranged in the bag filter after the clean air side to prevent the metal foreign body and the fan high-speed rotation of the blade collision spark, and to prevent flammable and explosive dust and high-speed rotating blade friction heating. Finally, the wind speed in the pipe network should be reasonable, and the high wind speed can accelerate the wear of the dust. The test shows that the wear rate is related to the wind speed, so as to bring more metal material to the dust collector.

(3)Static electricity generated mechanism has not yet clear out, but can take the necessary measures anti-static. It is possible to suppress the generation of static electricity to a maximum extent by selecting a substance that is close to the charged sequence or a substance that is opposite to the charged sequence and minimizing the contact potential difference. Take the positive and negative charge self-neutralization, to eliminate the purpose of static electricity. Followed by grounding is one of the most important and most common leakage measures. Equipment, containers, pipelines, etc. should be maintained equipotential. According to the actual situation, the use of decentralized or centralized grounding system for reliable grounding, the grounding resistance requirements within the range of 1-2Ω. In addition to increasing the conductivity, with a conductor or conductive material instead of high insulation material. In particular, the use of anti-static filter, which is mainly test that the filter is the most concentrated place to produce static electricity, in addition, stacked on the filter bag dust layer to increase the intensity of the space electric field, there may be a breakdown of the spark spark discharge. Finally, you can use the way to improve the environmental humidity to leak static electricity can also be directly in the production process water.

(4)Keep the dust collector shell temperature can not be too high, due to a large number of dust is the shell wall adsorption, the shell temperature is too high so that the dust surface heat, get energy after melting and gasification burst out of hot micro-proton particles or sparks, source. So the control of the ambient temperature can not put the bag filter outside the house.

3.Install the bleach film.

For the bag filter, the most effective and most economical explosion-proof measures is to install the leak film, install the leak film is the key to the calculation of the area, vent area is too small does not work, too much will increase the cost. In the international most commonly used area of the calculation of the area is Kst promise map method, St Nuo Tu method. Bag filter is also very important location, mainly close to the point of explosion, vent effect better.

4.Explosion and explosion.

Flameproof device, using an emergency shut-off valve, which is achieved by the infrared flame sensor quick start pneumatic spring valve. Capable of triggering an emergency shut-off valve mounted far enough away from the sensor to prevent flames or explosions from spreading to other places to propagate secondary explosions to explode specific areas of the accident control to avoid deterioration of the situation. If the small bag filter is easy to use a passive pressure water bag or flame retardant powder device, the dust is a hydrophilic material easy to use pressure water bag, the other use of flame retardant powder device; if the large bag filter easy to use intelligent high pressure spray device.

Explosive device, is the equipment within the combustible material explosion in the initial stage, a passive, such as water bags and flame retardant powder device, such devices is the explosion pressure rose to a certain extent, automatic rupture throwing water or flame retardant powder; The other is the active, by the detection of the initial explosion sensor, control unit and high-pressure driven high-speed spray (HRD) suppression device composed of intelligent suppression device.

5.Others.

(1)Protection interlock. Dust removal system should be set to protect the interlock device, when the monitoring device issued sound and light alarm signal, and flameproof, explosion suppression device is activated, the protection interlock device should also start control protection.

①Temperature detection alarm device, temperature sense to reach the limit when the sound and light alarm, cut off the fan.

②The wind speed detection alarm device, the tube wind speed below the limit when the sound and light alarm, cut off the fan.

③The pressure detection alarm device, the vacuum pressure reaches the limit when the sound and light alarm, cut off the fan.

④Electrostatic ground alarm device, static conductivity guide when the sound and light alarm, cut off the fan.

⑤Spark detector fault detection alarm device, when the spark detection device failure sound and light alarm, cut off the fan.

⑥Other monitoring linkage alarm device.

(2)The vast majority of dust explosion is caused by the negligence of personnel, to strengthen the management of personnel is the most fundamental and important.

① The operator of the theoretical and practical knowledge of the training, so that the operator aware of the risk of dust explosion and how to effectively dust and explosion;

② Strengthen labor discipline, the work must always pay attention to the operation of bag filter; In the bag filter working time for its welding, gas cutting and other operations and fire into or near the work area.