Design and Selection of Industrial Electric Furnace Dust Collector

Resistance furnace, induction furnace, vacuum furnace, electron beam furnace, heat treatment (or smelting) unit, heat treatment auxiliary equipment, combustion furnace.

Industrial electric furnace dust removal mainly uses bag filter, and the dust hood is designed according to different working conditions on site. Therefore, the difficulty of industrial electric furnace dust removal lies in the design and arrangement of the dust hood.

In recent years, electric furnaces have been improved by adding gas (oil) oxygen lances and hot charging molten iron, resulting in faster production rhythm, shorter smelting time, and corresponding increase in output. The dust removal system also has the phenomenon of insufficient capacity and reduced effect. Therefore, three key issues are proposed and analyzed for the electric furnace dust removal system.

1. Commonly used process flow

The primary exhaust in the electric furnace, the secondary exhaust in the closed hood of the electric furnace and the roof of the workshop, and the exhaust of the refining furnace, the exhaust of the feeding system, the pressure of the fan into the main pipeline of the electric furnace dust removal system, the combination of flue gas capture and filter bag filtration. Process flow of dust removal method and negative pressure operation.

2. PLC automatic control

(1) Pulse (set time or pressure difference) backflush to clean the dust.

(2) Automatically adjust the air volume, air pressure and fan power of each soot collection point according to the smelting conditions.

1. The quality of the bag filter material of the dust collector

The quality selection of filter material determines the operating resistance, operating cost and investment cost of the dust collector, which directly affects the emission concentration of smoke and dust.

2. Cleaning technology

The quality of cleaning performance directly affects the filtration efficiency and the life of the bag.

3. Flue gas temperature

The flue gas temperature control directly affects the smoke exhaust effect of the airtight hood and the roof of the workshop, the formation of micro-negative pressure in the furnace and the life of the cloth bag.

1. Bag filter material

The commonly used bag filter material is polyester needle-punched felt, and its filtration principle is based on the primary dust layer (dust cake) on the surface of the bag to achieve filtration. The characteristics of electric furnace dust: light, fine, large dispersion and poor fluidity; it is easy to block the cloth bag, that is, “paste bag”. The main components and dust components in the flue gas.

FeO, FeO/Fe2O3 and CaO are easy to crystallize on the surface of the bag to cover the pores of the filter material, and the dust penetrates into the inner layer of the filter material to block the pores over time, so that the air flow through the bag decreases, the pressure loss increases, and the operating resistance of the dust collector increases. Each dust collection point is “powerless” to the dust collection, and the dust diffuses outward to pollute the environment; the cycle of backflushing and cleaning of the bag is shortened or even uninterrupted, which reduces the fatigue life of the bag and ruptures, causing the dust emission exceeding the standard (more than 100mg/ Nm3).

In order to meet the environmental protection emission requirements, the cloth bag has to be replaced, which increases the operating cost. Therefore, the principle of bag filter material selection is recommended:

a. Hydrophobic, water is not combined with the cloth bag, no sticky dust, dust and water will settle into the ash bin.

b. The breaking strength of the bag filter material fiber, it is suggested that the transverse rupture strength is greater than 120kg/5cm; the longitudinal rupture strength is greater than 70kg/5cm.

2. Cleaning technology

(1) Medium gas with adjustable pressure for cleaning appliances. In the initial use of the bag filter material, its filtration efficiency is high, the degree of blockage of the cloth bag is relatively light, and the backflushing pressure of ash cleaning can be controlled at 3-4kg. Avoid early fatigue caused by long-term operation of the cloth bag under high pressure; in the later period of use of the cloth bag filter material, the degree of blockage of the cloth bag becomes heavier and heavier, the operating load continues to rise, and it is difficult to clean the dust with low-pressure blowback. At this time, 5-7kg pressure can be used to remove dust. Reduce the filter pressure drop as much as possible, maintain a good cleaning effect, and achieve the effect of prolonging the fatigue life of the cloth bag. However, at this time, a venturi should be added to prevent the bag from breaking due to high-pressure gas blowing.

(2) The medium gas for ash cleaning should be free of water and oil, and nitrogen is ideal for steel mills. Because there is a certain amount of water in the compression control under a certain pressure and temperature.

(3) After the dust collector stops running, it should continue to blow back the dust for two cycles to avoid the combination of moisture in the air and the dust on the surface of the cloth bag to agglomerate and paste the bag.

3. Flue gas temperature

(1) The temperature (T) of the flue gas entering the dust collector is too high, and the bag filter material shrinks and deforms, which increases the running resistance. If the flue gas temperature (T1) exceeds the softening temperature of the filter material, the bag will fail or be burned. Therefore, there must be an accident-protected air mixing mechanism before entering the dust collector, so that the outside natural air can be fully mixed with the flue gas and cooled to ensure that the flue gas enters the dust collector below the softening temperature of the bag filter material.

(2) If the flue gas enters the dust collector in an accident state for a long time, the entire dust removal system pipe network will be “short-circuited”, which will greatly reduce the effect of collecting smoke and dust at each dust collection point; T2 temperature is too high, water cooling, sliding sleeve automatic Slip away from the flue gas elbow of the furnace cover, and it is difficult to form a slight negative pressure in the furnace. The flue gas pipeline is required to have sufficient cooling capacity; for example, the water-cooled flue has a sufficient length or diameter, and the mechanical cooler has sufficient cooling area.

Choose oil-proof and waterproof polyester needle-punched felt, adopt reasonable ash cleaning technology, and control the flue gas temperature of the electric furnace dust removal system, which will make the system run with low resistance, good dust removal effect, long life of the cloth bag, and low operating cost. The organic and reasonable matching among the three can meet the emission targets of the electric furnace dust removal system to meet the environmental protection regulations.