Keywords: melting, environmental protection, electric furnace, smelting, electric furnace dust removal, gas (oil) oxygen spray gun, hot charging iron, process, improvement, smelting time,

　　with the improvement and perfection of China is environmental protection laws and regulations and the improvement of people is awareness of environmental protection, electric furnace smelting technology and equipment should also consider the world is advanced electric furnace dust removal system. In recent years, the electric furnace additional gas (oil) oxygen spray gun, hot iron and other process improvements, the pace of production accelerated, smelting time shortened, the corresponding increase in production. The dust removal system also has the phenomenon of insufficient capacity and reduced effect. Each factory has also demonstrated technically and taken measures to meet the emission targets stipulated by the state. In this regard, the electric furnace dust removal system put forward 3 key issues, analysis.

Process flow of 1. dust removal system

1. The commonly used process flow

　　The process flow of flue gas collection combined with primary flue gas exhaust in the electric furnace, secondary flue gas exhaust in the closed cover of the electric furnace and the roof of the factory building, flue gas exhaust in the feeding system, dry dust removal method of filter bag filtration, and negative pressure operation.

2. PLC automatic control

　　(1) pulse (set time or pressure difference) back blowing ash.

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

2. key technical issues

1. Quality of bag filter material for 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. Ash cleaning technology

　　The 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 exhaust effect of the closed hood and the roof of the plant, the formation of micro-negative pressure in the furnace and the life of the bag.

3. Technical Analysis

1. Bag filter material

　　The commonly used cloth bag filter material is polyester needle felt, and its filtering principle is based on a dust layer (dust cake) on the surface of the cloth bag to achieve filtration. Electric furnace smoke dust characteristics: light, fine, large dispersion and poor fluidity; easy to block the bag, that is, \& quot; paste bag \& quot;. The main components and dust components in the flue gas.

　　FeO, FeO/Fe2O3 and CaO are easy to crystallize into blocks on the surface of the cloth bag to cover the pores of the filter material. In addition, dust penetrates into the inner layer of the filter material to block the pores over time, resulting in a decrease in air flow through the cloth bag, an increase in pressure loss and an increase in operating resistance of the dust collector. Each dust collection point traps smoke & ldquo; Weak air & rdquo;, smoke diffuses outward to pollute the environment; The cleaning cycle of cloth bag back blowing dust becomes shorter or even uninterrupted, which reduces the fatigue life of cloth bag and breaks, causing smoke emission to exceed the standard (more than 100mg/Nm3). In order to meet the environmental emission requirements, the bag has to be replaced, increasing the operating cost. In addition, the inevitable accident water of the system will also be the source of moisture in the flue gas. Therefore, the selection principle of bag filter material recommends special treatment of traditional polyester needle felt to meet the following requirements:

　　A. hydrophobic, water does not combine with the bag, does not stick dust, dust, water sink ash bin.

　　B. fiber breaking strength of cloth bag filter material, it is suggested that transverse fracture strength> 120kg/5cm; Longitudinal fracture strength> 70kg/5cm.

2. Ash cleaning technology

　　(1) medium gas with adjustable pressure of ash cleaning appliance. At the beginning of the use of cloth bag filter material, its filtration efficiency is higher, the degree of blockage of the cloth bag is lighter, and the cleaning pressure can be controlled at 3~4kg. Avoid long-term operation of the bag under high pressure and fatigue in advance; In the later stage of use of the bag filter material, the clogging degree of the bag becomes heavier and heavier, the operating load continues to rise, and it is difficult to clean the dust at low pressure blowback. At this time, 5~7kg pressure can be used to clean the dust, so as to reduce the pressure drop of the filter as much as possible, maintain a good cleaning effect, and prolong the fatigue life of the bag. But at this time should increase the venturi tube to prevent high-pressure gas blow caused by the bag rupture.

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

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

3. Flue gas temperature

　　(1) The temperature (T) of the flue gas entering the dust collector is too high, and the shrinkage and deformation of the bag filter material increases the operating resistance. If the flue gas temperature (T1) exceeds the softening temperature of the filter material, the bag will fail or burn. Therefore, before entering the dust collector, there must be a mixed wind mechanism for accident protection, so that the outside natural air is fully mixed with the flue gas, cooling, and ensuring that the flue gas enters the dust collector below the softening temperature of the bag filter material.

　　(2) If flue gas enters the dust collector in an accident state for a long time, it will definitely make the entire dust removal system pipe network & ldquo; Short circuit & rdquo;, resulting in a great reduction in the dust collection effect of each dust collection point; T2 temperature is too high, water cooling, sliding sleeve automatically slides away from the furnace cover flue gas elbow, making it difficult to form a slight negative pressure in the furnace. The flue gas pipeline is required to have sufficient cooling capacity; if the water-cooled flue is long enough or has a considerable diameter, the machine force cooler has sufficient cooling area.

4. Conclusions

　　Choosing oil-proof and waterproof polyester needle felt, adopting reasonable dust removal technology and controlling the flue gas temperature of the electric furnace dust removal system will make the system run with small resistance, good dust removal effect, long bag life and low operating cost. Organic and reasonable matching between the three, completely based on localization can meet the electric furnace dust removal system to meet the environmental protection requirements of the emission indicators.

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