The development trend of electrostatic precipitators
In 2000, the production capacity of aluminum electrolysis has reached 600,000 t/a, and the actual production of aluminum is 470,000 t/a, accounting for about 17% of the national aluminum production, ranking first. However, due to the small scale and low output of most electrolytic aluminum plants, there is no supporting carbon anode production system, and all anode products are purchased. The enterprises that provide carbon products (mainly carbon anodes for prebaked tanks) are scattered, and the scale is mostly small factories with an annual output of less than 10,000 tons. These small carbon plants are generally produced in the form of purchased green or incoming processing. Only 23 911 chamber intermittent open furnace type roasters are built. The main production content is the final process of the entire prebaked anode production process. The process is simple; the role played by the bitumen surface of the asphalt discharged from production is increasing. In the future, electrostatic precipitators will continue to be the main means of pollution control in large factories such as thermal power plants and smelters. Electrostatic precipitators have the following development trends in the future: (1) Develop new structures, reduce the space occupied by electrostatic precipitators, volume and steel consumption, and reduce initial investment. A special electrostatic precipitator with high negative pressure (-) and an electrostatic precipitator for high specific resistance dust.
(3) High-efficiency electrostatic precipitators for submicron particles have been developed with emphasis.
(4) Combined dust removal methods that combine other dust removal methods to improve dust removal performance will have great advantages.
(5) Development of other applications of electrostatic precipitators. For example, the dust-removing property is used to remove the adsorbing medium that adsorbs the gas contaminant, thereby removing the gas contaminant; and the plasma released by the pulse discharge can also be used to remove the gas contaminant while efficiently removing dust.
(6) Increasing the power supply level is an economical and convenient method, so it will be greatly developed in the future to replace the conventional power supply method.
2 Industrial safety and environmental protection technology is difficult and costly, and it is difficult for small enterprises to bear. Therefore, most of the pollution-free treatment facilities, natural pollutants, and serious pollution of the surrounding environment have become an urgent problem for local environmental protection departments. The use of cyclone washing and granular layer adsorption purification technology has the characteristics of low investment, short construction period and high efficiency, and is an effective treatment method for purifying and treating asphalt fume of small carbon roaster.
1 Production Overview 1.1 Production Process The small carbon calciner is a roasting of carbon anodes with petroleum coke and medium temperature coal pitch as the main raw material. The fuel is made of raw coal. The furnace structure and working principle are similar to tunnel kiln and downdraft kiln. . The production process is to install the green special clamp for the green body, and the metallurgical coke is used as the filler in the gap of the baking chamber. The calcination temperature is between 12201280e, and the finished product is prebaked anode after a certain production cycle, and the whole production cycle of the single furnace For 3545 days, the output is 1.2. The pollution of the anode carbon block roasting project uses the raw coal as the fuel. In the roasting process, in addition to the dusty exhaust gas generated by burning the raw coal, there is also the binder asphalt in the raw anode block. The pyrolysis exudes the asphalt smoke, and the exhaust gas passes through the reserved gap of the partition wall between the baking chamber and the combustion chamber, and is introduced into the combustion chamber for combustion, thereby reducing the content of the pitch tar and the benzo (a) bismuth in the roasting flue gas. The flue gas is then discharged directly from the exhaust pipe after being cleaned by simple spray. In the initial heating stage of calcination, the main pollutants are soot and SO2. The main pollutant in the volatilization period is asphalt fume. The main pollutants in the late roasting period are soot, SO and a small amount of asphalt fume.
This flue gas working condition has different effects on the four main methods of purifying asphalt fume: combustion method, electric trapping method, adsorption method and absorption method.
(1) Combustion method: Asphalt smoke is mainly composed of hydrocarbons. When the combustion temperature is >790e and the combustion time is >0.5s, it can be completely burned. This method requires strict combustion temperature and time, otherwise it will cause incomplete combustion or carbonization of bitumen smoke into particles, resulting in secondary pollution, and at the same time high requirements on the concentration of asphalt smoke. The actual process operation level and asphalt fume concentration of small roasters generally cannot meet the requirements of the combustion method.
(2) Electric catching method: The initial purification efficiency is high, but the temperature of the flue gas is high, and it needs to be between 70100e; if the temperature is too high, the specific resistance exceeds 10, which is good for electrostatic trapping, and the asphalt trapping of the gas phase components. The efficiency is low; the one-time investment is large and the floor space is large. Since the flue gas contains a high concentration of soot, and the electric tar catcher is not rapping, the trapped dust will adhere to the plate and cannot fall off, which affects the purification efficiency; at the same time, for small enterprises, it cannot withstand high One-time construction investment. Therefore, the electric trapping method is not suitable for the flue gas purification of a small carbon roaster.
(3) Adsorption method: physical adsorption of bitumen smoke is carried out by using various substances (coke powder, alumina, activated carbon, dolomite powder, talc powder, etc.) which are small or porous and have a large specific surface area as an adsorbent. The purification process and equipment are: particle layer dust collector purification and powder material adsorption bag filter dry purification 2 kinds. The specific implementation should be based on the conditions of purification of asphalt fume concentration, adsorbent properties, purification standards and other conditions. The utility model has the advantages that the process is simple and the purification efficiency is high (98%); the adsorbent does not need to be regenerated, and can be directly returned to the production system; the investment is saved, the operation cost is low, the operation and maintenance are convenient, and there is no secondary pollution. However, the system has a large resistance, and the workload when replacing the filter material or the adsorbent is large.
(4) Absorption method: an organic liquid is used as an absorbent, so that the mixed smoke of the asphalt smoke is sufficiently contacted with the absorbent in reverse flow and washed to remove the toxic components of the smoke to achieve the purpose of purification. However, there is secondary pollution, the purification efficiency is not high, and there are many problems in the operation of the dust-containing flue gas system, and it is still impossible to carry out industrial applications.
2.2 Purification technology and scheme selection Through the comparative analysis of the above purification methods, the adsorption technology is an ideal and effective method. At present, the domestic adsorption method is used to purify carbon roasting furnace asphalt flue gas for industrial production, mainly in large-scale ring roaster with heavy oil as fuel represented by Qinghai Aluminum Plant and Baotou Aluminum Plant. The agent is a pervaporation dry adsorption purification technology using a bag filter. This technology was introduced from France and Japan in the 1980s. The alumina powder loaded with pitch tar after adsorption is used as a raw material for electrolytic aluminum production, and is sent to an aluminum electrolytic tank matched with the carbon production system. The purification efficiency is high, but the process is complicated, the technical conditions are high, and the investment is large. This technology is difficult for small carbon calcining enterprises in terms of production, technical conditions, operation management, and investment.
According to the production process of the small roaster and the flue gas conditions, through the experimental research, the purification process using the wet scrubbing plus the particle layer adsorber can achieve the purpose of effective treatment. It has the characteristics of simple process, high efficiency, low investment, low operating cost and short construction period. It is suitable for use in small carbon roasting enterprises.
3 wet washing granular layer adsorption purification technology 3.1 purification system process This purification process uses a cyclone tower wet cooling dust removal plus particle layer adsorber purification process. After the high-temperature flue gas discharged from the roaster is taken out through the flue, it first enters the swirling plate tower for dust removal, desulfurization and partial asphalt fume removal, and then enters the granular layer dust collector to capture the asphalt tar by the physical adsorption of the adsorbent. To achieve the role of purifying smoke. The flue gas after the purification is up to standard is discharged into the atmosphere by the chimney. The wastewater flowing from the bottom of the swirling plate tower enters the circulating pool, and after two stages of classification and precipitation, it is re-sent to the cyclone tower for recycling by the circulating water pump.
Asphalt flue gas purification process 3.2 Swirl plate tower 3.2.1 Working principle The cyclone tower is based on the similarity and relative theory, using the change of the wind tunnel section to change the direction and speed of the airflow, and the flue gas is rotated at high speed in the working section. And the absorbing liquid injected into the working section is repeatedly rotated and cut to form a turbulent boundary layer on the wall surface, which enhances the exchange of mass and energy between the three phases of gas, liquid and solid soot, prolonging the physical and chemical reaction history and time, fully Neutralizing and absorbing smoke in organic and absorbing soot, especially for fine dust particles.
The flue gas enters the working section of the tower from the bottom of the tower and is in full contact with the water. The harmful substances in the flue gas increase the mass of the individual aerosol due to the effects of cooling and condensation, and are trapped by the action of centrifugal force. The wall slips into the ash bucket to eliminate. The purified flue gas is dehydrated by the mist eliminator and discharged from the top of the tower.
3.2.2 The role of the cyclone tower The cyclone tower is mainly used to remove dust and SO2 from the flue gas, and at the same time achieve the purpose of cooling, reduce the dust entering the particle layer adsorber, reduce the system resistance, and prolong the adsorption. The service life of the agent. In the structural design, the number of swirling plates in the tower should be determined according to the air volume, the temperature of the flue gas and the content of the pollutants. In addition, in order to avoid the adsorption effect due to the water droplets in the flue gas entering the particle layer adsorber, a demisting device should be provided at the outlet of the tower body. The resistance of the equipment is 1.21.5kPa. In order to save investment, the tower body can be made of refractory brick or masonry.
3.3 Granular layer adsorber 3.3.1 working principle Granular layer adsorber is based on the working principle of gas adsorption method, using various particles with small particles and large specific surface area (such as activated carbon, coke, alumina, etc.) as adsorbent . When the flue gas is in contact with the surface of the solid adsorbent, wherein one or more components of the organic gas can be attracted to the solid surface and aggregated thereon, an adsorption reaction occurs, which is a physical adsorption to purify Asphalt smoke in the flue gas.
3.3.2 The operation of the particle layer adsorber takes into account the factors of maintenance and repair operations, and on the premise of ensuring the purification effect, the design adopts the larger particle calcination post-focus fixed bed adsorption method. Calcined coke is the main raw material for the production of prebaked anode. It is a calcined product of petroleum coke. It has a large specific surface area and strong adsorption capacity, and is easily produced in the carbon industry. As the exhaust gas passes through the carbon bed of the adsorber, the bitumen smoke is adsorbed on the surface of the calcined coke and gradually reaches saturation. In the design, according to the concentration of asphalt smoke and the adsorbent layer, the medium-grained calcined coke is used, the particle size is in the range of 20@40mm, and the adsorption amount is 2.53.2kg of asphalt smoke per 100kg. The operating cycle of each set of adsorbers is generally designed to be about 30 days, which is similar to the production cycle of one roaster.
When the adsorption reaches saturation, the resistance of the device increases, the adsorption efficiency decreases, and the granular layer filter material needs to be replaced. The replacement time can be carried out in the stop of the roasting furnace. The replaced granular layer filter material can be incorporated into the raw coal and burned into the furnace.
In order not to affect the operation of the roaster, while ensuring the purification effect, the resistance of the adsorber should be minimized, and the size of the adsorbent and the thickness of the layer should be emphasized in the structural design.
4Industrial application situation A carbon anode roasting enterprise has two 9-chamber gap open roasting furnaces, and the annual processing prebaked anodes are 5kt. Only one set of simple water spray facilities treats flue gas, and pollutants exceed the standard. After adopting the purification process of the cyclone tower wet cooling dust removal and particle layer adsorber, the treatment effect is obvious, and the pollutants are monitored to achieve the standard discharge.
5 Conclusions and recommendations (1) The purification process using wet scrubbing plus particle layer adsorber can achieve effective treatment. It has the characteristics of simple process, high efficiency and low investment, and is suitable for use in small carbon roasting enterprises.
(2) With calcined coke as adsorbent, the adsorption efficiency is high, the raw materials are easy to obtain, the price is low, and it can be recycled.
(3) The granular layer filter material should be replaced in time to ensure the purification effect of the particle layer adsorption and the stable operation of the production system.
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