Problems and Countermeasures of air pollution prev

Problems and Countermeasures of air pollution prevention and control in flat glass industry

there is ash deposition and scaling in waste heat boilers in the operation of air pollution prevention and control technology in flat glass industry; The bag filter is difficult to remove dust, and high-temperature electrostatic precipitator often has short-circuit fault; Lack of successful application cases of SCR denitration technology; There are many problems in flue gas desulfurization technology, such as the blockage of desulfurization tower and auxiliary pipeline and the increase of flue gas dust concentration after treatment, which lead to the "regular" unstable emission and "periodic" abnormal emission of flue gas. Combined with the rectification of air pollution in the industry, this paper puts forward pollution control countermeasures and suggestions in theory and practice to meet the urgent needs of the current industry to achieve stable standards and in-depth governance

after the promulgation and implementation of the emission standard of air pollutants for flat glass industry in 2011, the air pollution control of the glass industry has presented unprecedented environmental pressure. In order to effectively control the emission of pollutants such as particulate matter, SO2 and NOx, glass production enterprises have successively invested in environmental protection facilities such as desulfurization, denitration and dust removal. Due to the large number of raw and auxiliary materials of glass kilns, involving quartz sand, soda ash, mirabilite, limestone, etc., the flue gas characteristics are complex, viscous, easy to scale, and easy to adhere to environmental protection facilities, resulting in high maintenance frequency of environmental protection system. It needs to be overhauled every 1 ~ 3 months, each time for 1 ~ 3D, which seriously affects the efficient operation of prevention and control facilities. Therefore, it is urgent to conduct in-depth analysis of the current situation, improve the pollution control technology level of the glass industry, and realize the stable and up to standard emission of the industry

1. Current situation of air pollution control in flat glass industry

the pressure of SO2 and NOx emission reduction in China's flat glass industry is still large, and energy-saving and emission reduction technologies need to be improved. At present, there are two main air pollution control processes for kiln flue gas: "dust removal + denitration + desulfurization" and "denitration + dust removal + desulfurization". Among them, the dust removal technology mainly adopts high-temperature electrostatic precipitation and bag dust removal. After treatment, the particle concentration is 20 ~ 30mg/m3; The desulfurization technologies used are mainly double alkali method, limestone/gypsum method and circulating fluidized bed technology. The limestone/gypsum method is the most widely used. After being treated by desulfurization facilities, the SO2 concentration in flue gas is 150 ~ 300mg/m3; The denitration technology of glass furnace is mainly copied from the power industry, and all adopt SCR technology. After treatment, the concentration of NOx is less than 400mg/m3

at present, due to the short operation time of the environmental protection facilities of flat glass, the lack of mature operation and management mechanism, the sticky flue gas, and the periodic "fire change" operation of the furnace, the emission concentration of waste gas from the glass furnace presents a prominent problem of periodic and unstable emission

2. Problems and Countermeasures of air pollution prevention and control technology

2.1 problems and Countermeasures of ash deposition in waste heat boiler

under normal circumstances, the exhaust gas temperature of glass furnace is 420 ~ 450 ℃, and the temperature range of SCR reactor corresponding to the smoke temperature is 320 ~ 420 ℃. Furnace flue gas needs to be cooled by waste heat boiler before and after entering SCR reactor. Ash deposition is easy to occur in the waste heat boiler, and the dust on the surface of the heat exchange pipe before SCR denitration is easy to clean, and water flushing is sufficient; After SCR denitration, the moisture content in the flue gas increases, making a part of viscous fly ash adhere to the heat exchange pipe in the waste heat boiler and the induced draft fan blades at the outlet of the waste heat boiler, and the surface of the heat exchange pipe will produce crystallization, which is difficult to clean

according to the research, in the denitration process, the runaway ammonia generated by the reaction reacts with SO3 to form ammonium bisulfate, which is easy to combine with the fly ash particles in the flue gas to form highly cohesive molten salt like ash crystals on the heat exchange tube. The production of ammonium bisulfate can be reduced by controlling the ammonia escape amount in SCR denitration process and the oxidation rate of SO2 in flue gas. The type, quantity and position of the guide vanes at the inlet of SCR denitration device can be optimized to make the inlet flue gas flow rate, temperature and concentration uniform. At the same time, adjust the ammonia dosing system, strictly control the limit of escaping ammonia, make NH3 mix evenly, and finally reduce the amount of ammonia escaping. The flue gas temperature can be adjusted and controlled, and the catalyst type can be reasonably selected to minimize the conversion of so2/so3, so as to reduce the reaction amount of SO3 and NH3, and also reduce the production of ammonium bisulfate. For boiler soot cleaning system, superheated steam soot blowing, compressed air soot blowing, shock wave soot cleaning and other methods have obvious effects

according to the current situation of facility operation, adding standby waste heat boiler or waste heat pipeline for waste heat boiler maintenance and switching during ash cleaning is the quickest solution to the problem in the short term

2.2 problems and Countermeasures of dust removal

2.2.1 bag dust removal

the flue gas of glass furnace has the characteristics of high temperature. Because the temperature fluctuates frequently within a certain range during production, the flue gas cooling system is generally arranged in front of the bag dust collector. However, the dust particles are small and sticky, and it is easy to block the bag filter at a certain temperature, resulting in "bag pasting" and "hardening" and other phenomena, resulting in difficulty in ash removal. In order to ensure the normal operation of bag filter, the control of flue gas temperature is very important. Qixiaofang et al. Proposed that the fuzzy control strategy is used to control the temperature of the flue gas of the bag type dust collector. When the flue gas temperature is instantaneously too high, the air mixing valve can be quickly opened to keep the inlet temperature of the dust collector within the allowable range and effectively maintain the bag type dust removal efficiency. Wang Zhong and others proposed that through the analysis and design of the pipe resistance of the bag filter, the purchase and selection of a suitable bag filter can also achieve a relatively ideal dust removal effect

the most direct and effective solution at present is to choose cloth bags made of high-temperature materials, improve the ash removal method, or replace the cloth bags with wet electrostatic precipitators. The calculated length of the sample is determined by the diameter of the sample

2.2.2 electrostatic precipitator

electrode plate short circuit is easy to occur inside the electrostatic precipitator, and discharge, flashover and other problems are easy to occur inside the electric field. The main electrode plate is easy to deform under the action of high temperature for a long time, and the accumulated ash adheres to the electrode plate, resulting in the short circuit phenomenon if the distance between the electrode line and the electrode plate is too close; The main reasons for voltage flashover are the excessive electrode spacing caused by cathode insulation distance, anode plate jamming, dust prevention plate condensation and dust deposition, and cathode wire disconnection

high temperature electrostatic precipitator has been applied in the glass industry for a short time. According to the above problems, we should further optimize the frame structure of electrostatic precipitator to reduce high temperature deformation; Reduce the wind speed of the electric field and reduce secondary dust; The anode and cathode rapping is changed to side rapping; Adopt "BS" tubular prick wire to reduce the linear change of cathode, reasonably control the rapping speed and reduce the secondary dust caused by rapping and dust removal. The application of high temperature electrostatic precipitator technology in glass furnace flue gas needs technical upgrading and improvement

2.3 existing problems and Countermeasures of denitration

2.3.1 physical blockage of catalyst

the flue gas treatment process route of glass enterprises adopts "denitration + dust removal + desulfurization". The denitration device is arranged in front of the dust removal device, which will cause serious ash deposition in the reactor, resulting in the blockage of the denitration reactor and physical poisoning of the catalyst. Therefore, the accumulated ash in SCR denitration device needs to be cleaned regularly, but some manufacturers have blown, weathered and collapsed catalyst fiberboard from time to time due to lack of operation experience

the forms of denitration catalysts mainly include honeycomb, flat plate and corrugated plate. At present, honeycomb catalysts are mainly used in the glass industry. This type of catalyst has large gas-solid contact area and long residence time of reactants, but its mechanical strength is low and it is prone to blockage. It is not suitable for denitration in the glass industry with high smoke concentration. Flat catalyst has good mechanical properties and strong corrosion and blockage resistance, which is more suitable for this industry. In addition, in the process of catalyst operation and management, pay attention to soot cleaning and temperature control, improve SCR soot blowing system, increase compressed air pressure, increase purging times, and reduce reactor blockage

2.3.2nox exceeds the standard and ammonia escape exceeds the standard

in the production process, when the gas "changes fire", the flue gas temperature rises quickly, the flue gas volume is large, the NOx fluctuation in the flue gas of glass furnace is large, the automatic ammonia injection system is imperfect, the manual ammonia injection is lagging, difficult to control, and the ammonia injection volume is large, which is easy to cause the catalyst to lose activity, reduce the denitration efficiency, and cause the problems of NOx exceeding the standard and ammonia escape exceeding the standard

in order to buffer the NOx concentration fluctuation caused by the "fire change" operation of the glass furnace, the flue gas pretreatment tower can be designed in front of the SCR device to maintain the stability of denitration efficiency. In addition, by improving the ammonia injection system, realize the automatic and accurate control of ammonia injection quantity; Enhancing the reaction activity of the catalyst and improving the reaction efficiency of ammonia and NOx can reduce the ammonia escape rate to a certain extent and ensure that NOx emission meets the standard. At present, there is a lack of mature application cases of SCR denitration technology in the flat glass industry, and the application research of SCR glass furnace flue gas needs to be strengthened

2.3.3 SO2 concentration increases

field test data show that SO2 concentration at the outlet of denitration facilities is significantly higher than that at the inlet of denitration facilities. The concentration of SO2 in glass furnace fueled by natural gas increases by 50% - 100%; The growth rate of furnaces using coal to gas as fuel is 40% - 70%. In particular, the concentration of SO2 in the furnace with natural gas as fuel for glassy materials is lower than 250mg/m3 steel before denitration, and SO2 can be discharged up to standard without desulfurization. After denitration, additional desulfurization facilities are required to meet the standard requirements

it is preliminarily judged that the furnace flue gas contains HS substances, which react to produce SO2 after catalysis. Therefore, it is necessary to carry out the composition analysis of glass furnace flue gas to further determine the type and concentration of sulfur-containing substances at the inlet of denitration device

2.4 desulfurization problems and Countermeasures

wet desulfurization such as double alkali method and limestone/gypsum method are mostly used in desulfurization devices in glass enterprises. In actual operation, the flue gas at the outlet of the desulfurization device contains part of the desulfurization slurry, and the desulfurization agent or desulfurization products are dissolved in the desulfurization liquid, resulting in the increase of flue gas particles; In addition, the nozzle in the desulfurization tower is blocked, the demister and rotating diaphragm are scaling, pipe crystallization and other phenomena are serious

so2 dissolution, limestone dissolution, oxidation reaction and gypsum crystallization will be affected by the pH value of the slurry to varying degrees, so operation management can be strengthened, the diameter of the agent injection pipeline of the desulfurization equipment can be increased, the manual dosing can be changed to mechanical dosing, and the pH value of the solution in the desulfurization tower can be adjusted to be stable between 6 and 8. In addition, increase the area of desulfurization circulating pool to achieve the best clarification effect, and reduce sediment blocking device components

while exploring practical experience, it is necessary to further strengthen the R & D and demonstration of semi dry desulfurization technology and desulfurization and other environmental protection integration technologies, limit the use of highly polluting fuels such as coal and heavy oil in this industry, reduce the proportion of Mirabilite in raw materials, and reduce the production of SO2 from the source

3. Conclusion

(1) driven by more stringent industrial policies and industry standards, the engineering practice of glass furnace flue gas treatment technology has made significant progress, but the construction and operation time of the facilities is relatively short, and the common problems of instability and reaching the standard are prominent. If the stable and up to standard emission is achieved, it still needs some time to explore and improve the relevant environmental protection technology

(2) the characteristics of glass furnace flue gas and pollutants are different from those of power plants, with the characteristics of fine particles, viscosity and high temperature. It is suggested to carry out the research on the mechanism of pollutant flue gas characteristics and the multi-functional coupling mechanism of multi pollutant control technology, and develop the integrated and stable emission technology of ultra-fine particles with high efficiency capture, multi pollutant desulfurization, denitration and dust removal

(3) after the glass furnace is equipped with SCR denitration facilities, the SO2 concentration of flue gas increases, and the dust concentration increases after adding desulfurization facilities, and then the wet electrostatic precipitator is added. The current situation of flue gas treatment of "headache cures the head and foot pains cures the foot" has led to the treatment of atmospheric environmental protection