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Problems And Countermeasures Of Air Pollution Control In Float Glass Industry

     There is ash and scale in waste heat boiler during the operation of air pollution control technology in glass industry. Bag dust collector is difficult to clean dust, high temperature electrostatic dust often short circuit fault; SCR denitration technology lacks successful application cases. The flue gas desulfurization technology generally has such problems as desulfurization tower and accessory pipe clogging and increased dust concentration after treatment, which leads to the flue gas to be "regular" unstable emission and "periodic" abnormal emission. Based on the air pollution rectification of the industry, the countermeasures and Suggestions for the pollution control of the industry are put forward theoretically and practically, so as to meet the urgent need for the industry to achieve stable compliance and carry out in-depth treatment.

    After the issuance and implementation of the air pollutant emission standards for plate glass industry in 2011, the glass industry has shown unprecedented environmental pressure in air pollution control. In order to effectively control the emission of particulate matters, SO2, NOx and other pollutants, glass manufacturers have successively invested and built environmental protection facilities such as desulfurization, denitration and dust removal. For glass kiln raw and auxiliary materials, quartz sand, soda ash, glauber's salt, limestone, etc., produce gas features more complex, good adhesion, easy fouling, easier to adhere to the environmental protection facilities, cause environmental system maintenance frequency is high, every 1 ~ 3 months to repair time, every time 1 ~ 3 d, seriously affected the prevention and treatment facilities run efficiently. Therefore, in-depth analysis of the current situation is urgently needed to improve the technical level of pollution control in the glass industry and achieve the stable standard emission in the industry.

1. Status of air pollution control in plate glass industry

China's sheet glass industry is still under great pressure to reduce emissions of SO2 and NOx, and energy conservation and emission reduction technologies need to be improved. At present, there are two main processes of air pollution prevention and control: "dust removal + denitrification + desulfurization" and "denitrification + dedusting + desulfurization". Among them, dust removal technology mainly adopts high-temperature electric dust removal and cloth bag dust removal. After treatment, the concentration of particulate matters is 20 ~ 30mg/m3. The desulfurization technologies adopted are mainly double alkali method, limestone/gypsum method and circulating fluidized bed technology. The most widely used is limestone/gypsum method. Glass furnace denitration technology is mainly copied from the power industry, all of which adopt SCR technology. After treatment, the concentration of NOx < 400mg/m3.

At present, due to the short operation time of the environmental protection facilities of the plate glass, the lack of mature operation management mechanism, the smoke is sticky, and the furnace need to periodically "change fire" operation, etc., resulting in the emission concentration of the waste gas of the glass melting furnace presents the prominent problem of periodic unstable emission.

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

2.1 problems and countermeasures of ash accumulation in waste heat boiler

Under normal circumstances, glass furnace exhaust temperature in 420 ~ 450 ℃, and the smoke temperature corresponding to the SCR reactor temperature range is 320 ~ 420 ℃. The flue gas of melting furnace is cooled by waste heat boiler before and after entering the SCR reactor. Ash accumulation is easy to occur in the waste heat boiler. Dust on the heat exchange pipe surface area is easy to be cleaned before SCR denitration and water can be flushed. As the moisture content of flue gas increases after SCR denitration, some of the sticky fly ash sticks to the induced fan blades of the heat exchanger pipe in the waste heat boiler and the outlet of the waste heat boiler, and the heat exchanger surface will produce crystallization phenomenon, which is difficult to clean up.

According to the research, in the process of denitration, the escaping ammonia generated by the reaction and SO3 will form ammonium sulfate, which is easy to combine with fly ash particles in the flue gas and form extremely cohesive and salt-like accumulative crystallization on the heat exchange pipe. The production of ammonium sulfate can be reduced by controlling the ammonia escape during SCR denitration and the SO2 oxidation rate in flue gas. The type, quantity and position of the inlet guide vane of SCR denitration device can be optimized to make the inlet flue gas velocity, temperature and concentration uniform, and at the same time, the ammonia feeding system can be adjusted to strictly control the escape ammonia limit, so that NH3 can be mixed uniformly, and finally reduce the ammonia escape. The flue gas temperature can be adjusted and controlled, the catalyst type can be reasonably selected, and the conversion rate of SO2/SO3 can be reduced to the maximum extent to reduce the reaction amount of SO3 and NH3, and the production of ammonium sulfate can also be reduced. For the boiler ash cleaning system, the superheated steam blowing, compressed air blowing, shock wave cleaning and other methods have been adopted.

According to the operation status of the facility, adding spare heat boiler or waste heat pipe for waste heat boiler maintenance and switching during ash cleaning is the fastest solution in the short term.

2.2 problems of dust removal and countermeasures

2.2.1 cloth bag dust removal

The flue gas of glass melting furnace is of high temperature, and the flue gas cooling system is usually arranged in front of the bag dust collector due to the frequent fluctuation of temperature in a certain range due to the production of heat exchange. However, soot particles are small and sticky, and it is easy to block the bag filter at a certain temperature. The control of flue gas temperature is very important for the normal operation of bag filter. Qi xiaofang et al. proposed the fuzzy control strategy for the temperature control of the flue gas of the bag filter. When the flue gas temperature is instantaneous too high, the mixed air valve can be opened quickly to keep the inlet temperature of the dust collector within the permitted range and effectively maintain the efficiency of the bag dust removal. Wang zhong et al. proposed that, through the pipeline resistance analysis design of bag-type dust collector, the selection of suitable cloth bag dust collector could also achieve a relatively ideal dust removal effect.

The most direct and effective solution at present is to select the high temperature resistant material cloth bag to improve the way of cleaning dust, or to replace the cloth bag with a wet electrostatic precipitator.

2.2.2 the electric

The problem of plate short circuit is easy to occur inside the electrostatic precipitator, and discharge and flashover are easy to occur inside the electric field. The main plates are prone to deformation under the action of long-term high temperature, and the accumulated ash adheres to the plates, resulting in a short circuit when the electrode line is too close to the plates. The main cause of voltage flashover is the distance between poles caused by cathode insulation distance, anode plate astringency, dust accumulation due to dustproof board, and cathode line break.

The application time of high temperature electric dust removal in glass industry is short. Reduce the wind speed of electric field, reduce the second dust; The yin-yang pole strike was changed to lateral strike; The "BS" tubular barbed wire is adopted to reduce the cathode line deformation, and the vibration speed is controlled reasonably to reduce the secondary dust caused by the vibration and ash cleaning. The application of high temperature electrostatic precipitator technology to the flue gas of glass melting furnace is to be upgraded and improved.

2.3 problems and countermeasures of denitration

2.3.1 physical blockage part of catalyst

The flue gas treatment process of glass enterprise adopts "denitration, dust removal and desulphurization". Before the denitration device is arranged in the dust removal device, serious dust accumulation will occur in the reactor, resulting in blockage of denitration reactor, resulting in physical poisoning of catalyst. Therefore, the ash accumulation in the SCR denitration device needs to be cleaned regularly. However, due to the lack of operating experience in some manufacturers, the phenomenon of blown up, weathering and collapse and dispersing of the catalyst fiber board often occurs.

There are three types of denitration catalyst: honeycomb, 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 reactant retention time, but has low mechanical strength and is prone to blockage, which is not suitable for denitration in glass industry with high dust concentration. The flat-plate catalyst has good mechanical properties and strong anti-corrosion and anti-clogging properties, which is more suitable for the industry. In addition, during the process of catalyst operation and management, attention should be paid to ash cleaning and temperature control, the SCR blowing system should be improved, the compressed air pressure should be increased, the number of purge times should be increased, and the blockage of reactor should be reduced.

2.3.2 excessive NOx and ammonia escape

In the process of production, gas "in fire smoke temperature increase fast, smoke flue gas volume is large, glass furnace flue gas in NOx volatility is larger, automatic spraying ammonia system is imperfect, the manual spraying ammonia with lag, difficult to control, ammonia injection quantity is big, easy to cause catalysts losing activity, reducing denitration efficiency, NOx overweight and excess ammonia escape problems.

The flue gas pretreatment tower can be designed in front of the SCR device to keep the denitration efficiency stable in order to buffer the fluctuation of NOx concentration caused by the operation of "heat exchange" of glass furnace. In addition, through perfecting the ammonia spraying system, automatic and precise control of the amount of ammonia spraying can be realized. Enhanced catalytic reactivity and improved ammonia water and NOx reaction efficiency can both reduce the ammonia escape rate to a certain extent and ensure the NOx standard discharge. At present, there is no mature application case of SCR denitration technology in plate glass industry, and the application research of SCR glass melting furnace flue gas needs to be strengthened.

2.3.3SO2 concentration increased

Field test data showed that the concentration of SO2 at the outlet of denitrification facility was significantly higher than that at the entrance of denitrification facility. In glass kilns with natural gas as fuel, the SO2 concentration increases by 50% ~ 100%. The increase rate of melting furnace with coal gas is 40% ~ 70%. In particular, the concentration of SO2 is lower than 250mg/m3 before denitration in the melting kilns fueled by natural gas. No need to go through the desulfurization link, SO2 can be discharged up to standard. After denitration, additional desulfurization facilities are needed to meet the standard requirements.

It was preliminarily judged that the flue gas of melting furnace contained HS substances, and SO2 was generated after catalytic reaction. Therefore, the flue gas composition analysis of glass melting furnace should be carried out to further determine the type and concentration of sulfur at the entrance of denitration device.

2.4 existing problems of desulphurization and its countermeasures

The desulphurization equipment of glass enterprises mostly adopts wet desulphurization such as double alkali method and limestone/gypsum method. In actual operation, the flue gas at the outlet of the desulphurization device contains part of desulphurization slurry, which is dissolved with desulphurization agent or desulphurization product, resulting in increased flue gas particulate matter. In addition, in the desulphurization tower, the sprinkler is blocked, the mist eliminator and rotary plate scale, pipe crystallization phenomenon is serious.

SO2 dissolution, limestone dissolution, oxidation reaction and gypsum crystallization are all affected by the pH value of slurry to different degrees. Therefore, the operation management can be strengthened, the diameter of spraying agent pipeline for desulfurization equipment is increased, manual dosing is changed to mechanical dosing, and the pH value of solution in desulfurization tower can be adjusted to be stable between 6 and 8. In addition, increasing the area of the desulphurization circulation tank can achieve the best clarifying effect of the circulation tank and also reduce the blockage device assembly of sediment.

While exploring the practical experience, it is necessary to further strengthen the research and development and demonstration of semi-dry desulfurization technology and desulfurization and other environment-friendly integrated technologies, limit the use of high-polluting fuels such as coal and heavy oil in this industry, reduce the proportion of glauber salt in raw materials, and reduce the generation of SO2 from the source.

3, conclusion

(1) driven by more stringent industrial policies and industrial standards, the engineering practice of flue gas control technology of glass melting furnace has made remarkable progress, but the equipment construction and operation time is short, and the common problem of unstable meeting the standard is prominent. If the discharge is stabilized, it still needs to be explored for a period of time and the improvement of relevant environmental protection technologies.

(2) and pollutant characteristics of glass furnace flue gas and power plant has a certain distinction, have the characteristics of particles small, high viscosity, temperature, Suggestions to carry out the mechanism of flue gas pollutants characteristics of multi-functional coupling mechanism and more pollutants control technology research and development of ultrafine particles efficiently capture, more pollutants desulphurization and denitration, dust removal integration standards emissions technology.

(3) the concentration of flue gas SO2 increases after the SCR denitration facility is equipped with glass melting furnace, and the dust concentration increases after the desulphurization facility is increased, and then the wet electrostatic precipitator is increased. The current situation of flue gas treatment with "head pain medicine, foot pain medicine" leads to the long process route of atmospheric environmental protection treatment, and it is trapped in the circulation of problems. It is suggested to strengthen the research and development of glass flue gas treatment process, especially denitration technology.