The prevention and control of flue gas pollution in glass melting furnaces is the key and difficult issue of pollution control in China's glass manufacturing industry. Chinese glass companies have basically completed the desulfurization technology transformation by the end of 2013; by the end of 2018, more than 80% of glass companies have completed the construction of denitration facilities. Due to the particularity of the glass production process, the furnace flue gas temperature is high, the composition is complex, the smoke dust viscosity is high, and the NOx concentration is high. During the operation of environmental protection equipment, it is necessary to ensure the balance of the furnace pressure in the furnace, and the periodic fire change of the furnace will cause PM2 .5, SO2, NOx concentration fluctuates greatly. At present, most of the flat glass production lines are equipped with waste heat power generation systems. The flue gas of the glass melting furnace also includes unconventional pollutants such as fluoride and chloride. The flue gas treatment technology is complicated, which increases the difficulty of the flue gas treatment of the glass melting furnace.
Glass melting furnace flue gas pollutant control technologies are divided into: primary measures, that is, to prevent and reduce the generation of pollutants, which belong to the source treatment technology; secondary measures, that is, to reduce the harmfulness of the generated pollutants, which belong to the end treatment technology. Current measures to reduce NOx emissions include: low-nitrogen combustion technology, oxy-fuel combustion technology, 3R technology, selective catalytic reduction technology (SCR), selective non-catalytic reduction technology (SNCR) and wet oxidation absorption method. Measures to reduce sulfur dioxide emissions include the use of low-sulfur fuels, reducing the use of sulfates in raw materials, and flue gas desulfurization through dry, semi-dry, and wet technologies.
For glass companies that use inferior fuels such as petroleum coke, since the concentrations of SO2, NOx and dust in the exhaust gas are much higher than other fuels, in order to meet the requirements of the new national and local glass pollutant emission standards, high-efficiency denitrification, desulfurization and desulfurization must be selected. Dust removal process. At present, SCR denitration technology has high efficiency. In the SCR device that has been in operation, the denitration rate reaches 80%~90%. The spray drying absorption desulfurization technology has the characteristics of quickly adapting to changes in flue gas composition, flow, temperature, and SO2 concentration, and desulfurization efficiency It can reach more than 90%. At present, the integrated technology obtained by optimizing the combination of desulfurization, denitrification and dust removal technology is the best choice to solve the problem of high-concentration sulfur dioxide and high-concentration nitrogen oxide glass furnace waste gas.
1 Pollution prevention technology
The nitrogen oxides in the flue gas of the glass melting furnace come from three aspects: ①NOx generated by the violent reaction of nitrogen in the combustion air with oxygen at high temperature is the main source of NOx; ②NOx generated by the reaction of nitrogen in the fuel with oxygen after combustion ③ NOx formed by the decomposition of a small amount of nitrate in the raw material. The NOx emission concentration of glass furnace is generally 1600 ~ 3600 mg/Nm3
According to the data in the "Environmental Assessment Report for the Flat Glass Industry (2017)", the compliance rates of the three major pollutants of nitrogen oxides, sulfur dioxide and particulate matter in the online monitoring data of flat glass companies in 2016 were basically about 80%. Therefore, the use of preventive technologies to reduce the original concentration of pollutants in the kiln flue gas, combined with the improvement of end treatment technology, to form a pollutant emission control technology that can operate economically and have a long-term and stable treatment effect is still an urgent solution for China's glass manufacturing industry. The problem.
From the perspective of pollution prevention, the flue gas pollution prevention technology in the glass manufacturing industry mainly considers three factors: the influence of raw materials, fuels and combustion technology.
1.1 Raw materials
In the glass preparation process, methods such as raw material substitution and raw material formulation optimization are adopted to control the usage of raw materials containing nitrates, sulfides, fluorides and chlorides, and reduce the content of nitrogen oxides produced by the chemical decomposition of raw materials.
1.2 Fuel
Use clean fuel or low-sulfur fuel. Clean fuel means that no substances harmful to the human body and the environment are produced during combustion, or harmful substances are very small, and the amount of pollutants produced is relatively small, such as natural gas, liquefied petroleum gas, clean gas, alcohol fuel (methanol, ethanol, dimethyl Die, etc.), biofuels, hydrogen fuels, etc., to reduce the amount of pollutants produced during the fuel combustion process. Among the various fuels currently used in the glass manufacturing industry, the clean fuel is mainly natural gas.
1.3 Combustion technology
1.3.1 Oxygen combustion technology
It is to change the air fuel combustion system into oxygen (purity greater than 90%)-fuel combustion system. During the oxy-fuel combustion process, about 79% of the nitrogen in the air no longer participates in the combustion, which can improve the combustion efficiency. The nitrogen oxide content in the flue gas is very high. Low, thereby reducing nitrogen oxide emissions.
Compared with regenerative air combustion kilns, oxy-fuel combustion has no regenerators, small furnaces, and reduced waste gas emission equipment, which reduces the floor space of oxy-fuel combustion kilns and reduces the investment in civil engineering and kilns. The cost has been reduced; the NOx emissions produced by the glass during oxy-fuel combustion are about 90% lower than that of the regenerative kiln; the energy consumption per unit of glass melting is significantly reduced by 20%-30% compared with air combustion; after the combustion flue gas volume is reduced, the coordination The loss of volatile materials in the material is reduced, and the amount of dust carried by the flue gas is greatly reduced.
1.3.2 Low-nitrogen combustion technology
The low-nitrogen combustion technology is to make the combustion reaction of the fuel in the same furnace divided into two stages: reducing flame and oxidizing flame, and proceed under a relatively dispersed temperature system, forming a staged combustion. The typical approach is that the first stage is oxygen-lean (fuel-rich) combustion, and the NOx flame is not produced due to lack of oxygen. In the second stage, pure oxygen, oxygen-rich, air or compressed air are used as combustion-supporting media to form complete combustion before the fuel leaves the kiln. It is not easy to form NOx due to the relatively low temperature.
Low-nitrogen combustion technology is a measure of NOx control in the exhaust gas of glass melting furnaces. The focus is on pollution source control, that is, strictly control the source of NOx and limit the formation of NOx. The main measure is to improve the combustion technology.
The staged combustion of the fuel is realized by using a dedicated low-NOx burner, and the flame shape and length can be adjusted by adjusting the angle and flow of the spray gun as needed, so that the fuel and the combustion-supporting air are fully mixed, so that the combustion reaction is relatively more in the kiln. Completed in a wide space, at the same time it can reduce the excess air coefficient and reduce the generation of NOx during the combustion process
1.3.3 Pure oxygen combustion-supporting low-nitrogen combustion technology
The oxygen-enhancing gradient combustion-supporting technology is a manifestation of low-nitrogen combustion. It is characterized by passing a certain amount of oxygen under the burner, which can effectively improve the heat transfer efficiency of the flame, reduce the emission of NOx and other pollutants, and improve the glass quality , Extend the life of the furnace. Gradient oxygen increase makes the combustion reaction in the first stage a fuel-rich incomplete combustion. Because the flame temperature is lower and the amount of O2 and N2 is small, the formation of NOx is reduced; the second stage is a complete combustion reaction with O2 combustion as the main component. , The flame temperature is high, but due to the lack of N2 participation and short combustion time, the amount of NOx generated is very small. On the other hand, the use of oxygen-enhancing gradient combustion-supporting technology can reduce the excess secondary air volume and ensure that the air excess coefficient reaches the ideal value, thereby reducing the NOx emission concentration by 20% to 35%.
2 Low-emission energy-saving glass furnace design
Combined with a company's 160 t/d kiln coal-to-gas and supporting facility design project, the glass melting furnace designed and constructed adopts a series of advanced and mature glass melting furnace energy-saving technical solutions. According to the production process characteristics of specific products, the glass melting furnace project was optimized and designed by utilizing advanced domestic and foreign melting furnace technology and equipment. In order to achieve the goals of improving melting quality, saving energy consumption, reducing NOx emissions, prolonging kiln life and stabilizing operations.
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Design Points:
(1) According to the numerical simulation and calculation results of fluid mechanics, optimize the structure of the furnace
The kiln sill set up on the basis of the optimized design and the adopted deep clarification tank technology can effectively reduce the reflux and molding reflux in the kiln tank, thereby reducing the energy loss caused by the reflux of the glass liquid, and at the same time, it can also improve the glass liquid Clarification effect and homogenization quality.
(2) Use fluid dynamics numerical simulation to optimize the structure of the furnace
Each side of the small furnace is equipped with a high-efficiency, energy-saving, low-NOx combustion natural gas spray gun, which can adjust the flame shape and length, and the flame coverage area is large. The combustion-supporting air flow and the natural gas flow are adjusted in cascade ratio or ratio to achieve complete fuel combustion and low flue gas. NOx emissions.
(3) Seal
The fully-sealed feeder, fully-sealed spray gun and fully-sealed observation hole are used to prevent cold air from infiltrating, which is beneficial to reduce energy consumption and reduce NOx generation.
(4) Material channel
Reasonably design the distribution channel and material channel to avoid secondary heating of the glass liquid. The distribution channel and the material channel are equipped with a natural gas heating system, and the operating temperature is adjusted according to the production needs.
(5) Regenerative structure
By rationally designing the structure of the regenerator, the melting ratio of the furnace is greater than 60:1, making full use of the heat of the flue gas.
(6) Furnace structure
The furnace adopts a full thermal insulation structure to help reduce energy consumption and extend the service life of the furnace.
(7) Refractory materials
Optimize the refractory material configuration of the kiln to ensure that the service life of the kiln meets the design requirements.
(8) Flame
The high-efficiency, energy-saving and low-NOx natural gas spray gun is used to precisely control the flame shape, so that the fuel is completely burned in the kiln, and to ensure that the big chute and the breast wall are not washed by the flame. Ensure that the fuel is not burnt in the regenerator for a second time to extend the service life of the regenerator.
(9) Bubbling technology
The pulse bubbling technology is used to improve the clarification effect of the molten glass and reduce the temperature difference between the upper and lower sides of the molten glass.
3 The operation effect of staged pure oxygen combustion-supporting technology of glass furnace
Before and after the adoption of staged pure oxygen combustion-supporting technology for a certain domestic 600 t/d float glass, the fuel consumption decreased from 200 kg heavy oil/t glass liquid to 180 kg heavy oil/t glass liquid, and the fuel consumption of the glass melting furnace was reduced by 10% to support combustion. The total amount of air decreased from 56 000 Nm3/h to 46 000 Nm3/h, the amount of combustion-supporting oxygen was 1 380 Nm3/h, the average NQ emission concentration decreased from 2 250 mg/Nm3 to 1 400 mg/Nm3, and the NOx concentration decreased 38%, the effect of energy saving and emission reduction is obvious.
4 Conclusion
Compared with the end treatment technology, the use of process treatment can reduce NOx emissions from the source, and the use of low NOx emission phased combustion technology can reduce the generation of NOx from the source, which can alleviate the pressure of glass companies to reduce emissions. It is currently reducing NOx emissions The process of governance means.
