Abstract : The principle of selective non-catalytic reduction (SNCR) denitration technology is introduced. The reasons for denitrification in the glass industry are introduced. The advantages and limitations of SNCR denitration technology are analyzed from the perspective of glass processing and furnace life, and the SNCR denitrification is proposed. The feasibility of using technology in the glass industry.
The main harmful components in the exhaust gas of glass factories are SO2, NOx, COx, HF and hydrocarbons. Among them, SO2 and NOx are contained in large amounts, causing serious damage to humans, animals, plants and the ecological environment, limiting the emission of harmful gases, and protecting humans. The ecological environment has become the primary task of national governance. With the continuous strengthening of the country's enforcement of environmental protection policies, the daily-use glass industry is facing a great deal of tests. Controlling the emission of NOx in flue gas is a key and difficult point in the treatment of exhaust gas. Since 2013, various companies have invested a large amount of funds for the treatment of nitrogen oxides. However, due to the unique characteristics of the process, combustion, and exhaust gas components, exhaust gas treatment technology still has certain defects and becomes a problem that plagues the development of the industry. .
1 Denitrification and denitrification methods
Denitrification is the reduction of nitrogen oxide (NOx) content in exhaust emissions. Denitrification technology is also the control of nitrogen oxide emission concentration technology. The current denitrification methods in the glass industry include low-nitrogen (fragmented) combustion, ozone oxidation, selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR).
Low-nitrogen combustion divides the entire combustion zone of the furnace into main combustion zone, reburn zone and burn-out zone. 80% to 85% of the fuel is sent to the main combustion zone, and the fuel is combusted in the main combustion zone to generate NOx, 15% to 20%. The fuel is fed to the reburn zone. The excess air ratio in the reburn zone is less than 1.0 (Î±<1.0). There is a strong reducing atmosphere. The NOx generated in the main combustion zone is reduced, and the reburn zone can not only restore the NOx generated, but also The generation of new NOx is suppressed, and a certain amount of air is supplied in the burnout zone (referred to as the overfire air) to ensure that the incomplete combustion product from the reburn zone burns out.
The principle of ozone oxidation and denitrification is to utilize the strong oxidizing property of ozone to oxidize NO into high-valent nitrogen oxides such as NO2, N2O3, and N2O5 that can be dissolved in water to generate HNO2 and HNO3, and then absorb it with a solution to convert NOx into N2. The purpose of removal.
Selective catalytic reduction is the use of reducing agent NH3 under the action of catalyst titanium, zirconium and other rare metals, selectively reacts with NOx in the flue gas to produce nitrogen and water.
Selective non-catalytic reduction refers to the selective use of a reducing agent to chemically react with nitrogen oxides (NOx, mainly NO and NO2) in the flue gas to produce harmless nitrogen and water without the need for a catalyst. In order to remove the smoke uric acid and various ammonium salts. The normal reaction temperature is between 800 and 1100Â°C, and the optimal reaction temperature is 950Â°C.
2 reasons for the difficulty of denitrification in the glass industry
Denitrification is not a sophisticated technology. In the United States 25 years ago, Chinaâ€™s steel, electricity, cement, and chemical industries started denitrification six or seven years ago, and their technology is mature. Why the technology is mature in other industries, it is not easy to use it in the glass industry. The main reasons are as follows:
(1) In the power, cement and chemical industries, the degree of denitrification is low, generally around 900Â°C. As we all know, nitrogen oxides are produced only when they are combusted. The temperature is high and the amount produced is greater. As the daily-use glass industry, the flame combustion temperature is generally about 1580C, and the glass temperature is about 1480C. Therefore, although the emissions are small, the concentration of nitrogen oxides is several times that of other industries.
(2) During the reversal of the glass melting furnace, the kiln temperature, the kiln pressure, and the fuel input into the kiln will all have significant changes. These changes also affect the production of nitrogen oxides. It can be seen through the on-line testing equipment that the concentration of nitrogen oxides in the combustion of the glass melting furnace is non-linear, and the difference between the high and low levels exceeds 30%. This means that it is difficult to solve the stability of emissions from a technical level.
(3) The components involved in the reaction in glass melting furnaces are relatively complex. In addition to the formation of glass, there are more than a dozen side reactions that generate a variety of other substances. The presence of these substances will have a certain impact on the denitrification process.
(4) The amount of flue gas in the new melting furnace and the old melting furnace varies greatly. Compared with the later period of use, a newly-built melting furnace has a difference of nearly 1 time in the amount of flue gas. The main reason is that the late melting furnace seal is not strict, the combustion air is large, the entire system runs under negative pressure, and there is more air inhalation.
(5) Excessive equipment costs and operating costs have, to a certain extent, led to the enthusiasm of glass companies. The industry is considered to be the most stable low-nitrogen (fragmented) combustion method and ozone oxidation method. If this technology is used for denitrification, it is estimated that each bottle needs to increase the cost of about 0.06 yuan, which is unsustainable as a daily-use glass for the low-profit industry. .
3 Selective non-catalytic reduction (SNCR) denitrification technology application in glass companies
The SCR denitrification technology, which is widely used in the solar glass industry, has obvious defects. The main performance is the high temperature requirements, and the catalyst is easily poisoned (alkali metal) or sticky package is invalid, the application is very troublesome, the overall efficiency is about 50%. In the first three months of equipment installation, the denitrification effect was obvious, reaching more than 80%, followed by rapid decay, and after six months of use, the activity was basically lost.
Selective non-catalytic reduction (SNCR) denitrification technology is based on the principle of spraying reducing agent (usually 870-950Â°C) in the condition of 850-1050Â°C, generally ammonia water or urea solution, reducing NOx in flue gas into N2 and H2O reduce NOx emissions.
The key issues are the following points.
3.1 The use of selective non-catalytic reduction (SNCR) denitrification technology can not meet the standard
The denitrification efficiency of the selective non-catalytic reduction (SNCR) denitration technology recognized by experts is 30% to 70%. Experts are not wrong in saying that this is because the full coverage of exhaust gas by reductants has not been solved. As long as this problem is solved, it is entirely possible to increase the denitration efficiency to 80%.
We know that the difference between catalytic (SCR) and non-catalytic (SNCR) methods lies in the absence of a catalyst. The role of the catalyst is to interfere with the reaction conditions. The catalyst itself does not participate in the reaction process. Therefore, as long as the reaction conditions are satisfied, there is no difference in the denitrification efficiency between catalytic (SCR) and non-catalytic (SNCR) processes.
In the case of both temperature and other reaction conditions, the removal rate of selective non-catalytic reduction (SNCR) denitration technology is beyond doubt. This conclusion is based on both theoretical evidence and data from installed companies.
3.2 Using Selective Non-catalytic Reduction (SNCR) Denitrification Techniques Will Not Affect Melt Furnace Service Life
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