On June 13, the "11th China Cement Energy Conservation and Environmental Protection Technology Exchange Conference-Equipment Renewal Forum" was held grandly. Ba Taibin, a professor-level senior engineer of Zhengzhou Tonghui Design Institute, a senior consultant of China Cement Network, made a theme report on "Discussion and Selection of Denitrification Technology Route for Cement Plants".
Bataibin explained in detail the current situation of denitrification technology in domestic cement industry from the aspects of the necessity of denitrification, the research of Nox, the discussion of out-of-stock technology and the selection of out-of-stock technology. The necessity
of out-of-stock < IMG SRC = "The https://img7.ccement.com/richtext/img/iuplqu9qsfl1718845878730. meeting stressed that the implementation of ultra-low emissions in the cement industry should be promoted." It is an important measure to defend the blue sky. We should reduce pollutant emissions from the source and promote the synergy of pollution reduction and carbon reduction. On January 19,
2024, the Ministry of Environmental Protection issued the Opinions on Promoting the Implementation of Ultra-low Emission in Cement Industry.
Time requirement: By the end of 2025, significant progress will be made in key areas. About 50% of cement < a href = "https://price.ccement.com/Price_list-1-s0-e0-p0-c0-k100059-b0.
index requirements: under the condition that the reference oxygen content is 10%, The hourly average emission concentration of flue gas particulate matter, sulfur dioxide and nitrogen oxides in the waste heat utilization system of cement kiln and kiln tail shall not be higher than 10, 35 and 50mg/Nm ³ respectively. At least 95% of the hourly average emission concentration of cement enterprises with ultra-low emission meets the above requirements.
From the point of view of the harm of nitrogen oxides to the environment, with the acceleration of economic development and urbanization in China, the emission of nitrogen oxides will continue to grow. For this reason, from the beginning of the "Twelfth Five-Year Plan" to now, the state has taken the reduction of nitrogen oxide emissions as a rigid target for energy conservation and emission reduction.
Nitrogen oxides, mainly nitric oxide and nitrogen dioxide, are an important cause of photochemical smog and acid rain, which will cause great harm to human body and the environment.
NO is a colorless and odorless gas, which can easily combine with heme in the blood, causing blood hypoxia and central nervous system paralysis. Various potential carcinogens destroy the ozone layer, which can destroy the ozone layer under certain conditions and affect the ultraviolet protection of the earth. Photochemical smog will reduce atmospheric visibility and affect environmental quality and traffic safety. Acid rain is formed, which is harmful to soil, vegetation and water.
According to the NOx emission of cement plants, the NOx emission coefficient is 1.5--1. The total NOx emission of cement industry accounts for about 10% of the total emission of the country, which is the third largest emission source after thermal power generation and iron and steel. Therefore, the national environmental protection department pays special attention to cement enterprises.
From the point of view of enterprise development, at present, the air pollutants dust and sulfur dioxide in cement plants have been basically controlled, and nitrogen oxides have become the main source of waste gas pollution.
The government's special funds for environmental protection and pollution control are time-sensitive, and enterprises should seize the opportunity. Through technological transformation,
enterprises can achieve emission standards (ultra-low emissions), enhance the overall image of enterprises, promote technological upgrading and enhance competitiveness.
Nitrogen oxide emissions are large, harmful to the environment, policy control is strong, ultra-low emission indicators have been clear, the completion time of technological transformation to achieve ultra-low emissions has entered the countdown, for enterprises, "denitrification technology, emission standards" is necessary to do, there is no other choice.
Nox research
is aimed at the source of nitrogen. According to Bataibin's analysis, the source of nitrogen in nitrogen oxide species is mainly divided into three parts. First, nitrogen in raw materials: the content of nitrogen-containing compounds from ore deposits is low, and the use of industrial solid wastes (such as fly ash, coal gangue, etc.) In raw material ingredients will bring in some nitrogen compounds. Nitrogen oxides in raw materials are mainly affected by the content of nitrate and nitrite in the ingredients, and the nitrogen oxides in raw materials can not be removed by conventional denitrification means; The second is nitrogen in the fuel: nitrogen compounds deposited during the formation of fossil fuels are generally 0.5-2.
For the formation of nitrogen oxides, Bataibin said that nitrogen oxides are divided into thermal NOx, fuel NOx and fast NOx. Thermal NOx
refers to the NOx produced by the oxidation of N2 in the air at high temperature. The yield mainly depends on the temperature. When the temperature is lower than 1500 ℃, there is almost no yield, but when the temperature is higher than 1500 ℃, there will be a large amount of yield. The yield is related to the combustion temperature, oxygen concentration, residence time in the high temperature zone, etc. It is mainly produced in the kiln, and the influencing factors include volatile matter of pulverized coal, KH value of raw meal, process operation, oxygen concentration, carbon monoxide concentration, etc.
Fuel NOx: a nitrogen compound in the fuel is thermally decomposed and oxidized during the combustion process. It is mainly produced in the calciner, and the influencing factors include the nitrogen content of pulverized coal, oxygen concentration (excess air coefficient), etc.
Fast NOx (Fenimore NOx): Nox is generated rapidly near the reaction zone by N2 in the air and hydrocarbon ion groups (CH, CH2, etc.) in the fuel, and its generation is relatively small, generally accounting for less than 5% of the total NOx.
NOx mainly comes from fuel combustion in rotary kiln and decomposition furnace. NOx of untreated flue gas is mainly distributed as follows:
NOx at the outlet of flue gas chamber: thermal and fuel NOx, with concentration of about 800 ~ 2600mg/Nm ³;
NOx at the outlet of decomposition furnace: fuel NOx, with concentration of about 800 ~ 1300mg/Nm ³; NOx at
C1 outlet: concentration is about 800-1200mg/Nm ³.
Ba Taibin discussed the relationship between Nox in smoke chamber and clinker strength. Ba Taibin pointed out that the level of NOx in the smoke chamber at the end of the kiln can reflect the quality of the calcination in the kiln. Generally, the high concentration of NOx in the smoke chamber indicates that the calcination in the kiln is good. On the contrary, the calcination in the kiln is not good, and the clinker strength in the kiln is high. On the contrary, the clinker strength is low. High temperature in the
kiln: large amount of NOx generated, high clinker yield and high strength. The temperature in the
kiln is low: the reducing atmosphere is dense, the NOx in the smoke chamber is low, the clinker strength is low, the output is not high, and the yellow core material is more. In order to control NOx,
some enterprises deliberately lower the kiln temperature and increase the reducing atmosphere, resulting in ugly clinker color and reduced clinker strength. It is not advisable to reduce the quality of
clinker to reduce the formation of NOx and achieve ultra-low emissions.
Ba Taibin introduced the current mainstream technology of denitrification. According to incomplete statistics, there are more than ten kinds of denitrification technologies at present. Under different conditions and different use scenarios, various denitrification technologies are playing their due roles, providing valuable experience for the progress of denitrification technology.
1、 source treatment: Nox generated in the kiln is solved by a process method; the technical scheme comprises low-nitrogen combustion, graded combustion and pipeline reduction; the implementation position: the source denitration is mainly between a smoke chamber and a decomposition furnace.
Low nitrogen combustion: reduce the primary air volume (8-10%), increase the swirl nozzle, improve the uniformity of flame temperature distribution, and reduce the generation of thermal nitrogen.
Staged combustion: Staged combustion is a technology that adds fuel, tertiary air and materials at different times to reduce the generation of nitrogen oxides and reduce nitrogen oxides to nitrogen. In the reducing area of the decomposition furnace, the fuel is combusted in an oxygen-deficient state to reduce nitrogen oxides, and then is combusted completely in an oxygen-rich state. Controlling the temperature distribution of the calciner by controlling the raw meal feeding is beneficial to the staged combustion. Both NOx and fuel NOx are reduced by staged combustion. The effect of
staged combustion is closely related to the characteristics of pulverized coal and the volume of the calciner. The effect of different production lines is quite different. It can reduce the initial NOx concentration and reduce the pressure of SNCR and SCR.
Pipeline reduction technology: the pipeline reduction furnace is arranged between the kiln tail smoke chamber and the decomposition furnace, the air inlet is connected with the kiln tail smoke chamber, the air outlet is connected with the bottom of the decomposition furnace, the CO generated by the coal entering the denitration furnace and the NOx in the kiln are fully reacted and reduced in the denitration furnace, and the flue gas after denitration enters the decomposition furnace. The measured value of NOx at the outlet of the denitration furnace is 0, and the denitration rate is 100%!
Technical highlights 1. Materials entering the denitration furnace are preheated and decomposed in advance while balancing the temperature, which prolongs the decomposition time, improves the decomposition rate of materials entering the kiln, and realizes production increase, energy saving, consumption reduction and emission reduction!Intermediate treatment of
2、: SNCR technology; technical scheme: traditional SNCR, intelligent SNCR; implementation location: intermediate denitration is mainly in the five-stage cyclone. Selective Non-Catalytic Reduction
(SNCR) reduces nitrogen oxides to non-toxic nitrogen and water without the use of a catalyst.
Technical features: the investment is low, the SNCR denitration efficiency is 40 ~ 60%, and the emission requirement of less than 100mg/m ³ can be achieved on the premise of increasing the ammonia water injection, but the ammonia water consumption is large and the ammonia escape is high.
Precise ammonia injection SNCR technology has made great progress in recent years, which can achieve lower emission targets, but is also limited by a variety of conditions.
3、 end treatment: mainly SCR technology; technical scheme: high temperature high dust SCR, high temperature medium dust (low dust) SCR, medium temperature low dust SCR, low temperature low dust SCR, wet LCR; Real-time position: The terminal denitration is mainly after
the C1 outlet, and the Selective Catalytic Reduction (SCR) is mainly used to promote the reaction of ammonia and nitrogen oxides under the action of catalyst.
According to the classification of dust, the flue gas dust entering the reactor is divided into high dust, medium dust and low dust, which are related to the means of dust removal. Classification
by temperature: the temperature of flue gas entering the reactor is divided into high temperature, medium temperature and low temperature, which is related to the location of the reactor. Different catalysts shall be selected for different temperatures.
Cost: The cost per ton of clinker with SCR system will increase by about 4 yuan, which will bring competitive pressure to the enterprise.
Hazardous waste: the catalyst is generally used for 2-3 years and needs to be replaced, and the replaced catalyst is hazardous waste, which is troublesome to treat.
Sensitive: The catalyst is sensitive to temperature, dust, SO2, etc., which is easy to cause blockage, abrasion and poisoning.
Ba Taibin said that the end treatment is a passive choice.
< IMG SRC = "https://img7.ccement.com/richtext/img/au27otve52e1718845908681. Through the analysis and comparison of various denitration technologies, practice has proved that: When the pipeline reduction technology is used together with the existing SNCR, the NOx emission is less than 50mg/Nm ³, which can meet the requirements of ultra-low emission and ammonia escape stably for a long time, and it is an ideal choice at present.
Through the research on the decomposition technology outside the kiln and the analysis on the change of flue gas composition at the kiln tail, the pipeline reduction deep denitration technology was introduced to minimize the use of reductant and catalyst and the generation of hazardous waste. After the application in many cement enterprises, good results were achieved, and the NOx emission was less than 50mg/Nm ³.
Pipeline reduction denitrification technology is a technological innovation, which uses the mechanism of NOx reduction in the pipeline to control from the source. The principle of
NOx reduction is to separate a part or all of the coal used in the decomposition furnace and inject it into the preheating area of the pipe furnace to form "anaerobic combustion" under the anoxic working condition of the pipe furnace. The generated CO reacts with the NOx in the flue gas at the kiln tail and reduces the NOx generated in the kiln to N2 gas harmless to the environment.
< IMG SRC = "The materials entering the denitration furnace https://img7.ccement.com/richtext/img/bglcf3j6yzt1718845922015. are preheated and decomposed in advance while balancing the temperature." Prolongs the preheating and decomposition time of the raw meal and improves the decomposition rate of the material entering the kiln.
The denitration furnace is arranged between the kiln tail smoke chamber and the decomposition furnace, an air inlet of the denitration furnace is connected with a necking opening at the top of the kiln tail smoke chamber, and an air outlet of the denitration furnace is connected with the bottom of the decomposition furnace. The inlet end of the denitration furnace is provided with a pulverized coal inlet and a material inlet, the coal feeding in the denitration furnace is mainly for generating CO, and the material feeding is mainly for balancing the temperature in the furnace.
The pipeline denitration technology has the following characteristics: realizing online self-denitration; increasing clinker output; reducing coal consumption and power consumption; using alternative fuels; NOx emission is less than 50mg/Nm ³; Under the same conditions, the consumption of ammonia water is lower. Can
reach 1.5-2.img/t clinker SRC = "Environmental protection benefits of https://img7.ccement.com/richtext/img/6d6xrajl2kj1718845937883.
: the pipeline denitration technology conforms to the relevant national policies." The advanced index of NOx emission concentration < 50mg/Nm ³ (10% O2) is realized, and no hazardous waste is generated during operation, which can effectively improve the local environmental quality and enable cement enterprises to become environment-friendly enterprises, with obvious environmental benefits.
Social benefit: Pipeline denitration is a new technical breakthrough to solve the problem of NOx in production by using process technology, which provides a new technical way for denitration in cement enterprises and has good social benefit.
Economic benefit: the application of pipeline denitration technology can improve the output and quality of clinker, reduce coal consumption and power consumption, without new operation cost, and the economic benefit is remarkable. Compared with a 5000t/d end treatment technology, the annual cost can be saved by about 6 million yuan. Ba Taibin introduced the selection
of denitrification technology, and the denitrification technology of pipe furnace was put into the market and received attention from relevant parties. In May 2023, the technical investigation team organized by the State Inspection and Quarantine Group investigated the technical transformation of Jiangshan, Shanya and Sanming companies, and found that the denitrification technology of the tube furnace was stable in operation, simple in operation, and achieved the ultra-low emission target. Compared with similar technologies, the investment was reasonable, the operation cost was low, and there was no catalyst consumption.
Hangzhou Shanya Cement 5000tpd Production Line Denitrification Technical Transformation Project (Phase II) was commenced on November 8, 2023, the kiln was shut down for docking on February 14, 2024, and the material was fed on March 13. After the project is put into operation, it runs stably and has good effect. NOx at the outlet of C1 is reduced to below 50mg/Nm ³, Ammonia consumption has decreased by 37.
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to find a denitration method in the cement process." It is a problem that cement workers have been discussing to achieve standard discharge without external reducing agents and catalysts. It is known that the research results of some companies at home and abroad in this area have been applied in many cement plants, and the measured data show that the concentration of nitrogen oxides at the outlet of the denitrification furnace can be reduced to zero! At present, due to the problem of air leakage, a small part of NOx-containing gas does not enter the reduction furnace, but enters the C5, as well as the NOx generated by combustion in the decomposition furnace, which needs to be combined with the existing SNCR system to achieve the emission index of NOx < 50 mg/Nm ³.
Ba Taibin pointed out that the pipeline denitration technology has obvious advantages and is a development direction. In order to achieve denitration with less ammonia or without ammonia, further research is needed:
1. Study how to reduce the air leakage of the air lock valve, so that the NOx gas in the smoke chamber does not enter or less enter C5; The research on the combustion mechanism of the precalciner should be strengthened
2、 to avoid the generation of thermal nitrogen oxides in the precalciner as far as possible.
3. The operation should be optimized to avoid or reduce the generation of fuel nitrogen oxides in the precalciner by feeding all the tailings into the denitrification furnace.
