Exploration of Selection of Low Temperature SCR Denitration Catalysts for Coking
Publishdate：2020-04-15 Views：42
With the continuous tightening of environmental emission standards, NOx emissions are also receiving increasing attention from the industry, and selective catalytic reduction (SCR) based denitrification methods are becoming a trend. Whether in the thermal power industry or non electric industry, synchronous construction or addition of SCR denitrification devices has become standard equipment. However, due to the different industries and processes used, the medium temperature SCR denitrification catalyst at 280-420 ℃, which is suitable for use in the thermal power industry, is not very suitable for non electric industries such as steel coking, sintering machines, waste incineration, glass, refractory materials, lime kilns, gas power generation, lithium batteries, silicon smelting, alumina and other industries, Due to the fact that the flue gas temperature in these non electric industries is lower than the range of use of medium temperature SCR catalysts, most flue gas temperatures are between 160~280 ℃. On the other hand, the composition of flue gas in non electric industries is more complex, with higher levels of alkali metals, moisture, and other harmful substances, which puts more stringent requirements on SCR denitrification catalysts as core equipment.
At present, in China, denitrification catalysts are divided into three types based on the usage temperature of SCR denitrification systems in different industries: low-temperature catalysts (160-280 ℃), medium temperature catalysts (280-420 ℃), and high-temperature catalysts (≥ 450 ℃). After determining the usage temperature of SCR denitrification systems, the type of catalyst is basically determined. Therefore, the operating temperature of the denitrification system is the basis for selecting the type of denitrification catalyst. This article focuses on exploring the selection of low-temperature SCR catalysts under temperature conditions. After determining the operating temperature of the denitrification system, catalysts should be selected from the following aspects: 1. Based on the actual working conditions of the flue gas, such as the required denitrification efficiency, NOx content at the inlet of the denitrification system, and the desired NOx emission value, the approximate amount of catalyst should be considered to determine the initial catalyst volume; Based on the actual dust content and characteristics in the flue gas working conditions, a comprehensive consideration should be given to which pore size catalyst to choose. If the dust content is high, a catalyst with a large pore size can be selected. On the contrary, use a small aperture. Adjust the production formula of the catalyst based on the content of SO2, moisture, and the presence of alkali metal heavy metals in the flue gas, so that it has different sulfur resistance, water resistance, and metal poisoning resistance, thereby ensuring the long-term operation of the catalyst. 4. As the usage temperature of low-temperature SCR denitrification catalyst is within the formation temperature range of ammonium bisulfate (ABS) and ammonium sulfate (AS), the engineering company or the owner should be reminded or advised to use relevant thermal analysis equipment during the actual catalyst selection process. Based on the designed catalyst dosage, the nature of the owner's industry, and the site, it is necessary to comprehensively consider whether to divide the denitrification system into compartments.
The coking industry is a typical non electric industry. Due to the characteristics of the coking industry, the design life of coke ovens is generally 30 years, and they cannot be stopped halfway. Environmental protection also requires an annual operation of 8760 hours. Regions with strict environmental requirements will require SCR systems to be divided into warehouses, which can achieve online single warehouse analysis, equipment maintenance, and catalyst replacement, thus putting higher requirements on environmental protection enterprises. For denitrification only, research has found that the waste gas generated by coke ovens varies greatly depending on the fuel used, resulting in significant differences in the exhaust temperature and pollutant content of the waste gas. Therefore, when selecting catalysts for denitrification systems, it is necessary to distinguish them based on the properties of the fuel.
If the fuel used in the coking plant is coke oven gas, its calorific value is higher, and its characteristic is that the exhaust temperature of the coke oven is generally between 250-310 ℃, which is greatly affected by production load. Relatively speaking, the flue gas conditions with higher pollutant content are more complex, with NOx content ranging from 700-1500mg/Nm3 and SO2 content ranging from 300-1000mg/Nm3. According to current standards, SO2 emissions are 30 mg/Nm3 and particulate matter emissions are 15 mg/Nm3. There are two processes to choose from, which are the existing wet desulfurization processes: coal tar pretreatment+medium and low temperature SCR denitrification+wet desulfurization. The advantage of this process is that it has a relatively low cost and a wide range of catalysts to choose from. However, the disadvantage is that the catalyst lifespan may not reach 3 years, and wet desulfurization does not meet the low temperature requirements for coke oven chimney hot standby, requiring heat exchange with the front end. After several years of actual operation, the chemical lifespan of the catalyst generally ranges from 2 to 3 years. The operating temperature of the catalyst can be selected as ≥ 230 ℃, ≥ 250 ℃, ≥ 270 ℃ depending on the sulfur content. There are many catalyst manufacturers with case studies available in the market. The second is the selection process without desulfurization system: SDS dry desulfurization+medium and low temperature SCR denitrification. The catalyst can operate under low sulfur and low dust conditions, and its chemical life can reach 3 years. The operating temperature of the catalyst can be selected as ≥ 180 ℃, ≥ 200 ℃, ≥ 220 ℃. The specific temperature can be selected based on the actual temperature of the desulfurization and dust removal system, and a suitable and experienced catalyst manufacturer can be selected.
The fuel used in the coking plant of a steel joint enterprise is blast furnace gas or mixed gas, which has a relatively low calorific value. Its characteristic is that the exhaust gas temperature of the coke oven is generally low, ranging from 200 to 260 ℃, and is greatly affected by production load. Relatively speaking, the pollutant content is also relatively low, with NOx content generally ≤ 500 mg/Nm3 and SO2 content generally ≤ 300 mg/Nm3. There are two process options: (semi) dry desulfurization+bag dust removal+low-temperature SCR denitrification. The second is carbon based dry desulfurization+medium and low temperature SCR denitrification catalyst. The key points of these two processes are that the temperature drop of dry desulfurization is 10-30 ℃ (depending on the desulfurization method, inlet SO2 concentration, and engineering insulation quality), and the temperature after denitrification meets the requirements of chimney hot standby, without the generation of wastewater and waste residue. The disadvantage is that there are few manufacturers to choose from for catalysts around 180-200 ℃, and the price is relatively high; But compared to heating up or heating up+heat exchange, a suitable low-temperature catalyst will save more energy and investment. Under low sulfur and low dust conditions, the early Baosteel Zhanjiang steel coking plant has been in operation for more than four years, and the catalyst life can reach 3-4 years, depending on the flue gas conditions and maintenance level. The operating temperature of the catalyst can be selected within the range of approximately 180-220 ℃. The specific temperature can be determined based on the temperature after desulfurization and dust removal. It is advisable to carefully choose a catalyst manufacturer with multiple years of experience.
In addition, due to the varying operating time of different coke ovens, the leakage of coke oven flue gas is also a factor affecting the selection of catalysts in the denitrification system. When designing catalysts, the actual usage of low-temperature SCR denitrification catalysts should be revised based on the coke oven leakage rate, in order to not only meet the qualified emissions of the denitrification system outlet indicators, but also ensure that the indicators detected by environmental protection are qualified.
In addition, due to the varying operating time of different coke ovens, the leakage of coke oven flue gas is also a factor affecting the selection of catalysts in the denitrification system. When designing catalysts, the actual usage of low-temperature SCR denitrification catalysts should be revised based on the coke oven leakage rate, in order to not only meet the qualified emissions of the denitrification system outlet indicators, but also ensure that the indicators detected by environmental protection are qualified. In summary, in the selection process of low-temperature SCR denitrification catalysts in the coking industry, not only should the influence of fuel be considered, but also relevant environmental protection process routes and the leakage situation of coke oven flue gas should be comprehensively considered.
For Fangxin Lihua, which is dedicated to the research and development of non electric low-temperature SCR denitrification catalysts, the research and development of SCR denitrification catalysts for coking is of utmost importance. At present, the performance of Fangxin Lihua low-temperature catalysts in coking has reached 88 sets, distributed in coke oven flue gas denitrification projects of large steel joint enterprises such as Baosteel Zhanjiang Steel Coking, Anshan Steel, Liuzhou Steel, Laiwu Steel Coking, Taiyuan Stainless Steel Coking, Hangang Group Coking, and Nanjing Steel, and has achieved good denitrification effects. Fangxin Lihua will continue to increase its research and development efforts, striving to provide assistance to coking enterprises in the selection of low-temperature catalysts.
With the continuous tightening of environmental emission standards, NOx emissions are also receiving increasing attention from the industry, and selective catalytic reduction (SCR) based denitrification methods are becoming a trend. Whether in the thermal power industry or non electric industry, synchronous construction or addition of SCR denitrification devices has become standard equipment. However, due to the different industries and processes used, the medium temperature SCR denitrification catalyst at 280-420 ℃, which is suitable for use in the thermal power industry, is not very suitable for non electric industries such as steel coking, sintering machines, waste incineration, glass, refractory materials, lime kilns, gas power generation, lithium batteries, silicon smelting, alumina and other industries, Due to the fact that the flue gas temperature in these non electric industries is lower than the range of use of medium temperature SCR catalysts, most flue gas temperatures are between 160~280 ℃. On the other hand, the composition of flue gas in non electric industries is more complex, with higher levels of alkali metals, moisture, and other harmful substances, which puts more stringent requirements on SCR denitrification catalysts as core equipment.
At present, in China, denitrification catalysts are divided into three types based on the usage temperature of SCR denitrification systems in different industries: low-temperature catalysts (160-280 ℃), medium temperature catalysts (280-420 ℃), and high-temperature catalysts (≥ 450 ℃). After determining the usage temperature of SCR denitrification systems, the type of catalyst is basically determined. Therefore, the operating temperature of the denitrification system is the basis for selecting the type of denitrification catalyst. This article focuses on exploring the selection of low-temperature SCR catalysts under temperature conditions. After determining the operating temperature of the denitrification system, catalysts should be selected from the following aspects: 1. Based on the actual working conditions of the flue gas, such as the required denitrification efficiency, NOx content at the inlet of the denitrification system, and the desired NOx emission value, the approximate amount of catalyst should be considered to determine the initial catalyst volume; Based on the actual dust content and characteristics in the flue gas working conditions, a comprehensive consideration should be given to which pore size catalyst to choose. If the dust content is high, a catalyst with a large pore size can be selected. On the contrary, use a small aperture. Adjust the production formula of the catalyst based on the content of SO2, moisture, and the presence of alkali metal heavy metals in the flue gas, so that it has different sulfur resistance, water resistance, and metal poisoning resistance, thereby ensuring the long-term operation of the catalyst. 4. As the usage temperature of low-temperature SCR denitrification catalyst is within the formation temperature range of ammonium bisulfate (ABS) and ammonium sulfate (AS), the engineering company or the owner should be reminded or advised to use relevant thermal analysis equipment during the actual catalyst selection process. Based on the designed catalyst dosage, the nature of the owner's industry, and the site, it is necessary to comprehensively consider whether to divide the denitrification system into compartments.
The coking industry is a typical non electric industry. Due to the characteristics of the coking industry, the design life of coke ovens is generally 30 years, and they cannot be stopped halfway. Environmental protection also requires an annual operation of 8760 hours. Regions with strict environmental requirements will require SCR systems to be divided into warehouses, which can achieve online single warehouse analysis, equipment maintenance, and catalyst replacement, thus putting higher requirements on environmental protection enterprises. For denitrification only, research has found that the waste gas generated by coke ovens varies greatly depending on the fuel used, resulting in significant differences in the exhaust temperature and pollutant content of the waste gas. Therefore, when selecting catalysts for denitrification systems, it is necessary to distinguish them based on the properties of the fuel.
If the fuel used in the coking plant is coke oven gas, its calorific value is higher, and its characteristic is that the exhaust temperature of the coke oven is generally between 250-310 ℃, which is greatly affected by production load. Relatively speaking, the flue gas conditions with higher pollutant content are more complex, with NOx content ranging from 700-1500mg/Nm3 and SO2 content ranging from 300-1000mg/Nm3. According to current standards, SO2 emissions are 30 mg/Nm3 and particulate matter emissions are 15 mg/Nm3. There are two processes to choose from, which are the existing wet desulfurization processes: coal tar pretreatment+medium and low temperature SCR denitrification+wet desulfurization. The advantage of this process is that it has a relatively low cost and a wide range of catalysts to choose from. However, the disadvantage is that the catalyst lifespan may not reach 3 years, and wet desulfurization does not meet the low temperature requirements for coke oven chimney hot standby, requiring heat exchange with the front end. After several years of actual operation, the chemical lifespan of the catalyst generally ranges from 2 to 3 years. The operating temperature of the catalyst can be selected as ≥ 230 ℃, ≥ 250 ℃, ≥ 270 ℃ depending on the sulfur content. There are many catalyst manufacturers with case studies available in the market. The second is the selection process without desulfurization system: SDS dry desulfurization+medium and low temperature SCR denitrification. The catalyst can operate under low sulfur and low dust conditions, and its chemical life can reach 3 years. The operating temperature of the catalyst can be selected as ≥ 180 ℃, ≥ 200 ℃, ≥ 220 ℃. The specific temperature can be selected based on the actual temperature of the desulfurization and dust removal system, and a suitable and experienced catalyst manufacturer can be selected.
The fuel used in the coking plant of a steel joint enterprise is blast furnace gas or mixed gas, which has a relatively low calorific value. Its characteristic is that the exhaust gas temperature of the coke oven is generally low, ranging from 200 to 260 ℃, and is greatly affected by production load. Relatively speaking, the pollutant content is also relatively low, with NOx content generally ≤ 500 mg/Nm3 and SO2 content generally ≤ 300 mg/Nm3. There are two process options: (semi) dry desulfurization+bag dust removal+low-temperature SCR denitrification. The second is carbon based dry desulfurization+medium and low temperature SCR denitrification catalyst. The key points of these two processes are that the temperature drop of dry desulfurization is 10-30 ℃ (depending on the desulfurization method, inlet SO2 concentration, and engineering insulation quality), and the temperature after denitrification meets the requirements of chimney hot standby, without the generation of wastewater and waste residue. The disadvantage is that there are few manufacturers to choose from for catalysts around 180-200 ℃, and the price is relatively high; But compared to heating up or heating up+heat exchange, a suitable low-temperature catalyst will save more energy and investment. Under low sulfur and low dust conditions, the early Baosteel Zhanjiang steel coking plant has been in operation for more than four years, and the catalyst life can reach 3-4 years, depending on the flue gas conditions and maintenance level. The operating temperature of the catalyst can be selected within the range of approximately 180-220 ℃. The specific temperature can be determined based on the temperature after desulfurization and dust removal. It is advisable to carefully choose a catalyst manufacturer with multiple years of experience.
In addition, due to the varying operating time of different coke ovens, the leakage of coke oven flue gas is also a factor affecting the selection of catalysts in the denitrification system. When designing catalysts, the actual usage of low-temperature SCR denitrification catalysts should be revised based on the coke oven leakage rate, in order to not only meet the qualified emissions of the denitrification system outlet indicators, but also ensure that the indicators detected by environmental protection are qualified.
In addition, due to the varying operating time of different coke ovens, the leakage of coke oven flue gas is also a factor affecting the selection of catalysts in the denitrification system. When designing catalysts, the actual usage of low-temperature SCR denitrification catalysts should be revised based on the coke oven leakage rate, in order to not only meet the qualified emissions of the denitrification system outlet indicators, but also ensure that the indicators detected by environmental protection are qualified. In summary, in the selection process of low-temperature SCR denitrification catalysts in the coking industry, not only should the influence of fuel be considered, but also relevant environmental protection process routes and the leakage situation of coke oven flue gas should be comprehensively considered.
For Fangxin Lihua, which is dedicated to the research and development of non electric low-temperature SCR denitrification catalysts, the research and development of SCR denitrification catalysts for coking is of utmost importance. At present, the performance of Fangxin Lihua low-temperature catalysts in coking has reached 88 sets, distributed in coke oven flue gas denitrification projects of large steel joint enterprises such as Baosteel Zhanjiang Steel Coking, Anshan Steel, Liuzhou Steel, Laiwu Steel Coking, Taiyuan Stainless Steel Coking, Hangang Group Coking, and Nanjing Steel, and has achieved good denitrification effects. Fangxin Lihua will continue to increase its research and development efforts, striving to provide assistance to coking enterprises in the selection of low-temperature catalysts.
