Development of low-temperature catalytic denitrification technology
Publishdate：2018-05-03 Views：13
At present, the research on low-temperature selective catalytic reduction technology using NH3 as the reducing agent is relatively in-depth in low-temperature catalytic denitrification technology. The characteristics of low temperature and high efficiency make this type of catalyst suitable for low dust and low sulfur environments. However, the research on low-temperature catalysts for non ammonia catalytic denitrification has only become a hot topic in recent years. Due to the incomplete reaction of hydrocarbons in the low-temperature stage and the high production rate of N2O, there are still many problems that need to be solved urgently, Here is a summary of the catalysts and applications of low-temperature catalytic denitrification technology.
(1) For NH3-SCR technology, due to the high activation energy of the reaction between NH3 and NOx, the decrease in temperature window requires high activity of the catalyst, which requires the catalyst to have a good morphology and more active sites. Therefore, improving the catalyst preparation process and adjusting the catalyst metal ratio is a hot research topic. Due to the decrease in temperature, NH4SO4 is easy to form and adhere, so low-temperature NH3-SCR is not easily placed in front of the desulfurization tower. However, the low-temperature flue gas after desulfurization contains high moisture, so the low-temperature NH3-SCR catalyst needs to improve its water resistance performance.
(2) In terms of non ammonia catalytic denitrification technology, although nitrogen oxide direct cracking technology does not require reducing agents, its efficiency is difficult to meet practical requirements. HC-SCR technology has high efficiency but faces two major challenges: when the temperature is too low, hydrocarbons are prone to decompose into solid carbon, causing carbon deposition deactivation; Secondly, oxygen will competitively react with hydrocarbons, consuming reducing agents. CO catalytic denitrification technology solves the problem of low-temperature carbon deposition, but the negative effect of oxygen cannot be solved. The nitrogen oxide adsorption reduction technology not only solves the problem of low-temperature carbon deposition but also the negative impact of oxygen, but the currently used catalysts have a smaller adsorption volume. Therefore, the future research on low-temperature non ammonia catalytic denitrification technology can focus on the following aspects. To address the negative effects of oxygen, it is necessary to develop highly selective catalysts to avoid the oxidation of hydrocarbons and CO; The second is innovation in denitrification processes, such as the development of nitrogen oxide adsorption reduction catalysts. At present, research mainly focuses on molecular sieve supported catalysts, and compared with carbon materials, molecular sieves have complex preparation processes, higher prices, smaller NOx adsorption volumes, and must minimize space velocity in the adsorption area; Carbon materials, especially natural source carbon materials with activated carbon and activated semi coke as the main body (prepared by high-temperature pyrolysis of coal or biomass), due to their simple preparation process, complex surface active groups, and higher NOx adsorption capacity after metal loading, can achieve higher adsorption efficiency at high altitudes, and are expected to become a research hotspot in the future. In addition, the water vapor content in the flue gas is relatively high (>8% [1]), and water vapor has a certain negative impact on non ammonia catalytic denitrification. Therefore, improving the water resistance performance and extending the service life of the catalyst are also the focus of research.
At present, the research on low-temperature selective catalytic reduction technology using NH3 as the reducing agent is relatively in-depth in low-temperature catalytic denitrification technology. The characteristics of low temperature and high efficiency make this type of catalyst suitable for low dust and low sulfur environments. However, the research on low-temperature catalysts for non ammonia catalytic denitrification has only become a hot topic in recent years. Due to the incomplete reaction of hydrocarbons in the low-temperature stage and the high production rate of N2O, there are still many problems that need to be solved urgently, Here is a summary of the catalysts and applications of low-temperature catalytic denitrification technology.
(1) For NH3-SCR technology, due to the high activation energy of the reaction between NH3 and NOx, the decrease in temperature window requires high activity of the catalyst, which requires the catalyst to have a good morphology and more active sites. Therefore, improving the catalyst preparation process and adjusting the catalyst metal ratio is a hot research topic. Due to the decrease in temperature, NH4SO4 is easy to form and adhere, so low-temperature NH3-SCR is not easily placed in front of the desulfurization tower. However, the low-temperature flue gas after desulfurization contains high moisture, so the low-temperature NH3-SCR catalyst needs to improve its water resistance performance.
(2) In terms of non ammonia catalytic denitrification technology, although nitrogen oxide direct cracking technology does not require reducing agents, its efficiency is difficult to meet practical requirements. HC-SCR technology has high efficiency but faces two major challenges: when the temperature is too low, hydrocarbons are prone to decompose into solid carbon, causing carbon deposition deactivation; Secondly, oxygen will competitively react with hydrocarbons, consuming reducing agents. CO catalytic denitrification technology solves the problem of low-temperature carbon deposition, but the negative effect of oxygen cannot be solved. The nitrogen oxide adsorption reduction technology not only solves the problem of low-temperature carbon deposition but also the negative impact of oxygen, but the currently used catalysts have a smaller adsorption volume. Therefore, the future research on low-temperature non ammonia catalytic denitrification technology can focus on the following aspects. To address the negative effects of oxygen, it is necessary to develop highly selective catalysts to avoid the oxidation of hydrocarbons and CO; The second is innovation in denitrification processes, such as the development of nitrogen oxide adsorption reduction catalysts. At present, research mainly focuses on molecular sieve supported catalysts, and compared with carbon materials, molecular sieves have complex preparation processes, higher prices, smaller NOx adsorption volumes, and must minimize space velocity in the adsorption area; Carbon materials, especially natural source carbon materials with activated carbon and activated semi coke as the main body (prepared by high-temperature pyrolysis of coal or biomass), due to their simple preparation process, complex surface active groups, and higher NOx adsorption capacity after metal loading, can achieve higher adsorption efficiency at high altitudes, and are expected to become a research hotspot in the future. In addition, the water vapor content in the flue gas is relatively high (>8% [1]), and water vapor has a certain negative impact on non ammonia catalytic denitrification. Therefore, improving the water resistance performance and extending the service life of the catalyst are also the focus of research.
