One Question per Day in Applied Chemistry 8-10

　In waste gas treatment equipment, flue gas desulfurization technologies include gas-phase reaction methods, liquid absorption methods, adsorption methods, liquid film methods, microbial methods, and others. 　　I. The gas-phase reaction methods are further divided into 3 categories: 1. Electron beam irradiation method and pulsed corona plasma method; 2. Selective catalytic reduction method, selective non-catalytic reduction method, and hot carbon reduction method; 3. Low-temperature and normal-pressure plasma decomposition method, etc. The first category involves using radicals generated by high-energy electrons to oxidize NO to N2O2, which then reacts with H2O and NH3 to produce NH4NO3, which can be recovered and reused, thereby enabling both desulfurization and denitrification. The second category consists of methods in which reducing agents such as NH3 and C are used, under catalytic or non-catalytic conditions, to reduce nitrogen compounds to harmless N2. The third category utilizes high-energy active particles produced by ultra-high-pressure narrow-pulse corona discharge to strike NOx molecules, breaking their chemical bonds and causing them to decompose into O2 and N2. 　　II. There are many methods for absorbing NOx using the liquid absorption approach, and these methods are widely applied. NOx can be absorbed using water, alkaline solutions, dilute nitric acid, and concentrated sulfuric acid. Since NO is extremely insoluble in water or alkaline solutions, the efficiency of wet denitration is generally not very high. Therefore, oxidation, reduction, or combined absorption methods are employed to improve the purification efficiency of NO. Compared with dry methods, wet methods have advantages such as simpler process equipment and lower investment; some of these methods can also recover NOx, offering certain economic benefits. The downside is that the purification effect is slightly poor. Flue gas desulfurization process flow Flue gas desulfurization process flow III. Removal of NOx by adsorption; common adsorbents include molecular sieves, activated carbon, natural zeolites, silica gel, and peat. Some of these adsorbents, such as silica gel, molecular sieves, and activated carbon, also possess catalytic properties; they can catalytically oxidize NO in exhaust gases to NO2, which can then be recovered by absorption with water or alkali. The adsorption method achieves high denitration efficiency and can recover NOx, but it is not widely used due to reasons such as low adsorption capacity, high consumption of adsorbents, large-sized equipment, and frequent regeneration. 　　Overall, the methods currently used in industry are mainly divided into two categories: gas-phase reaction methods and liquid absorption methods. Among these two categories of methods, catalytic reduction and alkaline absorption are the main approaches. The former can reduce the NOx emission concentration in exhaust gases to low levels, but it consumes large amounts of NH3; in some cases, fuel gas is also used, resulting in economic losses. The latter allows for the recovery of NO as nitrates and nitrites, offering certain economic benefits, but its purification effect is not high enough to reduce NOx to low levels. The commonly used methods all have their shortcomings; therefore, greater efforts are still needed to identify one or several denitration technologies that are technically feasible, economically reasonable, and suitable for China’s national conditions.

　In waste gas treatment equipment, flue gas desulfurization technologies include gas-phase reaction methods, liquid absorption methods, adsorption methods, liquid film methods, microbial methods, and others. 　　I. The gas-phase reaction methods are further divided into 3 categories: 1. Electron beam irradiation method and pulsed corona plasma method; 2. Selective catalytic reduction method, selective non-catalytic reduction method, and hot carbon reduction method; 3. Low-temperature and normal-pressure plasma decomposition method, etc. The first category involves using radicals generated by high-energy electrons to oxidize NO to N2O2, which then reacts with H2O and NH3 to produce NH4NO3, which can be recovered and reused, thereby enabling both desulfurization and denitrification. The second category consists of methods in which reducing agents such as NH3 and C are used, under catalytic or non-catalytic conditions, to reduce nitrogen compounds to harmless N2. The third category utilizes high-energy active particles produced by ultra-high-pressure narrow-pulse corona discharge to strike NOx molecules, breaking their chemical bonds and causing them to decompose into O2 and N2. 　　II. There are many methods for absorbing NOx using the liquid absorption approach, and these methods are widely applied. NOx can be absorbed using water, alkaline solutions, dilute nitric acid, and concentrated sulfuric acid. Since NO is extremely insoluble in water or alkaline solutions, the efficiency of wet denitration is generally not very high. Therefore, oxidation, reduction, or combined absorption methods are employed to improve the purification efficiency of NO. Compared with dry methods, wet methods have advantages such as simpler process equipment and lower investment; some of these methods can also recover NOx, offering certain economic benefits. The downside is that the purification effect is slightly poor. Flue gas desulfurization process flow Flue gas desulfurization process flow III. Removal of NOx by adsorption; common adsorbents include molecular sieves, activated carbon, natural zeolites, silica gel, and peat. Some of these adsorbents, such as silica gel, molecular sieves, and activated carbon, also possess catalytic properties; they can catalytically oxidize NO in exhaust gases to NO2, which can then be recovered by absorption with water or alkali. The adsorption method achieves high denitration efficiency and can recover NOx, but it is not widely used due to reasons such as low adsorption capacity, high consumption of adsorbents, large-sized equipment, and frequent regeneration. 　　Overall, the methods currently used in industry are mainly divided into two categories: gas-phase reaction methods and liquid absorption methods. Among these two categories of methods, catalytic reduction and alkaline absorption are the main approaches. The former can reduce the NOx emission concentration in exhaust gases to low levels, but it consumes large amounts of NH3; in some cases, fuel gas is also used, resulting in economic losses. The latter allows for the recovery of NO as nitrates and nitrites, offering certain economic benefits, but its purification effect is not high enough to reduce NOx to low levels. The commonly used methods all have their shortcomings; therefore, greater efforts are still needed to identify one or several denitration technologies that are technically feasible, economically reasonable, and suitable for China’s national conditions.

SNCR, SCR, activated carbon adsorption, electron beam denitration.

Flue gas desulfurization technologies include gas-phase reaction methods, liquid absorption methods, adsorption methods, liquid film methods, and microorganisms

For SCR, SNCR, and SNCR/SCR combined technologies, the denitration efficiency of SCR can generally reach 80–90%, enabling the NOx emission concentration to be reduced to below 100 mg/m3 (under standard conditions, on a dry basis, with 6% O2)

The main methods are as follows: SCR (for power plants), SNCRA, and staged combustion (for the cement industry). Acid absorption method, alkali absorption method, selective catalytic reduction method, non-selective catalytic reduction method, adsorption method, plasma activation method, etc

Acid absorption method, alkali absorption method, selective catalytic reduction method, non-selective catalytic reduction method, adsorption method, plasma activation method, etc

SNCR, SCR, activated carbon adsorption, electron beam denitration. We use the activated carbon adsorption method; the nitrogen oxides level is around 100 mg/cubic meter, and the sulfur dioxide level is around 10 mg/cubic meter. There’s no particular reason for this – experience proves everything

　1) Selective Non-Catalytic Reduction for Denitration (SNCR) 2) Selective Catalytic Reduction for Denitration (SCR) 3) Activated carbon adsorption 4) Electron beam denitration 1. SNCR (Selective Non-Catalytic Reduction) technology: Selective non-catalytic reduction is a method that reduces NOx without the use of a catalyst, at temperatures ranging from 850 to 1100°C. It has a low construction cost, is easy to install, and requires little space; it is suitable for the renovation of existing factories, and can be used in conjunction with boiler designs in new factories. 　　 2. SCR (Selective Catalytic Reduction) technology: SCR is the most mature flue gas denitration technology available today; it is a post-furnace denitration method. The currently popular SCR processes in the world are mainly divided into two types: ammonia-based SCR and urea-based SCR. Advantages: This method features high denitration efficiency and relatively low costs; it is widely used in projects both domestically and internationally, and has become the mainstream technology for flue gas denitration in power plants. Disadvantage: The fuel contains sulfur, which can produce a certain amount of SO3 during combustion. After adding the catalyst, under aerobic conditions, the amount of SO3 produced increased significantly, and NH4HSO4 was formed together with the excess NH3. NH4HSO4 is corrosive and sticky, and can cause damage to the equipment in the tail flue. 3. Activated carbon adsorption: Used in combination 　4. Electron beam denitration: A new technology

Activated carbon powder is used to adjust the coal blend for coking