The purification method of flue gas pollutants in desulfurization, denitrification and dust removal equipment: 1. The difficulty of flue gas purification treatment is that the flue gas is the gas released after the combustion of coal and other fuels. It is usually treated by desulfurization, denitrification and dust removal equipment after dust removal. At this time, the flue gas has the characteristics of high temperature, mixed components, and fast flow rate. Due to the fact that flue gas is a gas immediately emitted after combustion, its temperature is relatively high, and even after preliminary dust removal treatment, its temperature usually exceeds 100 ℃. Coal and other fuels contain a large amount of impurities, and the smoke generated after combustion also contains various pollutants, such as dust, sulfur dioxide, nitrogen oxides, mercury and other heavy metals. Coal fired power plants and other units have a large scale, generate a large amount of flue gas during the combustion process, and work continuously without interruption. The flue gas flow rate is large and fast. The several characteristics of flue gas determine that there are several difficulties in its purification process. If the flue gas temperature is too high and directly purified, it will cause the purification substance to become inactive. And there are many pollutant components in the flue gas, so it is better to choose a purification process that can simultaneously remove multiple pollutants, which can simplify the operation, reduce capital investment, and shrink the footprint. The fast flow rate of flue gas requires the purification material to have the ability to remove pollutants, which can be achieved through short-term contact with the flue gas, reducing the pollutant content of the flue gas purified by the desulfurization, denitrification, and dust collector to a low level and minimizing the harm caused. In summary, in the process of flue gas purification treatment, it is necessary to find technical methods that can regulate the flue gas temperature and simultaneously remove multiple pollutants. 2. The research on flue gas desulfurization (FGD) process related to desulfurization technology began as early as 1927. In order to protect high-rise buildings in London, the United Kingdom adopted limestone desulfurization technology at two power plants on the banks of the Thames, Batfoon and Banziside. The desulfurization process can be divided into pre combustion, combustion, and post combustion desulfurization treatments. Pre combustion treatment is mainly aimed at desulfurization of fuel coal, so that it no longer produces sulfur-containing flue gas during the combustion process. During combustion, combustion processes such as circulating fluidized beds are used to remove SO2 generated by combustion immediately before emission. Post combustion treatment, also known as widely used flue gas purification treatment. At present, researchers have proposed various technical methods for removing SO2 from flue gas. One method is to mix coal and other fuels with dry alkaline materials before combustion, or inject atomized alkaline substances directly into the gas produced by combustion - to adsorb or oxidize pollutants such as SO2 after adsorption. The disadvantage of this method is that the mixed contact surface is prone to forming dirt, the removal efficiency is moderately low, the utilization rate of reagents is low, and the increased particulate matter in the flue gas may require additional treatment (such as humidification or using electrostatic precipitators for downstream particle collection). The other method is the spray drying chemical adsorption process, which is often called "dry purification". The alkaline aqueous solution or slurry that has been atomized through a mechanical, dual fluid or rotary atomizer is sprayed into the hot exhaust gas to remove pollutants such as SO2. The disadvantage of this method is that: with the spray drying of the air intake distribution device, there will be a medium to high pressure side drop; When the saturation temperature of exhaust gas is reached, the spray temperature will be limited, which requires equipment conditions that can be controlled stably. Another method is the chemical adsorption process under liquid conditions, commonly known as "wet scrubbing". At the gas-liquid contact surface, the slurry is used to "scrub" the hot exhaust gas, thereby removing pollutants such as SO2. A typical wet flue gas scrubbing system involves the injection of mud from the tower and the injection of gas from the bottom of the tower. Gas and liquid come into contact to remove pollutants. The disadvantages of this method are: for gas and sludge generated in the process, both flue gas and spray have saturation, so there must be liquid loss; The construction of the adsorption model itself and related downstream equipment (such as primary and secondary dehydration and wastewater treatment systems) require additional financial support for materials. At present, most detergent slurries are replaced with liquid oxidants. 3. The nitrogen oxides (NOx) in the flue gas of denitrification process are mainly composed of nitric oxide (NO) and nitrogen dioxide (NO2), with the main component being NO (over 90%). N02 can be absorbed by some aqueous solutions, but NO cannot. However, most of the NOx in the flue gas is NO. Therefore, for the control of NOx emissions, the removal of NO becomes a key step in the purification system. There are many methods applied to control NO emissions. Selective Catalytic Reduction (SCR) is a common method. During the SCR process, ammonia water is injected into the flue gas and mixed with it under low to medium temperature conditions. The mixed gas flows through a catalyst (usually stainless steel based vanadium), and NO is reduced to N2. The problem with the SCR system is that the initial input is high, ammonia water is easily decomposed and consumes a large amount, and it will be emitted into the atmosphere along with the flue gas. The selective non catalytic reduction (SNCR) method is also applied in the removal of NO from flue gas. This method involves injecting ammonia or urea into hot flue gas to directly generate the N-In5] oSNCR system. The challenge is to maintain stable time and operating conditions so that the reaction proceeds sensitively with changes in operating mode; Ammonia water is prone to decomposition and consumes a large amount (even more severe than SCR systems), and it is also emitted into the atmosphere along with the flue gas. Wet oxidation method is also applied to the removal of NO in flue gas, which requires the use of oxidants such as hydrogen peroxide (H2O2), sodium chlorite (NaClO2), sodium hypochlorite (NaClO), and potassium permanganate (KMnO4). In addition, strong oxidizing agents such as ozone (O3) and chlorine dioxide (ClO2) can be injected into the flue gas to improve the removal efficiency of NOx through their interaction with the flue gas.
