Common desulfurization technologies for flue gas desulfurization

Flue gas desulfurization (FGD) is an effective desulfurization method widely used in industry. According to the forms of sulfide absorbents and by-products, desulfurization technologies can be divided into dry, semi-dry and wet methods. Dry desulfurization process mainly uses solid absorbent to remove SO2 from flue gas. Generally, limestone fine powder is sprayed into the furnace and decomposed into CaO by heating, so as to absorb SO2 in flue gas and generate CaSO3 _ 3, which is collected together with fly ash in a dust collector or discharged through a chimney. Wet flue gas desulfurization is a gas-liquid reaction of liquid absorbent under ionic conditions, and then SO2 in flue gas is removed. The equipment used in the system is simple, stable and reliable, and the desulfurization efficiency is high. The biggest advantage of dry desulfurization is that there is no discharge of wastewater and waste acid during treatment, which reduces secondary pollution; Disadvantages are low desulfurization efficiency and huge equipment. Wet desulfurization uses liquid absorbent to wash flue gas to remove SO2. The equipment used is relatively simple, easy to operate and has high desulfurization efficiency. However, the temperature of flue gas after desulfurization is lower, and the corrosion of equipment is more serious than that of dry method. CFB process consists of absorbent preparation, absorption tower, absorbent recovery, dust collector and control system. Untreated boiler flue gas enters from the bottom of fluidized bed. The bottom of the fluidized bed is connected with a Venturi device, so that the flue gas passes through the Venturi tube at a faster speed and is combined with fine absorbent powder. Severe friction will occur between particles and between gas and particles. The absorbent reacts with SO2 to generate calcium sulfite and calcium sulfate. Flue gas containing a large number of solid particles after desulfurization is discharged from the top of the absorption tower and enters the absorbent recovery dust collector, which can be mechanical or mechanical pre-dust collector before electrostatic precipitator. Most of the solid particles in the flue gas are separated and returned to the absorption tower through the middle ash bin. Because most particles circulate many times, the retention time of absorbent is very long, which can generally reach more than 30 minutes. According to the supply of absorbent and dust removal efficiency, a part of the ash in the middle ash bin is discharged from the solid recovery loop in proportion and sent to the ash bin for transportation. The process is shown in Figure 2.

If the flue gas discharged by the recirculation dust collector cannot meet the requirements of emission standards, another dust collector needs to be installed. The clean flue gas after dust removal is discharged into the atmosphere through the induced draft fan and chimney. Generally speaking, the absorbent is Ca(OH)2 dry powder. When the fine particles are below 10μm, the absorbent is input into the absorption tower of the fluidized bed, and a certain amount of water is injected to improve the desulfurization efficiency. In this way, the flue gas temperature after water spraying can be very close to the water dew point, and high desulfurization efficiency can be achieved under various working conditions. Circulating fluidized bed flue gas desulfurization technology has a good application prospect in desulfurization industry because of its different characteristics from traditional desulfurization technology. The circulating fluidized bed flue gas desulfurization process system is simple and reliable; High desulfurization efficiency; When the flue gas load changes, the system can still work normally; Desulfurization by-products are dry powder, without a lot of wastewater, which is beneficial to comprehensive utilization; There are basically no serious problems such as corrosion, scaling and blockage in wet absorption tower; It can remove some heavy metals, especially some mercury, which is of great significance to the further treatment of flue gas.