The FGD wet desulfurization system consists of multiple subsystems responsible for different processes to achieve desulfurization effects, and the subsystems are composed of specific components, including limestone slurry system, spray absorption tower system, gypsum dehydration collection system, flue gas operation system, emergency slurry system, process water system, and compressed air system.
2.1 Limestone pulping system
The limestone slurry system is used as an absorbent for SO2 preparation. Absorbent, also known as slurry, is prepared by tanker truck using compressed air to feed powder into the powder bin. It enters the slurry preparation tank through the feeding valve and mixes with the filtrate in the tank. The limestone slurry is then prepared by stirring with a mixer. The agitator can only be started when the height of the filtrate reaches 0.8m or above. The liquid level of the limestone slurry tank should be maintained at 2.5-3.3m, and the density should be controlled at around 1200kg/m3; Finally, set the limestone slurry pump to constant start and adjust the slurry supply through a frequency converter to transport the slurry to the absorption tower through the slurry pump. As it is the main component that undergoes chemical reactions, its content ratio should exceed 90% and its content should be less than 2%. Therefore, the particle size of limestone powder is required to be 250 mesh. To ensure the efficient operation of the pulp making system, the storage capacity of limestone should meet the amount of slurry consumed by the system for 72 hours of operation. One slurry tank can be set up, with a capacity that meets the amount of slurry consumed by the system for 5 hours of operation.
2.2 Absorption Tower System
Absorption tower, also known as washing tower, mainly purifies and dries flue gas, and processes the generated products. Installing three absorption towers can maintain stable system operation. To withstand high temperature flue gas, the inlet flue must be corrosion-resistant, so a corrosion-resistant high nickel based alloy lining was selected. The tower body is made of carbon steel lined with glass flake resin material. The three-layer spray layer adopts spray technology, which can expand the spray coverage rate to over 130% and ensure sufficient mixing of gas and liquid. The nozzle is made of silicon carbide material, which is corrosion-resistant, wear-resistant, and not easily clogged. The defogger is installed on the upper part of the spray layer for easy maintenance and repair, and its material is polypropylene. Four agitators are installed in the slurry pool to ensure sufficient reaction between the slurry and SO2. In order to maintain a constant pH value of the slurry, three 400TL-50 slurry circulation pumps are required to bring the slurry into the absorption tower to neutralize the hydrogen ions and circulate it inside the absorption tower.
2.3 Gypsum Dehydration System
The gypsum dewatering system mainly concentrates the discharged gypsum slurry through a cyclone, and then produces gypsum cake and filtrate through the dewatering process. Since gypsum can only be extracted through dehydration treatment when the concentration of gypsum slurry is around 15%, the gypsum dehydration system needs to be started when the slurry density reaches 1130 kg/m3, and stopped when it is less than or equal to 1070 kg/m3; The inlet pressure of the gypsum cyclone is controlled at around 180KPa; The vacuum degree of the gas-liquid separator should not be lower than 40KPa; The dehydrated gypsum cake falls into the gypsum silo, and the moisture content of the gypsum product should be less than 10%.
2.4 Smoke system
The flue gas system mainly purifies and dries the flue gas, while also diverting and cooling the flue gas in case of accidents. The bypass baffle is of the single axis double louver sealed type, made of Q235B material, and is installed on the flue entering the absorption tower to discharge flue gas in the event of a failure of the FGD device; To prevent high-temperature flue gas from damaging the absorption tower in case of accidents, the desulfurization system is specially equipped with an accident spray cooling system [3], which can reduce the average temperature of the flue gas from 180 ℃ to 100 ℃. Two baffle sealed fans are selected with centrifugal fans of model 9-19-4.5A; The sealed air heater is a horizontal heater model JMDYK-60; Three induced draft fans use single-stage centrifugal fans with model CGY-48No.26.5D.
2.5 Other systems
The accident slurry system is mainly used for storing the slurry in the tower during system shutdown. It requires one slurry return pump for slurry reflux and a storage tank that can accommodate one slurry in the absorption tower. The process water system includes a 30m3 water tank and two IS100-65-200 centrifugal process water pumps. The compressed air system includes two air compressors, air filters, and supporting instruments. Two air compressors, one in use and one as backup, model SE180A-7/D single-stage, air-cooled, box type low-noise oil injected screw air compressor; The air filter and supporting instruments include a pre filter model SF-360/P, a precision filter model SF-360/A, a compressed air buffer tank, and an air storage tank used for denitrification, desulfurization, and dust removal systems.
