Absorber System

After entering the absorber, the raw gas rises and goes through the tray with uniform speed. Limestone/gypsum slurry spray in a mist hood shape from nozzles of the two spray layers towards absorber bottom, spray zone with liquid mist highly overlapped is formed. The slurry drops fall rapidly in converse flow against rising gas, through which most of the pollutant contained in gas is washed into slurry and remove by reaction with slurry.

While the limestone absorbent is being consumed, SO2, SO3, HCL and HF in the flue gas are separated, the same with most of the fly ash, and byproduct gypsum (CaSO4•2H2O) is produced.

In absorber, the slurry pH value in its lower slurry tank is determined by limestone slurry amount added into it, which is controlled between 5 and 6. The limestone slurry volume is adjusted based on predicted boiler loading, SO2 content and actual absorber slurry pH value.

When going through absorber, moisture in hot flue gas is taken away by vaporization, which causes fluctuation of solid concentration and liquid level of absorber slurry. Through mist eliminator and process water supply and desulphurization reaction product emission, the system controls the absorber slurry density and liquid level.

The desulphurization reaction product and the added limestone slurry and process supply water form gypsum slurry in the absorber slurry tank, circulating inside through absorber circulation pump.

Oxidation air system provides oxidized air for the absorber slurry, and forcibly oxidize the CaSO3•1/2H2O generated by desulphurization reaction into CaSO4•2H2O, which generates gypsum (CaSO4•2H2O) through crystallization. Three oxidation fans (two for the two absorbers respectively and one for standby) are set for two absorber oxidation systems.

Slurry spray layer is set in absorber upper flue gas area. 3 layers are set (2 for use and 1 for standby) for one absorber, each of which has 1 slurry circulation pump. Under normal BMCR operation situation, 2 spray layers are started and 1 layer is for standby. In actual operation, take turns to start 2 spray layers in the 3 periodically (less than 3 days), avoiding deserting a certain one and making the spray nozzles of it blocked by slurry carried by the flue gas.

In the upper part of the absorber, two-level mist eliminator are set, which can separate most of liquid drops in the slurry. Mist drop content in absorber outlet flue gas < 75mg/Nm3. The mist eliminator can be washed with process water system to avoid scaling. The wash way is pulse type and in automatic control (or manual control).

In absorber slurry tank, 5 agitators are arranged horizontally and radially to remove the stagnant matters and keep slurry in even suspending status without deposit. They also evenly distribute the oxidized air in the slurry tank with the oxidation air ejection bank, ensuring desulphurization absorption reaction effect.

1 sealing tank is set on the overflow pipe of absorber slurry tank, which can contains the overflow caused by absorber in pressure sealing. The liquid level of the sealing tank is maintained by periodical process water makeup. The absorber sealing tank is to prevent absorber slurry overflow enters into flue duct and to provide pressurization protection.

On absorber top, automatic deflation valve is set. Under normal operation, this valve is closed; when FGD device pauses, this valve will open to delete pressure difference with outer atmosphere in respect that absorber oxidation fan continues operation or flue gas cools down.

For absorber slurry discharge, there are two sets of gypsum bleed pump (one for use and one for standby). After absorber system starts, start the gypsum bleed pump that we can know the gypsum slurry density and pH value. When gypsum density achieves dewatering requirements (>1120kg/m3), the gypsum bleed pump will take the gypsum slurry to the dewatering system. If dewatering system fails, or gypsum slurry is not eligible or FGD system is stopped for overhaul, the slurry will be discharged into emergency tank system.