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Application of decanter centrifuge in gypsum dehydration

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Application of  decanter centrifuge in gypsum dehydration 

 

Desulfurization usually adopts limestone-gypsum wet flue gas desulfurization process. And decanter centrifuge is an important part in the process.

FGD uses a furnace and tower desulfurization device, 100% flue gas desulfurization. The desulfurization rate is not less than 95%.

The waste water treatment capacity of the waste water treatment device is designed according to 4 furnaces (4 × 300MW) of the whole plant.

1. Wastewater generation

The flue gas desulfurization project uses the limestone-gypsum wet desulfurization process. The limestone is crushed and ground into a powder, which is mixed with water and stirred to make an absorption slurry. In the absorption tower, the absorption slurry is contacted and mixed with the flue gas. The SO2 in the flue gas is removed by chemical reaction with the calcium carbonate in the slurry and the oxidized air blown in. The final reaction product is gypsum.

The gypsum slurry with a concentration of 15% in the slurry tank of the absorption tower is transported by the discharge pump to the primary dehydration device-gypsum hydrocyclone. The gypsum hydrocyclone has the dual functions of pre-dehydration and classification of gypsum crystals. The gypsum suspended tangential flow entering the hydrocyclone produces centrifugal motion, and the heavy solid particles are thrown toward the wall of the cyclone and flow down to form an underflow. The fine particles flow upward from the center of the cyclone to form a top flow. The solids content of the slurry leaving the cyclone underflow slurry to the gypsum slurry buffer tank is 40% to 50%. The slurry in the gypsum slurry buffer tank is pumped to the vacuum belt dewatering system through the gypsum slurry pump. Part of the slurry overflowing from the top of the gypsum hydrocyclone flows into the hydrocyclone tank, and is driven into the waste water cyclone by the hydrocyclone pump; partly flows into the slurry tank. The underflow of the waste water cyclone enters the slurry tank and returns to the tower through the slurry pump. The overflow part of the waste water cyclone is divided into two ways, one way enters the filtrate tank, one part enters the slurry tank return tower, part returns to the grinding system, and the other way enters the waste water tank, and the waste water is pumped to the waste water treatment system.

2. Wastewater treatment system

Waste water treatment process:

Wastewater pump—neutralization tank—reaction tank—flocculation tank—clarifier—sludge hopper—centrifugal dehydrator—slurry pump—sludge buffer tank—discharge—outlet pump—outlet tank    

In the neutralization tank, add Ca (OH) 2 to adjust the PH value, so that the heavy metal ions in the desulfurization wastewater form hydroxide precipitation. Add polymerized iron to produce flocculation reaction, add coagulant in the flocculation tank to enhance the flocculation effect. Organic sulfur is added to the flocculation tank to further remove heavy metal ions, especially mercury (Hg2 +).

The clarifier has the functions of coagulation, clarification and sludge concentration at the same time. After entering the clarification tank, the wastewater passing through the flocculation tank is further flocculated and precipitated. The clarified liquid overflows to the outlet tank and is discharged to the outside of the desulfurization island by the outlet pump discharge pump.

3. Sludge treatment system

 

The sludge at the bottom of the clarifier is discharged to the sludge buffer tank, and then pumped into decanter centrifuge by the sludge transfer pump for dehydration. The dehydrated sludge first enters the mud bucket and is then transported away by truck.