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Flue Gas Desulfurization System

Flue Gas Desulfurization System
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Flue Gas Desulfurization is commonly known as FGD and is the technology used for removing sulfur dioxide (SO2) from the exhaust combustion flue gases coming from the boilers to produce steam that burn coal /oil/ pet coke.
The FGD offered is the dual- or double-alkali scrubbing process which contacts the flue gases with an alkaline sorbent of lime or limestone and a sodium-based alkali solution to remove SO2 from combustion exhaust gas.

Product Details :
MaterialStainless Steel, Carbon Steel
GradeSS 304, 316

The steps involved in the process is as follows:
The SO2 in the flue gas passing through the absorber column / scrubber reacts with the alkaline solution (naoh, caustic soda) sprayed from top through distributor nozzles to primarily form Sodium Sulfite and Sodium Bisulfite (NaHSO3). The following are the main absorption reactions :
  • 2 NaOH + SO2->Na2SO3+ H2O
  • NaOH + SO2->NaHSO3

In addition to the above reactions, some of the SO3 present may react with alkaline components to produce sodium sulfate:
  • 2NaOH + SO3->Na2SO4+ H2O

Throughout the system, some sodium sulfite is oxidized to sulfate by:
  • 2Na2SO3+ O2->2Na2SO4

Later the sodium bisulfite and sodium sulfate are reacted with lime or limestone (CaCO3) slurry solution to produce a calcium sludge in the form of calcium sulphate ( gypsum ) and a regenerated sodium solution. This regenerated sodium solution is re-used in the absorption column and the sludge from the reactor is then sent to a clarifier, or thickener, where the calcium sludge is drawn off the bottom, filtered, and washed with water. From the filter, the sodium solution is recycled to the clarifier, and the sludge is discarded. From the clarifier, the regenerated sodium solution is sent to a mixing tank where the sodium compounds and makeup water are added.

The sodium alkali solution absorbs SO2 , and the spent absorbing liquor is regenerated with lime or limestone. Using both sodium- and calcium-based compounds is where the name dual or double-alkali comes from. Calcium sulfites and sulfates are re-precipitated and discarded as sludge. The regenerated sodium scrubbing solution is returned to the absorber loop. The dual-alkali process has reduced plugging and scaling problems in the absorber because sodium scrubbing compounds are very soluble. Dual-alkali systems are capable of 95% SO2 reduction.

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