Flue gas desulphurization systems
FGD (Flue Gas desulphurization) systems can be divided into three categories, based on the state in which you carry out the desulphurization reaction:
1) "wet" process (wet scrubbers)
2) "dry" process (dry scrubbers)
3) "semi-dry" process (spray-dry scrubbers)
Among these three categories of desulphurizing equipment those who are mostly employed are wet scrubbers, especially on large projects not only for their neutralization yield often above the 95%, and considering their reliability <99% but also for the possibility (prevented to others) to obtain gypsum (often marketable) as reaction product if fed with calcium-based reagents, whereas normally, other FGD (dry and semi-dry) produce wastes for landfills.
Sorbents used in this type of installation can be:
• Calcium-based sorbents:
- calcium carbonate – CaCO3
- calcium oxide – CaO
- lime – Ca(OH)2
- dolomite – CaCO3·MgCO3
• Potassium, magnesium and sodium-based sorbents:
- magnesium oxide and hydroxide – MgO and Mg(OH)2
- soda - NaOH
- soda ash - Na2CO3
- sodium bicarbonate - NaHCO3
- potassium sulphate – K2SO3
• Sea water (magnesium carbonate included into this kind of water – MgCO3)
The wet FGD systems will require water treatment (absent in other cases), which is used to separate the products of the desulfurization from water excess.
Semi-dry FGDs generally use sorbents based on calcium oxide or calcium hydroxide (hydrated lime is generally more reactive), this apparatus does not require water treatment but produces materials that must be disposed in landfills. ATS is able to provide "sprying dryer" systems with yields <98%.
Those are the most simple and economical FGD equipments, they do not include any special item due to the fact that the injection of sorbent (calcium or sodium-based) takes place directly in the boiler or in the case of an injection at medium temperatures in the "Venturi throat" of a reactor. The effectiveness of those systems is highly variable depending on the conditions of the process and the reagent used for the reaction.