Question 5.27: Dry scrubbing is a feasible process FGD (32,66,67). Discuss ...
Dry scrubbing is a feasible process FGD (32,66,67). Discuss the following:
1. The process description, performance, and future of the dry scrubbing FGD process.
2. The chemical reactions of the dry scrubbing FGD process.
1. The following presents the process description, performance, and future of the dry scrubbing desulfurization process. Dry scrubbing is a modification of the wet scrubbing FGD technology. As in other FGD systems, the exhaust gases combine with a fine slurry mist of lime or sodium carbonate. This system, however, takes advantage of the heat of the exhaust gases to dry the reacted slurry into particles of calcium sulfite and sodium sulfite.
The particles generated by this dry scrubbing process are then collected along with other particles from coal combustion in a baghouse collector. This collector uses fabric bags that function similarly to those in a vacuum cleaner, which collect particles while permitting cleaned gases to escape.
Dry scrubbing typically removes 70\% of the sulfur dioxide in a waste gas stream. It is 15–30\% less expensive to install and operate than a conventional wet scrubbing system. However, because dry scrubbing is less efficient than wet scrubbing, the technology has been limited to use with low-sulfur coal.
Plans for future research include evaluating the performance and reliability of a fullscale utility boiler equipped with a spraydryer SO_{2} control system. Improvements could make these dry scrubbing systems acceptable for general use by the early 2000s.
2. The chemical reactions of the dry scrubbing desulfurization process are as follows:
SO_{2} + CaO → CaSO_{3}
SO_{2} + Na_{2}CO_{3} → Na_{2}SO_{3} + CO_{2}
where CaO = lime, calcium oxide, CaSO_{3} = calcium sulfite, Na_{2}CO_{3} = sodium carbonate, and Na_{2}SO_{3} = sodium sulfite.
