8
2.3. Control techniques for SOx emissions reduction
On the contrary to NOx, SO
x
emissions are directly linked to the initial sulfur content of the
fuel and the combustion parameters do not influent on the amount of SOx emitted. Two
strategies can be used to reduce SOx emissions: the formation prevention (low sulfur fuel
usage, fuel desulfurization) or the flue gas desulfurization (wet or dry scrubbing, dual-alkali,
spray drying, Wellman-Lord process, etc.).
There are many postcombustion flue gas desulfurization techniques. Almost all techniques are
based on the acid-alkaline reaction between SO
2
(and SO
3
) and an alkaline agent such as often
lime or limestone, caustic soda, magnesium hydroxide or ammonia. Other techniques are
selective adsorption or absorption.
Flue gas desulfurization is mostly used in thermal power plant. Few refineries have a flue gas
desulfurization, except in Japan where principally dry processes are used. The principles of
four major techniques are given below.
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