CCC/210 ISBN 978-92-9029-530-3

November 2012

copyright © IEA Clean Coal Centre

Abstract

Conventional flue gas desulphurisation (FGD) systems require large supplies of water. Technologies

which reduce water usage are becoming more important with the large number of FGD systems being

installed in response to ever tightening emission regulations. Reducing water loss is particularly

important in arid regions of the world. This report reviews commercial and near commercial low

water FGD processes for coal-fired power plants, including dry, semi-dry and multi-pollutant

technologies. Wet scrubbers, the most widely deployed FGD technology, account for around 10–15%

of the water losses in power plants with water cooling systems. This figure is considerably higher

when dry/air cooling systems are employed. The evaporative water losses can be reduced by some

40–50% when the flue gas is cooled before it enters the wet scrubber, a common practice in Europe

and Japan. Technologies are under development to capture over 20% of the water in the flue gas

exiting the wet scrubber, enabling the power plant to become a water supplier instead of a consumer.

The semi-dry spray dry scrubbers and circulating dry scrubbers consume some 60% less water than

conventional wet scrubbers. The commercial dry sorbent injection processes have the lowest water

consumption, consuming no water, or a minimal amount if the sorbent needs hydrating or the flue gas

is humidified to improve performance. Commercial multi-pollutant systems are available that

consume no water.