ABSTRACT
One of the most widely used technologies for removing pollutants such as sulfur dioxide from flue gas emissions produced by coal-fired power plants is the limestone-forced oxidation scrubbing system. More commonly known as flue gas desulfurization (FGD), this process employs gas scrubbers to spray limestone slurry over the flue gas to convert gaseous sulfur dioxide to calcium sulfate.1 Unfortunately, many of the contaminants from the coal, limestone, and make-up water are concentrated in the circulating water of the scrubbing system. So, in order to maintain appropriate plant operating conditions, a constant purge stream of water containing these contaminants has to be discharged from the scrubbers while fresh limestone slurry is fed in. This purge stream is extremely acidic and saturated with high concentrations of gypsum, heavy metals, alkali earth metals, chlorides, and dissolved organic compounds. A schematic of a typical FGD process is shown in Figure 20.1.
