FGD and DeNOx
NEWSLETTER       

                                                                                                                    February  2002
                                                                                                                          No. 286

Wet vs. Dry FGD for New Coal-Fired Plants

It is likely that a number of coal-fired generating units will be installed in the United States over the next few years. The new units will utilize flue gas desulfurization systems to limit sulfur dioxide emissions. Either dry FGD or wet FGD systems could be utilized depending upon a variety of site-specific factors. Stephen Bjorklun of Burns & McDonnell discussed these factors at Power-Gen 2001.

The first consideration in evaluating wet versus dry FGD system is establishing the regulatory limitations for sulfur dioxide emissions. It is likely that PSD (Prevention of Significant Deterioration) modeling or the Best Available Control Technology evaluation will establish emission requirements for a new facility that are substantially more stringent than New Source Performance Standards.

The next factor to consider in evaluating wet versus dry FGD is the coal sulfur content. With medium- and high-sulfur coals, wet FGD is clearly the preferred technology. Reagent costs make dry FGD extremely costly at higher fuel sulfur levels. A dry system's capability to achieve the high SO₂ removal requirements that are needed with higher sulfur fuels is also questionable.

Both wet and dry FGD systems can achieve low emission rates with low sulfur coals. A dry system will have lower capital and fixed operating costs. A wet FGD system will have lower variable operating costs. Other factors to consider include unit size and capacity factor (with larger unit size and higher capacity factor making wet systems more practical), reagent costs, the availability and cost associated with landfilling the combustion products (with disposal of waste being a major drawback for dry FGD), the availability of markets for sale of the combustion and waste products, and wastewater discharge limitations.

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