User:Milton Beychok/Sandbox

Flue gas desulfurization

Partial flue gas desulfurization (FGD) can achieve about 50-70 % removal of sulfur dioxide by the injection of dry limestone just downstream of the the air preheater. The resultant solids are recovered in the ESPs along with the fly ash.

In power plants burning pulverized coal, wet flue gas desulfurization (FGD) that contacts the flue gases with lime slurries (in what are called wet lime scrubbers) can achieve 95% sulfur dioxide removal without additives and 99+% removal with additives. Wet FGD has the greatest share of the FGD usage in the United States and it is commercially proven, well established technology.

The typical older FGD units in power plants burning pulverized coal within the United States achieve emission levels of 0.21 to 0.23 lb SO₂ /10⁶ Btu, which meets the level to which those units were permitted.[12]

Recently permitted units have lower limits, ranging from 0.08 to about 0.12 lb SO2/million Btu for low-sulfur coal to 0.15 to 0.20 lb SO2/million Btu for high-sulfur coal. Lower emissions levels can be expected as permit levels are further reduced. FGD technology has not reached its limit of control and can be expected to improve further. Figure A-3.D.3 shows the twenty lowest SOx emitting coal-fi red PC units in the U. S. as reported in the EPA CEMS Database [13]. Coal sulfur level impacts the SOx emissions level achievable. Th e best PC unit in the U.S. burning high-sulfur coal, such as Illinois #6, in 2005 had demonstrated emissions performance of 0.074 lb SO2/million Btu [11]. For low-sulfur coals, the best performance was 0.03 lb SO2/million Btu. Th e best units in Japan operate below 0.10 lb SO2/million Btu [9].

Coal-fired power plants also emit large quantities of carbon dioxide (CO₂) which is not a pollutant in the traditional sense. In fact, it is essential for all plant life on Earth through photosynthesis. However, it is a greenhouse gas considered to have a major role in so-called global warming. 50% of the electricity generated in the U.S. is from coal.2 � Th ere are the equivalent of more than fi ve hundred, 500 megawatt, coal-fi red power plants in the United States with an average age of 35 years.2 � China is currently constructing the equivalent of two, 500 megawatt, coal-fi red power plants per week and a capacity comparable to the entire UK power grid each year.3 � One 500 megawatt coal-fi red power plant produces approximately 3 million tons/year of carbon dioxide (CO2).3 � Th e United States produces about 1.5 billion tons per year of CO2 from coal-burning power plants. � If all of this CO2 is transported for sequestration, the quantity is equivalent to three times the weight and, under typical operating conditions, one-third of the annual volume of natural gas transported by the U.S. gas pipeline system. � If 60% of the CO2 produced from U.S. coal-based power generation were to be captured and compressed to a liquid for geologic sequestration, its volume would about equal the total U.S. oil consumption of 20 million barrels per day.