The generation of electric power from fossil has seen continuing, and in some cases dramatics technical advances over the last 20-30years. Today most large power plants worldwide burn coal though many generating companies are adding natural gas plants, particularly where the cost of gas fired generation, and the long term supply favorable.
Fossil steam pulverized coal (PC) plants are dominant in the expanding nations of the east as China and India. In fact for developing world there is a good reason why the coal fired power plant may still be primary choice for many generation companies. Fuel is plentiful and inexpensive, and sulfur dioxide scrubbers have proved to be more reliable and effective than early plants indicated. In the fact up to 99% SO2 removal efficiency is now possible. Removal of nitrogen oxide is also well advanced with over 95% removal possible using selective catalytic reduction (SCR), Ways to remove mercury are currently under study, and the issue of carbon dioxide control and sequestration from fossil power plant is receiving renewed attention as ways to control global warming are pursued.
Coal as a Fuel for Electric Power.
Low rank coal, such as lignite and sub bituminous coals are typically softer, friable materials with a dull, earthy appearance. They characterized by high moisture levels and a low carbon content, and hence a low energy content. Increasing rank is accompanied by a rise in the carbon and energy content and a decrease in the moisture content of the coal. Anthracite is at top of rank scale and has a correspondingly higher carbon and energy content and a lower level of moisture.
NOx Control.
Low NOx burner especially when combined with staging of over fired air, are currently deployed most often. In an SCR, ammonia is injected into the boiler exhaust gasses ahead of the catalyst bank (at about 550F-750F. The reaction can result in a potential NOx removal capability off more than 90%.
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Sulfur Dioxide Control.
The most common wet system bring lime or limestone slurries into contact with the flue gas is a spray tower. SO2 in the flue gas is absorbed in the slurries and collected in a reaction tank, where it precipitates to produce calcium sulfite or calcium sulfate (gypsum) crystal. Flue gas desulphurization gypsum can be sold for use in wallboard, cement or agricultural products.
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