of 90%. In spray drying and dry injection systems, the flue gas must first be cooled to about 10–20 °C above adiabatic saturation to avoid wet solids deposition on downstream equipment and plugging of baghouses. The capital, operating and maintenance costs per short ton of removed (in 2001 US dollars) are: For wet scrubbers larger than 400 MW, the cost is $200 to $500 per ton For wet scrubbers smaller than 400 MW, the cost is $500 to $5,000 per ton For spray dry scrubbers larger than 200 MW, the cost is $150 to $300 per ton For spray dry scrubbers smaller than 200 MW, the cost is $500 to $4,000 per ton Alternative methods of reducing sulfur dioxide emissions An alternative to removing sulfur from the flue gases after burning is to remove the sulfur from the fuel before or during combustion. Hydrodesulfurization of fuel has been used for treating fuel oils before use. Fluidized bed combustion adds lime to the fuel during combustion. The lime reacts with the to form sulfates which become part of the ash. This elemental sulfur is then separated and finally recovered at the end of the process for further usage in, for example, agricultural products. Safety is one of the greatest benefits of this method, as the whole process takes place at atmospheric pressure and ambient temperature. This method has been developed by Paqell, a joint venture between Shell Global Solutions and Paques. See also Incineration Scrubber Flue-gas emissions from fossil-fuel combustion Flue-gas stacks Wellman–Lord process References External links Schematic process flow of FGD plant 5000 MW FGD Plant (includes a detailed process flow diagram) Alstom presentation to UN-ECE on air pollution control (includes process flow diagram for dry, wet and seawater FGD) Flue Gas Treatment article including the removal of hydrogen chloride, sulfur trioxide, and other heavy metal particles such as mercury. Institute of Clean Air Companies – national trade association representing emissions control manufacturers Air pollution Pollution control technologies Air pollution control systems Acid gas control Incineration Chemical processes Environmental engineering Environmental impact of the energy industry Gas technologies Sulfur