FGD Scrubber Material

The burning of pulverized coal in electric power plants produces sulfur dioxide (SO2) gas emissions. The 1990 Clean Air Act and its subsequent amendments mandated the reduction of power plant SOj emissions [66-70]. The Best Demonstrated Available Technology (BDAT) for reducing SOj emissions is wet scrubber flue gas desulfurization (FGD) systems. These systems are designed to introduce an aUcahne sorbent consisting of lime or limestone in a spray form into the exhaust gas system of a coal-fired boiler. The aUcaU reacts with the SOj gas and is collected in a liquid form as calcium sulfite or calcium sulfate slurry. The calcium sulfite or sulfate is allowed to settle out as most of the water is recycled [66-80]. 

FGD scrubber sludge is the wet solid residue generated from the treatment of these emissions. The wet scrubber discharge is an off-white slurry with soUds 

As of December 1994, there were at least 157 coal-fired boiler imits at 92 power plants with wet scrubbing systems operating. These plants are located in at least 32 states [66,72-75]. Additional scrubbers are planned or under construction in order to achieve compliance with the Clean Air Act requirements. As of 1996, the operating scrubber systems at coal-fired power plants generated approximately 21.4 million metric tons (23.8 million tons) of FGD sludge aimuaUy [71-80]. 

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Stabilization of FGD scrubber material refers to the addition of a sufficient amount of dry material, such as fly ash, to the dewatered FGD filter cake so that the stabilized material can be handled and transported by construction equipment without water seepage and can also support normal compaction machinery when placed into a landfill. 

Dewatered flue gas desulfurization (FGD) scrubber material is most frequently generated as calcium sulfite, although some power plant scrubbing systems have the forced oxidation design, resulting in a calcium sulfate (or by-product gypsum) material. Calcium sulfite FGD scrubber material is oxidized to sulfate and used for road base, while the calcium sulfate FGD scrubber material is frequently used for wallboard or as a cement additive [66-80]. 

The degree to which FGD scrubber material is treated influences its physical properties. Basic physical properties include solids content, moisture content, specific gravity, and wet and dry density [67]. When dewatered, the calcium sulfite FGD sludges become a soft filter cake with a solids content typically in the 40-65% range. Calcium sulfate FGD sludges can be dewatered much more easily and may achieve solid contents as high as 70-75% after dewatering [67]. 

FGD scrubber material Stabilized base - Stabilized or fixated FGD scrubber material has been used successfully for road base construction, at a number of different sites in Florida, Pennsylvania, Ohio, and Texas - Stabilization or fixation of FGD scrubber material can be accomphshed by the addition of quicklime and pozzolanic fly ash, Portland cement, or selfcementing fly ash - The FGD scrubber sludge is dewatered before the addition of stabilization or fixation reagents - Additional fixation reagents may need to be added for stabilized base construction in order to meet compressive strength or durability requirements 66-80... 

FGD scrubber material Embank- ments - Small amounts of fixated FGD scrubber material have been used for embankment construction in western Pennsylvania - The material was reclaimed from a landfill and used in conjunction with a fly ash embankment project - No additional reagents were needed for embankment construction 66-80... 

Flue gas desulfurization (FGD) scrubber material - In 1996,0.8 million metric tons (0.9 million tons) of calcium sulfate FGD scrubber material were used to produce wallboard and approximately 0.06 million metric tons (0.07 million tons) of this material were used as feed material for cement production - In 1996,0.04 million metric tons (0.05 million tons) of primarily fixated calcium sulfite FGD scrubber material were used for structural fill. Also, approximately 0.11 million metric tons (0.12 million tons) were used for road base construction 66-80... 

Flue gas desul- - Fixated or stabilized calcium sulfite FGD scrubber furization material has been used as an embankment and... 

The sulphate FGD residues often contain unreacted sorbent, that is, CaO or Ca(OH)2, which acts as in internal source of lime and produces a high pH (12.5) when these materials come in contact with water. The amount of unreacted sorbent varies considerably depending on whether or not the power plant recycled the residues back through the scrubbers (McCarthy et al. 1989). Research has shown that these... 

FGD material Solid/semisolid material obtained from flue gas scrubbers Fine to coarse (dry or wet) 350 Ca, S, Si, Fe, Al ... 

FGD materials Derived from a variety of processes used to control sulfur emissions from boiler stacks. These systems include wet scrubbers, spray dry scrubbers, sorbent injectors, and a combined sulfur oxide (SOx) and nitrogen oxide (NOx) process. Sorbents include lime, limestone, sodium-based compounds, and high-calcium coal fly ash. 

Ferritic, austenitic, or ferritic-austenitic cast alloys are used in preference as materials for pumps in scrubber circuits of flue gas desulphurisation plants (FGD... 

Flue gas desulfurization (FGD) plants have been in service since the 1970s, when all coal-fired power plants had to install a flue gas cleaning system to reduce SO2 output. The design material depends on the desulfurization process and the fossil coal which is used. One of the main components of an FGD plant is the absorber or scrubber. Several factors determine the severity of corrosion of the media ... 

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