Scrubbers dry

Dry scrubber pollutant gas equilibrium concentration over sorbent ... 

Sodium carbonate reacts with sulfur oxides in a dry scrubber to form sodium sulfite and CO2. Sodium sulfite is then removed with a baghouse. 

Dry scrubber systems applied to the pot fumes and to the anode baking furnace result in the capture of 97% of all fluorides from the process. 

Semidry Scrubbers The advantage of semidry scrubbers is in that they remove contaminants by way of a solid waste that is easier to dispose of (less expensive). Initially, the scrubbing medium is wet (such as a lime or soda ash slurry). Then a spray dryer is used to atomize the slurry into the gas which evaporates the water in the droplets. As this takes place, the acid in the gas neutralizes the alkali material and forms a fine white solid. Most of the white solids are removed at the bottom of the scrubber while some are carried into the gas stream and have to be removed by a filter or electrostatic precipitator (discussed later). Although semidry systems cost 5-15% more than wet systems, when combined with a fabric filter, they can achieve 90-95% efficiencies. Dry scrubbers are sometimes used in a very similar fashion, but without the help of gas-liquid-solid mass transfer, these systems use much higher amounts of the solid alkali materials. 

Dry scrubber An absorption system which uses a dry solvent directly injected into the gas stream. 

Piping, Ducting, Dampers and Fans 8300-8399. .Waste Disposal and Recovery 8900-8999. .Hlace1laneoua (Wet Scrubbers) 8500-8599 -Dry Scrubbers 6550-8580. Precipitators... 

Bag houses These are employed to follow dry scrubbers and/or precipitators in coal burning plants. 

Wet and dry scrubbers Dry scrubbers are generally preferred today. Scrubbers can be used for the removal of both particulate matter and toxic sulfur gases (dry scrubber or spray dryer desulfurizers). 

The facility would use a dry scrubber system for emission control, which would eliminate the need for wastewater treatment. Any water from emission control and from decontamination procedures would be treated in the on-site groundwater treatment system. The residual soil and collected ash is assumed to be nonhazardous and can be disposed of in a solid waste disposal facility in compliance with subtitle D of RCRA. In the event that they cannot be delisted due to the presence of metals, the residuals will be managed as part of the closure of Area 2 shown in Figure 16.21 (lead-contaminated soil). 

The description of the workings of the control technologies is beyond the scope of this article. However, it is worth noting that many of these technologies create substantial amounts of solid or liquid waste that needs to be disposed of properly. For example, in the USA the total amount of fly ash produced from coal combustion alone is about 57 Mt/y (Kalyoncu 2000). About one-third is utilized as secondary raw material (e.g., for aggregate and asphalt), but the rest is usually disposed of in landfills. The wet and dry scrubbers for S02 control produce a sludge or dry waste that finds little secondary use, and a large amount is disposed in landfills. 

Exhaust gases are treated to minimize SO2 emissions into the atmosphere. Removal of SO2 is achieved by the utilization of a scrubber system and will be discussed below in greater detail. Although numerous variations of both wet and dry scrubbers are commercially available, most rely on the adsorption of S02 onto A1-, Na-, or Ca-based adsorbents. Ca-based adsorbents, such as lime (CaO) or calcite (CaC03), are usually preferred due to their low cost and high availability. 

During MSW combustion in a modern mass burn combustor with reciprocating grates, 11 of MSW is converted to heat gases such as C02, NOx, SOx, and H20 and about 350 kg of ash residuals partitioned into the various ash streams. For every tonne of MSW combusted, about 5 kg of grate siftings, 295 kg of grate ash, 5 kg of boiler/economizer ash, 20 kg of ESP ash, and 12 kg of dry scrubber solids are produced (Chandler et al. 1997). 

Element Fresh bottom ash Ivsimeter extracted pore water and leachates (Chandler el al. 1997 Cranncll et al. 2000) Aged boiiuiit ash extracted pore waters (Mciina 1997) Dry and semi-dry scrubber residues low LS (0.0-0.2) column leachates (Chandler et al. 1997) Wet scrubber residue low LS 10.0-0.2) column leachates (Chandler et al. 1997)... 

Table 7. Identified phosphate mineral reaction products in phosphate-stabilized AfS lV dry scrubber residues... 

Ecke, H., Menad, N. Lagerkvist, A. 2002. Treatment-oriented characterization of dry scrubber residue from municipal solid waste incineration. Journal of Material Cycles Waste Management, 4, 117-126. 

Eighmy, T. T., Crannell, B. S. et al. 1997. Heavy metal stabilization in municipal solid waste combustion dry scrubber residue using soluble phosphate. Environmental Science Technology, 31, 3330-3338. 

Bresowar, G.E. Borsare, D.C. Walki, K.W. "Dry Scrubber Design and Application. The C-E Approach", presented at Joint Power Generation Conference, 1981. 

---