Scrubber process

S02 and NOx in flue gas from coal combustion contribute to smog and acid rain. Methods to remove these pollutants include alkaline wet scrubber systems that fix S02 to solid CaS04, and selective catalytic reduction by metal/metal oxide systems of NO/NOz to N2 and steam in the presence of ammonia. Particulate active carbons have also been used in flue gas decontamination, especially as they avoid costly scrubber processes and can operate at lower temperatures. The potential of active carbon fibers in this application has been explored by a... 

Measurements of total odour strength in combustion processes imply sampling challenges. Beside the chemical scrubber process, combustion of odorous air is the best odour reducing method. The disadvantage of this process is the high energy costs. Treatment at apropriate conditions, however, will destroy the odorous compounds extensively. Temperatures about 850 C and contact time up to 3 seconds are reported (2, 3). 

When using a scrubber, an additional acid treatment must be implemented, preferably afterward. If an HF bath is used prior to the scrubber to improve global particle removal [24], the metallic cleanliness obtained can be preserved if a complexing agent is used in the scrubber process—EDTA in water or choline instead of ammonia. The acid treatment can be introduced in the second scrubber station citric acid or HF. In the latter case, the scrubber has to be especially designed for corrosion and security reasons. 

The simple scrubber process is very efficient to eliminate slurries but does not remove the metallic contamination or the damaged layer. The simplest additional process is to use an HF-based step which removes both of them. The use of an HF-compatible scrubber saves an additional wet bench with a dryer and a wafer transfer. The chemistries used must avoid loading effects. 

Si02 slurries are quite easy to remove and do not produce any brush-loading effect since the commercial slurry used does not contain too many foreign particles. The simplest scrubber process consists in a... 

FIGURE 16.9 Belco LABSORB regenerative scrubber process diagram. (With permission from Belco Technologies.)... 

Fig. 5 Flow diagram of the dual-alkali scrubber process, using lime to regenerate the sodium alkali. The clarified liquid from the thickener contains dissolved calcium sulfate, which would produce calcium carbonate scale in the scrubber when it contacts the carbon dioxide in the flue gas. It is therefore precipitated in the softening reactor by a combination of carbon dioxide and sodium carbonate, and the resulting calcium carbonate precipitate is removed by the hydrocyclone.

In general, the performance of a scrubber process will be improved if the sulfur content of the feed coal... 

The key public concern about plasma arc processes for the destruction of non-stockpile CWM in the United States centers on whether plasma arc offers a true alternative to incineration. Depending on the type of plasma gas used and the configuration of secondary oxidation zones, quench, and scrubber processes, plasma arc systems may produce gas volumes and reaction products that are quite similar to or quite different from those associated with incinerators. 

Oxidation of potassium compounds to the sulfate form occurs in the Recovery Scrubber process licensed by Passamaquoddy Technology, which was originally developed for cement plant applications. The process uses waste cement kiln dust, which contains limestone, alkali, and calcium sulfate, in an aqueous slurry as a flue gas scrubbing reagent The first commercial appUcation of the process began operating at the Dragon Products Company cement plant in Thomaston, Maine in December 1990 (Morrison, 1991). 

The Passamaquoddy Recovery Scrubber process offers several advantages for cement plant use it recovers a major fraction of the waste cement kiln dust in a form suitable for... 

Other applications of the Recovery Scrubber process have been proposed by Morrison (1991). In general, these are based on the use of biomass ash from pulp and paper plants and other wood burning facilities. Biomass ash is rich in potassium and ery alkaline, so its use presents the possibility of both SO2 mnoval and potassium sul te recovery. 

Screen printing inks Screen-process inks Screens Screw dislocation theory Scrip set Scrubbers... 

Dust entrained in the exit-gas stream is customarily removed in cyclone cohectors. This dust may be discharged back into the process or separately cohected. For expensive materials or extremely fine particles, bag collectors may follow a cyclone collector, provided fabric temperature stability is not hmiting. When toxic gases or solids are present, the exit gas is at a high temperature, the gas is close to saturation as from a steam-tube diyer, or gas recirculation in a sealed system is involved, wet scrubbers may be used independently or following a cyclone. Cyclones and bag collec tors in diying applications frequently require insulation and steam tracing. The exhaust fan should be located downstream from the cohection system. 

Vapors (from drying) are removed at the feed end of the dtyer to the atmosphere through a natural-draft stack and settling chamber or wet scrubber. When employed in simple drying operations with 3.5 X 10 to 10 X 10 Pa steam, draft is controlled by a damper to admit only sufficient outside air to sweep moisture from the cylinder, discharging the air at 340 to 365 K and 80 to 90 percent saturation. In this way, shell gas velocities and dusting are minimized. When used for solvent recovery or other processes requiring a sealed system, sweep gas is recirculated throu a scrubber-gas cooler and blower. 

By-product processing CO, H2S, methane, ammonia, H2, phenols, hydrogen cyanide, N2, benzene, xylene, etc. Electrostatic precipitator, scrubber, flaring... 

Rendering plants Feedstock storage and housekeeping Cookers and percolators Grinding Odors SO2, mercaptans, ammonia, odors Particulates (dust) Quick processing, washdown of all concrete surfaces, paving of dirt roads, proper sewer maintenance, enclosure, packed towers Exhaust system, condenser, scrubber, or incinerator Exhaust system and scrubber... 

A fluid-bed incinerator uses hot sand as a heat reservoir for dewatering the sludge and combusting the organics. The turbulence created By the incoming air and the sand suspension requires the effluent gases to be treated in a wet scrubber prior to final discharge. The ash is removed from the scrubber water by a cyclone separator. The scrubber water is normally returned to the treatment process and diluted with the total plant effluent. The ash is normally buried. 

Shared equipment Design to avoid or minimize use of (e.g. auxiliary process- common equipment for incompatible ing scrubbers ). Pos- materials sihility of incompatible, Implement proper cleaning procedure materials coming between incompatible uses to prevent together. cross contamination Prescrub or treat process streams before transfer to common equipment API RP 750 CCPS G-11 CCPS G-22 Kletz 1991 Lees 1996 NFPA-91... 

Consider common scrubbers, vents, sumps, drains, off-gas treatment and other opportunities for inadvertently mixing process materials. Cross-contamination potential at transfer stations should not be overlooked. 

The principal technological developments in the control of air pollution by engineering during the nineteenth century were the stoker for mechanical firing of coal, the scrubber for removing acid gases from effluent gas streams, cyclone and bag house dust collectors, and the introduction of physical and chemical principles into process design. 

Figure 30-lA presents the integrated environmental control potential for maximum control of particulate matter and SO2. Cooling tower water blowdown and treatment by-products may be used to satisfy scrubber makeup requirements. Fly ash and scrubber sludge will be produced separately. If the catalytic NO, process is required, the integration issues will be increased significantly. 

Figure 30-lE includes a hot ESP for fly ash collection prior to a catalytic NO , unit. Having a hot ESP dictates the use of a conventional wet scrubber and perhaps the need for a second particulate matter control device at the end of the system. Fly ash and scrubber sludge would be separate byproducts, but sludge could be contaminated with NH4 from the catalytic NO process. 

Thermal process HiP04, HjS Mist eliminators, alkaline scrubbers... 

Refractory metals Zirconium Hafnium Titanium Kroll process, chlorination, and magnesium reduction Chlorine, chlorides, SiCli Wet scrubbers... 

The electric arc furnace process accounted for about 25% of the 1982 U.S. steelmaking capacity (14). Most of the raw material used for the process is steel scrap. Pollutants generated by the electric furnace process are primarily particulate matter and CO. The furnaces are hooded, and the gas stream containing the particulate matter is collected, cooled, and passed to a bag-house for cleaning. Venturi scrubbers and ESPs are used as control devices at some mills. Charging and tapping emissions are also collected by hoods and ducted to the particulate matter control device. 

Collecting a sample is a costly and timecosts minimized consistent with other objectives. It makes little sense to spend 5000 on an extensive stack testing analysis to decide whether to purchase a 10,000 scrubber of 95% efficiency or to try to get by with a 7000 scrubber of 90% efficiency. 

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