Scrubbing operation particulate removal

Make a list of all the costs associated with running a wet scrubbing operation to remove particulates and SO,. What cost factors could be eliminated or reduced if a pollution prevention technology or practice that used about the same energy and manpower requirements was applied. 

Removal of a solid or liquid particulate involves a physical capture by wetting after the particle has penetrated the liquid surface. There is no limit to the amount of particulate capture that can be achieved, as long as the liquid-film properties remain unchanged during the scrubbing operation. 

The scrubbing liquid is controlled to a neutral pH with reagent addition to drive SO2 absorption. Caustic soda (NaOH) is typically used as the alkaline reagent. However, other alkalis, such as soda ash, magnesium hydroxide, and lime have also been utilized with excellent results in terms of performance and reliability. For FCCU applications, however, where a 5-7 year continuous operation is required, the use of lime as a reagent is not recommended. Multiple levels of spray nozzles provide sufficient stages of gas/liquid contact to remove both particulate and SO2. An illustration of the spray tower and the spray nozzles is provided in Figure 16.6. 

Satriana (2) provides a summary of the development of flue gas treatment technology. The first commercial application of flue gas scrubbing for sulfur dioxide control was at the Battersea-A Power Station [228 MW(e)] in London, England, in 1933. The process used a packed spray tower with a tail-end alkaline wash to remove 90 percent of the sulfur dioxide and particulates. Alkaline water from the Thames River provided most of the alkali for absorption. The scrubber effluent was discharged back into the Thames River after oxidation and settling. A similar process was also operated at the Battersea-B Power Station [245 MW(e)] beginning in 1949. The Battersea-B system operated successfully until 1969, when desulfurization efforts were suspended due to adverse effects on Thames River water quality. The Battersea-A system continued until 1975, when the station was closed. 

Material Balance. Material balances for a low and high sulfur content gas to the RC/Bahco CTB-100 module are illustrated in Table IV. Operating data from actual installations indicate 93-99% SO2 removal and particulate emissions as low as 0.01 grain/SCFW. Scrubbing reagent consumption is about 1.1 times the stoichiometric amount. 

Qince the first large sulfur dioxide control system was installed at the Battersea plant in London, it has taken almost 50 yrs for calcium-based scrubbing technology to become commercially acceptable. In 1926, the 125 MW coal-fired Battersea power plant was equipped with a spray packed tower and final alkaline wash section which removed more than 90% of the sulfur dioxide and particulate (I). Thames River water provided most of the alkali for absorption, and about 20% was made up from lime addition. The process operated in an open-loop manner, returning spent reagent to the Thames. 

Particulate matter may be removed from gas products by a number of means such as (1) water scrubbing or (2) a cyclone separator. Part of the ash from a conversion operation occurs as fly ash and is removed with particulate matter. Some gasifiers produce a melted bottom ash (slag) which is quenched in water while other processes produce a self-agglomerating ash consisting of softened particles. 

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