Dowa process

An alternative is to pass Boliden Norzink exit gas through a column of activated PbS coated pumice (Dowa Process). This precipitates solid HgS and keeps Hg-in-sulfuric acid below 0.05 parts per million (Lossin and Windhager, 1999). 

Dowa process Similar to dual alkali except J.A12(S04)3 solution used in scrubber. 

The Dowa process is claimed to offer sevoal advantages in comparison with both conventional limestone/lime and sodium dual alkali systems (Nolan and Seaward, 1983). These include... 

Nolan, P. S., and Seaward, D. O., 1983, The Dowa Process Dual-Alkali Flue Gas Desulfurization with a Gypsum Product, Proceedings of Seminar on Flue Gas Desulfurization sponsored by the Canadian Electrical Association, Ottowa, Ontario, Canada, September. 

The Dowa process is another dual alkali system. It uses basic aluminum sulfate solution for SO2 removal and low-cost limestone to regenerate the aluminum sulfate. A gypsum by-product is produced. The process is common in Japan. 

In iadustry, chemical reductioa is preferred over electrolytic processes for potassium productioa. AppHcatioa of the Dowa s electrolytic sodium process to produce potassium has aot beea successful. Potassium—sodium ahoy is easily prepared by the reactioa of sodium with molten KCl, KOH, or sohd K2CO3 powder (see Sodiumand sodiumalloys). 

Dowa A flue-gas desulfurization process in which the sulfur dioxide is absorbed in a basic aluminum sulfate solution. The product solution is oxidized with air and reacted with limestone to produce gypsum. Developed by the Dowa Mining Company, Japan, in the early 1980s. In 1986 it was in use in nine plants in Japan and the United States. 

The Dowa Mining Company (K9) in Kosaka, Japan has developed a hydrometallurgical process shown in Fig. 15 to treat 2400 metric tons/ month of copper-zinc sulfide flotation concentrates. The microscopically fine mixture of copper and zinc sulfides was separated from lead sulfide and barite by flotation. The flotation concentrate analyzed 8.7% Cu,... 

Conparing the results from Parts (a) and (c), we can see that with the current prices for these two chemicals it is not economical to produce benzene from toluene. Historically, the price differential between benzene and toluene has been greater than the 0.009/kg shown in Table 8.4. and this is the reason why this process has been used, and is currendy being used, to produce benzene. Clearly, if this low price differential were to exist for a long period of time, this process might have to be shut dowa... 

The Dowa Dual Alkali Process uses a solution of basic aluminum sulfate to absorb SO2, air injection to oxidize sulfite to sulfate, and limestone to precipitate the resulting excess sulfate in the form of gypsum. 

The process was developed by the Dowa Mining Company of Japan in the eariy 1980s and, by 1983, ten commercial systems were operating on a variety of smelters, sulfuric acid plants, and one oil-fired boiler (Nolan and Seaward, 1983). The process was dononstrated in the United States by UOP at TVA s Shawnee Steam Plant (Hollinden et al., 1983A). 

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