Ferrox process

Manchester A variation on the Ferrox process for removing hydrogen sulfide from industrial gases in which several absorbers are used, and delay stages permit completion of the reaction with the iron oxide absorbent. Developed by the Manchester Corporation Gas Department in the 1940s and installed in several British gasworks. 

Removal of larger amounts of hydrogen sulfide from gas streams requires continuous processes, such as the Ferrox process or the Stretford process (Mokhatab et al., 2006 Speight, 2007, 2008). The Ferrox process is based on the same chemistry as the iron oxide process except that it is fluid and continnons. The Stretford process employs a solution containing vanadinm salts and anthraqui-none disulfonic acid (Maddox, 1974). 

The Ferrox process represented a marked improvement over dry-box purification because the plants occupied only a fraction of the ground area necessary for dry boxes treating equivalent volumes of gas. In addition, the labor cost was reduced appreciably, and the initial... 

Rgure 9-1. Typical flow diagram of Ferrox process. 

One of the major drawbacks of the Ferrox process is the corrosiveness of the treating. solution which causes fairly rapid destruction of carbon-steel equipment. The use of alloys is uneconomical in most installations, but lining of the major vessels with luhher and the possible use of coated wooden tanks for thionizers was routinely considered. 

A modification of the Ferrox process was developed in England in the 1950 at the Rochdale Works of the Manchester Corporation Gas Department and is known as the Manchester process. This process, which is covered by British Patents 550,272 and 611,917, was subsequently used in several British gas works installations. A large plant, with a capiacity to handle 80 million cu ft air/day, was also built to remove hydrogen sulfide from the exhaust air in a viscose cellulose manufacturing plant. In this installation, the hydrogen sulfide content of the air was reduced from 255 to approximately 5 ppm (Roberts and Farrar, 1956). 

The Konox process is a liquid-phase oxidation process based on the use of an iron complex. The process was developed in Japan in 1975 by Sankyo to replace the Ferrox process in the treatment of coke oven gas. 

Some of the commercial processes comprising this group include Stretford, Takahex, Giammarco-Vetrocoke, Ferrox and others. 

Various other techniques have also been developed particularly the Ferrox. Manchester, Perox, Lacy-K.eller. Lo-Cat. Freeport sulfur processes, etc. 

In this sector, the Stretford Process offered by British Gas Corp. and the Takahax Process of Tokyo Gas Cie. Ltd. have prevailed over the older processes of this type such as Giammarco-Vetrocoke, Ferrox, Thylox and others [2.4]. A certain preference for the former can be observed in the USA and Europe, whereas the latter is more frequently used in Japan. The Takahax process, which exists in 4 versions in combination with the Hirohax process developed by Nippon Steel, is specifically tailored to coke oven gas cleaning and may therefore be left unconsidered here. 

Design and Operation. The absorber used in Ferrox installations has a lower section, or saturator, and an upper section, the absorber proper, llie saturator contains a continuous liquid phase, several feet high, through which the raw gas is bubbled before it enters the upper section. The function of the saturator is to provide sufficient contact time to complete the reaction between sodium hydrosulfide and ferric oxide before regeneration of the solution. If essentially complete reaction is achieved, thiosulfate formation in the regenerator is kept at a minimum. The upper part of the absorber contains sprays and wooden hurdles similar to those used in the Seaboard process and usually has a total height of 60 ft (Sperr, 1926). 

The solids obtained in the filters contain from 30 to 50% elemental sulfur, approximately 50% moisture, and 10 to 20% salts, mostly entrapped ferric hydroxide and sodium carbonate. Because of this loss of. sodium carbonate and ferric hydroxide, these chemicals have to be added continuously to the solution. This affects the economics of the process, and for plants where the gas capacity is low and the quantity of recoverable sulfur is small, solution regeneration is uneconomical. In general, this consideration was not a major factor in the United States since there was no market for the sulfur obtained from a Ferrox plant. Therefore, most American plants were operated on a non-regenerative basis. 

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