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The Otto-Hoffman system for making coke.
Dr. C. Otto, of Dahlhausen transformed the Coppee oven into a sort of huge gas retort installation, so that the volatile products could be treated for by-products, and only the waste gases used for heating purposes. By this treatment, however, the gases became cooled, and therefore, as there appeared to be some danger of cooling the ovens below the high temperature required to produce good coke and good by-products by the admission of cool gas along with the six or seven volumes of cold air for combustion, it occurred to Gustav Hoffmann to adapt the Siemens regenerator to the Otto-Coppee oven. As a result four regenerator chambers were added, two for re-heating the gas and two for heating the air. Subsequently it was found that the heating of both gas and air was unnecessary and had other disadvantages. So the Otto-Hoffmann-Coppee oven was designed to produce coke, tar, benzol, ammonia, etc., and utilise some of the heat of the waste gases in heating regenerators for the air supply. The two main additions and the various incidental modifications rendered this very unlike the original Coppee so it was known as the Otto-Hoffmann system.