Form coke production with recovery of medium BTU gas

#This invention relates to the production of medium BTU product gas, particularly in conjunction with the manufacture of form coke.

#In U.S. Pat. Nos. 3,140,241 and 3,140,242 to Work, et al, there is described a form coke product which comprises briquettes made by briquetting a reactive coal calcinate with oxidized coal tar pitch, curing the resulting green briquettes in an oxidizing atmosphere and then coking the cured briquettes in an inert atmosphere to reduce the volatile content to less than about 3%. The product is a highly reactive, physically strong carbonaceous material eminently satisfactory for use in metallurgical furnaces including iron smelters. For instance, during commercial blast furnace runs, these briquettes proved generally equal in performance to conventional high temperature coke. In fact, they were superior to oven coke in that their uniform size and shape tend to facilitate furnace operation. Moreover, the briquettes can be manufactured from non-coking coals, an especially attractive feature since it promises to ease the steel industry's dependence on coking coals which are becoming increasingly scarce. In addition, plants for producing the briquettes meets all Federal and State environmental standards whereas coke ovens are highly polluting. Nor is it presently feasible to equip coke ovens with the requisite pollution abating devices.

#All things considered, the form coke briquette of the aforecited patents is an ideal carbon reductant for commercial metallurgical purposes.

#In carrying out the invention herein, the process of the Work, et al patent is followed generally except that the carbonizing and calcining vessels are fluidized with steam and/or carbon dioxide which are then separated from the vessel overheads and the resulting fuel gases recovered. Heat for the carbonization and calcination is provided by partial combustion of carbonaceous materials in the reaction vessels with oxygen incorporated in the fluidizing medium. The oxygen should be added only in an amount as required for the combustion to supply the heat demand of these stages. In general, the concentration of oxygen in the fluidizing atmosphere is about 18 to 30%, preferably about 20 to 25%. Surprisingly, it was found that by operating in accordance with the invention a detailed description of which follows, calcination can be effected in a fluidizing atmosphere of steam or carbon dioxide while preventing gasification of the calcinate from approaching levels at which the coke quality and yield is impaired.

#Where the fluidizing medium in the carbonizing zone is a mixture of oxygen and steam, cooling of the evolved gaseous components results in the tar vapors being condensed to tar and the steam condensed to water. This leaves a crude carbonizer gas comprising an essentially nitrogen free mixture of fuel gases and carbon dioxide plus a small amount of nitrogen, usually about 1 to 2%. The heating value of the crude carbonizer gas is about 500 to 600 BTU/SCF.

#Freeing the crude carbonizer gas of carbon dioxide is effected in the known manner such as by absorption in an alkaline or amine solution followed by stripping using known techniques. Since carbon dioxide is always formed during carbonization, it is evident that it might be advantageous to treat the crude carbonizer gas as above described even if carbon dioxide is not added to the fluidizing atmosphere. The purified carbonizer gas which can be used by itself or combined with calciner gas to give a mixed by product gas having a heating value of about 500 to 600 BTU/SCF on a N.sub.2 free basis and 900 to 1000 BTU/SCF on a N.sub.2 --CO.sub.2 free basis.