Steam cracking Hydrodesulfurization

Thermal processes such as coking, cat cracking, hydrodesulfurization, and hydrocracking ail produce both NF 3 and H2S. The resulting aqueous-phase ammonium hydrosulfide is antagonistic to carbon steel heat-exchanger tubes. Most of the ammonium hydrosulfide winds up in sour-water streams. Before disposal, the sour water must be steam stripped. The overhead condenser used for this stripper has an extremely corrosive environment. Titanium is preferred for this service. 

Flow diagram of the process for hydrogen and distillate fuel production from residual oil using iron oxides and steam. 1 = Cracking reactor, 2 = distillation column, 3 = hydrogen generator, and 4 = hydrodesulfurization reactor. 

In the process, a residuum is desulfurized and the nonvolatile fraction from the hydrodesulfurizer is charged to the residuum fluid catalytic cracking unit. The reaction system is an external vertical riser terminating in a closed cyclone system. Dispersion steam in amounts higher than that used for gas oils is used to assist in the vaporization of any volatile constituents of heavy feedstocks. 

Such second-order kinetics are observed in some refinery operations including catalytic cracking and hydrodesulfurization. Others, such as steam deactivation upon coke bum-off, however, occur at reaction orders of 2 to 5, indicating an initial distribution that diverges at k- 0 [33]. 

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