Multistage residual oil hydrodesulfurization process with an interstage flashing step

摘要

In the hydrodesulfurization of residual oil the amount of hydrogen consumed per atom of sulfur removed is relatively low until the desulfurization becomes deep, whereupon the amount of hydrogen consumed per atom of sulfur removed becomes relatively high. The present invention provides a multistage catalytic hydrodesulfurization process capable of producing products of low sulfur level while avoiding deep desulfurization of the heavy portion of the residual oil so that hydrogen consumption is diminished. The feed oil and hydrogen are passed through an upstream hydrodesulfurization stage and the upstream stage effluent is flashed to separate a distillate oil fraction from a concentrated residual oil fraction. A portion of the concentrated residual oil fraction is diverted from the process for use as refinery fuel and the remaining portion of the flash residue and hydrogen are charged to an upstream stage together with the flash distillate. Since the sulfur in distillate oil is less refractory than the sulfur in residual oil, removal of a portion of the concentrated residual oil fraction provides a nonaliquot distillate-residual oil downstream stage feed stream which is easier to desulfurize to a low sulfur level than an aliquot distillate- residual oil stream. The dilution of the high sulfur residue in the downstream stage diminishes the depth of hydrodesulfurization required for residual components in the downstream stage, thereby reducing the level of hydrogen consumption required to produce a product having a low sulfur level.