Patent ID: 8084660

Claim:
A method for increasing the efficiency and/or expanding the capacity of a new or existing dehydrogenation unit for dehydrogenating of alkyl aromatic hydrocarbons to alkenyl aromatic hydrocarbons, comprising: providing at least one dehydrogenation reactor and a feed stream comprising said alkyl aromatic hydrocarbons; adding at least one direct heating unit (DHU) to a new or existing dehydrogenation unit having a reheater, whereby the DHU and reheater are positioned before or after at least one reactor, and wherein the DHU and reheater are operated in parallel arrangement with respect to each other; diverting between 0.5% and 85% of a reactor effluent from the reactor to the DHU for heating and feeding the remainder of the reactor effluent to the reheater for heating; feeding the heated streams from the DHU and the reheater to a subsequent reactor, wherein there is an energy savings for operating the new or existing dehydrogenation unit with an added DHU as compared to operating a dehydrogenation unit with only a reheater and no added DHU; wherein the energy saving is a usage of 0.1% to 50% less energy when at least one DHU and at least one reheater are used to heat a process stream.