A Technoeconomic Analysis of Different Options for Cogenerating Power in Hydrogen Plants Based on Natural Gas Reforming

摘要

Steam methane reforming is the most common process for producing hydrogen in the world. It currently represents the most efficient and mature technology for this purpose. However, because of the high investment costs, this technology is only convenient for large sizes. Furthermore, the cooling of syngas and flue gas produce a great amount of excess steam, which is usually transferred outside the process, for heating purposes or industrial applications. The opportunity of using this additional steam to generate electric power has been studied in this paper. In particular, different power plant schemes have been analyzed, including (ⅰ) a Rankine cycle, (ⅱ) a gas turbine simple cycle, and (ⅲ) a gas-steam combined cycle. These configurations have been investigated with the additional feature of CO_2 capture and sequestration. The reference plant has been modeled according to state-of-the-art of commercial hydrogen plants: it includes a prereforming reactor, two shift reactors, and a pressure swing adsorption unit for hydrogen purification. The plant has a conversion efficiency of ～75% and produces 145,000 Sm~3/hr of hydrogen (equivalent to 435 MW on the lower-heating-volume basis) and 63 t/hr of superheated steam. The proposed power plants generate, respectively, 22 MW (ⅰ), 36 MW (ⅱ), and 87 MW (ⅲ) without CO_2 capture. A sensitivity analysis was carried out to determine the optimum size for each configuration and to investigate the influence of some parameters, such as electricity, natural gas, and steam costs.