Process simulation and economic analysis of the Calcium Looping Process (CLP) for hydrogen and electricity production from coal and natural gas

摘要

The Calcium Looping Process (CLP) is being developed to facilitate carbon dioxide (CO_2) capture during the production of hydrogen (H_2) from syngas. The process integrates CO_2, sulfur, and halide removal with the water-gas shift (WGS) reaction in a single-stage reactor. In the CLP, a regenerable calcium oxide (CaO) sorbent is used to chemically react with and remove CO_2 and other acid gases from syngas at high temperature (i.e., 550-700℃). The removal of CO_2 drives the WGS reaction forward via Le Chatelier's principle, obviating the need for a WGS catalyst and enabling the production of high-purity H_2. The spent sorbent is heated in a calciner to regenerate CaO for reuse in the process and to release a concentrated CO_2 stream, which can be dried and sequestered. The regenerated sorbent is then reactivated in a hydra-tor, to improve its recyclability, before being reintroduced into the H_2 production reactor. Techno-economic analyses were performed to evaluate the application of the CLP to a coal-to-H_2 plant, a steam methane reforming (SMR) plant, and an integrated gasification-combined cycle (IGCC) plant, all including ≥90% CO_2 capture. In each case, use of the CLP resulted in a 9-12% reduction in the cost of H_2 or cost of electricity when compared with the use of conventional CO_2 capture and WGS technologies. The economic advantage afforded by the CLP is realized because of the large amount of high-quality heat produced in the process, which is recovered to raise steam for electricity generation. This heat arises from the combustion of supplemental fuel in the CLP calciner and from the exothermic CO_2 removal, WGS, and hydration reactions, which are carried out at high temperature (i.e., ≥500℃) in the CLP. As a result of recovering this heat, the CLP-based coal-to-H_2 and SMR plants, which are designed to produce 26,000 kg/h H_2, necessarily co-produce 320 MW_e and 190 MW_e of net electric power, respectively. Although the CLP can reduce the cost of producing H_2 from coal, the resulting cost is still about 26% greater than the cost of H_2 produced from natural gas using conventional WGS and CO_2 capture technologies, assuming coal and natural gas prices of $1.55/GJ and $6.21/GJ, respectively. The lowest cost of H_2 with CO_2 capture for these fuel prices is achieved by applying the CLP to an SMR plant.