Conceptual design of a hydrogen production process from natural gas with CO2 capture using a Ca–Cu chemical loop

Abstract

This work presents a conceptual design of a novel method to obtain hydrogen and/or electricity from natural gas and a concentrated stream of CO2 suitable for permanent geological storage. The method is based on the well known Sorption Enhanced Reforming (SER) principles for H2 production using a CaO/CaCO3 chemical loop. A second chemical loop of Cu/CuO is employed to solve the problem of endothermic CaCO3 calcination in order to regenerate the sorbent and release the concentrated CO2. The reduction reaction of CuO with natural gas, CO or H2 is shown to be feasible for providing the necessary heat for calcination. A preliminary design of the process has been carried out based on the principles of fixed bed operation and high temperature PSA, making use of the information offered by the literature to define the operating best conditions for the key gas-solid reaction steps and assuming ideal plug flow behaviour in all the reactors during the chemical reactions and gas-solid heat transfer. This makes it possible to define the precise operating windows for the process, so that the reactors can operate close to neutrally thermal conditions. Special material properties (particularly the Ca/inert and Cu/inert ratios) are required, but these are shown to be within the limits of what have been reported in the literature for other gas/solid reaction processes using the same reactions. The conclusion is that there is a great potential for achieving a high degree of energy efficiency with the proposed process by means of a sequence of reactions under the conditions described in this work.