Abstract
The Ca-Cu process is a novel concept for hydrogen production with inherent CO2 capture that has received great attention in the last years as potential low-CO2 emission technology for power generation and hydrogen production from natural gas. The process is based on the reforming of natural gas in the presence of a CaO-based sorbent and a Cu/CuO chemical looping combustion loop that provides the energy needed for CaCO3 calcination. The process is proposed to be carried out in adiabatic, dynamically operated fixed bed reactors operating in parallel. Simulations with a 1D dynamic pseudo-homogeneous reactor model were performed for the different stages of the Ca-Cu process, considering a reasonable set of process assumptions. It has been demonstrated that the formation of a high temperature plateau during the sorption-enhanced reforming stage of the process, caused by the decoupling between the steam methane reforming and the carbonation reactions in different positions along the bed, decreases the carbon capture efficiency that can be achieved in this process. Concretely, a maximum overall carbon capture efficiency of almost 82% could be obtained with selected operating conditions in the Ca-Cu process. With the aim of overcoming this limited capture efficiency, a novel alternative scheme for the Ca-Cu process has been proposed, consisting in splitting the sorption enhanced reforming stage into two steps with intercooling. Simulations of this case demonstrated that an overall carbon capture efficiency of 88% can be achieved.
Highlights
Most of the hydrogen produced worldwide is used as feedstock within the chemical and refinery industries, while showing a growing interest in the coming years as energy carrier for conversion into electricity, mechanical energy or heat [1]
It has been demonstrated that the formation of a high temperature plateau during the sorption-enhanced reforming stage of the process, caused by the decoupling between the steam methane reforming and the carbonation reactions in different positions along the bed, decreases the carbon capture efficiency that can be achieved in this process
As demonstrated from the results shown in this analysis, the capture efficiency (CCE) obtained for stage A is not significantly influenced by the shape of the initial bed temperature profile
Summary
Most of the hydrogen produced worldwide (i.e. around 65 million tons per year) is used as feedstock within the chemical and refinery industries, while showing a growing interest in the coming years as energy carrier for conversion into electricity, mechanical energy or heat [1]. Natural gas represents the principal feedstock for hydrogen production, accounting for more than 48% of the worldwide production, followed by petroleum and coal as primary energy sources. Large scale hydrogen production worldwide represents only 3% of the global emissions [2], the expected growth in the hydrogen demand in the coming years makes the development of large fossil fuels hydrogen production plants integrated with CO2 capture technologies interesting [3]. Despite the fact that the steam methane reforming (SMR) process of natural gas is the dominant and most economic technology for large scale H2 production, it presents important drawbacks associated to its demanding operating conditions of high pressure and high temperature in the reforming reactor.
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