Design of a Compact Heat Exchanger in a Methanation Plant for Renewable Energy Storage

Power-to-Gas (P2G) is a viable technology for renewable energy storage. In one of its preferred configurations, a hot gaseous mixture of H2O and CO2 is fed to a high temperature electrolysis module (SOEC) and gets converted to CO and H-2, which are subsequently converted into methane in a methanation module. Here the SOEC is powered by using the excess energy of the renewable source. For such a system to work efficiently, it is necessary that the gaseous mixture enter the SOEC at a sufficiently high temperature. The present study aims at designing a compact heat exchanger (HE) to heat the inlet mixture to the required temperature of 850 degrees C, using a regenerative solution. The design process consists of two complementary steps. The first step involves an analytical sizing procedure based on the known epsilon-NTU method along with semi-empirical correlations, which rapidly provides a cost-effective, preliminary heat exchanger design (construction type, flow configuration and fin geometry). In the second step, the preliminary design is refined and optimized using 3-D CFD simulations, resulting in an ultra-compact HE with elliptical fin shape. The optimization procedure was aimed at maximizing the device thermohydraulic performance and compactness index, benchmarked with respect to other notable designs so as to highlight the current design soundness. The optimum HE design has an effectiveness of 96%, pressure losses as low as 5.5 and 4.3 mbar on the cold and hot sides, respectively, and a heat transfer area density of 3600 m(2)/m(3). (C) 2017 Elsevier Ltd. All rights reserved.