Design and thermodynamic analysis of a novel methanol, hydrogen, and power trigeneration system based on renewable energy and flue gas carbon dioxide

Abstract

In this paper, a new trigeneration system is proposed to decrease atmospheric carbon dioxide emission and produce methanol, hydrogen, and power. The system is composed of an organic Rankine cycle, a direct methanol fuel cell, a carbon capture unit, a proton exchange membrane electrolyzer, and a methanol synthesis unit. A flue gas stream with a defined composition, solar energy, and the atmospheric air are the system's inlets. In the design step, special attention is paid to heat and mass integration between different components so that its waste can be lowered as much as possible. Then, mass balance law, energy conservation principle, exergy relations, and auxiliary equations are applied for each subsystem to investigate the system's thermodynamic performance. Also, the effect of changing operating parameters on the performance of each subsystem is studied. The obtained results show that the proposed system has the energy and exergy efficiencies of 66.84% and 55.10%, respectively. Furthermore, 94% of the total exergy destruction rate belongs to the water electrolyzer, while the contribution of the organic Rankine cycle is negligible. The performance of the methanol synthesis reactor depends strongly on its inlet temperature. Maximum equilibrium methanol concentration and carbon dioxide conversion are achieved at the inlet temperature of 210 °C. The parametric studies reveal that there is an optimum fuel cell current density in which its produced power density is maximized.