Process simulation and optimization of H2 production from ethanol steam reforming and its use in fuel cells. 2. Process analysis and optimization

Abstract

The feasibility of power cogeneration through fuel cells using bioethanol with different concentration has been considered. Data and layout have been inspired by an existing unit Helbio, GH2-BE-5000 (5kWelectrical+5kWthermal) system for combined heat and power generation (CHP). The system is constituted by six reactors connected in series for hydrogen production and purification and by a fuel cell of the mentioned capacity.To evaluate process efficiency and the possibility to operate with diluted bioethanol feed, characterized by lower purification cost, different process layouts have been tested. Particular attention is paid to the intensification of the heat exchange network, to increase the overall plant efficiency. Heat supply to the steam reformer has been accomplished by burning part of the reformate, since diluted ethanol is not suitable to feed the burner as in the experimental process layout.The water/ethanol feeding ratio has been taken as major parameter for simulation. An increase of this variable improved H2 yield due to promotion of the water gas shift reaction and lower impact of the hydrogen-consuming methanation step. However, higher heat input was required by the reformer, implying the delivery of a higher fraction of the reformate to the burner instead than to the fuel cell. This means lower electric output and efficiency. However, the presence of a high enthalpy steam exhaust increased the available thermal output, with consequent increase of the thermal and overall efficiency of the plant.