When to switch from heat-up to start-up in the warming-up process of a solid oxide fuel cell: A numerical study and multi-objective planning

Abstract

Solid oxide fuel cells (SOFCs) at rest need to undergo warming-up process to reach normal performance. This process begins with cell heating (so called heat-up process) and continues with the activation of electrochemical reactions (so called start-up process) until the cell performance reaches steady state. This paper develops a transient numerical model to investigate the influence of the switching temperature (ST), defined as the electrolyte average temperature at the beginning of the start-up process, on the SOFC warming-up process. Also, an optimal ST is proposed by considering the different combinations of the objectives of warming-up time duration, energy efficiency and thermal shock. The results indicate that a lower ST (or an earlier onset of start-up process) results in a shorter warming-up time duration and a greater energy efficiency (as two desirable impacts), but causes a higher thermal shock (as a negative point). Using a multi-objective decision making approach (namely, linear programming technique for multi-dimensional analysis of preference), a ST of 823 K is proposed as an optimal compromise among the three mentioned objectives. However, when the energy efficiency is disregarded, a ST of 998 K is found to be optimum.