Abstract
A fuel cell system needs to be designed in consideration of frequent start-up, shutdown and load change operations, since it is generally operated on demand manner. The conventional design approach such as a heat integration technique gives us the optimal structure of a heat exchanger network of a fuel cell system during the steady state operation. However, the extra units need to be added in the derived structure later for the transitional operations, when the fuel cell system is designed based on the steady state operation mode. In this research, the process synthesis method is proposed for the fuel cell systems considering start-up operation. The proposed method mainly consists of two optimization steps. In the first step, the optimal heat exchanger network and operation profiles are derived so that the fuel cell system can follow the predefined temperature profile. The transshipment model used in the conventional heat integration technique is extended to the dynamic transshipment model which can handle the heat accumulation to the devices during the transitional operation. In the second step, the operation profile is optimized as a function of time using more detailed dynamic models of the process. The proposed two-step optimization method is demonstrated through a case study. The proposed method has wide applicability to other processes where frequent start-up and shutdown are requested.
