Design and Optimization of Flexible Hydrogen Systems in Refineries

With the increasing demand for hydrogen resulting from fierce market competition and stringent environmental legislation, the hydrogen system has become an important component of a refinery. It is vital for the hydrogen system to be operated economically and safely under varying operating conditions. This calls for a systematic approach to the design and optimization of flexible hydrogen systems, which is the aim of this article. The hydrogen distribution network is designed at the minimum total annual cost subject to constraints on the flow rates and pressures of both existing and new equipment during the payback period. Varying hydrogen demands, different pipeline levels, and the possibility of hydrogen units being shut down are considered as operating conditions in the design optimization task, leading to the formulation and solution of a mixed-integer nonlinear programming (MINLP) problem. Using a linearization method, the MINLP formulation is approximated by a mixed-integer linear programming (MILP) problem, resulting in an acceptable quality and high efficiency. An industrial hydrogen system is taken as a case study. As shown in the case study, the proposed approach can handle high-dimensional and complex hydrogen system problems and gain significant economic improvements in comparison to an existing design.