Plant flexibility of a pre-combustion CO2 capture cycle

Abstract

Abstract The aim of the paper is to investigate plant flexibility for a pre-combustion cycle. That is, answering the question: how flexible is the plant to changes in operating conditions? Steady-state off-design simulations was the key component of the plant flexibility analysis. Specifically, part load behavior and dual-fuel operation of the integrated reforming combined cycle (IRCC) were studied. The idea of the plant was to use hydrogen-rich decarbonized fuel as the primary fuel and natural gas as back-up fuel. If a problem would occur in the reforming, water-gas shift, or CO 2 capture processes there might be a need to switch to a natural gas feed for the gas turbine. This led to design challenges for the heat recovery steam generator (HRSG). The design of the HRSG for the IRCC process was different from an HRSG design in a natural gas combined cycle (NGCC) plant because of the significant amount of steam production from the heat generated in the reforming process. In addition, preheating (within the HRSG) of some of the process streams could add to the complexity in HRSG design. For the concepts studied it was of importance to maintain a high net plant efficiency on both fuels. Therefore the HRSG design had to be a compromise between NGCC and IRCC operation modes. In the analysis performed, part load behavior was good with efficiency reductions from base load operation comparable to that of the reference combined cycle plant. Based on the analysis performed in the present work, it was possible to operate a complex plant like an IRCC at loads down to 60 gas turbine load while capturing 85% of the CO 2 . During start-up and operation at lower loads, CO 2 would not be captured. The investigation was done by using process simulation tools Aspen Plus by AspenTech and GT PRO/GT MASTER by Thermoflow.