Energy, exergy and optimization of a binary hydrogen-power production system with net zero emissions
Javad Jeddizahed, Paul A. Webley, Thomas J. Hughes
Abstract
• The NZC system efficiency increases by from 53.7 to 62.8%. • Key system influencers are: electrolyzer recirculation molar flow, COT, TOP, and COP. • The optimized integrated system is found to achieve a maximum efficiency of 68.1%. • The electrolyzer causes the most exergy destruction, followed by the combustor. This study investigates a novel dual-generation system producing electricity and hydrogen with zero net carbon emissions, utilizing natural gas, water, and renewable energy. It explores the system integration of a Net Zero Cycle (NZC) oxy-combustion power plant with a renewable-powered hydrogen electrolyzer, eliminating the need for an Air Separation Unit (ASU). Process simulations were conducted using Aspen Plus and Aspen Custom Modeler. Sensitivity analyses and optimization was conducted via Particle Swarm Optimization combined with Latin Hypercube Sampling, and an exergy analysis was performed. In the linked process, the energy consumption of turbomachinery in the NZC increases by 16.9% due to the need for compressing electrolyzer-produced oxygen to combustion levels. Nevertheless, the net power output of the NZC increases by 17%, mainly due to the elimination of the energy-intensive ASU, increased heat provision by the electrolyzer to the regenerator, and the combustion of hydrogen mixed with the oxygen output. Consequently, the efficiency of the NZC improves from 53.7% to 62.8% with this integration. The research also highlights the electrolyzer’s efficient use of condensed water from the NZC process without the risk of salt precipitation. Sensitivity analyses revealed that the system’s efficiency is predominantly influenced by the electrolyzer’s recirculation molar flow, combustion outlet temperature (COT), turbine outlet pressure (TOP), and combustor outlet pressure (COP), by factors of 1.9%, 1.5%, 0.8%, and 0.7%. The hydrogen-power system achieves a maximum first law efficiency of 68.1%. The research shows that the electrolyzer is the main cause of exergy losses, followed by the combustor at 15.8% and 9.3%, respectively.