Closed-Loop Zero Emission H2-O2-Liquid Water Combustion for Power Generation (CloZE)

Electricity demand in the UK varies from a low of 1 TWh/day to a peak of up to 4 TWh/day in the winter. The difference is currently met mostly by natural gas supplies, and represents about 100 TWh/year. A zero-carbon scenario requires that the balance comes from either large installed capacity or storage. This cannot be met by batteries, as the largest facilities are smaller than 4 GWh, so other means of storage are necessary. Hydrogen is considered a key energy storage vector for seasonal applications in a fully renewable energy system. Key to the successful utilisation of hydrogen as a seasonal energy vector are high efficiencies in the round-trip generation via electrolysis (typ. 60-70%) and equally efficient conversion back into electricity. Importantly, it should also generate zero NOx emissions, which are produced in combustion processes with air. The use of pure hydrogen and oxygen instead of air would produce very high temperatures incompatible with normal materials. Liquid water offers the ideal combination of high heat of vaporisation to lower the temperature, high availability and zero environmental impact. We propose to investigate a closed-loop, zero-emissions (CloZe) energy conversion system based on Hydrogen-Oxygen combustion diluted by Water injection as Liquid (HOWL). The liquid is used first for cooling the combustor walls, then sprayed and vaporised as a diluent. The generated steam is expanded to ambient pressures and condensed to ambient temperatures as in a conventional steam cycle, either in one stage or via reheat. The remaining water vapour is condensed, and brought back to the system via a liquid pump. The expected power cycle efficiencies are of the order of 50-70% depending primarily on the combustor pressure. The price to be paid is the compression and storage of both hydrogen and oxygen, consuming a few percent of the total energy available. The challenges in the HOWL cycle are associated with the effective design of water-based evaporative cooling systems and spray delivery leading to complete combustion and uniform temperatures, primarily to ensure the safe and efficient operation at stoichiometric conditions at maximum performance. The work in this project will develop the tools for design, validation and testing of the liquid water injection, mixing, and cooling in a HOWL combustor, allowing de-risking of the detailed design and deployment of such systems in the future. Advanced laser based imaging for measuring instantaneous local species and temperatures will be used to acquire scalar, velocity and spray data. High performance numerical methods will be deployed to validate and interpret the behaviour of these systems at pressure, creating models for use in the design of new generation high efficiency, zero-emissions closed-cycle energy production systems.