Highly Flexible Zero-Carbon Electricity Generation Using an Innovative Oxy-Fired Supercritical CO2 Power Cycle

Along with renewables and nuclear power, carbon capture and storage (CCS) is expected to play a vital role in decarbonising electricity production. In future electricity systems, CCS power plants will be required to respond to the fluctuating supply of renewable energy by varying their output and through rapid shut-downs and start-ups [1]. This concept of flexible operation initially proposed by academics at the University of Edinburgh [1, 2] allows CCS plants to time-delay the financial and energy output penalty of carbon capture processes. Whilst the concept was developed for conventional fossil fuel power cycles with post-combustion capture, this project is the first to apply it to the Allam Cycle, a recent breakthrough in low-carbon energy generation. The Allam Cycle is an oxy-fired supercritical CO2 power cycle, currently undergoing pilot scale testing as part of a $140m scheme led by NET Power [3]. It is designed to produce zero carbon electricity at competitive efficiency and costs compared to unabated fossil fuel plants, thus exhibiting a step-change in performance compared to state of the art CCS power generation. In the Allam Cycle, shown in Figure 1, an Air Separation Unit produces oxygen which is combusted with natural gas, producing a high-pressure working fluid above 90% supercritical CO2 in volume, which is then used to drive an electricity generating turbine. Most of this CO2 is then compressed and fed back into the cycle, while surplus is removed at the required pressure and quality for pipeline transport. Thus, the cycle inherently captures all CO2 produced, without the expense of an add-on capture system. The potential for enhanced operational flexibility in the Allam Cycle arises from the opportunity to decouple the highly energy intensive step of oxygen production from power generation. The limiting Figure 1 Simplified Allam Cycle Schematic [4]