Integrating alkaline electrolysis with oxyfuel combustion for hydrogen and electricity production

The present study explores the potential of integrating the NET Zero Cycle (NZC) with hydrogen production by alkaline electrolyzers. To achieve this, an Aspen Plus model was developed for the NZC, and its accuracy was first confirmed by comparing it with literature data. The creation of a model for an alkaline electrolyzer was achieved using Aspen Custom Modeler and later imported into Aspen Plus. A comprehensive simulation was conducted in Aspen Plus to examine the synergies between the NZC and the alkaline electrolyzer. In this integration, the oxygen demand of the NZC is met by a combination of an air separation unit (ASU) and the electrolyzer. The electrolyzer not only partially fulfills the oxygen requirements but also acts as an external heat supplier for the regenerator. Additionally, the NZC supplies deionized water to the electrolyzer. A thermodynamic analysis indicates that the integration of the NZC and alkaline electrolyzers results in a higher efficiency of 56.5 % compared to the stand-alone NZC, an improvement of 2.3 %. Assuming that the NZC and alkaline electrolyzer operate at the same power production and input levels, the alkaline electrolyzer can generate substantial oxygen to reduce the energy consumption of the ASU significantly. This aspect represents one of the primary reasons for the enhanced efficiency observed in this study. However, the ASU still needs to be operated to provide the full oxygen demands of the process. To identify the key parameters influencing the integration of the NZC and alkaline electrolyzers, a sensitivity analysis was performed. To enhance the system efficiency, a comprehensive investigation was conducted to analyze the influence of key parameters such as combustor outlet temperature (COT), turbine outlet pressure (TOP), and combustor outlet pressure (COP) on the thermodynamic first law efficiency of the cycle. An increase in electrolyzer input power and a reduction in electrolyzer inlet feed were associated with a higher cycle efficiency. The results also highlight that the TOP, COT and the electrolyzer input power have a more significant impact on the cycle thermodynamic first law efficiency within the range of 5.7, 4.0, and 2.6 % respectively, while COP only causes a 0.4 % change in cycle efficiency. The integrated system demonstrates an impressive system first law thermodynamic efficiency of 62.5 % and exergy efficiency of 60.6 %.