Industrial waste heat recovery using supercritical carbon dioxide cycles (SCOTWOHR)

减少能源密集型工业（如炼油、钢铁、水泥、石油和天然气）的碳足迹的压力越来越大，大量的废热流导致需要开发高效且具有成本效益的废热回收技术。由于废热流的温度通常低于500摄氏度，并且低流速意味着商业上可用的蒸汽发电系统是不合适的，因此注意力集中在其他废热回收技术上。因此，重大的研究工作集中在下一代的热电系统，与新的工作流体，如有机流体和超临界二氧化碳（sCO2）的操作。ORC使用有机工作流体，已被证明可将约100至350摄氏度的热量转化为电力，并且商业系统可用。然而，ORC系统仍然与高投资成本相关联，而有机流体通常是易燃的，在高操作温度下不稳定，并且与有害的环境影响相关联。或者，CO2是一种非常有前途的候选物，其优点包括成本低，不易燃，并且对环境的影响低于有机流体。由于流体密度高，它有助于紧凑的部件，并且可以在中等热源温度下获得高循环效率。尽管具有巨大的潜力，但由于需要克服重大的技术挑战，用于废热回收应用的sCO2系统尚未商业化。这包括开发合适的热交换器和换热器，以及确定最佳系统，充分解决性能和复杂性之间的权衡。该提案的重点是进行原创性研究，以提高对sCO2循环性能和关键部件（即压缩机、膨胀机和热交换器）设计方面的基本理解。计算和实验方法将被用来调查的性能和设计特点，在广泛的操作条件。这些研究必须考虑到使用sCO2的复杂性，这些复杂性表现出在传统流体（如空气和蒸汽）中未观察到的复杂流体行为，此外还要考虑高速流动、压缩机入口处接近临界点的两相条件以及sCO2在低湿度下对热交换器材料的腐蚀性。最终，这些研究的结果将改善现有的科学认识，并将促进循环和部件的新性能预测方法的开发。了解这些方面不仅可以改进性能预测，还可以改进未来的组件设计。在这个项目中，新的预测方法将用于调查和比较不同的循环架构和组件设计的性能。这些比较的结果将能够确定可以在广泛的热输入和负载条件下运行的最佳系统，从而最好地促进sCO2系统的改进。这项研究的主要成果将是提高对sCO2循环性能的基本理解，以及压缩机和膨胀机的组件设计和经验证的性能模型。此外，还将就最合适的系统配置提出建议，以改进操作方面，从而使未来小规模sCO2废热回收技术商业化。因此，该项目有可能刺激低碳能源市场的投资并创造新的就业机会，同时为英国现有的能源密集型行业余热回收研究做出积极贡献。

Increased pressure on reducing the carbon footprint from energy intensive industry such as glas, iron and steel, cement and oil and gas, with substantial waste heat streams is leading to the need to develop efficient and cost-effective waste heat recovery technologies. With waste heat stream at temperatures typically below 500 deg C, and low flow rates that mean commercially available steam power generation systems are unsuitable, attention is focused on other waste heat recovery technologies. Thus, significant research efforts have focused on the next generation of thermal-power systems, operating with novel working fluids such as organic fluids and supercritical carbon dioxide (sCO2). The ORC, which uses an organic working fluid, has been proven for conversion of heat between approximately 100 and 350 deg C into electricity, and commercial systems are available. However, ORC systems remain associated with high investment costs, whilst organic fluids are often flammable, unstable at high operating temperatures, and associated with a detrimental environmental impact. Alternatively, CO2 is an extremely promising candidate with benefits including low cost, is non-flammable and has a lower environmental impact than organic fluids. It facilitates compact components owing to high fluid densities, and high cycle efficiencies can be obtained at moderate heat-source temperatures. Despite its significant potential, sCO2 systems for waste heat recovery applications have not been commercialised yet, due to significant technical challenges that need to be overcome. This includes the development of suitable heat exchangers and turbomachinery, as well as the identification of optimal systems that adequately address the trade-off between performance and complexityThe focus of this proposal is to conduct original research to improve the fundamental understanding of the performance sCO2 cycles and the design aspects of the key components, namely compressors, expanders and heat exchangers. Computational and experimental methods will be used to investigate the performance and design characteristics across a wide range of operating conditions. These studies must account for the complexities of using sCO2 that exhibit complex fluid behaviour not observed in conventional fluids such as air and steam, in addition to considering the high-speed flows, and two-phase conditions close to the critical point at the compressor inlet, and the corrosive nature of sCO2 with low level of humidity to the heat exchanger materials. Ultimately, the results from these studies will improve the existing scientific understanding, and will facilitate the development of new performance prediction methods for the cycle and components. Understanding these aspects will not only lead to improved performance prediction, but could also lead to improved component design in the future. Within this project the new prediction methods will be used to investigate and compare the performance of different cycle architectures and component designs. The results from these comparisons will enable the identification of the optimal systems that can operate across a wide range of heat input and load conditions, and therefore best facilitate improvements to sCO2 systems. The primary outcomes of this research will be improved fundamental understanding of the performance of sCO2 cycles and component designs and validated performance models for compressors and expanders. Furthermore, recommendations will be made on the most appropriate system configurations that offer improvements to operational aspects, thus enabling the future commercialisation of small-scale sCO2 technology for waste heat recovery. Therefore this project has the potential to stimulate investment and create new jobs within the low carbon energy market, whilst positively contributing to the UK's existing research portfolio in waste heat recovery from energy intensive industry.