The UK has set a target to cut its greenhouse gas emissions by at least 80% by 2050, relative to 1990 levels. To achieve this target, a reduction in energy consumption of around 40% will be required, and therefore significant improvements in energy efficiency are necessary. Energy recovery from industrial waste heat sources is considered to offer a significant contribution to improving overall energy efficiency in the energy-intensive industrial sectors. In the UK, a report recently published by the Department of Energy & Climate Change (DECC) identified 48 TWh/yr of industrial waste heat sources, equivalent to around one sixth of UK industrial energy consumption. Although waste heat recovery is broadly welcomed by industry, there is a lack of implementation of waste heat recovery systems in UK industrial sectors due to a number of barriers, the most important being poor efficiency. The forecast for global waste heat recovery systems market value is growth to 53 billion US Dollar by 2018, with a compound annual growth rate of 6.5% from 2013 to 2018. Needless to say, there is a huge national and global market for innovative waste heat recovery technologies. Although there are several alternative technologies (at different stages of development) for waste heat recovery, such as heat exchanger, heat pump, Stirling engine and Kalina Cycle power plant, the Organic Rankine Cycle system remains the most promising in practice. Large Organic Rankine Cycle systems are commercially viable for high-temperature applications, however, their application to low-temperature waste heat (<250 Degree C) is in its infancy. Yet more than 60% of UK industrial waste heat sources are in the low temperature band (<250 Degree C). There is clearly a mismatch between Organic Rankine Cycle technology supply and demand, so innovative research and development are highly in demand. This First Grant Scheme project, in response to the challenge of industrial waste heat recovery identified by DECC, aims to develop an innovative Dynamic Organic Rankine Cycle (ORC) system that uses a binary zeotropic mixture as the working fluid and has mechanisms in place to adjust the mixture composition dynamically during operation to match the changing heat sink temperatures, and therefore the resultant system can achieve significant higher annual average efficiencies. The preliminary research shows that a Dynamic Organic Rankine Cycle system can potentially generate over 10% more electricity from low temperature waste heat sources than a traditional one annually. The research will firstly develop a novel Dynamic Organic Rankine Cycle concept by integrating a composition adjusting mechanism into an Organic Rankine Cycle system, so that the mixture composition can be adjusted during the operation of the power plant. A steady-state numerical model will be developed to simulate and demonstrate the working principle and benefits of such a Dynamic Organic Rankine Cycle system. A dynamic numerical model will then be developed to simulate and optimise the control strategy of mixture composition adjustment. Finally, a prototype of such Dynamic Organic Cycle system will be designed and constructed. The Dynamic Organic Rankine Cycle concept and the two numerical models will be validated through a comprehensive experimental research. The Dynamic Organic Rankine Cycle power plants developed through this project can be widely applied to energy intensive industrial sectors such as the iron and steel industry, ceramic manufacturers, cement factories, food industrial, etc. As such power plants can achieve a much higher efficiency; the payback period can be significantly reduced, which would make energy recovery from industrial waste heat sources more profitable. The wide installation of such waste recovery power plants will ultimately reduce the energy demand of these industrial sectors, and therefore improve our energy security.

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 complexity The 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.

Commercial steam power plants pressurise and heat water to produce steam which is then expanded to produce electricity. However, using an organic fluid permits low temperature heat sources, typically between 80 and 350 degrees Celsius, to be converted into mechanical power more economically than steam. Organic Rankine Cycles (ORC) therefore have a great potential to contribute to the UK's mix of low carbon technologies with promising applications such as combined heat and power, concentrated solar power and waste heat recovery from reciprocating engines and other industrial processes with waste heat streams. However, despite successful commercialisation of ORCs for industrial scale applications, more development is required at the commercial and domestic scales before its potential can be realised. More specifically, at these small-scales, the challenge lies in the design of systems that are efficient but are also low cost. One approach to achieving this is to develop systems that operate efficiently over a range of different conditions. This will enable the high-volume, low-cost production of ORC systems, enabling significant improvements in the economy-of-scale. Furthermore, at this scale, different expander technologies, such as turbo and screw expanders, and system architectures can be considered. However, it is not clear which expander technology or system architecture is the optimal choice to achieve the desired improvements in the economy-of-scale. To answer this question it is important to improve the understanding of how different ORC expanders perform across a wide range of operating conditions, and to investigate how these systems respond to changes in the working fluid. The focus of this proposal is to conduct original research to improve the fundamental understanding on the performance of two different types of ORC expander, namely turbo and screw expanders. Computational and experimental methods will be used to investigate the performance of these expanders across a wide range of operating conditions and with a variety of organic fluids. These studies must account for the complexities of using organic fluids 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 that are expected in turbo and screw expanders respectively. Ultimately, the results from these studies will improve the existing scientific understanding, and will facilitate the development of new performance prediction methods for these expanders. 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 expanders within different ORC system architectures. The results from these comparisons will enable the identification of the optimal systems that can operate across a wide range of operating conditions, and therefore best facilitate improvements in the economy-of-scale of small-scale ORC systems. The primary outcomes of this research will be improved fundamental understanding of the performance of ORC expanders and validated performance models for turbine and screw expanders. Furthermore, recommendations will be made on the most appropriate system configurations that offer improvements in the economy-of-scale, thus enhancing the future commercialisation of small-scale ORC technology. 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 turbomachinery and screw expanders.