FUNDAMENTAL STUDIES ON ORGANIC RANKINE CYCLE EXPANDERS (NextORC)

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.

This project will deliver an improved understanding of the performance of small-scale ORC systems leading to higher system efficiency and potentially reduced costs in particular through the opportunity to improve the economy-of-scale.
Firstly, impact is expected in the two areas of the economy and knowledge transfer. A defined deliverable from this research program are recommendations on the most appropriate system configurations that can be implemented within different applications. This will give industries such as commercial and domestic combined heat and power, concentrated solar power, and waste heat recovery a clear direction from which to proceed with future commercialisation. Furthermore, of the existing international ORC manufacturers, none develop systems within the considered power range, highlighting the potential for the UK to lead in the manufacture of these systems. Furthermore, results can be used for the validation of existing simulation tools will improve understanding of system behaviour. This will ultimately lead to better component design; either measured through higher efficiency at the design point, or higher efficiency over a wider range of operating conditions.
The widespread implementation of ORC technology could impact society in many ways. Not only will it help the UK government to meet its targets for renewable energy production and reductions in greenhouse emissions, thus positively impacting our climate, but it will also help reduce reliance on imported fossil fuels. This will improve the UK's future energy security. Furthermore, ORC technology at this scale is well suited for the sustainable supply of power and heat to remote, off-grid regions, particularly using locally produced biofuels such as woodchip, which can help to support commitments to international action on climate change in developing countries.
Through the proposed research programme, and improvements to the existing test facility at City, it is expected that this project will maintain, and further enhance City's international reputation as a leading research centre for ORC technology. This will help in attracting leading students and staff to the university who will benefit from the extensive knowledge of ORC systems, which will ultimately help in the development of leading ORC research engineers in the future.
The transfer of knowledge to industry will be obtained through regular progress meetings with beneficiaries and obtain feedback to ensure that this research remains highly relevant to the requirements of the industry. A workshop will be arranged to disseminate key findings to relevant industries and researchers, whilst also providing a springboard from which to direct further research and development activities. City hosts the International Conference on Compressors and their Systems, which also covers expanders, and is well attended by industry. This will provide an additional platform from which disseminate important results, and offers the opportunity to arrange a technical session focusing specifically on ORC systems and waste heat recovery expanders.
The specialist knowledge developed as a result of this research will be actively used during taught courses at the university. This will ensure the development of highly skilled graduates trained in the design and analysis ORC systems and ORC expanders. This will be obtained by bringing relevant material into lectures, in addition to using the background of this project to define industrially relevant undergraduate and MSc research projects.
Wider disseminations will be achieved through Journal and conference publications in addition to a project website to provide updates, reports and links suitable for the lay audience. Furthermore, digital media will be utilised to both inform the public about research activities and upcoming events, to explain the various aspects of technology to the public.