In the UK, power generation is achieved mostly through the combustion of fossil fuels from remote power stations at a low-efficiency rate of 40%. This can lead to a large depletion of energy resources and pollution to environment. In reality, after taking into consideration long-distance power transmission and distribution losses, the generation efficiency tends to be further reduced to around 32% at the power supply end. To combat this problem, a local and decentralised combined heat and power (CHP) system may be used to attain not only 30% electrical efficiency but also over 50% heating efficiency, which would significantly improve the energy utilisation rate. In areas with simultaneous heating and electricity demand including supermarket and district heating, such systems would be a viable economic option. However, currently most CHP systems still require fossil fuel energy resources, which diminish both their energy-saving merit and potential CO2 emission reductions. Therefore, it would be highly desirable to promote the use of localised renewable resources, such as biomass fuels, with optimised CHP system engineering designs. Currently, there are two main biomass CHP systems: biomass gasification with gas/steam turbines and biomass combustion with Organic Rankin Cycles (ORC). However, these biomass CHP systems cannot be further developed or extensively applied before the resolution of certain critical issues. These include achieving an acceptable thermal efficiency, compact system size, environmentally-friendly working fluid, advanced thermodynamic power cycles, optimal system design and control, and flexible operation etc. On the other hand, for power generation with medium to high temperature heat sources, CO2 supercritical Brayton cycles (S-CO2) can predominate over conventional ORCs in terms of thermal efficiency, environmental impact and system compactness. The S-CO2 systems have been applied in large-scale waste heat recovery of nuclear power plants but have not yet been utilised in biomass power generations due to various unsettled challenges. In this proposed project, a small-scale biomass power generation system with advanced CO2 supercritical Brayton cycles and novel heat exchanger designs will be investigated experimentally and theoretically. The investigation will address the challenges involved in the proposed system including innovative designs of thermal drive CO2 supercritical compressors, precise CO2 parameter controls at the S-CO2 compressor inlet, novel designs of supercritical CO2 heat exchangers and comprehensive understanding of the complex heat transfer and hydraulic processes involved. In addition, a detailed transient model of the biomass S-CO2 power generation system will be developed which will enable the system to be further optimised and scaled up for actual design and operation.

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.

In the UK, power generation is achieved mostly through the combustion of fossil fuels from remote power stations at a low-efficiency rate of 40%. This can lead to a large depletion of energy resources and pollution to environment. In reality, after taking into consideration long-distance power transmission and distribution losses, the generation efficiency tends to be further reduced to around 32% at the power supply end. To combat this problem, a local and decentralised combined heat and power (CHP) system may be used to attain not only 30% electrical efficiency but also over 50% heating efficiency, which would significantly improve the energy utilisation rate. In areas with simultaneous heating and electricity demand including supermarket and district heating, such systems would be a viable economic option. However, currently most CHP systems still require fossil fuel energy resources, which diminish both their energy-saving merit and potential CO2 emission reductions. Therefore, it would be highly desirable to promote the use of localised renewable resources, such as biomass fuels, with optimised CHP system engineering designs. Currently, there are two main biomass CHP systems: biomass gasification with gas/steam turbines and biomass combustion with Organic Rankin Cycles (ORC). However, these biomass CHP systems cannot be further developed or extensively applied before the resolution of certain critical issues. These include achieving an acceptable thermal efficiency, compact system size, environmentally-friendly working fluid, advanced thermodynamic power cycles, optimal system design and control, and flexible operation etc. On the other hand, for power generation with medium to high temperature heat sources, CO2 supercritical Brayton cycles (S-CO2) can predominate over conventional ORCs in terms of thermal efficiency, environmental impact and system compactness. The S-CO2 systems have been applied in large-scale waste heat recovery of nuclear power plants but have not yet been utilised in biomass power generations due to various unsettled challenges. In this proposed project, a small-scale biomass power generation system with advanced CO2 supercritical Brayton cycles and novel heat exchanger designs will be investigated experimentally and theoretically. The investigation will address the challenges involved in the proposed system including innovative designs of thermal drive CO2 supercritical compressors, precise CO2 parameter controls at the S-CO2 compressor inlet, novel designs of supercritical CO2 heat exchangers and comprehensive understanding of the complex heat transfer and hydraulic processes involved. In addition, a detailed transient model of the biomass S-CO2 power generation system will be developed which will enable the system to be further optimised and scaled up for actual design and operation.

In the UK, power generation is achieved mostly through the combustion of fossil fuels from remote power stations at a low-efficiency rate of 40%. This can lead to a large depletion of energy resources and pollution to environment. In reality, after taking into consideration long-distance power transmission and distribution losses, the generation efficiency tends to be further reduced to around 32% at the power supply end. To combat this problem, a local and decentralised combined heat and power (CHP) system may be used to attain not only 30% electrical efficiency but also over 50% heating efficiency, which would significantly improve the energy utilisation rate. In areas with simultaneous heating and electricity demand including supermarket and district heating, such systems would be a viable economic option. However, currently most CHP systems still require fossil fuel energy resources, which diminish both their energy-saving merit and potential CO2 emission reductions. Therefore, it would be highly desirable to promote the use of localised renewable resources, such as biomass fuels, with optimised CHP system engineering designs. Currently, there are two main biomass CHP systems: biomass gasification with gas/steam turbines and biomass combustion with Organic Rankin Cycles (ORC). However, these biomass CHP systems cannot be further developed or extensively applied before the resolution of certain critical issues. These include achieving an acceptable thermal efficiency, compact system size, environmentally-friendly working fluid, advanced thermodynamic power cycles, optimal system design and control, and flexible operation etc. On the other hand, for power generation with medium to high temperature heat sources, CO2 supercritical Brayton cycles (S-CO2) can predominate over conventional ORCs in terms of thermal efficiency, environmental impact and system compactness. The S-CO2 systems have been applied in large-scale waste heat recovery of nuclear power plants but have not yet been utilised in biomass power generations due to various unsettled challenges. In this proposed project, a small-scale biomass power generation system with advanced CO2 supercritical Brayton cycles and novel heat exchanger designs will be investigated experimentally and theoretically. The investigation will address the challenges involved in the proposed system including innovative designs of thermal drive CO2 supercritical compressors, precise CO2 parameter controls at the S-CO2 compressor inlet, novel designs of supercritical CO2 heat exchangers and comprehensive understanding of the complex heat transfer and hydraulic processes involved. In addition, a detailed transient model of the biomass S-CO2 power generation system will be developed which will enable the system to be further optimised and scaled up for actual design and operation.

In the UK, heat accounts for over a third of the nation's greenhouse gas emissions. Most of the heating and cooling in our industries and buildings are delivered directly or indirectly by fossil fuels. Apart from the greenhouse emissions, the extensive consumption of fossil fuels can also lead to a large depletion of energy resources, waste heat production and pollution to the surrounding environment. To meet the target of Net Zero greenhouse gas emissions by 2050, there is an urgent need for decarbonising heating and cooling by utilising renewable energy and industrial waste heat with advanced technologies. Compared to renewable energy such as solar, the resources from industrial waste heat have clear advantages including greater stabilisation, less cost and larger temperature ranges. Therefore, industrial waste heat recovery for decarbonised heating and cooling is an attractive concept that could simultaneously reduce fossil fuel consumption and CO2 emissions. Evidently, in the UK, based on a recent report, it was identified that around 48 TWh/yr industrial waste heat sources were available of which about 28 TWh/yr could be potentially used to meet the heating and cooling demands. All heat-intensive industrial sectors including iron & steel, refineries, ceramics, glass, cement, chemicals, food and drink, paper and pulp can contribute to this potential. Even so, high efficient energy conversion systems need to be designed and applied so as to maximize the waste heat utilisations for heating and cooling. On the other hand, the locations of industrial waste heat providers such as steel plants are mostly far away from the utilisers for heating and cooling. Conventionally, hot water heated by the industrial waste heat is transported through long distance water pipe to the end user site which can cause huge pump power consumption and heat losses due to significant friction pressure drop for the water flow and large temperature difference between water flow and ambient. There are therefore challenges to the long-distance waste heat transport and high-efficient and innovative energy conversion technologies for the decarbonising heating and cooling. To address these challenges, in this proposal, strategies for a novel concept of decarbonising district heating and cooling system (H2-heat) will be developed with the integration of metal hydride (MH) heat pump on site, long distance hydrogen and heat transport, and MH heating and cooling for end users. In such a system, low grade heat (~210C) and extra low grade heat (~40C) from TATA Steel plant or a similar industry site will be used as heat sources while building heating and cooling spaces are applied as heat sink and low temperature heat source respectively at end user side. Technologies of MH heat pump, a thermal driven chemical compressor with MH, long distance hydrogen and heat transport, MH space heating and cooling, MH alloys and reactors applied in the systems and processes, controls for space heating and cooling etc. will be identified and investigated. Ultimately, a decarbonising district heating and cooling test system with industrial waste heat from TATA Steel plant or other industrial sites will be constructed in lab with 5 kWth heating or cooling capacity and high heat transport efficiency. Furthermore, a detailed mathematical model will be developed and validated for the established system; this can be used for a system scale-up into actual application in TATA Steel plant or other industrial sites where low grade waste heat is available. As yet, no research activity on such a system can be found either nationally or internationally. Important reasons include the difficulty in choosing a thermal driven long distance hydrogen and heat transport system and associated MH alloys for space heating and cooling and complicated designs of MH reactors in the H2-heat system. These challenges and issues will be addressed and solved by this proposed project.