SCOTWOHR: Industrial waste heat recovery using supercritical carbon dioxide cycles
SCOTWOHR is an UK EPSRC-funded research project investigating supercritical carbon dioxide (sCO2) power cycles for industrial waste-heat recovery. It brings together leading academic experts from the two academic institutions and four industrial partners.
- Funder: EPSRC
- Duration: January 2021 – December 2023
- Total: £1,465,784 (EP/V001752/1 ; EP/V001795/1)
- Academic partners:
- City, University of London
- Brunel University London
- Industrial partners:
- EscherTec AG
- Heliex Power Ltd
- Innovatium Group Limited
- Kelvion Searle
Currently, there are a large number of energy intensive industries that have waste heat at temperatures and flow rates that are unsuitable for existing commercial power generation systems. Supercritical CO2 technology is an extremely promising candidate, but the technology has not been widely commercialised due to significant technical challenges that need to be overcome.
The focus of this project is to conduct original research to improve the fundamental understanding of the performance of 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. The results from these studies will improve 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.
Potential application areas for sCO2 technology 
- To identify the optimal cycle configuration for sCO2 power systems with power outputs of a few hundred kilowatts for WHR applications (~400-800 C) based on multi-objective techno-economic optimisation accounting for design and off-design operation with variable or intermittent heat streams
- To explore design innovations for small-scale sCO2 turbomachines that can extend beyond current state-of-the-art operating conditions, and improve fundamental understanding of condensation, non-ideal gas effects, and stability of sCO2 compressors operating near the critical point
- To investigate innovative heat exchanger designs, materials and fabrication methods for different cycle configurations and develop heat exchangers for direct high temperature (up to 800 C) waste heat to supercritical fluid heat recovery
- To characterise the transient operation of small-scale sCO2 power systems operating at design and off-design conditions with variable or intermittent heat streams and identify suitable real-time control strategies to maximise system performance across a wide range of operating conditions
Programme and methodology
The project will involve a combination of computational and experimental research to investigate the influence and interactions between the key components and design and control parameters on the performance of sCO2 systems for WHR applications. To this end, the project is divided into four closely linked work packages each designed to address one of the four stated objectives.
Overview of the SCOTWOHR work packages.
WP1: Optimisation of thermodynamic cycle
The necessary tools to optimise the design of the whole system will be developed, including the configuration of the sCO2 system and its constituent components. These will allow a rigorous investigation of the advantages and limitations of WHR using sCO2. A key outcome of the research will be a greater understanding of optimal component design and sizing for a range of WHR applications.
WP2: Turbomachinery innovation for small-scale sCO2 power systems
This WP focuses on the main challenges identified in relation to turbomachinery for sCO2 power systems. This includes the design and optimisation of high pressure-ratio turbines for sCO2 systems, an investigation into non-ideal gas effects, condensation and operational stability of compressors and the development of a stationary blowdown test facility to study sCO2 behaviour in close proximity to the critical point.
WP3: Innovative heat exchanger development
Building on the state of the art and work done by the Brunel team to date, WP3 will investigate and develop innovative heat exchanger designs for sCO2 WHR system. The investigations will cover the three principal heat exchanger types: i) primary heat exchanger (heater) for direct exhaust gas heat recovery to sCO2 in the power cycle; ii) recuperator for sCO2 to sCO2 heat transfer; and, iii) heat rejection heat exchanger, sCO2 heat rejection to water and direct to air.
WP4: Model-based control for optimal transient and off-design operation
For optimised configurations identified in WP1, control strategies will be developed to optimise performance during off-design and transient operation to cater for variations in waste heat stream temperature and flow characteristics. Such variations are common in industrial exhausts.
Simplified schematic of the blowdown facility that will be commissioned to City to investigate the behaviour of sCO2 in proximity to the critical point.
sCO2 test loop installed at Brunel University London.
References and further reading
- White, M., Bianchi, G., Chai, L., Tassou, S., Sayma, A., 2021, “Review of supercritical CO2 technologies and systems for power generation”, Applied Thermal Engineering, 185, 116447. doi: https://doi.org/10.1016/j.applthermaleng.2020.116447