Dynamic Organic Rankine Cycle for Recovering Industrial Waste Heat

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.

The project's outputs will include the developed Dynamic Organic Rankine Cycle technology and the design tools for the resultant power plants. The wide installation of such plants will deliver significant economic, social, and environmental benefits to the society. Several major categories of beneficiaries can be identified as follows:

(1) Energy-intensive industrial sector as end user. The obvious users of this technology will be a variety of energy-intensive industrial sector across UK such as cement factories, steel makers, oil refineries, glass factories, and the food industry. Once the Dynamic Organic Rankine Cycle power plants are installed, the overall energy efficiency of these manufacturers will be significantly improved. The direct benefit will be twofold: first, the energy demand will reduced, and thus the level of fossil energy import of UK will be reduced. This will certainly contribute to the energy security of UK in the future. Second, as the energy efficiency is improved, the manufacturing cost of products will be brought down, and thus the UK products will have more competitive prices in the international market.

(2) Equipment manufacturers as suppliers. The project's industrial partners are the immediate beneficiaries of the developed Dynamic Organic Rankine Cycle technology. The four industrial partners, DRD power, Star Refrigeration Ltd, Wellman International, and Heliex Power Ltd are all specialists in designing and supplying energy equipment. The construction of future plants will naturally involve collaboration with these UK equipment manufacturers, as any new plants will need to draw on their products and fabrication facilities. In the longer term, these industrial partners will form an ideal consortium to commercialise this Dynamic Organic Rankine Cycle technology, which will ultimately generate new jobs for manufacturing, installing, and operating such power plants in the UK and globally.

(3) Energy users. The general energy users will also benefit due to the energy availability and savings on energy bills as a result from the installation of such power plants in energy intensive industrial sectors. The exploitation of waste heat will also reduce the absolute demand for energy across the UK economy, and thus reduce the need for imported fossil fuels, improving energy security and making future power cuts less likely.

(4) Policy makers. The technology developed through this project will offer energy policy makers a more efficient waste heat recovery technology. The policy of subsidising energy recovery may be reshaped as this high efficiency Dynamic Organic Rankine Cycle technology becomes available.

(5) Environmental impacts. Furthermore, in the UK, a report recently published by the Department of Energy & Climate Change identified 48 TWh/yr of industrial waste heat sources, equivalent to around one sixth of UK industrial energy consumption. The report further identified 11 TWh/yr of them are technically recoverable, which is equivalent to 2.2 MtCO2/yr. The scale of this problem is such that enabling the recovery of even a fraction of this waste heat would lead to significant reductions in greenhouse gas emissions by displacing generation by fossil fuel power plants. The Dynamic Organic Rankine Cycle power plants offering a more efficient (and thus commercially viable) technology to exploit sources of waste heat could thus eventually make a significant contribution to the UK's efforts to reduce greenhouse gas emissions by at least 80% by 2050.