Extensive Techno-economic Assessment of ORC and Inverted Brayton Cycle Combined for High-temperature Waste Recovery

orc2019 Tracking Number 117

The general trend to the decarbonisation stimulates the continuous development of waste heat recovery technologies. Nowadays, the most deployed solution in this field up to certain installed capacity is the organic Rankine cycle (ORC). However, for high-temperature cases, above 400 oC, this technology has essential limitations on exploited temperature because of the properties of available working and intermediate heat-transfer fluids. As a sequence, waste heat recovery based on the ORC technology has lower efficiency than it could have from the thermodynamic viewpoint. This work continues the study of a combined scheme based on the coupling of the ORC with the inverted Brayton cycle (combined IBC-ORC) which enables to use the high-temperature waste heat potential more effectively. In this scheme, hot gas from a heat source expands in the IBC turbine to the subatmospheric pressure created by a compressor which follows in the downstream of the gas duct. Before the compressor, gas transmits heat via heat exchangers to regenerative ORC and partially to the atmosphere. The scheme may be employed for waste heat recovery from high-temperature heat sources such as internal combustion engines and some technological processes such as cement kilns or heat treating furnaces. In the paper, the analysis of the scheme performance under different ambient temperatures is presented, showing the negative effect of high ambient temperature. Specificities of the optimisation results are explained with the analysis of IBC performance, considering water condensation issues. Pareto fronts for system electric efficiency and levelized cost of energy for several temperatures of the primary heat source provide valuable insight for techno-economic assessment, recommending the most suitable sets of parameters in the trade-off between electrical power and investment results.