11:10
Session 7A: Novel/advanced architectures (2)
Chair: Oliver Dingel
11:10
20 mins
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Extensive Techno-economic Assessment of ORC and Inverted Brayton Cycle Combined for High-temperature Waste Recovery
Kirill Abrosimov, Andrea Baccioli, Aldo Bischi
Abstract: 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.
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11:30
20 mins
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Potential of a Regenerative Transcritical Series Two Stage Organic Rankine Cycle for Dual Source Waste Heat Recovery
Anandu Surendran, Satyanarayanan Seshadri
Abstract: IC engine waste heat recovery is the most common application of Organic Rankine Cycle (ORC) systems, which were mostly pre-heated or dual loop[1]. Recent studies on dual pressure organic Rankine cycle (ORC) architectures shows series two stage ORC (STORC) to have improved exergetic efficiency compared to single pressure ORC[2][3]. Studies have also shown that adopting partial evaporation in ORCs architecture improves exergetic efficiency than the simple ORC[4]. So far, only a few studies have focussed on the use of two stage evaporation architectures for dual source heat recovery in which maximum heat source utilization is desired[5]. Adopting a supercritical evaporation processin the high pressure (HP) stage combined with partial evaporation in the low pressure(LP) stage could lead to improved thermal matching and increased heat source utilization. The regenerative use of superheated vapour from the exit of HP turbine could also lead to improved thermal efficiency. In this study, a regenerative transcritical STORC (RT-STORC) is analysed for waste heat recovery from a 2.97 MW natural gas IC engine. The HP and LP evaporator extracts heat from the exhaust gas (primary heat source) and jacket water(secondary heat source)respectively.
A thermodynamic model of the system in developed in MATLAB, for which the HP stage pressure, vapour outlet temperature and LP stage evaporation temperature are specified. Based on this, the model optimizes the vapour quality in the LP stage evaporator, so as to satisfy the saturated vapour condition in the LP turbine inlet. The effect of vapour outlet temperature and evaporation pressure in HP stage is analysed for a given LP stage evaporation temperature. For the HP stage, higher evaporator pressures and lower vapour outlet temperatures leads to increase in net work output.There exists an optimum LP stage evaporation temperature that maximises the utilization rate of secondary heat source. The optimum vapour fraction in the LP stage increases with decrease in HP stage pressure and outlet temperature. At the engine design point, the RT-STORC delivers 419kW, which is 13.6% and 25.8% higher than the sub critical STORC and pre-heated ORC respectively.
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11:50
20 mins
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Model, Simulation and Experiments for a Buoyancy Organic Rankine Cycle
Jeroen Schoenmaker, Pâmella Gonçalves Martins, Guilherme Corsi Miranda da Silva, Julio Carlos Teixeira
Abstract: Organic Rankine Cycle (ORC) systems are increasingly gaining relevance in the renewable and sustainable energy scenario. Recently our research group published a manuscript identifying a new type of thermodynamic cycle entitled Buoyancy Organic Rankine Cycle (BORC) [1]. Although the cycle itself is not necessarily organic, the publication aimed a renewable energy solution for low temperature systems. In BORC systems, the height of the column-fluid reservoir influences its operation temperature and determines the efficiency of the system. For operation temperatures under the boiling point of water we estimated efficiencies up to 26% for n-pentane (in a 51 m tall water column) and 26.2% for Dichloromethane (in a 71.4 m tall water column). In this work we present two main contributions. First, we propose a refined thermodynamic model for BORC systems accounting for the specific heat of the working fluid. Considering the refined model, the efficiencies for both above mentioned working fluids at temperatures up to 100°C were estimated to be 17.2%. Second, we show a proof of concept BORC system using a 3 m tall, 0.06 m diameter polycarbonate tube as a column-fluid reservoir. We used water as a column fluid. The thermal stability and uniformity throughout the tube has been carefully simulated and verified experimentally. After the thermal parameters of the water column have been fully characterized, we developed a test body to allow an adequate assessment of the BORC-system’s efficiency. According to our BORC model, the working and column fluids are in thermal equilibrium during the expansion. Our experiments focused on test trials tending to the lowest possible temperature of operation, estimated to be 44ºC for a 3 m water column. For the sake of reliability, we reduced the usable height of the column to 2.3 m and we obtained 0.84% efficiency for 46ºC working temperature. This corresponds to 27% of a Carnot cycle working in the same temperature difference. Limitations of the model and the apparatus are put into perspective, pointing directions for further developments.
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