21 results found
Le Brun N, Simpson M, Acha S, et al., 2020, Techno-economic potential of low-temperature, jacket-water heat recovery from stationary internal combustion engines with organic Rankine cycles: A cross-sector food-retail study, Applied Energy, Vol: 274, Pages: 1-14, ISSN: 0306-2619
We examine the opportunities and challenges of deploying integrated organic Rankine cycle (ORC) engines to recover heat from low-temperature jacket-water cooling circuits of small-scale gas-fired internal combustion engines (ICEs), for the supply of combined heat and power (CHP) to supermarkets. Based on data for commercially-available ICE and ORC engines, a techno-economic model is developed and applied to simulate system performance in real buildings. Under current market trends and for the specific (low-temperature) ICE + ORC CHP configuration investigated here, results show that the ICE determines most economic savings, while the ORC engine does not significantly impact the integrated CHP system performance. The ORC engines have long payback times (4–9 years) in this application, because: (1) they do not displace high-value electricity, as the value of exporting electricity to the grid is low, and (2) it is more profitable to use the heat from the ICEs for space heating rather than for electricity conversion. Commercial ORC engines are most viable (payback ≈ 4 years) in buildings with high electrical demands and low heat-to-power ratios. The influence of factors such as the ORC engine efficiency, capital cost and energy prices is also evaluated, highlighting performance gaps and identifying promising areas for future research.
Olympios A, Hoisenpoori P, Mersch M, et al., 2020, Optimal design of low-temperature heat-pumping technologies and implications to the whole energy system, The 33rd International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems.
This paper presents a methodology for identifying optimal designs for air-source heat pumps suitable for domestic heating applications from the whole-energy system perspective, accounting explicitly for a trade-off between cost and efficiency, as well as for the influence of the outside air temperature during off-design operation. The work combines dedicated brazed-plate and plate-fin heat-exchanger models with compressor efficiency maps, as well as equipment costing techniques, in order to develop a comprehensive technoeconomic model of a low-temperature air-source heat pump with a single-stage-compressor, based on the vapour-compression cycle. The cost and performance predictions are validated against manufacturer data and a non-linear thermodynamic optimisation model is developed to obtain optimal component sizes for a set of competing working fluids and design conditions. The cost and off-design performance of different configurations are integrated into a whole-energy system capacity-expansion and unit-dispatch model of the UK power and heat system. The aim is to assess the system value of proposed designs, as well as the implications of their deployment on the power generation mix and total transition cost of electrifying domestic heat in the UK as a pathway towards meeting a national net-zero emission target by 2050. Refrigerant R152a appears to have the best design and off-design performance, especially compared to the commonly used R410a. The size of the heat exchangers has a major effect on heat pump performance and cost. From a wholesystem perspective, high-performance heat pumps enable a ~20 GW (~10%) reduction in the required installed power generation capacity compared to smaller-heat-exchanger, low-performance heat pumps, which in turn requires lower and more realistic power-grid expansion rates. However, it is shown that the improved performance as a result of larger heat exchangers does not compensate overall for the increased technology cost, with
Pantaleo A, Simpson M, Rotolo G, et al., 2019, Thermoeconomic optimisation of small-scale organic Rankine cycle systems based on screw vs. piston expander maps in waste heat recovery applications, Energy Conversion and Management, Vol: 200, ISSN: 0196-8904
The high cost of organic Rankine cycle (ORC) systems is a key barrier to their implementation in waste heat recovery (WHR) applications. In particular, the choice ofexpansion device has a significant influence on this cost, strongly affecting the economic viabilityof an installation. In this work, numerical simulations and optimisation strategies are used to compare the performance and profitability of small-scale ORC systems using reciprocating-piston orsingle/two-stage screw expanders whenre covering heat from the exhaust gases of a 185-kWinternal combustion engine operating in baseload mode. The study goes beyond previous work by directly comparingthese small-scaleexpanders fora broad range of working fluids, and by exploring the sensitivity of project viability to key parameters such as electricity price and onsite heat demand.For the piston expander, a lumped-massmodel and optimisation based on artificial neural networks are used to generate performance maps, while performance and cost correlations from the literature are used for the screw expanders. The thermodynamic analysisshows that two-stage screw expanders typically deliver more power than either single-stage screw or piston expanders due to their higher conversion efficiencyat the required pressure ratios. The best fluids areacetone and ethanol, as these provide a compromise between the exergy losses in the condenser and in the evaporatorin this application. The maximum net power output isfound to be 17.7kW, from an ORC engine operating withacetone anda two-stage screw expander. On the other hand, the thermoeconomic optimisation shows that reciprocating-piston expandersshow a potential for lowerspecific costs, and sincesuchan expander technology is not mature, especially at these scales, this finding motivates further consideration of this component. A minimum specific investment cost of 1630€/kW is observed for an ORC engine with a pisto
Simpson M, Chatzopoulou M, Oyewunmi O, et al., 2019, Technoeconomic analysis of internal combustion engine - organic Rankine cycle systems for combined heat and power in energy-intensive buildings, Applied Energy, Vol: 253, Pages: 1-13, ISSN: 0306-2619
For buildings with low heat-to-power demand ratios, installation of internal combustion engines (ICEs) for combined heat and power (CHP) results in large amounts of unused heat. In the UK, such installations risk being ineligible for the CHP Quality Assurance (CHPQA) programme and incurring additional levies. A technoeconomic optimisation of small-scale organic Rankine cycle (ORC) engines is performed, in which the ORC engines recover heat from the ICE exhaust gases to increase the total efficiency and meet CHPQA requirements. Two competing system configurations are assessed. In the first, the ORC engine also recovers heat from the CHP-ICE jacket water to generate additional power. In the second, the ORC engine operates at a higher condensing temperature, which prohibits jacket-water heat recovery but allows heat from the condenser to be delivered to the building. When optimised for minimum specific investment cost, the first configuration is initially found to deliver 20% more power (25.8 kW) at design conditions, and a minimum specific investment cost (1600 £/kW) that is 8% lower than the second configuration. However, the first configuration leads to less heat from the CHP-ICE being supplied to the building, increasing the cost of meeting the heat demand. By establishing part-load performance curves for both the CHP-ICE and ORC engines, the economic benefits from realistic operation can be evaluated. The present study goes beyond previous work by testing the configurations against a comprehensive database of real historical electricity and heating demand for thirty energy-intensive buildings at half-hour resolution. The discounted payback period for the second configuration is found to lie between 3.5 and 7.5 years for all of the buildings considered, while the first configuration is seen to recoup its costs for only 23% of the buildings. The broad applicability of the second configuration offers attractive opportunities to increase manufacturing volumes an
Song J, Simpson M, Wang K, et al., 2019, Thermodynamic assessment of combined supercritical CO2 (SCO2) and organic Rankine cycle (ORC) systems for concentrated solar power, International Conference on Applied Energy 2019
Concentrated solar power (CSP) systems are acknowledged as a promising technology for solar energy utilisation. Supercritical CO2 (SCO2) cycle systems have emerged as an attractive option for power generation in CSP applications due to the favourable properties of CO2 as a working fluid. In order to further improve the overall performance of such systems, organic Rankine cycle (ORC) systems can be used in bottoming-cycle configuration to recover the residual heat. This paper presents a thermodynamic performance assessment of a combined SCO2/ORC system in a CSP application using parabolic-trough collectors. The parametric analysis indicates that the heat transfer fluid (HTF) temperature at the inlet of the cold tank, and the corresponding HTF mass flow rate, have a significant influence on the overall system performance. The results suggest that the combined system can offer significant thermodynamic advantages at progressively lower temperatures. Annual simulations for a case study in Seville (Spain) show that, based on an installation area of 10,000 m2, the proposed combined cycle system could deliver an annual net electricity output of 2,680 MWh when the HTF temperature at the cold tank inlet is set to 250 °C, which is 3% higher than that of a stand-alone CO2 cycle system under the same conditions. Taking the size of the thermal storage tanks into consideration, a lower HTF temperature at the cold tank inlet and a lower mass flow rate would be desirable, and the combined system offers up to 66% more power than the stand-alone version when the HTF inlet temperature is 100 °C.
Li X, Song J, Simpson M, et al., 2019, THERMO-ECONOMIC COMPARISON OF ORGANIC RANKINE AND CO2 CYCLE SYSTEMS FOR LOW-TO-MEDIUM TEMPERATURE APPLICATIONS, 5th International Seminar on ORC Power Systems
Simpson M, Schuster S, Ibrahim D, et al., 2019, Small-scale, low-temperature ORC systems intime-varying operation: Turbines orreciprocating-piston expanders?, 32ND INTERNATIONAL CONFERENCE ON EFFICIENCY, COST, OPTIMIZATION, SIMULATION AND ENVIRONMENTAL IMPACT OF ENERGY SYSTEMS
Chatzopoulou MA, Simpson M, Sapin P, et al., 2019, Off-design optimisation of organic Rankine cycle (ORC) engines with pistonexpanders for medium-scale combined heat and power applications, Applied Energy, Vol: 238, Pages: 1211-1236, ISSN: 0306-2619
Organic Rankine cycle (ORC) engines often operate under variable heat-source conditions, so maximising performance at both nominal and off-design operation is crucial for the wider adoption of this technology. In this work, an off-design optimisation tool is developed and used to predict the impact of varying heat-source conditions on ORC operation. Unlike previous efforts where the performance of ORC engine components is assumed fixed, here we consider explicitly the time-varying operational characteristics of these components. A bottoming ORC system is first optimised for maximum power output when recovering heat from the exhaust gases of an internal-combustion engine (ICE) running at full load. A double-pipe heat exchanger (HEX) model is used for sizing the ORC evaporator and condenser, and a piston-expander model for sizing the expander. The ICE is then run at part-load, thus varying the temperature and mass flow rate of the exhaust gases. The tool predicts the new off-design heat transfer coefficients in the heat exchangers, and the new optimum expander operating points. Results reveal that the ORC engine power output is underestimated by up to 17% when the off-design operational characteristics of these components are not considered. In particular, the piston-expander isentropic efficiency increases at off-design operation by 10–16%, due to the reduced pressure ratio and flow rate in the system, while the evaporator effectiveness improves by up to 15%, due to the higher temperature difference across the HEX and a higher proportion of heat transfer taking place in the two-phase evaporating zone. As the ICE operates further away from its nominal point, the off-design ORC engine power output reduces by a lesser extent than that of the ICE. At an ICE part-load operation of 60% (by electrical power), the optimised ORC engine with fluids such as R1233zd operates at 77% of its nominal capacity. ORC off-design performance maps are generated, for characterising a
Driker J, Juggurnath D, Kaya A, et al., 2019, Thermal energy processes in direct steam generation solar systems: Boiling, condensation and energy storage, Frontiers in Energy Research, Vol: 6, ISSN: 2296-598X
Direct steam generation coupled with solar energy is a promising technology which can reduce the dependency on fossil fuels. It has the potential to impact the power-generation sector as well as industrial sectors where significant quantities of process steam are required. Compared to conventional concentrated solar power systems, which use synthetic oils or molten salts as the heat transfer fluid, direct steam generation offers an opportunity to achieve higher steam temperatures in the Rankine power cycle and to reduce parasitic losses, thereby enabling improved thermal efficiencies. However, this is associated with non-trivial challenges, which need to be addressed before such systems can become more economically competitive. Specifically, important thermal-energy processes take place during flow boiling, flow condensation and thermal-energy storage, which are highly complex, multi-scale and are multi-physics in nature that involve phase-change, unsteady and turbulent multiphase flows in the presence of conjugate heat transfer. This paper reviews our current understanding and ability to predict these processes, and knowledge that has been gained from experimental and computational efforts in the literature. In addition to Rankine cycles, organic Rankine cycle applications, which are relevant to lower operating temperature conditions, are also considered. This expands the focus to beyond water as the working fluid and includes refrigerants also. In general, significant progress has been achieved, yet there remain challenges in our capability to design and to operate effectively high-performance and low-cost systems with confidence. Of interest are the flow regimes, heat transfer coefficients and pressure drops during the thermal processes present in direct steam generation systems including those occurring in the solar collectors, condensers and relevant energy storage schemes during thermal charging and thermal discharging. A brief overview of some energy storage
Simpson M, Chatzopoulou MA, Oyewunmi O, et al., 2019, Technoeconomic analysis of internal combustion engine – organic Rankine cycle cogeneration systems in energy-intensive buildings, 10th International Conference on Applied Energy, Publisher: Elsevier, Pages: 2354-2359, ISSN: 1876-6102
Organic Rankine cycle (ORC) systems are a promising technology for converting heat to useful power, especially in combined heat and power (CHP) applications with significant quantities of surplus heat that would otherwise be wasted. Beyond the technical performance of these systems, their economic feasibility is crucially important for their wider deployment. In this study, a technoeconomic optimisation of CHP systems is performed in which ORC engines convert heat recovered from internal combustion engines (ICEs), and specifically from both the ICE hot-water output and exhaust-gas stream. The overall aim is to evaluate the impact of the ORC power output and of the components’ design and capital cost on the financial viability of a relevant project, while evaluating a range of candidate working fluids. Results indicate that ORC designs optimised for maximum power output correspond to higher specific investment cost (SIC), with the best performing fluids achieving a SIC of £2100 per kW. In contrast, optimisation for minimum SIC returns values as low as £1700 per kW, or 20% lower. For systems designed and optimised for maximum power, a large fraction of jacket water heat is recovered, while for minimum SIC the utilisation drops to minimise the size and cost of the heat exchangers. The best-performing ORC designs for minimum SIC have discounted payback periods (DPPs) of 4 – 5 years, while those optimised for power output have DPPs of 6 – 7 years, however, the net present values (NPVs) of the latter designs are up to 27% higher than the former. Therefore, there is a trade-off to consider over the project life between high-capacity ORC engines with a high SIC and longer DPP, and designs with minimal SIC but lower power output, shorter DPP and lower NPV. The effect of increasing the amount of hot water required by the building is also analysed, and the ORC engine is shown to be sensitive to this factor for some work
Simpson M, Pantaleo AM, De Palma P, et al., 2018, Design and thermo-economic optimisation of small-scale bottoming ORC systems coupled to biomass CHP gasification cycles, ECOS 2018 - 31st International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems., Publisher: ECOS
Optimisation of a small-scale bottoming organic Rankine cycle (ORC) engine is carried out for a combined biomass-gasifier-CHP system, drawing heat from the syngas conditioning unit of the gasifier and the exhaust gas of the internal combustion(IC) engine. The optimisation considers different working fluids and selection of a positive-displacement expander. Single-and two-stage screw expanders and single-stage reciprocating-piston expanders are modelled in order to capture the variation in their performance at a range of design points.Double-pipe heat exchangers are employed for both evaporator and condenser, leading to a low-cost but bulky design.The system is optimised first for maximum electrical power output, and second for minimum specific investment cost(SIC). Cost correlations are used for each of the principal ORC components. The optimal design for minimum SIC is found to be a two-stage screw expander withethanol as the working fluid, which produces a 13.6% increase in the electrical power output relative to the system without an ORC.The investment attractiveness of the whole system with and without the bottoming ORC is assessed and the system is found tobe profitable for avoided electricity costs above 150 $/MWheland biomass costs of 50 $/t, with the ORC making the system more attractive in all cases studied.Discounted payback periods range from 12years at 150 $/MWhelto 3.5years at 250 $/MWhelforthe system with ORC.
Sapin P, Simpson M, Kirmse C, et al., 2018, Dynamic modeling of water-droplet spray injection in reciprocating-piston compressors, ECOS 2018 - 31st International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems
Sapin P, Simpson M, Kirmse C, et al., 2018, A lumped-mass analysis of water evaporation in reciprocating-piston compressors
Davenne TR, Garvey SD, Cardenas B, et al., 2017, The cold store for a pumped thermal energy storage system, JOURNAL OF ENERGY STORAGE, Vol: 14, Pages: 295-310, ISSN: 2352-152X
Cardenas B, Garvey SD, Kantharaj B, et al., 2017, Gas-to-gas heat exchanger design for high performance thermal energy storage, JOURNAL OF ENERGY STORAGE, Vol: 14, Pages: 311-321, ISSN: 2352-152X
Simpson M, Sapin P, Rotolo G, et al., 2017, Efficiency map of reciprocating-piston expanders for ORC applications, 4th Annual Engine Organic Rankine Cycle Consortium Workshop 2017
Simpson M, Rotolo G, Sapin P, et al., 2017, Thermodynamic performance maps of reciprocating-piston expanders for operation at off-design and part-load conditions, 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Publisher: ICHMT
Renewable energy sources, such as solar-thermal or geothermal heat, and low-/medium-grade industrial waste-heat can be converted into useful power and/or heating with a variety of technologies, including organic Rankine cycle (ORC) and vapour-compression heat-pump systems. The thermodynamic performance and cost of these technologies depends crucially on the efficiency of key components, including the compressor or expander used. Reciprocating-piston machines can be advantageous over turbomachines and other positive-displacement machines at intermediate scales (~10s-100s of kW) thanks to their ability to operate with relatively high isentropic efficiencies at large expansion ratios. However, modelling the thermodynamic losses in reciprocating-piston expanders, with a view towards designing high-performance machines, is a complex undertaking. The aim of this paper is to develop a spatially-lumped, yet dynamic model of a piston expander suitable for early-stage engineering design, that can provide simplification without sacrificing accuracy. The unsteady heat transfer between the gas and the cylinder walls, and the mass leakage are predicted independently with correlations available in the literature and simplified one-dimensional models, respectively. However, the turbulence induced by the mass intake through the piston rings can affect the gas-to-wall heat transfer. In order to address this dependency two complementary approaches are used. Compression and expansion processes are simulated in a gas spring configuration (i.e. without valve systems) using a computational fluid dynamics (CFD) model developed using the open-source code OpenFOAM, where the loss mechanisms are solved directly. The results are then compared with predictions from the heuristic lumped model based on heat tr
Sapin PMC, Simpson M, White AJ, et al., 2017, Lumped dynamic analysis and design of a high-performance reciprocating-piston expander, 30th International Conference on Efficiency, Cost, Optimisation, Simulation and Environmental Impact of Energy Systems., Publisher: ECOS
A spatially-lumped dynamic model of a reciprocating-piston expander is presented in this paper. The model accounts for the three main loss mechanisms in realistic piston machines, namely: pressure losses through the intake and exhaust valves, heat transfer between the gas and the surrounding cylinder walls, and the mass leakagebetween the compression/expansion chamber and the crankcasethrough the piston rings. The model also accounts for real-gas effects with the fluid properties calculated from the NIST database using REFPROP. The numerical calculations are first compared with experimental pressure-volume-temperature data obtained on a custom reciprocating-piston gas spring over a range of oscillation frequencies. The comparison between numerical and experimental results shows good agreement. It also allows the most accurate heat transfer correlationto be selectedfor calculating the gas-to-wallin-cylinderheat transfer. The semi-heuristic modelling tool is thenused to design an expander forspecific pressure ratiosand mass flowrate, and to predict the thermodynamic performance of the piston device over arange of part-load conditions.
Pantaleo, Rotolo G, De Palma P, et al., 2017, Thermo-economic optimization of small-scale ORC systems for heat recovery from natural gas internal combustion engines for stationary power generation, 4th Annual Engine ORC Consortium Workshop for the Automotive and Stationary Engine Industries
Cárdenas B, Pimm AJ, Kantharaj B, et al., 2017, Lowering the cost of large-scale energy storage: High temperature adiabatic compressed air energy storage, Propulsion and Power Research, Vol: 6, Pages: 126-133, ISSN: 2212-540X
Cardenas B, Garvey S, Kantharaj B, et al., 2017, Parametric investigation of a non-constant cross sectional area air to air heat exchanger, APPLIED THERMAL ENGINEERING, Vol: 113, Pages: 278-289, ISSN: 1359-4311
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