Simulation of Organic Rankine Cycle – Quasi-steady state vs dynamic approach for optimal economic performance

Pili, Roberto; Romagnoli, Alessandro; Jiménez-Arreola, Manuel; Spliethoff, Hartmut; Wieland, Christoph Martin

doi:10.1016/j.energy.2018.10.166

Cited by 37 publications

(10 citation statements)

References 34 publications

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“…It is interesting to compare these results to those in Ref. [70], where a reduction of 37% in the U-values was reported when the heat-source mass flow rate decreased to 50% of the design point. • Although the U-values deteriorate at off-design operation, the evaporator effectiveness remains constant or even increases.…”

Section: Discussionmentioning

confidence: 68%

Off-design optimisation of organic Rankine cycle (ORC) engines with piston expanders for medium-scale combined heat and power applications

et al. 2019

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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 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 its nominal point, the offdesign ORC engine power output reduces by a lesser extent than that of the ICE. At an ICE part-load operation of 60% (by power), the optimised ORC engine with fluids such as R1233zd operates at 77% of its nominal capacity. ORC off-design performance maps are generated, predicting system performance and can be used by ORC system designers, manufacturers and plant operators to identify optimum performance under real operating conditions.

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Section: Discussionmentioning

confidence: 68%

Off-design optimisation of organic Rankine cycle (ORC) engines with piston expanders for medium-scale combined heat and power applications

et al. 2019

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“…The ORC unit was designed by using a MATLAB design routine previously presented in [9]. In this work, the design and off-design routines have not been integrated in the same global optimization loop, but used sequentially for simplicity.…”

Section: Orc Modelmentioning

confidence: 99%

Dynamic modelling of an Organic Rankine Cycle Compressed Heat Energy Storage (ORC-CHEST) system integrated with a cascaded phase change materials (PCM) based packed bed unit

Alessio¹,

Tafone²,

Пили³

et al. 2022

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“…14), or exclude ORC designs with two-phase expansion (Eqs. [15][16], by monitoring the quality of the working fluid through the expansion process (quality is defined as the ratio of the vapour mass over the total mass of the working fluid). The heat-source fluid temperature when leaving the evaporator HEX is constrained by the dew point of the exhaust gases, to avoid condensation.…”

Section: Nominal Operation (Design) Optimisationmentioning

confidence: 99%

“…[13], in an effort that was mainly concerned with off-design control strategies for the turbine. Koppauer et al [14] considered the off-design performance of ORC engines with a double-stage evaporator, PHEXs and a turbine, without optimisation on the working-fluid side, while Pili et al [15] considered the off-design performance of an ORC engine with turbine expanders and PHEXs in waste heat applications, and Guopeng et al [16] performed an off-design performance analysis of an ORC engine recovering heat from the exhaust-gas stream of an ICE. In this study, a turbo-expander and PHEXs were designed for the rated ICE capacity, and the system was subjected to off-design operation, accounting for varying expander and HEX performance.…”

Section: Introductionmentioning

confidence: 99%

Off-design optimisation of organic Rankine cycle (ORC) engines with different heat exchangers and volumetric expanders in waste heat recovery applications

et al. 2019

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Organic Rankine cycle (ORC) engines in real applications experience variable heat-source conditions. In this paper, the off-design performance of small/medium-scale ORC engines recovering heat from a stationary internal combustion engine (ICE) is investigated. Of interest are the employment of screw vs. piston expanders, and two heat exchanger (HEX) architectures. Unlike previous studies where the expander and HEX performance are assumed fixed during offdesign operation, we consider explicitly their varying and interacting characteristics within the overall system. Nominal sizing results reveal indicated isentropic efficiencies >80% for twin-screw and >85% for piston expanders. Following nominal design, ORC engine operation is optimised for ICE part-load (PL) operation. Although the heat transfer coefficients in the evaporator decrease by 30% at PL, the effectiveness increases by 20% due to the larger temperature differences in this component. The screw expander efficiency reduces by up to 3% at off-design operation, whilst that of the piston expander increases by up to 16%. Optimised off-design maps indicate that the ORC engine power output reduces to 77% (piston) or 68% (screw) of full-load when the ICE operates at 60% PL, and that ORC engines with plate HEXs generate 5-11% more power than those with double-pipe HEXs. Under variable ICE operation, smaller ORC engines with piston expanders generate more power than larger engines with screw expanders, highlighting the resilient off-design operation of piston machines. The tool can predict ORC performance over a wide operating envelope and provides performance maps that can be used by operators to optimise ORC engine operation in variable conditions and by ORC vendors to inform component design decisions.

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Simulation of Organic Rankine Cycle – Quasi-steady state vs dynamic approach for optimal economic performance

Cited by 37 publications

References 34 publications

Off-design optimisation of organic Rankine cycle (ORC) engines with piston expanders for medium-scale combined heat and power applications

Off-design optimisation of organic Rankine cycle (ORC) engines with piston expanders for medium-scale combined heat and power applications

Dynamic modelling of an Organic Rankine Cycle Compressed Heat Energy Storage (ORC-CHEST) system integrated with a cascaded phase change materials (PCM) based packed bed unit

Off-design optimisation of organic Rankine cycle (ORC) engines with different heat exchangers and volumetric expanders in waste heat recovery applications

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