Integrated computer-aided working-fluid design and thermoeconomic ORC system optimisation

Abstract

The successful commercialisation of organic Rankine cycle (ORC) systems across a range of power outputs and heat-source temperatures demands step-changes in both improved thermodynamic performance and reduced investment costs. The former can be achieved through high-performance components and optimised system architectures operating with novel working-fluids, whilst the latter requires careful component-technology selection, economies of scale, learning curves and a proper selection of materials and cycle configurations. In this context, thermoeconomic optimisation of the whole power-system should be completed aimed at maximising profitability. This paper couples the computer-aided molecular design (CAMD) of the working-fluid with ORC thermodynamic models, including recuperated and other alternative (e.g., partial evaporation or trilateral) cycles, and a thermoeconomic system assessment. The developed CAMD-ORC framework integrates an advanced molecular-based group-contribution equation of state, SAFT-γ Mie, with a thermodynamic description of the system, and is capable of simultaneously optimising the working-fluid structure, and the thermodynamic system. The advantage of the proposed CAMD-ORC methodology is that it removes subjective and pre-emptive screening criteria that would otherwise exist in conventional working-fluid selection studies. The framework is used to optimise hydrocarbon working-fluids for three different heat sources (150, 250 and 350 °C, each with mcp = 4.2 kW/K). In each case, the optimal combination of working-fluid and ORC system architecture is identified, and system investment costs are evaluated through component sizing models. It is observed that optimal working fluids that minimise the specific investment cost (SIC) are not the same as those that maximise power output. For the three heat sources the optimal working-fluids that minimise the SIC are isobutane, 2-pentene and 2-heptene, with SICs of 4.03, 2.22 and 1.84 £/W respectively

Design and Analysis of Domestic Micro-Cogeneration Potential for an ORC System Adapted to a Solar Domestic Hot Water System

“…For this particular study, was considered a pump efficiency, = 65 % [11,14,15,51,52]. The power required by the pump can be calculated by:…”

Expanding the Applications of the SAFT-γ Mie Group-Contribution Equation of State: Prediction of Thermodynamic Properties and Phase Behavior of Mixtures

“…(We note also the works of Contreras et al 128 and Aasen et al 129 in developing the SAFT-VR Mie and SAFT-γ Mie formalism to take account of quantum effects when modeling hydrogen or other fluids for which quantum effects are important.) Markides and co-workers applied SAFT-γ Mie in the context of CAMD for working fluids in organic Rankine cycle engines 95,104,107,122 and diffusion-absorption refrigerators; 113 Bowskill et al 130 independently used SAFT-γ Mie within CAMD for ORC systems. Watson et al 115 used SAFT-γ Mie in the design of crystallization solvents.…”

A New Predictive Group-Contribution Ideal-Heat-Capacity Model and Its Influence on Second-Derivative Properties Calculated Using a Free-Energy Equation of State

“…Thermodynamic properties for which the importance of the ideal contribution is most easily observed are the isochoric and isobaric heat capacities, however, as will be discussed later in this study, the importance of the ideal contribution extends beyond heat capacities to other second-order derivative properties as well. In recent years, the ability to calculate properties such as these using engineering equations of state has become increasingly important, as is exemplified by a substantial number of works − using Statistical Associating Fluid Theory (SAFT) in one of its different incarnations. ,− Among these examples we highlight works illustrating the growing interest in the calculation of thermal properties of working fluids in organic Rankine cycles (ORCs) − and other thermodynamic cycles.…”