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Integrating working fluid design into the thermo-economic design of ORC processes using PC-SAFT
Johannes Schilling, Dominik Tillmanns, Matthias Lampe, Madlen Hopp, Joachim Gross, André Bardow
Session: Session 2C: Working Fluid Selection
Session starts: Wednesday 13 September, 14:20
Presentation starts: 14:20
Room: Building 27 - Lecture room 03

Johannes Schilling ()
Dominik Tillmanns ()
Matthias Lampe ()
Madlen Hopp ()
Joachim Gross ()
André Bardow ()

To exploit the full thermo-economic potential of an Organic Rankine Cycle (ORC) application, the process, equipment and working fluid have to be optimized simultaneously. Today, working fluid selection and thermo-economic process optimization are commonly separated: In a first step, working fluid candidates are preselected based on heuristic knowledge. The process and equipment are thermo-economically optimized for each preselected working fluid, in a second step. However, if the preselection fails, the thermo-economically optimal working fluid is excluded and the approach leads to suboptimal solutions. In this work, we present an approach for the integrated thermo-economic design of ORC process, equipment and working fluid using consistent thermodynamic modelling. The approach is based on the Continuous-Molecular Targeting–Computer-aided Molecular Design (CoMT-CAMD) [1] framework. In CoMT-CAMD, the properties of the working fluid are modelled by the physically-based Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) equation of state [2]. A CAMD formulation allows the design of novel fluids during the process optimisation. So far, CoMT-CAMD was limited to equilibrium thermodynamics and thus thermodynamic cycle optimization. Recently, we developed models for the transport properties viscosity [3] and thermal conductivity [4] based on entropy scaling of PC-SAFT which allow designing the equipment within the CoMT-CAMD framework. In particular, the heat exchanger of the ORC can be designed using detailed correlations for single phase, evaporation and condensation heat transfer. Based on the equipment sizing, a thermo-economic objective function can be considered in the resulting mixed-integer nonlinear optimisation problem. Thereby, the thermo-economically optimal working fluid is identified in one single optimization problem jointly with the corresponding optimal process and equipment. The resulting approach is demonstrated for the design of a subcritical ORC for waste heat recovery. We show that the predicted specific purchased-equipment costs are in good accordance with real ORC applications. References [1] Schilling, J., Lampe, M., Gross, J., and Bardow, A., 1-stage CoMT-CAMD: An approach for integrated design of ORC process and working fluid using PC-SAFT, Chem. Eng. Sci., 2016, http://dx.doi.org/10.1016/j.ces.2016.04.048. [2] Gross, J. and Sadowski, G., Perturbed-chain SAFT: An equation of state based on a perturbation theory for chain molecules. Ind. Eng. Chem. Res., 2001, 40(4):1244–60. [3] Lötgering-Lin, O., and Gross, J., Group Contribution Method for Viscosities Based on Entropy Scaling Using the Perturbed-Chain Polar Statistical Associating Fluid Theory, Ind. Eng. Chem. Res., 2015, 54(32):7942–52. [4] Hopp, M., and Gross, J., Group-contribution method for thermal conductivity using PC-SAFT and entropy scaling, in: Proceedings of PPEPPD 2016, Porto, Portugal, 2016.