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14:40   Session 4: Thermoeconomics I
Chair: Christoph Wieland
14:40
20 mins 		System-search THERMO-ECONOMIC ANALYSIS OF ZEOTROPIC MIXTURES AND PURE WORKING FLUIDS IN ORGANIC RANINKE CYCLES FOR WASTE HEAT RECOVERY
Florian Heberle, Dieter Brüggemann
Abstract: We present a thermo-economic analysis of an Organic Rankine Cycle (ORC) for waste heat recovery using a low-temperature heat source. A case study for a heat source temperature of 150 °C and a subcritical saturated cycle is performed. As working fluids R245fa, isobutane, isopentane and the zeotropic mixture of isobutane and isopentane are considered. The minimal temperature difference in the preheater and condenser as well as mixture composition are chosen as variable parameters. The aim is to identify the most suitable working fluid in combination with optimal process parameters under thermo-economic criteria. In the present study, shell and tube heat exchanger are designed based on simulation results. Depending on the capacity respectively heat transfer surface, cost estimations for the major components of the ORC system are conducted. Finally, specific costs of the power plant and of the generated electricity are determined. In general, the most cost effective systems show a high minimal temperature difference ΔTPP,C at the pinch-point of the condenser and a low minimal temperature difference ΔTPP,E at the pinch-point of the evaporator. Exemplarily, the design parameters ΔTPP,E = 1 K and ΔTPP,C = 13 K lead to minimal costs of 56.82 €/GJ for R245fa. Choosing isobutane as working fluid leads to the lowest specific costs of electricity with 51.97 €/GJ at ΔTPP,E = 1.2 K and ΔTPP,C = 14 K. Considering only the major components, specific costs for the ORC module range between 1150 €/kWel and 2250 €/kWel. In case of the mixture isobutane/isopentane as working fluid, a mole fraction of 90 % isobutane leads to lowest specific costs of electricity. Although a higher power output is obtained, the specific costs are 2 % higher compared to isobutane. An overcompensation of the additional expenses for heat exchange equipment occurs for higher process integration costs. Finally, a sensitivity analysis for an ORC system using isobutane as working fluid is performed to identify particularly relevant boundary conditions. Based on standard conditions, the specific costs of electricity show the highest sensitivity for a variation of process integration costs and isentropic efficiency of the turbine. Especially for the evaluation of fluid mixtures as potential working fluids, a comprehensive analysis of fluid properties and heat transfer characteristics is required to minimize uncertainties of heat exchanger design and cost estimations.
15:00
20 mins 		System-search TECHNO-ECONOMIC ANALYSIS OF THE SUB-CRITICAL ORC WITH OPTIMIZED HEAT TRANSFER PROCESS
Wei Liu, Dominik Meinel, Christoph Wieland, Hartmut Spliethoff
Abstract: A techno-economic analysis of a sub-critical ORC designed for the utilization of geothermal heat is performed. The thermodynamic optimization of the investigated ORC system is based on a new approach, in which thermal match between the heat source and the working fluid is improved by operating an optimal working fluid at near-critical pressures. The Optimal Heat Source Temperature (OHST) method is used to identify suitable fluids for which the pinch point is located at the inlet (or an intermediate point) of the preheater. As a result, R227ea is selected, which performs best under certain defined conditions, while R245fa is also considered as a reference fluid for further thermo-economic comparison. A heat transfer model is proposed for the plate heat exchanger system in order to determine the pinch point position in the case of near-critical fluid parameters, as well as to obtain the heat transfer area which is required for the calculation of Purchased Equipment Cost (PEC). The economic optimization is based on the minimization of the Levelized Cost of Electricity (LCOE) for the considered fluids. Results from the techno-economic optimizations show that for R245fa the optimum is obtained with a system efficiency of 7.306% and a LCOE of 205.7 €/MWh. In comparison, the proposed approach for R227ea leads to an optimum with a system efficiency of 8.607% and a LCOE of 185.9 €/MWh. The comparison suggests that although the proposed approach aims to improve the thermodynamic performance of the sub-critical ORC, it is also promising in terms of the economic profitability.
15:20
20 mins 		System-search INFLUENCE OF THE HEAT-SOURCE COST ON GEOTHERMAL ORC'S
Daniël Walraven, Ben Laenen, William D'haeseleer
Abstract: One of the biggest costs in geothermal ORCs is the drilling of the wells. The costs of these wells depend on the region and they have an influence on the optimal configuration of the power plant. The higher the cost of the wells (for a given wellhead temperature), the higher the efficiency of the ORC has to be for a profitable project and thus the higher the cost of the ORC will be. In this work, it is investigated what the influence of the cost of the heat source is on the performance and configuration of the economically optimal ORC. This optimal ORC is obtained by performing a system optimization, as already performed in our previous work [1,2]. In such a system optimization, the configuration of the most important components (heat exchangers, cooling system and turbine) are optimized together with the configuration of the cycle. In this way, components are optimal to be used together and optimal to be used in the obtained cycle. Minimization of the LCOE (Levelized Cost of Electricity Production) is chosen as the objective function. This LCOE is the fixed electricity price needed to obtain break even at the end of the project. As a result, the LCOE for both water and air-cooled ORCs is given as a function of the heat-source cost and heat-source-wellhead temperature. With this data, an estimation of the LCOE of a geothermal project can be made based on the depth of the wells and the expected wellhead temperature. Comparison with expected electricity prices, the profitability of the project can be estimated. Other results, like the heat-exchanger surface, cooling-system cost, etcetera as a function of the heat-source cost, are also given.
15:40
20 mins 		System-search A PERSPECTIVE ON COSTS AND COST ESTIMATION TECHNIQUES FOR ORGANIC RANKINE CYCLE SYSTEMS
Sanne Lemmens
Abstract: The main goal of this paper is to provide information specifically about the cost aspects of ORC systems. The knowledge from literature on ORC costs is summarised, various cost estimation methods are discussed and their real-life validity is put into perspective.