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15:00   Session 12: Thermoeconomics II
Chair: Florian Heberle
15:00
20 mins 		System-search THERMO-ECONOMIC EVALUATION OF ORC'S FOR VARIOUS WORKING FLUIDS
Pardeep Garg, Matthew Orosz, Pramod Kumar, Pradip Dutta
Abstract: Disparity between electricity demand and its generation motivates to utilize every possible energy resource to bridge the gap to the extent of realizing the marginal potential of the low temperature heat (< 200 °C) such as geothermal, waste heat from industrial processes or low concentration (< 100) solar collector systems. Though available in plenty, these sources are distributed in space, thus making power generation inherently distributed by nature. In this regard, organic Rankine cycle (ORC) with its ability of scalability, promises reasonable thermodynamic efficiencies. A number of fluids have been proposed in the literature and optimized based on their thermodynamic performance. However, it is worth noting that a cycle with slightly higher efficiency need not necessarily result in lower capital cost.. This paper presents a detailed thermo-economic analysis for various fluids. The criterion is to select zero OPD working fluids having positive condenser pressures at 35 °C (condenser temperature). A total of 20 fluids are shortlisted based on above criteria. Parametric studies are performed by varying working fluid, source side temperature, pinch temperature in heat exchangers namely boiler, regenerator and condenser, condenser area and power generation capacity ranging from 5 to 500 kWe. Various components considered on working fluid side are a plunger pump, plate type of heat exchangers for both regenerator and boiler, a scroll expander and an air cooled condenser. A limit of 60 bar is imposed on high side pressure in view of the pressure rating of plate heat exchangers. Similarly, components considered on heat source side are gear pump and heat transfer fluid. Ethylene glycol is selected for temperatures below 180 °C and Therminol VP-1 for higher temperatures up to 250 °C. The thermo-economic model accounts for basic instrumentation required from a control perspective which also includes variable frequency drives for working fluid pump and HTF pump. Cost functions are generated for the above mentioned components for various power capacity ranges. Finally, a Matlab code is developed to evaluate the thermodynamic performance of a given working fluid for the various parameters considered above along with the associated economic implications to arrive at a $/We (Figure of Merit, FOM). A one to one comparison is performed among the various fluids to minimize the $/We associated with them. The following observations made: i. Condenser pinch point, its area and fan power are the most significant parameters driving the figure of merit. ii. $/We for a given fluid under the given operating conditions inversely scales with the power generation capacity approaching an asymptote around 100 kWe. iii. Condenser pressure and FOM are found to be inversely related. For a particular power capacity and operating conditions (source and sink temperature) increase in condenser pressure reduces $/We. However, it is not recommended to have condenser pressures beyond 15 bar which would result in lower expansion ratio in the expander due to upper pressure limit of 60 bar. In this aspect, R-134a and R-152 are found to have lower initial investment.
15:20
20 mins 		System-search THERMOECONOMIC ANALYSIS OF ORGANIC RANKINE CYCLE USING ZEOTROPIC MIXTURES
Muhammad Imran, Muhammad Usman, Dong Hyun Lee, Byung Sik Park
Abstract: Depletion of fossil fuel resources and their environmental impact have accelerated research work in the area of renewable energy and energy efficiency. Utilization of low temperature renewable energy resources or low grade waste heat can reduce the environmental impact and energy cost. Organic Rankine Cycle (ORC) is a viable option for efficient recovery of medium to low temperature renewable energy and waste heat. Working fluids with lower boiling point enable ORC to recover low grade heat effectively. Selection of the working fluid has a significant impact on ORC system performance. The current study aims to investigate the performance of ORC system using pure working fluids and zeotropic mixtures, based on thermodynamic and thermo-economic parameters of ORC system under different sink and source conditions. Low temperature geothermal water is used as heat source in simulation. Evaporator, expander, condenser and feed pump models are developed in MATLAB. The discretized LMTD method is employed for evaporator and condenser model with appropriate database of heat transfer and pressure drop correlations. The effects of temperature glide and pinch point temperature are analysed on the basis of exergy loss and cost of evaporator and condenser. For comparison, pure working fluids are taken as the base case. The results show that the exergy destruction in evaporator and condenser for zeotropic mixtures is less than pure working fluids. Exergy efficiency of system with zeotropic mixture is higher than pure working fluids. For the same power output, the heat transfer area of evaporator and condenser is reduced considerably and so the cost.
15:40
20 mins 		System-search INFLUENCE OF HEAT DEMAND ON TECHNO-ECONOMIC PERFORMANCE OF A BIOMASS/NATURAL GAS MICRO GAS TURBINE AND BOTTOMING ORC FOR COGENERATION
Sergio Camporeale, Antonio Pantaleo
Abstract: This paper presents a thermo-economic analysis of small scale Combined Heat and Power (CHP) plants composed by a micro gas turbine (MGT) and a bottoming Organic Rankine Cycle (ORC). The focus is to improve the flexibility of the plant through a bottoming ORC that can increase the electric power production despite reducing the useful heat for cogeneration. For the topping cycle three different configurations are examined: 1) a simple recuperative micro gas turbine fuelled by natural gas, 2) an externally fired gas turbine (EFGT) with direct combustion of biomass, and 3) a dual fuel EFGT cycle, fuelled by biomass and natural gas. For the bottoming cycle, a saturated recuperative Rankine cycle is examined under two different condensation temperatures for applications of heat and power generation. The simulation results show that, at low condensation temperature, higher electric efficiency can be obtained but heat rejected by the ORC cycle cannot be used for cogeneration while, with high condensation temperature, lower electric efficiency but higher plant cogeneration efficiency can be obtained. The research assesses the global energy efficiency and profitability of the different schemes, as a function of the thermal energy demand intensity, represented by the annual equivalent heat demand hours. For this purpose, the following factors are considered: (i) lower energy conversion efficiency, higher investment cost and lower fuel costs of biomass vs natural gas fuel; (ii) revenues from feed-in tariff available for biomass electricity fed into the grid; (iii) revenues from heat distribution to end users.
16:00
20 mins 		System-search SIZING AND PARAMETRIC OPTIMIZATION OF A WASTE HEAT TO POWER PLANT BASED ON TRANSCRITICAL ORGANIC RANKINE CYCLE
Van Long Le, Michel Feidt, Abdelhamid Kheiri, Vincent Lemort
Abstract: In recent years, the transcritical (also called supercritical) organic Rankine cycle (Trans-ORC) has more and more aroused the attention for power generation from low-temperature heat source thanks to the better thermal matching between the heating and the cooling fluids of the high pressure heat transfer process. The absence of isothermal evaporation in transcritical ORC enables the heat source to be cooled down to a lower temperature despite an identical pinch point as in a comparable subcritical cycle. This leads to a greater utilization of the heat source. In other words, the transcritical cycle could produce more power with higher exergy efficiency compared to the subcritical one. This paper aims at sizing a transcritical ORC to recover energy from a cooling circuit of turbine exhaust gas and optimizing the operating conditions of the cycle from a thermoeconomic point of view. Indeed, several potential organic fluids, which satisfy the screening criteria (e.g. safety, environment, thermophysical properties and availability), will be used as working fluid to evaluate the performance and the specific investment capital (SIC) of the plant. The operating conditions (i.e. turbine inlet temperature and pressure, condensing temperature and heat sink outlet temperature) of the plant will also be optimized to find out the most suitable working fluid for the studied cycle.
16:20
20 mins 		System-search PRELIMINARY INVESTIGATION INTO THE CURRENT AND FUTURE AFFORDABILITY AND GROWTH OF ORC ELECTRICITY GENERATION SYSTEMS
Michael Southon, Susan Krumdieck
Abstract: The Organic Rankine Cycle (ORC) provides a way to produce power from heat resources that are at too low of a temperature to be competitively converted using steam-Rankine cycles. While ORC systems using geothermal, biomass, waste-heat, and solar resources currently provide less than 0.1% of worldwide electricity generation, their market growth has been historically steady, with new resource opportunities helping to marginally increase the installed capacity growth rate in recent years. This paper explores the current growth of ORC electricity generation systems, the theoretical limit of their future growth, and to what extent a policy-based market change will push ORCs towards meeting this potential. The results from a survey of ORC manufacturers are presented, looking into the prevalence of existing ORC systems and the heat resources which they use. Estimates for the potential for future growth are made based on existing literature, and this is compared with current development. The historic trend for the growth of ORC generation capacity is presented, and it is proposed that if the low current annual growth rate continues, then ORCs are unlikely to become a globally significant energy conversion technology at current electricity demand levels. The final part of this paper looks at the competitive advantage that ORCs get from GHG pricing, a non-technological factor that affects the growth rate of installed capacity. It is concluded that a truly significant penetration of ORC generation into the global energy mix would require a step change in the amount of resources that can be affordably developed; either through the introduction of new ways to cheaply access and convert resources, or through a massive shift in expenditure on energy systems, which may be infeasible in future economic scenarios.