Organic Rankine Cycle Engine Research Articles

Performance of the Coolidge Solar Thermal Electric Power Plant

Energy performance and equipment evaluation results are presented for the grid-connected Coolidge solar thermal-electric power plant. Performance was determined for each of the major subsystems—line-focus collector array, thermal energy storage and 200 kW, organic Rankine cycle engine and generator. Day-long collector array efficiency was about 32, 26, and 9 percent in June, September, and December, respectively. Energy conversion efficiency was about 20 percent; electrical parasitics reduced this by 12 percent. Operation and maintenance required about 90 h/mo, only 20 percent requiring special skills or training. Operating supplies and repair services cost about $6300 per year. Major equipment problem catagories were fluid leakage and electric motor and electronic component failures. The presented operating data provide a basis for improved design and analysis.

Operational evaluation of the grid-connected Coolidge solar thermal electric power plant

Results of the operation and evaluation of the grid-connected Coolidge solar thermal-electric power plant are reported. Performance was determined for each of the major subsystems—line-focus collector array, thermal energy storage and 200 kW organic fluid Rankine cycle engine and generator. Daily collector array efficiency (based on total direct solar radiation) was nominally 32% in June, 26% in September and 9% in December. Rankine cycle engine-generator conversion efficiency was about 20%; electrical parasitic losses reduced the efficiency by 12%. Operation and maintenance required about 90 h/mo, only 20% requiring special skills or training. Operating supplies and repair services cost about $6300 per year.

Multi-Vane Expanders as Prime Movers in Low-Grade Energy Engines

Multi-vane expanders possess many advantages, over turbines and other positive-displacement machines, as prime movers for low-grade energy engines of small power outputs. It has been found that the performances of such expanders can be improved considerably by optimizing their design and operating variables. For an organic Rankine-cycle engine, utilizing low-temperature heat as the input, a multi-vane expander with isentropic efficiencies exceeding 73 per cent at rotational speeds up to 3000 r/min was designed, built and demonstrated.

Selection of operating conditions and optimisation of design parameters for multi-vane expanders

Multi-vane expanders possess many advantages as prime movers for organic Rankine-cycle engines utilising low-grade heat as the energy inputs. The performances of these devices can be improved considerably by the proper selection of the operating conditions for existing units and by optimising their designs proposed for specified applications. Computer programs, composed for predicting the behaviours of multi-vane expanders, were employed to ascertain the most suitable operating conditions for two existing designs. A simple formula for selecting the optimal working pressure ratios of the expanders, using R-113 as the working fluid, is presented. Optimal values of the design parameters of the expanders were determined for selected operating conditions. The performances of the optimised designs of the considered expanders are relatively insensitive to changes in the operating conditions of the machines in the vicinity of their optimised values. This is a desirable feature of prime movers in Rankine engines utilising fluctuating low-grade energy sources, such as solar energy.

Influences of vane design and lubricant on a multi-vane expander's performance

Multi-vane expanders possess advantages as prime movers for organic Rankine-cycle engines stimulated by low-grade heat, particularly for low-power output applications. The behaviours of the vanes in these devices influence radically their overall performances. In this study, the effects of the percentage of the lubricating oil mixed with the working fluid, the arrangement of the pressurising slots machined into the vanes and the vane material upon the performance of a multi-vane expander are investigated. The experimental results indicate that the performances and operation reliabilities of multi-vane expanders can be improved considerably by optimising these design and operational variables.

Multi-vane expanders: Geometry and vane kinematics

A multi-vane expander (MVE) offers considerable promise as a prime mover for organic Rankine-cycle engines utilising solar energy or waste heat to provide the power input. 1 Therefore, mathematical models describing an expander's behaviour have been constructed; these models are applicable to a wide range of MVEs. For two existing designs, the geometrical characteristics and the vane kinematics have been evaluated using the computer sub-routines composed. The results indicate that the neglect of the vanes' thickness when evaluating the geometrical characteristics of the expanders can lead to considerable errors in their predicted volume expansion ratios, especially when numerous vanes and small inlet angles are employed. The expected effects of the geometrical parameters of the expanders on their performances are discussed.

Heat pump enhanced gas turbine cogeneration

A significant fraction of the gaseous fuel supplied to industry will be used in medium- and small-size cogeneration plants. In this paper, a gas turbine and a gas engine of about 800 kW power output are compared at full and part load operation. When low-temperature heat (e.g., for space heating) is produced, the higher exhaust losses of the gas turbine yield a lower system efficiency, particularly at part load. A scheme is proposed to recover the exhaust gas energy by cooling to a temperature near ambient. The system features a heat pump to raise the recovered heat temperature to a usable level and an organic Rankine cycle (ORC) engine to drive the heat pump. The ORC engine uses the high-temperature fraction of the heat recovered from the exhaust. The data for the ORC engine are derived from an actual experimental engine. The performance is calculated for the system at full load.

Multi-vane expanders as prime movers for low-grade energy organic Rankine-cycle engines

The behaviour of the prime mover in a low-grade energy Rankine-cycle engine is one of the most important factors affecting the overall system performance. A survey of published data concerning various types of expander in use in Rankine engines and an analysis based on the concept of similarity shows that, for the low power outputs, positive-displacement expanders have potential advantages when compared with turbines. However, the multi-vane expander (i.e. the MVE) offers considerable promise as the most appropriate prime mover for organic Rankine-cycle engines utilizing solar energy or waste heat as energy inputs, especially in the developing countries. The features and characteristics of the appropriate MVE's are discussed, together with the operational problems remaining to be solved.

Selection of a Working Fluid for an Organic Rankine Cycle Coupled to a Salt-Gradient Solar Pond by Direct-Contact Heat Exchange

An analysis was conducted of power production by an organic Rankine cycle engine coupled to a solar pond with direct-contact heat exchange. Use of a direct-contact boiler reduced the projected plant cost by 25 percent. The choice of a working fluid affects plant efficiency, turbine size, and working fluid losses. Pentane was shown to be the working fluid best suited to this application.

High-Performance Photovoltaic Systems

Photovoltaic systems generating electric power and thermal energy can operate at high efficiency if the thermal energy is generated at temperatures compatible with the operation of organic Rankine cycle engines. GaAs solar cells are well suited for such systems, since the cell can operate at relatively high functional temperatures without considerable performance degradation. System efficiencies in excess of 20% are predicted based on the use of an efficient 'stagnation point' solar cell cooling concept.

Heat recovery in a ceramic kiln with an organic rankine cycle engine

The process of ceramics firing, as well as many other high temperature processes, is highly inefficient and it is possible to recover an important fraction of the heat input. However, the recovery of heat is not practical because heat finds little use in the factory and its transport to other users is expensive. A recovery system has been proposed by the authors and funded by EEC, which transforms part of the heat of the kiln exhaust gases into electricity by means of an Organic Rankine Cycle Engine. The generated electricity can often be utilized directly in the oven for driving the air and exhaust fans. A thermodynamic study has led to the selection of tetrachloroethylene as the working fluid, with a rated power output of 40 kW at the turbine shaft, at an evaporation temperature of the work fluid of 110°C. In the paper, the design criteria for the most significant plant components are briefly outline; some experimental results, obtained in a series of tests carried out at Gemmindustria, are presented: They show that most of the technical goals of the research (engine efficiency, power output, behaviour in transient conditions, etc.) have been met. Recently the engine has been installed on the oven of a large ceramic industry, and will be continuously operated for testing the engine reliability in an industrial environment.

The CNPM thermal heat pump. Part 1 — general description and thermodynamic analysis

A research programme, funded by CNR (National Research Council), has been undertaken by CNPM since 1973. The aim of the programme is the construction and testing of a prototype thermal heat pump. The most significant component is an organic Rankine cycle engine, driving the compressor of a heat pump. Since the heat rejected by the engine is supplied to the user — water for domestic heating — the whole system performs as a ‘heat multiplier’, converting the high temperature heat given to the engine into a larger amount of low temperature heat, to be used for domestic heating. In this paper, the selection criteria for the working fluid — a completely fluoro-substituted hydrocarbon — and the main thermodynamic data of both power and heat pump cycles, are discussed; the finally adopted plant configuration is described, with particular emphasis on the influence exterted by the working fluid nature on the heat exchangers and turbo-machinery dimensions and performance. A discussion on the merits of the single fluid solution (ie the same working fluid in the power and the heat pump cycle) and dual fluid solution is also carried out. The feasibility of a low-temperature heat distribution, based on compact-surface, natural-draft convectors, with the relevant advantages on the Rankine and heat-pump cycles, is also investigated. Finally, the expected overal; system performance is given, both at design and part-load conditions. As a premium for the rather complex but efficient thermodynamicscv of the system, significant energy savings are obtained in all situations.

Current costs of solar powered organic Rankine cycle engines

Solar energy can be used to heat and cool buildings, drive irrigation pumps, make electrical power, desalt sea water, and, in general, reduce energy demands on conventional energy sources. The organic Rankine cycle engine will play an important part in the conversion of solar energy to useful shaft power. Technical feasibility is here now, as shown by several demonstration projects; however, economic feasibility may be some years away. This paper addresses the technical and cost aspects of the organic Rankine cycle and its interaction with the solar collector as a power system. The efficiency and practical considerations of the combined collector and Rankine system show that collector temperatures of 93°C (200°F), 150–200°C (300–400°F), and 315°C (600°F) are optimum operating conditions for flat plate, concentrators, and tracking concentrators respectively. The peak solar conversion efficiencies of these systems are approximately 5, 10 and 11 per cent respectively. When comparing the cost of solar power systems, it is shown that the dominant factor in the system cost is the collector cost. It is estimated that in a production unit the Rankine cycle cost will be approximately one-third of the total system cost with two-thirds going to the collector component. Consequently, low-cost collectors are crucial for commercialization of solar Rankine systems. It is estimated that the installed cost of mass produced solar power systems would be in the neighborhood of $1600–$2500/peak kW output. These values do not relate to a solar cooling system since not all the collectors are charged to the cooling system; hence, the relevant cost comparison is the production costs of the Rankine and the absorption cooling systems. Therefore, the conclusions presented here relate primarily to power systems. Solar power systems are technically feasible now; however, when will they be economically feasible? It is this author's opinion that this will occur when there is no other alternative, which may not be long in coming. When this time does arrive, the organic Rankine engine is available to convert the Sun's heat into useful power.