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Publication Title | Efficiency of Compact Organic Rankine Cycle System with Rotary-Vane-Type Expander for Low-Temperature Waste Heat Recovery

Organic Rankine Cycle

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Abstract—This paper describes the experimental efficiency of a compact organic Rankine cycle (ORC) system with a compact rotary-vane-type expander. The compact ORC system can be used for power generation from low-temperature heat sources such as waste heat from various small-scale heat engines, fuel cells, electric devices, and solar thermal energy. The purpose of this study is to develop an ORC system with a low power output of less than 1 kW with a hot temperature source ranging from 60°C to 100°C and a cold temperature source ranging from 10°C to 30°C. The power output of the system is rather less due to limited heat efficiency. Therefore, the system should have an economically optimal efficiency. In order to realize such a system, an efficient and low-cost expander is indispensable. An experimental ORC system was developed using the rotary-vane-type expander which is one of possible candidates of the expander. The experimental results revealed the expander performance for various rotation speeds, expander efficiencies, and thermal efficiencies. Approximately 30 W of expander power output with 48% expander efficiency and 4% thermal efficiency with a temperature difference between the hot and cold sources of 80°C was achieved.

Keywords—Organic Rankine cycle, Thermodynamic cycle, Thermal efficiency, Turbine efficiency, Waste heat recovery, Power generation, Low temperature heat engine.

I. INTRODUCTION

TO mitigate the world’s energy problems and the extent of global warming, renewable sources of energy must be used. Waste heat is one such renewable source of energy. In industries around the world, a large amount of low-temperature heat is lost in the form of waste heat. According to a report by the Energy Conservation Center of Japan [1], industrial waste heat in Japan amounts to 2.7 × 105 Tcal/year. This is equivalent to approximately 70% of the annual commercial and residential energy consumption in Japan. The report also mentions that the

Musthafah MT is with the Graduate school of Energy and Environment Science, Nagaoka University of Technology, 1603-1 Kamitomioka-machi, Nagaoka-shi, Niigata 940-2188, Japan (phone: +81-258-47-9748; fax: +81-258-47-9748; e-mail: musmt@stn.nagaokaut.ac.jp). He is also an academic staff of Malaysia University of Technical, Melaka (UTeM).

Noboru Yamada is with Nagaoka University of Technology, Nagaoka-shi, Niigata, Japan. (e-mail: noboru@nagaokaut.ac.jp).

Tetsuya Hoshino was with Nagaoka University of Technology, Nagaoka-shi, Niigata, Japan. He is now with ADTEC Engineering, Niigata, Japan (e-mail: t_hoshino@adtec-eng.co.jp).

temperature level of 45% of the total waste heat is 100°C and below. Therefore, it is important to develop an economically efficient waste heat recovery system that can generate power and/or electricity from low-temperature heat sources (less than 100°C). Furthermore, the recovery system must have a compact size because waste heat is a highly distributed energy source. The power generated by the recovery system would be less due to limited heat efficiency.

Thus far, various waste heat recovery systems have been proposed and developed. The most feasible and common used waste heat recovery system is the organic Rankine cycle (ORC). The ORC uses an organic fluid with a low boiling point. Yamamoto et al. [2] described the effects of the thermal properties of an organic working fluid on the turbine power output of an ORC system. Free Power Co., Ltd., introduced a commercial ORC system that converts waste heat into electricity [3]. Yamaguchi et al. [4] developed a unique Rankine cycle system using supercritical carbon dioxide (CO2) as the working fluid, and they elucidated its potential as a solar thermal energy conversion system. Advanced cycles such as the Kalina cycle and the Uehara cycle have been developed in order to generate power from a small temperature difference between hot and cold sources (e.g. 15 K to 25 K in an ocean thermal energy conversion (OTEC) system) [5]. Most of the research and development related to waste heat recovery systems has been carried out for a power output greater than 10 kW. For example, the turbine power outputs of the ORC system developed by Ebara Co., Ltd., [6] and Free Power Co., Ltd., are approximately 50 kW and 120 kW, respectively; those of OTEC systems and geothermal plants are usually above 30 kW. An ORC system with a power output of less than 1 kW has not yet been extensively studied and developed. However, the current energy and environmental conditions worldwide are such that there will soon be a requirement for a compact ORC system that can be easily installed at the location where waste heat is generated.

The purpose of this study is to develop an economically efficient ORC system with a turbine power output of less than 1 kW. In order to realize such a system, an efficient and low cost expander is indispensable. In this study, we developed an experimental ORC system using a rotary-vane-type expander, which is one of possible candidates of the expander. Other commercially available components were also used. The system is equipped with a hot source with a temperature range of 60–100°C and a cold source with a temperature range of

International Journal of Civil and Environmental Engineering 2:1 2010

Efficiency of Compact Organic Rankine Cycle System with Rotary-Vane-Type Expander for Low-Temperature Waste Heat Recovery

Musthafah b. Mohd.Tahir, Noboru Yamada, and Tetsuya Hoshino

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