Research Papers: Gas Turbines: Microturbines and Small Turbomachinery

Siloxanes as Working Fluids for Mini-ORC Systems Based on High-Speed Turbogenerator Technology

[+] Author and Article Information
Antti Uusitalo

e-mail: antti.uusitalo@lut.fi

Teemu Turunen-Saaresti

e-mail: teemu.turunen-saaresti@lut.fi

Juha Honkatukia

e-mail: juha.honkatukia@lut.fi
Laboratory of Fluid Dynamics,
Institute of Energy Technology,
Lappeenranta University of Technology,
Lappeenranta, Finland

Piero Colonna

Process and Energy Department,
Delft University of Technology,
Delft, The Netherlands
e-mail: P.Colonna@tudelft.nl

Jaakko Larjola

Laboratory of Fluid Dynamics,
Institute of Energy Technology,
Lappeenranta University of Technology,
Lappeenranta, Finland
e-mail: jaakko.larjola@lut.fi

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Engineering for Gas Turbines and Power. Manuscript received February 28, 2012; final manuscript received June 25, 2012; published online March 18, 2013. Assoc. Editor: Joost J. Brasz.

J. Eng. Gas Turbines Power 135(4), 042305 (Mar 18, 2013) (9 pages) Paper No: GTP-12-1051; doi: 10.1115/1.4023115 History: Received February 28, 2012; Revised June 25, 2012

This paper presents a study aimed at evaluating the use of siloxanes as the working fluid of a small-capacity (10kWe) ORC turbogenerator based on the “high-speed technology” concept, combining the turbine, the pump, and the electrical generator on one shaft, whereby the whole assembly is hermetically sealed, and the bearings are lubricated by the working fluid. The effects of adopting different siloxane working fluids on the thermodynamic cycle configuration, power output, and on the turbine and component design are studied by means of simulations. Toluene is included into the analysis as a reference fluid in order to make comparisons between siloxanes and a suitable low molecular weight hydrocarbon. The most influential working fluid parameters are the critical temperature and pressure, molecular complexity and weight, and, related to them, the condensation pressure, density and specific enthalpy over the expansion, which affect the optimal design of the turbine. The fluid thermal stability is also extremely relevant in the considered applications. Exhaust gas heat recovery from a 120 kW diesel engine is considered in this study. The highest power output, 13.1 kW, is achieved with toluene as the working fluid, while, among siloxanes, D4 provides the best simulated performance, namely 10.9 kW. The high molecular weight of siloxanes is beneficial in low power capacity applications, because it leads to larger turbines with larger blade heights at the turbine rotor outlet, and lower rotational speed if compares, for instance, to toluene.

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Fig. 1

Process flow diagram of the ORC power system based on high-speed turbogenerator technology

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Fig. 2

Cutout of a typical high-speed ORC turbogenerator developed and manufactured at the LUT fluid dynamics laboratory

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Fig. 3

Temperature diagram of the evaporator. The working fluid is siloxane D4.

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Fig. 4

Temperature diagram of the recuperator. The working fluid is siloxane D4.

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Fig. 5

Temperature diagram of the condenser. The working fluid is siloxane D4.

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Fig. 6

ORC process net electric power, Pe,net

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Fig. 7

ORC process net electric efficiency, ηe,net

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Fig. 8

The effect of the condensation temperature, Tc, on the net electric power output, Pe,net (pressure losses are neglected)

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Fig. 9

The effect of the condensation temperature, Tc, on the net electric efficiency, ηe,net (pressure losses are neglected)

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Fig. 10

The effect of the condensing temperature, Tc on the turbine volume ratio vt,out/vt,in

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Fig. 11

The effect of the condensing temperature, Tc on the pressure ratio pt/pc

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Fig. 12

The effect of the condensing temperature, Tc on the condensing pressure, pc

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Fig. 13

The effect of the turbine efficiency, ηt on the electric power output, Pe,net



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