Research Papers: Gas Turbines: Microturbines and Small Turbomachinery

Evaluation of the Energy Performance of an Organic Rankine Cycle-Based Micro Combined Heat and Power System Involving a Hermetic Scroll Expander

[+] Author and Article Information
Jean-François Oudkerk

e-mail: jfoudkerk@ulg.ac.be

Ludovic Guillaume

Thermodynamics Laboratory,
University of Liège,
Campus du Sart-Tilman, B-49,
B-4000 Liège, Belgium

Eric Winandy

Emerson Climate Technologies GmbH,
Pascalstrasse 65,
52076 Aachen Germany

Vincent Lemort

Thermodynamics Laboratory,
University of Liège,
Campus du Sart-Tilman, B-49,
B-4000 Liège, Belgium

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 29, 2012; final manuscript received October 11, 2012; published online March 18, 2013. Assoc. Editor: Paolo Chiesa.

J. Eng. Gas Turbines Power 135(4), 042306 (Mar 18, 2013) (10 pages) Paper No: GTP-12-1056; doi: 10.1115/1.4023116 History: Received February 29, 2012; Revised October 11, 2012

This paper evaluates the performance of an organic Rankine cycle (ORC) based micro- combined heat and power (CHP) unit using a scroll expander. The considered system consists of a fuel boiler coupled with an ORC engine. As a preliminary step, the results of an experimental campaign and the modeling of a hermetic, lubricated scroll compressor used as an expander are presented. Then, a fluid comparison based on several criteria is conducted, leading to the selection of R245fa as working fluid for the ORC. A simulation model is then built to evaluate the performance of the system. The model associates an ORC model and a boiler model, both experimentally validated. This model is used to optimize and size the system. The optimization is performed considering two degrees of freedom: the evaporating temperature and the heat transfer fluid (HTF) mass flow rate. Seasonal simulation is finally performed with a bin method according to the standard PrEN14825 for an average European climate and for four heat emitter heating curves. Simulation results show that the electrical efficiency of the system varies from 6.35% for hot water at 65 °C (high temperature application) to 8.6% for a hot water temperature of 22 °C (low temperature application). Over one entire year, the system exhibits an overall electrical efficiency of about 8% and an overall thermal efficiency around 87% without significant difference between the four heat emitter heating curves. Finally, some improvements of the scroll expander are evaluated. It is shown that by increasing the maximum inlet temperature (limited to 140 °C due to technical reasons) and using two scroll expanders in series, the overall electrical efficiency reaches 12.5%.

Copyright © 2013 by ASME
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Fig. 1

Evolution of the overall isentropic effectiveness with the pressure ratio imposed to the expander

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Fig. 2

Efficiency of the generator and CVexp versus shaft power for a typical scroll expander

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Fig. 3

Contribution of electromechanical and under- or overexpansion losses

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Fig. 4

Configuration of ORC-based CHP

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Fig. 5

Evolution of the cycle net efficiency with the evaporating temperature for different fluids (Tcd = 50 °C)

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Fig. 6

Volume ratio in term of Tev for different fluids (Tcd = 50 °C)

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Fig. 7

Evolution of the volume coefficient with the evaporating temperature for different fluids (Tcd = 50 °C)

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Fig. 8

Influence of Tev on the electrical efficiency

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Fig. 9

Temperature profile in the evaporator

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Fig. 10

Average climate (PrEN14825)

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Fig. 11

Heat emitters heating curves

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Fig. 12

Electrical efficiency for each bin in term of outdoor temperature for four heat emitter heating curves (very high, high, medium, and low temperature application)

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Fig. 13

Net ORC efficiency versus Tev with actual scroll expander (Tcd = 50 °C)

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Fig. 14

Isentropic effectiveness of the actual scroll expander in terms of Tev for different fluid (Tcd = 50 °C)

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Fig. 15

Improvement of the isentropic effectiveness for toluene and n-pentane (Tcd = 50 °C)

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Fig. 16

ORC net efficiency with improvement for toluene and n-pentane (Tcd = 50 °C)




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