Research Papers: Gas Turbines: Microturbines and Small Turbomachinery

Influence of Condenser Conditions on Organic Rankine Cycle Load Characteristics

[+] Author and Article Information
Tobias G. Erhart

e-mail: tobias.erhart@hft-stuttgart.de

Ursula Eicker

e-mail: ursula.eicker@hft-stuttgart.de
Sustainable Energy Technology Research,
University of Applied Sciences Stuttgart,
Schellingstrasse 24,
70190 Stuttgart, Germany

David Infield

Department of Electric and Electronic Engineering,
University of Strathclyde Glasgow,
204 George Street,
Glasgow, Scotland G1 1XW, UK
e-mail: david.infield@eee.strath.ac.uk

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 January 27, 2012; final manuscript received August 13, 2012; published online March 18, 2013. Assoc. Editor: Paolo Chiesa.

J. Eng. Gas Turbines Power 135(4), 042301 (Mar 18, 2013) (9 pages) Paper No: GTP-12-1026; doi: 10.1115/1.4023113 History: Received January 27, 2012; Revised August 13, 2012

A 7 MWth combined heat and power plant (CHP) based on an organic Rankine cycle (ORC) with 5.3 MWth and 1 MWel nominal output is analyzed. A district heating system serves as heat sink; the entire system is heat-led. Two examples for winter and summer operation are shown. The observed characteristics of the condenser are compared to results of a theoretical model. Variable mass flows, temperature levels (72 °C–95 °C) and temperature spreads result in varying condensation temperatures and pressure levels in the condenser (90 mbar to 150 mbar). High mass flows on the secondary side and related low temperature spreads improve the heat transfer and increase the condensation rate in the condenser. The monitoring data support the findings of a steady-state condenser model. As a consequence, advantageous load profiles according to the pressure characteristic of the system can be reached. Live steam pressure, pressure difference across the turbine, and flow rate increase. The effect on the electric efficiency is one percentage point in summer and 1.5 percentage points in winter, which translates to a difference in the electric yield of the cycle of about 10%. Furthermore, the data show that the transient sink conditions cause unsteady operation for the entire cycle.

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Fig. 1

Heat meters in the power plant

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Fig. 2

Location of sensors in the ORC

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Fig. 3

Electric gross efficiency versus thermal input (hourly means, 2008)

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Fig. 4

Characteristic pressure curve of cycle

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Fig. 5

Isentropic efficiency of turbine versus mass flow (7 days/10 seconds)

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Fig. 6

Scheme of shell tube type condenser

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Fig. 7

Condensation on multiple tubular surfaces

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Fig. 8

Expected U value versus cooling water mass flow

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Fig. 9

Summer case—condenser conditions over one day period (June 2, 2011)

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Fig. 10

Summer case—electric gross efficiency versus electric output

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Fig. 11

Summer case—condenser pressure versus feeding temperature and volume flow of sink side

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Fig. 12

Summer case—electric gross efficiency versus feeding temperature and spread

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Fig. 13

Summer case—electric gross efficiency versus feeding temperature and volume flow

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Fig. 14

Winter case—condenser conditions over one day period (Dec. 10, 2011)

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Fig. 15

Winter case—condenser pressure versus feeding temperature and spread

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Fig. 16

Winter case—electric gross efficiency versus feeding temperature and spread

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Fig. 17

Winter case—electric efficiency versus electric output



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