Research Papers: Gas Turbines: Cycle Innovations

Evaluation of Property Methods for Modeling Direct-Supercritical CO2 Power Cycles

[+] Author and Article Information
Charles W. White

3168 Collins Ferry Road,
Morgantown, WV 26505
e-mail: CWWhite@keylogic.com

Nathan T. Weiland

National Energy Technology Laboratory,
626 Cochrans Mill Road,
Pittsburgh, PA 15236
e-mail: nathan.weiland@netl.doe.gov

Contributed by the Cycle Innovations Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 3, 2017; final manuscript received July 14, 2017; published online September 19, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(1), 011701 (Sep 19, 2017) (9 pages) Paper No: GTP-17-1264; doi: 10.1115/1.4037665 History: Received July 03, 2017; Revised July 14, 2017

Direct supercritical carbon dioxide (sCO2) power cycles are an efficient and potentially cost-effective method of capturing CO2 from fossil-fueled power plants. These cycles combust natural gas or syngas with oxygen in a high pressure (200–300 bar), heavily diluted sCO2 environment. The cycle thermal efficiency is significantly impacted by the proximity of the operating conditions to the CO2 critical point (31 °C, 73.7 bar) as well as to the level of working fluid dilution by minor components, thus it is crucial to correctly model the appropriate thermophysical properties of these sCO2 mixtures. These properties are also important for determining how water is removed from the cycle and for accurate modeling of the heat exchange within the recuperator. This paper presents a quantitative evaluation of ten different property methods that can be used for modeling direct sCO2 cycles in Aspen Plus®. Reference fluid thermodynamic and transport properties (REFPROP) is used as the de facto standard for analyzing high-purity indirect sCO2 systems, however, the addition of impurities due to the open nature of the direct sCO2 cycle introduces uncertainty to the REFPROP predictions as well as species that REFPROP cannot model. Consequently, a series of comparative analyses were performed to identify the best physical property method for use in Aspen Plus® for direct-fired sCO2 cycles. These property methods are assessed against several mixture property measurements and offer a relative comparison to the accuracy obtained with REFPROP. The Lee–Kessler–Plocker equation of state (EOS) is recommended if REFPROP cannot be used.

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Fig. 1

Block flow diagram of a simplified direct sCO2 cycle

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Fig. 2

Comparison of LK-PLOCK calculations to saturated CO2 vapor and liquid-specific volume data

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Fig. 3

Relative errors of property methods in calculating saturated vapor (upper) and liquid (lower) CO2 specific volumes

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Fig. 4

Pure saturated CO2 vapor and liquid molar volume evaluation

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Fig. 5

Relative error (bubble area) in superheated CO2 molar volume. Solid bubbles are positive deviations from REFPROP, and empty bubbles are negative deviations.

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Fig. 6

Data used for property assessment of CO2:H2O binary mixture [10]

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Fig. 7

CO2:H2O binary property evaluation

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Fig. 8

Relative differences in key performance variables from REFPROP. Numbered variables defined in Table 5.

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Fig. 12

Calculated versus experimental data for BWRS

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Fig. 13

Calculated versus experimental data for BWR-LS

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Fig. 14

Calculated versus experimental data for SRK

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Fig. 15

Calculated versus experimental data for RK-SOAVE

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Fig. 9

Calculated versus experimental data for REFPROP

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Fig. 10

Calculated versus experimental data for LK-PLOCK

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Fig. 11

Calculated versus experimental data for PR-BM

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Fig. 17

Calculated versus experimental data for GRAYSON

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Fig. 18

Calculated versus experimental data for PC-SAFT

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Fig. 16

Calculated versus experimental data for SR-POLAR



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