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Research Papers: Gas Turbines: Cycle Innovations

Postcombustion CO2 Capture for Combined Cycles Utilizing Hot-Water Absorbent Regeneration

[+] Author and Article Information
Klas Jonshagen1

Department of Energy Sciences,  Lund University, SE-22100 Lund, Swedenklas.jonshagen@energy.lth.se

Majed Sammak

Department of Energy Sciences,  Lund University, SE-22100 Lund, Swedenmajed.sammak@energy.lth.se

Magnus Genrup

Department of Energy Sciences,  Lund University, SE-22100 Lund, Swedenmagnus.genrup@energy.lth.se

1

Corresponding author.

J. Eng. Gas Turbines Power 134(1), 011702 (Oct 27, 2011) (7 pages) doi:10.1115/1.4004146 History: Received April 12, 2011; Revised April 13, 2011; Published October 27, 2011; Online October 27, 2011

The partly hot-water driven CO2 capture plant offers a significant potential for improvement in performance when implemented in a combined-cycle power plant (CCPP). It is possible to achieve the same performance with a dual-pressure steam cycle as in a triple-pressure unit. Even a single-pressure plant can attain an efficiency competitive with that achievable with a triple-pressure plant without the hot-water reboiler. The underlying reasons are better heat utilization in the heat recovery unit and less steam extraction to the absorbent regenerating unit(s). In this paper, the design criteria for a combined cycle power plant utilizing hot-water absorbent regeneration will be examined and presented. The results show that the most suitable plant is one with two steam pressure levels. The low-pressure level should be much higher than in a conventional combined cycle in order to increase the amount of heat available in the economizer. The external heat required in the CO2 capture plant is partly supplied by the economizer, allowing temperature optimization in the unit. The maximum value of the low-pressure level is determined by the reboiler, as too great a temperature difference is unfavorable. This work evaluates the benefits of coupling the economizer and the reboiler in a specially designed CCPP. In the CO2 separation plant both monoethanolamine (MEA) and ammonia are evaluated as absorbents. Higher regeneration temperatures can be tolerated in ammonia-based plants than in MEA-based plants. When using a liquid heat carrier the reboiler temperature is not constant on the hot side, which results in greater temperature differences. The temperature difference can be greatly reduced by dividing the regeneration process into two units operating at different pressures. The possibility of extracting more energy from the economizer to replace part of the extracted steam increases the plant efficiency. The results show that very high efficiencies can be achieved without using multiple pressure-levels.

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Figures

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Figure 1

The proposed circuit between the economizer and the reboiler

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Figure 2

Schematic simplified picture of the CCPP with CO2 capture utilizing the economizer–reboiler loop

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Figure 3

Temperature versus heat flux for the single-pressure CCPP with carbon capture and the economizer–reboiler loop. Note the small temperature difference in the economizer.

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Figure 4

Temperature versus heat flux for the dual-pressure reheat CCPP with carbon capture and the economizer–reboiler loop

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Figure 5

The chilled ammonia CO2 separation unit and the reboiler heat configuration

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Figure 6

Efficiencies of different CCPP with CO2 capture. The pile to the most left and to the most right does not use the economizer–reboiler coupling. All plants except the sixth from the left uses MEA as absorbent.

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