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Research Papers: Gas Turbines: Cycle Innovations

HRSG Design for Integrated Reforming Combined Cycle With CO2 Capture

[+] Author and Article Information
Lars O. Nord

Department of Energy and Process Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim, Norwaylars.nord@ntnu.no

Olav Bolland

Department of Energy and Process Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway

J. Eng. Gas Turbines Power 133(1), 011702 (Sep 14, 2010) (7 pages) doi:10.1115/1.4001822 History: Received April 08, 2010; Revised April 10, 2010; Published September 14, 2010; Online September 14, 2010

This article illustrates aspects of heat recovery steam generator (HRSG) design when employing process integration in an integrated reforming combined cycle (IRCC) with precombustion CO2 capture. Specifically, the contribution of this paper is to show how heat integration in a precombustion CO2 capture plant impacts the selection of HRSG design. The purpose of such a plant is to generate power with very low CO2 emissions, typically below 100 g CO2/net kWh electricity. This should be compared with a state-of-the-art natural gas combined cycle (NGCC) plant with CO2 emissions around 380 g CO2/net kWh electricity. The design of the HRSG for the IRCC process was far from standard because of the significant amount of steam production from the heat generated by the autothermal reforming process. This externally generated steam was transferred to the HRSG superheaters and used in a steam turbine. For an NGCC plant, a triple-pressure reheat steam cycle would yield the highest net plant efficiency. However, when generating a significant amount of high-pressure steam external to the HRSG, the picture changed. The complexity of selecting an HRSG design increased when also considering that steam can be superheated and low-pressure and intermediate-pressure steam can be generated in the process heat exchangers. For the concepts studied, it was also of importance to maintain a high net plant efficiency when operating on natural gas. Therefore, the selection of HRSG design had to be a compromise between NGCC and IRCC operating modes.

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Figures

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Figure 1

Schematic of natural gas precombustion capture

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Figure 2

Overall simulation overview with software linking

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Figure 3

Net electrical efficiency (including transformer losses) for combined cycle plants with GE 9FB gas turbine. Steam cycles include: single-pressure (1P), dual-pressure (2P), dual-pressure with reheat (2PR), triple-pressure (3P), and triple-pressure with reheat (3PR).

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Figure 4

Natural gas fired combined cycle plant with external HP steam generation. For reference, 90 kg/s (2PR, 3PR) and 105 kg/s (1P, 2P, 3P) of steam was generated in HRSG evaporator at the 0 kg/s external HP steam mass flow point.

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Figure 5

T-Q diagram for single-pressure HRSG without external HP steam generation. Dashed lines refer to HRSG flue gas, solid lines to water/steam cycle.

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Figure 6

T-Q diagram for dual-pressure reheat HRSG without external HP steam generation. Dashed lines refer to HRSG flue gas, solid lines to water/steam cycle.

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Figure 7

T-Q diagram for single-pressure HRSG with 70 kg/s of external HP steam generation. Dashed lines refer to HRSG flue gas, solid lines to water/steam cycle.

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Figure 8

T-Q diagram for dual-pressure reheat HRSG with 70 kg/s of external HP steam generation. Dashed lines refer to HRSG flue gas, solid lines to water/steam cycle.

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Figure 9

Natural gas fired combined cycle plant with external HP economizer and evaporator. For reference, 90 kg/s (2PR) and 105 kg/s (1P) of steam was generated in HRSG evaporator at the 0 kg/s external HP steam mass flow point.

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Figure 10

T-Q diagram for single-pressure HRSG with 70 kg/s of external HP steam economizing and evaporation. Dashed lines refer to HRSG flue gas, solid lines to water/steam cycle.

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Figure 11

Net plant efficiency as a function of HP steam pressure level for a dual-pressure reheat steam cycle in an NGCC plant.

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Figure 12

IRCC process flow sheet. Stream numbering and temperatures (in °C) are indicated for certain streams.

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Figure 13

GT PRO power cycle schematic including HRSG design. Annotations: pressure p in bar, mass flow m/M in kg/s, and temperature T in °C. For example, air extracted from the GT compressor with annotation 16.22 p, 380 T, and 91.96 m, refer to a pressure of 16.22 bar, a temperature of 380°C, and a mass flow of 91.96 kg/s.

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