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Research Papers: Gas Turbines: Electric Power

# Highly Efficient IGFC Hybrid Power Systems Employing Bottoming Organic Rankine Cycles With Optional Carbon Capture

[+] Author and Article Information
R. J. Braun, S. Kameswaran, J. Yamanis, E. Sun

Engineering Division, Colorado School of Mines, Golden, CO 80401 United Technologies Research Center, East Hartford, CT 06108

This cost reflects an overnight installed capital cost that can be 50% lower than actual turn-key plant cost.

The estimation is made by taking the 250% excess process thermal energy and generating power through either ORC or SRC power cycles at the efficiencies employed in this analysis.

Ejector efficiency is defined as $ηejector=V˙2V˙1P2⋅ ln⁡(P3/P2)(P1−P3)$ , where $V˙$ is the volumetric flow rate and P is the static pressure at the denoted location in the ejector. The subscripts 1, 2, and 3 refer to the primary driving flow (fresh air), the secondary flow (recycle), and the mixed flow at the ejector outlet, respectively.

J. Eng. Gas Turbines Power 134(2), 021801 (Dec 14, 2011) (15 pages) doi:10.1115/1.4004374 History: Received June 18, 2010; Revised May 18, 2011; Published December 14, 2011; Online December 14, 2011

## Abstract

This study examines the performance of a solid oxide fuel cell- (SOFC-) based integrated gasification power plant concept at the utility scale (>100 MW). The primary system concept evaluated was a pressurized ∼150 MW SOFC hybrid power system integrated with an entrained-flow, dry-fed, oxygen-blown, slagging coal gasifier and a combined cycle in the form of a gas turbine and an organic Rankine cycle (ORC) power generator. The analyzed concepts include carbon capture via oxy-combustion followed by water knockout and gas compression to pipeline-ready CO2 sequestration conditions. The results of the study indicate that hybrid SOFC systems could achieve electric efficiencies approaching 66% [lower heating value (LHV)] when operating fueled by coal-derived clean syngas and without carbon dioxide capture. The system concept integrates SOFCs with the low-pressure turbine spool of a 50 MW Pratt & Whitney FT8-3 TwinPak gas turbine set and a scaled-up, water-cooled 20 MW version of the Pratt & Whitney (P&W) PureCycle ORC product line (approximately 260 kW). It was also found that a system efficiency performance of about 48% (LHV) is obtained when the system includes entrained-flow gasifier and carbon capture using oxygen combustion. In order to integrate the P&W FT8 into the SOFC system, the high-pressure turbine spool is removed which substantially lowers the FT8 capital cost and increases the expected life of the gas turbine engine. The impact of integrating an ORC bottoming cycle was found to be significant and can add as much as 8 percentage points of efficiency to the system. For sake of comparison, the performance of a higher temperature P&W ORC power system was also investigated. Use of a steam power cycle, in lieu of an ORC, could increase net plant efficiency by another 4%, however, operating costs are potentially much lower with ORCs than steam power cycles. Additionally, the use of cathode gas recycle is strongly relevant to efficiency performance when integrating with bottoming cycles. A parameter sensitivity analysis of the system revealed that SOFC power density is strongly influenced by design cell voltage, fuel utilization, and amount of anode recycle. To maximize the power output of the modified FT8, SOFC fuel utilization should be lower than 70%. Cathode side design parameters, such as pressure drop and temperature rise were observed to only mildly affect efficiency and power density.

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## Figures

Figure 1

Schematic overview of coal-based IGFC hybrid system with ORC and post-combustion CO2 capture

Figure 2

Simplified schematic diagram of PW FT8-series gas turbine power generator

Figure 3

SOFC stack model overview

Figure 4

SOFC V-j model performance characteristic

Figure 5

Hybrid IGFC plant concept flowsheet depicting gasifier, SOFC, GT-ORC, and CC&S subsystems

Figure 6

Effect of cell voltage on system parameters associated with the hybrid IGFC system

Figure 7

Effect of fuel utilization on system parameters associated with the hybrid IGFC system

Figure 8

Effect of system pressure ratio on system parameters associated with the hybrid IGFC system

Figure 9

Effect of anode S/C ratio on system parameters

Figure 10

Effect of cathode-side pressure drop on system parameters

Figure 11

Effect of stack ΔT on various system parameters in the hybrid IGFC system

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