Performance Analysis of a Retrofitted Reversible Solid Oxide Cell and a Combined Cycle Gas Turbine

Abstract

The vast amounts of greenhouse gas (GHG) emissions, surging gas prices, and increasing proportion of intermittent energy sources force the energy sector to structurally modify the energy system. The reversible Solid Oxide Cell (rSOC) is considered to be part of the solution due to its high efficiency, good scalability, and ability to balance the energy grid. The rSOC is a high-temperature, electrochemical device that can convert both power-to-gas and gas-to-power during its Solid Oxide Fuel Cell (SOFC) and Solid Oxide Electrolysis Cell (SOEC) modes. The integration of the SOFC with a combined cycle gas turbine (CCGT) features exceptional synergies. Although the synergies of the SOFC and CCGT have already been widely reviewed, the combination of an rSOC and a CCGT has remained unexplored.

The research objective of this study is to assess the benefits of retrofitting an rSOC to an existing CCGT by simulating its exegetic performance, relative GHG emissions and gross profit, and comparing these results to those of an existing CCGT. During the integration of the rSOC (operating in SOFC mode) with the CCGT, the performance of the reversed SOEC mode must be taken into account because it will have to operate with the same operating conditions and the same system components. In order to decrease the system investment cost, this work examines to what extent the rSOC can be retrofitted into the currently deployed CCGTs.

This research optimizes the process plant design and scrutinizes the effect of various operating conditions on the system performance. The optimization is performed through exergy analyses of a zero-dimensional Aspen Plus model. A case study, in which the proposed system is inserted into an energy resource allocation model of the Amsterdam metropolitan area, is used to examine the gross profit of the proposed multi-energy system.

The optimization of the SOFC-CCGT system results in an exergy efficiency of 61.5%, generating 518 MWe, which enhances the performance of the existing CCGT by 3.8% and decreases the GHG emissions [CO2e t/MWh] by 21.3%. When the combined heat and power (CHP) mode of the CCGT is considered, the resulting SOFC-CCGT CHP system achieves an exergy efficiency of 61.2%, while generating 474 MWe and 103 MWth. The SOFC-CCGT CHP outperforms the exergy efficiency of the original CCGT CHP with 4.2%, while emitting 13.2% less GHG emissions. The same operating conditions of the SOFC were applied to the SOEC, which manages to operate with an exergy efficiency of 84.3%.

Implementing the rSOC-CCGT CHP system into the energy resource allocation model results in a 118% increased net present value (NPV) of the gross profit compared to the original CCGT. The proposed multi-energy system is able to adjust its operating mode to anticipate the price variations in the energy grid and thereby increases the gross profit. Adding a thermal energy storage system decouples the consumption and production of heat, which enhances the NPV of the gross profit by an additional 1.4%.