https://doi.org/10.3390/en15020425
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A more appropriate way to present performance may not be in absolute values but in percentages. Therefore, the cost reduction potential of the systems was assessed on percentage basis. However, in comparisons here and in subsequent sections where cost saving potentials are reported, all comparison is made with the reference case. The reference case is the case of using FTS-STHX as the lean/rich heat exchanger with a “ΔTmin of 10 °C”, and for the lean MEA cooler and DCC cooler. This means all other ΔTmin trade-off analyses of the FTS-STHX are compared with FTS-STHX of ΔTmin of 10 °C to show if there is cost reduction potential at other ΔTmin with the same heat exchanger type. All ΔTmin trade-off analyses of the other specific types of heat exchanger cases were also all compared with the reference case, FTS-STHX of ΔTmin of 10 °C. The results are presented in Figure 11 and Figure 12 using curves to concisely give overviews of the performance of utilising each specific type of heat exchanger at different ΔTmin as well as the impact of choosing the lean vapour compression CO2 capture process.
Figure 11. Cost reduction analysis at different ΔTmin for different heat exchanger types compared with FTS–STHX of ΔTmin = 10 °C in the NGCC power plant capture process.
Figure 12. Cost reduction analysis at different ΔTmin for different heat exchanger types compared with FTS–STHX of ΔTmin=10 °C in the cement plant capture process..
In the NGCC power plant standard CO2 capture system, despite the significant energy demand reduction in the LVC process, the standard PHE system dominated over the lean vapour compression processes of the FTS-STHX and FH-STHX at ΔTmin of 5 °C and 6 °C. It also competes with the lean vapour compression process of the UT-STHX at 5 °C. The cost optimum ΔTmin (5 °C) of the PHE standard process achieved 4.7% cost reduction, while it was 9.6% for the lean vapour compression PHE process. This implies the lean vapour compression doubles the performance of the cost optimum PHE over the reference case. All the STHXs cases achieved significant cost reduction at all ΔTmin in the lean vapour compression CO2 capture process.
In the cement plant flue gas treatment, the PHE system reached cost savings of 5% and 11.6% in the standard and lean vapour compression CO2 capture configurations, respectively. In both industrial flue gases treatments, the most robust FH-STHX process was not economically viable at all ΔTmin in the standard capture processes. The FTS-STHX process could only realise very marginal cost savings between ΔTmin of 11 °C (0.04%) and 14 °C (0.2%), with a maximum of 0.3% at the optimum ΔTmin of 12 °C, in the NGCC power plant standard capture process. The standard UT-STHX process only achieved a maximum of 1%. The results revealed that while the lean vapour compression process achieves very good cost reduction for all specific types of heat exchanger studied, using the PHE as the lean/rich heat exchanger, lean MEA cooler and as cooler for the DCC circulation water dominates as the best choice for CO2 capture cost reduction, irrespective of its higher pumping cost requirement. With PHE, we can take advantage of the considerable energy reduction at lower ΔTmin. Since steam is usually the major cost driver, operating at lower ΔTmin between 4 °C and 7 °C and using PHE will provide the possibility of significant cost reductions.
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