Environmental performance of ammonia based CO2 capture

The values of the impact indicators quantify the emissions from the two stages of the fuel life cycle, namely extraction, processing, transport (stage 1) and combustion (stage 2). For ADP, only the mass of fuel from the extraction step was taken into account.
Table 7 presents the results for the impact indicators for the functional unit considered (1 MWh of electricity).
Table 7. Values of impact indicators relative to 1 MWh.
Impact Indicator Case 1 Case 2 Case 3 Case 4 Case 5 Case 6
ADP, kg_Sb_eq/MWh 3.71 5.93 4.93 4.75 4.51 5.31
GWP, kg_CO2_eq/MWh 823.83 149.15 123.91 119.44 113.37 133.42
EP, kg_PO43−_eq/MWh 0.55 2.25 4.62 6.89 23.94 0.78
AP, kg_SO2_eq/MWh 8.02 14.18 14.54 16.45 33.01 11.46
POCP, kg_C2H4_eq/MW 0.35 0.56 0.47 0.45 0.43 0.50
HTP, kg_1.4DCB_eq/MWh 5.53 8.83 7.34 7.07 6.71 7.90
The ADP indicator increased compared to the baseline scenario (steam power plant without CO2 capture technology) for all variants where the CO2 capture process was integrated. If ammonia was used, the highest increase in the ADP indicator was recorded for a mass concentration of 2%, since in this case, the amount of heat required for regeneration was the highest, and therefore, a greater amount of fuel was used to produce electricity. When comparing the process of chemical absorption using NH3 with the MEA process at 30% mass concentration, it should be noted that for MEA, the ADP indicator was the highest, with an increase of 24.3% over the baseline.
In terms of GWP, the highest value was obtained for the case without CAP, since the other cases included CO2 capture process, and thus reduced CO2 emissions by 90% at the combustion stage. For CO2 capture, the GWP values did not differ significantly, ranging from 149 to 134 kg_CO2_eq/MWh, with a decrease of between 85% and 89% of this life cycle indicator. For this indicator alone, the percentage of emissions in the combustion phase that contributed to the total value was 87.43% while the remaining 12.57% represented the emissions from the extraction, processing, and transport stages. For the other indicators, the combustion stage emissions had a percentage greater than 96%.
The results obtained for EP shows that the increases are significant for this indicator during the integration of the chemical absorption process NH3, as the amount of ammonia lost in the CO2 capture process is taken into account based. Compared to the case without CCS, for a mass concentration of NH3 = 2%, there was an increase of 206.6%; for a mass concentration of NH3 = 5%, an increase of 579.7%; for a mass concentration of 7%, an increase of 924.3%; and an increase of 3533.2% for a mass concentration of 15%. All this indicates that in terms of this indicator, the NH3 capture process is less advantageous compared to the MEA capture process, with only a 24.3% increase in EP compared to power generation without carbon dioxide capture technology.
For the AP indicator, as for the EP indicator, a significant increase was noted in all cases of ammonia. However, in this case, such large increases were no longer present, as SO2 emissions were also taken into account. Thus, the percentage increases varied between 24.3 and 243.9%, with the highest value for NH3 = 15 wt.%, and the lower value for MEA = 30 wt.%.
In the case of the POCP impact class, it should be noted that the highest value was obtained with MEA, because in this case, a greater amount of fuel was used to provide the necessary heat to the chemical solvent regeneration, while the lowest value was obtained when NH3 was used at a mass concentration of 15%. The same variations were observed for the HTP impact class as for the POCP impact class. Compared to the variant without CAP, both for POCP and HTP, there was a 24.3% increase in MEA, while in NH3 = 15 wt.%, there was an increase of 1.5%.

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