Base Case Variable Operating Cost

The varying heat duties in the reboiler and in the lean MEA cooler with varying ΔTmin of the lean/rich heat exchanger in Table 10, Table 11, Table 12 and Table 13 have variable operating cost implications. An increase in reboiler heat consumption implies an increase in energy (steam) cost. Meanwhile, changes in the duty of the lean MEA cooler mean changes in both the amount of cooling water needed and electrical energy consumption for pumping of water, as the situation demands. Figure 4 shows that these variables which are influenced by the ΔTmin of the lean/rich heat exchanger are the most important variable cost drivers in both the NGCC power plant and cement plant flue gas CO₂ capture systems. At a ΔTmin of 10 °C, they account for 82% and 84% of the variable costs in the NGCC standard and lean vapour compression processes, respectively. Meanwhile, the energy cost accounts for 82% and 81% of the variable cost in the standard configuration and the lean vapour compression process, respectively, in the cement plant systems.

Since the PHEs have small channels, the pressure drop is higher than for the STHXs. Higher pumping duties by the rich pump and lean pump are incurred by the PHE system [3]. The allowable pressure drops in the tubes of the STHXs is between 0.5 and 0.7 bar [62]. According to [63,64], the allowable pressure drop is 1 bar. To account for the higher pumping pressure in the PHE system, the outlet pressure of the rich pump and lean pump were made 1 bar higher than when any STHX was selected for the lean/rich heat exchanger function.

Figure 5 shows the electricity consumption cost in both the STHX and the PHE systems for the NGCC power plant lean vapour compression. Figure 5 also shows that the two energy (steam and electricity) consumption costs slightly increase with an increase in the ΔTmin of the lean/rich heat exchanger. The cost of electricity consumption of the PHE system is about EUR 70,000 more than those of the processes with STHXs as the lean/rich heat exchanger.