https://doi.org/10.3390/en15020425
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A 30 wt% monoethanolamine (MEA) process simulation for 90% CO2 capture from the two flue gases was performed in Aspen HYSYS Version 12. The lean amine stream entered the top of the absorber at 40 °C and at 1.013 bar. The reflux ratio in the desorber was 0.3. The first process for CO2 capture concerned exhaust gas from a natural gas combined-cycle (NGCC) power plant in Mongstad, close to Bergen in Norway. The second capture process concerned flue gas from Norcem Cement plant in Brevik in Norway.
The NGCC power plant exhaust gas and the cement plant’s flue gas specifications are given in Table 1 and Table 2, respectively. The simulation strategy was the same as in our previous works [34,35,37]. The absorber in the NGCC case was simulated with 17 packing stages (1 m per packing stage) with Murphree efficiencies of 11–21% from the bottom to top, as was carried out in [31,35]. The cement plant’s case absorption column was simulated with 29 packing stages (0.6 m per packing stage) with a constant Murphree efficiency of 15% based on [24]. Thus, the cement plant’s case absorption total packing height was 17.4 m. In both cases, the desorption column was simulated with 10 packing stages (1 m per packing stage) each and a constant Murphree efficiency of 50%. The desorber was maintained at 2 bar, and the reboiler temperature was specified as 120 °C. The minimum temperature approach of the lean/rich heat exchanger was 10 °C in the base case.
Table 1. NGCC power plant exhaust gas specification.
| Parameter | Value | Reference |
|---|---|---|
| CO2 mole% | 3.75 | [37] |
| H2O mole% | 6.71 | [37] |
| N2 mole% | 89.54 | Calculated |
| Molar flow rate, kmol/h | 85,000 | [37] |
| Flue gas temperature, °C | 80 | [35] |
| Flue gas pressure, kPa | 110 | [35] |
| Temperature of flue gas into absorber, °C | 40 | [34] |
| Pressure of flue gas into absorber, kPa | 121 | [31] |
Table 2. The cement plant flue gas specification.
| Parameter | Value | Reference |
|---|---|---|
| String 1 | ||
| CO2 mole% | 22 | [38] |
| O2 | 7 | [38] |
| H2O mole% | 9 | [38] |
| N2 mole% | 62 | [38] |
| Molar flow rate, kmol/h | 5785 | [38] |
| Flue gas temperature, °C | 80 | [3] |
| Flue gas pressure, kPa | 101.3 | [3] |
| Temperature of flue gas into absorber, °C | 40 | [31] |
| Pressure of flue gas into absorber, kPa | 121 | [31] |
| String 2 | ||
| CO2 mole% | 13 | [38] |
| O2 | 7 | [38] |
| H2O mole% | 10 | [38] |
| N2 mole% | 70 | [38] |
| Molar flow rate, kmol/h | 5682 | [38] |
| Flue gas temperature, °C | 80 | [3] |
| Flue gas pressure, kPa | 101.3 | [3] |
| Temperature of flue gas into absorber, °C | 40 | [31] |
| Pressure of flue gas into absorber, kPa | 121 | [31] |
The DCC section and compression section of both processes were modelled in the same way. The flue gas fan raised the flue gas pressure from 1.01 bar to 1.21 bar to cover for the pressure drop in the absorber. Each of the compression stages had a pressure ratio of 2.8. The inlet pressure of the first stage was at 1.5 bar, and the final compression pressure was 75.9 bar. With the aid of the intercoolers, the temperature of the CO2 stream was maintained at the supercritical temperature of 31 °C. The CO2 streams, each having a purity of 99.74%, were then pressurised to 110 bar, as carried out by [39].
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