Equipment Dimensioning and Assumptions

The absorption and desorption columns were dimensioned based on superficial gas velocity using the Souders–Brown equation with a k-factor of 0.15 m/s [44]. Structured packing was selected as advocated by [22] to reduce operating cost by reducing the pressure drop. A shell tangent-to-tangent height (TT) of 40 m was specified for both systems’ absorption columns to account for the water wash section, even though its details were not included in the study. The desorption columns’ shell tangent-to-tangent heights were also specified as 25 m.

The flue gas fans, pumps and compressors in both processes were sized based on their duties in kW and flow rates in m³/h, except the pumps in l/s. The values were obtained directly from the simulation.

The separators were dimensioned as vertical vessels; the vessel diameter was calculated using the Souders–Brown equation with a k-factor of 0.101 m/s [44,45]. A corrosion allowance of 0.001 m, joint efficiency of 80%, stress of 2.15 × 10⁸ Pa, and a tangent-to-tangent to diameter ration of 3, i.e., TT = 3Do [35,45] were specified. The direct contact cooler (DCC) unit was dimensioned in similar manner, with the shell tangent-to-tangent height specified to be 15 m and a 4 m packing height.

The reboiler, coolers and condenser were sized based on the required heat exchange area, as carried out for the main heat exchangers in the next section. All the cooling water inlet and outlet temperatures were specified to 15 °C and 25 °C, respectively, and were controlled using adjust functions. The overall heat transfer coefficients of 1200 W/m²·K and 1000 W/m²·K [35] were specified for the U-tube kettle-type reboiler and condenser (UT-STHX)m respectively. Meanwhile, 800 W/m²·K [35] and 1600 W/m²·K were used for the coolers with STHXs and PHE, respectively. The conditions of steam supplied to the reboiler were 145 °C and 4 bar, while it exited at 130 °C and 3.92 bar.