## 2 Experimental  
### Test Rig Setup  
Figures 1 and 2 show an absorber test rig that was constructed at the Technical University of Darmstadt. The absorber test rig consists of four main parts: an absorber column, a regeneration unit, a gas mixing unit, and a gas analysis unit. The absorber consists of a glass column with an inner diameter of 152 mm and a height of 1500 mm. The upper and lower parts of the column were closed by suitable metal flanges. The lower flange contains the outlet of the liquid and the upper flange contains the outlet of the gas. The column has 12 glass nozzles to which metal flanges can be connected, 10 nozzles of which are used to measure the temperatures and pressures in the absorber, and 2 nozzles for the entrance of the liquid and gas into the absorber. Figure 3 shows a cross section of the sieve tray used in the absorber, five sieve trays are fixed with threaded rods and inserted into the absorber. The diameter of the sieve tray is 150 mm, the space between the sieve tray and the glass wall is sealed with rubber seals. The percentage of the sieve holes area in the active area is 0.071, the diameter of the hole in the sieve tray is 2 mm, the vertical and horizontal pitch between the holes is 6 mm, and the height of the weir is 15 mm. The tray spacing is 240 mm. The mixing unit consists of two lines connected to a manifold in front of the absorber. One of the lines is connected to cylinders filled with CO\({}_{2}\) gas, while the other is connected to an air compressor. The MFC is used to control the flow rate of the gases introduced into the absorber. A gas analyser is connected to the gas outlet line to measure the volume fraction of CO\({}_{2}\) at the outlet of the absorber.  
Figure 1: Side view of the absorber test rig: 1, absorber column; 2, control panel; 3, Coriolis device; 4, pressure difference transmitter; 5, make-up pump; 6, liquid level control valve; 7, recycling pump; 8, re-boiler; 9, packed column; 10, gas outlet; 11, pressure control valve; 12, gas analysis unit.  
The regeneration unit is used to regenerate the absorbent and recycle it to the absorber as a lean absorbent. It consists of a packed column, a reboiler, two heat exchangers, a recycle pump and a make-up pump. The packed column was made of a glass column with a height of 1300 mm and a diameter of 152 mm. The packed column is filled with a metallic packing of the Pall-Ring 15 mm type with a specific surface area of 360 m\({}^{2}\)/m\({}^{3}\) and a free  
Figure 3: A cross-section of the sieve tray used in the absorber.  
Figure 2: Schematic diagram of the absorber test rig.  
volume of 95%. The height of the packed column is 1 m. The rich absorbent enters the packed column through a liquid distributor to uniformly distribute the absorbent over the top of the packed column. The shaped liquid distributor is of spray type, which contains 13 holes uniformly arranged on the liquid distributor. The packed column is installed on the reboiler, a heating coil with a heating capacity of 4.5 kW was inserted into the reboiler to heat and regenerate the absorbent. A circulation pump is connected to the reboiler, which draws the water from the reboiler and pumps it into the absorber. The lean hot absorbent is cooled by two heat exchangers. In the first heat exchanger, the lean hot absorbent is precooled by heat exchange with the absorbent leaving the absorber, while in a second heat exchanger the precooled absorbent is cooled by heat exchange with cold water.