Capture of CO2 using a lab-scale bubble-column scrubber

The experimental device used is shown in Figure 4. The inside diameter of the column is 5 cm and the gas distributor is a perforated plate designed with four holes per square centimeter and each hole is 1 mm in diameter. Initially, a known amount of aqueous ammonia solution (14%) is introduced into the column, into which a pH electrode is inserted. The solution is adjusted to the desired pH value by adding a known concentration of aqueous solution (28%). The experiment starts when the mixed N₂–CO₂ gas, in the range of 15–60% CO₂ gas, begins bubbling through the column. The gas flow rates are in the range of 3 to 5 L/min. A gas heater and circulating cooling water tank are used to control the gas and solution temperatures. The mixed gas is delivered to the heater, which maintains the inlet gas temperature at 55 °C. The operating pH value is in the range of 9.5–11.5. The temperature in the bubble column is maintained at 25–60 °C by a water cooling system (Deng Yng, D-620, New Taipei, Taiwan). The operating time is 5–7 h, depending on the operating conditions. During the operation, the pH of the solution is decreased due to absorption in the scrubber. In order to hold the pH value of the solution at a desired value during operation, an aqueous ammonia solution is introduced into the column through the action of a pH controller (Suntex, PC-310, New Taipei, Taiwan). The overflow solution automatically flows out to the reservoir. The volume of added solution is recorded every ten minutes during the operation. A digital gauge pressure meter measures the inlet gas pressure. A CO₂ gas meter (Guardian Plus, D600, Hartford, USA) is used to measure the concentration of the CO₂ gas at the outlet of the bubble column (y₂). When the concentration of CO₂ gas changes to a steady state, the solutions are withdrawn using a syringe to measure the total dissolved CO₂ in the solution. At the end of the operation, the solution is poured into a vessel and the volume of the solution (V_L) is measured. In addition, the slurry solution is separated using a filter. The crystal size distribution is measured by a particle size analyzer (Galai, CIS-50, Or Akiva, Israel). The crystals obtained are characterized by X-ray (Rigaku, D/MAX-2200/PC, Tokyo, Japan), FESEM (Jeol, JSM-6500F, Tokyo, Japan) and EA (Thermo, Flash EA1112, Cambridge, UK ), respectively. A total of twenty runs are carried out in this work. The operating conditions and physical properties of ABC are, as shown in Table 3.