Carbon Dioxide (CO2), one of the universal industrial gases, is mainly produced during the combustion of hydrocarbons also known as fossil fuels. Due to a growing demand for CO2 as a commercial product, it is captured and purified, for transport and beneficial uses at other locations. Among many different uses, refrigeration, and cooling, the casting of molds and oil extraction are few that utilizes the properties of CO2. In chemical industries, various technologies and processes are employed to separate CO2 from either the gas stream or liquid stream, which then can be further purified. This article discusses three different methods of separation of CO2 from the feed stream;
- CO2 Absorber
- CO2 Stripper
Pre-condenser is used to remove any impurities from the CO2 gas before it is sent to the absorption tower. The hot flue gas is cooled inside the quench tower. Gas with 96 % CO2, 1.3 % Ethanol, 0.03 % Acetaldehyde and rest water gets in contact with the liquid, which is mainly composed of H2O and at a temperature as low as 75 °F. With the help of process simulation and hydraulics calculation, the scrubber is designed to have a pressure drop across the packing of less than or equal to 0.25 psi. Also, the flooding is set to not exceed 70 % at design rates. The low-pressure drop characteristic of MACH’s Tri-Pack and careful design of the internals results in a lower flue gas temperature that enhances CO2 absorption in the absorber.
The absorber operates at atmospheric pressure and can be carried out with different solvents. Water was the first solvent to be used in this process but recently chemicals like Potassium Carbonate, Sodium Carbonate, and MEA are used to achieve high removal efficiency. The temperature at which CO2 is absorbed with a chemical solvent varies between 40 and 60 °C, depending on the solvent. To treat a process gas flow ranging between 7 to 8 CFM and composed of 40% CO2 and 20% CO, water can be used as a suitable solvent along with MACH’s 5/8’’ Rings in 304SS to generate a low-pressure drop across the packing and to achieve a 90% removal.FF
The most common use of a CO2 Stripper is to regenerate the solvent. If CO2 is being stripped out of the water, then it can be grouped with aeration and deaeration tower. The latter accompanies the addition of O2 into the water with the removal of CO2 in the same piece of equipment. A very common design that MACH comes across is the stripping of CO2 from Ethanol feed stream. An Ethanol feed stream at 250 °F, is first flashed into separate gas and liquid phases and then sent to the Stripper tower. A high-performance random packing such as 40 mm VSP in 304 SS is used for a low-pressure drop across the packing and greater mass transfer characteristics. Also, third generation random packings like VSP and Tri-pack allows a reduction in tower diameter and height compared to other random tower packings.