In the field of gas separation and purification, with the strengthening of environmental protection, coupled with the current demand for carbon neutrality, CO2 capture, absorption of harmful gases, and reduction of pollutant emissions have become more and more important issues. At the same time, along with the transformation and upgrading of our manufacturing industry, the demand of high purity gas further expands. Gas separation and purification technologies include low temperature distillation, adsorption and diffusion. We will introduce the two most common and similar processes of adsorption, namely pressure swing adsorption (PSA) and variable temperature adsorption (TSA).
Pressure swing adsorption (PSA) main principle is based on the differences in the adsorption characteristics of gas components in solid materials and the characteristics of adsorption volume changes with pressure, using the of periodic pressure transformation to complete the gas separation and purification. Variable-temperature adsorption (TSA) also takes advantage of the differences in the adsorption performance of gas components on solid materials, but the difference is that the adsorption capacity will be affected by temperature changes, and using of periodic variable-temperature to achieve gas separation and purification.
Pressure swing adsorption is widely used in carbon capture, hydrogen and oxygen production, nitrogen methyl separation, air separation, NOx removal and other fields. Because the pressure can be changed quickly, the cycle of pressure swing adsorption is generally short, which may complete a cycle in a few minutes. And variable temperature adsorption is mainly used in carbon capture, VOCs purification, gas drying and other fields, limited by the heat transfer rate of the system, heating and cooling time is long, variable temperature adsorption cycle will be relatively long, sometimes can reach more than ten hours, so how to achieve rapid heating and cooling is also one of the directions of variable temperature adsorption research. Due to the difference in operation cycle time, in order to be applied in continuous processes, PSA often requires multiple towers in parallel, and 4-8 towers are common parallel numbers (the shorter the operation cycle, the more parallel numbers). As the period of variable temperature adsorption is longer, two columns are generally used for variable temperature adsorption.
The most commonly used adsorbents for variable temperature adsorption and pressure swing adsorption are molecular sieve, activated carbon, silica gel, alumina, etc., because of its large specific surface area, it is necessary to select the appropriate adsorbent according to the needs of the separation system. Pressurization adsorption and atmospheric pressure desorption are the characteristics of pressure swing adsorption. The pressure of pressurization adsorption can reach several MPa. The operating temperature of variable temperature adsorption is generally near room temperature, and the temperature of heating desorption may reach more than 150℃.
In order to improve efficiency and reduce energy consumption, vacuum pressure swing adsorption (VPSA) and vacuum temperature swing adsorption (TVSA) technologies are derived from PSA and PSA. This process is more complex and expensive, making it suitable for large-scale gas processing. Vacuum swing adsorption is adsorption at atmospheric pressure and desorption by pumping vacuum. Similarly, vacuumizing during desorption process can also reduce the desorption temperature and improve desorption efficiency, which will be conducive to the utilization of low-grade heat in the process of vacuum variable temperature adsorption.
Post time: Feb-05-2022