Pressure swing adsorption plant

Figure 4. Schematic of nitrogen pressure swing adsorption plant.

The adsorbents usually have a long lifetime. The impurities are adsorbed at high partial pressure. Then the adsorber is depressurised in two steps firstly, co-current to the adsorption process down to a medium pressure level, followed by counter-current depressurisation to the low pressure level of the desorption step. While a minimum of two adsorbers is required to run the process, industrial pressure swing adsorption plants consist of up to 12 adsorbers and along with the number of valves required, this makes the systems complicated [421]. 

Pressure Swing Adsorption. Carbon dioxide can be removed by pressure adsorption on molecular sieves. However, the molecular sieves are not selective to CO2, and the gases must be further processed to achieve the high purity required for "over the fence" use as in the urea process. Use of pressure swing adsorption for CO2 removal appears most appHcable to small, stand-alone plants (29). 

In most hydrogen plants, a pressure-swing adsorption (PSA) system is used for hydrogen purification. In these plants, a major portion of reformer fuel is PSA offgas with a hydrocarbon stream for makeup fuel. 

The pressure at the outlet of the pressure-swing adsorption (PSA) plant is 1.5 MPa. The specific electricity requirement for the compression from 1.5 to 88 MPa at the compressed gaseous hydrogen (CGH2) filling station (required for 70 MPa on-board vehicle storage) amounts to about 0.077 MJei/MJ of CGH2. 

The gas is then cooled to 30-50 °C and the carbon dioxide is removed by amine absorption or other processes. The remaining impurities - carbon monoxide, methane, nitrogen, argon - are removed in a final pressure-swing adsorption (PSA) step to yield >99.5% pure hydrogen. One of the main problems with this process is that the carbon dioxide is removed by the amine unit as a low-pressure gas. This gas must be compressed to 80 bar to be pipelined for sequestration. This compression step alone requires massive compressors and uses 4—5% of the total power output of the plant. The amine treatment step itself uses even more energy, so the total energy consumption is 15% of the power produced by the plant. 

Air Products and Chemicals, Inc. has been selected to supply a hydrocarbon and nitrogen recovery system for a new polyethylene manufacturing plant in Baytown, TX. The plant will be owned by Chevron Phillips Chemical Company and Solvay Polymers, Inc. The recovery system uses partial condensation in conjunction with Air Products pressure swing adsorption technology to recover hydrocarbons in the polyolefin plants, and recycle nitrogen with a purity of greater than 99%55. 

In modern plants, a Pressure Swing Adsorption (PSA) unit replaces the complete LTS, the CO2 stripping section and the final purification. 

Of course, use of Pressure Swing Adsorption for C02 removal would produce equivalent ultra-high purity hydrogen from either SGP or SMR-based plants. 

Oxygen can be supplied from an air separation plant, as well as from the cost-effective pressure swing adsorption (PSA) process. The Vinnolit oxychlorination process is also able to handle ethylene and/or anhydrous HCI containing vent streams from direct chlorination, acetaldehyde, monochloroacetic acid and other processes. 

We have synthesized carbon materials from hydrolysis lignin and tested them in the separation of gaseous mixtures He-CR. The a orbents show a helium concentration capacity of up to He no 95-99 %vol. They appear proved to be promising for application in the pressure swing adsorption (PSA) plants for Hj h He concentration. 

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