Pressure swing absorption

Within such a plant, depending on the pressure of the syngas, the separation can be performed by chemical absorption (usually with amine solvents) under lower pressure conditions or by physical absorption (e.g., with methanol) under higher pressure conditions (see also Chapter 6). Likewise, pressure-swing absorption can be employed. With the special properties of hydrogen, membrane separation processes could also be a very promising solution for the separation task. 

The redox process (RP) development was eventnally abandoned as other technologies such as pressure swing absorption (PSA) and cryogenic separation began to dominate. In recent years there has been a renewed interest in developing the RP. 

The BYAS (Bypass Ammonia Synthesis) process can be used for economical expansion of existing ammonia synthesis plants. This process introduces additional natural gas at an intermediate stage in the process. The additional nitrogen in the air, which also has to be introduced, is removed by PSA (pressure swing absorption). The process was developed and offered by Humphreys and Glasgow in the UK1. 

X. Assumes Pressure Swing Absorption to obtain desired H 2 purity. ... 

Since Texaco syngas process was not being used to make ammonia, some of the steps would have to be modified to apply it to ammonia production. A CO Shift step might be needed upstream of the C02 Removal unit the membrane unit might be replaced by a Pressure-Swing Absorption (PSA) unit and a methanation unit might be needed to remove residual CO and C02. 

A Pressure Swing Absorption step to Replace the Conventional CQ Removal step, and... 

Fig. 7.14. The catalytic synthesis of hydrogen from natural gas using hydrodesulfurization, steam reforming, water gas shift, and pressure swing absorption (PSA).

Nitrogen production via PSA (pressure swing absorption) is based on the principle that nitrogen and oxygen have different absorption rates on carbon molecular sieves (CMS). Some of the nitrogen production processes that use this technology are described in References 1 and 3-6. 

The Haldor Topsoe Convection Reformer (HTCR) is a relatively small piece of equipment that combines the radiant and waste heat sections of the conventional reformer. It uses PSA (pressure swing absorption) to make 99.9 percent hydrogen purity. It is best for small and medium-sized hydrogen plants (500 to 10,000 Nm3/hr).75... 

There is a recent trend in refineries away from the first option and toward the second, because of the falling cost of hydrogen separation from gas mixtures via pressure-swing absorption. If the C02 from refinery production of hydrogen... 

Fig. 5a. Pressure swing absorption beds for the dehydration Fig. 5b. Packed bed used in adsorber, of alcohols (courtesy of Howe-Baker Engineers)...

As for a comparison of membrane gas separation technologies, such as pressure swing absorption (PSA) and low-temperature or cryogenic separations, the last chapter in (Paul and Yam-pol skii, 1994) must remain somewhat inconclusive, given the... 

Product purification. In a liquid absorption system, carbon dioxide is removed. The product gas undergoes a methanation step to remove the residual traces of carbon oxides. Recent SMR plants use a pressure swing absorption (PSA) unit instead, producing 99.99% pure hydrogen. 

The process then involves a water-gas shift step, which produces CO2 and H2. The CO2 and H2 gas streams are further separated using a pressure swing absorption (PSA) process. 

Separation technologies, such as pressure swing absorption, are commercially available, but would add complexity and cost. 

Depending on the downstream process (H2, CO, oxosynthesis, ammonia, etc.), the product gas goes to the different unit operations as described in the section Overview. In the case of hydrogen production, this usually involves a shift reactor and a pressure-swing-absorption reactor (PSA) (Fig. 4). For CO production, the scheme involves a CO2 removal section and a low temperature separation unit (so-called cold box). CO2 is recycled to the reformer. If in this case, H2 product is also desired, a PSA unit may also be present (Fig. 5). 

After scrubbing the exiting acidic gases, that is, CO and traces of H S, under pressure by an alkaline aqueous solution containing either diethanolamine or sodium carbonate, all the carbon dioxide and impurities are removed below acceptable levels for the final purification of the hydrogen gas. Usually, the final purification utilizes pressure swing absorption (PSA). 

Industrially, the above reaction is conducted at atmospheric pressure and at 800-900 C with nickel or iron catalysts. The hydrogen-rich gas mixture (i.e., 75 vol.% and 25 vol.% N ) that contains only traces of unreacted ammonia can be used as-is or purified by pressure swing absorption, or gas permeation through Pd-Ag membrane. 

---