Cryogenic separation

Clodic and Younes [11,12] have developed a cryogenic CO2 capture process, in which CO2 is desublimated as a solid onto surfaces of heat exchangers, which are cooled by 

In the following a process will be described that purifies krypton and xenon by means of cryogenic rectification in five columns. 

The feed gas is cooled before it is fed to the first column. It contains mostly oxygen with typical 4000 ppm of Kr and 400 ppm of Xe and additional impurities of hydrocarbons and greenhouse gases with concentrations below 1 ppm. 

In Column 1 oxygen and CH4 is separated to the top of the column, while Kr/Xe together with all other low volatile components collect in the bottom fraction. A strong enrichment of all low volatile components occurs in this bottom fraction. With the flows indicated in Fig. 3.2, the enrichment factor amounts to 3000/14 = 124. Column 2 splits krypton from xenon. Column 3 separates the less volatile components from krypton and isolates the latter as a pure product at the columrfs top. Column 4 segregates xenon from its less volatile companions and column 5 isolates xenon as pure sump product. 

The flow to the Xe-flne-purification column 5 is by about a factor 10 smaller than the flows involved with the columns of the air separation unit. The rectiflcation on such a small scale requires special solutions  

The Kr and Xe product obtained in the cryogenic plant is warmed up and stored and supplied to the consumers in cylinders at pressures of about 60 bar for Xe and about 140 bar for Kr. The pressure of a Xe-cylinder must be lower, because Xe is near its critical state = 289.8 K, = 58.4 bar). Thus when a Xe-cylinder is heated, its pressure will increase more than the pressure in a Kr-cyhnder (T rit = 209.4 K, P it = 55.0 bar). A preceding cleaning of the cylinders by evacuation and purging is necessary to obtain the product purities as specified in Table 3.4. 

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Nitrogen is used for pressure maintenance in oil and gas reservoirs for enhanced recovery. It is sometimes used as a miscible agent to reduce oil viscosity and increase recovery in deep reservoirs. Other appHcations include recovery of oil in attic formations, gas cap displacement, and a sweep gas for miscible CO2 slugs. Nitrogen competes with CO2, a more miscible gas with hydrocarbons (qv), in most of these appHcations. The production mode is typically by on-site cryogenic separation plants. In 1990, nitrogen production in enhanced recovery operations was 20 x 10 m /d (750 million SCF/d)... 

The dephlegmator process recovers a substantially higher purity C2+ hydrocarbon product with 50—75% lower methane content than the conventional partial condensation process. The C2+ product from the cryogenic separation process can be compressed and further separated in a de-ethanizer column to provide a high purity C3+ (LPG) product and a mixed ethylene—ethane product with 10—15% methane. Additional refrigeration for the deethanization process can be provided by a package Freon, propane or propylene refrigeration system. 

The process begins with a gasification process that converts coal into carbon monoxide and hydrogen. Part of this gas is sent to a water-gas shift reactor to increase its hydrogen content. The purified syngas is then cryogenically separated into a carbon monoxide feed for the acetic anhydride plant and a hydrogen-rich stream for the synthesis of methanol. 

Cryogenic separation, which can provide multiple pure products and is especially used for separation of pure carbon monoxide... 

Besides absorption processes, adsorption processes, cryogenic separation or membrane separation can be applied. Adsorption processes are based on the physical attachment and bonding of components from the gas mixture on the surface of solid sorbents. As with absorption a distinction can be made between physical and chemical adsorption the first one is referred to as pressure-swing adsorption (PSA), where... 

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. 

Most commercial oxygen at present is obtained from air by cryogenic separation processes. Although design of oxygen manufacturing plants and process conditions may vary depending on production capacity, purity desired, and cost, basic steps are similar. 

Usually, high-purity CO is manufactured on a large scale by means of costly cryogenic separation or absorption from syngas. The above approach could be attractive for small production. Also based on Equations 14 and 15, an easy source of oxogas (C0 H2 = 1 1) can be imagined. Indeed, we could demonstrate that methyl formate and methanol can be used to hydroformylate olefins in good yields and selectivities (37). 

As can be seen in Table III the Synthol process produces a large amount of C to C- hydrocarbons which are predominantly olefins. At Sasol tne C stream from the cryogenic separation unit is fed to a standard ethylene plant. The feed is first dried and then fractionated to remove the small amounts of C-. and C products. The C stream is then selectively hydrogenated to remove acetylene... 

Effect of vaporization equilibrium ratios, K, and enthalpies on cryogenic separations. 

Thus POLYBED PSA can be thought of as a process which alms for maximum recovery of the less-adsorbed component in very high purity at the expense of a complex flowsheet Its growing commercial acceptance suggests that it competes quite successfully with cryogenic separation in many cases ... 

The pressure swing separation of CH4/N2 is economically viable for small plant sizes, but cryogenic separation is more attractive at larger plant sizes. 

A comparison of the cost of oxygen-enriched air produced by membranes and by cryogenic separation shows that current membranes are generally uncompetitive. The only exception is for very small users in isolated locations, where the... 

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