Pumps and compressors for supercritical extraction

The challenge for the high pressure engineer is to cope with the problems of sealing, fatigue, wear, installation and vibration which arise in each specific application. The solvents to be pumped in supercritical extraction plants show poor lubrication properties and therefore require special seals. The co-solvents which are sometimes used are hydrocarbon-based in many cases, so that leakage must be prevented to avoid pollution and the risk of explosion. 

Another problem is that, in the near-critical and supercritical region, the solvents must be regarded as somewhat compressible. Consequently pulsations can be excited if reciprocating pumps are used. 

The high pressures - up to 400 or even 600 bar - generate high stresses and strains in the liquid-containing parts combined with cyclic changes. This leads to fatigue. Special materials and techniques of design and manufacture are required to combat this. 

The principal solvent is usually CO2, though various organic entrainers or co-solvents such as CsHg, C4H10, C2H4, C3H6 and many others [7, 8, 9] may also be present. 

Supercritical extraction processes show similar requirements with regard to high pressure fluid machinery as do high pressure processes for reactions. However, since the principal solvent is usually CO2 the corrosion and erosion aspects are less demanding than is the case in reaction processing. Also the temperature will not usually be high since a limit to the allowable temperature is often set by the properties of the components and the required quality of the products. 

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Pumps and compressors for supercritical extraction design, characteristics and installation... 

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