Oscillating displacement pumps for extraction with Carbon Dioxide

Carbon dioxide is used particularly in the food, beverage, cosmetics and pharmaceutical industry for extracting natural substances, aromas, fats, oils, waxes, polymers, enzymes and colourants in their supercritical physical state. For despite its bad reputation as a greenhouse gas, CO2 is a natural and environmentally-friendly solvent which has advantages over synthetic and harmful media such as n-hexane when it comes to sustainability.

Oscillating displacement pumps are ideal for supercritical CO2 extraction.

In recent years, the pressure in extraction processes increased from approx. 300 bar to approx. 1,000 bar. This leads to a reduced processing time, allowing more efficient ingredients to be produced in a gentler manner. This makes commercial use overall more economically efficient and more effective. The current general trend among consumers towards biological products supports this development.

One classic application of this process is beer brewing: The selective extraction of alpha and beta acids changes the spectrum of bitter substances in the naturally grown hops according to the desired flavour. This type of “beverage design” can influence how aromatic, mild or bitter a beer tastes. The resulting flexibility allows breweries to adapt to consumer trends and to manufacture healthy products which are tailored to customer requirements.

Furthermore, in medicine there is also a growing focus on sensitive substances from naturopathy. Ever more intelligent and finely-tuned processes are being developed and used for extracting these substances for preventive medicine or therapeutics. In the same way, natural cosmetics, which are becoming increasingly popular among consumers, contain a variety of different allergens which have to be extracted from the substances.

Challenge for CO2 high pressure pump technology

CO2 has to be constantly kept in a liquid state through precise monitoring of the process parameters to prevent cavitation damage in the pump. Poor lubrication properties and the high compressibility of liquid CO2 require specially developed pumps with a high level of process reliability. The power end has to be able to withstand the rod forces resulting from the high suction pressure and optimum lubrication of the bearing points has to be ensured. At the same time, pressure increases up to 1,000 bar create a correspondingly higher temperature increase: This requires effective cooling of the fluid section with cooling channels in the stuffing boxes and valve blocks. As some components cannot be cooled directly, it is important to adapt the materials and the design so that as little as possible of the generated compression heat is absorbed. Because the CO2 is alternately subjected to compression and expansion, it is necessary to minimise or avoid the temperature rise and the resulting losses.

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