One of the most overlooked aspect of any extraction system is the CO2 supply. It’s generally provided as a single CO2 cylinder, manifolded cylinder bank (12 -16 bottles manifolded) or by bulk storage (≥500 L @ 20 bar). The type of delivery depends on the size of the system and the ultimate flow rate you require.
Most systems use compression pumps that require CO2 in the liquid phase (55 bar) and compress this to the desired pressure needed for the extraction.
The most common problem found by customers is that “the pressure does not increase in the extractor” which is usually related to the CO2 feed.
As we consume the CO2 the pressure begins to drop, resulting in a phase change from liquid to gas. At this point, it is worth considering what is happening to the density.
As with performing an extraction, temperature also plays an important factor (see part2). To simplify this, consider the CO2 is maintained at a constant 15 °C within the CO2 bottle. Below is a table of density as the pressure in the bottle begins to drop:
| Pressure (bar) | Temperature (°C) | Density (kg/m3) | Phase |
| 55 | 15 | 826 | Liquid |
| 54 | 15 | 825 | Liquid |
| 53 | 15 | 823 | Liquid |
| 52 | 15 | 822 | Liquid |
| 51 | 15 | 821 | Liquid |
| 50 | 15 | 167 | Gas |
As demonstrated above a small drop in pressure of 5 bar results in a phase change from a liquid to a gas and a significant drop in density. Most pump manufacturers quote flow rates at a density of 1000 kg/m3, density of water. A pump that is quoted at 500g/min trying to compress a gas with a density of 167 kg/m3 is now only working at 16 % efficiency assuming it can compress it at all!
One of the best tools for this type of diagnosis is the addition of a flow meter to monitor the incoming CO2 supply. Although its not required to run an extraction system the amount of process data it can provide is invaluable.
At Core separations we believe in collecting and analysing as much data as possible.
To enhance this process, we need a reliable flow meter which assists us in collecting this data. Bronkhurst is a worldwide leader is mass flow measurements offering a variety of Coriolis flow meters at different flows. Using these flow meters, we can observe the in-coming CO2 densities in real time into the system which helps us quickly diagnose problems with the incoming CO2 supply, either on site or remotely. We look for solutions to help our customers deliver their requirements and we would be happy to discuss this further with you.
Please get in touch if you want to talk to us further about how we can assist you with CO2 extraction system.