Dual-pump CO2 Extraction Systems
The dual-pump system was designed and patented by a company called Critical Fluid Solutions in the 1980’s. Several variations of this design were used by various manufacturers of CO2 extraction equipment for many years. Ultimately the design was rejected by all major companies because of the vaporized terpenes which pass into the gas booster pump, shredding it and leading to constant maintenance issues.
In a curious development, several new startup CO2 extractor companies catering to the cannabis industry have revived this design in the last couple years. Touting it as a radical new invention, these companies have managed to convince many innocent investors that this is the best way to extract botanical oils with CO2.
The dual-pump concept is an awkward combination of liquid pumping and gas booster vapor recovery. A liquid pump pushes the CO2 through the extraction vessel just like a conventional liquid design. As the oil-saturated CO2 depressurizes and extracts the oil in the separator, the vapor then exits the separator and enters the gas booster just like in a conventional gas booster extractor. The booster compresses it back to liquid so it is ready to enter the inlet of the liquid pump. The compression and liquefaction of the CO2 is usually assisted by a chiller.
The False Benefits of Dual-pump Systems
On Stability. Both booster and liquid systems will operate with complete stability if engineered and operated properly.
On Temperature. It is true that the separators can be operated at lower temperatures - but this will have no effect on the extracted product in a properly designed system. A liquid system may have an outside heating jacket set at 140F, but the interior, extracted oil is sitting in a pool of cool, liquid CO2 in the bottom of the separator. Liquids can only be heated to their boiling point. More heat only makes them boil faster. So in a typical liquid system separator where the pressure is 900 psi and the temperature of the heating jacket is 140F, the boiling CO2 pool is only approx 60F. This is not a temperature that will overheat anything.
Some liquid designs on the market use separators which are too small and have too much heat on them. This results in a system lacking a pool of liquid CO2 in the bottom of the separator resulting in burnt oil.
On Energy Dual-pump systems use less energy than a liquid system to condense the CO2 vapor back to liquid. This minor advantage, however is greatly outweighed by the disadvantages and the related expenses of a dual-pump design.
The Problems with Dual-pump Systems
The pump is always the weak link in any system in which it is required. Pumps are far more likely to break than other parts within any piece of equipment. Having two pumps doubles the chances of equipment breakdown.
If there is a fluctuation in voltage the system’s stability is compromised. The two pumps must be kept in perfect flow rate balance meaning the liquid pump and the booster pump must be moving CO2 at the same rate. Voltage fluctuations will throw this rhythm off. Furthermore, the gas booster pump within this design is prone to the same problems as a single booster design as mentioned previously.