The three most important components of a supercritical CO2 extraction machine are the extraction vessel, CO2 high-pressure pump, and control system. In this article, we will discuss what needs to be considered during the design and manufacture of CO2 extraction machines.
CO2 Extraction Vessels
The supercritical CO2 extraction process is mostly a semi-batch operation. The extracted biomass is loaded into the extraction container at one time, and the supercritical CO2 fluid is continuously fed. The biomass in the extraction container needs to be replaced frequently, and the extraction container also needs to be opened frequently for cleaning, that is, high pressure The extraction vessel must be opened and closed frequently. In order to facilitate the operation and shorten the intermittent time, the extraction vessel should adopt a quick-opening structure.
Filter Device of Biomass Load Basket
There are many differences between industrial CO2 extraction machines and small CO2 extraction machines used in laboratories. One of them is that industrial production pays special attention to efficiency, requiring less downtime and continuous production. One of the reasons why the supercritical CO2 extraction equipment cannot operate continuously is clogging, but if a multi-functional filter device is installed at the inlet and outlet of the extraction vessel and the upper and lower parts of the biomass load basket, it can not only effectively prevent the biomass from entering the pipeline and cause clogging, but also improve the CO2 fluid. The condition of entering and exiting the extraction vessel can avoid channeling and improve mass transfer efficiency.
Note: During our actual CO2 fluid extraction process, filter paper is usually used. Method: Cut the filter paper into a size suitable for the diameter of the container, and pad it on the upper and lower inlet and outlet ports of the container. When extracting essential oils, we tried to use a layer of medical cotton pad under the filter paper to enhance the filtering effect.
CO2 high-pressure pump
The function of the high-pressure pump is to deliver high-pressure CO2 fluid. fluid and adjust the flow rate. To realize the CO2 extraction process, it is required that the pressure is stable, the pulse is small, and the step-less speed regulation can be realized according to the production needs. Because supercritical CO2 fluid has strong dissolving and permeation ability, a special CO2 high-pressure pump must be used. If an ordinary plunger high-pressure pump is used, the following structural modifications are required:
Three Improvement Measures
- Improvement measures 1# – Pump head cooling system: A cooling water system should be added outside the pump head to effectively ensure that the conveying medium does not vaporize, otherwise the normal operation of the pump cannot be guaranteed and the purpose of boosting cannot be achieved.
- Improvement measures 2# – Sealing gasket: Generally, the sealing gasket of the plunger CO2 high-pressure pump is oil-resistant rubber or polytetrafluoroethylene. In the case that the extracted product contains oil, the supercritical CO2 fluid will also contain a small amount of oil, due to CO2 under high pressure. It has strong permeability, which makes the oil-resistant rubber expand quickly. PTFE is easily damaged by fluid cutting under high pressure and leaks, and the phenomenon of non-pressurization occurs. Therefore, the sealing gasket must be made of metal material.
- Improvement measures 3# – Plunger pump packing: The packing of an ordinary plunger pump is graphite and PTFE, the applicable medium is water, and the medium used is changed to supercritical CO2, which is easy to causes the deterioration of sealing performance and leakage, so use high carbon fiber And metal filler, can better meet the requirements.
Automatic Control System for CO2 Extraction
The control system of supercritical CO2 extraction must follow the principles of practicality, practicality, and effectiveness.
4 automatic control requirements
- Automatic Control Requirements 1# – Automatic Pressure Regulating: Use an automatic pressure regulating valve to achieve automatic pressure control.
- Automatic control requires 2# automatic temperature adjustment: use reliable solenoid valves, thermocouples, etc. to realize automatic adjustment of process temperature.
- Automatic control requires 3# to automatically control the flow of CO2 fluid: realize automatic control of the pressure and speed of the high-pressure pump to control the flow of CO2 fluid and realize overpressure protection of the extraction container and the high-pressure pump.
- Automatic control requires 4# automatic alarm: According to the requirements of the CO2 extraction process, realize the automatic alarm of shutdown, start-up, and failure of the refrigeration process, etc., to achieve the purpose of energy saving and safe operation.
The supercritical CO2 extraction process has high operating pressure, and safety factors such as production, maintenance, and explosion-proof must be fully considered, and accidents must be strictly prevented to avoid component explosions. A pressure gauge with good performance and a matching safety valve must be used, and the high-pressure pump must be protected against overpressure. When the process pressure exceeds the specified pressure, the high-pressure pump must be able to automatically stop running.
For high-pressure equipment such as extraction containers and separation containers, corresponding safety measures should be taken according to different working pressures. For example, a manual vent valve should be set for each CO2 extraction container. Before opening the CO2 extraction container, the valve must be used to reduce the pressure in the container to 0. For CO2 condensers, an explosion-proof membrane should be installed.
Note: In practical applications, the CO2 extraction vessel will have 3 explosion-proof pressure points.