The supercritical CO2 fluid extraction device mainly includes three parts: pretreatment equipment, extraction equipment, and separation equipment.
Four main equipment of supercritical extraction plant
The main equipment (static equipment) used in the supercritical CO2 fluid extraction device includes: heat exchanger, extraction kettle, separation kettle, storage tank, etc.
Heat exchangers are widely used in chemical production. According to different heat transfer methods, they can be divided into partition wall heat exchangers, direct heat exchangers and regenerative heat exchangers. The direct contact heat exchanger is a direct contact between two fluids (cold and hot) after entering the heat exchanger to transfer heat and have high heat transfer efficiency, but its use is limited and it is only suitable for occasions where the two fluids are allowed to mix. The regenerative heat exchanger is a space (regenerator) filled with regenerators.
Two fluids with different temperatures pass through the regenerators alternately to achieve indirect heat transfer. This heat transfer method is inefficient and requires two The fluids are allowed to mix. The most widely used in chemical production is the partition wall heat exchanger, which refers to the heat transfer between two fluids with different temperatures through the wall (tube wall) through which the fluid flows, and the two fluids do not contact each other.
This method of heat transfer is most suitable for chemical production. According to the shape of the partition wall, the partition wall heat exchanger can be divided into a shell-and-tube heat exchanger for heat transfer on the tube wall and a plate heat exchanger for heat transfer on the plate wall.
The main function of the heat exchanger in the supercritical CO2 fluid extraction process is to make the fluid and the extraction material reach the operating temperature before entering the extraction tank, and raise the temperature before entering the separator to facilitate separation.
The extraction kettle is one of the key equipment in the supercritical CO2 fluid extraction device. According to the different extraction process and feeding method, it can be divided into continuous countercurrent extraction and batch operation extraction kettle. At present, for liquid materials, continuous countercurrent extraction equipment is generally used, which has the advantages of simple operation, good material contact, and easy temperature control. For solid materials, batch extraction equipment is mostly used, because solid materials are not easy to achieve continuous operation.
At present, the design and manufacturing capacity of domestic supercritical fluid extraction energy is very low, and most of the small production devices are produced domestically, but the large supercritical fluid extraction devices of more than 500L are usually imported from abroad, because domestically produced large devices are not technically The level is still lower than that of foreign devices in terms of production quality and so on.
Because the structure design of the extraction kettle directly affects the production cost and product quality, many manufacturers at home and abroad are actively researching new extraction kettles with more reasonable structures. The supercritical extraction kettle designed by German Uhde company, its top cover and bottom head adopt automatic quick-opening device, which is very convenient for material loading and unloading.
At present, the volume of the extraction kettle produced by the company can reach more than 3800L. The multi-layer cylinder extraction kettle designed in Japan adopts an inner wall heating and cooling structure, that is, there are many longitudinal grooves on the inner wall of the cylinder, and circulating water is introduced into it, which can make temperature control easier.
In China, such as Xiangdong Chemical Machinery Factory has produced a supercritical fluid extraction kettle with a design pressure of 42Mpa and an inner diameter of 500mm. Jacket to ensure the stability of the extraction temperature during operation
The supercritical fluid carrying a large amount of solute coming out from the top of the extraction tank first enters the heat exchanger, the temperature of the supercritical fluid rises, and the pressure further decreases after reaching the separation tank, the solubility of the supercritical fluid decreases rapidly, and a large amount of solute is transferred from the supercritical fluid to the separation tank. It is released from the critical fluid and flows out from the bottom of the separation tank. Therefore, the role of the separation tank is to effectively separate the extract and the extractant.
Storage tanks are essential in the supercritical CO2 fluid extraction process. According to their uses, they mainly include storage containers, metering containers, reflux containers, intermediate turnover containers, buffer containers, and mixing containers.
The main purpose of the buffer container is to accumulate a certain amount of substances, so as to ensure the stability of the flow operation in the process flow. Therefore, the extraction agent, entrainer, and liquid materials need to enter the buffer after pretreatment. In supercritical fluid extraction, a mixing vessel is sometimes required, such as the mixing of the extractant and the entrainer before entering the extraction tank.