Two types of supercritical CO2 fractionation columns
The supercritical CO2 fractionation column purifies substances by using the difference in volatilities of the components in the liquid mixture. In the fractionation column, the liquid flows from top to bottom by gravity, while the gas flows counter to the liquid from bottom to top by pressure difference. The good contact of the two-phase fluid is formed by the column plate or packing installed in the fractionation column. Therefore, the fractionation column can be divided into a plate fractionation column and a packing fractionation column according to the internal structure.
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The structure of the fractionation column equipment determines the fluid dynamics and mass transfer performance of its operation to a certain extent. The plate fractionation column and the packed fractionation column have their own characteristics:
Plate fractionation column
A certain number of trays are installed in the plate fractionation column, and the gas passes through the liquid layer on the fractionation column plate in the form of a bubbling jet from the bottom of the fractionation column to make the two phases contact and carry out mass transfer; the component concentration of the two phases increases along the height. Changes in steps.
Packed fractionation column
The packed fractionation column is equipped with a certain height of packing, and the gas-liquid two-phase conducts countercurrent mass flow along the surface of the packing. The component concentrations of the two phases vary continuously along the column height.
Plate type vs packed fractionation column, 6 major differences
- Packed CO2 fractionation columns generally have a lower pressure drop than plate CO2 fractionation columns. Less pressure drop means less power consumption and lower operating costs.
- The empty column gas velocity of the plate CO2 fractionation column is generally larger than that of the traditional packed column. A large gas velocity in the empty column means a large production capacity, and abnormal phenomena such as liquid flooding will not occur even at a relatively high gas velocity. However, the empty column gas velocity of the new packing CO2 fractionation column has been greatly improved.
- The plate-type CO2 fractionation column has greater operating flexibility and is more suitable for occasions where the gas and liquid loads fluctuate greatly, especially the float valve CO2 fractionation column has the greatest operating flexibility. Plate-type CO2 fractionation columns are also suitable for occasions where the liquid-gas ratio fluctuates greatly.
- The efficiency of the plate supercritical CO2 fractionation column is relatively stable, and the diameter of the supercritical CO2 fractionation column increases, and the efficiency will increase. A packed supercritical CO2 fractionation column has high efficiency when the column diameter is small, and the efficiency will decrease when the column diameter increases, but the new regular packing is an exception.
- When the diameter of the plate supercritical CO2 fractionation column is large, the cost is lower than that of the packed supercritical CO2 fractionation column, but for the supercritical CO2 fractionation column with a diameter less than ∅800, the cost of the packed supercritical CO2 fractionation column is lower;
- The installation and maintenance of the plate supercritical CO2 fractionation column is easier than that of the packed supercritical CO2 fractionation column, especially the larger diameter supercritical CO2 fractionation column.
How to choose the suitable form of a supercritical CO2 fractionation column, 5 factors
When choosing the form of a supercritical CO2 fractionation column, various factors should be considered comprehensively, and the appropriate form of supercritical CO2 fractionation column should be selected according to the main contradiction.
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Packed supercritical CO2 fractionation column
- Factors 1#: For corrosive materials, a packed supercritical CO2 fractionation column should be selected, because the packing can be made of ceramic or other corrosion-resistant materials;
- Factors 2#: Packed supercritical CO2 fractionation columns should be used for materials that are prone to foaming because the packing is not easy to form foam;
- Factors 3#: Materials with heat sensitivity should be operated under reduced pressure to prevent overheating, so a packed supercritical CO2 fractionation column with a small pressure drop should be selected;
Plate supercritical CO2 fractionation column
- Factors 4#: Plate-type supercritical CO2 fractionation column is suitable for materials with suspended solids or easy scaling because most of the packed columns are easy to block;
- Factors 5#: If the material system is accompanied by thermal effects during the mass transfer process, heat needs to be extracted, and a plate-type supercritical CO2 fractionation column is suitable.
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