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Four Types of Combined Cylinders for Supercritical CO2 Extraction Vessels

As the pressure increases, the thickness of the CO2 extraction vessel increases, and the distribution of stress along the wall thickness becomes more and more uneven. The stress on the inner wall of the CO2 extraction vessel is large, while the stress on the outer wall is small. When the ratio of the outer diameter to the inner diameter of the CO2 extraction vessel K is greater than 1.5, the inhomogeneity of the stress distribution becomes more prominent. In order to improve the bearing capacity of the CO2 extraction vessel cylinder, double-layer and multi-layer cylinder structures appeared to achieve the purpose of uniform stress distribution along the wall thickness.

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Type 1: Multi-layer wrapped cylinder

This is the combined cylinder structure with the most widely used CO2 extraction container and the richest manufacturing and use experience in the world. Multi-layer wrapped CO2 extraction container combined cylinder consists of two parts: an inner cylinder with a thickness of 12-25m and a multi-layer laminate with a thickness of 4-12mm. In order to prevent cracks from extending along the thickness direction, the longitudinal welds between the laminates should be staggered by 75° from each other. The multi-layer wrapped cylinder has a simple manufacturing process and does not require large-scale and complicated processing equipment. Compared with the single-layer cylindrical CO2 extraction vessel, it has higher safety and reliability. the possibility of brittle failure. However, the multi-layer wrapped cylindrical CO2 extraction container has many manufacturing processes, long cycle time, low efficiency, and low utilization rate of steel plate materials. Read More: Pressure Vessel – Wikipedia

Type 2: Double-layer thermal sleeve body

CO2 extraction vessels
CO2 extraction vessels

The double-layer thermal sleeve body of the CO2 extraction vessel consists of two concentric cylinders. The outer surface of the inner cylinder and the inner surface of the outer cylinder need to be precision machined so that the outer diameter of the inner cylinder is slightly larger than the inner diameter of the outer cylinder, and the inner cylinder is fitted by heating the outer cylinder to achieve an interference fit. In this way, the inner cylinder is pre-compressed and the outer cylinder is pre-stretched, achieving the purpose of homogenizing the stress of the cylinder during operation.

Type 3: Multi-layer thermal sleeve body

When the total thickness of the CO2 extraction vessel remains constant, increasing the number of layers of the thermal sleeve can improve the uniformity of stress distribution along the wall thickness and reduce the thickness of each layer of the cylinder. The number of layers of the multi-layer thermal sleeve body can be up to 5 layers. Too many layers will affect the heat transfer of the cylinder wall and increase the manufacturing process. In high-pressure situations, different materials are often used for the multi-layer cylinder, in which the inner cylinder is often made of materials with high tensile strength and low fracture toughness, and the outer cylinder is made of materials with slightly lower tensile strength and high fracture toughness.

Type 4: Tape-wound barrel

For example, in the flat steel belt inclined angle staggered winding cylinder, which is a new type of CO2 extraction vessel belt-wound cylinder structure pioneered in China, the thickness of the inner cylinder accounts for about 16~1/4 of the total thickness. With the simple “prestressing Cold winding” and “pressure roller pre-bending and sticking” technology, the flat steel strip is staggered outside the thin inner cylinder at an inclination angle of 15°~30° relative to the container ring direction. The first and last ends of the steel strip are welded to the bottom head and the end flange respectively. This kind of cylinder structure is very safe for the pressure extraction kettle. When the inner cylinder is damaged, the strength of the steel belt is not lost, and it can still carry the load, which can achieve the effect of only leaking and not bursting.

Read More: CO2 Extraction Process: Basics, 5 Advantages, 7 Features, 4 Applications