Closed-circuit cyclone ("pin", "safety pin") - principle of operation and advantages of the solution

Cyclone dust collectors are devices commonly used in industry for the separation of solid particles from gases (usually air). One of the interesting solutions is a closed system cyclone, also known by the colloquial names "safety pin" or "pin". This type of system is commonly used in the wood industry (mainly in pellet lines), plastics processing (pellet loading, raw material dedusting) and recycling (plastics and foam mills, separator collection). How does this solution work and why should it be used where possible? We answer in this article.

Principle of cyclone operation in a closed loop system

The same cyclones can be used for closed-circuit systems as in open-circuit systems, but the way they are connected is distinguished by the fact that the air from the cyclone's upper outlet (containing a certain amount of unseparated dust) is fed back into the suction section of the pipeline instead of into the environment or into the filters. This is usually implemented by means of two cellular sluices, one of which is installed under the cyclone and the other under the material loading point.

In the case of material input at more points, further cellular sluices are used with appropriate transfer ports. The second solution, which is often used, is to force air flow through the machine generating the material (sawdust, chips, dust, milling, pellets) by connecting two pipes to it on opposite sides of the working chamber (left+right, up+down, etc.). For this to be possible, the working machine (e.g., mill, grinder, screen) must be suitable for this.

Advantages of using a cyclone in a closed system

• No emission of dust and pollutants - dust that could not be separated in the cyclone is returned to the cyclone in the next cycle until final capture.
• No loss of material - thanks to full recovery, raw material losses can be reduced and production costs can be reduced.
• No need for filters - which reduces both investment and operating costs.
• Energy savings - pressure losses in the return pipeline are significantly lower than those generated in the filters, allowing the use of a lower-power fan.
• Simplicity of the system, virtually maintenance-free operation - reducing the need for frequent maintenance and filter replacement affects long-term savings.

Summary

Closed system cyclone, or the popular "safety pin" or "pin", is a solution with many advantages. Thanks to its effective separation of particles, reduction of dust emissions and process optimization, it is widely used in industry. It is an ecological and economical solution that saves raw materials and improves the quality of the working environment.