Screw heat exchanger with cryogenic application

Wednesday 14 December 2011

°Celsius has developed a nitrogen cooled screw conveyor for a German customer with which fresh herbs can quickly be deep frozen. By freezing the soft herbs become hard and can be ground (cryogenic grinding).

Upon grinding a product may change shape and structure due to friction. Examples are plastics with a low melting point or products containing moisture, such as fresh herbs in this case. By injecting nitrogen at a temperature of -195.8 °C during transport of the herbs, the fresh herbs are immediately deep frozen and so hard enough to grind.

The screw heat exchanger freezes the herbs over a distance of 2500 mm with a capacity of 1.6 m³/hour. Liquid nitrogen is injected into the product at 4 points during the transport to the grinder. Liquid nitrogen is a good option for immediate cooling. The nitrogen gas produced is odourless, colourless, tasteless and it is inert.

There are paddles on the screw that mix the herbs well with the nitrogen. The casing of the screw heat exchanger has twin walls with a vacuum between them for insulation. The screw is easy to dismantle using a clamp structure on the outlet side and is easy to clean.

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