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The Pulva Corporation
Grinding and Pulverizing Services

Cryogenic Screw Feed Conveyor


The cryogenic feeder is a specially constructed stainless steel heat exchanger designed to optimize heat transfer, using liquid nitrogen as a refrigerant. The feeder is suitable for precooling a wide variety of materials, including plastic, rubber, food and drugs to their embrittlement temperature for cryogenic grinding operations. Heavy-Duty components and simplicity of construction assure a durable and reliable cryogenic cooling system.

The cooling conveyor operates with high thermal efficiency resulting in lower nitrogen consumption. The material is cooled to it's embrittlement temerature traveling through the cooling conveyor. When the material is passed through the pulverizer it is reduced to the required size. Some products can be reduced to as low as -325 mesh.

The material to be ground is loaded into a feed hopper. From the hopper, the material enters the cooling conveyor where liquid nitrogen at -320 F is sprayed directly onto the material. The liquid nitrogen vaporizes to a gas by absorbing the required heat of vaporization from the feed material. Seeking thermal equilibrium, the cold nitrogen gas continues to cool the feed material to its embrittlement point.

A thermocouple and temperature controller are used to control and monitor the temperature within the cooling conveyor and the grinding mill discharge hopper. The material enters the Pulva-Sizer® Grinding Machine where the material is ground into a powder. During the grinding stage, additional liquid nitrogen may be injected into the Pulva-Sizer® to remove heat caused by grinding.

When using the cryogenic conveyor, measurable and repeatable results are obtained for lab or productions calculations. Grinding mills range in size from 7-1/2 HP to 200 HP. With our cryogenic grinding unit an understanding develops with interaction of equipment components and operating parameters. Factors such as consistent feed rate, precise temperature measurement, mill operating parameters and pressure control are critical to the evaluation of cryogenic grinding and cryogenic grinding systems.

Testing is available in Pulva's Testing Lab.

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