Ground freezing with


For nitrogen freezing, deep-cold liquid nitrogen is used as a refrigerant. It is produced on a large scale in air liquefaction plants. Nitrogen is a non-toxic, non-inflammable gas which makes up 78 % of air. As a deep-cold liquefied gas, nitrogen has a temperature of -196° C at the pressure of 1 bar. Using special vacuum-insulated tankers, liquid nitrogen is transported to the construction site and temporarily stored there in tank facilities. It is then fed through high-quality insulated pipelines into the down pipes. As the deep-cold liquid leaves the downpipe, it evaporates when it makes contact with the relatively warm freeze pipes and then exits the pipe in gaseous form. This evaporation process absorbs energy from the surrounding soil and the ground freezes as a result. When using nitrogen as refrigerant, the freezing process takes place very quickly, and is referred to as shock freezing. The amount of nitrogen required for freezing or maintaining the frost body is determined for each individual freeze pipe by a control circuit consisting of a magnetic valve and a temperature sensor. The valves are controlled by monitoring the temperature of the nitrogen gas escaping from the freeze pipes.
Each individual freeze pipe can be operated with a different freezing capacity by specifying a different exhaust gas temperature. Within a central measuring and control unit, temperatures and switching operations can be observed, documented, assessed and changed, thus making the production of tailor-made frost bodies possible. The physical properties of the refrigerant and sophistication of the control system makes ground freezing with liquid nitrogen a highly flexible method with a wide range of applications. The individual plant components such as the supply tank, the pipelines as well as the measuring and control unit can be installed quickly and made ready for operation. Unlike ground freezing using brine, nitrogen as a refrigerant is used up as it escapes in gaseous form back into the atmosphere. Especially in the larger-scale and lengthy ground freezing projects, the volumes of liquid nitrogen used, a consumable item, becomes the most important cost factor.


When getting into contact with the relatively warm freeze pipes the liquid nitrogen vaporizes and then escapes from the pipes in gaseous form.



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