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Cold boxes

Many industrial applications use gases such as oxygen, nitrogen and argon. These gases are obtained using cryogenic gas separation technology, whereby air is condensed and converted into a liquid. Afterwards, the various elements can be separated using fractional distillation. So-called air separation plants are characterised by an extremely low temperature of as low as approximately -200°C.

 

The importance of insulation

In addition to the risk of water and ice formingat this cryogenic temperature, there is also the risk of pure oxygen condensing against the cold parts of thesystem. The presence of oil and grease may be enough to cause the high concentration of oxygen to spontaneously combust. This is obviously an extremely hazardous situation. The presence of oil and grease must thereforebe avoided at all times.

It is vitally important to well insulate all cold parts of the system, such as vessels andpipes. Strict specifications regarding the insulation are therefore essential. A frequently applied standard for theinsulation of air separation plants is the AGI Q 118 standard “insulation work on air separation plants”.This standard describes in detail the various parts of the installation and the insulation to be applied.The construction method naturally depends on the application. The following instructions are limitedto the insulation of so-called cold boxes.

Cold boxes

An important component in gas separation plants are the so-called “cold boxes”. Cold boxes are (pressure) vessels that hold a gas or liquid at a very low temperature. The distinctive feature of cold boxes is the double-wall construction, which allows the insulation to be fitted between the inner and outer walls. The cold box is sealed after the insulation has been fitted, so the insulation can no longer come into contact with, for example, water, snow, dust and contaminants.

Choice of insulation

The choice of insulation material depends on a variety of parameters, including the user requirement, standards (e.g. AGI Q118), the operating temperature and the accessibility of the installation. In many cases, mineral wool fibres are used (e.g. ProRox GR 903 (ROCKWOOL Granulate)), which contain a very low proportion of organic substances- the so-called “Linde Quality”. This can be easily injected into the vessel and has a very long lifespan. The material is easily removed for inspection purposes

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