US3092283A - Means for insulating elements of a low temperature unit - Google Patents

Description

c. TREPP 3,092,283

MEANS FOR INSULATING ELEMENTS OF' A LOW TEMPERATURE UNIT June 4, 1963 Filed July 20, 1961 United States Patent @ffice 3,092,283 Patented June 4, 1963 3,092,283 MEANS FOR INSULATING ELEMENTS F A LOW TEMPERATURE UNT Christian Trepp, Zurich, Switzerland, assignor to Sulzer Freres, SA., Winterthur, Switzerland, a corporation of Switzerland Filed July 20, 1961, Ser. No. 125,440 Claims priority, application Switzerland July 29, 1960 6 Claims. (Cl. 2210-16) The present invention relates to means for improving the insulation of elements of low temperature apparatus such as that which is employed for example in the liquefaction of diflicultly liqueiiable gases such as hydrogen or helium.

The practice of protecting elements of devices which operate at low temperatures from absorbing external heat is quite common. 'Ihis is particularly true of those elements where an appreciable temperature dilerential is maintained such as heat exchangers, rectifying columns and the like. One manner in which this may be accomplished is to place the elements in a vacuum jacket or vessel and then to further insulate them by employing a timely-divided insulating material to fill the open space in the vacuum jacket and to surround the elements being insulated. In order to inspect elements which are insulated in this way it is then necessary to remove the insulating material completely from the jacket. In addition, the elective operation of these low temperature units is somewhat hindered and eiective operation is delayed after start up because of the presence of appreciable quantities of the insulating material in the vacuum jacket since the heat content of this material must be removed before the elements can function at optimum capacity.

It is, therefore, an important object of this invention to provide improved insulating means adapted for use as additional insulation for elements which are normally operated at low temperature and within an evacuated vessel maintained at subatrnospheric pressure.

Another object of this invention is to provide such auxiliary insulating means which may be readily applied to and removed from said elements for easy inspection and access.

Other objects of this invention will appear from the following detailed description and the accompanying drawing.

It has now been found that the disadvantages of the insulating methods and materials heretofore employed in the insulation of low temperature elements may be overcome and highly ecient insulation achieved if several elements of a low temperature device are each enclosed within a shaped jacket formed of a rigid porous insulating material and the enclosed elements are then maintained and operated in a vacuum vessel held at a pressure of 10-1 to 10-3 millimeters of mercury.

As the rigid porous insulation material used in forming the shaped jacket there may be employed :any one or more of those materials which are generally employed as protective agents for refrigeration equipment such as, for example, naturally occurring organic material such as cork particles, granular plastic materials or inorganic substances, sheets or 'batts of foamed synthetic plastic resin materials or sheets or batts formed of brous materials such as mineral wool. In accordance with the present invention the required degree of insulation can be readily attained by maintaining a vacuum of from l0-1 to iiD-3 millimeters of mercury in the vessel containing the insulated elements since the insulating material contains pores whose dimensions are less than the maximum distance of the mean free path of the gaseous molecules of the air at the indicated pressures.

Advantageously, the jacket or casing which serves as the insulation material is so assembled and mounted as to `be removable at least in part so that when inspection is required the insulated elements are readily accessible. By employing a concentric arrangement powdered, granular or iibrous materials such as easily pourable kieselguhr or easily laminated asbestos, spun glass bers or rock wool may be utilized and in each case the outer protective shell is advantageously formed of a screen-like material which is provided with a suitable removable bonnet or header. lf the insulating casing is formed of sheet materials such as oamed plastic, this is likewise mounted on the equipment so as to be easily removable. For example, by means of catches at the margin of the sheet or by the use of wire strapping or with clasps the insulating sheet material can be brought into very close contact with the equipment. The protective casing cau also be so designed that no particular fastening agents `are required.

In order to reduce heat absorption due to radiation a metal powder may conveniently be incorporated into the outer layer of the casing to deect radiant heat and, similarly, a metal foil may be applied to the outer surface of the casing or jacket for the same purpose.

Other `features of the invention will be apparent upon reference to the description and the accompanying drawing which comprises a `schematic diagram Iwhich illustrates one method whereby the invention may be carried out.

Referring to the drawing, the reference numeral 1 iudicates a vacuum tank provided with a removable cap 2. Connected to the tank 1 is a pipe 3 which is further connected to sa pump, not shown, such as a rotary pump, capable of producing and maintaining a vacuum of 10 1 to 10-3 mm. of mercury within the tank. The tank 1, as shown, contains a heat exchanger 4 and a rectifying column 5 which are supported by but are insulated from the walls of said tank by suitable brackets. The rectifying column 5 is enclosed within a jacket or casing 6 formed of a granular insulating material. 'Ihe outer layer of the casing is formed of a screen-like or foraminous sheath 7 which may be, for example, a perforated metal foil. The foraminous sheath may be formed in sections, the upper portion consisting of a removable bonnet or header, as described above, which may be attached to the lower portion by means of suitable anges in the manner shown in the drawing, similar to the manner in which removable cap 2 is attached to the lower portion of tank 1. An opening for introducing lthe powdered, granular or fibrous insulating material into sheath 7 and having :a removable closure may be provided in the top of the removable bonnet or header. Surrounding the heat exchanger 4, as shown, is a sheet material formed of a foamed plastic -material 8 which is held in position in close proximity to the outer surface of said heat exchanger by means of clamps 9 and 10, or by other fastening means. As shown, sheet material S is slit beneath clamps 9 and 10 respectively so that by opening said clamps the top and bottom caps formed by said slits can be removed.

I claim:

1. In an apparatus having a plurality of elements operating at low temperatures, an outer casing for each of said elements, said casings being formed of porous heat insulating material, and a vessel maintained at a vacuum of from 10-1 to 10-3 mm. of mercury containing said elements.

2. In an apparatus in accordance with claim l and wherein the outer surface of said outer casings contains a metal powder yas 'a shield against absorption of heat radiation.

3. In an apparatus in accordance with claim l and wherein the outer surface of said outer casings is provided with Ia metal foil as a shield against absorption References Cited in the file of this patent of heat radiation. NIT

4. In an apparatus in accordance with claim 1 and U ED STATES PATENTS 5. In an apparatus in accordance with claim 1 and 2,962,867 Seidel Dec. 6, 1960 'wherein said outer casings are formed by Yremovably 2,970,452 Beckman et al. Feb. 7, 1961 mmd Sheetmaals: s OTHER REFERENCES In an apparatus 1n accordance w1th clalm 1 and l wherein the heat insulating material employed is a granu- 10 Progress In CfY0gDlCS (lVIeIldelSSOhll),` Published Ylar material; and a screen-like sheath is provided surround- 'by Academic Press, Incorporated (New York), 1960, ing the granular material. (pages 78-85 relied on).

Claims (1)

1. IN AN APPARATUS HAVING A PLURALITY OF ELEMENTS OPERATING AT LOW TEMPERATURES, AN OUTER CASING FOR EACH OF SAID ELEMENTS, SAID CASINGS BEING FORMED OF POROUS HEAT INSULATING MATERIAL, AND A VESSEL MAINTAINED AT A VACUUM OF FROM 10-1 TO 10-3 MM. OF MERCURY CONTAINING SAID ELEMENTS.

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