Low-temperature vessels

June 6, 1961 η. o. mcmahon 2,986,891

LOW-TEMPERATURE VESSELS

Filed Feb 10, 1958 2 Sheets-Sheet 1

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Howard O. McMahon INVENTOR.

BY

ATTORNEY

June 6, 1961

Η. O. MCMAHON

2,986,891

LOW-TEMPERATURE VESSELS

Filed Feb. 10, 1958

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INVENTOR.

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2,986,891

Patented June 6, 1961

United States Patent Office

2,986,891 LOW-TEMPERATURE VESSELS

Howard O. McMahon, Lexington, Mass., assignor to Arthur D. Little, Inc., Cambridge, Mass., a corporation of Massachusetts

Filed Feb. 10, 1958, Ser. No. 714,122 5 Claims. (Cl. 62—45)

This invention relates to maintaining an enclosed space at a low temperature and more particularly to minimizing possible heat transfer from the surrounding atmosphere into the enclosed space.

It is desirable to be able to maintain enclosed spaces, 'either large or small, at temperatures below those of the atmosphere surrounding the enclosed space. Thus for example, it is necessary to maintain large spaces such as cold storage houses, refrigeration plants, and domestic refrigerators at temperatures around 0° C.; while it is necessary to maintain the interior of storage vessels, tank cars, and dewar-type containers at temperatures as low as —269° C. to be able to handle, transport, and store liquefied gases. Although these enclosed areas vary in size, design and performance characteristics required of them, they are all subject to heat losses by reason of heat transferred from their surroundings into the enclosed space which must be kept at a low temperature.

Many complicated systems having been devised to minimize these heat leaks from the surroundings, and they include evacuating a space surrounding the area to be cool'ed and Using various insulations, some being evacuated. The necessity of evacuating an annular space about the enclosed area introduces complications in manufacture and of course is hot practical for large enclosed spaces such as refrigerators and cold storage units.

It would therefore be desirable to provide a refrigeration system which is simple in construction and which, at the same time, is more effective in preventing the inflow of heat from the surrounding atmosphere.

It is therefore an object of this invention to provide a system wherein the heat leak from the surrounding atmosphere into an enclosed space maintained at a low temperature is minimized. It is another object to provide containers for liquefied gases in which the loss of liquid due to boil-off is maintained at a minimum. Another object is to provide a refrigerating system which employs simple auxiliary equipment, has no internal coil system, and maintains a consistent temperature throughout the cold space while at the same time does not dehumidify items stored therein.

Briefly, this invention involves economically and ef- 5θ ficiently maintaining an enclosed space at a low temperature by venting cold gas from the enclosed space into a passage surrounding substantially all of the enclosed space, and in a direction countercurrent to the flow of space maintained at a low temperature and using the process of this invention without insulation; and

FIG. 5 is a cross-sectional view of an enclosed space such as a cold storage room maintained at a low temperature in accordance with the practice of this invention, in which cold gas is supplied from an external source.

In order to achieve the improved performance in the storage of cold liquids, or in the maintaining of low temperatures in relatively large areas, in accordance with the practice of this invention, it is necessary that a fluid, normally a gas, at a temperature below that of the surrounding atmosphere be vented or released from the enclosed space into a passage extending around substantially all of the enclosed space or directly from the enclosed space radially outward and in a direction countercurrent to the direction of normal heat influx from the surrounds. The passage may or may not be surrounded with porous insulation, or the insulation may serve also as the passage. It is preferable that the vented gas reach a temperature approximating the temperature of the atmosphere at the point where it is finally drawn off.

This invention may be further illustrated with reference to FIGS. 1 through 5 in which three different arrangements are shown.

FIG. 1 represents a cross-sectional view of a flask or container suitable for storing liquefied gases according to the teaching of this invention. In FIG. 1 container 10 is placed within an outside protective vessel 12 which may in turn be surrounded by any convenient configuration 3θ such as box 14 for additional protection. Vessel 12 is held in place by any suitable supporting means such as supports 16. Surrounding substantially all of flask 10 and iff concentric relationship therewith is passage 18 which is defined by the outside wall of flask 10 and by a perme³⁵ able wall 20 (such as screening) which also substantially surrounds flask 10 and is in concentric relationship therewith. Concentric with permeable wall 20 is another permeable wall 22 and these define an annular space between them, said space containing insulation 26. Ports 24 ⁴⁰ lead out from the neck of flask 10 into space 18. These ports are placed abbve the normal line of liquid 34 stored in flask 10. The spacing 18 between flask 10 and permeable wall 20 is maintained by any suitable way such as supports 28 and the spacing between permeable wall 22 arid protective wall 12 is also maintained by any suitable means such as supports 28α. A lead-off line 32 is connected with space 30 to permit gas to pass out of the storage system either into the atmosphere or into a suitable recovery system not shown.

The arrangement shown in FIG. 1 is particularly well suited to the storing, handling, and transporting liquefied gases at very low temperatures. It will be seen that it combines the use of an annular passage surrounding the „„„ _{___}_______________________ _________ storage vessel 10 and insulation 26. When a portion of heat from the surroundings. The gas which is vented 55 the liquid 34 in flask 10¹ bojls off to form cold gas, the from the enclosed space may be supplied through boiloff of liquefied gas stored therein or it may be supplied from external sources. The passage may in turn be surrounded with porous insulation or may contain porous insulation.

This invention will be described in detail with reference to the accompanying drawings in which

FIG. 1 represents a cross-sectional view of a flask suitable for storing liquefied gases according to the process of this invention;

FIG. 2 represents a tankcar, partly in cross-section, partly in plan view, designed in accordance with this invention; _____o„ ..............,_______r_________,____

FIG. 3 is a cross-sectional view of the tankcar of FIG. ₇θ the teriiperature of the surrounding atmosphere. 2 taken along lines 3—3 of FIG. 2; ^T ‘ ^{: :1}'¹'

FIG. 4 represents a cross-section view of an enclosed gas passes through ports 24 into annular space 18 and then in a radial direction (as indicated by the arrows) through permeable wall 20, insulation 26 and finally through permeable wall 22 into space 30. It will be seen go from this arrangement that the cold gas vented from flask 10 is continually passing in a direction countercurrent to the direction of incoming heat from the surroundings. This heat from the surroundings is flowing inwardly through box 14 and thence through the protective vessel 12. By this system of heat exchange it is possible to make lise of the entire refrigerating content of the vented gas if it is directed in this manner to sweep out the incoming heat. By the time the gas leaves the system through lead-off line 32, it has preferably been raised to

Inasmuch as the incoming heat is responsible for the boil-off of the liquefied gas, the practice of this invention

2,986,891 makes possible the reduction of liquid loss to a minimum. If ideal conditions were obtained, there should not of course be any liquid boil-off. However, this is not entirely practical; but I have found that under nearly ideal conditions, with the gas diffusing evenly through the insulation 26 and leaving the system at ambient temperature, that liquid hydrogen boil-off, for example, will be only 27 % of the boil-off rate of a conventionally vented system in which the gas would leave the storage vessel at a temperature only slightly above that of the liquid hydrogen.

FIG. 2 shows essentially the same arrangement as that illustrated in FIG. 1 except that FIG. 2 applies the arrangement to a tankcar suitable for transporting liquefied gases. Thus in FIG. 2 the inside tank 11 is surrounded first by annular space 19 and then by insulation 27 which is contained in permeable walls 21 and 25. Outside tank wall 13 and permeable wall 25 provide an annular space 13α for drawing off the gases comparable to space 30 of FIG. 1. Ports 23 are provided to vent the boil-off gas into annular space 19. Line 15, including valve 17, is provided to introduce liquefied gas 37 into the tankcar while vent 33, including valve 35, is provided to release the warmed gas from the system. Suitable supports to maintain the various elements in their proper position 25 such as 29 and 31 are supplied. Such a tankcar would of course be equipped with wheels 39 and coupling 41. Inasmuch as FIGS. 1 and 2 illustrate vessels for storing liquefied gases, the cold gas necessary to the practice of this invention is supplied from an internal source; i.e., 30 the liquefied gas itself.

In FIG. 4 it is shown how an enclosed space 38 may be maintained at a low temperature by the use of concentric containers 40, 41 and 43 having ports 42, 46 and 50, respectively, at alternating and opposite ends of the con- 35 tainers. Such concentric containers form in this arrangement annular passages 44 and 48 which achieve the effect of countercurrent heat flow of the vented gas with respect to the direction of heat flowing in from the surroundings. Thus cold gas leaving port 42 flows completely around 40 container 40 as indicated by the arrows, leaves by way of port 46 and flows in an opposite direction through space 48 to be vented to the atmosphere or to any other sytsem (not shown). Suitable supports such as 45 and 47 may be placed at different points to maintain the necessary spacing between the containers. In the arrangement of FIG. 4 the cold gas to be vented may be supplied from an internal source if it is used to store liquefied gases or from an external source if it is used as a cold storage unit or the like.

FIG. 5 illustrates how the practice of this invention may be adapted to a refrigerator or to a cold storage unit. In this arrangement the cold gas is supplied from a source external to the space to be cooled as contrasted with the . . . ---------------------____r arrangement in FIGS. 1 and 2 in which the cold gas is 55 °^. introducing said cold gas into said first passage comsupplied from an internal source. ™

In FIG. 5 the space 38 to be maintained at a cold temperature is defined by a permeable structure 52. Surrounding permeable structure 52 is an outside permeable . . . --,----_r-----_o structure 54 which defines therewith space 53. Structure 60 vessel, an outer gas-tight vessel surrounding said 52 and 54 may be permeable walls in which case they - -- *—

Would contain within the passage defined therewith insulation 53. However, it is also possible that structures 52 and 54 and insulation 53 may be an integral unit such as . _ ---------------------a rigid insulation material which needs no additional walls 65 ^{VeSSel adapted t0 vent} S^{as from a} P^oint in the wall thereof, to contain it. For example, this integral unit may be a ^{nnrl r}' ^!J fairly thick glass fiber mat, bonded if necessary with a suitable binding agent. Structure 54 and outside wall 56 in turn define an annular passage 55 which leads to port 60. An incoming line 58 connects with space 38 and also 70 with a source of cold gas which may include compressor 62, cooler 64 and expansion engine 66. Gas which is to serve as the coolant may be compressed in compressor 62, passed through cooler 64 in which condensibles such as water and CO₃ are removed and then into expansion 75 engine 66 for expanding and further cooling. The then cooled gas is introduced by line 58 into space 38 where it circulates and from which it passes radially through porous structures 52-54 into annular spaces 55 and out through port 60. The temperature and flow rate of the incoming gas may be so controlled that the outgoing gas at port 60 is at approximately the same temperature as the surrounding atmosphere. Again as in the case of the arrangements discussed above, it will be noted that by i directing the flow of cooled gas in the manner described, i.e., counter-current to the influx of heat from the surroundings, the maximum amount of refrigeration is obtained from the cold gas. Furthermore, in the practice of this invention as it may be applied to refrigerators and cold storage units, it should be noted that several other advantages are obtained over the usual arrangement wherein coolants are introduced and passed through coils contained in the space to be cooled. First of all, the temperature throughout the space is constant, and the air itself is the coldest element within the space, not the usually employed coils. Since the water and other condensibles have been removed and no coils are used, there can be no frost formed and hence there is no defrosting problem. Moreover, there is no tendency in this system to dehydrate the materials stored within the space, a problem which is always present in conventional refrigeration.

From the above descriptions of this invention it will be seen that a method and apparatus are provided which make possible the maintaining of an enclosed space at a low temperature while minimizing the heat leak in from the surroundings and minimizing the heat loss from within, thus achieving improved refrigeration.

The wide use of liquefied gases in industrial and military application requires that such liquefied gases be handled and stored with a minimum loss.