US2148109A - Method and apparatus for handling gas material - Google Patents

Description

Feb. 21, 1939. L, l. DANA El AL 2,148,109

METHOD AND APPARATUS FOR HANDLING GAS MATERIAL Filed May 16, 1935 Z4 INVENTORS LEO DANA TF2 BY ODD ARNOLD HANSEN ATTORNEY.

' Patented Feb. 21, 1939 UNITED STATES METHOD AND APPARATUS FOR. HANDLING GAS MATERIAL Leo I. Dana and Odd Arnold Hansen,

Y., asslgnors, by mesne assignments, to Union Carbide and Carbon Corporation, a corporation of New York Application May 16, 1935, Serial No. 21,784

13 Claims.

This invention relates to a method and apparatus for handling gas material, having particular reference to a method and apparatus for storing and transporting dimcultly liquefiabie gases,

such as acetylene, air, oxygen, and carbon dioxide, especially in the liquid phase at temperatures below 273 Kelvin.

It is known practice to store and transport diflicultly liquefiable gases, such as air, oxygen,

and carbon dioxide, at low temperatures in the liquid phase in heavily insulated containers at either high or low pressure, allowing the heat which inevitably leaks into the container through the insulation to be dissipated by the evaporation of such an amount of the stored liquid as is necessary to keep the temperature of the liquid so low that the maximum desired pressure is not exceeded. The liquid which evaporates in this manner for cooling purposes is ordinarily lost, and if the gas is stored for long periods of time and/or at relatively low pressures, this evaporation loss may be considerable. Furthermore, certain gases are of such a nature that their vaporization into the atmosphere is undesirable or dangerous since their vapors may create an explosion or poison hazard. Acetylene, for example, which has heretofore generally been stored under pressure in solution in acetone, cannot safely be handled in the liquid phase at high pressure without a stabilizer because of its instability, and cannot safely be allowed to evaporate into the atmosphere because of its infiammability. Hence, in order to avoid the losses and other disadvantages of evaporation and still obtain the advantages of 35 handling gases in the liquid phase, chief of which is increased handling efiiciency resulting in decreased storage and transportation costs, it is necessary that some means be devised for avoiding the evaporation of the liquefied gas. 40 Generally, therefore, it is the object of this invention to provide a. novel method and apparatus for handling gases in the liquid phase at any desired constant pressure wherein evaporation of the liquefied gas shall be substantially avoided.

More specifically, objects of this invention are to provide a method and apparatus of the character indicated wherein the heat which normally leaks into the liquefied gas shall be dissipated by some other means than the vaporization of a portion of the liquefied gas; wherein use shall be made of the change in state at constant temperature of a refrigerating medium to absorb and dissipate the heat which would otherwise leak into the liquefied gas; wherein the refrigerating efiect of the refrigerating medium and the liquefied gas shall be conserved, so that a high handling eificiency is obtained; and wherein the insulation used to minimize heat leakage shall be preserved from deterioration, so that its heat insulating properties remain unimpaired.

These and other objects of this invention, together with the novel features thereof which achieve these objects, will become evident-in the following detailed description, having reference to the accompanying drawing, in which:

Fig. 1 is a diagrammatic arrangement of apparatus embodying the principles and illustrating the methodof this invention; and

Fig. 2 is a similar arrangement of apparatus illustrating another embodiment of this invention and having special means for conserving the refrigeration of the refrigerating medium and the liquefied gas and for preserving the insulation used to minimize heat leakage and increasing its insulating effectiveness.

In accordance with the broad principles of this invention, gas material is handled as follows: The gas is first obtained in liquid form either directly from the manufacturing process or by liquefaction by any one of a number of well-known processes. The liquefied gas is then charged into a'suitable receptacle or container, and the receptacle is packed or substantially surrounded with a refrigerating medium which by a change in state, as for example solid to gaseous, maintains a substantially constant low temperature. The temperature of the refrigerating medium should be the same as or below the maximum allowable temperature or the liquefied gas corresponding to the maximum pressure desired; that is, the refrigcrating medium should at all times maintain the temperature of the liquefied gas at such a value that the vapor pressure of the liquefied gas does not exceed the maximum pressure desired. The liquefied gas then assumes a. temperature corresponding to the temperature of the refrigerating medium and a pressure corresponding to its vapor pressure at that particular temperature, and any heat tending to leak into the gas is intercepted and dissipated by the gradual change in state, e. g. vaporization of the refrigerating medium. Thus evaporation of the liquefied gas is substantially avoided.

In order to control the pressure of a liquefied gas being handled in accordance with this invention, two alternatives are possible. Diflerent refrigerating mediums differ widely in the constant temperatures at which they change from one state into another. Thus, solid carbon dioxide sublimes at 'l8.5 C. at atmospheric pressure while ice melts at 0 C. at atmospheric pressure. Hence such a medium must be selected as will maintain a substantially constant temperature corresponding to the temperature of the particular liquefied gas at the desired pressure. Also, the temperature of any one refrigerating medium is capable of a certain amount of control by varying the pressure under which the change in state takes place. Thus, ordinarily, an increase in pressure will increase the sublimation tempera ture of a solid or the vaporization temperature of a liquid. Hence, the pressure of the liquefied gas will vary accordingly. Then both the selection of the refrigerating medium and the pressure under which it changes state may be used to control the pressure of the gas being handled.

In order to minimize heat leakage to the refrigerating medium, it may desirably be surrounded by an insulating space filled with a suitable thermal insulation, such as a gas or a porous solid, and the residual refrigeration of the refrigerating medium in its final state (usually vaporous) may be conserved by passing it in heatconducting relation to this insulation to remove quantities of heat therefrom. Likewise, the refrigerating effect of the liquefied gas may be conserved by passing it, when withdrawing gas from the receptacle in either the liquid or vapor phase, in heat-conducting relation to the insulation. Furthermore, means may be provided for preserving the insulation from deterioration by contact with the moisture in atmospheric air, as will hereinafter more fully appear.

Acetylene may advantageously be handled in the liquid phase with substantially no evaporation in accordance with the principles of this invention. Solid acetylene at normal atmospheric pressure sublimes at a temperature of 83.'7 C. in a manner similar to solid carbon dioxide. It becomes liquid at a temperature of -82.4 C. and at a pressure of 1.5 pounds per sq. in. gage. Solid carbon dioxide sublimes at a constant temperature of -78.5 C. at atmospheric pressure, which corresponds to a vapor pressure of about 5.7 pounds per sq. in. gage for liquid acetylene. Solid carbon dioxide thus serves as an ideal refrigerating medium for handling liquid acetylene at low pressures without evaporation. The liquid acetylene is charged into a receptacle which is packed or surrounded with solid carbon dioxide which in turn may be surrounded with suitable insulation. The heat which inevitably leaks in through the insulation is intercepted and dissipated by the sublimation of the solid carbon dioxide at a constant temperature of '78.5 C., so that the liquid acetylene is maintained at this temperature and at a corresponding pressure of 5.7 pounds per sq. in. gage without evaporation.

It is possible to increase the sublimation temperature of solid carbon dioxide by increasing the pressure under which it sublimes, which decreases the rate of sublimation since the temperature gradient is not so extreme. The pressure of the liquid acetylene would increase correspondingly. Thus, at a pressure of 10 pounds per sq. in. gage, solid carbon dioxide sublimes at a temperature of about 72.1 C., which 'corresponds to a vapor pressure of about 13.4 pounds per sq. in. gage for liquid acetylene.

Referring now to the drawing, in Fig. 1 is shown one arrangement of apparatus embodying the method of this invention. The apparatus is shown as comprising a container denoted generally by C having a base It and a cover or closure member ll removably secured to the base in in a preferably fluid-tight manner by any suitable means. The base lil may comprise an outer wall or casing l2 and an inner wall It positioned apart to enclose an insulating space. The cover ll may similarly comprise outer and inner walls It and 15 respectively, positioned apart to enclose an insulating space. These insulating spaces are preferably filled with any suitable thermal insulation it, such as magnesium carbonate, charcoal, asbestos, slag wool, sheep's wool, or silk, or mixtures thereof, to minimize the leakage of heat into the container.

Supported in any suitable manner within the container C and spaced therefrom is a receptacle or vessel I! for holding a liquefied gas l8, such as liquid acetylene. Associated with the receptacle I! may be a liquid filling conduit l9 discharging into the receptacle at a point near the top thereof, a liquid withdrawal conduit 20 discharging from the receptacle at a point near the bottom thereof, and a vapor withdrawal conduit 2| discharging from the receptacle at a point near the top thereof. The vapor withdrawal conduit 2| may be provided with a safety valve 22 which may be adjusted to any desired maximum pressure.

In the space between the receptacle l1 and the inner wall of the container C and surrounding the receptacle is disposed a suitable refrigerating medium 23, such as solid carbon dioxide, which maintains a substantially constant low temperature by a change in state. In the case of carbon dioxide, this change is from solid to gaseous by sublimation. The heat which leaks into the container through the insulationlis intercepted and dissipated by the heat of sublimation of the solid carbon dioxide and hence does not reach the liquid acetylene, which therefore remains at the constant temperature of the carbon dioxide without evaporation. The carbon dioxide vapor is discharged at atmospheric pressure through a conduit 24, which is preferably disposed in the insulating space between the inner and outer walls of the container in a series of convolutions in heat-conducting relation to the insulation to transfer quantities of heat therefrom. The residual refrigeration of thevapor is thus conserved. The solid carbon dioxide may be readily replenished by removing the cover ll of the container C, and any excessive or dangerous rise in pressure due to exhaustion of the solid carbon dioxide is prevented by the safety valve 22.

If it is desired to increase the sublimation temperature of the solid carbon dioxide so that the liquid acetylene will have a correspondingly high temperature and pressure, the carbon dioxide vapor discharge conduit 24 may be provided with a safety valve which may be set to open at any desired discharge pressure.

In the embodiment of this invention shown in Fig. 2, the refrigerating medium denoted here by 23' is shown as comprising a mixture of solid carbon dioxide and a suitable low-freezing liquid, such as acetone or alcohol. The liquid must have a freezing point below the sublimation temperature of solid carbon dioxide, and acetone, methanol, and ethanol meet this requirement since they freeze at about 94.6 C., 97.1 C., and 114 C., respectively. The liquid facilitates thermal contact between the solid carbon dioxide and the receptacle l1, thus preventing local variations in temeperature which might otherwise occur, for example, when the supply of solid carbon dioxide becomes low. Acetone or a liquid having a high solvent power for acetylene is particularly suitable when handling liquid acetylene according to the present invention because any acetylene that may accidentally escape from the inner container would be held in solution thereby.

In order to-minimize heat leakage into the container C and thus minimize the rate of vaporization of the solid carbon dioxide, special means are provided in Fig. 2 for conserving the refrigeration of the carbon dioxide vapor and :the acetylene liquid and vapor. A body of high heat conductivity and high heat capacity is supported in the insulation and interposed between the outer and inner walls of the container, surrounding at least a substantial part of the receptable W. This body acts to store quantities of heat which may be continuously or intermittently transferred from the body by the discharging carbon dioxide vapor and the discharging acetylene liquid and vapor when, acetylene is withdrawn. The body may preferably comprise a metal thermal shield 25, having the carbon dioxide vapor discharge conduit 24, the liquid acetylene discharge conduit 20 and the acetylene vapor discharge conduit 2| coiled in heat-conducting relation thereto. During periods of acetylene withdrawal, the thermal shield becomes relatively very cold, giving upits heat to the acetylene, and thereafter it acts to absorb heat leakage into the container, which heat would otherwise penetrate to the solid carbon dioxide to be dissipated by sublimation.

Certain insulation deteriorates and decreases in effectiveness if it becomes wet. If such an insulation is used between the inner and outer walls of the container C, means should be provided for maintaining it in a substantially dry state. The insulating space between the inner and outer walls of the container is subject to wide variations of contraction and expansion as a result of the wide temperature changes between periods when the apparatus is in use and when it is idle. If moist atmospheric air is allowed to be drawn into this space when the temperature decreases, some of the moisture in the air will condense on coming in contact with the cold insulation and other cold parts, thus wetting the insulation. This may be avoided by constructing the inner and outer walls of the container to be fluid-tight as shown in Fig. 1. However, the

walls must then be sufliciently strong to with-.

stand the pressure stresses set up as a result of the alternate contraction and expansion before referred to. If the outer container is not fluidtight, means may be provided for removing moisture from the air drawn into the insulating space. Such means may preferably comprise moisture traps 26 and 21 shown in Fig. 2, communicating with the insulating space and containing some strongly hygroscopic material, such as calcium chloride or barium oxide, for drying the air drawn therethrough. A dehydrating breather trap of the type disclosed in the patent to L. I. Dana and G. H. Zenner No. 1,976,688 has been found very satisfactory. Of course, such a device is unnecessary if insulation which does not suffer from such breathing action is used.

In order to further minimize heat leakage into the container C and to further conserve the residual refrigeration of the carbon dioxide vapor, means may be provided for diffusing the carbon dioxide vapor through the insulating space between the inner and outer walls of the container C. Such means may conveniently comprise a perforated conduit 24' inserted in the carbon dioxide vapor discharge conduit 24, as shown in Fig. 2. A closure cap 28 may then be provided at the end of conduit 24, instead of which a safety valve may also be used. The carbon dioxide val r permeates the insulation and discharges through the breather trap 26. Since carbon dioxide is heavier than air, the air will be removed from the insulating space and be replaced by an insulating layer of carbon dioxide. The flow of carbon dioxide keeps the insulation dry and materially reduces the total thermal conductivity of the insulation, since the prime thermal conductivity of a porous insulation resides in the gas present in its interstices and since carbon dioxide has a considerably lower thermal conductivity than air. In such an embodiment the carbon'dioxide then serves a triple purpose: the solid carbon dioxide by its heat of sublimation intercepts and dissipates all the heat tending to leak into the liquefied gas, thereby preventing evaporation thereof; the carbon dioxide vapor keeps the insulation dry by maintaining a dry carbon dioxide atmosphere in the insulating space, whereby deterioration of the insulation is minimized; and the carbon dioxide vapor forms an insulating layer in the insulating space, which increases the insulating effectiveness and thus decreases the flow of heat to the solid carbon dioxide and the liquefied gas. Furthermore, the residual refrigeration of the carbon dioxide vapor is conserved by transfer of its cold to the thermal shield and to the insulation.

The embodiment shown in Fig. 1 may also be arranged to diffuse the carbon dioxide vapor through the thermal insulation IS in the insulating space. It is merely necessary to insert a diffuser in the carbon dioxide vapor discharge conduit 24, to plug the end of this conduit, and to insert a one-way valve or safety valve in the outer wall I2 of the container C. A valve rather than a breather trap as in Fig. 2 is used, since the inner and outer walls of the container in I Fig. l are constructed to be fluid-tight and hence some means must be provided for permitting the carbon dioxide vapors to escape from the insulating space while still preventing atmospheric air from entering this space.

The several parts of the apparatus in accordance with this invention as before described may be constructed of any materials and in any manner suitable for the purpose. The outer wall or casing of the container C is preferably alumimum and the inner wall which serves as a vessel for the refrigerating medium 23 or 23' is preferably stainless steel. The receptacle ll for the liquefied gas may also desirably be stainless steel and is preferably of integral welded construction with the filling and withdrawal conduits welded in place. The thermal shield 25 is preferably a metal of high heat conductivity and capacity, such as aluminum or copper, and the carbon dioxide vapor vent and the acetylene filling and withdrawal conduits, whether or not they are used in conjunction with the thermal shield, are preferably stainless steel. The base l0 and the cover H of the container C are each preferably separate units of integral construction.

The use of the novel method and apparatus of this invention for handling acetylene carries with it many advantages. Formerly, acetylene was distributed either in the form of calcium carbide or dissolved in acetone under pressure in cylinders. The distribution of acetylene in the form of calcium carbide necessitates the installation,

operation, and maintenance of an acetylene generator by the consumer, which is troublesome, and expensive. Moreover, the acetylene from such a generator generally contains water vapor, air, and other undesirable impurities such as phosphene and ammonia. The distribution of acetylene dissolved in acetone under pressure in cylinders is objectionable because the acetylene is only about 8% by weight of the total filled container, which results in high handling costs, and because, unless special precautions are taken, appreciable amounts of acetone may come off with the acetylene especially at the lower ranges of pressure in the cylinder and at high atmospheric temperatures, which seriously aifects the temperature of combustion and heat available. On the other hand, handling acetylene in accordance with the method and in the apparatus of this invention eliminates the necessity oi. maintaining a generator on the consumer's premises. Moreover, acetylene so handled represents about 25% by weight of the total filled container, which results in an increase in storage and transportation efllciency over the former cylinder method and a corresponding decrease in handling costs. Furthermore, the present method delivers acetylene substantially free from any of the impurities previously mentioned; in fact, the acetylene is so much purer than that distributed by previous methods and has such marked advantages commercially that it may be considered a new product'.

Liquid acetylene handled in accordance with the method and in the apparatus of this invention may be dispensed by any of the methods heretofore proposed for dispensing liquefied gases which are adapted to handle acetylene.

It is contemplated that certain changes may be made in practicing the hereindescribed method and in the construction and arrangement of apparatus shown for carrying out the method without departing from the principles or exceeding the scope of this invention as indicated in the appended claims.

We claim:

1. Method for handling acetylene, which comprises liquefying acetylene, charging said liquid acetylene into a receptacle, and substantially surrounding said receptacle with a mixture of solid carbon dioxide and acetone.

2. Method for handling acetylene, which comprises liquefying acetylene, charging said liquid acetylene into a receptacle, substantially surrounding said receptacle with a mixture of solid carbon dioxide and a. liquid having a freezing point below the sublimation temperature of carbon dioxide and a solvent power for acetylene substantially equal to that of acetone, and maintaining the pressure within said receptacle at the pressure corresponding to the boiling point of acetylene at the temperature of said mixture so that said liquid acetylene will not evaporate at the temperature maintained by said solid carbon dioxide.

3. Apparatus for handling liquefied gases, comprising a container having outer and inner walls enclosing an insulating space having thermal insulation therein, a receptacle for the liquefied gas supported within said container and spaced therefrom, a refrigerating medium in the space between said receptacle and the inner wall of said container which maintains a substantially constant low temperature by vaporization and a conduit for conducting the vapor from said refrigerating medium uniformly through the insulation in said insulating space and in indirect heat exchanging relation therewith.

4. Apparatus for handling liquefied gases, comprising in combination a container having spaced outer and inner walls, a receptacle supported within said container and spaced therefrom, a refrigerating medium in the space between said receptacle and the inner wall of said container which maintains a substantially constant low temperature by a gradual change in state, a body of relatively high heat conductivity insulatingly supported and interposed between said outer and inner walls, and. means for transferring quantities of heat from said body.

5. Apparatus for handling liquefied gases, comprising in combination a container comprising spaced outer and inner walls having thermal insulation therebetween, a receptacle for the liquefied gas supported within said container and spaced therefrom, a refrigerating medium in the space between said receptacle and the inner wall of said container, means interposed between said walls and in said insulation for intercepting and carrying away a portion of the heat fiowing inward through said insulation and means for maintaining said insulation in a substantially dry state.

6. Apparatus for handling liquefied gases, comprising in combination a container comprising spaced outer and inner walls enclosing an insulating space having thermal insulation therein, a receptacle for the liquefied gas supported within said container and spaced therefrom, a refrigerating medium in the space between said receptacle and the inner wall of said container, 9. body of relatively high heat conductivity and capacity supported in said insulation and interposed between said outer and inner walls, means for transferring quantities of heat from said body, and means for excluding moisture from said insulating space.

7. Apparatus for handling liquefied gases, comprising a container having outer and inner walls enclosing an insulating space, a receptacle for the liquefied gas supported within said container and spaced therefrom, solid carbon dioxide in the space between said receptacle and the inner wall of said container, and a carbon dioxide vapor vent comprising conduit convolutions in said insulating space for transferring quantities of heat therefrom.

8. Apparatus for handling liquefied acetylene, comprising an insulated container, a receptacle for the liquefied gas supported within said container and spaced therefrom, and a refrigerating medium comprising a mixture of solid carbon dioxide and acetone in the space between said receptacle and said container.

9. Apparatus for handling liquid acetylene, comprising in combination a container comprising outer and inner walls enclosing an insulating space having thermal insulation therein, a receptacle for the liquid acetylene supported within said container and spaced therefrom and provided with filling and withdrawal means, solid carbon dioxide in the space between said receptacle and the inner wall of said container, and means including a thermal shield for intercepting and uniformly diffusing the heat entering said insulation and for conducting the vapor from said solid carbon dioxide uniformly through the insulation so as .to carry away a portion of said heat.

10. Apparatus for handling liquid acetylene, comprising in combination a container comprising outer and inner walls enclosing an insulating space having thermal insulation therein; a receptacle for the liquid acetylene supported within said container and spaced therefrom; solid carbon dioxide in the space between said receptacle and the inner wall of said container; a thermal shield of relatively high heat conductivity and capacity supported in said insulating space and interposed between said outer and inner walls, surrounding at least a substantial part of said receptacle; and a carbon dioxide vapor vent and acetylene liquid and vapor phase withdrawal conduits coiled in heat-conducting relation to said thermal shield for transferring quantities of heat therefrom. l

11. Method for handling liquefied gases, which comprises charging the liquefied gas into a closed receptacle while isolated from the atmosphere,

surrounding at least a substantial portion of said receptacle with a refrigerating medium, utilizing vapors from said refrigerating medium to assist in impeding the flow of heat thereinto, controlling the refrigerating eflect of said medium to maintain the temperature of said liquefied gas at a substantially constant value above the triple point temperature of said gas but below its boiling point temperature corresponding to the pressure, and maintaining said pressure below one atmosphere gauge pressure.

12. Method for handling liquefied acetylene which comprises charging liquefied acetylene into a closed receptacle while isolated from the atmosphere, substantially surrounding said receptacle with a refrigerating medium comprising solid carbon dioxide and a liquid having a melting point temperature below the sublimation temperature of carbon dioxide and having a solvent capacity for acetylene substantially equal to that of acetone whereby a constant "low temperature is maintained which is above the freezing point of said liquefied gas, maintaining the pressure on said liquefied gas at least equal to its vapor pressure corresponding to the temperature maintained by said refrigerating medium, and utilizing the vapors from said refrigerating medium to decrease the fiow of heat thereto.

13. Method for handling acetylene, which comprises charging liquid acetylene into a receptacle, substantially surrounding said receptacle with a refrigerating-medium, utilizing vapors from said refrigerating medium to assist in impeding the flow of heat thereinto, controlling the refrigerating effect of said refrigerating medium to maintain a substantially constant low temperature between --82 C. and -73 C., and maintaining a pressure on said liquid acetylene at least equal to its vapor pressure corresponding to the temperature maintained by said refrigerating medium butbelow one atmosphere gage pressure whereby to conserve the liquiiied acetylene without loss.

LEO I. DANA. onn' mom HANSEN.

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