US3012408A - Method and apparatus for vaporizing liquefied gases - Google Patents

Description

Dec. 12, 1961 w, PERKlNs r 3,012,408

METHOD AND APPARATUS FOR VAPORIZING LIQUEF'IED GASES Filed July 22, 1958 2 Sheets-Sheet 1 GAS I0 I STAYS OXYGEN 34 I 2 PASSAGES 40a 1 BRINE COMPARTMENT LIQUID INVENTORS WARREN E. PERKINS CHARLES F. FAILS LYLE E. FULLER ATTORNEY United States Patent 3,012,408 METHOD AND APPARATUS FOR VAPORIZING LIQUEFIED GASES Warren E. Perkins, Grand Island, and Charles F. Fails, Tonawanda, N.Y., and Lyle E. Fuller, Indianapolis, Ind., assignors to Union Carbide Corporation, a corporation of New York Filed July 22, 1958, Ser. No. 750,149 6 Claims. (CI. 62-52) This invention relates to method and apparatus for vaporizing volatile liquids and more particularly concerns apparatus for vaporizing low boiling, volatile liquids such as oxygen and nitrogen at service pressures above atmospheric pressure.

Several difiiculties have been encountered in the vaporization of liquefied gas at relatively low rates of flow for delivery at warm temperature and superatmospheric pressure to a consumer. For example, many Vaporizers are heated by steam or electrical means, and whereas the provision of such utilities may be justified for a large consumer, it is often not convenient or desirable for the small consumer. Furthermore, it may be advantageous to make the supply of gas independent of a utility since this improves the dependability of the supply, and facilitates the use of Vaporizers on mobile equipment. Dependability is of special importance to consumers desiring a guaranteed supply, such as hospitals.

Atmospheric Vaporizers are not necessarily dependent upon a utility for heat and are frequently employed for small demands. However, such Vaporizers are normally relatively bulky and must frequently be provided with large excess capacity to accommodate momentary peak demands at the desired pressure and temperature levels. To obtain dependability and to ensure adequate delivery rates under all conditions, it may be necessary to provide an expensive auxiliary equipment as a source of heat or have in readiness additional sources of heat supply.

Another problem involved in the design of atmospheric Vaporizers is the achievement of rated performance under a wide variety of weather conditions. Normally, the atmospheric vaporizer unit is located out of doors where the deposition of snow, ice, or frost on the vaporizer walls can reduce heat transfer and impair the proper functioning of the unit, particularly when the humidity is high and the ambient air temperature is about 30 F. to 40 F.

For these and other reasons, such problems are difficult to solve in atmospheric Vaporizers and have added to the need for a low cost atmospheric vaporizer which can meet the requirements of small industrial users.

It is therefore an important objectof the present invention to provide an improved atmospheric vaporizer apparatus for the out-of-doors conversion of valuable liquefied gas products and adapted to absorb sensible heat from the atmosphere under varying weather conditions for dispensing gaseous product from said vaporizer.

Another object of the invention is to provide an improved low pressure atmospheric vaporizer apparatus for converting relatively small amounts of valuable low boiling liquefied products and dispensing same in gaseous form at a temperature and pressure suitable for use by small industrial users without using utility power such as gas, steam, or electricity.

Another object of the invention is to provide a low pressure atmospheric vaporizer for valuable low boiling liquefied gas material which is simple to manufacture, easy to operate and low in cost.

Other objects, features and advantages ofthe present invention will be apparent from the following detailed description of a preferred embodiment thereof taken in conjunction with the drawings, in which:

FIG. 1 is a perspective view of a cold converter apparatus embodying the principles of the present invention;

FIG. 2 is an enlarged schematic view taken along line 2-2 in FIG. 1 of the vaporizer portion of the converter unit;

FIG. 3 is an enlarged front elevational view looking in the direction of the arrows along the line 3-3 of FIG. 2;

FIG. 4 is an enlarged partial isometric view of the vaporizer unit taken approximately along the line 44 of FIG. 3; and

FIG. 5 is a schematic flow diagram of the apparatus of the invention.

In FIG. 1 is shown an assembly of a gas material holding container or vessel 10 embodying the features of the present invention. By the term gas material is meant a low temperature product, such as oxygen or nitrogen in the liquid or gaseous state. The vessel 10 may be of more or less conventional construction for stationary or portable use of the type having a double walled, thermally insulated pressure vessel for holding a supply of liquefied gas material, for example oxygen. The intervening space between the vessel walls may be filled with a comminuted insulating material and evacuated to reduce heat leakage from the outside to the body of liquefied gas in the vessel.

For simplicity, the operation involving the conversion of liquid oxygen will be described but it is to be understood that the invention is not limited to this service.

' For filling or replenishing the supply of liquid oxygen in the vessel 10, a suitable liquid phase pipe 12, see FIG. 5, provided with a filling connection 14 and controlled by a liquid fill valve 16, extends through suitable gas tight openings into liquid space in the lower portion of the vessel 10.

Liquid oxygen, supplied through the fill connection 14, may also be passed through a gas phase connecting line 12a controlled by a valve 16a and which is gas-tightly joined at one end to the liquid fill line 12 and at the other end to the gas space in the upper region of the vessel 10. The valves 16 and 16a are'used to proportion the flow of liquid oxygen supply between the liquid and gas spaces of the vessel 10 so that the pressure in the vessel 10 can be controlled during filling to maintain a desired operating pressure as is disclosed in U.S. Patent No. 2,368,215. Relief valve 18 in communication with fill lines 12 and 12a allows vapors which may become entrapped between control valves 16 and 16a to escape.

The vessel 10 is customarily supplied with auxiliary devices such as liquid level and pressure indicating means.

The proper filling level may be indicated by a trycock line 28 at the upper filling level and including an external trycock' valve 30.

Suitable pressure building means indicated generally at 31 may also be provided to prevent reduction in the container pressure, such as might occur in periods of sustained liquefied gas withdrawal. Such pressure builder circuit maybe of the type disclosed in U.S. Patent No. 2,500,249, and may include suitable heat exchanger and regulator equipment.

The oxygen material from either the liquid or gas line is passed through a conversion apparatus, or'vaporizer which when combined with the container 10 and the necessary controls, forms an apparatus known as a cold converter. The conversion apparatus of the invention illustrated in FIGS. 1, 2, 3, 4, and 5 comprises an atmospheric vaporizer 32 having at one end a liquid withdrawal line conduit 20 which joins liquid phase line 12 below the fill valve 16, and at the other end a discharge line 3 4 having interposed near the end thereof a check valve 36, at the outer end of which is a service coupling 38. By opening the liquid withdrawal valve 24 in line 20, liquid oxygen is passed to the vaporizer 32 where it is evapo- 7 rated andsuperheated for delivery at the conditions required by the consumer.

To prevent excessive gas pressure buildup in the vessel 10, provision is made for gas withdrawal through a gas phase line 20a in communication with the gas space in the vessel 10. having therein a gas phase pressure relief valve .22. A back pressure gas valve 24a is set to open at a predetermined higher pressure within the desired operating range. Gas thus withdrawn may also be passed through vaporizer. 32. to superheat the gas to near amient temperature. v o g I An acute problem in atmospheric vaporizers employing warm air for heat exchange with the liquefied gas, is that of evaporatingthe liquefied gas and suitably superheating it under severe weather conditions without using any utilities such as steam, gas, or electricity, either for supplying heat of vaporization or for the operation o-f circulating fans, pumps, or defrosting heaters. In accordance with this. invention, a low temperature liquid such as liquid oxygen is converted to a warm gas in a vaporizer employing only atmospheric heat as a source of energy. The process and apparatus may readily be made independent of all industrial sources of power, yet it will perform satisfactorily even under adverse weather conditions and is capable of supplying a widely fluctuating demand .with more severe peak loads than could be accommodated with known atmospheric vaporizer.

1 As a means of accomplishing this, the vaporizer unit is provided with a heat storage system for supplying latent and. sensible heat from the atmosphere to liquid oxygen and'for. minimizing the effect of cold moist weatherconditions upon the proper functioning of the vaporizer unit. Asshown-in FIGS. 2 and 4, the vaporizer 32 comprises a pair of elongated thermally conductive'plates. 40, 4011 preferably of aluminum orrother heat conductive metal, disposedin spaced contact to form a cellular structure having therebetween a labyrinth of internal- passages 42, 58, 60, 62 and 64-for oxygen flow. These passages may be formed by placing fiat sheet 40 upon flat sheet 40a, and bonding together in suitable manner the marginal edges and registering areas 44, illustrated here in the form ofrectangular and square buttons, and hydraulically expanding the, areas adjacent. thereto to form walls 46 and 40a of'the internal passageways. This expansion can be accomplished by providing inlet and an outlet connections openinginto the unbond'ed areas between the sheets 40 and40a, and through which hydraulic fluid is introduced for expanding such areas to provide passages. The internal passages formed'thereby may be of varying shape and dimension'through the length ofvaporizer 32' to suit the character of the fluid flowing in the passages at each point therein. The passages adjacent the liquid inlet are preferably of the type'shown' in FIGURE 4- which permit low and approximately equal flow resistance in either vertical; or horizontal directions. Such pattern is conducive to good distribution ofthe liquid across'the width of the vaporizer so that theoperatingloadis. uniform.

Above the liquidv distributingsection containingpassages 42, the. passages arepreferably formed as-long, vertical channels 58: comprising the. vaporizing section. Such passages are advantageous in promotinga priming action wherein the fluid with increasing vapor content accelerates upward through the channels and by its turbulence brings; the fluid in good heat exchanger relation with the vaporizer walls. 7

As the fluid emergesfrom the upper ends of, vaporizing channels58, any remaining unvaporized liquid will either be disengaged from the vapor in passages 60 above, or will be reduced to tiny vapor-borne droplets or mist. The passages 60 forming the separator section are somewhat similar to passages 42 providing low flow resistance in vertical anclhorizontalv directions favorable to disengagement of remaining liquid. Passages 60 also provide 'much extended wall surfaces on which any disengaged liquidis held and vaporized.

A vapor superheating section above the separator section contains long vertical passages 62 similar to vaporizing channels 58. If desired, passages 62 may be interrupted by one or more horizontal passages 66 for assuring good distribution of the fluid among the superheating channels.

Above the superheating section, a gas collecting section is formed of passages 64 similar to passages 42. The warm gas leaving passages 62 flows upwardly and horizontally to the withdrawal. connection 34, and the horizontal flow must be accompanied by very low pressure difference across the width of the vaporizer so as not to upset the flow distribution.

It will be noted that the vaporizer section (passages 58) and superheating section (passages 62) of FIGURE 3 are fore-shortened. These sections provide the majority of the heat transfer into the gas material and comprise the major portion of the vaporizer length.

Spaced from the inner wall 40a is a solid flat plate 50 which, together with wall 40a forms a thin rectangular heat storing container 54 for holding a heat storing liquid.

7 The atmospheric vaporizer of the invention is adapted to; function V satisfactorily under temporary adverse weather conditions during which heat transmitted directly from the atmosphere to the gas material is insuflicient for the delivery of gas at the required rate and heat content. This is accomplished. by employing inthe container 54 a low-freezing or low-boiling heat storing liquid having a Zreasonably high latent heat of fusion or-vaporizati0n within the low temperature range expected to be encountered, such as brine. or ethylene, glycol solution. Brine is the preferred liquid, having a low cost, high specific heat capacity and a freezing temperature of about 2 F. Using approximately a;.22% brine solution as the heat storing liquid, the gas delivery range for oxygen should be preferably between; about 40 C. andv ambient temperature. A

It is. to be understood thatthisinvention is not limited to brine as the'heat storing liquid, and:that the choice of heat storing fluidmay bedetermined by the conditions under which the'vaporizer of? the invention is expected to function.- Someof the factors which will affect the selection of a; heat storing liquid are weather conditions, the boiling pointof the heat storing liquid and the desired outlet. temperature of the gaseous material to be dispensed.

The. container: 54 andthe cellular wall structure 40, 40a, forming a side of said container, are suitably braced by metalreinforcing stays or hands 56- to avoid bulging.

In. operation under normal atmospheric conditions, relatively'low rates of flow of liquefied gas material may be vaporized and superheated in the atmospheric va= porizer' 32 at equilibrium conditions; i.e., the heat absorbed by the gas-material beingbalanced by the ambient heattransferred primarily through cellular walls 40, 40a, and secondarily through" plate SO and'the brine solution. Whenthe unit'is vaporizing gas material at such equilibrium rate the brine's'olution in the vicinity of the liquid distributing passages 42 may freeze, but since only a minorpart of the total heat is transferred from the atmosphere through the brine solution, the insulating'effect of the ice .on the overall heat transfer rate from the atmosphere not be serious.

During; other periods, it is expected that the vaporizer will'be called upon to vaporize and superheat gas material' more rapidly than the requisite heat can be suppliedthrough cellular walls 40, 4011.. Such condition may result from an increase in demand'for gaseous material or from the development'of unfavorable Weather conditions. During such periods,.the operation of the atmospheric vaporizer of the invention is as follows:

ture dropsfto its freezing point.*- Thereafter, the brine freeze, releasing'a large amount of latent heat for transfer to the wall 40a. As long as such non-equilibrium condition exists, the brine will continue to cool and freeze, thereby supplying the heat deficiency and maintaining near-normal vaporizer service. Freezing progresses upwardly from the bottom of the vaporizer, and the solid-liquid interface slopes downwardly from the cold wall 40a to the warmer wall 50.

If the heat deficiency is only minor, the vaporizer may establish a new equilibrium but with a higher ice level. Such new equilibrium is maintained by the generally lower wall temperatures existent throughout the vaporizer which tend to increase the AT between the walls and the surrounding atmosphere. Thus, the vaporizer can adjust itself to changes in weather conditions and to moderate fluctuations in vaporizing rates.

When the heat deficiency is considerable, as may reasonably result from a momentary demand for gaseous material far in excess of the equilibrium capacity of the vaporizer, the freezing progression line will continue to advance within the vaporizer. The duration and frequency of such peak loads are usually predictable from experience, and if the vaporizer is properly constructed for its intended serw'ce, the heat capacity of the brine will not be exhausted before normal vaporization rates are resumed.

When the vaporization rate of the gas material returns to normal or is discontinued altogether, there follows a warming period during which the heat capacity of the brine is restored; and the vaporizer is prepared to supply the next period of heat deficiency. If the flow of gas material ceases altogether, heat from the atmosphere enters the brine through wall 50 and also through extended surface walls 40, 4011. If a moderate vaporizing load continues, wall 40 will supply the heat for vaporization and for superheat, while wall 50 supplies the heat for thawing the brine.

An alternative method of construction is to replace fiat wall 50 with a duplication of wall 40, 40a so that both faces of the vaporizer contain vaporizing and superheating passages. Such construction has the disadvantage that if both vaporizing faces are used elficiently a-t moderate vaporizing rates, then a warm wall will not be available for restoring heat to the brine solution.

Another alternative is to enclose the brine compartment with flat walls 50 on both sides and with vaporizer element 40, 40a located midway between. The vaporizing passages are then completely immersed in the heat storage liquid with no surfaces exposed to the atmosphere. The disadvantage of this arrangement is that the heat capacity of the brine solution cannot be conserved as effectively at low rates of vaporization since all the heat transmitted to the gas material must be absorbed from the solution regardless of vaporization rate. The brine also acts as a thermal insulation and the overall heat transfer rate, inherently low due to the poor convection coeflicient, is still further reduced by the resistance of the enveloping layer of brine. Finally, the extended surface area of wall 40 is not utilized effectively to improve heat transfer at the principal resistance, namely, the surface exposed to the atmosphere.

In order that the frozen brine may thaw completely between freezing periods, it is clear that the thickness of the brine compartment must not be too great. On the other hand, maximum heat storage is desirable in the brine compartment and for this reason, it should be as thick as practical. We have found that a thickness of about 2 in. is suitable for most services encountered, although thinner or thicker compartments may be used if so desired.

From the above, it will be seen that the atmospheric vaporizer of the present invention provides a fluctuating demand for gaseous material in which momentary loads may far exceed the continuous rating of the unit. The vaporizer is also admirably suited to provide a relatively steady vaporization rate for an extended period of time.

An obvious advantage of the invention is that momentary peak loads considerably in excess of the continuous rating of the vaporizer can be satisfactorily vaporized and superheated provided such peaks are followed by adequate intervals of low demand to permit restoration of the heat storing capacity of the compartment 54. Similarly, a consumer who withdraws gasified gas material only during a part of the day can withdraw at higher rates than the continuous rating of the vaporizer. For example, a consumer may require 1,000 cu. ft. per hr. gaseous material for one 8-hour shift only, in which case the conventional vaporizer will represent idle investment 16' hours of each day. In contrast, a vaporizer embodying the principles of the present invention and having a continuous rating of only about 700 cu. ft. per hr. will be capable of supplying the customers full requirements for the 8-hour.period. The heat capacity of the unit will be restored during the 16-hour intervals, thus making continuous, round-the-clock use of the atmospheric heat absorptive capacity of the unit.

From the above, it will be seen that the present invention provides an atmospheric vaporizer for a cold converter, the vaporizer including a heat storing unit for improving the rated capacity and peak withdrawal rates of gasified gas material without resorting to gas, electric, steam or other utilities.

It will be understood that modifications and variations may be effected without departing from the spirit and scope of the novel concepts of the present invention.

What is claimed is: v

l. A cold converter including a vessel having. an inlet at one end thereof for the supply therein of low-boiling liquefied gas material, an outlet at the other end thereof for the discharge therefrom of gasified gas material, said vessel having at least two non-planar side walls closely spaced, being arranged and constructed to form a cellular structure with a labyrinth of internal passages for the flow of gas material, one of said non-planar side walls being disposed in direct thermal association with the atmosphere for absorbing heat therefrom for the vaporization and superheating of said liquefied gas material; a heat storing compartment for a liquid having a freezing point below atmospheric temperature and above the vaporization temperature of said liquefied gas for transferring heat to the gas material in said vessel during periods when the heat in the surrounding atmosphere is insufficient to fully vaporize said gas material, the other of said non-planar side walls of said vessel forming one side wall of said heat storing compartment and a fiat surface being provided in direct thermal association with the atmosphere so as to form a second side wall of such compartment.

2. A cold converter including a vessel having an inlet at the lower end thereof for the supply therein of lowboiling liquefied gas material, an outlet at the upper end thereof for the discharge therefrom of gasified gas material, said vessel having at least two non-planar side walls closely spaced, being arranged and constructed to form a cellular structure with a labyrinth of internal vertically and horizontally interconnected passages for the flow of gas material, one of said non-planar side walls being disposed in direct thermal association with the atmosphere for absorbing heat therefrom for the vaporization and superheating of said liquefied gas material; a heat storing compartment for a liquid having a freezing point below atmospheric temperature and above the vaporization temperature of said liquefied gas for transferring heat to the gas material in said vessel during periods when the heat in the surrounding atmosphere is insufficient to fully vaporize said gas material, the other of said nonplanar side walls of said vessel forming one side wall of said heat storing compartment and a flat surface being provided in direct thermal association with the atmosphere so as to form a second side wall of such compartment.

3. A cold converter according to claim 1 wherein saidtnon-planar. side wallshave irregular; wafiie-like external surfaces. A

4. A method for vaporizing and super heating liquefied oxygen comprising the steps of providing and flowing said liquefied oxygen in simultaneous heat exchange with atmospheric air and a heat storingliquidhaving a freezing point below atmospheric temperatures and above the vaporization temperature of the liquefied oxygen, thereby vaporizing and superheating' such liquefied oxygen and cooling said heat storing liquid for freezing thereof, soas to transfer the heat of fusion to said liquefied oxygen; and thereafter warming the frozen heat storage material sufiiciently by atmospheric'heat so as to melt such material. for reuse as a heating medium for. said liquefied oxygen. g I

5. A method for vaporizing and. superheating: a'lowboiling-liquefied gas according to claim 4 wherein said superheating raises the temperature. of the oxygen to between approximately ambient temperature and 40t C.

6. A method for vaporizing and superheating liquefied gas having a normal boiling point no higher than the a heating such liquefied gas and cooling said heat storing liquidfor freezing thereof, so as to transfer the heat of fusion to said liquefied gas; and thereafter warming the frozen heat storage material sufliciently by atmospheric heat so as to melt such material for reuse as a heating medium for said liquefied gas;

References Cited in the file of this patent UNITED STATES PATENTS 2,271,648 Kleist Feb. 3, 1942 2,576,985 Wildhack Dec. 4, 1951 2',638,754' Kleist May19, 1953 2,795,114" Kleist June 11,1957

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