US3091096A

US3091096A - Delivering vapors of low boiling liquids

Info

Publication number: US3091096A
Application number: US804749A
Authority: US
Inventors: John J Rendos; Donald L Smith
Original assignee: Air Reduction Co Inc
Current assignee: Airco Inc
Priority date: 1959-04-07
Filing date: 1959-04-07
Publication date: 1963-05-28
Anticipated expiration: 1980-05-28

Description

May 1963 J. J. RENDOS ETAL 3,091,096

DELIVERING VAPORS OF LOW BOILING LIQUIDS Filed April 7, 1959 2 Sheets-Sheet 1 F I G. I

I 38 34 35 36 l l 8 0 egg MI- 32 I I 2 is so l 28 4 64 37 I I 42 I 44 S 50 1 U III I I 40 v I I I7 48 I 49 a 66 I l I FIG. 4 I

W? INVENTORS JOHN J. RENDOS DONAL D L. SMITH ENTROPY AGENT TEMPERTURE y 1963 J. J. RENDOS ETAL 3,091,096

DELIVERING VAPORS OF LOW BOILING LIQUIDS 2 Sheets-Sheet 2 Filed April 7. 1959 FIG.

FIG. 3

, INVENTORS JOHN J. R-EN DOS DONALD L. SMITH AGENT 3,091,096 DELZVERHIG VAPGRS 01F LOW BOILING LIQUIDS .lohn J. Rendos, Miliington, and Donald L. Smith, Berkeley Heights, NJ, assigners to Air Reduction Company, Incorporated, New York, N.Y., a corporaion of New York Filed Apr. 7, 1959, Ser. No. 804,749 '16 Claims. (Cl. 6252) This invention relates to methods and apparatus for supplying the vapors of low boiling liquefied gases at a specified state or condition, and, more particularly, concerns the delivery of such vapors in a predetermined state at desired delivery pressures and at varying rates of delivery.

The invention is particularly adapted for the delivery of oxygen and nitrogen under desired specified conditions, although it may be used advantageously in connection with other low boiling liquefied gases. By low boiling liquefied gases are meant those gases having boiling points substantially below about 233 K. The rapid growth and development in the field of cryogenics has created an urgent demand for apparatus particularly suited for the handling of fluids at extremely low temperatures and especially for such types of apparatus and fluid systems that are capable of delivering these fluids at a specified state which may be accurately maintained and controlled for various delivery pressures and flow rates. Such systems may be used, for example, to supply vapors of low boiling liquefied gases under simulated conditions, such as exist in cryogenic Work, so thatthe apparatus, such as valves and the like, used therein may be tested under specified Working conditions. While there are available standard types of converters for vaporizing low boiling liquefied gases and devices for metering such fluids in the liquid state, there have notbeen heretofore any completely satisfactory apparatus or systems for furnishing such fluids under specified conditions Which may be maintained reliably within closely prescribed limits. This is particularly true Whereit is desired to supply a relatively low boiling, liquefied gas at a predetermined pressure and either exactly at or close to its point of saturation.

Accordingly, it is an object of the present invention to provide means for delivering a relatively lowboiling point liquefied gas at a controllable pressure and at a predetermined state.

A further object of the present invention is to provide means for delivering the vapor of a low boiling liquefied gas at a controllable pressure at or substantially near its point of saturation.

One significant difliculty which is encountered in delivering such fluids at, or substantially at, their point of saturation is the absence of the sensitivity of the temperature of the fluid as a reflection of the quality or condition of the fluid at the saturation pressure. Thus, the fluid, even though at saturation temperature, may be a mitxure of gas and liquid of indeterminate quality inasmuch as the temperature of such fluids remains substantially the same for all quality mixtures between vapor saturation and liquid saturation at any given pressure;

Accordingly, it is a further'object of the present invention to deliver a low boiling liquefied gas substantially at its vapor saturation point, or as a liquid-vapor mixture of a specified quality, by admixing a superheated vapor of said liquefied gas with a predetermined corresponding quantity of low temperature liquid so as to reliably produce a saturated vapor stream, or partially liquefied stream of a prescribed quality, without reference to the temperature of the resulting mixture.

It is a still further object of the present invention to n ut Patented May 28, 1963 provide a method and apparatus for delivering vapors of a predetermined condition, particularly substantially at about saturation, and maintaining such conditions substantially constant over a range of variable flow rates,

A still further object of the present invention is to provide means foradmixing a superheated vapor and a liquid of a low boiling liquefied gas wherein the commencement of the flow of said liquid is responsive to a predetermined temperature of the resulting fluid mixture and the delivery of said vapor and said liquid are adapted to be substantially simultaneously terminated in the event of an increased pressure in the delivery pressure of the resultant fluid mixture above a predetermined value.

A still further object of the present invention is to provide an improved fluid supply system including low boiling liquefied gas storage means, vaporizing means, conduits and control means eifectively constructed and arranged to admix liquid and vapor constituents in accordance with the preceding objects and deliver .a fluid stream at a controllable, substantially constant thermodynamic state or condition.

In accordance with the present invention, a method and apparatus are provided for delivering a stream of a relatively low boiling liquefied gas at a desired constant con- .dition wherein a supply of superheated vapor and of liquid are maintained separately, respectively, at prede termined initial conditions and streams of each thereof delivered in predetermined proportions, said streams being admixed and delivered at the desired final state of the resulting fluid stream such that the sensible heat of the vapor available between the initial state of the vapor and the desired final state of the combined vapor and liquid substantially equals the heat required to change said liquid from its initial state to the desired final state of the admixed constituents. In an advantageous embodiment of the present invention, the separate liquid and vapor streams are maintained substantially constant at initial conditions, respectively, of substantially predetermined enthalpy and at an elevated pressure, reduced in pressure substantially isenthalpically substantially to about the desired delivery pressure of the fluid mixture and the prescribed relative proportions thereof brought together at said pressure and maintained in a substantially fixed ratio. A fluid stream maintained uniformly substantially at its saturation point may be supplied in accordance herewith at varying rates by admixing said vapor and liquid in a prescribed fixed relative proportion such that the available sensible heat of the vapor and the necessary latent heat of vaporization of the liquid are substantially equal. In a preferred embodiment of the invention, a desired fluid stream may be delivered by providing a source of liquefied gas stored under pressure in a suitable insulated vessel and obtaining the liquid and vapor streams for admixture in accordance with the invention by withdrawing liquid from said vessel, separately vaporizing a portion of the Withdrawn liquid and recombining the liquid and vapor to produce a combined stream at the desired constant conditions.

The admixture, in accordance with an advantageous embodiment of the invention, of separate vapor and liquid streams in predetermined fixed proportions to achieve a predetermined desired final state of the fluid depends to a large extent upon the suitable maintenance of the initial states, respectively, of the admixed vapor and liquid at substantially constant values.' Accordingly, in carrying out such embodiment of the present invention, the respective vapor and liquid streams are delivered at a point preceding admixture thereof at respective initial states which are maintained substantially constant during the delivery of the desired fluid stream. Such initial 3 conditions may be maintained advantageously, for example, by deriving the vapor and liquid from a single insulated vessel under a predetermined vapor pressure. A portion of such liquid may be withdrawn and heated a predetermined extent in conventional vaporizer means at substantially constant pressure so as to thereby provide an adequate source of such vapor at a fixed initial condition of substantially constant enthalpy. Such vapor then may be reduced in pressure in one or more successive stages substantially isenthalpically, without variably altering the heat content of the vapor, to substantially the desired delivery pressure. Such pressure reductions may include throttling through a prop'ortioning orifice across which a substantially constant pressure difierential is maintained so as to provide a substantially predetermined flow. Similarly, the liquid will be available from the storage vessel normally at a substantially constant subcooled condition. Such liquid may be throttled to the desired delivery pressure or substantially to a slightly higher pressure to allow for further throttling through a liquid proportioning orifice, and thence combined in a predetermined fixed portion with the vapor stream. Inasmuch as the throttling of the liquid is substantially isenthalpic, the maintenance of a fixed condition of the liquid at the point of its admixture with the vapor stream is achieved by maintaining the source of the subcooled liquid, or initial condition thereof, substantially constant.

In a further alternative embodiment of the invention, streams of admixed liquid and vapor combined in a suitable ratio in accordance herewith to produce saturation, are advantageously passed through a mixing column containing a body of said liquid in excess of the liquid stream constantly brought together for admixture with the flowing vapor stream. Such excess body of liquid may be arranged to act as a reservoir to compensate for minor intermittent fluctuations from the desired saturated condition of the final fluid mixture by adjusting the relative flow rates of said liquid and vapor streams so as to maintain the volume of such body of liquid substantially constant. In a further advantageous embodiment of the invention, particularly suited for delivering a fluid stream at saturation at a'predetermined delivery pressure and over a relatively Wide range of permissible flow rates, separate streams of vapor and liquid are controllably admixed in the presence of a body of saturated liquid substantially at the desired delivery pressure and the relative flows of the vapor and liquid streams, respectively, adjusted to maintain such liquid body substantially constant.

In accordance with a furtherfeature of the present invention, a system eflective to carry out the method herein described includes a pressure regulating device for controlling the delivery pressure of the vapor constituent and 'a valve device for controlling the delivery of the liquid'constituent each of which is responsive to a predetermined delivery pressure of the resultant mixture such that upon an increase in said delivery pressure above such predetermined value, each'of the vapor and liquid flows simultaneously is cut off.

Other features and advantages of the present invention, as well as a betterunderstanding thereof, may be had by reference to the following description and accompanying drawings, in which:

FIG. 1 illustrates schematically a system for the storage and delivery of the vapors of a low boiling liquefied gas under controlled conditions of temperature and pressure, wherein the superheated vapor and subcooled liquid of said stored liquefied gas are admixed in fixed relative proportions;

FIG. 2 is a schematic illustration of an alternative embodiment of the invention, particularly adapted for delivering the vapors of a stored low boiling liquefied gas at saturation by combining predetermined proportions of the superheated vapor and subcooled liquid in the presence of an excess store of substantially saturated liquid in a mixing chamber or column, maintained actually subcooled or at liquid saturation.

substantially at about the desired delivery pressure and adjusting the flow of the subcooled liquid so as to maintain a desired amount of said store of liquid in said mixing column; 7

FIG. 3 illustrates an alternative mode of carrying out the invention, involving a modified arrangement for deliven'ng the liquid and vapor constituents to the mixing column seen in FIG. 2;

FIG. 4 is a partial reproduction of a temperatureentropy diagram showing the state of the fluid in the successive stages of its delivery as carried out in connection with an illustrative embodiment of the invention; and

FIG. 5 is a cross-sectional view illustrating the construction of the flow proportioning device, or eductor, used in the apparatus shown in FIGS. 1 and 2.

Referring now to FIG. 1, a system is shown which is advantageously adapted for the delivery of a low boiling liquefied gas, such as nitrogen, at a specified condition of temperature and pressure. The sphere 10 in the drawing may be of a conventional design constituting an insulated container in which a substantial volume of liquefied nitrogen 11 is stored. The pressure within the vessel 10 is determined by the pressure of the gas in the vapor space 12 above the liquid, which vapor is substantially in equilibrium at least with the surface strata of the stored liquid while the remainder generally will be relatively in a subcooled state. The operation of the system does not depend on whether the stored liquid is The stored liquid, however, constitutes a source of liquid at a substantially fixed condition which may be mixed in a pre- 7 determined ratio with a vapor as hereinafter described. The liquid phase is withdrawn through the outlet 14 con.- nected in the conventional manner at the bottom of the container and is heated in a vaporizing coil 16 and superheating coil 17. The vapors produced in the coil 16 may be returned to the vapor space 12 of the container through the conduit 18 connecting the vaporizing coil with the top of the container. A pressure switch 20' arranged in the vapor line 18 regulates a solenoid valve 22 in the liquid outlet so as to maintain a suitable pressure within the sphere 10 for operation of the supply system. The switch 20, for example, may be set to mainta1n the pressure of 150 p.s.i.g. in the container. It may be seen that as the pressure Within the container drops below this value, such as when the contents thereof are depleted, the opening of the solenoid valve 22 permits the vaporization of liquid and return of Vapor to the container until the desired container pressure is restored.

Similarly, in the event of an excess vapor pressure, the

vapor, preferentially, will be delivered to the superheating coil 17 from the top of the storage vessel, with valve 22 closed. Such means for maintaining a desired storage vessel pressure are well known for stored liquefied gases and need not be described in any further detail.

The vaporized liquid from coil 16 is conducted through the heating coil 17 and thence to a vapor outlet line 26 having a pressure reducing regulator 28. The combined eifect of the

coils

16 and 17 as to the fluids delivered therethrough is to vaporize the liquid from the bottom of the vessel'and heat such resulting vapors or the vapor from the vapor space in the vessel uniformly to a predetermined constant temperature, such as F., independently of the flow. Air or other suitable heating fluid may be employed in heat exchange with the

coils

16 and 17 in conventional vaporizing means to vaporize and heat the liquid a predetermined amount.

The pressure reducing regulator 28 may, for example, be of a conventional socalled pilot-loaded type having a valve element 30 operated in response to the movement of a control diaphragm 32 to open and close the regulator nozzle and thereby control the flow of vapor therethrough. The delivery pressure of the regulator is determined by loading the, control diaphragm 32 with a pressurizing gas. Such pressurizing gas is delivered through a pilot loading regulator 34 which is connected to a suitable source of pressurized actuating fluid such as air or nitrogen. Preferably, the actuating fluid is obtained from the delivery line 26 through a tap 34'. The loading fluid delivered at a predetermined pressure from the pilot regulator is delivered to the pressurizing chamber of the diaphragm 32 and is allowed to bleed off through a venting passage 35 to the atmosphere at a rate controlled by solenoid valve 36. With this control system for regulating the loading of the flow control regulator 28, restriction of the flow of gas through the bleed conduit 35 produces an increase in the diaphragm loading pressure and a reduction in such restriction reduces the loading pressure. The setting of the pressure regulator 34 and the capacity of the bleed conduit 35 and control valve 36, are such that when the valve 36 is fully opened the loading pressure on the diaphragm 32 is sufiiciently reduced to permit the regulator ZS-to close. Also the pilot regulator 34 may be set so that, with the bleed valve 36 totally closed, its output constitutes the loading pressure on the diaphragm 32. The valve 36, however, may be operated in such a manner as to produce varying loading pressures on the diaphragm and to thereby control the delivery pressure of the regulator 28 in a desired manner. It will be seen that various known types of pressure regulating means may be employed in place of the specific regulating device 28 which will sat isfactorily deliver the vapor at adesired pressure. The operation of the solenoid valve 36 and thereby of the pressure delivery regulator 28 is controlled by a pressure responsive switch 37 through connecting control circuit means 38 as shown in dotted lines. The pressure switch 37 is connected to a delivery line 40 through which the final fluid mixture to be delivered in accordance with the present invention is supplied as will be more fully understood from the following description.

The vapor delivered by the regulator 28 is conveyed through a conduit 41 connecting with the vapor inlet 41 of an eductor device shown at 42. The eductor is a device whose general type and construction are known to those skilled in the art and is characterized by operations such that predetermined proportionate amounts of two or more respective'fluids are admixed to form a combined fluid stream. Liquid is delivered to the eductor through the liquid inlet shown at 44. In the system herein shown, liquid withdrawn from the vessel through the line 14 is delivered through a liquid line 46 to the inlet 44 of the eductor. Desirably, the static head of liquid, by arrangement of the level of the mixing eductor relative to the level of liquid in the storage vessel, is either substantially zero or slightly positive, so that substantially no pressure drop is required in the eductor to aspirate the liquid stream. Where the liquid may be delivered as the primary fluid to the eductor, the elevated pressure at which the vapors are supplied, similarly, eliminates any necessity for aspiration.

The liquid supply line 46 is equipped with a solenoid operated shut-off valve 47 and with a manually adjustable throttling valve 48 whose operation will be described hereinafter. It may be seen, however, that the solenoid valve 47 is responsive to the operation of pressure switch 37, connected in the delivery line 40, and may be operated to close and open simultaneously with the bleed valve 36. In addition, the solenoid 48 may be independently operated by a temperature responsive switch 49 which is connected in the fluid delivery conduit 50 of the eductor device.

A suitable construction of the eductor device 42 is illustrated in the cross-sectional view of a typical eductor shown in FIG. 3. Referring thereto, it may be seen that the eductor includes a main tubular housing 51 in which is formed an elongated mixing chamber 52 and into which the respective fluids delivered from the vapor delivery line 41 and the liquid delivery line 46 are introduced.

The vapor from the eductor inlet 41' is throttled through an inlet orifice 54 which is shown as an annular space surrounding an inwardly extending nozzle 55. The annular orifice for the vapor is of a predetermined crosssectional area which determines the flow of the vapor to the mixing chamber of the eductor depending upon the diflerential pressurev between the pressure P at the vapor inlet and the pressure P in the mixing chamber 52. The liquid enters the mixing chamber. 52 through an orifice 56'at the end of the nozzle 55, which is of a preselected cross-sectional area and whichdetermines the flow of the liquid into the chamber depending upon the differential pressure between the liquid inlet pressure P and the pressure P of the mixing chamber. It will be seen that by selecting the

delivery orifices

54 and 56 and maintaining the pressures P and P at the vapor and liquid inlets to the eductor respectively, and the delivery pressure P reasonably constant, the streams of the liquid and vapor mixed in the eductor will remain in a predetermined substantially fixed ratio.

It has been found that this can be achieved by providing the respective orifices so thatat the lower limit of the flow range for which the system is intended to be.

may be made to increase, for example, the delivery pressure of the vapor at the inlet 41 as increased flow rates are required which, however, is preferably limitedto some maximum pressure which will not noticeably alter the desired predetermined ratio of the vapor relative to the liquid delivered to the eductor. It may be seen that where such an eductor device is employed to provide the desired mixing of fixed proportions of the vapor and.

liquid in carrying out the present invention and where a relatively wide range of delivery flows may be required, such that with a single eductor device, the limitations in its performance may incur changes either. in the proportions of the fluids or in the delivery pressure, that a plurality of two or more such eductors may be arranged in parallel so that the vapor and liquid flows through any single one of them will remain within a range of optimum performance.

Desirably, the vapor and liquid undergo some agitation to facilitate mixing in the chamber 52 which is advantageously of slightly converging and diverging crosssection to facilitate achievement of this result. The slight pressure drop which may be incurred by such contour of the flow passage is substantially negligible. The combined streams discharge through the delivery outlet of the eductor 60 in which is received the delivery conduit 50. The manner in which the respective vapor and liquid delivery orifices are detenrnined in carrying out the present invention will be described in greater detail hereinafter.

The combined vapor and liquid streams discharged from the outlet of the eductor are conducted through the conduit 50 to a separating chamber 64 which is of relatively large cross-sectioual area. The chamber 64 is so arranged as to facilitate thorough intermingling of the admixed streams and enable completion of the heat exchange therebetween so that the desired resultant condition of the final stream may be brought about. The construction and arrangement of such types of devices to produce thorough mixing of vapors and liquids are generally known and need not be described in any detail. A drain line 66 is provided at the bottom of the chamber to allow any excess droplets of liquid in the admixed streams which tend to settle as the stream velocity is reduced, to be precipitated and withdrawn from the chamber. The resultant fluid stream at the pressure corresponding substantially to the fixed delivery pressure rnospheres absolute.

control by the regulator 28 is delivered to the intended point of use from the chamber through the delivery line 40.

The following example will serve to illustrate the operation of the system hereinabove described in connection with FIG. 1 for delivering a desired saturated vapor at a predetermined delivery pressure. Reference is made to the temperature-entropy diagram shown in FIG. 4 showing the coordinates representing the condition of the fluids at various stages in the system. In this illustrative embodiment, the system is employed for delivering nitrogen at saturation at a delivery pressure of about 1.5 atmospheres absolute. The specified flow to be provided at these conditions may be taken as approximately 3,000 cubic feet per minute, with accommodation of an overload in delivery of about twenty-five percent without undesirably affecting the resulting fluid conditions. In the embodiment shown in FIG. 1, the liquid nitrogen in the container will be assumed to be subcooled to about 81 K. and to have a vapor pressure within the storage vessel of about 10 atmospheres absolute.

Referring to the temperature-entropy diagram, the point shown at A identifies the mass of subcooled liquid Within the storage vessel which being at 10 atm. and subcooled to about 81 K. has an enthalpy, or heat content, of 26.5 cal./gm. The values for the thermodynamic properties of the nitrogen may be obtained from standard published tables such, for example, as given in the Summary Technical Report of Division 11, NDRC, vol. 1, Improved Equipment for Oxygen Production, 1946.

Depending upon the source of such data which is used, the quantitative values assigned to the various conditions may diifer slightly but generally will be in suflicient agreement for the purposes of carrying out the present invention. Specific values given in the present example have been obtained from tables compiled by the assignee of the present invention which are based generally upon the data published by Kamerlingh Onnes Laboratory, Leyden, Belgium. It Will be seen that the point A lies on the saturation curve represented by the dome-shaped curve S on the diagram. The liquid taken from the container and delivered to the vaporizing coils 16 and 17 is heated at constant pressure to the liquid saturation point shown at A, temperature of 113 K., thence to the vapor saturation point D and thence to the state of superheat represented substantially by the point B which, for example, corresponds to a temperature of 804 F. (300 K.) and 10 atmospheres absolute pressure. The enthalpy of the vapor at the point B is substantially 127 cal./ gm. The heating of the fluid as represented on the diagram from point A to B occurs substantially isobarically. The condition of the fluid at point B corresponds to the condition of the vapor at the inlet to the pressure regulating device 28 in FIG. 1. Through the regulator 28, the pressure may drop substantially to a value which may be represented by the point C on the isenthalpic curve B-V The vapor then undergoes a further drop in pressure from C to the point V which is the pressure corresponding substantially to the delivery pressure existing Within the outlet of the eductor device 42 in FIG. 1. Such pressure in the present example is substantially about 1.5 at- The reduction in pressure of the heated fluid from 'B to V, may be taken as being substantially isenthalpic such that the heat content of the vapor delivered to the mixing chamber of the eductor 42 is substantially about 127 cal./ gm. In admixing with the liquid delivered to the mixing chamber of the eductor so as to produce a resultant stream at the satunation point, the vapor must undergo cooling so as to change its state from the point V on the diagram to the point M which corresponds to the'saturation point of nitrogen at substantially 1.5 atmospheres. At the point M the heat content of the fluid is about 72.5 cflj gm. The differ- V ence in enthalpy in the fluid between the point V, (which able periods to permit sustained operation.

is the same as at the point B) and the final condition M is, therefore, about 54.5 cal./gm.

Considering now the delivery of the liquid from the container 19 for admixture with the vapor furnished in the manner above described, such liquid under the condition at A may undergo a slight degree of heating to the point represented at A due to normal heat leakages in the liquid conduit system which, it will be apparent, will be relatively constant for any given system. The point A or A may, therefore, be taken as corresponding substantially to the intial state of the liquid. At point A, the heat content of the liquid is 27.8 cal./gm. and its temperature is 84 K. The liquid thence undergoes a reduction in pressure along the line A, L, through the manual valve shown at 48 and the liquid orifice 56 of the eductor. Such reduction in pressure may be taken as being substantially isenthalpic so that the heat content of the liquid remains substantially unchanged between the point A and L' However, it will be seen that as a result of such throttling from 10 atmospheres to the final delivery pressure corresponding substantially to 1.5 atm., vapor will be produced corresponding substantially to a saturated vapor so that the actual available liquid for admixture with and cooling of the vapor stream corresponds to the quality of the fluid at the point L, which in the present instance is substantially about 98% liquid. Such fluid which is introduced through liquid inlet 44 of the eductor upon heat exchange with the vapor stream delivered as above-described, is supplied with the required latent heat of vaporization and heated thereby to the point 'Mf at constant pressure. The difference in heat content of the liquid between the points A and Mg is 44.7 ca1./ gm. multiplied by the quality of the throttled liquid (.98) to give a latent heat of vaporization of 43.7 cal./ gm.

To produce a final stream at the desired delivery pressure of 1.5 atmospheres and at saturated conditions, the amount of liquid required for a given amount of vapor will correspond to the amount of the vapor supplied multiplied by the heat content of such fluid between the conditions represented by V, and M on the diagram divided by the difierence in the heat content of the liquid to be in the present example, for unit volume or mass of vapor about 1.24 equivalent units of liquid are required. It may be seen that the desired proportions of vapor and liquid for producing a resultant stream of any other desired condition may be similarly determined. Thus, the proportions required to produce a resultant stream at any condition such as represented by the point M in FIG. 4, would be similarly determined by the differences between the initial states of the liquid and vapor and the final state M "Having determined the respective proportions of vapor and liquid that are to be admixed inthe above illustrative example, the desired sizes of the

proportioning orifices

55 and 56 of the eductor may be computed. In the present example, a vapor inlet orifice of 1.33 square inches and a liquid inlet orifice of 0.49 square inch may advantageously be employed to deliver the desired flow rate. of resultant mixture with a reasonable accommodation of flows in a range above and below such rate.

It will be apparent that in the foregoing example, in which the proportioning of the vapor and liquid is maintained in a desired fixed ratio, the method relies, in part at least, upon the constant condition of the mass of liquid in the storage vessel. The condition of such liquid has been found to remain substantially constant for reason- However, such liquid does undergo. a change in condition particularly as the vessel is gradually depleted of its supply so that if successively greater amounts of the liquid are consumed the liquid becomes less and less subcooled and gradually increases in temperature toward its saturation temperature of 103.8 K. As the temperature of the liquid increases, relatively greater amounts of the liquid are required in proportion to the vapor. To compensate for this gradual change, it is merely necessary in carrying out the inventionin connection with the system shown in FIG. 1 to open the manual throttling valve 48 through which the liquid is suppliedto the liquid inlet of the eductor. Such manipulation has the effect of increasing the liquid inlet pressure to the eductor orifice thereby permitting a comparable adjustment in the relative flow of liquid introduced to the eductor. The proper setting of the manual valve may be determined by observation of the temperature in the outlet of the eductor, the setting being correct when this temperature is reduced from a slight degree of superheat to approximately the temperature at the point of saturation.

It will be seen that upon cessation of a demand in the delivery line 40, such as by closing a downstream supply valve, the pressure in the line 40 will increase. Upon increase to a suitable value of the pressure in the delivery line pressure switch 37 is actuated to simullaneously close off the respective vapor and liquid supplies. This action, thus, affords a safety control which prevents the delivery or accumulation of liquid in the vaporizing portions of the system which could readily become heated and expand so as to produce excessive vapor pressures, beyond those values for which the system has been safely designed. The temperature responsive switch 49, it will be seen, affords an additional degree of safety and may be set so that upon the appearance of temperatures in the delivery line 50 corresponding to liquid conditions therein the liquid supply solenoid valve 47 may be closed.

Referring now to FIG. 2 of the drawings, a system similar in many respects to that shown in FIG. 1 is shown. The identical portions of. the system in FIG. 2 are identically labeled. The vapor regulator in this system to which the superheated vapors from the coil 17 are delivered is shown at 68. This device may be of a slightly different type from the control regulator 28 shown in FIG. 1 and may, for example, be of the type provided with diaphragm loading gas from its downstream outlet such as illustrated by the line 68. The regulator, however, is of a conventional design and need not be described in detail, except to indicate that it is effective to maintain a predetermined delivery pressure in any suitable fashion. The vapor from the regulator is delivered through the conduit 41 to an eductor device shown at 42', which is substantially identical to the eductor 42 seen in FIG. 1. Liquid from the storage vessel which is delivered through conduit 46 to the liquid inlet of the eductor 42' is controlled by a solenoid valve 70. The eductor 42 is substantially the same as the eductor previously described in that it is provided with respective vapor and liquid inlet orifices of predetermined cross-sectional flow areas, such that with the respective fluids at their prescribed inlet pressures, the resultant fluid mixture contains the admixed vapor and liquid constituents in substantially desired proportions. Such admixed fluid stream is delivered from the eductor through an outlet conduit 59 to the base of a mixing column shown at 72.

The mixing column is provided with a predetermined desired volume of liquid corresponding to the liquid which is to be supplied substantially at its point of saturation. The liquid may, for example, be provided in the column to the level indicated at L. It may be seen that the mixing column 72 is maintained substantially at a pressure corresponding substantially to the exit pressure of the eductor which corresponds to about the desired delivery pressure of the resultant saturated fluid stream. The upper portions of the column above the liquid L may advantageously be filled with a suitable porous packing to facilitate heat exchange and the removal of liquid droplets contained in the vapor rising to the top of the column for discharge through the outlet 74. The resulting fluid stream delivered by the conduit 74 is conveyed through a suitable separator chamber 76 which corresponds substantially to the chamber shown at 64 in FIG. 1 wherein minute liquid particles that might remain may be separated and returned to the base of the mixing column 72 through a return conduit 78. The resulting fluid stream is elfectively delivered through a delivery conduit 80 at a closely maintained desired delivery pressure by means of a suitable pressure regulating device 82. It will be understood that the necessary reduction in pressure for operation of the regulating device 82 is desirably relatively small so that the slight degree of superheating which occurs by expansion of the saturated vapors therein is negligible and that, therefore, the final fluid stream at a closely maintained delivery pressure may be substantially at saturation.

The level of the liquid in the mixing column 72 is indicated by a level indicator gauge 84 which may be arranged to automatically operate the liquid solenoid valve 70 as indicated by the dotted line 86 so as to controllably open or close such liquid control valve to maintain a desired level of the liquid L in the mixing column. A pressure responsive switch shown at 88 also is arranged to be responsive to the pressure within the mixing column and to close the liquid valve 70 through control means represented by the dotted lines 90 in the event that the mixing column exceeds a predetermined desired pressure.

In the embodiment of FIG. 2, it will be seen that the flow of liquid to the eductor 42' may be efl'ectively varied by opening and closing the liquid solenoid valve 7% in response to the level indicator 84 so as to maintain the volume of the liquid in the mixing column constant. In the event, therefore, during any specified interval, that an excess of the vapor relative to the liquid is supplied so that the resultant fluid mixture thereof tends to be relatively superheated, an equivalent amount of the liquid shown in the mixing column will be caused to vaporize which will be manifested by a reduction in the level of the liquid therein. Accordingly, the level control device 84 will manipulate the liquid valve 79 so as to increase slightly the liquid flow to return the liquid level L to its predetermined level and, thereafter, to maintain such level substantially constant. A reverse operation of the liquid valve 70, of course, occurs when the relative proportion of the liquid delivered to the eductor is excessive. It may be seen that the pressure in the mixing column 72 is maintained substantially at about the delivery pressure at which the saturated vapors are to be supplied and that the residual liquid which is maintained in the bottom of the column comprises a volume of substantially saturated liquid such that the equilibrium vapors evolving from such volume of liquid and rising up in the column will be substantially in a saturated condition. The column is constructed of suflicient vertical extent and preferably packed with a suitable packing such as Raschig rings so that substantially all of the liquid that might be entrained in the rising vapors is substantially effecuvely separated and returned to the lower portion of the column.

Referring now to FIG. 3, an alternative embodiment of the system shown in FIG. :2 is illustrated. In this system, all of the component elements are identical to that shown in FIG. 2 with the exception that the eductor shown at 42 in FIG. 2 has been eliminated. As shown in FIG. 3, the liquid delivery line 46 from the li uid control valve 70 is connected directly to the mixing column at an intermediate level therein preferably at a point slightly above the normal level of the liquid L therein. The vapor delivery line 41 is in turn directly connected to the lower end of the mixing column at substantially the same point as the line 50 in FIG. 2 was previously connected which corresponds preferably to a point below the normal level of the liquid L. It will be seen, by this arrangement, respectively, of the liquid and vapor inlets to the mixing column, that a more 1 1 effective reflux of ascending vapor with descending liquid may be obtained. In this embodiment of the invention, it will be seen that the respective liquid and vapor streams are introduced to the column 72 and mixed in the presence of a predetermined volume, of substantially saturated L FIG. 2 is thus effective to reduce the flow of liquid to readjust the desired proportions to produce a substantially saturated stream and to reestablish and maintain the initial or desired predetermined volume of liquid at the bottom of the mixing column. Substantially the same control occurs in the event that the vapor stream becomes'out of balance or in the event that the supply of liquid becomes warmer or temporarily flows at a reduced rate, which results in a reduction of the excess volume of liquid which is normally maintained in the bottom of the column due to the increased rate of vaporization caused by the delivery of the superheated vapor to the column. Consequently, an increased flow of liquid by opening of the control valve 70 will occur.

It will be seen, however, that the column is maintained substantially constant at a predetermined pressure and that the vapor evolving from the liquid body at the bottom of the column will remain at the desired saturated condition even though the initial conditions of the respective vapor and liquid constituents, or the relative flows thereof, may temporarily vary. This embodiment, furthermore, aliords advantages in readily accommodating wide ranges of delivery ranges.

Having now described the above advantageous embodiments of the present invention and the modes of carrying out the method and operation of such apparatus, it will be apparent that this invention alfords a highly useful, efficient and economic means for controllably delivering a low boiling liquefied gas at a predetermined desired condition to meet varying demands. Moreover, streams of such fluids may be reliably reproduced and maintained for substantial intervals by use of the invention. While not specifically indicated herein, it will be understood that for economic reasons, as well as for facilitating control of the fluid conditions, the various portions of the system, other than the Vaporizers, carrying low temperature fluids are advantageously insulated and arranged in the conventional manner to reduce heat leakage 'to the surrounding atmosphere to a minimum.

The invention is not necessarily limited to the specific embodiments herein illustrated and described, but may be used in other Ways without departure from its spirit as defined by the following claims.

We claim:

1, The method of delivering a low boiling liquefied gas at a predetermined thermodynamic condition at a desired delivery pressure comprising maintaining separate streams respectively, of a superheated vapor and a liquid of a low boiling liquefied gas at respective initial thermodynamic states at elevated pressures, delivering and admixing said streams to produce a resultant stream of the predetermined thermodynamic delivery condition at said "desired delivery pressure, said streams being expanded substantially isenthalpically from said elevated pressures to said delivery pressure, and controlling the relative proportions of said superheated vapor and liquid streams to balance the available heat of said vapor stream with the required heating of said liquid stream to effect the change, respectively, of said liquid and vapor from their respective initial thermodynamic states to said thermodynamic delivery condition.

2. The method of delivering a low'boiling liquefied gas at a predetermined condition at a desired delivery pressure comprising maintaining separate streams of a superheated vapor and a liquid, respectively, of a low boiling liquefied gas, at constant, initial conditions at relatively elevated pressure, throttling said streams substantially isenthalpically to lower pressure, admixing said streams substantially at said delivery pressure to produce a resultant stream of the desired delivery condition and delivery pressure, and controlling the relative proportions of said vapor and liquid streams to balance the available heat of said vapor stream with the required heating of said liquid stream to effect the change, respectively, of said liquid and vapor from their initial states to said delivery condition.

3. The method of delivering a low boiling liquefied gas at a predetermined condition according to claim 2, wherein said liquid and vapor streams, respectively, are obtained from a common source of low boiling liquefied gas stored as a liquid in an insulated vessel under elevated pressure and a portion of said liquid is vaporized and heated in a controlled manner to provide said vapor stream. I

4. The method of delivering a fluid stream of" a low boiling liquefied gas at a desired thermodynamic condition comprising maintaining separate sources of superheated vapor and liquid, respectively, of said low boiling liquefied gas at substantially constant respective thermodynamic conditions, delivering streams of said vapor and liquid and admixing said streams in a predetermined substantially constant proportion to form said delivery fluid stream, said liquid source being a body of liquid stored at a substantially constant, relatively elevated pressure in an insulated vessel and a portion of said liquid being vaporized and heated a predetermined extent substantially at constant pressure to provide said separate source of vapor, and said streams of liquid and of vapor being throttled substantially isenthalpically to a desired delivery pressure.

5. The method of delivering a fluid stream of a low boiling liquefied gas according to claim 4, wherein said vapor and liquid streams, respectively, are throttled by passage through orifices relatively proportioned to effect the desired proportions of said admixed streams.

6. The method of delivering a fluid stream of a low boiling liquefied gas comprising maintaining separate sources of vapor and liquid, respectively, of said low boiling liquefied gas at substantially'constantconditions, delivering streams of said vapor and liquid and admixing said streams in a predetermined substantially constant proportion to form said delivery fluid stream, said liquid and vapor streams being admixed and contacted with an excess volume of said low boiling liquefied gas at substantially saturated condition. i

7. The method of delivering a fluid stream of a low boiling liquefied gas, comprising maintaining a volume-of said liquefied gas substantially at a desired delivery pressure, delivering and admixing in the presence of said liquid volume separate superheated vapor and liquid streams of said low boiling liquefied gas, Withdrawing the vapors resulting therefrom and adjusting the relative flows of said liquid and gas streams to maintain said liquid volume substantially constant.

8. The method of delivering a fluid stream of a low boiling liquefied gas, comprising maintaining a volume of said liquefied gas substantially at a desired delivery pressure, admixing in the presence of said liquid volume separate vapor and liquid streams of said low boiling liquefied gas, withdrawing the vapors resulting therefrom and adjusting the relative flows of said liquid and gas streams to maintain said liquid volume substantially constant, said liquid and vapor streams being derived from a common source of liquid maintained at an elevated pressure in an insulated vessel, a portion of said liquid being vaporized and superheated to produce said vapor stream and said liquid and said vapor streams being reduced to said pressure at which said streams are admixed.

9. The method of delivering a fluid stream of a low boiling liquefied gas according to claim 8, wherein said liquid stream is controlled to maintain said liquid volume substantially constant.

10. The method of delivering a fluid stream of a low boiling liquefied gas at a desired delivery pressure and thermodynamic condition, comprising maintaining separate sources of a superheated vapor and a liquid of said low boiling liquefied gas at substantially constant predetermined, respective, thermodynamic states, delivering streams of said liquid and superheated vapor, respectively, controllably admixing said streams to produce said desired fluid stream and terminating the delivery of said streams in response to an increase in the delivery pressure of said fluid stream above a predetermined value.

11. The method of delivering a fluid stream of a low boiling liquefied gas at a desired delivery pressure, comprising maintaining separate sources of a vapor and a liquid of said low boiling liquefied gas, delivering streams of said liquid and vapor, respectively, admixing said streams to produce said desired fluid stream, terminating the delivery of said streams in response to an increase in the delivery pressure of said fluid stream above a predetermined value, and preventing the delivery of said liquid stream in response to temperatures of said fluid stream below a predetermined value.

12. Apparatus for delivering fluids at relatively low temperatures comprising an insulated storage vessel adapted to hold a supply of a low boiling liquefied gas at an elevated pressure, means for maintaining the vapor pressure in said vessel substantially constant, means for withdrawing liquid firom said vessel and delivering a stream of said liquid at a controllable rate at a predetermined elevated pressure, means for simultaneously withdrawing a further portion of liquid from said vessel and vaporizing and heating said further portion of liquid and delivering a stream of the vapors resulting therefrom at a controllable rate at -.a predetermined elevated pressure, means for throttling substantially isenthalpically said vapor and liquid streams from said respective predetermined elevated pressure thereof to substantially a desired predetermined delivery pressure, and means for admixing said liquid and vapor streams in desired proportions substantially at said desired predetermined delivery pressure and delivering the resulting admixed stream.

13. Apparatus for delivering fluids at relatively low temperatures, according to claim '12, wherein said liquid and vapor stream delivery means, respectively, include restricting orifices and said orifices are relatively propor- :tioned so as to maintain the proportions of said vapor and liquid streams, respectively, substantially constant.

14. Apparatus for delivering fluids at relatively low temperatures comprising an insulated storage vessel adapted to hold a supply of a low boiling liquefied gas at an elevated pressure, means for maintaining the vapor pressure in said vessel substantially constant, means for withdrawing liquid from said vessel and delivering a stream of said liquid, means for Withdrawing a further portion of liquid from said vessel and vaporizing and heating said further portion of liquid and delivering a stream of the vapors resulting therefrom, a chamber containing a body of said low boiling liquefied gas, means for introducing said respective vapor and liquid streams into said chamber, means for delivering the resulting vapors from said chamber and means responsive to the level of said body of liquid in said chamber to control the relative flow rates of said liquid and vapor streams.

15. Apparatus for delivering fluids at relatively low temperatures in accordance with claim 14, wherein said means for introducing said respective vapor and liquid streams into said chamber includes means for combining said vapor and liquid streams prior to introduction into said chamber.

16. The method of delivering a low boiling liquefied gas :at a predetermined thermodynamic condition at saturation, comprising maintaining separate streams, respectively, of a superheated vapor and a liquid, of a low boiling liquefied gas, at respective initial thermodynamic states, delivering and admixing said streams to produce a resultant stream of the predetermined thermodynamic delivery condition at saturation and controlling the relative proportions of said superheated vapor and liquid streams to balance the available heat of said vapor stream with the required heating of said liquid stream to effect the change respectively of said liquid and vapor from their respective initial thermodynamic states to said thermodynamic delivery condition at saturation.

References Cited in the file of this patent UNITED STATES PATENTS 2,037,673 Zenner Apr. 14, 11936 2,729,948 Northg-raves Jan. 10, 1956 2,747,374 Thompson May 29, 1956 2,933,901 Davison Apr. 26, 1960 2,938,576 Cox et a1 May 31, 1960

Claims

1. THE METHOD OF DELIVERING A LOW BOILING LIQUFIED GAS AT A PREDETERMINED THERMODYNAMIC CONDITION AT A DESIRED DELIVERY PRESSURE COMPRISING MAINTAINING SEPARATE STREAMS RESPECTIVELY, OF A SUPERHEATED VAPOR AND A LIQUID OF A LOW BOILING LIQUEFIED GAS AT RESPECTIVE INITIAL THERMODYNAMIC STATES AT ELEVATED PRESSURES, DELIVERING AND ADMIXING SAID STREAMS TO PRODUCE A RESULTANT STREAM OF THE PREDETERMINED THERMODYNAMIC DELIVERY CONDITION AT SAID DESIRED DELIVERY PRESSURE, SAID STREAMS BEING EXPANDED SUBSTANTIALLY ISENTHALPICALLY FROM SAID ELEVATED PRESSURES TO SAID DELIVERY PRESSURE, AND CONTROLLING THE RELATIVE PROPORTIONS OF SAID SUPERHEATED VAPOR AND LIQUID STREAMS