US2973629A - Method and apparatus for pumping liquefied gases - Google Patents

Description

March 7, 1961 E. R. LADY 2,973,629

METHOD AND APPARATUS FOR PUMPING LIQUEFIED GASES Filed Dec. 27, 1956 INVENTOR ATTORNEY E 0%4/170 R. LADY BY 6 METHOD AND APPARATUS FOR PUMPING LIQUEFIED GASES Edward R. Lady, Epsom, England, assignor to Air Products Incorporated, a corporation of Michigan Filed Dec. 27, 1956, Ser. No. 630,976 13 tllaims. (CI. 62-41 This invention relates to a method and an apparatus for pumping liquefied gases from a reservoir at low pressure to a utilization or storage system at high pressure.

In the pumping, storage and use of liquids having extremely low boiling points at atmospheric pressure, it is highly desirable to transfer them in liquid rather than gaseous phase. When pumping these liquefied gases, difficulty is encountered in keeping pumps from vapor locking unless the liquefied gases are at temperatures below their boiling points under the pressure conditions present. Since liquefied gases normally exist at their boiling points, pumping systems in the past have included provision for subcooling the liquefied gas entering the pumping cycle. These subcooling arrangements are sometimes expensive and always inconvenient. Pumping systems requiring no subcooling have been heretofore proposed but they have had practical limitations which have limited their acceptance by the industry. One form of pumping system re- Uniteci tates Patent quiring no subcooling is that in which a floor pump raises the pressure of the liquefied gas to a relatively low value and the liquefied gas thus in effect subcooled is introduced into a pump which raises the pressure to the desired point. Here again, difiiculties have been encountered in practice which have detracted from the commercial value of this type of system.

In all prior liquefied gas pumps which raise the liquid to high pressure, a high pressure packing has been necessary in order to reduce blow-by to a degree consistent with the requirements of most commercal installations. Where close tolerance pumps have been relied upon to eliminate the need for a high pressure packing, the appreciable blow-by results in the waste of gas or in complicated arrangements for recovering such gas. It is well known that where high pressure packing is used, frictional heat generated introduces a problem which can be handled only by pump refrigeration and this, in turn, complicates the pumping system.

It is therefore an object of the present invention to provide a method of pumping and a pumping system which can handle liquefied gases at their boiling points and which can raise the pressure on the liquefied gas to a high pressure without introducing objectionable amounts of frictional heat and without objectionable blow-by losses.

It is a further important object of the present invention to provide a two-stage pumping method and apparatus stage.

It isa further important object of the present invention to provide a two-stage pumping method and system in which an accumulator between stages assures liquid supply to the inlet of the second stage.

A still further object of the present invention is to provide a piston pump having a frictionless support for the plunger which prevents wear on the pump cylinder walls.

In accordance with one feature of the illustrated embodiment of my invention, a stream of liquefied gas at its boiling temperature and near atmospheric pressure is withdrawn from a reservoir, e.g., the collecting zone of a fractionating device, and is introduced into a confined space from which it is displaced at an increased pressure without a substantial increase in temperature and then the pressurized liquid is introduced into a second confined space from which it is displaced at a still higher pressure into a storage or transmission system.

In accordance with further features of my invention, provision is made in my pumping cycle for the recovery of gases evolved from the boiling liquid withdrawn from the reservoir; for the intermediate storage of pressurized liquid displaced by the first displacing operation under controlled conditions and for the withdrawal and further utilization of excess liquid which may accumulate in the intermediate storage means.

Another feature of my invention is the provision of an arrangement of apparatus for pumping a liquefied gas of the character indicated with a two-stage close tolerance pump wherein friction is held to a minimum thereby to reduce the heat transferred to the fluid during the pumping operation. The elimination of sliding friction between the pistons and cylinder walls at all times not only eliminates heat generated by this friction so that only an insignificant amount of heat is transmitted to the liquid during the pumping but it also adds to the serviceable life of the pump.

In accordance with another feature of the illustrated embodiment of my invention, boiling liquefied gas at atmospheric pressure is fed into a two-stage close tolerance pump having no inlet valve in the initial stage and in which all the pumping parts are submerged in a body of liquefied gas feeding the first stage. With the present invention, a limited quantity of liquid escapes past the pistons on the compression strokes and into the body of liquefied gas.

The above and other features of the invention will be apparent from the following detailed description taken in in which blow-by from both stages returns to the initial connection with the attached drawings in which:

Figure 1 is a partly diagrammatic view of a system embodying the present invention and adapted to carry out applicants method, in which a portion of a pump is shown in longitudinal section; and

Figure 2 is a perspective of the ball bushing employed in the pump shown in Figure 1.

While the invention is applicable to handing all liquefied gases, it is found especially useful in connection with the pumping of liquid oxygen, nitrogen, hydrogen and the like, because of the very low atmospheric pressure boiling points of these liquids. The invention will be described in connection with the manipulation of oxygen, it being understood that such description is illustrative and not limiting.

In the practice of the present invention, two principal steps are employed in association with a two-stage close tolerance pump in which the pistons are in close-fitting but spaced relation to their cylinder walls. Thefirst step involves the introduction of boiling liquid oxygen at atmospheric pressure into the low pressure stage of the pump from which itis discharged under an increased pressure without a significant rise in temperature thus in effect subcooling the liquid. In the second step, the pressurized liquid is introduced into the high pressure stage of the pump from which it may be discharged at an extremely high pressure into a storage or transmission system.

Referring to the drawings, the system shown includes a liquid oxygen container 10 connected to a fractionating column 12, the latter being constructed to collect liquid oxygen in a pool in its base 14. The liquid oxygen container and fractionating column may be of conven tional construction and operation and, hence, their de tails which do not form a part of this invention will not be described. Liquefied oxygen can be led from the pool I in the base 14 of the fractionating device through a conduit 15 into the container. A conduit 16 connects conduit 15 to the inlet 18 of a two-stage close tolerance pump 20.

Pump 20 consists of a barrel 22 having a low pressure cylinder 24 formed in one end and a high pressure cylinder 26 in the other, the cylinders 24 and 26 being in axial alignment. Reciprocating in the cylinders 24, 26 "are pistons 28, 30 which are slightly smaller in diameter than the bores of their respective cylinders. The low pressure piston 28 has a pair of ring-shaped members 29 which are receivable in close-fitting but spaced relation to the walls of the cylinder 24 while the high pressure piston 30 which is likewise in close-fitting but spaced relation with the walls of the high pressure cylinder 26, 'is provided with a series of spaced grooves 32 which give a labyrinth seal that permits only a small amount of liquid to escape past the piston on its compression stroke.

The pump barrel 22 is provided with an enlarged cavity 34 that extends between cylinders 24, 26 and in which is mounted a ball bushing 36. Slidably supported in the ball bushing 36 is a reciprocating rod 38 which is connected at its opposite ends to pistons 28, 30 and supports them in their close-fitting but spaced relation to their respective cylinder walls. The pistons are reciprocated back and forth by a piston rod 40 which is connected to a power source 42 by a coupling 44. The reciprocating rod 40 is in turn slidably supported by graphite bushings 46, 48 mounted in the low pressure end of the pump barrel 22. Rod 40 is sealed by conventional means consisting of primary packing 50, gland .52 with a vented blow-by 54, secondary gland 55, and secondary packing 56, all secured by primary packing nut 57 and secondary packing nut 58. The pump may be mounted on any convenient support 60.

Mounted on the high pressure end of the pump is a head 62 having an inlet check valve 64 connected to the high pressure cylinder by a port 66 and a high pressure discharge valve 68 which is likewise connected to the high pressure cylinder by a port 70.

Surrounding the pump barrel 22 is a casing 72 which is connected at its ends to the head 62 and a flange 74 on the pump barrel to form a liquid tight compartment 76 around the pump barrel 22. Inlet port 18 is connected to the underside of the casing 72 while an outlet port 78 is provided on the upper side of the casing. When the liquid oxygen has entered the compartment 76 through the inlet port 18, any vapors in the liquid bubble out and are vented through the outlet port 78 from whence they are returned to the fractionating column 12 by a conduit 80. A liquid level may be maintained as shown in the drawing, which is slightly below the outlet port 78; however, in the event the liquid level in the oxygen reservoir is higher, the liquid may extend into the outlet 78. Conduit 80 connects with the column 12 in which vapors can be condensed and recovered. At times, the vapors can be sent to the liquid oxygen container through a conduit 81 by operating the valves shown in an obvious manner. In such instances, the column may not be operating and the liquid oxygen being pumped is supplied from the reservoir presented by container 10, the valves shown in line being operated in an obvious manner.

Liquid oxygen from the compartment 76 enters the low pressure cylinder 24 through ports 82, 84 in the pump barrel 22 when the low pressure piston 28 is in its extreme left position as shown in the drawing. At this time, any vapors which have previously been formed in the cylinder may bubble out through the port 82 to the outlet 78. As the low pressure piston 28 is moved to the right on its compression stroke, its rings 29* sea f e liquid t pp in the cylinder when they pass the ports 82, 84 and further movement of the piston pressurizes the, liquid to an intermediate pressure of, for example, 50 p.s.i.g. when it is discharged through an outlet 86 to a conduit 88. The pressurized liquid passes through a check valve 90 in the conduit and into an intermediate storage tank 92 where it is kept under controlled conditions until it is drawn into the high pressure cylinder 26. The storage tank is provided with a gauge 94 and a pressure relief valve 96 which vents excess gas or liquid back to the inlet 18 through a conduit 98 thereby controlling the pressure and volume of liquid in the storage tank. When piston 28 moves to the left the small amount of liquefied gas remaining in cylinder 24 may be partly vaporized by the resulting pressure drop but except for heat leakage into the pump at this end, all this gas would be liquefied on contact with the bodyof supply liquid in the pump inlet. Any unliquefied gas evolved at this point bubbles out through outlet 78.

As the high pressure piston is moved to the right from the position shown in the drawing on the compression stroke of the low pressure piston 28, pressurized liquid flows from the storage tank 92 through a conduit 100 to the inlet check valve 64 and thence through the port 66 into the high pressure cylinder 26. Upon its return or compression stroke, the high pressure piston 30 further compresses the liquid to the pressure of the transmission system or the cylinder bank, which may be as high as 3000 p.s.i.g., when it is discharged through the outlet check valve 68 to a conduit 102, vaporizer 104 and storage cylinders 106. The high pressure piston 30 never completely retracts from cylinder 26 on its intake stroke and therefore there is a close tolerance seal in effect at all times.

Because of the close-fitting but spaced relation of the pistons 28, 30 to their cylinders, there will be a small amount of liquid escaping from the cylinders past the pistons upon their compression stroke. This liquid reenters the body of liquid supplying the pump, the liquid escaping past the piston 28 directly entering the low pres- .sure suction cavity while the liquid escaping past the high pressure piston 30 passes through the cavity 34, ball bushing 36 to the low pressure suction area, the cavity 34 and openings in the bushing forming passages for the movement of the liquid. The escaping liquid is then utilized on the subsequent operation of the low pressure piston 28. With this arrangement, leakage back past the pistons is no problem as the blow-by liquid is utilized in an ensuing pumping cycle. Thus, the arrangement eliminates the need for high pressure packing. I Since the high pressure inlet must at all times be supplied with liquid during pumping operations, the displacement of the low pressure stage must at least equal that of the high pressure stage. From a practical viewpoint, this means the low pressure stage must pump a very slight excess of liquid over that pumped in the second stage but valve 96 will pass and recycle this excess to the inlet 18 through conduit 98.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In an apparatus for pumping a highly volatile liquid having a low boiling point, a low pressure supply of such liquid, and a pump arranged to transmit the liquid, said pump comprising a low pressure stage and a high pressure stage each having aligned cylinders, reciprocating pistons in said cylinders, a rod interconnecting the pistons, and roller bearings for slidably supporting said connecting rod and arranged to support said pistons in closing fitting but spaced relation from their cylinder walls thereby to eliminate sliding friction between the pistons and cylinder walls.

I 2. In an apparatus for pumping a highly volatile liquid having a low boiling point, means -for providing a low pressure supply of such liquid, a pump having low pressure and high pressure stages for pumping said liquid, accumulator means between the low pressure stage and the high pressure stage for storing liquid pumped by the low pressure stage until utilized by the high pressure stage, control mechanism for regulating the liquid in the accumulator, and means for returning excess liquid from the accumulator to the low pressure supply.

3. In an apparatus for pumping a highly volatile liquid having a low boiling point, a low pressure supply of said liquid and a pump for pumping the liquid, said pump comprising a low pressure stage and a high pressure stage having aligned cylinders in each stage, a reciprocating piston assembly for compressing the fluid in each cylinder including pistons slidably mounted in each cylinder and a reciprocating rod connecting said pistons, antifriction means for slidably supporting said connecting rod and arranged to support said pistons in close fitting but spaced relation from their cylinder walls thereby to eliminate sliding friction between the pistons and cylinder Walls and passages for returning liquid escaping past said pistons to the low pressure supply of the pump. 7

4. In an apparatus for pumping a highly volatile liquid having a low boiling point, a low pressure supply of said liquid and a pump for pumping the liquid, said pump comprising a low pressure stage and a high pressure stage, cylinders in each stage, pistons for compressing the fluid in each cylinder arranged in close fitting but spaced relation from their cylinder walls, and means for returning liquid escaping past said pistons to the supply.

5. In an apparatus for pumping a highly volatile liquid having a low boiling point, a low pressure supply of said liquid and a pump for pumping the liquid, said pump comprising a low pressure stage and a high pressure stage, aligned cylinders in each stage, pistons for compressing the fluid in each cylinder arranged in close fitting but spaced relation from their cylinder walls, and passages for returning the liquid escaping past the high pressure piston to the low pressure supply.

6. In a method wherein a compressed and cooled mixture of low boiling gases is separated in a fractionating operation producing a liquid product and a gaseous product, the steps comprising withdrawing a stream of liquid product at its boiling temperature from a collecting zone in the fractionating operation and introducing it into a confined space, eflecting positive displacement of a major part of the liquid product from the confined space at an increased pressure without a substantial increase in temperature, introducing the pressurized liquid product into an accumulation zone, transferring liquid from the accumulation zone to a second confined space and effecting positive displacement of a major part of the liquid product from the second confined space to a transmission system at a still higher pressure, and conducting vapor from the accumulation zone to the fractionating operation.

7. In a method wherein a compressed and cooled mixture of low boiling gases is separated in a fractionating operation producing a liquid product and a gaseous product, the steps comprising withdrawing a stream of the liquid product at its boiling temperature from a collecting zone in the fractionating operation and introducing it into a confined space, efiecting positive displacement of a major part of the liquid product from the confined space at an increased pressure without a substantial increase in temperature, storing and maintaining the pressure of the liquid product displaced from the confined space, introducing pressurized liquid product from storage into a second confined space, effecting positive displacement of a major part of the liquefied product from the second confined space to a transmission system at a still higher pressure, and returning stored vapor under reduced pressure to the fractionating operation.

8. In an apparatus for pumping a highly volatile liquid having a low boiling point, means for providing a low ing cylinders spaced by a chamber in fluid communication with the cylinders, pistons for compressing fluid in the cylinders, the pistons having external diameters slightly less than the internal diameter of respective cylinders, rod means joined to the pistons and traversing the chamber between the cylinders, means carried by the casing and located within the chamber for slidably supporting the rod means to position the pistons in close fitting but spaced relation from the walls of respective cylinders, and means for reciprocating the rod means.

10. Apparatus for pumping a highly volatile liquid having a low boiling point comprising a casing presenting cylinders spaced by a chamber in fluid communication with the cylinders, pistons for compressing fluid in the cylinders, the pistons having external diameters slightly less than the internal diameter of respective cylinders, rod means joined to the pistons and traversing the chamber between the cylinders, anti-friction bearing means carried by the casing within the chamber and extending along the rod means for slidably supporting the rod means to position the pistons in close fitting but spaced relation from the walls of respective cylinders, and means for reciprocating the rod means.

11. Apparatus for pumping a highly volatile liquid having a low boiling point comprising a casing presenting aligned first and second cylinders spaced by a chamber in fluid communication with the cylinders, a first piston for compressing fluid in the first cylinder, a second piston for compressing fluid in the second cylinder, the pistons having external diameters slightly less than the internal diameter of respective cylinders, a rod joined to the pistons and traversing the chamber between the cylinders in spaced relation with the walls of the chamber, means carried by the casing and located within the chamher and extending along the length of the rod for slidably supporting the rod to position the pistons in close fitting but spaced relation from the walls of respective cylinders, and means for reciprocating the rod.

12. Apparatus for pumping a highly volatile liquid having a low boiling point comprising a casing presenting aligned first and second cylinders spaced by a chamber in fluid communication with the cylinders, a first piston for compressing fluid in the first cylinder, a second piston for compressing fluid in the second cylinder, the pistons having external diameters slightly less than the internal diameter of respective cylinders, a rod joined to the pistons and traversing the chamber in spaced relation with the walls of the chamber, means carried by the casing and located within the chamber for slidably supporting the rod to position the pistons in close fitting but spaced relation With the walls of respective cylinders, means for reciprocating the rod, the distance between the first and second pistons being less than the space between the first and second cylinders so that one of the pistons is moved into the chamber and out of its respective cylinder upon reciprocation of the rod, and means forming a port in the casing and communicating with the chamber adjacent the one cylinder.

13. Apparatus for pumping a highly volatile liquid having a low boiling point comprising a casing presenting aligned first and second cylinders spaced by a chamber in fluid communication with the cylinders, a first piston for compressing fluid in the first cylinder, a second piston for compressing fluid in the second cylinder, the pistons having external diameters slightly less than the internal diameter of respective cylinders, a rod joined to the pistons and traversing the chamber in spaced relation with the walls of the chamber, means carried by the casing and located within the chamber for slidably supporting the rod to position the pistons in close fitting but spaced relation with the walls of respective cylinders, means for reciprocating the rod, the distance between the first and second pistons being less than the space between the first and second cylinders so that one of the pistons is moved out of its cylinder and into the chamber upon reciprocation of the rod, a compartment surrounding the casing and overlying at least a portion of the first and second cylinders adapted to receive a liquid to be pumped, and means forming a port located in the casing in communication between the chamber and the compartment adjacent the one cylinder. 7

References Cited in the file of this patent I UNITED STATES PATENTS 618,004

Faulkner Jan. 17, 1899 947,613 Gothmann Jan. 25, 1910 1,261,061 Seymour Apr. 2, 1918 1,299,478 Kendall Apr. 8, 1919 1,976,388 Eichelman Oct. 9, 1934 2,655,415 Briney Oct. 13, 1953 2,698,576 Strub Jan. 4, 1955 2,785,544 Levin et al. Mar. 19, 1957

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