US2680352A - Apparatus and method for pumping liquefied gaseous fluids - Google Patents

Description

June 8 1954 H. o. MCMAHON 2 680 APPARATUS AND METHOD FOR PUMPING ,352

LIQUEFIED GASEOUS FLUIDS Filed Dec. 29, 1950 2 Sheets-Sheet 1 35 I7 3 I I I5 1 i i I E I IO i l I I' '4 5 15 u i p 5 I E I 5 E l A I l I i i I n i /5 i I l l I /9 g I s I 1: 5 1;: 45 1i la INVENTOR AG NT June 8, 1954 H. 0. MCMAHON 2,680,352

APPARATUS AND METHOD FOR PUMPING LIQUEFIED GASEOUS FLUIDS Filed Dec. 29, 1950 2 Sheets-Sheet 2 FIG. 5

INVENTOR HOWARD 0. MC MAHON Patented June 8, 1954 APPARATUS AND METHOD FOR PUMPING LIQUEFIED GASEOUS FLUIDS Howard 0. McMahon, Lexington, Massl, assignor to Arthur D. Little, Inc., Cambridge, Mass., a corporation of Massachusetts Application December 29, 1950, Serial No. 203,403

12 Claims.

This invention relates to means and method for pumping a liquefied gaseous fluid from a relatively low pressure to a relatively higher pressure without the expenditure of a corresponding amount of mechanical work. More particularly, this invention relates to a pump means whereby the aforesaid pumping is performed primarily by thermal rather than by mechanical action.

' It is well known that this objective can be accomplished by any one of a number of devices known as warm converters. One such device may be visualized as a cylinder filled with a liquefied gaseous fluid and fitted with suitable check valves, into which a warm plunger is im mersed. The heat from the plunger serves to vaporize a sufficient amount of the liquefied gaseous fluid to elevate the pressure to any desired level. Such a device is irreversible in the thermodynamic sense and also in the operational sense because after one stroke the plunger is cooled off and requires reheating before it can be used again. From the thermodynamic point of view, heat is transferred irreversibly (i. e. through a large temperature difference) from the heating member (the plunger) to the fluid receiving the heat. Heat flowing across such a temperature difference occasions a larger entropy increase, which of course means that the device is very inefficient in the thermodynamic sense.

The pump of this invention is superficially similar to a warm converter of the type just described, to the extent that a plunger is used as a source of sensible heat which serves to raise the pressure of the liquefied fluid. It diifers, however, from the warm converter type of pump in the fundamental respect that the heat interchange which occurs at every temperature level between liquefied fluid temperature and room temperature does so with a minimum temperature difference. In this respect it resembles a cold accumulator or regenerator, its function. being to minimize entropy changes. Stated in another way, it permits a close approach to reversibility both in the thermodynamic and in the operational sense.

At the present time it is understood that successful pumps have been developed for pumping small quantities of liquid oxygen, or other liquefied gaseous fluid, to relatively high pressure by means of a fairly standard reciprocating mechanism, and for pumping relatively large volumes to low pressures by fairly standard centrifugal mechanisms; however no suitable pump exists for transferring large quantities of such a liquefied fluid to high pressures. A reciprocating pump satisfactory than a reciprocating pump if a suitable design for the former could be worked out. in the pump described in the present invention, however, the action is reciprocating rather than rotary. Nevertheless the need for a closely fitting piston and cylinder has been eliminated and, since no appreciable amount of mechanical work need be done, no heavy forces need be applied. It follows that the chief objections to a reciprocating pump for raising a liquefied gaseous fluid to a high pressure are eliminated by mechanism of the present invention.

In order to pump a fluid from a lower pressure to a higher pressure, which is a primary object of this invention, work must be done on the fluid. In the case of the standard reciprocating pump this work is supplied mechanically directly to the fluid. In the present invention work is done indirectly, as in any heat engine, by absorbing heat at a higher temperature and discharg ing a portion of it at a lower temperature.

The present invention is useful in the treatment of any liquefied gaseous fluid, and while it is primarily useful for treating liquefied normally gaseous fluids such as oxygen, nitrogen, carbon dioxide, argon, hydrogen, Freon, sulfur dioxide, etc., which are gaseous at normal temperatures and pressures and are liquid at various subatmospheric temperatures, it is also applicable to the treatment of fluids which are normally in liquid form (e. g. water, ethyl alcohol, and various petroleum fractions) when there is present in the apparatus a source of heat sufiicient to convert a part of said fluids to gaseous form. However, for convenience, the term liquefied gas will generally be used hereinafter, for convenience, in designating all such fluids.

This invention will now be described in more detail by reference to the accompanying drawings, wherein Fig. 1 represents a side elevational view of a preferred form of the pump of the present invention, partly in section;

Fig. 2 is a view similar to that of Fig. 1 but with the plunger at the other end of the stroke;

Fig. 3 is a side elevational view of the upper end of the pump showing one type of provision for increased heat exchange at the upper (warm) end;

Fig. 4 is a top view, somewhat enlarged, of one form of upper disk for the plunger of the pump; and

Fig. 5 is a schematic diagram showing the pump of the present invention in association'with other apparatus suitable for transforming relatively low-pressure liquefied gas to relatively high-pressure liquefied gas and then vaporizing the latter.

The pump of this invention, as shown in detail in Figs. 1, 2, and 3, is indicated generally'by the numeral 10. It comprises a pressure-resistant chamber H, which will ordinarily be in the form of a cylinder but which may, if desired, have a cross-section other than strictly circular. For convenience, however, this chamber will be generally referred to herein as a cylinder. This cylinder is entirely closed except for openings presently to be described, and is built to withstand the top pressures to which it is desired to compress the liquefied gas. Within this cylinder is a piston or, more properly, a plunger, l3, which is hollow and is filled with a. heat-conductive packing [5, such as metal turnings, chips, or pellets Which are of such character and so packed as to provide high heat capacity, low resistance for fluid flow, small free volume, and low longitudinal heat conduction. The ends of the plunger are closed by foraminous disks ll, i9, which may be made of punched metal or of wire cloth, for example, in such a way as to permit ready passage of the fluid being pumped (either in liquid or gaseous form) while still retaining the packing [5 within the plunger. To upper disk ll is attached a piston rod or plunger rod 2!, which actuates plunger I3 and which passes through hole 23 in top 25 of cylinder 1 i; this hole 23 is sealed by stufiing box 21. Also positioned at the top of cylinder H are the safety valve 29 and the blow-down line 3|, both communicating with the interior of cylinder It. Line 31 is provided with pressure gauge 83 and controlled by valve 35. 7 Rod 2! may be reciprocated to actuate plunger I3 by any conventional means, such as a manually operated handle 31 (Fig. 2) or any suitable crank means 39 (Fig. 3).

The bottom end of cylinder H is provided with an intake port 4! and an outlet port 43, controlled by valves and 41 respectively.

If the top disk I? is made of wire cloth, reinforcernent means is desirable (unless the cloth is very heavy) to provide proper rigidity between rod 2! and plunger 13. One form of reinforcement is shown in Fig. "4, wherein axial braces 51 are fixed firmly at their ends to the upper edge of the walls of plunger l3, said braces crossing at point 53 at which rod 2! is attached; wire cloth 55 is positioned either over or under said braces and is attached at its periphery to the upper edge of the walls of plunger i3. It is not necessary to attach the wire cloth to the braces, although that may be done if desired.

Both cylinder H and plunger l3 are quite long in proportion to their diameters; the plunger is shorter than the cylinder so that the former is free to move longitudinally. The plunger has substantially the same cross-sectional area and shape as that of the inside "of the cylinder but fits sufiiciently loosely therein that there is no 4 wall friction, or substantially none, in moving it up and down within the cylinder.

The lower end of the cylinder H and the fluid therein are maintained at substantially the temperature of the liquefied gas being pumped, while the upper end and the fluid therein are made relatively much warmer, say at room temperature, although this temperature may be appreciably higher or lower depending upon the nature of the liquefied gas being handled and the conditions of operation and results desired. The temperature at the lower end of cylinder l i may be controlled by immersing the same in a bath of the same kind of liquefied gas as that to be pumped or by any other suitable means. Temperature at the upper end may be controlled by any suitable means, such as by exposing the same to air at a suitable temperature; the effects of this air may be promoted by providing fins 57 around the upper end of cylinder H and blowing air of the desired temperature over the fins by means of fan 59. On the other hand, if the liquefied gas is normally a liquid and becomes a gas only at higher temperatures than normal room temperature, a still higher temperature may be employed for heating the upper end of the cylinder, e. g. a blast of highly heated air.

In the flow diagram shown in Fig. 5, the numeral 6! represents a hollow-walled vessel (Dewar) filled with a body63 of the same kind of liquefied gas as that to be pumped. Within this liquid body 83 is immersed the lower end of the pump i l. Safety valve 2%], line 3!, gauge 33, and valve 35 are provided, as already described, at the top of cylinder H; and 2E connects with the plunger within cylinder II, also as already described.

A source 65 of liquefied gas to be pumped is provided, and leading from it is pipe Bl passing through supercooling coil 69 and vapor trap ll, both immersed in the liquid body 53. The vapor trap is provided, if desired, to minimize the possibility of vapor lock. Pipe B? then enters the bottom of pump It through inlet 4!. Also adjacent the bottom of pump I0 is outlet 43; both this and inlet 41 are valved as already described. From outlet 43 another pipe '13 leads out of the liquid body 63 to a vaporizer 15, which may be any conventional type of coil or the like capable of providing adequate heat-exchange surface to cause the high-pressure liquefied gas therein to vaporize. The resulting gas, under the same high pressure, passes thereafter through pipe TI to receiving bottles or cylinders 19, which after filling are removed for storage; shipment, and use, as desired. Pipe TI is preferably provided with pressure gauge 8! and also with a blow-down valve 83.

Briefly stated, the operation-of the pump of this invention comprises moving the plunger 13 repeatedly down and then up throughout its free stroke within cylinder H, whereby the fluid being pressurized is-caused to fiowrespectively'upward and then-downward through the plunger packing thereby becoming alternately heatedand cooled. The plunger acts as a thermal accumulator, passing as it does back andforth between the warm end and the cold end of the pump.

In the operation of the present invention, the liquefied gas from source -65 flows through pipe- 67, coil 69 and trap H into cylinder H through inlet M, under pressure sufiicient to cause such fiow and to open valve "45. Plunger leis-positioned at the top of its stroke, and the'space below it within cylinder H fills with the liquefied ature as that of the top of cylinder II. As the plunger I3 approaches the bottom of its stroke, the liquefied gas within cylinder II enters into progressively warmer zones of the plunger where its vapor pressure consequently rises and the pressure throughout the entire interior of the cylinder finally reaches a value which causes the liquefied gas in the bottom part to be ejected through valve 47. Valves 45 and 4'! are so set and arranged that the former closes when the pressure within cylinder II exceeds that in pipe 61, and the latter (4'!) opens when the pressure of liquefied gas has been raised to the desired higher eve At the completion of the discharge stroke the plunger I3 has moved fully to the bottom of cylinder I I, and the free volume thus created in the upper part of the cylinder is filled with warmed gas at the pressure of the discharge through valve 41. The plunger is then raised to the top of the cylinder, by an upward pull on rod 2 l, whereupon the warmed high-pressure gas flows back downwardly through foraminous disk I? and packing l5. In so doing, it reaches progressively colder parts of the plunger and packing, and thereby a substantial part thereof (in particular that which passes into and through the lower parts of the plunger and packing) becomes liquefied again. Accordingly, the pressure throughout cylinder I I drops as the upstroke proceeds, valve 41 closes when the pressure drops below the desired output level, and finally the pressure reaches suction level, whereupon valve 45 opens and the free volume at the bottom of the cylinder again fills with liquefied gas from source 55, as before. This cycle is repeated as often as necessary to obtain the desired amount of high pressure product- It is here again emphasized that the pressure is at all times the same both above and below plunger I3 hence the only force required to move the plunger is that needed to overcome the inevitable slight amount of friction. This slight friction is due almost entirely to stuffing box 21 and to the movement of liquid and gas through the foraminous disks and the packing. There is substantially no wall friction between plunger I3 and the interior of cylinder II, as these are so constructed as to fit rather loosely.

The following will serve as an example of a specific operation of the present invention: Cylinder II was constructed of stainless steel, 2 inches i. e. and inch thick wall. Plunger I3 consisted of a thin brass shell closed at both ends by perforated disks I'I, I9 and filled with aluminum pellets so shaped and packed as to provide a void volume of 32%. The plunger length was 30 inches and its free stroke 6% inches. Clearance between interior cylinder wall and plunger was about 0.02 inch. The plunger was caused to move up and down by means of a thin stainless steel rod 2i entering through stuffing box 21 and actuated by hand. Simple ball check valves were used as valves 45 and 41, the balls being 0.025 inch in diameter and their seats 0.187 inch in diameter. The pump was operated as already described above, with associated apparatus as shown in Fig. 5. The supply of liquefied gas was liquefied nitrogen, at about 10 p. s. i. g.; the body of liquid 63 was also liquefied nitrogen, but at atmospheric pressure. The pressure of the gas delivered to cylinders I9 was 1750 p. s. i., and was prevented from bein higher by the operation of safety valve 29. A complete up and down stroke of the plunger required a time of about minute. This could be speeded up by increasing the size of the ball check valves and their orifices, and by warming the upper end of cylinder II (as shown in Fig. 3, for example)since that end became appreciably colder than room temperature during the continuance of the operation described above. Another way of increasing the frequency of stroke is to vent a small amount of the warmed gas from cylinder ii through valve 35, while the cylinder is filling with liquid from source 65.

Various modifications of the above-described invention may be made within the scope of the present invention. For example, the plunger may be any permeable mass of heat-conducting metal which will permit ready flow through it of the fluid being treated, in both liquid and gaseous form. And while the plunger preferably conforms generally to the inside walls of the cylinder, for best operation and efficiency, it may be of different shape and still permit operation in the manner herein described.

I claim:

1. Apparatus for pumping a liquefied gaseous fluid comprising an elongated chamber, a plunger fitting within said chamber and of substantially the same cross-sectional area and shape as that of the inside of said chamber, said plunger being of lesser length than said chamber and freely movable lengthwise within said chamber, said plunger being filled with a packing of discrete pieces of heat-conductive material, and provided with foraminous ends adapted to hold said packing in place, said packing and said ends permitting ready flow of said fluid from one end to the other of said chamber through said plunger, means for reciprocating said plunger in said chamber, a source of said liquefied fluid, first conduit means leading from said source to a first port adjacent one end of said chamber, a second port adjacent said end of said chamber, and second conduit means leading from said second port for conveying liquefied fiuid under pressure away from said chamber.

2. Apparatus according to claim 1, wherein said first port is provided with valve means adapted to admit said liquefied fluid into said chamber and to prevent reverse flow of said fluid, and said second port is provided with valve means adapted to permit fluid egress from and to prevent fluid entrance into said chamber.

3. Apparatus according to claim 1, further characterized in that means are provided for coolingthe fluid in said chamber adjacent said one end thereof and for warming the fluid in said chamber adjacent the other end thereof.

4. Apparatus for pumping a liquefied gaseous fluid comprising an elongated cylinder, a shorter cylindrical plunger loosely fitting in and freely movable lengthwise of said cylinder, said plunger being filled with a packing of heat-conductive material, and provided with foraminous ends adapted to hold said packing in place, said packing and said ends permitting ready flow of said fluid from one end to the other of said chamber through said plunger, means for reciprocating said plunger within said cylinder, two ports jacent one end of said cylinder, conduit means leading from a source of supply of said liquefied fluid to one of said ports, and conduit means connected with the other of said ports for cohveying fluid under pressure away from said cylinder.

5. Apparatus according to claim a, which comprises means for cooling the fluid in said cylinder adjacent said one end thereof.

6. Apparatus according to claim 5, wherein said cooling means comprises a bath of the-same kind of liquefied fiuid as that being pumped, in liquefied form and at substantially atmospheric pressure.

7. Apparatus according to claim 4, which comprises means for cooling said cylinder and the fluid therein adjacent said one end thereof, and means for warming said cylinder and the fluid therein adjacent the other end thereof.

8. Apparatus for converting a liquefield gaseous fluid under relatively low pressure into gaseous form at high pressure comprising a source of said liquefied fluid under relatively low pressure, a bath of said liquefied fluid, pump means comprising a chamber and a plunger reciprocable therein, said plunger being filled with heat-conductive material and freely permeable throughout is entire length to said fluid, the lower end of said chamber being immersed in said bath and the upper end of said chamber being outside of said bath, conduit means for conveying liquefied fluid in said source from said source, through said bath in out-of-contact relation therewith, to the interior of said chamber adjacent the lower end thereof, said conduit means comprising heatexchange means for supercooling said liquefied fluid by out-of-contact heat exchange with the liquefied fluid in said bath, check valve means in said conduit means for assuring flow of liquefied fluid only toward said chamber, second conduit means leading away from the interior of said chamber adjacent the lower end thereof, said second conduit means being provided with check valve means for assuring passage of said liquefied fluid only away from said chamber, and heat-exchange means in said second conduit means for vaporizing said liquefied fluid.

9. Apparatus in accordance with claim 8, further characterized inthat means are provided for supplying heat to the fluid in the upper end of said chamber.

10. Apparatus in accordance with claim 8, further characterized in that valve means are provided in the upper end of said chamber for venting gas from within said chamber.

11. Apparatus for increasing the pressure of a liquefied gaseous fluid, comprising an elongated chamber, means for maintaining one end of said chamber at a temperature which is below the liquefaction point of said fluid at atmospheric pressure, means for maintaining the other end of said chamber at a temperature which is above the liquefaction point of said fluid at atmospheric pressure, a plunger loosely fitting in and freely movable lengthwise of said chamber, said plunger being shorter than said chamber and being in the form of a permeable mass of heat-conducting metal and permitting ready flow of said fluid from one end to the other of said chamber through said permeable mass, means for admitting liquefied gaseous fiuid into said chamber at its colder end, and means for discharging said fluid at a higher pressure from said chamber at its colder end.

12. Apparatus for pumping a liquefied gaseous fluid comprising an elongated chamber, a shorter plunger loosely fitting in and freely movable lengthwise of said chamber, said plunger being in the form or" a permeable mass of heat-conducting metal and permitting ready flow of said fluid from one end to the other of said chamber through said plunger, means for reciprocating said plunger in said chamber, a source of said liquefied fluid, first conduit means leading from said source to a first port adjacent one end of said chamber, a second port adjacent said end of said chamber, and second conduit means leading from said second port for conveying liquefied fluid under pressure away from said chamber.

References Cited in the file of this patent UNITED STATES PATENTS

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