US2522638A - Gas compressing apparatus - Google Patents

Description

P 1950 H. R. RICARDO E'I'AL 2,522,638

GAS COMPRESSING APPARATUS Filed June 13, 1945' 4 Sheets-Sheet 1 L F/G.

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(1,6 M \r m A ttorney pt 19, 1950 H. R. RICARDO EIAL 2,522,638

GAS COMPRESSING APPARATUS- Filed June 13, 1945 4Sheets-Sheet 2 Attorney Sept. 19, 1950 I H. R. RICARDO ETAL 2,522,538

GAS COMPRESSING APPARATUS Filed June 13, 1945 4 Sheets-Sheet 3 4 BI 55 A D A3 Sept. 19, 1950 H. R. RICARDO EIAL 2,522,633

GAS COMPRESSING APPARATUS Filed June 13, 1945 4 Sheets-Sheet 4 lllllllllllllllllllmm Patented Sept. 19, 1950 GAS COMPRESSING APPARATUS Harry Ralph Ricardo,

Thomas Evans, Worthing, England; said Evans assignor to said Ricardo Application June 13, 1945, Serial No. 599,268 In Great Britain May 3, 1944 4 Claims.

This invention relates to gas compressing apparatus adapted more particularly for ,use in the compression of oxygen and has for its object to provide a compressing plant and also an improved construction of compressor to be used therein, the compressor being of the type in which water for the purpose of lubricating the pistons is admitted with the gas to be compressed.

In known oxygen compressing apparatus in which compressors of this type are used the separation of the water supplied for lubrication of the cylinders from the gas after compression has been effected in a separator constructed and arranged so that the accumulated water must be removed therefrom periodically and passed into a separate water reservoir or allowed to run to waste. This procedure is avoided in the present improved plant which is compact, simple in construction and capable of continuous automatic operation in that there is no need for the intermittent evacuation of accumulated water.

According to this invention in the improved compressing apparatus the water following a closed circuit enters the cylinders with the gas to be compressed and leaves these cylinders with the compressed gas passing thence through a cooler to a gas and water reservoir from which the water flows back to re-enter the cylinders with the incoming gas. The water used in this circuit flows to the cylinders through a metering device and is in such quantity as to abstract substantially all the heat of compression and friction while also lubricating the cylinders so that all the cooling necessary is effected internally and as the water passes with the gas through the cylinders. The metering device is constituted by a fixed resistance in the path of the water flowing in the closed circuit from the gas and water reservoir to the cylinders and takes the form of a length of capillary tube through which the water has to pass.

The path of the gas through the apparatus and the circuit followed by the water as it is used in the compressor comprise the following features, the compressor having for example two stages. The gas is drawn into the cylinder of the first stage and with it enters the water as it issues under pressure from the capillary tube metering device. The gas and water pass from this low pressure cylinder into the cylinder of the second stage and are delivered together thence through a cooler into the gas and water reservoir. The gas from this reservoir is led through a drier and then taken for storage or use. The water, under the pressure in the reservoir can flow con- London, and Aubrey tinuously through a filter to the metering device from which is issues to again enter the cylinder of the first stage with the fresh supply of gas. Means are provided for shutting off the gas delivery from the drier and leading the gas by a short-circuiting pipe back to the supply pipe, an. arrangement which is of use when it is desired to change a fully charged storage cylinder for an empty or partially empty one.

The accompanying drawings illustrate by way of example a compressor constructed according to this invention and the circuit in which this compressor is intended to be used. In these drawings:

Figure 1 is a vertical sectional elevation of a two-stage compressor. v

Figure 215 a similar view showing the cylinders of the first and second stages on a somewhat larger scale.

Figure 3 is a section through the cylinder of the first stage on the line 3-3 in Figure 2 looking in the direction of the arrows.

Figure 4 is a transverse section through the first and second stage cylinders the section being on the line 4-4 in Figure 3.

Figure 5 is a vertical sectional elevation through the high pressurev or second stage cylinder the section being mainly on the line 5-5 in Figure 4, but as to the part of the first stage cylinder which appears in Figure 5 the section is on the line 5a-5a in Figure 4.

Figure 6 is a longitudinal sectional elevation of the end of the second stage or high pressure cylinder showing an alternative arrangement of the delivery valve at the end of the cylinder.

Figure 7 is a longitudinal section through the water supply pipe showing an arrangement of the capillary tube which functions as a metering device.

Figure 8 is a diagrammatic representation of the compressing apparatus.

As mentioned the compressor here more particularly described by way of example is a twostage one having the first stage or low pressure cylinder'A and the second stage or high pressure cylinder B. The piston C which is shown as of the trunk type in the low pressure cylinder A and the piston D of the plunger type in the high pressure cylinder B are respectively connected to the crank shaft E which is driven from some suitable source of power. A rod C couples the piston C to one end of a guide member C from whose other end a connecting rod C runs to a crank on the shaft E, the guide member C reciprocating in what is in effect a crosshead guide Ihe plunger D is directly connected to one end of a similar guide member I) at the other end or which is a connecting rod D extending to the crank shaft, the guide member D reciproeating in a guide D. In a cylinder A is a liner A in the wall of which are the inlet ports A leading from an annular space or inlet belt A into which the gas and water enter from the lateral chamber F. Delivery of the gas and water is through the end of the cylinder where is a nonreturn valve constituted by a disc G which is acted on by a spring G and is seated on the end of the liner A Delivery past the valve G is through the passage A seen in Figure 5, to the high pressure cylinder B. In some cases the inlet ports A may lead tangentially into the cylinder A. The piston C carries no packing device reliance being placed on the relatively close fit of the long trunk in the liner A and the packing effect of the water.

In the high pressure cylinder B is a liner B in the wall of which are the inlet ports 13 leading from the annular space or inlet belt B into which runs the passage B communicating, asseen in Figure 5, with the delivery passage A from the low pressure cylinder A. The gas and water are delivered through the end of the cylinder B past the non-return disc valve H to the pipe B which leads ofi laterally. The valve H on which acts the spring H is seated on a ring H which in turn rests on the end of the liner B When the seating of the valve H on the ring H becomes worn this arrangement enables the seating to be renewed by inserting a new ring thus avoiding the need for removing the liner B as might be necessary if the valve was seated directly on the end of the liner; it also allows the seating to be made in a material difierent from that of which the liner is made.

The valve H may be variously arranged, two alternative constructions being shown in Figures 5 and 6. In that seen in Figure 5, which is also shown in Figures 1 and 2, the valve disc H is formed on the end of a sleeve H which is guided in a cylindrical member H fixed in the end of the cylinder B beyond the end of the liner B The spring H which tends to keep the valve disc H on its seat on the ring 1-1 is guided by a central pin H which also acts as a stop to limit the lift of the valve and at its end abuts against a shoulder on this pin. In the alternative arrangement shown in Figure 6, the valve disc H is not guided, but floats freely except for the spring H which bears against the back of the disc with its other end abutting against a plug H fixed in the end of the cylinder B.-

The manner in which the capillary tube, which serves as a metering device for the water, is arranged is shown in Figure 7. This tube J near one end passes through and is held by a plug J which is fixed in the end J of the pipe J through which the water flows under pressure to the chamber F into the side of which projects the end of the tube J. A suitable length of the capillary tube lies within the pipe J where it is subjected externally as well as internally to the high pressure at which the water is supplied. Such a length of capillary tubing, which for example may be made from stainless steel, will satisfactorily resist erosion and corrosion when employed in the delivery and for the purpose of metering highly oxygenated water passing through the tubing at high velocity for use in an oxygen compressor.

Diiierence oi. pressure lbs. Flow in per sq inch gallons gauge between per hour ends of pipe 0 0 500 6 l, 000 9. 5 l, 500 ll. 5 2,000 13.5 2, 500 15. 5 3, 000 17. 5 3, 500 19. 3

This tube will satisfactorily control the flow of highly oxygenated water in an oxygen compressor of a determined size and constructed as above described. The tube may be arranged in various ways as found convenient, but in each case the water will be delivered through it at a substantially constant rate for a constant pressure difference into the chamber F while the compressor is being driven at a fixed speed. The water is drawn from the chamber through the ports A into the cylinder A with the gas from the source of supply which enters the chamber F through the piping L and as described the gas and water then pass together through the compressor cylinders. It will be perceived that tube J constitutes a fixed; low velocity, distributed resistance to the fiow of water, the term distributed resistance" being employed hereinafter to designate a resistance eflective at a plurality of points spaced substantially in the direction of flow. The use of such a resistance is of outstanding importance in the practice of the invention, owing to the high pressures employed in oxygen compressors and the like. At such pressures, the metering of the water by the use of a conventional orifice is wholly impractical, the size of orifice required being so .small that choking with fine particles, as well as rapid erosion, is inevitable. These defects are overcome by distributing the resistance to flow over a substantial length of the supply conduit, whereby the desired total resistance may be achieved without unfavorably 10w dimensioning of the passage.

Suitable stufling glands or other devices may be provided to prevent lubricating oil from working past the crosshead guides C D towards the glands of the compressing cylinders A and B. The cylinder liners are formed of bronze and .preferably in the case of the high pressure liner of chromium bronze and the piston C and plunger D of stainless steel chromium plated. As mentioned each piston or plunger carries no packing device but relies for gas-tightness on the water and the close fit of the piston in its'liner. A suitable clearance is 0.001 inch for a low pressure piston of 2 inch diameter and 0.0005 inch for a high pressure plunger of inch-diameter. At the outer end of the liner A is a stufllng gland A through which runs the trunk of the piston C. In the case of the high pressure cylinder B there is a similar gland B, but it is convenient to provide some means whereby water and gas which may leak past the plunger D may be trapped and dealt with. For this purpose, and as an example, a lantern B may be provided between the outer end of the liner B and the gland packing B and from the trap thus formed any gas and water which finds its way along the plunger D will be returned through the passage B to the inlet belt A around the liner A of the low pressure cylinder and so to the inlet ports A. In this way these glands may be subjected only to the inlet pressure of the first stage.

Since in each stage'the inlet ports in the wall of the cylinder liner are spaced from the inner or high pressure end of the cylinder bya distance representing a substantial portion of the stroke of the piston at the time of maximum pressure, a long seal is provided and any gas or water which may find its way along the surface of the plunger is received into the inlet ports. Hence in the second stage the contacting portion of the plunger D and liner B beyond the inlet ports B" and towards the stufiing gland B can be subjected only to a pressure difference represented by the interstage pressure and the inlet pressure to the first stage.

It may be noted that by constructing and arranging the automatic discharge valves G and If so that each forms in effect the whole end, of its cylinder it becomes impossible for a lock-up of water to occur in the cylinders A and B and the end of each piston can be brought close to the face of the valve in the end of the cylinder at the end of the in-stroke. This arrangement in combination with the water which will be present on the face of the plunger reduces the clearance losses to a negligible amount.

It is desirable to provide a safety or relief valve M in the passage A B between the low and high pressure cylinders. This avoids any risk at starting-up of a lock-up with any water between the delivery A from the low pressure cylinder A and the inlet to the high pressure cylinder B which may have leaked past the water metering device while the compressor is standing still with the reservoir under pressure.

Turning now to Figure 8 this shows diagrammatically the general arrangement of the improved compressing plant in a form which is particularly suitable for use in transferring oxygen from a partially empty storage cylinder and compressing the oxygen into an empty or partially empty storage cylinder. In the gas supply pipe L there is a non-return valve L and a reducing valve L and through this pipe and the water supply pipe J wherein is the metering device. gas and water fiow to the inlet belt A of the low pressure cylinder A. The gas and water are delivered past the valve G on the instroke of the piston or plunger C and pass through the passage A B to the inlet belt B and through the ports into the high pressure cylinder B. As mentioned a safety valve M is arranged in the passage A B and there is an additional reason for this beyond its function as indicated above. The quantity of water delivered by the capillary metering device J in unit time is dependent on the pressure existing in the water supply pipe J whereas the capacity of the compressor to receive water is determined by the volume displacement of the second stage Plunger D in unit time. Therefore if the rotational speed of the compressor should fall appreciably below the speed assumed when determining the proportions of the capillary tube J for a given reservoir pressure, then more water may be fed into the compressor than the displacement of the second stage can accommodate.

The gas and water delivered from the high pressure cylinder B past the valve H is led by the pipe I? through a cooler N which may be some known form of heat exchange apparatus, or in some cases may be constituted by a cooling Jacket surrounding the pipe B Thence the gas and water enter the reservoir 0 wherein they separate, the water collecting in'the lower part of the reservoir the form of which is preferably such that its height is materially greater than its diameter. The reservoir may be provided with a safety valve 0 From the bottom of the reservoir, the water, under the pressure existent in the reservoir, is taken back by a pipe J to a filter J whence it flows once more through the pipe J and the metering capillary tube J to enter the low pressure cylinder A with a fresh supply of gas.

In those cases in which it is desirable that the compressed gas shall be delivered from the reservoir O in a reasonably dry state the gas leaving the reservoir through the pipe P is taken to a drying device Q such as a silica-gel drier. In the pipe P is a spring-loaded valve P so that when in operation a, pressure of a predetermined minimum value, for instance not less than 200 lbs. per square inch, will be maintained in the reservoir to ensure that a sufficient amount of water is supplied to the compressor to maintain the compressor at a safe temperature at normal speed. There is a valve P in a branch from the pipe P to enable the gas pressure to be blown down before stopping the compressor so that the supply of water to the compressor may cease when the compressor is stopped. The gas is led off from the drier through the pipe R in which is a valve R Between this valve and the drier a pipe R in which is a valve R runs back into the gas supply pipe L entering that pipe between the non-return valve L and the reducing valve L There is a valve P in the pipe P between the spring-loaded valve P and the drier Q. If before stopping the compressor the valves P and R are shut the silica-gel in the drier Q will be locked up under the maximum pressure existing in the plant before it is stopped.

A compressor plant as described above may be used in various ways. For example it may be employed as a transfer pump to take the contents of partly filled storage vessels and transfer the gas from them at high pressure to another partly filled storage vessel, or it may be used to receive gas at a low or at atmospheric pressure and pump the gas into a storage vessel at a high pressure. In the latter case the reducing valve L is conveniently removed from the position in which it is shown in the pipe L and placed in the pipe R because reducing valves suitable to receive gas at high pressure will not function if fed with gas at very low or at atmospheric pressure. By moving the reducing valve to a position in the pipe R low pressure gas can pass to the first stage inlet while any gas by-passed through the pipe R will be reduced in pressure before passing to the first stage inlet for re-circulation.

When using the apparatus as a transfer pump the procedure at starting is as follows. Before starting up, the quantity of water in the system is checked and if necessary more Water is added to the reservoir through a filling plug provided in the top of the reservoir. The vessel in which the gas is to be stored is connected to the pipe R and its valve is opened. One or more partly empty vessels from which the gas is to be taken are connected to the pipe L. The valves P R P and R are all closed and the valves of the partly empty vessels are opened. The compressor, driven conveniently by an electric motor, is then started up and quickly brought to its normal running speed, As it continues running the pressure in the reservoir will rise and when this pressure reaches a value equal to or slightly higher than the pressure in the vessel connected to the delivery pipe R the valves P and R are opened. When the desired maximum pressure has been reached in the vessel into which the gas is being transferred, or when the pressure in the vessels from which it is being removed has fallen to the permissible minimum, the plant must be unloaded so that the vessels to which it is connected may be removed and others substituted for them. To unload the plant the valve R is first shut and the valve R is then opened. This allows the gas leaving the drier Q to flow back through the pipe R to the inlet pipe L. Owing to the non-return valve L the gas cannot flow back and escape through the supply pipe L, and the reducing valve L whether this is in the pipe L or in the return pipe R ensures that the pressure of the gas flowing back in the pipe R will be brought down to a suitable value before the gas enters the inlet belt A of the low pressure cylinder on its way to being again circulated in the plant. When the plant is to be stopped, the valves R 1 and R. are closed thereby shutting 01! delivery through the pipes P and R and R. and thus locking up the pressure in the drier Q, and the blow-down valve P is opened. When the pressure in the reservoir 0 has fallen to a low value the compressor can be stopped.

Owing to the internal cooling of the plant which is effected by the passage through the cylinders of a sufllcient quantity of water to perform the cooling and the subsequent cooling of this water before it again passes through the cy1-. inders, the need for performing external cooling, as by arranging a water jacket or radiating fins or the like on the outside of the cylinder block, is obviated.

It is to be understood that while it is convenient to use a compressor comprising the features indicated above and described hereunder more in. detail, the improved gas compressing apparatus may be operated with the closed water circuit and automatic internal cooling by employing some other construction of compressor. The present construction, however, provides an effective plant especially suitable for the compression of oxygen. v

What we claim as our invention and desire to secure by Letters Patent is:

1. Gas compressing apparatus comprising in combination at least two cylinders with pistons therein which are reciprocated from a source of power and constituting a multi-stage compressor,

means for delivering water in measured quantity with the gas entering the cylinder of the first stage of the said compressor, a cooler through which passes the compressed gas leaving the cylinder of the last stage and also water which is carried over with the gas this v water having served to lubricate the pistons in the cylinders of the said compressor and also to abstract substantially all the heat of compression and friction, a reservoir in which the gas and water accumulate after passing through the cooler and whence the compressed gas is taken for use, and a pipe through which the water in the reservoir is taken to a metering device comprising a fixed low velocity distributed resistance through which it passes and is again taken into the cylinder of the first stage of the said compressor with the gas so that this water continuously follows a closed circuit.

2. Gas compressing apparatus comprising in combination the features set out in claim 1 and in which the close fitting surfaces in contact of each piston and rod and plunger in the cylinders of the said compressor are sealed solely by the water passing through the cylinders no packing being provided.

3. Gas compressing apparatus comprising in combination the features as set out in claim 1 and in which in the said pipingthrough which the water is conveyed from the said reservoir back to the cylinder of the first stage of the said compressor there is fixed a length of capillary tube through which the water has to pass and which acts as a fixed distributed resistance metering device for the water taken into the first stage of the compressor with the gas.

4. In gas compressing apparatus, the combination with amulti-stage compressor, each stage comprising a cylinder having a piston therein, and driving means for reciprocating said pistons, 01 devices delivering water in measured quantity with the gas entering the first stage cylinder, a cooler. means delivering the compressed gas and entrained water from the last stagepylinder to said cooler, and a reservoir receiving the cooled gas and water from said cooler, said devices receiving water from said reservoir and including a capillary tube. constitutin a, fixed low velocity distributed resistance by which the water returned to said first stage cylinder is metered.

HARRY RALPH RICARDO. AUBREY THOMAS EVANS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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