US2282675A - Controller for flowing gases - Google Patents

Description

May- 12, 19 42. R. J. 5. PIGOTT GONTRQLLER FOR FLOWING GASES Fil-ed Nov. 5, 194o Patented May 12,1942

con'rnornsa ron nowmo cases Reginald I. s; Pigott, l ittsburgh, Pa., asaignor to Gulf Research a Development Company, Pittsburgh, Pa., a corporation of Delaware Application November 5, 1940, Serial No. 364,469 9 Claims. (CI- 138 -46) This invention relates to controllers for flowing gases; and it comprises apparatus for substantially adiabatically reducing the pressure or high pressure gas discharged from flowing gas wells and the like, said apparatus including an elongated casing or conduit adapted to be connected in series with a source of high pressure gas and a low pressure gas discharge line, the casing enclosing a space increasing in cross-sectional area in the direction of flow of the gas, and said space being filled with porous material such, for instance, as sand, or shot, orother porous medium for providing a multiplicity of small labyrinth like passages offering relatively high frictional resistance to the flow 0! gas therethrough, and the invention further comprises means for by-passing portions of the porous medium for accomplishing different rates of flow, or for use with gas flows of difierent initial high pressures; all as more fully hereinafter set forth and as claimed.

Many gas wells, especially during their initial stages of flow, deliver gas at extremely high pressures; pressures of the order of 3,000 pounds per square inch are typical, with production of a v million or more cubic feet of gas per day (measured at atmospheric pressure and normal room to the low temperature of the gas in the jet as a result of the high velocity of the gas. Ice and snow forming at the control causes the gas to flow/erratically and may result in stopping the flow entirely. Freezing is more troublesome during cold weather since there is no absorption of heat from the atmosphere. In attempting toovercome this. dimculty steam and hot water jackets-have been applied to the pressure reducing device or sometimes a plurality of chokes or orifices have been provided'arranged in series for reducing the pressure of the ga gradually,

in steps, so as to minimize the temperature drop temperature). In the practical utilization of such flows it is necessary to reduce the pressure to a moderate value for transmission to pipe lines, or for other purposes. conventionally this is accomplished at or adjacent the well by permitting a reduced or limited flow of gas to expand freely at high velocity into an enlarged space, a low pressure pipe line or a gas main, but the procedure is complicated owing to the presence of moisture and corrosive and abrasive substances normally present in the gas. Ordinarily throttle valves such as are used for controlling low pressure gas flows are not practical to control high pressure gas because of the severe wear on the mechanical parts caused by the rushing of the gas stream through the valve. For this reason it is customary to use chokes or flow beans, as they are sometimes called, to reduce the pressure of the gas. The usual choke or flow bean consists simply of a nipple or short length of pipe of small bore, provided with thick, solid walls. An improved form of choke consists of a thin, hard steel disk or plate positioned crosswise in the flow line and provided with a small orifice permitting passage of a limited flow of gas.

A serious dimculty attending the use of such devices however, is the freezing of the moisture present in the gas in and about the control due in the jets. Also it has been proposed to reduce the pressure or the gas by simply passing it through great lengths of coiled tubing where the force of the gas is expended in. overcoming the frictional resistance to passage offered by the tubing. None of these prior methods have proven entirely satisfactory. Heating jackets are inefficient and troublesome. The use of greatlengths of tubing is impractical and series chokes are costly and complicated in construction and operation although satisfactory in most other respects. i

A further diiilculty with the devices of .,the priorart is that of reducing the well head pres? sure of the gas to relatively low pipe line pressures and still attain the desired flow of gas without freezing. With the devices of the prior art the greater the quantity of gas expanded to a reduced pressure the greater is the cooling effect produced by the gas.

According to the present invention the above diiilculties are avoided by the provision of apparatus for reducing the pressure of the gas by substantially adiabatically expanding the gas at a constant, relatively low velocity. This is ac, complished by passing the gas through a ,porous medium such as a bed of sand, or shot, or other porous material of suitable gas permeability, increasing in cross-sectional area advantageously substantially as the square of the distance from the inlet end. With such apparatus, the pressure energy dropof the gas is not utilized in creating high velocity but is absorbed largely by friction in the small, capillary passages in the sand or other porous medium andby impact loss of head due to changes in direction of flow. The velocity characteristic of the gas is in the viscous flow region rather than in the turbulent flow region and there is no appreciable exchange. of energy with the surrounding medium. Thus the volume of the gas as it travels from the inlet to the outlet is approximately inversely proportional to its to the inner wall of pipe as shown at I8.

absolute pressure, and the temperature throughout the operation remains substantially uniform. It is of course, not necessary that the gas during expansion and reduction of pressure be maintained at the temperature before expansion so long however as the temperature does not drop below the freezing point of the moisture in the gas. For the purpose of adapting the apparatus for use with gas flows of diflierent initial pressures, or for securing different rates of flow, means is provided for by-passing more or less of the porous material used. I

In the accompanying drawing, wherein'there is illustrated one form of a specific embodiment of the invention:

Fig. 1 is a plan view of the controller shown partly in longitudinal section, and

Fig. -2 is a transverse sectional view taken along line 2-2 of Fig. 1 looking in the direction of the arrows.

Referring to the drawing, the flow controller consists of a section of tubular metal pipe I of uniform cross-sectional area provided with a flange coupling member 2 at one end adapted for attachment to a high pressure gas well discharge pipe, not shown, and joined a't-the other end, as by welding 3, to the small end of a tapering expansion nipple or pipe coupling memher It. The opposite end of the expansion nipple grating 9. Welded to the. outer end of the sleeve, at the face of the coupling member, is a combined sealing ring and retaining collar I0. Flanged coupling member 6 is also provided with a screened grating as shown-at II; the grating in this case being removably secured in the coupling member by internal screw threaded engagement therewith. Diametrically opposed pins expand, as will be more fully explained hereinafter.

For the purpose of by-passing portions of pipe I the pipe is tapped at suitably spaced intervals and providing with three relatively short pipe nipples I9, 20 and 2|, respectively, which project outwardly from the pipe at right angles thereto. Nipple I9 joins pipe I through sleeve 1 at a point immediately ahead of screened grating 9 as shown, while nipple 2| is located at a point on the pipe opposite'rod but near the small end thereof. Nipple joins pipe I at a point I in its length about midway between nipples I9 and 2|. To secure strong, gas tight joints, the nipples are welded to the pipe as shown at 22. Nipples 20 and 2| are provided with screened gratings 23 and 24, respectively, where they join with pipe I, and are valved as at 25 and 26, respectively. The nipples are connected for operation to a feeder or by-pass conduit -designated generally by the numeral 21. As shown, this conduit is made up of short lengths of pipe connected together and to the nipples by means of pipe elbows 28, pipe .T 29 and unions 30 in a manner well known in the art.

In operation of the device, screened grating II is removed by means of a suitable tool as heretofore explainedand pipe I, expansion nipple 3 and coupling 6 filled with sand or other porousmaterial 3I ofsuitable known gas permeability.

The grating is then replaced and the device, with I2 are provided on the outer rim face of the grating for engagement with. a suitable tool for rotation of the grating when applying or removing the same from the coupling.

Supported within pipe I by means of spiders I3 and I4 is a centrally disposed, tapered metal rod I5 positioned with its large diameter end adjacent grating 9 at the upstream end of pipe I and its small diameter end adjacent the weld 3 connecting pipes I and 4. In manufacturing the device, rod I5 with its spacing and supporting spiders secured thereto at each end by means of stud bolts I6 and I! respectively, is inserted -within pipe I before butt welding the end of the pipe with the end of expansion nipple 4. The assemblage is secured in place in pipe I by circumferentially welding'the rim of spider I4 In use. rod I5 serves as a displacement member in pipe I, its taper being such as to vary the cross-sectional area of the space between it and the inner walls of the tubing substantially as the square of the distance from the large end of the rod to the small end of the rod. Thus gas passing through pipe I between the rod and the walls of the pipe in the direction from the large end of the rod to the small end of the rod may valves 25 and 26 closed, connected by means of flanged coupling 2 to a high pressure gas line leading from a gas well or the like and by means of flanged coupling 6, at the other end, to a low pressure gas main or pipe line. The apparatus shown is designed for three diiferent rates of fiow at three dilferent head pressures by operation of the valves 25 and 26 connecting pipe I with by-pass 21, for example, as' follows:

When both by-pass valves are closed, approximately 200,000 cubic feet of gas at F. will flow through the device in 24 hours, with an inlet or head pressure of 1500 pounds per square inch and an outlet or line pressure of pounds per square inch. With by-pass valve 25 open and.

valve 26 closed, approximately 500,000 cubic feet of gas per 24 hours at 80 F. will flow with an inlet or head pressure of 1200 pounds per square inch and a corresponding outlet or line pressure of 140 pounds per square inch. With by-pass valve 26 open, approximately 1,400,000 cubic feet of gas per 24 hours at 80 F. will flow through this device with an inlet pressure of 1000 pounds per squareinch and a corresponding outlet pressure of 140 pounds per square inch. The above figures apply when the device is used in connection with reduction of. the pressure of natural gas from natural gas wells. Results with other gases vary slightly, depending upon the character of the gas.

With the controller of the present invention difficulties due to freezing of the moisture present in the gas by rapid expansion of the gas are not present, for the reason that the gas is expanded gradually with no sudden large drop in temperature as the result of high velocity of the gas. In addition, the controller is much smaller and more compact than controllers of the multiple disk, orifice type for accomplishing the same pressure drop and flow, because the resistance to gas flow is muchgreater and no enlarged spacesinexpensive of manufacture and adapted for wide flexibility of operation. Large or small gas flows may be handled simply by regulating the quantity, quality and disposition of the porous material employed.

While the controller has been described principally in connection with gas wells, it is useful to control gas flows from oil wells as well as from high pressure stills, autoclaves, etc. The usefulness of the invention to reduce the pressure of high temperature, high pressure gas from hot stills and autoclaves is in the provision of low pressure gas at still or autoclave temperature, and in the securing of such reduction in pressure without possible chemical reaction or condensation of possible high boiling constituents in the gas.

c In one aspect of the invention, the friction developed by the gas in passing through porous material of known permeability is controlled by coordination of the diameter, length and degree of taper of the device to provide for expansion of the gas without substantial reduction in temperature. When the gas is expanded adiabatically, the taper of an elongated, uniformly porous medium will, of course, be such that its cross-sectional area will vary as the square of the distance from the inlet end. vUnder these conditions the volume of the gas is inversely proportional to its absolute pressure at all times and the velocity of the gas is maintained constant and at a lowlevel.

area in the direction of flow of the gas substantially as the square of the distance from the inlet end, and porous means in said space, substantially coextensive therewith, for reducing the pressure of the gas by frictionally resisting its 3. The subject matter of claim 2 wherein the porous means in said space is sand.

4. Apparatus for reducing the pressure of high pressure gas which comprise an elongated conduit adapted for passage of gas therethrough, displacement means in the conduit, said displacement means and said conduit being spaced to provide a passage for flow of gas through the conduit, and gas pervious, porous means in said space substantially coextensive therewith, for frictionally resisting the flow of gas therethrough, said porous means increasing in crosssectional effective pore area in the direction of flow of the gas at a rate sufficient to maintain the velocity of the gas passing therethrough subreducing the pressure of, high pressure gas from stantially constant and at a low value.

5. Apparatus for substantially adiabatically flow of gas through said medium, said porous It is however within the purview of the present invention to use a conical tube of appropriate dimensions for holding the porous material rather than acylindrical tube provided with a conical core. Likewise porous material varying in fineness or permeability from fine grain, low permeability at the inlet end of the device to course grain, high permeabilityat the outlet end may be used with advantages such for instance.

as enabling the use of a cylindrical casingwithout a core for holding the material. Here, the increase in effective porosity of the material alone provides the desired space for expansion of the gas. Thus, when the permeability of the porous material is known, its proper length and diameter for reduction of the pressure of a gas without substantial change in temperature can be determined to give any desired capacity of flow for known inlet and outlet pressures.

What I claim is:

1. Apparatus for reducing the pressure of high pressure gas which comprises an elongated gas permeable porous medium and means for directing a flow of gas through said medium, the total cross-sectional effective pore area of the medium increasing in the direction of flow of the gas at a rate such as to maintain the velocity of flow medium increasing in cross-sectional area in the direction of flow of the gas at a rate such that the degree of enlargement of said medium, acting in cooperation with the frictional resistance to flow of gas offered by the medium, results in expansion of the gas at a substantially constant low velocity and reduction in pressure without substantial temperature change.

6. The apparatus of claim 5 wherein by-pass means is provided adapted for selective introduction of the high pressure gas at different points along the length of the porous material.

7. Apparatus for reducing the pressure of gas flows which comprises an elongated laterally confined gas permeable column of porous material adapted to impose frictional obstruction to flowing gas and means for admitting a gas flow t0 one-end of the column, the cross-sectional area 1 of the column increasing gradually from said end of the gas therethrough substantially constant conduit being provided with an inlet end and enclosing a space increasing in cross-sectional to the other end at a ratesuch that the velocity of the gas throughout the colunm is substantially constant and at a low value, whereby as the flowing gasexpands in the column an increasingly greater cross-section of material is presented to it, the length of the column being such that the gas issues at the large end substantially completely expanded to the desired low pressure.

8. The subject matter of claim 7 wherein the ,capacity of the apparatus is controlled by bypass means provided forselective introduction of high pressure gas at different points along the length of the column.

9. The subject matter of claim 7 wherein the porous medium is sand.

REGINALD J. S. PIGOTT.

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