US2570965A - Variable automatic clearance pocket - Google Patents

Description

Oct. 9, 1951 Q MEYERS 2,570,965

VARIABLE AUTOMATIC CLEARANCE POCKET Filed Dec. 19, 1946 COMPRESSED GAS CONTROL SECTlON PULSATION DAMPENER GAS TO BE PRESSED PRESSOR INTAKE COMPRESSOR CYLINDER COMPRESSOR DISCHARGE /NVENTOR C4 0. MEYERS ATTORNFYS Patented Oct. 9, 1951 VARIABLEAUTOMATIC CLEARANCE PUCKET) Charles .Myers;.-Bartlesville, -Okla.,.,assignor to Phillips Petroleum Company, a .corppration of Delaware ApplicationDecember-P19, 1946;21S'erial N0;-'-.7-17;263:

Claims.

This invention relates. ta reciprocating vcome pressors. In. one. of itsimoreespecific aspectssit relates. to a. variable. automatic clearance. pocket. for useewith' reciprocatingcompressors.

The :petroleum rindustrvin general, and .speci,-- ficall-y the-naturai gas sandgasoline industry uses large-numbers. of. reciprocating or. pistontype. compressors: This. latter. industry.-. uses these. compressors for, among other things; compressing hydrocarbon. gases prior, to: extraction ofco-ndensible or. gasoline. boiling range: hydro! carbons.:.

Power units for operating sucngascompressors: may beselectedto. o.perateat orvery nearly; capacity-forz maximum operating Aefiiciency and. for -'savings in capital investment. And further,- these power units. may, be. selected to operate at capacity for compressing gasfrom.- an available intake pressure to a.desired ou-tlet pressure; For example;..a compressor. installation. may be designed for compressing-gasfrom'arnewly drilled: field,. from which. a smal-liamountof gasgmayr-be available: for: compression; at? as relatively; low pressure. After. the. field is. fully developed; or: the-gas/oil ratio -increases=-the: .pressure .of the gasfrequently. startsLtog-increase. This-increase. field pressure often effects-1am increase in. pressure in the zsuction-manifoldioia compressor; system; Such-"a: pressureerisesmeans that the compressor; cylinders twill.- receive-, an increased. quantity got? gas on-. each-. intake .l-stroke; If..- the: compressor: is.--v dischargingagainsta constant pressure,;the-;compression .of :this. increased; (1113,11? tit-y: oi. gasswill increase-thee'horsepower demand on the-powerzunit which was originally-operating at its full iratedx p9wer,-. output. This: increased. horsepower; demand: willvthereforegoverload .the: power-unit.

Anothen. compressor installation-.. may; be de signed .-for 1compressing gassfrom. a :newly drilled. field which-is inv a.:flush..period.-of- -.productiom. During ,-this initialaperiod theega pressure=.availableeinz-thell suctionemanifold :oi theev compressor-z. installationqmayjbe relatively v-highi. However,,it, isaknownsthat thisgas pressure :Will; decline and. that. .thefieldsmay subsequentlymroduce at-loweri pressures and over a long period of time.

. stilliother-compressoriinstallationslmay receive gas.:-.at-,-a-.pressure1.which1.may change. from-day; to; day, or. evemfrom hour. tothourr. Most; oil. producing; states; such; as Texasestablish. monthly;- allowable: crude oil. production? for, producing; wells: Under" such circumstances, sems producersfrequently/- pump ..wellsscontim1= ously ot;atgleastieight ahourssazaday: forlthe first:

. part ofatheimonth o-rluntilthe allowableaoil. has been;.-.produced-.:a:nd. then -.the well. is shutdown during the-remainder of" the month. Suchopem ations make for variable production .gas pres! sure:

For. any type of gasproduction: compresson cylinders are usuallyyselected so that the power; units :will .be ,fully loaded :when .the compressors-t are operating at-the. expected lower inlet-pressure. Thus it is necessarytoad'just the volue metric efiiciency of the compressor:cylindersrsor as to load fully but not overload-the powerunifl during higher pressure production. periods. a

Several methodshaveheretoforebeen available for solving such anlengineeoverload problem first; installation of. a larger power engine;- second,- replacement of. .thecompressorlunit with one having asmaller. cylinder; third; replace-: ment oftheboriginaicompressor. cylinder and piston witha-smaller cylinder and. pistonmwhichl proceduremay-sometimes be followed since many.- compressors g are adapted for such alterations" and fourths installations of external clearance. pockets, a clearance pocket=being -definedflas an attached, gas receiving: space in direct connection withcthe compressor. cylinder; suchthatsthereeisan increase in residual gasgvolume. atrtheend. of. the. compression. stroke... The. first V two'sof these methods involves considerable. investment whilethe third. involves less, yet appreciable "ex.- pense.. r The H last .method requires. .the "least Vex! penditure; but .its range-- of applicationv is. some! What limited.

Someattempts have been. made. to utilizeaonh and .ofi or manuallyiadjustable clearancepockets to solve the above I mentioned, problem... Such clearance pockets offer-only aapartial solutionitd the problemsince an .operatormust recognize the engine: overload. condition. and. then. manuallm open; one-ormore valvesto onea or more clears ance pockets, and this operation to be efie'ctive-l. mustebe done before. an nengineestalls ..when=an increasein manifold, gasapressurehas-overloaded: thepower unit. The reverse .is .also' true that ispan operatormust observe by pressure ga eiorr a recording chart when .gas manifold-r pressure: has. decreased, .then .closeofioneor ,more clear? ance pockets to, keep; theengine. operating, at maximunnefficiency. I

An operator of a gas compressionplantlm whichthere gare 12..toZ 15 201 .11.10.18 compressors would frequentlyneed .a helper ortwo designated. as clearance pocket-operators? in case .gasmanli; fold pressure fluctuates andzemanuall y, operated" pockets-were i-used.

I have developed a variable and automatically operated clearance pocket for gas compressors o erating under variable intake pressure conditions.

An object of my invention is to provide an automatically operable means for reducing the volumetric efficiency of gas compressors.

Another ob 'ect of my invention is to provide a variable and automatically operable means for reducing the volumetric efficiency of gas compressors.

Still another object of my invention is to provide a variable and automatically operable means for reducing the volumetric efliciency of gas compressors when compressor suction pressure has become increased, in order to maintain the compression load within the rated power output of the prime mover driving such compressors.

Man other objects and advantages of my invention will be apparent to those skilled in the art from a careful study of the following disclosure and attached drawing which respectively describes and illustrates a preferred embodiment of my invention.

The figure illustrates diagrammatically, partly in cross section and partly in elevation, a preferred form of my automatic and variable clearance pocket attached to a compressor cylinder. Referring now to the drawing, a compressor cylinder I is fitted with a gas inlet pipe 2 and a compressed gas outlet pipe 3. A second connection 4 is provided for attachment of my Variable automatic clearance pocket mechanism 5. The gasinlet pipe 2 is intended to conduct gas to be compressed from a suction manifold line (not shown) to a compressor cylinder. Pipe 3 conducts compressed gas from the compressor cylinder I to a control chamber 6 of the clearance pocket mechanism; This control chamber discharges the compressed gas through a pipe 1 which in turn conducts the compressed gas to a storage tank, to a process step or to other disposal, as desired, and not shown on the drawing for purposes of simplicity.

My clearance pocket mechanism is composed of two main parts, the control chamber 6 and a variable clearance section 8.

The variable clearance section 8 is composed of a cylindrical wall 9, the interior surface of which is machined so as to accommodate and permit movement of a carefully fitted piston [2. A space or volume l6 directly under the piston I2 is the variable volume clearancespace. This cylindrical wall 8 has a side outlet with a flange I] for connection to flange 4 of the compressor cylinder. The bottom end of the wall 8 terminates in a flange l3 to which may be attached a'cover plate I4, the connection being made gas tight by use of a paper gasket, not shown. Flanges! and l l of course are fitted with gaskets also.

Into the upper end of the piston i2 is inserted byscrew threads or other means a connecting rod I5 to the top end of which is attached a conical shaped bob l6. This bob l6 may be made integral withthe rod l5, if desired or may be attached by threads or other means. On account of rapid movement and vibration during operation it maybe preferable to make the bob and rod as one unit.

The cylindrical wall 9 is intended to act as a cylinder in which the piston l2 fitted with one or more piston rings, may move freely.

The upper end of the cylindrical wall 9 has a closure member I! which in turn is fitted with;

a packing gland l8 in such a manner that some oil 20 in the space between the piston and the closure member [1 cannot leak around the connecting rod IS. A coil spring I9 is attached to the underside of the closure member I! and to the upper side of the piston l2 or to the connecting rod H5 at a point near the upper surface of the piston. This spring is intended merely to carry the dead weight of the bob, piston, connecting rod and the weight of the oil 20.

A reservoir 25 also contains oil 20 which may pass into or out of the cylinder by way of a tube 26 as the piston l2 falls or rises.

The control chamber 6 is tapered as shown so that the higher the bob I6 is in the tapered chamber the greater is the area of the annular space between the periphery of the base of the bob I6 and the side wall of the chamber. The upper end of the chamber 6 is made with an outlet carrying a flange 22 to which a flange of the discharge pipe I may be connected.

My clearance pocket apparatus may be used on substantially any size compressor cylinder where clearance pockets are need. The sizes of the pocket cylinder. piston and bob portions may be the same for some different sizes of compressor cylinders, and the control chamber memher 6 may be varied in size to suit requirements. That is, a 20 inch diameter compressor cylinder will. require a larger control section member 6 than will an 18 inch diameter cylinder of the same stroke. The 20 inch cylinder will pass a larger volume of gas than an 18 inch cylinder while clearance volume requirements will be of the same order of magnitude and the volume adjustments for both cylinders may be accomplished with the use of the same size clearance section 5. By providing a flange 24 at the contact between the control section 6 and the piston section 8 different sizes of control sections 6 may be used with one piston section.

A tube 26 connects the bottom of an oil reservoir 25 with the volume between the piston l2 and the cylinder closure member IT. This volume, tube 26 and a portion of the reservoir 25 contain the oil 20. A tube 2! establishes fluid communication from the space above the oil in reservoir 25 to the clearance volume I0.

In the operation of my variable automatic clearance pocket, a gas to be compressed may be conveyed to the compressor cylinder at 2 pounds per square inch gage pressure and compressed to say 50 pounds per square inch gage pressure. Many gas compressors have spring loaded discharge valves or such other type of discharge valve that when a predetermined pressure of the gas is reached the valve will open' and the remainder of the compression stroke will then serve to discharge the compressed gas. Under such conditions the engine driving the compressor may be operating at capacity.

When the pressure of the gas to be compressed is increased to say 5 pounds per square inch more power is required to compress gas from this pressure to 50 pounds than from 2 pounds to 50 pounds. Thus the power engine will be overloaded.

During normal compressor operation the compressed gas passes through the compressor discharge pipe 3 and passes into and through the control section 6 of my apparatus. The surface area of the underside of the bob l6 and the area of the annular space between the bob l6 and the wall of the control chamber 6 are so chosen that when this normal volume of gas passes by asaowca through the annular-space between-bob le and" this wall of ich'amb'en the-=bob 6- is: exposed :to a; pressure differential for a-longen-per-iod of time than 1 when" compressing 1 the one to two pound; gas andthis pressured-i'fieren-tial acting ion b'ob lfi -fo'r' a--'- longer period of 'timewilr move -th'e bob agreaten'distance -in=the d6wnstream d-irec tion" than when the bob -is'exposedts the same. pressure difierenti-al=-for a--shorter per-iod of time-:

When the bob is raised the-piston-l2 is raised:

also-and 'the volume lfifmore accurately called the"learance volthneg increases and "this in-- creases-in clearance volumeunloads the driving engine si-nce it permits discharge of a=smaller= volumeot compressed gas-from the cylinder to the compressor dis-charge pipes in volume ofthe discharged gas is accordingly proportional to theincrease-in clearance volume. lfi caused by the -rise-of the piston l 2 Y Thetube V 2 T permits pressure from withirrthe clearancechamber A W to be communicatedto the oil 2a. Thus any; pressure acting'on the bottom 'side of the piston l 2-is-alsoacting-on the top sideof the-piston l2, or in ot-h'en-words' the piston is not moved by-"th'e-pressurepf 'gas'-inthe :clearanceyolumei N31: The only force acting to move the piston is the passage of gas around the bob [6.

The spring I9 need .not be especially strong since it is used merely to supporttheweight. of the bob-connectingrod-piston assembly and to assist in returningthe bob toitsoriginal and normal position after abnormal inlet gaspres sure has sceasedl to exist...andzthelzvoluine-eofa" as passingathelb'ob. at. each discharge stroke .issithe normal intended volume.

The oil 28 serves as a pulsation dampener. Tube 26 is sized so as to prevent the rapid flow or surging of oil from the cylinder to oil reservoir 25. In some instances it may be desirable to place a choke or orifice in tube 26 to control the fiow of oil. Since the oil is relatively viscous any movements of the bob are dampened and the overall result is during times of 2-pound inlet gas pressure the bob remains substantially at its initial position, and during times when the inlet gas pressure is 5 pounds (or any other pressure greater than 2 pounds) the bob rises and remains substantially fixed at its new position until the inlet gas pressure changes. If the gas pressure further increases, the bob will rise further or if the inlet gas pressure drops the bob will fall also to decrease the clearance volume. In this manner the load on the engine driving a compressor equipped with the clearance pocket of my invention will remain remarkably constant.

The clearance pocket assembly described herein is for one end of a compressor cylinder, and if the compressor is double acting, a similar apparatus may be installed on the other end of the cylinder. It is preferable to have clearance pocket operation on both ends of such a cylinder, otherwise an unbalanced operation results and such unbalanced operation is not conducive to longer compressor life.

The decrease Th'e diameter: of 'the piston-.- l2; and the-dis ameter'and the conical pitchuof th'eawalls of the control chamberli relative to the diameterof Y the bob It 'may :be determined :for: each size of "compressor cylinder taking further intov con sideration: the compressor inletand. outlet-press sures. The-diameter :-of the: piston l 2i and "distance of it's-upwardmovementtprovides the in crease incclearance volumea=- The slope-:onconical pitch, among other factors;determines the disa tance the bob -rises for-- the passage of a: given volume of gases through a given central chamber. The-smaller the conical pitch, the greater will be-the bob movement for thepassageof a given,

' volume of gas.-

Theoil used-in the pulsation chamber 25 may be a lubricating oil, as mentioned hereinbefore; and ifalubricating oil it should possess arela-. tively high viscosityindex-z In place of oil, glycerin or-ot-her type-oi hydraulicfiuid may be Hsedybutwhatever fluid is used, it should exhibit relatively-constant characteristics as to viscosity, etc.',, at atmospheric conditions, winter-or summer; as Well"; as at' corn-pressor operating'temperatures; This fluid should not form sludge nor wax'to plug the;tu-be-2ii-'-or to:interierewith-the movementiof piston; l2' against the-wallet theclearance ch'amber'or with the movement of the rod l5 in the packing gland iii.

If desired and 'to save first cost; the control chamber. may. be made relatively small'in comparison, to .,the .size ofth'e bob" lfiand through this.small,controlfchamber then may be passed alconstant frjaction offlth'e, compressor output. For example, if theccompressor discharge pip is a A inch. diameter pipe; a. 2 .inch take-off Tpipe maygbe. installed .andjrom. the. ratio of the. ,cross sectionalareasof these..two ,pipes,.,the smaller should permitfiow. of about. one-fourth. the volume of rcompressedsgas all ofwhich. would otherwisemass-throughthe 4, inch pipe. This smallerv volumegof compressed .gas :then may be. passed .through a relatively; small ,control. cham.-.. her to operate;-a .clearance pocket as ereinabove described.

Example,

A compressor cylinder of size 18 inches D' y -ZOF inches is compressing gas at the rate of 1,735 M. C. F. D. (thousand cubic feet per day) from an intake pressure of 2 pounds per square inch gage to a discharge pressure of 43 pounds per square inch gage. Loading is approximately brake horsepower. The cylinder clearance is 3.87% atmospheric pressure 14.4 pounds per square inch and the n value of the gas is 1.26. The intake pressure is suddenly increased to 5 pounds gage pressure thereby throwing a compression load of 138 horsepower. on the power unit. At this increased intake pressure, the compressor passes gas at the rate of 2,070 M. C. F. D. This increased flow of gas actuates the controlling mechanism and increases the clearance volume to 8%, thereby decreasing the gas flow and unloading the engine to its normal 125 horsepower loading. At this 8% clearance and '5 pounds inlet gage pressure 1,950 M. C. F. D. of as is passed.

The clearance volume remains at 8% as long as the intake pressure is 5 pounds. Upon decrease of intake pressure to 2 pounds, less gas is passed and the apparatus actuates to decrease the clearance volume to 3.87% with an engine loading of 125 brake horsepower.

Materials for use in the construction of my variable automatic clearance pocket may be selected from among those commercially available. No special material is needed.

It will be obvious to those skilled in the art that many variations and modifications Of my clearance pocket mechanism, such as, dimensions of mechanical parts, the slope or angle of the side wall of the control section, etc., may be made and yet remain within the intended spirit and scope of my invention.

Having disclosed my invention, I claim:

1. A variable, automatic clearance pocket for use in conjunction with reciprocating gas compressors comprising a cylinder adapted to be attached at one end to a compressor cylinder, the first mentioned cylinder fitted with a piston, means to equalize pressure on both sides of said piston, and means attached to said piston and extending beyond the other end of its containing cylinder for moving said piston, a housing means surrounding the extended portion of said piston moving means, a further means attached to said housing means and to said gas compressor cylinder and adapted to convey compressed gas from said compressor cylinder into said housing means, said extended portion of said piston moving means adapted to move said piston in response to the flow of gas through said housing means.

2. A variable, automatic clearance pocket for use in conjunction with reciprocating gas compressors, comprising a cylinder adapted to be attached at one end to a compressor cylinder having an intake and an outlet, the first mentioned cylinder fitted with a piston, means attached to said piston and extending beyond the other end of its containing cylinder for moving said piston, and means for equalizing pressure on both sides of said piston, a housing means surrounding the extended portion of said piston moving means, a further means attached to said housing means and to said gas compressor cylinder and adapted to convey compressed gas from said compressor cylinder into said housing means, said extended portion of said piston moving means adapted to move said piston in response to the flow of gas through said housing means.

- 3. The variable, automatic clearance pocket of claim 2 wherein said means for equalizing pressure on both sides of said piston comprises means,

for communicating fluid pressure from one side of said piston to the other side.

4. A'cylinder for a reciprocating gas'compressor having an intake and an outlet, and means for varying the efiective clearance volume of the cylinder, comprising in combination a clearance volume chamber in communication at one end with the head of the compressor cylinder, the clearance volume chamber being fitted with a piston to vary the efiective volume of said chamber, a gas flow bob in said outlet and attached to said piston and being responsive to the volume of discharge through said outlet to position the piston so that the effective volume of the clearance chamber will be varied directly as the volume of said discharge.

5. A cylinder for a reciprocating gas compressor having an intake and an outlet, and means for varying the eiTective clearance volume of the cylinder, comprising in combination a clearance volume chamber in communication at one end with the head of the compressor cylinder, the clearance volume chamber being fitted with a piston to vary the effective volume of said cham ber, means to equalize pressure on opposite faces of said piston, a gas flow bob in said outlet and attached to said piston and responsive to the volume of discharge through said outlet to position said piston so that the effective volume of the clearance chamber will be Varied directly as the volume of said discharge.

CHARLES O. MEYERS.

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

UNITED STATES PATENTS Number Name Date 2,004,474 Schaer June 11, 1935 2,121,534 Aikman June 21, 1938

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