US3096926A - Compressor control - Google Patents

Description

y 9, 1963 D. T. KOCH ET AL 3,096,926

COMPRESSOR CONTROL Filed March 19, 1962 5 Sheets-Sheet 1 MM, 22 55 33 6 Ak L ANA kk T A KK K.K. K.K. PP P mm mm PP 2 l2 l2 I2 I2 cc c co cc cc LL LL LL LL L| YY YY Y cc cc um mm c N m mHN TCA S fl a W m 1T.R. m mm m AU L y 9, 1963 D. T. KOCH ET AL 3,096,926

COMPRESSOR CONTROL Filed March 19, 1962 5 Sheets-Sheet 2 INVENTOR. DONALD T. KocH WILLIAM R. BOHANNAN FE? gfi BY 2 22 ATTORNEYS y 9, 1963 D. T. KOCH ET AL 3,095,926

COMPRESSOR CONTROL Filed March 19, 1962 3 Sheets-Sheet 3 mag.

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INVENTOR.

DONALD T. Kocn WILLIAM R. BOHANNAN QULQL A'TTO RNEYS United States Patent 3,096,926 CfiMPRESSOR CONTRGL Donald T. Koch, Birmingham, Mich, and William R.

Bohannan, Caracas, Venezuela, assignors to The Cooper-Bessemer Corporation, Mount Vernon, Ohio,

a corporation of Ohio Fiied Mar. 1%, 1962, Ser. No. 180,767 4 Claims. (Cl. 230-4) This invention relates to a control for reciprocating compressors and is particularly directed to a control that is intended for use with relatively large, engine driven compressors in service wherein the suction and discharge pressures are both subject to substantial variation. Such compressors are commonly used on gas transmission pipelines and in gas storage service.

It is desirable that the engine driving a reciprocating gas compressor be held very close to its point of optimum loading and performance, and that it be not overloaded. Commercial considerations suggest that the engine load be held within +3 percent and percent of constant loading. Control within this narrow range is very difficult to accomplish manually, and present automatic systems with which we are familiar are unsuitable and unreliable. Most automatic systems are sensitive only to discharge pressure and to engine speed and torque so that they control the engine load after the overload has occurred, and do not anticipate it. The present invention provides means to control the compression ratio of a reciprocating compressor in accordance with variations of both suction pressure and discharge pressure. By this expedient, a conventional form of engine governor may be used to control engine speed and it will be found that the horsepower output of the engine remains constant within the above described commercial limitations.

The primary object of the present invention, therefore, is to provide means to control the compression ratio of a reciprocating compressor in accordance with variations in both the suction and discharge pressures with which the machine is operating.

Other objects and advantages of the invention will become apparent from the following detailed description of a preferred embodiment thereof, reference being had to the accompanying drawings, in which:

FIG.1 is a diagrammatic view of a compressor and a control therefor embodying the present invention;

FIG. 2 is a plan view, with parts in section and parts broken away of a control embodying the present invention;

FIG. 3 is a section on line 3-3 of FIG. 2;

FIG. 4 is a diagrammatic view of a modified form of the invention; and

FIG. 5 is a diagrammatic plan View of a modified form of sensing plate.

The drawings show the present invention in conjunction with an engine which may be, for example, a gas fueled engine having angle compressor cylinders 12 and 13. This engine-compressor configuration is conventional and widely used. If the compressor is used for gas transmission service, it will take gas from a suction line 14 at a relatively high pressure, for example, 600 psi. and will discharge it into a discharge line 16 at a higher pressure, for example, 850 psi. A conventional compressor of this type is provided with regulating devices in the form of clearance pockets at each end of the compressor cylinder (the cylinder being double-acting) and with unloading valves by which either end of a cylinder may be opened to the suction line during both the suction and compression strokes so that no energy is expended in the cylinder. Opening of a clearance pocket changes the compression ratio of the afliected end of the cylinder and therefore pumps a greater volume of gas at a lower pressure rise, while opening of an unloading valve, of course, effectively puts the load on the affected end of a cylinder at zero.

No specific disclosure of the construction of the valves for step-unloading of the compressor need be made herein, since these valves are conventional. The step-unloading devices are designated A1 to A-6 inclusive and are duplicated in each compressor cylinder. It will be readily apparent that a greater or lesser number of step-unloading devices may be used without departing from the teachings of the present invention.

In the operation of engine driven compressors it is always desirable to take full advantage of the full rated horsepower of the engine whenever possible. At the same time it is highly undesirable to overload the engine even for a short time in the event of a change of the pressure conditions. Normally, the only way an engine can be operated at optimum efficiency when both the suction and discharge pressures vary is to attempt to follow the horsepower curve of the engine as reflected in these pressures. Such a curve has heretofore required the operator to make manual changes in the percent clearance in the compressor cylinders by opening or closing the clearance pockets and unloading valves. The present invention analyzes the prevailing pressure conditions, and does automatically what has heretofore been accomplished very inetfectively by manual operation so that the present invention is capable of operating with much greater pre cision.

The present invention includes means responsive to a variation of both suction and discharge pressures, and may comprise a movable contact member 20 carried in a suitable holder and biased outwardly into electrical contact with a plate by a spring 21. A cylinder 22 is connected to the compressor discharge line 16 by a pipe 24. A piston 26 in the cylinder 22 is connected to a yoke 28 having a slot 30 therein, in which the stem of the contact member 20 is received. Movement of the piston 26 will, therefore, cause a movement of the contact member 20 in one direction. Since cylinder 22 contains gas at discharge pressure the position of the contact member will be determined by and responsive to changes in this pressure.

Disposed at right angles to the discharge pressure cylinder 22 is a second cylinder 32 connected by a pipe 34 to the suction line 14 of the compressor, and having a piston 36 therein connected to a second yoke 38. Yoke 38 has a slot 40 in which the stem of the contact member 24? is also received. As the suction pressure increases or decreases the left-to-right position of the contact member 24 will be adjusted by the yoke 38, and if the dis charge pressure is constant the stem of the contact member 20' will merely slide in the slot 30 of the discharge pressure yoke. Similarly, as the discharge pressure is changed, the stern of the contact member 20 will slide in the slot 40 of the suction pressure yoke 38. Thus, be-

. 3 cause the contact member is received in the perpendicularly disposed slots 30 and 40 of the yokes 28 and 38 its position will depend on the magnitude, at any time, of both the suction and discharge pressures, and the position reflects the algebraic sum of the pressures.

The contact member 20 is moved over a stationary contact plate 44, and the point of the member 20 is in electrically conductive contact with the surface of the plate. The contact plate 44 is divided into a plurality of seg ments 45, 46, 47, 48 and 4,9 shaped in accordance with the horepower output requirement of the engine ltl for given ranges of variation of suction and discharge pressures, as will become apparent. The subdivision of the contact plate 44 can be carried :to any desired degree to give greater or less precision to the operation of the engine.

When the suction and discharge pressures bear a predetermined relationship to each other, all of the step-unloading .devices can be closed and the full horsepower ,output of the engine utilized in the compressor. In the event that the discharge pressure should increase beyond a predetermined value while the suction pressure remains the same, it would become desirable, to prevent overloading, .to open one or more of the step-unloading devices, probably in the form of one or more clearance pockets. This increase in discharge pressure, however, might be accompanied by a decrease in suction pressure. In this event no .change in the effective volume of the compressor cylinder needbe .made unless the relationship of the pressures causes a substantial load change on the engine. From the configuration of the division lines between the segments of contact plate 44 it will be noted that, at low suction pressures, the discharge pressure may vary substantially without changing the load on the engine or prime mover. At high suction pressures, however, a small variation in discharge pressure requires a change in the compression ratio by the operation of one or more step-unloading devices. As the suction pressure increases a reduction in the compression ratio would occur if the discharge pressure were to he held constant, and the flow of gas through the compressor would be reduced, and the horsepower output of the engine would fall off. By opening one or more clearance pockets the flow can be raised which, in turn, raises the horsepower requirement of the prime mover since it is required to pump more gas through the line.

A suitable mechanism :for opening and closing the stepunloading devices in response to a movement of the contact 20 over the segmented plate 44 is shown diagrammatica'lly in FIG. 1. As shown, the step-unloading devices are fluid operated and the flow of fluid thereto is controlled by an appropriate series of solenoid operated valves. The disclosure of the valves is in accordance with the conventions of the American Standards Association.

in the energized position permits fluid to flow through it (this "is symbolized by the upper square having the horizontal arrow). In the de-energized position the spool or other movable valve element stands in such a position that the flow of fluid is cut oil, as symbolized by the slanting arrow'in the lower square. A dotted line 51 connects the valve 50a with a diagrammatically shown solenoid 52a indicating which of the several solenoids operates the respective valves.

The fluid control valves similar in form and operation to valve 50a are given the reference numerals 50b, 50c, 50d and 50a in FIG. 1. Similarly, solenoids for operating the respective valves are indicated at 52a, 52b, 52c, 52d and 52e. The operating contact segments of the contact plate are given the reference characters a, b, c, d and e, and these are connected electrically to relays 53a, 53b, 53c, 53d and 53e. The relays carry the additional designations TDa, TDb, TDc, TDd and TDe. The TD designation indicates that the relay has a time delay opera- .tion, :and in this instance the delay occurs upon opening. The relays are fast-closing, slow-opening devices.

' Except for relay 53a which has a single contact pair, each of the relays 53b, 53c, 53d and 53a is provided with two sets of operating contacts, one in each series with its respective solenoid and the other in parallel with the coil of its preceding relay to act as holding contacts. Thus, relay 53b has a set of contacts 54b in series with solenoid 52b to close the circuit through the solenoid and has an additional set of contacts 55b in parallel with the coil of relay 53a which, when closed, will maintain the relay 53a closed even though its circuit from contact segment a should be opened.

The effect of the delayed opening relay system shown is to make the operation of the step-unloading devices cumulative. Thus, if a set of clearance pockets is opened by valve Stla, operation of valve b opens an additional set of clearance pockets while those previously opened by valve 50a remain open.

The electrical circuit for the operation of relays 53a to 53c inclusive may comprise a simple D.C. circuit, one side of which is connected to ground (or negative) while the positive side is connected to the movable contact member 20. When contact member 20 is electrically in contact with operating segment a, for example, the circuit to ground is completed through relay 53a, and when contact 20 moves to segment b the circuit to relay 53b is completed, relay 53a being held closed by contacts b as explained above.

As indicated in FIG. 1 of the drawing each of the compressor cylinders C1 and C-2 is provided with clearance pockets A-l, A-2 and A-3 at the head end, clearance pockets A-4 and A-6 at the rod end and an unloader valve A-S at the suction manifold. Clearance pockets A-1 and A-4 in each cylinder are opened by fluid pressure supplied from a header through valve 50a when the latter is open. Valve 50b, when opened, will pass operating fluid from the header to clearance pockets A2; valve 500 when opened will pass operating fluid to clearance pockets A-S; valve 5001 when opened will pass operating fluid to clearance pockets A3; and the unloading valves A'5 in each cylinder are opened when operating fluid is passed from the header 60 through valve 50c.

If desired, a conventional speed governor 62 may be used to control engine speed and may take its operating power from the header 60 and its sensing function from a line 64 connected to the discharge manifold -16.

In operation, assuming that the compressor is running at normal suction and discharge pressures, these pressures will be reflected respectively in cylinders 32 and 22 and the yokes 38 and 28 will cause the movable contact member 20 to stand over that portion of contact plate 44 above and to the left of segment a as these segments are shown in FIGS. 1 and 3. The engine will be running under normal governor control with all of the compressor step-unloading devices closed.

A If the discharge pressure of the compressor increases so that the load on the engine increases (suction pressure remaining constant) the increase in pressure in cylinder 22 will move yoke 28 downwardly in FIGS. 1 and 2 and if the magnitude of the increase is sufficient, movable contact 20 will enter segment a of the contact plate 44. The circuit to relay 53a will be completed, contacts 54a will be closed, solenoid 52a will be energized, and valve 50a will shift to its energized position. Control fluid can now flow from header 60 to clearance pockets A1 and A-4 in each compressor cylinder. The engine is now running at full load with a lower compression ratio, and the horsepower output of the engine remains unchanged Should the discharge pressure continue to rise, the increased pressure in cylinder 22 will move the contact member 20 from segment a to segment b of the plate 44. The circuit to relay 53b will be completed, contacts 54b will be closed to energize solenoid 52b and at the same time contacts 55b will close to establish a holding circuit for the relay 53a. As previously noted, the relays 53a to 53c are of the delayed opening type so that there is time for the holding circuit to be established before the previously closed relay can open. Since the circuits to solenoids 52a and 53b are now both closed, valves 50a and 50b will both be energized and clearance pockets 1, 2 and 4 will be opened, further reducing the compression ratio of the compressor.

If the discharge pressure continues to increase, the movable contact member 20 will successively enter segments 0, d and e to maintain the horsepower output of the engine substantially constant.

Assuming now that the discharge pressure were to remain constant, and the suction pressure were to increase, the movable contact member 20 will be moved first by the yoke 38 into segments a, b and c with the same effect as described above.

In the event that both suction and discharge pressures vary, which is the more usual case, the position of the movable contact member 20 will be established by the combined effect of both pressures, through the movement imparted thereto by both yokes 28 and 38, and its position is the algebraic sum of the movements caused by the two pressures.

The operation of the parts upon a decrease in pressure is, of course, the reverse of that described above. As the movable contact 20 moves from segment d to the lower segment 0, for example, relay 53d opens after a predetermined time interval, solenoid 52d is de-energized and valve SM is closed, closing clearance pockets 43.

The drawings show a control which depends for its operation on an electrical contact between a moving stylus and a segmented contact plate. It is, however, Within the purview of the invention to provide a control which does not depend on an electrical contact, but which operates electronically by a change in output of a circuit including a moving pick-up and a segmented stationary control element. For example, a photoelectric scanning device comprising a light source 100 and a movable photoelectric cell 101 having its output varied by varying the optical density of a segmented stationary control plate 102 can be readily substituted. Such an electrical output from the photocell 101 can be used to trigger consecutive zener diodes 163a, 103b, 1630, 103d and 103e biased by resistors 104a, 1041:, 104e, 194a and 104e to different levels of operation for consecutive operation. In this system, a strong light 100 placed behind the segmented stationary control plate 1il2 would be used, the plate being progressively shaded in optical density from segment to segment. As the photocell is moved over the pattern by the variation in suction and discharge pressures, it passes from area A to area B to area C, etc, which are shaded respectively darker. The result of this scanning operation is a variation in the photocell output from one area to another. This variation can easily be sensed by diodes 103a, 103b, 103e, 103d and 1032 and translated into voltage outputs corresponding to the particular scanned areas. These voltage outputs can then be fed directly or in an amplified condition to the circuits comprising relays 53a, 53b, etc. Similarly, separate p'hotocells may be placed behind each of the segmented stationary plate areas and a single light source moved by the yokes 28 and 38 to feed the relay system. In such a system the segmented plate would have a uniform optical density.

It is also intended that the appended claims shall include pneumatic or hydraulic means for sensing the movement of the stylus or movable control element from one segment to another of the stationary control element, in which case the segments may be physically spaced from each other at different elevations.

While reference has been made throughout the specification to an engine driven compressor, the term engine is intended to embrace other known prime movers such as a gas or steam turbine. Thus, while the invention has been described in conjunction with a specific form and disposition of the parts, it should be understood that the disclosure is highly diagrammatic and is simplified for purposes of understanding the principles of the invention and of one form thereof. It will be apparent to those skilled in the art that numerous modifications and changes may be made therein without departing from the scope of the appended claims.

What we claim is:

1. In a control system for a compressor having means to change the compression ratio of the compressor While running, the combination of (1) a single movable control element,

(a) moved in one direction by a change in compressor discharge pressure and (b) moved in a direction at right angles to said first movement by a change in compressor suction pressure,

(2) a stationary control element operatively associated with said movable control element,

(a) having its surface segmented .into areas representing l3. summation of suction and discharge pressures at which the compressor operates at substantially constant horsepower,

(3) means to sense the presence of said movable concontrol element over any of the segments of said stationary control element, and

(4) means responsive to said sensing means to change the compression ratio of the compressor to maintain the power input to the compressor substantially constant.

2. In a control for a reciprocating compressor having a plurality of independently operable step unloading .devices in each cylinder, the combination of (a) means responsive to compressor suction pressure;

(b) means responsive to compressor discharge pressure;

(c) a stationary contact plate having (1) a plurality of segments insulated from each other (a) each of said segments representing a summation of suction and discharge pressures at which the compressor operates at substantially constant horsepower;

(d) a movable contact member in electrical contact with said stationary contact plate;

(e) means to move said movable contact member along a first axis by said means responsive to suetion pressure;

(7) means to move said movable contact member along an axis perpendicular to said first axis by said means responsive to discharge pressure;

(g) a plurality of valve means to control the flow of operating fluid to said step-unloading devices (1) and corresponding in number to the number of segments in said stationary contact plate;

(h) and means initiated by engagement of said movable contact with each of said insulated segments to operate a respective one of said valves whereby said valves are operated sequentially as the algebraic sum of suction and discharge pressures increases and said step-unloading devices are operated sequentially to maintain the power requirement of said compressor substantially constant.

3. The combination of means defined in claim 2 and holding means to [retain in an open position a previously opened valve as the algebraic sum of pressures increases.

4. In a control system for a compressor having means to change the compression ratio of the compressor While running, the combination of (1) a single movable element (a) moved in one direction by a change in compressor discharge pressure and ([2) moved in a direction at right angles to said firstmovement by a change in compressor suction pressure '(2) a stationary control element operativeiy associated with said movable control element,

(a) having its surface segmented into areas of substantially constant compressor power input, (3) means 'to sense the presence of said movable control element over any of the segments of said stationary control element, and (4) means responsive to said sensing means to change the compression ratio of the compressor to main- References Cited in the 'file of this patent UNITED STATES PATENTS Wallene Apr. '9, 1935 Paul'lin July 25, 1939 Miller Nov. 14, 1939 G'arbaccio July 8, 1952 Corson et a l. May 2, 196-1 Emmel Mar. 13, 1962

Claims (1)

1. IN A CONTROL SYSTEM FOR A COMPRESSOR HAVING MEANS TO CHANGE THE COMPRESSION RATIO OF THE COMPRESSOR WHILE RUNNING, THE COMBINATION OF (1) A SINGLE MOVABLE CONTROL ELEMENT, (A) MOVED IN ONE DIRECTION BY A CHANGE IN COMPRESSOR DISCHARGE PRESSURE AND (B) MOVED IN A DIRECTION AT RIGHT ANGLES TO SAID FIRST MOVEMENT BY A CHANGE IN COMPRESSOR SUCTION PRESSURE, (2) A STATIONARY CONTROL ELEMENT OPERATIVELY ASSOCIATED WITH SAID MOVABLE CONTROL ELEMENT, (A) HAVING ITS SURFACE SEGMENTED INTO AREAS REPRESENTING A SUMMATION OF SUCTION AND DISCHARGE PRESSURES AT WHICH THE COMPRESSOR OPERATES AT SUBSTANTIALLY CONSTANT HORSEPOWER, (3) MEANS TO SENSE THE PRESENCE OF SAID MOVABLE CONCONTROL ELEMENT OVER ANY OF THE SEGMENTS OF SAID STATIONARY CONTROL ELEMENT, AND (4) MEANS RESPONSIVE TO SAID SENSING MEANS TO CHANGE THE COMPRESSION RATIO OF THE COMPRESSOR TO MAINTAIN THE POWER INPUT TO THE COMPRESSOR SUBSTANTIALLY CONSTANT.

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