US2490493A - Attenuation pulsation dampener - Google Patents

Description

1949 H. N. WADE 2,490,493

ATTENUATION PULSATION DAMPENER Filed March 18, 1946 I0 Y ll F IG'. 1

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Patented Dec. 6, 1949 UNITED STATES'PATENT OFFICE ATTENUATION PULSATION DAMPENER Henry N. Wade, Los Angeles, Calif.

Application March 18, 1946, Serial No. 655,057

7 Claims.

This invention pertains to means for the suppression or the substantial elimination of pulsations in the rate of flow of gases through pipes.

The ultimate purpose of the invention is to protect from dangerous vibration pipe systems receiving the discharge from piston type compressors.

The outflow of gas from conventional piston type, positive displacement compressors is necessarily intermittent, due to the peculiarities of the compression cycle. At the end of the suction stroke the cylinder is filled with gas at approximately the suction pressure. During the earlier part of the compression stroke this gas is compressed until its pressure slightly exceeds that against the discharge valves. When this point is reached and the discharge valves lift, discharge of gas from the cylinder begins and continues to the end of the piston stroke.

Taking a commonly occurring example in which the ratio of the absolute discharge pressure to the absolute suction pressure is of the order of three to one, the piston will travel through approximately two-thirds of displacement stroke before discharge of gas begins, and consequently the entire quantity of gas delivered during a complete stroke cycle will pass out of the cylinder during a relatively short time near the end of the displacement stroke. In cases where the clearance volume is relatively large, as is common in commercial compressors, the actual delivery of gas into the discharge system may occur during only one-fourth or onefifth of the total displacement movement of the piston.

It follows from these factors that the gas from ordinary compressor cylinders, operating at or-' dinary compression ratios, is delivered to the discharge system in a succession of short spurts.

These spurts begin and end suddenly and, consequently, have an extreme tendency to cause vibration in the piping or other apparatus through which the gas is delivered.

In the natural gas industry, in connection with;

a straight line as shown, in a spiral or in an irreggas processing plants and gas transmission lines, difiiculties due to pulsation from compressors have been greatly increased by the introduction to this industry of machines operating at relatively high speeds.

Up to about the last ten years, the types of compressors mainly used for handling natural gas operated at rotative speeds ranging fromi 125 R. P. M. to 200 R. P. M. With machines running at these speeds the frequeny of gas pulsation was such that the piping systems usually 1 and I2 a discharge valve.

connected with them had natural frequencies outside the range of the pulsation frequencies. For this reason, a dangerous degree of vibration seldom occurred.

At the present time, however, the tendency is to the use of compressors operating at much higher speeds, up to 300 to 330 R. P. M., and also to build larger units. Whereas the amount of power applied to a single cylinder rarely went above to H. P. in the earlier practice, it is now not uncommon to find 500 H. P. concentrated in a single cylinder. Both of these factors have increased greatly the difiiculty in designing discharge piping systems which will not be vibrated to a dangerous or even destructive eX- tent by gas flow pulsations.

The present invention suppresses or eliminates the effect of pulsation by breaking up each advancing wave into a multiplicity of minor waves, displaced in space, the multiple waves interfering and mutually nullifying each other.

The invention is described with reference to the attached drawings, in which Fig. 1 is a diagrammatic representation of the simplest form of the invention, illustrating the principle on which it is based;

Fig. 2 is a longitudinal section through a somewhat modified form of the invention;

Fig. 3 is a cross section taken on the line 33 of Fig. 2, and

Fig. 4 is a cross section through another modified form.

Referring first to Fig. 1, ll] represents the discharge end of a compressor cylinder, II a piston A pipe or pipes l3, preferably as short as possible, connects the compressor with the pulsation dampener which in this form consists of an outer shell M and an inner tube l5 having one end closed as at I 5. This 4- tube passes out of the end of the outer shell as at I! and connects with the piping system into which the compressed gas is delivered. The inner tube is provided with one or more longitudinal rows of perforations, which may be arranged in ular pattern.

As piston ll moves toward the right, pressure increases in clearance space 19 until the discharge valve IZ opens against the back pressure in the piping system. The sudden opening of the discharge Valve creates a pressure wave which, unless otherwise dampened, travels away from the compressor until it is absorbed by friction or the resilience of the discharge piping. In the use of the device illustrated in Fig. 1,

this wave is transmitted along the length of space 25 between shell l4 and tube l5. As the perforations l8, each of relatively small area, lie at progressively increasing distances from the point 'of initiation of the wave, there is a pressure surge through each perforation as it is reached, and the pressure wave within the outer shell decreases in intensity until at the farther end of the shell it has disappeared. The dotted line 2| in this figure represents such waves, A, B, and C, at three stages of dissolution.

The minor waves created within the inner tube M5 by the surge of pressure through adjacent per forations travel toward each other and do not synchronize. In consequence, provided the number of perforations be sufiicient, the flow of gas from the outlet end of the inner tube is substantially or entirely free from pressure pulsation.

A slight modification of the above described structure, adapted particularly to large compressor units, is illustrated in Figs. 2 and 3 in which the various elements are numbered as in Fig. 1. In this form, the clearance space I 9 of the compressor is connected with the outer shell Hi by a plurality oi downcomers l3.-l3, spaced along the length of the shell. The gen-\- eral directions of gas flow through the shell, perforations and inner tube are indicated by arrows. As shown in Fig, 3, a plurality of rows of perforations are so placed as regards the line of attachment of the downcomers that there is a minute time interval between the surges through circumf erentia lly spaced perforations as well as between those longitudinally spaced. Thus the pressure surges and the minor waves created by them within theinner tube are out of step in both directions of wave propagation.

In practice it has been foundthat the pressure drop across the perforated area required to produce substantially complete suppression of pulsatiori, even at compression pressures as high as 800 poun au e, nee v no x e e to w pounds per square inch. Neither. the number nor the spacing of the perforations is critical, but the free area must be divided among a considerable n r f p fo ionss parated y appreciable distances, and these must be so arranged that they li t pro r ssively increa ing distan es from the point or points at which the pressure wave enters the outer chamber. In the form of gl t mp essor dischar eenters the chamber at one end and the pressure wave travels through its entire length. In the form, of Fig. 2, in w h h ompressor ischar e enters at spaced points, the pressure waves initiated at adjacent points of entry travel toward each other, but the flow of gas through the inner tube is constantly in one direction.

The concentric arrangement of inner and outer tubes shown in Figs. 1 to 3 is convenient but not essential. Fig. 4 illustrates in cross section amodified form in which a tube [4 is divided into two chambers 23 and 24 by a septum 22 having one or more lines of perforations l8. The basic requirement is for a chamber receivingthe compressor discharge, a chamber communicating with the discharge piping system, and a septum separating the chambers and provided with perforations arranged at progressively increasing distances from the points at which the compressor discharge enters the receiving chamber.

These requirements may be met in numerous.

modifications of form,

A characteristic of this structure which distinguishes it sharply from the prior art pulsation dampeners of which I am aware is that its proper functioning is substantially independent of any consideration of volume. In all previous dampener structures known to me, dependence is placed largely on the elasticity of the compressed gas to absorb pressure pulsations, and that principle becomes effective only when the retained volumes are very large. In the device herein described the cross sectional areas of the passages through the two chambers should be such as to avoid any restriction of gas flow other than that aiiorded by the perforations, in other words each may be no greater in area than the discharge piping into which the device delivers, producing a structure of extreme compactness at a very small fabrication cost.

I claim as my invention:

1. Apparatus for suppressing pulsations in a stream flowing under pressure comprising an elongated gas-tight chamber having inlet and outlet openings therein; an elongated conduit disposed within said chamber having the dischar e end thereof extending in pressure-tight arrangement through the outlet opening of said chamber, said conduit being provided with a plurality of openings through the walls thereof at points spaced longitudinally of said conduit asthe sole means for intercommunicating flow between said chamber and conduit, means for introducing a pulsating flow of gas under pressure through an inlet opening of said chamber so as to align the resultant wave pattern in said gas longitudinally of said chamber, said gas passing through said openings into the conduit and out of the discharge end thereof at substantially constant pressure.

2. Apparatus for suppressing pulsations in a stream of flowing gas comprising an elongated gas-tight chamber having inlet and outlet openingstherein, an elongated conduit disposed within said chamber having the discharge end thereof extending inpressure-tight arrangement through the outlet opening of said chamber, said conduit being provided with a plurality of openings through'the walls thereof atpoints spaced 1ongitudinally of said conduit as the sole means for intercommunicatingunidirectional flow between said chamber and conduit, means for introducing a pulsating flow of gas under pressure through aninletopening of said chamber so as to align the resultant wave pattern insaid gas longitu-' dinally of saidchamber, said gas passing through said openings into the conduit and out of the discharge end thereof at substantially constant pressure.

3. Apparatus for suppressing pulsations in a stream of gas flowing under superatmospheric Pressure comprising an elongated gas-tight chamber having inlet and outlet openings therein, an elongated cylindrical conduit disposed within said chamber having the discharge end thereof extending in pressure-tight arrangement through the outlet opening of said chamber, said conduit being provided with a plurality of openingsthrough the walls thereof at points spaced longitudinally of said conduit as the sole means for intercommunicating flow between said chamberand conduit, means for introducing a pulsating flow of gas under pressure through an inlet opening ofsaid chamber so as to align the resultant wave patter in said gas longitudinally of said chamber, said gaspassing through said openings into the conduit and out of the discharge end thereof at substantially constant pressure.

4. Apparatus for suppressing pulsations in a stream of gas flowing under pressure comprising an elongated gas-tight chamber having inlet and outlet openings therein, an elongated cylindrical conduit disposed Within said chamber having the discharge end thereof extending in pressure-tight arrangement through the outlet opening of said chamber, said conduit being provided with a plurality of openings through the walls thereof at points spaced longitudinally of said conduit as the sole means for intercommunicating unidirectional flow between said chamber and conduit, means for introducing a pulsating flow of gas under pressure through an inlet opening of said chamber so as to align the resultant wave pattern in said gas longitudinally of the chamber, said gas passing through the openings and into the conduit in a direction substantially normal to the direction of flow through the conduit, and said flow through the apparatus being at substantially constant pressure.

5. Apparatus for suppressing pulsations in a stream of flowing gas comprising an elongated gas-tight chamber, a partition member disposed longitudinally of the chamber to divide said chamber into separate elongated entrance and discharge portions, said partition having a plurality of openings therethrough at spaced points along said partition as the sole means for intercommunication between said entrance and discharge portions, means for introducing a pulsating flow of gas under pressure into said entrance portion so as to align the pulsating wave movement in said gas longitudinally of said entrance portion, said gas passing through said openings and into said discharge portion in a direction substantially normal to the direction of flow through the discharge portion, and said flow through the apparatus being at substantially equal pressure.

6. Apparatus for suppressing pulsations in a stream of flowing gas comprising an elongated gas-tight chamber, a partition member disposed longitudinally of the chamber to divide said chamber into separate elongated entrance and discharge portions, said partition having a plurality of openings therethrough at longitudinally spaced points along said partition as the sole means for intercommunication between said entrance and discharge portions, means for introducing a pulsating flow of gas under pressure into said entrance portion so as to align the pulsating wave movement in said gas longitudinally of said entrance portion, said gas passing through said openings and into said discharge portion in a direction angularly disposed to the direction of flow through the discharge portion, and said flow through the apparatus being at substantially equal pressure.

7. A method for suppressing pulsations in a stream of flowing gas comprising the steps of passing said pulsating stream of gas into a first elongated zone wherein the wave movement in said gas is aligned longitudinally of said zone, dividing said stream into a multiplicity of minor streams flowing in directions substantially normal to the direction of wave movement in said first zone, said division being effected at points varying in distance from the point of gas introduction into said zone, and recombining said minor streams in a final discharge zone to form a second stream of gas flowing out of said zone to a point of discharge and substantially in a direction normal to the direction of flow of said minor streams.

HENRY N. WADE.

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

UNITED STATES PATENTS Number Name Date 1,707,912 Heindorf Apr. 2, 1929 2,278,688 Caminez Apr. '7, 1942 2,290,337 Knauth July 21, 1942 2,401,570 Koehler June 4, 1946 2,401,792 Overbeke June 11, 1946 FOREIGN PATENTS Number Country Date 3,470 Great Britain Mar. 7, 1887 558,021 Germany Aug. 18, 1932

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