US 3793888 A
Apparatus for collecting a sample of fluid which includes a piston slidable in a cylinder and displacable by the sample. A mixing element is provided within the cylinder. The piston, mixing element and end wall of the cylinder are all so configured that virtually no dead space remains when the piston is slid toward the inlet end wall prior to a sample being taken.
Claims available in
Description (OCR text may contain errors)
United States Patent Rosenwald [451 Feb. 26, 1974 CELL FOR COLLECTING AND MIXING FLUIDS lnventor: Gary W. Rosenwald, Tulsa, Okla.
Cities Service Oil Company, Tulsa, Okla.
Filed: Aug. 2, 1972 Appl. No.: 277,442
US. Cl. 73/421 R, 73/42l.5 R, 73/422 R, 259/98 Int. Cl. .1 G01n l/l4 Field of Search ..73/422 R, 422 TC; r ..V.S.Z. i G-ifl5 983222216 2.
References Cited UNITED STATES PATENTS Rousseau 222/243 3,390,580 7/1968 Taylor 73/422 TC Primary Examiner-S. Clement Swisher Attorney, Agent, or Firm-Elton F. Gunn [5 7] ABSTRACT Apparatus for collecting a sample of fluid which includes a piston slidable in a cylinder and displacable by the sample. A mixing element is provided within the cylinder. The piston, mixing element and end wall of the cylinder are all so configured that virtually no dead space remains when the piston is slid toward the inlet end wall prior to a sample being taken.
8 Claims, 3 Drawing Figures ///////////////////I/l//l.
' sum 2 or 2 ll I00 ,r L ,//////////l////////////////WZWIWWIWW ////////////////l CELL FOR COLLECTING AND MIXING FLUIDS BACKGROUND OF THE INVENTION In the production of natural gas liquids such as ethane, propane, and butane, a stream of the mixed liquids is sampled to determine the quantity of each component contained in the stream. In accordance with prior practice, small samples are taken from the stream periodically. Multiple samples have been required for buyer, seller, transporter and a referee. Attempts to collect separate yet identical samples for analysis by the different parties has required many pieces of hard ware and electronic devices which need frequent maintenance, and has also resulted in disagreement between the parties regarding analytical results of the supposedly identical samples.
By taking numerous small samples into a collecting cell incrimentally over a long period of time, a large component sample can thus be accumulated and later subdivided into numerous small portions. Many problems could thus be eliminated provided the large composite sample is homogeneously mixed and is thus representative of the composition of the steam over the entire sampling period.
It was learned prior to the present invention that homogeneous blending of the fluid components in such large composite samples does not occur readily by diffusion alone; complete blending cannot be assured in the absence of mechanical agitation within the collecting cell. This problem is further complicated by the fact that a cell which contains internal means for agitating the fluids must nonetheless be designed so that the fluid sample can be completely displaced therefrom mechanically.
It is therefore an object of this invention to provide a cell for collecting samples of mixed fluids, which also includes means whereby the fluids can be quickly and easily blended once they have been drawn into the cell, and also completely displaced from cell after the mixing has been completed. Other objects and advantages of the invention will become apparent from the following description and the appended claims.
SUMMARY OF THE INVENTION The present invention is a collecting cell for mixed fluids which includes means whereby crudely mixed fluids are homogeneously blended within the cell prior to quantitative analysis of a collected sample.
The present collecting-mixing cell comprises a cylinder having a free piston coaxially aligned therein, a head plug in one end of the cylinder and a tail plug in the other end thereof, and with the piston being located between the plugs. Each plug has a passageway for fluids which leads from the interior of the cylinder to the outside. A plunger is located inside of the cylinder and is adapted for back and forth movement therein between opposed faces of the head plug and the piston when the piston is displaced from the plug by injection of fluid into the cylinder. The outer periphery of the plunger is closely fitted to the inside circumferential wall of the cylinder. A front face on the plunger opposes an inner face on the head plug and has a surface area substantially equivalent to the inner face of the plug. Similarly, a rear face on the plunger opposes a face on the piston and has a surface area substantially equivalent to that of the piston face. The plunger is actuated within the cylinder by means of a stem which is attached to one of the faces of the plunger and extends through a stem channel in one of the plugs to the outside. Back and forth movement of the plunger inside of the cylinder is thus accomplished by reciprocating the stem along its longitudinal axis.
An essential feature of the invention is a series of mixing orifices which extend through the plunger from the front to the rear faces thereof. Upon moving the plunger back and forth within the cylinder, crudely mixed fluids are forced through these orifices and are homogeneously mixed by shearing and turbulence caused by the resulting extrusion of fluids through the orifices. Since one object of the invention is to effect complete discharge of the composite sample from the cell after it has been collected and mixed, it is important that any residual fluid contained in the mixing orifices be completely emptied therefrom when the piston is displaced all the way over toward the head plug for compression of the plunger against the plug by pressure applied with the piston. For this purpose pins project inwardly into the cylinder from the inner face of the head plug and extend through the mixing orifices of the plunger when the front face thereof is abutted against the opposed inner face of the plug.
Substantially complete emptying of the cell is other wise assured by the fact that the front and rear faces of the plunger have surface areas which are substantially equivalent to the opposed faces of the piston and the head plug, and since this arrangement is in conjunction with the close fit of the periphery of the plunger with the inner wall of the cylinder, void volume between the members becomes practically nill when the plunger is compressed against the head plug by full displacement of the cylinder in the direction of the plug.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates an apparatus arrangement whereby samples of fluids are drawn into and discharged from the collecting cell of this invention.
FIG. 2 is a sectional view of one end of the collecting cell and shows the cylinder, the head plug, the free piston and plunger assembly.
FIG. 3 is an end view of the plunger showing the rear face thereof which opposes the piston.
DETAILED DESCRIPTION OF THE INVENTION In FIG. I a pipe line for natural gas liquids is shown at I. The cylinder of the collecting cell is shown at 2. Fluid from the pipe line is fed into the cylinder through tap lines 3 and 4, which are provided with stopcock valves 5, 6, and 7. To draw a sample into the cylinder 2, stopcock valves 5, 6, and 7 are opened and pump 8 is activated. By means of the intensified pressure provided by the pump, fluid from line 1 is driven into the sample cylinder 2, displacing the free piston 11 from a seated position against the head plug 10 and toward the tail plug 10a at the opposite end of the cylinder. To accomplish filling of the cylinder in this fashion, valves 5, 6, and 7 must be open. Once the desired quantity of fluids has been injected into the cylinder, valves 5 and 6 are closed to seal the fluid within the cylinder and the pump is then stopped. Subsequent incrimental injection of samples into the cylinder is accomplished by restarting the pump and opening valves 5, 6, and 7, followed by sealing off of the cylinder, as previously explained.
The fluid sample is removed from the cell and passed to an analyzer by closing valve 5 and opening valves 6 and 9 so that the sample can be discharged from the cell into an analyzer through line 9a. (Valve 9 remains closed during the filling sequences.) Complete discharge of fluid from the cylinder is accomplished by driving the piston against the head plug 10 with pressure supplied from the line I through line 4 and valve 7.
Referring to FIGS. 2 and 3, the cylinder of the cell is shown at 2. Head plug 10 is threadably inserted into one end of the cylinder and has a fluid passageway 12 which extends through the body of the plug from the interior of the cylinder to the outside. A free piston 11 is fitted within the cylinder 2.
The plunger-mixer is generally represented at 13. The plunger, which in the illustrated case has the shape of a disc, is shown at 14, and is attached to a plunger stem 15 through a solid frusto-cone 16. To closely accomodate the surfaces 14a and 14b of the front face of the plunger, at equivalent angle and surface area, the head plug 10 has matching facial surfaces 10a and 101) which abut the front facial surfaces of the plunger when it is pressed against plug 10 by complete lateral displacement of the piston 11 to the left.
The plunger disc 14 is provided with mixing orifices 17, more clearly represented in FIG. 3. These orifices are aligned axially with respect to the disc 14 and the cylinder 2, and have a diameter matched to that of the pins 19 which project inwardly into the cylinder 2 from the inner face 10a of the head plug. The pins are sufficiently long to extend through the mixing orifices 17 when the front face of the plunger is abutted against the opposed face of the head plug.
The plunger stem 15 extends through a stem channel 18 in the body of the head plug 10. The diameter of the stem is about the same as the diameter of the channel so as to result in a close fit between the two. (The terms close fit and closely fitted as used herein are with reference to a close tolerance machine fit, e.g., a clearance of only a few thousandths of an inch.) The purpose of the close fit between the plunger stem and stem channel is to nullify void volume so that no gas is re tained within the channel when the endeavor is to empty the cell. Furthermore, this close fit is intended to inhibit leakage of gas through the channel from the interior of the cell to the outside, but the fit is not so close as to prevent back and forth movement of the plunger by binding of the stem. To further prevent leakage of gas through the stem channel, a stuffing box or seal gland 19 can also be provided. As shown in FIG. 2 the stuffing box can be located within the body of the plug. Where preferred however, the stuffing box can be mounted on the outside of the plug for more convenient repacking of the gland when such becomes necessary. A lock nut 20 can also be provided on the outside of the plug for securing the plunger from undesired movement.
The plunger shown in FIG. 2 is a disc attached to the plunger stem by means of the solid frusto-cone 16. However, it will be understood that other types of plungers can be employed. For instance, the frustocone section 16 can be dispensed with and in which case the head plug 10 can be provided with a flat inner 6 section on the plunger is preferred since it facilitates sealing of pressurized fluids within the collecting cell. i.e., the pressure of the fluid wedges the conical section into the matching recess in the head plug 10 and provides a substantial sealing effect by forceful inserting of the cone into the recess of the plug when the plunger is not being moved back and forth for mixing of the fluids. Therefore, most of the time that the cell is in use for storing a composite sample, the sealing effect between the plunger and plug can be used to advantage so that sealing between the stem 15 and the stem channel, on the packing gland 19, do not have to be totally relied upon for maintaining pressurized fluids within the cell.
The number of mixing orifices 15 which should be employed is subject to variation but it will be appreciated that a large number of small orifices will affect thorough mixing at a faster rate than can be accomplished with a lesser number of larger orifices. In the embodiment shown in FIGS. 2 and 3 the series of orifices is located near the periphery of the disc, but the orifices could also be placed in any suitable location over the face of the disc, especially when the frustocone section 16 is not employed.
Best sealing between the piston and the wall of the cylinder 2 can be accomplished by means of piston rings. O-rings 21 are preferred and use of two or more rings which are substantially spaced apart from one another prevents wobbling of the piston during movement along its axis. Similarly, O-rin'gs can be used for sealing members in the stuffing box 19.
Reciprocating movement of the plunger stem can be accomplished by hand; otherwise simple mechanical means can be adapted to this purpose.
It will be apparent from the drawings that placement of the pins 18 must be such as to permit alignment with the orifices 18 so that the pins will slide into the orifices when the plunger is bottomed against the head plug 10. Alignment of the fluid passageway 12 with at least one of the orifices 15 is also advantageous in facilitating emptying of the gaseous contents from the cell during displacement of the piston 11 against the plunger.
When preparing to gather a large composite sample the piston is first displaced all the way to the left in order to drive the plunger against the head plug 10, thus emptying the cell of any fluids which it may contain. Subsequently, samples of fluid can be incrimentally introduced into the cell through the fluid passageway 12, thus causing displacement of the piston to the right. When the incrimental sampling has been completed the fluids contained in the cell are then stirred and thus mixed by movement of the plunger back and forth using the stem 15. The fluid contents of the cell can then be discharged therefrom in the manner previously described.
While the present invention has been described with reference to particular materials, apparatus and arrangements thereof, it will nonetheless be understood that still other embodiments will become apparent which are within the spirit and scope of the invention defined in the following claims.
What is claimed is: g
1. Sample collecting cell comprising:
a. a cylinder having free piston coaxially aligned therem,
b. a head plug in one end of the cylinder and a tail plug in the other end thereof, said piston being l0- cated between the plugs, each of the plugs having a passageway for fluids which leads from the interior of the cylinder to the outside,
0. a plunger located inside of said cylinder which is movable back and forth between opposed faces of the piston and the head plug, said plunger having, an Qll9 l2 l9 Q 3 ,@5539 hrifl f fi ameter of the cylinder,
2. a front face whi ch gpposes aninner face of the head plug and which has a surface area substantially equivalent to said face of the plug,
3. a rear face which opposes a face on the piston and which has a surface area substantially equivalent to said face of the piston,
a e i Qtm a ns orifices whish aeasl thou h the plunger from the front face to the rear face thereof,
d. a plunger-actuating stern attached to a face of the plunger and extends through a closely fitting stem channel which leads through the one of said plugs to the outside,
e. pins which project inwardly into the cylinder from the inner face of the head plug and extend through said orifices when the front face of the plunger is abutted against the opposed inner face of the head plug.
2. Apparatus as in claim 1 and further comprising fluid sealing means located between the plunger stem and the head plug;
3. Apparatus as in claim 1 and further including at least two piston rings which seal between the piston and the wall of the cylinder.
4. Apparatus as in claim 3 wherein the rings are 0 rings.
5. Apparatus as in claim and further comprising:
a. valve means for starting and stopping a flow of pressurized fluid through the passageway of the head plug, and
b. valve means for starting and stopping a flow of pressurized fluid through the passageway of the tail plug.
6. Apparatus as in claim 1 and including at least two piston rings which seal between the piston and the wall of the cylinder.
7. Apparatus as in claim 6 wherein the rings are 0- rings.
8. Apparatus as in claim 1 wherein the front face of the plunger include the outer surface of a frusto conical section of the plunger and the inner face of the head plug includes the surface of a frusto-conical recess which matches the frusto-conical section of the