US2955457A - Apparatus for continuous instrument sampling - Google Patents

Description

Oct. 11, 1960 v W. D. PETERS ET AL APPARATUS FOR CONTINUOUS INSTRUMENT SAMPLING Filed April 18, 1955 "2 Sheets-Sheet 2 P64 I 1 66 I I 79 8| I FIG. 2.

Q J Y J J v J v22' u J 74 dd) J U J JJJJ I04 I03 I06 I 87 I07 INVENTORS W. D. PETERS D. E. LUPFER ATTORNEYS APPARATUS FOR CONTINUOUS INSTRUMENT SAMPLING William D. Peters and Dale E. Lupfer, Bartlesville, Okla.,

assignors to Phillips Petroleum Company, a corporation of Delaware Filed Apr. 18, 1955, Ser. No. 501,878 I 5 Claims. (Cl. 73--23) This invention relates to a apparatus for providing a sample from a process stream for an automatic analyzer. A specific aspect of the invention pertains to a process and apparatus for controlling the flow of a sample stream to an analyzer.

Various types of instruments have recently been developed for the analysis of fluid streams. These instrur'nents include infrared analyzers, differential refractometers, ultraviolet spectrophotometers and mass spectrometers, for example. In many of these instruments the sample stream to be tested must be supplied as a gas at substantially a constant pressure. Quite often the sample streams are contaminated by materials which must be removed before the stream can be analyzed for a selected component. One procedure for removing the objectionable contaminants is to dissolve the same in a selective solvent material. When this procedure is followed, the solvent in turn must be removed from the vapor stream. In general, any liquids entrained in a gas stream to be analyzed rnust be removed before the stream is passed to the analyzer.

In accordance with the present invention there is provided a system for removing sample streams from a chemical process and for supplying these streams as a vapor to an analyzer instrument. When the stream to be tested is a liquid at the point of sampling, a vaporizer and a pressure regulator are employed. If the sample stream contains undesirable constituents which can be dissolved by a selective solvent, then 'such a solvent is added to the sample stream and is removed as a liquid together with other condensibles present. A condenser in combination With a liquid trap is disposed in the sample stream line upstream from the analyzer to remove entrained liquids and condensible vapors. This liquid trap comprises an elongated upright chamber which is provided with an inlet port at an intermediate point thereon. A contact bed comprising a large number of balls or to the condensing chamber is vented or rejected therefrom thru a backpressure regulator, along with the conden sate. In this manner the time lag between the taking of the sample from theprocess line and the analysis in,

the automatic analyzer is substantially reduced, dependingupon the flow rate of the sample in the line leading 1 into the condensing chamber as compared to the flow rate of the gas Sample in the line leading from the condensing chamber to the analyzer instrument. It'is preferred to withdraw at least twice as much materialat the sampling 7 point as is passed from the condensing chamber to the analyzer so that the discarded stream of gas flowing out of the condensing chamber as rejected material is at least. How-- ever, the rejection of any portion of the initialsarnpleg as great as the material passed to the analyzer.

from the condensing chamber decreases the time lag between the taking of the sample and the analysis thereof; so as to improve the sampling technique and the accuracy;

of the control to which the instrument is directed and is. within the scope of the invention. 5

One of the objects of the invention is to provide an improved apparatus for passing a process stream sample.

' tion to provide apparatus for passing a continuous repre,

sentative sample of a process stream to an automatic con.- tinuous'analyzer'. A further object is to provide apparatus for continuously passing a representative sample of a process stream to a continuous analyzer with less time lag between the taking of the sample and the analysis; Other objects of the invention will become apparent from a consideration of the accompanying disclosure;

A broad aspect of the invention process-wise comprises passing a gas sample in a continuous stream at a con-. stant rate to a condensing chamber or column and passing only a portion of the gas therefrom to the analyzer while venting or-rejecting the remaining portion of gas and. any condensate formed therein. In this manner the time lag between the taking of the sample from the process stream and the analysis is decreased appreciably so as to obtain more accurate control of the process being regulated in accordance with the analysis. 7 l V 1 More complete understanding may be had of the invention by reference to the accompanyingdrawing of which Figure 1 is a flow diagram in accordance with the other particles having a large surface area is positioned :5-

above the inlet port to provide a liquid coalescing surface. A cooling coil is disposed above the balls to condense 'water vapor and/ or other readily condensible materials which remain in the gas stream. A backpressure regulator or flow-control valve is connected with an outlet in a lower portion of the trap or condenser to maintain a constant pressure in the condenser and remove gas and condensate against the regulator backpressure. The liquids condensed on the balls and cooling coil fall to the lower region of the chamber.

Utilizing the system described herein a relatively large sample is continuously taken from the sample point in the process line which carries the streamto be analyzed and this sample in vapor form is passed to the condensing column or trap wherein readily condensible material is condensed and is removed from the bottom of the column. Only a portion of the sample vapor passed into the condensing chamber is passed to the analyzer instrument so that a substantial portion of the sample passed invention showing one arrangement of apparatus for etfecting the flow; and Figure 2 is an elevation, partially in section, of a condensing column and backpressure regulator or valve for use in the arrangement shown in 'Fig' ure 1. The drawing is schematic and corresponding parts are correspondingly designated. Referring to Figure 1, a stirred reactor 5 provided with stirring means 6 is utilized in the polymerization of low boiling l-olefins in which process a slurry of suitable catalyst is passed via line 7 into the reactor and the olefin is passed via line 8 under the control of motor valve 9 into the reactor. The reaction is effected at pressures which. maintain the reaction mixture, including a suit,- able hydrocarbon solvent for the polymer, in liquid phase. The reaction effluent is passed via line '12 to a flash chamber 10 containing a heating coil 11 which supplies the heat for flashing the unreacted normally gaseous olefin which was fed to the process via line 8. The solvent and polymer product of the process is passed via line 15 to purification and recovery means not shown. The overhead fraction from flash chamber 10 is passed via line 16 to any suitable disposal and may be recycled to the polymerization process via line 8. n

In order to control the polymerization process a sample Patented Oct. 11, 1960 form of balls 74, is disposed on screen 71.

chamber or column 22. Steam line 24 passes thru va-' porizer-flow-controller 18 and thence around lines 20, 32, 3 6, and 40 to beat them and facilitate flow of fluid therethru. Vaporizer-flow-controller 18 is of any suitable design which passes a completely vaporized sample at a constant flow rate from line 17 to line 20. A preferred device for this purpose is fully disclosed in application Serial No. 429,463, filed May 13, 1954 in the U.S. Patent Office, now Patent No. 2,826,180.

Condenser 22 contains a cooling means (shown in Figure 2) which is connected with inlet line 26 and outlet line 28 for circulating a coolant therethru. A conduit 30 leads from the upper end of condenser 22 to analyzer instrument 31 which may be any type of instrument adapted to measure the concentration of a component in the gas stream or of any characteristic of the gas stream which is useful in controlling a pnocess variable. A vent line 33 is provided on instrument 31 to dispose of the gas sample after analysis.

An effiuent line 32 from the bottom of condenser 22 connects with a constant pressure relief valve 34 which maintains a predetermined pressure within condenser 22. Line 36 connects valve 34 with a liquid-vapor separator 38. Line 40 vents vapor from the separator and line 42 carries condensate or liquid to any suitable disposal. Separator 38 may be of any conventional design and construction. A solenoid valve 46 in line 30 provides for cutting off the flow of vapor in line 30 from condenser 22 to analyzer 31 and cutting in the flow of a standard gas (or other gas stream) for comparative purposes thru line 48. Valve 46 is operatively connected with a source of electric power and a timer (not shown) which operate the valve at regular intervals, such as one hour periods, to pass standard gas to the analyzer for a short period. A constant flow controller 50 of any conventional design and construction is positioned in line 30 so as to effect accurate regulation of the flow of vapor in this line at a desired predetermined rate. A flow indicator 52 is also positioned in line 30 so as to permit reading of the flow at any time. Flow controller 50 and flow indicator 52 are usually built into instrument 31 but may be detached therefrom as shown in the drawing.

Obviously the lines or conduits connecting the sampling point with the analyzer should be as short as possible in order to reduce the time of travel of the sample thru the system.

In the specific application of the invention shown in Figure 1, instrument 31 is an infrared anlyzer which determines the olefin (ethylene) content of the vapor stream flowing from flash chamber via line 16 and is connected by control line 54 (generally an air line) with controller 56 on motor valve 9, thereby controlling the feed rate of olefin to reactor 5.

Referring to Figure 2, condenser 22 comprises a metal shell 60 having an inlet 62 intermediate its ends. Line 20 of Figure l connects with inlet 62. Shell 60 is closed at the ends by means of closure members 64 and 65 which are conveniently threaded onto the ends of the shell against sealing rings 66.

Intermediate the ends of the condenser and opposite inlet 62 is positioned a filter and support assembly on ring 68 which is fixed by any suitable means to the shell 60. The filter assembly comprises rings 69 and 70 supporting screens 71 and 72, respectively. Rings 69 and 70 are separated and spaced apart by a series of rods 73. A bed of particulate contact material, preferably in the Balls 74 may be constructed of metal, porcelain, ceramicmaterial or any hard material inert to the fluid stream passing thru the condenser. The principal function of balls 74 is to provide a coalescing or condensing surface for the readily condensible material in the vapor stream passing thru the condenser. Raschig rings, saddles, or contact material of other shapes may be utilized in lieu of balls 74.

Cover member 64 contains a threaded outlet 76 which connects with line 30 and threaded ports 77 and 78 which connect with lines 26 and 28. A condenser coil 79 is spiraled around condenser vessel 80 and leads into this vessel at 81 thereby providing flow of heat exchange fluid from port 77 port 78. Rings 82 are disposed on tubing 79 so as to increase the heat exchange surface thereof.

Bottom closure member 65 contains an outlet port 84 which is connected thru conduit 32 to a pressure flowcontrol valve 34 comprising a lower housing section 86 and an upper housing section 87. A flexible diaphragm 88 is disposed between sections 86 and 87 which are attached in sealed relation thru diaphragm 88 by means of screws 89. This construction provides an upper valve chamber 90 and a lower valve chamber 91. An inlet port 93 containing a filter screen 94 provides a passageway from conduit 32 to chamber 91. An outlet port 95, which connects with line 36 of Figure 1, leads into an angular channel 96 extending upwardly thru valve seat nipple 97. A valve head assembly comprising thimble 98, containing passageways 99, core 100, and plate 101 are assembled by threads as shown. Plate 101 is attached to the upper surface of diaphragm 88 by screws, rivets, or other suitable means so as to move with the diaphragm. A flexible valve seat sealing member 102 is held in position on core by shoulders on thimble 98 and makes a seal with nipple 97. A helical spring 103 is axially positioned around the upper end of valve head assembly in contact therewith and is adjustably retained by threaded cap 104 which fits against flexible washer 106.

A vent 107 opening into valve chamber 90 provides for breathing of the valve while in operation. Flow of fluid thru valve 34 via passageways 99 in thimble 98 is permitted when pressure in valve chamber 91 is suflicient to force diaphragm 88 upwardly so that the valve head assembly including seat 102 is moved away from valve nipple 97 thereby allowing fluid to pass thru passageways 99 into the annular space between thimble 98 and nipple 97 from which it passes to channel 96 and out thru port 95.

In practice valve 34 may be constructed and set to open at any desired pressure in chamber 91, the pressure in valve chamber 90 of course being atmospheric because of vent 107. A valve of the construction shown in Figure 2, designed and set to open at about 8 p.s.i. pressure has been utilized with good results in a system substantially as shown in Figure 1. In this system ethylene was polymerized in stirred reactor *5 and the efliuent was passed via line 12 to flash chamber 10 which was controlled so as to flash the light constituents, including ethylene, overhead via line 16. A continuous sample of the efiluent in line 16 was taken thru line 17 by means of vaporizerflow-controller 18 which passed the same at a constant rate of 5,000 cc. per minute. All of the sample taken was passed in vapor form thru line 20 to inlet 62 and into condenser 22. Flow-controller 50 was set to pass the efiluent in line 30 at the rate of 2,000 cc. per minute to infrad red analyzer 31 which automatically and continuously determined the ethylene content of the sample and regulated the flow of ethylene in line 8 by controlling valve 9 so as to substantially maintain a predetermined ethylene content in the overhead stream from flash chamber 10.

It was found that the time lag between taking the sample at thesampling point and the analysis of the sample at instrument 31 was reduced about /2, thereby permitting closer control of the polymerization process,

as compared with the time lag when passing the entire vapor sample admitted to the condenser thru line 20 to the analyzerthru line 30, without rejecting any substantial portion of the sample.

The sampling system substantially as shown and described and operated in accordance with the invention can also be utilized with similar improved results in controlling the operation of an extractive: distillation column on operation in the separation of C hydrocarbons comprising normal butane, butene-l, and butene-Z utilizing a selective solvent comprising furfural. In this application of the invention it is essential to remove the furfural prior to the analysis and this is accomplished by dissolving the furfural in water or steam. To this end, a steam line (not shown) connected to line 20 is utilized to pass steam admixed with the sample stream into condenser 22 so as to remove furfural from the sample be fore the same passes thru line 30 to the analyzer. The water, furfural, and other readily condensible material in the sample are then removed together with the rejected portion of the sample stream via lines 32 and 36, the gaseous portion escaping thru line 40 and the liquid fraction thru line 42. This type of process is disclosed fully but with a diflferent sampling technique in US. application S.N. 431,702, filed May 24, 1954, now abandoned.

It should be understood that the sampling system and method of operating same as disclosed herein are applicable to any chemical process in which it is desirable to control a process variable by analysis of a process stream which is aifected by the process variable.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

We claim:

1. Apparatus comprising in combination a vaporizerflow-controller having an inlet, an outlet, and heating means; a condenser connected with said outlet having an inlet at an intermediate level, a gas outlet at an upper level, a fluid outlet at a lower level, and cooling means in an upper section thereof; and a pressure-relief valve connected with said fluid outlet adapted to pass both liquid and gas from said condenser at a predetermined pressure therein.

2. The apparatus of claim 1 including a vapor-liquid separator connected with said pressure-relief valve.

3. The apparatus of claim 2 including a gas analyzer connected by conduit means with the gas outlet of said condenser and a flow-controller in said conduit means.

4. The apparatus of claim 1 including a gas analyzer connected by conduit means with the gas outlet of said condenser and a flow-controller in said conduit means.

5. The apparatus of claim 4 including a three-way valve in said conduit means intermediate said flow-com troller and said condenser which in one position connects said analyzer to a source of standardization gas while cutting off the sample stream.

References Cited in the file of this patent UNITED STATES PATENTS 2,119,786 Kallam June 7, 1938 2,299,899 Houghland Oct. 27, 1942 2,306,606 Hirsch Dec. 29, 1942 2,350,006 Wolfner May 30, 1944 2,356,845 Hines Aug. 29, 1944 2,429,555 Langford et al. Oct. 21, 1947 2,720,788 Sibley Oct. 18, 1955 FOREIGN PATENTS 661,636 Germany June 23, 1938

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