US3021199A

US3021199A - Instrument to measure combustibles in liquid oxygen

Info

Publication number: US3021199A
Application number: US696252A
Authority: US
Inventors: Kapff Sixt Frederick; Ginsburgh Irwin
Original assignee: Standard Oil Co
Current assignee: Standard Oil Co
Priority date: 1957-11-13
Filing date: 1957-11-13
Publication date: 1962-02-13
Anticipated expiration: 1979-02-13

Description

Feb. 13, 1962 s. F. KAPFF ETAL 3,021,199

INSTRUMENT TO MEASURE COMBUSTIBLES IN LIQUID OXYGEN Filed Nov. 13, 1957 3 Sheets-Sheet 1 gar-W4 Jim 3 zwmgww a liar/1g Feb. 13, 1962 s. F. KAPFF EFAL 3,021,199

INSTRUMENT TO MEASURE COMBUSTIBLES IN LIQUID OXYGEN Filed Nov. 13, 1957 5 Sheets-Sheet 2 @4474 5201/ jzrwv'n/ 49m; mg 2M0. 9M

QW/cey Feb. 13, 1962 KAPFF ET AL 3,021,199

INSTRUMENT TO MEASURE COMBUSTIBLES IN LIQUID OXYGEN' Filed Nov. 13, 1957 3 Sheets-Sheet 5 6Q HRH/Y I v? Nf W 61 I 63 W F29 2 [Ma 67 .512? 69 PM i 1 45 8 W FILL P0 WEE SUPPL Y Pl/HP RECORDER WSTRUWNT TU MEASURE COMBUSTIBLES EN LEQUID GXYGEN Sixt Frederick Kapfi, Homewood, and Irwin Ginshurgh,

Chicago, Ill assignors to Standard Gil Company, Chicago, 111., a corporation of Indiana Filed Nov. 13, 1957, Ser. No. 696,252 6 Claims. (Ci. 23-230) This invention relates to method and means for accumulating and monitoring the concentration of hydrocarbons in liquid oxygen or oxygen-rich liquid streams in liquid air plants.

The operation of plants for the production of pure oxygen or nitrogen from air basically involves a liquefaction of the air and subsequent fractionation of the components in a distillation tower. This distillation is performed at low temperatures and produces an overhead product of pure nitrogen and a bottoms product of liquid oxygen. In the liquid oxygen will be found any substances present in the entering air which are not trapped out in the early cooling stages and have boiling points higher than oxygen. Some of the materials of interest are the hydrocarbons in the C C and 0.; range of molecular weights. The presence of sizable quantities of these in the liquid oxygen presents a serious explosive hazard.

The safe operation of such a plant, therefore, involves maintaining the hydrocarbon concentrations as low as possible in the liquid oxygen. The concentrations considered tolerable vary for the different hydrocarbons. Acetylene is by far the most dangerous since in concentrations of a few p.p.m. it reaches its solubility limit in liquid oxygen. The solid acetylene which then separates can detonate under certain conditions causing serious explosions. The concentrations of other hydrocarbons from ethylene to the butanes are not so critical since these are much more soluble in liquid oxygen. However, it is desirable to hold their concentrations as low as possible since, if any explosion should occur, these would furnish an additional fuel supply.

Monitoring the liquid air stream in the process is desirable for early detection of hydrocarbon concentration. An object of this invention is, therefore, to provide an instrument capable of measuring combustibles in liquid oxygen. A further object of the invention is to provide a method and means whereby the hydrocarbon component can be concentrated for subsequent detection and measurement. These and other objects of the invention will become apparent as the description thereof proceeds.

Briefly, the instrument depends upon the adsorption of hydrocarbons from gaseous oxygen stream (obtained by evaporation of liquid oxygen) upon cold silica gel, their subsequent desorption by heating, and their detection by combustion on a catalytic heated platinum wire. Cooling is provided by contact with the liquid oxygen under test, the pressure generated providing the pumping necessary to drive the vaporized sample through the column. A Wheatstone bridge circuit including such platinum wire comprises the measurng means. Further details and advantages of our invention will be described by reference to a preferred embodiment illustrated in the accompanying drawings wherein:

FIGURE 1 is a diagrammatic illustration of one system, partly in section, of the hydrocarbon concentration cell;

FIGURES 2, 3 and 4 are views illustrating hydrocarbon detector apparatus;

FIGURE 5 is a circuit diagram of the instrument; and

FIGURE 6 is a diagram of the detector bridge circuit 3,Zl,l% Patented Feb. 13, 1962 employed with the detector apparatus of FIGURES 2, 3 and 4.

Referring to the drawings, FIGURE 1 shows the details of the refrigerated vessel 10 having a cover 10:: and an air-tight gasket seal 10b containing the silica gel adsorber 11. To analyze a liquid oxygen sample, the operator pours the sample into the funnel 12 until liquid is observed issuing from valve 13. He then presses start switch 31 (FIGURE 5) and the instrument does the remainder of the operations automatically. The cartridge heater 15 turns on after the

valves

13 and 46 close and remains on as long as there is liquid oxygen present in the lower portion of the vessel 10 to keep the thermocouple 17 cold. The gaseous oxygen and hydrocarbons which fill the upper part of the vessel 10 enter inlet 16 and pass upwardly through the gel column 18 and the oxygen exhausts through line 58 and valve 19. When all the liquid oxygen has been evaporated in vessel 10 and the thermocouple 17 begins to warm up, the cartridge heater 15 turns oif and theinstrument prepares to go through the desorption and analysis steps as described below.

In FIGURE 1, the column 18 comprises an annular gel bed 18a with glass wool distribution plugs 18b at the upper and lower ends of annular vessel 11. The top of the vessel is closed by cap ring 11b, lead gaskets 11c and 11a providing necessary seals. Port 11e in cap ring 1112 permits free access of the refrigerating gas through and about the annular vessel.

The adsorbed hydrocarbons are desorbed from column 18 into an oxygen-containing carrier gas stream 20 and detected with a catalytic platinum wire detector 21 similar to that shown in FIGURES 2, 3 and 4. The

platinum wires

22 and 23 are connected in the bridge circuit shown in FIGURE 6. A selector switch 25 permits operation of the recorder 26 at two sensitivties to cover a wide range of hydrocarbon concentrations.

The calibration of this instrument depends upon the catalytic activity of the

platinum wires

22 and 23 used as detectors. Since these change their activity from time to time, it is necessary to supply a standard signal to check them. This is done by permitting a small quantity of combustible gas to enter the oxygen stream 20 passing to the detectors 21. It has been found that a flow of 2.9 cc. of ethylene per minute into the oxygen stream 20 flowing at 0.10 c.f.m. gives a recorder signal corresponding to that obtained from 6 ppm. of hydrocarbon in a liquid oxygen sample. This standardization occurs during every determination and all concentrations are calculated relative to it.

A cylinder 27 of dry gas, such as gaseous ovygen, is connected to this instrument and provides a gas flow for three purposes: (1) During the time when the liquid oxygen is being evaporated, the cylinder gas is pumped through the detecting cell 21, thus permitting the bridge current and zero to be adjusted and a good zero to be obtained. (2) During the desorption period when the pump 28 is pulling gas from the refrigerated vessel 10 through the gel column 18, the dry cylinder gas flow passes through the refrigerated vessel 10 to protect against the entrance of humid room air which in this cold system would soon cause ice blockage. (3) The third function of the cylinder gas is to serve to flush out the refrigerated vessel 10 after a sample containing high concentrations of hydrocarbons has been run.

Before starting any test, the device is connected to gaseous oxygen cylinder 27 through reducing valve 32 and to standardizing gas (ethylene) cylinder 27a through reducing valve 34 which is adjusted to 10 p.s.i.g.

If instrument has not been used for a period of several hours, flush switch 29 is placed in the "flush position. This energizes valves 13 and 45 causing gaseous oxygen from cylinder 27 to pass through vessel 10, sweeping out any moisture which may have diifused in as well as any residual hydrocarbon vapors from previous tests. The range switch 25 is set for high or low concentration. Switch 29 is returned to the run position closing valve 45 and switch 31 is placed in the fill position. This opens

valves

46 and 13 so that sample liquid may be poured through funnel 12 to a level determined by outlet conduit 47. When liquid is seen to issue from valve 13, the instrument is ready to begin a test.

Switch 31 is placed in the start position. This closes

valves

46 and 13 and opens valve 48. Switch 31 is a spring-return type and remains in start only momentarily. At the same time, relay 49 is reset by coil 50 opening switch 51. Relay 52 (used as a time-delay relay) actuates about one second after relay 4-9 has been reset and provides power to contacts of switch 51. At the same time, power is supplied by self-locking relay 54 to pilot light 66, pump 28, and to the power supply for the detecting and recorder circuits of FIGURE 6.

Thermal delay relay 53 is energized through relay 54, relay 53 providing current to the motor of recorder 26 when energized. A delay of 60 seconds in relay 53 is used to reduce the large recorder deflection sometimes obtained while the recorder and detector circuits are warming up.

By relay 54- power is supplied to cartridge heater '15 which heats and evaporates the liquid oxygen sample in vessel 10. During this evaporation, the operator set the flow through pump 2% by adjusting valve 32 and observing flow meter 33. The detecting bridge current and recorder zero are also set at this time. The bridge current is set at 0.60 ampere and the zero of recorder 26 is adjusted by zero adjust helipot 35 in FIGURE 6.

When evaporation of the liquid oxygen sample has been substantially completed, thermocouple 17 in vessel 10, being no longer immersed in cold liquid, heats up and actuates relay 49. This removes power from the cartridge heater 1S and normally closed valve 48 by means of relay 55. At the same time, (a) the timer motor 56 is started by the action of coil 57 and switch 66; (b) valves 45 and 13 (by action of switch 64) are opened, permitting a stream of gaseous oxygen from cylinder 27 to pass through the vessel and (c) valve 19 is energized to connect pump 28 to line 58, thus drawing gas through the gel column 18.

Closing of timer switch 59 actuates pilot light 67 and opens valve 42 permitting standardizing gas from cylinder 27a to enter the oxygen stream flowing in line 20 through the high resistance leak 60 to check the detector 21. Switch 59 then opens. Referring to FIGURE 5, timer switch 61 is next actuated by the action of the timer to provide power to transformer 62 and pilot light 68, the secondary of which is connected to gel heater 63. Resistance 69 in the primary circuit of the transformer 62 is chosen to provide the proper heating current to gel heater 63 via leads from the kovar seals 100 in cover 10a.

At the completion of the preset time for desorption of the adsorbed hydrocarbons, timer switch 65 operates to de-energize relay '54. Timer switch 65 returns to the closed position just before switch 66 opens ending the test.

When the pilot light 66 goes out, the test has been completed and the hydrocarbon concentration can be calculated from the ratio of the height of the desorb peak to the standardizing peak of 6 p.p.m. on a chart record. If the sample has shown a hydrocarbon concentration greater than p.p.m., the flush switch 29 is held in the flush position for at least three minutes. This clears out any remnants of the previous sample and prepares the instrument for another test.

In summary, the timer starts after the liquid oxygen has all evaporated in 10 and has the following sequence:

(1) The cylinder oxygen from 27 is diverted to the refrigerated vessel 19 and the pump 28 is opened to the outlet of the gel column 11;

(2) The standardizing gas valve 42 is opened to check the activity of the

platinum filaments

22 and 23 and to provide a reference signal; and

(3) The gel column 11 is heated to desorb any adsorbed hydrocarbons. The timer then turns oif and the test is concluded.

Samples of liquid oxygen containing known concentrations of hydrocarbons were prepared and used to standardize the instrument. Our technique has been to fill a small 1.6 cc.) gelatin capsule with hydrocarbon gas by means of a hypodermic syringe. This capsule is then immersed in liquid oxygen. After the capsule has come to liquid oxygen temperature, it is broken beneath the surface of the liquid, the hydrocarbon gas dissolving V in the liquid oxygen quantitatively.

The calibration with different hydrocarbons shows some instrument sensitivity to hydrocarbon type. For example, for a given hydrocarbon concentration, the instrument will give about twice as large a signal for ethylene as for ethane. This may be a unique property of the Us since propane and propylene give essentially the same instrument response.

It has been found that if the gel column 18 is heated gradually, the various hydrocarbons adsorbed thereon will desorb at characteristic temperatures. This gradual heating may be accomplished, for example, by inserting between switch 61 and gel heater 63, by means of a stepping rel y, suitable resistances in predetermined sequence to vary the current flowing in heater 63. Hence calibration with known gases will permit qualitative and quantitative estimation of the gases adsorbed.

If an analysis of the gas being desorbed from a gel is desired, the output of the detector 21 is plotted on one axis of an X-Y recorder with the other axis representing the temperature of the silica gel column. The record so obtained indicates hydrocarbon concentrationas a function of the temperature of desorption.

It is contemplated that adsorbents other than silica gel may be used including molecular sieve-type adsorbents, activated carbon and alumina, and the like. A double column system may be used in series for the adsorption and in parallel for desorption. Thus molecular sievetype adsorbents may be used to accumulate methane after the C -C hydrocarbons have been retained by the silica gel column. suitably programmed and two desorption signals shown on the recorder.

The invention has been described in terms of a system for concentrating dilute hydrocarbons from oxygen-rich streams. The invention has further been described in connection with a detector for the concentrated hydrocarbons comprising a device wherein they are oxidized. However, in some circumstances it may be desirable to preserve the hydrocarbon components and the detector may comprise non-destructive detectors, such as thermal conductivity cells, gas gravity balances, chromatographic analyzers, and the like. of the hydrocarbons as taught makes possible the use of rugged and less sensitive detectors and makes unnecessary expensive apparatus utilizing techniques such as involved in mass spectrometers, infrared analyzers, and the like.

Although the invention has been described With reference to embodiments thereof, it should be understood that these are by way of illustration only and that the invention is not necessarily limited to such embodiments. Alternative components and operating techniques will become apparent to those skilled in the art in view of the foregoing disclosure and, accordingly, modifications in the construction and operation of the apparatus are contemplated without departing from the spirit of the invention.

The desorption of the two columns may be In any event, the concentration What we claim is:

1. An apparatus for analyzing liquid oxygen for its hydrocarbon content which comprises chamber means for vaporizing a quantity of a sample of oxygen-rich liquid, adsorption means in said chamber means and in communication therewith for selectively adsorbing vaporized hydrocarbons, means for cooling said adsorption means by said liquid sample in heat exchange therewith, means for flowing a stream of gaseous oxygen into said chamber means and through said apparatus, temperature-responsive means responsive to the temperature in said chamber adapted to control said means for flowing said stream of gaseous oxygen, means for heating said adsorption means to desorb said adsorbed hydrocarbons into said stream, and hydrocarbon detector means including a catalytic element adapted to effect combustion of said desorbed hydrocarbons and thereby indicate the concentration of hydrocarbons in said flowing stream.

2. An apparatus for monitoring small quantities of dissolved hydrocarbons in an oxygen-rich liquid sample comprising in combination a vaporizing chamber, means for supplying said sample to said chamber, a column of an adsorbent mass in said chamber cooled by said sample, said column being in communication with said chamber, conduit means for flowing a gasiform sample stream into said chamber and through said column, means for heating said column periodically to desorb hydrocarbons therefrom, means for flowing gaseous oxygen through said apparatus to sweep the desorbed hydrocarbons from the said column, and detector means including a catalytic element adapted to effect combustion of said desorbed hydrocarbons in said flowing gaseous oxygen, the combustion being a measure of the concentration of hydrocarbons in said oxygen-rich liquid sample.

3. An apparatus for analyzing an oxygen-rich liquid sample for small concentrations of hydrocarbons which comprises adsorption column means for accumulating the hydrocarbons, chamber means for vaporizing a liquid sample in heat exchange with said adsorption column means, one end of said adsorption column means being open to the interior of said chamber means, means for sensing when vaporization of the sample is complete, means for flowing gaseous oxygen from a separate source into said chamber means and through said adsorption column means at a uniform rate when such vaporization has taken place, means for heating the said adsorption means to desorb hydrocarbons therefrom, and means including a catalytic element for effecting combustion of said desorbed hydrocarbons to indicate the concentration of hydrocarbons in said flowing gaseous oxygen stream as a measure of the concentration of hydrocarbons in said liquid oxygen sample.

4. The apparatus of claim 3 wherein the adsorption means contains silica gel, said chamber means is a Dewar vacuum flask, and the means for effecting the combustion of hydrocarbons includes a heated platinum filament in a bridge circuit.

5. A method for monitoring the concentration of hydrocarbons in liquid oxygen-rich streams flowing in air liquefaction plants which comprises vaporizing a sample of such liquid oxygen within a confined space to produce a gasiform stream of gaseous oxygen and hydrocarbon vapors, flowing the gasiform stream through an adsorption zone, maintaining said zone at a low temperature by heat exchange contact with the liquid sample and said gasiform stream, separating hydrocarbons from said stream in said adsorption zone, heating said zone to desorb the adsorbed hydrocarbons, simultaneously with said heating flowing a stream of gaseous oxygen through said zone as a sweep gas, and effecting combustion of the desorbed hydrocarbons in said gaseous oxygen on a combustion-catalyzing element, said combustion being a measure of the concentration of hydrocarbons in said liquid oxygen-rich streams.

6. An apparatus for monitoring an oxygen-rich stream containing dissolved hydrocarbons comprising thermally insulated vessel means, column means in said vessel for concentrating said hydrocarbons, said column means having an inlet in communication with said vessel, means for vaporizing a sample of such stream in said vessel, conduit means for flowing said vaporized sample through said column, control means within said vessel responsive to the complete vaporization of said sample, means for heating the said column means to liberate the hydrocarbons therefrom, said control means actuating said heating means, means for flowing an oxygen carrier gas through said vessel and said column means to sweep the concentrated hydrocarbons from said vessel, and a catalytic platinum filament in a bridge circuit adapted to effect combustion of said hydrocarbons in said oxygen carrier gas and detect such combustion as a measure of the hydrocarbon content of said oxygen-rich stream.

References Cited in the file of this patent UNITED STATES PATENTS 2,398,818 Turner Apr. 23, 1946 2,429,555 Langford et al Oct. 21, 1947 2,826,908 Skarstrom Mar. 18, 1958 OTHER REFERENCES Gas Chromatography in Plant Streams, by D. H. Fuller, in ISA Journal, November 1956, pages 440-444.

Chromatographic Analysis of Hydrocarbon Mixtures, by Bradford et al., in Journal of Institute of Petroleum, vol. 41, 1955, pages -88.

Book, Vapor Phase Chromatography, Desty. Butterworth Scientific Publications, London, 1956, page 215. (Article by Drew et al.)

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,021,199 February 13, 1962 Sixt Frederick Kapff et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 61, for "measurng" read f-- measuring column 2,v line 51, for "'ovygen'= read oxygen column 4, line 23, for "C's": read C s Signed and sealed this 3rd day of July 1962.

(SEAL) Attest:

DAVID L. LADD Commissioner of Patents ERNEST W. SWIDER Attesting Officer

Claims

5. A METHOD FOR MONOITORING THE CONCENTRATION OF HYDROCARBONS IN LIQUID OXYGEN-RICH STREAMS FLOWING IN AIR LIQUEFACTION PLANTS WHICH COMPRISES VAPORIZING A SAMPLE OF SUCH LIQUID OXYGEN WITHIN A CONDINED SPACE TO PRODUCE A GASIFORM STREAM OF GASEOUS STREAM THROUGH AN ADSORPVAPORS, FLOWING THE GASIFORM STREAM THROUGH AN ABSORPTION ZONE, MAINTIANING SAID ZONE AT A LOW TEMPERATURE BY HEAT EXCHANGE CONTACT WITH THE LIQUID SAMPLE AND SAID GASIFORM STREAM, SEPARATING HYDROCARBONS FROM SAID STREAM IN SAID ADSORPTION ZONE, HEATING SAID ZONE TO DESORB THE ADSORBED HYDROCARBONS, SIMULTANEOUSLY WITH SAID HEATING FLOWING A STREAM OF GASEOUS OXYGEN THROUGH SAID ZONE AS A SWEEP GAS, AND EFFECTING COMBUSTION BEING A MEASURE SORBED HYDROCARBONS IN SAID GASEOUS OXYGEN ON A COMBUSTION-CATALYZING ELEMENT, SAID COMBUSTION BEING A MEASURE OF THE CONCENTRATION OF HYDROCARBONS IN SAID LIQUID OXYGEN-RICH STREAM.