US2782103A - Analyzer for gaseous mixtures - Google Patents

Description

s. s. PRENTISS 2,782,103 ANALYZER FOR GASEOUS MfXTURES Filed Oct. 12, 1951 Feb. 19, 1957 FIG. 3

FIG. 4

INVENTOR.

S. S. PRENTISS BY HUM qr A TTOR/VE VS United States Patent-O ANALYZER FOR GASEOUS MIXTURES Spencer S. Prentiss, Bartlesville, kla., asslgnor to Phillips Petroleum Company, 'a corporation of Delaware Application October 12, 1951, Serial No. 251,115 1 Claim. (Cl. 23-455 such as in mines and around petroleum and chemical processing plants, for example. Efiiciency studies of internal combustion engines, jet engines, and the like often require an analysis of the exhaust gases therefrom or of the fuel-air ratio of the input feed mixture. In pe troleum exploration and drilling operations it is desirable to analyze soil and mud particles, since the detection of changes in the combustible gas contained therein often gives valuable information as to oil bearing strata. From the foregoing illustrations, which obviously include only a few of the many applications of combustible gaseous mixture analysis, it should be apparent that there is a widespread need for eflicient analyzers.

For some time it has been known quite generally that. certain substances, in the presence of a combustible. fluid mixture, have the property of promoting combustion along their surfaces which results in the combustible constituents of the fluid mixture uniting with any airor oxygen which may be present. An example of such a substance is platinum which is a catalyst of combustion under certain temperature conditions. When a combustible material is brought together with air or oxygen in the presence of such a catalyst of combustion, the temperature of the latter isincreased by an amount depending upon the proportion of combustible constituents present. By measuring this increase in temperature there is provided an indication of thepercentage of combusti-' bles present in the mixture. In accordance .withjthis principle, apparatus has been provided for detecting combustion of a gaseous. mixture on the surface: of aheated platinum filament. Heat generated by the oxidationxof the gas increases the temperature of the filament thereby resulting in an increase in the electrical resistance of said filament. This change in resistance is measured by means of a Wheatstone bridge circuit wherein the platinum filament constitutes one of the resistance arms of said bridge. analysis based upon this catalytic property of platinum employs a strip of platinum wire positioned around the bulb of a thermometer device. Any increase in temperature of the platinum due to combustion taking place on its surface is indicated by the reading of the thermometer. While these various known devices operate in a satisfactory manner under certain conditions, most of these devices lack the desired degree of portability and rigidity which is needed in many testing operations. A further limitation is that these devices usually require that the gaseous mixtures under analysis be-maintained within an analysischamber.

Another known method of gaseous paratus;

It is toward providing an improved form of gaseous analyzer and detector that the present invention is directed. In accordance therewith, a catalytic agent 1s disposed upon the surface of a flame detecting dev ce which can be positioned directly in the region of a mixture under analysis. The improved form of flame detecting device employed in this manner is essentially of the form described in the copending application of D. R. De Boisblanc, Serial No. 220,113, filed April 9, 1951, entitled Detecting Device.

Accordingly, an object of this invention is to provide.

means for safely and accurately indicating the presence of an explosive or gaseous mixture.

Another object is to provide means for analyzing gaseous mixtures to determine the proportions of combustible components present therein.

A further object is to provide means for analyzing the fuel-air ratio of feed streams to internal combustion and other type engines.

- A still further object is to provide apparatus for carrying out the above-mentioned objects which is simple to construct, easy to operate, and which is capable of giving rapid reliable results.

7 Various other objects, advantages, and features of this invention should become apparent from the following detailed description taken in conjunction with the accompanying drawings illustrating a preferred embodiment of this invention in which:

Figure 1 is a schematic view of a combustible gaseous mixture detecting probe together with suitable electrical indicating circuitry;

' Figure 2 illustrates a second form of the testing ap-' Figure 3 shows a modification of the apparatus of Figure 1 especially adapted to detect the presence of explosive vapors; and

Figure 4 illustrates an application of this analysis instrument for studying the fuel-air input mixtures to internal combustion engines. 1

. An improved form of combustion detecting device recently has been developed which relies upon the principle that in any given electrical resistance element having two electrodes connected thereto, one of which is grounded,

there exists a constant distribution of potential at all.

points throughout said element. If an electrically charged particle is brought into contact with the surface of this element electrical current will flow therein until.

all points within the element are once again at zero or ground potential.

the ungrounded electrode exhibits a potential variation which is dependent upon the magnitude of the charge of the particles striking said element, the electrical resistance of the element, and the geometric relation of the ungrounded electrode with respect to the second grounded,

propriate apparatus which can be usedin this manner for flame detection.

Referring now to the drawings in detail and to'Figure l in particular, there is shown a combustion detecting element 10 comprising a cylindrical metallic casing 11 having a metallic electrode 12 positioned therein and'electrically insulated from casing 11 by means of suitable in-- sulating support such as 13. A ceramic refractory tip.

Patented Feb. 19, 1957 During the time when current is flowing, the region of the'element in the neighborhood of 14; into which, While plastic, is inserted the hook 'shaped end of electrode 12, is positioned across one end of casing 12 and anchored thereto by suitable holes 15 drilled near the tender casing 11. Tip 14 preferably is cdhst ructe'd or a baked and hardened rerractor' f material seen as aluminum oxide. Electrode 12 is fitted somewhat'lo'osely into casing 10 so as not to work loose from tip 14 due to thermal expansion at elevated temperatures. .Upon the surface of refractory tip 14 there is formed a partial coat ing of suitable combustion promoting catalytic material such as, for example, thin strips 16 of platinum or other combustion supporting materials which are discussed fully hereinafter. Electrical leads 17 and 18 are attached to casing 11 and electrode 12, respectively, to; connect cumbustion detecting element 10 into the associated electrical circuitry which comprises an alternating current amplifier 21 and an output indicating device or meter 22.

The operation of the flame detecting probe per se, which" is not the subject of the present invention, can be ex-. plained in the following manner. Assuming that tip 14' is positioned in the region of a flame, then the ions con tained within said flame will bombard the surface of tip I4 and in so doing generate electrical voltage fluctuation across said tip. Each ion that strikes tip 14 introduces a small burst of current therein. It is believed that the voltage fluctuations generated between casing 11 and elec node 12 by the individual bursts of current have a sta tistical fluctuation in magnitude over .a Wide frequency range. However, these electrical signals must be amplified many fold by amplifier 21 before being' of sufficient magnitude to give a readable signal on meter 22.

The present invention, however, is directed to the ad dition of a suitable combustion supporting catalyst such as platinum strips 16 to tip 14. When probe 10 is inserted into the region of a combustible mixture there iswith amplifier 21 by means of connecting leads 27 and 28, respectively. The output of amplifier 21 is indicated on meter 22. Partial coatings 29 and 30 of combustion supporting catalytic material are formed on the opposing surfaces of electrodes 25 and 26, respectively. The operation of this second form of detecting device is essentially the same as that of the probe in Figure 1, it having been found that the air gap between electrodes 25 and 26 serves essentially the same function as the ceramic noise resistance element 14 positioned between casing 11 and electrode 12 in Figure l, and that coatings 29 and 30 serve the same function as coating 16 on element 14.

In Figure 3 there is shown a portable combustion detecting unit which is particularly adapted to determine the existence of an explosive mixture such as may be encountered in mines, for example. Probe unit 10 contains an elongated casing 11 which can serve as a handle for conveniently carrying the probe unit into a region containing what may be an explosive atmosphere. Tip portion 14, upon which combustion readily takes place due to platinum coating 16 thereon, is completely enclosed within a screen of an effective heat conducting material such as copper wire. Screen 35 serves to prevent any flame which may be initiated upon the surface of tip 14 from escaping outward therefrom, said screen 35 forming essentially a Davys safety lamp. Probe 10 is connected by means of a flexible conduit 36 to a portable indicating unit 37 which contains amplifier 21 and output meter 22. In place of, or in addition to, output meter 22, a suitable warning device such as a bell or buzzer can This sur- In this manner the air input mixture through intake manifold 41. Inserted within manifold 41 is a probe element 10 surrounded by a protecting wire screen 35. Electrode 12 is connected to the input of amplifier .21 by an electrical lead 42, the input circuit being completed by a grounded lead which portion thereof.

can be applied directly to a manifold 41. The input fuel-air mixture which enters engine thus surrounds probe 10 which is employed to initiate combustion of a Protective screen 35 preventsthis combustion from taking place throughout manifold '41. Since the reading on output meter 22 is indicative of the degree of combustion taking place upon probe 10, this meter reading can becalibrat'ed to give an indication of the prope'r fuel-air mixture enteringengine 40. This is true hecause the degree of combustion is influenced by the ratio of fuel to air supplied engine 40. In addition to its use asanindicating device, the output signal of amplifier 21 can be applied to suitable control mechanism to regulate the fuel-air input' supplied by the carburetor, not shown; In this manner engine 40 can be operated at the condition of maximum efficiency by proper regulation of its fuelair input ratio. Approximately the same results can be obtained by positioning the combustion detecting probe 10" within theexhaust fumes of engine 40. By measuring the cbmbnstible' content of the output exhaust fumes, a

, various other materials can be employed as combustion supporting catalytic agents;

It has been found that even the stablest organic substances when mixed with air and passed over suitable catalytic surfaces will commence to oxidize at quite moderate temperatures. Particularly active in this respect are the various metals of the platinum group which include platinum, palladium, iridium, rhodium, osmium and ruthenium. In addition, the oxides of iron, cobalt, nickel, chromium, copper, manganese, silver, and cerium are catlytic in somewhat the same manner.

- Platinum black, platinum sponge and the corresponding forms of palladium also are quite active as well as the metallic elements themselves. For the detection of carbon monoxide, the catalyst I-Iopcalite" is particularly elfective'. Hopcalite is a mixture of the following approximate composition: cupricoxide, 30 percent; manganese peroxide, 50 percent; cobaltic oxide, 15 percent; and

silver oxide, 5 percent.

The detecting elements of this invention can be constructed in various manners; one of which comprises depositing a coating of the catlytic active material upon a portion of the surface of the probe element itself. This coating can be in the form of thin strips or wires of the catalytic material disposed either directly on the surface of the probe or protruding therefrom like whiskers. A

' second mode of construction comprises mixing a quantity of the catalytic material with the material of which the probe tip is formed, the latter procedure resulting in catalytic points being formed on the surface of the probe whichserves toisolate the combustion at said individual has a greater safety factor when used in the detection of explosive vapors.

In constructing the probe element of Figure 1 various ceramic refractory materials can be used in addition to aluminum oxide to form the tip element 14. Examples of these substances which have been found effective include the oxides of calcium, magnesium, zirconium, beryllium, and thorium; and the carbides of titanium, zirconium, columbium, tantalum, silicon, tungsten, and hafnium. The probe element itself can be constructed in various configurations as illustrated in the copending application of R. S. Marsden, Jr., Serial No. 220,116, filed April 9, 1951, entitled Electrical Noise Element. As therein illustrated casing 11 can be formed of a ceramic material as can electrode 12; in addition two electrodes can be positioned within casing 11 thereby eliminating casing 11 as one of the output electrodes. A still further example comprises a mass of ceramic material having two metallic electrodes positioned therein.

Amplifier 21 can be any conventional alternating current amplifier adapted to pass a wide band of frequencies. Since the detected noise signals are of relatively small amplitude amplifier 21 must have high gain and should have little electrical noise introduced therein in order that a maximum signal can be transmitted thereby. The output of amplifier 21 can be indicated on any suitable metering device such as a thermocouple voltmeter or can be rectified to actuate any direct current control or recording mechanism.

While this invention has been described in conjunction with present preferred embodiments thereof, it should be apparent that various changes in details of the apparatus can be made without departing from the scope of the invention; and, further, that the theory set forth, although believed to be accurate, is not considered as the sole basis of the operativeness of this invention. This apparatus does operate successfully and effectively whether or not upon the principles described herein.

Having described my invention, I claim:

Apparatus for indicating the presence of a combustible gaseous mixture comprising a metallic casing having an electrode positioned within and electrically insulated from the casing, a tip of electrically conductive refractory material positioned between and electrically connecting said casing and said electrode, a catalytically active agent positioned on said tip, said agent being capable of initiating combustion of a gaseous mixture to be analyzed, alternating current amplifying means having the input terminals thereof connected to said electrode and said casing, respectively, and means to indicate the output signal of said amplifying means which is representative of electrical voltage fluctuations that are generated by combustion of the mixture to be analyzed taking place in the region of said tip.

References Cited in the file of this patent UNITED STATES PATENTS 262,054 Kitsee Aug. 1, 1882 1,421,720 Toberts July 4, 1922 1,880,941 Erickson Oct. 4, 1932 2,219,540 Miller Oct. 29, 1940 2,285,866 Markle June 9, 1942 2,298,288 Gerrish et al. Oct. 13, 1942 2,363,478 Boeke Nov. 28, 1944 2,437,720 Ackley Mar. 16, 1948 2,508,588 Waltrnan a May 23, 1950 2,511,177 Richardson June 13, 1950 2,577,435 Siebenthaler Dec. 4, 1951 2,581,812 Page Jan. 8, 1952 2,583,930 Cotton Jan. 29, 1952 2,617,716 Hartline Nov. 11, 1952 2,688,648 McIlvaine Sept. 7, 1954 FOREIGN PATENTS 11,101 Great Britain July 16, 1890 398,722 Great Britain Feb. 1, 1933 591,808 Great Britain Aug. 29, 1947 OTHER REFERENCES Cook et al.: Physical Review, vol. 74, No. 11, Dec. 1, 1948, pages 1714-1719. (Copy in Scientific Library.)

Chem. Engineering, vol. 57, No. 8, page 149, August 1950, item 149A. (Copy in Scientific Library.)

Garrison et al.: Review of Scientific Instruments, vol. 20, No. 11, November 1949, pages 785-794. (Copy in Scientific Library.) 7

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