US2273981A

US2273981A - Analysis of gases

Info

Publication number: US2273981A
Application number: US239794A
Authority: US
Inventors: John D Morgan; Alan P Sullivan
Original assignee: Cities Service Oil Co
Current assignee: Cities Service Oil Co
Priority date: 1938-11-10
Filing date: 1938-11-10
Publication date: 1942-02-24
Anticipated expiration: 1959-02-24

Description

Patented Feb. 24, 1942 UNITED STATES' PATENT OFFICE ANALYSIS OF GASES John D. Morgan, South-Orange, andl Alan P. Sullivan, Elizabeth,. N. J., assignors,.by mesne assignments, to Cities Service Oil Company, New' York, N. Y., a corporation of Pennsylvania Application November 10, 1938, Serial No. 239,794

7 Claims. (C1. ,2s- 232) This invention relates to the analysis of gases, and morel particularlyto apparatus adapted for checking the operating efficiency of domestic and industrial heating furnaces and Diesel engines in accordance with the-temperature and composition of gaseous products of combustion dis- `ing application, ignition of a gas under analysis is effected at the surface of a hot catalytic platinum or platinum-alloy wire forming one leg, of a Wheatstone bridge. Any increase in temperature of the wire resulting from catalytic combustion of the gas increases the electrical resistance of the Wire by ,an amount proportional to the combustion constituents in the gas under analysis. The catalyst wires which are used in this type of gasanalyzer mayhave an operating life of several thpusand hours if they are not heated to ,a -temperature higher than about 1600 F.1'7 00 F. However, it has been found that when such catalyst wires are employed in the analysis of gases containing parafli'nic .hydrocarbons or their derivatives, the catalyst wire gradually suffers a loss in activity at the optimum operating temperature of 14004600".4 Such loss in activity of the catalyst is apparently the erroneous readings which might otherwise be obtained as a result of variations in the pressure of the gas to be analyzed at the point where the sample is taken for analysis. With this object in View a feature of the invention contemplates improvement in apparatus whereby the gas to be analyzed and any combustion constituents which are added thereto for the purpose of promoting combustion reactions, are fed to the analyzing unit of the apparatus at a uniform rate.

Essentially the apparatus of the'present invention is designed to effect Asubstantially simultaneous measurements of the factors of flue or exhaust gas temperature, amounts of unburned combustible, and amounts of excess'oxygen in the flue or'exhaust gases under test, at several points on the load curve of the furnace or engine between high and low load. After such measurements are made, the operation ofthe combustion apparatus under test can then lbe regulated in accordance with such measurement by proportioning the air'and fuel supplies to the furnace or engine so that the temperature of the products result of poisoning of the catalyst by aldehydes or other intermediate partialoxidation products of such parafllnic hydrocarbons and derivatives. Poisoning of the catalyst can be avoided if the catalyst is operated continuously -at` a higher' temperature in the neighborhood of 20009 F. However, the life of a catalyst wire operating at 2000 F. is extremely short, sometimes being only a few hours.

The primary object of the present invention .is

,to provide improved `gas analyzing apparatus which shall be adapted for use in adjusting all4 `v such combustion operations asl occur in furnaces,

Diesel engines, and the like to a condition. of

optimum operating eciency with respect to the particular combustionapparatus and fuel under test.

-A more specic object of the presenti invention is to provide gas analyzing apparatusoper-V ating by catalytic combustion -and so designed as to avoid difficulties with catalystpoisoning heretoforeY referred to.;

Another object of the invention is to provide bustion leaving the combustion chamber may contain small amounts of unburned combustible and relatively large amounts of excess l .air. On

the other hand, certain industrial furnaces are frequently-operated under conditions ofv underventilation, wherein the products of combustion may contain very little if. any unreacted oXvgeIl.

but relatively large amounts of unburnedcom- `bustible. The apparatus of the present invention is .de-

signed for useeven-by anv unskilled operator in effectingl accurate and substantially simultaneous measurements of tine temperature and com'- position.v ofgaseous products of combustion containing either or both unreacted oxygen and unburned combustible. This apparatus has been particularly designed for making continuous teml perature measurements of the ue gas or ex haust gas adjacent the point at which Ait leaves the combustion chamber, and for the simultane- ,y ous removal of a sample stream'of exhaust gas at the point of temperature measurement. The gas sample is thereafter divided into two streams, "and a uniform portion of each stream is quantitatively analyzed respectively for `excess oxygas analyzing apparatus designed `to avoid any 55 ,gen rld for unburned combustible. 1

With the above and other objects and features in view, the invention consists in the improved apparatus which is hereinafter described and more particularly dened by the accompanying claims.

In the following description of the invention, reference will be had to the attached drawing, in which:

Fig. 1` is a diagrammatic `ow sheet of the apparatus assembly showing the gas analyzer and a hydrogen cell in section, and other parts of the apparatus in perspective and elevation; and

Fig. 2 is a wiring diagram.

Referringto Fig. 1, numeral I designates a gas sampling tube having an apertured sampling nozzle I2 at its inlet end, said nozzle being adapted for introduction into the exhaust. pipe of an engine or the waste gas ue I4 of a furnace for securing a continuous sample of the engine exhaust gas or furnace ilue gas to be analyzed. A thermocouple I6 is mounted in flue I4 at a. point closely adjacent the point of location of the gas sampling nozzle I 2, and lead wires I8 and 20 connect the thermqcouple I6 through a switch 22 to a millivoltmeter 24 which iscalibrated for measuring the temperature of the ue gases.

Gas which is withdrawn from the ue I4 through the sampling tube I8 is conducted into a gas iilter and liquid separator 26. Filter 26 may be iilled with copper iilings, cotton, glass wool, or other dry filtering material. From lter 26, the gas sample is conducted' by a tube 28 to an aperture 38 in the housing or bearing of a rotatably journaled multi-apertured gas ow regulator valve 32. With the valve 32 set in the position illustrated diagrammatically in Fig. 1, all of the gas sample which reaches aperture 38 flows through a peripheral groove 34 in the valve to an aperture 36 in the valve housing, and thence through a conduit 38 by which the gas is conducted to an inlet port 40 of a rotary suction pump 42.

Pump 42 is a rotary sliding vane type pump, and it will be understood that this type of pump normally discharges gas from/its discharge portv at a rate which varies with variations in pressure at the inlet port 40. For the satisfactory operation of the gas analyzing apparatus of the present invention it is important that so much of the gas sample as is subjected to analysis should be delivered to the analyzing apparatus at a substantially constant rate, irrespective of variations in pressure at the point at which the gas sample is taken. Accordinglythe pump 42 has been provided with two discharge ports 44 and 46 spaced about 90 apart inthe direction of rotation of the pump. 'l'he discharge port 44 is connected directly to an atmospheric discharge orice 48 and is. proportioned to effect discharge of at least three-quarters of the gas introduced to the pump through the inlet port 48. Since the second'discharge port 48 handles only the gas which is left within the pump chamber after a major portion of the gas has been discharged by the port 44, that gas which is discharged from the pump through the port 46 leaves the pump at a substantially constant pressure closely ap-l proximating atmospheric, and at a substantially constant rate. v

The gas which is discharged from the pump 42 through the exhaust port 46 is conducted by a conduit 50 directly to an inlet aperture 52 of a gas analyzer chamber 54. After passing through the chamber 54 the stream of, gas which is introduced thereto through aperture 52 exits to atmosphere through a discharge aperture 56.

Analyzer 54 serves, according to the present invention, for the quantitative analysis of the gas sample by combustion to determine the amount of uncombined oxygen carried by the gas, Another analyzer 58 may be simultaneously operated on another part of the gas sample to determine how much uncombined combustible constituents are present in the gas sample.

The sample of gas which is taken by tube I0 may or may not carry both uncombined oxygen and uncombined combustible. A second gas and air mixing pump 68 is accordingly provided which operates to withdraw a minor portion of the original gas sample, mix air at a uniform rate in excess of the amount necessary to burn any uncombined combustible therein, and deliver such air-gas mixture through a conduit 62 to inlet aperture 64 of chamber 58. Inlet or suction port 66 of pump 68 is connected by a pipe 68 with the discharge port 44 of pump 42. Thus a part of the gas which exits from pump 42 through discharge port 44 is withdrawn at a substantially constant rate into pump 60, and is admixed within the pump 60 with air introduced thereto through an atmospheric air inlet port 10. The uniformly proportioned mixture of gas and air thus formed in pump is delivered at a constant rate to the chamber 58 through the discharge port 'I2 and conduit 62. After passing through chamber 58 the gas is discharged to atmosphere through an orifice 14.

An electrolytic hydrogen generatingcell 'I6 is provided for the purpose of supplying hydrogen at a uniform rate and'in suiiicient quantity to mix with thel sample of gas which is to be analyzed for uncombined oxygen to insure combustion of any oxygen in that portion of the gas sample which contacts the catalyst wire in analyzer 54. 'I'he hydrogen cell 'I6 consists essentially of two electrodes immersed in an electrolyte bath and separated by a diaphragm. Thus cell I6 is provided with an inner cylindrical anode 'I8 constructed of sheet nickel which is in Hydrogen which is generated in the cell 16l exits therefrom through a pipe 84, while oxygen whichis simultaneously liberated by the cell exits from the interior of the anode through a pipe 88. The interior of the cell I6 is completely sealed except for pipes 84 and 86, and these may be' closed off, when the cell is not in use, by an apertured valve 88.Y With the valves 88 and 32 in the positions shown in Fig. 1, oxygen liberated by the cell 'I6 is discharged to atmosphere through a valve aperture 90. At the Sametime hydrogen generated by the cell is passed by a valve aperture 82 to the inlet en'd of a pipe 34. From pipe 94 the hydrogen passes through connecting apertures 86-91--98 in valve 32 and in its housing, which apertures i`n turn communicate by a pipe |00 with conduit 50; so that the hydrogen is admixed with the gas flowing to analyzer 54 through conduit 50 for the purpose of insuring reaction of uncombined oxygen in the gas sample with the hydrogen.

With the valve 32 turned clockwise 90 from ply pipe. |02 lthroughv a. peripheral groove |04 'in valve 32, and thence through conduit 38,.l

With the valve -32 in the position under discussion, any hydrogenfwhlch is delivered to the valve 32 by pipe 94 is exhausted to atmosphere through volume in the products of combustion under analysis. 'I'he catalyst wire |20 may for example consist of a wire of platinum-S-per-centiridium alloy, r's inch in length and .0035 inch a peripheral groove |06 and arelief aperture |08,

Thus with the valve in this positiononlyair is handled by the two pumps 42 and 60, and only air is passed through the two combustion chambers 54 and 58.

4Withthe valve 32 turned 90 counterclockwise from the positie illustrated in Fig. ,1 toanother new position (n t illustrated), the instrument is set at the position for lcalibrating'the, analyzer 54 for the temperatures developed by reacting the uniform supply of hydrogen furnished by the electrolytic cell 16 'with air. Thus with the valve in this position thev gas sample is bypassed to atmosphere through peripheral groove |04, and air only is ysupplied to the pump 42 through air intake pipe |02, groove 34 and pipe 38. Also with the valve in this position, hydrogen is admixed with the air delivered by pump 42 to cell 54, the hydrogen being in. this case conducted from the hydrogen cell through. pipe 94, groove ||0, housing groo/ve 01, groove ||2, and thence to conduit 50 through pipe |00.

Valve 88 has only two normal positions. In

the position illustrated in Fig. 1 the valve is open to pass hydrogen from'the hydrogen generator to the apertures of valve 32. With the valve 88 turned 90 clockwise from the position illustrated in Fig. 1', the hydrogen generator cell is completely sealed. The stem of valve 88 is equipped with a handle and with a coil spring |3 which alyzer 58.

is under tension lwhen the valve is in the position illustrated in Fig. 1, such tension tending to rotate the valve clockwise 909 from the position illustrated., An electric switch ||4 is operatively connected tothe stem of valve 88 by a pivoted pawl "I I6, the purpose of this hook-up being to insure that whenswitch ||4 opens the circuit supplying current to energize the hydrogen generator cell 16, the pawl 6 simultaneouslyunlocks valve 88 from the position illustrated in Fig, 1 and'permits rotation of the valve in a clockwise direction under thetension of spring H3, thereby sealing4 the hydrogen generator cell against escape of ga's or liqudtherefromthrough either of the pipes 84 andl86. The gas analyzers A54 and 58 are embodied in a unitary housing comprising a block of dielectric heat insulating material. Centrally apertured dielectric plugs I8 form quickly detachable bottom closures for each of the chambers 54, 58, extending upwardly into the respective chamber. Each or these plugs in turn carries at .its top a plurality ofV upright wire supporting Legs |20 and |24 are mounted inY spaced hori inV diameter. The wire |26 should have the same diameter and length as the wire |20. The Wires |24 and |28 may be platinum5percent rhodium alloy wires Tag inch in length and gcld plated to a final diameter of .0038 inch. A bridge' embodying wires of the dimension and composition stated will stand up for long periods when operated at temperatures in the range 1400-1600 F., and the conductivities of the legs of the Vbridge remains substantially bal-g ancedwhen operating in the specified tempera-A 132-134 in the same bridge may be constructed of 1% inch lengths of platinum-five-per-centrhodium alloy wires .0035 inch in diameter, which latter wires have a nickel oxide coating. Catalyst wire |22 and non-catalyst wire |32 are mounted in spaced parallel relation within, an-

The central apertures 52 .and 64 in the respective plug closures ||8 at tle lower ends of the chamber 54 4and 58 communicate at their lower ends with the respective gas supply pipes 50 and 62, and at their upper ends communicate through radial apertures |36 with the interiors of the respective chambers 54 and 58. The c'atalyst and non-catalyst wires in the respective combustion chambers are enclosed within cylindrical metal shields |38 which are open at the top and which are `closed at the base by the tops of the plugs ||8. A iine mesh metal screen |40 is disposed transversely as a closure within each Ashield |38 at a point closely spaced'above the respective catalyst wires |20 and |22. Any gas llowing through the respective combustion chambers `54 and 58 can only come into contactl with the respective catalyst wires |20 and |22by diffusion and convection through the metal screens |40. According to the preferred design, the shields |38 are dimensioned with approximately 1/2 inch internal diameter, so that the catalyst wires are closely surrounded on all sides 4by metal.

lAn important construction feature of the gas analyzerI hereinl described resides in the means employed for avoiding diii'iculties heretofore encountered with catalyst poisoning. Among the principal elements contributing to this resultare the metal screens |40 (for example, 100 mesh Monel metal screen) located inclosely spaced heat transfer relation to the electrically heated wires'|20,|24, |22 and |32, where the screens function as gas preheaters to preheat the gas mixtures under analysis,-` prior to contact with the catalyst surface, to a temperature in the range-65,0?- F.1200 F. It has been found that .by thus preheating vthe gas mixture under analzontal parallel relation within chamber 54..-J`I'he y other two legs ofthis Wheatstone bridge are des- A ignated in Fig. 2 by the numerals |26 and |28. The analyzer 54 is designed to measure amounts of uncombined oxygen'up to ten percent by ysis 'either'.by means of the screens |40 orby .other independently operated preheliing ele ments such as forv example' electrically heatedl wire coils or preheating chambers, catalytic com' bustion of almost any normally catalyst poisonkying combustible'constitueni; can be effected at theoptimum temperature range of 14400-1600u F. without ldiiilcultlywith poisoning.

In order to insure against poisoning *of* the catalyst in analyzing any gas, the analyzer herein described may be provided with another means of inhibiting poisoning; said means consisting of a coating of alkaline earth oxide applied to one or both of the catalyst wires |20, |22. Application of such a. coating to the wires has the elect of increasing the electron emission rate at temperatures above 300 F. It is important that the oxide coating be applied in such a way that it will not be blown olii by immersion of the coated wires. in a moving current of hot gas. The coating is preferablyapplied to a wire by enclosing the wire in a chamber while passing electric current through the wire to heat it to a high temperature (yellow heat), and while the chamber is lled with a dust cloud or atmosphere containing approximately 90 per cent barium oxide and ten per cent'l cerium oxide. The dust cloud is made up of particles ground to a fineness greater than 300 mesh. Some of the dust settles on, or is directed to, the surface of the wire and is apparently aflxed thereto by chemical action at the high temperature at which the Wire is coated. After cooling the wire, the coated wire is subjected to a further heat treatment in an atmosphere of reducing gas containing for example up to five per cent hydrogen and 95 per cent nitrogen, or in an atmosphere consisting primarily of combustible gas. This treatment of the oxide coated wire'in a reducing atmosphere seems to definitely improve and affix the coating in a way in which it is not aiiixed by the rst heating and coating treatment. Other alkaline earth oxide coatings have been successfully used, including coatings of barium oxide, cerium oxide, strontium oxide and thorium oxide'.

The rotors of pumps 42 and 60 are keyed to the drive shaft of electric motor 15. Motor '|5 is powered by current supplied by an electric circuit |42 controlled by a switch ||4; and theelectric energy for heating the catalyst wires 20 and |22 of the gas analyzer is also taken from the circuit |42, the voltage being reduced by a transformer |44 to an approximate value of about 5.5

volts. As shown in Fig. 2,v provision is made for supplying current at a constant rate from the low voltage side of the transformer |44 to both sides of the gas analyzer, as well as tothe hydrogen cell 16. To, accomplish this -the current iiows from the l'ow voltage side of the` transformer to a pair of `full wave bridge rectifers |46-l48, through an adjustable rheostat |50. `The rectilied D. C. current of approximately 2.4 ampres is taken from secondary points on the rectiers |46|48, to pointsl |52|54 of the respective Wheatstone bridges embodying as legs catalyst wires |20 and |22. The current flowing through each of the Wheatstone bridges is controlled by zero adjustment rheostats ISB-|58 which are connected in shunt circuit respectively across the catalyst legs |20 and |22.' The fixed iesist` ances |26|28|30 and |34 are preferably mounted on spools secured within the analyzer units, and may be balanced as to dimensions and composition with the corresponding legs |20- |24|22 and |32. The rheostats ISB- |58 are employed for adjusting the initial or zero electrical balance of the bridges embodying the catalyst legs |20, v|22 respectively.

The double pole double'throw switch 22 is used to alternatively connect millivoltmeter 24 either with the thermocouple I6 through leads |8 and.

20 or with the Wheatstone bridge embracing catalyst |22 as one leg. Thus the millivoltmeter 24 is provided with tworscales, one of which is calibrated to measure temperatures obtaining in flue 4, while the other scale is calibrated to mea'sure percentages of combustible gas in the gas stream flowing through analyzer chamber 58 and in contact with catalyst wire |22. A corresponding millivoltmeter |60. is operatively connected across the Wheatstone bridge embracing `catalyst Wire |20 as one leg, and is calibrated to vfor` each half unit of oxygen in the gas under analysis. Experience has shown, however, that in operatinga gas analyzer having the optimum dimensions and construction previously referred to, at an optimum temperature in the range 1400-1600 F., the most accurate readings on the percentage of excess oxygen in the gas under analysis have been obtained when the volume ratio of added hydrogen to oxygen in the gas sample passed through the excess oxygen ana'- lyzer, is approximately 1:1. With this volume ratio of hydrogen to oxygen the analyzer is operative for giving accurate quantitative measurements of amounts of excess oxygen up to 20 per cent by volume of the gas under analysis.

Having thus described the invention in its preferred form, what is claimed as new is: l

1. A` gas analyzer for quantitatively measuring a combustion constituent in a gas comprising a vertically disposed combustion chamber, means for passing a continuous stream of gas to be analyzed at a uniform' rate upwardly through the chamber, a metal cup mounted centrally within the chamber with imperforate base and side Walls positioned in ballling relation to the stream of gas flowing therethrough, a Wheatstone bridge electric circuit embodying a catalystkA wire leg and a non-catalyst wire leg of approximately balanced electrical conductivity mounted in closely spaced parallel relatidn within said cup, and a preheater mounted in the'path of gas flowing downwardly through the open end of the cup toward said catalyst and non-catalyst legs.

2. Apparatus as defined in claim 1, in which the preheater comprises a multi-apertured metal screen disposed as a closure at the open end of said cup at a spaced distance of not to exceed 1A inch from the catalyst and non-catalyst wire legs.

3. A gas analyzer for quantitatively measuring a combustion constituent in a gas comprising a combustion chamber, means for passing 'a continuous stream of gas to be analyzed at a uniform rate upwardly through the chamber, a metal cup mounted centrally within the chamber with im- I perforate base and side walls positioned in ballling relation to the stream of gas flowing therethrough, and a Wheatstone bridge electric circuit embodying a catalyst wire leg anda noncatalyst Wire leg of approximately balanced electrical conductivity lmounted in closely spaced relation within said cup, said catalyst wire leg having a coating of alkaline earth oxide fixed thereto by hea't in a reducing atmosphere.

4. In analyzing gas to determine the amount of" oxygen therein up to 20% by volume, the steps comprising passing a continuous stream of the gas upwardly through a combustion chamber admixing hydrogen with the gasy prior to its entrance to the chamber in lamount sucient to provide a hydrogen-oxygen volume ratio in the mixture less than 2:1, passing electric current through a metal catalyst wire within said chamber in amount suilicient to heat said wire to a. temperature above the ignition temperature ofA said hydrogen-oxygen constituents, bailling the gas stream against direct ow contact withl the catalyst Wire, allowing some gas from the stream to reverse direction of iiow to contact the catalyst solely by diffusion and convection, and preheating the gas prior to contact with the catalyst to a temperature in the range 650 F. to 1200 F.

5. In analyzing a gas to determine quantitatively amounts of oxygen therein up to 20 per cent by volume of the gas, the steps comprising passing a continuous stream of the gas at a uniform rate through a combustion chamber, admixing with the gas prior to its entrance to the ,combustion chamber a continuously ilowing hydrogen stream in the proportion to provide a hydrogen to oxygen volume ratio in the mixture of approximately 1:1, heating a catalyst wire within said combustion chamber by passing there- ,through an electric current in amount suicient to heat said wire to a temperature in the range 1400-1600" F. when immersed in air, and bailling the gas stream against direct flow contact with the catalyst wire, while allowing some gas from the stream to reverse direction of owto contact the catalyst solely by diffusion and convection.

6. A gas analyzer" adapted for quantitatively measuring the amount of oxygen in a gas comprising a combustion chamber, means for passing a continuous stream of gas to be analyzed at a uniform rate through the chamber, a. metal cup imperforate base and side walls positioned in bailling relation to the stream of gas owing therethrough, a Wheatstone bridge electric circuit embodying a catalyst wire leg and a, noncatalyst wire leg of approximately balanced electricai conductivity mounted in closely spacedv parallel relation within said cup, a preheater mounted in the path of arfraction of the main gas stream flowing in reverse direction through the open end of the cup toward said catalyst and non-catalyst legs, an electrolytic-hydrogen generator cell operatively connected to continuously add to said gas stream prior to its entrance to the chamber a uniformly proportioned increment stream of hydrogen, and means for supplying energizing current at a controlled rate both to.

\oii` from said cell and adapted respectively for mounted centrally within the chamber having v removal of hydrogen and oxygen therefrom, an electric switch for controlling supply of electric current to the hydrogen cell, and means operatively connected with the switch for 'automatically preventing release of gas and electrolyte liquid from the cell through. said conduits during periods when the switch is open.

JOHN D.`MORGAN.

ALAN P. SULLIVAN.