US2310435A

US2310435A - Method of and apparatus for gas analysis

Info

Publication number: US2310435A
Application number: US243496A
Authority: US
Inventors: Arthur C Jenkins
Original assignee: Linde Air Products Co
Current assignee: Linde Air Products Co
Priority date: 1938-12-02
Filing date: 1938-12-02
Publication date: 1943-02-09
Anticipated expiration: 1960-02-09

Description

lllll Feb. 9, 1943. A. c JENKINS METHOD OF AND APPARATUS FOR GAS ANALYSIS Filed Dec 2, 1938 Patented Feb. 9, 19.43

UNITED STATES, PATENT OFF] METHOD OF AND APPARATUSFO lt GAIS, ANALYSIS Arthur C. Jenkins, Kenmore, N. Y.,. 'assignor to I The Linde Air Products Company, a corporation of Ohio -Application December 2 1938, Serial No. 243,496 12 Claims. (o1. 23-232) This invention relates to a method of and apparatus for gas analysis, and more particularly to a method of and apparatus for indicating continuously the oxygen content in a given atmosphere and intermittently the carbon dioxide require the frequent handlingof chemical solutions, which factor may be a source of danger to inexperienced persons. While analyzers. have been constructed which will the oxygen concentration, these analyzers can not be used to determine the carbon dioxide concentration without seriously aifecting the calibration ofthe analyzer and hazarding a serious disruption of the delicate and ments of the analyzer.

In one type of apparatus used heretofore for gas analysis, the gas tobe analyzedand a standard gas, which may be air, are passed respectively through two tubes so constructed and arranged that the composition of the gas under analysiscan' be determined through comparison oi? pressures existing at certainpoints ineach of the respective tubes.

what more satisfactory than intermittentlyopere 1e of alternately deter This apparatus, while someating analyzers, 'is incapab mining the concentration of more than one.ele-, ment in the gas'under analysis without the disadvantageous plienomena sgt forth above.

It is therefore among the I bjects of this invention to provide a method oband apparatus for continuously, directly, accurately and rapidly indicating the concentration of one constituent in a givenatmosphere; which apparatu'sis readily convertible to indicates ilarly the concentration of another constituen of said atmosphere;

in which'apparatus the. indications are dependent only .upon the physical properties of thegas be-' ing analyzed; which apparatus maybe converted readily toindicate either' oxygen concentration or carbon dioxide concentration without afiecting' proven satisfactory. Among sensitive component ele continuously indicate the calibration of the apparatus or hazar 4 ethod' ruption of'its component parts; which 3 and apparatus do not require'the frequent hanin part be obvious and in part become apparent from a consideration of the following description and accompanying drawing, in which:

Fig. 1 diagrammatically illustrates the general arrangement of the apparatus; Fig. 2 is a longitudinal sectional view through a valve used to adjust the apparatus; and

Fig. 3 is a'longitudinal sectional view of a two-- sway-valve used-to convert the apparatus to indicate either the oxygen or the carbon dioxide concentration ,without interrupting the new oil as throughthe apparatus. I

In the emmdiment Of theinvention illustrated v in the drawing, the gas to be analyzedland a standard gas such as air, are drawn through a gas comparing means or analyzer comprising a viscosity-effusion bridge B by means of a suitable exhaustingapparatus or means such as a vacuum pump P,. shown d agrammatically. The bridge comprises a pair of capillary comparison tubes C, (2' each connected, on the doWn-stream side, by T-piegesT, T- to orificed plates formed. with orifices 0, v0' and mounted in an evacuating'chamber E connected to the vacuum pump.- Also connected to each T-'-piece is a differential manometer M, the liquid level of which,- in 00- operation with a suitable scale 8, indicates the concentration ofoxygen or carbon dioxide in the gas undergoing analysis.

the physical laws The. operation of tgie apparatus is based on through orifices and apillary tubes. The rate of .flow of gas through an orifice varies inversely as the capillaries C and C and-throu h the orifices O 'and' O, when any particular gas is drawn through. the bridge. Thus, if the same gasisi drawn simultaneously through, each side of the bridge; and both sides have the same, dimensions,

the pressures in the T-pieces T, T willbe equal,- i

i and the liquid level in each arm of thediflerential manometer M -will be at the same elevation.

If now, a standar gas, such as-air or any "other gas whose comp sition is known oripredeerningthe flow of gases ing 34.

use of other elements of the apparatus described hereinafter, the liquid level may be used to compare the respective viscosities and densities of the gases and thus indicate the percentage concentration of one or more elements of the sample gas.

Operatively associated with the viscosity- 1 efiusion bridge B, is a gas absorbing medium such as a carbon dioxide remover R, which may be filled with a suitable absorbent such as Ascarite," which is a sodium hydrate asbestos absorbent. Although an absorbent of this type is preferred, other well known materials for absorbing carbon dioxide may be used. The remover R may be provided with a novel two-way by-pass valve V (Figs. 1 and 3) which maybe used 'ical seating portion It in the diflerential manometer in order to prevent the liquid in the manometer from being withdrawn into the capillaries and orifices in case the end of the tubing 22 is accidentally shut of! or restricted in any way. The reservoir 14 is large axial with the chamber 48 is a small diameter central passage 52 terminating in a right angle passage 54. The stem 42 is formed with 'a con- 56 adapted to partially enter the passage 52 and engage the walls thereof at the intersection of this passage with the chamber 48 to restrict or prevent communication between the chamber 48 and the passage 52. Through adjustment ofthe stem 42 by means of a hand wheel 58, gas passing between the passage 54 and to cut the remover in and out of circuit with the bridge without interrupting the flow of gas through the latter. An adjusting valve A (Fig. 2) is provided to adjust the manometer M to an arbitrary zero point on the scale S and a gauge G is connected to the chamber E to indicate the degreeof vacuummaintained by the pump. Dust removers D, D' are associated, respectively, with each tube C, C. a 4

Referring more specifically to the drawing, the manometer M comprises a left hand arm l0 and a right hand arm l2, connected respectively to the 'T-pieces 'I', T. A suitable reservoir l4 containing indicating liquid is connected to the manometer by a branch passage i6, and the amount of liquid may be increased or decreased by removal of a ground glass stopper I8 which is greased before reinsertio in the reservoir l4 to provide an air-tight seal erefor. The scale S is provided with two sets of graduations, one for indicating oxygen concentration and the other for indicating carbon dioxide concentration.

The standard gas, which may be air, enters I through a tube or conduit 20 in which is located the adjusting valve A, passes through the dust remover D, the capillary tube C, the T-piece T;

and the orifice 0' into the evacuating chamber E.- The sample gas enters through tubing or conduit '22 and by means of adjustment of the valve V may pass through a tube or conduit 24 and the carbon dioxide remover R intoa branch the orifice 50 through the chamber 48 maybe throttled to any desired value in order to adjust the level of the fluid in the manometer tube to the" proper point on the scale S.

Tomaintain continuityof operation of the apparatus when it is desired to change the indication from percentage oxygen to percentage carbon dioxide, or vice versa, and to prevent damage to the delicate parts otthe apparatus, it is necessary to provide some means for cutting the carbon dioxide remover R into and out of circuit with the viscosity-efiusion bridge B without interrupting the flow or gas through the bridge.

, If the flow of gas were suddenly initiated or sud:

denly interrupted, the liquid. in the diiferential manometer might now into the capillary tubing or be drawn through the orifices.

To prevent these conditions, a special two-way valve V, shown in Fig. 3, is provided to selectively by-pass the gas absorbing medium R. This valve is so designed that the, flow. of gas may be diverted from the inlet to either of two outlets tube or conduit 26 connected to tubing or con- 7 duit 28. If it is ihesired to have the sample gas by-pass the carbo dioxide remover, the valve V may be turned to theposition shown in Fig. 1 and the sample gas to be analyzed then passes from;

this valve through a by-pass tubing or conduit 30 into the tubing 28. From the tubing 28, the sam- Dle gas passes through the dust remover D, the

capillary tube C, theT-piece T, and the orifice 0 into the evacuating chamber E. Connected to the evacuating chamber is one end of atubing 32 which is connected at its other end to the vacuum pump P, which should be capable of maintaming a vacuum in the chamber E of 25 inches of mercury or better. The gauge G is connected to the tubing 32 by means of a short piece of tubv A special check valve 36'is provided in the arm without the valve passing through an ofi" position.

Referring more specifically to Fig. 3 of the drawing, the valve V comprises a body 60 formed with a valve chamber 62, a packing chamber 44 and a partially threaded bore 66 connecting these chambers and forming a valve seat 88 at its intersection with chamber 62. The lower end of the valve body 60 is closed by a threaded plug 10 formed with a spring recess 12 communicating with the valve chamber 62 and with an outlet port 14. The upper or inner end of the plug-ll forms a second valve seat 16 in the chamber 82. A ball valve 18 is mounted in the valve chamber *62 and is resiliently urged in an upward direcs tion by a spring seated in the recess 12. The ball valve '18, in cooperation witheither of are valve seats 68 or 16, controls communication be tween an inlet port 82 in ,the body BI] and either an outlet port 84 in the valve body or the outlet port I4 in the plug 10, respectively. The ball valve 18 is operated by means of a stem 88 threadedly engaging .bore 66. On the outer end of stem 85 is" an operating handle 88 and the irv ner end of the stem engages the ball valve 18'. Suitable packing 90 is held in the packing cham-v ber 64 around the stem 86 by a combined packing nut and valve mounting stud 92.

It will be observed readily that, irrespective of the liquid level in the manometer indicates the I carbon dioxide percentage. This indication is the position of ball valve .18, gas may always flow from inlet port 82 to either of the

outlet ports

14 or 84. At no time during the movement of the ball valve from one seat to the other is the flow of gas through the valve chamber interrupted.

The method of operating theabove described apparatus to indicate the oxygen concentration in the sample gas is as follows: The stopper I8 is removed and manometric liquid is added to the reservoir i4 until the level of the liquid reaches apoint on the oxygen scale corresponding to 21%, which is the .(approximate proportion of oxygen in normal air. The stopper I8 is then greased and replacedto seal the manometer M.

The vacuum pump P, connected to the tubing 32, is then started and the valve V is adjusted so that the tubing 22 communicates with the remover R through the tubing 24. i

In order to permit proper adjustment of the liquid level with respect to the scale S, the standard gas side of the apparatus is "constructed to permit a slightly greater fiowof gas than is permitted by the sample gas side. Thus, when the vacuum pump is started, and air enters both sides of the bridge at atmospheric pressure or at equal pressures approximately atmospheric, the

liquid level will first rise and then fall as the maximum vacuum is obtained. The liquid level is then adjusted to the 21% oxygen mark through manipulation of the adjusting valve A. The 'vacuum should be maintained between 2 5 and inches of mercury to assure stableindications.

When the above adjustments have'been made, the tubing 22 is connected by means of a suitable length of tubing of rubber or other material to the oxygen tent or room containing the sample gas to be analyzed as to oxygen content. Withgas minus the 'carbon dioxide content. HOW? ever, if the percentage of carbon dioxide islsmall, the indicated 'oxygen percentage may be accepted as correct for all practical purposes.

To condition the apparatus for indicating the carbon dioxide concentration, the vacuum pump is stopped. Next, the

tubings

20 and 22 are conindependent of the relative volumes of oxygen and nitrogen in the mixture.

, To recondition the apparatus to indicate oxygen concentration, the FIT-piece is removed from tubings 20 and 22 and the liquid level is adjusted tothe 21% point on the oxygen scale through the medium of valve A, with air entering tubes.

20 and 22. When tubing 22 is inserted in the sample gas, the apparatus will indicate the oxygen concentration. 7

While the effect ofthe capillary length on the sensitivity is small, within certain limits, there is a definite ratio between the orifice diameter andthe capillary diameter which will assure optimum sensitivity; Thus, the orifice diameter should be three-quarters oi the capillary diameter, and the pressure at the outlet of the capillary about one-half the inlet pressure. As a specific example, witheach-tube C, C having a uniform diameter of 0.5 mm. and a length of 9 inches, and with the orifice having a diameter of 0.375 mm., the sensitivity of. the apparatus for the oxygen indication is 2.3 mm. and for the carbon dioxide indication is 13 min. The, se'nsitivity is given as the change inlevel for a 1% change in composition. The accuracy of indication is, respectively, 12% and 195% for oxygen and carbon dioxide and is not/affected, within these limits, by variations in the humidity oi the air. Furthermore, if both the standard gas and the sample gas are'approximately equal in temperature, a variation or afew degrees be-. tween the respective gas temperatures will not afl'ect the accuracy within the above limits. The indications are not affected by the degree of vacuum provided a minimum vacuum of 25 inches of mercury is maintained. No air leak to maintain the vacuum at a definite value is nec-' 'essary provided the conditions of critical flow through the orifices are maintained.

In order'that, the accuracy of indication may be independent gof changes in barometric pressure, interchangeable scales S may be provided,

, each corresponding to a definite barometric pressure. Since the efiect of a change in barometric pressure .is to displace the entire calibration curve as a unit, it is. only necessary to select the scale which gives the correct reading for 100% oxygen content at the given barometric pressure; The apparatu Ids thus suitable for use at any altitude; The only handling of chemicals required is the occasional replacement of a cartridge type unit nec'ted by meansof a T-piece to a suitable length of tubing and this is inserted in the tent or room containing the sample gas. After the 'valve V hasbeen adjusted to permit the gas to bypass the remover Rkthe vacuum pump is. restarted and the liquid level in manometer M adjusted to the zero point on the carbon dioxide scale by manipulation of the adjusting valve is, The

valve V is now adjusted to place the remover R in circuit with the manometer M, andthe liquid level will then indicate the carbon dioxide concentration.

'In effect, the zero adjustment is made when the same gas is passing through both sides of the viscosity-effusion bridgeB, and enters both sides 'of the bridge at equal pressures approximately atmospheric. When the carbon dioxide remover R. is placed in'circuit, the bridge compares the mixture containing-the carbon dioxide with the same mixture minus the carbon dioxide. Thus,

P of

. carbon dioxide, in the carbon dioxideremove'r R.

Ascarite, or other suitable absorbent for Furthermore, all elements of the apparatus except the vacuum pump may be mounted in a simple cabinet and easily transported. to difierent i locations.- 1

While the apparatus is intendedto give a con tinuous indication of the oxygen concentration and only intermittent indications of 'the'earbon dioxide concentration, it can be used, equally well,

to give a continuous indication of the carbondiore, it is apparent thatf,

oxide content. "Further while the apparatus is designed primarily toIin-v d cate oxygen and carbon dioxide concentrations, by a suitable change of scales it may be used to indicate concentrations of other constituents of a sample gas. I

While a. specific embodiment of the invention has been illustrated and described in detail, it

will be obvious that the invention maybe otherwise embodied and certain dimensions and in-,

terrelations of parts changed so long as the objects of the invention are attained.

What is claimed is:

1. A gas analyzer comprising, in combination, two comparison tubes, each having a capillary portion; a conduit connected to the inlet side of each tube and extending respectively to a source of standard gas and to a source of gas under test; a chamber connected to the outlet sides'of said tubes; an orificed plate in each tube on the downstream side of the capillary portion; a differential manometer having its arms connected, respectively, to each of said tubes between the capillary portion and the oriflced plate; exhausting apparatus connected to 'said' chamber; a 'gas absorbing medium interposed in the conduit which extends between said source of gas under test and its associated comparison tube; and means operatively associated with said last-named conduit for selectively by-passing said gas absorbing medium without interrupting the fiow of gas through said associated comparison tube.

2. A gas analyzer comprising, in combination, two comparison tubes, each having a capillary portion; a conduit connected to the inlet side of each tube and extending respectively to a source of standard gas and to a source of gas under test; a chamber connected to the outlet sides of said tubes; an orificed plate in each tube on the downstream side of the capillary portion; a differential manometer having its arms connected, respectively, to each of said tubes between the capillary portion and the orificed plate; exhausting apparatus connected to said chamber; means, connected in the conduit extending between said source of gas under test and its associated comparison tube, for removing a given constituent of said gas under test; means, operatively associated with the conduit extending between said sourcepf gas under test and its associated comparison tube, for selectively by-passing such removing means; and means operatively associated with said manometer for indicating the percentage of two difierent constituents of said gas under test.

3. A gas analyzer comprising, in combination, two comparison tubes, each .having a capillary portion; a conduit connected to the inlet side of each tube; means for connecting each of said conduits to a source of gas under test; a chamber connected to the outlet sides of said tubes; an orificed plate in each tube on the down-stream side of the capillary portion; a differential manometer having its arms connected, respectively, to each of said tubes between the capillary portion and the oriflced plate; exhausting apparatus capillary portion and the oriflced plate; exhausting apparatus connected to said chamber; a gas absorbing medium interposed in said second conduit; means operatively associated with said second conduit for selectively by-passing said gas absorbing medium; and an interchangeable scale associated with said manometer and calibrated to indicate selectively the percentages of two constituents of said gas under test.

5. A gas analyzer as claimed in claim 4, in which such by-pass means comprises a valve interposed in the conduit between said gas absorb ing medium and said source of gas under test for selectively by-passlng said gas absorbing medium.

6. A gas analyzer comprising, in combination, means for comparing a gas under test with a standard gas; a first conduit extending between said means and a source of standard gas; a second conduit extending between said means and a source of gas under test; a gas absorbing medium interposed in said second conduit between said means and said source of gas under test; and means, including a valve interposed in said second conduit between said medium and said source of gas under test and a by-pass conduit connected to said valve and to said second conduit between such cbmparison means and said medium, to by-pass said medium selectively without interrupting the flow of gas from said source of gas under test to said gas comparison means.

'7. The gas analyzer claimed in claim'6, in

v X which said valve comprises a valve chamber havconnected to said chamber; a gas absorbing medium interposed in one of said conduits; and

means operatively associated-with said one contube and to a source of gas under test; means.

for connecting said first conduit to either said source of gas under test or'a source of standard gas; a chamber connected to the outlet sides of said tubes; an orificed plate in each tube on the down-stream side of the capillary portion; a differential manometer having its arms connected, respectively, to each'o'f' said tubes between the ing a plurality of ports adapted to be connected respectively to that portion of the second conduit extending to said source of gas under test, that portion of the second conduit. extending to said gas absorbing medium and said by-pass conduit and a valve member in said chamber operable to close selectively said ports connected to said gas absorbing medium and said by-pass conduit, respectively, without interrupting the flow of gas from said source of gas under test to said gas comparison means.

8. The gas analyzer claimed in claim 6, in

which said valve comprises a valve chamber former with an inlet port connected by that portion of the second conduit extending to said source of gas under test and two outlet ports connected, respectively, to that portion of the second conduit extending to said medium and to said by-pass conduit, and means disposed in said valve chamber for selectively closing either of said outlet ports without substantial interruption of the flow of gas from said inlet port through said chamber to said gas comparison means.

9. A method of continuously analyzing a gas under test which comprises separately and continuously withdrawingtwo samples from a source of gas under test, chemically absorbing one constituent of said gas from one of the samples, and comparing the viscosity and density of such sample with the viscosity and density of the other of the samples to indicate the percentage concentration of said chemically absorbed constituent in said gasunder test.

10. A'method of indicating the percentage concentration of a given constituent of'a gas under test which comprises passing a standard gas through both sides of a viscosity-effusion bridge and adjusting said bridge to indicate the normal percentage concentration of said given constituent in said standard gas; then continuously passing said standard gas' through one side of said bridge, and a sample from a source of said gas 2,310,435 under test through the other side of said bridge,

while hemically absorbing a different constituent of said gas under test before said gas under test enters said bridge; and comparing the viscosity and density of said standard gas with the viscosity and density of said gas under test to indicate the percentage concentration of said given constituent in saidigas under test.

11. A method of continuouslyiindicating the percentage concentration of a given constituent of a gas under test which comprises passing samples of said gas through both sides of a viscosity efi'usion bridge; adjusting said bridge to indicate a zero percentage concentration of said given constituent; then chemically absorbing said given constituent from the sample of gas passing through one side of said bridge without interrupting the continuous flow of gas through said bridge; and comparing the Viscosity and density of one sample with the viscosity and density of the other sample to indicate the percentage concentration of said given constituent in said gas under test.

12. A gas analyzer comprising, in combination, a viscosity-efiusion bridge provided witlime'ans for indicating the percentageconcentrations of two constituents of a gas under test; an exhaust ing mechanism connected to the outlet side of said bridge; means for connecting one side of said bridge to a source of gas under test; means selectively operable to connect the other side of said bridge to said source of gas under test and to a standard gas; a gas absorbing medium in circuit with said one side of said bridge; and means, operatively associated with said means for connecting one side of said bridge to a sourcev of gas under test, for selectively-by passing said gas absorbing medium without afiecting the flow of gas through said bridge.

ARTHUR C. JENKINS.