US2170056A - Method for automatic indication of inflammable gas admixtures - Google Patents

Description

Aflg 1939 G. KEINATH ET AL METHOD FOR AUTOMATIC INDICATION OF INELAEIZMABLE GAS ADMIX TURES Filed June 283 1957 Patented Aug. 22, 1939 PATENT OFFICE METHOD FOR AUTOMATIC INDICATION OF.

INFLAMMABLE GAS ADMIXTURES Georg Keinath, Berlin-Charlottenburg, and Heinz Griiss, Berlin-Wannsee, Germany, assignors to Siemens & Halske, Aktiengesellschaft, Siemensstadt, near Berlin, Germany, a corporation of Germany Application June 28, 1937, Serial No. 150,782 In Germany May 23, 1936 14 Claims.

The invention relates to a method of automatic indication of inflammable gas'admixtures which excels by heretofore unattained reliability. It is for this reason also especially suited for continuous determination of the methane percentage in the air of pits or mines? The special advantage resulting from this method is that a given specific arrangement only responds to inflammable gas and thus in the case of examining pit air is only and solely sensitive to methane. In consequence thereof also with other mixtures of inflammable gases or vapors, for instance in' case of illuminating gas, the mixture is according to the Le Chatelier law the .point of response indicated in fractions of the explosion limit concentration. --Besides, the occurrence or non-occurrence of. an explosion caused accordingto the method forms a pronounced limit of reactiomensuring highest possible accuracy, and is to a large extent independent of attendant circumstances, such as ignition tension, temperature etc. In addition, the invention excels insofar as high operating temperatures are avoided and the stress on the measuring deviceis re-' duced to a minimum in consequence thereof.

These various advantages are attained in ac-- cordance with the invention by making a certain percentage of the inflammable gas explosive by automatically regulated vapour concentration by means of evaporating an additional combustible. The explosiveor non-explosive character is preferably made use of as indication for exceeding or remaining below the limiting concentration. There is used in this case as additional combustible in particular a solid body for which purpose naphthalene has proved to be especially suited. point of naphthalene, to mix it with beta naphthol.

The use of additional evaporating substances, viz. liquids or solid bodies: is especially suitable since with them only the one condition has to be complied with, that a, certain temperature of the evaporating substance be ensured. For this purpose there may be provided, for instance, an overflow in the case of liquids so as to. attain a considerable constancy of the liquid level independent of the tank filling. For enlarging the surface of the evaporating liquid use may be made of a wick arranged at the element regulating the temperature to a constant value.

But especially simple and suitable has roved the use of-solid combustible substances having sufficient vap'or'pressure so as to permit of convenient and simple handling and to ensure con- It isadvisable, for raising the melting stancy of the action of the saturation equipment. It has been shown that with the low gas velocities required only a few cubic centimeters of a loosely heaped solid substance, for instance, naphthalene, will sufilce for full saturation with naphthalene vapor, independent of the gas velocity. Tests have been carried out in which the substance was placed in a supply container from which the substance automatically trickled down according to the vaporisation into the considerl0 ably smaller saturation space. It is hereonly necessary to maintain this small Space at a constant temperature while the spaces following in the gas path must have at least the temperature of the saturation space. Thus it has been shown, v for instance, when using naphthalene, that a gasair mixture,-having 1.8% methane contents, at.- tains its explosion threshold value when saturated with naphthalene at 77 C.,while a mixture having a 2.7% methane *contents saturated with naphthalene attains this value already at 71 C. From this follows, that a difference of 6 C. corresponds to a difference of methane contents of 0.9%. Since there is no difiiculty encountered in maintaining a given temperature constant within 1 C., this tolerance would correspond to an indicating accuracy of i 0.15% methane contents which is entirely. sufiicient for all practicalpurposes.

' The use of naphthalene in flaked form hasv however a, disadvantage insofar as, owing to the desirable operating temperature being close to the melting point of naphthalene (805) sintering of the flakes is difficult to avoid, so that in this case it cannot be guaranteed that the naphthalene follows into the space which'has been gradually evacuated through consumption of naphthalene by evaporation. But this drawback may be avoided according to the invention by using the substance in the solid form, of a candle, for instance, in the form of a cast cylinder, which exactly fits the evaporation space and during its consumption is shoved into the Space evacuated by the evaporation of the material, preferably with the aid of spring action. This ensures entirely uniform consumption of the solid substance and any unutilised space at the end surface of the solid substance is avoided thereby, so that retardation of the indication cannot occur, which otherwise would be the case due to the fact that by the gradual consumption of the solid substance, without the latter moving forward, the evaporation space, and in consequence thereof the gas quantity to be examined, would be increased.

The gas to be examined is preferably introduced into the evaporation space with as low a velocity as possible so as to keep, on the one hand, the dimensions of the apparatus and, on

5 the other hand, the consumption of the additional solid substance as small as possible. Such low gas velocity has the further advantage that the surfaces, at which the gas current is saturated with the vapor of the solid substance,

may be very small. For the introduction of the gas to be examined is used a conventional diaphragm pump which has proved to be especially well suited for this purpose.

The application 'of the method according to the invention has shown, that the explosion pressure and the threshold values of ignition are to a large extent independent of the size of the explosion space and the energy and the tension of the ignition spark. But of some importance is the influence of the external air pressure on the explosion pressure. The evaporating naphthalene causes in the mixture a constant partial pressure independent of the level of the barometer. The explosion threshold per se of a naphthalene-air mixture is determined, however,

depths in mines, also the concentration of the vapor varies at constant vapor pressure and thus it also varies for a given constant quantity of naphthalene evaporated per volume unit. This has after all the effect that the response thresh- 5 old of the relay in per cent of methane depends upon the air pressure. This applies also in the presence of a constant percentage of inflammable gases, for instance, methane. The thus arising dependence of the. admixed naphthalene concentration on air pressure, .which is of importance especially in mining, may, however, be easily removed. If for controlling the heating of the evaporating substance a membrane box is used which is filled with a liquid of high vapor pressure, the temperature point, at which this box closesthe heating current in consequence of the .vapor pressure, will be dependent on the air pressure in obedience to the same law according to which the percentage of a substance evapcrating at constant temperature in air, depends on the level of the barometer. For this reason the evaporation space should practically not be maintained at a constant temperature, but be regulated to a temperature, from which results a constant vapor pressure difference of the expansion liquid with respect to the prevailing atmospheric pressure. In order that the percentage of the admixed vapor may remain independent of the external air pressure, the following conditions must be complied with:

Phi l pa- 2 and I where 9 represents the vapor pressure of the 66 liquid regulating the temperature, I) the level of the barometer at the time and P the vapor pressures of the evaporating combustible at the temperatures I .and 2, respectively. When using naphthalene as evaporating substance a given 70 slope ofthe vapor pressure curve of the substance employed for the regulation of the temperature shows, for instance, a mixture of pentane and hexane.

In the following will be described with the aid of Figures 1-3 an apparatus which is especially suited for the application of the method in accordance with the invention. Figure 1 is a transverse section on line I'I in Figure 2, while Figures 2 and3 are sectional elevations following the lines 2-2 and 3-3, respectively, of Figure 1; Figure 2 represents the contact arm I3 of Figure 2 in plan view, and Figure 4 represents a wiring diagram of the circuits used in the operation of the device.

Referring to Figures 1-3, in a metal block i is provided a. cylindrical chamber I for the naphthalene candle 2 which is contained in a guide tube 3, suitablyfixed in the chamber, and from which it is forced against the retaining screen l near the bottom of the evaporating space 4 by means of a spring 3. Tube 3 is heat-insulated from block I by an annular air space 3' so as to protect the candle 2 from the temperature variations of block I which occur'during the operation of the device. Alongside chamber I? is the explosion chamber 5 connected with the saturation space 4 by a duct 6. A spark plug I arranged at the bottom of chamber 5 serves for igniting the mixture. The pressure, due to an explosion occurring when a certain methanepercentage is exceeded, is transmitted to a contact 9 by means of a Sylphon bellows manometer 8. In order that this contact, which may set into action any suitable connections, warning signals or similar apparatus, as will be referred to later, may not remain closed too short a time in accordance with the only short duration of an explosion, the manometer is preferably accorded retardation lasting a few seconds by the insertion of a conventional check valve III which quickly opens and flies against stop pins I8 in response to the explosion gas pressure and admits gas into the manometer, thereby rapidly closing contact 9, while it is-then immediately reciosed by the gas pressure in the manometer which at that time exceeds the pressure in chamber 5, because the latter in the meantime has been vented at 5 The gas is discharged from the manometer only gradually through a conventional vent it in the valve body. Thus the opening of contact 9 is slightly retarded. The voltage for the igniting spark is derived from the transformer II, rigidly attached to the metal block I. A synchronous motor I2 and a timing element I 3 rotated thereby serve for intermittent connection of the spark plug to the transformer terminal II and the frequency of this connection and the duration of the sparks may be determined at will depending on the construction of the timing element ii, i. e., upon its circumferential length and whether it has one or several contact fingers which contact with the spark plug terminal. In the present case only one contact finger I3 is shown in Figure 2. I

Tests have shown that naphthalene vapor, if subjected to prolonged electrical discharges, burns up and forms phthalic acid which is deposited on the walls of the explosion chamber 5.

But if with the aid of the timing element I3, which may be run at the proper speed discharges are used of durations of a few hundredths parts of a second the phthalic acid remains in a gaseous state in consequence of its sl'ight concentration. Besides, the discharge must take place "only so seldom, that in the meantime the exploded gas mixture may be completely replaced through diaphragm pump I6 by a fresh mixture as otherwise the possibility exists that a fresh mixture, notwithstanding its explosive character, will yield an explosion but seldom, due to contamination by' the residues from the previous explosion.

For the completion of the apparatus is inserted in the block I in a bore I4 a cartridge heating element 22 controlled by the temperature regulator I5 contained in chamber 20 which cooperates with a contact spring I5' controlled by adjusting screw l8. The desired temperature value, corresponding to-a given percentage of inflamm mable gas, may be adjusted by the screw I8 which controls the distance between thermostat capsule l5 and spring l5 and which may be located in a suitable circuit, such as is shown at 22, H3 in Figure 4. This circuit inclLdes the current source 15 S and the previously mentioned heating element 22 in block I. The temperature regulator screw l8 may be provided with a scale, not shown, permitting of adjusting the various concentrations of the inflammable gas by turning the screw l8.

go It thus becomes possible by adjusting screw is to vary the closing of the contact. The voltage transformer II is also used, apart from generating the igniting spark, for oscillating the diaphragm l6 of the diaphragm pump whichpumps the gas mixture to be examined into the saturation space 4. The magnetic flux of this transformer, as Figures 2 and 3 show, is closed by diaphragm it which, as will be noted, is spaced from the transformer core by an air gap. The diaphragm is; mounted in front of the lower nozzle ll. Thus the diaphragm oscillates at the frequency of the supplied alternating current and produces in this case an air current in the two nozzles ll, due to their shape and relative positions, which in the upper nozzle is augmented by an action based on the ejector principle to such an extent that the air attains the required velocity thereby and is forced through the saturation space 4. The air is taken in through the intake passage l'l provided in block I. Diaphragm pumps of this character are well known in the art and therefore the detail description of this pump and the principle on which it is based-has been omitted.

All gas inlet and outlet openings such as H and 5 in this device should be protected, as is customary in mining lamps with fine capillaries or slots, not shown here, which form the communication between the external atmosphere and the explosion space which in known manner prevents the explosion from extending outwardly.

If the dependence on air pressure, which often has no disturbing effect, is disregarded, the method according to the inventionmay, apart from the manner described, also be applied by adjusting the heating value to a constant value in such a manner, that when the mixture exceeds a certain percentage of inflammable gas, explosion and in consequence thereof indication will result.

60' In this case also the degree of the temperature to be maintained at a constant value may beselected according to the desired permissible limit of the percentage of the inflammable gas.

The described apparatus solves the problem of 65 automatically reporting in the manner of a relay when a certain percentage of inflammable gas or vapor is exceeded or not reached. If however, the problem is to be dealt with to determine or record the often varying percentage of inflam- 70 mable gases, the heating serving forthe evaporation of the additional combustible may be automatically stopped or-be put out of commission by. an explosion, until at further ignition attempts no further explosions occur, whereby the which this may be accomplished is shown dia-. grammatically in-Figure 4. In this figure a tilting toggle relay 25 is provided which is held by its armature 28 and springs 3| in the position shown by the intermittent energizing of core 29 through the intermittently operating contact l3 previously described with reference to Figure 2, but which in this case more conveniently controls the primaryof transformer II by way of intermittently short circuiting a resistance 32, whereby the voltage of .the transformer primary is intermittently raised sufliciently to produce a spark at the spark plug 1, and to energize at the same time coil 29. In this position of relay 25, contact 30, which controls the heating current of cartridge 22, remains closed, except that it is subject to the control of contact l8, previously described. Thus the temperature in the evapora- .tion chamber 4 is raised until by the repeated production of sparks an explosion occurs; whereby as previously described a contact is made at 9 by the Sylphon bellows manometer 8, and a local circuit is closed which contains the current source D and the other energizing coil 29 of relay 25 which is thereby energized. Its armature is now attracted and relay 25 is pulled down at the left, and thus heating contact 30 is opened. This cools the evaporation chamber until by the continued ignition attempts no further explosions occur. As a consequence, as also described before, the manometer contact at 9 is opened and the left-hand coil 29 of relay 25 is deenergized, so that by the continued repeated energization of the right-hand coil 29 the relay 25 is tilted back into the position shown in Figure f1, in which it recloses heating contact 30 and in which it remains until again an explosion occurs. The temperature of the apparatus will in consequence thereof vary in the vicinity of a value corresponding to a certain percentage of inflammable gas. By indicating this temperature forinstance by a thermometer 26 in block 'I it is possible to continuously indicate the composition percentage of the gas exploding for the time being by the indications of the thermometer.

It will be advantageous, under certain circumstances, to release the ignition process in any other manner than the one described. It has been especially advantageous, however, to combine the drive of the diaphragm pump IS with the current transformer I I, generating the igniting tension, so that the latter normally operates with a small voltage output, sufficient to continuously operate pump l6 but which does not continuously cause discharge of the secondary circuit over the spark plug but only, if from time to time, for instance by short circuiting seriesresistance 32 by element l3, as shown in Figure 4, the increased primary voltage applied to the transformer sufficiently increases the secondary voltage to produce a spark at the gap I.

It is also possible to cause ignition by mechanical movement of one of the live parts of the spark plug, a so-called make and break movement actuated by the motor l2, which will result in the advantage that reliable ignition will be ensured with considerably lower tensions. Devices of this character are well known in the art and illustration thereof is omitted here since it does not form part of the present invention.

What we claim is:

1. Method of automatically and continuously 7 testing for the presence of a dangerous amount of combustible in anatmosphere, consisting in solid stored combustible to the saturation point combustible into the test gas at constant vapor concentration to render the latter explosive, and supplying intermittently an ignition spark to the entire gas and vapor mixture.

3. Method of automatically and continuously testing for the presence of a dangerous amount of combustible in an atmosphere, consisting in passing the gas to be tested continuously through a reaction chamber, evaporating an additional into the test gas to render the latter explosive, and supplying intermittently an ignition spark to the entire gas and vapor mixture.

4. Method of automatically and continuously testing for the presence of a dangerous amount of combustible in an atmosphere, consisting in passing the gas to be tested continuously through a reaction chamber, evaporating solid naphthalene into the test gas at constant vapor concentration to. render the gas explosive, and in supplying intermittently an ignition spark to the entire gas and vapor mixture.

5. Method of automatically and continuously testing for the presence of a dangerous amount oicombustible in an atmosphere, consisting in passing the gas to be tested continuously through a reaction chamber, evaporating solid naphthalene admixed with beta naphthol into the test gas at constant vapor concentration to render the gas explosive, and in supplying intermittently an ignition'spark to the entire gas and vapor mixture.

6. Method 01 automatically and continuously testing for the presence of'a dangerous amount of combustible in an atmosphere, consisting in passing the gas to be tested continuously through a reaction chamber, evaporating solid naphthalene into the test gas at constant vapor concentration to render the gas explosive, in supplying intermittently an .ignition spark to the entire gas and vapor mixture, and in continuously feeding the naphthalene, so that at all times the sameamount of evaporated solid is contained in the gas mixture.

7. Method of automatically and continuously testing for the presence of a dangerous amount of combustible in an atmosphere, consisting in pass ing the gas to be tested continuously through a reaction chamber, evaporating an additional solid stored combustible to the saturation point into the test gas to render the latter explosive, supplying intermittently an. ignition spark to the entire gas and vapor mixture, and in controlling the evaporation temperature of said combustible to a given value, so that when the inflammable gas admixture exceeds a permissible percentage an explosion of the entire mixture by the spark will occur.

8. Arrangement for automatically indicating the permissible percentage of inflammable gas admixtures to a surrounding atmosphere, including a mixing. chamber, a combustion chamber communicating with said mixing chamber and means for supplying the test gas through said mixing chamber to said combustion chamber, means for constantly supplying a solid combustible to said mixing chamber, heating means for evaporating said solid combustible at a constant vapor concentration into the test gas in said mixber communicating with said mixing chamber and means for supplying the test gas through said mixing chamber to' said combustion chamber, means for constantly supplying a solid combustible to said mixing chamber, heating means for evaporating said solid combustible at a constant vapor concentration into the test gas in said mixing chamber, intermittently actuated ignition means in said combustion chamber to explode the entire mixture when it contains a given amount of inflammable gas admixture, means controlled.

by the intermittent actuation of said ignition means for normally maintaining said heating means operative, and means actuated by an explosion in said combustion chamber for cutting ofi said heating means for a given period after an explosion.

10. Arrangement for automatically indicating the permissible percentage of inflammable gas admixtures to a surrounding atmosphere, including a mixing chamber, a combustion chamber communicating with said mixing chamber and means for supplying the test gas through said mixing chamber to said combustion chamber, means for constantly supplying a solid combustible to said mixing chamber, heating means for evaporating said solid combustible at a constant vapor concentration into the test gas in said mixing chamber, intermittently actuated ignition means in said combustion chamber to explode the entire mixture when it contains a given amount of inflammable gas admixture, a diaphragm capsule containing a liquid mixture having a given vapor pressure curve and means controlled by the response of said capsule to varying atmospheric pressures for actuating said combustible heating means in accordance with the pressure conditions of the atmosphere, so that the combustible vapor concentration variations due to varying atmospheric pressure are compensated .by the reactions of the pressure on said capsule.

1i. Arrangement for automatically indicatin the permissible percentage of inflammable gas admixtures to a surrounding atmosphere, including a solid block of suitable material, having a mixing chamber, a combustion chamber communicating with said mixing chamber, a solid combustible disposed in the upper portion of said mixing chamber and means for constantly pushing said combustible toward the lower end of said mixing chamber, a heating chamber in said block containing a heating device for evaporating said combustible substance into said mixing chamber and a temperature control chamber in said block containing a temperature control device, means connected with said block of inflammable gas admixture, and means actuated by said temperature control device for controlling said combustible heating means in accordance with the pressure conditions of the atmosphere, so that the combustible vapor concentration variations due to varying atmospheric pressure are compensated by the reactions of said pressure on said temperature control device and said heating means. i

12. Arrangement for automatically indicating the permissible percentage of inflammable gas admixtures to a surrounding atmosphere, including a solid block' of suitable material, having a mixing chamber, a combustion chamber communicating with said mixing chamber, a solid combustible disposed in the upper portion of said mixing chamber and a spring for constantly pushing said combustible toward the lower end of said mixing chamber, a heating chamber in said block containing a heating device for evaporating said combustible substance 'into said mixing chamber and a temperature control chamber in said block containing a temperature control device, means connected with said block for constantly supplying the test gas through said mixing chamber into said combustion cham-' ber, intermittently actuated ignition means in said combustion chamber for exploding the entire mixture when it contains a given amount of inflammable gas admixture, and means actuated by said temperature control device for controlling said combustible heating means in accordance with the pressure conditions of the atmosphere, so that the combustible vapor concentration variations due to varying atmospheric pressure are compensated by the reactions of said pressure on said temperature control device and said heating means.

13. Arrangement for automatically indicating the permissible percentage of inflammable gas admixtures to a surrounding atmosphere, in-

cluding a mixing chamber, a. combustion chamber communicating with, said mixing chamber and means for supplying the test gas through said mixing chamber to said combustion chamber, means for constantly supplying a solid combustible to said mixing chamber, heating means for evaporating said solid combustible at a constant vapor concentration into the test gas in said mixing chamber, intermittently actuated ignitionpmeans in said combustion chamber to explode the entire mixture when it contains a given amount of inflammable gas admixture, means for controlling said combustible heating means in accordance With the presure conditions of the atmosphere, so that the vapor concentration variations due to varying atmospheric pressure are compensated by the reactions of said pressure on said heating means, and a Sylphon bellows manometer connected to said combustion chamber and having a contact element actuated by said manometer at the occurrence of an explosion, and aneIectric circuit arrangement including said contact and said heating means for cutting out said heating means when an explosion occurs.

14. Arrangement for automatically indicating the permissible percentage of inflammable gas admixtures to a surrounding atmosphere, including a mixing chamber, a combustion chamber communicating with said mixing chamber d a diaphragm pump for supplying the test gas through said mixing chamber to said combustion chamber, means for constantly supplying a solid combustible to said mixing chamber, heating means for evaporating said solid combustible at a constant -vapor concentration into the test gas in said mixing chamber, intermittently actuated ignition means in said combustion chamber to explodethe entire mixture when it contains a given amount of inflammable gas admixture, and means for controlling said combustible heating means in accordance with the pressure conditions of the at mosphere, so that the vapor concentration variations due to varying atmospheric pressure are compensated by the reactions of said pressure on said heating means.

GEORG KEINATH;

nnmz Gauss.

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