US 3918880 A
An improvement in safety devices for gas-consuming equipment, such as catalytic heaters, which include a pilot-burner with a metastable flame which displaces itself from its burner when the oxygen content of the ambient air drops below a predetermined limit, thus causing a detector to shut off or greatly reduce the gas supply to the gas-consuming equipment. The improvement comprises the addition of a chamber for ensuring through mixing of the combustible gas with the combustive air prior to combustion, and further including the use of a plurality of flames around the detector.
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Description (OCR text may contain errors)
Unite States Patent [191 Risse 5] Nov. 11., 1975 SAFETY DEVICE FOR GAS-CONSUMING EQUIPMENT  Inventor: Roger Paul Pierre Risse,
Caluire-et-Cuire (Rhone), France  Assignee: Societe Lyonnaise des Applications Catalytiques, Rhone, France 1 Filed: Dec. 27, 1973  Appl. No.: 428,628
 Foreign Application Priority Data Apr. 16, 1973 France 73.14492  US. Cl. 431/22; 431/76; 73/26  Int. Cl. F23N 5/24; GOIN 31/00 158} Field of Search 431/22, 59, 80, 76; 73/25, 73/26  References Cited UNITED STATES PATENTS 658,891) 10/1900 Brooks 431/355 3,295,585 1/1967 Kovach et al 73/26 yllllllllllllllllz v 11112- 3,610,792 10/1971 Risse 431/22 3.683.670 8/1972 Iriondo 73/25 FOREIGN PATENTS OR APPLICATIONS 1,251,364 12/1960 France 73/25 Primary E.\'aminer'Carroll B. Dority, Jr. Attorney, Agent, or FirmBrowdy and Neimark [5 7 ABSTRACT An improvement in safety devices for gas-consuming equipment, such as catalytic heaters, which include a pilot-burner with a metastable flame which displaces itself from its burner when the oxygen content of the ambient air drops below a predetermined limit, thus causing a detector to shut off or greatly reduce the gas supply to the gas-consuming equipment. The improvement comprises the addition of a chamber for ensuring through mixing of the combustible gas with the combustive air prior to combustion, and further including the use of a plurality of flames around the detector.
6 Claims, 5 Drawing Figures SAFETY DEVICE FOR GAS-CONSUMING EQUIPMENT FIELD OF INVENTION The present invention relates to safety devices for gas-consuming equipment which will automatically shut off or reduce the gas supply to the gas-consuming equipment when the oxygen content of the ambient air drops below a predetermined value. More particularly, the present invention relates to improvements on such devices which operate under the principle of flame displacement in which the evenness of operation is greatly increased.
BACKGROUND OF THE INVENTION U.S. Pat. No. 3,610,792, hereby incorporated by reference, describes a safety device forgas-consuming apparatus lacking evacuation systems, said device being used to shut off or reduce the gas supply to the equipment when the oxygen percentage of the ambient air falls below a predetermined limit.
The originality of this previously described safety device is characterized in that, contrary to other prior art apparatus, the pilot flame will not be deformed, blown out or lengthened, butrather it will displace from its burner from which it becomes detached and will be retained on an obstacle when the oxygen of the ambient air drops below a predetermined minimum value. The pilot flame keeps the gas circuit open by means of a thermostat or bulb system.
The above mentioned patent well shows and proves all the advantages inherent in this principle of operation and furthermore indicates the potential possibilities for rendering this pilot flame anti-deflagrating, inaccessible and, if necessary, discrete. As will be noted, the overall device is particularly well designed for adaptation to catalytic heaters.
The object of the present invention is a particular mode for implementing the previous invention, which, while conserving the set of advantages initially achieved, does furthermore introduce improvements with respect to them.
The present invention is based on the well-known phenomenon that the displacement of the flame of a burner occurs at that moment when the velocity of propagation of this flame falls below the velocity of the combustible mixture. This is precisely the phenomenon made use of in systems using a flame to control the composition of the atmosphere. When the ambient oxygen ratio drops appreciably, the speed of propagation of the flame also drops; but the speed of the gaseous mixture prior to combustion remaining essentially constant in such conditions, the flame will depart from the top of the burner. It is understood, of course, that in such conditions, the mixture must always be homogeneous. If perturbations otherwise arise, the system will be impaired as regards regularity of operation.
In the application of the preceding principle in connection with a gas apparatus, the same phenomenon takes place for the control of the composition of the atmosphere by means of a pilot burner. The apparatus in such case, as is represented by FIG. 1, comprises, or substantially comprises, in knowm manner, a tube 1 with a flame 2 set up at the open end and with a closed bottom traversed by an injector 3 above which is located an orifice 4 providing the primary air introduction to a venturi tube 5. The gaseous jet traverses the 2 pilot-burner along its axis, and, the pilot-burner bulk being required to be as small as possible on practical grounds, the tube extending the venturi generally will be very short. In the course of this fairly short passage, unevenness in the gaseous mixture frequently is encountered, so that the mixture is of uncertain and variable homogeneity. This lack of homogeneity is serious, because it appreciably disturbs the overall operation of the device and makes regulation difficult, such safety devices generally requiring a high degree of constant sensitivity.
SUMMARY OF THE INVENTION As already stated above, the object of the present application is the improvement of the safety device which is the object of the above mentioned patent.
To do this, a chamber ensuring thorough mixing of the combustible gas with air prior to combustion and thus causing high evenness of operation will be incorporated in the pilot-burner.
BRIEF DESCRIPTION OF THE DRAWING The schematic drawing attached hereto illustrates several embodiments of the invention.
FIG. 1, discussed hereinabove, is an elevation in section of a prior art pilot-burner for a system to control the composition of the atmosphere;
FIG. 2 is an overall view of the pilot-burner in elevation, in accordance with the present invention;
FIGS. 3 and 4, also in elevation, show the top of the anti-deflagrating mechanism, which is provided with a shutter-equipped window, respectively open and shut;
FIG. 5 is a top view of another incorporated lighting system.
DESCRIPTION OF PREFERRED EMBODIMENTS As shown in FIG. 2, the pilot-burner consists of an injector 6 at the end of a tube 7 in which the kinetic energy of the gas arriving through the injector 6 creates a depression which causes the entry of primary air through an orifice 14. This tube 7 leads to a mixing chamber 8. This chamber, the volume of which is adjusted to the burning rate of the pilot-burner, greatly facilitates obtaining a constant homogeneous gas mixture. The top of mixing chamber 8 is sealed by a thin steel plate 9, which may also be made of any other material inert under the operating conditions of the pilotburner. The combustion orifice(s) 10 in plate 9 may be of diverse shapes, but preferably they should be circular and of suitable diameters.
In a preferred embodiment, plate 9 comprises a plurality of combustion orifices 10, for instance two or three.
In another preferred embodiment, the sensing component l1 acting as detector, for instance a thermocouple or a bulb thermostat, passes through the center of the sealing plate 9 of mixing chamber 8 and along the vertical axis of the latter. The previously mentioned detection system 11 is preferably located between orifices 10, that is, between flames 12.
It will be noted that there is considerable advantage in having the detection component 11 be perpendicular to the axis of the expansion system, such a position causing disruption of the gas mixture jet and thereby improving its homogeneity by means of the many turbulences so caused.
This pilot-burner technique also facilitates miniaturization, the gas flow rate being as low as 4 gm/hr if de- 3 sired for butane or propane, for instance.
in conformity with the details listed in the above mentioned patent, the burner top is provided with an anti-deflagrating mechanism 13 which may consist either of a tube with a metal-screen gas escape window or ofa sleeve entirely made of metal screen of appropriate mesh size.
The effective crosssection of the primary air intake passage 14 is adjusted in a manner known per se by means of an adjusting collar 15.
It must further be observed that the pilot-burner so improved allows eliminating the obstacle provided for in the above mentioned patent and which is meant to retain the flame at the time of flame displacement. Nevertheless, the elimination of this obstacle does not at all impair the back and forth motion of the flame in sleeve 13, as shown by the above mentioned patent. On the contrary, much empirical work has shown that the present novel concept of a pilot-burner very clearly enhances this back and forth phenomenon.
One of the very important characteristics of the safety device as described above is the feasibility of perfect and even operation for fine-control setting with respect to any variations of oxygen ratio in the ambient atmosphere. It is quite easy to effect flame displacement, that is, shutting off or reducing the gas supply to the gas appliance, for a very slight reduction of the oxygen ratio in the ambient air, if use is made of the easily accessible primary air control system 14-15; thus, such control is possible if the oxygen percentage drops from a normal 21 to 20.2 percent; similarly, fine-control still is very sensitive if a signal is desired only when the ambient oxygen content drops to 18 percent, for example.
This fine control also is favored by the fact that the whole of the pilot-burner remains at a fairly moderate and only slightly variable temperature. It is known in this regard that the temperature variations of the apparatus significantly affect the characteristics of the gas- /air mixture, so that the initial settings would become imbalanced, these settings being determined by the magnitude of the primary air intake.
Several temperatures monitored at the gas mixing chamber and relating to different sensitivity settings are illustratively reproduced below:
Another important advantage of the system consists in its simple execution. The entire pilot-burner assembly may be made of a light alloy because of its moderate operational temperature; only the upper anti-deflagrating piece is a component to be joined.
Lighting of the pilot-burner may advantageously be effected by flame or spark or any other suitable means that are in contact with the upper part of the anti-deflagrating sleeve 13, which in this instance is provided with a lighting window 16 equipped with a shutter 17 which is automatically closed by means of a bimetallic strip 18, thus providing the anti-deflagrating state when the pilot-burner is lit (FIGS. 3 and 4). It is equally feasible to provide a spark-lighting system 19 within the anti-deflagrating sleeve 13 and near the flame zone l2,
4 for instance of the piezo-electric type (FIG. 5), whereby one achieves the advantage of not needing the above mentioned window 16 with shutter 17.
It will be obvious to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown in the drawings and described in the specification.
What is claimed is:
1. In a safety device for gas-consuming equipment comprising a pilot-burner with a metastable flame which moves by displacing itself from its burner when the oxygen percentage of the ambient air drops below a predetermined limit, and a thermosensitive detector means for shutting off or greatly reducing the gas supply to said gas-consuming equipment upon sensing displacement of the burner flame of the said pilot burner, the improvement wherein:
said pilot-burner includes a combustible gas inlet, an
air inlet, a combustion plate with at least one combustion orifice at which combustion occurs under normal operating conditions and a mixing chamber means between said gas and air inlets and said combustion plate for ensuring thorough mixing of the combustible gas and the air; and
an anti-deflagrating sleeve mounted on said pilotburner over said combustion plate, said anti-deflagrating sleeve including a window at the top thereof and shutter means for opening said window when the pilot flame is not burning and automatically closing said window when the pilot flame is burning.
2. A safety device in accordance with claim 1 wherein said detector means is located on the vertical axis of said mixing chamber means and traverses the latter from one end to the other, thereby aiding the mixing therein.
3. A safety device in accordance with claim 1 wherein said pilot-burner further includes a sensitivity setting means comprising a movable collar for covering any predetermined portion of said air inlet.
4. A safety device in accordance with claim 1 further including lighting means for igniting the pilot burner incorporated within said pilot burner.
5. A safety device in accordance with claim 1 wherein said pilot burner is in the form of a tube having a horizontal axis with said combustible gas inlet and said air inlet at one end and said mixing chamber means at the other end, said combustion plate comprising the top wall of said mixing chamber means.
6. A safety device for gas-consuming equipment comprising a pilot-burner with a metastable flame which moves by displacing itself from its burner when the oxygen percentage of the ambient air drops below a pre-determined limit, and a thermosensitive detector means, having a tip, for shutting off or greatly reducing the gas supply to said gas-consuming equipment upon sensing displacement of the burner flame of the said pilot burner, the improvement wherein:
said pilot-burner includes a combustible gas inlet, an
air inlet, a combustion plate with a plurality of combustion orifices at which combustion occurs under normal operating conditions, wherein the tip of said thermosensitive detecter means is located between said combustion orifices and thus is not in contact with the combustion, and a mixing chamber means between said gas and air inlets and said combustion plate for ensuring thorough mixing of when the pilot flame is not burning and automatically closing said window when the pilot flame is burning.