FR2504648A1 - SAFETY DEVICE FOR GAS HEATING APPARATUS AND APPLICATION THEREOF - Google Patents

Abstract

THIS APPLIANCE INCLUDES AN ELEMENT 9 SENSITIVE TO THE TEMPERATURE, ACTING ON THE ELECTRIC CIRCUIT 5 CONNECTING THE THERMOCOUPLE AND THE ELECTROVALVE, SO AS TO CLOSE IT IN NORMAL OPERATING CONDITIONS, AND TO OPEN IT WHEN THE TEMPERATURE OF THE BURNER IS AT PREDETERMINED MINIMUM VALUE. APPLICATION TO CATALYTIC HEATING APPLIANCES.

Description

The subject of the present invention is a device for

  safety for gas heater.

  The gas heaters and in particular the catalytic heaters are most often equipped with two start-up disengageable safety systems, one of which prevents the burner gas supply when the latter is not at a sufficient temperature and the other of which cuts the gas supply of the burner when the oxygen level

  ambient reaches a predetermined minimum value.

  The first security, called "thermostatic security"

  can be realized in different forms.

  According to a first possibility, the thermal safety

  can be performed by a linear expansion thermostat consisting essentially of two rods with

  of very different dilation that act on a valve.

  If this arrangement gives satisfactory results,

  however, it is not without disadvantages.

  Indeed, a linear expansion thermostat has the disadvantage of being bulky, delicate adjustment and singularly complicates the gas circuit Its reliability is also sometimes questioned because, given the temperatures of use and thermal shocks caused by the ignition and extinguishing of the burner, there are crystalline rearrangements substantially modifying the coefficients of expansion of the components and consequently the

original setting.

  According to another possibility, the thermostatic safety is filled by a thermocouple placed near the burner, developing an electromotive force which maintains, when it is sufficient, an electromagnetic valve

in open position.

  The thermoelectric torque system is interesting in terms of its reliability However, when the device to be controlled is of the catalytic combustion type, the measurement obtained by the thermocouple may not be

  representative of the operating conditions of the burner.

  Indeed, if, as a result of any phenomenon, a

  hot spot subsists in the only zone close to

  couple, while the rest of the surface is at a temperature

  the thermocouple will not react to this malfunction, and the gas supply of the apparatus will remain, although most of the catalytic mass is at a temperature substantially lower than the reaction initiation temperature. , and without it spreading from the hotspot for various reasons such as poisoning or

  partial fouling of the catalyst.

  It should also be noted that, if the inertia of a thermo-

  torque is low when in contact with a flame, it is much greater when it is close to a catalytic panel In addition, a contact between the thermocouple and the panel hinders the reaction at the level of

  this one, and increases the inertia of the thermocouple.

  There are other thermostatic safeties as

  those exploiting the dilatation of a liquid or a gas.

  However, these systems are less and less used in catalytic devices, on the one hand, because of their high price and on the other hand, because of their thermal inertia incompatible with the time required for ignition of This inertia also appreciably prolongs the response time to safety. Atmosphere control is often performed by a metastable flame acting on a thermocouple developing an electromotive force that remains in the open position under normal conditions. operating, a solenoid valve

  placed on the burner gas supply circuit.

  When the heater has double safety, the thermocouple and solenoid components must be doubled.

  The present invention aims to remedy these drawbacks.

  by providing a device with a double safety of the type in which the atmosphere control is carried out by a thermocouple subjected to the action of a

  metastable flame and acting on an electronic valve

  magnetic. According to the invention, this device comprises an element

  temperature-sensitive, acting on the electrical circuit

  connecting the thermocouple and the solenoid valve, so as to close it in normal operating conditions, and to open it when the temperature of the br

predetermined minimum value.

  If, for any reason, the percentage of oxygen reaches a predetermined minimum value, the pilot flame extinguishes or shifts causing the thermocouple to cool down, which no longer supplies the solenoid valve, resulting in a power failure. in gas

burner.

  If, for any reason, the burner temperature drops abnormally or if the burner goes out even though the pilot light remains on, the temperature sensitive element opens the electrical supply circuit of the solenoid valve causing it to close. and

  as a result the shutdown of the gas supply of the burner.

  The device according to the invention therefore provides double security with the aid of a single thermocouple and a single

  solenoid valve in excellent conditions of reliability.

  According to a first possibility, the temperature sensitive element is constituted by a bimetallic element actuating a microswitch mounted on the electrical circuit

  containing the thermocouple and the solenoid valve

  contact may be independent of the bimetallic element or

integrated into it.

  The bimetallic element is advantageously of planar shape of small thickness and of simple geometry, which considerably simplifies its implementation and confers on it over time a certain stability ensuring the reliability of the device. The bimetallic element can have a surface

  function of the burner surface power (ie

  say power per unit area of the burner), so as to capture the maximum heat energy in the form

of radiation.

  After calibration of the system, it is sufficient that the radiation ceases or is reduced to a limit value corresponding to the proper functioning of the burner so that the safety

  the latter intervene quickly.

  The interest of this arrangement is to provide general burner control and not spot control, as is the case with a thermocouple, and with a very high degree of accuracy.

low inertia of the system.

  According to another possibility, the temperature-sensitive element is constituted by a thermistor which, inserted in the electrical circuit containing the thermocouple and the solenoid valve, has a low internal resistance allowing a passage of current sufficient to allow the current supply. the solenoid valve when the burner is in temperature, and an internal resistance sufficiently high to limit the passage of this current until closing of the solenoid valve when the temperature

  burner reaches a predetermined minimum value.

  Advantageously, the thermistor is made in one

circuit called "thick layer".

  This characteristic gives the device a very low inertia As in the case of a bimetallic element, the position and the surface of the thermistor can be

  function of the pfd of the burner.

  In any case, the invention will be well understood

  using the following description with reference to the drawing

  schematic annexed representing, by way of non-limiting examples, two embodiments of this device: Figure t is a view of a first embodiment of this device comprising a bimetallic element; Figures 2 and 3 are two perspective views of the bimetallic element, respectively in the rest position and in normal operating conditions; Figure 4 is a view of a second embodiment of this device having a different thermosensitive element. The burner of the gas heater equipped with the device according to the invention is designated by the reference g 6 N 6 Rale 2 On the gas supply pipe 3 of the burner is placed a solenoid valve 4 supplied with current by a circuit 5 on which is mounted a thermocouple 6 reacting to the metastable flame of a nightlight 7 of

control of atmosphere.

  On the electrical circuit 5 is mounted 6 a microswitch 8 may be opened by action of an element

  bim 6 tallique 9 mont 6 in a frame 10 near 6 burner.

  The operation of this device is as follows: The brick and the night light m 6 tastable being 6 dyed, the bim 6 metal element 9 is in tension, as shown in Figure 3, so that the electrical circuit 5 of the thermocouple is open, the 6 solenoid valve 4 is not so 6

  feed 6 e running and closing the tubing 3 of food

burner.

  To reset the ignition of the burn, it is sufficient to act m 6 canically on the solenoid valve 4 to supply the burner and the nightlight 7 gas The night light being

  light 6 e, by any procedure 6 d 6 ignites the burner 2.

  After a time of the order of 30 seconds, the metal element 6 is shaped by the action of the heat of the solder and releases the control lever of the microswitch 8, ensuring the closure of the latter. ci, as shown in Figure 2 The electromotive force 6 developed by the thermocouple is sufficient to maintain the solenoid valve

4 in open position.

  In the embodiment shown in FIG. 4, the thermosensitive element consists of a thermistor 12, constituted by a "thick layer 6" type circuit.

  inserted into the electrical circuit 5.

  When the burner is at a temperature lower than a predetermined temperature, the resistance of the thermistor is large enough to limit the passage of the current supplied by the thermocouple, which results in a high temperature. need to supply the solenoid valve 4

and by closing it.

  Under normal conditions of operation of the brick, the resistance of the thermistor 12 is low enough not to oppose the passage of the supply current

of the solenoid valve 4.

  As is apparent from the foregoing, the invention provides a great improvement to the existing technique by providing a device capable of providing double security, extremely reliably with much lower inertia than systems

  existing and implementing a limited number of

  nes. It goes without saying that the invention is not limited to the embodiments of this device, described above as examples; she embraces it, at

  contrary, all the variants.

  Thus, in particular, the bimetallic element could have an accordion shape, or be folded or differently shaped, to capture the maximum radiated energy and to benefit from the lowest thermal inertia possible, without the 'so we leave the framework

of the invention.

Claims (4)

CLAIMS -   1 Safety device for a gas heating appliance of the type comprising means for cutting off the supply of gas to the burner when the latter is not at a sufficient temperature, and means for cutting off the gas supply to the burner when the oxygen content of the ambient medium reaches a predetermined minimum value, the latter means being constituted by a thermocouple (6) which, subjected to the action of a metastable flame, develops a sufficient electromotive force, under normal conditions, for maintaining in the open position an electromagnetic valve (4) arranged on the gas supply circuit (3) of the burner (2), characterized in that it comprises a temperature-sensitive element (9),   acting on the electrical circuit (5) connecting the thermo-   torque and the solenoid valve, so as to close it in normal operating conditions, and open when the burner temperature reaches a predetermined minimum value. 2 Device according to claim 1, characterized in that the temperature-sensitive element is constituted   by a bimetallic element (9), actuating a micro-   contact (8) mounted on the electrical circuit containing the thermocouple and the solenoid valve.   3 Device according to claim 2, characterized in that the bimetallic element (9) is of flat shape and   of surface adapted to the surface power of the burner.   4 Device according to claim 1, characterized in that the temperature-sensitive element is constituted by a thermistor (12) which, inserted into the circuit   (5) containing the thermocouple (6) and the electro-   valve (4) has a low internal resistance   a current flow sufficient to allow the   current flow of the solenoid valve when the burner is in temperature, and an internal resistance sufficiently high to limit the passage of this current until closing of the solenoid valve when the temperature of the burner (2)   reaches a predetermined minimum value.   Device according to claim 4, characterized in that the thermistor is constituted by a "thick layer" type circuit, so as to adapt its surface to the surface power of the burner. 6 Application of the device according to any one   Claims 1-5 to Equipment Equipment   for producing heat energy from a catalytic oxidation reaction of hydrocarbons or the like fuels.