EP2354653B1 - Flashback prevention for a gas heater - Google Patents

Description

description

The invention relates to a heater with a back burner.

Heaters, in particular gas heaters for mobile devices such as campers, caravans, boats and cabs are known. Such a heating device has a combustion chamber with a combustion air inlet and a flue gas outlet. In the lower region of the combustion chamber, a burner device, in particular for gaseous media, is provided. The fuel gas flows with a certain intrinsic pressure in the burner device and is burned there with the incoming combustion air. Due to the rising and to Rauchgasauslass, for example, a chimney, flowing flue gases creates a negative pressure, which sucks more combustion air from the environment. The combustion air supply can be assisted by a blower.

The burner device usually has a main burner and a pilot burner, wherein both burners each have their own fuel gas supply. The pilot burner is ignited once when starting the system and then burns usually with a small flame permanently. The main burner can be switched on and off at any heat demand by opening and closing the fuel gas supply, without the need for an independent ignition. Rather, the fuel gas flowing out of the main burner ignites directly at the ignition flame of the pilot burner. In addition, devices are also known which do not have a pilot burner, such as e.g. modulating burners or burners where only the main burner can be switched on and off.

In order to prevent unburned combustion gas from escaping unrecognized in the event of undesired extinguishment of the flame, a thermocouple is provided in the area of the pilot burner. The thermocouple is heated by the ignition flame of the pilot burner, thereby generating a current. This current is sufficient to hold a spring-loaded solenoid valve against the action of the spring in the open position, wherein the solenoid valve is disposed in the fuel gas supply of the pilot burner and the main burner. When the ignition flame goes out, the thermocouple can no longer generate electricity, so that the solenoid valve automatically moves into the closed position and interrupts the fuel gas supply to the main and pilot burners. As a result, no fuel gas can escape if the ignition flame does not burn.

To start the system, the operator must manually hold the solenoid valve in the open position for a few seconds until a pilot ignites, e.g. has formed by a spark ignited flame, which generates the necessary holding current for the solenoid valve via the thermocouple.

For devices that do not have a pilot burner, the thermocouple is located in the area of the main burner.

Especially in the case of so-called atmospheric gas burners, in which the combustion air from the environment is sucked into the interior of the combustion chamber exclusively by the negative pressure generated by the outflowing flue gases, there is the problem that under unfavorable pressure conditions, for example, when the wind presses outside on the flue gas fireplace , can lead to pressure changes and finally to a backflow inside the combustion chamber. In a return flow, gas, e.g. Air and flue gas against the intended direction of operation flow direction. In critical cases, this can lead to a so-called "burn back" in which the flame generated by the burner device strikes back into the combustion air inlet.

During burn-back, it can be observed in particular that the pilot flame of the pilot burner can continue to burn stably while the main flame on the main burner strikes downwards, in the direction of the combustion air inlet, which is usually located at the bottom or at the side. The gas-air mixture can pass through the secondary air vane strongly heated due to the backflow and spread into the combustion air duct.

In the case of a burn-back, a flame can either form below the burner, ie below the space actually intended for the premix, or, depending on the strength of the backflow, only in the intake region of the fresh air supply. In extreme cases, a flame escapes from the combustion air intake area and accordingly may result in fire damage to the vehicle and / or the environment.

It is therefore important to prevent such re-burning or to notice in time. Then, when a burn back is detected, the burning should be stopped so that the flames (main flame and pilot flame) go out, or at least the main burner is turned off.

From the DE 100 24 511 C1 It is known to hold a pivotable flap with a melting element in the open position in the combustion air inlet. As soon as a burn back condition sets in and a flame strikes the combustion air inlet or combustion air supply, the melting element is heated and melted. As a result, it can no longer hold the flap in the open position so that the flap closes and thus prevents the supply of combustion air - or the discharge of flue gas in the case of a burn-back - via the combustion air inlet. Accordingly, the flames in the combustion chamber are stifled. In this case, the thermocouple on the pilot burner can no longer detect a flame and no longer generate a holding current so that the solenoid valve interrupts the fuel gas supply. However, by melting the fusible element and closing the flap in the combustion air inlet, the heater is disabled so that it can only be re-started by a person skilled in the art. At least the melting element must be renewed.

The invention has for its object to provide a heater with an improved backup fuse.

The object is achieved by a heating device with the features of claim 1. Advantageous embodiments are specified in the dependent claims.

A heating device according to the preamble of claim 1 is known from US 5 984 663 A known.

A heating device according to the invention comprises a combustion chamber with a combustion air inlet and a flue gas outlet, a combustion device arranged in the combustion chamber and a fuel gas feed for supplying fuel gas to the burner device. For monitoring a flame at the burner device, a flameproofing thermocouple is provided, which is arranged in the region of the burner device, wherein in a state in which the flameproofing thermocouple is heated by the flame, an electrical flameproofing current or a flameproofing voltage can be generated by the flameproof thermocouple. In the fuel gas supply, a solenoid valve device is arranged, which has a magnet excitable by the flameproof current, wherein upon application of the flameproofing current, the solenoid valve device is held in an open position, so that the fuel gas supply is open and fuel gas can reach the burner device. An additional thermocouple is located in the combustion air inlet.

The heater is characterized in that the additional thermocouple is a backfire thermocouple for monitoring a burn back flame in the combustion air inlet, wherein in a state in which the burn back thermocouple is heated by the burn back flame in the combustion air inlet, an electric burn back stream or a burn back voltage can be generated by the backfire fuse thermocouple. The flameproof voltage and the burnback voltage are combined by reverse polarity such that a holding voltage resulting from the reverse polarity of the flame fuse voltage and the burnback voltage is lower than a voltage required for holding the solenoid valve in the open position, so that Solenoid valve automatically assumes a closed position and interrupts the fuel gas supply.

Thus, in the heating device according to the invention, in addition to the existing flame arrestor by the arranged on the burner device flame retardance thermocouple a return fuse in the form of a second thermocouple (Rückbrennsicherungs thermocouple) is provided, which is introduced into the combustion air supply of the heater. The backfire thermocouple is reverse polarity to the flameproof thermocouple, so that a current generated by the backflush thermocouple counteracts the flameproof current and reduces it overall. Accordingly, the resulting, applied to the solenoid valve voltage is reduced.

The solenoid valve device has a spring-loaded solenoid valve, which is held by an excitation of its magnet against the action of the spring in the open position, while it is held in the closed position in the absence or insufficient excitation by the spring.

If, during operation, an undesirable flame burnback occurs while at the same time a portion of the flame, such as the pilot flame, remains stable and the flameproof thermocouple is heated, the flashback flame in the combustion air stack heats the backflush thermocouple. Due to the reverse polarity switching, the thermovoltage corresponding to the burnback current is drawn off from the thermal voltage of the flameproofing thermocouple, at least in the case of a series connection, which means that the solenoid valve device can no longer be held in the open position, but automatically by the action of the built-in spring closes. As a result, the fuel gas supply is interrupted and transferred to the heater in a safe state.

The flameproof thermocouple and the back-fusing thermocouple can be connected in reverse polarity in parallel or reverse polarity.

If the thermocouples are connected in reverse polarity in series, the holding voltage, which results from the polarity reversal as the sum of flameproof voltage and burnback voltage, may be less than the voltage required to hold the solenoid valve device in the open position, in particular less than that Be flame retardant voltage.

When the thermocouples are connected in reverse polarity, an electrical holding current supplied to the solenoid valve device resulting from reverse polarity of the flameproofing thermocouple and the backflushing thermocouple may cause the solenoid valve device to maintain a holding voltage that is less than the voltage required to hold the Solenoid valve device is required in the open position, which is therefore in particular lower than the flameproof voltage.

The electrical connection of the thermocouples ensures that a voltage generated by the back-fuse thermocouple or a generated current counteracts the flameproof voltage or the flameproofing current of the flameproofing thermocouple and reduces this, so that in sum only one more low voltage or too low a current to the solenoid valve device is applied and this therefore can not be held in the open position.

The combustion air inlet may include an air supply passage for supplying combustion air from the environment to the burner device, wherein the backfire protection thermocouple may be disposed in the air supply passage. In this case, it is free to arrange the back-fusing thermocouple relatively close to the burner device in order to detect it even with a small burn-back of the flame, or to arrange the back-fusing thermocouple farther away, for example in the combustion air suction region further away.

The burner device may have a main burner and a pilot burner. This arrangement has proven itself in practice diverse and allows - with permanent pilot light on the pilot burner - a convenient switching on and off of the main burner.

The flameproof thermocouple may be disposed in the region of the pilot burner and serve to monitor a flame of the pilot burner. For proper operation of the heater, it is a prerequisite that at least the flame is present at the pilot burner and thus escaping gas can be burned immediately as intended. The flameproof thermocouple monitors the presence of this flame at the pilot burner.

The solenoid valve device may be electrically connected to the flameproof thermocouple and the backflush thermocouple. This makes it possible in a simple manner to transfer the information obtained from the two thermocouples information directly into an effect on the solenoid valve device.

The solenoid valve device may have a so-called magnetic insert. Such is for example from the DE 20 2005 021 724 U1 known. In this case, a valve provided in the region of the fuel gas supply is coupled to an armature cooperating with a magnet, which holds the valve open against the action of a spring, provided that the magnet is excited by a suitable voltage (here: flameproof voltage or holding voltage). When the tension falls below a value dictated by the stiffness of the spring, the spring force is greater than the magnetic force, so that the spring moves the armature against the action of the magnetic force and closes the valve. Such a solenoid valve device can be installed as a unit in the fuel gas supply.

Fig. 1

eine schematische Schnittdarstellung einer erfindungsgemäßen Heizvorrichtung;

Fig. 2

ein Beispiel für eine verpolte Parallelschaltung der beiden Thermo-elemente; und

Fig. 3

ein Beispiel für eine verpolte Reihenschaltung der beiden Thermo-elemente.

These and other advantages and features of the invention are explained in more detail below by way of example with the aid of the accompanying figures. Show it:

Fig. 1

a schematic sectional view of a heating device according to the invention;

Fig. 2

an example of a reverse polarity connection of the two thermo-elements; and

Fig. 3

an example of a reverse polarity series connection of the two thermo-elements.

Fig. 1 shows a schematic sectional view of a gas heater eg for a caravan or a motorhome, with a heat exchanger 1, in the interior of which a combustion chamber is formed. The combustion chamber 2 or the heat exchanger 1 have a combustion air inlet 3 and a flue gas outlet 4.

Inside the combustion chamber 2, a burner device 5 with a main burner 6 and a pilot burner 7 is arranged.

The main burner 6 and the pilot burner 7 fuel gas can be supplied via a fuel gas supply 8.

The combustion air inlet 3 has an air supply channel 9, which couples the heat exchanger 1 or the combustion chamber 2 with the environment. In the example shown, the air supply channel 9 penetrates a bottom wall 10 of a caravan or motor caravan so that the combustion air can be supplied via the bottom region of the caravan to the heat exchanger 1 and the combustion chamber 2. The combustion air is then burned by means of the burner device 5 and the fuel gas supplied via the fuel gas supply 8. The hot flue gases rise in the combustion chamber 2 and are led either directly or through several diversions to the flue gas outlet 4, which opens into a chimney, not shown.

In the area of the pilot burner 7, a flameproof thermocouple 11 is arranged. The flameproof thermocouple 11 should be placed so that a flame above the pilot burner 7 heats the flameproofing thermocouple 11 such that a flameproofing voltage or a corresponding electric current can be generated therefrom.

The voltage is conducted via an electrical line 12 to a magnetic insert 13 serving as a solenoid valve device. Such a magnetic insert 13 is for example from DE 20 2005 021 724 U1 known.

The magnet insert 13 is arranged in the fuel gas supply 8 such that it interrupts the fuel gas supply 8 in an energized state and prevents the flow of fuel gas to the burner device 5. When the flame-proofing voltage generated by the flame-retardant thermocouple 11 is applied, the magnet of the magnet insert 13 is able to hold the armature of the magnet insert 13 and thus keep the fuel gas supply 8 open. The opening itself is carried out by external force, for example by a depression of an actuating element by the operator. The magnet insert 13 only serves to hold the open position thus achieved.

During operation of the heating device, this means that in a state in which a flame is present at the pilot burner 7, the flameproofing thermocouple 11 is heated and generates the required holding voltage for the magnetic insert 13. As a result, the magnet insert 13 is held in the open position, so that the burning process is maintained.

As soon as the flame extinguishes at the pilot burner 7, the voltage drops from the flameproof thermocouple 11 and can no longer hold the magnet insert 13 in the open position. Accordingly, the fuel gas supply 8 is closed by the magnetic insert 13 and the fuel gas supply is interrupted.

In the region of the combustion air inlet 3, a further thermocouple is arranged as a back-fuse thermocouple 14, which is also connected to the magnet insert 13 via an electrical line 15.

The two thermocouples, namely the flameproofing thermocouple 11 and the backflushing thermocouple 14 are reversed to each other. This will be in Fig. 1 among other things also symbolized by the two differently drawn conductors of the electrical lines 12 and 15.

In principle, the back-fusing thermocouple 14 operates in the same way as the flame-retardant thermocouple 11. Accordingly, in a (undesired) case in which a backflow in the combustion chamber 2 causes the flame, in particular the flame, from the main burner 6 to burn back into the combustion air inlet 3 This backfire flame is detected by the back-fuse thermocouple 14, which then applies a voltage across the electrical lead 15 to the magnet insert 13. The polarity reversal circuit reduces the voltage present across the flameproofing thermocouple 11 with a stable ignition flame on the pilot burner 7, or removes it altogether, so that the resulting voltage applied to the magnetic insert 13 is no longer sufficient to secure the magnet insert 13 in FIG To hold open position. The magnetic insert 13 thereby closes the fuel gas supply 8 and moves the heater into a safe state. After that If necessary, the system can be restarted if a proper flame history is restored.

Fig. 2 shows an example of a reverse polarity connection of the flameproofing thermocouple 11 and the back-fusing thermocouple 14 in relation to the magnetic insert 13th

In Fig. 3 is a verpolte series connection of the two thermocouples 11, 14 shown with the magnetic insert 13.

In both FIGS. 2 and 3 It can be seen that the poles of the two thermocouples 11, 14 are interchanged. In the case of reverse polarity Fig. 2 ), the currents generated by the two thermocouples 11, 14 act against each other and thus lead to a reduction of the total current and thus the holding voltage applied to the magnetic insert 13. In the reverse polarity series connection ( Fig. 3 ), the voltages generated by the thermocouples 11, 14 against each other, so that the total voltage at the magnetic insert 13 is reduced.

Claims (8)

1. Heating device, with

   - a combustion chamber (2), with a combustion air inlet (3) and a flue gas outlet (4);

   - a burner equipment (5) arranged in the combustion chamber (2);

   - a burner gas supply (8) for supplying fuel gas to the burner equipment (5);

   - a flame safety thermocouple (11), that is disposed in the region of the burner equipment (5) and serves to monitor a flame at the burner equipment (5) whereby, in a condition in which the flame safety thermocouple (11) is heated by the flame, an electrical flame safety voltage can be generated by the flame safety thermocouple (11); and with

   - a solenoid valve device (13), arranged in the combustion gas supply (8), which has a magnet excitable by the flame safety voltage, whereby the solenoid valve device(13) is held in the open position when the flame safety voltage is applied, so that the fuel gas supply (8) is opened and fuel gas passes to the burner equipment (5);

   - a thermocouple (14) disposed in the combustion air inlet (3);

   characterised in that

   - the thermocouple (14) is a flashback safety thermocouple (14) for monitoring a flashback flame in the combustion air inlet (3), wherein, in a condition in which the flashback safety thermocouple (14) is heated by the flashback flame in the combustion air inlet (3), an electrical flashback voltage can be generated by the flashback safety thermocouple (14); and that

   - the flame safety voltage and the flashback voltage are combined by a polarity reversal so that a holding voltage resulting from the polarity reversal of flame safety voltage and flashback voltage is smaller than a voltage which is required to hold the solenoid valve device (13) in the open position, so that the solenoid valve device (13) automatically adopts a closed position and interrupts the supply of fuel gas.
2. Heating device in accordance with claim 1, characterised in that

   - the flame safety thermocouple (11) and the flashback safety thermocouple (14) are connected in series with polarity reversed, and that

   - the holding voltage, which results from the polarity reversal as the total of flame safety voltage and flashback voltage is smaller than the voltage that is required to hold the solenoid valve device (13) in the open position, in particular smaller than the flame safety voltage.
3. Heating device in accordance with claim 1, characterised in that

   - the flame safety thermocouple (11) and the flashback safety thermocouple (14) are connected in parallel with polarity reversed, and that

   - an electric holding current, which results from the polarity reversal of the flame safety thermocouple (11) and the flashback safety thermocouple (14), brings about a holding voltage at the solenoid valve device (13) that is smaller than the voltage that is required to hold the solenoid valve device (13) in the open position, in particular smaller than the flame safety voltage.
4. Heating device in accordance with one of the claims 1 to 3, characterised in that

   - the combustion air inlet (3) has an air supply channel (9) for supplying combustion air from the environment to the burner equipment (5); and that

   - the flashback safety thermocouple (14) is disposed in the air supply channel (9).
5. Heating device in accordance with one of the claims 1 to 4, characterised in that the burner equipment (5) comprises main burner (6) and an ignition burner (7).
6. Heating device in accordance with one of the claims 1 to 5, characterised in that the flame safety thermocouple (11) is disposed in the region of the ignition burner (7) and is used to monitor a flame of the ignition burner (7).
7. Heating device in accordance with one of the claims 1 to 6, characterised in that the solenoid valve device (13) is electrically connected to the flame safety thermocouple (11) and to the flashback safety thermocouple (14).
8. Heating device in accordance with one of the claims 1 to 6, characterised in that the solenoid valve device has a magnet insert (13).

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