EP1479973B1 - Method and device for controlling the tightness of a gas fired radiant tube - Google Patents

Description

The invention relates to a method and a device for monitoring the tightness of a jet pipe fired by a gas burner.

Gas-fired ceramic jet pipes are becoming increasingly popular, especially in industrial furnaces because of their long service life.

A disadvantage of the use of ceramic radiant tubes is that in case of damage, the jet breaks and immediately a large free cross-section of the furnace chamber is available. A damage of the jet pipe is not readily apparent so far and can lead to significant disadvantages in the process, since the furnace atmosphere is changed accordingly. Also, there are significant safety problems.

If an industrial furnace has several jet pipes and a break occurs, this will not be recognized immediately. The interior of the oven is usually closed by the inlet and outlet not close to the outside environment, so that no pressure increase occurs. If the furnace is filled with protective gas, the atmosphere is changed in the event of a jet pipe break, which can develop creeping and can only be determined by constant analysis or other measuring methods. In addition, it is not immediately apparent which jet pipe is broken. Only by switching off the jet pipe associated burner can be made a limitation. This takes time, since only a reaction of the furnace atmosphere or an effect of it must be maintained. Also analyzes of protective gas components of the jet pipe can be very time consuming. If there is only air in the furnace chamber, a jet pipe break in the production process is barely noticeable.

All of these problems are detrimental to the use of ceramic radiant tubes. In contrast, steel nozzles are exposed to greater corrosion and less temperature resistant. Damage to jet pipes made of steel usually develops creepingly.

From the US-A-4,219,324 It is known to monitor the operation of a burner by means of a flame detector. Furthermore, in this case the composition of the exhaust gas flow is monitored in order to determine an error state in the event of deviation from predetermined nominal values.

From the US-A-4 508 501 In addition, it is known to monitor the tightness of a jet pipe fired by a gas burner, in which the control of the burner monitors the oxygen content in the exhaust gas stream of the burner. If there is a deviation from a specified setpoint, an error signal is output.

Finally it is off the JP-A-55066729 (Patent Abstracts of Japan), in which also the exhaust gas flow of the burner is monitored and from this a signal for monitoring is derived. Again, the exhaust gas composition is monitored.

In the prior art, monitoring the leakproofness of the radiant tube requires elaborate monitoring of the gas composition, which is complicated and expensive and also involves the problem of aging of sensors.

The invention is therefore an object of the invention to provide a method and an apparatus for monitoring the tightness of a jet burner fired from a gas burner, which results in a simple and inexpensive construction and a fast response in case of failure.

This object is achieved by a method for monitoring the tightness of a jet pipe fired by a gas burner dissolved, is monitored in the on state of the burner and an indicative of the on-state burner signal is generated, which can occupy at least the conditions BURNER OFF with the burner off and BURNER ON with the burner on, in which also the exhaust gas flow of the burner is monitored and thereof an exhaust gas signal which is capable of assuming at least the exhaust gas out with insufficient volumetric flow and exhaust gas with the exhaust flowing properly, and wherein the combustor signal and the exhaust gas signal are combined to provide an error signal if the combination of the burner signal and the exhaust signal is not allowed issue.

The object of the invention is further achieved by a device for monitoring the tightness of a jet burner fired by a gas burner, with a sensor for monitoring the exhaust gas flow of the burner, which outputs a characteristic exhaust gas signal when a predetermined threshold value is exceeded, and with a monitoring circuit, the exhaust signal and indicative of a burner signal indicative of the on-state of the burner, and outputting an error signal upon improper combination of the burner signal and the exhaust gas signal, the sensor being configured as a sensor for monitoring exhaust gas volumetric flow.

The invention is completely solved in this way.

If the burner is switched on, as indicated by the burner signal, then the exhaust gas flowing out of the jet pipe must flow with a characteristic exhaust gas volume flow characteristic for the burner. If this waste gas flow volume does not reach or does not reach the required size, then there is a leak to go out the beam pipe. By linking the exhaust gas signal, which indicates a sufficient volume flow of the exhaust gas, with the burner signal can be easily detect in this way a leakage of the jet pipe.

The burner signal can be derived for example from the on / off switch of the burner, provided that it should only indicate the switch-on state. However, preferred is a derivative of a control of the burner, which usually not only indicates a turn-on state of the burner, but also at the same time monitors a correct operation of the burner, which is indicated by a signal BURNER ON. Alternatively, it is conceivable, for generating the burner signal, a separate monitoring device in the form of a sensor, e.g. a flame sensor to provide.

The monitoring of the exhaust gas flow can be monitored, for example, by a volumetric measurement, by a differential pressure measurement, by a flow velocity measurement using an inductive or ultrasound method or by a pressure probe measurement.

A particularly simple embodiment results when the exhaust gas flow is monitored by means of a differential pressure method by constriction of the flow cross section by means of a throttle device, in particular by means of a differential pressure diaphragm. It can then be carried out a differential pressure measurement between the input and the output of the throttle device. If the measured differential pressure is below a predetermined threshold value, the obtained exhaust gas signal is set to exhaust gas OFF. If the differential pressure is higher than this, the exhaust gas signal ABGAS ON results.

As a threshold value, for example, a value of 10 mbar, preferably of 5 mbar, more preferably of 3 mbar, in particular of 2 mbar, between input and output of the differential pressure diaphragm can be used.

In an additional development of the invention, an error signal is output even when the combination BURNER OFF and exhaust gas ON.

If, for example, an exhaust gas signal of sufficient magnitude is measured without the BRENNER ON signal characteristic for switching on the burner being present, it can be assumed that such a high volume flow will be sucked out of the furnace via a leaking jet pipe in the case of a broken jet pipe through an exhaust fan the signal EGR ON is generated.

In addition, a monitoring can be performed when the burner is turned off and works in the cooling air mode for the jet pipe for cooling the furnace chamber, wherein the cooling air is preferably that which serves as a combustion air during burner operation. For this purpose, a fan running even when the burner is switched off can supply the cooling air. Optionally, a separate cooling air duct can be mounted on the burner, via which additional cooling air is fed into the jet pipe, in order to achieve greater furnace cooling.

The function of the cooling air and possibly the additional cooling air can be monitored and a cooling air signal derived therefrom and possibly additional cooling air signal can be linked to the exhaust gas signal in order to output an error signal in the event of an impermissible combination.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Fig. 1

eine vereinfachte Darstellung eines Industrieofens mit einem Brenner und einem Strahlrohr in Form eines Mantelstrahlrohres und einer zugeordneten Einrichtung zur Überwachung der Dichtheit des Strahlrohres; und

Fig. 2

eine mögliche Ausführung einer Schaltung mit Leuchttaster zur Anzeige und Quittierung einer Meldung, die eine Undichtheit des Strahlrohres anzeigt.

Further features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the drawings. Show it:

Fig. 1

a simplified representation of an industrial furnace with a burner and a jet pipe in the form of a radiant tube and an associated means for monitoring the tightness of the jet pipe; and

Fig. 2

a possible embodiment of a circuit with illuminated button for displaying and acknowledging a message indicating a leakage of the jet pipe.

In Fig. 1 is an industrial furnace, which is heated with a gas-fired jet pipe and is equipped with a monitoring device according to the invention for monitoring the tightness of the jet pipe, shown schematically and generally designated by the numeral 10.

The industrial furnace 10 has an only schematically indicated by a dot-dash line furnace chamber 11 which is heated by a gas burner 12. The gas burner 12 has a projecting into the oven chamber 11 jet pipe 14 in the form of a jacket tube. The recirculated via the jet pipe 14 exhaust gases via a purely schematic indicated output of the jet pipe 14 in an exhaust pipe 18 and are passed into an exhaust passage 20.

According to the invention, the exhaust gas volumetric flow flowing via the exhaust gas line 18 is monitored to monitor the tightness of the jet pipe 14 and linked to a burner signal derived from the burner control 28, which indicates proper functioning of the burner. If the burner is working properly and there is no exhaust gas volume flow which has the characteristic size for the burner type used, then it can be assumed that there is a leakage in the jet pipe.

For this purpose, a differential pressure diaphragm 22 is inserted into the exhaust pipe 18. At the input and output of the differential pressure shutter, i. immediately before and behind, a pressure measuring device 24 is connected via measuring lines 26. If the burner 12 is operating properly, a differential pressure Δp of sufficient magnitude, e.g. 2 mbar, it can be assumed that there is no leakage of the jet pipe 14. Otherwise, an error signal is generated. For this purpose, a monitoring circuit is provided, which is indicated only schematically with the numeral 38. The monitoring circuit 38 is supplied with the exhaust gas signal 34 obtained from the pressure measuring device 24 and the burner signal 32 obtained from the burner control device 28. The monitoring circuit 38 generates an output signal 36 which, in the simplest case, can only assume the states OK or ERROR.

Also, in the simplest case, the exhaust gas signal 34 obtained from the pressure measuring device 24 can only be the states EXHAUST EXHAUST ON or EXHAUST OFF. Likewise, the burner signal 32 is preferably configured as a binary signal that can only accept the BURNER ON and BURNER OFF states.

It is understood that the connections of the exhaust signal 34 and the burner signal 32 by the monitoring circuit 38 can be done either by a conventional hard-wired circuit or by a digital switching logic, which is executed in the simplest case, for example. By means of TTL logic devices.

The output 36 obtained in response to the various possible combinations of the burner signal 32 and the exhaust signal 34 could then be represented by a truth table, for example, as shown in Table 1 below. Table 1 Brenner signal exhaust signal output Status 0 0 0 0 1 0 (1) 1 0 1 1 1 0

The input signals have a "0" for the state OFF or LOW, ie BURNER OFF or EXHAUST OFF and a "1" for the state ON or HIGH, ie BURNER ON or EXHAUST ON.

The output signal has a "0" for the condition OK or OK, while a "1" indicates an error.

In the simplest embodiment of the circuit, an error signal is generated only at the combination of BURNER IN and OFF GAS OFF, i. issued a logical "1". In an alternative embodiment, an error signal will also be output for the combination BURNER OFF and DISCHARGE ON, which is indicated in brackets by the logical "1" for this combination.

In the latter case, it must be assumed that, in the case of a broken jet pipe, such a high volume flow is sucked out of the furnace chamber by means of an exhaust fan, that the signal EXHAUST ON is generated.

If burners are also used for cooling furnace chambers via the associated jet pipe, which can take place with the cooling air (combustion air) and / or by additional cooling air via a cooling air duct attached separately to the burner, then monitoring can also take place in this case.

For cooling, simply the cooling air flow (combustion air volume flow) can be used, which also runs when the burner is not switched on. This, in turn, can be monitored with a differential pressure measurement to produce a COOLING ON or COOLING OFF signal indicating the flow of cooling air or the absence of cooling air flow. Likewise, the flow of additional cooling air may be monitored to provide an ENTIRE COOLING AIR ON or OFF signal. EXTERNAL COOLING AIR to produce, indicating a flow of additional cooling air or a lack of flow of additional cooling air.

In addition to Table 1, Table 2 shows possible states that may result when the burner is switched off in cooling mode. In a manner corresponding to Table 1, in the case of the cooling air signal, a "1"("0") means the signal COOLING AIR ON (COOLING AIR OFF) and, for the auxiliary cooling air signal, a "1"("0") the signal AUC. COOLING AIR ON (ADDITIONAL COOLING AIR OFF). Table 1 Brenner signal Cooling air signal Additional cooling air signal exhaust signal output 0 1 0 1 0 0 1 0 0 1 0 1 1 1 0 0 1 1 0 1 0 0 1 1 0 0 0 1 0 1

It is understood that the purely exemplary by way of Fig. 1 and Tables 1 and 2 can be used to monitor the tightness of a radiant tube not only in a single jet tube furnace but also in multi-jet tube furnaces. In this case, a pressure monitoring can be carried out at each jet pipe and the resulting exhaust gas signals can be linked by means of individual monitoring circuits or by means of a single monitoring circuit with the relevant burner signals.

It is further understood that the method according to the invention and the device according to the invention can be used for monitoring any jet pipes. So it can, for example, mantle jet pipes, P-beam tubes and double P-beam tubes are monitored. But even with through and U-beam tubes, the principle of the invention can be used. In this case, the exhaust gas flow is monitored at the outlet of the passage of the U-tube by means of the differential pressure diaphragm and the pressure measuring device.

One possible embodiment for the monitoring circuit 38 with conventional components is shown in FIG Fig. 2 shown. With this monitoring circuit 38, an error signal is output only when the combination BURNER ON and OFF GAS OFF is obtained. In addition, however, a light button for displaying and acknowledging the error message is provided here.

The monitoring circuit 38 may, for example, be accommodated in a separate housing, which is additionally accommodated in each case on the associated burner.

The monitoring circuit 38 has an input 56 for the burner signal (220 V signal) received from the burner controller 28, which can assume the conditions BURNER ON or BURNER OFF. This input 56 is connected to a relay K1, which is connected with its control circuit 40 at the other end to the neutral conductor N via the terminal 64. Likewise to the neutral conductor N, a relay K2 is connected to its control circuit 42, which is in series with the make contact 41 of the relay K1 and in series with the pressure measuring device 24, which is connected via the terminals 58 and 60 and via a line 50 with the 220 received from the burner control 28 V-phase connected via the terminal 62 is connected. The pressure measuring device 24 opens the in Fig. 2 schematically indicated NC contact when the differential pressure exceeds the preset threshold of eg 2 mbar.

Parallel to the control circuit 42 of the relay K2, an indicator lamp 44 is connected, which lies with its one end to the neutral and with its other end via the control circuit 43 of the relay K2 and a button 46 with the line 50 and the terminal 62, ie with the 220V Phase is connected. Through a line 48 between the control circuit 42 and the circuit 43 of the relay, the indicator lamp 44 is connected in parallel to the control circuit 42 of the relay K2.

When the burner signal BURNER ON is received and the exhaust signal, i. If the normally closed contact of the pressure measuring device 24 does not open the connection between the circuit 41 of the relay K1 and the line 50, this is indicated by the illumination of the indicator lamp 44, and an error signal is output at the output 66. The error signal can be acknowledged by the button 46.

Claims (13)

1. A process for monitoring the imperviousness of a radiant tube (14) fired by a gas burner (12), wherein the operation of the gas burner (12) is monitored and a burner signal (32) is generated that comprises at least the states BURNER OFF when the burner (12) is switched off and BURNER ON when the burner (12) is switched on, wherein further the exhaust gas flow of the burner (12) is monitored and an exhaust gas signal (34) is generated that comprises at least the states EXHAUST GAS OFF, when there is no sufficient exhaust gas volume flow, and EXHAUST GAS ON, when there is a suitably flowing exhaust gas flow, and wherein the burner signal (32) and the exhaust gas signal (34) are coupled with each other for generating a failure signal (36) when there is a non admitted combination of the burner signal (32) and the exhaust gas signal (34).
2. The process of claim 1, wherein the burner signal (32) is derived from a control (28) of said burner (12).
3. The process of claim 1 or 2, wherein the failure signal (36) is generated when the signals BURNER ON and EXHAUST GAS OFF are received.
4. The process of any of claims 1, 2 or 3, wherein coolant air is fed to said radiant tube (14) for cooling a furnace room heated by said radiant tube, the flow of said coolant air is monitored and a coolant air signal is generated that comprises the states COOLANT AIR ON and COOLANT AIR OFF, respectively, and wherein a failure signal (36) is generated when there is an inadmissible combination with said burner signal (32).
5. The process of claim 4, wherein additional coolant air for cooling said furnace room is fed to said radiant tube, the flow of said additional coolant air is monitored and an additional coolant air signal ADDITIONAL COOLANT AIR ON or ADDITIONAL COOLANT AIR OFF, respectively, is generated there from, wherein a failure signal is generated when there is an inadmissible combination with said burner signal, said exhaust gas signal and said coolant air signal.
6. The process of any of the preceding claims, wherein the monitoring of said flow is performed by a volumetric measuring, by an effective pressure measuring, by a flow velocity measuring using an inductive method or an ultrasonic method or a pressure probe method.
7. The process of claim 6, wherein said flow is monitored by an effective pressure method using a flow constriction by a throttle device, in particular by a differential pressure disk (22).
8. The process of claim 7, wherein the signal (34) is set to "OFF" when the detected pressure differential falls below a certain threshold.
9. The process of claim 8, wherein a threshold of 10 mbar, preferably of 5 mbar, more preferably of 3 mbar, in particular of 2 mbar is selected as the pressure differential Ap between the pressure differential disk inlet and outlet.
10. The process of any of the preceding claims, wherein a failure signal (36) is generated in case of the combination BURNER OFF and EXHAUST GAS ON.
11. A device for monitoring the imperviousness of a radiant tube (14) fired by a gas burner (12), comprising a sensor (24) for monitoring the exhaust gas flow of said burner (12) and, when exceeding a certain threshold, for generating an exhaust gas signal (34) characteristic therefor, and further comprising a monitoring circuitry (38) into which said exhaust gas signal (34) and a burner signal (32) characteristic for the on/off state of said burner (12) are fed and which outputs a failure signal (36) when there is an inadmissible combination of said burner signal (32) and said exhaust gas signal (34), characterized in that said sensor (24) is configured as a sensor for monitoring the exhaust gas volume flow.
12. The device of claim 11, characterized in that there is provided a throttle device, in particular a differential pressure disk (22) within the exhaust gas flow, wherein said sensor (24) is configured as a differential pressure detector for measuring the pressure differential between the inlet of said differential pressure disk (22) and the output of said differential pressure disk.
13. The device of claim 11 or 12, characterized in that said monitoring circuitry (38) generates a failure signal (36) with the combination BURNER ON and EXHAUST GAS OFF.

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