GB2242514A

GB2242514A - Adjustable premixing gas burner

Info

Publication number: GB2242514A
Application number: GB9106581A
Authority: GB
Inventors: Peter Luebke; Martina Hansmann; Konrad Weber; Heinz Thomas; Rainer Otminghaus
Original assignee: Joh Vaillant GmbH and Co
Current assignee: Vaillant GmbH
Priority date: 1990-03-27
Filing date: 1991-03-27
Publication date: 1991-10-02
Anticipated expiration: 2011-03-27
Also published as: CH682951A5; IT1245564B; NL9100526A; GB9106581D0; DE9103563U1; PT97143A; ITMI910756A0; DE4109580A1; FR2660414A1; BE1004667A6; FR2660414B1; ITMI910756A1; ES2056756A6; GB2242514B

Abstract

An atmospheric premixing gas burner comprises at least one gas nozzle (8) and at least one mixing tube (6), which are adjustable relative to one another by automatic distance control means (13) in dependence upon a temperature which is derived from the burner to reduce variation in the burner air-fuel ratio with change of gas flow. The gas nozzle may be moved along (Figs 1 to 3, not shown) or transversely of the mixing tube axis. Damper plates (46, 48) are adjustable by bimetallic devices to control airflow into mixing tube as the nozzle (6) is moved. <IMAGE>

Description

Premixina gas burner This invention relates to a premixing gas burner comprising at least one gas nozzle and at least one mixing tube.

Such premixing gas burners in the form of atmospheric burners have already been proposed. These are supplied with gas through a nozzle under a supply pressure (for example from natural gas, liquefied gas or town gas) in which the air is entrained by the impulse of the gas jet through a gap between the gas nozzle and the inlet of the mixing tube, and is admixed.

It has been found that the mixing ratio of the gas and primary air will fluctuate in dependence on the operating conditions of the burner, that is to say on the magnitude of the impulse of the gas jet and on the temperature of the burner.

As the requirements regarding the stability of the flames and regarding a combustion producing pollutants only at a low rate become more stringent, the mixing ratio of the fuel gas and primary air are desirably very precisely adjusted and maintained throughout the range of the load and operating conditions of the burner.

Accordingly, the present invention is directed to a premixing gas burner comprising at least one gas nozzle and at least one mixing tube, in which automatic position control means are provided for varying the relative'position between the gas nozzle and the inlet of the mixing tube in dependence upon a temperature that is derived from the burner.

With such a burner, it is possible to adjust the mixture of gas and primary air very precisely and then to maintain that mixture constant so that the emission of pollutants comprising CxHy, NOx and CO will be low.

The position control means may be distance control means comprising an expansion element having a sensor which is associated with the combustion chamber or with a medium that is heated by the combustion chamber and a final control element that is associated with the mixing tube or the gas nozzle.

It is desirable to provide a burner with a simple design for the control means.

Accordingly, the mixing tube and the gas nozzle may be displaceable relative to each other transversely of their longitudinal axes to change the distance between the gas nozzle and the centre of the mixing tube.

This results in a relatively simple design and it would be possible to alter existing burners of the kind described first hereinbefore. Another advantage which is afforded resides in that in a burner having a plurality of mixing tubes extending parallel to each other it will be sufficient to provide only one final control element.

A displacement of the gas nozzle and the mixing tubes relative to each other may change the distance between the mouth of the gas nozzle and the centre of the inlet of the mixing tube, and will change the flow conditions so that the effect of the change of the distance will be increased.

The gas nozzle may be held on a line which is displaceable transversely of the longitudinal axis of the gas nozzle and hinged dampers may protrude from the said line.

In that case the gas nozzle may be interconnected by very simple means and the nozzles can be adjusted in unison so that the design is very simple.

In principle, the mixing tubes might alternatively or in addition be interconnected and adjusted in unison although this will involve a higher expenditure because the mixing tubes have a larger mass than the gas nozzles.

The dampers may be plates which cooperate with stationary stops. In that case the displacement of the line will result in a change of the position of the damper plates.

The damper plates may be made of or connected to a bimetal strip. In that case the position of the damper plates may be directly influenced by the temperature in the combustion chamber so that the flow in the range between the gas nozzle and the mixing tube will be influenced and an influence will thus be exerted on the operation of the burner.

Examples of premixing gas burners made in accordance with the present invention are illustrated in the accompanying drawings in which: Figure 1 is an elevational diagrammatic view of an atmospheric gas burner comprising a single burner tube for a boiler or a water accumulator; Figure 2 is an elevational diagrammatic view of a gratelike burner which is intended for use in a circulating water heater and comprises a multiplicity of burner chambers, each of which is fed through at least one mixing nozzle; Figure 3 is an elevational diagrammatic view of a premixing gas burner for a room-heating stove; Figure 4 is a top plan view showing a further premixing gas burner; and Figure 5 is a diagrammatic top plan view of a modified premixing gas burner.

The atmospheric premixing gas burner shown in Figure 1 comprises a burner tube or a burner chamber 1, which is provided in a certain region 2 of its top with outlet openings 3 for the fuel-air mixture so that burner flames 4 will be formed at said openings. A mixing tube 6 opens into the interior 5 of the burner chamber and has an inlet 7 which is tapered like a funnel. A gas nozzle 8 is associated with the inlet 7 of the mixing tube 6, and is spaced therefrom by a distance s. The longitudinal centre line 9 of the gas nozzle 8 is aligned with the longitudinal centre line of the mixing tube 6. The gas nozzle 9 is connected to a gas supply line 10 for town gas, liquefied gas or natural gas.

The line 10 is provided with a solenoid valve 12, which is controlled by an electromagnet 11. The solenoid valve 11/12 can be used for an infinitely adjustable or stepwise control of the gas flow rate through the nozzle between zero load flow rate and full load flow rate, so as to include in its range a flow rate for a partial load.

The distance s between the outlet of the gas nozzle 8 and the inlet 7 of the mixing tube 6 is adjustable. This is accomplished by distance control means 13, with which a set point adjuster 14 is associated. An actual value signal is delivered to the distance control means 13 from a temperature sensor 15 via a signal line 16. In the embodiment shown in Figure 1 the temperature sensor measures the temperature of the burner chamber 1, preferably the temperature of that portion of the burner chamber which is associated with the region 2 in which the outlet openings 3 for the fuel-air mixture are provided.

By the operation of the distance control means the distance s will be minimized when the burner is cold and will be maximized when the burner is at an operating temperature under its maximum load. Under a partial load the distance s will be controlled infinitely variably or in steps between said two values.

In the embodiment shown in Figure 1 the gas nozzle 8 is rigidily associated with a housing and is screwed into that housing. The inlet 7 of the mixing tube 6 is movably mounted so that its distance from the housing can be adjusted. The entire mixing tube may be moveable in unison with the burner chamber 1. It would be sufficient however if only a part of the mixing tube were adjustable to change its distance from the nozzle 8. In that case the remaining burner may be rigidly fixed in position if a bellows seal or a sliding seal is provided for the gas-air mixture flowing in the interior 5 of the mixing tube 6.

Such a sliding seal comprising a cuff 18 is indicated in Figure 1. In that case the burner chamber or chambers may be accommodated in the housing, particularly if the housing encloses also the combustion chamber in which the burner chamber(s) is or are accommodated.

A circulating water heater, shown in Figure 2, comprises a heat exchanger 19, which is connected by a circulating pump 20 to the return line 21 and to a flow line 22, which is provided with the temperature sensor 15.

The temperature sensor 15 senses a temperature which is derived from the burner and is in fact the flow temperature of the water which has been heated by the atmospheric premixing gas burner 23. That atmospheric gas burner comprises a so-called gratelike burner, which comprises a multiplicity of individual burner chambers 1, which extend one beside another. Each individual burner chamber is fed froni a mixing tube 6, which constitutes an injector and has an inlet 7 that is spaced a distance s from an associated gas nozzle 8. Each gas nozzle 8 is associated with a gas-distributing pipe 24 which extends, as part of the gas line 10, wholly downstream of the valve 12. Each gas nozzle is slidably mounted on the associated gas-distributing pipe.The distance control means 13 vary the distance s between the gas nozzle and the inlet of the mixing tube 6 in dependence on the temperature of the flow line, and in this embodiment are effective at each nozzle.

If only one gas nozzle is provided that nozzle will be suitably displaced and if a plurality of gas nozzles are provided all said nozzles will be suitably displaced in unison towards the stationary inlets of the mixing tube.

For this purpose a nozzle carrier will be provided, which carries all the nozzles so that they will all be displaced in unison. The distance will be controlled in the manner which has been described with reference to Figure 1. The present embodiment affords the advantage that a displacement is not imparted to the burner chamber or chambers 1 of the atmospheric premixing gas burner 23, which burner chambers are relatively heavy, but it will be sufficient to displace only the nozzle or nozzles, which is or are relatively light in weight.

The distance control means 13 comprise an expansion element, such as is known from a thermostat valve of a heating system. The expansion element is provided with a sensor, which corresponds to the temperature sensor 15. The connection between the sensor and the expansion element is constituted by a capillary passage, which corresponds to the line 16. The higher the temperature to which the head is heated, the larger will be the displacement of a piston of the expansion element.

That displacement will be transmitted by a final control element to the mixing tube 6 and/or the nozzle 8.

There is a controller 25, with which an outdoor temperature sensor 26 is associated by a signal line 27.

The outputs of the controller are connected to the electromagnet 11 and to a drive motor 28 of the pump 20.

Figure 3 shows an air heater. The heat exchange 19 comprises an exhaust gas-air heat exchanger, which is supplied with fresh air through an air inlet line 30, which contains a fan 32 that is driven by a motor 31.

Heated fresh air is withdrawn from said heat exchanger through an air outlet line 33 and is used to heat one or more residential rooms. The other part of the heat exchanger is included in the exhaust gas flow path 34 from a combustion chamber 35, which is heated by the atmospheric premixing gas burner 23. The exhaust gas flow path 34 has associated with it the temperature sensor 15, the capillary passage 16 of which is associated with one or more mixing tubes 6 of the burner 23. In that case the distance control means 13 displace the entire burner, which is slidably mounted and is adjustable to change the distance s. The gas nozzle(s) 8 is or are stationarily mounted in the housing.

It is emphasized here that the decision whether the gas nozzle 8 and/or the mixing tubes 6 are displaced will be independent of the nature of the use. Either of the distance control means can be used in any of the embodiments shown in Figures 1 to 3. It is also possible to have one or more nozzles 8, or one or more mixing tubes 6, in any of the embodiments shown in Figures 1 to 3, and it is possible to make the entire burner, or the entire mixing tube, or only a part thereof, namely, the inlet, displaceable, in any of the embodiments.

Instead of hydraulically operated distance control means it is possible to provide such means which are actuated by an electric motor or which operate pneumatically or simply mechanically. For instance, the actuator of the distance control means may comprise a bimetal device. It is also possible to use a stepping motor. Finally, the distance may be controlled in dependence on the result produced by the combustion. In that case an exhaust gas sensor for measuring the emission of pollutants will be required and the distance will so be controlled that the pollutants will be minimized.

In a burner made in accordance with Figure 4 or Figure 5, the mixing tube 6 is provided in its inlet portion with a portion 40, which flares towards the gas nozzle and merges into a further portion 41, which flares towards the burner, the other parts of which are not shown in Figure 4 or Figure 5. A cylindrical portion 42 disposed between the above-mentioned portions is formed with windows 43, which are constituted by apertures in the wall of that portion 42.

The portion 42 is followed by a portion 41, which flares towards the burner. A holder (not shown) for a baffle member is provided in the interior of the mixing tube 6 in the transitional region between the portion 41 and the portion 42.

When the burner is cold in its initial position the axis of the mixing tube 6 will be aligned with the axis of the gas nozzle 8, which is mounted on a line 10.

That line 10 is controlled by means of the final control element 13, which is influenced by the temeprature of the burner 1, which temperature is measured by the sensor 15, and is also influenced by the load on the burner.

That line 10 is mounted to be displaceable in its axial direction (as indicated by the arrow heads) to the maximum extent s' from an initial position, in which the axes of the gas nozzle 8 and the mixing tube 6 are aligned. This is also apparent from Figure 5.

With reference to Figure 5, a damper plate 46 is hinged to the line 10 and cooperates with stationary stops 47 so that a displacement of the line 10 will result in a change of the flow conditions in the region between the mouth of the gas nozzle 8 and the inlet of the mixing tube 6. The operation of the burner will thus be changed.

More than one damper plate 46 may be provided. The or each plate 46 may comprise or may be attached to a bimetal strip or other bimetal device.

As the temperature of the burner increases, the line 10 will be increasingly displaced so that the gas nozzle 8 will be increasingly displaced out of alignment with the mixing tube 6 and the distance s from the centre of the mouth of the gas nozzle to the centre of the inlet of the mixing tube 6 will be increased.

The displacement of the gas nozzle 8 will also displace the region in which the gas jet 49 discharged by the gas nozzle 8 contacts the mixing tube 6 so that the operating performance of the burner will also be influenced in a favourable sense.

With further reference to Figure 5, one or more further damper plates 48 are provided at the inlet portion of the mixing tube 6 and comprise bimetal strips. They change their position in dependence on the temperature which prevails in that region so that the conditions for the flow of the fresh air towards the inlet of the mixing tube 6 will be favourably influenced.

Claims

1. A premixing gas burner comprising at least one gas nozzle and at least . one mixing tube, in which automatic position control means are provided for varying the relative position between the gas nozzle and the inlet of the mixing tube in dependence upon a temperature that is derived from the burner.

2. A premixing gas burner according to claim 1, in which the position control means comprise a sensor and a final control element, the sensor is associated with the combustion chamber or with a medium that is heated by the burner, and the final control element is associated with the mixing tube or the gas nozzle.

3. A premixing gas burner according to claim 1 or claim 2, in which the position control means comprise an expansion element having a sensor, which is associated through a capillary passage with a burner chamber, a flow line or an exhaust gas path of the premixing gas burner, and a final control element which is associated with a displaceable gas nozzle or a displaceable inlet of a mixing tube.

4. A premixing gas burner according to any preceding claim, in which the position control means comprise a stepping motor or a bimetal actuator.

5. A premixing gas burner according to any preceding claim, in which the inlet of the mixing tube is connected to the mixing tube by a cuff, a bellows or the like, which permits an adjustment of the distance between the gas nozzle and the inlet of the mixing tube.

6. A premixing gas burner according to any preceding claim, in which the mixing tube and the gas nozzle are displaceable relative to each other transversely of their longitudinal axes in order to change the distance between those axes.

7. A premixing gas burner according to claim 6, in which the gas nozzle is held on a line which is displaceable transversely of the longitudinal axis of the gas nozzle and serves to supply the gas, and at least one hinged damper protrudes from the said line.

8. A premixing gas burner according to claim 7, in which the damper cooperates with an associated stationary stop.

9. A premixing gas burner according to claim 7 or claim 8, in which the damper comprises or is connected to a bimetal strip or other bimetal device.

10. A premixing gas burner, substantially as described hereinbefore with reference to and as shown in any one of Figures 1 to 5, or any one of Figures 1 to 3 modified in accordance with Figure 4 or Figure 5 of the accompanying drawings.