Gas burner and gas supply control depending on the pressure in the combustion chamber

Abstract

 The present invention relates to a gas burner (10) comprising a cylindrical burner head (11) having a plurality of burner orifices (15) in a cylindrical surface thereof, fan means (23, 24, 25) for supplying a gas air mixture to said burner head (11) gas supply means (26) for supplying a combustible gas within the vicinity of the fan inlet (25) so that the fan means (23, 24, 25) takes in atmospheric air and gas from said supply means and a zero governor (40) included in the gas supply means, said governor (40) being connected between the outlet for said fan means (23, 24, 25) and a combustion chamber for the burner (10) so that when the pressure in the combustion chamber relative to the fan supply means (23, 24, 25) increases above a predetermined datum the gas supply is shut off.

Description

[0001] The present invention relates to gas burners and has particular reference to gas burners suitable for use in combination with boiler fed heating systems.

[0002] In industrial boiler systems presently in use, where a gas burner is employed, it maybe a power gas burner in which air is forced as a draught over a gas nozzle to provide a ball flame about a burner head which is then projected into a combustion chamber or combustion cavity. This arrangement has the advantage that combustion can be controlled by the rate of supply of air and has the disadvantage that the heating pattern within the combustion chamber is uneven. In view of the force air draught provided about the combustion head itself in order to produce combustion of the gas, substantial uneven heating takes place within the combustion chamber with the result that complex construction of the combustion chamber itself within the boiler is necessary. This is expensive and on occasions the life of the boiler itself may be shortened by excessive heat in a localised area within the chamber itself.

[0003] An alternative has been to use a grid bar burner through which a gas/air mixture is supplied to provide generally an upwardly directed heat. In a domestic boiler, this provides an adequate and reasonably efficient means of heating water, v but in an industrial environment in which upwards of one million BTU is required this is inefficient and again only half the available combustion chamber surface is in fact effectively heated by such an arrangement.

[0004] British Patent Specification No. 1,286,356 discloses a multi-port gas burner comprising an array of ports in the curved wall member and a rotary blower adapted to blow a substantially uniform mixture of gas and air through the ports to form, when operated under a constant temperature conditions, jets with an angle of divergence greater than the angle of divergence between the centre lines of adjacent ports caused by the curvature of the wall member.

[0005] This specification specifically describes an arrangement in which gas and air are supplied separately to a fan unit and mixed therein and then fed to the burner head which comprises a plurality of holes spaced in a pattern to provide gas outlets and a generally cylindrical flame for the burner head.

[0006] Such an arrangement suffers from the disadvantage that gas and air are supplied via a fan and mixed therein for supply to the burner head.

[0007] According to the present invention there is provided a gas burner comprising a cylindrical burner head having a plurality of burner orifices in a cylindrical surface thereof, fan means for supplying a gas air mixture to said burner head, gas supply means for supplying a combustible gas within the vicinity of the fan inlet so that the fan means takes in atmospheric air and gas from said supply means and a zero governor included in the gas supply means, said governor being connected between the outlet for said fan means and a combustion chamber for the burner so that when the pressure in the combustion chamber relative to the fan supply means increases above a predetermined datum the gas supply is shut off.

[0008] Such an arrangement has the advantage that the flame is directed around a cylindrical burner head extending into a combustion chamber. This provides more even heating of the surfaces of the combustion chamber and the combustion chamber can, therefore, be configured to accept such an arrangement and to provide a more compact boiler installation for a given heat output.

[0009] Furthermore, such a burner is fully modulated since the heat output of the burner can be controlled merely by varying the speed of the fan.

[0010] In a typical embodiment of the present invention, the cylindrical burner head may have in its cylindrical surface a plurality of holes extending over a major part of its longitudinal length and a layer of metal gauze covering each hole. The gauze may be disposed either outwardly of the burner head or interiorly thereof and serves to stabilise the flame pattern about the head itself and to provide a back pressure within the burner. The burner head may comprise a cylindrical tube closed at a first end and open at a second end for communication with said fan means. The burner head may include guide means disposed therein to ensure substantially uniform combustion of the gas air mixture along said surface of the burner head. The guide, means is preferably conical in form and is disposed within the cylindrical tube with a portion of the cone of greatest diameter disposed towards the first end thereof.

[0011] A zero governor may be included in a gas supply means the governor being connected between the fan means outlet and the combustion chamber so that when the pressure in the combustion chamber relative to the fan supply pressure increases above a predetermined datum the gas supply is shut off. The gauze serves to maintain a pressure barrier whereby the pressure maintained by the fan means within the burner is, under normal conditions, greater than the pressure within the combustion chamber.

[0012] In practice, such a device has been found to be quieter in operation and may be modulated merely by adjusting the fan speed to rate between the specified limits. By incorporating the zero governor the device is self-compensating for conditions within the combustion chamber for example.should the flue outlet be blocked, the unit shuts down automatically.

[0013] Following is a description by way of example only and with reference to the accompanying informal drawings of methods of carrying the invention into effect.

[0014] In the drawings:-

Figure 1 is a diagrammatic cross-section of a burner assembly in accordance with the present invention.

Figure 2 is a modification of Figure 1 showing the operation of the zero governor.

Figure 3 is a perspective view of a burner in accordance with the present invention.

Figure 4 is a perspective view of the gas control means and the fan assembly of the burner of Figure 3.

[0015] Turning firstly to Figure 1 the burner indicated generally at 10 comprises a burner head 11 comprising a substantially cylindrical tube 12 closed at a first end 13 by means of a plug 14. The cylindrical tube 12 is provided with a plurality of radially disposed holes 15 disposed in circumferentially spaced rows, each row extending longitudinally of tube 12.

[0016] The plug 14 carries a frustoconical guide 16, the base portion of which is contiguous plug 14 and the narrow portion 17 is disposed within tube 12 and towards a second end 18 of cylindrical tube 12. The narrow end 17 is supported by means of a spider 19 so that the frustoconical guide 16 is substantially coaxial with the tube 12.

[0017] The second end 18 of the cylindrical-tube 12 is open and is provided with a sealing gasket 20 on the inner surface. The burner head 11 communicates with a cylindrical supply tube 21 which is connected with . the outlet of a centrifugal fan 23. The centrifugal fan 23 is disposed so that its rotor 24 rotates about a substantially vertical axis and the inlet therefor is disposed in the lower surface of the fan 23, the arrangement being such that on operation of the fan, air is drawn in through inlet 25 and supplied via the supply tube 21 to the interior of burner head 11.

[0018] A gas nozzle 26 is disposed beneath inlet 25 and spaced downwardly thereof so that on operation of the fan and with gas issuing from the nozzle 26, a mixture of gas and air is taken into the fan, substantially uniformly mixed and supplied to supply tubes 21. The supply tube 21 is mounted in a carrier plate 30 which also supports an ignition electrode 31.

[0019] The internal surface of burner head 11 is provided with a sheet of gauze 32.

[0020] In operation the fan 23 is driven to commence the air supply to the nozzle head 11. At the same time, the ignition electrode 31 is caused to spark and gas is . supplied by nozzle 26 to the fan inlet 25. The gas air mixture is supplied to the internal surface of the cylindrical nozzle head 11 where it passes through the gauze 32 which serves to maintain a back pressure within the apparatus and passes out of the holes 15 to provide, on ignition a substantially cylindrical flame. The frustoconical guide plate 16 serves to maintain a substantially uniform gas supply along the length of the nozzle.

[0021] Figure 2 illustrates the emodiment of Figure 1 including a zero operation governor 40 having an upper case portion 41 and a lower case portion 42. Each upper and lower case portion carries a mounting for a vertically slidable plunger 43 which is fixedly connected to a diaphragm 44 spring loaded by means of spring 45 in an upward direction (in Figure 2).

[0022] The cavity defined by the upper casing portion 41 is connected by means of conduit 46 to supply conduit 21 and the lower cavity defined by the lower case portion 42 is connected by means of second supply conduit 47.

[0023] In operation plunger 43 is connected to a pressure switch in the main gas supply line. The spring depresses diaphragm 44 and hence the plunger 43 to maintain the pressure switch (not shown) in the "off" position. On starting the fan the pressure in the supply conduit 21 builds up to a level greater than the pressure within the combustion chamber itself. This produces a pressurp differential between conduits 46 and 47 with a result that the greater pressure 46 acts on the diaphragm to depress the diaphragm downwardly against the loading of spring 45 thereby moving plunger 43 downwardly to operate the pressure switch and thereby providing a gas supply to nozzle 26 (see Figure 1). Thereafter, the apparatus operates in a manner described with respect to Figure 1. In the event of an imbalance or a build up of pressure within the combustion chamber, to an extent greater than that permitted by virtue of the loading of spring 45 the plunger 43 moves upwardly under the influence of the pressure applied to diaphragm 44 to operate the pressure switch and stop the supply of gas to nozzle 26.

[0024] The embodiments illustrated in Figures 3 and 4 show in perspective a prototype of the device and in practice it has been shown that the burner is quieter in operation and is fully modulating since the heat output of the burner can be varied by simply adjusting the fan speed to rate between certain limits. The burner is also self-compensating for conditions within the combustion chamber by virtue of the zero governor described above. Thus, for example, in the event of a blocked flue the pressure build up in the combustion chamber is such that the zero governor 40 is caused to operate to close the gas supply rendering the device safe.

Claims

1. A gas burner comprising a cylindrical burner head having a plurality of burner orifices in a cylindrical surface thereof, fan means for supplying a gas air mixture to said burner head, gas supply means for supplying a combustible gas within the vicinity of the fan inlet so that the fan means takes in atmospheric air and gas from said supply means and a zero governor included in the gas supply means, said governor being connected between the outlet for said fan means and a combustion chamber for the burner so that when the pressure in the combustion chamber relative to the fan supply means increases above a predetermined datum the gas supply is shut off.

2. A gas burner as claimed in claim 1 including means for varying the speed of the fan means, thereby varying the heat output of the burner.

3. A burner as claimed in claim 1 or claim 2 wherein the burner head has in its cylindrical surface a plurality of holes extending over a major part of its longitudinal length and a layer of metal gauze partially obturating each hole.

4. A burner as claimed in claim 3 wherein the gauze is disposed externally of the burner head.

5. A burner as claimed in claim 3 wherein the gauze is disposed interiorally of the burner head.

6. A burner as claimed in any preceding claim wherein the burner head comprises a cylindrical tube closed at a first end and open at a second end for communication with said fan means.

7. A burner as claimed in any preceding claim including guide means disposed within the burner head to ensure substantially uniform combustion of the gas -air mixture along the surface of said burner head.

8. A burner as claimed in claim 7 wherein the guide means is conical in form and disposed within the cylindrical tube with a portion of the cone in greatest diameter juxtaposed a closed end thereof.

9. A burner as claimed in any preceding claim wherein the datum position for sut-off of the gas supply is selected such that in normal operation the pressure maintained by the fan means within the burner body is greater than the pressure within the combustion chamber.

Drawing