GB2254413A

GB2254413A - Gas burner assembly and waterheating apparatus incorporating it

Info

Publication number: GB2254413A
Application number: GB9206277A
Authority: GB
Inventors: Keith Francis Hyland
Original assignee: IMI RANGE Ltd
Current assignee: IMI RANGE Ltd
Priority date: 1991-03-21
Filing date: 1992-03-23
Publication date: 1992-10-07
Anticipated expiration: 2012-03-23
Also published as: GB9206277D0; GB2254413B

Abstract

A gas burner assembly (5) especially for use in a gas-fired thermal storage type of waterheater comprises a cylindrical ribbon type of burner (14) mounted in a casing (13) to which premixed natural gas/air is fed under pressure by a fan (10). A conduit (12) that connects the fan (10) with the casing (13) includes a pair of flat plates (23A, 23B) arranged in cruciform fashion and these serve to reduce the turbulence of combustion air fed into the conduit (12) by the fan (10), the air entraining natural gas injected into the conduit (12) by an injector (24) located in the conduit (12) adjacent to the burner (14) and having a scarfed outlet end (25). The casing (13) houses a diffuser (27) in the form of a hollow cylinder (28) that is open at its rear end and closed at its front end, adjacent to the burner (14), by an apertured plate (29). The plates (23A, 23B), scarfed injector (24) and diffuser (27) all serve to improve mixing of the combustion air with the gas and the performance of the burner. <IMAGE>

Description

Gas Burner Assembly and Waterheating Apparatus Incorporating It This invention relates to a gas burner assembly for use in fluid heating apparatus, especially but not exclusively waterheating apparatus, and more particularly is concerned with improvements to fan-assisted, premixed gas/combustion air burner assemblies, for example of the type described and claimed in our prior UK patent No 2 214 629, the disclosure of which is incorporated herein by way of reference thereto.

According to the present invention, there is provided a gas burner assembly including a gas burner comprising a casing having at one end a plurality of burner ports and connected to combustion air supply ducting, there being in communication with the ducting, and therefore with the casing and the burner ports, a fan for inducing air flow along the ducting to the burner, the assembly being characterised by one or more of the following: a) a gas injector tube extending into the supply ducting, upstream of the gas burner, substantially perpendicularly to the axis of the ducting, the end of the tube within the ducting being scarfed so as to provide a gas outlet orifice that faces generally upstream of the injector tube; b) an air flow straightening device, located in the supply ducting upstream of the gas burner, for reducing turbulence of air flowing through the ducting towards the burner; and c) a gas/combustion air diffuser/baffle located in the casing for improving distribution of the gas/air mixture to all of said burner ports.

In an assembly of the invention, the fan is preferably arranged to blow air along the supply ducting and thence, after admixture with gas, to the burner, ie the fan is located upstream of the burner.

In that case, the assembly advantageously includes at least feature (b) specified above, the air flow straightening device preferably being located in the supply ducting immediately adjacent to the fan which is located at the inlet end of the ducting.

Alternatively, the fan may be arranged to suck combustion air into and along the supply ducting and thence, after admixture with gas, to the burner. As such, the fan will be disposed downstream of the gas burner within the latter's flue arrangement. In either case, the fan serves to expel flue gases from the burner and then to atmosphere through a flue terminal.

In any event, the fan is preferably an electric motor-driven centrifugal fan.

As previously noted, the gas burner may generally be of the type described and claimed in our prior UK patent No 2 214 629, that is to say a burner preferably constituted by two metal strips, one flat and one corrugated laid flat in face-to-face contact and then wound spirally around a cylindrical, cup-shaped boss, the closed end of which is located on the flame side of the gas burner. Such burner therefore comprises a multiplicity of axially directed gas/flame ports with a non-ported central area. The flat metal strip is preferably of heavier gauge than the corrugated strip and the width of the two strips is preferably so chosen that the length of the wound assembly is substantially less than its diameter, say, for example, about 2 cm compared with about 13 cm.

Preferably, the air flow straightening device comprises two plates defining together an X-configuration and located in the supply ducting, which is preferably of circular cross-section, upstream of the gas burner and, as noted earlier, downstream of the fan in the case where the latter is arranged to blow the air, via the supply ducting, to the burner.

The gas injector tube (see feature (a) above) is preferably located in the supply ducting adjacent to the burner with the centre of the ellipse defined by the scarf lying on the axis of the ducting whereby, in use, gas (eg natural gas) supplied through the injector becomes entrained by combustion air flowing through the ducting towards the burner. Thus, a combustible mixture of gas and air is fed to the burner. In order to improve mixing of the gas and air and its distribution to all ports of the gas burner, the burner casing preferably contains a diffuser/baffle device (feature (c) referred to above). Preferably, such device is in the form of a cylinder which is open at one end (such end defining a gas/air mixture inlet) and "closed" at the other end by a circular forminate plate through which the gas/air mixture flows to the burner ports.

The present invention also provides waterheating apparatus including a burner assembly as defined above. The apparatus is preferably of the thermal storage type, the thermal storage medium, typically water, being contained in a vessel, for example a cylinder, and being directly heated by the burner of the aforementioned burner assembly, the burner being located in a plenum chamber extending within the vessel and being connected to one or more flue pipes that extend through the vessel to a position outside the vessel. In other words, the or each flue pipe is, over a part of its length, surrounded by the thermal storage medium thereby improving the heat exchange efficiency of the apparatus.Reference is made to our co-pending UK patent applications Nos 2 241 052 and 2 240 615 which describe in detail a thermal storage type of waterheater in which the burner assembly of the present invention may be used with advantage.

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings of which: FIGURE 1 is a schematic diagram of a thermal storage waterheating apparatus of the invention; and FIGURE 2 is an exploded, perspective view, together with detailed views, of the gas burner assembly, constructed in accordance with the invention, embodied in the apparatus shown in Figure 1.

Referring firstly to Figure 1, the waterheating apparatus includes a lagged cylinder 1, for example of copper or stainless steel, which is filled with primary water 2 (the thermal storage medium). Typically, the capacity of the cylinder 1 will be from 100 to 200 litres. Mounted in the upper part of the cylinder 1 is a high efficiency heat exchanger in the form of coiled INTEGRON (Registered Trade Mark) internally rifled/externally finned tubing 3. The lower, inlet end of the tubing 3 is connected to the cold mains, as shown, and the upper outlet end is connected, via a thermostatic mixing valve 4 to the domestic hot water (DHW) distribution pipework, again as shown, of the premises served by the apparatus.

The primary water 2 is heated, typically to 80 "C or higher, by an "integrated" premixed air/gas burner 14 forming part of a burner assembly 5, described in more detail below, mounted in the side of the cylinder 1 adjacent to its base. The burner 5 is sealed into one end of a plenum chamber 6, located wholly within the cylinder 1, from which a number of, for example four, flue pipes (only two of which, 7, 7' are visible in the drawing) extend vertically through the cylinder 1 and communicate collectively, outside the cylinder 1, with a single flue pipe which terminates on the outside of an external wall of the premises at a balanced flue terminal 8 that additionally defines a combustion air inlet 9 communicating with the gas burner assembly 5. Because flow of the flue gases and the combustion air are induced by a fan 10 (see below) the single flue pipe and the incoming air pipe may both be of small internal diameter, say 45 mm or less and of large length, say up to about 7 metres. This means that the apparatus may be sited virtually anywhere in the premises and not necessarily adjacent to an external wall.

The principle of operation of the apparatus depicted in Figure 1 will be familiar to those skilled in the art. Briefly, however, when there is a demand for domestic hot water, cold water at, or at reduced, mains pressure passes through the tubing 3, whereupon it instantaneously becomes heated by virtue of heat exchange with the primary water 2, and thence, at a pre-set temperature as determined by the valve 4, to the point of demand. A substantial demand for domestic hot water will, of course, result in a reduction in temperature of the primary water 2 and when that temperature drops below a pre-set value, say about 80 "C as mentioned above, as determined by the setting of a cylinder thermostat (not shown), the burner 14 is fired whereby the temperature of the primary water 2 is raised to about the cylinder thermostat's pre-set value.This cycle is repeated as necessary whereby the temperature of the primary water 2 is continually maintained at about the temperature pre-set on the cylinder thermostat.

In addition, the primary water 2 may serve to heat a wet central heating ('CH') circuit by being pumped therearound by an electric pump operable in response to the usual room thermostat (not shown).

A more detailed description of the construction, operation and control of waterheating apparatus of the type shown in Figure 1 may be found, for example, in our aforementioned co-pending UK patent applications.

The gas burner assembly 5, to aspects of which the present invention particularly relates, will now be described in more detail with reference to Figure 2 of the accompanying drawings.

The gas burner assembly comprises a blower fan 10, driven by an electric motor 11, in communication via a tubular air supply duct 12 with a cylindrical gas burner casing 13 housing a gas burner 14.

The blower fan 10 is a centrifugal fan enclosed in a housing in communication with an end of the tubular duct 12 which is provided with a lateral branch 15 to accommodate the sensor of an air pressure switch (not shown) that forms part of the electrical control system of the apparatus.

The tubular duct 12, at its other end, fits and is secured into a tangential extension tube 16 of the gas burner casing 13.

The gas burner 14 is constituted by two metal strips of different gauge, one metal strip 17 being flat and the other and thinner gauge strip 18 being corrugated. The strips 17, 18 are in face-to-face contact and are coiled into an annular configuration about a central cup-shaped boss 19 to provide a multiplicity of spaced, axially directed gas or flame ports 20 (see scrap detail III).

The gas burner 14 is enclosed in a surrounding wall 21 which extends slightly beyond the gas burning and gas inlet faces of the gas burner 14 defined by the strips 17, 18. The wall 21 may be cut away at one or more places, for example as indicated at 22, to permit location of a gas/air mixture ignition device and a flame sensing and/or monitoring device (both not shown).

The gas burner assembly 5 is provided with a number of air and gas/air mixture conditioning devices, as will now be described.

Within the tubular duct 12 in'the region of the pressure sensor location 15 is an air flow straightening device comprising two axially extending, flat plates 23A, 23B disposed in X-configuration and each extending diametrically across the duct 12.

A gas inlet supply pipe 24 extends into the tangential extension tube 16 adjacent to the end into which the tubular duct 12 fits and this pipe 24 is scarfed at its outlet end as indicated at 25. The centrepoint of the thus generally elliptical orifice defined by the outlet end of the pipe 24 lies substantially on the axis of the tubular duct 12. It has been found that this arrangement enhances intimate mixing of the gas and air.

Such mixing is enhanced by a pair of baffles 26A, 26B downstream of the gas inlet pipe 24. This aspect is described in detail in our aforementioned co-pending patent application No 2 241 052. Briefly, however, each baffle 26A, 26B comprises a multi-apertured, substantially semi-circular plate and the baffle 26A occupies one half of the cross-sectional area of the extension tube 16 while the other baffle 26B, which is axially spaced from the baffle 26A, occupies the other half of the cross-sectional area of the extension tube 16. Thus, the gas/air mixture is caused to flow both through the baffles 26A and 26B and in a sinuous path past the baffles 26A, 26B thus causing futher vigorous and intimate mixing and turbulence of the gas/air mixture. In addition, the baffles 26A, 26B serve to reduce operational noise of the burner assembly, ie as a silencing device.

The extension tube 16 has a portion 16A which extends tangentially into the casing 13 and this configuration serves to impart a swirling effect to the gas/air mixture as it enters the casing 13. The mixture than passes through a diffuser 27 which comprises a cylinder 28 whose rear end is fully open and whose front end comprises a forminate plate 29.

The external diameter of the cylinder 28 is somewhat less than the internal diameter of the burner casing 13 and its length is such that when it and the burner 14 are located in place in the casing 13 (with the plate 29 abutting the rear face of burner 14), there is a gap between the rear end of the cylinder 28 and the rear, closed end of the casing 13. There will also be an annular space between the external surface of the cylinder 28 and the internal, cylindrical surface of the casing 13. Accordingly, the gas/air mixture, having entered the casing 13, can pass to the ports 20 of the burner 14 via the open end and interior of the cylinder 28 and then through the apertures formed in the plate 29. The diffuser 27 serves further to mix the air and gas and more especially to distribute, substantially evenly, the mixture to all of the ports 20 of the gas burner 14.

Whilst a burner assembly of the invention is especially useful in the context of the thermal storage type of waterheating apparatus described above, it will be appreciated that it could be used in other contexts where a highly efficient and compact gas burner is required.

Claims

CLAIMS:

1. A gas burner assembly including a gas burner comprising a casing having at one end a plurality of burner ports and connected to combustion air supply ducting, there being in communication with the ducting, and therefore with the casing and the burner ports, a fan for inducing air flow along the ducting to the burner, the assembly being characterised by one or more of the following: a) a gas injector tube extending into the supply ducting, upstream of the gas burner, substantially perpendicularly to the axis of the ducting, the end of the tube within the ducting being scarfed so as to provide a gas outlet orifice that faces generally upstream of the injector tube; b) an air flow straightening device, located in the supply ducting upstream of the gas burner, for reducing turbulence of air flowing through the ducting towards the burner; and c) a gas/combustion air diffuser/baffle located in the casing for improving distribution of the gas/air mixture to all of said burner ports.

2. A gas burner assembly according to claim 1 wherein the fan is located upstream of the burner at the inlet end of the supply ducting.

3. A gas burner assembly according to claim 2 wherein the air flow straightening device is located in the supply ducting adjacent to the fan.

4. A gas burner assembly according to any one of claims 1 to 3 wherein the air flow straightening device comprises one or more flat plates extending longitudinally and diametrically of the supply ducting.

5. A gas burner assembly according to claim 4 wherein the air flow straightening device is of cruciform configuration.

6. A gas burner assembly according to any one of claims 1 to 5 wherein the scarfed end of the gas injector tube defines a substantially elliptical gas outlet and wherein the centre of the ellipse lies substantially on the axis of the supply ducting.

7. A gas burner assembly according to any one of claims 1 to 6 wherein the gas injector tube is scarfed at an angle of from 30 to 600, preferably about 45, to the axis of the gas injector tube.

8. A gas burner assembly according to any one of claims 1 to 7 wherein the diffuser/baffle comprises a hollow cylinder coaxially mounted in the burner casing so as to afford an annular space between the external surface of the cylinder and the internal, cylindrical surface of the casing, the end of the cylinder remote from the burner ports being open and spaced from the rear, closed end of the casing and the other end of the cylinder being closed by an apertured wall located adjacent to the burner ports, the arrangement being such that, in use, the gas/air mixture enters the burner casing from the supply ducting and flows to the burner ports via the open end of the cylinder and thence through the apertured wall thereof.

9. A gas burner assembly according to claim 8 wherein the apertured wall comprises a foraminate plate.

10. Waterheating apparatus comprising a vessel for containing water to be heated and a burner assembly according to any one of claims 1 to 9, the burner ports defining one end of a plenum chamber extending into the vessel and being connected to one or more flue pipes that extend through the vessel to a position outside the vessel whereby, in use, said water is directly heated by the burner and its flue gases.

11. Waterheating apparatus according to claim 10 which is of the thermal storage type and said water constitutes the thermal storage medium thereof.

12. A gas burner assembly substantially as hereinbefore described with reference to, and as illustrated in, Figure 2 of the accompanying drawings.

13. Waterheating apparatus substantially as hereinbefore described with reference to, and as illustrated in, Figures 1 and 2 of the accompanying drawings.