Gas Burners

Abstract

A gas burner comprises an annular chamber surrounding the fuel and air inlet end of a throated nozzle, with a circular slit orifice opening from the chamber into the nozzle upstream of the throat, and a flame stabilizer at one end of the nozzle, fuel gas passing through the slit expanding to form a Coanda wall jet around the inlet peripheral converging wall of the nozzle and inducing a flow of air down the center of the nozzle, the radial pressure gradient created by the jet sheet following the converging wall of the nozzle to its throat bringing about a high degree of air entrainment, whereby stable combustion results, at a point determined by the flame stabilizer.

Description

This invention relates to gas burners of the injector type in which air for combustion is entrained by the flow of the fuel gas under pressure.

In the usual injector type burner, the gas is fed through one or more nozzles directed in the desired direction of gas/air flow, and air is entrained around the peripheral surface of the expanding gas jet issuing from a nozzle, and mixed with the gas by the turbulence there created. Such burners may operate using primary air only, induced in the manner described, or they may use both primary and secondary air, the latter being entrained into the flame already produced by the combustion with the primary air.

The word gas as used throughout this specification is intended to embrace any artificially produced or natural gas, or any vapor that is suitable for combustion with air.

The principle object of the invention is to provide a burner of simple design in which there is a greater rate of air entrainment than is possible with a conventional injector burner, so that for a given duty a smaller burner may be used than is possible with a conventional burner.

A further object is to provide a burner in which the air/gas mixture boundary velocity gradients at the nozzle exit are higher than in a conventional injector burner so that a higher turndown ratio and a higher combustion intensity can be achieved.

Yet another object is to provide a burner with a gas inlet orifice that is readily adjustable, so that a wide variety of gases can be burned efficiently by the same burner, with the possibility of remote control of the adjustment.

Arising from the simple design of the burner, the invention also permits easy removal from the burner of grit or particles present in dirty gases.

According to the present invention a gas burner comprises an annular chamber, a throated nozzle surrounded near its inlet end by the chamber, a circular slit orifice opening from the chamber into the nozzle upstream of the throat, for the expansion of gas through the slit to form a Coanda wall jet around the inner peripheral converging wall of the nozzle, for the induction of air down the center of the nozzle, and a flame stabilizer mounted at one end of the nozzle. By the Coanda effect, the jet sheet follows the converging wall and the radial pressure gradient created by the curvature of the wall to its throat brings about a high degree of air entrainment. Stable combustion then results, at a point determined by the flame stabilizer.

The flame stabilizer may be mounted at the next exit end of the nozzle. Thus, it may be a tunnel stabilizer of larger diameter than the exit end, to provide return eddy currents by the toroidal vortex created by the gas and air immediately on leaving the exit. Alternatively, the exit stabilizer may be formed of an array of angled blades.

The flame stabilizer may however be mounted at the inlet end of the nozzle in the form of a vortex chamber with non-radial air inlet slots. This enables a highly turbulent helical vortex to be formed at the nozzle exit, for the stabilizing of the flame.

By suitable proportioning of the relative dimensions of the circular slit diameter and gap, and the diameter of the nozzle throat, the whole of the air for stoichiometric combustion can be induced down the center of the nozzle or the air as induced may be primary air, secondary air being entrained into the flame region itself by the flame turbulence. For any given gas and burner configuration there is an optimum slit gap width for maximum flame intensity, and preferably the burner has means for adjusting the gap, for tuning to this optimum during operation. Once the gap has been set, the gas/air entrainment ratio is comparatively insensitive to gas pressure over a wide range, and down to comparatively low pressures. At very low gas pressures approaching pilot light operation, the pressure drop across the gap from the annular chamber into the nozzle may be insufficient to produce an effective Coanda wall jet and therefore the burner tends to burn over-rich as insufficient air is entrained. To overcome this, a further feature of the invention consists in the provision of a flexible annular diaphragm forming one wall of the annular orifice. At low gas pressure, the diaphragm limits the effective gap width appropriately, but at higher gas pressures the diaphragm is forced towards one side of the orifice to increase the gap width, until eventually it abuts one side of the orifice, so that the effective gap width remains fixed, appropriate to the normal working pressure of the gas. AT lower pressures than this, the diaphragm flexes to reduce the gap width and increase the pressure drop necessary to maintain the necessary entrainment.

Whether or not such a flexible diaphragm is provided, the gap width may be adjustable, manually or remotely. Thus, the inlet end of the nozzle may be axially adjustable with respect to an outer sleeve that forms one wall of the annular slit. The adjustment may be manual, as by a screwthreaded connection between the nozzle and the sleeve or it may be controlled by fluid pressure, as by providing a chamber within the outlet sleeve, this making it possible for the adjustment -- of one burner or a plurality of burners simultaneously -- to be remotely controlled.

The invention will now be further described with reference to several embodiments shown in the accompanying diagrams, in which:

FIG. 1 is a longitudinal section of a burner, showing its annular orifice and other essential features of construction in diagrammatic manner;

FIG. 2 is an end view taken in the direction of arrow A in FIG. 1;

FIG. 3 is a longitudinal section of the inlet end of a burner provided with means for manually controlling the width of its annular orifice;

FIG. 4 is a longitudinal section through the inlet end of a burner provided with fluid-pressure operated means for controlling the width of its annular orifice, the burner, also being fitted with an inlet vortex chamber;

FIG. 5 is a section taken to a smaller scale, on the line 5--5 of FIG. 4, and

FIG. 6 is a fragmentary longitudinal section through the inlet end of another burner provided with means for automatically controlling the width of its annular orifice.

In FIG. 1, a fuel gas inlet 1 leads to an annular chamber 2 provided with an annular orifice 3 (see also FIG. 2) from which the gas flows into a converging inlet 4 of a nozzle 5, to form a Coanda wall jet in the nozzle the jet flowing through a throat 6 and along a diverging length 7 of the nozzle to an exit 8. Primary air for combustion is induced by the wall jet from the atmosphere into the inlet 4. The inlet may be fitted with a vortex chamber 9, to provide for stabilization of the flame burning at the nozzle exit 8. Such a vortex chamber is also shown in FIG. 4. Alternatively, a tunnel type stabilizer 10, or a swirl type stabilizer, may be fitted on the nozzle exit 8 to stabilize the flame.

The gas and air flowing into the stabilizer 10 form return eddy currents beyond the shoulder formed by the larger diameter of the stabilizer as compared with the exit end of the nozzle 5.

The efficient burning of different gases necessitates an appropriate gap width for the orifice 3. The burner is therefore preferably adjustable as to gap width. One adjustable construction is shown in FIG. 3. The annular orifice 3 is formed between an outer sleeve and an inner nozzle plug 12, these being axially movable one relative to the other by means of screw threads 13, so that rotation of the sleeve 11 alters the gap proportionally to the pitch of the threads. To take up thread backlash and provide a resistance to the rotary motion, a spring 14 is compressed between the ends of the two components 11, 12. An O-ring seal 15 prevents gas leakage. A pointer 16 carried by the plug 12 protrudes from a slot 17 in the sleeve 11 and enables the gap width to be set in relation to scale markings (not shown) on the outside of the sleeve.

In FIG. 4, a pressure chamber 18 is formed by a sleeve 11A and a nozzle plug 12A. O-ring seals 15A, 15B prevent leakage from the chamber 18. Pressure fluid admitted to the chamber 18 by an inlet 19 acts against the spring 14 and controls the width of the orifice gap 3 to an amount proportional to the force generated by the fluid pressure in overcoming the spring. The pressure of the fluid in the chamber 18 should be such that the net axial force caused by changes in fuel gas pressure in the chamber 2 is negligible compared to that generated by the control pressure, thus rendering the gap width insensitive to changes in fuel gas pressure.

The construction of FIG. 4 has the advantage that the orifice gaps on a large number of burners can be rapidly and similarly altered from a location remote from the burners, by inter-coupling the fluid chambers 16 to a common control source of pressure fluid.

FIG. 4 also shows the vortex chamber 9, for inducing into the primary air, formed integrally with the sleeve 11A. Air approaches the vortex chamber as shown by the arrows B, and is then sucked into the chamber by the Coanda wall jet of the nozzle. It enters the chamber 9 through oblique slots 20 (see FIG. 5), and is caused to produce a vortex, which continues to and beyond the nozzle exit (FIG. 1).

The construction of FIG. 6 provides for automatically increasing the air entrainment ratio, at very low fuel gas pressures. A flexible annular diaphragm 21 is clamped between an outer sleeve 11B and an end cover 11C (providing the nozzle inlet 4), so as to form one wall of the annular orifice 3. At zero pressure difference between the annular chamber 2 and the atmosphere, the width of the orifice gap is the distance between the end 22 of a plug 12B providing the nozzle proper, and the inner edge 23 of the undistorted diaphragm. As the fuel gas pressure increases, the diaphragm distorts towards the end cover 11C until it eventually contacts a point 24 on the latter, to leave between the diaphragm and the point 22 the maximum gap width required for the efficient operation of the burner at the normal working pressure of the gas supplied to the chamber 2.

Where the flame stabilizer 10 is mounted at the exit end, the annular slit 3 is readily accessible for cleaning. For cleaning purposes, a flame stabilizer 9 mounted at the inlet end may be made dismountable, e.g., separate from the sleeve 11A of FIG. 4.

Claims

What we claim is:

1. A gas burner comprising:

a source of fuel gas,

an annular chamber for receiving a supply of fuel gas under pressure from said source,

a convergent-divergent throated nozzle surrounded near its inlet end by said annular chamber,

said burner including a circular slit orifice opening from the chamber into the nozzle upstream of the throat, said nozzle and said slit being arranged to produce a Coanda effect entraining air as an oxidizer as a result of fuel gas under pressure issuing from said slit,

a flame stabilizer mounted at one end of the nozzle, said flame stabilizer being mounted at the inlet end of the nozzle and is in the form of a vortex chamber with non-radial air inlet slots,

whereby expansion of gas through the slit forms a Coanda wall jet around the inner peripheral converging wall of the nozzle for the induction of air down the center of the nozzle.

2. A gas burner comprising:

a source of fuel gas, an annular chamber for receiving a supply of fuel gas under pressure from said source,

a convergent-divergent throated nozzle surrounded near its inlet end by said annular chamber,

said burner including a circular slit orifice opening from the chamber into the nozzle upstream of the throat, said nozzle and said slit being arranged to produce a Coanda effect entraining air as an oxidizer as a result of fuel gas under pressure issuing from said slit,

means for adjusting the gap where the slit opens into the nozzle,

a flame stabilizer mounted at one end of the nozzle,

whereby expansion of gas through the slit forms a Coanda wall jet around the inner peripheral converging wall of the nozzle for the induction of air down the center of the nozzle.

3. A gas burner as in claim 2, wherein the flame stabilizer is mounted at the exit end of the nozzle.

4. A gas burner as in claim 3, wherein the end stabilizer is a tunnel stabilizer of larger diameter than the exit end, to provide return eddy currents by the helical vortex created by the gas and air immediately on leaving the exit.

5. A gas burner comprising:

an annular chamber,

a throated nozzle surrounded near its inlet end by the chamber, a circular slit orifice opening from the chamber into the nozzle upstream of the throat,

a flexible annular diaphragm forming one wall of the annular orifice,

a flame stabilizer mounted at one end of the nozzle, and

a fuel gas inlet to the annular chamber, whereby expansion of gas through the slit will form a Coanda wall jet around the inner peripheral converging wall of the nozzle, for the induction of air down the center of the nozzle.

6. A gas burner as in claim 5, wherein the inlet end of the nozzle is axially adjustable with respect to an outer sleeve that forms one wall of the annular orifice.

7. A gas burner as in claim 6, wherein the adjustment is manual, as by a screwthreaded connection between the nozzle and the sleeve.

8. A gas burner as in claim 6, wherein said nozzle and said chamber are movable axially thereof and include piston means for displacing said chamber selectively relative to said nozzle, whereby the adjustment of the gap is made by said piston means.