IMPROVED INSULATION FOR RADIANT BURNER

Abstract

A radiant burner (1) which comprises at least one radiant burner plate (2) and at least two layers of radiant screens (3) enclosed by a peripheral band (4) associated with a body (6) defining a premixing chamber for said burner. The peripheral band (4) comprises an upper flange (5). The radiant burner further comprises an insulation (7) lying under and extending downwardly from said upper flange of said peripheral band. The insulation (7) has an internal peripheral structure permitting limited movement of the layers of radiant screens (3). The insulation is a multilayer structure wherein each insulation layer engages and supports at least one screenlayer (3).

Description

TECHNICAL FIELD

The present invention relates to radiant burners comprising a radiant plate and a screen.

BACKGROUND ART

Radiant burners comprising a radiant plate and a screen are known e.g. from U.S. Pat. No. 4,799,879 or EP0539279. The screen together with the radiant burner plate provides the radiative output of the burner, which amounts up to about 50% efficiency. In the past the radiative output of the burners has been increased by modification of the radiant burner plate as described in e.g. U.S. Pat. No. 4,569,657 or U.S. Pat. No. 4,799,879. This or similar modifications of the radiant burner plate increased the temperature level and consequently also the radiative output of the burner. Another way to increase the radiative output of the burners was proposed by using two layers of screens as e.g. in U.S. Pat. No. 3,847,536. Here the radiant screens are kept in place by metal means. These metal connections cause thermal bridges and thermal losses, causing thermal stresses and thereby early emitter failure.

DISCLOSURE OF INVENTION

The object of the present invention is to provide a new radiant burner which combines the advantage of using two layers of radiant screens with limiting the lateral heat losses through the thermal bridges, thereby providing a radiant burner wherein the thermal energy is concentrated on the inside of the combustion chamber which results in a greater amount of energy radiated at the front of the radiant burner.

An aspect of the claimed invention provides a radiant burner which comprises at least one radiant burner plate and at least two layers of radiant screens enclosed by a peripheral band associated with a body defining a premixing chamber for said burner. The peripheral band comprises an upper flange. The radiant burner further comprises an insulation lying under and extending downwardly from said upper flange of said peripheral band. The insulation has an internal peripheral structure permitting limited movement of the layers of screens. The insulation is a multilayer structure wherein each layer engages and supports at least one screenlayer. This provides an insulation which enables the different screenlayers to expand freely in the radiant burner and at the same time provides the fact that the insulation is a multipiece, multilayered structure, and preferably that each layer is insulating one screenlayer, that the different levels can expand freely with respect to one another as the different levels are subjected to different expansions due to their distance to the radiant burner surface of the radiant burner plate. A further advantage of this multilayer insulation is an easier assembly of the radiant burner, a simplified production. Moreover, if one layer of the insulation is broken, other insulation layers will keep the broken part in place and the radiant burner can stay in operation.

Preferably, the insulation is made of ceramic, e.g. cordierite or zirconia; partially stabilised zirconia (PSZ), alumina, silicon carbides or other high level technical ceramics. The ceramic insulation layer is obtained by extruding ceramic material, it is preferable to mold them when aiming at more complex ceramic insulation layers.

The insulation has an equal thickness in the complete depth of the radiant burner. In an alternative embodiment, the insulation is thicker at the level of the radiant burner plate(s) and obliquely narrows down to smaller thickness. In another alternative embodiment, the insulation narrows gradually from the radiant burner plate(s) upto the upper flange of the peripheral band. These alternative embodiments provide as an extra advantage that a better insulation is obtained on the closer to the radiant burner plate lying screenlayers which are also at higher temperatures and require a thicker insulation. At the same time is this narrowing insulation (away from the radiant burner plate(s)) also provides more free radiant surface to the outside.

The different layers of the insulation all have the same depth. In an alternative embodiment, the different layers of the insulation have a gradually or obliquely lowering depth from the radiant burner plate upto the upper flange of the peripheral band. In another alternative embodiment, insulation layers with same depth are combined with insulation layers with differing depth.

In another preferred embodiment, the insulation is also enclosing the radiant burner plate(s).

In a preferred embodiment, the surfaces of the insulation layers wich are in contact with the other layers of the insulation (which will be called further on “contacting surfaces”) are very smooth. Allowing a tension free movement of the contacting surfaces with respect to one another. In another preferred embodiment, each insulating layer comprises one smooth contacting surface and one profiled contacting surface. This provides as further advantage that the contact surface of these contacting surfaces is lowered to the surface of these profiles. Whereas the smooth and flat surface of the neighbouring insulation layer still provides a tension free movement of the contacting surfaces with respect to one another. Preferably, the profiles on one of the contacting surfaces of the insulation layer are ribs. More preferably, these profiles ribs are parallel to the peripheral band, in an alternative preferable embodiment, these ribs are in zig-zag or sinuous form and parallel to the peripheral band.

It is self evident that the succession of profiled surface and flat, smooth surface can also be used in one insulation layer wherein this insulation layer is construed of multiple building blocks.

Preferably, the radiant screens are produced from highly heat resistant materials such as ceramics, especially aluminium or zirconium oxide, aluminium titanate, silicon oxide, corundum or mullite, silicon carbide, silicon nitride or metal infiltrated ceramics, such as silicon-infiltrated silicon carbide. Alternatively, the radiant screens can also be fabricated from heat-resistant materials of other nature such as e.g. materials which contain more than 50% by weight of a metal silicide, such as molybdenum disilicide (MoSi₂) or tungsten disilicide (WSi₂). Alternatively the radiant screens are fabricated from highly heat resistant steel grades, such as high level stainless steel grades like Kanthal APM or APMT, different grades of FeCrAl alloy designed for high temperature corrosion, Chrome/Nickel steel grades like Avesta 253 MA, 153 MA, Inconel 601, Incoloy 800HT, Incoloy MA956.

In a preferred embodiment, at least one of the screenlayers is a metal grid, preferably woven. In an alternative preferred embodiment, at least one of the screenlayers is made of an arrangement of parallel spaced round rods or square bars. In a further preferred embodiment, the different screenlayers are arranged in the same direction and parallel with respect to one another. In an alternative preferred embodiment, the different screenlayers are arranged in shifted angles, but parallel, with respect to one another. More preferably, the first and second radiant screens are at a 90° angle.

The radiant burner plate is preferably made of a ceramic material with high temperature resistance, and excellent mechanical and thermodynamic properties such as e.g. cordierite or zirconia; partially stabilised zirconia (PSZ), alumina, silicon carbides or other high level technical ceramics.

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

Example embodiments of the invention are described hereinafter with reference to the accompanying drawings in which

FIG. 1 shows a cross section through an example radiant burner which comprises 2 screenlayers.

FIG. 2 shows a cross section through an alternative example radiant burner which comprises 2 screenlayers.

FIG. 3 shows a cross sectional view of another embodiment of insulation of the present invention.

FIG. 4 shows a cross sectional view of another embodiment of insulation of the present invention.

FIG. 5 shows a cross sectional view of another embodiment of insulation of the present invention.

FIGS. 6 and 7 show a cross sectional view of further alternative embodiments of insulation layer of the present invention.

FIGS. 8 to 10 show cross sectional views of differing embodiments of insulation layer of the present invention.

FIGS. 11 shows a perspective view of an exemplary preferred embodiment of insulation layer of the present invention.

FIG. 12 shows a cross sectional view of a stack of two insulating layers according to a preferred embodiment.

FIGS. 13 and 14 show perspective views of further alternative embodiments of insulation layer of the present invention.

MODE(S) FOR CARRYING OUT THE INVENTION

As shown in FIG. 1 the radiant burner 1 according to the invention comprises at least one radiant burner plate 2 and, in this example, two layers of radiant screens 3 enclosed by a peripheral band 4 associated with a body 6 defining a premixing chamber for said burner. The peripheral band comprises an upper flange 5. The radiant burner further comprises an insulation 7 lying under and extending downwardly from said upper flange 5 of said peripheral band 4. The insulation 7 has an internal peripheral structure permitting limited movement of the layers of screens 3. The insulation 7 is a multilayer structure wherein each layer engages and supports at least one screenlayer. This provides an insulation 7 which enables the different screenlayers 3 to expand freely in the radiant burner and at the same time provides the fact that the insulation is a multipiece, multilayered structure, and preferably that each layer is insulating one screenlayer, that the different levels can expand freely with respect to one another as the different levels are subjected to different expansions due to their distance to the radiant burner surface of the radiant burner plate. In this example, the insulation has an equal thickness over the complete depth of the combustion chamber. The depth of both insulation layers are equal although the distribution of the internal peripheral structure permitting movement of the screenlayers varies, in this example the upper screenlayer, being a metal mesh, is placed in the middle of the upper insulation layer, whereas the lower screenlayer, being round rods, is placed in the upper part of the insulation layer.

The illustrated example of FIG. 2 comprises an alternative insulation according to the present invention. In this example the insulation has an obliquely increasing thickness starting under said upper flange and extending downwardly to said radiant burner plate(s). In FIG. 3 the insulation has a gradually increasing thickness. The screenlayers in the exemplary embodiment of FIG. 2 are both arrangements of parallel spaced round rods which are arranged parallel to one another, but are shifted in a 90° angle with respect to one another.

FIGS. 4 and 5 show some examples of insulation layer stacks according to the present invention. FIG. 4 shows an insulation stack wherein the different insulation layers have the same depth. FIG. 5 shows an insulation stack wherein the different insulation layers have the same and differing depths.

FIGS. 6 and 7 show some examples of alternative insulation layers which are mainly used on the top of such an insulation stack.

FIGS. 8, 9 and 10 show alternative embodiments of insulation layers in cross section.

FIGS. 11 shows a perspective view of a exemplary preferred embodiment of insulation layer of the present invention. The insulation layer of FIG. 11 has ribs protruding the upper contacting surface of the insulation layer, these ribs are parallel to the peripheral band.

FIG. 12 shows a cross sectional view of a stack of two insulating layers according to a preferred embodiment, wherein the lower insulation layer is according to FIG. 11.

FIGS. 13 and 14 show perspective views of further alternative embodiments of insulation layer of the present invention. The insulation layer of FIG. 13 has zig-zag patterned ribs protruding one contact surface. In FIG. 14 the ribs are in sinuous form and substantially parallel to the peripheral band.

Thus there has been described a radiant burner which comprises at least one radiant burner plate and at least two layers of radiant screens enclosed by a peripheral band associated with a body defining a premixing chamber for said burner. The peripheral band comprises an upper flange. The radiant burner further comprises an insulation lying under and extending downwardly from said upper flange of said peripheral band. The insulation has an internal peripheral structure permitting limited movement of the layers of screens. The insulation is a multilayer structure wherein each insulation layer engages and supports at least one screenlayer.

Claims

1. A radiant burner (1) comprising at least one radiant burner plate (2) and at least two layers of screens (3) enclosed by a peripheral band (4) associated with a body (6) defining a premixing chamber for said burner, said peripheral band comprising an upper flange (5), said burner further comprising an insulation (7) lying under and extending downwardly from said upper flange of said peripheral band, said insulation (7) having an internal peripheral structure permitting limited movement of said radiant screens (3), characterised in that said insulation (7) is a multilayer insulation structure comprising more than one insulation layer, each insulation layer engaging and supporting at least one screenlayer (3).

2. A radiant burner according to claim 1, wherein said insulation (7) has an increasing thickness starting under said upper flange (5) and extending downwardly to said radiant burner plate(s) (2).

3. A radiant burner according to claim 1, wherein said insulation layer having at least two contacting surfaces which could provide contact with a neighbouring insulation layer, characterised in that one contacting surface has at least one flat surface and at least another profiled contacting surface.

4. A radiant burner according to claim 1, wherein at least one of said radiant screenlayers is a metal grid.

5. A radiant burner according to claim 1, wherein at least one of said radiant screenlayers is an arrangement of parallel spaced round rods or square bars.

6. A radiant burner according to claim 1, wherein at least two of said radiant screenlayers are an arrangement of parallel spaced round rods or square bars.

7. A radiant burner according to claim 6, wherein said radiant screenlayers, which are an arrangement of parallel spaced round rods or square bars are in parallel directions.

8. A radiant burner according to claim 6, wherein said radiant screenlayers, which are an arrangement of parallel spaced round rods or square bars are in crossing directions, preferably at 90°.

9. A radiant burner according to claim 1, wherein said multilayer insulation structure is made of ceramic material.