AU534443B2 - Non-warping radiant burner construction - Google Patents

Description

NON-WARPING RADIANT BURNER CONSTRUCTION

BACKGROUND OF THE INVENTION

The present invention relates to infrared radiant gas burners or heaters of the type shown and described in U.S. Patents Nos. 3,785,763; 3,824,064; and 4,035,132.

In this type of burner, the gas-air combustion mix¬ ture is blown through a porous refractory board or matrix and caused to burn very efficiently at the outside or burning face of that matrix. The matrix is held on the frame of a burner box by a metal retaining rim extending around the periphery of the outside or burning face of the matrix. The temperatures reached at the burning face of such burners are in the order of 1600 F. (870 C.) or more, which means that the metal frame of the burner box and the matrix retain¬ ing rim reach comparable temperatures and are subject to severe distortion from such heat. Any distortion or warping of the frame of the burner box in turn affects the plane burning face of the matrix and the seals around the edges of the matrix, with the result that combustion takes place at seal leaks and burns out the burner, or combustion is not even across the face of the burner and the infrared radiation or heating effect is uneven. Whenever any of these events occur, the burner must be replaced.

One of the principal uses of these types of burners at this time is in textile mills where they are used to dry moving webs of fabric as the webs emerge from tanks of liquid dyes, sizings, or the like. The burner matrix is faced ver¬ tically, parallel to, and about eight inches away from, the moving fabric web. One of the known advantages of this type of burner is that it heats evenly and, when combustion ceases, cools off rapidly. In textile mill applications of the type described, it can readily be seen that any warping of the burner box frame causing unevenness in the matrix face plane with a resultant unevenness in heating effect cannot be tolerated.

SUMMARY OF THE INVENTION

In the present invention, the edges of the matrix are beveled and the matrix is retained on the burner box frame edge shelf by a wedge of refractory material in combi¬ nation with spaced holding clips and high temperature sealant-adhesive. The beveled edges of the matrix are coated and sealed with refractory material so that cooling air, which is blown through such refractory material wedge, does not interfere with combustion.

The objects of the present invention are to provide a radiant gas burner in which there is minimal distortion of the burner box frame from the heat of combustion, in which there is suitable edge air cooling of the burner box frame without interference with combustion at the burner face, and in which there is steady and even combustion across the plane burning face of the matrix.

BRIEF DESCRIPTION OF THE DRAWING These and other objects of the invention will be understood from the description in the specification and dis¬ closure of the drawings, in which:

O FIG. 1. is a perspective view of a burner box, with the matrix mounted therein in accordance with the present invention. In this instance, the matrix is in a vertical plane.

FIG. 2 is a sectional view of the burner of FIG. 1, taken through line 2-2.

FIG. 3 is an enlarged section of the edge of the matrix and burner box frame, taken through line 2-2.

FIG. 4 is an enlarged section of the edge of the matrix and burner box frame, taken through line 4-4 at the matrix retaining clip.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The general construction of burners of the present invention is illustrated in FIGS. 1 and 2, and comprises a rectangular burner box 1 which supports a porous, gas- permeable, refractory board panel or matrix 2 having an inner face, outer face, and peripheral edge separating the faces. A combustible gas-air mixture enters into the back of the burner box through an inlet pipe nipple 3 and blows against a baffle 4 inside the burner box so as to be distributed evenly under pressure throughout a combustion mixture plenum chamber 5. The combustion mixture plenum chamber 5 is defined by the matrix inner face and an inner box 6 which is welded to a number of spaced support brackets 7, which, in turn, are welded to the sides and ends of an outer cooling air box 8. The inner box and outer box together make up the burner box with an open end to receive the matrix 2. The inner box is nested within the outer box and is generally equidistantly spaced from the sidewalls of the outer box, with the open ends of the boxes opening outwardly in the same direction, the open end of the inner box defining the combustion mixture plenum chamber being closed by the matrix.

A shelf or flat ledge portion 9 about the open-end periphery of the inner box 6 supports and abuts the edge area of the matrix 2. This shelf or ledge 9 is preferably dis¬ posed inwardly from the outer burning surface of the matrix a distance which approximates the thickness of the matrix.

A cooling air plenum chamber 10 is defined by the space between the inner box 6 and outer box 8, and is sup¬ plied with cooling air by an inlet pipe nipple 11 at the back of the burner box.

The gas-air combustion mixture is under a pressure in the plenum chamber 5 of from about 3-1/2 to 8 inches (8.9-20.3 cm.) water column pressure from a blower or other supply means, as is well known in the art. The cooling air is under a pressure in its plenum chamber 16 of about 3 to 8 inches (7.6-20.3 cm.) of water column pressure, likewise from a blower or other supply means, as is well known in the art. The pressures of both the supply of the combustion mixture and the cooling air should be constant and accurately con¬ trolled and adjusted.

The matrix 2 is a porous refractory ceramic fiber- board, preferably made of type 130 Cera Form board, manufac¬ tured by Johns-Manville Company. The matrix is a single uni¬ tary board of substantially equal porosity throughout so that it burns and heats equally. The boards are manufactured from Cera Form refractory fibers and a multicomponent binder sys¬ tem which burns out at approximately 500° F. (260° C.) The composition of the Cera Form type 130 board is approxi¬ mately 36% alumina, 54% silica, and 3.5% chromic oxide. The specified density is 13.5 pounds per cubic foot and the spe¬ cified thermal conductivity is from .28 Btu/in., hr., sq. ft. at 400° F. (204° C.) to 1.98 at 2000°F (1093° C). The boards lose around one-third of their strength when the binder is burned out. One face is sanded and that, prefer¬ ably, is the outward or burning face at which combustion takes place. The boards are preferably from about 1 inch to about 1-1/2 or 2 inches (2.54-5.0 cm.) thick.

The matrix 2 should have good insulative properties so that heat from the burning surface is not conducted back into the combustion mixture chamber 5. Actual combustion takes place at or within about 1/8 inch (.32 cm.) inwardly of the outside burning surface. The porosity of the matrix is generally equal throughout to fully homogenize the combustion mixture. The pressure of the combustion mixture has to be adjusted to the porosity of the matrix. Preferably, the air for both the combustion mixture and cooling is filtered before introduction into the burner.

An important feature of the present invention is that there is no metal retaining rim or frame member as in the burners of patents 3,824,064 (the retaining rim 18) or 4,035,132 (upper frame members 21, 22, 23, and 24). This, in turn, means that there is no heat absorbing metal part adja¬ cent to the edge of the burning surface of the matrix to con¬ duct heat into the burner box and cause it to warp and other¬ wise distort as it is heated and cooled in the normal opera¬ tive cycle.

When a burner operates in a vertical position, as shown in FIG. 1, the distortion at the top edge of the burner box tends to be greatest because the flame rises against it and heats that area much more than the bottom area.

In accordance with the present invention, the edges of the matrix 2 are beveled at an angle of from about 10 up to 25 from the plane of the matrix as shown in FIGS. 3 and 4. In other words, when disposed on the shelf 9 around the edges of the inner box, the beveled edge makes an angle of from 65 to 80 with the plane of the shelf edge por¬ tion 9, whereby the planar area of the outside burning sur¬ face is less than the planar area of the opposed non-burning surface of the matrix 2. The beveling operation may be done with a saw or very sharp knife.

The -beveled edge is then treated with suitable seal¬ ers and rigidizing materials which are refractory in nature or at least have high heat resistance so that a permanent gas-impermeable seal or barrier against passage of the com¬ bustion mixture is made. The matrix is next sealed and adhered to the shelf or flange support 9 formed by the pe¬ ripheral portions of the inner box with suitable rubbery sealing and adhesive material. Metal clip means 13 (FIG. 4) -are then inserted in the generally continuous channel 14 formed between the matrix edge and the outer box sides and ends, as shown in FIG. 4, and held in place with sheet metal screws 15 or other suitable fastening means. The clip angle corresponds to the bevel angle and otherwise fits the channel 14 formed between the edge of the matrix 2 and the sidewalls of the outer box 8.

Finally, a retaining means in the preferred form of packing 16 of resilient, porous, refractory material is placed inside the channel 14 and tamped or pressed therein to also help retain the matrix 2 in place on the shelf-edge por¬ tion 9. The packing 16 engages and interfaces with the pe¬ ripheral edge of the matrix which is spaced from the side- walls of the outer box 8, and overlaps at least a portion of the peripheral edge wherein such portion is sandwiched between the inner box shelf or flange support 9 and the pack¬ ing 16. The packing extends between the matrix peripheral edge and the sidewalls of the outer box. If desired, the pieces of Cera Form removed from the matrix in the beveling operation may be used as the packing material 16.

Alternatively, a refractory fiber strip of higher densities, preferably at least about 8 lbs. (3.63 kg.) per cu. ft., may be used, such as Kaowool, manufactured by the Babcock & Wilcox Company, or Fiberfrax, manufactured by the Carborundum Company. Both Kaowool and Fiberfrax are alumina-silica fibrous refractory materials. These materials should be tamped or packed into,the channel 14 and preferably coated with a colloidal silica rigidizer such as Ludox HS-40, manufactured by E. I. DuPont de Nemours & Company. Since the burner box 1 is alternately heated and cooled as the burner is ignited and turned off, there is cyclical expansion and contraction in operation of the burner and the packing 16 for the matrix 2 should have sufficient resiliency to adjust to these conditions. A turned edge 17 of the outer box helps to keep the refractory packing in position. The minimum straight-line distance along the sidewall of the outer box between the turned edge 17 and the shelf 9 is less than the thickness of the matrix, preferably by about 1/8 inch (.32 cm.), wherein the burning surface of the matrix is spaced outwardly away from and set off from the edge 17 to lessen its radiant heating by the burning surface of the matrix 2.

The matrix is thus held and positioned on the shelf 9 by retaining means which comprise a combination of clip 13, sheet metal screw 15, shelf seal and adhesive 12, packing 16, and turned edge 17. There is thus no heat absorbing metal or other heat absorbing material adjacent the edge of the outer or burning surface of the matrix.

OMPI The cooling air 18 from the chamber 10 flows through a slot opening or passageway 19 formed between the outer edge 20 (FIG. 3) of the inner box 10 and the sidewalls of the outer box 8 and into the channel 14 through the porous pack¬ ing 16 and is exhausted out, as shown by the arrows in FIG. 3. Air flow through the passageway is necessarily restricted by the packing wherein the restricted and diffused air flow¬ ing through the packing advantageously absorbs heat to pro¬ vide cooling at the matrix edge by carrying heat away from the adjacent packing. The only interruptions to this air flow are the spacers or brackets 7 and clips 13, which inter¬ fere with the passage of cooling air to the extent of their widths. In a typical burner construction, the spacers 11 might be 1 to 1-1/2 or 2 inches (2.54-5 cm.) wide and the clips less than the widths or the spacers 11, and these obstuctions are therefore of no significance.

The beveled edge of the matrix 2 is treated for the purpose of creating a gas-impermeable barrier or seal inter¬ face between the packing and the matrix edge which separates the cooling air from the burning surface and prevents the combustible mixture from penetrating through or around it and burning somewhere other than the outside or burning surface of the matrix 2, for instance, at the shelf 9 or in the chan¬ nel 14. The treatment comprises first impregnating the beveled edge with a refractory sealing and penetrating silica compound, such as Ludox HS-40, manufactured by E. I. DuPont de Nemours & Co. Ludox HS-40 is an aqueous colloidal silica dispersion of discrete particles of surface-hydroxylated silica, alkali stabilized.

The silica penetrates the edge portions of the matrix. Two or more coats may be applied with suitable dry¬ ing in between. Over the silica, it is advisable to apply a mixture of about equal parts of alumina-silicate refractory cement, such as Whiteline'cement, manufactured by Fireline, Inc. of Youngstown, Ohio, and colloidal silica. Whiteline cement is an alumina-silicate mixed with about 50% colloidal silica. The Whiteline cement/Ludox mixture stiffens the matrix edge and may also be used to help bond it to the packing wedge 16. The Whiteline cement/Ludox mixture is also preferably applied to the surfaces of the packing wedge 16 prior to inserting it in the channel 14.

As will be apparent to those skilled in the art, other refractory sealers and bonding materials may be used for these purposes, such as agnesite (MgO) , forsterite (MgO-Si0₂) t burned dolomite (CaO-MgO) , and alumina (A1₂0₃). We prefer materials which do not crack or spall and are resistant to thermal shock. Kaowool surface coating cement, manufactured by the Babcock & Wilcox Company, may be used on the beveled edge over a Ludox HS-40 coating layer.

The Ludox HS-40 colloidal silica sealer should also preferably be applied to the inner surface of the matrix where it is to be cemented to the shelf 9. The cement for that purpose may be a rubbery, high-temperature-resistant silicone cement such as Dow Corning clear silicone, Catalogue Number 732-CL 111. The contact between the shelf and inside edge of the matrix, that is, the inside surface of the matrix which is opposite to the outer burning surface, in normal operation, is not heated to such an extent that a refractory-type cement is needed. If in use it is discovered that the temperatures are too high for the silicone cement, then a refractory cement may be used. The rubbery silicone cement has a greater holding power than a refractory cement and that is why we prefer it^" in this circumstance. One advantage of the structure of the present inven¬ tion is that the matrix may be replaced should it lose its shape or be damaged. We contemplate that the matrix need not be a flat board but could be a hat or other non-planar shaped matrix.

This invention is not restricted to the slavish limitation of each and every one of the details described above by way of example. Obviously, devices may be made which change, eliminate, or add specific details but which do not depart from our invention.

Claims (7)

WHAT IS CLAIMED IS:

1. A radiant burner comprising an inner box which has a shelf around its edges, an outer box, a refractory fiberboard matrix, porous resilient refractory means to retain the edge portions of the matrix on the inner box shelf, the insi-de of the inner box and the matrix defining the plenum chamber for the combustion mixture, the outside of the inner box and the inside of the outer box defining the plenum chamber for the cooling air, the inner box and outer box together forming the burner box for the burner, means to supply a combustion mixture and cooling air respectively to the combustion plenum chamber and cooling air plenum chamber, slot openings between the edges of the inner box and the sides of the outer box for the passage of cooling air through said porous refractory means, and a refractory sealant on the edges of the matrix to seal against the combustion mixture, the said sealed edges being inwardly disposed from said porous refractory means, whereby the combustion mixture burns in the outside surface of the matrix inwardly from the sealed edges, and there is no heat absorbing structure to retain the matrix in the burner box.

2. A radiant burner comprising an inner box, an outer box, and a porous refractory board matrix mounted on a shelf which is integral with the inner box around the edges of the matrix, porous resilient refractory material which helps to hold the matrix on said shelf disposed between the edges of the matrix and the sides of the outer box, and metal clip means which help to hold the matrix on said shelf dis¬ posed between the edges of the matrix and the sides of the outer box, the inside of the inner box and the matrix defin¬ ing the plenum chamber for the combustion mixture, the (claim 2 continued) outside of the inner box and the inside of the outer box defining the plenum chamber for the cooling air, the inner box being supported on brackets integral with the outer box to provide openings for the passage of cooling air from the cooling air plenum chamber through the porous refractory material, the edges of the matrix being sealed to the sup¬ porting shelf and being refractorily sealed against the combustion mixture.

3. A burner having a porous refractory fiber matrix which covers a combustion mixture plenum chamber, means for introducing the combustion mixture into the. lenum chamber so that the mixture flows through the matrix and burns at its outer surface, an inner box the inside of which with the matrix defines the combustion mixture plenum chamber, means for introducing a separate stream of cooling air into a cool¬ ing air plenum chamber, an outer box, the inside of the outer box and the outside of the inner box defining the cooling air plenum chamber, the inner box and outer box together forming the burner box, means to mount the inner box inside of the outer box, a shelf disposed around the edges of the inner box inwardly to receive the edges of the matrix, refractory seal¬ ing material around the edges of the matrix, porous resilient refractory fiber material around the edges of the matrix to help hold it on said shelf, openings from said cooling air plenum chamber into said porous resilient refractory fiber material to permit cooling air to flow through said material adjacent the edges of the burner box to cool the same, and additional means to help hold said matrix on said shelf.

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4. A burner comprising a burner box with an open face and a porous refractory fiber matrix disposed on said face which covers a combustion mixture plenum chamber, means for introducing the combustion mixture into said plenum cham¬ ber so that the mixture flows through the matrix and burns at its outer surface, an inner box, the inside of which defines, with the matrix, the combustion mixture plenum chamber, means for introducing a separate stream of cooling air into a cool¬ ing air plenum chamber, an outer box, the inside of the outer box and the outside of the inner box defining the cooling air plenum chamber and the inner box and outer box together form¬ ing the burner box, means to mount the inner box inside of the outer box, a shelf which is an integral portion of the inner box and is formed around the edges of the inner box a distance inwardly from the outer surface of the matrix approximately equivalent to the thickness of the matrix, the edges of the matrix being beveled at an angle of from 65 to 90 degrees from the plane of the shelf, and being sealed against the combustion mixture with a refractory sealant, retaining metal clip means to help hold said matrix on said sftelf, porous resilient refractory fiber material mounted between said beveled edges and the sides of the burner box, a sealant and adhesive on said shelf to seal and adhere the matrix edges to it and prevent the passage of any combustion mixture therethrough, and slot openings around the edges of said outer box to permit the passage of cooling air there¬ through from said cooling air plenum chamber into said porous resilient refractory fiber material to cool the edges of the burner box.

5. A gas-fired radiant burner comprising an outer box having sidewalls and at least one open end, an inner box nested within and generally equidistantly spaced from the sidewalls of the outer box, the inner box having at least one open end, the open ends of the inner and outer boxes opening outwardly in the same direction wherein a generally contin¬ uous channel is formed between the boxes at their open ends, a gas-permeable refractory fiberboard unitary matrix closing the open end of the inner box, the peripheral edge of the matrix being spaced from the sidewalls of the outer box, a porous resilient refractory packing press-fitted into the channel, the packing extending between the peripheral edge of the matrix and the sidewalls of the outer box, the r-efractory packing engaging and overlapping at least a portion of the peripiheral edge of the matrix to hold the matrix in position against the open end of the inner box, the refractory packing extending around the matrix and substantially closing the channel, means for supplying a combustion mixture to pressur¬ ize the inner box wherein the mixture is exhausted through the matrix for burning at the outer surface thereof, and -means for supplying a non-combustible pressurized cooling gas to the outer box wherein the cooling gas is exhausted and diffused through the porous refractory packing to provide cooling to the peripheral edge of the matrix.

6. A burner according to claim 5, including a gas- impermeable seal located at the interface area between the refractory packing and the peripheral edge of the matrix, the seal establishing a barrier to the passage of the combustion mixture from the matrix peripheral edge to the porous refrac¬ tory packing.

7. A gas-fired radiant burner comprising a gas- permeable matrix of refractory fiber material providing a generally equal degree of porosity throughout, the matrix having an inner face, outer face, and gas non-permeable peripheral edge area separating the faces, plenum means sealed against the inner face of the matrix to supply a pres¬ surized combustible gas thereto for burning at the outer face of the gas-permeable matrix, a porous gas-permeable refrac¬ tory packing fixed relative to the plenum means and engaging the peripheral edge area of the matrix, at least a portion of the peripheral edge area of the matrix being sandwiched between the plenum means and the packing wherein the packing retains the matrix to maintain it in sealing engagement with the plenum means against the force of the pressurized combus¬ tible gas supplied to the inner face of the matrix, and sup¬ ply means providing pressurized non-combustible cooling gas to the refractory packing, the cooling gas flowing and dif¬ fusing generally throughout the packing to carry heat away from the packing.