TECHNICAL FIELD

The invention relates to a liner device for mounting between a burner box and a tube interface plate of a furnace, to a furnace including such a liner device, and to a method of manufacturing such a liner device.

BACKGROUND ART

Hot air furnaces are a common component of many commercial and residential heating, ventilation, and air conditioning (HVAC) systems. Such furnaces typically include at least one burner for combusting a liquid or gaseous hydrocarbon fuel, such as natural gas. The burner in such a system is typically located external to a set of heat exchanger (HE) tubes, and receives a flow of fuel from a fuel source. An ignition source inside the burner ignites the fuel, to create a flame and hot flue gasses that project from the combustion region into the HE tubes. The hot flue gasses flowing inside the HE tubes, transfer their thermal energy via the walls of the HE tubes to a flow of air that is conveyed along outer surfaces of the HE tubes.

A known type of furnace burner is a “premix burner”, in which fuel and air are mixed inside a burner inlet valve, before being injected into a combustion zone where an ignition source ignites the mixture. Premix burners typically emit lower levels of nitrogen oxides (NOx), compared to inshot burners that do not have such an air-premixing stage. Pre-mix burners are preferred to be used in heating systems, particularly in those countries in which stricter regulations on NOx emissions apply.

Patent document US 2019/0101282 A1 describes a known pre-mix type burner box assembly for a furnace burner, which forms part of a HVAC system. This assembly includes a heat-resistant liner, which lines an interior of an outer cover that defines a box-shaped recess with apertures. This cover forms an interface structure between an array of HE tubes mounted on one side, and the burner box mounted on an opposite side. This liner is composed of panel members, which are formed into a box-shaped structure with an open rear face that is exposed to the flames inside the pre-mix burner, and which are made of heat-resistant material such as nickel/chromium alloy or ceramic wafer board. The liner additionally includes tubular members, designed to be placed through the apertures of the outer cover in order to line the HE tubes on their inner sides. This known liner is said to reduce peak temperatures and formation of hot spots within the burner box assembly.

However, US2019/0101282 fails to reveal details on how the various parts of this known liner have to be constructed, in order to ensure that peak temperatures and hot spots are indeed avoided and that this liner has good mechanical and thermal insulation properties.

It would be desirable to provide a liner device for a furnace, which is easy to manufacture yet retains its mechanical robustness and heat insulating properties when subjected to harsh high-temperature conditions inside the furnace for prolonged times.

SUMMARY OF INVENTION

Therefore, according to a first aspect of the invention, there is provided a liner device that is adapted to be mounted between a burner box and a tube interface plate of a furnace. The liner device includes a base section, at least one tube section, and one or more angle fasteners. The base section includes a shielding layer formed from a first flexible mesh of flame-resistant fibers. This shielding layer defines a first surface that is configured to face the burner box, a second surface opposite to the first surface, and a medial region with a through-hole forming a passageway through the shielding layer. The tube section consists essentially of a second flexible mesh of flame-resistant fibers formed into a tubular shape that defines an internal channel around a nominal axis. The tube section is positioned with its proximal end at the base section, such that the channel opens into the through-hole and that the tube section projects from the second surface and in a direction faced by the second surface. The angle fastener has a base portion that is positioned along and fixed to the second surface of the shielding layer. The angle fastener further has a leg portion that projects towards the second direction, and which is positioned along and is fixed to an outer surface of the tube section at or near the proximal end thereof.

This angle fastener forms a structure that is distinct from the tube and base sections. By not forming the fastener as a continuation of the materials from which the tube and base sections are made, the probability of exerting local stress onto the tube or base sections when the fastener is folded and attached—which may cause the tube and base sections to warp and/or misalign during manufacturing—is reduced. The separate angle fastener on the rear side of the base section and on the outer lateral side of the tube section provides a reliable mechanical interconnection between these sections, while the base section and tube section(s) shield the angle fastener from direct exposure to flames and excessive heat during furnace operation. This yield a robust liner device with good thermal insulation properties, which is flexible and easy to install and replace.

In this context, the term “mesh” is used to refer to a network of interconnected strands/wires. On a macroscopic scale, this network extends as a surface contour in three dimensions, for instance as a planar surface or as a more complex folded/curved surface structure. The strands/wires may be formed by continuous fibers (i.e. mono-filament), by continuous yarns (i.e. intertwined fibers), or by continuous twines (i.e. intertwined yarns or bundles of fibers) made of such fibers. These strands/wires are arranged in a periodic and structured orientation relative to each other, while extending with their elongated direction predominantly along the direction of the mesh surface. The strands/wires may be interconnected in a rigid manner (e.g. by intersecting in preformed single body node points, or by welding/adhering to each other), or in a loose indirect manner (e.g. by abutting each other at crossing points, while allowing for some relative sliding motion). The mesh strands/wires may be arranged closely together in a tightly packed manner i.e. without defining openings in-between the strands/wires, or may be arranged further apart so that openings are defined in-between the strands/wires.

In this context, the phrase “flame resistant material” is used herein to refer to materials (e.g. fabrics) that consist entirely or predominantly of materials that are inherently non-flammable i.e. which, when in close proximity to flames inside a furnace, will not melt, combust, or fracture, and will not burn or only burn to such minor extent that the material is able to extinguish the burning by itself. A “flame resistant object” can be entirely made of flame resistant material, or partially made of flame resistant material and partially made of burnable material. When subjected to flames in a furnace, the burnable material will burn away, but the remaining structure defined by the flame resistant material will remain intact.

The base section (in particular the shielding layer) is preferably formed into a planar shape or a curved developable shape. This rest shape (i.e. in absence of net forces) substantially matches the local surface contours of the tube interface plate onto which the device is installed.

The fibers of the shielding layer are preferably interwoven to form a closed mesh, in order to prevent impinging combustion flames from passing through shielding layer. Alternatively, the shielding layer may be formed by an open mesh, although this leaves the subsequent layer(s) exposed to flames, and might render the shielding layer plastically stretchable along its plane.

In embodiments, the base portion of the angle fastener forms an integral part of an attachment layer that covers the second surface of the shielding layer along at least the medial region. This attachment layer includes a cutout having a shape that is circumscribed by the periphery of the through-hole. The cutout extends locally and radially inwards to define at least one tab, which forms the leg portion of the angle fastener when it is flexed towards the second direction.

A continuous attachment layer, forming a unitary base portion from which the one or more leg portions of the angle fastener(s) protrude, allows the angle fastener(s) to be quickly and accurately aligned with the shielding layer. In device embodiments with multiple tube sections, the base portions of angle fasteners for distinct tube sections may be in a contiguous arrangement and be connected together, so as to form a unitary attachment layer that extends across the entire base section.

In alternative embodiments, the angle fasteners may form unconnected and mutually separated units that are associated with individual tube sections. An angle fastener may for instance be formed as an annular patch with a single cutout that matches the through-hole, and with one or more tabs forming flexible leg portions as described above. Alternatively, the angle fastener may be shaped as an L-bracket, or as a flanged bush.

In further embodiments, the attachment layer defines at least three tabs that protrude from the edge of the through-hole. These tabs are arranged in an approximately regular angular distribution around the edge of the through-hole, forming leg portions of three respective angle fasteners associated with the same tube section.

Placing the three tabs in a regular distribution (i.e. in a mirror and/or rotationally symmetrical arrangement) around the through-hole yields good stability of the mechanical connection with minimal use of material. The three tabs may for instance be arranged in a 120°-degree rotationally symmetric manner around the through-hole. However, in device embodiments with multiple tube sections and through-holes close to each other, this symmetry may be slightly deviated from, by placing two of the tabs about 5°-20° closer to each other. This ensures that a staple/sewing device for fixing the tubes will not be obstructed by adjacent tube sections.

In embodiments, the attachment layer is formed by an open mesh or punched sheet. This open mesh or punched sheet has a low bending resistance against out-of-plane flexing, and a high shear resistance against in-plane deformation.

An open mesh or punched foil facilitates creating interconnections by sewing or stapling techniques, without having to align the attachment layer accurately with predetermined attachment points in the other layers.

In embodiments, the leg portion of the angle fastener is fixed to the outer surface of the tube section using flame-resistant staples or stitches made of flame-resistant yarn. Alternatively or in addition, the base portion of the angle fastener may be fixed to the second surface of the shielding layer using flame-resistant staples or stitches made of flame-resistant yarn.

Using flame-resistant stitches and/or staples for mechanically fixing the various parts together obviates the need for chemical bonding agents (e.g. adhesives), thus avoiding associated risks of chemical bond failure and pollution.

In embodiments, the shielding layer further defines a peripheral region that surrounds the medial region. The liner device may then further include an insulating layer that is fixed to and overlaps with the second surface of the shielding layer along at least the entire peripheral region. This insulating layer is compressible and is configured to form a gasket between the mounting flanges of the burner box and the interface plate of the furnace.

The provision of a compressible insulating layer along the peripheral region of shielding layer will reduce leakage of combustion gasses from the burner box, without having to install a separate gasket.

In further embodiments, the flexible and compressible material of the insulating layer consists essentially of thermally insulating mineral wool. The insulating layer defines a further through-hole and overlaps the second surface of the shielding layer along the medial region such that the through-hole and further through-hole align. The insulating layer also overlaps the base portion of the angle fastener, such that the shielding layer and the insulating layer enclose the base portion on opposite sides thereof.

The mineral wool layer extending across the peripheral and medial regions of the shielding layer improves the thermal insulation capability of the liner device, and forms a flow barrier along the engaged edges of the burner box and tube interface plate. Sandwiching the base portion(s) of the angle fastener(s) in-between the shielding and insulating layers restricts the ability of the angle fastener(s) to move in out-of-plane directions, thus preventing excessive displacement of the tube section(s) relative to the base section, when subjected to mechanical loads. Here, the term “mineral wool” may also cover materials obtained directly from such wool, for instance felt.

In yet further embodiments, a cross-sectional dimension of the through-hole in the shielding layer is smaller than a further cross-sectional dimension of the further through-hole in the insulating layer, so that an annular edge region of the shielding layer associated along the inner periphery is not covered by the insulating layer. An annular recess or void is formed in this part of the insulating layer that directly surrounds the outer surface of the tube section. This recess/void terminates on the base portion of the angle fastener and on the second surface of the shielding layer.

The annular recess in the base section and directly around the tube section allows a protruding edge of a heat exchanger conduit to be accommodated by the liner device, so as to prevent such a conduit edge from exerting compressive forces on the base section and/or shear forced on the angle fastener(s).

In device embodiments including an attachment layer in the base section, the liner device may further include a stitch connection that extends in a continuous path across the medial region and around the inner periphery of the base section. This stich connection passes repeatedly back-and-forth through the shielding layer and the attachment layer.

This stitch connection fixes the shielding and attachment layers together in regions where the angle fasteners reside, thus preventing excessive displacement of the angle fasteners and tube sections relative to the base section, when subjected to mechanical loads. In embodiments that also include the insulating layer, the stitch connection may also pass repeatedly through the insulating layer, to improve mechanical robustness and further immobilize the angle fasteners and tube sections.

In further embodiments, the liner device includes at least two tube sections, and the base section includes at least two corresponding through-holes. In this case, the continuous path of the stitch connection may be composed of concave path sub-sections that extend partially around respective through-holes. These path sub-sections are interconnected in series such that consecutive path sub-sections extend alternatingly along corresponding halves of the through-holes on opposite sides thereof, and such that the continuous path intersects itself in-between the through-holes.

This stitch connection extends in a continuous and self-intersecting path around all the tube sections, and terminates on its starting point. Such a closed self-intersecting pattern facilitates manufacturing by minimizing the efforts required for aligning the starting position of a sewing device with the base section and each of the tube sections.

In embodiments, the device includes a further stitch connection that extends in a continuous pattern along the peripheral region of the base section, thereby passing alternatingly and repeatedly through the shielding layer, through the insulating layer, and around an outer periphery of the base section.

The stitch connection along and through the outer periphery holds layers together, and simultaneously confines these layers from lateral directions ±X, ±Y in order to lower the probability that fiber filaments become separated from the base section52. This stitch connection preferably is applied along the entire periphery of the base section.

In embodiments, the tube section is formed by bending an initially planar sheet of flexible mesh of flame-resistant fibers around the nominal axis into a tubular shape, and by attaching two overlapping edges of the initially planar sheet to each other using staples or stiches.

The tube section(s) can be manufactured easily and reliably, by rolling up fiber mesh and sewing or stapling together the overlapping edges of this mesh. The tube section(s) may be made from the same fireproof mesh material as is used for forming the shielding layer.

In further embodiments, the liner device includes at least one further tube section with an associated nominal axis. Here, the nominal axes of the tube sections may be mutually parallel and may span a sagittal plane transverse to the base section, and the overlapping edge portions of the tube sheets may be at substantially identical orientations while facing transversely away from the sagittal plane.

In embodiments wherein the leg portion of the angle fastener is fixed to the outer surface of tube section using flame-resistant staples or stitches, these staples/stitches preferably extend through only a single layer of tube mesh sheet. The above-mentioned orientation of overlapping sheet edge portions creates asymmetry between the two sides of sagittal plane, while simultaneously ensuring that all flame-resistant staples or stitches remain accessible/visible along in-plane directions. The asymmetric geometry can be exploited to optimize the orientation of the device inside the furnace and relative to gravity, while the accessibility of the staples or stitches ensures that the sewing or stapling device used during manufacturing will not be obstructed when applying these staples/stitches.

In a second aspect, and in accordance with the advantages and effects described herein above, there is provided a furnace accommodating a liner device according to the first aspect. The furnace includes a heat exchanger housing, one or more conduits, an interface plate, a burner unit, and the liner device placed between the burner unit and the interface plate. The heat exchanger housing encloses a plenum, and is configured to allow a flow of gas to pass through the plenum. The burner unit is configured to receive and ignite a flammable fluid inside a burner chamber, in order to produce a flow of heated fluid. The one or more conduits are configured to receive the flow of heated fluid from the burner unit via inlets, and to convey the heated fluid through these conduits and through the plenum, while allowing heat from the heated fluid to be conducted through walls of the conduits, in order to transfer the heat to the gas in the plenum. The interface plate mechanically supports the at least one conduit on one side of the interface plate, and is configured to support the burner unit on an opposite side of the interface plate, so that the conduit and the burner unit are in fluid communication via the inlet. The base section of the liner device is placed on the opposite side of the interface plate, in-between the burner unit and the interface plate, with the first surface of the shielding layer facing the burner chamber and the second surface facing the interface plate. The tube section(s) of the liner device project away from the second surface, via the inlet, into the conduit(s). The base portions of the one or more angle fasteners are positioned along and fixed to the second surface, and the leg portions are positioned along and fixed at or near proximal tube end to the outer surface of the tube section, such that the base section and the tube section shield the angle fastener from the burner chamber.

According to a third aspect, with advantages and effects described herein above, there is provided a method of manufacturing a liner device according to the first aspect. The method includes:providing a shielding layer formed from a thin planar sheet that consists essentially of a flexible mesh of flame-resistant fibers, this layer defining first and second surfaces on opposite sides thereof;providing a through-hole that extends from the first surface to the second surface through the shielding layer, said hole being bounded by an inner circumference;providing a tube section consisting essentially of a flexible mesh of flame-resistant fibers formed into a tubular shape that defines a channel around a nominal axis;placing the tube section with a proximal end at the base section, so that the channel opens into the through-hole and that the tube section projects away from the second surface in a direction faced by the second surface;providing angle fasteners and fixing leg portions of said angle fasteners along an outer surface of the tube section, andfixing base portions of said angle fasteners along the second surface of the shielding layer.

In embodiments, the outer surface of the tube section has at the proximal end with a cross-sectional shape that is essentially identical to a cross-sectional dimension of the inner circumference of the through-hole in the shielding layer. The step of placing the tube section with its proximal end at the base section may then include:coaxially aligning the nominal axis of the tube section with a center of the through-hole, andsliding the tube section with its proximal end in the through-hole.

Snugly fitting the tube section with its proximal end in the through-hole of the shielding layer maximizes the available cross-sectional area for combustion flames to project into the tube section and heat exchanger conduit, and ensures that no openings are formed in-between the tube and base sections.

In embodiments, the tube section defines a distal end on a side opposite to the proximal end, and the base portions of the angle fasteners form an integral part of an attachment layer that covers the second surface of the shielding layer along at least the medial region thereof. This attachment layer may include a cutout that defines tabs extending locally and radially inwards relative to the periphery of the through-hole. In this case, the manufacturing method may further include:placing the shielding layer and the attachment layer in an abutting layered arrangement, so that the through-hole and cutout become aligned, thereby forming a base section;positioning the tube section on a side of the base section faced by the first surface, such that the nominal axis of the tube section aligns co-axially with the through-hole and the cutout, and such that the distal end is directed towards and located near the first surface;moving the tube section relative to the base section along an axial direction faced by the second surface, such that the distal end enters the through-hole and the cutout, and such that the tabs flex towards the axial direction;continue moving the tube section relative to the base section, through the through-hole and the cutout, and along the axial direction, until the proximal end of the tube section becomes level with the shielding layer, andfixing the tabs to the outer surface of the tube section near the proximal end, using staples or stitches.

This manufacturing procedure allows angle fasteners to be formed merely by cutting openings with tabs into a planar sheet, and allows these tabs to be placed automatically in the correct positions and orientation merely by sliding the tube section(s) from the first surface side into the hole(s) of the base section (or vice versa, for this motion between base section and tube section(s) should be understood to be relative).

In embodiments, the method further includes:providing an insulating layer with a further through-hole, the insulating layer consisting essentially of a flexible and compressible of sheet of thermally insulating wool or felt material;positioning the insulating layer in an abutting arrangement along a medial region of the shielding layer, so that the through-hole lines up with the further through-hole, and that the shielding layer and the insulating layer enclose the base portions of the angle fasteners on opposite sides thereof, andfixing the base portions of the angle fasteners, the insulating layer, and the shielding layer to each other, using staples or stitches.

In further embodiments, a cross-sectional dimension of the further through-hole in the insulating layer is larger than a cross-sectional dimension of the through-hole in the shielding layer. The method may then further include:leaving an annular edge region of the shielding layer along the inner periphery uncovered by the insulating layer, when positioning the shielding layer along the insulating layer, thereby forming an annular recess in the insulating layer that is bounded by the outer surface of the tube section, by the base portion of the angle fastener, and by the second surface of the shielding layer.

