Patent ID: 12215861

DETAILED DESCRIPTION

The harsh environment within a glass melting furnace—attributable primarily to the corrosive nature of molten glass and the high temperature maintained in the furnace—can lead to wear, cracking, erosion, and/or the failure of furnace components. Temperatures in the melting furnace typically range from 1200° C. to 1650° C. or higher. What is more, in a submerged combustion melter, the combustion burners, or at least the portions of the burners that extend into the glass melt, are submerged and are thus in direct contact with the glass melt, and the glass melt is agitated by the discharge of combustion products from the submerged burners to create turbulent flow patterns within the melt.

Because the submerged combustion burners installed on a SCM are exposed to the harsh environment associated with glass melting, especially since the burners are in direct contact with the agitated glass melt, the operational lifetime of the burners is a concern. To address this concern, each of the burners typically includes a cooling tube that has a wall surrounding the coaxial fuel and oxidant flow conduits of the burner. The wall thickness of the cooling tube can be small, often in the range of 1-5 millimeters. An upper portion of the cooling tube, or the tip of the cooling tube, extends into the melter and is exposed to molten glass, and the heat flux received at this location of the cooling tube fluctuates over a wide range, for example, between 35-80 W/cm2(350-800 kW/m2). Conversely, a lower portion of the cooling tube is typically located outside of the melter in a more moderate ambient environment. Water is circulated upwards into the cooling tube to the tip, over an internal divider wall, and then back down to the lower portion of the tube, and ultimately out of the cooling tube, to absorb heat and manage the temperature at the tip of the cooling tube.

The different thermal exposures experienced by the cooling tube can adversely affect the life and operation of the associated submerged burner. For example, temperature gradients may develop across the wall of the cooling tube due to the transfer of heat from the upper portion of the cooling tube to the lower portion, and from the outside of the cooling tube to the inside of the tube, which can induce thermal stresses within the wall. These thermal stresses can cause cracking on the outside surface of the cooling tube when the cooling tube wall becomes thermally fatigued. Once formed, these cracks can propagate quickly across the cooling tube wall and the circulating coolant can leak therefrom. Furthermore, the upper portion of the coolant tube may erode over time as a result of being constantly exposed to the corrosive and high temperature glass melt contained in the SCM, which can render the cooling tube wall more susceptible to crack formation and propagation.

To reduce the tendency for cracking of the cooling tube wall, previous practices sought to minimize the temperature along the upper portion of the cooling tube as much as possible. One way to decrease the temperature of the upper portion of the cooling tube as well as the thermal gradient across the cooling tube wall is to increase the thermal conductivity of the material used to construct the cooling tube wall. The thermal conductivity of copper, for example, is about sixteen to thirty-three times higher than the thermal conductivity of stainless steel. To that end, when the cooling tube wall is constructed of copper, the average temperature at the outside surface of the upper portion of the copper tube would be expected to be about 95° C.-100° C. when exposed to molten glass, while the same portion of a stainless steel cooling tube would be expected to have an average temperature of about 180° C.-185° C. under the same conditions. The problem with a copper cooling tube, however, is that the melting temperature of copper (1084° C.) is lower than the temperature of the glass melt contained in a SCM and other furnace types as well (>1200° C.). Other solutions are therefore needed.

In the present disclosure, a submerged combustion burner, a submerged combustion melter, and a method for cooling the combustion burner is disclosed. The combustion burner includes a fluid-cooled heat pipe that surrounds and extends beyond a terminal end of a central burner tube. When the combustion burner is received in a burner opening defined by a floor of the submerged combustion melter, the heat pipe is disposed between the central burner tube and the floor of the melter to cool the central burner tube while experiencing a mitigated potential for the types of damage (e.g., fracturing and erosion) that often accompany a conventional cooling tube. In particular, the heat pipe transfers heat away from the terminal end of the central burner tube of the submerged combustion burner to a convective cooling fluid. And since the flow of the cooling fluid extracts heat from the heat pipe outside of the melter, the likelihood of having to shut-down the melter on account of a cooling fluid leak is greatly reduced compared to conventional submerged combustion burner designs.

Referring now to the drawings,FIG.1illustrates a submerged combustion melter100that includes a melting tank102in which a vitrifiable batch material is melted into molten glass. While the submerged combustion melter100is describe herein in the context of manufacturing glass, the melter100may be employed to melt other materials that do not produce glass such as, for example, metal(s) and waste products. The melting tank102receives the vitrifiable batch material, which may include virgin raw materials (sand, soda ash, limestone, etc.) and recycled glass (i.e., cullet), plus other raw materials and minors additions as is well known in the art, from a batch charger (not shown) or some other device that can controllably feed batch material into the tank102.

The melting tank102includes a floor104that defines at least one burner opening106. The burner opening106traverses a thickness of the floor104. Each burner opening106receives a corresponding submerged combustion burner108and enables the burner108to discharge combustion products G directly into a glass melt M that is contained within an interior110of the tank102. AlthoughFIG.1illustrates two burner openings106in the floor104, more or less burner openings106may be disposed in the floor104to accommodate any desired number of submerged combustion burners108. Each of the submerged combustion burners108installed in the melting tank102receives separate flows of a fuel and an oxidant, which in turn combust before exiting the burner108or immediately upon exiting the burner108to produce the forceful discharge of the combustion products G.

Referring now toFIG.2, the floor104may include at least one cooling panel112configured to internally circulate a cooling fluid such as water. The cooling panel(s)112provide structure to the melting tank102and cool a portion of the glass melt M adjacent to the floor104to form a layer of frozen glass114in contact with the floor104. The term “frozen glass” is meant to broadly include glass that is resistant to flow including glass that is not technically frozen but nonetheless has a high enough viscosity that it behaves like frozen glass and forms a definitive layer of glass against the floor104. In some instances, a refractory layer (not shown) may be included in the floor104between the cooling panel112and the layer of frozen glass114. Here, the frozen layer of glass114protects the underlying refractory layer and/or the cooling panel112from erosion and/or corrosion that stems from contact with the glass melt M.

In the embodiment shown inFIG.2, the submerged combustion burner108includes a central burner tube118that extends along a longitudinal axis A and defines an internal passage162. The central burner tube118has a terminal end164located proximate the floor104of the melting tank102and an opposite distal end166. Defined in the central burner tube118is a first inlet116, which may be defined in the distal end166as shown, but is not required to be, and a first outlet124, which is defined in the terminal end164and is centered on the longitudinal axis A of the central burner tube118. Each of the first inlet116and the first outlet124fluidly communicates with the internal passage162of the central burner tube118. The submerged combustion burner108also includes an outer tube168that surrounds a portion of the central burner tube118. The outer tube168is coupled to the central burner tube118and defines a second inlet120. The outer tube168, which extends along the outside of the central burner tube118along the longitudinal axis A of the central burner tube118, does not cover the terminal end164of the central burner tube118; in other words, the terminal end164of the central burner tube118extends beyond the outer tube168. A flow of one of a fuel (e.g., methane or propane) or an oxidant (e.g., oxygen, air, or an oxygen-enriched gas containing at least 85 vol % O2) is provided to the internal passage162of the central burner tube118through the first inlet116and exits the internal passage162at the terminal end164of the central burner tube118through the first outlet124. Additionally, a flow of the other of a fuel or an oxidant is provided around the central burner tube118through the second inlet120of the outer tube168.

The submerged combustion burner108further includes a heat pipe128that surrounds a portion of the central burner tube118that is axially forward of the portion of the tube118surrounded by the outer tube168. Specifically, the heat pipe128connects to and extends axially from the outer tube168, and further surrounds, and extends beyond, the terminal end164of the central burner tube118. The heat pipe128and the outer tube168therefore define an annular space122exterior to the central burner tube118and interior to the outer tube168and the heat pipe128. The annular space122runs along the longitudinal axis A of the central burner tube118and is provided with the flow of the fuel or the oxidant, whichever the case may be, through the second inlet120. The heat pipe128may be integrally formed with the outer tube168or it may be separable from but fluidly sealable with the outer tube168to facilitate easy disassembly and replacement of the component parts.

To facilitate the combustion reaction between the fuel and the oxidant, the heat pipe128and the central burner tube118further define a mixing zone132axially beyond the terminal end164of the central burner tube118and radially inboard of the heat pipe128. In the mixing zone132, the flows of the fuel and oxidant that pass through and emerge from the internal passage162of the central burner tube118and the annular space122outside of the central burner tube118can mix, ignite, and combust to produce combustion products G. When the heat pipe128is installed in the floor104of the melting tank102and, thus, is received in its respective burner opening106, the heat pipe128is disposed between the terminal end164of the central burner tube118and the floor104of the melting tank102. In this way, the combustion products G are discharged into the glass melt M from the mixing zone132, which is surrounded by the heat pipe128.

The heat pipe128includes a forward end126and a rearward end130. The forward end126is positioned axially beyond the terminal end164of the central burner tube118and is disposed within the burner opening106, or extends though the burner opening106into the interior110of the melting tank102, when the burner108is installed in the floor104of the tank102. The rearward end130overlaps the central burner tube118and is positioned axially below the terminal end164of the central burner tube118. The rearward end130is connected to the outer tube168and, when the submerged combustion burner108is installed in the floor104of the melting tank102, the rearward end130of the heat pipe128is positioned outside of the melting tank102as shown best inFIG.2. As for the construction of the heat pipe128, it may be a vacuum-tight, two-phase heat transfer device configured to pump heat from the forward end126to the rearward end130of the pipe128during operation of the submerged combustion burner108. For instance, in the embodiment shown here inFIG.2, the heat pipe128includes a housing134, a wick136, and a working fluid140in fluid communication with the wick136and sealed within the housing134.

The housing134is a sealed outer wall that encompasses the wick136and contains the working fluid140. The housing134is composed of a material having a high effective thermal conductivity that is also heat and corrosion resistant such as, for example, stainless steel, copper, silica, nickel, titanium, iron, aluminum, brass, or combinations thereof. The wick136is a porous capillary structure that is supported by the inside surface of the housing134and defines a vapor chamber138interiorly of the wick136in the center of the housing134. The wick136may be a homogenous and/or a composite capillary structure. Some examples of structures suitable for use as the wick136include a screen-type (e.g., a wrapped screen) capillary structure, a sintered metal capillary structure, a capillary structure having axial grooves, a composite screen, screen covered grooves, and/or a porous composite slab.

The working fluid140is a fluid that can undergo repeated phase transitions between liquid and gas as part of a cooling or heat pump cycle. When present within the housing134and over the course of a cooling cycle, the working fluid140includes a liquid portion that soaks the wick136proximate the rearward end130of the heat pipe128and a vapor portion proximate the forward end126of the heat pipe128. The working fluid140, in liquid form, and is able to flow upwards towards the forward end126of the heat pipe128through the wick136by way of capillary action where it can evaporate to form a vapor. From there, the vaporized working fluid returns downwards towards the rearward end130through the vapor chamber138wherein it condenses back into liquid form. Some examples of a material suitable for use as the working fluid140include water, ammonia, acetone, methanol, ethanol, toluene, and combinations thereof.

The heat pipe128includes an evaporator region148and a condenser region150, as shown generally inFIG.3, when the cooling or heat pump cycle has been established. The evaporator region148forms adjacent to the forward end126of the heat pipe128and the condenser region150forms adjacent to the rearward end130of the pipe128. In the evaporator region148, heat is transferred through the housing134of the heat pipe128from the glass melt M and is absorbed by the working fluid140that has traveled up the wick136. The absorption of heat causes the working fluid140to evaporate into a vapor form (i.e., vaporized working fluid), thereby capturing the latent heat of vaporization. The vaporized working fluid then flows downwards through the vapor chamber138towards the condenser region150. When the vaporized working fluid reaches the condenser region150, which is cooler than the evaporator region148, the vaporized working fluid condenses into a liquid form (i.e., liquefied working fluid) and releases the previously-captured latent heat of vaporization. The liquefied working fluid140then travels back towards the evaporator region148through the wick136via capillary action.

The flow of the working fluid140is shown inFIGS.2and3by the directional arrows within the wick136and the vapor chamber138. The phase change process of the working fluid140and the two-phase flow circulation continues so long as the temperature gradient between the evaporator region148and the condenser region150is maintained. Additionally, when the two-phase flow circulation of the working fluid reaches steady-state, an adiabatic region152may form between the evaporator region148and the condenser region150, depending on length of the heat pipe128. The adiabatic region152is a region in which the net heat transfer in and the net heat transfer out is zero. For example, in a heat pipe having a length of anywhere between 0.1 meters and 1.5 meters, an adiabatic region ranging from 0 meters to 0.8 meters may form between the established evaporator and condenser regions148,150.

To cool the rearward end130of the heat pipe128so that the vaporized working fluid can be condensed in the condenser region150and the latent heat released by the condensation of the working fluid140can be removed through the housing134, the submerged combustion burner108may include or be associated with a cooling jacket142located exterior to the melting tank102, as shown inFIG.2. The cooling jacket142surrounds at least a portion of the heat pipe128and encompasses at least the rearward end130of the heat pipe128, preferably extending towards the forward end126to cover between 10% and 60% of an axial length of the pipe128to help ensure adequate cooling. The cooling jacket142defines an interior flow space170as well as a cooling fluid inlet144and a cooling fluid outlet146. Each of the cooling fluid inlet144and the cooling fluid outlet146fluidly communicate with the interior flow space170so that a cooling fluid can be introduced into and removed from the interior flow space170, respectively, so that the flow of the cooling fluid through the interior flow space170can contact and convectively extract heat from the heat pipe128through the housing134. The cooling fluid used here may be water, a propylene glycol, ethylene glycol, or any other suitable heat-transfer fluid.

In operation, the heat pipe128functions as a good heat flux transformer with an effective thermal conductance significantly greater than copper alone due to its cooling cycle and the convective transfer of heat to the cooling fluid flowing through the cooling jacket142while also maintaining a high-power handling capacity. For example, when water is used as the working fluid (boiling point of 100° C.), the heat flux through the heat pipe128can reach approximately 400 W/cm2. As a result of the high thermal conductance of the heat pipe128, the temperature gradient between the evaporator region148and the condenser region150can be minimized along the axial length of heat pipe128, which in turn reduces the thermal stress on the surrounded central burner tube118. This reduced thermal stress helps reduce the occurrence of crack formation and propagation in the central burner tube118by slowing the onset of thermal fatigue, thus allowing the central burner tube118to operate for periods of time without replacement.

The submerged combustion burner108shown inFIGS.2-3includes a single heat pipe128that has one vapor chamber138for directing vaporized working fluid from evaporator region148to the condenser region150as well as a cooling jacket142that partially surrounds the heat pipe128. However, other submerged combustion burner constructions that include at least one heat pipe having at least one vapor chamber and an approach for cooling the heat pipe outside of the melting tank102that are consistent with the description above and operate in the same general manner are possible. Certain of these alternate embodiments are shown inFIGS.4-7. In the alternate embodiments disclosed herein, corresponding numerals among the embodiments designate like or corresponding elements throughout the several views of the drawing figures. To that end, the above descriptions of features identified in the embodiment shown inFIGS.1-3apply equally to features shown inFIGS.4-7that are identified with a corresponding reference numeral and, accordingly, the description of that common subject matter will not be repeated.

Referring now toFIG.4, a heat pipe228is shown that has more than one vapor chamber. In this embodiment, the wick236contained within the housing234of the heat pipe228defines a first vapor chamber238aand a second vapor chamber238b. Here, the first vapor chamber238aand the second vapor chamber238bare radially spaced apart and separated by a portion of the wick236. While two vapor chambers238a,238bare shown inFIG.4and described here, the wick236may define more than two vapor chambers if desired. Each of the several vapor chambers238a,238bpresent in this embodiment of the heat pipe228functions similarly to direct vaporized working fluid from the evaporator region148of the heat pipe228to the condenser region150.

Referring now toFIGS.5A-5D, there are shown several different embodiments of a submerged combustion burner (in top cross-sectional views) that may be used in the submerged combustion melter100according to the present disclosure. In the embodiment shown inFIG.5A, a heat pipe328is shown that surrounds the central burner tube318and partially defines the annular space322as described above. The heat pipe328is unitary in construction and may include one vapor chamber138or multiple vapor chambers238as described above inFIGS.1-3andFIG.4, respectively. In the embodiment shown inFIG.5B, a heat pipe428is shown that includes a plurality of arcuate sections fastened together. Here, the heap pipe428is constructed from four arcuate sections454a,454b,454c,454d, each of which forms a circumferential part of the heat pipe428as a whole. Each section454a,454b,454c,454dmay include a wick that defines a respective vapor chamber, thereby providing the pipe428with a plurality of circumferentially spaced vapor chambers (i.e., one per section), or the several sections454a,454b,454c,454dmay include respective wicks that together define a single circumferentially continuous vapor chamber when sections454a,454b,454c,454dare fastened together. The heat pipe528shown inFIG.5Cis similar to the heat pipe shown inFIG.5Bexcept that the plurality of sections554a,554b,554c,554dare linear in shape and arranged to provide the heat pipe528with a rectangular cross-section when sectioned perpendicular to the axial length of the heat pipe528rather than a circular cross-section. Lastly, in the embodiment shown inFIG.5D, a plurality of heat pipes628is included in the submerged combustion burner. The plurality of heat pipes628includes an inner heat pipe628aand an outer heat pipe628bdisposed radially outwardly of the inner heat pipe628a. Here, the inner heat pipe628asurrounds the central burner tube618and partially defines the annular space622, as described above, while the outer heat pipe628bsurrounds the inner heat pipe628ato provide an additional layer of thermal protection to the central burner tube618.

Referring now toFIG.6, a submerged combustion burner708is shown that has a modified cooling jacket742relative to the burner108shown inFIGS.1-3. In the submerged combustion burner708shown here, one or more cooling fins756are coupled to the heat pipe728within the interior flow space770of the cooling jacket742that encompasses the rearward end730of the heat pipe728. The cooling fin(s)756are formed from a material having high thermal conductance—such as, for example, stainless steel, copper, silica, nickel, titanium, iron, aluminum, and brass—and is preferably configured to provide a large surface area for the transfer of heat out of the heat pipe728and into the cooling fluid being passed through the cooling jacket742. Specifically, when present, the cooling fluid thermally communicates with the cooling fin(s)756via direct or indirect contact as the cooling fluid passes through the cooling jacket742and, in doing so, the cooling fin(s)756help extract heat through the housing734of the heat pipe728from the working fluid740as the working fluid740condenses and additionally help deliver the extracted heat to the cooling fluid, possibly more efficiently than if the cooling fin(s)756are omitted. Each of the one or more cooling fins756may be an integral projection that extends outwardly from the housing734of the heat pipe728. For example, as shown here, the cooling fin(s)756may include a first cooling fin756that extends axially from the rearward end730of the heat pipe728and a second cooling fin756that extends radially outwardly from a side of the heat pipe728with both fins756further surrounding the central burner tube718.

Turning now toFIG.7, a submerged combustion burner808is shown that omits the cooling jacket shown in the embodiment ofFIG.6but adds an air circulation device858, such as a fan, to pass a flow of air860over and in thermal communication with the heat pipe828and the cooling fin(s)856that extend from the heat pipe828exterior to the melting tank102. The air circulation device858may be part of or separate from the melting tank102and the flow of air860it distributes over the heat pipe828and the cooling fin(s)856convectively remove heat from the heat pipe828and the fin(s)856and transfer the heat to the ambient environment.

FIG.8illustrates a method900of cooling a submerged combustion burner108,208,308,408,508,608708,808that includes a heat pipe128,228,328,428,528,628728,828. For purposes of illustration and clarity, the method900will be described in the context of the submerged combustion melter100and the submerged burner108depicted inFIGS.1-4. The described method900is of course applicable to each of the other submerged burners208,308,408,508,608,708,808described above, as well as others not described herein and shown in the drawings, in the same manner as will be apparent to a person of ordinary skill in the art.

Method900includes a step902of providing a flow of either a fuel or an oxidant through the internal passage162of the central burner tube118, and providing a flow of the other of the fuel or the oxidant through the annular space122outside of the central burner tube118such that the flow of the fuel and the flow of the oxidant mix together downstream of the terminal end164of the central burner tube118to create a fuel and oxidant mixture that is directed into the glass melt M contained within the submerged combustion melter100. In one arrangement, the fuel is introduced into the internal passage162of the central burner tube118through the first inlet116and exits the internal passage through the first outlet124, while the oxidant is introduced into the annular space122through the second inlet120and flows along the outside of the central burner tube118. The fuel and the oxidant mix together in the mixing zone132and the resultant combustion products G are discharged into the glass melt M.

Method900also includes a step904of providing the cooling fluid to the heat pipe128that is disposed between the central burner tube118of the submerged combustion burner108and the floor104of the submerged combustion melter110and is configured to cool the central burner tube118. The cooling fluid may be a liquid or a gas that flows through the cooling jacket142that surrounds part of the heat pipe128exterior to the submerged combustion burner108or, in an alternate embodiment, the cooling fluid may be a flow of air supplied by the flow circulation device858. Because the combustion products G provide a large amount of heat to the glass melt M, and thermal gradients induced in the portion of the burner108that contacts or is in very close proximity to the glass melt M can be damaging, the ability of the heat pipe128to pump heat from the central burner tube118by the mechanisms described above to help minimize the formation and steepness of any thermal gradients may help protect the burner108and extend its operating lifetime.

The disclosure has been presented in conjunction with several illustrative embodiments, and additional modifications and variations have been discussed. Other modifications and variations readily will suggest themselves to persons of ordinary skill in the art in view of the foregoing discussion. For example, the subject matter of each of the embodiments is hereby incorporated by reference into each of the other embodiments, for expedience. The drawings are not necessarily shown to scale. The disclosure is intended to embrace all such modifications and variations as fall within the spirit and broad scope of the appended claims.