Patent Application
20220153622
Disclosed aspects relate to oxygen fuel burners for a forehearth system of a glass manufacturing system.
A glass manufacturing system is used in the production of glass, where molten glass is produced in a glass melting furnace which then passes along a forehearth system (or forehearth section) in a continuous stream to a feeder bowl from which the molten glass is fed in mold charges or gobs into a glass forming apparatus. The glass forming apparatus processes the molten glass received into a desired form or shape.
The forehearth system is designed to condition the molten glass during conveyance between the glass melting furnace and the glass forming apparatus, rendering the molten glass more suitable for forming or shaping. In particular, the forehearth system is designed to heat or cool the molten glass to the temperature required for processing by the glass forming apparatus. For some glass products, the temperature of the molten glass after processing by the forehearth system needs to be maintained within about 1° C. of a target temperature, such as around 1200° C., at the inlet to the glass forming apparatus.
Conventional forehearth systems provide temperature control through a series of relatively small sized oxygen fuel forehearth burners placed longitudinally on either side of the forehearth duct. The spacing between the respective oxygen fuel forehearth burners is typically between six and eighteen inches. A single forehearth system can contain several hundred oxygen fuel forehearth burners and a single glass furnace may have one or multiple forehearth systems. A typical forehearth system comprises a refractory material (e.g., Alumina Zircon Silica) trough along which the molten glass flows, and which is generally provided with a thermally insulating crown or roof.
This Summary is provided to introduce a brief selection of disclosed aspects in a simplified form that are further described below in the Detailed Description including the drawings provided. This Summary is not intended to limit the claimed subject matter's scope.
Disclosed aspects recognize the forehearth system of a glass manufacturing system is in several ways more challenging to design for oxygen fuel forehearth burners as compared to designing a glass melting furnace. These design challenges include proper cooling of the oxygen fuel forehearth burner, and efficient and effective management of the discharge velocities of the fuel and the oxygen.
One disclosed aspect comprises a forehearth system comprising a superstructure including a plurality of refractory bricks that frame a molten glass tank. A burner block comprising a refractory material includes a discharge throat that extends to its distal end, where the burner block is within the superstructure above the molten glass tank. At least one oxygen fuel forehearth burner is within the burner block having a long axis along a length direction. A fuel pipe is within the burner body having a fuel inlet for receiving fuel on one end and a fuel outlet on an opposite end. An oxygen pipe is within the burner body having an oxygen inlet for receiving oxygen and an oxygen outlet. The oxygen pipe is positioned coaxially outside the fuel pipe. The fuel outlet extends beyond the oxygen pipe and the burner body so that the oxygen first reaching the fuel and thus a flame when operating is delayed until the discharge throat.
Disclosed aspects are described with reference to the attached figures, wherein like reference numerals are used throughout the figures to designate similar or equivalent elements. The figures are not drawn to scale and they are provided merely to illustrate certain disclosed aspects. Several disclosed aspects are described below with reference to example applications for illustration. It should be understood that numerous specific details, relationships, and methods are set forth to provide a full understanding of the disclosed aspects.
The arrangement shown for the oxygen fuel forehearth burner 100 is a coaxial pipe arrangement comprising an inner disposed fuel pipe 101 and an outer disposed oxygen pipe 102, where the fuel pipe 101 is contained inside the oxygen pipe 102. This arrangement delays the combustion process (reflected in the flame 107) for the oxygen fuel forehearth burner 100 so that combustion first occurs beyond the burner body 135 to be generally in the discharge throat of the burner block (see the burner blocks including a discharge throat shown in
The oxygen, or oxygen-containing gas, enters its oxygen pipe 102 through an inlet path 103 formed through the burner body 135 shown optionally oriented at a right angle to the length direction of the oxygen fuel forehearth burner 100 and the oxygen pipe 102. The fuel enters the fuel pipe 101 axially (length direction) through a fuel inlet 104 also formed in the burner body 135. The fuel generally comprises natural gas known to be primarily methane, or propane, and the oxygen source generally comprises O2.
The fuel pipe 101 can be seen to extend in the length direction 109 beyond the burner body 135 and beyond the oxygen pipe 102, generally a distance anywhere between 0.25″ (inches) to 6″ beyond the oxygen pipe 102. The flame 107 resulting from the combustion of the fuel with the oxygen generally has a low velocity laminar layer of O2 105 shown surrounding flame 107. It may be possible for the discharge throat to be replaced by a direct discharge into the atmosphere. The laminar flow of fuel output by the fuel pipe 101 shown as 106 which is introduced near or at the center of the flame 107 emerging from the fuel outlet 101a, is generally moving at a velocity of 75 to 300 ft/s.
Disclosed aspects recognize there are two factors which should be accounted for in a design of an oxygen fuel forehearth burner for a forehearth system for a glass manufacturing system. The function of the forehearth system comprising at least one oxygen fuel forehearth burner in a glass manufacturing system is to maintain the temperature of the molting glass, or to slightly cool the molten glass received from the glass melting furnace. It is recognized herein that the heat input needed for the forehearth system is significantly less as compared to the heat input needed for the glass melting furnace. This results in a lower volume of fuel and oxygen gas being passed through the oxygen fuel forehearth burner(s).
This lower volume flow rate of reactant gas presents a challenge for oxygen fuel forehearth burners which are designed to be cooled almost entirely by the flow of reactants, the reactants being O2 or an oxygen-containing gas mixture, and a fuel. As the flow rate of unburnt gases goes down, so does the total amount of heat that can be carried away from the oxygen fuel forehearth burner. This challenge is met by disclosed oxygen fuel forehearth burners as described below.
It is also recognized that the current state of the art for oxygen fuel burner for a forehearth system of a glass manufacturing system does not adequately address the unique challenges of the oxygen fuel burner in the forehearth environment, and this results in oxygen fuel forehearth burners which can overheat and thus prematurely fail. By applying disclosed aspects, an oxygen fuel forehearth burner 100 can be expected to remain within the operational limits of the materials of construction including the material of the burner body 135 which as noted above generally comprises stainless steel, at essentially every reasonable operating condition, and also operate normally for the life of the glass manufacturing system.
The current state of the art for forehearth systems is recognized to also not adequately address the varied shapes of burner blocks that customers may use. It is common for customers to design their own forehearth burner blocks. When these customer-designed burner blocks are combined with a current state of the art oxygen fuel forehearth burner, it can cause unintended consequences. A poorly matched oxygen fuel forehearth burner and burner block can cause the oxygen fuel forehearth burner to prematurely fail due to excessively high temperatures in the burner block created by poor flow dynamics. Disclosed forehearths burners are generally essentially invariant to the particular shape of the burner block, generally ensuring cooler operation no matter the specific installation of the oxygen fuel forehearth burner.
As described above, the forehearth system comprising at least one oxygen fuel forehearth burner transports the molten glass received from the glass melting furnace to the glass forming apparatus. Therefore, the forehearth system is recognized to be the last opportunity to affect the quality and the temperature of the glass. Temperature uniformity in the molten glass is recognized to be important for the forehearth system. The oxygen fuel forehearth burner can have a significant effect on both temperature control and temperature uniformity. If the oxygen fuel forehearth burner is designed for maximum flame luminosity, more of the heat produced by the combustion is absorbed by the top of the molten glass through thermal radiation. The top portion of the molten glass is thus recognized to need more heat input as compared to the bottom of the molten glass, which is in contact with the burner block. This creates a more uniform temperature for the molten glass being received by the glass forming apparatus.
Beyond temperature uniformity of the molten glass, another major benefit of a luminous flame (a burning flame which is brightly visible) provided by a disclosed oxygen fuel forehearth burner is the generation of more useful heat generated per unit of fuel consumed. If one compares an oxygen fuel forehearth burner with a yellow luminous flame and an oxygen fuel forehearth burner with a blue flame, the oxygen fuel forehearth burner with the yellow luminous flame (relatively lower temperature) can be operated at a lower flow rate of both O2 and fuel, and still heat the same volume of molten glass.
To ensure the oxygen fuel forehearth burner does not overheat in the forehearth environment which can cause catastrophic damage to the oxygen fuel forehearth burner and also potentially to the glass batch moving through the furnace, it is recognized that the oxygen and the fuel should not be mixed in the oxygen fuel forehearth burner. This is because it is recognized there is generally not enough volume flow to eliminate the heat generated when using a metallic pipe as a combustion chamber for the oxygen fuel forehearth burner. Known oxygen fuel forehearth burners are recognized to not allow for the creation of a flame with maximum luminosity. In order to provide a maximum flame luminosity for an oxygen fuel forehearth burner, it is recognized herein that the flame should be configured to be relatively long and the fuel should be introduced to the oxygen at a relatively low velocity.
In order to ensure the material of the burner body 135, which as noted above typically comprises stainless steel, stays within its safe operating temperature, the introduction of O2 to the fuel as disclosed herein is delayed by the fuel pipe 101 extending beyond the burner body 135 into the discharge throat of the burner block. The point of fuel ignition is thus not the same as the point of O2 injection. O2 is instead injected into the oxygen fuel forehearth burner at the back of the oxygen fuel forehearth burner, while the fuel is not introduced until after the oxygen fuel forehearth burner (into the discharge throat), where the point of the fuel ignition should also be a sufficient distance from the burner body 135 of the oxygen fuel forehearth burner, this will also serve to keep the oxygen fuel forehearth burner cooler. To create a luminous flame during oxygen fuel combustion it is recognized herein that the fuel velocity should be controlled to be within a defined velocity range, such as 75 to 300 ft/s.
Disclosed aspects are further illustrated by the following specific Examples, which should not be construed as limiting the scope or content of this Disclosure in any way.
A prototype oxygen fuel forehearth burner for a forehearth system resembling oxygen fuel forehearth burner 100 described above was built with the above-described features that was installed in a burner block 210 or 220 of the working forehearth system 400 depicted in
The customer replaced an entire zone of the forehearth system 400 with disclosed oxygen fuel forehearth burners resembling the design of the oxygen fuel forehearth burner 100 shown in
The customer compared the performance of oxygen fuel forehearth burner 100 (labelled “new type burner” in
The customer noted this with their evaluation comments which can be seen in the scanned images shown in
While various disclosed embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Numerous changes to the subject matter disclosed herein can be made in accordance with this Disclosure without departing from the spirit or scope of this Disclosure. In addition, while a particular feature may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application.
