Glass manufacturing – Processes – Fining or homogenizing molten glass
Reexamination Certificate
2001-03-02
2004-03-16
Griffin, Steven P. (Department: 1731)
Glass manufacturing
Processes
Fining or homogenizing molten glass
C065S134600, C065S136300, C065S356000, C431S010000, C432S010000, C432S020000
Reexamination Certificate
active
06705117
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the use of roof mounted oxy-fuel burners for glass melting. This invention further relates to the use of at least one oxygen-fuel burner that utilizes internal or external combustion staging in the roof of a glass melting furnace. The invention applies both to 100% oxygen-fuel fired furnaces and to furnaces heated by electric or non oxygen-fuel means, such as air-fuel burner(s) or their combinations.
BACKGROUND OF THE INVENTION
In one embodiment, this invention relates to the use of at least one oxygen-fuel burner in the roof of a glass melting furnace to boost production capacity or maintain current production capacity with either reduction of electro-boost or as a result of deterioration of existing heat recovery equipment such as recuperators or regenerators. The process involves the replacement of a portion of existing or previously existing air-fuel or electrical energy capacity with oxy-fuel energy. With the exception of end-fired regenerative furnaces and electric furnaces, the process involves the blocking of regenerative ports or isolation of recuperative burners. In particular the design selection, angling and positioning of the burners over the raw batch materials entering the furnace improves the rate of melting, increases product yield, provides better energy efficiency and improves glass quality. Accurate control of the stoichiometric ratio of combustion in the burner, rich-lean interaction of burners, and furnace zonal fuel/oxygen staging are used to optimise heat transfer while minimizing oxides of nitrogen and sulfur dioxide emissions.
Regenerative, recuperative, electric and direct fired furnaces have been commonly involved in the manufacture of glass and related frit products.
Air-fuel regenerative furnaces fall into two categories: cross-fired and end-fired. Cross-fired regenerative furnaces have multiple ports, typically three to eight on each side of the furnace that connect to either a common or compartmentalized regenerator to preheat the combustion air. The regenerators, which come in various shapes and sizes, reverse every 15-30 minutes dependent on furnace operation. During each reversal cycle combustion air from a fan passing through one passage in a reversal valve enters the base of the regenerator on one side of the furnace and is preheated prior to entering the ports which connect to the furnace. Fuel in the form of oil and/or gas is injected either under, over, through or side of port to produce a flame which is combusted in the glass melting furnace. The hot products of combustion exit the furnace through the opposing side port, down through the regenerator checker bricks, releasing heat and then exiting to the exhaust stack through a second passageway in the reversal valve. As the incoming combustion air-side regenerator cools, the exhaust regenerator heats until the reversal valve reverses and combustion air enters the previously hot exhaust regenerator.
The glass is melted partly due to the radiation of the air-fuel flame but mainly by re-radiation from the roof and walls which are heated by the products of combustion. To obtain higher furnace glass production capacity, many furnaces use electric boost by means of electrodes immersed in the glass. This is costly and can cause damage to the glass contact tank walls. Through time, regenerators can become blocked due to thermal/structural damage and/or carry-over of raw glass forming materials, also known as batch materials or batch, or condensation of volatile species released from the glass batch. As the regenerators start to block or fail, the preheat temperature of the air in the furnace will decrease, and the atmospheric pressure within the furnace will increase, reducing the thermal efficiency of the furnace. More fuel and combustion air would be required to maintain the same glass production rate. More importantly, because of the increase in furnace pressure, the rate of glass production must be decreased so as not to damage the refractory materials that make up the superstructure of the furnace.
To recover production capacity lost to preceding regenerator issues or to increase production in a non-encumbered furnace, oxygen has been used by four means: general air enrichment with oxygen, specific oxygen lancing under the port flames, installation of an oxy-fuel burner between first port and charging end wall, and water-cooled oxy-fuel burners installed through the port. The capacity increases from these technologies are limited by access, process requirements or refractory temperature limits.
The End-Fired Regenerative furnace is similar in operation to a cross-fired furnace; however, it has only two ports in the end wall which connect to individual regenerators. Regenerator deterioration can occur by the same mechanism as in cross-fired furnaces and similarly, electric and oxygen boost is utilized.
To recover production capacity lost to the aforementioned regenerator issues or to increase production, oxygen has been used by three means: general air enrichment with oxygen, specific oxygen lancing under the port and installation of oxy-fuel burners through the furnace. These technologies are typically capacity limited due to temperature limitations within the furnace, because of location and concerns for overheating of the furnace.
The recuperative furnace utilizes at least one recuperator type heat exchanger. Unlike the regenerator, the recuperator is continuous with a hot concurrent flow heat exchanger where exhaust gases preheat combustion air, which is ducted to individual air fuel burners along the sides of the furnace. Recuperative furnaces can also use electric boost. As with regenerative furnaces, recuperators can start to lose their efficiency and ability to preheat the air. They can become blocked or develop leaks between the walls separating the combustion air and exhaust gases.
To recover production capacity lost from the aforementioned recuperator issues or to increase production, oxygen has been used by three means: general air enrichment with oxygen, specific oxygen lancing under the air fuel burners and installation of oxy-fuel burners either through the furnace breast walls. These technologies are typically limited on capacity because of burner location limitations and concerns for overheating of the furnace.
Direct fired furnaces do not utilize preheated air and are therefore less efficient than the preceding examples of furnace design. To improve thermal efficiency or increase production capacity, side wall oxy-fuel burners have replaced air fuel burners.
Electric furnaces or furnaces which utilize electricity for the majority of melting are typically costly to operate and are subject to a shorter campaign life than the typical fossil fuel fired furnaces. Once designed, it is difficult to increase the production capacity. This invention relates to what are commonly referred to in the industry as hot top and warm top electric furnaces and does not apply to cold top furnaces.
U.S. Pat. No. 5,139,558 to Lauwers discloses the use of a water cooled, high-momentum roof-mounted auxiliary oxygen fired burner in a glass melting furnace, which is directed to the interface of the melted and solid glass forming ingredients at an angle directed upstream relative to the glass flow, whereby the solid glass forming ingredients are mechanically held back, thus being prevented from escaping the melting zone.
U.S. Pat. No. 3,337,324 to Cable discloses a process for melting batch material in a glass furnace using a burner positioned to fire substantially down over the feed end of a water-cooled furnace.
In the past, roof-mounted burners were considered in the glass industry, but were disregarded. It was perceived that the heat release from roof mounted burners was too great, resulting in the melting of the furnace crown (roof). In addition, high momentum flames from the burners would blow the batch materials around, harming the furnace walls, and generating a layer of gaseous bubbles, commonly referred to as foam, on the glass melt surface.
Clayton Thomas G.
LeBlanc John R.
Prusia Greg Floyd
Richardson Andrew Peter
Simpson Neil George
Cohen Joshua L.
Griffin Steven P.
Hug Eric
The BOC Group Inc.
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