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Show . The fabrication processes are different for each product category, but they use combustion processes for control~mg the mO.lten glass. temper~ture. Many products are thennally or chemically tl Jted after fabrication by temper.tng, annealIng, labehng, coatIng, or dccorating. Tempering of flat glass is very energy intensive. For the annealing of flat glass or containers, energy intensity depends on the efficiency of the annealing lehrs. . . The major use for gas in the container glass sector is in melting, with some consumption in annealing and fllUshmg. Ave~ag~ fuel conswnption for melting is about 4.5 to 6 MMBtuiton. The flat glass segment also consumes energy for lrurunatmg, autoclaving, annealing, and tempering. Typical funlace fuel consumption is between 8 and 10 M~BtuJton mel~ed. Fuel consumption in the fiberglass melting furnaces also run in the 8- to lO-MMBtu range. Unlike the contamer and flat glass segments, a large amount of energy is used in fabrication. Fiberizing can consume 6 to 1 0 M.M~tulton. Pressed and blown glass melting furnaces have a capacity of about 5 to 25 TPD. Fuel consumptIon In these plants can run 12 to 16 MMBtuiton shipped. . The bas.ic design of conventional fuel-fired furnaces has remained unchanged for many years. The raw ma~enal charge IS melted in large gas-fired reverberatory type furnaces . High heat losses and inefficient regenerator deSigns formally resulted in thenllal efficiencies of less than 30 percent in many older furnaces . The efficiency of these types of furnac.es has been increased significantly in the last 15 years in response to the rapid increase in energy costs. Fuel consumptIon has decreased by more than 25 percent through a variety of design changes. More efficient regenerators have been used to increase combustion preheat temperatures to 2,200 to 2,300°F. This may require the use of more expensive refractories in the hot end of the regenerator and some increase in size and design complexity to obtain the higher effectiveness. More efficient insulation of the furnace itself reduces heat loss and decreases its fuel consumption, but the savings are limited by the size of the furnace. 4.5.1 Combustion-Related Problems 4.5.1.1 Environmental. With melting energy representing approximately 150/0 of manufacturing costs and considerable efforts necessary to meet expanding envirorunental regulations, the industry must find alternative melting technologies to remain competitive. Environmentally driven process changes for reducing emissions of criteria air pollutants (HC, CO, NO,O and particulate matter) sometimes do not lead to increases in productivity and thus have increased operating costs. Investments in environmental control equipment are viewed as nonproductive and as leading to further pressures on the industry's low operating margins. Therefore, there are real opportunities for the development of technologies that can meet applicable regulations without increases in capital requirements or operating costs. One key issue for combustion space characterization and modeling for glass melting furnaces involves understanding the heat input to the batch/glass, the relationship with pollution production (NOJ and combustion products, and glass fluid dynamics (refractory erosion resulting from flow, entrairunent of particulates, etc.). Present combustion models are limited in their ability to accurately predict chemical reactions, radiant heat transfer (spectral effects, etc.), and the turbulent reacting flow. For example, the Fluent, Inc., code is frequently used by many organizations but it has limited sub models and a simplified radiation heat transfer sub-model. There is very limited linkage between the combustion enviroIUnent and chemical species interaction at the melt interface. Another major issue is that there are very few experimental data to validate nunlerical models. An effort in the glass industry is underway to gather detailed measurements within an operating glass melter. Measurements will include the collection of local gas compositions, including O2, CO2, CO, NOx, and SOx, their temperatures and gas velocities. Measurements of wall radiant and convective heat flux will also be made. Process variables will be altered (such as different burner angles, gas flow rates, etc.). The local data will be used to experimentally validate compute~ models. The va~idate~ mod~l will t.hen be used to optimiz.e prese~t operat.ing conditions examine possible deSIgn changes, and mvestIgate uillovatlve concepts and examme pOSSIble deSIgn changes, s~ch as gas reburn, staged .combust.i~n, oxygen/fuel combustion, etc. These. validated models will allow an investigation of the effects of changmg condItIOns and geometry on both the combustIOn process and molten glass. Although the concept behind low NOx burners may be applicable to glass melting, the burners cannot be directly retrofitted to glass furnaces . Thi~ is a consequen?e .of a basic di~erence between industrial boilers and glass furnaces . In boilers, mixing of fuel a~d aIr takes place wlthm .the b.urner It.self. In a glass furnace., ~owever, the bllf!ler is really a fuel injector, injecting fuel mto the flo\\' of combustIOn atr entenng the furnace. ~e lluxmg of fuel an~ aIr takes place within the furnace. Consequently, there are no oIT the shelf low NOx burners aVailable for glass meltIng furnaces. 14 |
