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Show three model furnaces: a 500 ton per day flat glass furnace, a 250 ton per day container glass furnace, and a 125 ton per day fiber glass plant. Next, the impacts of reburning on the overall thermal efficiency and NOx emissions for each furnace were evaluated using computerized computational process models. Finally, the cost effectiveness of gas reburning technology was calculated and compared to other available NOx control technologies. The re·sults of this assessment for the flat and container glass furnaces are summarized in the following sections since these plants represent the majority of the glass manufacturing industry. Further details on the feasibility study and the results for the fiber glass plant are found elsewhere 1. Model Glass Furnaces Model glass furnaces were developed to permit evaluation of gas reburning for a representative cross section of equipment used in the United States. Model furnaces representing the two main types of glass manufacturing processes-flat and container glass-were defined based upon information in the open literature and discussions with industry experts and glass furnace manufa<;turers. The model furnace definitions included furnace size, operating parameters, and NOx emissions. Furnace sizes were selected based upon averages of those used in industry and to allow comparison t0 2 the EPA Alternative Control Technology Document for NOx emissions from glass manufacturing . The model furnaces are briefly described below. Flat Glass Model Furnace Hat glass manufacturing accounts for approximately 20 percent of the glass produced in the United States. Most of the furnaces utilize the float glass method rather than the energy and labor intensive rolled glass method. Furnaces producing flat glass are generally much larger than their container and fiber glass counterparts, with production ranging from 300 to 1000 tons per day. For the flat glass model furnace, a production rate of 500 tons per day has been assll:med. To maintain high temperatures in the melter and to improve thermal efficiency, flat glass furnaces utilize regenerators to recover heat from the melter flue gases and to provide high air preheat temperatures. The products of combustion pass through a "regenerator", which typically consists of a stack of refractory bricks, transferring heat to the bricks. Every 15 to 20 minutes, the firing and exhaust ports are reversed. Combustion air passing through the regenerators on the reverse cycle is preheated to high temperatures. Figure 2 shows a plan view of the flat glass model furnace. The furnace is of the side port design with twin regenerators. The burners are fired perpendicular to the direction of glass melt flow. Firing sides (six port) are assumed to switch every 20 minutes to maintain air preheat. The furnace thermal efficiency is 6.0 million Btus of natural gas per ton of melted glass. The average combustion air preheat temperature is 2300°F. The gas temperature is 2850°F at the exhaust ports. Baseline NOx emissions are assumed to be 14 pounds of N02 per ton of glass melted, which corresponds to 1,839 ppm NO (dry, corrected to 3 percent 02). Container Glass Model Furnace Container glass furnaces produce approximately 65 percent of all the glass manufactured in the United States. The majority of these furnaces utilize natural gas in addition to electric boosting to achieve high pull rates. Two primary furnace designs, side and end port, are utilized in container glass manufacturing. An end port design, shown in Figure 3, was chosen for the container glass 3 |