OCR Text |
Show door was opened to allow inspection of the tank. The walls were coated with a frozen layer of basalt to a depth of 0.5 to 2.5 inches. N o damage was done to the refractory, the walls, or the burners. A continuous test was conducted next using the oxy-gas burners and a feed blend of 75% basalt and 2 5 % dolomite. The dolomite was added to decrease the melt viscosity and to generate a product similar to a mineral wool composition. Batch feeding and discharge through the tap piece was maintained uninterrupted for more than four hours. Firing, feeding, and discharge proceeded smoothly during this time. The tap piece design prevented pieces of unmelted batch from entering the molten product stream which was collected at a steady rate of approximately 100 lb/hour. The oxy-gas burners again operated smoothly and provided stable combustion over a wide range of firing rates. The basalt-dolomite blend was changed somewhat during testing, and the melt viscosity and bath turbulence were both decreased with increasing dolomite content. A heat balance was calculated for the continuous pilot-scale test. Thermal efficiency, defined as percent heat transfer to the melt was 5 percent of the total available energy input. Thermal efficiency increases with higher production rate, increased melter size, recuperation, and batch preheating. In the continuous test, 76 percent of the heat input was lost to the water-cooled walls and 10 percent was lost to the droplet separator. These heat losses are constant, and the percentage of heat transfer to the walls would increased with higher production rate. If production rate is increased from 100 to 500 lb/hour, calculations show thermal efficiency will increase from 5 to 22 percent. A commercial unit with a capacity of 120 tons/day of melt is determined to have thermal efficiency above 40 percent. Calculations also show that increasing melt capacity to 240 tons/day and including batch preheat will result in a thermal efficiency of 65 percent using oxy-gas firing. These calculations show the high thermal efficiency and energy savings capabilities of submerged combustion melting. Emissions measurements of the offgas were made during continuous testing. The exhaust gas compositions were not steady during the duration of the testing. However, C O and N O x emissions, corrected to 3 percent O 2 , were below 50 vppm and below 100 vppm, respectively, and were similar to the very low emissions observed in the commercial air-fired S C M units producing mineral wool. SUMMARY Submerged combustion melting is an advanced melting technology with wide potential applications in industrial mineral melting processes. The technology has been developed through conceptual and demonstration phases and is now commercial for mineral wool production in two 75 ton/day melters. Mineral wool production in the United States is 500, 000 ton/year and relies entirely on outdated and costly coke-fired cupolas. W The first commercial applications focused on demonstrating a reliable air-fired melting technology. IGT has licensed the SCM technology from its developer, the Gas Institute of the National Academy of Sciences of Ukraine. IGT is pursuing further applications of the technology and has constructed and operated a 6 ton/day S C M unit in its laboratories. This pilot-scale S C M unit is equipped with both air-fired and oxy-fired burners as well as feed systems for coarse and fine batch material. The first successful oxy-gas fired S C M operation has now been conducted in this pilot-scale melter. Oxy-gas operation has proven to be reliable. Melt was produced from basalt and basalt-dolomite mixtures and then collected on a continuous basis. The melter operation was robust enough to allow high turndown on the submerged burners. 8 |