| OCR Text |
Show • a unifying zoned system model to integrate the results from the C F D and gas reburn physical flow modelling into a prediction of performance attributes including thermal and production efficiency, and final N O emissions. Concepts Background Oxygen-enrichment (OEA) concepts are being used to improve the performance of high temperature pyroprocessing processes in the energy intensive industries. It is important to note that experience with O E A in many of these industries has lead to the development of specific burner technologies. One example is the tube bundle burner commonly seen today on the electric arc furnace as well as the Clean Fire H R burner system, which has been successfully applied to glass and aluminum melters. Productivity gains up to 4 0 % have been achieved as well as a 3 0 % decrease in N O x . Newly developed O 2 injection methods for the iron cupola have shown significant reductions in % coke in the charge. Limited experience, mostly overseas, has shown that oxy-fuel burners in the heating zone of a billet furnace can increase productivity by 3 0 % . O E A (3%) applied to the heating zone of a billet reheat furnace decreased fuel consumption by 2 0 % , all at the expense of higher N O emissions. Gas reburn technologies for NOx control are being commercially offered for large boilers and M S W incinerators. In a study for the Gas Research Institute [GRI] (Pearson, Moyeda & Koppang, 1994) the feasibility and effectiveness of applying gas reburning technology to industrial equipment was established for the pyroprocessing industries, and specifically, steel reheat furnaces. The combined technologies should obtain the following attractive features: • greater production throughput with associated furnace efficiency improvements; • low NOx emissions, particularly when raw off-gases contain fuel N or OEA increases gas path temperatures; • better control over scale formation. Concept Implementation Continuous reheat furnaces are used to raise the temperature of the steel shapes for further high temperature processing. The product flow in a reheat furnace is countercurrent to the flue gas flow as shown in Figure 2. It is c o m m o n for reheat furnaces to have multiple heating zones or banks of burners. Zone flue gas, with temperatures ranging from 2150°F to 2650°F, is ultimately exhausted through a recuperator to the stack at 700 to 1200°F. Even with recuperation overall furnace efficiencies are low (45 to 6 0 % ) and stack gas sensible heat losses relatively high. This and the need to transfer heat by radiation in the heat zones suggest that oxygen enrichment of these zones would offer some significant benefit in thermal efficiency and productivity. Three concepts shown in Figure 3 are under evaluation: 1) oxygen lancing into fuel rich combustion zones, 2) oxygen enrichment into the primary burner combustion air, and 3) additional oxy-fuel boost burners strategically placed in the heat zones. 4 |
