OCR Text |
Show Fuel ^^ N2 in 02 Figure 4. Schematic of oxy/fuel. There are many other possible sources of N2 in an OEC system. One is air infiltration into the combustion chamber which may come from leaks through openings and by air that is entrained in with the feed materials being heated in the combustor. Air leakage through openings can be minimized by operating at positive furnace pressures. However, this is not always possible with all processes. Even in relatively tight systems, such as batch processes, significant amounts of air m a y enter the combustion system when the charging door is opened. Air leakage from feed material charging doors can be minimized with proper seals, inert gas curtains, and the like. Another source of N 2 can be in the feed materials themselves. In the production of glass, sodium and potassium nitrates ("niter") are used in certain glass batch formulations. These nitrates can be a source of N O x [8]. ECONOMICS OF OXYGEN-ENHANCED COMBUSTION OEC has been used for many years to improve a variety of high temperature heat applications such as the production of both ferrous and non-ferrous metals and the production of glass and ceramics. Since using oxygen in the combustion process is an added operating expense, the benefits of using O E C must outweigh the costs. Depending on the specific application and on the needs of the user, O E C can provide a number of benefits. One common reason for using OEC is to increase the production using existing equipment. For a given size furnace, the throughput can be increased significantly using O E C due to the dramatic increase in the flame temperature. Figure 5 shows the theoretical adiabatic flame temperature (AFT) for the stoichiometric combustion of C H 4 with an oxidizer containing 0 2 and variable amounts of N2. The figure shows that the A F T for an air/CH4 flame is about 2200K (3500°F), while the A F T for an 02/CH4 flame is over 3000K (5000°F). In most high temperature furnaces, the primary mode of heat transfer is by radiation which is proportional to the difference between the absolute temperatures of the source and the sink raised to the fourth power: _rad ^(^source-^sink) (2) Then, the heat transfer from the flame (source) to the load (sink) increases dramatically as the temperature of the source increases. For example, if the average load temperature is assumed to be 810K (1000°F), then raising the flame temperature from 2200K (3500°F) to 3000K (5000°F) would increase the radiation from the flame to the load by 266%, assuming everything else was 4 |