OCR Text |
Show 2 . The reduced volume of the oxidant per unit of fuel lowers the momentum of the flame . This, in turn, reduces the amount of mixing and recirculation of the gases within the furnace . Good gas circulation in the furnace is usually desired to obtain uniform heating of the charge and to prevent localized hot spots . BURNER DESCRIPTION In order to overcome the disadvantages noted above, the Aspirator Burner or "A" Burner was developed(1&2) . The burner is described below using the operation of a conventional burner as a reference point. A schematic view of a conventional air burner in a furnace is given in Figure 1. The fuel and air mix and burn close to the burner face or within a burner block . By varying the mixing pattern a long or short flame can be achieved . The flame temperature is slightly below the theoretical adiabatic flame temperature (about 3S00°F). The combustion products form a jet aspirating in furnace gases resulting in the gas recirculation pattern in the furnace indicated in Figure 1. As a result of the gas recirculation, the temperature and heat transfer distributions within the furnace are quite uniform. If this type of burner were used with 100~ oxygen, the flame temperature would be very high (about SOOO°F) and the gas recirculation would be greatly reduced because of the low flow rate of oxygen as compared to air . The temperature and heat transfer distributions within the furnace would not be uniform. OXIDANT FLUE GAS FUEL OF COMBUSTION PRODUCTS Fig . 1 - Schemati c view of a conventional air burner in a furnace . t 330 A key feature of the "A" Burner is that the furnace gases are aspirated into the oxidant jets prior to mixing with the fuel . A sketch of the "A" Burner is given in Figure 2. In the following discussion, the operation of the "A" Burner is examined with respect to flame temperature, furnace gas recirculation, flame stability, and operating flexibility. For all of the examples and test results, the oxidant is 100~ oxygen. However, it should be kept in mind that oxygen enriched air could also be used. FUEL OXYGEN oxy~~~J~ ~NVELOPE ;t~~I~'i OXYGEN TO NOZZLES • FUEL ---.. :==~~ OXYGEN NOZZLES OXYGEN TO ANNULUS Fig . 2 - Schematic sketch of t he "A" Burner Referring to Figure 2, fuel gas is supplied at the burner axis as a relatively low velocity jet . Host of the oxygen (90 - 9S~) is supplied as a ring of high velocity jets surrounding the center fuel s tream . The purpose of the oxygen annulus ( containing the remaining S - 10~ oxygen) around the fuel stream is covered further on . The aspiration of furnace gases into the oxygen jets prior to mixing with the fuel is indicated in Figure 2 by the small |