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Show BENCH SCALE REBVRNING EXPERIMENTS ON A 50 KWt FURNACE Trials were conducted using the 50 KWt test rig available at the £NEL-CRIN experimental station at Leghorn . This vertical down-fired pulverized coal or oil capable experimental furnace is shown in Figure 1 . The coal feed rate varies from 4 to 8 kg/hr and the oil rate from 3 to 6 kg/h . The combustion air can be pre-heated up to 600·C and when coal is burned , the primary transport air is heated up to 200·C . All inlet and outlet rates, temperatures and pressures can be measured to check heat and mass balance . C,. C, ... PRIMAR COMBUSTION ZONE REBURNING ZONE POST-COMBUSTION ZONE Fig 1 SO Wt furnace and main expenmental variables It is possible to sample or to introduce probes, such as pyrometers , at six axial distances from the burner Temperature, gas composition and solids concentration may be measured all along the furnace axis by introducing probes from the bottom . The experimental tests (detailed in (3» were conducted using oil as the primary fuel and gas as the reburn fuel with the final objective of investigating the effect of these principal process variables : a ) oxygen concentration in the main combustion zone, b) reburn fuel percent , and c) NO. initial concentration . Figure 2 shows the effect of variabl a) which determines the stoichiometry of the main zone . The importance of stoichiometry in the main zon is evident with maximum NO. reduction obtained with minimum oxygen level at the exit of the primary zone The NO. reduction by reburning increases also with the percentage of reb urn fuel, as shown in Figure 3 . Th effect of reburning zone temperature (Tr ) is not important when reburn fuel X is low, but is increasingly important as gas flow increases Th l means that the kinetics of the process are es s nt la l l y dominated by the partial pressure of the rad icals 2 w~-----------------------------------------, 30 ~~-----r----'-----~----r---~~--~-----r----~ 02 06 08 10 12 I . O2, ~ Fig. 2 DeNOx Efficiency vs Oxygen Concentration of Pnmary COOlbustlOn Zone (SO KWt) ~-r------------------------------------------~ 70 ,Ga •• 17" l20C 1300 I~ 1 soc TR 'C Fig 3 DeNOx Efficiency vs Temperature of Reburnlng Zone (50 I) generated with the reb urn fuel . When there is an abundance of radicals, temperature is important, while when radical formation is low, they ar immedia el ' con ~ umed by the r duc tlon proc nd t mperatur do ~ no t pI y an impoltant rol Figur 4 shows th t proc 5S efficiency is r lativ lv ind p ndent from N inltia values. This 1s n extrem Iy importan finding which supports th application of r burning t chno ogy in combination with primary combustion modtflcation and low-NO. burn r without any reduction 1 tffl c i nc) of th proc s |