| OCR Text |
Show -5- AIR STAGED COMBUSTION FOR NOx EMISSIONS CONTROL WITH PULVERISED COAL FLAMES Work commenced at Umuiden in the general field of NO emmision x control in the early 1970's and has been reported mainly as the AP (Atmospheric Pollution) investigation series. Towards the end of the last decade, this research tended to become concentrated on pulverised-«oal firing and concerned the concept of air staged low NO burners particularly for application to wall fired boilers, x either in retrofit situations or in new boilers. The most recent work in this field executed at the IFRF and partially reported in reference 2, has been recently completed experimentally and the final reporting is now in progress. This investigation was executed in three parts referred to as APll, 12 and 13 and was concerned with the operation of air staged combustion burners for a wide range of pulverised coals varying in rank from sub-bituminous to low volatile bituminous. For the semi-industrial scale, APll and AP13 investigations, the number 1 experimental furnace was used, set up as a water tube boiler combustion chamber simulator with respect to heat extraction characteristics as shown in figure 1. Scaled-down experimental burners were fired in this furnace, normally at a total thermal input of 2.3 MW in order to achieve a firing density typical of a full scale boiler combustion chamber. For the more fundamental AP12 phase, a reduced scale burner/flame simulator as shown in figure 2, was used through which it was possible to study independently, the effect of a number of parameters such as primary and secondary mixing, primary zone stoichiometry, residence time and heat extraction and overall stoichiometry upon NOx formation and reduction. For this work a total thermal input of 0.185 MW was used. |
