| OCR Text |
Show 3 temperature for selective noncatalytic NOx reduction. The amount of natural gas that must be burned to achieve the desired turbine inlet temperature can be reduced if air heater design can be improved to reduce the required approach temperature and radiant air heater panels can be used in the primary combustion zone. The basic idea of our design is to control NO emissions and wall ash problems by using multiple, long axial flamesxwhich minimize the conversion of fuel nitrogen to NO by virtue of their fuel rich center core. Figure 3 illustrates the overall process flow sheet for this concept which is designed to support the baseline power cycle. It consists of the following major design elements: Primary Zone: The primary zone will have an overall residence time of approximately one second and an axial length of approximately thirty meters to facilitate the long, pulverized coal flames. The primary zone would be operated slightly air deficient (primary zone stoichiometries between 0.85 and 1.0). The secondary air would be both preheated (to 1,0000F) and vitiated (to 17% oxygen). The walls of the combustor would be used to provide air passages for the remaining portion of the working fluid from the turbine exhaust (termed dilution air in this configuration). The mass flow rate of this stream is more than twice that required for combustion in the primary zone, but it is not desirable to put all of the turbine exhaust air through the primary zone. (Doing so would greatly enhance NO formation; it would also reduce our ability to transfer heat from fhe core of the axial flame via radiation). Burnout Zone: A small portion of the dilution air would be added to the main combustion stream in this zone to raise the stoichiometry to approximately 1.10 and drop the overall gas temperature to about 2700F. This zone is designed to ensure oxidation of any remaining carbon or CO in a controlled manner such that secondary formation of NO can be minimized. A residence time of approximately 400 ms would ~e required. Dilution Zone: In this zone the remaining dilution air would be mixed with the combustion products to produce the required air heater inlet temperature of approximately 2400F. This zone would be designed to facilitate the mixing of the dilution air, the solidification of sticky ash particles, and subsequently the rejection of a significant portion of the fly ash. Segmented Air Heater: The air heaters for the turbine working fluid have been divided into two (physically adjacent) segments which will provide overall air preheating from 730F to 1800F. They have been segmented to provide the proper inlet temperature for the SNCR zone. |
