| OCR Text |
Show 2.0 REACTOR DESIGN 2.1 General Procedure The starting point in making a reactor design is the characteristics of the flue gas system to be treated: • quantity of flue gas • flue gas temperature • flue gas composition, in particular; percentage water vapor percentage oxygen quantity of NO /N02 quantity of S02 and/or other catalyst poisons (metals, As, etc.) • desired final NOx level and permitted NH3 slip • available pressure drop • (for retrofits) orientation and dimensions of the existing ducting Prospective clients are customarily sent a questionnaire so that the denox system can be tailored to the specific unit and to the client's requirements. A remark is in order about the temperature of the flue gas. In applications where significant amounts of S02 (say > 5 ppm) are present, one does not have complete freedom in selecting the flue gas temperature. The reason is that S02 acts as a catalyst poison, the rate of catalyst decline being strongly dependent on flue gas temperature (see Refs. 1 and 2). If the temperature is high enough, there will be some initial decline of catalyst activity, followed by an essentially stable plateau. The required minimum temperature depends on the amount of S02 in the flue gas. In general, laboratory testing is necessary to establish this temperature level. The required amount of catalyst (or, stated otherwise, the required space velocity) is determined in a complex way by the kinetics of the reaction. The existing knowledge of the kinetics is as yet incomplete, so that in practice one is obliged to determine the space velocity by laboratory tests. (A discussion of denox kinetics is presented in Ref. 3). These lab tests must be done under conditions that are as realistic as possible, as far as the flue gas composition is concerned (especially H20, 02 and SO~. 4 |
