OCR Text |
Show reduction of N O x and the oxidation of C O and Dioxins. In municipal solid waste incinerators, cross jet flow mixjng is used. This study focuses on the effect of the design parameters relating to cross jet mixing on the mixing performance in the simplified model incinerator. 2. INCINERATOR MODELING Figure 1 shows typical diagram of fluidized bed incinerator with reburnng gas jet nozzle. The incinerator was equipped with natural gas injectors and secondary air nozzles. The secondary air is injected from the nozzle to promote the oxidation of unburned species like CO. Reburning gas is injected from the nozzle upward to the secondary air. Reburning natural gas was mixed with E G R (exhaust-gas recirculation) gas before injected into the incinerator to promote the mixing with the primary combustion product. In the reburning technology, the flow rate of reburning gas. E GR gas and burnout air are determined by various factors such as excess air ratio. temperature and natural gas input. The present study focuses on the effect of the design parameters relating to cross jet mixing on the mixing performance in the simplified model incinerator. Three-dimensional flow simulations are applied to the model geometry of the injection nozzles. Figure 2 shows a typical cross jet configuration in the combustion chamber of an incinerator. Secondary air or reburning natural gas is injected as a multi-jet into the combustion gas stream. The angle between the jet axis to the transverse combustion gas stream is one of the major design variable, which influences the mixing in the reburning zone and burnout zone. For the simplicity of the current study, the angle is held constant at 90° to the transverse flow. 3. GEVERNING EQUATIONS For the prediction of the flow field in the model incinerator . The C F X 4.2 was employed with the standard k-e turbulence model. The required governing equations are those of mass, momentum and species concentration conservation in the time-averaged form. The k-e turbulent model also includes two additional conservation equations for the average turbulent kinetic energy and its dissipation rate. The governing equations are outlined below. Conservation of mass: OX, Conservation of momemntum: |