RESIDENCE TIME CALCULATIONS USING THE NUMERICAL-SIMULATION OF INCINERATOR FLOWS

The value of knowing residence time distributions (RTD's) in mass bum incinerators and the serious limitation imposed by the use of gas volu me-flow rate based average residence time with regard to these inciner ators are recognized. The utility for understanding macromixing of hav ing detailed RTD-information about the incinerator overfire region is demonstrated by estimating RTD's using transient numerical simulation of tracer injection into the 2-D, isothermal flow field of a typical m ass bum incinerator configuration. Several numerical experiments are c onducted to determine the effect of overfire jets on the RTD's of trac er flows introduced into different grate streams. The results indicate that valuable diagnostic information on the state of mixedness in the overfire region can be extracted from these RTD's by mapping them ont o a macromixing scale whose extremes are the RTD of a plug flow and th at of a stirred tank. Further, they not only underscore the critical r ole played by jets in achieving desirable states of macromixing in the overfire region but also point to the significance of the geometry ef fects. Lastly, the opportunity created by the RTD studies for experime ntal validation of incinerator overfire mixing simulations is identifi ed.