Estimation of Burning Rates in Solid Waste Combustion Furnace

The author provides an interesting one-dimensional ap­ plication of Essenhigh's bed combustion models to munici­ pal waste combustors. Some of the model's limitations are recognized when the author explains that this work only considers chemical heat release and that radiative and con­ vective heat release may be significant and should be con­ sidered as well. In the mid 1970s, I was part of a team that used Essenhigh's model frame work and finite element tech­ niques to model the Landguard Process (a counter-current rotary kiln gasifier). The Landguard modeling was part of the EPA-sponsored technical evaluation of the Baltimore plant to help us understand why the roughly 30: I scale-up from prototype to commercial unit failed. We learned that the Essenhigh model had to be expanded to separately consider the heat transfer modes and losses the author notes, solidand gas-phase reactions, and that the solids had to be modeled along the lines of conventionally defined combustion zones (i.e., drying, ignition, rapid burn­ ing, char burn-out, and cooling) before we could get the model to match the measured end conditions. This means that we had to consider volatilization (gasification) effects as well as the diffusion-limited fixed carbon burn-out. Consequently, I believe that the author's conclusions should be considered preliminary until further work is done to incorporate, at least on a heuristic basis, additional known significant parameters into the model. I also suggest that the model be compared to field data on furnace residue carbon and the chemistry of the off-gases at the system boundaries. Such comparisons and validations becomes particularly important if the author wants to compare modular (starved air) combustors and conventional mass burning units. Modular combustors are designed to introduce 80-90% of theoretical air into the primary chamber to gasify the waste and inherently produce a carbon-rich char as residue. In the case of a mass burning unit, more than theoretical air is in-