1984-National-Waste-Processing-Conference-18-00011984-National-Waste-Processing-Conference-18-00021984-National-Waste-Processing-Conference-18-00031984-National-Waste-Processing-Conference-18-00041984-National-Waste-Processing-Conference-18-00051984-National-Waste-Processing-Conference-18-00061984-National-Waste-Processing-Conference-18-00071984-National-Waste-Processing-Conference-18-00081984-National-Waste-Processing-Conference-18-00091984-National-Waste-Processing-Conference-18-00101984-National-Waste-Processing-Conference-18-00111984-National-Waste-Processing-Conference-18-00121984-National-Waste-Processing-Conference-18-00131984-National-Waste-Processing-Conference-18-00141984-National-Waste-Processing-Conference-18-00151984-National-Waste-Processing-Conference-18-00161984-National-Waste-Processing-Conference-18-0017NUMERICAL SIMULATION OF ENERGY RECOVERY INCINERATORS c. A. KODRES Mechanical Systems Division Naval Civil Engineering Laboratory Port Hueneme, California ABSTRACT A mathematical model is developed to simulate the dual combustion chamber energy recovery incinerator. The key to the model is the analysis of the incinerator by components; conservation of energy is applied to the flame and primary combustion chamber, secondary combustion chamber, and heat exchanger, in sequence, to predict temperatures and heat transfer rates throughout the system. Application of the model is illustrated by using it to conduct a limited parametric examination of this type of incinerator. The importance of combustion air control and heat exchanger performance is demonstrated. A BD Cp (1) hCONV NOMENCLATURE -surface area -blow down - specific heat at temperature T - convection heat transfer fUm coeffi-cient t!.h (1) - enthalpy at temperature T relative to enthalpy at TREF K = thermal conductance k - coefficient of thermal conductivity LMTD -logarithmic mean overall temperature difference M - mass flow rate nJ through n12 - molar coefficients • q - heat flux • qFLAME • qPCC T t:.T fJ. a Subscripts AIR ASH AVe COND CONY DRY FEED FLAME FUEL 178 -energy liberated to the flame - energy liberated to the primary com-bustion chamber - temperature -temperature relative' to the reference temperature; t:.T = T -TREF = overall heat transfer coefficient of heat exchanger = emissivity at temperature T = efficiency - viscosity - Stefan-Boltzmann constant - refers to airflows, combustion or leakage as applicable -refers to incinerator ash - average value -by conduction heat transfer = by convection heat transfer = refers to fuel (waste) conditions with all moisture removed = refers to feed water entering the heat exchanger -refers to incinerator flame - refers to the waste fed into the incin-eratorF�W G�W HTEXC LEAK MIX PCC RAD REF SCC SHELL STACK STEAM WALLS W�OO 00 = from the flame to the combustion products (gases) = from the flame to the incinerator walls = from the combustion gases to the incinerator walls -refers to heat exchanger = air leakage, into the PCC or down the dump stack as applicable = refers to products of combustion in the PCC or SCC as applicable = primary combustion chamber = by radiation heat transfer -reference = secondary combustion chamber -refers to outer skin of incinerator walls = refers to combustion products exiting the heat exchanger -refers to steam generated by the energy recovery heat exchanger - refers to inner surface of incinerator walls = from the outer skin to surrounding atmosphere = ambient condition INTRODUCTION Energy reco\rery incinerators are a solution to two problems. Landfill disposal requirements are reduced by decreasing the volume of the refuse and, simultaneously, conventional fuels are conserved by utilizing the energy liberated in the combustion of the solid waste. There are some drawbacks. Incineration can be expensive, both in terms of initial costs and operating and maintenance costs. Some environmental problems are inherent in these devices. A potential for air pollution exists. Particulate emissions and/or undesirable products of combustion may have to be faced. The ash must be disposed of, a problem if it is not completely inert or if hazardous nonorganic components were present in the waste. Finally, energy recovery, the generation of steam, for example, is often sporadic and unpredictable. Nevertheless, events of the last decade have acceler.ated the construction of energy recovery incinerators. Land available for mls has been neady exhausted in many areas. Thus, the cost of the service and the distance to an 179 available site have increased, pushing up the cost of landml disposal. The oil crises have created an awareness of energy limitations, spawning the development of unconventional sources. The physics of incineration is extremely complex, coupling heat, mass, and momentum transfer to the chemical kinetics of solid waste combustion. Energy recovery further complicates the problem. Therefore, most incinerator designs are based on experience and empirical correlations rather than theoretical predictions. Yet, with assumptions, it is possible to theoretically examine an incinerator to the extent of, at least, getting a valid "feel" for its operation. Questions such as "What are the most important parameters?" and "What are the ranges of these parameters?" can often be answered. For new construction, the answers help determine where the design effort should be concentrated. Some of the trial and error can usually be avoided. An approximate theoretical analysis can also be used for troubleshooting existing facilities. The Navy has developed a theoretical model to use as a tool for troubleshooting the three 20 TPD energy recovery incinerators located at the Naval Air Station (NAS) in Jacksonville, Florida [1]. These incinerators are dual combustion chamber devices. In this paper, the model is described. Application of the model is illustrated by using it to conduct a limited parametric examination of the Jacksonville incinerators. DUAL COMBUSTION CHAMBER INCINERATORS Figure 1 is a schematic of a dual combustion chamber energy