Combustion efficiency improvement in a rotary furnance using a post combustion chamber

Abstract

Combustion Efficiency Improvement in a Rotary Furnace using a Post Combustion Chamber. Luwaya Edwin. Department of Mechanical Engineering, University of Zambia.Geometric parameters, of a rotary furnace, necessary for the improvement of combustion efficiency are analysed using Computational Fluid Dynamics (CFD). The simulation is based on a real Rotary Furnace at Kabwe Power and Metals Limited in Kabwe. A Post Combustor Chamber (PCC) was incorporated in the numerical model at the exit of the combustor and the results compared with the case where no post combustor was used. Performance optimisation of the furnace was done by varying the fuel-air ratio and the size of the PCC. The flow characteristic results obtained, for the case of PCC and no PCC incorporated were contrasted. Flow characteristics were looked at in the wake of combustion,focusing on convection, temperature distribution, conduction, and radiative heat transfer. The k-e model is used for turbulence flow prediction. Combustion of premixed fuel is simulated by the Simple Chemical Reacting Scheme (SCRS). The eddy break-up (EBU) model is used to determine the rate of the reaction. The six-flux model is used for the radiative heat transfer without turbulence-radiation interaction i.e. only the products of combustion are participating in radiative heat transfer. The SIMPLEST algorithm is employed to solve the transport equations of momentum and other scalar variables. Radiation field is determined using a modification of the SIMPLEST scheme. The computation has shown that improvement of the thermal performance of the Rotary Furnace can be done using the post combustion chamber. The PCC improves the thermal performance of the furnace by increasing the intensity of recirculation and mixing of hot vitiated products with fresh charge in the primary combustion zone thus increasing residence time of combusting materials in the furnace space. This reduces the exhaust gas loss therefore increasing the useful heat value in the combustor. The heat flux to the sink is equally increased. The combustion efficiency improved by 0.53 percent. For the rotary furnace at Kabwe the PCC should be optimised as demonstrated in this study