Arnaud R. A.A Valea’s scientific contributions

The present work concerns the study of the influence of combustion air flows on the thermal potential during the combustion of a 2 kg mixture of solid model waste from the city of Ouagadougou. This mixture consists primarily of wood, cardboard and plastic. The prototype model is a natural laterite internal-walled grate furnace. During these investigations, we were interested in the temperature variation measured by 4 thermocouples K1 to K4 placed respectively from the waste bed to the top of the furnace. These variations are considered according to a variable primary and secondary air flow. The maximum primary and secondary airflow is 3000 L/min. Measurements are taken throughout the experiment at a step of 18 seconds and a maximum duration of 3 minutes for each case of flow considered. Maximum temperatures reaching 450oC are observed following the injection of secondary air only. This is explained by the supply of oxygen making the combustion more complete. The results show that the injection of primary and secondary air at a flow rate of 1500 L/min gives a more stable temperature result, i.e. 362,18oC 186,82oC 109,27oC 72,41oC respectively for the thermocouples K1, K2, K3, K4. An increase in the primary and secondary air flow to a maximum of 3000 L/min leads to a drop in temperatures due to the dilute internal atmosphere. These results allow to set the optimal operating parameters of the furnace in order to produce more heat for its recovery into electricity through a heat exchanger and a steam turbine.

The valorization of municipal waste is a good option for energy production. Our work consists of a numerical study of the heat equations in a fixed-bed centimetric grate furnace modeled by a natural laterite inner wall and a kaolin laterite wall. Simulation results showed that the kiln filling rate at 100% is 5 kg of fuel. From 500o C as the starting point for heating, the temperature reaches a maximum of 1225o C and 1050o C respectively for natural and kaolin laterite at 30 minutes of operation. In addition, the internal temperature is optimal around 35 ± 5 hgs-1 of internal air flow. A drop in internal temperature was observed after 35 minutes due to mass degradation and convection of the outlet gas. Natural laterite tends to retain heat inside the kiln more than kaolinite, which dissipates too quickly. These results show that, depending on how heat is converted into energy, the right materials and operations need to be chosen to optimize the process.