Abstract
As part of economic and environmental solution, cement industries massively involved on fuel and material substitution. Due to its economic and environmental performance, solid waste has been largely preferred for fuel and raw material substitution. But no cement facilities operated in Ethiopia still engaged on yet. To this effect, this research intended to find best possible strategy for solid waste fuel substitution in cement kiln: for case specific cement plant of National Cement Share Company (NCSC) and solid waste material (SWM) generated from Dire Dawa City Administration (DDCA).
Accordingly, the research investigated the potential and performance of solid waste resource along with operational restriction and product specification. This information was thus used for evaluating optimal rate of solid waste fuel substitution. Data for operational restriction and product specification of the cement plant were collected through interview & document review. Whereas, the potential & performance of solid waste resource were determined through waste quantification and characterization surveys conducted at point of waste stream. Samples were collected through interview and observation of 180 households and business units from systematically selected two urban kebeles. Observations were made based on weight recording and visual inspection after sorting. Data from waste surveys were analyzed using descriptive statistics. The result revealed that the daily waste generation rate was found about 262ton. Of which the amount of waste components, which is suitable for material and energy recovery in cement plant, accounted for 39.86% (68.77ton/day). The empirical analysis of heating value for net calorific value on dry base was found about 19500kJ/kg. Accordingly, an optimization model with linear problem was developed to find optimal rate of solid waste substitution with maximum economic benefit subject to operational and quality restriction constraint. Micro-soft Solver was used to optimize. The model result showed that at 13% substitution rate: clinker production cost-which is a function of cost of fuel and raw material-was minimized; quality and operational restriction was satisfied. Effects of 13% substitution on emission and combustion air demand were also evaluated. The results revealed that emission (CO2 and SO2) and combustion air demand was reduced by marginal fraction. This indicate that it would be economically as well as environmental feasible for NCSC to substitute 13% SWM generated from DDCA without even affecting the product quality and operation.
Key Words: waste quantification and characterization, material and energy recovery, solid waste fuel substitution, cement plant, operational restriction, product specification, Dire Dawa City
