Evaluation of dewatered and partially dried sewage sludge combustion based on energy balance and carbon footprint

Calbay, Emin
Aim of this thesis is to evaluate dewatered (wet) and partially dried sludge combustion, based on energy balance, carbon footprint and cost estimations. Thermal processes have advantage of converting sludge into energy. Transition from environmentally risky disposal methods to environmentally friendly innovative thermal processes is crucial. Until innovative technologies are proven to be robust and efficient, mono-incineration is evaluated as the transition technology in sludge management. Sufficient data and easy operation due to being conventional makes mono-incineration an available and applicable thermal process for sewage sludge. Besides, electricity generation has potential to avoid carbon dioxide (CO2) emissions. Only mono-incineration is evaluated in this study because in co-combustion applications, sludge disposal is directly dependent on the sectoral dynamics of cement plants or power plants where co-combustion occurs. In this study, six different mono-incineration scenarios are developed. Generally, an autogenous combustion, combustion of a substance without external fuel supply, cannot be achieved for dewatered sludges. Therefore, scenarios are differing by additional fuel consumption in furnaces or partial drying application prior to furnaces. Besides, electric generation is applied in half of the scenarios. For each scenario and each sludge selected, mass and energy balances, carbon footprints and initial cost estimations are conducted. Evaluation criteria are; fossil fuel consumptions, electric consumptions, electricity generations, net CO2 emissions and initial cost estimations. Scenarios including direct combustion of dewatered sludge with natural gas or partial drying by recovered energy from combustion are advantageous regarding the evaluation criteria. Scenarios including partial drying with external fuel supply do not show any advantage for any of the evaluation criteria.