A simulation-driven feasibility study of multicomponent organic solid waste incineration with low NOx emissions in grate-fired beds using an advanced BASIC code

Municipal sewage sludge and landfill waste are challenging auxiliary fuels for co-combustion in municipal solid waste (MSW) incinerators because of their unfavourable fuel properties. Sewage sludge is characterized by high moisture and nitrogen contents and a low heating value, whereas landfill waste contains high ash content and variable combustible fractions. These properties may reduce combustion stability, delay burnout, and influence pollutant formation during co-firing with MSW. Therefore, adding a suitable high-heating-value waste stream can help improve combustion stability while maintaining the disposal capacity of existing incinerators. In this study, MSW co-firing with sewage sludge and landfill waste is numerically investigated in a 500 t/d moving-grate MSW boiler. Co-combustion stability and nitrogen oxides (NOx) emissions are the main concerns; different waste blends and under-grate primary air (PA) distributions are examined and compared. A validated in-house bed model, which describes solid-fuel conversion and heat- and mass-transfer phenomena on moving grates, is extended to include NOx formation and used to simulate the combustion of different blends on the grate. The results indicate that landfill waste blending should not exceed 30 wt%, while sewage sludge co-firing should be limited to 10 wt% under the investigated conditions to avoid unstable combustion and incomplete burnout. A decoupled combustion strategy with a PA ratio of 20-23-27-30 enhanced the reducing atmosphere and NO reduction reactions, achieving a maximum NO reduction of 11.6%. This reduction is mainly attributed to the enhanced reduction of nitric oxide (NO) through reactions with ammonia (NH3) and char. These findings may support the operation of existing incineration facilities for stable, low-NOx co-combustion of MSW with sewage sludge and landfill waste.