Surrogate model for improved simulations of small-scale sludge incineration plants

Although various modelling approaches exist for the simulation of solid fuel combustion, no specific model has been developed for the accurate description of gas-phase combustion in small-scale combustion devices. This is particularly limiting in scenarios when volatile-rich, complex and incompletely described solid fuels such as sewage sludge are used. To address this issue, an accurate description of combustion from the fuel bed onwards is required as well as an improved description of emitted volatiles. This paper introduces an innovative surrogate-based combustion model that combines data on sludge devolatilisation and measured combustion characteristics to offer a new surrogate composition. The composition includes heavy hydrocarbon species to accurately describe combustion evolution. A sensitivity analysis revealed that H2 contributes significantly to combustion evolution, while the most robust surrogate composition is obtained when ethanol is used as a leading representative of heavier hydrocarbons. The model can be used to produce suitable surrogates for the main sludge combustion interval, offering the required improvement in fuel descriptions and accuracy of simulations in the vicinity of the fuel bed. Hence, this model is particularly suitable for the optimisation of temperature, heat release rate, and concentration field in combustion chambers with limited volumes.