Environmental assessment by dynamic full-field synergy model in co-combustion of coal and sludge with high water content

The management of industrial sludge generated considerable interest for environmental protection. The cost associated with the treatment of sludge with high water content is considerably higher before the discharge of a clean effluent. In order to reduce this cost, this study developed the co-combustion of coal and sludge with high water content in a 220 t/h boiler, to tackle the sludge and control the SO₂, NO_x, and CO₂ emissions from the boiler. The idea at the basis of this study was to directly eject the sludge with high water content into the boiler. A dynamic full-field synergy model was developed to perform the environmental assessment, which considers the dynamic characteristic and the full-field synergy over two co-combustion fields. Industrial field data were used to validate the model. It was found that boiler efficiency decreased only by 0.1% with sludge ejection, while flue gas moisture was almost unvaried. The SO₂ and NO_x emissions were reduced by 14.27% and 8.23% respectively, if compared with emissions without co-combustion of coal and sludge. The results are attributed to the improved synergy effects. The drive forces of liquid and solid particles are the dominant steps for the fluid flow field transformation between the W-shape and the M-shape. The dynamic full-field synergy model, presented in this study, allows the characterization of co-combustion with 92% water content and a nozzle diameter of 1.5–3.5 mm. It accurately describes the full-field synergy effects of the field number over two, a result that could not be obtained by the conventional multi-field synergy model.