Wastewater treatment
produces a large amount of sludge,
where the
minimizing of the disposed sludge is essential for environmental protection.
The co-combustion of sludge with coal is a preferable method for sewage
sludge disposal from the economic and environmental perspective. The
co-combustion of sludge has been widely used in the industry with
the advantages of large processing capacity. The melting characteristics
of ash are an important criterion for the selection of the co-combustion
methods and furnace types. In this study, two types of sludge and
four types of coal with different ash melting points were selected,
where the ash melting behavior upon co-combustion is investigated
by experimental and thermodynamical approaches. Especially, the slag
fluidity upon co-combustion is explored via a modified inclined plane
method. It has been found that the presence of SiO2 and
CaO in sludge substantially enhances its fusion temperature owing
to the high content of CaO, while SiO2 acts as a solvent,
facilitating the co-melting of other oxides and raising the sludge
fusion temperature. Fe2O3 exhibits a specific
mass fraction within the range of 10–20%. Furthermore, the
presence of CaO and SiO2 prohibits the flow ability of
the slag at high temperatures, and Fe2O3 promotes
the flow ability for sludge at high temperatures. With increasing
base/acid ratio, the sludge flow velocity increases remarkably and
peaks at 1.6. The interaction between Fe–Ca and Si–AI
significantly affects the fluidity significantly. The findings are
expected to optimize the condition of co-combustion and desirable
furnace design for the incineration of sludge.