Recycling Residual Carbon from Gasification Fine Slag and Its Application for Preparing Slurry Fuels

Residual carbon can be recycled from the solid-waste gasification fine slag by froth flotation which is suspended into bio-oil to produce a new type of slurry fuel, so the comprehensive utilization of recovered carbon and bioenergy can be realized. The flotation process on gasification fine slag has potential economic and environmental benefits. The carbon content in recycling residual carbon is elevated from ∼24% in fine slag to ∼65%. Residual carbon below 106 μm accounts for 84% of the total recovered flotation residual carbon, and the mass ratio of −75 μm fractions is over 80%, which meets the particle size distribution requirements for the preparation of slurry fuel. The 4–12 wt % of flotation residual carbon was added into bio-oil to prepare the residual carbon bio-oil slurry (RCBS) fuel. The RCBS fuel has desired fuel and rheological properties that meet the requirements in boiler combustion aspects. The volume energy density of RCBS fuel with 12 wt % residual carbon is elevated to 21.56 GJ/m3. As the residual carbon added, the TAN (total acid number) value per unit mass of RCBS fuel is decreased. The RCBS fuels with 4–12 wt % of residual carbon present pseudoplastic property and the apparent viscosities at shear rate 100 s–1 are no more than 370 mPa·s, and the maximum flotation residual carbon loading in bio-oil is 17.45% according to comprehensive consideration of pumping requirements and safer application.