Fuel mixtures of oil sludge and waste oils: comprehensive ignition and combustion analysis

• Ignition and combustion characteristics of composite fuels were determined. • Waste oil additives improved the characteristics of oil sludge. • Ignition mechanisms were determined for oil sludge and composite fuels. • The composition of flue gases during combustion were determined. • A feasibility study of oil sludge fuels combustion was performed. Oil residues and industrial waste are among the most promising feedstocks for energy conversion. However, many key processes of thermal conversion of low-grade mixed oil-containing fuels remain insufficiently studied. This study focuses on determining the stability and combustion performance of oil sludge of three types blended with additives (waste cooking oil, waste motor and pump oils, and methanol). It was found that waste cooking and pump oils reduce the viscosity of oil sludges by 5–35 %. Methanol, on the contrary, increased the viscosity of oil sludge by 12 % and worsened storage stability. The addition of waste compressor oil demonstrated the most comprehensive effect on oil sludge combustion, increasing the integral combustion efficiency by 5–7 %. The experiments in a spray-type combustion chamber demonstrated the advantages of the mixed fuel with the waste oil additive over the original oil sludge in terms of combustion efficiency. The estimated payback period for investments in re-equipping fuel storage and handling systems of a diesel boiler to burn oil sludge and its fuel mixtures is no more than 6 months. The obtained results indicate a high potential for the conversion of oil-containing waste and mixtures into energy.