Effect of modified sludge on the rheological properties and co-slurry mechanism of petroleum coke–sludge slurry

Poor stability and low gasification reactivity of petroleum coke–water slurry (PCWS) significantly limit large-scale gasification applications of PCWS. Co-slurry of sludge and petroleum coke can be used to solve the problems of poor stability and low gasification reactivity of PCWS. In this study, petroleum coke–sludge slurry (PCSS) samples were prepared by mixing petroleum coke with three kinds of sludge, namely, petrochemical, sewage, and paper mill paper. The rheological properties and co-slurry mechanism of PCSS were analyzed with different sludge modifiers and sludge mixing proportions. Results showed that the lowest apparent viscosity of PCSS could be obtained by using Ca(OH)2 modifier for the three kinds of sludge. Optimal dosage was approximately 8 wt.% to 10 wt.% based on dry sludge. Maximum mass concentration of PCWS with no stabilizer was 71.3 wt.% and the slurry exhibited shear-thickening behavior. However, PCSS exhibited shear-thinning behavior when approximately 6 wt.% to 8 wt.% of the sludge was added based on dry petroleum coke. Flow behavior of PCSS fitted the Herschel–Bulkley model perfectly. Good stability of PCSS could be obtained despite reducing maximum mass concentration of PCSS to approximately 8 wt.% compared with PCWS after almost 10 wt.% of sludge was added. The co-slurry mechanism of PCSS may have a significant relationship with the physical and chemical properties of sludge. The network structure of sludge floc and the network structure formed by a chemical bond between petroleum coke and sludge determined the rheological properties of PCSS.