Preparation of the modified sludge-semi-coke water slurry and analysis of its slurring performance and mechanism

Abstract

The sludge-semi-coke water slurry (S-SCWS) and modified sludge-semi-coke water slurry (MS-SCWS) can be used as liquid fuels for combustion and gasification. These slurries have apparent economic advantages in sludge recovery and utilization. High concentration MS-SCWS can be prepared by low-temperature thermal alkali-modified sludge. In this paper, the modified sludge was characterized by Fourier transform infrared spectrometry (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM), and nitrogen adsorption-desorption methods. The adsorption experiments of composite anionic dispersant (NNO/PCE) on semi-coke, sludge and modified sludge demonstrate that low temperature thermal alkali method changes the properties of sludge particles including hydrophilicity, pore structure, surface properties, mineral composition and zeta potential. The apparent viscosity of MS-SCWS prepared from modified sludge was investigated under different modification conditions, such as temperature (25 °C–90 °C), time (60 min–150 min), and the does of sodium hydroxide (15 wt%-30 wt%). Under the optimized low-temperature thermal alkali experimental conditions, the maximum solid concentration of MS-SCWS reached from 66.67% to 68.1%, when the amount of NNO/PCE dispersant dosage was 0.8 wt%, the apparent viscosity decreased from 711.2 mPa·s to 434.2 mPa·s, and the water separation rate (WSR) declined from 6.09% to 0%, while the stability improved significantly. The adsorption kinetics of NNO/PCE dispersant on the surface of semi-coke, sludge, and modified sludge particles showed that the quasi-second-order adsorption kinetic equation can better describe the adsorption process of dispersant on the particle surface. The result of isothermal adsorption experiment showed that the saturated adsorption capacity of NNO/PCE on the surface of semi-coke particles was significantly higher than that of sludge and modified sludge. The adsorption of NNO/PCE on all particle surfaces was monolayer adsorption. The low-temperature thermal alkali pre-treatment of municipal sludge could change its physical and chemical properties. This method is an effective way to develop and utilize sludge on a large scale. • MS-SCWS was prepared by semi-coke powders, modified sludge and dispersant. • The maximum solid concentration of MS-SCWS reached from 66.67% to 68.1% • The electrostatic interaction of particles improved the stability of the MS-SCWS. • The adsorption of dispersants on semi-coke powders was monolayer adsorption. • The interaction mechanism between the dispersants and particles was proposed.