Mass transfer research on solid-liquid separation of extracted coal tar residue based on diffusion model

Abstract

A large amount of coal tar residue (CTR) produced in the process of coal coking and tar processing is recognized as hazardous industrial waste with a high carbon content and strong carcinogenic polycyclic aromatic hydrocarbons. Through solvent extraction, CTR can be separated into economically valuable tar and fixed carbon, and waste recycling can be realized. In this paper, a mathematical model of CTR solid-liquid extraction is established based on a diffusion model and experiments, and the mass transfer law, mass transfer equation, and influence of different conditions of solid-liquid separation of CTR from toluene extraction are studied. First, the empirical formula is used to derive the change in the mass transfer coefficient kf outside the particles during extraction, and the kf gradually decreases as the extraction progresses. The particle swarm optimization is used to obtain the best effective diffusion coefficient Deff, inside the particles, which is 9.65 × 10−14 m2/s. The effective diffusion coefficient, Deff, was determined and corrected based on experimental data. A second-order function was fitted to describe the variation of Deff with temperature. MATLAB software was used to solve the model the concentration change law and extraction law during extraction were obtained. According to the model simulation, the influence of different conditions such as agent residue ratio, stirring speed, particle radius, and temperature on the extraction process is calculated.