The discrete element method coupled with the computational fluid dynamic (CFD-DEM) method is effective for studying the micro-flow process of lignin particles in ceramic membranes. Lignin particles may exhibit various shapes in industry, so it is difficult to model their real shapes in CFD-DEM coupled solutions. Meanwhile, the solution of non-spherical particles requires a very small time-step, which significantly lowers the computational efficiency. Based on this, we proposed a method to simplify the shape of lignin particles into spheres. However, the rolling friction coefficient during the replacement was hard to be obtained. Therefore, the CFD-DEM method was employed to simulate the deposition of lignin particles on a ceramic membrane. Impacts of the rolling friction coefficient on the deposition morphology of the lignin particles were analyzed. The coordination number and porosity of the lignin particles after deposition were calculated, based on which the rolling friction coefficient was calibrated. The results indicated that the deposition morphology, coordination number, and porosity of the lignin particles can be significantly affected by the rolling friction coefficient and slightly influenced by that between the lignin particles and membranes. When the rolling friction coefficient among different particles increased from 0.1 to 3.0, the average coordination number decreased from 3.96 to 2.73, and the porosity increased from 0.65 to 0.73. Besides, when the rolling friction coefficient among the lignin particles was set to 0.6–2.4, the spherical lignin particles could replace the non-spherical particles.
The separation and recovery of lignin in black liquor is a hot topic in current research. Ceramic membrane technology has become the main method of lignin separation in black liquor due to its advantages of green environmental protection, high efficiency and high recovery rate. However, in the separation process, the problem of ceramic membrane fouling has always existed and has become the key to hinder its continuous separation. Aiming at the problem that the existing filtration methods can not meet the continuous separation of lignin in black liquor, this paper proposes to apply the blade dynamic cross-flow filtration device to the separation process of lignin in black liquor, and the influence of blade rotation speed on the separation performance is studied experimentally. The results showed that increasing the rotating speed of the blade could effectively reduce the accumulation of filter cake on the membrane surface and achieve the purpose of improving the filtration flux.
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