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The dust cake is critical to improve the fine particle collection efficiency in the gas-solid separation process of the granular bed filter (GBF). In this work, the dust cake formation and the corresponding filtration characteristics in a cyclone-granular bed filter (C-GBF) were investigated by experiments under a constant-velocity filtering condition. It was found that cake filtration, deep-bed filtration and the corresponding transitional phenomena could be observed in the C-GBF. A critical porosity was defined to identify the transition from cake filtration to deep-bed filtration. A following parametric study showed that a higher filtration gas velocity could increase the critical porosity and made it more difficult to form a dust cake. It was also demonstrated that the critical porosity was little affected by the dust concentration. However, the time point of the transition of different filtration modes was earlier with a higher dust concentration. The inlet gas velocity ultimately resulted in the different dust concentrations into the GBF. The similar dynamic processes of cake formation were obtained for different granular sizes. These results provided a deeper understanding of the dynamic behaviors of cake formation and filtration mode transition, which played an important role in the design and the scaling-up of the C-GBF filtration systems.

The rapid and efficient filtration of particles from high temperature pyrolysis vapors is of crucial importance for enhancing yields and quality of pyrolysis oil. In this work, an integrated dust removal technology of cyclone-granular bed filter (C-GBF) was designed. A computational fluid dynamics (CFD) simulation of the flow pattern of the C-GBF was carried out. The Reynolds stress model (RSM) and discrete phase model (DPM) were used to describe the gas-solid flow behavior in the C-GBF. The simulated results demonstrated that the flow pattern characterized by a free vortex in the C-GBF was observed. The location of maximum tangential velocity was found to be at the inlet section and the maximum value was about 1.2 times larger than the inlet gas velocity. The pressure drop of the C-GBF was mainly affected by the granular bed with the free vortex playing a trivial role. Based on the understanding of flow characteristics of the free vortex, the effects of the inlet gas velocity and filtration gas velocity on separation performance of the C-GBF were analyzed. The feasibility of the C-GBF was further examined by laboratory experiments under a constant-velocity filtration condition. The matching condition of the C-GBF was obtained with an inlet gas velocity of 30 m/s and the corresponding filtration gas velocity of 0.4 m/s.

The filtration of flying char particles from coal pyrolysis vapors plays a very important role in enhancing yields and quality of pyrolysis oil. In this work, the performance of coal pyrolysis flying char particles in a granular bed filter (GBF) was studied in cold model experiments. A filtration model was developed using a macroscopic phenomenological method that describes the filtration of the GBF. The polynomial expression of the relative filter coefficient (F) and the nonlinear expression of the relative pressure drop ratio (G) were applied in the new model. The unsteady state of granular filtration was captured, demonstrating that the GBF performance could be predicted by the new model. Effects of superficial gas velocity, thickness of granular layer, and dust mass concentration on collection efficiency and pressure drop were analyzed. An excellent performance of the GBF was obtained and the total collection efficiency could reach a span between 98% and 99.9%. In the case of lower dust mass concentra...