Haifeng Lu

Entrained-flow gasification is one of the most promising technological routes for efficient biomass conversion. A critical bottleneck restricting its rapid development lies in the efficient preparation of biomass powders. An ideal biomass powder preparation process should combine low energy demand with favorable particle properties conducive to conveying. However, direct comminution (DC) alone cannot meet these requirements. Here we systematically compare four comminution strategies─DC, multistage comminution (MC), screened comminution (SC), and blended comminution (BC)─and quantify the trade-offs among particle size distribution, morphology, bulk density, and energy demand for micron-scale feedstocks in entrained-flow gasification. MC produces moderate sphericity (0.60) and bulk density (273.2 kg/m3) but the broadest size distribution (span = 2.00); SC yields the narrowest size distribution (span = 1.34) at the cost of the lowest sphericity (0.50) and bulk density (223.8 kg/m3); BC achieves the highest sphericity (0.62) and bulk density (280.0 kg/m3), while DC falls between these extremes. In terms of comminution energy demand, MC, BC, and SC reduce the specific energy demand by 5.8%, 11.1%, and 41.0%, respectively, compared to DC (102.04 kWh/t). Energy allocation analysis reveals that heat loss from moisture evaporation accounts for 44.2–53.8% of the total energy input, underscoring the importance of predrying treatment. These findings highlight feedstock drying as a general principle for energy-efficient comminution, providing a quantitative framework for selecting comminution strategies based on specific industrial priorities and establishing a mechanistic basis for designing energy-efficient biomass pretreatment tailored to entrained-flow gasification.

Biomass particles with low density and pronounced anisotropy tend to form periodic dynamic arches during hopper discharge, which severely affects flow stability and controllability and has become a critical bottleneck restricting their large-scale and efficient utilization. In this study, the complete evolution of dynamic arches of corn stover and corn cob was revealed with the help of high-speed image processing and signal analysis techniques. The results reveal a clear transition from long-period intermittent arching to short-period rapid arch collapse and finally to arch-free stable flow with increasing gas velocity. By conducting force analysis on arch formation and collapse processes, it clarifies the intrinsic driving mechanism of the periodic arch-collapse behavior of biomass particles, where the periodic alternating evolution of pressure difference directly dominates the arch structure. Based on this, a semi-empirical model integrating gas seepage and arch dynamics was established to calculate the arch period, and the model-calculated values are in good agreement with the experimental results. This study conducts an in-depth analysis of the arch-breaking mechanism of corn stover and corn cob in a conical hopper under aeration conditions. The results can provide a reference for the aeration optimization of biomass feeding systems with similar material characteristics and hopper configurations.

Powder compression is essential in the storage and transportation processes. The compression characteristics of pulverized coal, rice husk and lignocellulose were compared under mechanical and gas pressurization respectively. The experimental results showed that the descending order of relative packing density was lignocellulose > rice husk > pulverized coal under mechanical pressurization, while an opposite trend was observed under gas pressurization. The effect of cohesion properties on compression results, such as inter-particle adhesion force and powder bed cohesion, was also investigated. For mechanical pressurization, the powder bed of cohesive biomass had higher void fraction, which was directly linked to larger relative packing density. On the contrary, gas permeated easily into the biomass powder bed, and the lower pressure drop decreased the compression capacity of gas pressurization. In addition, a model for predicting the relative packing density was proposed with an error of ± 5%.

In this paper, the relationship between the conveying pressure drop and the gas velocity were firstly characterized based on pressure signal analysis. The critical gas velocity was obtained to classify the transfer bottle into stationary station and motion state, and pressure fluctuation characteristics in each state were determined. Further, derived from the traditional additional pressure drop method, the model for pressure drop prediction was developed. The gas pressure drop was further divided into four terms, including those in the conveying pipe, through the sudden contraction from the pipe to the head of the transfer bottle, through the sudden expansion from the end of the transfer bottle to the pipe, and through the gap between the bottle and the pipe. The solid-phase friction pressure drop was determined based on correctly estimation of the dynamic friction coefficient.The model can satisfactorily predict the pressure drop, giving errors mostly smaller than ±10%.