Study on flow characteristics of pneumatic conveying of stiff shotcrete materials by CFD-DEM

• The long-distance pneumatic conveying of stiff shotcrete materials has been investigated. • The influencing factors of long-distance pneumatic conveying are clarified. • CFD-DEM is used in long-distance pneumatic conveying simulation. • The linear function relationship between minimum conveying velocity and feeding rate is obtained. Long-distance pneumatic conveying of stiff shotcrete materials (SSM) is critical for modern mining and tunnel engineering but remains underexplored, with existing studies limited to short-distance systems. This work addresses this gap by employing a novel computational fluid dynamics-discrete element method (CFD-DEM) coupled model to analyze SSM flow dynamics, focusing on air compressibility, elbow spacing, and pipe material effects—factors pivotal for industrial-scale optimization but previously unquantified. The model integrates particle morphology approximations and is validated through parameter calibration and field experiments. Key results reveal a linear correlation between feeding rate and minimum conveying velocity, while elbow spacing >1.5 m prevents flow instability. Ceramic-lined steel pipes reduce unit pressure drop by 23 % compared to rubber hoses, with restitution and static friction coefficients increasing stable-section pressure drop by 8–15 %. Power-law relationships between air velocity and pressure are established for pipes (51–70 mm diameter), yielding working pressures of 132–1074 kPa. These findings provide the first comprehensive framework for designing energy-efficient long-distance SSM systems, directly addressing industrial challenges in reducing blockages and wear. The study advances multiphase flow modeling by bridging granular mechanics and compressible aerodynamics, offering actionable insights for sustainable infrastructure development.