Enhanced motion behavior and heat transfer performance of boiler slag in a rotary drum with heat exchange half-pipes

• A novel rotary drum with half-pipes was experimentally investigated. • Half-pipes structure promotes the radial movement of boiler slag. • Rotational speed, filling level, and quantity of half-pipes were studied. • Comparative results revealed improved motion behavior with half-pipes. To improve the efficiency of waste heat recovery from high-temperature boiler slag, a novel rotary drum with heat exchange half-pipes was proposed and systematically evaluated. The effects of rotational speed, filling level, and the quantity of half-pipes on boiler slag motion behavior were analyzed using the angle of repose and active layer thickness as key indicators, and the comparison of the motion behavior of boiler slag in smooth-walled rotary drum was carried out. As the rotational speed increased from 1 rpm to 5 rpm, the smooth-walled rotary drum showed a maximum angle of repose rising from 37.5° to 41.0°, and active layer thickness from 8 mm to 17 mm. In contrast, the rotary drum with heat exchange half-pipes achieved a higher maximum angle of repose, from 43.5° to 46.0°, and the active layer thickness from 10 mm to 20 mm, indicating stronger boiler slag lifting and radial mixing. When the filling level increased from 5 % to 25 %, the maximum angle of repose increased from 40.0° to 43.0° in the smooth-walled rotary drum, and from 42.5° to 46.5° in the rotary drum with heat exchange half-pipes, showing a more significant rise in the latter. The maximum angle of repose peaked at 46.5° when 32 half-pipes were installed, and further increases in the quantity of half-pipes reduced the spacing between adjacent pipes, weakening their ability to carry particles and resulting in diminished boiler slag mobility. Crucially, Discrete Element Method (DEM) simulations established a direct quantitative link between the enhanced motion behavior and superior thermal performance. The effective heat transfer coefficient in the rotary drum with heat exchange half-pipes has been proven to be higher than that the smooth-walled rotary drum. This study conclusively demonstrates that the rotary drum with heat exchange half-pipes not only augments boiler slag motion but also decisively improves heat transfer efficiency, providing a scientifically grounded and practical strategy for designing high-efficiency boiler slag cooling systems in coal-fired power plants.