On the degradation of wood pellets during pneumatic conveying: Experiments and DEM-CFD simulations

In the present thesis, the dependence of wood pellet degradation and fines formation during pneumatic conveying on operating conditions like air and product mass flow or shape of pipe components is investigated. Both the size reduction of the cylindrical pellets during pneumatic transport caused by mechanical impacts and the prevailing pressure losses are analysed experimentally and numerically. Single particle impact tests are performed for investigating the breakage behaviour of wood pellets including the effect of particle length, impact velocity and collision angle. Based on the empirical correlations derived, a numerical degradation model is developed and implemented into the in-house DEM code of the Department of Energy Plant and Technology of the Ruhr-University Bochum. Experimental and numerical investigations are conducted using coupled DEM-CFD simulations to obtain detailed insights into flow conditions, particle motion and the mechanical loads on the pellets during pneumatic conveying. Numerical results show good qualitative agreement with the experimentally determined degradation rates and prevailing pressure losses. The degradation model developed allows detailed investigation into wood pellet degradation and fines formation during pneumatic conveying and enables the design of pipe configurations and operating conditions to prevent particle size reduction and excessive pressure losses.