Degradation of Biomass Pellets during Transport, Handling and Storage: An experimental and numerical study

Presently, biomass pellets play a significant role in energy transition scenarios worldwide. Due to the lack of local supplies, many countries import their pellets from countries with enormous resources. For instance, in Europe, a big share of pellets is imported from the USA, Canada, and Asian countries. Pellets are normally transferred in bulk using ocean vessels with a capacity of up to 40,000 metric tons. Due to mechanical forces and environmental changes throughout the transport and storage steps, pellets are prone to degradation. This may degrade pellets physically or chemically. As a result, fines and dust are generated. Moreover, as pellets absorb and adsorb moisture from the environment, the moisture content and the heating value of pellets may change, and this may also weaken the physical structure because of swelling. The presence of fines and dust may lead to self-ignition and dust explosion, material loss, equipment fouling, and environmental and health issues. The goal of this dissertation is to investigate to what extent biomass pellets degrade during transport and storage. To achieve this, first, we conducted an extensive literature review to reveal the factors that affect the extent of degradation of pellets. Moreover, we studied the commonly used methods to assess the quality parameters and the degradation behavior of pellets in detail. Then, we carried out a series of experiments on physical and chemical degradations of pellets from laboratory to large-scale and analyzed them in the operational and environmental context. By conducting these experiments, we unveiled the relationship between the laboratory test results and the pilot or large-scale transport impact on the proportion of generated fines. Furthermore, a model in the discrete element method (DEM) was developed and used to simulate the breakage pattern of individual pellets under the compression test. The model shows high fidelity in simulating the breakage behavior of pellets under compressive forces in two directions.