Evaluation of the Concentrated Spatial Dust Distribution in Cylindrical Silo during the Filling Process for Predicting Dust Explosion Hazards

Biomass was identified by the industry as suitable fuel for reducing CO₂ emissions in coal fired power stations. Companies such as DRAX power stations in the UK with a plant capacity of around 3870 Mega Watt (MW) handle around 7 million tonnes biomass per annum. The handling of the biomass in the plant required significant investments in the handling and storage infrastructure because biomass has different flow and storage properties than coal. One significant difference is that biomass cannot be stored outside in the reclaim areas for coal because of the nature of the biomass which could cause self-ignition and environmental parameters e.g. moisture could degrade pellets. The storage of pellets at DRAX was realised by building 50 m high domes with a capacity of 112,000m³. These domes are filled with wood pellets via pneumatic conveying lines and conveyer belts which introduce air into the storage silos. The air starts to circulate and entrains fines (particles smaller than 100 microns) which are broken off particles from the pellets. These fines accumulate in certain areas of the silo and at high dust concentrations it can cause dust related health and safety issues such as dust explosions. To investigate the dustiness of the pellets and the air entrainment characteristics of the material a small scale experimental silo was designed. Material e.g. wood dust was fed centrally into the silo and the circulation pattern was recorded with a video camera. The camera recorded illuminated particles in a light plane which was generated with a laser. The laser produced a green light sheet of around 5 mm thickness and the concentration of the illuminated particles was evaluated using Matlab ®. The Matlab code calculated the concentrated spatial dust distribution and results were plotted in a colour map. The colour map provided insides in the formation of dust clouds which may have the potential to cause dust explosions. These information are useful for practitioners to design safety equipment for the biomass storage silos and evaluate hazards for plant operators. The scalability of the experimental results obtained in the small scale silo was evaluated using computational fluid dynamics (CFD) simulations using Fluent. The developed analysis showed that results from simulation and experiments can be compared easily. The findings can be used by academics and practitioners alike to build a better understanding of the complex nature of the dust formation in different sized silos to help to evaluate risks and to operate biomass storage and handling facilities safely.