Fine particle separation in a riser with flow modifications

Abstract

Fine particle separation is of great interest in industry. Coal and mineral processing industries are currently very interested in particle separation for its potential in cleaning coal matter. A circulating fluidized bed riser system has been constructed to investigate possible separation of coal containing pyrite from clean coal. The system was constructed to operate using compressed air in which an air-solid mixture would pass through the riser and the solids would enter in to a dense, product, or filter collection bin. Several different variables were investigated during the project such as the collection ring wall height, particle entrance size into the riser, and mass flux of particles into the riser. By changing the particle entrance into the riser, and changing the ratio of nozzle flow and particle mass flux, a jet style flow could be achieved. The objective of this investigation was to observe how changing the flow field in a circulating fluidized bed would affect particle separation. The first experiment was conducted using a mixture of sand and steel shot with particles sizes between 250 and 500 micron. Results from using the sand and steel shot proved to be very promising as more than 90% of the steel shot could be collected from the sand. The results were then used to determine the experimental conditions that were to be used while separating pyrite laden coal particles from clean coal. There was approximately 1% initial pyrite in the mixture and size ranges for the particles were between 105 and 210 micron. The results using the run-of-mine coal were not as promising as those of the sand and steel shot as a maximum of 25% of the pyritic laden coal could be separated from the cleaner coal. A third experiment was then performed in which chunks of pure pyrite were crushed and then added into clean coal and run through similar separation conditions to the run-of-mine coal. The mixture contained 4% pyrite, and both the pure pyrite and clean coal size ranges were between 105 and 210 micron. The results from this test proved to be very good as up to 77% of the pure pyrite could be recovered from the clean coal.