INFLUENCE OF THE OPERATING CONDITIONS ON GAS AND SOLID FLOW PATTERNS INTO A LOOP-SEAL OPERATED IN A CIRCULATING FLUIDIZED BED

The dual interconnected fluidized bed (DIFB) technology has recently risen to renewed interest for process applications whenever distinct reactive environments need to be established while sharing a solid stream acting as reactant or thermal carrier. Loop-seals are commonly used in CFBs and DIFBs to control the mass flow rate of solids or to seal gaseous streams. Despite empirical or semiempirical criteria for correct loop-seal design have been laid, thorough characterization of the hydrodynamics of loop-seals, especially under large solid throughput conditions, is still lacking. The hydrodynamics of a loop-seal operated as solids re-injection device between a 40 mm ID downcomer and a 102 mm ID riser in a lab-scale cold CFB apparatus has been investigated. The experimental procedure includes measurement of the pressure time series along the CFB loop and in the loop-seal and solids mass flux along the riser. The gas flow patterns have been characterized by CO2 continuous injection/measurement into different locations along both loop-seal chambers. Solids flow patterns have been characterized by impulsive injection of dye-coloured particles into the supply chamber followed by ad-hoc particle tracking procedure. The characterization of the gas and solids flow patterns has been carried out by varying: i) the fluidization velocity in the riser; ii) the fluidization velocity in the loop seal; iii) bed solids size.