Effect of low‑grade coal on hydrodynamics and heat transfer in a cyclone separator for different operating conditions in a circulating fluidized bed

In the present work, experimental study of hydrodynamics and heat transfer in cyclone separator of a circulating fluidized bed has been completed successfully. Low‑grade coal was used as bed material having calorific value in the range of 3500–4000 Kcal/Kg and size in the range of 450–850µm. The hydrodynamics study was analyzed for mean particle size of 580 µm and 780 µm. Bed inventories of 600 g, 800 g, and 1000 g were used for both particle sizes. The main effort that has been addressed is the variation of suspension density distribution along the cyclone axis. Suspension density decreases along cyclone axis and maximum at cone exit. The fluid velocity increases rapidly in the convergent section of cyclone. This acceleration converts static pressure energy into kinetic energy, resulting in a sharp drop in manometric head difference). The drag force exerted on the particles force rapidly sweeps the particles out of the zone in the conical portion. While fewer particles occupy the space per unit volume at any given millisecond in the converging zone. Dilution of the solid phase causes a sharp change in the bulk suspension density. The converging walls act as a funnel, forcing more particles to deflect from the boundaries. Simultaneously high‑velocity differentials create a turbulence which maximizes the relative velocity between individual particles, leading to inter particle collisions. Steady‑state heat transfer experiments were carried out by providing heat in the cyclone separator and consequently examining wall to bed heat transfer in the cyclone separator. Effect of parameters such as superficial velocity of air and heat flux on heat transfer characteristics was investigated for particle mean size of 580 µm and inventory of 1000 g. Local heat transfer coefficients along the height of cyclone separator were evaluated and heat transfer behavior has been expressed in terms of Nusselt number. Local heat transfer coefficient and Average Nusselt number increase with increase in heat flux and superficial velocity of air.