Transient hydrodynamics and heat transfer behaviour in a pressurized circulating fluidized bed during abrupt changes in operating pressure

Abstract

Pressurized circulating fluidized beds (PCFB) are subjected to various fluctuating conditions due to fluctuations in load demands owing to its vast utilization as a combination of heat and power generating unit. As such, analysis of transient heat transfers and hydrodynamics during these fluctuations in PCFB is very important. The present work includes experimental investigation on the transient behaviour of a PCFB unit during abrupt changes in operating pressure. The experiments are performed on a laboratory scale PCFB set up consisting of a stainless-steel riser of height 2 m and an inner diameter of 54 mm. The operating pressure is regulated by a pressure regulator and is measured using a piezo resistive pressure sensor attached to the inlet of the riser. Static pressures and temperatures are also measured along the riser column at various heights. Experiments are performed with 500 g sand as bed inventory at two operating pressure of 2 and 3 bar. Drastic changes in voidage values were observed mostly in the upper region of the riser column for transient conditions in the operating parameters. The experiments showed that with a sudden drop in operating pressure, the heat transfer coefficient momentarily increase and subsequently decrease steadily. The reverse is observed for a sudden increase in operating pressure.