On the comprehension of the gas split in loop seal devices

Abstract

Gas distribution through the chambers of a loop seal in circulating fluidized bed (CFB) units is still difficult to predict and often misunderstood. Dedicated experiments were carried out in an isolated loop seal to assess how the gas fed into a loop seal is distributed under different aeration modes (through the recycle chamber, the supply chamber and both chambers), aeration flowrates and solids fluxes. Experimental results shed light on the non-ideality of the gas-solids flows occurring in these units and, in combination with theoretical considerations, it is demonstrated why semi-empirical models cannot effectively describe the performance of loop seals operating as non-mechanical valves. Recommendations are given for the optimization of the operation of a loop seal as a non-mechanical valve in a solids circulating loop. A method is proposed to characterize the performance of a loop seal in a CFB unit from measurements of that loop seal in isolation mode.