Investigation of Loop Seal Operation By Pulse Air Injection for Improving the Performance and Stability

In this study, the solid recirculation characteristics of loop seal have been tested in a Fluidized Bed cold model system, and the hydrodynamic behavior in downcomer and riser section in various operating conditions. The aim of this work is to fix the appropriate structure and operation of actual scale loop seal installed in a cold model of dual bubbling fluidized beds(DBFBs) system.

The hydrodynamics of solids material recycle through a loop seal (size 70 x 28 cm) in the downcomer and riser section of the DBFBs cold model have been measured in various operation conditions. Silica sand was applied as bed material and tested the fluidization characteristics in a reactor chamber (gasifier: 80 cm, combustor: 93 cm) with 70 cm in height. A reactor chamber was connected to stand pipe then to a loop seal with several riser pipes without mechanical valves. Solids circulation rate (G_s) experiment have been performed in various outlet riser pipe size (6 inches and 4 inches) and various aeration velocity in the loop seal in this study. Some experiments were carried out by flowing solids particle from reactor chamber through standpipe by continuous aeration to obtain the solids particle behavior in the circulating fluidized bed system. Solid flow rate through the loop seal increases linearly with increasing aeration rate of loop seal gas. At the same aeration rate, the solid circulation rate can be obtained by applying 10 or 6 inches riser pipes. The obtained solid circulation rate has been calculated from total amount of solid flow out from loop seal with the operation time. According to the result, the most influence factor to reach high solid circulation rate is aeration velocity of the loop seal, especially in the downcomer section. The higher circulation rate can be obtained by increasing in gas velocity in downcomer in this experiment, influence of fluidization regimes in riser was also investigated by changing standpipe size from 10 inches to 4 inches. It can be concluded from the experimental and theoretical considerations that superficial velocity should be more than the transport velocity to make particle flow steady. The higher aeration velocity in loop seal can be obtained by changing standpipe size in outlet of riser section, from 10 inches initially to be 6 inches and 4 inches. And also in this study, it was proposed a pulse operated loop seal (POLS) using pulse injective flow to loop seal for to establish simple operation method. Performance of continuous flow and pulse flow of loop seals was examined to check on the validity. It was observed that averaged particle circulation rate could be achieved by application of POLS in similar aeration gas injection. The result of particle circulation in POLS will be reported in the presentation.