Investigation of Loop Seal Performance in Cold Model Circulating Fluidized Bed

In this study, the particle recirculation characteristics of loop seal have been tested in a Fluidized Bed cold model system, and the hydrodynamic behaviour in downcomer and riser section in various operating conditions. The aim of this work is to develop a hydrodynamic model for a cold model of fluidized bed gasification incorporating with loop seal and stand pipe to predict the basic hydrodynamic properties such as pressure drop, minimum fluidization velocity and bed material circulation rate. The hydrodynamics of solids material recycle through a loop seal (size 70 x 28 cm) in the downcomer and riser section of CFB cold model have been determined. Fluidization testing was conducted in a reactor chamber (gasifier  80 cm, combustor 93 cm) and filled by solids particle up to around 70 cm in height. The reactor chamber was connected to stand pipe and a loop seal as non-mechanical valve. Particles 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 (V_J,RD and V_J,RU) in this study. Some experiments were carried out by flowing solids particle from reactor chamber through standpipe and a loop seal, 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 fluidizing gas. At the same aeration rate, the solid circulation rate can be obtained by using standpipe of downcomer 10 inches and 6 inches for riser pipe. A number factors influenced to the solids material behaviour, such as solid inventory, fluidizing gas velocity, and outlet standpipe size. The obtained solid circulation rate has been correlated with bed inventory height in the reactor and correlation between total amount of solid flow out from loop seal with the operation time. The solids circulation rate through the loop seal increases linearly to a maximum value with increasing aeration rates of downcomer up to 4Umf and riser up to 120Umf, due to the increase of frictional drag on the particles. Therefore, the most influenced factor to reach high solid circulation rate is aeration velocity of the loop seal, especially in the riser section. 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. As a result, it was found that the operability was improved by POLS. It was also suggested that the particle circulation rate can be controlled by low pulse average rate.