Gas residence time distribution in a conical spouted bed

• Gas RTD in a conical spouted bed are characterized by radioactive technique.
• Inlet gas flow partitioning between spout and annulus is characterized and evaluated.
• A predictive model for the gas flow split between spout and annulus is developed.
• Gas flows from the spout into the annulus all along the spout height.
• Mean gas velocities in spout and annulus are evaluated.

Conical spouted beds (CSB) are considered as promising contacting devices for several applications such as drying. One of the most critical parameters influencing the performance of a CSB is the gas partitioning between the spout and annulus regions. This study presents results from gas residence time distribution (RTD) experiments carried out using a radioactive tracer measurement in a fully instrumented laboratory CSB. RTD measurements were done in the conical empty vessel and in the CSB operating with and without a draft tube. Comparisons between the RTD curves obtained clearly show the influence of the operating parameters on the gas partitioning between the spout and annulus regions. It is highlighted that the fraction of total gas injected in the CSB that passes through the annulus reaches values up to 90% for large bed height. The fraction of total flow that passes through the spout and the annulus regions appears to be independent of the operating value of U/Ums. The gas penetration in the annulus occurs along the entire interface between these two regions.A predictive model for the partitioning of gas between the annulus and the spout is also developed based on the expression of mass and momentum balances for the gas in the different regions of the conical spouted bed. Experimental results are compared to the model's predictions in term of gas residence time distribution in the annulus and spout regions. The model is also successfully used to highlight gas-partitioning parameters.

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