(473b) Process Fundamentals in a Counter-Current Moving Bed

The counter-current moving bed has been widely applied in industry, e.g., solvent removal for polyolefins and food products, and moisture reduction for biomass or plastics. ExxonMobil applied the purge bin for their polyolefin technology. After being generated in a reactor, these polyolefin materials are known to have high levels of dissolved hydrocarbon content, and adequate purging is required for safe operations and regulatory compliance. On the other hand, excessive purge gas flow rate could introduce unwanted N2, and increase flaring. This work focuses on understanding the multiscale, fundamentals of a moving bed purge bin.

A phenomenological model based on process fundamentals is developed which incorporated the hydrodynamics, kinetics, and thermodynamics to understand the performance of a purge bin. These components are modeled in a transient manner (not just simulated at steady state) in the gPROMS software platform. After comparing with the literature data, a sensitivity study is presented to understand the effects of operating parameters such as purging dimensions, temperature, pressure, purge gas flow rate and composition, and purge gas injection location, on the purging performance. The mal-distributions of gas and solids mass flux in a purge bin were shown to have a large effect on purging performance.