Measurement of solids circulation rate in a high temperature dual fluidized bed pilot plant

Conference Dates

May 22-27, 2016


A pilot scale dual fluidized bed gasification system, consisting of a riser as combustor and a bubbling bed as gasifier, is being operated at high solid circulation fluxes to provide necessary heat from the combustor to the gasifier in support of endothermic steam gasification reactions. Since the circulation rate strongly affects mass and energy balances, and therefore greatly influences hydrodynamics and performance of the system, a reliable technique for its accurate measurement is needed. However, there are no reported techniques suitable for measuring solid circulation rates at elevated temperatures typical of gasification systems.

A novel thermal-tracing technique for measuring solids circulation rate is being developed. Particles at room temperatures (cold particles) are injected into a downward-moving packed bed of solids at elevated temperature (hot particles), creating cold zones inside the moving bed which are tracked using thermocouples along the vertical flow path of solids. The descent of the cold zone over the known distance between two adjacent heights gives the velocity of solids particles, from which the circulation rate is estimated.

The values measured so far are satisfactory as the technique provides solids circulation rate information beyond the capability of other techniques. A pressure balance in circulation loop during each batch of tests is used to interpret the results. A novel butterfly valve, currently under construction, will be employed to provide results for comparison with those obtained using the thermal-tracing technique.

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