Gas Mixing in a Pilot Scale (500 kWth) Air Blown Circulating Fluidised Bed Biomass Gasifier

Abstract

To study the gas mixing capacity of circulating fluidised bed (CFB) biomass gasifiers, radial and axial gas concentration profiles have been measured and interpreted in a hot pilot scale biomass gasifier (100 kg/hr fuel). The presented data of the pilot scale gasifier are unique and provide new insight in the radial gas mixing capacity of circulating fluidised bed gasifiers. Considerable radial gas phase concentration gradients have been observed in the pilot plant gasifier, with a difference between wall and centre concentrations up to a factor 3. It must be concluded that the radial gas mixing is far from ideal. On basis of these pilot plant data and the standard dispersion model (to describe gas mixing) it can be concluded that the radial Peclet number of the dilute region is in the order of 1000. Such a value excludes the radial mixing of gases almost entirely.