A system for heating and feeding of free-flowing powders at high temperatures and high mass flow rate constancy

A high-temperature feeding system has been developed for continuous heating and discharge of fine, free-flowing powders with typical median particle diameters between 50 and 150 μm. It is capable of heating the material up to a temperature of 600 °C at mass flow rates up to 60 g s-1 (depending on solids density) with a feeding constancy of approximately 1% on average, thus making it a suitable device for solids discharge into a downflow reactor. This heating/feeding system consists of a combination of a fluidized bed with electrical heating coils and a small silo with interchangeable orifice at the exit. Using orifice plates with different hole diameters a wide range of mass flow rates can be accommodated. The pressure drop over the orifice is continuously recorded and is a measure for the mass flow rate. Pressure transducers at the top and bottom of the fluidized bed are used to monitor total system pressure and bed height during operation. The system was characterized using two different powders, iron and FCC catalyst, with median particle diameters of 138 and 82 μm, respectively. The experimental data of mass flow rate and orifice pressure drop were found to be well-correlated with an expression of the general form W = C1√g+C2Δporifice. Temperature did not have a great influence on the relationship between mass flow rate and orifice pressure drop. Whereas for FCC a slight decrease in mass flow rate was determined, iron showed the opposite behaviour.