Particle Residence Time Measurement in Dual Fluidized Bed Pyrolysis Unit

A measurement system for particle tracking is designed and implemented in a scaled dual fluidized bed cold-flow model. A riser operating as combustion section, is connected to a bubbling fluidized bed operating as pyrolysis section. The riser provides the energy for the pyrolysis section transported by the hot bed material circulating in the system. This system can be applied to produce a high calorific value fuel gas out of waste plastic material. The majority of the feedstock material is converted to gaseous as well as liquid products which can be directly utilized e.g. in burners for rotary kilns (cement industry, waste incineration, …). Solid residues such as char can be utilized as energy carrier and ash as well as metal fraction is sorted out of the system.

The particle tracking system consists of two inductors, which are placed upstream and downstream of the pyrolysis section. Metal particles with a mass fraction of 1 percent of the bed material are used as tracking particles. The particles are released on the upstream side of the pyrolysis zone and increase the inductance when passing the inductors. The inductance change is measured with two measurement bridges. Residence time distribution and circulation rates are analyzed for different operating points. Moreover, the behavior of the dual fluidized bed systems for different geometries of the pyrolysis section is determined. The measurements are set into reference to calculation of mass and energy balances of the conversion of feedstock to syngas respectively thermal energy. Optimal process operation window is determined as basis for the design of a hot pilot scale unit.