Dolomite decomposition in a high temperature fluidised bed reactor

The decomposition of dolomite was investigated in a bench-scale fluidised bed reactor (30 cm diameter) at temperatures between 600°C and 1000°C in batch and continuous operations. The composition of the solids was determined by X-ray analysis, the gas composition by infrared (i.r.) spectroscopic analysis. The reaction kinetics were investigated in a small fluidised bed (2.6 cm diameter) as well as in the bench-scale equipment and compared with kinetic data evaluated from differential thermal gravimetric (DTG) curves. The measurements were carried out by adding small amounts of dolomite into the isothermal fluidised bed. The resulting CO₂ concentration within the gas could then be very low, thus MgCO₃ and CaCO₃ decompose as parallel reactions (singlestage reaction). At somewhat higher CO₂ gas concentrations prevailing in technical operational conditions the decomposition mechanism changes into a two-stage reaction where MgCO₃ decomposes first. The bed temperature, pressure drop, superficial gas velocity, solid conversion, and specific interfacial area of solids were determined as functions of time and/or reactor wall temperature with a constant temperature increase rate for batch runs. The distributions of the residence time of solids indicate that in the continuously operated fluidised bed well-mixed conditions prevail. The concentrations of dolomite, CaCO₃, MgO, CaO, and solid conversion as well as the specific surface area of particles were determined as functions of the mean residence time in the continuous reactor. By means of the CO₂ concentration in the gas phase and the mean residence time the conversions of the consecutive reactions can be controlled.