Energy-saving strategy for a transport bed flash calcination process applied to magnesite

A transport bed flash calcination (TBFC) process applied to magnesite is systematically investigated through process simulation to optimize the energy-saving strategy. The high-temperature calciner flue gas is used to preheat the fed magnesite, while the sensible heat with the caustic calcined magnesia (CCM) product is cooled by air sent to the calciner. Pre-decomposition of magnesite during preheating is considered on basis of the kinetics measured using a micro fluidized bed reaction analyzer that allows the minimized effect of external diffusion on reaction. With staged fuel gas supply the TBFC process allows the equivalence ratios around 1.2 for combustion. The preferred arrangement of stages for magnesite preheating and CCM cooling are respectively 4 and 2, leading to the energy consumption of 4100 kJ/kg-CCM and the energy efficiency of 66.8%, which is almost doubly higher than the 33.9% of the conventional reverberatory furnaces (RF). The pre-decomposition occurs mainly in the 1(st)-stage preheater, and the maximal conversion is about 13%. Varying the stages of preheating appears more influential on the energy saving than varying the cooling stages, while residence time above 1 s in the preheaters has limited effect.

Automated summary

The TBFC process applied to magnesite optimizes energy-saving strategies by preheating the fed magnesite with high-temperature calciner flue gas and cooling the CCM product using air sent to the calciner. By pre-decomposition of magnesite and staged fuel gas supply, the process achieves an energy efficiency of 66.8%, significantly higher than conventional RF furnaces. Preheating stages have a greater influence on energy saving than cooling stages, with limited effect of residence time above 1 second in the preheaters.