Multi stage combustion furnace and process for the thermal expansion of mineral particles

A multistage combustion furnace system for an open furnace for thermal expansion of mineral particles, the open furnace being open to atmosphere and comprising an expansion chamber for receiving the mineral particles, the multistage combustion furnace system comprising:

• a burner head connected at a burner distance from and below the expansion chamber for operating the expansion chamber, the burner distance providing an atmospheric coupling of the burner head and the expansion chamber with the atmosphere;
• a furnace device connected at a furnace device distance from and below the expansion chamber, in the atmosphere, the furnace device and the expansion chamber being installed separated by a gap extending below the expansion chamber, the gap being open to both the expansion chamber and the atmosphere, where unexpanded mineral can fall out of the open furnace, and to provide an atmospheric coupling of the furnace device and the expansion chamber with the atmosphere, the furnace device comprising a ring portion installed peripherally from said burner head and comprising a channel directed toward the gap to generate an air curtain extending through the gap to offset the quenching effect of ambient air from the atmosphere normally drawn in an open furnace, wherein said furnace device is installed between said burner head and a tuyere kit;
• and
• the tuyere kit connected between said expansion chamber and said furnace device at a lower portion of the expansion chamber, the tuyere kit comprising an air inlet installed inside said tuyere kit to provide a preheated air intake causing a tertiary combustion stage surrounding a burning flame with higher oxygen air;
• wherein an inlet of preheated air is connected to each one of the burner head and the furnace device.