Apparatus for the expansion of mineral matter, especially perlite and vermiculite

An apparatus for the expansion of particles of a mineral such as perlite and vermiculite, comprising:

• means forming an upwardly extending fluidized-bed furnace for expanding said particles;
• a burner opening into a lower end of said furnace for generating a flame therein, said furnace being closed at said lower end except for said burner;
• and
• a pipe opening upwardly into said furnace at said lower end for feeding a mixture of said particles and a carrier gas into said flame whereby said particles pass generally in the direction of propagation of said flame through said flame into said furnace, said burner opening axially from below into said furnace and consisting of an annular fuel inlet duct coaxially surrounding said pipe and directed upwardly into said furnace, a combustion air duct opening axially upwardly into said furnace and at least one fuel inlet and coaxially surrounding said fuel inlet assembly, means for feeding fuel exclusively to said fuel inlet duct and means for feeding exclusively air to said combustion air duct, and said combustion air duct being formed with a ceramic ring around said fuel inlet duct and provided with a plurality of spaced apart axially extending bores opening into said furnace and parallel to said pipe and said fuel inlet duct, said ring having a planar horizontal upper surface, said pipe projecting upwardly beyond said surface.