Method for producing anhydrous alumina

A method for producing substantially uniform anhydrous alumina having a controlled degree of alpha conversion from alumina trihydrate comprising:

• (1) heating said alumina trihydrate to a temperature range between about 150.degree. C. up to but not exceeding about 450.degree. C. in a precalcining zone to remove any free or combined water;
• (2) at least partially recrystallizing said precalcined alumina to alpha alumina in a reaction chamber by:
• (a) feeding said precalcined alumina onto a downwardly and inwardly inclined annular bottom wall of said reaction chamber;
• (b) introducing said precalcined alumina and said fuel at the bottom of said reaction chamber in intersecting directions to cause intimate mixing thereof;
• (c) introducing an oxygen containing gas upwards through the bottom of said reaction chamber to suspend said mixture of precalcined alumina and fuel;
• (d) subjecting said precalcined alumina to a rapid increase in temperature of at least 600.degree. C. during a period of less than 0.2 times the particle retention time in said reaction chamber, by burning said fuel in said oxygen containing gas in a hot combustion zone to initiate exothermal recrystallization of said precalcined alumina;
• (e) converting said precalcined alumina to alpha alumina at temperatures from about 1100.degree. to 1600.degree. C. in about 0.5 to 5 seconds in entrained suspension in a combustion gas stream to form the desired content of alpha alumina in the final product;
• and
• (f) withdrawing said recrystallized alumina suspended in said combustion gas stream at the top of said reaction chamber;
• (3) separating said recrystallized alumina from said combustion gas stream;
• and
• (4) rapidly cooling said recrystallized alumina in a cooling zone;
• thereby producing substantially uniform alumina particles having the desired degree of alpha conversion.

A method for producing substantially uniform anhydrous alumina having a controlled degree of conversion from alumina trihydrate comprising:

• (1) heating said alumina trihydrate to a temperature range between about 150.degree. C. up to but not exceeding about 450.degree. C. in a precalcining zone to remove any free or combined water;
• (2) at least partially recrystallizing said precalcined alumina to alpha alumina in a reaction chamber by:
• (a) feeding said precalcined alumina onto a downwardly and inwardly inclined annular bottom wall of said reaction chamber;
• (b) introducing said precalcined alumina and said fuel at the bottom of said reaction chamber in intersecting directions to cause intimate mixing thereof;
• (c) introducing an oxygen containing gas upwards through the bottom of said reaction chamber to suspend said mixture of precalcined alumina and fuel;
• (d) subjecting said precalcined alumina to a rapid increase in temperature of at least 600.degree. C. during a period of less than 0.2 times the particle retention time in said reaction chamber, by burning said fuel in said oxygen containing gas in a hot combustion zone to initiate exothermal recrystallization of said precalcined alumina;
• (e) converting said precalcined alumina to alpha alumina at temperatures between about 1290.degree. and 1590.degree. C. in about 0.5 to 5 seconds in entrained suspension in a combustion gas stream to form an alpha alumina content of between about 14.5 and 77% in the final product;
• and
• (f) withdrawing said recrystallized alumina suspended in said combustion gas stream at the top of said reaction chamber;
• (3) separating said recrystallized alumina from said combustion gas stream;
• and
• (4) rapidly cooling said recrystallized alumina in a cooling zone;
• thereby producing substantially uniform alumina particles having the desired degree of alpha conversion.