A process of calcining aluminium hydroxide (Al.sub.2O.sub.3.3H.sub.2O) to form alumina (Al.sub.2O.sub.3), for example in an alumina plant, such as a Bayer process plant, is disclosed. The process comprises combusting hydrogen and oxygen and generating steam and heat 5 and using the heat to calcine aluminium hydroxide and form alumina and more steam. An apparatus is also disclosed.

A process of calcining aluminium hydroxide (Al.sub.2O.sub.3.3H.sub.2O) to form alumina (Al.sub.2O.sub.3), for example in an alumina plant, such as a Bayer process plant, is disclosed. The process comprises combusting hydrogen and oxygen and generating steam and heat 5 and using the heat to calcine aluminium hydroxide and form alumina and more steam. An apparatus is also disclosed.

A method for producing abrasive particles includes: i) providing a starting mixture which contains at least aluminum hydroxide and which can be converted at least into aluminum oxide by a heat treatment, ii) extruding the starting mixture in order to form an extrudate, iii) separating the extrudate into intermediate particles, and iv) heat-treating the intermediate particles. The intermediate particles are converted into abrasive particles which contain aluminum oxide, and the starting mixture is pressed through at least one nozzle element with a plurality of substantially parallel nozzle channels. The nozzle channels are preferably arranged in a mutually spaced manner over the course of the extrusion process, and the extrudate has a spiral or hollow cylindrical shape at least in some sections.

A method for producing abrasive particles includes: i) providing a starting mixture which contains at least aluminum hydroxide and which can be converted at least into aluminum oxide by a heat treatment, ii) extruding the starting mixture in order to form an extrudate, iii) separating the extrudate into intermediate particles, and iv) heat-treating the intermediate particles. The intermediate particles are converted into abrasive particles which contain aluminum oxide, and the starting mixture is pressed through at least one nozzle element with a plurality of substantially parallel nozzle channels. The nozzle channels are preferably arranged in a mutually spaced manner over the course of the extrusion process, and the extrudate has a spiral or hollow cylindrical shape at least in some sections.

An improved apparatus for steam calcining aluminium trihydroxide (Al(OH).sub.3) to produce alumina (Al.sub.2O.sub.3) is disclosed. The apparatus comprises an Al(OH).sub.3 preheater configured to heat an Al(OH).sub.3feedstock by contacting it with steam. The Al(OH).sub.3 preheater comprises at least one gas solid separator for separating preheated Al(OH).sub.3 from carrier steam. The apparatus further comprises a calciner configured to accept preheated Al(OH).sub.3 from the Al(OH).sub.3 preheater and to produce heated Al.sub.2O.sub.3 by steam calcination. The apparatus also comprises an Al.sub.2O.sub.3 cooler configured to remove heat from the heated Al.sub.2O.sub.3 and produce Al.sub.2O.sub.3 product. The Al.sub.2O.sub.3 cooler comprises at least one gas solid separator. The apparatus further comprises a steam compressor in fluid communication with the Al(OH).sub.3 preheater, the calciner and the Al.sub.2O.sub.3 cooler and configured to accept and pressurise carrier steam from the Al(OH).sub.3preheater and to provide pressurised carrier steam to the Al(OH).sub.3 preheater and pressurised carrier steam the Al.sub.2O.sub.3 cooler to transfer Al(OH).sub.3 feedstock to and within the Al(OH).sub.3 preheater, and pressurised carrier steam to transfer preheated Al(OH).sub.3 from the Al(OH).sub.3 preheater to the calciner, and to transfer heated Al.sub.2O.sub.3 from the calciner to and within the Al.sub.2O.sub.3 cooler.

An improved apparatus for steam calcining aluminium trihydroxide (Al(OH).sub.3) to produce alumina (Al.sub.2O.sub.3) is disclosed. The apparatus comprises an Al(OH).sub.3 preheater configured to heat an Al(OH).sub.3feedstock by contacting it with steam. The Al(OH).sub.3 preheater comprises at least one gas solid separator for separating preheated Al(OH).sub.3 from carrier steam. The apparatus further comprises a calciner configured to accept preheated Al(OH).sub.3 from the Al(OH).sub.3 preheater and to produce heated Al.sub.2O.sub.3 by steam calcination. The apparatus also comprises an Al.sub.2O.sub.3 cooler configured to remove heat from the heated Al.sub.2O.sub.3 and produce Al.sub.2O.sub.3 product. The Al.sub.2O.sub.3 cooler comprises at least one gas solid separator. The apparatus further comprises a steam compressor in fluid communication with the Al(OH).sub.3 preheater, the calciner and the Al.sub.2O.sub.3 cooler and configured to accept and pressurise carrier steam from the Al(OH).sub.3preheater and to provide pressurised carrier steam to the Al(OH).sub.3 preheater and pressurised carrier steam the Al.sub.2O.sub.3 cooler to transfer Al(OH).sub.3 feedstock to and within the Al(OH).sub.3 preheater, and pressurised carrier steam to transfer preheated Al(OH).sub.3 from the Al(OH).sub.3 preheater to the calciner, and to transfer heated Al.sub.2O.sub.3 from the calciner to and within the Al.sub.2O.sub.3 cooler.