A Quintessential Guide To Calcination Of Bauxite In Industries

Calcination is the process of subjecting a substance to the action of heat, but without fusion to cause some change in its physical or chemical constitution, The objects of calcination are usually.

  • To drive off water present or absorbed moisture as water of crystallization or as water of constitution.
  • To drive off carbon dioxide Sulphur dioxide or another volatile constituent.
  • To oxidize a part of the whole of the substance.

In this process, the raw bauxite which is mixed is converted to calcined bauxite. The following reaction takes place Al2O3.2H2O → Al2O3 + 2H2O (at 1300 deg.) Other materials that can be calcined in this unit are clay, fireclay, etc.

The calcination unit can be divided into 5 parts:

  • Raw material crushing and storage
  • Kiln and cooler conveying section
  • Calcined bauxite storage system
  • Coal crushing and storage or Petcoke/ other fuels storage.
  • Pollution control.

Technology for Bauxite Calcination 

CPG also supplies a special range of small and medium-capacity Rotary Kilns across the world with numerous applications.

CPG has already supplied Kiln for calcination of:

  • Lime Sludge
  • Bauxite
  • Petcock
  • Dolomite
  • Clay

Our design & production experts provide high-quality, innovative & cost-effective solutions according to the requirements of customers.

This material is fed to the rotary kiln from the storage hopper through the elevators and conveyors. A rotary kiln is a device used to raise materials to high temperatures (calcination) in a continuous process. The kiln is a cylindrical vessel, inclined slightly to the horizontal which is rotated slowly about its axis. Material that is to be processed is fed in the upper end of the cylinder. As the kiln rotates, the material gradually moves down towards the lower end and may undergo a certain amount of stirring and mixing. A very high temperature from 850 deg. C to 1600 deg. C continuously flows in the kiln. The fuel for this may be Gas, oil, Pulverized Petroleum Coke, or Pulverized Coal.

By Vertical Shaft Kiln

In the process of calcination by vertical shaft kilns, the raw material is loaded from the top of the kiln together with coal powder and combustion improver, the fire of calcination comes from the kiln bottom, and a temperature of about 1300 – 1400 deg C is achieved in the kiln.

FEATURES OF ROTARY KILN SUPPLIED BY US:-

  • Better inlet and outlet sealing to ensure minimum false air entry
  • Hydraulic thruster provides control to the Kiln axial movement.
  • Three support roller stations are provided for better distribution of forces on the shell.
  • Ensures optimal safety of material elasticity at operating temperature.
  • A throat adjuster is provided to optimize Kiln/Calciner fuel

POLLUTION AND CONTROL:-

Rotary Kiln → Single Cyclone → Dust Collector → I.D. Fan → Chimney

USES OF CALCINED BAUXITE :-

  • Refractory grade calcined bauxite (CB-I and CB-II Grade): To make the refractory grade, bauxite is thermally treated at 1600 deg C to produce calcined bauxite where the alumina content is mostly above 80%.
  • Brown fused alumina, proppants, and road surfacing: To make the above grades bauxite is thermally treated at 1000 deg C – 1200 deg C to produce calcined bauxite where the alumina content is anywhere between 75 – 85 % depending on the requirement.
  • Anti-skid protection: Calcined bauxite is an ideal aggregate for anti-skid applications. It is used extensively for vehicle skid prevention and on surfaces requiring additional safety. The bauxite may be trowelled into fresh concrete, added to paints, or applied to surfaces using resin types of cement and adhesives.
  • High Friction Surface Treatment (HFST): HFST is a cost-effective method to reduce skidding and is mainly used to make roadways safer. It is used on horizontal curves or ramps, intersections, steep grades, bridge decks, roundabouts, and pavement surfaces. Studies have indicated that the application of HFST reduces vehicle crashes by up to 100%. The material is applied to surfaces using a polymer binder.
  • Refractories: Refractories are insulating materials that maintain their strength and chemical properties at high temperatures. They are used to line boilers, furnaces, kilns, reactors.