Major Cost Component in Manufacture of Calcined Alumina

Hi Friends,

We covered a variety of techno-commercial  issues with regard to production of calcined alumina. In present post, we will discuss the major cost components and their optimum level to control manufacture cost of alumina.

Production cost of calcined alumina is directly impacted by process efficiency figures due to higher consumption of input materials. Requirement of energy and consumption of Caustic soda are the main challenges for the process engineers to monitor on continuous basis so as to minimize the manufacture cost of calcined alumina. Total cost component of energy and caustic soda is estimated at around 70% of manufacture cost of alumina. Energy requirement for bauxite mining ranges from 0.40 US$ to 0.50 US$ per tonne of ROM Bauxite which is purely dependent on stripping ratio (meters of overburden : meters of Bauxite) and haulage (distance between Bauxite deposit to point of loading for despatch to Alumina refinery). Land area used for mining Bauxite ranges from 50 to 60 m2 per 1000 tonnes of ROM Bauxite or 5 to 6 hectares land per million tonnes of ROM Bauxite.

In Alumina refinery, energy is used in three forms- (i) Solid / liquid / gaseous fuel for raising  saturated steam to be used in digestion and evaporation stages and (ii) Liquid / gaseous fuel for Calcination and (iii) Electrical power for running the rotating equipment. Though the electrical power consumption is equivalent to about 1.0 GJ per tonne of calcined alumina which accounts for about 10% of total energy consumption for production of alumina. Various methods for controlling the energy consumption have already been elaborated in previous posts.


The other main challenge is to minimize caustic soda consumption. Presence of high reactive silica in Bauxite, lower alumina recovery, poor washing efficiency figures of residue and hydrate are the main reasons for higher caustic soda consumption. Thus steady plant operation with optimum temperature profile of the process circuit attributes in reducing the caustic soda consumption. 


All information presented here are the personal views of the author and thus advised not to act upon these data / information without taking professional advice from experts as it  is essential to take care of consequences on other efficiency figures.


Please put your views / remarks / comments, if any.
Regards.


Kunwar Rajendra 
www.bauxite2aluminium.blogspot.com