Saturday, October 14, 2017

Key Controls for Improving Settling Characteristics of Bauxite Residue

Hi Friends,

We are well aware that Bauxite residue is the waste generated in Alumina refinery. The residue generation rate is dependent of Bauxite quality and alumina extraction efficiency. In Bayer process Bauxite with around 40% Al2O3 and less than 5% total silica (Module > 8) is preferred which generally causes generation of about 1.15 to 1.35 tonnes of dry residue per tonne of alumina.

It is a known fact that storage and disposal of Bauxite residue is a big problem for all Alumina producers with stress and emphasis of concerned Governments to store it in well protected area so as to combat probable environmental problems and health hazard for the community around because of the passage of alkaline water to natural streams and acute dusting in the area during summer. Though attempts are being made by researchers and scientists to find commercial utilization of residue but very limited utilization has been made possible so far because of economic disadvantages. The laboratory scale development of various processes were done till 1980s for its utilization in manufacture of red mud bricks, cement, red mud PVC plastic, pigment and many other products but only a few has been commercialized till date. 

In present post, we will discuss the key contributing parameters to improve the settling characteristics of Bauxite residue in Alumina refinery. As such, there are unlimited variables which affect the settling rate of residue but we will like to highlight the major parameters to improve the settling rate of residue particles in settlers and washers of Alumina refinery thereby improving the production rate due to steady operation, improved product quality due to less carry over of suspended solids in filtrate during polishing filtration and lower soda loss with residue due to increased residue washing efficiency in residue washers. The major parameters are briefly described in subsequent paragraphs-

1. Mineralogical composition of Bauxite: The mineralogical composition of Bauxite clearly reflects that oxide of iron is present in the form of hematite, goethite and siderite where as Oxide of titanium in the form of anatase and rutile in addition to oxides of other minor metals. The presence of goethite badly affects the settling rate of residue. Thus the ratio of hematite to goethite is preferably maintained more than 3 by adopting suitable blending techniques before processing in the Bayer circuit. 

2. Granulometry of Bauxite in ground slurry: The specific gravity of Bauxite ranges from 2.50 to 2.75 depending on the chemical and mineralogical composition of Bauxite. As such, the bauxite particle of minus 60 mesh has been found to be okay for satisfactory extraction as well as recovery of alumina but to ensure the same the granulometry in ground slurry is controlled over 85% of minus 60 mesh fraction. The slurry contains about 1 to 2% of plus 10 mesh fractions. With this particle size distribution, the specific surface area of dry bauxite is observed between 12 to 15 m2 per gram. This figure is also used as a guideline for required granulometry in ground slurry. Over grinding of bauxite is avoided as it badly affects the settling rate of residue because of further disintegration of particles during digestion and slurry flashing circuit of Alumina refinery. 

3. Selection of suitable flocculants: It has been seen that mixed natural and synthetic flocculent gives better result than any individual flocculent for desired level of overflow liquor clarity as well as compactness of underflow residue. However, the ratio of mixture varies widely depending on mineralogical composition as well as settling characteristics of Bauxite. Thus, the ratio of mixing is finalized by carrying out settling rate test in Laboratory with digested blow-off slurry under the plant operating conditions. The dosing rate of natural flocculent generally varies from 0.25% to 1% of dry bauxite residue entering the settlers and washers.

4.Temperature profile of Settling and Washing circuit: Though, there may not be wide fluctuations in temperature profile of thickeners and washers but at times even the minor deviations in temperature profile either due to ignorance of operating personnel or malfunctioning of instrumentation and control system may cause serious problem in the settling rate as well as overflow liquor clarity due to increase in viscosity of aluminate liquor at lower temperature. Thus close watch on steady temperature profile is considered as one of the major factors.

5. Monitoring and control on P2O5 content in process liquor: This is one of the very important parameters which requires constant vigil for steady control within limits by taking required preventive measures in the upstream of the process. For the purpose, suitable chemical is added continuously to the process circuit.

Thus, close watch on these critical parameters must be kept for trouble-free as well as steady and efficient operation of Alumina refinery. We would like to have your views / remarks / suggestions / comments, if any, for further improvements in quality of future articles.

Kunwar Rajendra

Wednesday, August 9, 2017

Design Calculations for Chemical Cleaning Heat Exchangers for Alumina Refinery

Hi Friends,

Hard scale formation in Red and White areas of Alumina Refinery causes interruptions in plant operations badly affecting the production, productivity and efficiency of the plant. Manual cleaning of these scale is time taking which causes huge loss time for the plant. Adoption of chemical cleaning system attributes in faster cleaning process by dissolving hydrates in hot caustic soda forming Sodium aluminate.

In present post, we will discuss the detailed sample calculations for design of heat exchangers used in white area of Alumina refinery for cleaning of vessels, equipment and process lines. In some Alumina refineries, these heat exchangers are also known as Caustic cleaning heat exchangers. Here, we have taken certain assumed input figures required for a typical Alumina refinery for explanation purposes. Please follow these engineering calculations for the plant of any capacity of your choice. You will find these calculations unique blended with simplified methodology for carrying out equipment design calculations accurately. Step by step derivations and used formula have also been presented here as guideline and reference for easy understanding-

You will appreciate the efforts put by our team in developing such complicated design calculations in simplified manner. You will find it as an asset in your knowledge bank as such unique derivations are not available in any published literature. In case, you find similar derivations any where please let me know for my reference.

Please put your views / suggestions / remarks / comments, if any, for further improvements in methodology and method of presentation as well for easy understanding by our young generation. In case of any doubt, please feel free to contact us at

Kunwar Rajendra
Founder of this Technical Blog.

Tuesday, July 4, 2017

International Benchmark of Energy Consumption for Alumina Production in Bayer Alumina Refinery

Hi Friends,

In earlier posts, we have covered various issues pertaining to design, engineering, execution and cost estimation of plant, equipment and facilities of Alumina refinery. In present post, we will discuss the International benchmark of energy consumption for production of Metallurgical grade calcined alumina.

As per the literature published by United Nations Industrial Development Organization (UNIDO) available on public domain, typical energy consumption data presented below clearly reveal that specific thermal energy consumption per tonne of alumina produced in various Alumina refineries across the globe ranges from 10.2 GJ/t to 24.5 GJ/t alumina. The thermal energy consumption figures for different regions are presented in following graph-

Data Source : International Aluminium Institute

It is evident from the above graph that specific energy consumption for production of calcined alumina in South America is the lowest at 10.2 GJ/t whereas it is highest in China at about 24.5 GJ/t of alumina. Reasons for wide range of variation in energy consumption figures have already been described in earlier posts. On comparative analysis of these figures, it can be concluded that Asian and American Alumina refineries have the potential to improve the performance of plants for reduction in specific energy consumption by 23 to 25% from the present level. However, Chines Alumina refineries have tremendous scope for further reduction in energy consumption by about 50% through modifications and modernisation in the existing plants. As such, many Alumina refineries under execution in the World have set their total thermal energy consumption target at 8.5 GJ/t alumina.

On critical analysis of plant efficiency figures, process control parameters of operative Alumina refineries and technological advancements in the World, the global benchmark for specific thermal energy consumption in new Alumina refinery has been set by the International Expert Committee as 7.80 GJ/t of calcined alumina.

It may be a little difficult to achieve the set benchmark figure in existing Alumina plants because of inefficient heat recovery system. However, it is challenging and achievable target for modern Alumina refineries with installation of efficient heat recovery system, high degree of automation and continuous monitoring of thermal energy consumed in various units of Alumina refinery. Let us join hands to save unwanted thermal energy and get additional advantage on production cost of alumina. Please put your views / suggestions / remarks / comments, if any.

Kunwar Rajendra

Tuesday, May 23, 2017

Minimum Feasible Capacity of Specialty Grades of Alumina Refinery

Hi Friends,

In earlier post, we have already discussed about minimum feasible capacity of smelter grade Alumina refinery which is techno-economically viable to set up in any part of the globe. In present post, we will briefly discuss about minimum feasible capacity of specialty grades of  Alumina Plant.

It is well known fact that specialty grades of hydrate and alumina are marketed at premium price ranging from three times to five times of those of chemical grade hydrate and standard calcined alumina where as the production of specialty grades of hydrate and special alumina are approximately 15% to 20% higher than those of chemical grade hydrate and smelter grade alumina respectively. Because of increasing demand of specialty grades of hydrate and calcined alumina for various non-metallurgical applications all over the World has tremendous market potential with reasonably high profit margin. Thus, it gives us opportunity to think about the minimum feasible capacity of specialty grade alumina plant which can give high returns resulting in low pack back period. 

The preliminary study reveals that specialty grade alumina plant with 25,000 tonnes per annum production capacity is the minimum feasible capacity considering the availability of basic technological equipment for continuous operation on commercial scale. The estimated capital investment for such plant will be around US$ 25 million excluding the investment towards land and infrastructure facilities. The average manufacture cost of specialty grade alumina is estimated at around US$ 310 per tonne inclusive of all financial charges where as minimum  selling price will be ranging from US$ 600 to US$ 1000 per tonne of specialty grade alumina. Taking average level of sales realization at around US$ 800 per tonne of specialty grade alumina, the pay back period for total capital investment works out to less than 3 years. Specialty grades of hydrate have more profit margin compared to specialty grades of calcined alumina.

The preliminary financial indices prompt us to go ahead for execution immediately. However, It is always advisable to check the following basic information before taking final decision for execution-
  1. Availability of about 3.0 million tonnes of chemical grade bauxite,
  2. Required utilities and services,
  3. About 20 hectares of land for plant,
  4. About 50 cubic meters per hour of industrial grade water,
  5. Other basic input raw materials and skilled workforce.
In addition to all stated above requirements, the detailed feasibility study is a must to confirm the market scenario, fixing of product-mix, finalizing the required process technology and re-look at outcome of final financial parameters. Execution of such plants definitely require technical competence in process expert as a process technology supplier for the project, otherwise execution with superficial knowledge about the process may be detrimental for the stake holders in the project - this is just a word of caution from our expert team.

These are just the basis to initiate working on this lucrative project. Please put your views / suggestions / remarks / comments, if any.

If you like this article, then please press your rating as  +1  .
Thanks and regards.

Kunwar Rajendra

Friday, April 21, 2017

Design and Motor Rating Calculations for Bauxite Grinding Mills

Hi Friends,

In continuation to our earlier post on Efficient grinding system for Bauxite in Alumina refinery, we will discuss the methodology along with design calculations for sizing of Ball mill including the estimated motor rating with reference to a known mill operative in identical process conditions.The cross section of a typical Ball mill has been shown below just to have the physical feel of the main components of Ball mill and movement of grinding media inside in running condition. I am thankful to my friend who has developed this animation for schematic cross section of the ball mill in operation-

Schematic Cross section of Ball mill in Operation

It is evident from the above schematic diagram that size reduction of bauxite takes place due to impact action of balls and rubbing action of particles as well. The actual operating rotational speed of ball mill is controlled at around 60 to 80% of the critical speed of the mill derived on the basis of effective diameter of the mill as elaborated below. We have already discussed about the material of construction for ball mill liner and balls used as grinding media. We are presenting here the systematic approach to work out the dimensions (Diameter and Length) and motor rating of ball mill for successful operation for a typical capacity Alumina refinery as given below-
We have put all out efforts to present the calculations in simplified manner for easy understanding by one and all related to the subject. Hope, you will appreciate our attempts in preparing the concise and systematic derivations for such a complicated topic. Please put your views / remarks / suggestions / comments, if any, for further improvement.

Kunwar Rajendra

Saturday, August 1, 2015

Grand Success of Bauxite, Alumina and Aluminium Fraternity

Hi Friends,

In present post, we are presenting the grand success of our bauxite-aluminium fraternity in subsequent paragraphs.
Our efforts of exchanging our knowledge on the technical platform of Alumina Technology blog has fetched us to a new height of success. All of us who contributed directly or indirectly in achieving this grand success deserves our heartiest Congratulations! We congratulate all members of bauxite-alumina-aluminium fraternity for setting up such a new record of of success in achieving the target of 100,000 viewers of our popular technical blog on Alumina Technology i.e. across the globe today, the Sunday 1st August 2015.
The editorial team of Alumina Technology blog is thankful to you all of you for your continued co-operation, support, feed back and contribution in improving the quality of technical articles published on regular basis.
We celebrate every success and thus we are now aiming for the grand occasion for reaching to  a further milestone of success to cross the total viewer target of 200,000 within short duration.We have observed that our younger generation of bauxite-alumina-aluminium fraternity have started taking keen interest in analyzing the articles with due care and expressing their views and suggestion by putting their remarks in the space provided under "Comments" column located just below each technical article of the above mentioned technical blog. We have truly realized that exchanging knowledge has helped us in enriching the knowledge of all involved persons in the field of operation, design, engineering, process improvements, execution, troubleshooting and other related issues of bauxite mining, Alumina refinery and Aluminium Smelters..
Trust, we will continue to have your cooperation / supports in days to come for further improvements in quality of articles published on this blog. Your comments encourages our team to be more careful while publishing any new article on this popular technical platform. Knowledge sharing, positive attitude towards our assignment and improving skill are the key to success. Let us remember these tools of success for achieving our goals.
Rajendra Kunwar

Friday, July 17, 2015

Footsteps for Enhancing Data Bank on Bauxite, Hydrate, Alumina & Alumina Chemicals

Hi Friends,
In present post, we have put forward our aggressive steps to enhance the inventory of technical data bank pertaining to bauxite, hydrate, alumina and alumina chemicals covering all spheres of activities for all friends of our professional fraternity.
It's my natural temperament to exchange ideas particularly on technical topics. It is also the truth that blessings of my superiors and best wishes of my friends have attributed in enriching my knowledge base which further encouraged me to move forward with accelerated pace in exchanging ideas and opinions. I do not believe in diary culture in hiding information unnecessarily in my desk. I know, I have very limited data / information with me compared to many others in the World. My this approach has given me more than 2500 trust-worthy friends who are directly or indirectly associated with bauxite, hydrate, alumina and aluminium including specialty chemicals. As such, I have faced many road blocks in my career path so is impossible for me to forget the blessings of society and almighty God. Majority of my life, I have enjoyed with smile. What ever work I do, I get immense pleasure in contributing to my fullest satisfaction.  
During early days of my professional careers, I faced acute problems in learning technical things as limited people had the desire to exchange their fresh or outdated perceived ideas as they used to keep those data as very confidential just like keeping the personal property in the Bank lockers. Those days i.e in early eighties, internet in India was available to defense people only. You can imagine the extent of difficulties faced by me in learning the basics and design aspects of process, calculations, equipment, capex, opex and profitability aspects. Truly, it was hard time for me when I recall. I struggled a lot for finding even tiny technical information. You will be astonished to know that people were reluctant to tell even the basic process and operating parameters of Alumina refinery. Can you think of doing process design engineering calculations using scientific calculators and preparation of drawings using Mini Drafters on the Drawing boards. For the first time in 1984, I got opportunity to work on computer that to with 640 kb RAM. Those days, Word star and Lotus-123 were the basic software for  word processing and calculations respectively. In 1990, I got the computer with MS-Excel on which I initiated to take up the assignment for developing a mathematical model for Design of Alumina Refinery during extra hours. I was fortunate to be awarded for development of that mathematical model sometime in 1995. I kept on updating the mathematical model considering it as my person achievement. If I see the model today, I am surprised on myself for completing this unique and wonderful developmental work alone. The outcome of this model has been well tested with the results provided by other leading technology suppliers in the World. This mathematical model has been developed on MS-Excel platform and requires only 150  basic input data and it gives detailed process calculations like material balance, thermal energy balance, water balance, caustic soda balance, alumina balance etc and sizing calculations for all major technological equipment, tailor made equipment and requirement of utilities and services within no time. Utmost accuracy in outcome is the essence of this mathematical model. Since this Mathematical model has been awarded by Internationally reputed Engineering & Consultancy Organization and they are using the same even today for design of Alumina refinery. Thus, I consider it as their asset but as an originator, I keep on updating the Mathematical model incorporating advancements in process technology. 
To summarize the facts of my professional life, I had to face a lot of difficulties which can not be expressed in words. All of us know the fact of our life that we are not going to remain alive on this earth for more than 200 years under any circumstance. Thus, it would be a wiser decision to dissipate the knowledge and expertise acquired by all of us. Though our first forefathers were monkeys, but we can not behave like monkeys today in keeping intact the assimilated information with us as the World has become very small because of advancements in communication technology. I feel proud of myself as I initiated this move of exchanging the ideas of public domain nature among my friends about a decade back which was appreciated by almost all across the globe. Now, I have observed that my friends are contributing much more than what I could and what I am. I have always advised one and all to share the information of public domain nature and never disclose any data, information and drawings of proprietary and confidential nature. My interest  has remained at the same level among the global team but I am contributing little less because of paucity of time due to other pressing assignments.Till date, I have published 283 technical articles on this specialized subject and could present few papers in national and International seminars covering all aspects starting from concept to commissioning of Alumina Refinery.
No matter, I am always (24x7) available for serving the community around and specifically to bauxite, hydrate, alumina, aluminium and alumina chemical fraternity on techno-commercial issues across the globe even during odd hours.
If any individual particularly the young professionals / Entrepreneurs has any question with regard design, engineering, execution, commissioning, process calculations and costing (such as bauxite mining cost, alumina production cost, specific capital cost etc.) related to Bauxite, mining, Hydrate, Alumina and Specialty grades of hydrates and aluminas including Alumina chemicals, please feel free to ask any information / clarification clearly indicating your e.mail ID for receiving your reply. Our team of Experts will definitely put efforts for reply to you. Sometimes, you may be required to wait a while for the reply. Simplicity in our language and authenticity in information are major strength. 
We wish to have your opinion / comments / remarks on our new move on the very specialized subject like alumina. We will welcome your suggestions.
Kunwar Rajendra