Reasons for Coloration in Product Hydrate & Corrective Measures to Improve Whiteness & Brightness

Hi Friends,

First, we would like to share the background of this technical blog. Till the end of 20th century, generally people were reluctant to share their technical knowledge particular on hydrates and alumina. In the back of their mind, it was a general feeling that only a few have particular data / information. But the advancement in communication technology revolutionized the knowledge sharing approach. In order to get advantages of technology and knowledge sharing approach among bauxite, alumina and aluminium professionals, we started this specialized technical blog couple of years ago with aggressive impulse and approach for achieving the difficult goal set by involved team of professionals. Fortunately, we could maintain the accelerated pace so far with our keen interests, enthusiasm and pleasure in publishing wide range of 273 technical articles pertaining to bauxite, alumina and aluminium. Now, when we look back towards the trajectory of our progress path traveled so far , we find that we have surpassed all our targets and goals well ahead of our planned schedule without compromising on quality. This reflects the grand success of one and all associated with this technical blog. Till date, we have more than 60,000 members and 75 Key Members who are closely connected who made their contribution by way of sharing their knowledge, data and information of public domain nature through this unique platform / web site. Today, we are ourselves astonished on our achievements of set goals. On the eve of this grand success day, we would like to express our sincere thanks to renowned Alumina Expert, Mr. George Banvolgyi of Hungary, for his blessings, guidance, inspiration and support during our journey of publishing variety of technical papers on this technical blog. Everybody deserves applaud and congratulations on this eve for bringing this platform to a new higher level of popularity. It gives me immense pleasure to be associated with this site as the founder member among the friends of bauxite, alumina and aluminium fraternity.Our each tiny achievement is the outcome of our efforts and as we consider it as the golden gift of God and hence we must celebrate the same with full enthusiasm and happiness. On similar lines, on achievement of every thousand of added viewers of our technical blog, we make our efforts to publish at least one special technical article on every special occasions. 

Today, we have achieved the total viewers of 60,000 with 76 Key Members across the globe closely associated and contributed in the grand success of this specialized technical blog. This day will definitely remain memorable for all of us and particularly for each member of bauxite-alumina-aluminium fraternity. All viewers and key members of this technical blog deserves congratulations on the eve of this new height of success as every body has contributed directly or indirectly in achieving this sky high target. On this great occasion, we are publishing this unique and special technical article for value addition to product hydrate by making it dazzling white and bright adopting corrective measures in process steps as described here under.

There are several grades of Hydrated alumina (Hydrates) manufactured and marketed across the globe. These hydrates are generally known as Specialty grade hydrate or Non-metallurgical grade hydrate. These are marketed at 2 to 5 times the price of Standard chemical grade hydrate. It has been seen practically that over and above desired chemical composition, brightness or whiteness of hydrates has premium market. Thus it becomes important to address the issue of coloration of hydrate and remedial measures for improving the whiteness so as to add more value to it. 

In present post, we will briefly cover the most probable reasons for coloration of product hydrate and appropriate technical solutions as remedial measures to improve whiteness and brightness as well.

There are two main reasons for coloration in product hydrate and appropriate solutions opined by many process experts as described here in subsequent paragraphs-

1. High soda content in product hydrate
2. High suspended solids in Thickener overflow pregnant liquor.

Step-I: With our experience in different Alumina refineries in the World, we have experienced the high soda content in product hydrate as one of the basic reasons. The identification of this issue is confirmed through simple analytical technique by analyzing the Na₂O content in product hydrate ready for dispatch to respective customers. If total Na₂O content in Hydrate is found more than 0.30% then it confirms that Hydrate generated in precipitators / decomposers / crystallizers has not been washed properly on product filter wherein the maximum component of leachable soda is removed. After observing this high soda content, vigorous washing of hydrate using steam /  hot water at temperature around 95-98^oC helps in achieving total Na₂O content below 0.30%. This step easily improves the product whiteness. For further improvement on washing efficiency, steam-hood at the discharge side of product filter can also be considered.

Step-II: High Fe₂O₃ content in product hydrate above 0.010% is the key indication of high suspended solids in filtered aluminate liquor feeding to Decomposers (Crystallizers / Precipitators). The suspended solids must be controlled below 15 mgpl (i.e. 15 milligrams per litre of pregnant liquor) in feed to Decomposers. Higher solids in pregnant liquor happens because of inadequate settling of suspended red mud particles in Liquor thickener for the major reasons listed below-

(a) High generation of fines during grinding of Bauxite:  Control fineness of Bauxite at optimum level to ensure higher settling rate of red mud particles in thickener. Generally, minus 60 mesh fraction in ground bauxite slurry is maintained more than 85%. Check and control it accordingly.

(b) Higher viscosity of thickener overflow liquor because of its lower temperature: Temperature of Thickener overflowliquor must be controlled at around 100-102 degree C if  the concentration of liquor in thickener overflow is at around 140-145 gpl Na₂O or above. High concentration profile is the need of modern Alumina refinery in order to have improved productivity so as to minimise thermal and electrical energy consumption.

(c) Selection of right settling agent: Settling agent used for faster settling of residue particles play vital role in achieving desired quality of product. There are different types of natural and synthetic high density polymers are available for different application. It has been observed that mixed natural starch with particular type of synthetic floccullent are  cost effective for Alumina refinery. 

(d) Selection of proper filter cloth for polishing filtration equipment: Selection of proper filter cloth is equally essential for controlling suspended solids in filtered aluminate liquor fed to crystallizers. Polypropylene filter cloth of more than 30 and 32 EPI and PPI have been found to be the most suitable cloth for security filtration.

(e) Controlling ingress of P₂O₅ content in Bauxite: At times, high P₂O₅ content in Bauxite affects the settling rate of residue (Red mud) in thickener. To eliminate this issue, start adding small quantity of Burnt lime (CaO) in Bauxite being fed to Grinding mill. This results in reducing the Phosphorus content in liquor forming Calcium Phosphate.

(f) Control Filter feed pressure below 2.0 kg/cm2.g: Lower the fitration pressure better is the filtrate quality. Pressure around 2.9 kg/cm2.g has been found to be optimum.

(g) Control solids in Thickener overflow Liquor well within 100 mgpl: Suspended solids in feed liquor to filter should be controlled well within 100 mgpl so as to avoid extra load of residue on polishing filtration unit thereby improving the filtrate quality to crystallizers,

(h) Optimize dosing of TCA: TCA (Tri calcium aluminate) addition to filter feed liquor results in improved fitrate quality. It has been established in various plants across the globe that mass flow of TCA equal to 10 times of suspended solids in Thickener is optimum.

Step-III: Check & Replace Security Filters in Service: Even after checking and monitoring all the above mentioned parameters stated under Step-I & II, if there is no appreciable improvement in filtrate clarity, then it concludes that some thing wrong with filtration equipment itself. In such situation, replacement of Polishing filters with suitably sized and designed security filters is the ultimate solution to this problem. Since this step requires additional capital expenditure fot the plant, thus decision needs to be taken only after thorough investigations of results obtained during Step-I and Step-II under the guidance of process expert who has operated the similar systems in any Alumina refinery across the globe.

Trust, all major possible reasons for poor filtrate clarity have been covered here and desired solutions have been presented with utmost care. In case, we have missed out any major reason, please come forward and put your views under Comments just below the article. Our team of experts will welcome your valuable comments / remarks in the benefit of readers across the globe. Everybody will like to have hydrated alumina with whiteness and brightness as shown here in the pictorial view. The major chemical constituents and coarseness / fineness are given below-
Fe2O3: 0.007%, SiO2: 0.007%, Na2O:0.23% and Minus 45 microns: ~ 90%. This hydrate is the basic input material for producing American Diamond for jewelry, Thread guides, Sealing rings for pumps and many other valuable products. The author was deeply involved in development of this product, project engineering, trial run and manufacture of this product in the plant. Thus, if you can feel this product, you can definitely produce it in your own plant. Trust, our learned friends of alumina fraternity will put their valuable remarks and opinions under comments paragraph which will help in enriching our knowledge base towards our approach and methodology in achieving better results in future. Your views / remarks / comments matter for us for improvements in forthcoming articles. Please never be hesitant in expressing your opinions. We seek your continued support and welcome your suggestions.

Kind regards.

Kunwar Rajendra

Capex, Opex and Techno-economic Viability for Green-Field Alumina Refinery in India

Hi Friends,

Today is the great day for all of us who are deeply associated with this knowledge sharing technical blog on Alumina processing technology. It is needless to mention here that our blog has earned a prestigious position among the people of Bauxite-alumina-aluminium fraternity in short span of time. Congratulations to all concerned on the eve of crossing the total viewer mark of 130,000 today. This glorious moment is remarkable and memorable as we are proceeding ahead in setting the new height of success. We are continuously receiving appreciations from our learned friends for high level of quality of content published so far and feedback for further improvements. 

In present post, we are bringing out some special facts which will be useful for the top notch officials in taking strategic decisions with regard to capital investments, Operating cost and techno-economic viability aspects for setting up new Alumina refineries in India. 

As such, only a few Alumina refineries were constructed and commissioned across the globe during last decade. Broad details and present status of new refineries executed over last 15 years / under execution presently  in India are outlined in subsequent paragraphs-

1. 1.4 Mtpa Vedanta Alumina Refinery, India: This plant was designed for 1.4 Mtpa alumina with two streams each stream having 0.70 Mtpa production capacity. One of the stream of this plant was commissioned  in 2006 with non-designated source of bauxite as Niyamgiri deposits could not be cleared  by the Government of India for carrying out bauxite mining activities.  The specific capital investment for this plant was very low as the company took advantage of volatile market of equipment and facilities during execution period. But processing of low alumina content and high reactive silica content in bauxite of unidentified areas during commissioning itself made the plant uneconomical. Finally, the shutdown of the plant was forced on 9th December 2012 because of non-availability of bauxite. Plant remains shutdown as yet. However, the Vedanta management is striving to restart the operation of this plant shortly even with imported bauxite.
2. 1.4 Mtpa Anrak Alumina Refinery, India: This plant is located at about 70 km from Visakhapatnam in the state of Andhra Pradesh in India. This Alumina refinery has two streams of 0.70 Mtpa each and the execution is expected to be completed for commissioning by end of the current year - 2013. Most of the equipment and facilities of this plant have been installed and one of the process streams out of two are in readiness for trial but no adequate bauxite available as the earmarked Jarrella bauxite deposits are yet to be cleared by the Government. The trial run for Stationary calciner supplied by Outotec Germany was done in early first week of April 2013 with purchased hydrate and a few thousand tonnes of calcined alumina could be produced. HSD was used as the fuel for firing followed by HFO for calcination during commissioning trial. The estimated specific capital investment of this plant was much higher than that of Vedanta. But this plant could save substantially on technology, engineering and site activities during implementation.
3. 1.5 Mtpa Utkal Alumina Refinery, India: This plant is owned by Aditya Birla group of companies. The execution of this plant was conceived sometime in 1996. The construction of this plant is in advance stage and mechanical completion of this plant is expected by the end of 2013. This plant has been designed by Rio Tinto Alcan Australia who are considered leader in process technology across the globe. But because of inordinate delay in implementation because of various socio-political reasons, the capex of this project has increased substantially. Thus the specific capital investment of Utkal alumina plant was much higher than targeted figure. 
4. 1.4 Mtpa JSW Alumina Refinery, India: Under diversification plan, JSW group company decided to set up alumina refinery in Vijaya Nagaram district of Andhra Pradesh with state of the art and most modern plant associating Rio Tinto Alcan Australia as technology supplier in the year 2005. The company has acquired adequate land but execution of project is under hold awaiting clearance from Government of India for bauxite mining from Araku group of deposits.
5. 1.0 Mtpa NALCO Alumina Refinery, India: National Aluminium Company (NALCO) has initiated studies for setting up 1.0 Mtpa Alumina refinery near Mandavi in Gujarat. As per our estimates, the specific capital investment for this project will be high at around US$ 1000 per   tonne of Calcined alumina mainly because of Lignite based Co-generation plant, required Desalination plant, marginally bigger size equipment requirement because of lower alumina recovery from available bauxite in Gujarat and additional expenditure towards development of infrastructure facilities like port etc. for the project.

The capital expenditure data analysis clearly reveal that specific capital investment in setting up Alumina refineries in India varies from US$ 650 to US$ 1000 per tonne of calcined alumina depending on geographic location of the plant in the country. The capex will be lowest for the plant in Orissa, Gujarat and Jharkhand where as the same will highest in Gujarat.  The reasons are well known to all concern as elaborated in above paragraph. Also, the opex will be higher mainly because of poor plant efficiency figures due to wide variation in mineralogical and chemical composition of basic input material, Bauxite. Also, the volume effect of plant capacity because of low reserve of Bauxite in Gujarat is the other reason. It will be prudent to mention that comparatively lower grade of bauxite, non-availability of desalinated water, availability of low calorific value solid fuel source (Lignite) for co-generation plant are the main reasons for highest capex. Again, on opex part, the same will be abnormally high because of poor plant efficiency figures coupled with low grade of bauxite in Gujarat. At current price level of Caustic soda, Heavy furnace oil and Lignite, even the economic viability for Alumina refinery in Gujarat is a question mark because of high specific capital investment of around US$1000 per tonne and estimated operating cost excluding financing charges (interest & depreciation) at around US$ 200 per tonne of Calcined alumina as per preliminary estimates.However, the actual figures of Capex and Opex can be ascertained by Project Owner with detailed studies before taking financial decision on the matter. In spite of all these facts stated above, Green-field Alumina refineries will be installed mostly in India and Vietnam in coming decade because of huge bauxite reserves of comparatively improved quality than other countries across the globe. In other words, India and Vietnam are the future destinations for green-field Alumina refineries in years to come.

Trust, the above deliberation will give a glimpse of required capex, opex and economic viability aspects for setting up green-field Alumina refinery to one and all across the globe. The author of this technical article will welcome your comments on the subject, if any. Please feel free in sharing your views.

Regards.

Rajendra Kunwar
rajendra@ceti.co.in
www.ceti.co.in

Major Requirements for Successful Commissioning of New Alumina Refinery

Hi Friends,

In continuation to our earlier post, we would like to discuss the requirement of critical facilities, quantity of input materials and documents in readiness for successful commissioning of new Alumina refinery as described here under.

Readiness of plant and facilities:

It is essential to keep the keep following plant, equipment and facilities before starting the commissioning of Alumina refinery-

• Bauxite receipt, unloading, stacking and reclaiming system.
• Readiness of Bauxite crushing, Grinding, Predesilication, Digestion, Residue settling & washing, Security filtration, Heat interchange unit, Precipitation, Classification, Evaporation, Hydrate storage, Calcination  and alumina handling system.
• Major infrastructure facilities like co-generation plant, raw water supply system, cooling towers, compressed air station, emergency power supply system, railway and road network.
• Readiness of Process water storage and Drinking water distribution network.
• Storage vessels for Caustic lye, Fuel oil and other consumables.
• Availability of filter cloth, lubricants and other consumables.
• Adequate stock of input materials like Bauxite, Caustic soda, Coal, Fuel oil, Diesel, Burnt lime, Acids, Flocculent and Seed hydrate.
• Availability of experienced technical executives and operating workforce.

Materials Requirement:

Adequate quantity of major input raw material must be ensured in the stock for smooth commissioning of Alumina refinery as stoppage of plant after commissioning may cause losses for the company. Major raw materials are Bauxite, Caustic soda, water, lime, seed hydrate, flocculent and furnace oil / LSHS.

Documentation Requirement:

Following documents are required for systematic commissioning of Alumina refinery-

• Detailed commissioning procedures.
• Step by step process commissioning sequence.
• Safety and risk management Plan.
• Broad schedule for commissioning.
• Organization chart of Commissioning team.
• Training of commissioning team.
• Formats for recording various parameters and activities.

The above information will suffice the commissioning requirement of new Alumina refinery. Please put your views / suggestions / remarks / comments, if any, further improvements in planning the required activities.
Regards.


Kunwar Rajendra
www.bauxite2aluminium.blogspot.com

Technology Suppliers of Existing Alumina Refineries in India

Hi Friend,

In previous post, we have discussed about the Installed capacity of Alumina refineries in India as on today and proposed additions in capacities in the years to come. In present post, we thought of sharing with you the name of process technology suppliers who have contributed in installation and operation of these alumina refineries. As such, it may not be proper to mention that which company has supplied the best technology as each plant has got certain technology features which are missing in the other plant. 

The list of technology suppliers of existing Alumina refineries in India are tabulated here under-

We have analysed the technological features of the operative Alumina refineries and observed the following-

• Alumina refinery designed by Monte Cartini have efficient security filtration and Hydrate classification system.
• Aluterv FKI plants have better liquor decantation system which gives overflow liquor clarity at around 50 to 60 mgpl only.
• Worley Parson plants have improved digestion circuit compared to others.
• Alcan has efficient residue settling and washing system with proprietary equipment and improved hydrate precipitation circuit for achieving higher liquor productivity as well as consistency in product coarseness.

The information presented here are purely the personal observations and remarks of the author to the best his knowledge and experience in the field without any bias, favor or prejudice. If you have additional information on the subject, please come forward in sharing your views with members of Alumina fraternity.

We will welcome your views / suggestions / remarks / opinions / comments, if any.

Regards.

Kunwar Rajendra

Emerging challenges in design & engineering of new Alumina refinery

Hi Friends,

In earlier posts, we have already discussed the design criteria, process & engineering design calculations and basic requirements for setting up green-field Alumina refinery and methodology for their expansions in phases there after. We have covered all major crucial issues starting from conceptual stage to execution including commissioning procedures of Alumina refinery. In present post, we wish to address the design and engineering challenges in setting up new Alumina refineries in any part of the globe with due consideration of emerging issues being raised all over the World. Major challenges have been briefly described in subsequent paragraphs-

1. Efficient process technology: We can not afford to compromise on efficiency of the plant for judicious utilization of limited natural resources and minimum generation of bauxite residue as waste. Thus we have have to target for all plant efficiency figures better than the best achieved so far in the World. Each process unit should be evaluated in isolation with regard to efficiency irrespective of upward or downward units. The key efficiency parameters like overall alumina recovery at 94% (min.), liquor productivity across precipitators at 92 gpl Al2O3 (min.) and total energy consumption at 8.5 GJ per tonne of alumina (max.) must be kept in mind while designing the new Alumina refinery. Though, it may be little difficult but well achievable target for an efficient Alumina refinery.
2. Rugged design of residue storage pond: Recent failure of earthen dyke of residue storage pond of one of the Alumina refineries in Hungary has created fear psychosis among the people residing in the vicinity of all Alumina refineries in the World. This may be taken as a word of caution by designers and manufacturers of hydrates and alumina. Thus, design of bauxite residue pond to be done with utmost care leaving no chance for any dyke failure as well as percolation of alkaline fluid to nearby natural streams. In addition,   adequate future provisions in the foundation of base must be kept for raising the dyke height at least upto 50 meters from ground level.  
3. Compact design of equipment: Dimension and number of equipment & vessels  are directly proportional to land requirement for installation. Thus bigger capacity equipment & vessels with highest possible H/D ratio should be preferred. All out efforts should be made to maximize the installation of selected process equipment on 1st and 2nd floors of the unit areas wherever possible. During equipment sizing calculations we have to remember that sky is not the limit for designers. These steps will drastically reduce the land requirement for the plant proper. 
4. Optimized plant layout: General layout of the plant plays vital role in operational ease as well as overall space requirement. Thus the general layout and shop layout of the plant should be finalized by working out various permutations and combinations for installation of equipment and facilities to ensure optimum utilization of space within the premises.
5. Zero effluent discharge: As per the recent environmental norms and guidelines, dry residue stacking at more than 50% solids (w/w) and zero effluent discharge outside the premises of plant are essential design parameters for setting up new Alumina refinery. Thus, these issues should be taken up with due care during design and engineering stages of the plant. The residue disposal at higher solid consistency will result in increased pond life as well as faster drying of residue. Similarly, adoption of zero effluent discharge will combat the surface pollution problems and will attribute in reducing the total raw water requirement for the plant.
6. Development of green belt: Under environmental protection measures to prevent threat of global warming, development of green belt in and around the plant is a must in more than 30% of total plant area. This aspect need to be kept in mind and strictly followed while designing the Alumina plant.

These are major emerging challenges in design and engineering of new Alumina refinery. Hope, the topic has been covered in simple words with clarity in expression. The information presented here are purely based on my personal experience in the field. Please put your views / remarks / comments, if any.

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

Kunwar Rajendra