Operational Sequence for Start up & Commissioning of Alumina Refinery

Hi Friends,

In present post, we will discuss the operational sequence for starting and commissioning of Alumina refinery. As such, there may be many permutations and combinations of operational sequence for starting and commissioning of Alumina refinery. We are presenting here one of them which may be simple and most appropriate. The schematic diagram is presented here under-

Start up and commissioning of Alumina refinery is taken up after following activities-

• Thorough checking for Mechanical completion,
• Readiness of raw water supply system and DM plant,
• Synchronization of boilers and turbo-generators,
• Cold water run and 
• Hot water run.
• Ensuring the availability of adequate input materials.

Caustic concentration build up and raising its temperature to around 85 degree centigrade are pre-commissioning activities required for start up of Alumina refinery. Sequence of caustic concentration build up, temperature raising, start up and commissioning steps are taken up in following sequence-

1. Fresh caustic lye received by road / rail tankers are stored in Caustic storage tanks (CSTs) and 6 or 7 nos. precipitators of 2nd line as 1st line precipitators shall be taken into range for commissioning.
2. Initially, Evaporator feed tank, Liquor preparation tank, Digesters, Flash tanks, Heaters and one of the Decanters are taken into range for concentration build up and temperature raising. Accordingly closed circuit with these equipment is made by temporary connections for circulation of liquor before start up. 
3. Water is taken in Evaporator feed tank through temporary lines and operation of evaporator is initiated at low vacuum and operation is stabilized slowly with boiling. This ensures the adequate condensate supply to boilers as well as hot water for dilution of caustic lye to around 150 to 200 gpl caustic in Liquor preparation tank. 
4. Run the Test tank pump at about 50% flow for filling Heaters, Digesters and Decanter connected in the circuit. Keep the drain valves of Heaters in open condition in the beginning  for purging out entrapped air in pipelines otherwise it may cause damage to chambers of heaters.
5. Open steam in Live steam heater maintaining the outlet temperature below 100 degree centigrade. 
6. Circulation of liquor in this circuit is continued for about 24 hours for checking the readiness of process circuit.
7. Start Bauxite charging to grinding mill at about 50% digestion liquor flow and taking charging ratio at around 0.300. Bauxite charging to grinding circuit is considered as start of plant commissioning i.e. Zero hour of plant commissioning.
8. Two desilication tanks will be filled up with slurry taking Bauxite slurry heaters into service. After attaining about 16 hours of desilication time, temporary circuit of Red area will be discontinued and permanent process circuit will be energized for generation of spent liquor.
9. Start flocculent preparation and dosing to settler as required.
10. Initially Security filters will be operating as a spool but will be taken into range afterwards for ensuring required purity of plant liquor.
11. Heat Interchange Unit will be kept bypassed and filling of precipitators shall be started taking only five (5) precipitators in range for the purpose of adequate seed generation.
12. Continue circulation of Precipitation liquor through Evaporators and Digesters for slowly raising the temperature profile of liquor.
13. Slowly increase the digestion liquor concentration to around 250 gpl caustic and step up charging ratio to around 0.620 level for raising the ratio profile of aluminate liquor to the level of pregnant liquor. 
14. Take Residue washers into circuit.
15. After attaining the aluminate liquor ratio above 0.600 in feed liquor of Precipitation tanks, start seeding with purchased solid hydrate at controlled rate for generation of seed hydrate. For the purpose, solid hydrate will be mixed in Seed mixing tank with Pregnant liquor and pumped to those five (5) Precipitation tanks taken in range.
16. Maximize charging ratio to the desired saturation level and increase Bauxite charge at increase digestion liquor flow.
17. Hydrate generated in Precipitation circuit will be used as seed till adequate hydrate is built up in the process.
18. Discontinue all temporary connections and continue operation as normal by taking desired number of equipment and vessels of one line of process circuit.
19. Start hydrate classification circuit and transfer of product hydrate to Hydrate storage shed.
20. After making a stock of about 20,000 tonnes of hydrate in storage shed, commission Calciner for production of calcined alumina.
21. Stabilize plant operation for maximizing alumina production level.

Hope, starting and commissioning procedure for Alumina refinery has been covered with clarity in understanding.

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

Regards.

Kunwar Rajendra

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

Methodology for Checking Mechanical Completion of New Alumina Refinery

Hi Friends,

In present post, we will discuss the major activities carried out for checking the construction completion and readiness of equipment and facilities for conducting testing and commissioning trial runs. Major activities are listed here under-

1. Verifying the installation of all equipment and completion of construction activities as per PFDs, P&IDs, ISOs and design drawings.
2. Readiness of operating and maintenance platforms.
3. Installation of sampling valves, scoop and other required system.
4. Hydro-static / pneumatic testing of vessels, lines, cranes and equipment in line with statutory guidelines.
5. Cable continuity test for electrical power supply.
6. Statutory clearances from Government officials for equipment, lines and pressure vessels.
7. Calibration as well as function checking of instruments, controls and interlocks.
8. Proper leveling and alignment of the equipment.
9. Direction of rotation of motors, fans and other rotating equipment.
10. Flushing of equipment with water for removal of foreign materials.
11. Checking the equipment for initial fill of grease and lubricants.
12. Checking of tools and tackles for normal operation and maintenance.
13. No load checking of motors in decoupled condition.
14. Dry running of all rotating equipment in circuit.
15. Vibration checking of rotating equipment.
16. Preparation of punch list of outstanding items / deviations and required changes / modifications including their priority level for changes / modifications and planning for incorporation in final as-built drawings.

These are the major activities carried out for checking the mechanical completion of the Alumina refinery project before taking up testing and commissioning of Alumina refinery.

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

Regards.

Kunwar Rajendra

Congratulations for Achieving the New Record of Over 35,000 Viewers

Hi Friends,

Please accept my heartiest congratulations for achieving a new height of success of our technical blog on bauxite, alumina and alumina chemicals including aluminium metal. Today, we have crossed the record number of viewers of over 35,000 in short span of time. It's a fact that we do not give any cosmetic effect on the posts because of our various limitations and paucity of time as well. But it's also the truth that raw technical data and information without any cosmetic effect has its own importance, beauty and essence. 

This blog has been developed as independent think tank for the mutual benefits of each member of Bauxite-alumina-aluminium fraternity. The technical articles published on this site has proved that we can enrich our technical strength and capability just by exchanging our thoughts and experiences with our known or unknown friends of bauxite-alumina-aluminium fraternity. Let us  continue to put our concerted efforts for benefit of ourselves and the community around. We are committed to ensure that global community is fully informed about the technological advancements in the field of bauxite, alumina and aluminium.

On the eve of this new record, I would like to express my sincere thanks to Google for providing us such a wonderful platform, free of cost, for the benefit of global community. 

As concluding remarks, I would like to invite you to put your views / suggestions / remarks / feedback / comments, if any, for further improvements in strengthening this unique platform.

Thanks again for your continued support.  

Best regards. 

Kunwar Rajendra

Typical Schedule for Testing & Commissioning of New Alumina Refinery

Hi Friends,

In earlier posts, we have discussed the methodology for design, engineering and execution of  Alumina refinery adopting different technology suiting the Bauxite quality specifications. Soon after declaration of Mechanical completion, construction completion checking is carried out  which includes erection of equipment and facilities, lubrication, no load testing of decouple drive motor  and its direction of rotation including hydraulic testing of vessels, equipment and pipelines as per statutory guidelines. Soon after checking the mechanical completion, cold water run, hot water run and commissioning of individual equipment and facilities of Alumina refinery are taken up. Generally, checking of mechanical completion including cold water run requires about two weeks time. Cold water run, hot water run and caustic concentration build up activities are considered as pre-commissioning stage of the Alumina refinery. However, the Bauxite charge to process is considered as the Zero hour for commissioning of the plant. Commissioning stage of the plant requires about 8 to 10 weeks time from start up to calcined alumina production.


In present post, we will broadly discuss the schedule for pre-commissioning and commissioning stages of Alumina refinery clearly indicating the major activities for shortening its commissioning and stabilization period. Since alumina production is a complex and continuous chemical process, hence it's commissioning is also tedious and thus requires systematic planning and a team of experienced professionals as well. A typical schedule for testing & commissioning of Alumina refinery is given below-

It is evident from above graphical presentation that generally the total time for testing & commissioning of green-field Alumina refinery is about 16 weeks after the mechanical completion i.e. 6 weeks for pre-commissioning and 10 weeks for commissioning of entire Alumina refinery up to production of alumina in calciner. There is a scope for further compressing the commissioning schedule by systematic planning and involvement of experienced personnel as elaborated above. Planning for required input materials like Bauxite, caustic soda, water, lime, flocculent, fuel and consumables as well as required technical professionals are the key to successful commissioning of Alumina refinery.


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


Kunwar Rajendra

Specifications, Industrial Applications and Production of Kaolin Clay

Hi Friends,

In present post, we will discuss the specifications, industrial applications and production process route for manufacture of Kaolin clay as described here under.

Kaolin is the pure clay popularly known as China clay or Porcelain clay or White cosmetic.  It is100% naturally occurring material in earth crust which is mined, washed, crushed to desired size, processed and despatched in high density polyethylene (HDPE) bags to manufacturers of various industrial products. It is stiff having high refractoriness. It is generally known as Kaolinite chemically known as Hydrated aluminium silicate. It has unique features like high opacity, luster and chemical resistivity. Its fine powder swells in water which makes a great thickening ingredient.

Typical specifications:

Total Kaolinite: 97% min.

Aluminium oxide : 37% min.

Silicon oxide: 46% max.

Iron oxide : 1.0% max.

Titanium oxide : 0.30% max.

Calcium oxide:0.05% max.

Sodium oxide:0.50% max.

Volatile matters: 1.0% max.

Water soluble salts:1.0% max.

LOI: 15% max.

Physical properties:

Colour: White,

Whiteness: 65-67

Specific gravity: 2.5 to 2.7

Oil absorption: 25 to 35.

pH of 10% aqueous solution: 7 to 8

Shelf life: 5 years.

Granulometry:

Varying from 100 Mesh to 35 mm lumps required as feed stock for manufacture of various end products.

Major Industrial applications:

Ceramics, Paints, Pigments, Paper making, Coatings, Colour stabilizers, Catalyst carriers, Cosmetics, Skin care products, body powder and deodorants.

Production process route:

Kaoline clay is produced by adopting series of unit operations like crushing, grinding, thickening, classification, filtration, drying and calcination. Required unit operations are purely dependent on quality specifications and granulometry of desired product. It is generally packed in HDPE bags for despatch to desired destinations.

Hope, the subject has been covered adequately. 
Please put your views / suggestions / remarks / comments, if any.
Regards.

Kunwar Rajendra

Alumina Plants Processing Boehmitic Bauxite by Tube Digestion System

Hi Friends,

In continuation to earlier posts, we will outline here the technological features of various Alumina refineries in the World processing boehmitic bauxite adopting Tube digestion technology. It would be prudent to mention that plants processing Diasporic bauxite using Tube digestion system have not been covered here.

These are the plants processing Boehmitic bauxite using Tube digestion technology in the World. It is learnt that initial design and engineering activities were taken up for Ma'aden Alumina refinery by Hatch-Outotec JV but finally Ma'aden has placed the order on Hyundai Engineering & Construction Company South Korea for execution of their Alumina refinery project on EPC basis.  


Because of improved energy efficiency, Tube digestion technology has edge over other digestion technology in the World thus it may be the preferred choice for future Alumina refineries due to lower capex, opex and other added advantages of the system. This is purely the personal opinion of the author without any favor, bias or prejudice rather supplemented by factual information based on in-depth studies and experience acquired on the subject.


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


Kunwar Rajendra

Congratulations for the Glorious Success Beyond Our Imagination

Hi Friends,

It's a fact that we started this specialized technical blog with aggressive impulse for achieving the goal set by us within certain time frame. We could maintain the accelerated pace during our journey with our keen interests, enthusiasm and pleasure in publishing wide range of over 245 technical articles pertaining to bauxite, alumina and aluminium. Now, when we look back the trajectory of our 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. It is the success of one and all associated with this blog. Till date, we have more than 31,000 members who are closely connected with this web site. 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.


Now, we have to take this site to the next level covering solutions of complicated technical issues in all facets of design, engineering, execution and operation of units and plants. At this juncture, our team is working out the detailed planning for publication of forthcoming articles. Meanwhile, we solicit your views / suggestions / remarks for inclusion in forthcoming posts.


We would like to share with you this joyous moments of glorious success beyond our imagination. We seek your continued support. I take the opportunity to wish you & your family Merry Christmas and a very happy, healthy and prosperous New Year-2012. May God bring a golden feather of success on your cap in the new year.
Thanks and regards.


Kunwar Rajendra

Material Flow for Digestion and Slurry Flashing Circuit of Alumina Refinery

Hi Friends,

In earlier post we have presented the Material flow balance for Bauxite grinding and Pre-Desilication Units. In continuation to the earlier post, we are presenting here with the material flow balance for digestion and slurry flashing circuit for 1.0 Mtpa Alumina refinery.

In this flow balance presentation, only main streams have been presented with calculated figures based on chemical engineering principles. Calculations for all these figures definitely require the fair knowledge of process circuit and related basic process parameters adopted for steady operation of Alumina refinery. 


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


Kunwar Rajendra

Material Flow Balance for Bauxite Grinding & Pre-Desilication Units

Hi Friends,

You will appreciate the efforts put by us in exchanging views on many complicated technical issues pertaining to Bauxite, Alumina and Aluminium metal. Now, we have reached to a reasonably high level of discussions on the subject. The project engineering involving sizing of equipment as well as pipelines, material flow calculation for each stream is a must. Thus, we thought of sharing the simplified  methodology for carrying out material flow balance calculations for a typical 1.0 Mtpa Alumina refinery. 

In present post, we have just presented a sample of material flow balance for Bauxite grinding and Pre-desilication units of Alumina refinery. 

Using basics of Chemical engineering and mineral processing techniques, material flow balance for all units followed by thermal energy balance calculations for the plant may be developed by individuals for taking up assignments pertaining to design, engineering and execution of Alumina refinery. 

Hope, you will like this approach of systematic learning of process and plant design calculations for setting up Alumina refinery of any capacity.

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

Regards.

Kunwar Rajendra

Method to Calculate Operating Expenses (OPEX) for Production of Alumina

Hi Friends,

In present post, we will discuss the methodology to arrive at manufacture cost (Opex) of calcined alumina with certain basic assumptions and considered issue price of input materials-

The above tabular data fairly gives the idea about the consumption pattern of various input  materials, utilities and services required for producing  calcined alumina in Alumina refinery and elaborate method to estimate the manufacture cost of calcined alumina. With indicated assumptions, the manufacture cost works out to US$174.60 per tonne of calcined alumina.  Here, the figure does not include the financing charges on capital investment. It is evident from above presented data that cost towards mining and transportation of Bauxite accounts for about 25% of manufacture cost of calcined alumina. It is advised not to take the calculated figure on face value as the manufacture cost varies from plant to plant depending on the landed price of raw materials and other variants. Please put your views / suggestions / remarks / comments, if any. 


If you like this article, please press your rating as +1  appearing in blue colour at the footer of this page.

Regards.

Rajendra Kunwar

Heartiest Congratulations for the New Record of 29,000 Viewers

Hi Friends,

Please accept my heartiest congratulations for associating yourself with our technical blog in achieving this new height of success in short span of time. I am delighted to express my sincere thanks to all of you for your cooperation and supports on every steps of our journey in stepping beyond  the prestigious record of 29,000 viewers. So far, our journey had been joyous and adventurous as well particularly in maintaining the quality standard set since start of this technical blog. Till date, we have published over 235 technical articles on this blog and will continue to add variety of new technical articles full of technical data, information and calculations in days and years to come. We are confident to honor our commitments with our valued viewers.

You must have observed and realized that each and every member of our team has made concerted efforts in improving the quality of articles in all respect. We have published many unique articles which have been developed by our team and well appreciated by our learned viewers. Many of our viewers have expressed on several occasions that such technical documents / articles / papers on such a very specialized topics are rarely available in any published literature other than this particular platform. It is an honor to our team. We are thankful for your appreciation.

On continual basis, our team will put efforts in presenting articles with enriched data, information and calculations pertaining to project and equipment engineering in particular. We will welcome and appreciate your valuable remarks / comments on published articles for further improvements. As a routine, we keep on updating our old articles with modified and latest information. Hence, you are advised to keep a track of updated old articles also. You may find something better than what you have experienced earlier. In case, you have paucity of time because of your busy schedule, just run through the articles, I am sure, you will love the article and will enjoy the content as well. Never ignore the presented articles as we have put lot of efforts for sharing these data, information and calculations with you only.

Please put your valued suggestions / remarks / comments, if any. 


If you like this article, then please press your rating as  +1   appearing at the footer of this page.

Regards.


Kunwar Rajendra

Energy Balance Calculations for Specialty Grade Alumina Production Unit

Hi Friends,

In previous post, we have briefly described the material balance calculations for a typical 3000 tpa Specialty grade alumina production unit. Here, we are presenting the sample energy balance calculations across all associated facilities like Kiln, Air cooler and Water cooler installed for calcination as well as cooling of alumina for production of 3000 tpa Refractory grade calcined alumina. On the basis of this basic calculations, it becomes very easy to arrive at estimated fuel requirement for calcination, air requirement for combustion of fuel and generation rate of flue gases released to atmosphere through stack. In the proposed system, the feed hydrate with about 10% physical moisture will be entering to Rotary Kiln at about 30^oC and calcined alumina will be leaving the Kiln at about 1400^oC. From hot end side of the Kiln, preheated air and furnace oil will be entering to the Kiln at around 95^oC and 80^oC respectively. The furnace oil temperature will be very close to its flash point while entering the Kiln through the burner.


'As is' Hydrate feed rate to Kiln = 1720 kg/hr and
Calcined alumina coming out from Kiln = 1000 kg/hr.


Energy Balance across Rotary Kiln:

Assumed composition of Heavy furnace oil -

C = 87.0%          H = 10.5%          S = 1.0%.

O = 0.10%          N = 0.20%           Moisture = 1.20%.

Calorific value = 9600 k.cal/kg.

Specific gravity = 0.92

Specific heat = 0.56 k.cal/kg.

Taking the basis of 1 kg of HFO-

Element     Composition        Moles               O₂ Requirement

C                    0.87 kg        0.0725 kg. mole    0.0725 kg. mole       

H                    0.105 kg      0.0525 kg. mole    0.0262 kg. mole

S                    0.010 kg      0.0003 kg. mole    0.0003 kg. mole.

In order to ensure complete combustion of fuel oil inside the Rotary Kiln, 10% excess O₂ will be required.

Thus O₂ requirement = 1.10*0.0990 kg. mole = 0.1089 kg. mole

Considering 21% O₂ in air,

Air requirement = 0.1089/0.21 = 0.5186 kg. mole.

N₂ in air = 0.79*0.5186 kg. mole = 0.4097 kg. mole.

Now the composition of Flue gas may be derived as-

CO₂ = 0.0725 kg. mole = 0.0725 * 44 = 3.19 kg.

SO₂ = 0.0003 kg. mole = 0.0003 * 64 = 0.0192 kg.

O₂ = 0.01 kg. mole = 0.01 * 32 =0.320 kg. 

N₂ = 0.4097 kg. mole = 0.4097 *28 = 11.472 kg.

Thus total dry flue gas= 3.19+0.0192+0.32+11.472 = 15.00 kg.

Water vapour generated on combustion of Hydrogen= 0.0525*18 = 0.945 kg.

Mass of vapor due to moisture in HFO = 0.012 kg.

Hence total water vapour = 0.945 kg + 0.012 kg = 0.957 kg of water vapour per kg of HFO burnt.
Let x kg of HFO is required per tonne of product alumina.
Hence air requirement = 0.5186*x kg.
Mass of Flue gas = 15.00*x kg.
Mass of water vapour=0.957*x kg.


Heat Input to Rotary Kiln:-
Total heat value of HFO per tonne of product =9600*x k.cal.
Sensible heat of HFO = x*0.56*(30-0) k.cal. = 16.8* x k.cal.
Mass of water with HFO = 0.012*x kg.
Enthalpy of water vapour = 0.012*x*539 k.cal. = 6.5* x k.cal.
Enthalpy of air = 15*x*0.24*(95-0) k.cal = 342* x   k.cal.
Enthalpy of input feed hydrate = 1720 * 0.20*(30-0) k.cal = 10320 k.cal.
Therefore, total heat input to Kiln = 9600*x + 16.8*x + 6.5*x + 342*x + 10320.
Thus total heat input to Kiln = 9965.3*x + 10320 k.cals.


Heat Output from Rotary Kiln:-
Heat with dry stack gas = 15.0*0.24*(250-0) k.cal = 901 k.cal.
Enthalpy of calcined alumina = 1000*0.27*(1400-0) k.cal = 378000 k.cals.
Heat of vaporization of free moisture=170*1.08(100-30)+170*0.45*(250-100).
= 11900 + 91630 + 11475 k.cal. = 115005 k.cals.
Heat of vaporization of combined water = 0.55*1000*0.45*(1400-250).
= 284625 k.cal.
Heat of vaporization of water formed during combustion of Fuel oil
= 0.945*1.0*(100-30)+0.945*539+0.945*0.45*(250-100) k.cal. = 639 k.cal.
During operation of Rotary Kiln, substantial thermal energy is lost by radiation.
Assuming 20% of heat given by HFO is lost by radiation,
Heat loss by radiation = 0.20*9600*x k.cal. = 1920*x  k.cals.
Therefore, total heat output=901+378000+115005+639+284625+1920*x.
Thus, Total heat out = 779170 + 1920x  k.cals.
Since Heat Input = Heat Output.
Therefore, 9956.3*x + 10320 = 779170 + 1920*x.
or, 9956.3 *x - 1920*x  = 779170 - 10320.
or, 8036.3 *x = 768850.
or, x = 768850 / 8036.3 = 95.67 kg.
Taking design margin as 15%,
Specific HFO requirement=1.15*95.67 kg/t=110 kg HFO per tonne alumina.
Air requirement = 110 * 15 kg per hour. = 1650 kg per hour.
Flue gas generation rate = 110*15.0+110*0.957 = 1755 kg per hour.


Conclusions:
Specific HFO requirement = 110 kg per tonne of alumina.
Air requirement for calcination = 1650 kg per hour.
Flue gas generation rate = 1755 kg per hour.


Trust, all associated technical aspects have been covered systematically. In case you have some better method for carrying out energy balance calculations, please feel free to share with us. Your valued suggestions / remarks / comments, if any, shall be welcomed.


If you like this article, then please press your rating as  +1   appearing at the footer of this page.


Thanks and regards.

Kunwar Rajendra

Generation Cost of Electrical Power in Coal Based Thermal Power Plant

Hi Friends,

In earlier posts, we have already discussed about the Technological Advancements in Electrical Power Generation System with regard to overall thermal efficiency and other related technical issues of Thermal Power Plants. As production of aluminium metal in Aluminium Smelters is a power intensive metallurgical process wherein the cost component of electrical power in production cost of aluminium metal ranges from 50 to 55%. Thus, the unit price of electrical power becomes the key factor for execution and operation of Aluminium Smelters. As we all are well aware that shutdown and permanent closure of many Aluminium Smelters in the World were forced in the past mainly due to high power cost.  Thus, it becomes essential to judiciously work out the unit rate of electrical power for the specific Aluminium Smelter project. In present post, we will broadly discuss the methodology to estimate the generation cost of electrical power in coal based  Thermal Power Plants clearly stating the major assumptions as outlined here under-

Major assumptions include the capital investment, specific consumption factors, overall thermal efficiency figure applicable for considered type of power plant and landed price of input materials. Here, the methodology have elaborated clearly. The power generation cost in coal based Thermal Power Plant works out to US$ 43.12 per Mega watt hour of electrical power. The above derivation clearly reveals that the cost of input fuel accounts for over 56% in generation cost of power. Thus, fuel price is the key contributing factor in improving the profitability of Thermal power plant and thereby Aluminium smelter as well.

Trust, the methodology has been clearly described for easy understanding and can be used for any capacity simply by replacing the basic assumptions with the new figure.Please put your views / suggestions / remarks / comments, if any.


If you like this article, please press your rating as +1  appearing at the footer of this page.
Thanks and regards.


Kunwar Rajendra  

Key Considerations for Design of Bauxite Residue Storage Pond

Hi Friends,

In earlier posts, we have already discussed about the specifications and generation rate of Bauxite residue (Red mud) in Alumina refinery. The residue generation rate is generally 15 to 30% more than the production rate of product alumina. Thus, even for a typical Alumina refinery of 1.0 Mtpa calcined alumina, residue generation will vary from 1.15 Mtpa to 1.30 Mtpa. In a few cases, the residue generation rate is even higher where poor quality Bauxite is processed. This simply reveals that requirement of residue storage will be very high. Hence, it becomes essential In present post, we will discuss the major considerations while design of Bauxite storage pond (red mud pond) as outlined below.

1. Location: Site for construction of Bauxite residue storage pond (Red mud pond) is located close to the Alumina refinery to minimize the energy consumption for movement / transportation of residue but at the same time away from the habitation.
2. Natural Topography: It is preferred to locate the Bauxite residue storage pond in low lying area surrounded by hills to save on construction cost of dyke. The excavated soil is used to minimize the requirement of borrowed earth for construction of dyke / dam.
3. Characteristics of Soil: Soil having lower porosity with more of clay is considered better for construction of residue storage pond as it gives improved strength and less chance for percolation of alkaline water outside.
4. Volumetric Capacity: Volumetric capacity is decided based on residue generation rate and life of storage pond. As such base width is taken in to account for keeping in mind the final height of storage pond but phasing of dyke raising is done accordingly.
5. Rain Water Drainage: All along the dyke, proper drainage is made for diverting the rain water outside so that erosion of dyke will be minimal. 
6. Geo-Textile Lining: Entire storage pond including dykes are provided with geo-textile lining to ensure no percolation of water from storage pond to underground natural stream as it may cause harm to humanity.
7. Adequate Free Board: Minimum free board of 1.5 meter is is considered while designing the residue storage pond. This provides additional capacity and safety provision for the future. 

These are a few major issues which are taken care of during design of Bauxite residue storage pond. Please put your views / suggestions / remarks / comments, if any.

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Kunwar Rajendra

Methodology to Estimate the Land Requirement for Residue Storage

Hi Friends,

In present post, we will cover the simplified method to work out the estimated land requirement for construction of Bauxite residue storage for a typical Alumina refinery of 1.0 Mtpa production capacity processing gibbsitic Bauxite using Medium pressure digestion technology. The assumptions made for calculations have been clearly stated and may undergo change depending on capacity and quality of input materials.

Broad calculations are tabulated below-

Trust, the systematic approach presented above gives fair idea to work out the estimated land requirement for construction of Bauxite Residue Storage for Alumina refinery of any production capacity.

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

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Thanks and regards.

Kunwar Rajendra

Plate Thickness Calculations for Digesters and Other Pressure Vessels

Hi Friends,

In earlier posts, we have discussed in detail the process design and equipment design calculations for various technological equipment including pressure vessels used in Alumina refineries. I admire your level of stamina and patience in going through such complicated calculations with utmost interest. In present post, we wish to present the design calculations used for estimating the plate thickness of the pressure vessels like Digesters and Flash tanks operative in Alumina refineries. We have carried out sample calculations for Digester vessel installed in medium pressure digestion circuit of Alumina refinery.

As such, many methods and empirical relations have been developed by designers and equipment manufacturers based on their rich experience on the subject. Here, we will discuss the simplified  formula which gives most authentic and reliable results compared to others. Since the plate thickness of pressure vessels is directly proportion to its pressure and diameter and inversely proportion to allowable stress of material of vessel, thus the engineering formula used for thickness calculation can be presented as follows-

                                                                      P x D

                                                  t = -----------

                                                        2 x J x f

Here, P = Design pressure of vessel in kg per cm2,

          D = Diameter of vessel in mm,

          J  = Joint efficiency of welding,

          f  = Maximum permissible stress for material of plate in kg per cm2.
          t  = Plate thickness of vessel in mm.

Welding of pressure vessels are done by duly qualified and certified welders. The welding joint efficiency figures for thickness calculations is taken as per the following norms-
J = 1.00 for class-A type, J = 0.85 for class-B type and  J = 0.50 for class-C type.
The maximum permissible stress for plates of carbon steel as well as stainless steel ranges from 1000 kg/cm2 to 1800 kg/cm2 thus for design calculation purpose, lower value at 1000 kg/cm2 is generally considered. The sample calculations for estimation of plate thickness of Digester vessels are given below for clarity in explanation.


Sample Calculation:
Let us work out the plate thickness for the Digester vessels for Alumina refinery adopting Medium pressure digestion technology. The maximum operating pressure for such Digesters is 7.0 kg per cm2,
Thus design pressure for Digesters, P = 1.20 x 7.0 = 8.40 kg per cm2.
Diameter of Digester = 4.00 meter = 4 x 1000 mm (assumed),
For class-A type welding, Joint efficiency J = 1.00,
Maximum permissible stress of steel plate, f = 1000 kg/cm2,
                                                                                 8.4 x 4.0 x 1000
Thus the plate thickness of Digester vessel, t = ------------------------  = 16.80 mm.
                                                                                  2 x 1.0 x 1000 
Taking the design margin of 15%, 
Plate thickness = 1.15 x 16.80 = 19.32 mm.
Hence, the minimum plate thickness for Digester vessels operative for Medium pressure digestion technology must be 20 mm.


The specifications, drawings and fabrications of pressure vessels are carried out as per the guidelines and standards of American Society of Mechanical Engineers (ASME). Trust, the subject has been elaborated in simplified manner. Please put your views / suggestions / remarks / comments, if any.


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Thanks and regards.


Kunwar Rajendra