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

Method for Estimating the Volume of Work for Boundary Walls

Hi Friends,

In present post, we will discuss the methodology to arrive at volume of work and capital cost estimates for construction of boundary walls for a typical Alumina refinery of about 1.0 Mtpa capacity. As such there are many assumptions and variables depending on location and design of boundary walls but the methology for estimation will remain the same. let the total length of boundary wall for the considered plant works out about 10 km accommodating all technological, infrastructure and services facilities. The calculations have been presented in simplified manner for easy understanding as outlined here under-

The capital cost estimates for construction of boundary wall works out to around Rs. 2.5 Million per km which corresponds to around US$ 50,000 per km of running length of boundary wall. Using this method, capital cost estimate for boundary wall for Alumina refinery of any capacity can be calculated very easily just by relacing the assumptions and variables applicable for particular location of project site.

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

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Thanks and regards.

Kunwar Rajendra

Key Considerations for Development of Plant Layout for Alumina Refinery

Hi Friends,

In earlier posts, we have discussed many design, engineering and operational issues pertaining to Alumina refinery. In present post, we will discuss the major considerations for development overall plant layout of a new green-field Alumina refinery as outlined below.

• Location of Project Site :  Site selection of project site plays a vital role in capex and opex of Alumina refinery. If the site is located near the sea coast then minimum elevation level of plant should be 5 meters above the high tide level observed in last 100 years.
• Natural Site Conditions : Following parameters are of utmost importance which have direct bearing in the long run on successful operation of Alumina refinery-

• Topography of land,
• High flood level,
• Maximum wind velocity,
• Predominant direction of wind,
• Maximum rain fall,
• Safe bearing capacity (SBC) of soil,
• Total natural evaporation and
• Elevation of site from MSL.
• Natural topography of land should be utilized for gravity flow of process streams so as to minimize the expenses towards cutting and filling during site grading and expenses towards pumping energy during normal operation of the plant.

• Process Technology : Each and every Alumina refinery is the combination of tailor-made equipment and facilities depending on the plant capacity and technology considered.  Depending on technological requirement and flow sequence of process streams, drastic reduction in length of piping network and their structural supports can be achieved. Thus, Plant layout must be frozen after finalization of process technology with due consideration of Bauxite quality and process efficiency figures.
• Finalization of Plant and Equipment : Finalization of capacity and dimensions of equipment are essential to work out the preliminary shop layouts for developing the overall plant layout.
• Space for Operational and Maintenance Convenience : Adequate space must be kept in every area of the plant for safe movement of operating personnel and mechanized maintenance equipment.
• Storage for Input Raw Materials and Products : The storage sheds and vessels should be adequately considered for the plant. The inclination of belt conveyor for movement of bulk solid materials should not exceed the dynamic angle of repose of the material. This parameter is important for deciding the height of storage and space requirement.
• Adherence to Safety and Environmental Protection Norms : Statutory requirements with regard to safety and environment protection guidelines are strictly followed while  developing the layout of Alumina refinery.
• Capex and Opex of Alumina refinery : Lower Capex and Opex are considered as prime objectives for development of final layout  of Alumina refinery.

These are a few major parameters  considered essential in developing the overall layout of Alumina refinery.

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

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Thanks and regards.

Kunwar Rajendra

Calculations for Requirement of Wagon Tipplers for Unloading Bauxite

Hi Friends,

In earlier posts, we have already dicussed the various modes of transportation of ROM Bauxite from Mines to the premises of Alumina refinery. In most of the Alumina refineries in the World, preferred mode of transportation of Bauxite is Railway. If the Alumina refinery is in the close proximity of Mines then either cable belt conveyor or pipe conveyor system has been found to be most economical solution. 

Manual unloading of Bauxite from Railway wagon is time consuming as well as workforce intensive. Thus, Wagon tipplers are installed for unloading Bauxite from Railway wagons. In present post, we will describe the systematic approach to arrive at required number of Wagon tipplers for a typical Alumina refinery of 1.0 Mtpa production capacity as outlined below- 

Though, similar method is applicable for calculating the required number of Truck tipplers in case of movement of Bauxite from Mines to Alumina refinery by road due to non-availability of Railway linkage for small capacity plant. However, it is better to have captive Railway movement facilities rather than road movement for Alumina refineries having more than 0.50 Mtpa capacity as it will require a fleet of truck which may be unmanageable on public roads and parking at Alumina refinery site.

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

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Kunwar Rajendra

Design of F. D. Fan and I. D. Fan for Calciners in Alumina Refinery

Hi Friends,

In earlier posts, we have discussed the design calculations for sizing the HFO unloading pumps and HFO storage vessels based on certain applicable assumptions. In present post, we will discuss the methodology to work out the capacity of Primary air fan (F.D. fan) and Flue gas exhaust fan (I.D. Fan) required for Calcination system in Alumina refinery.

These calculations have been developed by the author based on the principles of chemical engineering for design and engineering of critical equipment for Alumina refinery. Your suggestions for further improvements in above design calculations shall be appreciated and welcomed.

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

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Thanks and regards.

Kunwar Rajendra

Sizing Calculations for HFO Unloading Pumps and HFO Storage Vessels

Hi Friends,

In present post, we will present the methodology for sizing of Fuel oil unloading pumps and its storage vessels required under calcination system in Alumina refinery. The sample calculations have been carried out for a typical Alumina refinery of 1.0 Mtpa calcined alumina.

The calculations have been presented in simplified form for easy understanding and can be developed for Alumina refinery of any capacity just by replacing the basic assumptions and input data where ever required.

The above design calculations include typical cost estimate for in-situ fabrication of required storage vessels for HFO or LSHS or any other liquid fuel.

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

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Thanks and regards.

Kunwar Rajendra

Sizing of Hydrate Storage Shed with Major Facilities for Alumina Refinery

Hi Friends,

In present post, we will discuss the methodology to arrive at the capacity and indicative dimensions of Hydrate storage shed required for a typical Alumina refinery for storage of washed hydrate to take care of any eventualities like sudden outage of Calciner for refractory failure or break down of any other major equipment in calcination section. The basic assumptions and calculations are outlined below-


Annual capacity of Alumina refinery =1000,000 tpa,
Net operating days for refinery = 336 days per year,
Moisture in washed and filtered hydrate = 6% max.,
Bulk density of washed and filtered hydrate = 1.0 t/m3,
Minimum storage capacity of Hydrate storage shed = 7 days of normal plant operation,
Design margin = 15%,
Storage capacity of Hydrate storage shed = 30,000 tonnes hydrate (say),
The angle of repose for dry hydrate varies from 33 to 35 degree,
Thus volumetric capacity of storage shed = 30,000 x 3 = 90,000 cubic meter,
Let  the material height in storage shed below conveyor = 10 meter,
If we take the width of storage shed = 60 meters,
Then length of storage shed = 90,000 / (10 x 60) = 150 meters.
Therefore, the size of Hydrate storage shed works out to 150 m x 60 m.


As such, there are two methods for reclaiming the hydrate from storage shed for feeding to calciner-

• Dry hydrate reclaimed using reversible belt conveyor system for direct feeding to calciner through feed hopper,
• Hydrate is reclaimed by making slurry with water and pumped to horizontal rotary disc table filter (Table filter or Pan Filter) for  filtration and there after feeding to calciners.

Major facilities required for transfer of washed hydrate to storage shed and recovery of hydrate from storage shed back to hydrate filters for feeding to calciners using 2nd method described above are tabulated below-

1. Belt conveyor from table filter to stockpile,
2. Mobile tripper conveyor for hydrate stacking,
3. Hopper for hydrate reclaiming,
4. Hydrate slurry tank with agitator,
5. Belt conveyor from hopper bottom to Hydrate slurry tank,
6. Hydrate slurry pump for pumping slurry to table filter for filtration.

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



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Thanks and regards.

Kunwar Rajendra

Calculations for Process Design of Inter Stage Coolers in Alumina Refinery

Hi Friends,

In continuation to our earlier posts pertaining to design of critical equipment of Alumina refinery, we are presenting here the calculations for Inter stage coolers used for sharp temperature drop of seed mixed aluminate liquor for improving the liquor productivity across precipitators. We are aware that only a few manufacturers are there for this specialized equipment  and thus utilize their expertise in designing this equipment. We have developed this design calculations with lot of efforts and the results of this mathematical model presented below are comparable and close to the heat transfer area worked out by specialized equipment suppliers. The details are presented below-

The inlet and outlet temperature of hot stream hydrate slurry are 70 and 60 degree C respectively which you may find missing in above tabulated data and calculations.

We will appreciate your views / suggestions / remarks / comments, if any, on the subject.

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Thanks and regards.

Kunwar Rajendra