Minimum Feasible Capacity for Specialty Grades of Hydrate and Alumina Plant

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

Production of Pharmaceutical Grade Hydrate

Hi Friends,

Here, we will discuss about specifications, production process route and applications of Pharmaceutical grade hydrate. 

Specialty grade of hydrated alumina used in formulation of pharmaceutical products are known as Pharmaceutical grade hydrate. Highest purity level particularly with respect to lowest level of alkali and fineness are the prime requirements in the product.

Product Specifications:

Typical quality specifications of Pharmaceutical grade hydrate are outlined below-

Al(OH)₃ : 99.5% min.

Al₂O₃: 64.0% min.

Fe₂O₃: 0.012% max.

SiO₂: 0.012% max.

Na₂O: 0.05% max.

Moisture: 0.40% max.

LOI at 1100^oC: 34.5%

Median particle size (d₅₀): 1 micron.

Production Process:

Pharmaceutical grade hydrate is produced using Chemical grade hydrate as the feed stock. The hydrate is ground in ceramic lined ball mill and ground hydrate is washed using very dilute acidic water (acid not more than 1% in water) in order to minimize the alkali content in the product. The properly washed hydrate is dried and packed for despatch to destination.

Industrial Applications:

Major applications Pharmaceutical grade hydrate are listed below-

• Manufacture of toothpaste as hardness of hydrate is matching with the hardness of our tooth enamel,
• Medicinal application as Antacids.

Request to kindly put your views / suggestions / remarks / comments, if any.

Regards.

Kunwar Rajendra

Production of Fire Retardant Filler Grade Hydrate

Hi Friends,

In present post, we will discuss about specifications, production process route and applications of Fire retardant filler grade hydrate.

Fire retardant grade hydrate releases over 30% water vapors on heating at more than 200^oC, thus it has more fire retardancy because of formation of water vapour cloud as per following reaction-

2Al(OH)₃  = Al₂O₃ + 3H₂O

The above reaction is endothermic absorbing about 280 k. calories per kg of hydrate. The maximum decomposition rate occurs at around 350^oC.

The hydrated alumina also imparts better surface finish. It has improved mechanical properties because of larger surface.

Product Specifications:

Typical quality specifications of Fire retardant filler grade are outlined below-

Al(OH)₃ : 99.5% min.

Al₂O₃: 64.0% min.

Fe₂O₃: 0.012% max.

SiO₂: 0.012% max.

Na₂O: 0.20% max.

Moisture: 0.40% max.

LOI at 1100^oC: 34.5%

Median particle size (d₅₀): 2-10 microns.

Production Process route:

The basic principle for manufacture of Fire retardant filler grade hydrate involves surface treatment of superfine hydrate.

The Superfine hydrate is mixed with small quantity of Stearic acid in dry mixer and dried at around 110^oC. The dried hydrate is dispersed in Air jet mill with adjustable classification mechanism for production of Fire retardant filler grade hydrate. This specialty grade has following advantages-

·         Large reduction in viscosity,

·         Improved dispersability,

·         Improved physical properties to composites,

·         Higher loadings.

Industrial Applications:

Major applications Fire retardant filler grade hydrate are listed below-

• Fiber glass products,
• Artificial marbles,
• Glass and glazed tiles,
• Carpet backing,
• Smoke suppressant fillers in rubber products,
• Fiber cement boards,
• Cables,
• Thermosetting plastics..

The data / informations published here are purely personal experience in the field and no way related to any company / organization.


We seek your views / suggestions / remarks / comments on above.
Regards.


Kunwar Rajendra

Specifications and Applications of High Purity Hydrate

Hi Friends,

In present post, we will discuss the broad specifications of high purity hydrate, its production process route and major industrial applications.

High purity hydrate (H.P. Hydrate) is one the special grades of hydrated alumina  primarily used as feed stock for manufacture of synthetic gem bowls.

Product Specifications:

Typical quality specifications of HP grade hydrate are outlined below-

Chemical constituents as impurities:

Fe₂O₃: 0.006% max.

SiO₂: 0.006% max.

Na₂O: 0.23% max.

Particle size analysis:-

Minus 45 microns: over 90%.

Production Process:

High purity hydrate is produced using small stream of pregnant liquor of standard Bayer circuit of alumina. The saturated aluminate liquor is cooled and crystallized in two step precipitation circuit at very stringent process control parameters. Hydrate produced in first step of crystallization is totally discarded and transferred to Bayer circuit of standard alumina. The liquor of the first step precipitators are used as purified liquor containing very lower level of iron and silica impurities. This liquor on crystallization results in production of HP hydrate. The hydrate thus generated is classified, washed, filtered and dried up before packing for transportation. Production of high purity hydrate is possible only in existing Alumina refinery as the main feed liquor is drawn from the existing process stream. Our team has the capability to design, engineer and commission the equipment and facilities for required plant capacity.

Industrial Applications:

High Purity grade hydrate is used for manufacture of synthetic gem bowls for-

 (i)  Ornamental jewelery

(ii) Watch jewels,

(iii) Industrial bearings.

It will be my pleasure to have your views / remarks / comments on above.

Regards.

Kunwar Rajendra

In previous post, we have developed the Design and motor rating calculations for Ball mill. In present post, we will discuss the systematic procedure for starting a Ball mill for taking into operation as well as stopping the Ball mill for taking out of circuit in Alumina refinery. Ball mill is one of the very critical equipment installed in Alumina refinery. Since the mass of the rotating cylinder with liners and balls is very high, thus the starting torque for the mill is enormously high. The drive motor for the Ball mill ranges fro 0.5 MW to 2.5 MW depending on the hardness of Bauxite, feed size and operating capacity of the mill for meeting the hourly alumina production requirement as described in earlier post. Generally squirrel cage induction motors are installed as drive motor for the Ball mill.  The mill is also provided with hydraulic pumps for lifting the Ball mill to provide a jerk to swing so that inertia of rest of the mill is broken for its rotation. The hydraulic pumps of Ball mills in Alumina refinery are popularly known as inching device for the mill. Since the drive motor rating of the mill is the highest among all the high tension (HT) motors of Alumina refinery, so it is connected with high voltage electrical supply line at about 6.60 kV. Hence all precautionary measures are taken to start the Ball mill for normal operation. Sudden start of the mill by direct power supply to its drive motor may cause serious damage to the equipment and power supply system as well.

Ball mill start up procedure: 

The systematic start up procedures for Ball mill are briefly outlined here under-

1.     Check the readiness of upstream and downstream equipment in the process circuit,

2.     Inform the turbine house of Co-generation plant to ensure the stable operation of Turbo-Generators (TGs) and connected boilers. During steam pressure fluctuations in boilers, the ball mill should not be started.

3.     Check hydraulic oil level in oil tank,

4.     Start hydraulic pumps for lifting the mill to swing,

5.     When hydraulic oil pressure reached above 2 kg/cm2 and mill swings, start the drive motor of the mill. The temperature of hydraulic oil should remain less than 40 degree centigrade,

6.     Keep close watch on voltage, amperage, temperature and sound of drive motor,

7.     Open aluminate liquor to the mill at controlled rate,

8.     Start the ground slurry pump,

9.     Start bauxite weigh feeder with low feeding rate to Ball mill,

10.   If everything is normal, put the operation of grinding circuit in auto mode with normal grinding rate.

Ball mill stoppage procedure: 

The sequence of operation for stopping the Ball mill from normal running condition are given below-

1.     Stop the bauxite feeder for stopping the feed to Ball mill first,

2.     Continue flow of digestion liquor to mill for a few minutes to ensure flushing of slurry from the Ball mill,

3.     Stop the Ball mill,

4.     Stop the slurry pump,

5.     Drain the slurry from pump including its suction and delivery lines.

Broadly, the above sequence of operations are followed for starting and stoppage of ball mills. Grinding section operators must be provided with written down procedures in order to avoid any confusion and thereby mishaps. Also, while starting the mill, presence of Area supervisor is considered essential as any small lapse during start up may cause serious damage to equipment as well as unsafe to the working personnel. Sudden start up may also cause damage to mill foundation and its alignment creating acute crisis for Alumina refinery. 

Hope, all major points have been covered under the topic. Please put your views / suggestions / remarks / comments, if any. We will always welcome your suggestions and recommendations.

Is Low Silica in Bauxite a Problem?

 Hi Friends,

After a long gap, I have appeared before you to interact on a small but very critical process issue of Bayer Alumina Plant.

In the past, we have always discussed about the negative impact of high silica in bauxite specifically with regard to operational problems, process control issues, higher consumption of input materials and deterioration in quality of product hydrate or alumina. In previous articles, this issue was elaborated at length with measurable / quantifiable approach so as to focus on its importance in Bayer Alumina Refineries.

In present post, we will briefly discuss about the advantages and disadvantages of low silica in processing bauxite for production of calcined alumina. The question mark (?) on the subject itself forces us to think and re-think about the positive and negative aspects of low silica in bauxite.

It’s a well-known fact that all Alumina producers wish to have low silica bauxite for obvious reasons discussed earlier. Now, before coming to the subject directly, following questions arise-

(i)                What type of silica is harmful for Bayer’s process?

(ii)              What should be the cut-off silica content in bauxite for acceptable quality of alumina in International market?

Though we have discussed these issues in several articles, still it is prudent to freshen up with salient features as outlined below-

There are two types of silica in bauxite designated with regard to Bayer process of alumina – (a) Non-reactive silica and (b) Reactive silica. ROM bauxite mined adopting either open cast or underground mining methodology contains a number of metallic oxides including silica. This mined silica as percentage of total dry bauxite is termed as total silica. The part of total silica which reacts with caustic soda and forms sodalite complex through sodium silicate route is termed as Reactive silica. Majority of Reactive silica is found in form of Kaolinite. And thus, the non-reacting component of total silica with caustic soda is popularly known as Non-reactive silica. Quartz is non-reactive silica. The silica being abrasive in nature causes erosion in components of various process equipment like heat exchangers, pipelines, valves, pump casing and impellers etc. Thus higher silica content affects the capital investment of Alumina refinery because robust material of construction for equipment component in contact with bauxite slurry. Hence higher silica in bauxite causes higher initial investment for the plant and higher repair maintenance cost for routine replacement of critical components of equipment.

Generally it has been seen from bauxite analysis that Reactive silica in bauxite ranges from 50% to 80% out of Total silica in bauxite. Plant operation is affected because of high silica in bauxite as it has high settling velocity and abnormally high abrasive nature.

Now coming to the topic with raised question mark, it’s true that low reactive silica in bauxite is considered as a serious process problem as it directly affects the quality of product alumina because of higher silica content in alumina. The SiO₂ content in calcined alumina produced in all modern alumina a refinery is controlled at around 0.015%. The alumina having higher silica content is considered as inferior quality. For achieving 0.015% SiO₂ in alumina, the SiO₂ in aluminate liquor feeding to crystallizers / precipitators should be around 0.45 gpl.  The saturation level of silica in aluminate liquor is about 3.80 gpl SuO2 which is achieved within an hour in desilication circuit. The delay in achieving super-saturation of silica across desilication tanks results in inefficient desilication thereby increasing gpl SiO₂ in liquor increases to much higher level which ultimately deteriorates the product alumina quality.

The above elaboration concludes that moderate level of Reactive silica in bauxite at around 1.5% in bauxite is considered to be the best with regard to plant efficiencies and product quality as well.

Trust, the subject has been covered here to your desired level of satisfaction in understanding the criticality of the subject issue. We would welcome your  valued comments / remarks to further substantiate the subject.

Regards.

Rajendra Kunwar

Founder & CEO

CETI Enterprises, Delhi NCR, India

Cell: +91 8380043065

Efficient Bauxite Grinding System for Alumina Refinery

Hi Friends,

Size reduction of mined ROM bauxite is essential for improving its reaction with caustic soda for dissolution of alumina (Al₂O₃) forming sodium aluminate (NaAlO₂). Coarser bauxite particles affect the alumina extraction efficiency however fine bauxite creates acute problems in settling of residue in decanters and washers. Thus optimum particle size is the basic requirement for efficient Alumina refinery. Generally, particle size in ground product slurry of bauxite is minus 10 mesh  with over 80% of minus 65 mesh fraction is considered as optimum operating parameter.

Selection and sizing of bauxite grinding equipment is carried out on the basis of following major input parameters-

• Bond index of bauxite,
• Grinding rate,
• Feed size (F₈₀),
• Product size (P₈₀)

In most of the existing Alumina refineries, ball mills are operative. Few plants in the World have rod mills and a few have two stage grinding system with combination of rod mill in first stage and  ball mill in the second stage. It has been practically seen that ball mill generates more fines compared to rod mills.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 the mill in running condition. I acknowledge with thanks the efforts of my unknown friend who has developed this animation for schematic cross section of the ball mill presented here-

Schematic cross section of Ball mill in running condition

Considering the uniformity of desired particle size in ground slurry and energy consumption, single drum grinding mill having two compartments with rods and balls as grinding media in 1st and 2nd compartment has been found to be the best option as per recent studies. Thus, this system is the preferred choice for bauxite grinding for upcoming Alumina refineries in the World because it has the advantages in uniformity of product fineness as well as substantial reduction in electrical energy requirement by about 10 to 15% less compared to total electrical energy requirement in conventional single stage grinding system. The specific electrical power consumption for wet grinding in efficient system ranges from 4.6 to 4.8 kwh per tonne of bauxite.

It is, therefore, essential to evaluate all pros and cons of techno-economic features for all possible alternatives before taking final call to go ahead with the best suited option of grinding system meeting the process requirement with optimum energy consumption.
Kindly put your views / suggestions / remarks / comments, if any on the subject.

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

Kunwar Rajendra