Specifications and Applications of Dry Coarse Hydrate

Hi Friends,

In continuation to our earlier discussions on specialty grades of hydrate, we will discuss here the specifications, broad process route and applications of dry coarse hydrate. Dry coarse hydrate is the special hydrated alumina  having wide range of applications in industries.

Product Specifications:

Typical quality specifications of Dry coarse hydrate are tabulated below-

Al₂O₃: 64.0% min.

Fe₂O₃: 0.012% max.

SiO₂: 0.012% max.

Na₂O: 0.25% max.

Moisture: 0.50% max.

LOI at 1100^oC: 34.0% min.

Minus 45 microns: 6-8%

Production Process:

Chemical grade hydrate produced in Bayer’s circuit is used as feed stock for production of dry coarse hydrate. The process for production of dry hydrate suitable for various non-metallurgical applications envisages the removal of physical / superficial moisture from feed Bayer hydrate. However, the chemically bound water of crystallization and structure of hydrated alumina molecules will remain unaffected.

Hydrate being granular, powdery and porous material; Steam Tube Rotary Dryer is the most appropriate choice to be used as main drying equipment because of under mentioned key advantages over others:

§           No fear of contamination of the product.

§           No material losses.

§           No environmental problem.

§           Ease of operation.

§           Low capital investment and

§           Lower operating cost.

Steam tube rotary dryer is considered as the basic equipment taking into account the physical characteristics of Bayer hydrate as feed material and desired quality of dry hydrate as product. Chemical grade being mild sticky in nature, a combination of chute and screw feeder is the right choice for feeding moist hydrate to dryer.

In Steam tube dryer, method of constant temperature drying is adopted and saturated steam at suitable pressure used as heating media for removal of unbound moisture. Mode of heat transfer from steam to hydrate takes place through conduction only. The dried product hydrate is discharged to the product storage using belt conveyor. In storage shed, the product hydrate is stacked in packed form using High Density Poly Ethylene (HDPE) bags with poly- liner for dispatch. Storage of dry hydrate in loose form is avoided as it may absorb moisture from atmosphere because of its hygroscopic properties.

Industrial Applications:

Major applications of Dry coarse hydrate are listed below-

(i)   Manufacture of glass,

(ii)     Glazed ceramic tiles,

(iii)    Catalyst.

 I presume, you are satisfied with the elaborated facts and figures. I have broadly presented the data / informations of public domain nature because of my limitations. However, I will welcome your views / suggestions / remarks / comments for further improvements in future.

  Regards.

  Kunwar Rajendra

Methods for minimizing unaccounted soda loss in Alumina refinery

Hi Friends,

We are aware that caustic soda is the basic input material used for dissolution of alumina present in bauxite for production of calcined alumina in Alumina refinery. In present post, we will briefly discuss one of the critical issues for operative Alumina refineries.

The specific consumption of caustic soda per tonne of alumina production is generally termed as overall soda loss in Alumina refinery which is ascertained on the basis of plant inventory carried out twice or thrice every month. The plant inventory is based on volumetric measurement of process liquor / slurry and analysis of collected samples to arrive at total production during the period and consumption of input raw materials.  Accounting of total soda loss is further assessed by estimating the consumption / losses under following sub-heads:

• Chemical soda loss,
• Soda loss with products,
• Soda loss with bauxite residue and
• Unaccounted or physical soda loss.

Caustic losses under first three subheads are estimated based on analysis and systematic calculations. But the difference of total soda loss and losses accounted under first subheads is indicated as unaccounted soda loss. At times, it becomes very difficult to technically justify the abnormally high figure on account of  unaccounted soda loss. The abnormally high figure has always bothered me to investigate this issue by tracking all possible factors so as to minimize the losses on this count in particular. I would like to share my personal experience in this regard. 

The specific unaccounted soda loss works out to around 3 to 4 kg per tonne of calcined alumina depending plant capacity. For bigger capacity plants, the figure is on the lower side, however, it may be little higher for smaller capacity alumina plants because of volume effect. In simple words, unaccounted soda loss means physical losses of soda from the plant through unknown sources. Following steps will contribute in reducing the unaccountable soda loss in Alumina refinery are outlined below-

1. Ensure correct receipt of fresh caustic lye in tankers received by rail or road,
2. Avoid accumulation of liquor on floors and immediate repair / steel cladding of drains and sump tanks minimizing seepage of caustic liquor to ground,
3. Recycling the washing of sample bottles and laboratory equipment to process circuit,
4. Ensuring no overflowing of process vessels and spillages of plant liquor outside process areas.

These are the main steps which will contribute in reduction of unaccounted soda loss significantly. Each individual must be vigilant to take care of these factors in Alumina refinery seriously and sincerely for minimizing unaccounted losses.

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

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.