Systematic Approach for Design of Slurry Mixing Agitators

         Hi Friends,

In various technical forums, process experts as well as equipment manufacturers have opined that the design of agitators for mixing process slurry handled in Chemical industries is complicated and tricky issue. In this paper, we would like to discuss the subject in very simplified manner with systematic approach starting with brief description of involved terminology, associated design parameters and methodology with sample motor rating calculations for the slurry mixing agitator.

Basic Formula Drive Rating Calculations for Agitator:

Power Required for Agitator Drive Motor = N_p X ρ x N³ x D⁵ watt for 1 Impeller.

Where Np = Power number (Dimensionless number dependent on type of impeller),

ρ = Density of Fluid in kg/m3,

N = Revolution per second and

D = Diameter of Impeller in m.

Indicative Power Numbers for Various Types of Impellers:

S.No.	Type of Agitator Impeller	Power Number (Np)
1.	Four bladed 45 degree Pitch Turbine	2.1
2.	Rushtom Turbine	5.5
3.	Propeller Type Impeller	0.70
4.	Hydro-Foil Type Impeller	0.30 to 0.51

Sample Calculations to Arrive at Drive Motor Rating for Agitator: 

Simplified sample calculations have been presented to arrive at the drive motor rating for the agitator of a Process tank having around 3000 m³ gross capacity with key input figures as well as realistic assumptions-

Fluid height in the tank, H = 16 m and Diameter of tank, D_t = 14 m

Slurry volume in tank   = π *D_t²*H/4 =  π * (14)²*16 /4 = 2463 m³   

Solid consistency in Slurry = 50 % (w/w),   Density of slurry, ρ = 1602 kg/m³,

Viscosity of slurry, μ = 550 cp

Agitator Impeller Diameter, D_i= 33 % of tank diameter = 14 * 33% m = 4.62 m

Tip speed of Impeller = π *D_i *N = 3.1416 * 4.62 *20 = 290 m/minute,      

 Drive motor RPM = 1500 rpm, Gear Box Reduction Ratio = 75

∴ Agitator RPM = Drive Motor RPM/Gear Box Reduction Ratio = 1500/75 = 20 rpm,

Thus revolution per second of impeller, N = 20/60 = 0.333 Revolution per second.

Flow Number N_q   = 0.56 and Power Number,     N_p  = 0.51 (assumed figures for Impeller)

∴ Pumping Capacity  =  N_q * N * D_i³  m³/ second

= 0.56 * 0.333 * (4.62)³ = 18.41 m³/sec.

Area of Tank               = π  * D_t²   = π  *(14)² / 4 = 153.94 m²

Bulk fluid Velocity      = pumping capacity/area of tank

= 1104.44 / 153.94= 7.18 m/min. = 23.55 ft./min.

Degree of Agitation   = bulk fluid velocity / 6     

(For 6 ft/min., degree of agitation =1 and Degree of agitation varies from 0 to 10)

= 23.55 / 6 = 3.93 ~ 4

Annular Area = π  * (D_t²- D_i² ) /4  

Where D_t = Diameter of tank      and        D_i = Diameter of impeller in meters.

= 3.14 * (14² – 4.62²) / 4 = 137.18 m²

Rising velocity of particles = pumping capacity / annular area

= 1104.44 / 137.18 = 8.051 m/min.  = 0.1342 m/sec. 

Tank Turnover rate   = Pumping capacity / tank capacity

= 1104.44 / 2463 = 0.45 times / min.

Power Number N_p    = 0.51

Shaft Power,      P      = N_p* ρ *(D_i)⁵ * N³ /1000 kW

Where N_p = Power number of impeller (Dimensionless number),

D_i = Diameter of impeller in meters, Shaft RPS,             N = revolutions per second,

∴ Shaft Power, P   = 0.51 * 1602 * (4.402)⁵ * (0.333)³ /1000 kW = 49.86 kW

Taking Gear Box Efficiency   = 80% and Drive Motor Efficiency = 95%,

Design margin           = 1.15

∴ Drive Motor Rating = 1.15 * 49.86/(0.80 * 0.95) =73.95 kW.

Thus the drive motor of about 75 kW shall be adequate for successful operation of agitator of 3000 m³ Process tank containing fluid of considered solid content. 

Conclusions:

The developed methodology clearly reveals that motor rating calculations for any slurry mixing agitator can be carried out easily by simply replacing the associated input process conditions, operating parameters, dimensions of tanks / vessel and appropriate power number for impeller in above simplified derivation. 

Trust, you will like the methodology adopted in this technical paper. We would like to have your comments.

In case, your company needs assistance of our team in resolving any technological, process, engineering or operational problems of your plant; we may be contacted. We are operating out of Gurugram, India. You may like to have a look at our website.

Regards.

Rajendra Kunwar

E.Mail: rajendra@ceti.co.in

Our Website: www.ceti.co.in

CONGRATULATIONS TO ALL MEMBERS OF BAUXITE-ALUMINA-ALUMINIUM FRATERNITY !

Hi Friends,

Our efforts of exchanging our knowledge on the technical platform of Alumina Technology blog has fetched us to a new height of success. All of us who contributed directly or indirectly in achieving this grand success deserves our heartiest Congratulations! We congratulate all members of bauxite-alumina-aluminium fraternity for setting up such a new record of of success in achieving the target of 95,000 viewers of our popular technical blog across the globe today, the 19th June 2015.

The editorial team of Alumina Technology blog is thankful to you all of you for your continued co-operation, support, feed back and contribution in improving the quality of technical articles published on regular basis.

We celebrate every success and thus we are now aiming for the grand occasion for reaching to  a further milestone of success to cross the total viewer target of 100,000 within couple of months from now. We have observed that our younger generation of bauxite-alumina-aluminium fraternity have started taking keen interest in analyzing the articles with due care and expressing their views and suggestion by putting their remarks in the space provided under "Comments" column located just below each technical article. We have truly realized that exchanging knowledge has helped us in enriching the knowledge of all involved persons.

Trust, we will continue to have your cooperation / supports in days to come for further improvements in quality of articles published on this blog. Your comments encourages our team to be more careful while publishing any new article on this popular technical platform. Knowledge sharing, positive attitude towards our assignment and improving skill are the key to success. Let us remember these tools of success for achieving our goals.

Regards

Kunwar Rajendra

PROCESS CALCULATIONS FOR 10,000 TPA ZEOLITE- A PLANT

Hi Friends,

In earlier post, we have already discussed about the specifications, applications and market potential of Zeolite-A. In present post, we will concentrate ourselves on basic theory and principles to develop most economic production process route and also present basic calculations involved in production of Zeolite-A after analyzing the pros and cons of various process routes using hydrate and bauxite as the basic input material along with sodium silicate.  

Process and Involved Reactions:

Zeolite-A is chemically represented as Na₁₂(AlO₂)₁₂(SiO₂)₁₂.27H₂O. It is evident from  its chemical formula that one mole of sodium aluminate and one mole of silica will be required along with 27 moles of water for production of one mole of Zeolite-A. In other words, combination of one mole of alumina with one mole of silica will produce one mole of Zeolite-A in presence of sodium hydroxide.

As highlighted in earlier post, bauxite based Zeolite-A plant is more profitable as bauxite is the cheaper source for generating sodium aluminate which in turn result in production of Zeolite–A with aqueous sodium silicate. In this process, alumina present in bauxite forms sodium aluminate on heating with NaOH and reactive silica present in bauxite will get converted to sodium silicate on combination with caustic soda as per following reactions-

Al(OH)₃ + NaOH = NaAlO₂ + 2H₂O.

SiO₂ + 2NaOH = Na₂SiO₃ + H₂O.

In further steps, sodium aluminate on reaction with sodium silicate will result in formation of Zeolite-A as shown in following reactions-

12NaAlO₂ + 12Na₂SiO₃ + 12H₂O = Na₁₂(AlO₂)₁₂(SiO₂)₁₂ + 24NaOH

Na₁₂(AlO₂)₁₂(SiO₂)₁₂ + 27 H₂O = Na₁₂(AlO₂)₁₂(SiO₂)₁₂ .27 H₂O

Estimated Input Material Requirement:

The above reactions clearly reveal that twelve moles of hydrated alumina and twelve moles of sodium silicate in aqueous solution produce one mole of Zeolite-A.

Molar mass of Hydrated alumina = 27 + 3*(16+1) = 78 g per mole.

Molar mass of Sodium silicate = 2*23 + 28 + 3*16 = 122 g per mole.

Molar mass of Zeolite-A =12*23+12*(27+2*16)+12*(28+2*16)+27*18 = 2190 g per mole.

∴ Required Hydrate with 10% moisture = (12*78)/(2190*0.90) = 475 kg / t Zeolite-A.

Required Sodium Silicate = (12*122)/2190 = 668 kg/t Zeolite-A.

About 1% physical NaOH and 0.50% occluded NaOH will be lost per tonne of Zeolite-A.

∴ Loss of NaOH with product =1.5%*1= 0.015 t NaOH =15 kg NaOH per tonne of Zeolite-A.

Loss of NaOH with Bauxite residue = 10 kg per tonne of Product.

Chemical losses because of Reactive SiO₂ = 30 kg per tonne of product,

Physical losses of NaOH during production = 10 kg NaOH per tonne of Zeolite-A.

Thus total requirement of NaOH=15+10 + 30 + 10 = 65 kg NaOH per tonne of Zeolite-A.

Annual Requirement of Raw materials for 10,000 tpa Zeolite-A Plant:

Hydrate with 10% moisture = 4750 tonnes.

Sodium Silicate = 6680 tonnes,

Caustic soda as NaOH = 650 tonnes.

As such, the above elaborations are brief guidelines for the plant designers of Zeolite-A plant. These are the basic clues based on which development of plant design, basic and detailed engineering activities can be taken up to initiate the execution of project of optimum production capacity.

Trust, you will find these basic inputs as interesting. Please do not take any investment decisions based on the technical inputs published on our blog without carrying out techno-economic feasibility studies. The market for synthetic Zeolite-A is very fluctuating as China is dumping natural Zeolite in nearby countries so you may not get price advantage in present scenario. But for future, Bauxite based Zeolite plant may be a good project having pay back period for investment less than three (3) years.

We will welcome your comments / feed back on the subject for further improvements. 

Regards.

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

PROMISING ALUMINA REFINERY PROJECTS IN INDONESIA

Hi Friends,

As discussed in previous articles, about 89% of alumina produced in the World is used for manufacture of aluminium metal and remaining 11% for production of chemicals and other non-metallurgical applications. Thus calcined alumina as well as hydrated alumina (Hydrate) is broadly characterized in two categories-

•       Metallurgical grade alumina or Smelter grade alumina (MGA or SGA)) and
•       Non-metallurgical grade alumina or Chemical grade alumina (NMGA or CGA).

Though the volume of CGA market is less compared to that of SGA but the profit margin in CGA is much higher as its selling price ranges from 2 to 5 times of that of SGA. Presently, the market potential of CGA across the globe is estimated at around 5.8 to 6.0 million tonnes per annum. Out of total CGA demand in International market, specialty grade hydrates have market share of over 50% i.e. about 3.0 to 3.2 Mtpa being used as feed stock for manufacture of Aluminium sulphate, Fire retardant fillers, Tooth paste, Sealing rings for rotating equipment, Thread guides, Polish, Paints, Ceramics, Abrasive, High temperature refractory and American diamond. During last couple of years, selling price of CGA has shown increasing trend along with increase in its demand whereas selling price of SGA has shown downward trend hovering at the level of US$ 350-360 per tonne of calcined alumina because of lower LME price of aluminium metal. Now, let me give the brief account of bauxite reserves and alumina scenario with more focus on salient features of Alumina projects in Indonesia in subsequent paragraphs.

As per data available on public domain, bauxite is available in Tayan, Munggu Pasir, Mempawah and West Kalimantan region in Indonesia. West Kalimantan is having total bauxite reserves of over 2000 million tonnes with proven reserves of over 800 million tonnes of bauxite. The bauxite is predominantly gibbsitic in nature with average quality of about 43% total alumina, about 38.6% available alumina and around 3% reactive silica. The bauxite in Indonesia has been seen in low lying hills with overburden varying from 0.60 m to 3.8 m and nodular bauxite horizon from 2.2 to 5.2 m. The geographical studies indicate that these bauxite deposits were formed by in-situ weathering. Till last year, the country was exporting bauxite to china and other countries but in the recent past, the Indonesian government has totally banned the export of bauxite and putting more focus on processing of bauxite for production of value added products.

In Indonesia, there are two major Alumina projects in West Kalimantan namely Tayan Alumina Project and Mempawah Alumina Project under execution and active consideration as outlined here under.

Tayan CGA Project: Tayan bauxite mine commenced its operation in early 2010 and was exporting bauxite to China and Japan. Construction of Tayan Alumina Project was started in April 2011 aiming to mechanical completion schedule in December 2013 and trial production in January 2014. The capacity of this plant is 0.300 million tonnes for production of wide varieties of Chemical grade hydrates and aluminas. The estimated investment in this project was US$ 500 million with the technology supplied by Showa denko (SDK), Japan. The actual mechanical completion of this project was done in December 2014 and commercial production commenced in February 2015.

Mempawah SGA Project: The capacity of this plant is 1.2 million tonnes of SGA to be supplied as feed stock to Aluminium Smelter. The estimated capital investment will be about US$ 1.5 billion. The construction of this plant will be started by early 2015 with mechanical completion target of December 2017.

Both Alumina projects have promising future because of locational advantages, availability of good bauxite reserves, adequate coal reserves and adoption of advanced technology. I wish grand success of both projects.

We seek your valued comments / opinions / additional information, if any.

Regards.

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

BENEFICIATION OF BAUXITE FOR ENRICHMENT IN QUALITY

Hi Friends,

In continuation to my earlier posts, I thought of sharing my views on beneficiation of Bauxite with the objective to optimum utilization of natural resources available with us. I am presenting here my views on the subject as outlined here under in subsequent paragraphs.

The mineral, Bauxite, is a rich source of alumina for making aluminum. The aluminium metal and its alloys have strong growth potential in international market for wide range of industrial applications. Bauxite is also used in refractory, cement, absorbents, steel, abrasives, rubber, plastic, cosmetics, paints, paper, polishes, glass, enamel and ceramics.

Since bauxite is a mineral occurring in earth’s crust, it has a number of impurities, like iron, silica, titania, calcium, and small quantities of phosphorous, sulfur, zinc, magnesium and various carbonate and silicate minerals. These impurities create quality problems during processing thereby increase production costs. Therefore, the removal of impurities to the extent possible economically is essential before processing further for any application.

Most mines abroad subject their run of mine ore (ROM) to the mineral dressing operation most suitable for their material. Crushing the ROM, usually in hammer mills, is an operation practiced worldwide. Depending on the bauxite, and the quality/grade required, the next stages are screening, scrubbing and washing, magnetic separation and drying. Magnetic separation is done to remove iron, however, is normally practiced in a limited way to produce high value, special grade bauxites. At present, the production of bauxite in most operative mines in India is not sufficiently high as to warrant a capital-intensive beneficiation plant, which usually requires a large capacity to be really economical. Hence, ore dressing efforts have been mainly confined to removal of silica by manual and/or mechanized breaking, crushing, manual sorting and dry screening.

Efforts towards research are being emphasized in most bauxite producing countries to develop cheap and innovative bauxite beneficiation processes. Many new methods of magnetic separation are also being tried out. These include rare earth roll separators, super conducting high gradient magnetic separators and open gradient, non-cryogenic high gradient magnetic separators. Other methods being researched include fluidized bed acid leaching, hydrogen assisted beneficiation and bio leaching. However, despite decades of intensive studies, economical bauxite beneficiation technology for removal of impurities satisfactorily is not available as on date.

Research in India is along international lines but still confined to the laboratory. The Indian Bureau of Mines, Nagpur (IBM), the Jawaharlal Nehru Research Development and Design Center, Nagpur (JNARDDC), and the Regional Research Laboratory, Bhubaneswar (RRL), all claim to have laboratory scale processes that are ready to be up scaled to pilot plant levels. The IBM has done numerous beneficiation tests, using different methods, on various bauxites found in India. The RRL claims to have developed a beneficiation process to produce non-metallurgical grade bauxite, whereas the JNARDDC says it has processes for both metallurgical and non-metallurgical grades.

As per the available published literatures and analysis, the savings on raw ore cost brought by JNARDDC's process through beneficiating metallurgical grade bauxite appears to be over 17% and that of non-metallurgical grade at least 19%. Bauxite users in India have indicated that they are willing to pay between 10-50% higher for a reduction in impurities by a similar amount. This would make the production and marketing of beneficiated bauxite more profitable.

We will welcome your comments / remarks on the elaborated topic.

Regards.

                        Kunwar Rajendra

Reasons for Such a High Popularity of Alumina Technology Blog

Hi Friends,

It gives me immense pleasure to analyse the basic reasons for such a high popularity of this Alumina Technology Blog among the people across the globe. On this issue, we have received many views of our friends of alumina fraternity which we thought of sharing with you.

Main reasons for such a high level of popularity are listed below-

• It's a great deal of what the Author learnt in last three decades in the field.
• It's a simple compilation of technical thoughts based on practical experience in the field of conceptualization, design, engineering, execution, testing and commissioning of various plants in the World.
• The language of this blog is simple.
• Assimilation of authentic and reliable technical data / information.
• It covers all facets of bauxite, alumina and aluminium field available on public domain without disclosing any proprietary information.
• Unique platform to share the views of technical professionals on variety of subjects.

The Author has presented this blog as a Gift to the friends of Bauxite, Alumina and Aluminium fraternity across the Globe.

We will continue our efforts to cover the balance topics in future. We solicit your views for enriching this blog further.

Regards.

Kunwar Rajendra
www.bauxite2aluminium.blogspot.com

It's Right Time to Write Our Success Story

Hi Friends,

It gives me immense pleasure to share this moment of achieving a record number of viewers of over 50,000 of our popular technical blog in such a short span of time. With this achievement, we have reached to a new height of success. All of us have contributed in this remarkable  success thus it is the right time to celebrate.

Let us recall in brief the moments of this glorious event as Success Story. Initially, I had no idea about sharing the knowledge through known and unknown friends as I have limited knowledge about the computers and internet as well. I would like to express my sincere thanks to my elder son, Vivek, for educating me about the blog. Vivek being a Computer engineering professional inspired me to write something about my areas of expertise. 

Soon after, I took the lead and published a few lines assuring my friends to share the technical knowledge of public domain nature pertaining to bauxite, alumina and aluminium. Till date, we have followed this strict ethical principle in publishing each and every technical article on this blog. We have never copied any information from any published literature. We have always used our simple language in expressing our own personal thoughts. 

Of course, right in the beginning itself, I had a dream to achieve a number of 100,000 viewers in  a time span of five (5) years and today on auditing of data, we find that we made a very conservative target.

So far, we have published over 265 technical articles and from last few months we have not added new article because of paucity of time. However, my friends all over the World are enjoying the published articles every moment.

This blog has given me thousands of global friends in every corner of the World as this blog has the in-built translation facility to read in any international language.

At this moment, I would like to thank to Google Management to provide such a lovely platform free of cost for sharing our knowledge.

Let us join hands to assimilate technical data related to design, operation, engineering, technology, execution, commissioning and other related issues on bauxite, alumina and aluminium and enrich our knowledge by exchanging those data with one other. This technique will make all of us more knowledgeable in the field. Trust you will agree with my views.

I take the opportunity to wish you a very happy, healthy and prosperous new year.
Thanks and regards.

Kunwar Rajendra
www.bauxite2aluminium.blogspot.com

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