Outline for Calcium Carbonate Process

8/10/2019 Outline for Calcium Carbonate Process

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OUTLINE FOR CALCIUM CARBONATE PROCESS

1. INTRODUCTION

Calcium carbonate is an important inorganic chemical for a variety of chemical

industries. It is basically an Extender which enhances the properties of end product

by virtue of its characteristics and offers cost advantages also.

The crystal structure, shape and density are measure characteristics used for

various applications thus giving a choice of variety of grades that can be

manufactured.

The main raw material for producing Precipitated Calcium Carbonate (P.C.C.) is

Limestone of high purity (>98%).

2. APPLICATIONS

Various applications of P.C.C. are given below:

i. In natural and synthetic rubber for tyre/tube industry and in Hawai chappal - to

improve strength as well as whiteness.

ii. In Plastics - for PVC pipes, cables, profiles - as a filler to improve impact

strength and other physical & electrical properties.

iii. In Dentrifice industry - as cleaning and polishing agent (tooth paste).

iv. In Paints - for improving opacity and whiteness.

v. In Paper Industry - for brightness, opacity and ink receptivity.

vi. In Pharmaceuticals - as calcium source, as an antacid and as a bulking

agent.


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vii. In foods & beverages - as calcium supplement and filteration aid.

viii. In Sealant & Maskets - as rheology modifier.

ix. In Cosmetics - to control absorption characteristics & increase fluffiness.

x. In Printing inks - to control strength & body of the ink.

The specifications of each grade are altered/controlled during reaction to achieve

required particle size, density, shape of particles, viscosity of powder, oil absorption

and flow point, etc.

3. PROPERTIES

Structure Calcitic/Aragonitic

CaCO3 % 98

Density (gpl) 400 - 600

Average Particle Size() 2 - 10

Viscosity (cps) 3000 - 60000

Moisture (%) < 1

Surface area (m2/g) 10 - 20

Grits (%)


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ii. Slaking/Hydration of Quick Lime

iii. Carbonation of Lime Slurry (Calcium Hydroxide)

iv. Sieving/water leaching (decantation)

v. Drying

The process utilizes evolved CO2 from Lime Kilns for carbonation. Limestone is

presently from Himalayan ranges mainly from Himachal Pradesh Mines

(Sataun/Renuka).

CALCINATION

Calcination is done at Vertical Shaft Kilns. Limestone of 4"/6" size is fed to these Kilns.

Producer gas is used as fuel for Calcination which is obtained from Gas producers. The

Gas producers are charged with mixed fuel (Pearl Coke and Charcoal). The flue gas

from each kiln is drawn through a series of Water Scrubber, Soda Scrubber/Roots

Blower and sent for carbonation.

The composition of Producer Gas -

CO : 25-27%

CO2 : 4-6%

O2 : 1%

H2 : 10%

N2 : Balance

Typical analysis of Kiln gas -

CO2 : 25-28%


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O2 : 3%

N2 : Balance

SLAKING (HYDRATION OF QUICK LIME)

Lime drawn from kilns is charged into lime slakers in a batch process. Water is taken

into slakepot and batch of lime is charged in (2) lots. After completion of reaction, slurry

is diluted with water and pumped into process block through a vibratory 150 mesh

sieve. Concentration and temperature of Lime Slurry are adjusted as per set conditions

for various grades of Calcium Carbonate.

CARBONATION OF LIME SLURRY

Carbonation on reaction is carried out in Cylindrical/Rectangular wooden/Mild steel

barrels provided with Agitators. The Kiln gas is drawn by a Roots Blower (exhauster)

through a water scrubber/soda ash scrubber. This is done to wash and cool the gas to

our room temperature. Washed gas is then fed to carbonation barrels.

Carbonation is carried out in batch process by taking measured quantity of Lime Slurry

and reacting it upon Kiln Gas in the wooden barrel. Particle size and shape of various

grades are controlled by the following factors.

(1) Lime Slurry Temperature/Concentration

(2) Agitator Speed

(3) Gas flow

(4) Gassing Time


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(5) Leave (quantity of gassed slurry left out in barrel for seeding purpose in some

grades. In other grades barrel is thoroughly washed and cooled after completion

of every charge).

Primarily, two crystal forms of Calcium Carbonate are produced (i) the needle like

Aragonitic form based upon arthorhombic structure (ii) calcitic barrel shaped based

upon hexagonal rhombic structure.

SIEVING/DECANTATION (FILTERATION)

Chalk slurry is passed through 325 mesh screen and sent for settling. In case of

Precipitated grades, the chalk (CaCO3) slurry is stored in settlement tanks for a

particular time, after that top layer is drained out by decantation and thick slurry is

pumped to Film Dried feed tank after giving a thorough agitation.

For coated grades, their slurry is coated with a solution of Sodium Stearate at a

particular condition to make 1.5/3.0% coated grades. Coated slurry is filtered through

High Pressure Filter to produce thick cake having 35% moisture.

DRYING

Precipitated grades are dried in steam heated drum dryers (Film dryers). Chalk slurry is

fed from one side through wet trough and from other side of drier, the dry material is

removed by Doctor's knife. Finally, the product is conveyed to Silos after passing

through vibratory screen and roller magnets for final packaging in HDPE/PP bags.


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In case of Coated grades, the Calcium Carbonate cake discharged from the Press Filter

is fed into a back mixer where some dry powder is mixed with to make it free flowing

and suitable for feeding into Thermoventury Dryer. Hot air is generated in air heater by

burning superior Kerosene Oil. This hot air is fed to drying plant (Thermoventury Dryer)

where pulverizing and drying of coated Calcium Carbonate taken place. Outlet of drying

unit is led to cyclone, where larger particles are separated and taken for packing into 50

kg bags. Finer particles along with moist air goes into a Reverse PulseJet type bag filter

for collecting the product (Finer) and letting out clean air with combustion gases. Finer

particles from R.P. Jet Silos are separately packed into 50 kg bags.

The crystalline form of particles, size and degree of aggregation are regulated by

varying the process conditions giving many different grades designed to meet the

various needs of customers, viz. Plastics, Rubbers, Surface Coating, Paper,

Pharmaceuticals, Cosmetics, Dentrifice, Food & Beverages, Sealants, Printing Inks, etc.

5. QUANTITATIVE REQUIREMENTS

Basis 1 ton of Calcium Carbonate

Limestone 1.2 MT

Coke/Charcoal 250 kgs

Power 220 KWH

Water 5 KL

Diesel for drying 150 lts

Economic Plant Capacity 60 tons per day


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6. ECONOMICS OF PRODUCTION

Land 10000 sq metres

Building 3000 sq metres covered area

Plant & Machinery 7 crores

Power 1000 kVA

The breakeven points comes to 60% of plant capacity utilization and internal rate of

return works out to 27%.

7. MEASURE PROBLEMS

a. Selection of highly efficient equipments

b. Nearness to source of limestone

c. Nearness to source of water

d. Abrasion of pipelines and gas lines.

8. MARKET SCOPE

Worldwide precipitated calcium carbonate stands at 6 million tons/year. Present

capacity in India is 3 lac tons i.e. only 5% of total capacity.

With the growth in Industrial sectors mentioned in application, there exists good scope

of adding up the capacity. Also, special grades have good market for Export to far east

and middle east countries.

The demand of calcium carbonate has good relation with the growth of population which

can be considered while estimating the requirements.


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9. MAJOR PRODUCERS IN INDIA

a. M/s Citurgia Biochemical Ltd., Rishikesh

b. M/s Lime Chemical, Roha

c. M/s Gulshan Chemicals, Muzaffanagar

d. M/s Kavery Chemicals, Sahoranfia

e. M/s Dewan Chemicals, Meerut

f. M/s Sai Chemicals, Surat

g. M/s Indochem, Bhiwani

h. M/s Chemical & Solven, Jodhpur

10. MAJOR EQUIPMENTS

a. Lime kilns

b. Slakers

c. Reactors

d. Flash dryers

e. Refrigeration plant

f. Boiler

g. Vacuum filters

h. Rotary sieves

i. Settlement tanks

11. NEW PRODUCT INFORMATION

a. Paper filling grade - for writing papers


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b. Paper coating grade - For special fax paper

c. Adhesives

d. Oil base paints

e. Microbiological free grades

Above grades are under production in Europe and need to be developed for meeting

local demand and exports to middle east/far east.

12. CONCLUSIONS

A state of art plant for Precipitated Calcium Carbonate with ISO Certification, Quality

Circles, having good Automation and well equipped laboratory, supported by a Pilot

Plant for development is likely to have a good potential in Indian market giving boost to

different industries and meet our present import demand of Calcium Carbonate.

Outline for Calcium Carbonate Process

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