INTRODUCTION

The production process for cement consists of drying, grinding and mixing limestone and
additives like bauxite and iron ore into a powder known as “raw meal”. The raw meal is then
heated and burned in a pre-heater and kiln and then cooled in an air cooling system to form a
semi-finished product, known as a clinker. Clinker (95%) is cooled by air and subsequently
ground with gypsum (5%) to form Ordinary Portland Cement (“OPC”). Other forms of cement
require increased blending with other raw materials. Blending of clinker with other materials
helps impart key characteristics to cement, which eventually govern its end use.

There are two general processes for producing clinker and cement in India : a dry process and a
wet process.

The basic differences between these processes are the form in which the raw meal is fed into
the kiln, and the amount of energy consumed in each of the processes. In the dry process, the
raw meal is fed into the kiln in the form of a dry powder resulting in energy saving, whereas in
the wet process the raw meal is fed into the kiln in the form of slurry. There is also a semi-dry
process, which consumes more energy than the dry process but lesser than the wet process.

DRY PROCESS

The basic steps involved in the production process is set out below:

All Cement plants are dry process plants. Limestone is crushed to a uniform and usable size,
blended with certain additives (such as iron ore and bauxite) and discharged on a vertical roller
mill, where the raw materials are ground to fine powder. An electrostatic precipitator dedusts
the raw mill gases and collects the raw meal for a series of further stages of blending. The
homogenized raw meal thus extracted is pumped to the top of a preheater by air lift pumps. In
the preheaters the material is heated to 750°C. Subsequently, the raw meal undergoes a
process of calcination in a precalcinator (in which the carbonates present are reduced to
oxides) and is then fed to the kiln. The remaining calcination and clinkerization reactions are
completed in the kiln where the temperature is raised to between 1,450°C and 1,500°C. The
clinker formed is cooled and conveyed to the clinker silo from where it is extracted and
transported to the cement mills for producing cement. For producing OPC, clinker and gypsum
are used and for producing Portland [Pozzolana] Cement (“PPC”), clinker, gypsum and fly ash
are used. In the production of Portland Blast Furnace Stag Cement (“PSC”), granulated blast
furnace slag from steel plants is added to clinker.
PROCESS DESCRIPTION

Cement industries typically produce portland cement, although they also produce masonry
cement (which is also manufactured at portland cement plants). Portland cement is a fine,
typically gray powder comprised of dicalcium silicate, tricalcium silicate, tricalcium aluminate,
and tetracalcium aluminoferrite, with the addition of forms of calcium sulfate. Different types
of portland cements are created based on the use and chemical and physical properties
desired.

Portland cement types I - V are the most common. Portland cement plants can operate
continuously for long time periods (i.e., 6 months) with minimal shut down time for
maintenance.

The air pollution problems related to the production, handling, and transportation of Portland
cement are caused by the very fine particles in the product.

The stages of cement production at a portland cement plant:

1. Procurement of raw materials

1. Raw Material Acquisition

Most of the raw materials used are extracted from the earth through mining and quarrying and
can be divided into the following groups: lime (calcareous), silica (siliceous), alumina
(argillaceous), and iron (ferriferous). Since a form of calcium carbonate, usually limestone, is the
predominant raw material, most plants are situated near a limestone quarry or receive this
material from a source via inexpensive transportation. The plant must minimize the
transportation cost since one third of the limestone is converted to CO 2 during the
pyroprocessing and is subsequently lost. Quarry operations consist of drilling, blasting,
excavating, handling, loading, hauling, crushing, screening, stockpiling, and storing.

2. Raw Milling

Raw milling involves mixing the extracted raw materials to obtain the correct chemical
configuration, and grinding them to achieve the proper particle-size to ensure optimal fuel
efficiency in the cement kiln and strength in the final concrete product. Three types of
processes may be used: the dry process, the wet process, or the semidry process. If the dry
process is used, the raw materials are dried using impact dryers, drum dryers, paddle-equipped
rapid dryers, air separators, or autogenous mills, before grinding, or in the grinding process
itself. In the wet process, water is added during grinding. In the semidry process the materials
are formed into pellets with the addition of water in a pelletizing device.

3. Pyroprocessing

In pyroprocessing, the raw mix is heated to produce portland cement clinkers. Clinkers are
hard, gray, spherical nodules with diameters ranging from 0.32 - 5.0 cm (1/8 - 2") created from
the chemical reactions between the raw materials. The pyroprocessing system involves three
steps: drying or preheating, calcining (a heating process in which calcium oxide is formed), and
burning (sintering). The pyroprocessing takes place in the burning/kiln department. The raw
mix is supplied to the system as a slurry (wet process), a powder (dry process), or as moist
pellets (semidry process). All systems use a rotary kiln and contain the burning stage and all or
part of the calcining stage. For the wet and dry processes, all pyroprocessing operations take
place in the rotary kiln, while drying and preheating and some of the calcination are performed
outside the kiln on moving grates supplied with hot kiln gases.

4. Clinker Cooling

The clinker cooling operation recovers up to 30% of kiln system heat, preserves the ideal
product qualities, and enables the cooled clinker to be maneuvered by conveyors. The most
common types of clinker coolers are reciprocating grate, planetary, and rotary. Air sent through
the clinker to cool it is directed to the rotary kiln where it nourishes fuel combustion. The fairly
coarse dust collected from clinker coolers is comprised of cement minerals and is restored to
the operation. Based on the cooling efficiency and desired cooled temperature, the amount of
air used in this cooling process is approximately 1-2 kg/kg of clinker. The amount of gas to be
cleaned following the cooling process is decreased when a portion of the gas is used for other
processes such as coal drying.

5. Clinker Storage

Although clinker storage capacity is based on the state of the market, a plant can normally store
5 - 25% of its annual clinker production capacity. Equipment such as conveyors and bucket
elevators is used to transfer the clinkers from coolers to storage areas and to the finish mill.
Gravity drops and transfer points typically are vented to dust collectors.

6. Finish Milling

During the final stage of portland cement production known as finish milling, the clinker is
ground with other materials (which impart special characteristics to the finished product) into a
fine powder. Up to 5% gypsum and/or natural anhydrite is added to regulate the setting time of
the cement. Other chemicals, such as those which regulate flowability or air entrainment, may
also be added. Many plants use a roll crusher to achieve a preliminary size reduction of the
clinker and gypsum. These materials are then sent through ball or tube mills (rotating,
horizontal steel cylinders containing steel alloy balls) which perform the remaining grinding.
The grinding process occurs in a closed system with an air separator that divides the cement
particles according to size. Material that has not been completely ground is sent through the
system again.

7. Packing and Loading

Once the production of portland cement is complete, the finished product is transferred using
bucket elevators and conveyors to large, storage silos in the shipping department. Most of the
portland cement is transported in bulk by railway, truck, or barge, or in 43 kg (94 pound)
multiwalled paper bags. Bags are used primarily to package masonry cement. Once the cement
leaves the plant, distribution terminals are sometimes used as an intermediary holding location
prior to customer distribution. The same types of conveyor systems used at the plant are used
to load cement at distribution terminals.
CEMENT MANUFACTURING COMPANIES IN INDIA

o Birla Corporation
Birla Corporation Limited is one of the leading manufacturing company of multi-
products, like Jute, cement, PVC floor covering carbide and more.

o JK White Cement
JK White Cement is a perfect white cement with no colour impurities. Stronger than
Grey Cement grade-53 - with exclusive features of rapid hardening.

o Lafarge-India
Lafarge cement is famous all over the world for its premium quality and has been used
to build many landmark buildings globally. Lafarge cement is available, through a large
dealer network, throughout eastern India- in the states of West Bengal, Jharkhand,
Bihar, North-East States and Chattisgarh.

o Span Cements
Span Cements caters to requirements of various Cement Products. The products they
store are the finest in the market and are of genuine Quality.

o Tamilnadu Cement Corporation Ltd.,

o Zuari Cement
Zuari Cement has within a short time-span made its presence felt in the cement
industry. It has done so by making top quality cement.