Cement Industry in Pakistan: At the time of partition in 1947, there were four plants producing 3, 30,000 tons of cement every year. However, in 1953 – 54 the production of cement rose to 6, 60,000 tons. In 1956 P. 1.D.C. set up cement factories at Daud Khel and Hyderabad.
But even then the production of cement was not enough to meet the day to day increasing demand for the construction of buildings, roads, dams, bridges etc. In 1970 the demand for cement was about 4 million tons.
How many Cement Factories are in Pakistan?
Here is the complete and latest list of cement industry in Pakistan:
Cement Industry in Pakistan
The location of the existing cement factories and production capacity of each are given below:
|Name||Location||Year of Establishment||Process||Capacity (000 tonnes)|
|Public Sector: Punjab Associated cement||Wah.||1922||Wet||450|
|National cement||Dandot (Jhelum)||1940||Wet||50|
|Gharibwal cements||Gharibwal (Jhelum)||1964||Wet||540|
|Dandot cements||Dandot (Jhelum)||1983||Dry||330|
|Maple Leaf||Daud Khel||1956||Wet||300|
|D.G. Khan cements Sindh||Dera Ghazi Khan||1986||Dry.W/Calc||600|
|Kohat Private Sector||Kohat||1983||Dry||330|
|Dadabhoy||Dadu (Sindh)||1986||Dry, W/Cal||300|
|Anwarzaib (White cements)||Bholari (Sindh)||1987||Dry||50|
The development of cement industry depends on the mutual efforts of the pub and private sectors. This industry being fairly capital intensive, the initial investment in Pakistan came from the public sector. P.l.D.C. was entrusted with the job and it is acquitted itself well in the field. In 1972 the cement industry was taken over by the Government and until 1978 cement had been the exclusive domain of the public sector.
The situation is not changed with the advent of the private sector which competes with the State Cement Corporation_. State Cement Corporation has no started a joint advertising campaign by introducing one brand name (State Cement for all its 14 factories.
At present, there are 22 cement factories in Pakistan, 14 in the public sector and 8 in the private sector. The total annual installed capacity of these factories L 8.12 million tons. The country is likely to achieve self-sufficiency in cement.
Significance of Cement Industry
Cement industry has great significance in the development programmers of a country. Pakistan is a developing country and there is much scope for its expansion. The average annual increase of cement is 8 percent, which is based on the production performance of the units in public sector.
These units are running on the old process. Balancing, modernization and replacement are being carried out by almost all the companies in public sector.
In this connection, Dyekerhoff Engineers Limited of West Germany consultancy have prepared a feasibility study for conversion of “wet process” units to “dry process”. The new units are being set up on “dry process” due to economies of fuel.
Recent the Ministry of Production has chalked out an elaborate programme to increase domestic’ production by the modernization of old unit s in phases through a BBM plan. Besides BRM programmes, a Cement Research Institute established at Lahore to conduct modern research to increase cement production and minimizing the cost of production.
How is Cement made?
(Manufacturing & Production Process)
Cement is a very important building material which was first introduced d by an English Mason Joseph Aspdin. He found it when a strongly heated mixture of limestone and clay was mixed with water and allowed to stand, it hardened to a stone like mass which resembled Portland rock; a famous building stone of England. Since then the name of Portland Cement is given to the mixture of lime (obtained from limestone), silica, iron oxide and alumina.
This was the start of Portland cement industry as we know today. The cement is now low in cost, as it is applied everywhere in the construction of houses, public buildings, road’s, industrial plants, dams, bridges and many other structures.
Definition of cement
Cement is the material obtained- by burning an intimate mixture of calcareous and argillaceous materials at a sufficiently high temperature to produce clinkers. These clinkers are then ground to a fine powder.
The essential constituents are lime (obtained from limestone) silica and alumina (present in clay).
An average composition of a good sample of Portland cement is as follows:
|Iron Oxide (Fe2O3)||2.5|
|Sulphur Trioxide (SO3)||1.5|
|Sodium Oxide (Na2O)||1.0|
|Potassium Oxide (K2O)||1.0|
Manufacturing Raw Materials
The important raw materials used for the manufacture of cement are:
- Calcareous material (limestone, marble, chalks, marine shell) as a source of Ca.
- Argillaceous material (clay, shale, slate, blast furnace slag). They provide acidic components such as aluminates and silicates.
- Other raw material being used is gypsum.
The manufacturing process of cement involves either a dry process or a wet process. The choice of dry or wet process depends on the following factors:
- Physical condition of the raw
- Local climatic conditions of the
- The price of the fuel.
In the world, most of the factories use a wet process for the production of cement. Dry process needs excessive fine grinding and it is more suited for the hard material. Wet process, on the other hand, is free from dust, grinding is easier and the composition of the cement can easily be controlled.
In this process grinding is done in the presence of water. There are five stages in the manufacture of Portland cement.
- Crushing and grinding of the raw.
- Mixing the material in the correct ratio.
- Heating the prepared mixture in a rotary kiln.
- Grinding the heated product known as
- Mixing and grinding of cement clinker with
Crushing and Grinding
Soft raw materials are first crushed into a suitable size, often in two stages, and then ground in the presence of water, usually in rotating cylindrical ball or tube mills containing a charge of steel balls.
Mixing of the Raw materials
The powdered limestone is then mixed with the clay paste in proper proportion (limestone 75%, clay 25%); the mixture is finely ground and made homogeneous by means of compressed air mixing arrangement.
The resulting material is known as slurry. The slurry, which contains 35 to 45% water, is sometimes filtered to reduce the water content from 20 to 30% and the filler cakes are stored in storage bins. This reduces the fuel consumption for the heating stage.
Heating the Slurry in a Rotary Kiln
Raw meal or slurry prepared as above is introduced into the rotary kiln with the help of a conveyor. The rotary kiln consists of a large cylinder 8 to15 feet in diameter and 300-500 feet in length. It is made of steel and is lined inside with firebricks. The kiln rotates horizontally on its axis at the rate of 1-2 revolution per minute and it is inclined a few degrees. As the kiln rotates, the charge slowly moves downward due to the rotary motion.
Now the charge is heated by burning coal, oil or natural gas. In the rotary kiln, the charge passes through the different zones of temperature where different reactions take place. The charge takes 2-3 hours to complete the journey in the kiln.
1. Drying or pre-heating Zone (Minimum Temperature Zone)
In this zone, the temperature is kept at 500°C, whereby the moisture is removed and the clay is broken into Al203, Si02, and Fe203.
2.Decomposition zone (Moderate Temperature Zone)
Here the temperature goes up to 90 °C, In this zone, the limestone (CaCO3) decomposes into lime (CaO) and CO2
CaCo3 (S) → CaO (S) + CO2 (g) at 900°C
3.Burning zone (minimum temperature zone)
In this zone1 the temperature goes up to 1500°C and the oxides, e.g. Ca0, Si0 2, Al203 and Fe203 combine together and form calcium silicate, calcium aluminate, and calcium ferrite.
This is the last stage in the kiln where the charge is cooled up to 150-200°C.
The resulting product obtained from the kiln is known as cement clinker. This has the appearance of greenish black or grey colored balls varying in size from small nuts to peas.
Grinding the clinkers with gypsum
The cement clinkers are then air-cooled. The required amount of gypsum (2.0 %) is first ground to a fine powder and then mixed with clinkers. At this stage finished cement is pumped pneumatically to storage silos from where it is drawn for packing in paper bags or for dispatch in bulk containers.
Setting of cement
The use of cement in the construction of the building is based on its property of setting to a hard mass when its paste with water is allowed to stand for some time. The reactions involved in the setting are described as follows:
Reaction taking place in first 24 hours
A short time after the cement is mixed with water, tri-calcium aluminate absorbs water (hydration) and forms a colloidal gel of the composition, 3 Ca. Al2O3•6H2O, (hydrated tricalcium aluminate).
This gel starts crystallizing slowly, reacts with gypsum (CaSO4 .2H2O) to form the crystals of calcium sulfur-aluminate 3CaO.Al 2O3 .3CaSO4 .2H 2O.
Reaction taking place in 1 to 7 days
Tri-calcium silicate (3CaO.SiO3) and tri-calcium aluminate (3CaO.Al2O3) get hydrolyzed to produce calcium hydroxide and aluminum hydroxide. The calcium hydroxide thus formed, starts changing into needle-shaped crystals, which get studded in the colloidal gel and impart strength to it. Aluminum hydroxide, on the other hand, fills the interstices resulting in hardening the mass. The gel formed starts losing water partly by evaporation and sets to a hard mass.