Cement industry in India is highly centralized capital intensive industry with giant plants with one million tonne per annum capacity of each plant. Such 97 cement plants producing 97 million tonnes of cement are owned by 47 families only. Each such giant plant requires investment of Rs 900 crores of rupees. Entire cement industry is highly exploitative draining the wealth of 5 lakh crores of rupees annually from common masses to handful of super rich families. Government is playing crucial role in exploiting common masses and in protecting and promoting such giant plants by imposing huge taxes up to Rs 150 per bag.
In fact cement is primary need of the people for home building and hence it must be produced by common people everywhere in villages. But there is a general impression that cement cannot be made without giant cement factory. In fact, cement is not mysterious product which can not be produced without giant complicated cement plant. Cement is really simple product which can be made with very simple cheap equipments.
At present lime is produced in every village by very poor people without using any machinery. Cement is just a similar product but slightly a little advanced technology than lime. So it also can be produced with simple technology at every spot of the limestone. Simple cement plant of 1 ton per day will be most practical and most viable unit in rural area for common people producing 20 bags of cement by illiterate people. If you still go further to decentralize it up to 5 bags or 10 bags per day, it is quite possible to introduce solar energy to make cement at Rs 50/- per bag of 50 kg.
Let us understand what is cement. Limestone is main raw material of cement. Limestone has calcium carbonate which decomposes into calcium oxide and carbon dioxide by heating at 900 degree Celsius. Clay is added to calcium oxide. Clay contains silica which reacts with calcium oxide at very high temperature and forms di calcium silicate and tri calcium silicate and also some other compounds. Cement is a mixture of many such compounds. It is known as Portland cement.
For scientific production of Portland cement, first of all limestone is pulverized to a very fine powder. Similarly, clay is to be pulverized to a very fine powder and coal is also pulverized to a very fine powder. All these three ingredients are thoroughly mixed to get perfectly homogeneous mixture. Proportion for 1 ton of cement is approximately 1400 kg limestone, 250 kg clay and 200 kg coal. Precise proportions depend on the chemical analysis of all the three components and percentage of calcium carbonate, silica etc. which should satisfy certain formulas and parameters to get best quality of cement. In technical language of cement manufacturing, you have to control and balance Lime Saturation Factor (LSF), Silica Modulus, Alumina Modulus, Burnability Factor, Liquid content, Free Lime Percentage etc for getting best quality of Portland Cement. For this purpose one has to study basic principles of cement chemistry and cement technology which is not very hard. Those who are interested to study and make cement scientifically of best quality with simple equipments, I have added here some chapters from cement technology book. Please study it thoroughly and you will be master of cement technology.
All the powders of limestone, clay and coal can be thoroughly mixed in a double cone mixture or in inclined cylinder with skewed shaft which is very simple equipment but gives thoroughly homogeneous mixture. Once the mixture is ready, it is to be nodulized into about 1 cm dia balls by adding some water and revolving inclined pan which is a simple equipment called Nodulizer.
Once the nodules are ready it is to be filled up into vertical kiln for firing. Kiln can be continuous or batch type. It is fired on the top and heavy cold air blow is thrown from the bottom to get enough oxygen. At 900 degree C, CO2 is liberated and goes to the air. Exact cement is formed at about 1400 degree C. Immediately after burning process is over, we have to abruptly cool the entire mass of balls of clinker. So cold air is pushed from the bottom. As we have mixed coal thoroughly, every ball formed into nodulizer will have equal quantity of coal. It will be burnt. So clinker will have no coal and it will have mixture of several compounds out of which main is tri calicium silicate and dicalcium silicate.
After clinker is cooled, it is again pulverized into the pulverizer. While doing this process, about 3% pulverized gypsum is added to retard earlier setting of mortar.
This is now best quality usable cement. The sample of cement is sent to laboratory to examine its compressive strength, to examine expansion property, its fineness, to analyze magnesia content, total sulphur content, total loss on ignition, free lime content etc.
Only 4 small simple equipments are required to produce best quality Portland Cement:
- Pulverizer- Readily available in the market or it can be fabricated very cheaply in ordinary workshop.
- Double Cone Mixer OR skewed shaft horizontal cylinder- This can be fabricated by a village blacksmith very easily.
- Nodulizer- Which is simple revolving inclined pan and can be fabricated by village blacksmith.
- Cement Burning Kiln- Somebody should design it properly with proper dimensions. Then it can be fabricated by village fabricator.
But eventhough it is quite possible to produce best quality cement with simple and cheap equipments, I do not advocate to manufacture Portland Cement scientifically as described above. The reason is that it is possible to manufacture still simpler cement which is called Natural Cement from low grade lime stone having higher silica content without the need the knowledge of cement technology as described above. So all ordinary people manufacturing lime can easily make natural cement without caring various contents of calcium oxide, silica content, alumina content or any other parameter. Low grade lime stone which is rejected by cement manufacturers is the best naturally balanced raw material for natural cement. Another important reason is that rural people require 80 to 90 % cement for construction of walls and plastering it and for this purpose natural cement is more appropriate than Portland cement. Third important reason is that it will not require any big investment, no any special knowlege is required, no special raw material is required and so it will be the cheapest cement and automatically more scientific for construction purpose. So I do not emphasize to produce quality cement as described above. So whoever wants cement for construction purpose, that is for masonry work and plaster work etc , then best and simplest way is to pulverize and burn inferior quality of lime stone which will not require to add clay; because silica is already more in inferior quality of lime stone. This cement natural cement is best for construction work , for masonry and plastering. Such a cement may cost hardly 30 to 40 rupees per bag of 50 kg. Inferior quality cement gets maximum compressive strength after a few more days say 15 days to 30 days instead of 7 days. This is the only difference in the quality. Prudent rural people will tolerate this variation and while making the roof slabs bottom support will not be removed until one month. But anyhow cement industry must be decentralized to one million plants of 1 ton capacity or less. I have no accurate idea of investment in equipments, but surely it should not be beyond one lakh rupees for 1 tonne cement plant producing natural cement.
Limestone burning is exothermic process generating lot of heat. Somehow this generated heat should be utilized for running the cement plant and outside power should not be required. If decentralized cement technology is fully disseminated to every village, cement cost will be reduced to 25% of the present price and huge exploitation of 5 trillion rupees (5 lakh crores) will be saved by the people. It means that wealth of the common people will be increased by 500000 crores annually.
But still bigger benefit of decentralized cement industry will be eye opening to everybody. The present cement production is utilized for constructing big dams, big factories, big cities, big infrastructure, big highways etc. All this leads to slavery of common masses and ultimately it leads to the death of population. So that is technology for death or mass murder. Decentralized cement production will be utilized in villages to construct poor peoples home, for check dams, for wells, for cattle sheds, for small godowns for storing grains etc. All this leads to real prosperity and real Swaraj of the people. So this si technology for life.
Now let us understand how solar energy can be utilized for cement making. All the equipments involved in cement making can be driven by solar energy. Those farmers who install 10 kw solar power plant in their farms for water pumping and when no irrigation required, surplus solar power can be utilized for running cement manufacturing equipments. My large solar basket can be utilized to burn cement at focal point where there will be very high temperature. But heat generated in decomposition of lime stone must be fully utilized for cement burning process.
I invite the interested entrepreneurs to take up this activity of manufacturing tiny cement plants on mass scale level as a mission of decentralization or even for earning money. So this activity will entirely change India from poverty to prosperity in one decade only. This is real swadeshi of Mahatma Gandhi. If I get thousands of engineers fully dedicated to this cause, real miracle will happen and heaven will descent on the earth.
Similar to India there is a huge scope of this activity to spread throughout the world.