Satellite grinding units are cost-effective proposition
Which are the most efficient methods of cement grinding that are used now?
The most efficient way of handling grinding is with VRM technology and ball mill with roll press. The main criteria of selecting these are dependent on the raw materials availability, mainly slag and fly ash, and these are done to see the capex control as well as the opex control. So basically, the technology is based (today) on the selection of the high efficiency level and how it can sustain the capex investment for the next 10 to 15 year so that the investors andpromoters can make some money and also produce a sustainable quality of cement through this grinding process.
Any new technologies that have emerged in the field or process?
There are around two to three technologies.VRM technology is predominantly used by most cement plants today, followed by roll press and ball mill technology, and also the roll press for finished grinding technology. Other than that, two other grinding systems-horomill and beta mill-have the the latest technologies but are yet to be proven. The beta mill is installed in Dubai in National Cement. This technology has an advantage over VRM as well as ball mill vs roll press. It was invented and the technology was established by a German company. Similarly, horomill technology was also invented and the technology was being supplied from France. But these two technologies are yet to come to India in a big way and prove its worth for the use and better particle size distribution and better quality of cement.
How does the quality of cement get affected by the method of grinding?
The quality is governed by particle size distribution in cement, and that alone, the ball mill with a classifier or with a VRM with a high efficiency classifier or roll press with a classifier can generate the 32 and 45 microns, which contribute to the quality and strength of the cement. These are the factors that improves the quality and sustainability in terms of its longevity.
The present trend is to install grinding plants at many places. However, earlier that was not the case. How is this likely to boost the size of market servicing levels? A good idea is to take the satellite grinding units based on the mother plants. What is happening is that cement business is a logistics-oriented business and you have to transport cement bags or loose bulk cement. Instead you can take clinker and go towards fly ash-based or slag-based cement, which can be mixed or blended with clinker grinding, and the capacity can be increased to local market to the tune of 2:1. That means you take one tonne of clinker and you produce almost close to 2 or 2.1 tonne of cement with that clinker, if not more. So that is basically the cost saving on the logistics part, and these can be achieved through road network as well as the sea route or river route process.
Also, the secondary freight slightly changes. To reduce secondary freight, satellite grinding units are being promoted very near to the market so that the distributors can give it to the consumers locally within a 35-40 km radius instead of travelling from mother plant covering distance of 250-300 km. So cost effectiveness comes mainly by achieving these satellite grinding units, located in the consumption centres. Only thing is that we have to study the consumption centres as well as the availability of other additives and cementitious products, which can improve the quality of cement and also meet the local quality of the market.
...those factors have to be studied in advance?
Yes, those factors need to be studied in depth, and then only the decision can be taken on what basis the cement product can be designed for the local market and cater to the various requirements.
Today, the government is giving thrust to blended cement and composite cement - wherein apart from clinker you are adding substantial amount of these additives and these are available at different locations. Instead of bringing these additives all the way to the mother plant and producing the cement and transporting all the way to the consumption centres, it is much better that you bring in clinker component and where additives are available and you do grinding at the location and take it to the nearest market or consumption centre. So it gives you a lot of addition in terms of profitability and reduction of the freight.
The mini consumption centres, which are in the rural areas where the cement quality requirement can be met through the cementitious products like green cement or composite cement, are required only for plastering or for the flooring purposes, while the walls and other things can be achieved with low clinker consumption. Some of the plants in India and abroad have gone to a level of 32 per cent of clinker consumption and rest are all additives and cementitious products. So this way it becomes environment friendly as well as the carbon emission level also goes down quite a lot.
How far has India progressed in domestic design and manufacturer of grinding machinery?
Today, India is self-sufficient in cement machinery manufacturing, especially grinding units except for very few castings, which are imported from Europe or Germany. Nevertheless, about 99 per cent of all the plant and machinery are being manufactured in India under the "Make in India" programme. So India is self-sufficient as far as cement industry is concerned, and is one of the world's most efficient industry. India will continue to be the leader in the future.
How does grinding of slag differ from grinding of fly ash in terms of energy consumption?
Slag is a difficult material to grind, whereas fly ash can be grounded easily. There are technologies that fly ash can be taken into cement grinding not through the inlet of the mill but it can be added at the discharge of cement mill and it gets mixed in the bucket elevator and air slide and then it gets separated. The fine particles get mixed up with cement OPC and go into the final product. Whereas the coarse fly ash that comes back to the re-circulation method through cement mill inlet and again it is grounded to a level of 3,600 to 4,000 to achieve the real quality and strength of the cement. Whereas with slag, it consumes almost additional 30 per cent extra power to grind vis-a-vis PPC. So that is the difference but since the cementitious slag has a better property, it can be mixed almost to the tune of 60 per cent to a clinker that is OPC ground to a level of 3,500 to 3,600 with a fine ground slag to 4,000+, and that can give you an excellent quality of slag cement,i.e., PSC cement, which can be much better than any other PPC or OPC cement and it is more durable than OPC.
- BS SRINIVASALU REDDY