ICR engages Anirudh Dani, Grinding Unit Head, JK Cement Works, Jharli, in a discussion about the grinding processes at the plant.
Explain the grinding process in cement manufacturing.
Cement is a core ingredient in construction and is also the most widely used construction material because only cement has the ability to enhance the viscosity of concrete, which in return provides a better locking result of sand and gravel together in a concrete mix.
Fresh feed along with the coarse material from the separator is fed back into the grinding system. Fines from separator i.e. the product passes from the bag house through a fan. The material collected at the bottom of the bag house is transported through a set of air slides and bucket elevator to the cement silo.
Tell us about the equipment used for grinding raw material and clinker.
A closed circuit Ball Mill, VRM, Roller Press or a combination of these are used for the grinding of raw materials and clinker. At JK Cement works, Jharli Roller press and ball mill combo are used for cement grinding, which has a capacity of 2.0 MTPA.
Mills are selected according to the type, which is most suitable in terms of variables like desired capacity, investment, space availability and grinding efficiencies based on relevant raw materials. In our organisation, we are using all three available combinations at various locations. All available technologies of cement grinding have their own benefits and drawbacks. Looking at the advancement of technology we prefer the Roller Press with Ball Mill and VRM. Several types of separators are also used in mill circuits and there are numerous variations of each type available in the market.
What are the key functionalities that are looked at while installing a cement grinding plant in your organisation?
In general, cement grinding plants are installed with the clinkerisation plant. But cement grinding is also installed at different locations on the basis of various strategic variables like nearby market locations and raw material sources. By installing cement grinding at different locations, the cement industry is effectively utilising the ‘Hub and Spoke Model’.
Major key technical functionalities are production capacity, cement grade, special energy consumption, maintenance cost, construction cost etc., for the installation of the grinding unit.
Further major key strategic deciding factors are land availability, market demand, logistics optimisation, geographical analysis and raw material availability for the finalisation of the cement grinding location.
What is the contribution of the grinding unit in making the cement grinding process efficient and productive?
Cement grinding is an integral part of the cement manufacturing process. The main function of cement clinker grinding is to provide a finished cement product with a certain particle composition. The dispersion of cement can be expressed by fineness and specific surface area. Cement grinding is required for inter grinding of various raw materials like clinker, gypsum, fly ash, slag and performance improvers. Efficient cement grinding contributes to enhancing the quality of the cement by better particle size distribution.
How do cement grinding /grinding units contribute to profitability of the cement making process?
Cement grinding cost is 40 to 45 per cent of the variable cost of cement production. By effective control measures and minuscule innovations, we can achieve a significant impact on profit maximisation with environmental sustainability.
Major KPIs of cement grinding units are clinker factor, specific power consumption, MTBF and maintenance cost to contribute for the profit maximisation.
Clinker factor has a pivotal role in profit maximisation with GHG reduction that is environmentally sustainable. For example, the clinker factor in PPC varies from 55 per cent to 65 per cent at various plants.
In general, as an industry, we are more concerned about the reduction in heat consumption during the clinkerisation process but concerted efforts to optimise the clinker factor will give more benefits in a shorter time. For example, 1 per cent reduction in clinker factor achieves higher environmentally sustainable gain, compared to 1.5 per cent reduction of specific heat consumption in clinker.
Specific energy consumption of grinding varies from 18.5 Kwh/MT to 30 Kwh/MT in the industry. Optimisation of grinding efficiency helps us in increasing the profitability of the cement-making process. Earlier we were on the higher side of energy consumption however by optimisation and innovations we have surpassed the industry benchmark and achieved higher profitability and environmental sustainability.
Further logistics costs also can be optimised by placing cement grinding on the basis of various strategic variables as already explained.
What are the materials and equipment that aid in the process of cement grinding?
Other than the standard raw materials, grinding aids and performance improvers play an important role in cement grinding. Grinding aids are effective chemicals that are utilised for various applications like increasing the flow ability of cement, higher early/later mortar strength and higher concrete strengths. Grinding aids for cement are like ‘Few drops can make a huge impact’.
Weigh feeders, VFD, screw conveyors, high efficiency separators, bag houses, compressors and hot air generators are the types of equipment used in the cement grinding process.
How do you ensure standards in the process? How often is the same monitored?
We ensure that our processes are BIS and ISO compliant. Further, we have also well-established internal norms by benchmarking the global data.
Chemical analysis of cement, product fineness, blaine surface and 45-micron residue, cement sulphur trioxide (SO3), percentage of grinding aid usage, moisture percentage, production rate, specific power consumption (SPC) and MTBF are also continuously monitored.
To ensure we meet quality standards, we leverage various digital platforms for taking real time action. We have an expert control system, world class laboratory, energy management system, lab automation and mobile applications that are well placed for continuous monitoring of the same.
What challenges do you face in the cement process of grinding?
Largely, availability of good quality raw materials, periodic variation in composition and size of materials, low availability of fly ash, power outage, optimum utilisation of alternative raw materials like wet fly ash, chemical gypsum, mould gypsum, and flue gas desulphurisation (FGD) gypsum are the major challenges in cement grinding. But as we have seen several times, challenges present opportunities whereby we can become more efficient in our operations. The cement industry is looking at alternatives and gearing up to handle these challenges through innovative solutions.
What are the innovations you would like to see in the technology of the grinding process and grinding aids?
Innovation is a continuous journey and grinding technology is continuously evolving and has modernised since its inception. We like to see innovations like low-weight grinding media/liners in ball mill, low maintenance-based rollers, high-efficiency separators of more than 95 per cent of efficiency, spares having less maintenance and higher life, brushless direct current motor based air conditioners, low clinker-based cement like limestone calcined clay cement, online real-time quality monitoring equipment etc.
Currently, various grinding aids are available in the market claiming high early/later strength, flowability of cement, higher concrete strength etc. We have seen continuous innovation happening in this area and there’s ongoing research on some materials like graphene to increase the impact on the cement strength by 15 per cent to 20 per cent. Further, we would also like to see the grinding aids, which will reduce the water demand drastically in the cement manufacturing process.
-Kanika Mathur