Cement, Energy and Environment

17 Use of High MgO Limestone in Portland Cement Manufacture An Indian Perspective G C Mishra , K N Bhattacharjee, V K Singh Department of Cement Technology AKS University, Satna Abstract Indian Cement Industry is presently facing an acute problem for manufacture of quality cement from the existing marginal and sub-marginal grade limestone. These limestone are either siliceous (high silica) or dolomitic containing high MgO. The higher content of MgO in raw materials not only causes serious problem in pyroprocessing during the clinker manufacture but also makes cement unsound. Although presently number of measures have been taken by Indian cement industry to overcome such problems still it is a serious challenge to use high MgO limestone in manufacture of quality cement. In this article the authors not only discuss the causes and problems encounted due to high MgO in raw materials during production of the Portland Cement but also the remedial measures to overcome such problems in production of quality cement. It has been observed that if the MgO content is <2.0% in the raw meal it is incorporated into the crystal structure works like good mineralser by improving the burnability, promoting the absorption of free lime and improving the formation of C 3 S and C 4 AF. This increases the early strength of cement and shortens the setting time. Use of 04.0-0.8 % CaF as mineralizer can also control the higher periclase (MgO) during pyroprocessing. With increase the fineness of the cement, the late expansion of the MgO can also be controlled. Impact of the clinker cooling and particle size distribution in cement have been discussed for production of sound cement. Alternately, the production of blended cement, composite cement and sulfoaluminate cement provide elegant solution to this burning issue. 1.0 Introduction: With depletion of high cement grade limestone, presently Indian cement industry is facing an acute cement raw material problem for smooth plant operation and manufacture of higher grade cement. Although India is bestowed with huge limestone resources the most of the limestone deposits in India presently available for cement manufacture are either marginal grade or low grade, whereas the demand for high grade limestone has been increased in recent years for manufacture of higher grade cements. Some of the cement plant starts with a simple limestone deposit with more or less uniform quality of limestone, with the consumption of the high grade limestone, the deposit converted in to intricate and left with very low heterogeneous grade some times dolomitic with high MgO content. Hence a serious thought is essential not only for detailed exploration of limestone deposits to convert the resources to reserves (as per UNFC) but also for development of a cost-effective dry beneficiation technique for upgradation of the low and sub-marginal grade limestone in India and use of huge high MgO limestone to meet the increased demand of limestone in cement manufacture. 2.0 Scenario of Limestone Deposits in India: Limestone being the prime raw materials for cement manufacture the growth of the cement industry depends on the availability of cement grade limestone. India is having huge limestone deposits distributing throughout the geological stratigraphic horizon starting from Archaean to Tertiary formations. Thus, the quality variation of limestone from deposit to deposit is very wide in India. The geographical distribution of limestone deposits in India is also not uniform. Some of the states do not have any limestone deposits. It has been observed that more than 95% of cement grade limestone deposits are concentrated in 10 states, although the cement grade limestone is occurring in 23 states in India. The limestone deposits are not reported from state of Punjab, Mizoram, Goa, Sikkim and Tripura, whereas Haryana, Manipur, West Bengal, Andaman and Nicobar Islands have very meager reserves not suitable for large capacity cement plants. Based on the prima-facie availability of freehold cement grade limestone deposits, there is very limited scope for further addition of cement manufacturing capacity in state of Kerala, Tamil Nadu, Bihar, Uttar Pradesh and Orissa. However, the states of Andhra Pradesh(including Telengana ) , Assam, Gujarat, Himachal Pradesh, Karnataka, Chattisgarh, Meghalaya and Rajasthan have