Cement, Energy and Environment

74 INTRODUCTION JK White Cement is the first White Cement factory in India , which manufactured White Cement through dry process technology. The Gotan plant was commissioned in 1984 with an ini al produc on capacity of 50,000 tons. It uses technical exper se from F. L. Smidth & Co. of Denmark and state-of-the-art technology with con nuous on- line quality control by microprocessors and X-rays, ensuring the purest white cement. Over the years, con nuous process improvements and modifica ons have increased the plant's produc on capacity to 610,000 tons per annum . Owing to its constant R&D efforts and updated technology J.K. Wall Pu y, a new, value-added product was launched in 2002. Cement Manufacturing Process Cement is made from limestone and clay or shale and other materials. These raw materials are extracted from quarries, crushed to a very fine powder and then blended in the appropriate propor ons. This blended raw material is called 'raw mix' or 'raw meal' and is heated in a rotary kiln where it reaches a temperature of about 1400 °C to 1500 °C. The raw meal enters the kiln at the cool end and gradually passes down to the hot end, then falls out of the kiln on the clinker cooler and subsequently cools down. The material formed in the kiln is called clinker and is composed of rounded nodules between 1 mm and 25 mm across. A er cooling, the clinker is either stored temporarily in a clinker store, or passed on directly to a cement mill. The cement mill grinds the clinker to a fine powder. Gypsum (hydrated calcium sulphate) and other addi ves are added which controls the se ng proper es of the cement when water is added. Ball Mill Ball mills are predominantly used machines for grinding in the cement industry. Although ball mills have been used for more than one hundred years, the design is s ll being improved in order to reduce the grinding costs. A Ball Mill is a horizontal cylinder partly filled with steel balls that rotates on its axis. Material fed through the mill is crushed by impact and ground by a ri on between the balls. The grinding media are usually made of high- chromium steel. The smaller grades are occasionally cylindrical ("pubs") rather than spherical. There exists a speed of rota on (the "cri cal speed") at which the contents of the mill would simply ride over the roof of the mill due to centrifugal ac on. The cri cal speed (rpm) is given by: N = C 42.29/√ d , where d is the internal diameter in meters. Ball mills are normally operated at around 75% of cri cal speed, so a mill with diameter 3.5 meters will turn at around 17 rpm. The mill is usually divided into at least two chambers (although this depends upon feed input size - mills including a roller press are mostly single-chambered), allowing the use of different sizes of grinding media. Large balls are used at the inlet, to crush clinker nodules (which can be over 25 mm in diameter). Ball diameter here is in the range 50–90 mm. In a two-chamber mill, the media in the second chamber are typically Gajendra Panwar & Virendra Singh Rathore J.K. White Cement Works, Gotan (Rajasthan) SUCCESS STORY OF REDUCTION IN SPECIFIC ENERGY CONSUMPTION BY PROCESS MODIFICATIONS IN CEMENT MILL AT JK WHITE CEMENT WORKS, GOTAN