Cement Energy and Environment

Microstructure, morphology and grindability of Indian clinkers at aglance By S P Pandey and P K Tripathy Dalmia Bharat Ltd, New Delhi Introduction A substantial part of the energy required for cement production is used for clinker grinding. Hence it is important to understand the factors, which tend to govern the grindability of the clinkers. Grindability, in general, is a measure of how much energy is required to change a particle from one size to another. Thus increase in grindability is synonymous to lowering Bond's work index and vice versa. There are many methods for assessing grindability; hence various measures of grindability can have different units. However the majority of grindability measures are given in kWh/t. As far as effect of various parameters on the clinker grindability is concerned, considerable amount of information has been compiled over the years. The major micro-structural parameters affecting the grindability of clinkers include mineralogical constituents, their size and morphological characteristics. By far, the most important parameters that are practically observed to be governing the clinker grindability includes • Insufficient kiln feed homogenization • Coarse quartz grains in the kiln feed • burning characteristics • Coal ash absorption. • heating rates temperatures and maximum • Presence of minor components. firing In the present investigation an attempt has been made to characterize clinkers collected from different cement units of the group for their grindability using Bond work index. Further, differences in their grindabilities are examined in the light of mineralogical composition, microscopical features and their granulometry to find out most significant factors governing work index for given samples. Experimental: In order to study effects of variations in microstructures of clinkers, representative samples were collected from different group units and subsequently characterized in terms of their • Bond work index • actual mineralogical compositions using XRD • Mineralogical compositions, grain sizes, pore sizes, etc. using Optical Microscope to evaluate their effects on grindability, if any. The standard feed for carrying out Bond test is prepared by crushing the received samples using Jaw crusher to pass through 3.35mm sieve. The weight of 700 cc of the resulting product is placed in the Bond Index mill and ground at 250% circulating load. The ball mill work index (kWh/t) is Calculated from the equation: WI = 49.1 , where P1 is closing sieve size, Gbp is net grams of average product size generated per revolution, P 80 is size of the product corresponding to 80% cumulative passing and F 80 is the size of the feed corresponding to 80% cumulative passing. Results & discussion: Table 1 shows the work indices for the clinker samples examined along with their actual mineralogical composition and microscopically features evaluated using XRD & OM respectively. It should be noted that the mineralogical compositions reported in tables are actual compositions unlike those indicated in plant practice using XRF chemical compositions & Bogue method. Based on the test results, all the clinkers are found to be having work indices in the range of 11- 17 kWh/t indicating wide variation in their grinding behavior. • For a typical product Blaine of 3100 cm 2 /gm., the above work index range corresponds to cement mill specific energy consumption in the range of 24.8-38.4 kWh/t respectively. 3