CEE Oct-Dec 2002

- A CONCEPT THAT WORKS CS. Muthuraj, LV Technology Co. Ltd, Thailand Since ince ption in 1999, LV Technology Co. Ltd (LVT) has supplied classifiers to all types of grinding circuits, including raw grinding. coal/petcoke grinding, cement/s lag grinding and miscellaneous applications, such as lly ash classification. The article presents case studies of conversions carried out in a vertical roller mill for raw material grinding. The LV classi fier concept improves the gas and material :flows in vertical roller mills. The classifier is a cage wheel type that comprises pocket-like guide vanes arranged concentrically around a rotor. The pockets are placed with gaps for maintaining the gas ve loc it y through guide vanes. The unique design not only guides air flow towards the rotor, but collects coarser particles rejected by it. With this classification concept, the gas velocity through the guide vanes is almost equal to or less than the tip speed of the rotor. LV Technology secured an order for Ambuja Cement Eastern Ltd (ACEL) in October 1999, to modify a Polysius mill from a static separator to a LV Technology classifier and the mill was commissioned after the modification in August 2000. The specific power of RM 51/26 (m ill , mill fan) came down to 18.71from 21.0 kWh/t with capacities (tph) 260 -270 and 230. A second contract for the company was from M/s Kakatiya Cement and Industr ies Ltd, to en hance the grinding capacity of their existing raw mill no.2 (ball mill). The LV class ifier for gravity discharge ball mills has a fluidised bed at the bottom of the classifier. The uniform distribution ofmaterial fed into the classifier is ensured by this fluidised bed and the nibs generated in the system are also effectively separated and collected. A draining a rr angement is provided to periodically clean the collected nibs in the tludised bed. The upper part of the c lassifier is sim ilar in construction to the vertical rolle r miII. The output increased to 45 (39) tph with specific power (kWh/t) of21 (23.73). Courtesy: World Cement, Aug 02, Pp72-73 Email: mail@1-vorldcement. com Web: 1vww.worldcement. com QUALITY AND STANDARD BOGUE VS CHROMY Dr. Michael Clark Why the growing interes t in clinker mineralogy, which has been substantially understood for more than 70 years now? Two factors seem to be driving th is renewed interest. firstly, most cement companies wish to produce more extended cements as this boosts their production capacity and profits. Cement clinker is partially replaced by extenders in these cements, and the refore the cl inker produced from the ki ln translates into a greater quantity of cemen t to be sold. Cements extended with granulated blast furnace slag, nat ura l and industrial pozzolans and limestone are also better than pure Portland cements 111 many concre te applications. However, as less cement clinker is present in these cements, the quality and mineralogy of the clinker becomes all the more important. Less hydraulic clinker mine ra l has to produce more hydraulic activity, and substandard cli nker quality cannot be tolerated. Second ly, many cement companies are pursuing a strategy of replacing fossi l fuels with alte rn atives and byproducts of industry and society for firing their 35 kil ns . Th is is the overriding econom ic factor just ify ing the continued operation of a number of kilns. as total thermal energy costs can be reduced (to zero and beyond in the best cases). Alternative fuels are undoubtedly here to stay in the cement industry, but do bring some problems. fn many cases they conta in oxides and spec ies not normally present in cement raw materials and foss il fuels. These exotic oxides and spec ies are incorporated in the c linke r and change the mineralogy, hence the renewed interest 111 c li nke r mineralogy and its control. Alternative fuels and extended cements are among the key means for cement companies to offset their carbon emissions and improve the sustainabi lity of their operations. For many years cement chemists have known that the Bogue calculation of clinker mineralogy is unsatisfacto ry and does not represent the real mineralogy of the cli nker. In essence it is a formula for the conversion of the oxide composition of the clinker into a theoretical mineralogy, and in fact is just another way of representing the oxide composition. lt does not relate to the true mineralogy. Dr. Stanislav Chromy ofBrno in the Czech Rep ublic has bee n studyi ng and writing pa pers on clinker mi neralogy for more than 30 years. His findings are that the true Alite content o f cement clinker varies from 5 to +20 per cent of the Bogue C 1 S content, wi th the Alite content normally significantly higher than the Bogue C 3 S content at the expense of the interstitial material (C 4 AF and C 3 A). The Alite mineral produced on an industrial cement kiln is not pure C 3 S. Substantial quantities of oxides othe r than CaO a nd Si0 2 are contained in this industrial Alite in solid solution. It is no't surprising