Cement, Energy and Environment July-Sep 2002

. . I I DIETHYLENE GLYCOL~ AS·GRINDING AID- R&D at NCB I . I Use of grinding aids is very common in cement industry abroad and the commonly employed aids are glycol s, amines , organa– silicones, organic acetates, etc. Grinding aids are substances that facilitate grinding and are used to secure benefits like reduction in power consumption, increase in production, and improvement in cement properties. Basis of grinding aids' action The grinding process involves breaking of particles leading to formation of new surfaces. In this process chemical bonds also break causing development of electrostatic charges of opposite polarity on the newly generated surfaces. Under the influence of electrostatic charges of attraction, the fin e particles formed during grinding tend to agglomerate and thus reduce the efficiency of g rinding. The electrostatically charged tine particles tend to form a coating on the grinding media, mill walls and extraction screens, which furth e r hampe rs the grinding process. Grinding aids possess lubricating and/or dispersive properties and form a coating of mono-molecular thickness on the fine particles. This neutralizes the unbalanced electrostatic charges present on the particle surfaces and helps to prevent the agglomeration of fine particles on grinding media and mill walls, etc. Thus the grinding becomes more efficient than the soft grinding provided by heavily coated media. The reduced tendency of the fine particles to agglomerate also results in higher grinding efficie ncy . The mill retention time tor achieving a given fineness is reduced too, resulting in increased production and lower power consumption. NCB Study In a recent study, sponsored by M/s Reliance Industries Ltd, National Council for Cement and Bui ld ing Materials (NCB) investigated the use of diethylene glycol (DEG) as a grind ing aid -in cement manufacture. A batch-type ball mi ll was used in the study to prepare samples of OPC without an·d with DEG . The power consumption was recorded using an electronic energy meter. The dosage of DEG was varied in the range of 0.00-0.04 percent. Following are the find ings from the study: • For the same duration of grinding, use ofDEG resulted in higher fineness of cement. The increase in finenes s ranged from 7 to 31 m 2 /kg (see Figure I) depending on the dosage of DEG and th e grinding duration. • For the same finene ss of cement, use of DEG resulted in 4-1 6 percent lowering of power consumption during .grinding (see Figure 2). The laboratory findings are considered encourag ing for conducting plant scale trials to work out the actual measure of power saving and production inc rease achievable. NCB is in a position to undertake such trails on sponsored basis. Triethanolamine, Ce lex powder and sulphate lye (a waste product from paper industry) are some other substances that have been found effective as grinding aids. Courtesy : NCB Newsletter Vol IV, No.2, June 2002 ~ r---------------------------------~ "' !! -450 g ~ l _____________.__ ----.------4 ~ z 400 ..... w z ;;: .. ~ 350 3 ., '"" ------------------~--------.__ _______ . ··········--····-···········--·--~---~-·------+·········-··-·· ... ,.. f-------,----------- 0.01 o.oz 0.03 0 04 OEG DOSAGE (%) Fig. 1 Effect of dosage of DEG on cement fineness. I GRINDING I TIME(ffilll} I 0.05 1.4 ,------------------------------------, . ---. -~ ... l FINENESS (m"l!t 1.3 1.2 1.1 1.0 ···JI· .. ·······.A. 0.9 r--------.J-..__ _______ 0.8 i 0 7 ~ 0.6 r--- ---,____.._____ 0.5 0.4 +-----~------,.-------.--------,~-----1 D.01 0.02 0.03 0 04 DEG DOSAGE (%) Ftg 2 Etft'ct of dosage ol DEC onpower consumption for cement grinding. 0.05 ... ...