Energy consideration in cement grinding

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2 Introduction Reasons for energy considerations Introduction o Rising consumption depleting energy resources o Depleting resources escalating energy prices o Consumption generates increasing green house gases o Energy costs are a major expense in cement production 2

3 Statistics Energy consumption in cement production 3

4 Statistics Energy consumption in cement production o ~ 2 % of the global primary energy, or 5 % of global industrial energy, is consumed in cement production, of which: % is thermal energy & % electricity; o o ~ 25 % of cement cost is due to energy costs, of which: ~ 50 % is for electricity, mainly for grinding. 4

5 Consumption Consumption of energy in cement plant Dry process 5

6 Consumption Consumption of energy in cement plant Dry process o Modern plant able to achieve 3,000 kj/kg clinker & 90 kwh/t cement o Electricity required for crushing, raw materials / coal milling & finished grinding represents ~ 25% of overall primary consumed in cement production o 65% of the electricity consumed is used in the grinding operations 6

7 Consumption Power consumption in cement plant ~ 65 % of electricity in cement plants is consumed in the grinding processes 7

8 Consumption Typical power requirement of finished ball mill Example: Total consumption 3333 kw, 104 t/h product => Total Power Consumption = 32,0 kwh/t Mill Power Consumption = 27,5 kwh/t (85,8 %) 8

9 Performance Grinding inherently inefficient... Performance 9

10 Performance Grinding inherently inefficient... o Only < 2-5% of energy input is theoretically required to fracture particles; the bulk of the input energy ends up largely as heat & typically generates ~ 25 kcal of heat per kg cement ground o Mill temperature could rise to 140 C and causes gypsum to dehydrate & produces false set in cement, as well as media coating which impairs grinding efficiency o typically, ~ 0.8 m³ of cooling air is required to remove the heat 10

11 Performance Example: material grindability & correlation with ball mill Evaluation of performance with help of Zeisel test Guiding values for the grindability of an OPC cement 95/5 are o kwh/t at 3000 cm²/g acc. Blaine o kwh/t at 4000 cm²/g acc. Blaine o kwh/t at 5000 cm²/g acc. Blaine 11

12 Performance Detrimental effects of feed moisture on energy consumption TPH kwh/t o Typically, every 1% increase in moisture content above 0.5% increases energy consumption by >10%, especially at higher product fineness o At limiting moisture, eg. above ~ 5% in limestone, a ball mill may not be operable! 12

13 Performance Influence of media filling ratio on specific power consumption 13

14 Performance Influence of equipment / process design o Process / equipment configuration (mill L/D & speed, closed v open circuit, pregrinder & type, mechanical v pneumatic transport, ducting arrangement, dampers, etc) o Equipment design including the separator, mill internals such as liners (lifter/classifying), diaphragm (flow control), media, etc o Degree of automation such as fuzzy logic / total feed / sonic control, auto sampling, etc) 14

15 Performance Optimising mill internals Well designed / upgrade of mill internals may improve mill output, product quality & specific power consumption by %. 15

16 The new CPB separator generation: OptiTromp First results with the new QDK technology 16 High efficiency separator QDK

17 New QDK separator: design basis Result of CFD analysis: improvement of air flow pattern 17 High efficiency separator QDK

18 New QDK separator: design basis Changes in air guide vanes and rotating cage Air guide vanes (louvres) New design Former design Rotating cage Separation zone Guide vanes Cage rods New design Number increased, directed tangentially to rotating cage Number increased, free cage surface area appr. 90 %, backwards curved cage rods 18 High efficiency separator QDK

19 Former Actuel Separating zone 19 High efficiency separator QDK

20 New QDK separator: design basis Changes in design of spiral casing Approximation of an ideal spiral design Leading to an almost ideal distribution of separation air into the separation zone 20 High efficiency separator QDK

21 T(x) [%] Separator efficiency 100 Trompcurve T(x) CEM I 32,5R CEM I 42,5R CEM II/A-LL 32,5R Bypass [%] O m [cm²/g] rejects O m [cm²/g] cement CEM I 32,5 R CEM I 42,5 R CEM II/A- LL 32,5 R 3,9 6,9 5, O m [cm²/g] feed Particle Size x [µm] 21 High efficiency separator QDK

22 CPB Shell liners Functioning of mill shell liners 1 st compartment 2 nd compartment 22 Shell liners

23 1 st compartment liners: activator liners Conventional liner Lifting height -decreasing- Activator liner Lifting height -maintained- 23 Shell liners

24 1 st compartment activator liners 24 Shell liners

25 2 nd compartment classifying liners 25 Shell liners

26 CPB mill diaphragms Functions & requirements Intermediate Diaphragm (ID) Retain media in 1 st / 2 nd compartments for different grinding actions Regulate material flow & particle size to maximize grinding efficiency Mill ventilation not obstructed (low ΔP) Low maintenance (constant slot opening, no breakage or loosening of plates ) Structure stability & long useful life Discharge Diaphragm (DD) 26 Cement mill diaphragm

27 CPB Monobloc Diaphragm Structure A strong, rigidly welded steel frame afixed to mill shell via Tie Plates to avoid direct rotational stress transmission from mill shell & ensures an exceptionally long useful life & maintenance-free operation 27 Cement mill diaphragm

28 Flexible plates division Provides further cost reduction opportunity Easy conversion from 3 to 4 plates division 28 Cement mill diaphragm

29 Maximum free diaphragm area = Lower Δp & maximum mill ventillation / optimum air velocity Calculated air velocity above ball charge v = 1.8 m/s v = 1.8 m/s p = 2.4 mbar 29 Cement mill diaphragm

30 Material flow control Allows optimization of material levels in 1 st & 2 nd compartments & ensures maximum grinding efficiency 30 Cement mill diaphragm

31 Air-material separation Negates particles throw & maximizes effective grinding length Older design 旧的设计 Current design 现在的设计 31 Cement mill diaphragm

32 Performance Operations & maintenance considerations Efficient grinding can only be achieved by maximizing the feed throughput, rapid removal of the desired fines to avoid overgrinding, transferring of optimum impact / shearing forces from the grinding media to the materials being ground & minimize generation of wasteful heat, wear, vibration & noise. 32

33 Performance Relationship between power consumption & product fineness For every 100 cm²/g increase in fineness increases power consumption by 1-2 kwh/t for closed circuit mill & 2-3 kwh/t for open circuit mill Open circuit kwh/t Closed circuit kwh/t 33

34 Performance Good practices in operations & maintenance Maintain maximum, continuous feed without over-fill of material which cushions & absorbs the impact energy in 1 st chamber or lifts media & causes reverse or even de-classification of media in the 2 nd Chamber Avoid meal starvation -eg at feed inlet, in front & behind intermediate diaphragm- & wasteful metal to metal contact between the grinding elements causing wear & tear, generate heat & noise Conduct regular mill sampling/analysis to maximise feed & periodic technical audit to ensure optimum process conditions Maintain optimum milling temperature (ventilation/water spray) & use grinding aid (if cost effective) to minimise media coating & particles re-agglomeration Adhere to a well design planned maintenance programme 34

35 Performance Use of additives & grinding aids o Use appropriate grinding aid such as air entrainer or strength enhancer o Provide water injection to maintain optimum milling temperature; water also acts as a grinding aid o Reduce clinker factor & use filler such as limestone and/or extenders such as slag, fly-ash or other pozzolan 35

36 Performance Energy Improvement Potentials in Grinding o Pre-grinding (e.g. roll press) => % o Separator upgrade => 5-25 % o New mill internals (liners / diaphragm) => 5-20 % o Mill operations & maintenance => 5-10 % o Using grinding aids => 3-10 % o Using fillers / Extenders => %* * Based on total energy consideration 36

37 Performance Case example 1: Results of mill internal upgrade 37

38 Performance Case example 2: Results of conversion to high performnace QDK 38

39 Performance Case example 3: Operational results of QDK conversion & mill internals upgrade 39

40 Performance Case example 4: Results of the russian plant upgrade Before upgrade After upgrade Cement type CEM400 D0 CEM400 D0 CEM400 D0 Product fineness [Blaine] cm²/g cm²/g cm²/g Average production rate Specific energy consumption of mill drive (at counter) Cement strength after 28 days 76,0 t/h 103,0 t/h (- 35,5 %) 36,0 kwh/t 26,6 kwh/t (- 26,0 %) 88,0 t/h (- 15,8 %) 31,1 kwh/t (- 15,7 %) 44,2 MPa 44,2 MPa 44,2 MPa Significant reduction in specific power consumption of the mill was achieved despite relatively coarse products. 40

41 Conclusions Conclusions o makes sense: it decreases production cost, increases output & reduces green house gas emission; o Proven technology available for both new & existing plant / equipment upgrade to generate attractive ROI; o Energy consideration should be regarded a basic responsibility of cement producers to help conserve the fast depleting fossil fuels & minimize impact of GHG on the environment to ensure a sustainable development of the cement industry. 41

42 Any questions? Feel free to ask! Thank you for your kind attention. 42