PreprintPDF Available

Effect of Free Lime and Lime Saturation Factor on Grindability of Cement Clinker

Authors:
  • Umaru Ali Shinkafi Polytechnic Sokoto
Preprints and early-stage research may not have been peer reviewed yet.

Abstract and Figures

This research aims to investigate the effect of free lime and lime saturation factor on grindability of cement clinker. Cement is a powdered substance that develops strong adhesive and cohesive properties when mixed with water. Cement production involves a number of processes, these include; Preparation of raw materials, production of clinker, preparation of cement and its packaging. Clinker formed as a result of heating of well blended raw materials that undergo a chemical transformation inside the kiln. The methodology of this research work, are; 10g samples of clinker were collected on the apron conveyor chute with liter weights, (table 2.1), the weighted samples (10g) of clinker were milled and pelletized with the aid of pyridine and binding agent. The pelletized samples were subjected to XRF/XRD machine using thermo fisher analysis. They were done to determine the mineralogical compositions of the clinker samples and their respective elemental oxides. The result of the clinker minerals are; C 3 S (Tri calcium silicate), C 2 S (Di calcium silicate), LSF (Lime Saturation Factor) and other elemental oxide (table 2.2). However each of the sample were subjected to grinding for 40 minute using ball mill after adding 5% gypsum, these was done to determine the energy required to grind the clinker sample, and fineness was determined for each using the Blaine cell and air permeability apparatus (table 2.3). Correlation and regression analysis (statistical method) were applied on these results (table 2.4), the implication of the results shows there increase in energy requirement as FCaO (free lime) and LSF (lime saturation factor) increase in the clinker samples, there is also increase in energy requirement with the increase in Blaine (fineness). Therefore thus a clinker with low free lime would be grinded more easily than with high free lime, and also implies that the high the LSF and hence the harder the clinker to grind.
Content may be subject to copyright.
International Journal of Engineering Research and Reviews ISSN 2348-697X (Online)
Vol. 7, Issue 1, pp: (61-66), Month: January - March 2019, Available at: www.researchpublish.com
Page | 61
Research Publish Journals
Effect of Free Lime and Lime Saturation
Factor on Grindability of Cement Clinker
1Rikoto I.I, 2Nuhu, S
1Energy Research Centre Usman Danfodiyo University Sokoto, Nigeria
2Chemical Engineering Department, Umaru Ali Shinkafi polytechnic Sokoto state, Nigeria
Author email id: sanusin48@gmail.com
Abstract: This research aims to investigate the effect of free lime and lime saturation factor on grindability of
cement clinker. Cement is a powdered substance that develops strong adhesive and cohesive properties when
mixed with water. Cement production involves a number of processes, these include; Preparation of raw materials,
production of clinker, preparation of cement and its packaging. Clinker formed as a result of heating of well
blended raw materials that undergo a chemical transformation inside the kiln. The methodology of this research
work, are; 10g samples of clinker were collected on the apron conveyor chute with liter weights, (table 2.1), the
weighted samples (10g) of clinker were milled and pelletized with the aid of pyridine and binding agent. The
pelletized samples were subjected to XRF/XRD machine using thermo fisher analysis. They were done to
determine the mineralogical compositions of the clinker samples and their respective elemental oxides. The result
of the clinker minerals are; C3S (Tri calcium silicate), C2S (Di calcium silicate), LSF (Lime Saturation Factor) and
other elemental oxide (table 2.2). However each of the sample were subjected to grinding for 40 minute using ball
mill after adding 5% gypsum, these was done to determine the energy required to grind the clinker sample, and
fineness was determined for each using the Blaine cell and air permeability apparatus (table 2.3). Correlation and
regression analysis (statistical method) were applied on these results (table 2.4), the implication of the results shows
there increase in energy requirement as FCaO (free lime) and LSF (lime saturation factor) increase in the clinker
samples, there is also increase in energy requirement with the increase in Blaine (fineness). Therefore thus a
clinker with low free lime would be grinded more easily than with high free lime, and also implies that the high the
LSF and hence the harder the clinker to grind.
Keywords: Clinker, Lime saturation factor, Free lime, Belite, Alite Blaine, Correlation, Regression, Energy.
1. INTRODUCTION
Cement is a product obtained by the pulverizing clinker from the materials limestone, with cohesive and adhesive
properties which make it capable of bonding minerals fragment into a compact whole. Cement is produced by grinding a
mixture of a clay and limestone together and heating to a temperature of 1450oC, [Mohammed, 2012]. In which the partial
fusion occurs and nodules of clinker are formed with the addition of shale, iron ore and gypsum. [Wilcox & Simon, 1995].
Grinding of the raw meal can also be reduced leading to further reduce the energy requirement for grinding. And grinding
depends on many parameters and compositions which any slide deviation from these compositions can significantly affect
the performance of the instillation and quality of the cement. Clinker is formed from burning or kiln stage, it can be
described as nodules, or lumps usually 3 mm to 25 mm in diameter, and it is composition of four minerals: C3S, C2S, C3A
and C4AF and these minerals is as a result of the reaction of oxides in the kiln, which leads to the formation of lime
saturation factor (LSF). LSF is the ratio of CaO to SiO2, Al2O3 and Fe2O3. Clinker with LSF close or beyond to 1.0
indicate a likelihood of the presence of free lime, this will result to the high burn of clinker and hence difficult in grinding
(CCNN-Sokoto, 2013). And it controls the proportion of C3S to C2S, in clinker, the high the value of it cause free
lime(CaO) not to combine with oxide, such as SiO2, Al2O3 and Fe2O3. While free lime is the CaO that didn’t combine
with those oxides. Excess free lime results in undesirable effect such as volume expansion, increased setting time or
reduced strength.
International Journal of Engineering Research and Reviews ISSN 2348-697X (Online)
Vol. 7, Issue 1, pp: (61-66), Month: January - March 2019, Available at: www.researchpublish.com
Page | 62
Research Publish Journals
About 30% of the energy are required to manufacture one ton of cement is used up in grinding. It sums up to a substantial
percentage of the over- all cost of cement. The consumption of energy in cement mill varies within, 16.5 to 63.5
KWh/ton, having an average of about 36KWh/ton (M Tokyay, 1998). Several factors affect energy consumption during
the process of clinker grinding. Clinker hardness brings about a wide disparity to grindability. About 80% extra power is
usually required in processing hard clinker than the soft ones (Nwokedi, 20140.
The fineness of cement samples can be analyzed by a few methods which includes Dry sieve analysis and Blaine air
permeability analysis. The dry sieve analysis measures the fineness of cement by means of a standard sieve in which the
proportion of cement with grain sizes bigger than the specified mesh size of the sieve is collected and measures as the
residue. Blaine air permeability apparatus determines the fineness of Portland cement in terms of surface area in g/cm2 of
cement. It consists of a brass or stainless steel permeability cell and a U tube manometer column. The process is described
by an ASTM standard; it is based on the rate of air passage through a porous bed of cement particles under a specific
pressure gradient as a function of the surface area. The process consists of a chamber whose volume and cross sectional
area is known, filled with a known mass of cement. A specific volume of air is passed through the cement power and the
time taken is measured. The surface area is then determined by calculations. [Thomas, Jennings, 2008].
Laboratory testing procedures established for determining the grindability of clinkers. The generally used procedures for
this purpose are; determination of
The mill energy requirement to produce cement with a definite fineness.
Revolutions of the mill required to produce cement with definite fineness
Specific surface area (Blaine) of the ground clinker for a specified energy consumption of the mill
This is mainly based on procedures I and III.
A number of investigations have been carried out to correlate the chemical and mineralogical compositions of clinker with
the energy requirement. Table below shows this relationship, the equation drives for determining the energy requirement
are;
Energy requirement, K = XeBY
Where B is the Blaine (fineness) of the pulverized clinker simple in cm2, X and Y are correlation values and are given
below for a wide range of consumption factors.
[Nwokedi, 2014]
Relationships between major chemical parameters of clinker and constants X and Y of the exponential equation are;
Parameter
X
Y
FCaO
1.2In(1/FCaO)+8.91
0.029In(1/FCaO)+0.5
2. MATERIALS AND METHODS
2.1 Materials
10 samples of various weights of clinker
Water
Gypsum
2.2 Equipment Instrumentation
XRF/XRD Machine: Is the ideal tool for direct quantification of the mineralogical composition of raw materials,
clinker and cement products.
Crusher: Is a machine used to reduce the size of limestone/clinker
Ball mill: Is a key piece of equipment used for grinding crushed clinker/limestone
Blaine air permeability apparatus: Is used to determine the Blaine (fineness) of the pulverized samples clinker.
Weighing balance; It is used to measure the weight of the samples
Pyridine: is a chemical and organic compound used to dissolve samples
Spatula: A thin hand tool used for handling chemicals or other materials, when weighing.
International Journal of Engineering Research and Reviews ISSN 2348-697X (Online)
Vol. 7, Issue 1, pp: (61-66), Month: January - March 2019, Available at: www.researchpublish.com
Page | 63
Research Publish Journals
2.3 Experimental Procedure
Sample preparation: 10g each of the samples were weighed, milled and pelletized with the aid of pyridine ad binding
agent
The pelletized samples were subjected to XRF/XRD analysis using thermo fisher analysis incorporated with
Goniometric. They was done to determine the mineralogical compositions of the clinker samples and their respective
elemental oxides. The clinker minerals whose compositions were determined using XRDF/XRD are: C3S, C2S and C4AF,
while the elemental oxides compositions determined also are: CaO, SiO2, Al2O3, and MgO. The silica modulus, alumina
modulus, lime saturation factor were found from the elemental oxides compositions using Bogue’s equation stored as a
program in the XRF/XRD analyzer.
The free lime were determined using wet chemistry method, with the aid of free lime tester
Each of the sample were subjected to grinding for 40 minute using ball mill after adding 5% gypsum
The fineness were determined for each using the Blaine cell and air permeability apparatus
It is base on the rate of air passage through a porous bed of cement particles under a specific pressure gradient as a
function of the surface area.
The energy requirement, k for grinding is calculated using K = XeBY,
3. RESULTS
3.1 Results
Table 3.1: Collection of 10 sample of clinker with litre weights (Lt/Wt) as tabulated below
S/N
1
2
3
5
6
7
8
9
10
Lt/Wt
(g/cm3)
1140
1242
1214
1270
1252
1350
1325
1335
1300
Table.3.2: XRF/XRD Analysis of Clinker Samples
Clinker
Samples
CaO
%
SM
AM
C3S
%
C2S
%
C3A
%
C4AF
%
LSF
%
FCaO
%
1
66.79
2.20
1.47
59.73
15.03
9.52
11.52
97.21
4.75
2
66.80
2.20
1.47
63.07
11.14
9.67
11.86
98.56
4.37
3
66.60
2.15
1.48
54.21
17.82
9.92
12.77
99.33
3.99
4
66.10
2.10
1.32
60.22
12.92
8.64
12.79
99.51
2.81
5
66.79
2.06
1.34
63.06
11.29
8.77
12.09
99.65
2.66
6
66.40
2.16
1.37
60.68
13.10
8.89
11.47
99.72
2.47
7
66.30
2.18
1.50
59.64
13.81
9.20
11.37
99.88
2.47
8
66.96
2.20
1.48
60.90
11.94
7.54
10.21
100.33
2.41
9
66.72
2.27
1.63
59.01
15.55
8.23
9.78
100.52
2.35
10
65.89
2.30
1.81
63.17
25.85
8.34
9.76
102.65
2.29
Table 3.3: X, Y and Energy requirement, k value for free lime in clinker samples.
Clinker
Samples
X
Y
K(kWh/ton)
FCaO (%)
Blaine
(cm2/g)
1
7.04
0.443
45.25
4.75
4200
2
7.14
0.445
40.85
4.37
3920
3
7.25
0.447
41.07
3.99
3880
4
7.67
0.458
45.14
2.81
3870
5
7.74
0.459
37.19
2.66
3420
6
7.82
0.462
36.08
2.47
3310
7
7.82
0.462
32.90
2.47
3110
8
7.85
0.462
31.54
2.41
3010
9
7.88
0.463
29.62
2.35
2860
10
7.92
0.464
26.84
2.29
2630
International Journal of Engineering Research and Reviews ISSN 2348-697X (Online)
Vol. 7, Issue 1, pp: (61-66), Month: January - March 2019, Available at: www.researchpublish.com
Page | 64
Research Publish Journals
Table.3.4: Represent the regression and correlation result of the analysis.
RELATIONSHIP
CORRELATION (r)
REGRESSION
BLAINE(X) VS ENERGY REQUIREMENT(Y)
0.978
Y = 0.012x 4.404
FREE LIME(X) VS ENERGY REQUIREMENT(Y)
0.745
Y = 5.12x + 20.996
FREE LIME(X) VS BLLAINE(Y)
0.8606
Y = 483.56x + 1942.8
LSF(X) VS BLAINE(Y)
-0.8962
Y = 338.283x 30317.99
3.2 Discussion of results
Table.3.2; The results Shows the minerals composition of 10 samples of clinker subjected to XRF/XRD analysis, the
samples were collected at random because of the varying amount of lime (CaO) and the calcium oxides. The composition
factors AM, SM and LSF are factors relating the proportions of SiO2, CaO, Al2O3 and Fe2O3 in the clinker samples. It was
observed that, the free lime (FCaO) present in each samples of clinker decreasing, the LSF increased. This indicated that
the more burning of clinker, the higher the composition of belite (C2S) and hence less free lime is available for the
formation of alite (C3S) after the burning zone of the kiln. However, it is a known fact that stable glazy crystal structure of
belite are very hard to grind and hence clinker with very low free lime is not healthy to Ball mill during grinding.
Table 3.3; Contain X, Y and Energy requirement (K) values for free lime in clinker samples, where X and Y are the
correlation factors and are drives from the below empirical equation;
X = 1.2In (1/FCaO) + 8.91
Y = 0.029In (1/FCaO) + 0.488 and the Energy Requirement K calculated from this below Equation; K = XeBY.
Where B = Blaine (fineness)
It was also observed that there increases in the energy requirement as the free lime increases.
Table 3.4; Represent the entire calculated results of the regression and correlation analysis.
The calculation was done using the statistical equations below;
r(correlation) = 

This regression equation: (y = bx + a) was also used to find the best fit line between the two variables
Where b = 
 and a =  - b
Where  and  are the mean of the respect variables
However in the relationship between free lime and energy requirement, the correlation shows positive, which implies
increase in energy requirement as the free lime increase. And also indicated increase in energy requirement to achieve
fineness as the LSF or lime saturation factor increased. However there is negative correlation in the relationship between
LSF and Blaine (fineness), which implies decrease in Blaine (fineness) of the clinker as the LSF increase. This confirms
that the clinker is completely burnt in the kiln, the high the LSF and hence the harder the clinker to grind.
4. CONCLUSION AND RECOMMENDATIONS
4.1 Conclusion
Finally it has been concluded that, free lime and LSF (lime saturation factor) compositions have considerable effects on
cement clinker grindability. As the results indicated there increases in energy requirement as free lime & LSF increases in
the clinker samples. Thus a, clinker with low free lime would be grinded more easily than with high free lime. Also
indicate an increase in energy requirement with increase in Blaine. Thus in achieving finer particles, more energy is
required in grinding. The negative results indicate a decrease in Blaine of the clinker with increase of LSF. This confirms
that, the clinker contain a higher LSF in the kiln, the high the LSF and hence the harder the clinker to grind.
International Journal of Engineering Research and Reviews ISSN 2348-697X (Online)
Vol. 7, Issue 1, pp: (61-66), Month: January - March 2019, Available at: www.researchpublish.com
Page | 65
Research Publish Journals
4.2 Recommendations
In order to eliminate the problem of high free lime, during pre-calcination of kiln feed in the precalciner and sintering
zone of the raw meal in the kiln, the correlation between the kiln feed and clinker LSF should be carefully care. Therefore
the kiln operators should place more attention on the LSF target of the clinker/kiln chemistry by increasing burning and
hence, free lime of the kiln output will be relatively low. This therefore will guarantee cement quality, suitable and
profitable fuel and energy requirement at the cement mill to grind the clinker to a specified fineness and time, since the
production time can also affect the output and profit.
The balanced feed rate to fuel flow rate in the kiln should pay attention by the cement plant process engineer. This is to
improve the proper burning of the sintering raw material in the kiln, so that the resulting clinker has relatively low free
lime and suitable target of lime saturation factor and hence, suitable/profitable energy requirement for grinding the clinker
at the cement mill.
However, the grinding aid will increase the product fineness, reduce the power consumption and reduce ball coating.
Therefore the mill operators should ensure proper used of grinding aid.
ACKNOWLEDGEMENTS
I’m grateful to the cement company of northern Nigeria plc sokoto, for given permission to use the equipments required to
finish this research and due to their further cooperation. Also, the author would like to thank the Chief Engineer
Production, Engr Nasiru Muhammad Bada, and other staffs from production and process for supporting this project with
other materials till the completion.
REFERENCES
[1] Hills.M.L. (2007). Solid Fuel Grindability. www.cement.org. ©Portland Cement
[2] Gavel. V. (2013) Grinding theoretical and technological investigation to establish the production of environmental
friendly cement with reduced clinker content. Unpublished Ph.D, Thesis.
[3] Cement Manufacturers Association of Nigeria, Optimizing clinker production in Nigeria industrial Standard,
Standard of Cement pages 9, A publication of Standard Organization of Nigeria, Wuse Zone 7, Abuja Nigeria
[4] Cement Company of Northern Nigeria PLC Sokoto (2004), Cement Grinding Training Book page 11-13
[5] Cement Company of Northern Nigeria Plc Sokoto, (2003) Cement Production Course, Milling Technology, page 6-
16
[6] (Nwokedi, 2014). Investigation of the effect of Free Lime and Lime Saturation Factor on Grindability of Cement
Clinker. Research work. Federal University of Technology, Minna. Niger State, Nigeria. Unpublished
[7] Hashim. S, Hussin. Azizli. K.A, Palaniandy, S. (2008) Study of Clinker Characteristics and Grindability during
Cement Production. Final Report of short term Research project, University of Malaysia.
[8] Ted Krapkat, 2015. Note on effect of Free Lime and LSF on Burning of Clinker
[9] Tokyay. M. (1999). Effect of Chemical Composition of Clinker on Grinding Energy Requirement. Civil Engineering
Department, Middle East Technical University, 06531 Ankara, Turkey. Cement and Concrete Resarch (29) 531-535.
[10] Winter N.B (2005). Understanding Cement. 2005-2014 WHD Microanalysis Consultancy LTD. Pg 75.
[11] Gavel.V. (2003). Grinding theoretical and technological investigation to establish the Production of Environmental
Friendly and Cement with Reduced Clinker Content. Unpublished Ph.D. Thesis. University of Miskolc Faculty of
Earth Science & Engineering Institute of Raw Materials Preparation and Environmental Processing.
[12] Svinning. K. (2011). Design and Manufacture of Portland Cement Application of statistical Analysis. Ph.D. Thesis.
Faculty of Natural Science and Technology.
[13] Soumaya. I, N jib. B, Khaoula. M and Mohammed. B. (2011). Comparative Study for Grinding of Two Cement
Clinkers, International Journal of Concrete Structure and Materials. Vol.5, No.2, pp.113-117.
International Journal of Engineering Research and Reviews ISSN 2348-697X (Online)
Vol. 7, Issue 1, pp: (61-66), Month: January - March 2019, Available at: www.researchpublish.com
Page | 66
Research Publish Journals
[14] Gebhardt, 1988, Research on Free Lime Determination in Clinker
[15] Effect of Chemical Composition of Clinker on Grinding Requirement, [M. Tokyay, 1998] Where is the iron? Clinker
Microanalysis with XRD Rietveld, Optical Microscopy, Alison Crumie, 2006.
[16] Kebede, M.A (2010). Investigation of calcite and Volcanic ash for their Utilization as Cement Filling and additive
Materials. Unpublished M.Sc. Thesis Addis Ababa University School of Graduate Studies.
[17] Christian J. E. (2008). Quality Improvers in Cement making State of the art COIN Project report 2. Retrieved from
www.sintef.no/upload/.../coin-no2.pdf
[18] Mohammed, T.A. (2012). Composition and phase mineral Variation of Portland Cement in Mass Factory Sulaimani-
Kurdistan Region NE Iraq, International Journal of Basic & Applied Sciences, 12(06), pg 116 117.
[19] Cement Company of northern Nigeria plc Sokoto, September 2003, Milling Training Book.
ResearchGate has not been able to resolve any citations for this publication.
Article
Full-text available
The purpose of this work is the comparative study for grinding of two cement clinkers. X-ray fluorescence, physical and granulometric tests and optical microscopy were used to characterize the clinkers. Also grinding tests were carried out for ten samples to determine the parameters influencing grindability of its clinkers. The results of calculation of the energies of grinding according to the law developed by Von Rittinger and the study of the microstructure of the two clinkers shows good agreements. Indeed, frequent clusters of belite which indicate a lack of uniformity and fineness have an effect on lowering the grindability. The obtained analyses and the results enabled us to interpret the granulometry and the microstructure of clinker to control quality and resistance.
Article
Fifteen commercial Portland cement clinker samples with a wide range of chemical compositions were subjected to grinding tests and relationships between grinding energy requirement attained specific surface areas and various chemical parameters were found. Regression analyses of the test results revealed that the energy–fineness relationship is exponential, and grinding energy is correlated with Al 2O3, free CaO, liquid phase contents, silica moduli, and (C3S + C2S)/(C3A + C4AF) ratios of the clinkers.
Solid Fuel Grindability. www.cement.org. ©Portland Cement
  • M L Hills
Hills.M.L. (2007). Solid Fuel Grindability. www.cement.org. ©Portland Cement
Grinding theoretical and technological investigation to establish the Production of Environmental Friendly and Cement with Reduced Clinker Content
  • V Gavel
Gavel.V. (2003). Grinding theoretical and technological investigation to establish the Production of Environmental Friendly and Cement with Reduced Clinker Content. Unpublished Ph.D. Thesis. University of Miskolc Faculty of Earth Science & Engineering Institute of Raw Materials Preparation and Environmental Processing.
Study of Clinker Characteristics and Grindability during Cement Production. Final Report of short term Research project
  • S Hashim
  • Hussin
  • K A Azizli
  • S Palaniandy
Hashim. S, Hussin. Azizli. K.A, Palaniandy, S. (2008) Study of Clinker Characteristics and Grindability during Cement Production. Final Report of short term Research project, University of Malaysia.
Note on effect of Free Lime and LSF on Burning of Clinker
  • Ted Krapkat
Ted Krapkat, 2015. Note on effect of Free Lime and LSF on Burning of Clinker
Understanding Cement. 2005-2014 WHD Microanalysis Consultancy LTD
  • N Winter
Winter N.B (2005). Understanding Cement. 2005-2014 WHD Microanalysis Consultancy LTD. Pg 75.
Design and Manufacture of Portland Cement Application of statistical Analysis
  • K Svinning
Svinning. K. (2011). Design and Manufacture of Portland Cement Application of statistical Analysis. Ph.D. Thesis. Faculty of Natural Science and Technology.