In clinkers

Multi-stage preheating, pre-calciners, kiln combustion system improvements, enhancement of internal heat transfer in kiln, kiln shell loss reduction, optimize heat transfer in clinker cooler, use of waste fuels Blended cements, cogeneration... 

Cement kilns can handle quite a lot of different materials. In most cases the input material should be chipped or shredded. Licenses often limit the PVC and chlorine input to l%-2% chlorine in waste. It is said that chlorine also has a negative impact on the quality of the clinker if it is available in too high quantities. The content in clinker seems to be limited to some 0.1% at maximum, and hence the average chlorine content of all fuels used combined may have to be somewhat lower. This implies that waste with a high chlorine... 

Third, implementing output-based allocation in the cement sector raises a difficult dilemma, due to the fact that 90% of cement emissions occur during the production of cement s main input, clinker, and that lowering the proportion of clinker in cement is one of the main means of cutting C02 emissions. If allowances are allocated in proportion to cement production, a producer may import clinker to make cement in Europe in order to receive free allowances and sell them. Leakage would then not be addressed. Alternatively, if allowances are allocated in proportion to clinker production, the incentive to reduce the clinker rate in cement vanishes, and so does a large part of C02 abatement. This problem is not taken into account in our simulations, since we model only trade in cement, not in clinker. 

Pure C3S contains 73.7% of CaO and 26.3% of SiO. Alites in clinkers typically contain 3-4% of impurity oxides, i.e. oxide components other than those present in the pure compound. Boikova (B4) found a positive correlation between the total percentage of impurity oxides in the alite (/ ) and the percentage of MgO in the clinker (M ). Her re.sults are approximately lilted by the equation = 0.1 -1-2.1. 

Normal form in clinkers low in alkali and with AljOj/FejOj in the approximate range 1.0-3.0. 

Orthorhombic or pseudotetragonal forms, found in clinkers high in alkalis. Na,/K ratio varies with that of the clinker. 

A number of experimentally determined XRD powder patterns have been reported for CjS and alite polymorphs (PI), but because of uncertainties in the indexing and sometimes in identification of the polymorph, these are usefully supplemented by patterns calculated from the crystal structures (Appendix). The patterns of the polymorphs are closely alike, and in clinkers, interpretation is complicated by the fact that many peaks overlap ones of other phases. The pattern depends not only on the polymorph or... 

A substituted C3S has been found in nature and given the mineral name hatrurite (G5). The rock containing it is interesting because it contains other phases present in clinker and appears to have been formed under conditions somewhat similar to those existing in a cement kiln. 

Studies on synthetic belites suggest the possible occurrence of modulated structures, i.e. ones in which compositional or structural variations occur with a statistical periodicity that is not a rational multiple of that of the basic structure (H5). Such effects might occur in clinker belites. 

Clinker belites typically contain 4-6% of impurity oxides, of which the chief ones are usually AI2O3 and Fe203. Correlations have been reported to exist between the MgO contents of belite and clinker (Kl), the Fe20, contents of belite and clinker (Kl), and the total impurity content of the belite and the MgO content of the clinker (B4). Early reports mention a compound KC23S,2, but the K2O content of 3.5% corresponding to this formula is well above those found in clinker belites, and recent electron optical work indicates that the limit of K2O substitution is about 1.2% (C1). 

Regourd et al. (R3) synthesized several belites of P-C2S type with compositions similar to those found in clinkers and determined their cell parameters. With increased substitution, the crystallinity tended to decrease, causing broadening of XRD powder peaks. Two of their results are given in Table 1.5. 

Pollitt and Brown (P2) were unable to prepare an analogue of the orthorhombic phase with as the sole substituent, but obtained evidence that could stabilize it in clinker, probably because other substituents were also present. Maki (M12) also failed to prepare K forms of the orthorhombic or monoclinic phases under equilibrium conditions, but by moderately rapid cooling of melts he obtained orthorhombic crystals having cell parameters close to those of the corresponding sodium-containing phase. He considered that the presence of silicon in the clinker liquid would favour supercooling and thereby also non-equilibrium formation of the orthorhombic or monoclinic phase. 

The aluminate phase in clinkers can also be characterized by its composition, determined by X-ray microanalysis this is discussed in the next section. 

Because of the close admixture with other phases, which is often on a scale of lOpm or less. X-ray microanalysis of the aluminate phase in clinkers is frequently difficult or unreliable. Data have been reported for cubic, orthorhombic, pseudotetragonal or unspecified forms of the aluminate phases in ordinary clinkers (R1,K1,B2,H3) and for aluminate phase (G3,G4,S1,B3) and glass (B3) in white cement clinkers. Tables 1.2 and 1.3 include, respectively, average compositions based on these somewhat scanty data, and suggested site occupancies based on them. The values in both tables take into account both the experimental data and the requirement of reasonable site occupancies. 

Plots of unit cell parameters or XRD powder spacings against a for the pure Ca,(Al,Fe)205 series show changes in slope near a = 0..1, attributable to the structural change (S4). Such plots may be used to determine composition provided that oxide components other than CaO, A1,0, and Fe,0, are absent. They have often been applied to ferrites in clinkers, but this gives seriously inaccurate results because of the effects of other substituents (Sections 1,5.2 and 1.5.. ). 

Alite may be expected to form in clinkers as the R polymorph, and belite as u l, ot n or a, according to the temperature. Chromy (C9) and Hofmanner (H21) discussed DTA curves of raw meals (Fig. 3.4). The main exotherm is due to belite formation, and the main endotherm to melting. A small... 

The methods that have proved effective for quantitative determination of phases in clinkers are based on light microscopy (Section 4.2.1), X-ray diffraction (Section 4.3.2) and calculation from the bulk chemical analysis. The last two of these are applicable also to cements. SEM with image analysis (Section 4.3.1) shows promise, but other methods that have been investigated, such as IR spectroscopy, appear to have little potential. Sections 4.4.2 to 4.4.5 describe a method of calculation from the bulk analysis and Section 4.4.6 compares the results of the various methods. 

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