Clinker reduction

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... 

Once the thermal runaway had become established, the high temperature could allow a smelting reaction (reduction of lead oxides by carbon to metallic lead) to occur, and the low m.p. and high density (327°C, 10.6, respectively) would cause the molten lead to concentrate at the base of the reactor, decreasing the lead content and raising the manganese content of the bulk of the clinker residue, as was observed [2],... 

Cement clinker Air Organosilicon (0.01-0.05 ) 70 reduction in grinding time... 

Utilization of different blended cements leads to the highest reduction of the CO2 emissions during the cement production. This is realised by replacement of a portion of clinker in cement by granulated materials. Blast-furnace slag, fly ash with accelerators were used as additive materials. Practical decrease of the CO2 emissions from both fuel and raw material can reach a reduction by 50% or even more [5]. 

The CO2 emission reduction from both the fuel combustion and calcination in intergriding clinker with extenders is directly equal to the amount of the extender. It is proved, that mixing moderate amount of limestone with clinker up to 10% has not detrimental effect, but some characteristics of cement are improved. Therefore there are several countries, allowing mixing up to 5% of limestone to portland cement. Applying 5 % of limestone, which replaces the clinker in cement shall reduce CO2 emissions by 0.05 ton CO2 per ton of cement [6]. 

After the rotating tube furnace, the burnt clinkers are immediately transferred to a cooler, to ensure rapid cooling. Slow cooling leads to a reduction in the tricalcium silicate content and to crystallization of the melt. Grate, tube and planetary coolers are used. The cooling air is then utilized in the calcination process. 

The government s consultancy had identified significant potential for emission reduction in the cement sector by means of reducing the clinker content of finished cement. 

Fig. 5.59 Specific surface of the build-up (= accretion) and of the free charge as well as amount of the build-up (= accretion quantity) with and without the use of a grinding aid during size reduction of cement clinker in a rod mill.

Fig. 5.61 Agglomerates produced during the grinding of limestone and cement clinker in a roller mill with a high reduction ratio.

Due to the lack of understanding for the flame behavior in cement clinker rotary kiln, the Cemflame I Consortium was set up by the most important European cement producers and combustion system manufacturers for financially supporting the IFRF, now located in Pisa and Fivorno Italy, to develop an experimental program to evaluate the primary reduction measures of NOx in this specific industry. 

The NO, reduction techniques applied in the cement clinker rotary kiln are generally classified as primary and secondary measures. The primary methods are applied to the main burner to prevent NO generation ... 

The system Ca0-Fe203 is binary only in the part rich in calcium oxide. The mixture rich in iron, even heated in air, easily lost the oxygen at higher temperatures with the magnetite formation, in which part of iron is reduced to Fe(ll). Obviously, the iron reduction is much quicker in reducing atmosphere and then in the clinker-ing process even metallic iron can be formed (see Sect. 2.3.2 and 9.2). 

The exceptional situation can take place in the case of fuel mixing with raw mix, then when the nodulization of material in the kiln will cause the closing of part of coal in the nodule core. In this condition, despite oxidation atmosphere in the kiln, the oxidation reaction of this part of coal will be exceptionally difficult and we ean observe the reduction phenomena in the clinker nodule core. It is occurring especially when on the nodules siuface the shells of hardly sintered material are formed. These phenomena were observed in the case of the LepoTs grate [76]. The classic example of the fuel addition to the feed are the shaft kiln, but they are applied exceptionally seldom. 

The influence of reducing atmosphere on phase composition and clinker properties was studies by several authors [76-81]. They state unanimously the gradual iron reduction, which leads to ferrite phase decomposition with C3A and free CaO formation. Fe can substitute Ca in all clinker phases, obviously in accordance with its solubility in individual phases. Frequently the tendency of clinker to seU-powdering, linked with Y-C2S formation is listed. 

The reaction of clinker phases with water, together with the crystalUzation of hydrates, brings about the substantial changes of rheological properties of the paste. The formation of hydrated phases and, according to Locher [28], the morphology of hydrates crystallized in the liquid phase or on the surface of cement grains, leads to the reduction of distance between them and the viscosity of paste is enhanced. At... 

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