EP2582641A1

EP2582641A1 - Method for producing a clinker for hydraulic cement with low co2 emission and high resistance

Info

Publication number: EP2582641A1
Application number: EP11734177.6A
Authority: EP
Inventors: Homero Ramirez Tovias; Juan Carlos Martinez; Norma Leticia Garza Gonzalez; Karla Serrano Gonzalez
Original assignee: Cemex Research Group AG
Current assignee: Cemex Research Group AG
Priority date: 2010-06-18
Filing date: 2011-06-17
Publication date: 2013-04-24
Also published as: CO6660444A2; WO2011158109A1; WO2011158105A1; US8715411B2; MX2012014995A; US20130152825A1; FR2961505A1; FR2961505B1; BR112012033789A2; CR20120633A

Abstract

The invention relates to a method for producing a clinker for cement, characterised in that it is obtained by grinding a raw flour comprising, especially, Al₂0₃, Fe₂O₃and SO₃ in contents (A) such that S0₃= 0.261A12O3 - 0.638Fe2O3 + k or 2.5<k<3.5, then by sintering said flour in an oven wherein the temperature is between 1250° and 1350° and the oxygen content is between 2.5 and 10 volume %.

Description

Process for the manufacture of a clinker for hydraulic cement with low CO 2 emission and high resistance.

Field of the invention

The present invention relates to a new family of clinker produced industrially containing the phases alite (C3S), belite (C2S), calcium suifoaluminate (C4A3S) and calcium ferroaluminate (C4AF) which, by its composition emits less amount C0 ₂ during its manufacturing a current Portland cement clinker, has a high level of compressive strength and is suitable for the manufacture of a new family of hydraulic cements.

Background of the invention

The present invention relates to the manufacture of clinker in industrial furnaces, during which lower amounts of CO ₂ are emitted and which by its nature makes it possible to obtain a higher mechanical strength and in particular its compressive component in hydraulic cements. .

Portland cement clinker is normally manufactured using an intimate pulverized mixture of limestone, clay, iron ore and other minor components, this mixture is exposed in a rotary kiln at temperatures above 1450 ° C, ensuring the formation of the phases at the origin of the required characteristics of the cements. These phases are alite (C3S), belite (C2S), calcium aluminate (C3A), calcium ferroaluminate (C3A), calcium ferroaluminate (C4AF) and other minor phases. The alite (C3S) mainly ensures the resistance properties, which normally keep values higher than 50%, by requiring large quantities of limestone and therefore generating a high level of C0 ₂ emissions.

It is important to remember that C0 ₂ emissions linked to an industrial process for the production of clinker for Portland cement are mainly due to two phenomena: the decarbonation of limestone which goes from CaCO ₃ to CaO then to CO ₂ and combustion during combustion. the carbon conversion of the latter into C0 ₂ , effectively combined with 1 Ό ₂ of air. In the past, efforts have been made to reduce C0 ₂ emissions by modifying the chemical and mineralogical composition of clinker and Portland cement; these modifications made it possible to eliminate the alite phase of the clinker and to increase significantly the belite content with conversion to a variant of clinkers and belitic cements

It is known that with Belitic clinker low reactivity cement is obtained and, consequently, low resistance to initial compression, although at advanced ages 28 days and more, the resistance becomes higher without ever being comparable to high-grade cements (C3S).

This low resistance to compression during aging makes it difficult to market this type of cement, since this characteristic does not meet the requirements of modern building construction and the quality standards of cement. An example of this technology for the production of belitic cements is described in US Pat. No. 5,599,962 of April 23, 1996, in which Fluvio J. Tang describes the method of producing a cement consisting mainly of belite alpha, a more reactive class of belite. that is not usually found in cements produced under normal conditions. Tang shows in this patent how the use of Na, K and Fe ions makes it possible to activate and fix this category of belite, by trying to improve the initial resistance of belitic cements.

Another example is British Patent GB2013648 of August 15, 1979 entitled "Cement Manufacturing Process", in which Richard Schrader explains how, using the same Portland cement production process, and with an appropriate formulation of raw flour, which normally employs less quantity of calcareous matter (CaCO 3), a belitic beta clinker is obtained at a temperature as low as 1350 ° C., the belite being activated by an appropriate cooling technique.

Suifoaluminate cements are the result of efforts by scientists and technologists to find an alternative to Portland cements. This type of cement consists mainly of the C4A3S (calcium sulphoaluminate) phase replacing the C3A and C3S phases in clinker and cement and reducing the emission of CO2. Generally, the proportion of C4A3S in this type of clinker exceeds 40%, requiring raw materials rich in alumina and sulphates to be able to form said phase. While it is certain that high sulphate (S04) materials are common, as in gypsum, anhydrite and other materials, alumina-rich raw materials are not usual and may be considered special, resulting in a high supply cost; bauxite is an example. In addition, the distribution of deposits is heterogeneous geographically.

This type of clinker and cement uses less CaCO3, because of its composition and its special formulation, resulting in a significant reduction of C02 emissions that can nevertheless reach 50% during the decarbonation process, depending on the raw materials used and of their formulation. This type of cement has the particularity of presenting a high initial resistance due to the formation of large quantities of ettringite (C6ASH32). However, being manufactured under special conditions of cost and production, its use has been reserved for special purposes such as repairs and pavements.

Another characteristic of these cements is the temperature level at which they are manufactured. As this temperature is below 1300 ° C, the energy consumption is lower, thus reducing CO2 emissions.

Some examples of this manufacturing technology are disclosed in US patents US 6149724, of November 21, 2000 and US 7150786, of December 19, 2006. In these documents, Ulibarri and Kunbargi present to us

respectively their processes for manufacturing high calcium cements of calcium suifoaluminate (C4A3S), with a small proportion of belite (C2S) and for Ulibarri with at least 1% alite (C3S), in order to obtain a high initial resistance during the reaction of calcium suifoaluminate C4A3S to form ettringite (C6ASH32), which also reduces the setting time. This cement is often used mixed with Portland cement in different proportions to improve its role.

In the two cases mentioned above, special raw materials are used, that is to say materials that do not require installation to produce Portland clinker or at least in amounts recommended by these inventors. Under these conditions, raw materials with very high levels of alumina (A1203) are required, which are generally rare and high economic value, resulting in a very high cost of production of this type of cement.

In recent years, another group of scientists has developed new cements using the technologies (belitic and suifoaluminous cements) previously described in this paper, to improve the role of belitic cements, as well as the perception on the market of obtaining cements of this type with a slow evolution of compressive strength. Another example of this case is represented by US patent application US 2007/0266903, of November 22, 2007, in which Ellis Gartner shows us how a belitic cement, prepared with a clinker manufactured at a temperature of between 1150 and 1350 ° C. , composed mainly of alite-free alpha (C3S) grade, and the formulation of which uses a series of minor components, is enhanced by mixing it with calcium suifoaluminate (C4A3S). In this In this case, this component is incorporated in order to activate the belite and to increase the initial resistance, which is usually very low when using only a belitic cement. Description of the invention

The object of the present invention is to solve the technical problems posed by prior clinker compositions by proposing a process for the industrial production of this new clinker and of a cement with a high content of alite (alitic) and of calcium suifoaluminate, by resorting to to raw materials generally used by Portland cement factories.

The cement of the invention is composed of alite (C3S) in a proportion of 30% to 70% by weight, of belite (C2S) in a proportion of 10% to 40% by weight of calcium suifoaluminate (C4A3S) in a proportion of 5% to 15% by weight and ferrite (C4AF) in a proportion of 1% to 7% by weight, for the main phases, and, if appropriate, anhydrite (CS) and C3A for the minority phases or components.

The manufacture of this clinker and cement uses common raw materials already used in factories producing clinker and Portland cement, such as limestone, clay, kaolin, gypsum, fluorite (CaF2) and others. Its formulation frees itself from rare materials, such as bauxite and aluminous clays, which are difficult to obtain and generally of high commercial value. Fluorite is added to lower the temperature of the eutectic for the formation of liquid phases during clinkerization and to lower the required energy level. The the amount of fluorite is between 0.1% and 1.5% by weight and preferably between 0.2% and 1% by weight.

The formulation of this new clinker makes it possible to use a lower proportion of limestone and to have formulations of raw flour which, once calcined, generates less CO 2 during the decarbonation process. The sintering temperature of this clinker also decreases, since the temperatures of 1400 ° C. to 1450 ° C. normally used to manufacture the Portland clinker are lowered between 1250 ° C. and 1350 ° C. for the clinker of the invention, which reduces the amount of fuel needed and, therefore, CO2 emissions. The mechanical properties of this new cement made with the clinker of the invention improve the compressive strength at all ages of the product, from the first hours to 28 days and it is not uncommon to see increases in strength ranging from 25 at 50%.

The manufacture of this new clinker involves adaptations of the operating parameters of the rotary kilns used for the development of the product. The regulation of the temperature in the furnace and the content of O 2 (oxygen) in it are important parameters of the process for fixing the sulfur in the clinker by forming the calcium suifoaluminate (C4A3S), thus avoiding the formation of concretions in the furnace. the preheater and rings in the oven, common phenomena if we use materials rich in sulfur. Detailed description of the invention.

The present invention allows the alite (C3S) and calcium suifoaluminate (C4A3S) phases to coexist in a clinker, thereby producing high alite (C3S) and calcium suifoaluminate (C4A3S) cements. This alite content is an important difference with belitic cement technologies, suifoaluminous cements, and the combination of both technologies, where there is usually no alitis. In the invention, the coexistence of the alite and suifoaluminate phases is possible thanks to a rigorously controlled production process.

The raw materials used in the production of this new clinker are commonly available in cement plants where conventional Portland gray clinker is made and in their supply quarries. These raw materials generally comprise limestone (CaCO ₃ ), clay, kaolin or any material containing SiO ₂ and Al ₂ O ₃ and a sulfur material necessary for the formation of the calcium suifoaluminate phase, namely gypsum, natural anhydrite, gas desulphurisation ash, hydrofluoric acid industry residues, etc. The proportion of materials constituting the raw meal is defined according to clinker-specific control modules, namely the lime saturation factor (FSC), between 91 and 96, the silicic modulus (S), between 2 , 0 and 5.0, and the alumina modulus (AM), between 2.7 and 22, and strongly depends on the iron content of the materials employed.

The value of the lime saturation factor has a direct effect on the clinker content of free calcium oxide, due to the heat energy required for phase formation mineralogical compounds combining calcium ions with silica, alumina and iron, as shown in Figure 1.

The method of formulation of the raw or raw flour according to the invention makes it possible to reduce both the quantity of limestone and the quantity of fuels since the temperature at which the clinker is sintered is of the order of 1250 ° C. to 1300 ° C. C, resulting in a significant decrease in C0 ₂ emissions. An essential element in the formulation of raw flour is the content of SO ₃ : this is determined from stoichiometric calculations in which the amount of aluminum is considered equal to the total quantity of aluminum available for the formation of sulphoaluminate. of calcium, namely, the amount likely to react with iron oxide, to which is added an additional factor representing a slight excess of SO ₃ in the clinker and intended to improve both the stabilization of calcium suifoaluminate than obtaining a low content of free lime. The calculation formula (A) for the content of SO 3 available in the raw meal and in the fuel is written; according to the invention,

S03 = 0.261 X Al 2 O 3 - 0.638 X Fe 2 O 3 + k with 2.5 <k <3.5 and, preferably, 2.75 <k <3.25.

In the considered raw flours, the Fe 2 O 3 and Al 2 O 3 contents are in the following respective ranges (the% being by weight) of 0.5% to 2% and 3% to 10%. The clinker production process includes: grinding of raw flour, oven feeding, precalcination and the sintering of the raw flour, the cooling of the clinker and the grinding of the cement.

The grinding of the raw meal consists in the introduction of the preconcassed and mixed materials into the mill in appropriate proportions, making it possible to obtain particles retained by the sieve 200, in order to optimize the combustion in the oven, that is to say ie the conversion of all calcium oxide into mineralogical phases of silicates and calcium aluminates. The value of the FSC influences the degree of combustion of the raw product, as shown in Figures 2A and 2B.

During the feeding of the preheat tower in raw meal, it is necessary to control the temperature to facilitate the decarbonation process of the calcareous material included in the raw material while maintaining the evaporation of the volatile components (S0 ₃ , mainly) at same level and without hindering the operation of the oven by deposits in the preheater pipes or inside the oven. Controlling the evaporation of SO 3 in the furnace is the key to a stable and continuous operation. The evaporation control is based on the monitoring of the material retained in the fourth stage of the preheater, an area in which volatiles tend to concentrate (mainly, SO 3, Na 2 O, K 2 O). The combustion loss of said material is determined and the SO 3 evaporation in the furnace is calculated by the following formulas:

Evaporation of S03 in the furnace = _(BI S03 - S03 LK _C) / S03 _B i

S03 Bi = SO3 igneous base = S03 _IV X (100 / (100- P. Ign _IV )) Where S03 CLK is the material retained in the clinker and P. Ign rv the combustion loss determined at 950 ° C in the material of the fourth stage of the preheater. As described, the SO 3 content in the raw meal plays a predominant role in the invention. An insufficiency of SO 3 available, as shown in Examples 4 and 5 as a function of the contents of A1303 and Fe 2 O 3, will result, on the one hand, by an increase in the free lime CaO in clinker which according to the general practice of quality should not be higher than 1.5% and, on the other hand, does not promote the formation of desired calcium suifoaluminate levels. The clinkers according to the invention are therefore characterized by an excess of SO 3 according to equation (A), which makes it possible to guarantee the formation of the optimal amounts of calcium suifoaluminate while maintaining in the final clinker an amount of CaSO 4 anhydrite of between 3% and 10% by weight depending on the level of calcium suifoaluminate likely to form according to the levels of Al 2 O 3 and Fe 2 O 3 in the raw meal.

A controlled excess of available SO 3 makes it possible to promote the presence of CaSO 4 (anhydrite) in the final clinker with contents of 3% to 10% by weight, which have several advantages:

An excess of S3 in the form of CaSO3 in the raw meal or during the clinkering (sintering) makes it possible to maintain an excellent industrial operability at low temperature by promoting the mineralization of the mixture and by maintaining good fluidity and viscosity of the liquid phase which is formed, thereby obtaining a homogeneous final clinker and avoiding any problem of transporting the material in the treatment furnace. Anhydrite forming at temperatures above 800 ° C exhibit an allotropic form poorly soluble in water. The presence of anyhydrites thus makes it easier to regulate the additions of sulfur necessary to form cement from the clinker, acting as setting regulators.

Conversely, the SO 3 content is an essential element of the raw clinker flour, but too high values are detrimental to the mechanical properties of the cements produced, in particular by reducing the mechanical resistance to compression at 1 day and 7 days.

The evaporation must be controlled, ensuring that it does not fall, for example, below 40%, in order to avoid losses of sulfur.

In addition to the temperature, the oxygen content in the furnace is another critical parameter to control to avoid problems of deposition or formation of rings of sulfur. A suitable oxygen content in the furnace facilitating complete combustion and a strongly oxidizing atmosphere, in which the SO ₃ can be retained in the clinker and extracted from the furnace, is typically between 2.5% and 10% by volume in the furnace. oven atmosphere and preferably between 4% and 8%.

Unlike the conventional clinker production process, to obtain the product proposed in the present invention, it is necessary to control the sintering or clinkerization by acting on the rate of S0 ₃ retained, that of free lime and the mineralogical composition of the clinker.

Calcium sulfoaluminate is formed in a temperature range of 1000 ° C to 1250 ° C in which CaO, Al 2 O 3 and CaSO 4 present in the system combine and react. The monitoring of the presence of calcium suifoaluminate is carried out only in the laboratory by X-ray diffraction on the clinker produced in order to confirm that the alumina determined in the chemical analysis is combined in the mineralogical phase of interest. If the temperature is insufficient, 1Ά1203 stabilizes as calcium aluminate (C12A7) at about 1000 ° C, and not as calcium suifoaluminate, reactive phase for the development of compressive strength at advanced ages of the material and SiO 2 as Belite, and not as bedridden. In the case where the temperature is above 1250 ° C - 1300 ° C, SO3 evaporates by decomposing to C3A in C4A3S. The clinker obtained contains between 30% and 70% of C3S, 10% and 40% of C2S, 4% and 30% of C4A3S, 5% and 15% of C3A, and between 1% and 7% of C4AF and 3% 10% by weight CaSO 4 (anhydrite). As a result, unlike other low temperature clinkers containing the calcium sulphoaluminate active phase, the present invention contributes to the formation of an alitic clinker. Examples

EXAMPLE 1

The composition of a low carbon clinker comprises 73% limestone, 22% kaolin, in addition to promoters promoting the formation of low temperature clinker phases. The chemical analysis of clinker obtained is presented below:

An adequate control of the sintering temperature in the rotary kiln and its cooling, preferably by a grid heat exchanger makes it possible to obtain the mineralogical composition of the clinker, taking as basis the Bug equations for the potential phases:

NOTE: The distinction of the C3A and C4A3S phases is made by X-ray diffraction, which explains why the aluminum taken into account to calculate the potential phases of C4A3S and C4AF is free after formation of the C3A quantified by the Rietveld method. (by X-ray diffraction). In cement preparation, the S03 to be used is defined by the maximum compressive strength over 24 hours. Once the S0 ₃ content of the 7.3% cement was determined to obtain its optimum reactivity in this particular case, and after grinding of the 96% sieve material of 325, the compressive strengths on cubes of 2 "

(inches) mortar; the corresponding results are presented below:

EXAMPLE 2

Using 71.2% of limestone, 10.2% of a material rich in Al ₂ 0 ₃ , 11.5% of aluminous kaolin and clinker phase-promoting agents, crude flour is obtained which When heated at 1350 ° C in a rotary kiln, produces a low carbon clinker, the chemical composition of which is as follows:

After having confirmed by the X-ray diffraction technique the stabilization of calcium sulphoaluminate in the clinker, the potential phases of the clinker are calculated using the Bug equations, giving the following results:

Phase Uni Value

you

Alite o,

o 40

Belite% 32

Suifoaluminate of% 10

calcium

Aluminate of ¾,

o 1

calcium

Ferroaluminate of% 3

calcium

Anhydrite% 7

Free lime

o 1

NOTE: The distinction of the C3A and C4A3S phases is made by X-ray diffraction, which explains why the aluminum taken into account to calculate the potential phases of C4A3S and C4AF is free after formation of the C3A quantified by the Rietveld method. (by X-ray diffraction).

The clinker obtained made it possible to produce at industrial level in a ball mill, the cement with 6.4% of S0 ₃ determined as optimum for obtaining resistances with 96% passing through sieve d 325 and a surface of 4570 cm ² / g defined by the Blaine method.

The following resistances to compression were obtained in the mortar:

EXAMPLE 3

In the laboratory, a clinker is sintered using 75.7% limestone, 17.5% residual material rich in Al 2 O 3, and the promoter components of the clinker phases at low temperature; the material obtained has the following chemical composition:

Clinker analysis by ray diffraction technique

X confirms that virtually all of the aluminum is combined to form calcium sulphoaluminate, and that there is no C3A formation but only C4AF that stabilizes due to the Fe203 content in the raw meal. The mineralogical composition of the resulting clinker is as follows: Phase Uni Value

you

Alite% 33

Belite% 34

Suifoaluminate of 13

calcium

% 1 Aluminate

calcium

Ferroaluminate of 3

calcium

Anhydrite 9

Free lime 1

NOTE: The distinction of the C3A and C4A3S phases is made by X-ray diffraction, which explains why the aluminum taken into account to calculate the potential phases of C4A3S and C4AF is free after formation of the C3A quantified by the Rietveld method ( by X-ray diffraction).

The compression strengths on 2 "mortar cubes after 24 h determined that the optimal S03 content was 9% for this clinker, and obtained the following compressive strengths:

EXAMPLE 4 - Relation between S03 in raw meal and free lime in clinker

CAD free lime is maintained at high levels above 2% as long as the S03 content of the raw meal does not exceed a certain threshold. When the level of SO 3 in the raw meal reaches the recommended levels according to the formula (A) of the invention as a function of the levels of iron and alumina, (in this case 2.8%) the level of free lime in the clinker reaches acceptable values, as shown in Figure 3.

Composition of raw flour

4.9

Fe ₂ 0 ₃ 2.3

S0 ₃ according to

equation (A)% 2.8

% Clinker Clinker Clinker Clinker Weights 4A 4B 4C 4D

S0 ₃ flour

raw 1.6 2.0 2.5 2.8

Free lime

in the

clinker% 2.1 2.1 1.7 1.3 C4A3S in

clinker 2.0 4.1 5.4 5.8

EXAMPLE 5 Relation between S03 in Raw Flour and the Suifoaluminate Content in Clinker

It is found that the level of C4A3S that stabilizes in the clinker is also a function of the SO 3 content in the raw meal and that the levels above 7.5% are obtained with the recommended level of S03 in the raw meal according to the equation ( A) as shown in Figure 4.

Composition of raw flour

A1O3 4.9

Fe ₂ 0 ₃ 2.3

S0 ₃ according to (A) 2.8

% Clinker Clinker Clinker Clinker Weight 5A 5B 5C 5D

S0 ₃ raw flour 1.5 1.9 2.3 3.1

Free lime

in the

clinker 1.7 1.4 1.2 1.2

C4A3S in the

clinker 3.5 5.6 7.0 7.9

Claims

1. A method for producing a cement clinker characterized in that it is obtained by grinding a crude flour comprising, in particular, Al ₂ O ₃ , Fe ₂ O ₃ and S0 ₃ in levels (A). ) such that S03 = 0.261A12O3 - 0.638Fe2O3 + k where 2.5 <k <3.5 then by sintering said flour in an oven where the temperature is between 1250 ° and 1350 ° and the oxygen content is between 2.5% and 10%. % in volume.

2. Method according to claim 1 characterized in that the A1203 content is between 3% and 10% by weight and the Fe203 content between 0.5% and 2% by weight.

3. Method according to claim 1 or 2 characterized in that the oxygen content in the oven is between 4% and 8% by volume.

4. Clinker composition obtained by the method according to one of claims 1 to 3, characterized in that it comprises:

from 30% to 70% by weight of alite (C3S),

from 10% to 40% by weight of belite (C2S),

from 5% to 15% by weight of calcium suifoaluminate (C4A3S),

from 1% to 7% by weight of ferrite (C4AF)

from 3% to 10% by weight of anhydrite (CS)

the remainder being lime and / or C3A.

5. Composition according to claim 4 characterized in that it further comprises from 0.1% to 1.5% by weight of fluorite (CaF2).

6. Composition according to claim 5 characterized in that it comprises from 0.2% to 1% by weight of fluorite (CaF2).