RU2752767C1 - Method for producing white cement clinker - Google Patents

Abstract

FIELD: construction materials industry.SUBSTANCE: invention relates to methods for producing white cement clinker and can be used in the construction materials industry. The method for producing white cement clinker includes the preparation of a raw material mixture, the supply of a mineralizer, the baking of the raw material mixture with a mineralizer in a rotating furnace of the dry production method and the sharp cooling of the white cement clinker in water. Moreover, the raw material mixture is mixed with the dust of dust-collecting devices before baking, and baking occurs at a temperature of 1250-1350°C, and a dust-like mineralizer 2C2S·CaF2in an amount of 1.5-11% is fed into the rotating furnace of the dry production method through the dust nozzle in the amount of 1.5-11% to the temperature range of the material 845-1255°C, while the angle between the horizontal axis of the cross-section of the rotating furnace of the dry production method and the line passing through the axes of the dust nozzle and the fuel nozzle is 30-90°, the distance between the axles of the fuel nozzle and the dust nozzle is 250-2500 mm, the distance to which the dust nozzle is extended relative to the fuel nozzle is 0-2000 mm, the angle of inclination of the dust nozzle axis relative to the fuel nozzle axis is 0-30°.EFFECT: decrease in the baking temperature of white cement clinker, an increase in its whiteness, the stability of the quality characteristics of white cement clinker, the performance of rotating furnaces of dry and combined production methods, a decrease in the specific fuel consumption for baking white cement clinker.1 cl, 3 dwg, 2 tbl

Description

The invention relates to methods for producing white cement clinker and can be used in the building materials industry.

A known method of producing white Portland cement (cement), according to which, in order to increase whiteness, an additive of calcium nitrite-nitrate is introduced into the raw mixture before firing [USSR author's certificate for invention SU No. 307989].

The disadvantages of this method are low productivity, high specific fuel consumption and insufficient bleaching efficiency (whiteness increases by only 3-4%). The use of calcium nitrite-nitrate as a mineralizer causes an increase in emissions of harmful nitrogen oxides into the atmosphere during firing.

The known method, in which, in order to increase the whiteness of white cement clinker and intensify the firing process, a sodium silicofluoride mineralizer is introduced into the original raw mixture. [Grachyan A.N., Gaydzhurov P.P., Rotych N.V. White Portland cement technology. M .: Stroyizdat, 1970. - S. 15].

The disadvantage of this method is the low efficiency of bleaching and insufficient reduction in the firing temperature.

The closest solution to the technical essence, taken as a prototype, is a method of producing clinker for white cement, carried out by a dry method of production. According to this method, in order to reduce fuel consumption and reduce the firing temperature of white cement clinker, 0.4% of calcium fluoride is added to the raw mixture [Smart B. Increase the production of white cement / B. Smart // Cement and its application. - 1997. - No. 3. - P. 16].

The disadvantage of this method is that the use of the CaF ₂ mineralizer according to this method does not lead to an increase in the whiteness of the white cement clinker.

The invention is aimed at reducing the firing temperature of white cement clinker, increasing its whiteness, increasing the stability of the quality characteristics of white cement clinker, increasing the productivity of rotary kilns of dry and combined production methods, reducing the specific fuel consumption for firing white cement clinker.

This is achieved by the fact that the method for producing white cement clinker includes preparing a raw mixture, feeding a mineralizer, roasting the raw mixture with a mineralizer in a rotary kiln of the dry method of production, and quenching the white cement clinker in water. Wherein the raw material mixture before firing is mixed with dust dedusting devices, calcining occurs at a temperature of 1250-1350 ° C and the rotary kiln dry process is supplied through a dust burner pulverized mineralizer 2C ₂ S·CaF ₂ in an amount of 1,5-11% to temperatures of the material 845-1255 ° C, while the angle between the horizontal axis of the cross-section of the rotary kiln of the dry method of production and the line passing through the axes of the dust nozzle and the fuel nozzle is 30-90 °, the distance between the axes of the fuel nozzle and the dust nozzle is 250-2500 mm, the distance the dust nozzle is extended relative to the fuel injector is 0-2000 mm, the tilt angle of the dust nozzle axis relative to the fuel injector axis is 0-30 °.

A dust-like mineralizer 2C is used as a mineralizer.₂S CaF_2.It can be obtained by three-time firing of a mixture of reagents of "pure" grade: CaCO₃, SiO₂, CaF₂ at a temperature of 980 ° C. [D2. Mishin D.A., Kovalev S.V., Chekulaev V.G. Influence of the method of introducing a mineralizer on the strength characteristics, morphology and color of Portland cement clinker. Journal "Cement and Its Application". No. 4, 2016. - P. 114] or by firing a mixture consisting of natural components at a temperature of 950-1040 ° C: a carbonate component with a titer of at least 95% and a Fe content₂O₃ no more than 4% (limestone, marble, chalk, etc.); silica-containing component with SiO content₂ not less than 90% and Fe content₂O₃ no more than 2% (quartz sand, marshal, etc.); component containing calcium fluoride with CaF content₂not less than 75% (fluorspar not lower than FC-75 in accordance with GOST 29220-91, calcium fluoride "technical" and "pure"). The content of free calcium oxide after firing must not exceed 5%.

As an initial raw material mixture, a mixture is used to obtain white cement clinker, consisting of a carbonate component with a low Fe ₂ O ₃ content (for example, chalk from the CJSC Belgorodsky cement deposit) and a clay component with a low Fe ₂ O ₃ content (for example, kaolin from the deposit Zhuravliny Log). The characteristics of raw materials and raw mixtures based on them are presented in table. 1, where: LOI is the loss on ignition of the raw mixture; R ₂ O - the content of Na ₂ O and K ₂ O in terms of Na ₂ O; КН - saturation coefficient; n - silicate module; p - alumina module.

Table 1.

Characterization of the starting components and raw mix for the production of white cement clinker.

Modules Chemical composition, wt. % KN n p 0.9 3.63 21.75 RFP SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ CaO MgO SO ₃ R ₂ O Other Chalk CJSC "Belgorodsky cement" 42.40 1.86 0.38 0.14 54.74 0.23 0.01 0.08 0.16 Kaolin "Crane Log" 7.45 71.18 19.23 0.36 0.07 0.43 0 0 1.28 Raw mix 35.78 15.00 3.95 0.18 44.38 0.27 0.01 0.06 0.37

The invention is illustrated by a drawing, where FIG. 1 shows a schematic diagram of a rotary kiln for dry production; in fig. 2 is a cross-sectional view of a dry-process rotary kiln oven; in fig. 3 shows a longitudinal section of a dry-process rotary kiln.

According to the claimed method (Fig. 1), the raw mixture is mixed with the dust of the dust-collecting devices in the raw meal silo 1, from where it is fed into the gas duct between the I and II stages of the cyclone heat exchanger system 2. Through the cyclone heat exchanger system 2, the raw mixture enters the housing 3 of the rotary kiln of the dry method production. The raw mix moves from the cold edge of the dry-process rotary kiln to the hot edge. A fuel nozzle 4 and a dust nozzle 5 are installed on the hot edge of the rotary kiln of the dry method of production, which serves to supply the dust-like mineralizer 2C ₂ S · CaF ₂ to the rotary kiln of the dry method of production.

The position of the nozzle in the dry-process rotary kiln is illustrated in FIG. 2 and FIG. 3 and is described by the following parameters:

And - the angle between the horizontal axis of the cross-section of the rotary kiln of the dry method of production and a line passing through the axes of the dust nozzle 6 and the fuel nozzle 5;

B, C - displacement of the fuel injector 5 relative to the vertical and horizontal axis of the rotary kiln of the dry production method, respectively;

Г - the distance between the axes of the fuel 5 and dust 6 nozzles;

D is the distance by which the dust nozzle 6 is extended relative to the fuel nozzle 5;

E is the angle of inclination of the axis of the dust nozzle 6 relative to the axis of the fuel nozzle 5.

The method of producing white cement clinker is carried out as follows. The prepared raw mixture with a moisture content of about 1% is fed into the raw meal silo 1, where the dust from the dust collectors of the rotary kiln of the dry production method is supplied. In the raw meal silo 1, the raw mixture and the dust of the dust collecting devices are mixed. Further, the raw mixture is fed through a system of cyclonic heat exchangers 2 to the body 3 of a rotary kiln of the dry method of production from the cold edge. The body 3 of the rotary kiln of the dry method of production is a rotating steel drum with a slope of 3.0-4.5%. The drum rotation speed is 2-4 rpm. Due to the inclination and rotation of the drum, the raw mixture moves from the cold edge of the dry-process rotary kiln to the hot edge of the dry-process rotary kiln. In this case, there is a gradual heating of the raw mixture and its physical and chemical transformations. From the hot-trimming the rotary kiln dry process set 4 and the fuel injector nozzle 5. The dust through the dust nozzle 5 fed pulverized mineralizer 2C ₂ S·CaF _2, previously ground until a residue on sieve №02 not more than 5% residue on sieve №008 no more than 20%. Depending on the size of the rotary kiln of the dry method of production for feeding the dust-like mineralizer 2C ₂ S · CaF ₂ to the material temperature range 845-1255 ° C, the position of the dust nozzle 5 should have the following parameters: A = 30-90 °; B = B = 150-250 mm; D = 250-2500 mm; D = 0-2000 mm; E = 0-30 °. The outflow velocity of the jet of the dust-like mineralizer 2C ₂ S · CaF ₂ should be 30-150 m / s. Dusty mineralizer 2C ₂ S · CaF ₂ is introduced in the amount of 1.5-11%. Firing of white cement clinker is carried out at a temperature of 1250-1350 ° C. The temperature of the exhaust gases is 250-380 ° C. The content of R ₂ O in white cement clinker should not exceed 1.2%. Water cooling of white cement clinker.

The most important factor in increasing the whiteness of white cement clinker is to prevent crystallization of calcium aluminoferrites and the introduction of iron ions into the structure of silicate phases [D3 Zubekhin AP, Golovanova SP, Kirsanov PV. White Portland cement / Ed. A.P. Zubekhin. - Rostov n / a: Ed. f. "Izv. universities. North Caucasus. Region "2004. - P. 66]. Due to the return of dust from the dust collection devices in the rotary kiln of the dry method of production, there is a circulation and accumulation of alkali metal salts, [D4 - Klassen, V.K. Roasting of Portland cement clinker / V.K. Klassen. - Krasnoyarsk .: Stroyizdat, Krasnoyarsk. otd., 1994. - S. 12], which leads to an increase in the content of R ₂ O in white cement clinker. In the presence of R ₂ O bound with an oxygen-containing anion, at a firing temperature of up to 1250-1300 ° C, instead of calcium alumoferrites, sodium and potassium alumoferrites are formed according to the scheme

1) 4CaO Al ₂ O ₃ Fe ₂ O ₃ + R ₂ O → R ₂ O Al ₂ O ₃ + 2CaO Fe ₂ O ₃ + 2CaO

2) 2CaO Fe ₂ O ₃ + R ₂ O → R ₂ O FeO ₃ + 2CaO

3) R ₂ O · Al ₂ O ₃ + R ₂ O · Fe ₂ O ₃ → R ₂ O · (Al, Fe) ₂ O ₃ .

Sodium and potassium alumoferrites have a lower coloring ability and do not allow iron bound in sodium and potassium alumoferrites to penetrate into the structure of silicate phases. This leads to an increase in the whiteness of the white cement clinker. With an increase in temperature above 1300-1350 ° C, sodium and potassium alumoferrites lose R ₂ O with the formation of alumoferrites of the intermediate composition R ₂ O · nAl ₂ O ₃ · mFe ₂ O _3. With a further increase in temperature, sodium and potassium alumoferrites are destroyed. As a result of the release of Fe ₂ O ₃ from the bond with R ₂ O, calcium aluminoferrites begin to form, and Fe ₂ O ₃ is introduced into the structure of silicate phases. This leads to a sharp decrease in the whiteness of the white cement clinker. The introduction of the dust-like mineralizer 2C ₂ S · CaF ₂ into the material temperature range of 845-1255 ° C allows the firing temperature to be reduced to 1250-1350 ° C while preserving sodium alumoferrites. The limitation on the content of R ₂ O in white cement clinker, no more than 1.2%, is justified by the recommendations of world cement manufacturers [D5 L. Zongshou, X. Weihong, C. Wei. Cementitious materials science: theories and applications. Gruyter, Walter de GmbH, Edition 1, 2019, P. 39]. An increase in the R ₂ O content over 1.2% leads to a decrease in the strength of the cement.

The minimum Fe ₂ O ₃ content is one of the conditions for achieving high whiteness. To show the possibility of using the claimed method for obtaining white cement clinker of high whiteness at low and high content of Fe ₂ O ₃ in it, the initial raw mixture (composition is presented in Table 1) was corrected for Fe ₂ O ₃ to obtain the compositions of the raw mixture, when fired, white cement clinker is obtained, containing 0.28; 0.5; 0.7% Fe ₂ O _{3. A} qualitative assessment of the claimed method was carried out according to the content of free calcium oxide (CaO _sv ) in the white cement clinker, the degree of whiteness, assessed by the brightness coefficient of the white cement clinker fired at control temperatures (t _fired ), as well as by the compressive strength of white cement clinker cement measured in small samples of plastic cement paste at the age of 28 days (R _comp ). The composition of the raw mixes and the characteristics of white cement clinker based on them are presented in table. 2.

table 2

Characterization of white cement clinker obtained from mixtures by conventional and declared methods.

No. Raw mix composition Fe ₂ O ₃ content in clinker,% t _fridge , ° С CaOs content. in clinker,% Clinker whiteness,% R _compressed , MPa one Raw mix without additives 0.28 1500 0 79 43.83 2 Raw mix + 1.2% Na ₂ O 1500 0.72 79.5 48.06 3 Raw mix + 1.2% Na ₂ O + 8.11% 2C ₂ S CaF ₂ 1300 2.21 89 45.73 4 Raw mix without additives 0.5 1500 0 70 49.33 five Raw mix + 1.2% Na ₂ O 1500 0.48 69.5 48.11 6 Raw mix + 1.2% Na ₂ O + 8.11% 2C ₂ S CaF ₂ 1300 0.83 83 49.75 7 Raw mix without additives 0.7 1500 0 62 42.49 eight Raw mix + 1.2% Na ₂ O 1500 0.34 62 44.46 nine Raw mix + 1.2% Na ₂ O + 8.11% 2C ₂ S CaF ₂ 1300 0.61 78 44.13

Samples of white cement clinker without the introduction of a dust-like mineralizer 2C ₂ S · CaF ₂ (No. 1, No. 2, No. 4, No. 5, No. 7, No. 8 of Table 2) were fired at 1500 ° C. Firing white cement clinker samples without a dust-like mineralizer 2C ₂ S · CaF ₂ at temperatures below 1500 ° C leads to a high content of CaOf, which is unacceptable. Samples of white cement clinker, obtained by introducing a dust-like mineralizer 2C ₂ S · CaF _{2 by the} claimed method (No. 3, No. 6, No. 9 of Table 2), were fired at a temperature of 1300 ° C. According to the content of CaOf., When the dust-like mineralizer 2C ₂ S · CaF _{2 is} introduced by the claimed method, it can be concluded that at a temperature of 1300 ° C, the processes of clinker formation are completed. This allows the firing temperature to be reduced. There is an increase whiteness samples obtained pulverized input mineralizer 2C _{2 2} S·CaF the inventive method relative to compositions without the pulverized mineralizer 2C ₂ S·CaF _2. Preparation of white cement clinker profiled whiteness becomes possible at higher Fe ₂ O ₃ content therein ( up to 0.7% Fe ₂ O ₃ ). The compressive strength of cement samples from white cement clinker obtained by introducing a 2C ₂ S · CaF ₂ pulverized mineralizer by the claimed method is not inferior to the strength of control white cement clinker samples without a 2C ₂ S · CaF _{2 pulverized mineralizer.}

Obtaining clinker by the claimed method can also be carried out in rotary kilns of the combined production method. Rotary kilns for dry and combined production processes can be additionally equipped with a calciner.

The use of the claimed invention will allow:

1) increase the whiteness of white cement clinker by 10-16% abs. without reducing the strength characteristics of cement based on it;

2) reduce the firing temperature of white cement clinker to 1250-1350 ° C;

3) to increase the stability of the quality characteristics of white cement clinker by increasing the stability of the rotary kiln, which is regulated by changing the amount of the supplied mineralizer;

4) increase the productivity of rotary kilns for dry and combined production methods by 10-15% by reducing the firing temperature of white cement clinker;

5) to reduce the specific fuel consumption for the burning of white cement clinker in a rotary kiln of the dry method of production by 10%, and in a rotary kiln of the combined method of production by 5-7% by reducing the firing temperature of white cement clinker and increasing the productivity of the rotary kiln.

Claims (1)

A method for producing white cement clinker, including preparing a raw mixture, feeding a mineralizer, roasting a raw mixture with a mineralizer in a rotary kiln of a dry method of production, and rapidly cooling white cement clinker in water, characterized in that the raw mixture is mixed with dust from dust collecting devices before firing in a rotary kiln , calcination takes place at a temperature of 1250-1350 ° C and the rotary kiln dry process is supplied through a dust burner pulverized mineralizer 2C ₂ S·CaF ₂ in an amount of 1,5-11% in the temperature range 845-1255 ° C the material, wherein the angle between the horizontal cross-sectional axis of the dry-process rotary kiln and the line passing through the axes of the dust nozzle and the fuel nozzle is 30-90 °, the distance between the axes of the fuel nozzle and the dust nozzle is 250-2500 mm, the distance the dust nozzle is extended relative to the fuel injector, is 0-2000 mm, the tilt angle of the axis is dusty howl of the injector relative to the axis of the fuel injector is 0-30 °.

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