SK288177B6 - Method for production of portland cement - Google Patents

Abstract

Method for production of Portland cement wherein by firing of raw material powder in arotating kiln from production of clinker having predominance of alite over belite (alitic clinker) containing 0.01 to 1.5 % by weight of P2O5 and by adjusting of chemical composition of the raw material powder through changing degree of lime saturation SLP from 100 to 72 and with use of material containing P2O5 or through changing degree of lime saturation SLP from 100 to 72, changing silicate module MS from 1.7 up to 3.5 using materials containing P2O5, the process is changed to produce clinker having predominance of belite over alite (belitic clinker) with content 0.01 to 3 % by weight of P2O5. In the same manner through an inverted process the process is changed from production of belitic clinker to production of alitic clinker and the cement is produced by common grinding of the both clinkers in the weight ratio according to the required final properties of the Portland cement.

Description

The invention relates to a method for producing Portland cement.

BACKGROUND OF THE INVENTION

Portland cement is produced by grinding cement clinker with solidification regulator (gypsum CaSO ₄ .2 H ₂ O, anhydrite CaSO ₄ , gypsum CaSO _4. 1/2 H ₂ O) optionally with additives and admixtures (according to European standard EN 197-1) , wherein the phase composition of the clinker is critical to the quality and properties.

Portland clinker is characterized by different chemical proportions of four major oxides of CaO (55 to 70%), SiO ₂ (16 to 26%), AlO ₃ (4 to 8%) and Fe ₂ O ₃ (2 to 5%), which at high temperatures they react with each other to form the main clinker minerals in amounts ranging from 50 to 85% alite (C ₃ S), 15 to 30% belite (C ₂ S), 5 to 15% C _{3 a} and 5 to 15% C ₄ AF (C = CaO, S = SiO ₂ , A = Al ₂ O ₃ , F = = Fe ₂ O ₃ ), with C ₃ A and C ₄ AF forming a spherical melt. In special cases, the composition of the clinker is modified to a reduced to zero content of C ₃ A, belite, or a reduced content of alite.

Portland clinker is e.g. defined in EN 197-1 that it must contain at least two-thirds of calcium silicates, alite and belite and the weight ratio C / S must not be less than 2.

The American standard ASTM C-150 even differentiates between Portland clinker based on its composition different types of Portland cements, namely: type I general purpose cement with an alite content of 50 to 65% and belite of 10 to 30%; high early strength type III cement with an alite content of 55 to 65% and belite of 5 to 25%, which are produced from high alite clinkers; and a low hydration heat type IV cement with an alite content of 35-45% and belite of 28-35%, which is produced from high belite-type clinkers.

The more common belite content in high-cement cements is just above 50% by weight. and an alite content of just above 20 wt. (T. Sui et al., Journal of Advanced Concrete Technology, Vol. 2, No. 2, pp. 201-206, 2004).

The production of Portland clinkers is a routine matter in existing cement plants. The problem arises with further increasing the belite content above 35%. Since belite is a phase with a lower strength increase than alite in order to be sufficiently active, it must stabilize in the high-temperature, well hydraulically active modifications of PC ₂ S and a'-C ₂ S. If the structure of high-temperature, active modifications of belite pC ₂ S and d-C ₂ S does not occur, undesirable modification to inactive yC ₂ S occurs (Taylor, HFW, Cement chemistry, 2nd edition, Thomas Telford Publishing, 1997, pp. 13-19 (ISBN 0 7277 2592 0)), which is associated with the clotting of the clinker (the Portland clinker is an irregular ball shape) into powdered yC ₂ S, which exhibits no hydraulic properties. The dust fraction cannot be processed technologically, because in the clinker cooler, which is designed for common spherical clinker, the dust fraction floats and returns to the furnace by pressurized cooling air, congesting the kiln system and making production impossible (Bye, G.C, Portland cement, edition, Thomas Telford Publishing, 1999, pp. 11-12 (ISBN 0 7277 2766 4). It is practically impossible to produce belitic clinker without stabilizing the high-temperature C ₂ S modifications and, due to no hydraulic activity of C ₂ S, is desirable.

In the solution of US 5509962, the active belite content increased to 88-94% by weight. and stabilized with 3 to 5 wt. % Fe ₂ O ₃ , 1 to 4 wt. % Na ₂ O and 1 to 4 wt. K ₂ O. Stabilization of high temperature active modifications of belite pC ₂ S a'-C ₂ with Na ₂ O and K ₂ O and Fe ₂ O ₃ alkali (US 5509962) is one way to prevent modification to yC ₂ S and to produce active Belgian clinker. However, the introduction of alkali into the furnace system and cements presents problems. Alkalis in firing in modern cementitious rotary kilns with a cyclone heat exchanger are a serious obstacle. their chlorides and sulphates cause sticking in the furnace system, reduced performance and clogging of the heat exchanger (SK 287017). Furthermore, increasing the alkali content of cements leads to an increase in the susceptibility of the aggregate to the alkaline-silica reaction in concretes, ie to the alkaline expansion of the aggregate and to the destruction of concrete, therefore the alkali content of Portland cements is limited to Na ₂ O + 0,658 K ₂ O <0,6% . (STN EN 206-1 / NA).

Increasing the proportion of belite in Portland cements need not only be achieved by increasing the proportion of belite in alitic clinkers or producing high-grade clinkers, but it is also possible to produce Portland cements by combining two types of separately produced clinkers, high-grade and high-grade.

In the solution according to JP 6048789, an ultra-low-exothermic blast-furnace cement type B is prepared by mixing 15 to 30 wt. % alite component with 50 to 75 wt. % of belite component, 4 wt. % C ₃ A and 6 to 18 wt. C ₄ AF and gypsum is added to the resulting cement clinker. % 40 to 60 wt. of the cement obtained, a pulverulent blast furnace granulated slag is added in an amount of 60 to 40% by weight, thereby achieving a significant reduction in the exotherm and preventing a reduction in the resistance of the cured concrete.

The solution according to JP 7215742 produces a cement with a low hydration heat evolution, lower than that

2886 Portland cement with a slight development of hydration heat, and the same development of initial strengths up to 7 days as for Portland cement with a slight development of hydration heat. Low heat hydration cement is a mixture of 60 to 90% belite-type cement with a C ₂ S content above 50% and an alite type of cement with a Blain surface area above 4000 cm ² / gas with a C ₃ S content above 50% 40% C ₂ S and above 5 wt. C ₃ S.

The solution according to JP 8175854 provides a low-exothermic cementitious composition having low heat build-up and high initial strength by mixing and grinding belitic cement clinker and alitic cement clinker together with gypsum in a specified weight ratio. Belitic cement clinker containing mainly belite is mixed in an amount of 30 to 90 wt. % with 70 to 10 wt. alitic cement clinker containing mainly alite and grinding. The resulting mixture contained below 8 wt. C ₃ A and achieves the same thermal and strength properties as traditional two-component or three-component mixtures based on finely ground blast furnace granulated slag or fly ash with excellent stability and quality.

The solution in JP 2007223819 relates to high strength belite mixed cement and methods for producing high strength concrete products from the cement. The belite mixed cement is prepared by mixing a cementitious composition consisting mainly of alite and a cementitious composition consisting mainly of belite having a specific surface area of 5000 to 9000 cm ² / g.

Phosphates are found at levels up to 0.2 wt. P ₂ O ₅ . Phosphates influence the development of the clinker phases during firing, the onset and setting times of cements, as well as the development of cement strengths. Increasing the content of phosphates in the clinker, in particular above 1 wt. P ₂ O ₅ has a negative effect on the early strength increase since phosphates reduce the alite content by stabilizing belite (Puntke, S. and Schneider, M., Cement International, Vol. 6, No. 5, pp. 81-93,2008).

In the areas of CSP equilibrium diagrams (P = P ₂ O ₅ ) with a high content of P ₂ O ₅ , belites are stabilized to the extent that alite is not formed by the reaction of belite and free lime. Solid solutions of belites in the C ₂ S - C ₃ P series are stabilized at room temperature in high-temperature modifications β, ï and a (Salge, H. and Thormann, P., Zement-Kalk-Gips, No. 11, pp. 532-539) , 1973).

In the case of belite stabilized with P ₂ O ₅ , the hydraulics of d-C ₂ S was even higher than in the case of PC ₂ S (Matkovic, B. and Young, J., F., 8 ^, International Congress on Chemistry of Cement, Rio de Janeiro, Brasil, Vol. II, pp. 276-281 (1986).

a'-C ₂ S with P ₂ O ₅ exhibits higher hydration heat than pC ₂ S when hydrated, but PC ₂ S starts to hydrate considerably earlier than a'-C ₂ S (Muller, R., Neubauer, J. and Gotz- Neunhoeffer, F., 1l ^, International Chemistry on Cement, Durban, South Africa, pp. 1043-1053, 2003). The aC ₂ S modification did not exhibit hydraulic capabilities.

In the case of alite, P ₂ O ₅ phosphates promote the formation of M1 polymorphic form C ₃ S, which has better hydraulic properties and higher development of initial strengths than the second polymorphic form M3-C ₃ S from alite modifications commonly found in clinkers, which may increase cement pressure by up to 10% (Stanék, T. and Sulovsky, P., Cement and Concrete Research, Vol. 32, pp. 1169-1175,2002).

SK 286 325 describes a solution which can reduce the inhibitory effect of P ₂ O ₅ on the formation of clinker phases, in particular alite, and thereby produce a high-grade cement clinker with an increased phosphorus content without adversely affecting the cement quality. The high-alkaline clinker with an increased phosphorus content and a reduced P ₂ O ₅ inhibitory effect according to the solution of SK 286 325 normally achieves a high alite content, several times higher than that of belite, as disclosed in SK 4488U. Solution E 286 325 relates to the production of cement clinker vysokoalitického with increased content of P ₂ O ₅ with the use of phosphorus-containing materials. However, the content of P ₂ O ₅ in alitic clinker can only increase to a level at which the qualitative properties of cements due to excessive reduction of the alite content are not yet compromised.

The disadvantage of alitic clinker is that, despite the reduction of the P ₂ O ₅ inhibitory effect of SK 286 325, there is still an upper limit for the use of phosphorus-containing materials, in particular waste and by-products, above which the cement quality is already reduced.

The disadvantage of belitic clinker is that it cannot be used for cement production without stabilization of hydraulically active high temperature modifications of α'-C ₂ S and PC ₂ S.

Phosphorus-containing materials have been used in the production of Portland clinker to include phosphorus-containing wastes added either to cementitious raw material mixtures in the form of phosphorus slag WO 9003340 and in the form of waste from phosphate fertilizer production RU 2147016 or to furnace flames as alternative fuels in waste water treatment plants (Ad Takx, 5 ^lh VDZ Congress, Diisseldorf Germany, pp. 357-360, 2002) and animal waste PL 197240, in particular meat and bone meal (Pech, M. and Douillet, G., 5 ^lh VDZ Congress, Diisseldorf, Germany, pp. 352-356,2002).

Cement clinker is fired in a rotary kiln from raw meal and its phase composition is determined by the chemical composition of the raw meal. For the most important properties of cement, especially its strength, the ratio of alite to belite in clinker is decisive. As belite content increases in clinker, cement strength decreases, but at the same time fuel consumption and CO ₂ emissions are reduced, rotary kiln performance increases and production costs decrease.

The chemical composition of the raw meal is adjusted to the fractions of oxides - modules, namely the degree of lime saturation S _LP (1), which ranges from 90 to 100 for common alitic clinkers, the silicate module M _s (2), which ranges from 1 7 to 2.7 and an aluminate module M _A (3) ranging from 1.5 to 2.5.

With _LP = 100. C / (2.8. S + 1.18. A + 0.65. F) (1)

M _s = S / (A + F)

_M = A / F (3)

In the case of belitic clinker production, the degree of lime saturation S _L p decreases to 70-85, the silicate module M _s increases above 3 and the aluminate module M _A normally increases above 2.5.

Since the possibilities of deliberately influencing the properties of cement by changing the chemical composition of the raw meal and thus the belite content of the clinker are very limited with this technology, usually a high alite clinker is produced with a fixed phase composition and the cement properties are adjusted only by grinding and quantity of additives; admixtures, in particular the amount of granulated blast furnace slag, less already by other admixtures and supplementary constituents permitted by EN 197-1.

SUMMARY OF THE INVENTION

It is an object of the present invention to produce Portland cement with increased belite content, minimized production costs and CO ₂ emissions, and precisely adjustable properties. It is also an object of the present invention to achieve a partial replacement of granulated blast furnace slag in the production of Portland cement, Portland slag cement, Portland blend cement with blast furnace slag as the main constituent, blast furnace cements, blended cement and all blast furnace slag cements as supplementary such as sulphate-free cements, low hydration heat cements, low initial strength cements, mortar cements for masonry and plaster, and various cement containing blends with the addition of blast furnace granulated slag.

This object is achieved by the method of producing Portland cement according to the invention. The essence of the solution is that by burning in a rotary kiln, two types of clinkers are produced alternately by adjusting the chemical composition of the raw meal, a clinker predominantly alite over belite (alitic clinker) containing 0.01 to 1.5 wt. % Of P ₂ O ₅ and clinker with a predominance of belite over alite (belitic clinker) containing 0.01 to 3 wt. P ₂ O ₅ . The cement is produced by co-milling both clinkers in proportion to the desired resulting properties of Portland cement.

The chemical composition of the raw meal is modified by changing the degree of lime saturation and the use of P ₂ O ₅ containing materials when changing from alitic clinker to belitic clinker production so that by increasing the P ₂ O ₅ content of clinker from 0.01 to 3 wt. the lime content of S _LP decreases from 100 to 72.

Also, the chemical composition of the raw meal can be modified by changing the degree of lime saturation, changing the silicate modulus and using P ₂ O ₅ containing materials when changing from alitic clinker to belit clinker production by increasing the P ₂ O ₅ content of the clinker from 0.01 up to 3 wt. the lime saturation rate S _LP decreases from 100 to 72 and the silicate modulus M _s increases from 1.7 to 3.5.

The two clinkers are produced alternately, whereby the firing of belitic clinker, which itself does not form a stable furnace sticker in the sintering zone of the rotary kiln, utilizes the labels after the previous firing of the alitic clinker. By reducing the proportion of melt in belitic clinker to about 10%, the wear of the furnace stickers when firing belitic clinker is reduced to a minimum.

By co-grinding the clinkers with different contents of these phases, a more accurate alite / belite ratio setting in the cement is achieved. The properties of the cement are adjusted by the ratio of the two clinkers with the solidification regulator, possibly with additives and admixtures.

However, due to the very low hydraulic activity of belite, in this way it is not possible to increase the content of belite in cement to those of active belitic cements, and this has the nature of diluting alitic clinker similar to granulated blast furnace slag. it starts to hydrate and develop high strengths and increased hydration heat until delayed, much like granular blast furnace slag, and also the chemical composition of belitic clinker is close to the chemical composition of granulated blast furnace slag as opposed to alitic clinker.

The performance of the rotary kiln is considerably higher when firing belitic clinker. The firing temperature is lower and the sintering zone in the rotary kiln is considerably shorter than that of alitic clinker firing. The fuel consumption and CO ₂ emissions are also significantly lower with this firing. Separate firing of belitic clinker and lower firing temperature allow a significant increase of P ₂ O ₅ content in belitic clinker and consequently also in the resulting cement and stabilization of more hydraulically active modification of belit d-C ₂ S and 3-C ₂ S.

If P ₂ O _{5 is introduced by} partial replacement of primary fuel with meat-and-bone meal or sludge from sewage treatment plants, a significant increase in the content of belite in the final product and saving of primary fuel will be achieved simultaneously with the increase of hydraulic activity of belite. In addition, the burning of meat-and-bone meal and sewage sludge as a neutral-CO ₂ biomass biomass reduces CO ₂ emissions, since biofuel combustion does not increase CO ₂ emissions, but is relatively quickly consumed to produce and grow additional biomass. The use of biofuels as a renewable energy source effectively helps to replace natural non-renewable fossil fuels, which contributes to sustainable development.

The content of belite in conventional Portland cement can in this case be increased up to 25 to 30% by weight. while retaining the strength of the fired alitic clinker.

Up to about 25 to 30 wt. Belite in the blend of both clinkers is the production of conventional alitic-belitic clinker of common use, including its use for the production of Portland cements, Portland slag cements, Portland mixed cements with blast furnace granulated slag as the main component, blast furnace cements, mixed cements and all blast furnace granulated slags as a complementary component, specialty cements such as sulphate-free cements, low hydration heat cements, low initial strength cements, mortar cements for masonry and plaster, and various cement containing blends with the addition of blast furnace granulated slag. The various mixtures containing cement with the addition of blast furnace granulated slag are conventional concrete mixtures, concrete mixtures for the production of blocks and prefabricates, concrete mixtures for cement concrete pavements, tunnels, bridges, viaducts, cement containing mixtures for stabilizing substrates, cement reinforced aggregates, concrete for solid and Bulk constructions, sprayed concretes, screeds, cement adhesives for wall and floor tiles, cement adhesives for thermal insulation systems, heat-insulating mortars, waterproofing mixtures, jointing materials, masonry mortars, plastering mortars, trowels, stuccoes, dry plaster mixtures, leveling mixtures, mixtures, sealing suspensions, mixtures for protection and repair of concrete structures, remediation mixtures and the like.

Further increasing the content of highly belite clinker in the mixture and thus the content of belite in cement is a partial replacement of granulated blast furnace slag in the case of portland cements, portland slag cements, portland mix cements with blast furnace slag as the main constituent, blast furnace cements, mixed cements and all cements with blast furnace granulated slag as a supplement, specialty cements such as sulphate-free cements, low hydration heat cements, low initial strength cements, mortar and plaster mortars and various cement containing mixtures with the addition of blast granulated slag, and therefore associated with decrease of short-term strength of cement. The rate of this refund is individual for each cement plant, taking into account the transport costs and the price of granulated blast furnace slag and the cost of producing belitic clinker.

Since the reaction rate of belite formation is many times higher than the rate of alite formation, the possibility of coarser grinding of raw meal for the production of belitic clinker with corresponding grinding energy savings compared to the production of alitic clinker contributes significantly to the reduction of production costs.

In addition to the reduction of CO ₂ emissions due to reduced specific fuel consumption, the reduction of CO ₂ emissions due to the reduced proportion of limestone in the raw material is also significant.

The burning of belitic clinker also enables an increased proportion of secondary - alternative fuels combustion and the possibility of increased use of waste - alternative raw materials for the production of raw meal. The solution enables the large-scale efficient use of wastes containing P ₂ O ₅ in the production of cement clinker, which elsewhere has only a very small application potential.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

In a cement plant with a dry process for the production of alitic clinker with the usual 10 to 15 wt. % belite, 18 to 20 wt. % melt and 0.15 wt. P ₂ O ₅ without burning meat-and-bone meal, changing the degree of lime saturation S _L pz 97 to 75 and burning meat-and-bone meal and sludge from sewage treatment plants and using the waste from phosphate fertilizer production as a constituent 20 wt. % alite, 10 to 12 wt. % melt and having a P ₂ O ₅ content in the clinker of 2.50 wt. In this clinker, belite is made up of a highly hydraulically active modification of a'-C ₂ S and β-C ₂ S containing an overstoichiometric CaO, which makes it possible to mix Portland clinker cement with a high content of belite by mixing both clinkers.

Due to the altered degree of lime saturation, this belitic clinker will be suitable for partial replacement of granulated blast furnace slag and the blend of both clinkers will be suitable for the production of Portland cement, Portland slag cement, Portland cement cement with blast furnace slag as the main constituent, blast furnace cement, cement. all cements with blast furnace granulated slag as an additional component, special cements such as sulphurous cements, low hydration heat cements, low initial strength cements, mortar and plaster mortars and various cement containing blends with the addition of blast granulated slag.

Example 2

In a cement plant with a dry process for the production of alitic clinker with the usual 10 to 15 wt. % belite, 18 to 20 wt. % melt and 0.15 wt. P ₂ O ₅ increased the P ₂ O ₅ content in the clinker by burning meat-and-bone meal to 0.7% by weight. With a change in the degree of lime saturation S _L pz of 96 to 74 and a change of the silicate modulus M _s from 2.8 to 3.3, the firing of belitic clinker with 5 to 20 wt. % alite and 10 to 12 wt. gap melt. In this firing, by burning meat-and-bone meal and using phosphorus slag as an ingredient in the feedstock mixture, the P ₂ O ₅ content in the clinker increased above 1.8% by weight, and therefore this belitic clinker will consist of a hydraulically active modification <x'-C ₂ S; PC ₂ S. The strengths of the cement produced only from the belitic clinker thus produced will be comparable to the strengths of the alitic clinker after 28 days and in particular after 90 days of storage and therefore the ratio of the two clinkers in the mixture will be determined only by the initial cement strength requirements.

Up to about 25 wt. The belitic clinker in the mixture will be the production of Portland cement with the usual parameters at an increased belite content. Further increasing the belitic clinker content of the composition will reduce the initial strengths and also reduce the development of hydration heat.

For the production of Portland cements, Portland slag cements, Portland mixed cements with blast furnace granulated slag as the main constituent, blast furnace cements, mixed cements and all blast furnace granulated slag cements as an additional component, special cements such as sulphate-hydrated cements, low heat cements , low initial strength cements, masonry mortars and plaster mortars and various cement containing blends with the addition of blast furnace granulated slag will increase the content of belitic clinker by partially replacing the granulated blast furnace slag with a degree of substitution according to short-term strength requirements.

The very low hydration heat of belitic clinker and the relatively high strength after 28 days will make it possible in this cement plant to produce mixtures with a belitic clinker content well above 50%.

The foregoing exemplary embodiments of the invention are exemplary embodiments of the idea of the invention and do not exhaust all possibilities of carrying out the invention within the scope of the claims.

Industrial usability

The solution according to the invention can be used in all existing and newly constructed Portland cement plants. The solution can also be used in the production of Portland cement, where it is necessary or advantageous to form a partial replacement of granulated blast furnace slag as an admixture.

Claims (1)

PATENT CLAIMS Method for producing Portland cement, characterized in that the firing of raw meal in a rotary kiln is from the production of clinker with a predominance of alite over belite having a content of 0.01 to 1.5% by weight. P ₂ O ₅ by adjusting the chemical composition of the raw meal by changing the degree of lime S _LP from 100 to 72 and using P ₂ O ₅ containing materials, or by changing the degree of lime S _LP from 100 to 72, by changing the silicate module M _s from 1, 7 to 3.5, and using materials containing P ₂ O _5, it is converted into clinker with a predominance of belite over alite with a content of 0.01 to 3 wt. P ₂ O ₅ as well as the reverse process will change from the production of belitic clinker to the production of alitic clinker, and the cement is produced by grinding both clinkers together in proportion to the desired resulting properties of Portland cement.