RU2362748C1 - Method for preparation of anhydrite binder - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention refers to the technology of preparation and application of anhydrite binders based on the anhydrous calcium sulphate. The method includes the disintegration of the gypsum stone, its loading to the conveying lattice and layer burning by the updraft of hot gases from fuel burning with following fine grinding of the calcinated product. The gypsum stone is beforehand diluted with 5-10 wt % of limestone and ground up to the powdery condition. The obtained mixture is moistened with obtaining of the pellets having size 6-8 mm and undergoes the level burning on the conveying lattice with beforehand laying on the lattice of the "bedding" (the layer of calcinated product pellets with thickness 40-60 mm). The 5-8% of oil coke are additionally fed into the mixture of gypsum stone and limestone. Then the pellets layer made of cement raw mixture and oil coke is laid over "bedding" on the conveying lattice and atop of it the layer of pellets made of gypsum stone, limestone and oil coke is laid with ratio of the cement and gypsum layers being 1:1-1.2 respectively. The calcination products of these mixtures are ground up together with 10-12 wt % of the complex additive consisting of 1 part of plastifier and 9 parts of silica component - microsilica or acid CHP-plant ash.

EFFECT: more full raw materials use, simplification of the binder preparation technology, acceleration and cheapening of calcinations process, enhancing of the water stability and resistibility of anhydrite binder.

4 cl, 1 tbl, 4 ex

Description

The invention relates to technologies for the preparation and use of anhydrite binders, the basis of which is calcium sulfate in anhydrous form. Unlike the quick setting and quick hardening semi-aquatic forms of calcium sulfate, known in construction practice in two forms - “building gypsum” and “technical gypsum”, anhydrite binders have normal setting and hardening times. Anhydrite binders, like all types of binders based on CaSO ₄ , are characterized by relatively low strength and are not waterproof.

A known method of producing anhydrite binder by roasting in shaft furnaces with external furnaces (Gypsum materials and products (production and use). Handbook edited by A.V. Ferronskaya, Moscow: ASV Publishing House, 2004, p.127). The disadvantage of this method should be considered as the use of large fractions of gypsum stone as a raw material. At the same time, other types of calcining devices should be used for firing fine fractions.

A known method of producing anhydrite binder from fine fractionated gypsum (gypsum materials and products (production and use). Handbook edited by A.V. Ferronskaya, Moscow: Publishing House ASV, 2004, p.128) According to this method, gypsum stone in the form crushed stone is loaded onto a grate furnace (grate) moving at a speed of 0.5 m / min with a layer through which hot flue gases are sucked. Moreover, the firing temperature of the upper layers reaches 700, and the lower - 400 ° C.

The disadvantages of this method include:

- the exclusion from the process of small, less than 5 mm, particles of gypsum stone, which are either dumped or disposed of by burning in another roasting device, for example in a gypsum cooker;

- low firing intensity due to the low process temperature;

- the resulting product needs an additive that activates its hardening, in the form of lime or magnesium oxide or other mineral additives (gypsum materials and products (production and use). Handbook edited by A.V. Ferronskaya, Moscow: DIA Publishing House, 2004, p. 126);

- the product has low water resistance and insufficient strength.

The technical problems to be solved in the claimed method for producing an anhydrite binder, including grinding gypsum stone, fractioning it and loading fractionated gypsum stone onto the conveyor grill, then calcining it in a layer by sucking through a layer of hot gases from burning fuel and subsequent fine grinding of the calcined product with simultaneous introduction in its composition additives - activator of hardening, are:

- full use of raw materials, including its small fractions;

- simplification of the technology of obtaining a binder;

- acceleration and cheapening of the firing process;

- increase the water resistance and strength of the anhydrite binder.

To obtain this result, gypsum stone together with 5-10 wt.% Limestone is finely ground, then the mixture is moistened, granules 6–8 mm in size are obtained, they are laid on a conveyor grate over the “bedding” layer from the firing product in the form of anhydrite granules with a thickness of 40– 60 mm and fired at the horizon, and the surface horizons of the granule layer using the flare-layer regime of burning gas fuel with a coefficient of air consumption a = 1.0-1.05 and heating intensity I = 10-20 × 10 ³ KJ / m ² min, and the middle and lower horizons burn in mode c oevogo combustion gas at a = 2,5-3,0 when I = 1-5 × March ¹⁰ kJ / m ² min.

To reduce the need for gas fuel, solid fuel — petroleum coke — is introduced into the mixture of gypsum stone and limestone in the amount of 5–8 wt%, the average particle size of which is 0.4 mm. In this case, the gas after firing the upper horizons of the layer is turned off, and the firing of the middle and lower is carried out due to the heat from burning solid fuel in the mixture.

If it is necessary to obtain a high-strength and water-resistant binder, a cement clinker is used as a “bedding”, the mass of which is 60-80% by weight of the gypsum stone, and the firing product is crushed together with the “bedding” with an additional introduction of 10-12 wt.% Of a complex additive consisting of from 1 part of a plasticizer and 9 parts of a siliceous component, silica fume or acid ash TPP.

In the absence of ready-made clinker, a layer of granules from a cement raw mix and solid fuel is laid on top of a bed of granular anhydrite binder, and on top of it is a layer of granules from the specified mixture of gypsum stone, limestone and solid fuel with a layer height ratio of 1: 1-1.2, moreover, the firing products of these mixtures are crushed together with the additional introduction of 10-12 wt.% a complex additive consisting of 1 part plasticizer and 9 parts of a siliceous component, silica fume or acid ash TPP. Petroleum coke is used as solid fuel.

Experimental verification of the proposed method was carried out on materials whose chemical composition is given in table 1. In addition, we used the clinker of the Nevyansk cement plant, which had the following technical characteristics: saturation coefficient KN = 0.92, silicate module n = 1.8, alumina module p = 1.1.

Table 1 Components Content, wt.% P.p.p. SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ CaO MgO SO ₃ Gypsum stone 19.3 3.2 0.9 0.2 32,2 2,4 41.8 Limestone 43.3 0.15 0.09 0,03 55.51 0.13 0.4

For firing an anhydrite binder, a laboratory sintering apparatus was used having a firing chamber diameter of 200 mm and a height of 400 mm. The raw mixes were moistened and granulated on a laboratory plate granulator. The granule size was 6-8 mm. A layer of bedding in the form of granules of calcined anhydrite 50 mm thick was laid on a grate located in the lower part of the calcining chamber, on top of which a granular gypsum stone with limestone was placed. During the firing process, the temperature of the firing process was measured, which was measured with a thermocouple at the contact of the raw material and “litter”. Its level was for the prototype, firing 1, 760 ° C, and for all others from 920 to 985 ° C. The above-mentioned thickness of the "bedding" is in the range of 40-60 mm, sufficient to protect the grate of the grate from melting from temperatures of this level.

In all experiments, the products of firing and “bedding” were crushed together to a residue on sieve 008 of not more than 15%, and in experiments 4-8, not more than 5%.

The astringent properties of the calcined materials were evaluated on tablet samples with a diameter and height of 30 mm, made of dough with Suttard plasticity (GOST 125-79) 140 + 10 mm, which hardened in air-wet conditions in a desiccator for 28 days. The water resistance of the binder was evaluated by the softening coefficient (K _p ), which was determined as the ratio of the strengths of the dried samples of air-wet storage and samples of a similar composition, solidified in water. Table 2 contains comparative data on the compositions and properties of the anhydrite binder (AB), compositions based on it with Portland cement clinker (PCC) and an additional complex additive (CD) introduced, including 9 parts of a siliceous component and 1 part of a plasticizer. Table 2 contains data on the composition of raw mixes, astringent compositions and their properties.

table 2 No. The composition of the raw mix, wt.% Astringent composition Note composition, wt.% properties GK From to Coke AB CCC Cd Kszh, MPa K _p one one hundred - - one hundred - - eighteen 0.64 According to the prototype * 2 92 8 - one hundred - - 21 0.65 According to the application, paragraph 1.2 3 84 8 8 one hundred - - 23 0.67 --- "---, p.1,3 four 84 8 8 56.3 33.7 ¹⁰⁺ 31 0.85 --- "---, p. 4 5 84 8 8 48,4 39.6 ¹²⁺ 33 0.87 --- "---, p. 4 6 84 8 8 45 45 ¹⁰⁺ 36 0.92 --- "---, p. 5 7 84 8 8 45 45 10 ⁺⁺ 33 0.90 --- "---, p. 5 8 84 8 8 45 45 10 ^" 29th 0.91 --- "---, p. 5 * Raw materials are represented by gypsum stone fraction 5-10 mm.
+ - concrete modifier MB-0,1, containing 90% silica fume and 10% plasticizer S-3;
++ - a composition consisting of 90% acid ash and 10% plasticizer C-3.
"- a composition consisting of 90% acid ash and plasticizer LST.
In the note to experiments 2-8, the claims are indicated.

In the composition of the anhydrite binder obtained in experiment 1, 5 wt.% Ground quicklime was added as a hardening activator, and in others - 8 wt.% Limestone, which after calcination is 5 wt.%. An increase in the proportion of limestone in excess of 10 wt.% Increases the cost of heat. In experiment 2, the raw material mixture was fired with gas. The firing of the surface horizon was carried out with an air excess coefficient a = 1.05, heating intensity I = 15 kJ / m ² min. The middle and lower horizons of the layer were fired in the layer-by-layer gas combustion mode with an air excess coefficient a = 2.5 and a heating intensity of I = 3 kJ / m ² min. The indicated values correspond to the central values of the claimed intervals. The lower limit of the claimed intervals is limited to the zone of stability of the regimes of flare-layer and layer-by-layer combustion of gas fuel, and the upper limit is a sharp increase in the hydraulic resistance of the fired layer. The latter in the industrial implementation of the method will lead to a significant increase in the "suction" of external air at the contact of the moving conveyor grill and the stationary vacuum chambers, which will significantly increase the cost of electricity for the firing process.

In experiments 3-8, 8 wt.% Solid fuel, crushed petroleum coke with an average particle size of 0.4 mm was introduced into the mixture. The indicated level was chosen to the maximum, since petroleum coke is cheaper than the replaced gas, but with a higher content of it in the feed, "overheating" occurs when firing lower horizons. The accepted particle size of coke provides the necessary temperature regime of firing with minimal heat loss with chemical and mechanical under-burning of coke.

In experiments 4 and 5, the clinker of the Nevyansk cement plant in the amount of 60% and 80% by weight of the gypsum-limestone mixture was used as a “bedding”. When firing anhydrite binder and clinker, experiments 6-8, a cement raw mixture was placed between the anhydrite bed and granules based on gypsum stone. It included limestone, clay, copper slag and had the following technical characteristics: saturation coefficient KN = 0.9, silicate module n = 2.2, alumina module p = 1.2, and contained 12 wt.% Crushed petroleum coke. The firing products were milled to 50 μm with 10-12 wt.% Complex additives, including 1 part plasticizer and 9 parts silica additives.

The use of petroleum coke in firing increases the strength of the anhydrite binder, experiments 3-8, and the use of factory clinker as a part of the mixture, experiments 4 and 5, or the joint firing of cement and gypsum mixtures, experiments 6, 7, 8, allows to obtain a waterproof binder with a softening coefficient above 0.8. A comparison of the results of experiments 4 and 5 allows us to consider the claimed interval of the factory clinker content of 60-80% by weight of the gypsum component optimal, since 60% of the clinker significantly increase the strength and water resistance of the composition, and increase the proportion of the more expensive clinker component than anhydrite in the form of clinker over 80% impractical since the increase in strength and water resistance of the anhydrite composition is not proportional to the increase in clinker fraction. Given the weight loss of gypsum stone during firing, the ratio of clinker and gypsum component after firing increases in favor of clinker, as indicated in table 2.

The introduction of a complex additive into the composition of the binder mixture, including a plasticizer and a siliceous component, provides the binder with water resistance and an additional increase in strength. In experiments 6-8, the effectiveness of plasticizing and silica additives was compared. As expected, the replacement of highly effective silica fume and C-3 with less effective lignosulfonate and fly ash of TPPs was accompanied by a slight decrease in strength and water resistance. Since the effect of using a plasticizer is proportional to its content in the mixture, the upper limit is usually determined by the level of cost of the plasticizer. In relation to the claimed method, it is advisable to use a complex silica-plasticizing additive, the optimum of which due to its high cost usually does not exceed 10-12% by weight of the binder. A comparison of the results of experiments 4 and 5 is consistent with this statement.

Grinding the raw material to a powder state and its subsequent granulation make it possible to use the entire mass of the extracted raw material in a single process, while the prototype uses only a certain fraction of it, and fines in the form of screenings are either dumped or burned in gypsum boilers. In addition, in the inventive method combine the firing of the main product, gypsum stone and additives - activator hardening of anhydrite - lime or cement clinker, which simplifies the technology. Moreover, in the process it is possible to use limestone screenings, waste lime production in shaft kilns.

The use of flare-layer and layer-fired gas burning in firing allows high-quality firing of anhydrite binder with high intensity due to the higher firing temperature and with minimal heat consumption, which reduces the cost of the process. The use of petro-coke in the process allows intensive and high-quality firing of an anhydrite binder in the case when gas fuel is expensive or unavailable. In this case, the upper horizon is fired using gas or other fuel, and the lower and middle horizons are fired with petroleum coke. The factory clinker in a layer with gypsum raw materials combines the functions of a “bedding” and an anhydrite hardening activator, which increases the strength of the composition and its water resistance. With the joint firing of cement and gypsum raw materials with a layer height ratio of 1: 1-1.2, a waterproof combined binder is obtained, similar in properties to Portland cement, but with less heat by 25-30% in relation to it. With an increase in the proportion of cement raw materials relative to gypsum more than 1: 1-1.2, the indicated savings decrease due to increased energy consumption for decarbonization of limestone in the composition of the cement raw material mixture.

Using the invention will allow to obtain a high-strength and water-resistant anhydrite binder at a total cost of 30-35% lower than in traditional technology.

Claims (4)

1. A method of producing an anhydrite binder, including grinding and loading gypsum stone onto a conveyor belt, burning it in a layer by sucking it through a layer of hot gases from burning fuel and subsequent fine grinding of the calcined product, characterized in that the gypsum stone is pre-diluted with 5-10 wt. % of limestone and ground to a powder state, the resulting mixture is moistened to obtain granules with a size of 6-8 mm, and then subjected to horizontal firing on a conveyor grid, on which to protect the grate eshetki by melting previously laid "bedding" as a layer of pellets baked product 40-60 mm thick. 2. The method according to claim 1, characterized in that for firing surface horizons using a flare-layer regime of burning gas fuel with a coefficient of air flow equal to a = 1.0-1.05 and heating intensity I = 10-20 · 10 ³ kJ / m ² min, and for firing the middle and lower horizons, layer-by-layer combustion of gas fuel is used with an air flow coefficient a = 2.5-3.0 and heating intensity
I = 1-5 · 10 ³ kJ / m ² min. 3. The method according to claim 1, characterized in that 5-8% of a short-flame solid fuel - petroleum coke, crushed to an average particle size of 0.3-0.5 mm is introduced into the mixture of gypsum stone and limestone. 4. The method according to claim 3, characterized in that a layer of granules of a cement raw material mixture and solid fuel - petroleum coke is laid on a conveyor grill on top of said “bedding”, and on top of it is a layer of granules made of a mixture of gypsum stone, limestone and additionally injected solid fuel - Neftekoks, with a layer height ratio of 1: 1-1.2, respectively, the firing product is crushed together with the additional introduction of 10-12 wt.% of a complex additive consisting of 1 part plasticizer and 9 parts of a siliceous component - silica fume or acid ash TPP.