RU2832453C1 - Method of intensifying process of burning portland cement clinker with fluorine-containing wastes in furnaces by dry method - Google Patents

Abstract

FIELD: construction materials.

SUBSTANCE: invention relates to the industry of construction materials, in particular to the production of portland cement clinker and optimization of the burning process thereof, and can be used in the production of portland cement clinker by a dry method. Method for intensifying the burning process of clinker, consisting mainly of tricalcium silicate C₃S, dicalcium silicate C₂S, tricalcium aluminate C₃A and tetra-calcium alumoferrite C₄AF, includes preparation and homogenisation of raw components together with fluorine-containing wastes of electrolytic production of aluminium with subsequent process of sintering and cooling of clinker. As a fluorine-containing waste of electrolytic production of aluminium, electrode breakage is used, containing a combustible component – carbon and cryolite – Na₃AlF₆, which has undergone thermal treatment for oxidation of the combustible component, after which electrode scrap in composition of crude mixture enters furnace system of dry method of clinker production, namely to cyclone heat exchanger between I and II stages, in amount of 0.25-0.75 wt.% in terms of fluorine from the initial raw mixture, and the sintering process is carried out at temperature of 1375-1450 °C.

EFFECT: intensification of burning process of portland cement clinker, produced by dry method, which consists in reduction of specific fuel consumption for burning of portland cement clinker, in reduction of burning temperature, with preservation of finished product quality indices.

1 cl, 4 tbl

Description

The invention relates to the building materials industry, in particular to the production of Portland cement clinker and the optimization of the process of its firing by introducing fluorine-containing waste from the electrolytic production of aluminum, and can be used in the production of Portland cement clinker by a dry method.

The most expensive process in terms of fuel and energy resources is the firing of Portland cement clinker – the main stage of Portland cement production, which requires a constant search for ways to optimize it.

A method for producing white cement clinker is known (RU patent for invention No. 2752767, published on 03.08.2021, bulletin No. 22). The method includes preparing a raw mix, feeding a mineralizer, firing the raw mix in a rotary kiln using a dry production method, and rapidly cooling the clinker in water. The raw mix is pre-mixed with dust from dust collecting devices, and the mineralizer 2C ₂ S⋅CaF ₂ is fed through a dust nozzle.

The disadvantage of the known method is the use of _2C2S⋅CaF2 powdered material as _a mineralizer, obtained by triple firing from chemical reagents or high-purity natural components, including fluorite, which entails additional costs for the synthesis of the mineralizer, as well as its increased consumption from 1.5% to 11%.

The closest solution in technical essence, accepted as a prototype, is the method for obtaining Portland cement according to the first point (RU patent for invention No. 2383506, published 10.03.2010, bulletin No. 7). The known method includes obtaining Portland cement clinker containing tricalcium silicate, dicalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite, sintering the initial raw mixture, including calcium, aluminosilicate, iron components and a fluorine-containing mineralizer - fluorocarbon-containing waste from the electrolytic production of aluminum, cooling and grinding the clinker with gypsum. Fluorocarbon-containing waste is used as a mineralizer individually or in combination with calcium fluoride. Fluorocarbon-containing waste is understood to be a mixture of electrostatic precipitator dust, gas cleaning sludge and coal foam tailings or their individual use.

The disadvantage of the prototype is the insufficient efficiency of the mineralizer, consisting in high fuel consumption to maintain a high firing temperature, which can lead to clinker overburning and a decrease in the quality indicators of Portland cement. Another disadvantage is the unstable chemical and phase composition of the mixture of fluorocarbon-containing waste.

The invention is aimed at intensifying the process of firing Portland cement clinker produced by a dry method, which consists in reducing the specific fuel consumption for firing Portland cement clinker, in reducing the firing temperature, while maintaining the quality indicators of the finished product.

The technical result is achieved in that in the method for intensifying the process of firing Portland cement clinker consisting mainly of tricalcium silicate _C3S , dicalcium silicate _C2S , tricalcium aluminate _C3A and tetracalcium aluminoferrite _C4AF , which includes the preparation of raw components, their homogenization with a mineralizer, the sintering process and cooling of the clinker, in the dry production method, thermally treated fluorine-containing waste from the electrolytic production of aluminum is used as a mineralizer.

The method of intensifying the firing process in the dry method of producing Portland cement clinker consisting mainly of tricalcium silicate C ₃ S, dicalcium silicate C ₂ S, tricalcium aluminate C ₃ A and tetracalcium aluminoferrite C ₄ AF includes the preparation and homogenization of raw components together with fluorine-containing waste to obtain a raw material mixture with a moisture content of 1%, its feeding into the kiln system, specifically into the cyclone heat exchanger between the first and second stages of the cyclones, sintering the clinker at a low temperature and cooling it. In this case, electrode scrap is used as fluorine-containing waste - fluorine-containing waste from the electrolytic production of aluminum, most of which is carbon and cryolite - sodium hexafluoroaluminate Na ₃ AlF ₆ , which has undergone preliminary preparation, which consists of heat treatment, allowing to remove from its composition - the combustible component - carbon. The need for this preparation is caused by the danger of using the electrode scrap in its original form when feeding it into a cyclone heat exchanger in the high-temperature region, as well as the possibility of locally exceeding the optimum temperature in the cyclone heat exchanger or decarbonizer in places where the combustible component is oxidized, which can lead to partial sublimation of fluorine. To implement the proposed method, thermally treated fluorine-containing waste is introduced into the raw mixture in an amount of 0.25-0.75 wt.% in terms of fluorine.

The initial raw mix used is a mixture consisting of carbonate, aluminate, silicate and ferrous components, designed to obtain ordinary Portland cement clinker. The characteristics of the raw mix are presented in Table 1.

Table 1

Characteristics of the initial raw material mixture

Chemical composition of the initial raw mixture, % _{SiO2 Al2O3 ​ Fe2O3 ​} CaO PPP Sum 14.69 3.14 2.76 44,41 34.99 100 Modular characteristics KN n p 0.93 2.49 1.14

Electrode scrap is used as fluorine-containing waste – fluorine-containing waste from the dumps of industrial waste of an aluminum production plant, for example, in Krasnoyarsk Krai, most of which is carbon and cryolite – sodium hexafluoroaluminate Na ₃ AlF _6. According to the declared method, fluorine-containing waste – electrode scrap – is subjected to preliminary heat treatment for use in the dry method of Portland cement production. The composition of fluorine-containing waste after heat treatment is presented in Table 2.

Table 2

Chemical composition of electrode waste, %

_{SiO2 Al2O3 ​ Fe2O3 ​} CaO MgO SO _{3 TiO2} F⁻ _{K2O Na2O} G. Ch. 0.6-0.7 21.0-22.0 1.3-1.4 1.0-1.2 0.4-0.5 3.0-3.2 0-0.02 38.0-39.0 0-0.30 32.0-33.0 -

Fluorine-containing waste is introduced into the raw mix in an amount from 0.25 wt.% to 0.75 wt.% in terms of fluorine. The additive is not introduced in an amount of less than 0.25 wt.% due to insufficient efficiency, and in an amount of more than 0.75 wt.% in order to prevent the formation of an excessive amount of alkaline compounds in the clinker and overconsumption of fluorine-containing waste. The raw mix without the addition of mineralizing additives was used as a control sample.

The qualitative assessment of the claimed method is assessed by the completeness of the assimilation of free calcium oxide into clinker minerals by examining each sample using the ethyl-glycerate method. The results of the study are presented in Table 3.

Table 3

Effect of introduced fluorine-containing waste on the amount of free calcium oxide in roasting products

№p/p
sample Quantity of FS additive, wt.% Firing temperature, °C 1250 1300 1325 1350 1375 1400 1450 1 0 27,784 21,879 15,363 3,265 1,959 0.653 0.163 2 0.25 19,939 11,452 5,551 1,636 0.653 0.327 0 3 0.5 15,036 4,898 2,454 0.818 0.163 0 0 4 0.75 11,429 3,922 1,963 0.164 0 0 0

The analysis of the samples obtained during the firing process showed that the use of fluorine-containing waste by the proposed method contributes to the completion of clinker formation processes with the complete assimilation of free calcium oxide in the temperature range of 1375-1450°C, given that in the raw mix without the addition of fluorine-containing waste, the clinker formation processes at a temperature of 1450°C do not proceed to the full extent, as evidenced by the presence of undigested calcium oxide in the amount of 0.163%. Consequently, the proposed method for intensifying the clinker firing process makes it possible to reduce the temperature by 50-75°C when introducing thermally treated fluorine-containing waste into the raw mix in an amount of 0.5-0.75 wt%.

An example of the invention implementation (table 3, sample 3).

A raw mix is prepared using fluorine-containing waste from the electrolytic production of aluminum. The raw mix consists of calcium carbonate (79.56 g), silicon oxide (IV) (14.49 g), aluminum oxide (3.18 g), iron oxide (III) (2.77 g). Electrode scrap is used as fluorine-containing waste from the electrolytic production of aluminum in an amount of 0.5 g in terms of fluorine.

The raw material mixture averaged with fluorine-containing waste is pressed into cylindrical samples with a diameter of 2 cm and a mass of 2 g. The samples are fired in batches in a laboratory furnace at a heating rate of 6 degrees/min in a temperature range of 1250–1450°C with isothermal holding for 15 minutes and subsequent rapid cooling in air.

The calculated chemical and mineralogical compositions of the resulting clinker are given in Table 4.

Table 4

Characteristics of synthesized clinker

Calculated chemical composition, % Calculated phase composition, % _{SiO2 Al2O3 ​ Fe2O3 ​} CaO Sum With ₃ S C ₂ S C ₃ A C ₄ AF 22.6 4.83 4.25 68.31 100 67.85 13.62 5.59 12.92

The completeness of the processes of formation of clinker minerals in the products of firing is estimated by the assimilation of free calcium oxide into clinker minerals by studying each sample by the ethyl-glycerate method. The result shows that free calcium oxide is completely assimilated at a temperature of 1400°C.

The results of the studies confirm that fluorine-containing waste from the electrolytic production of aluminum has a mineralizing effect during the firing of Portland cement clinker, which makes it possible to reduce the firing temperature by 50°C when using electrode scrap in an amount of 0.5 wt.% in terms of fluorine.

Thus, with the help of the proposed method of intensifying the process of firing Portland cement clinker with fluorine-containing waste, the following is ensured:

- reduction of the firing temperature of Portland cement clinker by 50-75°C when introducing an additive of fluorine-containing waste in an amount of 0.25 - 0.75 wt.%;

- complete formation of the main clinker minerals tricalcium silicate C ₃ S, dicalcium silicate C ₂ S, tricalcium aluminate C ₃ A and tetracalcium aluminoferrite C ₄ AF, as evidenced by the absence of free calcium oxide in the firing products;

- reduction of specific fuel consumption for clinker firing in the production of Portland cement by the dry method using thermally treated fluorine-containing waste by 3.0...4.5%;

- reduction of specific heat stress on the lining of rotary kilns of dry production method, which should ensure an increase in its service life;

- efficient utilization of fluorine-containing waste from the electrolytic production of aluminum with the expansion of the base of additives used in the production of Portland cement clinker;

- an economically advantageous replacement for scarce, traditionally used mineralizing additives such as calcium fluoride.

Claims (1)

A method for intensifying the process of burning clinker consisting mainly of tricalcium silicate C ₃ S, dicalcium silicate C ₂ S, tricalcium aluminate C ₃ A and tetracalcium aluminoferrite C ₄ AF, including the preparation and homogenization of raw components together with fluorine-containing waste from the electrolytic production of aluminum, followed by the process of sintering and cooling the clinker, characterized in that the fluorine-containing waste from the electrolytic production of aluminum is electrode scrap containing a combustible component - carbon and cryolite - Na ₃ AlF ₆ , which has undergone heat treatment to oxidize the combustible component, after which the electrode scrap as part of the raw mixture is fed to the kiln system of the dry method of clinker production, namely to the cyclone heat exchanger between stages I and II, in an amount of 0.25-0.75 wt.% in terms of fluorine from the original raw mixture, and the process sintering is carried out at a temperature of 1375-1450°C.