RU2497766C1 - Method of obtaining cement clinker - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to cement industry, in particular to method of cement clinker production. In method of cement clinker production, which includes heating of powder-from raw material by discharge gases, its agglomeration in blow-through process through primer of fluidised bed due to fuel burning and cooling, synthesis-gas, obtained as a result of heat recuperation from clinker by chemical regeneration of traditional types of fuel is applied as fuel, and final product than is cooled in two stages: high temperature zone - by expulsion of hydrocarbon fuel and water - steam and/or carbon dioxide - CO₂ mixture, and low temperature zone - by air; discharge gases from cooling stages are supplied into zone of agglomeration and decarbonisation. Carbon dioxide and water steam are collected from furnace discharge gases.

EFFECT: reduction of energy consumption for production of clinker, increase of cement clinker cooling efficiency with simultaneous reduction of specific air consumption and improvement of clinker quality.

1 dwg, 2 tbl

Description

The invention relates to the cement industry, in particular to methods for the production of cement clinker.

A known method of producing cement clinker, which consists in the fact that through the layer of dry fine-grained raw material mixture located on the grate or porous base, hot flue gases are passed under pressure. Penetrating into the layer, they cause a continuous circulation of grains and the entire layer of material becomes similar to a boiling liquid. A comprehensive washing of small grains with hot gas creates the most favorable conditions for heat transfer and determines the high specific productivity of such plants. The clinker quality is high due to the uniform firing of small granules. As an analogue, we consider a method in which all stages — drying, calcining, and firing of cement clinker — are carried out in one apparatus — the reactor. (Kolokolnikov B.C. “Cement Production” M., Higher School, 1967).

The disadvantage of this method is the high consumption of fuel and electricity. High fuel consumption is caused by the lack of preliminary decarbonization of raw materials, and high energy consumption is caused by the need to create increased gas pressure for air to pass through the high-temperature clinker.

There is also a method for producing cemented clinker in a fluidized bed in a one-furnace system of the KHI firm (Kawasaki heavy industries), including granulation and agglomeration in one fluidized bed furnace, i.e. crushing raw flour to the desired particle size distribution and subsequent sintering of granules at high temperatures. Clinker is cooled in two stages, in the first - the clinker is sharply cooled in the fluidized bed, and in the second a densified layer is formed to ensure a high level of heat use (see. Zement-Kalk-Gips, 1999, No. 1 translation of this article was published in the journal "Cement and its Application", July - August 1999, pp. 10-18 - analogue).

The disadvantages of this method:

- large dimensions of the cooler due to the need for two-stage cooling and the associated additional heat loss,

- high energy consumption, caused by the need to create increased pressure by blower fans to supply air to cool the clinker through the high-temperature layer of clinker.

The closest technical solution adopted for the prototype is a method for producing cement clinker, which includes heating the powdered raw material with exhaust gases, decarbonization and sintering it during purging through the seed fluidized bed by burning fuel and cooling (see A.S., No. 437725, USSR, M. C. C04b 7/44, applicant - State All-Union Scientific Research Institute of the Cement Industry, inventors: A.P. Belov, N.E. Sereda and V.V.Usenko, publ. 30.07.74, bulletin No. 28). However, this method also has increased energy consumption - a high specific fuel consumption for clinker firing and increased energy consumption for clinker cooling, because the passage of air through a high-temperature clinker requires more high-pressure fans with increased drive power.

The proposed technical solution is aimed at a significant reduction in energy costs for the production of clinker and increase the cooling efficiency of cement clinker while reducing specific air consumption and improving the quality of clinker.

This problem is solved by the proposed method for producing cement clinker, including heating the powdered raw material with exhaust gases, decarbonization and sintering of the raw material during the purging process through the priming of the fluidized bed by burning fuel and cooling, the synthesis gas obtained during the cooling of clinker is used as fuel. After sintering, the finished product is cooled in two stages: in the first stage, cooling is performed in the high-temperature zone at a temperature of 1300 to 700 ° C due to chemical heat recovery by blowing hydrocarbon fuel and water (for example, steam or a mixture of carbon dioxide and steam). And the second stage is low-temperature, where the cooling is carried out with air at a temperature of from 700 to 90 ° C or to a predetermined one. Exhaust gases from the cooling stages are fed to the sintering and decarbonization zone for combustion.

The difference between the proposed solution from the prototype is that the fuel used is the synthesis gas obtained in the process of cooling the clinker, which allows us to conclude that the proposed solution meets the criterion of "novelty."

A comparison of the proposed solutions with similar solutions in this field, allows us to conclude that the use of synthesis gas as a fuel obtained during cooling in the high-temperature zone is unknown. The claimed invention allows to sharply increase the efficiency of clinker cooling while significantly reducing specific air consumption and energy consumption by increasing the energy level (exergy) of converted fuel, which could not be predicted on the basis of the existing level of technology, therefore it can be concluded that the proposed solution meets the criterion of "inventive step ".

The invention is illustrated by the diagram (see Fig. 1) of the method on the example of a fluidized bed unit, where 1 is the zone of preliminary heat treatment; 2 - calcination zone (decarbonization); 3 - firing zone, 4, 5 - reactor-cooler, where 4 - high-temperature zone of the reactor-cooler; 5 - low temperature zone of the reactor cooler.

The method of producing clinker is as follows: the raw material mixture in powder form is fed into the fluidized bed furnace (aggregate) in zone 1, where the preliminary heat treatment of the raw material mixture is carried out in a known manner - A.S., No. 437725, USSR, M. Cl. C04b 7/44, due to the exhaust gases coming from decarbonization zones 2 and sintering 3. Then, the heat-treated raw material is additionally heated and decarbonized in decarbonization zone 2 by burning part of the fuel and heated air taken from the low-temperature zone 5 of the cooling reactor. Further, from the decarbonization zone, the raw material enters the firing zone 3 - into the fluidized bed, formed due to the continuous circulation of the material, when hot flue gases are passed under pressure through the grate or porous base of the furnace. The temperature regime of the fluidized bed is selected so that the particles of the powdered raw material, filtered through the fluidized bed, adhere to larger particles of the layer and sinter on their surface. To improve heat transfer, to maintain the sintering process of raw materials and to regulate the size of the finished product, seed is fed into the furnace (in the layer) - particles of the finished product are larger than particles of the raw material, according to A.S., No. 437725, USSR, M. Cl. C04b 7/44. The seed (granules) is an activator of clinker synthesis and allows to stably conduct the firing process due to the absence of clogging of holes (or pores) in the furnace grate.

Burnt clinker, from the fluidized bed, in the form of granules enters the reactor-cooler (4, 5). The cooler-reactor (4, 5) is conventionally divided into two zones: high-temperature 4 and low-temperature 5. In high-temperature zone 4, for cooling incoming clinker granules, hydrocarbon fuel and water (steam) and / or carbon dioxide are supplied. When a mixture of fuel and water vapor (carbon dioxide) passes through a layer of hot clinker, the components react according to the following equations:

CH ₄ + H ₂ O↔CO + 3H ₂ - 9.196 MJ.

CH ₄ + CO ₂ ↔ 2CO + 2H ₂ - 11.1 MJ.

This reaction is characterized by the selection of a large amount of heat from the calcined clinker product and allows you to organize a sharp and effective cooling of cement clinker. As a result of the thermochemical reaction, CO and H ₂ gases (carbon monoxide and hydrogen) are formed - synthesis gas, which have a higher combustion temperature than the original fuel. So, the combustion temperature of the initial fuel - methane CH ₄ , is 2040 ° С, and the components of the synthesis gas, respectively, of carbon monoxide СО - 2370 ° С and hydrogen Н ₂ - 2230 ° С. An increase in the temperature of fuel combustion is a fundamental factor for accelerating clinker formation processes . According to Weber P. Abgasverluste beim Zementdrehöfen. "Zement-Kalk-Gips", 1957, No. 2., increasing the temperature of the torch by 20-40 ° increases the productivity by 2.5-4% and reduces the specific heat consumption for clinker burning by 2-4%. For every 100 ° increase in the clinker burning temperature from 1300 to 1600 ° С, the rate of the reaction rate 2CaO · SiO ₂ + CaO = 3CaO · SiO ₂ increases on average by 2–3 times. As a result, the productivity of the firing unit is increased. Subsequently, the synthesis gas enters the sintering zone 3 and decarbonization 2.

In the low temperature zone of the reactor 5, the clinker is cooled by air supplied under pressure, for example, by means of fans. During cooling, the clinker gives off heat to the air, which is then fed to the sintering zone 3 and decarbonization zone 2. Due to the fact that air is supplied only to the low-temperature zone of the reactor 5, where the clinker is cooled at a temperature of 700 to 90 ° C, the energy consumption for the drive blow fans is sharply reduced compared to the prototype, in which the clinker is cooled from 1300 ° C to 90 ° C, by several times reducing the viscosity and volume of air passing through the cooled clinker and leading to increased sweat at the same time, the required specific air flow for cooling the clinker is reduced, which leads to a decrease in environmental pollution by minimizing the emission of excess air into the atmosphere.

The effectiveness of using chemical heat recovery and synthesis gas is confirmed by calculations of material and heat balances, the results of which are given in Tables 1, 2.

Table 1. Material balance of the furnace Incoming articles Quantity, kg / kg cells Consumables Quantity, kg / kg cells Synthesis gas Natural gas Synthesis gas Natural gas 1. Clinker one one 1.Fuel 0.169 0.133 2. Rel. gases 3,967 3,986 2. Sludge 2,577 2,577 - from fuel 2,390 2,409 3. Air burning fuel 2,221 2,277 CO ₂ 0.335 0.343 H ₂ 0 0.314 0.281 N ₂ 1,702 1,745 O ₂ 0,038 0,039 - from raw materials 1,577 1,577 CO ₂ 0.529 0.529 H ₂ O 1,048 1,048 Total 4,966 4,986 Total 4,966 4,986

Table 2. Heat balance of the furnace Incoming articles Quantity, kJ / kg cl Consumables Quantity, kJ / kg cl Synthesis gas Natural gas Synthesis gas Natural gas 1. From fuel combustion 6490 6203 1. For clinker education 1813 1813 2. With fuel 256 7 2. To evaporate water 2577 2577 3. With raw materials 56 56 3. With flue gases 1154 1163 4. With secondary air 561 1106 4. With clinker 1378 1378 5. Into the environment 442 442 Total 7363 7372 Total 7363 7372

Replacing part of the fuel with water increases the exergy of the fuel mixture, which confirms an increase in heat input from fuel combustion to 6490 kJ / kg cell (Table 2) and a decrease in the total amount of heat in the furnace from 7372 to 7363 kJ / kg cell. Also slightly reduced heat consumption with exhaust gases. The amount and composition of exhaust gases varies as follows (Table 1): emissions of CO ₂ and N ₂ are reduced by an average of 2.5% and the content of H ₂ O is increased by 10.5%. The required amount of combustion air is reduced by 2.5%.

The saving of natural fuel is ≈4.2 million m ^{3 of} natural gas per 1 million tons of clinker.

The proposed method allows you to:

- reduce fuel consumption for clinker burning by replacing part of the fuel with water, which, together with hydrocarbon fuel, under the influence of high temperatures, decomposes into constituent gases CO and H ₂ ;

- reduce emissions of exhaust gases, namely carbon dioxide (CO ₂ ) and nitrogen oxides (NO _x ), which positively affects the environmental situation in the region, by reducing the overall fuel consumption;

- to increase the productivity of the furnace installation, by increasing the energy level (exergy) of the newly obtained gaseous fuel, its combustion temperature;

- due to the sharp cooling of the clinker, to increase the strength and quality of cement, due to the reduction of alite crystals and stabilization of high-temperature forms of calcium silicates, and to improve the grinding characteristics and sulfate resistance of the obtained cement;

- sharply reduce the cost of electricity for cooling cement clinker by cooling the clinker in a high-temperature zone without the use of air, as well as reduce heat loss with excess air.

Also, as a result of the application of this method, a change in the color of the clinker obtained from dark gray to sandy white was experimentally established, which positively affects the architectural and artistic (aesthetic) properties of the obtained cement.

Claims (2)

1. A method of producing a cement clinker, including heating the powdered raw material with exhaust gases, sintering it during purging through the seed of the fluidized bed by burning fuel and cooling, characterized in that the fuel used is synthesis gas obtained by recovering heat from clinker by chemical regeneration of traditional fuels, and the finished product is then cooled in two stages: high temperature zone - by blowing a mixture of hydrocarbon fuel and water - steam and / or carbon dioxide - CO ₂ , and low temperature - by air, the exhaust gases from the cooling stages are fed into the sintering and decarbonization zone. 2. The method according to claim 1, characterized in that carbon dioxide and water vapor are selected from the exhaust gases of the furnace.

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