RU2816467C1 - Method of burning solid fuel in rotary kilns of cement production - Google Patents

Abstract

FIELD: methods of solid fuel combustion.

SUBSTANCE: invention relates to methods of burning solid fuel in rotary kilns of cement production. Method includes feeding through a fuel nozzle a dusty fuel mixture consisting of a solid fuel and a mineralizer having moisture content of not more than 5%, obtained by joint grinding to a residue on sieve No. 008 from 5 to 20% of solid fuel and a mineralizer based on fluorine ions, the amount of which in terms of fluorine ions is 0.05–0.5% F^- of the weight of the clinker, and speed of discharge of dusty fuel mixture from fuel injector is 40–120 m/s.

EFFECT: reduction of NO_x emissions from the rotary kiln into the atmosphere during solid fuel combustion.

1 cl, 1 dwg, 2 tbl

Description

The invention relates to a method for burning solid fuel in rotary kilns for cement production, and is aimed at reducing _NOx emissions from rotary kilns into the atmosphere when burning solid fuel.

NO _x is the collective name for the nitrogen oxides NO and NO ₂ . The predominant part of NO _x emissions from the rotary kiln is NO, the share of which is 93-97%. The amount of NO ₂ is 3-7%. NO in the atmosphere quickly oxidizes to NO _2.

In the cement industry, _NOx is produced when any type of fuel (solid, liquid or gas) is burned in a rotary kiln. Increased concentrations of NO _x in the atmosphere lead to acid rain, deterioration of human health and contribute to the decline in the number of pollinating insects, and also contribute to the greenhouse effect. Therefore, _NOx emissions into the atmosphere are limited.

There are known methods in which, in order to carry out the process of burning Portland cement clinker (clinker) in a rotary kiln for cement production, solid fuel is used, supplied through a fuel nozzle [O.I. Avramenko, V.K. Klassen, V.M. Kopeliovich, A.F. Matveev. Construction materials industry. Ser. 1: Cement industry, Vol. 3: Solid fuel and its use in the cement industry. - M.: VNIIESM, 1980. P. 36-38]

One of the disadvantages of these methods is the high NO _x emissions from the rotary kiln during clinker firing.

To reduce NO _x emissions in the cement industry, special selective catalytic and non-catalytic NO _{x reduction systems,} which are separate systems, can be used. However, based on economic considerations, instead of installing such systems, technical solutions built directly into the clinker firing process are more appropriate.

The closest solution in technical essence, adopted for the prototype, is a method in which, during the firing of Portland cement clinker, solid fuel is supplied through a fuel nozzle into a rotary kiln, and a reduction in NO _x emissions is achieved through a special design of the fuel nozzle [L. Ricci. Reducing NO _x emissions on existing cement production lines / Cement and its application, No. 6. - 2015. P. 61-62. ISSN 1607-8837].

However, the use of this method does not sufficiently reduce _NOx emissions from the rotary kiln and requires a more complex design of the fuel injector.

The invention is aimed at reducing NO _x emissions from a rotary kiln into the atmosphere when burning solid fuel.

This is achieved by the fact that the method of burning solid fuel in rotary kilns for cement production involves feeding through a fuel nozzle a pulverized fuel mixture consisting of solid fuel and a mineralizer, having a moisture content of no more than 5%, obtained by joint grinding to a residue on sieve No. 008 from 5 up to 20% of solid fuel and a mineralizer based on fluorine ions, the amount of which in terms of fluorine ions is 0.05-0.5% F ^- by weight of the clinker, and the speed of departure of the dusty fuel mixture from the fuel nozzle is 40-120 m/s .

Solid fuel used in the cement industry can be used as the initial solid fuel: coal, oil shale, brown coal, coke breeze, etc., as well as their mixtures in various combinations. The solid fuel used must have a lower calorific value of the working mass of fuel ≥21 MJ/kg [D1 - Cement production. Information and technical guide to the best available technologies. ITS 6 - 2015, M.: NDT Bureau, 2015. - P. 94.]. To compare the operating efficiency of the claimed invention, three types of coal were used as solid fuel. Characteristics of coals are presented in Table 1, where C^R, N^R, N^R, ABOUT^R,S^R - carbon, hydrogen, nitrogen, oxygen and sulfur, respectively, contained in the working mass of the fuel; A^R - ash content of the working mass of fuel, W^R - humidity of the working fuel mass, - lower calorific value of the working mass of fuel.

Table 1
Characteristics of solid fuel Fuel Composition of the working fuel mass, wt. % S ^p N ^r N ^r O ^r S ^r A ^r W ^p kJ/kg Coal No. 1 69.8 3.8 0.7 7.7 0.2 16.8 1 26720.63 Coal No. 2 59.2 3.7 0.6 16.9 1.9 15.7 2 22196.3 Coal No. 3 78.8 1.6 0.8 1.3 1.8 13.7 2 28306.2

As a mineralizer, mineralizers can be used, for example, fluorspar, NaF, 2C ₂ S⋅CaF ₂ and other mineralizers based on fluoride ions F ^- used in the cement industry.

table 2
The influence of the mineralizer - fluorspar in the composition of the fuel mixture on the amount of NO _x emissions from a rotary kiln The amount of mineralizer in terms of F ^- ion, % of the clinker mass 0 0.05 0.1 0.3 0.5 Amount of fluorspar in the fuel mixture, % 0 1.43 2.82 8.02 12.68 Amount of coal No. 1 in the fuel mixture, % 100 98.57 97.18 91.98 87.32 Amount of NO _x emissions, % vol. 0.095 0.091 0.088 0.076 0.068

According to the claimed invention, the solid fuel and the mineralizer are crushed together to a residue of 5 to 20% on sieve No. 008, turning into a pulverized fuel mixture. The pulverized fuel mixture is fed at a speed of 40-120 m/s through a fuel nozzle into a rotary kiln, where combustion of the pulverized fuel occurs mixtures. The amount of mineralizer in the pulverized fuel mixture corresponds to the input of 0.05-0.5% of fluorine ion by weight of the resulting clinker.

The method of burning solid fuel in rotary kilns for cement production is carried out as follows. Solid fuel, for example coal No. 1 and a mineralizer, for example fluorspar with a CaF ₂ content of 15-97%, for example 30% CaF ₂ , are crushed together to a residue on sieve No. 008 from 5 to 20%, for example up to 5%. The resulting pulverized fuel mixture is fed at a speed of 40-120 m/s, for example 50 m/s, through a fuel nozzle for combustion into a rotary kiln, for example, a wet method of cement production measuring ∅4×118 m with a capacity of 30 t/h. The amount of fluorspar supplied through the fuel nozzle as part of the pulverized fuel mixture in terms of fluorine ion (F ^- ) is 0.05-0.5% F ^- by weight of the clinker, for example 0.5% F ^- . The amount of solid fuel in the composition of the pulverized fuel mixture is the amount of solid fuel calculated from the heat balance of the rotary kiln for the clinker firing process [D2 - V.K. Cool. Technology and optimization of cement production: a short course of lectures: textbook. allowance / V.K. Cool. - Belgorod: BSTU publishing house, 2012. - P. 104] or selected on the basis of experimental data from the plant. For the rotary kiln under consideration, the required amount of coal No. 1 is 7066 kg/h, and the input of 0.5% F ^- by weight of the clinker corresponds to the input of 1026 kg/h of fluorspar containing 30% CaF ₂ . Therefore, to ensure the supply of such an amount of fluorspar containing 30% CaF ₂ it is necessary to obtain, by co-grinding, a pulverized fuel mixture consisting of 87.32% coal No. 1 and 12.68% fluorspar containing 30% CaF ₂ . When burning such a pulverized fuel mixture, NO _x emissions are reduced from 0.095% vol. up to 0.068% vol. The influence of the mineralizer - fluorspar containing 30% CaF ₂ , as part of a pulverized fuel mixture with coal No. 1 on the amount of NO _x emissions from a rotary kiln for the wet method of cement production with a size of ∅4 × 118 m and a capacity of 30 t/h is presented in Table 2.

When burning solid fuel in rotary kilns in cement production, rational or irrational flares arise. They differ in the position of the temperature maximum at a distance from the hot edge of a rotating kiln for cement production. The temperature maximum of a rational flame is located at a distance of 12±2 m, and that of an irrational flame is 20±4 m. In these areas, the highest heat stress of the combustion space is achieved. The rate of combustion of solid fuel and the nature of the torch are significantly influenced by the rate of mixing of solid fuel with air to the ignition point. The involvement of a large amount of air in the fuel jet to the ignition point causes the formation of an irrational torch at a distance of 20±4 m, characterized by a shorter length and a higher temperature in the area of increased thermal stress. In the presence of dust-like solid particles of the mineralizer, mixing of solid fuel with air is difficult, as a result of which the combustion process of solid fuel slows down and the temperature of the torch in the area of increased thermal stress decreases. Additionally, the flame temperature decreases due to a decrease in the lower calorific value of the working fuel mass due to the dilution of solid fuel with a mineralizer, which is equivalent to an increase in the ash content of solid fuel, which reduces the temperature of the torch, and also due to the removal of heat from the torch to heat the dust-like solid particles of the mineralizer. NO emission quantity_x depends on the flame temperature, therefore, as the flame temperature decreases, the amount of NO decreases_xformed during fuel combustion.

The invention is illustrated by the drawing, where in FIG. Figure 1 shows the effect of fluorspar containing 30% CaF ₂ in the fuel mixture on the amount of NO _x emissions from a wet cement production rotary kiln with a size of ∅4×118 m and a productivity of 30 t/h, depending on the composition of the coal.

When feeding a fuel mixture through a fuel injector, the permissible amount of mineralizer is limited to the recommended amount for clinker synthesis processes, for example, the upper limit of the interval 0.05-0.5% F ^- it is not recommended to exceed due to a decrease in clinker activity. On the other hand, the amount of mineralizer is limited by the flame temperature sufficient to maintain the required temperature for the synthesis of Portland cement clinker. When firing clinker, the minimum possible flame temperature should be approximately 100°C higher than the temperature required to complete the clinker formation processes [D3 - Butt Yu.M., Duderov G.N., Matveev M.A. General technology of silicates. Textbook for technical schools. Ed. 3rd, revised and additional M.: Stroyizdat, 1976. - P. 146]. The usual firing temperature for Portland cement clinker is 1450°C. Mineralizer particles entering the rotary kiln intensify the firing process, which makes it possible to reduce the firing temperature of Portland cement clinker when introducing fluorspar, for example, to 1300°C, therefore, reducing the temperature of the torch when introducing the stated amount of mineralizer will not have a negative impact on the firing process of Portland cement clinker .

The use of the claimed invention will allow:

reduce NO _x emissions from the rotary kiln into the atmosphere.

Claims (1)

A method of burning solid fuel in rotary kilns for cement production, including supplying through a fuel nozzle a pulverized fuel mixture consisting of solid fuel and a mineralizer, having a moisture content of no more than 5%, obtained by joint grinding to a residue on sieve No. 008 from 5 to 20% solid fuel and a mineralizer based on fluorine ions, the amount of which in terms of fluorine ions is 0.05-0.5% F ^- by weight of the clinker, and the speed of departure of the dusty fuel mixture from the fuel nozzle is 40-120 m/s.