RU2407804C2 - Cupola heat on hard coal - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: procedure consists in charging fuel and materials into cupola and in supplying blast heated to 450-550 °C. As fuel there is used mixture out of 40 % of birch wood and 60 % of hard coal with height of charge 4.0-4.5 m into fuel furnace charge.

EFFECT: stability of melting and reduced cost of melting process.

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Description

The invention relates to foundry and production of mineral wool products, which are used shaft furnaces of small diameter of the same design and is intended for melting charge materials on lean coal.

The search for new types of cupola and blast furnace fuel has been going on for a long time. Known cupolas with partial replacement of coke with natural gas, cupolas using electricity. Technologies have also been developed for the use of pulverized coal (PUT) in cupolas, the use of fuel oil, oil, pitch coke, as well as emulsions and suspensions.

It is known that in the first blast furnaces charcoal was the main fuel. The output of charcoal from firewood usually ranges from 60 to 70 vol.%.

Charcoal has a high reactivity and combustibility, which is associated with its huge porosity (80-87%). In terms of chemical composition, charcoal compares favorably with coke in its low ash content (1-2% A) and purity in sulfur (<0.05% S) and phosphorus (0.1-0.07% P). However, at present it is almost not used due to the high cost, high consumption and low mechanical strength due to its high porosity.

Known technology for the production of foundry coke from lean and low-caking coals of the Kuznetsk coal basin. The main disadvantage of this technology is the high cost of coking.

Over the years, attempts have been made to use various grades of coal without any preparation for it in both blast furnace and cupola production.

, где Д_в - диаметр вагранки, причем дутье в кислородную зону подают подогретым до 450-550°С в равных количествах на двух горизонтах с расстоянием между ними (17,5-20)% от диаметра вагранки [патент RU 2335718. Пашков В.В., Селянин И.Ф. и др.].A known method for cupola melting of cast iron and oxide materials on anthracite, including loading materials into the cupola shaft and blowing into the oxygen zone, characterized in that the level of material loading in the furnace is

where D _in - the diameter of the cupola, and the blast in the oxygen zone is fed preheated to 450-550 ° C in equal amounts on two horizons with a distance between them (17.5-20)% of the cupola diameter [patent RU 2335718. Pashkov V. V., Selyanin I.F. and etc.].

, где Д_в - диаметр вагранки, а также то, что дутье в кислородную зону подают на двух горизонтах с расстоянием между ними (17,5-20)% от диаметра вагранки.This patent describes a technology that allows to eliminate the main disadvantage of anthracite - low thermal stability, as a result of which, when heated quickly in a cupola and high pressure of a column of a metal charge, it crackes into small pieces, which reduce the free section of the cupola and lead to disruption of the melting course. It is indicated that heating the blast to 450-500 ° C reduces the likelihood of cracking of anthracite, thereby contributing to the normal course of the process. The main disadvantage of this method is that the level of material loading in the furnace is limited by the ratio

where D _in - the diameter of the cupola, as well as the fact that the blast in the oxygen zone is fed at two horizons with a distance between them (17.5-20)% of the diameter of the cupola.

Closest to the claimed is a method of melting cast iron in a cupola with secondary blast, which allows you to replace part of the coke with a working fuel spike with coal [Selyanin I.F. Melting cast iron in a cupola with an expanded combustion zone using coal. / I.F.Selyanin, G.L. Marx // Resource-saving technological processes in foundry: abstracts of the II Republican scientific and technical conference; Ordzhonikidze. - 1988. - S. 32-33]. In this method, lean coal of the TK brand of the Kuznetsk basin was used. Experimental melting showed that the replacement of coke with coal positively affects the chemical composition of the resulting cast iron. The consumption of scarce coke during the melting of cast iron in a cupola with secondary blasting can be reduced. However, the replacement of 50% coke with coal in the working fuel spool leads to a slight decrease in the temperature of cast iron on the cupola of the cupola, and with a further increase in the proportion of coal, the temperature of cast iron drops significantly.

The disadvantage of this method is that it is impossible to completely avoid the use of coke.

The objective of the invention is to use instead of coke a mixture consisting of 60% lean coal and 40% birch firewood. Which leads to a stable course of melting and a cheaper process of smelting.

To do this, in the method of cupola melting of cast iron and oxide materials on lean coals, including loading fuel and materials into the cupola, according to this invention, 40% of birch wood and 60% of lean coals are added to fuel spikes, while the blast is heated to 450-550 ° C.

The essence of the method is that birch firewood does not lose its strength during combustion and has a high calorific value Q = (4 ÷ 4,5) · 10 ³ kcal / kg, lean coals Q = (7,5 ÷ 8,3) · 10 ³ kcal / kg, and coke Q = (6.2 ÷ 6.8) · 10 ³ kcal / kg.

During cupola melting, the optimum amount of heat is generated on coke.

For the normal course of the cupola process, it is necessary that, as a result of burning a mixture of wood and lean coal, the same amount of heat is released as when burning coke.

For a given percentage: 40% firewood and 60% lean coal, the amount of heat released during the combustion of the fuel spike is

Q _total = Q _firewood + Q _coal = 0.4 · 4.5 · 10 ³ + 0.6 · 8 · 10 ³ = 6.6 · 10 ³ kcal / kg.

Thus, one kilogram of the mixture - firewood (40%) and lean coal (60%) give the same amount of heat as one kilogram of coke. This replacement is thermally equivalent.

Firewood during burning and loading do not crack, hold pressure of the upper layers of the charge well, as the frame perceives the load on itself and unloads pieces of coal from the load. This allows you to significantly increase the level of loading of charge materials.

Also, firewood is a moderator of the combustion reaction, as a result, the height of the oxygen zone increases.

Starting at 150 ° C, wood pulp loses hygroscopic moisture. Starting from this temperature and with a further increase in temperature, the process of evolution and combustion of volatiles begins. Upon reaching a temperature of 270-280 ° C, a rapid reaction of enhanced decomposition of wood organic matter occurs with the release of a large amount of gas, accompanied by significant heat release, reaching up to 6% of the total initial calorie content of wood [L. Marienbach. The use of local fuels and substitutes for coke in the smelting of cast iron. MASHGIZ, 1943, p. 28-29].

Thus, heat evolution reactions begin to occur already at the upper horizons of the furnace. The carbon contained in the wood, while not fading.

Some cooling effect, when using raw firewood, is compensated by heating the blast to 450-550 ° C. It also favorably affects the resistance of coal against cracking.

The density and elastic modulus of lean coals is higher than that of coke. The resistance of coal against cracking in the oxygen zone increases when the blast is heated.

Heated blast contributes to the reaction

instead of reaction

which reduces the surface temperature of coke in the oxygen zone, temperature gradients and reduces the likelihood of cracking of coal.

The moisture that is released from the wood during combustion moisturizes the blast and also contributes to the course of reaction (I) with the same positive effect.

The invention proposes to blow the blast to 450-550 ° C.

Heating the blast below 450 ° C is not enough to effectively suppress reaction (II) and develop reaction (I). The surface temperature of a piece of coal in the oxygen zone remains high, about 2000 ° C, which causes high temperature gradients of the surface, increases the likelihood of cracking a piece of fuel.

Heating the blast over 550 ° C is impractical, since radiation-convective recuperators are installed on small shaft furnaces, in which heat-transfer pipes from heat-resistant steel quickly fail over this temperature.

Experimental swimming trunks were carried out on the cupola of the Novokuznetsk enterprise Izolit CJSC. The cupola had an internal diameter of 1250 mm and two loading holes at a height of 3.5 and 5.5 m from the level of the main row of tuyeres. The cupola is intended for the preparation of oxide melt from waste blast furnace slag and rock - diabase for the production of mineral wool. The fuel used was birch firewood and lean coals of the TPKO brand of OJSC PF Razrez Krasnogorsky (South of Kuzbass).

The cupola is equipped with a radiation-convective recuperator, which allows heating the blast to 550 ° C.

Two series of experiments were performed. First series: the material loading height was 4.0 m, the amount of firewood added to the fuel spikes varied between 20-60% by weight (Table 1).

Table 1 Temperature of oxide material depending on the amount of firewood in fuel spikes The number of firewood,% by weight twenty thirty 40 fifty 60 The temperature of the oxide melt, ° C 1310 1330 1360 1320 1270

Second series: the amount of added firewood in fuel spikes was 40% by weight, the loading height of materials varied between 3.0-5.5 m (table 2)

table 2 Temperature of oxide material depending on material loading height Loading height, m 3.0 3,5 4.0 4,5 5,0 5.5 The temperature of the oxide melt, ° C 1280 1345 1360 1365 1355 1320

The first series of experiments showed that optimal results are achieved with 40% birch firewood in fuel spikes. With a lower content of firewood, the strength of the frame of birch firewood is not enough to effectively withstand the load of the upper layers of the charge, and pieces of coal partially crack, despite the heating of the blast to 550 ° C. At a higher content, over 40%, the calorific value of the fuel is not enough to overheat the melt to the required high temperatures.

The second series of experiments showed that optimal results are achieved with 40% firewood in fuel spikes and with a material loading height of 4.0-4.5 m. At a lower loading height, the gases do not have time to transfer heat to solid materials, with incomplete heat transfer, the height of the melting zone decreases. the melt overheating temperature also decreases. At a loading height of more than 4.5 m, the frame of the firewood does not withstand mechanical stress from the upper layers of the charge, the pieces of coal begin to crack, the melting level decreases, and the melt temperature drops.

Iron smelting was carried out at OJSC “Universal” (Novokuznetsk). The experiments were carried out on a cupola with an internal diameter of 1350 mm and a maximum loading height of 5.2 m. The cupola is equipped with a pipe-in-pipe recuperator, which allows heating the blast to 450 ° С. The charge consisted of 60% pig iron, 30% battle molds and 10% steel scrap. The fuel used was birch firewood and lean coals of the TPKO brand of OJSC Open Society “Razrez Krasnoyarsky” (south of Kuzbass). Two series of experiments were also conducted.

First series: the material loading height was 4.0 m, the amount of firewood added to the fuel spikes varied within 30-50% by weight (table 3).

Table 3 The number of firewood,% by weight thirty 35 40 45 fifty Cast iron temperature, ° С 1350 1375 1380 1360 1300

The second series: the amount of added firewood in fuel spikes was 40% by weight, the loading height of materials varied between 3.5-5.4 m (table 4).

Table 4 The temperature of cast iron at the outlet, depending on the loading height of the materials. Loading height in meters 3,5 4.0 4,5 5,0 5,4 Cast iron temperature, ° С 1360 1380 1375 1355 1340

When melting oxide materials, birch chocks ⌀ 120-130 mm long 150-160 mm were used, while casting iron, the size of chocks was ⌀ 150-180 mm, length 200-220 mm.

The use of firewood in the melting of cast iron and oxide materials gives an optimal effect on the temperature of the melt being released at the same parameters for the consumption of firewood - 40% for the loading height of 4.0-4.5 m.

The thermophysical cause of this phenomenon is one and the same. The optimum temperature of cast iron was 20 ° C higher than that of the oxide melt. This is due to the fact that isolator is serviced by a 6/6000 m ³ / h VM blower at Izolit CJSC, and a universal blower with a larger VM capacity of 15/15000 m ³ / h is serviced by a universal blower. Therefore, when melting on cast iron, the cupola was better supplied with air, which led to an increase in the temperature of the melt.

Claims (1)

Method for cupola melting of cast iron and oxide materials on lean coals, including loading charge materials and fuel into fuel spikes, supplying blast heated to 450-550 ° C, characterized in that a mixture of 40% birch wood and 60% lean coal is used as fuel the height of loading materials into the cupola 4.0-4.5 m.