RU2606375C1 - Method of producing iron-rich lime - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, in particular, to a method of producing iron-rich lime. Method involves loading in tubular furnace in form of a mixture of limestone and iron-containing additive, firing and pelletizing. Prior to loading into furnace iron-containing additive is produced by granulation of converter sludge to level of humidity no more than 12.0 %, followed by mixing lime and iron-containing additive in ratio: limestone 99.0–99.9 %; iron-containing additive 0.1–1.0 %. Further, obtained charge is loaded in tubular furnace and annealed for 1.5–2 hours at furnace rotation of 1-1.5 rpm, wherein annealing is started at a temperature of 750–850 °C, and completed at temperature 800–900 °C. For preparation of iron-containing additive converter sludge is used with following chemical composition, wt%: Fe₂O₃ not less than 12.0; FeO not less than 29.0; Fe_total. not less than 40.0; balance – unavoidable impurities. Surface of lime pieces has a coating layer based on compounds CaO, MgO, FeO, Fe₂O₃ with thickness of 0.5–3.0 mm.

EFFECT: invention ensures reduction of costs for production of steel due to increased degree and rate of recovery of CaO slag.

3 cl, 1 ex

Description

The invention relates to the field of ferrous metallurgy, in particular to a method for producing flux based on lime and iron-containing material in a rotary kiln.

The closest in technical essence to the present invention is a method for producing flux of steelmaking, including firing in a rotary tube furnace a material consisting of a mixture of limestone and iron-containing material, with a ratio of 24: 1, with additives of 35-40% of the water by weight of the charge being loaded and crushed to a particle size of not more than 0.08 mm The resulting mixture is loaded into a rotary tube furnace, calcined at a torch temperature of 1450-1510 ° C and pelletized [Patent RU No. 2078832, IPC C21C 5/36, C22B 1/00, 1997].

The disadvantages of this method are the significant cost of preparing the mixture: the need for thorough grinding, mixing with water, energy costs for the evaporation of water, as well as a high proportion of iron-containing material.

The technical result of the invention is to increase the yield of lime by reducing the amount of screening of a fine fraction of limestone and lime, reducing losses during transportation of lime from the place of production to the steelmaking unit, as well as increasing the degree and rate of assimilation of CaO by slag and, as a result, reducing the cost of steel production .

The specified technical result is achieved by the fact that in the method for producing ironized lime, comprising loading a mixture of limestone and an iron-containing additive into a tube furnace, calcining and pelletizing it, according to the invention, before loading the iron-containing additive in the furnace, granulate the converter slurry to achieve a moisture level not more than 12.0%, then they mix limestone and an iron-containing additive in the ratio:

limestone 99.0-99.9%;

iron supplement 0.1-1.0%,

after that, the resulting mixture is loaded into a tubular furnace and fired for 1.5-2 hours at a rotational speed of the furnace 1-1.5 rpm, while the firing is started at a temperature of 750-850 ° C, and finished at a temperature 800-900 ° C.

To prepare the iron-containing additives, converter slurry with the following chemical composition is used:

Fe ₂ O ₃ not less than 12.0;

FeO not less than 29.0;

Fe _total not less than 40.0%

the rest is inevitable impurities.

The surface of the pieces of lime is covered with a layer based on compounds of CaO, MgO, FeO, Fe ₂ O ₃ with a thickness of 0.5-3.0 mm.

The essence of the proposed method is as follows.

It is known that lime production from limestones of low strength of a piece is accompanied by losses in the form of screenings of fine fractions up to 25% of the initial mass of the charge, limestones of high strength of the piece up to 10% of the initial mass of the charge. Transportation of lime from the place of production to the introduction of lime into the melt of the steelmaking unit is also accompanied by losses in the form of spills and dust extraction from gas cleaning of steelmaking units. Through losses of limestone and lime obtained from it, even without taking into account the mass loss during dissociation of limestone, reach up to 40%.

The main source of hydrogen entering the steel and producing steel defects associated with the level of hydrogen is lime, as a material with a very high absorption capacity of open and atmospheric moisture. The shelf life of the produced lime at metallurgical enterprises is therefore limited to 0.5-3.0 days.

It is also known that the degree and rate of assimilation of CaO lime by steelmaking slag directly depends on the level of iron oxides in the slag. FeO is the main CaO solvent in slag. An increase in FeO in the reaction zone of a piece of lime sharply increases the rate of dissolution of CaO in slag.

The use of the inventive method for producing ironized lime allows, during the passage of the mixture of limestone and iron-containing additives through the firing zone of the tube furnace, to form on the surface of the pieces of lime obtained by dissociation of limestone, a strong layer (crust) based on compounds of CaO, MgO, FeO, Fe ₂ O ₃ ( further - a layer). This layer has a sufficiently high strength and prevents the mechanical destruction of a piece of lime in the process of moving from the place of production to the melt of the steelmaking unit, and also protects it from contact with moisture from the surrounding air.

To implement the proposed method, it is necessary to create in the firing zone of the tubular furnace conditions that allow a solid layer to be obtained on the surface of the lime pieces, while maintaining the same level of energy consumption for the production of ordinary lime as the limestone dissociation, without reducing the furnace productivity and obtaining a decrease in the limestone consumption coefficient. Granular converter sludge, which is a waste of our own production, does not bear the cost of lime production.

Initially, converter sludge has a moisture level of 25-40%. During granulation, the converter sludge is dried. The necessity of granulating the converter sludge to a moisture level of not more than 12% is due to the fact that, with higher humidity, the lining resistance of the tube furnace decreases and the likelihood of premature failure of the furnace decreases, as well as the increased humidity of the iron-containing additive does not allow it to be transported using belt conveyors.

When mixing limestone and iron-containing additives in a proportion of greater than 99.9 to 0.1%, the layer obtained on the surface of a piece of lime is not continuous and the required strength of the piece is not achieved.

When limestone and iron-containing material are mixed in a proportion of less than 99.0 to 1.0%, an excessive amount of iron-containing additive sticks to the lining of the tubular furnace, the nastily prevents the normal firing process and leads to the need for the furnace to stop cleaning.

The firing process, which takes place in less than 1.5 hours, which corresponds to an increase in the rotational speed of the furnace over 1.5 rpm, does not allow lime to be obtained with the required CaO content, since it does not have time to dissociate the middle part of the volume of the limestone piece.

The firing, carried out for a time greater than 2.0 hours, which corresponds to a decrease in the rotational speed of the furnace below 1.0 rpm, leads to a decrease in the reactivity of lime or an increase in the time of its extinction.

At a temperature of the beginning of the process below 750 ° C and the end below 800 ° C, the completeness of the process of melting the iron-containing additive is not ensured, and part of the pieces of lime leave the furnace not covered by a layer, and part of the iron-containing material at the outlet has its initial state.

The temperature of the beginning of the process above 850 ° C and the end above 900 ° C leads to excessive energy consumption for its maintenance, as well as the soldering of several pieces of lime into one large one, which leads to the inability to use such lime along the supply paths of bulk materials of steelmaking workshops, which have limitations by fraction of materials used.

The chemical composition of the iron-containing additive affects the thickness and continuity of the layer formed on the surface of the piece of lime. When the content of Fe ₂ O ₃ , FeO and Fe _total . less than the declared values, this layer on pieces of lime will not have sufficient thickness and continuity.

With a layer thickness of less than 0.5 mm, lime pieces do not have sufficient strength. To obtain a layer thickness of more than 3 mm, it is necessary to increase the amount of iron-containing additives to a content of more than 1.0% of the mixture, which leads to the sticking of an excessive amount of iron-containing additives to the lining of a tubular furnace.

An example implementation of the method

Converter sludge with a moisture level of 38% and the following chemical composition, wt. %:

Fe ₂ O ₃ 22.4;

FeO 35.6;

Fe _total 43.4%;

the rest is inevitable impurities.

The converter sludge was dried and granulated for 20 minutes to a moisture level of 10%. After that, the obtained iron-containing additive was fed into the hopper in front of the furnace, limestone was fed into another hopper. Mixing was performed on a prefabricated conveyor by feeding limestone and sludge from different silos in the ratio:

limestone 99.5%;

iron supplement 0.5%.

The resulting mixture was loaded into a tubular furnace and fired for 1.8 hours at a furnace rotation speed of 1.3 rpm. Firing started at a temperature of 770 ° C, and ended at a temperature of 880 ° C.

At the outlet of the furnace, the presence of a layer on pieces of lime was visually evaluated. The layer thickness varied in the range of 0.5-3.0 mm. After cooling, the obtained lime was transported to the receiving hoppers of the bulk material supply path of the steelmaking shop for further use during the steelmaking process.

As a result of the implementation of the proposed method for producing ferruginous lime, the limestone consumption coefficient for lime production and conditionally variable energy consumption was reduced by 12.5%, CaO assimilation by slag from the steelmaking unit was increased by 8.0%, and the metal dephosphorization rate increased by 2.0%.

Claims (6)

1. A method of producing ironized lime, comprising loading a mixture of limestone and an iron-containing additive into a tube furnace, roasting and pelletizing, characterized in that an iron-containing additive with a moisture level of not more than 12.0% obtained by granulating a converter slurry is used, the mixture is obtained by mixing limestone and iron supplements in the ratio: limestone 99.0-99.9% iron supplement 0.1-1.0% wherein, the firing of the obtained mixture in a tube furnace is carried out for 1.5-2 hours at a furnace rotation speed of 1-1.5 rpm, and the firing is started at a temperature of 750-850 ° C, and finished at a temperature of 800-900 ° C . 2. The method according to p. 1, characterized in that the iron-containing additive is obtained from a converter slurry having a chemical composition, wt. %: Fe ₂ O ₃ not less 12.0 FeO not less 29.0 Fe _total no less 40,0 rest inevitable impurities. 3. The method according to p. 1, characterized in that the surface of the pieces of the obtained ironized lime has a coating layer based on compounds of CaO, MgO, FeO and Fe ₂ O ₃ with a thickness of 0.5-3.0 mm