COKED SOLID AGGLOMERATE AND METHOD FOR PRODUCING SAME

Description

FIELD OF INVENTION

The present invention relates to solid agglomerates. More specifically, the present invention relates to solid agglomerates for use in steelmaking furnaces.

BACKGROUND OF THE INVENTION

One of the main functions of metallurgical furnaces is iron reduction, where iron Fe is separated from its ore Fe₂O₃. This separation occurs by means of chemical reduction, which involves separating a metal from its oxide, and is carried out using a reducing agent. This reducer is a material that must be more attractive to oxygen, under the conditions of the operation, than the metal to be reduced. The main reducing agent used in the steel industry is coke, which comes from mineral coal.

The steel industry relies heavily on metallurgical coal, which accounts for a large proportion of the final cost of the steel produced. Mineral coal for integrated coking steelmaking is called coking coal, which is an essential substance in the reduction of iron ore to metallic iron, as it combines with oxygen to create carbon dioxide, iron, and slag.

The class of coal commonly used for steelmaking is bituminous coal (soft coal) which forms a solid mass when heated (coking coal); on the other hand, if it does not soften or aggregate when heated, it is called non-coking coal.

Today, the use of agglomerates in the steel industry is becoming increasingly common. The agglomeration process consists of grouping fine-grained materials with the aim of obtaining a larger product through the use of binders. Through this process it is possible to obtain, for example, high-quality metallic agglomerates or coal briquettes, taking advantage of the small fractions that are usually discarded. In some cases, coal pellets can replace coking coal and metal pellets can replace iron ore.

Among the different agglomeration processes, the coal briquetting technique is gaining ground in the industry. This technique, which can be used for both mineral and vegetable coal, generally involves the following steps: (i) granulometric balancing of the coal or biomass particles; (ii) mixing of binders (agglomerants); (iii) mechanical compaction; and (iv) drying of the briquettes. The documents below describe examples of coal briquettes and their respective production processes.

Document U.S. Pat. No. 8,585,786B2, for example, describes a method and system for briquetting solid fuel, such as coal. In this document, the solid fuel is transported through a continuous feed solid fuel treatment plant, treated with electromagnetic energy and briquetted after treatment.

Document WO2014098413A1 describes a coal briquette and a method for manufacturing it. This coal briquette manufacturing method comprises the steps of (i) pulverized coal supply, (ii) producing a mixture obtained by mixing between 1 and 5 parts by weight of a hardening agent and between 5 and 15 parts by weight of a binder in relation to 100 parts by weight of pulverized coal, and (iii) shaping the mixture. In the pulverized coal supply stage, the pulverized coal comprises (i) more than 0 and no more than 50% by weight of low-grade coal and (ii) a balance of coal ash. Low-grade coal has between 25% by weight and 40% by weight of a volatile fraction (dry basis) and has a crucible expansion number of more than 0 and less than 3.

Document WO2013152959A1 describes a process for the production of a briquette containing coals, in which the coals together with a binder system are subjected to mixing with the introduction of steam and the mixture obtained is subjected to pressing to form briquettes. Here, at least one of the steps: (i) drying the carbon carriers before mixing, (ii) setting the temperature of the carbon carriers to be mixed with the binder system before mixing in a predefined temperature range, (iii) heat treatment of the briquettes after pressing, is carried out by means of direct or indirect interaction with superheated steam. The residual steam obtained is used as at least part of the steam introduced during mixing.

Document AU2008203855B2 describes a process for forming a briquette comprising low rank coal and aggregate material, characterized in that it comprises: drying a low rank coal feed to produce a dry coal with a moisture content of between 8 and 16% by weight; mixing the dry coal with an aggregate material; and compacting the dry coal and aggregate material mixture into briquettes.

As mentioned above, coal briquettes can be used in the process of reducing iron ore or its agglomerates in steelmaking furnaces. Document WO2011108466A1, for example, describes a process to produce iron-coke by carbonizing an agglomerate comprising mineral coal and iron ore. The process produces iron-coke which, in a blast furnace, is more reactive than the coke it contains with CO₂. The iron-coke production process in document WO2011108466A1 comprises the carbonization at a temperature above 800° C. of a mixture composed of mineral coal and iron ore to produce iron-coke.

The process in document WO2011108466A1 turns out not to be ecologically sustainable, since it requires significant amounts of energy to carbonize the agglomerate and does not provide for the use of renewable carbon material.

This invention solves the problems described above in the prior art in a simple and efficient way.

SUMMARY OF THE INVENTION

The first objective of the present invention is to provide a coked solid agglomerate for use in a steel furnace and a process for manufacturing it, in which the coking process is carried out at relatively low temperatures.

The second objective of the present invention is to provide a coked solid agglomerate for use in a steel furnace and a process for manufacturing it that uses a reasonable amount of biocarbon, increasing the ecological sustainability of the fuel.

In order to achieve the objectives described above, the present invention provides a coked solid agglomerate for use in a steel furnace, comprising biocarbon, mineral coal and at least one binder. After the solid agglomerate has been mechanically formed, it is subjected to a pyrolysis stage at a temperature greater than or equal to 700° C. and less than 800° C.

The present invention further provides a process for manufacturing a coked solid agglomerate for use in a steelmaking furnace, comprising the steps of (i) mixing biocarbon, mineral coal and one at least one binder, (ii) mechanically forming the mixture of biocarbon, mineral coal and at least one binder to form a solid agglomerate, and (iii) pyrolyzing the solid agglomerate at a temperature greater than or equal to 700oC and less than 800° C.

DETAILED DESCRIPTION OF THE INVENTION

First of all, it should be noted that the following description will be based on a preferred embodiment of the invention. As will be evident to anyone skilled in the art, however, the invention is not limited to this particular embodiment.

The present invention provides a coked solid agglomerate for use in a steel furnace, comprising in its composition biocarbon, mineral coal and at least one binder. For the purposes of this description, biocarbon means any charcoal of plant origin produced according to substantially sustainable standards. Preferably, this biocarbon has a low inorganic content (less than 1%).

Once submitted to mechanical forming, the solid agglomerate undergoes a pyrolysis process at a temperature greater than or equal to 700° C. and less than 800° C. This heat treatment cokes the carbonaceous material in the mixture and increases the interaction and anchoring between all the components of the solid agglomerate, improving its mechanical strength. In addition, the pyrolysis of the solid agglomerate promotes its drying and pre-reduction, increasing its calorific value and preparing it for use in steel furnaces.

Preferably, the pyrolysis of the solid agglomerate is carried out in a rotating cylindrical reactor.

Preferably, the solid agglomerate of the present invention comprises 10 to 75% by mass of biocarbon. More preferably, the solid agglomerate of the present invention comprises 50 to 65% by mass of biocarbon.

Preferably, the solid agglomerate of the present invention comprises from 25 to 90% by mass of mineral coal. More preferably, the solid agglomerate of the present invention comprises 25 to 50% by mass of mineral coal.

Preferably, the solid agglomerate of the present invention comprises 5 to 10% by mass of a binder, which has the function of keeping the compounds of the solid agglomerate bound together. The use of a binder also allows for the use of smaller-grained compounds in the composition of the solid agglomerate.

Optionally, the solid agglomerate of the present invention additionally comprises 5 to 15% by mass of an iron-based compound, such as iron oxide or metallic iron. Mixing an iron-based compound with the agglomerate produces an iron-coke agglomerate. As is well known, due to the catalytic effect of the iron content of iron-coke, the reaction of the carbonaceous material starts from a lower temperature compared to conventional coke. As a result, one can expect a reducing effect on the reducing agent ratio (RAR) by lowering the temperature of the thermal reserve zone when iron-coke is used as a charge material in the steelmaking furnace.

The present invention also provides a process for manufacturing a coked solid agglomerate for use in a steelmaking furnace, comprising the steps of (i) mixing biocarbon, mineral coal and at least one binder, (ii) mechanically forming the mixture of biocarbon, mineral coal and at least one binder to form a solid agglomerate, and (iii) pyrolyzing the solid agglomerate at a temperature greater than or equal to 700oC and less than 800° C.

Preferably, the mixing stage is carried out with 10 to 75% by mass of biocarbon. More preferably, the mixing stage is carried out with 50 to 65% by mass of biocarbon.

Preferably, the mixing stage is carried out with 25 to 90% by mass of mineral coal. More preferably, the mixing stage is carried out with 25 to 50% by mass of mineral coal.

Preferably, the mixing stage is carried out with 5 to 10% by mass of a binder.

Optionally, the mixing step also involves mixing in 5 to 15% by mass of an iron-based compound such as iron oxide or metallic iron to form an iron-coke agglomerate.

The solid agglomerate and its manufacturing process, according to the present invention, has a mass yield of 95%, while the agglomerates of the prior art have a mass yield of around 70%. In addition, with temperatures lower than 800° C., considerable energy savings are achieved in the manufacturing process.

The coked solid agglomerate of the present invention can be used, for example, in blast furnaces, sintering ovens and coking plants. The solid agglomerate containing iron (iron-coke) can be used, for example, to replace small coke in blast furnaces.

Thus, as explained above, the present invention provides a coked solid agglomerate for use in a steel furnace and a process for manufacturing it in which the coking process is carried out at relatively low temperatures. In addition, a reasonable amount of biocarbon is used in the agglomerate and in the manufacturing process, increasing the ecological sustainability of the fuel and reducing CO₂ emissions.

Numerous variations in the scope of protection of this request are permitted. This reinforces the fact that the present invention is not limited to the particular configurations/concretizations described above.