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Abstract

Content

Introduction

Currently, with the constant growth rate of the industry significantly increases the level of consumption of natural resources. Iron and steel industry is one of the major consumers, in particular iron ore. However, with the growth of consumption of resources are growing and stricter quality requirements, which directly depends on the quality of the raw materials used. Due to the fact that in nature significantly reduced inventories rich iron ore, so there is a need to resort to the processing of iron ore with poor subsequent enrichment.

But the process of ore grinding provided a finely dispersed material, so the use of this material without prior agglomeration process was impossible.

With a large decrease in the level of content in the ore began to develop recycling technologies metallurgical waste is to use recycled materials (iron-containing waste) such as metallurgical sludge, mill scale, etc. for steel. With the development of this technology conventional sintering techniques such as agglomeration and balling can not provide the required performance and quality of the material since the metallurgical residues are located primarily in the pulverulent state. On this basis, the steel industry are beginning to use briquetted iron as a method of sintering waste.

Thus, at present, briquetting has received a new impetus to the development in the agglomeration of iron-containing waste.

Theme urgency

In recent years, the steel industry has become an urgent topic of recycling waste. One of these is a waste of mill scale. In the rolling mill produced a large amount of oily scale that accumulates in the chip catcher. Mill scale contains more than 60% of the iron, so it economically feasible to use in the blast furnace and steelmaking processes. However, the scale in its original state can not be used as smelting slag fines will burn, on this basis to get the issue of its agglomeration before melting. The most effective method of sintering mill scale is briquetting.

Thus the study of the process and apparatus briquetting mill scale at the present time is quite important.

Goal and tasks

The object of study: the process of forming device and briquettes from mill scale.

Objectives: To study the process of briquetting mill scale and the development of an apparatus for producing briquettes.

To achieve this goal it is necessary to solve the following problems:

1. The main directions of development of briquetting technology

At the present level of development of metallurgical production significantly increase the scale of consumption of material resources and the importance of the factor of completeness of their use, so the involvement of secondary material resources is of paramount importance. In this regard, improving the traditional and the development of new technologies is a prerequisite for sustainable development of industry [1].

There are three ways pelletizing iron ores agglomeration, balling, and briquetting.

Agglomeration – a process of agglomeration comprising finely divided particles sintering ore sintering machine and getting pieces of material that is subject to further fragmentation in the appropriate faction.

Balling – is the process of pelletizing moist fine ore particles which are formed by spherical beads of different sizes followed by hardening – pellets.

Briquetting – a sintering process comprising compacting fine particles of ore rich with and without the use of binders in the form of predetermined dimensions.

Sintering and pelletizing unlike briquetting were more prevalent as these technologies have had quite a performance.

Currently frequently used methods of agglomeration and sintering of raw balling largely exhausted their reserves and can not provide the necessary performance in the current circumstances.

Due to the fact that in nature significantly reduced inventories rich iron ore, so there is a need to resort to the processing of iron ore with poor subsequent enrichment. The process of deep iron-ore enrichment is only possible when the small of her grinding. Such micronized concentrate for direct smelting is not suitable as a column of small charge materials in a blast furnace has a low permeability, and accompanied by a very intense fusion dust removal. Sintering of such thin materials sinter machine is slow, leading to decreased productivity and poor quality tapes agglomerate. When working on getting when this fragile and different-sized pieces of sinter not provided with good gas permeability of the charge domain, and thus greatly reduces the technical and economic performance of blast furnaces [2].

Thus, under the current technical level is difficult to obtain sintered agglomerate or solid pellets with a high content of free carbon. At the same time, these materials are produced by briquetting. However, briquetting in the steel industry has not yet received appropriate recognition. Basically it is briquetted metallized materials, fluxes and ferro-alloys for steel production.

Briquetting has a number of advantages, which in the current situation of industry allow us to consider it a promising method of agglomeration. These include the following [1]:

These advantages are relevant to effectively solve the problem how to obtain new, complex raw materials including iron oxides, reducing agent and flux effective treatment for introduction of raw materials, such as metallization, reducing harmful effect of metallurgical processes on the environment.

The main disadvantages of briquetting usually include the following [1]:

To date, most of these problems are solved partly. Abroad formed several areas receiving strong briquettes, which include the "hot" briquetting, high-temperature processing of briquettes, the use of heat-resistant binder.

2. Brief description of the raw materials for briquetting

In metallurgical production use large amounts of material resources.

as application and briketiruemye metallurgical materials are divided into major and minor.

basic materials constitute the main content of the briquette, for example, ores, concentrates, smelter.

Auxiliary materials used in the production of briquettes as extensions that improve the process and quality of the briquettes. The auxiliary material includes fluxes, dopants, etc.

Fuel feed can be as basic and auxiliary material for briquetting. As fuel feedstock can be a pulverized coal, coke breeze, the battle of the electrodes, etc.

By source of education all the materials are divided into primary, fresh and circulating materials, secondary materials or waste. To current materials used include waste, spillage, returns, and side-by-products.

Under the smelter in the broadest sense should be understood raw materials and energy, due to various reasons are not used to produce the main products. Waste is an inevitable part of the existing technology of metals [1].

to ore raw materials such as ore include:

In particular, for iron and steel industrial significance of iron ore.

Iron ores are classified according to the type of ore mineral, the following are the most common varieties of minerals [2]:

to briketiruemym metallurgical wastes include:

Scale – a scaly particles of different thickness consisting of oxides of iron as well as hematite and magnetite. According to the chemical composition of the slag is close to pure magnetite (65-72% Fe). In metallurgical slag formed in steel production and in cold or hot rolled steel. For example, rolling mill scale output is the average of 1.0-3.0% by weight of the finished steel.

3. Brief description of the binders for briquetting

When briquetting many kinds of minced raw having insufficient autohesive properties even at high pressure (180 MPa or more) in the usual cold-pressed to get a strong briquettes without sintering is not possible. In such cases, the use of binders – supporting materials that improve the stickiness of the particles and increase the strength of the briquettes to a specified level [1].

Since additives such materials can range from a few to 10% or more, they must meet the following requirements [2, 3]:

Binders subdivided into three types:

To common inorganic binder should include hydrated lime, sodium silicate, aluminate and Portland cement. However, many of them have significant drawbacks. So, slaked lime, Portland cement hydration when heated give moisture and lose strength, water glass contains significant quantities of alkali and silica, alumina cement and besides extremely expensive.

To common organic binders include coal tar and oil, molasses, waste hydrolysis and pulp industry, etc. A common drawback of organic binders is their pyrolysis or burning at high temperatures with a loss of strength, and to make a significant amount of sulfur pellets.

Link refers to the combined mixture of different binders. These compounds can improve the positive and negative properties decrease. For example, a mixture containing waterglass and lignosulphonate making a reduced amount of alkali silica or sulfur than each link in isolation, while providing high mechanical strength of briquettes.

As binders is preferable to use the most common and well-studied materials:

Lime, or calcium oxide CaO in the technique known as quicklime or burnt lime, which is in contact with water forms a hydrated lime, has high astringent properties. Hydrated lime is relatively cheap, strong enough and well-miscible binder and at the same time flux material The main drawback of slaked lime is that when heated to about 580 oC hydrate moisture begins to move, causing the strength of briquettes falls [ 1].

Liquid glass sodium GOST 13078-81 contains an average of 30% SiO2, 13% Na2 O, 0,8% impurities Al2O3, SO3 and CaO, the rest – water. Additives waterglass amount of 5-7% (over 100%) yield after drying extremely durable preform and fayalite formed during heating promotes the formation of liquid phases. A significant drawback of water glass is a significant increase in the silica content of the cast and alkalis.

Bischofite MgCl2×6H2O, giving ignition moisture becomes extremely solid crystalline salt MgCl2, which can serve not only as a binder, but also the substance that carries the zinc in the volatile compounds. The disadvantage of this coupling is that it gradually after calcination, attaching the moisture out of the air, spreads, and the cake loses its original strength [4].

Bentonite has a good astringent properties. Its basis is the montmorillonite which Al1,67Mg0,33×[(OH)2Si4O10]0,33×Na0,33(Н2О)4, when dissolved in water forms a highly dispersed colloidal particles having a high autohesion properties, the surface of which is 600-900 m2/g it is widely used in the production of pellets. Fuel bentonite is generally 0.5-1.5% of concentrate used [4].

Molasses (molasses feed) is a waste product of sugar beet production, and therefore a readily available and relatively cheap. Sulfur moderate [5]. As a binder, molasses has a satisfactory astringent properties. Additive 7% molasses (over 100%) can be used not only durable cake, but also reduce the content of reducing by 2%. Recoverability of briquettes from the mold is satisfactory. The crush strength of briquettes laboratory additive 7% molasses, dried at about 250 oC for 0.5 h, up to 40 MPa.

Although significant disadvantage that part of the binder is the poor mixing of the basic components of briquettes molasses together with waterglass, is assumed to be the most effective types of binders. Combined binder composed of a mixture of these materials can be very promising [1].

Coal tar pitch is a hard, brittle material in black, which is the residue of the distillation of coal tar, coke plants exercised. The density pitch 1100-1240 kg/m3, the softening temperature of 50-140 oC (depending on the brand), the ignition temperature of 230-300 oC. It is commonly used for briquetting of coal [2, 3].


At the moment, master thesis is to be written. Final completion: January 31, 2013. Full text of the work and materials on the topic can be obtained from the author or his manager after that date.

References

  1. Ожогин В.В. Основы теории и технологии брикетирования измельчённого металлургического сырья: Монография. – Мариуполь, ПГТУ, 2010. – 442 с.
  2. Равич Б.М. Брикетирование в цветной и чёрной металлургии / Б.М. Равич. – М.: Металлургия, 1975. – 232 с.
  3. Лурье Л.А. Брикетирование в чёрной и цветной металлургии / Л.А. Лурье. – М.: Металлургиздат, 1963. – 324 с.
  4. Штрюбель Г. Минералогический словарь / Г. Штрюбель, З. Циммер. – М.: Недра, 1987. – 494 с.
  5. ГОСТ 30561-98. Меласса (патока кормовая). Технические условия. – М.: Изд-во стандартов, 1998.