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Abstract

Content

INTRODUCTION

All the steel plants are a source of contamination by dust, oxides of carbon and sulfur. Metallurgical conversions in terms of environmental pollution surpass many times over, all other types of industrial production.

In modern time, main way of producing steel are oxygen-converter, Martin open hearth furnaces and electrosteel-smelting (arc furnace process). Each of these ways of production are to some extent, has negative impact on the environment. Today, to lower impact on environment in areas of where metallurgical plants are located, it is necessary to choose more environmentally friendly ways of producing steel.

Before financial crisis of 2008 Ukraine was one of the few countries where the Martin furnace way of steelmaking was widely used, which is rather power expensive and ecologically harmful. Now the majority of Martin open hearth furnaces in Ukraine is taken out of service [1].

Big share of electric steel in industrially developed and developing countries are produced because of advantages of the arc steel-smelting furnaces (ASSF), working at firm furnace charge at a high speed of fusion. It results in less investment and energy consumption, more high efficiency, and smaller number of emissions of harmful substances in environment [2].

1. Topic of the day

For steel making industry, that has considerable negative impact on environment, is characteristic big consumption of fuel, electric power and raw materials, and as a result, huge volumes of emissions and dumpings are made, producing large amounts of solid waste[11]. Different ways of steelmaking have the advantages and disadvantages. Therefore comparison of the main ways of steelmaking and choosing the environmentally safest way are absolutely necessary for our region.

2. The purpose and task of research and expected results

The purpose of this study – the comparative analysis of ecological indicators in steelmaking process and development of better technical and economic ways, in order to reduce harmful effects on the environment.

Main goal of research:

  1. Comparison of technical, economic and ecological indicators of steel production, carried out in various units;
  2. Choose one of the environmentally safest ways of steel production for DMZ;
  3. Consideration for introduction of the new cleaning equipment;
  4. Development of methods, in order to reduce impact on surrounding environment.

Research object:the main ways of steelmaking process.

Research subject:Result of work will be development of the most ecologically a safest way of producing steel for the region of Donbass.

3. Steel production abroad and in Ukraine

3.1 The modern steelmaking technology abroad

Table 1 represents data on emissions into the environment (dust, CO, SO2 and NOx) Steelmaking for Ukrainian metallurgical companies and steel companies of the EU [23]

Production Dust СО SO2 NOx Total
Ukrainian metallurgical plants
Martin open hearth furnaces 0,81 – 2,9 0,63 – 4,1 0,28 – 0,61 1,34 – 4,3 3,06 – 11,91
Converter process 0,87 – 1,03 0,7 – 5,57 0,009 – 0,06 0,026 – 0,06 1,6 – 6,72
Electric furnace steelmaking 2,9 – 7,1 2,39 – 8,7 0,15 – 0,16 0,9 – 1,8 6,34 – 17,76
Metallurgical enterprises of the EU
Converter process 0,08 – 0,15 1,5 – 7,96 - 0,005 – 0,02 1,58 – 8,13
Electric furnace steelmaking 0,001 – 0,78 0,74 – 3,9 0,024 0,12 – 0,24 0,885 – 5,05

According to the data on the emissions of domestic steelmaking plants are several times higher than similar Western European plants.

Main research of steelmaking in the world focused on improving technology and designing better units. In recent decade, the most significant changes occurred in the electric furnace steelmaking production: improved structural design of electric arc furnaces, significantly increased their specific electric power has been used a great variety of forms of arc - an arc of DC and AC, plasma, with a hollow electrode burning in the foamed slag. Introduced technologies such as vacuum arc remelting and plasma, electron beam, and electro-induction melting.

The company «Siemens VAI MT», at the 9th European Conference on Elektrometallurgii, presented a report about the design features and options for adaptation SimetalCIS Ultimate DSP for remelting of cold and hot DRI DRI, as well as on the work of particle board with the application of up to 40% of liquid cast iron in the charge.

As an example of successful adaptation of particleboard using liquid iron in the charge of the experience electric steelmaking plant of Magnitogorsk Metallurgical plant. Application of oxygen input dispersed into the molten bath provides a decarburization rate 300 kg / h 4m2 bath surface and gives the opportunity to use up to 35% of liquid pig iron in the charge. Productivity of electric furnaces using up to 35% liquid iron in the mixture.

Productivity of electric furnace is 22% of liquid iron and 78% scrap outputs 32melting per day.

At present time, apart from two electro furnaces MMK is using, there is six more pits of liquid iron in the world to successfully operate, chipboard company «Siemens VAI MT»: two 120-ton electric furnace JSC "Severstal" (up to 35% of liquid iron), four 80/100- ton furnace in China. [18]

The company «Fuchs Systemtechnik» developed the environmentally friendly project of arc shaft furnace. To heat the scrap in the furnace is used for combined heating by the thermal energy of exhaust gases and the oxygen burners. In such furnaces the preheating temperature in the batch reaches about 800 - 900 ° C. An additional advantage of passing the exhaust gases through a duct filled with scrap, is partially removing dust from exhaust gases, which reduces the load on the filters.

The company BSW in 1997, has developed technology that recovers zinc from electric arc furnace dust [4]. Zinc recovery method is that the dust is mixed with the powder of coke and heated to 1100 ° C in a rotary kiln. Zinc in the form of zinc oxide collected in the filter, and iron-rich residue is returned to the arc furnace.

In addition, one should take into account the technology associated with the processing and recycling of steel slag. For example, in Japan, about 64% of the converter slag is recycled to raw cement. Cement production allows to increase, share of BOF slag in its composition to 45%, and reduce fuel consumption by 43% compared with the production of Portland cement.

The company «Nippon Kokan» (Japan) develops technology aimed at reducing the weight of the slag, and the use of slag recycling technology to convert them into secondary resources. Among the first in its place, is dominated by the development of the original withoutdross process based on technology of smelting iron low silicon cast iron . This process has reduced the output of slag in steel production in about three times compared to the technology that was used in the past. On the other hand, for efficient use of steel slags in manufacturing techniques such as the "sea units» («Marine Block») - in large-carbonate cubic products bond obtained by blowing carbon dioxide and suitable for planting algae and fish habitats, as well as technology for production on commercial scale potash fertilizers. [5]

3.2 The analysis of steel-smelting production in Ukraine

As of October 1, 2012 at the metallurgical plants of Ukraine in service was: 24 blast furnaces from 36; 17 converters from 21, 11 martin furnaces from 16 and 6 electric furnaces from 15.

In 2012 production of steelmaking decreased to the levels of 42 million tons a year. In 2012 conditions in steelmaking industry as a whole worsened (decrease in volumes of production on comparison since 2011), low prices for products, reduction in export, don't allow the plants of Ukraine to use available production capacity.

Martin furnace production of steel in Ukraine is shrinking. In recent years Martin workshops on Makeevsky metallurgical complex and on Donetsk metal works are closed. Production of steel in present time is carried out this way by only 3 plants: The Mariupol MK of Ilyich, Alchevsky MK and MK "Zaporozhstal" [6].

According to future plans, till 2015 increase in production of electric steel by plants is expected to be 3,6 million tons. per a year [7].

It is obvious that in near future (2015-2017) martin furnaces on "Arselor Mittal Krivoy Rog" and MMK of Ilyich, and probably (before 2017) on MK "Zaporozhstal" will be closed.

Plans are already been made to construct new capacities for production of steel (oxygen converters) [6].

Implementation of those programs that are planned by the plants till 2010-1015 will allow our steelmakers to come near levels, and on a number of the plants to reach technological, technical and economic levels of EU countries [7].

4 Characteristics and particularity of technological process of steelmaking

4.1 Steelmaking, martin open hearth process.

In the atmosphere a large amount of gas and a dust is formed.

Dust content of martin gases of 10 g/m3, and gases from two-bathing furnaces — to 15 g/m3. The dust consists generally of iron oxides. Besides, at it there are oxides of calcium, magnesium, manganese, aluminum, silicon, phosphorus, sulfur. Density of a martin dust is 4,5 — 5 g/cm3. Bulk density - 1,5 g/cm3. Corner of a natural slope 28 — 33 °. Hygroscopicity of a dust of 3 — 8%. The disperse structure of a dust depends on a consumption of oxygen in the furnace and technological process of melting [8].

For cleaning dirty air there is different methods: dry cleaning in dust deposition chamber, cyclones, inertial and fabric filters, cleaning in dry and wet electric precipitators, high-speed dust collectors with pipes Venturi.

It is most rational to apply hose filters.

Because, the equipment of the main units systems of effective gas purification will allow to minimize pollution of atmosphere.

It is recommended to use a thermal fuel that 15-20% reduces NOx emissions. When blowing the bath with oxygen is not highly recommended to raise the lance, as the output of nitric oxide increases sharply [12].

Also, the amount of harmful emissions can be substantially reduced as a result of the rationalization process of steel production and improving the design of the furnace. By using the "ladle-furnace" for secondary metallurgy and continuous casting machines.

4.2 Steelmaking basic oxygen process

The main methods of steel production in BOF way - it's from the top, combined blowing with post-combustion and post-combustion without a converter gas.

An approach to the unification of synthesis of Moore FSM

4 frames, 44.10 КB (45,160 bytes)

Figure 1 – An approach to the unification of synthesis of Moore FSM

a - blowing top b - bottom blowdown, in - combined purging; 1 - slag, 2 - emissions, 3 - metal, 4 - acceleration of slag-metal reactions, 5 - good mixing of the bath, 6 - the introduction of hydrocarbons, 7 - the introduction of a mixture of O2 + CaO powder 8 - additional mixing tubs, 9 - the introduction of an inert and cooling gas and powder CaO

Figure 1 - Comparison of the converter circuit with the top, bottom and combined blowing

The figure shows that the shortcomings inherent in the converter from the top and bottom blowing, disappears when combined blowing is used.

The converter combined with a blowing process comprises feeding through the bottom of the converter of small amounts of an inert gas (argon or nitrogen). Oxygen is fed through the top of a one-or two-tier lance (for post-combustion CO). Gases supplied from below through porous blocks (inserts). Submission of gas from below starts a few minutes before the purge oxygen from above and continues for several minutes after its completion.

When combined purge degree of desulfurization increases by 10 - 15%, while additional transient nitrogen or argon purging sulfur content reduced by 10 - 25% [19 - 21].

When operating the converter in the system post-combustion gas is formed after gas purification containing iron sludge. Because there is no simple and cost affective technologies that exists, utilization is not done and very often they remain unwanted and stored in sludge collectors. In operation, the converter without afterburner - converter dust is formed, which is sent for disposal at sinter plant.

Converter slag, which is a valuable by product is not used and builds on slag dump at the plants. Considerable reserves to organize low-waste production are available in oxygen- converter process. It is possible to increase ecological safety at the Ukrainian steelmaking plants at the expense of improvement and optimization of technology and technological techniques that are:

4.3 Output of steel in electric furnaces

The advantage of electro smelting compared with other production methods of steel is mainly the use of electrical energy for heating the metal. Heating occurs in electrically heated metal or in the immediate vicinity of its surface due to arcing. This allows a relatively small volume to concentrate the large heat capacity of the metal at a high speed and high temperatures. Thus, the duration of melting is significantly reduced compared to the open hearth process, and dust release is significantly lower than the melting converters. Consumption of heat and temperature changes during melting in an electric furnace is fairly easy to control and regulate. In contrast to the open-hearth and converter processes in electric heat is not associated with the consumption of oxidizing agent, which is also a positive development from an environmental point of view. Therefore, electric smelting may be performed in any atmosphere - oxidative, reductive or neutral. Furthermore, electric furnace better suited for the processing of scrap metal. All of the furnace charge can be loaded into one or two doses, significantly reducing emission. The period of melting in electric arc furnaces is considerably shorter than in the open-hearth furnaces operating scrapbook process [13].The most widely used electric arc furnace (EAF), which transforms electric energy into heat, it takes place in an electric arc. Thus, a relatively small amount of large arc power can be concentrated and have a very high temperature. High concentration of heat in the arc allows high speed metal is melted and heated to a high temperature. Despite the obvious advantages of electric furnaces, it is currently under active work to improve the design and intensification of smelting furnaces to achieve maximum results for reducing the duration of melting, reduce harmful emissions, and ensuring low consumption of energy and resources [14].

Conclusion

Steel production industry in the country is in need of significant investments. However, due to lack of funds the majority of Ukrainian metallurgical plants were not able to modernize existing facilities, even in the period of crisis, when production levels were low.

It was only in 2010 - 2011 years. the industry once again stepped up the implementation of various projects, most of which concerned the steelmaking and rolling processing. Steel making plants was able to resumed long-term projects, including the construction of electric steel plants. Actively investing in the development of metallurgical assets of the company in 2012 [6].

Remelting scrap in open Martin hearth furnaces is accompanied by increased energy consumption and high amounts of pollution of the environment. In addition, the use of open-hearth furnaces to produce steel makes significant impact on environment during whole cycle.

Recycling of scrap in converters is limited to the content of the pig iron oxidized contaminants. Increase the proportion of scrap by increasing silicon content in pig iron increases energy throughout the whole cycle, increases the output of slag and dust emissions at all stages of overflowing and melting iron.

Thus, we can conclude that the best way for melting scrap is to use new generation of electric arc furnaces with magnetodynamic mixing of steel bath. This will significantly reduce impact on the environment during melting process.

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