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Tolkachova Maryna

Maryna Tolkachova

Faculty: of Ecology and chemical technology

Speciality «Ecology of metallurgy»

Ways of reduction of emissions dioxins and furans in electric steelmaking process

Scientific adviser: candidate of engineerings sciences Michael Peristiy

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ABSTRACT


TABLE OF CONTENTS

  1. INTRODUCTION
  2. SURVEY OF RESEACH AND DEVELOPMENTS
  3. CONCLUSIONS
  4. LITERATURE

INTRODUCTION

Theme urgency. Electric steelmaking plants, are intensive sources of allocation of dioxins and furans. Frequently the metal scrap arriving as raw materials for a meltdown, is strongly polluted by the rests of organic substances (various coverings, a paint, the rests of oils, plastic), that leads to occurrence of dioxins in the departing gases formed at a meltdown.

Therefore, at the present stage, in connection with introduction of rigid ecological norms on extretion harmful substances and the further rise in price of all kinds of energy, is put the problem of finding the ways to eliminate the reasons of formation the basic sources of dioxins and furans at a steelmaking

The purposes and problems

Purposes:

To develop actions for reduction of formation of dioxins in electric furnace steelmaking for prevention of negative influence on surrounding environment, and also on decrease in power expenses of electric steelmaking plants

Problems:

– To study the reasons of formation dioxins in gas emissions of electric steelmaking plans;

– To offer ways of prevention new synthesis of dioxins in technology process.

Scientific novelty of work – consists in working out of the new combined process of hot conditioning of scrap which eliminates principal causes for the formation of dioxins and furans in electric furnace steelmaking, and results to decrease of consumption the electric power.

Practical value of results of work – consists in working out of technological methods which will provide decrease in emissions of dioxins to admissible size in the conditions of electric steel-smelting production. Use of these methods will allow the enterprise to organise more effective production of a steel, having ensured the minimum negative effect of production on environment, will allow to lower possible ecological payments for emissions, will lower product cost at the expense of decrease in power inputs and reduction of ecological payments, will allow to increase competitiveness of production and to increase production export capacities. Results of the given work can be applied to conditions of any factory [4].

Dioxin are a family of complex chemicals containing chlorine, known as polychlorinated-p-dioxins (PCDDs) and the related furans (PCDFs). There are several hundred dioxin substances. Some dioxin-type compounds are toxic at very low levels. The most toxic is 2,3,7,8-tetrachloro-dibenzo-p-dioxin, which is often referred to 2,3,7,8-TCDD, or just TCDD. Excessive exposure to dioxins may affect the heart, immune system, liver, skin, thyroid gland and the unborn child, and may cause cancer. The Environment Agency aims to ensure that environmental exposures are too low to harm human health. [1].

Picture 1 – Scheme of structure of dioxins

Picture 2 – Scheme of structure of furans

Dioxins have a high chemical firmness, they get to a human body through air, water and a foodstuff and concentrate in fatty fabrics. The big danger in connection with accumulation is represented by long receipt of dioxins to an organism in small quantities [1].

Question condition at local and national level

By results of scientific research a problem of presence of dioxins in gas emissions of electric steelmaking plants was engaged in the masters work Dolzhenko E.G. But it placed emphasis in the work directly on clearing of departing gases in the end of electrosteel-smelting process, without affecting the elimination of harmful substances at heating of scrap metal.

The review of researches the theme in the world

In various countries are being developed to reduce emissions of dioxins from the EAF furnaces

The enterprise «Fest-Alpine» (Linz, Austria) has in the early 1990s developed new system for clearing of departing gases of electric arc furnaces not only from a dust, but also from dioxins and other undesirable substances. Installation «Erfayn» wet type for clearing of departing gases is introduced on sinter plant the companies «Fest-Alpine Steel Linz». By means of the given system simultaneous extraction of a dust and other polluting substances, such as НСl, HF, NOх, SО2, heavy metals, dioxins and furans, is carried out in uniform process [5].

On firm «Daido Steel», Japan, is developed economic highly effective system to reduce of dioxins emission from arc furnaces which contains consistently connected two dedusters: for direct catching of high-temperature departing gases from the furnace and for catching low-temperature departing gases in plants where the arc furnace so departing gas after a direct deduster arrives on input of a plants deduster is established.

The electric steel-smelting process of firm BSW in Germany pays the big attention to preservation of the environment, in particular the maintenance of dioxins in emissions from the furnace. In 1991 the firm has entered new system of suction and processings of the departing gases, including chamber of high-temperature reburning of gas in which occurs partial dissociation molecules of dioxins, and the chamber of fast cooling of gas to 150 – 300 °С. As a result concentration of dioxins has decreased to 0,03 ng/m3 [8].

MAIN PLANNED RESULTS

The combined process of preheating scrap

The carried out analysis of existing processes of preheating scraps, perfection of a stream and heat exchange of departing gases, improvement of thermal performance of of the second generation have shown basic lacks of existing processes of preheating scraps on an example of the integrated installation. Preheating process is characterised by the large difference of temperature on height of a column of a heated scraps – from 930 °С in the bottom part and to 150 °С in the top part of a mine heater. The average temperature in preheating scraps is less than 520 – 560 °С. Such distribution of temperatures in scraps column creates favorable conditions for formation of various harmful substances, such as dioxins and furans (PCDD/F), flying hydrocarbons (VOC) and other substances which are formed at temperatures below 750 °С.

These harmful substances on existing installations are eliminated by means of reburning in special chambers of reburning at 850 °С, with the subsequent sharp cooling of departing gases to 250 °С. It follows the basic conclusion: for the decision of existing problems of preheating a scrap it is necessary to pass from secondary to primary actions which eliminate the causes formation of dioxins and furans and conduct to full of preheating scraps to average temperature of about 800 °С.

Picture 3 – Temperature limits and zones of allocation of harmful substances in height scrap

Essentially new method of the combined heating scrap which combines an existing method of use of heat of departing oven gases and input of additional heat through an external energy source is developed. Heat input is carried out in steps in each section of a mine heater for the purpose of prevention of temperature drop of departing gases below 850 °С and full of scrap preheating to 800 °С. This combination of heating scraps does not suppose temperature drop and excludes, thus, the basic source of formation of dioxins and furans, and flying hydrocarbons.

CONCLUSIONS

Thus, the combined process of preheating scrap metal promotes the complete combustion of organic impurity and prevents formation of dioxins and furans in the concentration exceeding admissible norms, allows to reduce the expense of the electric power and duration of fusion, to reduce the release of harmful substances into environment.

LITERATURE

1. Проблема диоксинов [Электронный ресурс]. – Режим доступа:
http://www.textronica.com/aplicate/articles/diox1.htm

2. Тимофеев И. Г. Удаление диоксинов и фуранов из технологических газов ДСП //Электрометаллургия. 2003. №8.   С.   29   –   33

3. Райле В. Т. Концепция комбинированного подогрева металлолома в шахтных дуговых сталеплавильных печах//Электрометаллургия. 2011. №6. С. 42 – 46

4. Киселев А. Д., Тулуевски Ю. Н. Повышение эффективности газоудаления дуговых сталеплавильных печей. М.: Металлургия, 1992 С. 11 – 20

5. Зотов Д. О., Медведь Л. Н. Диоксины – экологическая опасность. // Сталь. – 2000. – № 1. – C. 82 – 86.

6. Дунаев Е. Г. Уменьшение выбросов диоксинов из дуговых сталеплавильных печей. // Новости черной металлургии за рубежом. – 2003. – № 3. – C. 51 – 52.

7. Королев Т, Вернеров С., Вирлинг Ю. Уменьшение выбросов диоксинов в электросталеплавильном производстве. // Черные металлы. – 2005. №5. С. 61 – 67.

8. Краснов О. Н. Снижение образования диоксинов в электросталеплавильных цехах. // Новости черной металлургии за рубежом. – 2005. – № 7. – C. 42 – 43.

9. Юзов О. В., Харитонова М. А., Гурьев В. С. Эффективность охраны атмосферы от выбросов сталеплавильного производства. – М.: Металлургия, 1987. – 103 с.

10. Лопухов Г. А. Эволюция электросталеплавильного производства к 2010 году // Электрометаллургия. 2002. № 5. С. 2 – 3.


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