Dioxin

Private : Melatener Straße 103 52074 Aachen, Germany Tel.: + 49 (0) 241 872131 URL: http://www.hochofen.com

Heinrich Wilhelm Gudenau Univ.-Prof. Dr.-Ing. Dipl.-Wirtsch.-Ing.

p

Office: RWTH Aachen University Dept. of ferrous metallurgy Intzestraße 1 52072 Aachen, Germany Tel.: +49 (0) 241 8095788 Fax.: +49 (0) 241 8092368 e-mail: [email protected] URL: http://www.iehk.rwth-aachen.de

Mr. L. Capogrosso RIVA Group ILVA S.P.A. Via Appia Km 648 I-74100 Taranto/ Italy

Consulting Project

Taranto Dioxin Sinter Plant Emission Part I

2 1.

Introduction

At the visit of the Taranto Plant in October 2005 with a lecture and discussion the sinter plant was shown to the contractor. Further information especially by the visit of Mr. Quaranta and Mr. Di Tursi at 01.09.2006 in Aachen were given and discussed. According to the letters to Mr. Capogrosso at the 12.09.2006 and 05.06.2007 the contract of consult service was fixed with an annex. The final report has the following table of contents:

Table of Contents 1.

Introduction

2.

Dioxin -

3.

Review -

4.

Problems at Seveso (Italy), Start of Research about Dioxin Primary Sources Secondary Sources Dioxin at Iron and Steel Industry First Published Results

Iron Ore Sinter Process -

5.

Different Kinds of Dioxins and Furans Structures of PCDD and PCDF Chemical and Physical Properties Formation Mechanism Toxic Equivalency Factors Aims and Limits

Definition Sinter Strand Heat Transport Charged Materials

Experiments in a Sintering Pan - Experimental Apparatus at Institute of Ferrous Metallurgy in Aachen - Results and Discussions of Experiments in a Sintering Pan

3 6.

Measurement in Sinter Plants - Influence of Filter-Systems - Influence of Different Sintermaterials - Results of Dioxinemissions over the Length of the Sinter Strand

7.

Proposals of Dioxin Minimizing by Technological Changes -

8.

Air Fine EOS LEEP Partly Offgas Recycling Eposint Bag filter Injection of pulverized coke breeze Effect of Additives on the Dioxinemission in a Sinter Pan

Prediscussion of the Report Part I

4 2. -

Dioxin Different Kinds of Furans and Dioxins

The polychlorinated dibenzodioxins (PCDD) and polychlorinated dibenzofurans (PCDF) are in general incorrectly summarized as dioxins. The chemist assigns the dioxins to the group of cyclic halogenated aromatic ether. Typical characteristic of the dioxin compounds is the connection of two carbon atoms by an oxygen bridge. For PCDDs, the carbon atoms are connected by a pair of oxygen atoms. PCDFs are connected via a single oxygen atom. /1-3/ Group of dioxins and furans with analogue structure: Cyclical ether (furan) - chlorine-benzofuran - chlorine-dibenzofuran (PCDF) - chlorine-benzoaphthofuran - chlorine-dinaphtofuran - chlorine-phenyldibenzofuran Cyclical diether (dioxin) - chlorine-benzodioxin - chlorine-dibenzodioxin (PCDD) - chlorine-benzoaphthodioxin - chlorine-diaphtodioxin - chlorine-phenyldibenzodioxin -

Structures of PCDD and PCDF

The basic structure of dibenzodioxins and –furans are based on two benzene rings. The benzene rings are missing two hydrogen atoms each, so the carbon atoms can be connected to each other directly with one oxygen bridge (furans) or with two oxygen bridges (dioxins), see Fig. 1.

5 Mono or polychlorinated dibenzodioxins and –furans are nascented by the substitution of the hydrogen atom at the positions 1,2,3,4,5,6,7,8 and/or 9 by chlorine atoms. The number of the chlorine atoms in the molecule is shown by the prefix mono (1) to octa (8). Also characterizing beside the number is the position of the chlorine atoms to each other (isomers). dibenzodioxin

dibenzofuran detailed descreption

common descreption with number of position

Fig. 1: Structural formula of dibenzodioxins and dibenzofurans Compounds with different chlorination degrees are called congeners. There are 210 different congeners together, 75 congeners of dibenzodioxins and 135 of dibenzofurans, see Table 1.

chlorine atomicity 1 2 3 4 5 6 7 8 total congenere

homologues series mono di tri tetra penta hexa hepta octa

brief descreption ---------TCDD/F PCDD/F HxCDD/F HpCDD/F OCDD/F

number of dioxins and furans 2 2 10 16 14 28 22 38 14 28 10 16 2 4 1 1 75 135

Table 1: Composition of chlorinated dibenzodioxins and dibenzofurans

6 The toxicological properties of the mono to tri- CDD/F are under dosed, so the used term “polychlorinated dibenzodioxins/ -furans“ mostly contains only the homologous series tetra to octa. Congeners with chlorine substituents in the 2,3,7,8- position are called “2,3,7,8class” and their toxicological properties should be underlined. The so called “Seveso- poison” the most toxical of the 210 congeners should be pointed out as a special example, see Fig. 2. /14,15/

Fig. 2: Structural formula of 2,3,7,8- Tetrachlorodibenzodioxin The more formal notation of technical literatures dibenzo-p-dioxins or dibenzoparadioxin are pointing out the symmetric position of the oxygen atoms in the structure of the dibenzodioxins. Beside chlorine other halogens like bromine, iodine or fluorine and their mixtures also can be used as substitution atoms. Analogous to the polychlorinated dibenzodioxins/ -furans is the chemical structure and the nomenclature of the ploybrominated, -iodinated and fluorinated dibenzodioxins /-furans constructed. Also there is an equal toxicological level supposed, the report would not going into details of this compounds. -

Chemical and Physical Properties

The studies on the chemical and physical properties of dioxins are not completed; there are only exact facts of the well known compounds. Isomers of different homologous series have very different properties. The melting point of 2,3Dichlorodibenzodioxin is about 89°C and 332°C for octadibenzodioxin. Even in the same homologous series with similar chemical and physical properties exist big varieties in toxicity.

7 PCDD and PCDF are almost leach- and base-insoluble and have a low volatility under normal air pressure. On the other side they are lipophilic and concentrate in animal and human adipose tissues. Water and fat solubility as well as vapour pressure have following attitudes depend on the rate of chlorination: -

The water solubility decreases strictly logarithmical when the rate of chlorination increases. And is general very low between 1 μg/l and 7,4* 10

−5

μg/l. -

The fat solubility increases at higher rate of chlorination and is about 4 dimensions higher than the water solubility.

-

The vapour pressure of PCDD and PCDF shows a downward drift at higher rate of chlorination, it decreases about a factor of 8 for each substituted chlorine.

The important physical properties of 2,3,7,8- Tetrachlorodibenzodioxin, see Table 2: physical propertie molecular weight melting point vapour presure critical presure critical temperature critical volume boiling point solubility in: water methanol xylene chlorobenzene partition coefficient: n-octanol/ water soil/ water biota/ water

value 321,97 303-305 4,5 23,42 661,3 763 440

unit g/mol °C MPa (25°C) atm °C cm³/g mol °C

0,2 10 3580 720

µ g/l mg/l mg/l mg/l

1,4* 10 7 1,0* 10 7 2000-3000

Table 2: physical properties of 2,3,7,8-TCDD

8 The change of the state of aggregation of PCDD/F depending on the temperature is very important for the filtering. PCDD/F are emitted depending on the kind of facility, waste heat utilization and purification of waste gases at a temperature of 60°C to 400°C. On the way to chimney the exhaust gas cools down, condenses and will be absorbed by dust and sooty particle. Studies have resulted that with waste gases with temperatures above 300°C PCDD/F are mostly (>80%) gaseous, but if the temperature is under70°C they are sorbed by dust particle (>90%).

-

Formation Mechanism

Polychlorinated dibenzodioxins and –furans are man-made matters, as a byproduct of the industrial production of trichlorinephenol and –benzene or as combustion product. Formation mechanism of PCDD and PCDF can be split up in: - Condensation reaction - Substitution reaction - Radical reaction - de novo synthesis The condensation reaction is one of the “classic” formation mechanisms. It is the condensation of two chlorophenolmolecule. Phenolic compounds adsorbed on the fly ash surface are chlorinated to form the dioxin precursor, and the dioxin is formed as a product from the breakdown and molecular rearrangement of the precursor. Figure 3 shows the formation of 2,3,7,8-TCDD by sodium salt of 2,4,5-trichlorophenol as a example for condensation reaction. This kind of reaction prefers less than 350°C.

9

Fig. 3: Condensation reaction

The substitution of hydrogen from none- or single halogenated dibenzodioxins and – furans by chlorine forms the polychlorinated dibenzodioxins. The substitution prefers the 2,3,7,8-position at the chlorination with the present of a metalchlorid catalyst. The dechlorination e.g. of OCDD with the present of metal at higher temperature into TCDD and the dechlorination with UV-light are also counted as substitution reactions. Radical reactions are another important formation mechanism of PCDD and PCDF. At this reaction organic precursor’s combust with chlorine compounds at 300°C to 600°C. The de novo synthesis occurs at a temperature of 300 – 450°C as formation of dioxin and furan compounds form nonchlorinated materials with the present of chlorine compounds and carbon, supported by catalytic reactions with metal. Like the DEACON reaction the important start reaction is the formation of chlorine from cooper and other metal chloride with oxygen. The de novo reaction is characterized by his long reaction time. At flue gas cleaning formation of PCDD/F is possible because the fly ash stays many hours in the electric filter. The standard dioxin formation takes place at 400 to 800°C. Above 800°C the pyrolysis (thermal decomposition) and the reaction with oxygen start. At the cool down process dioxins can be formed by the de novo reaction. This opposite reactions leads to the typical dependence of dioxin on the temperature (Fig. 4). The formation velocity shows a saturation curve and the decomposition velocity are proportional to the temperature.

10

Fig. 4: Dioxin Concentration

Also there are many assays and theories about the formation mechanism the exact formation mechanism is still partly unknown. It is unsettled when chlorine and oxygen enter the molecule or how important catalytic effects are at the combustion. -

Toxic Equivalency Factors

One of the main questions at the rating of dioxins and furans is the toxicity and specially the effectiveness on human. To rate the toxical potential of PCDD and PCDF toxic equivalency factors were introduced. The toxic equivalency factors show the toxicity of a special compound in relation to the most toxic substance – 2,3,7,8TCDD – (Table 3).

11 Table 3: International toxic equivalency factor TEF is an international NATO CCMS-Code replacing the old common national factors. The TEF divided all PCDD/PCDF congeners into their respective homologue groups and assigned to each group a toxicity factor relative to TCDD. These numerical factors could then be applied to transform various concentrations of PCDDs and PCDFs into equivalent concentrations of 2,3,7,8-TCDD. The concentration of PCDDs and PCDFs would be analytically determined, the concentration of each congener would be multiplied by its respective TEF value, and all the products would be summed to give a single 2,3,7,8-TCDD equivalent. For example in an alloy are 2000 fg octadibenzodioxin. With the equivalency factor of 0,001 you get 2000 fg * 0,001 = 2 fg, that means the OCDD has a toxic effect equal to 2 fg of 2,3,7,8-TCDD. The toxic equivalency factor does not contain conclusions of cancer risk. Carcinogenic effects of 2,3,7,8-TCDD could be detected in animal experiments, for other compounds are only insufficient assays. -

Aims and Limits

To find a toxic limit for dioxins depends on the effect on human organism. There is no clear line between the appearance and missing of unhealthy effects. The bandwidth is influenced by age, initial level of pollution and state of health. /5/ The first German standard regulation about emission control of polychlorinated dibenzodioxin and –furans was published on 23.11.1990 (17. BImSchV). This regulation contains many requirements about the formation of dioxins and furans and emission. The core is the emission limit of 0,1 ng TE/ m 3 , in the most cases only reachable with special filtering systems. Operators of old facilities have to keep these conditions since December 1996. To control these regulations sampling and analyzing of samples are standardised, too.

12 The European Union published on August 3rd, 1993 a guide line for combustion of dangerous waste. The published requirements are similar to the 17. BImSchV in Germany. The limit of 0,1 ng TE/ m 3 for dioxins and furans have been taken over. 3.

Review - Problems at Seveso (Italy), Start of Research about Dioxin

In literature it was mentioned that already 1963 dioxin cloudes escaped after an explosion in a plant near Amsterdam – four people died and 50 more suffered with score health problems /1/. After the accident at Seveso (Italy) in 1976 intensive research started about dioxin /210/, although no human fatalities or defects occured /1/. Soon it was found that in the waste-gases of waste-incinerators tracers of dioxins were measured. In the following years in different waste gases of chemical and thermal processes dioxin were found, furthermore unwanted burning processes and fires. The detection limit was possible to be lowered. More and more knowledge was added to the origin of PCCD and PCDF in the environment. It was noticed that dioxins are not only a problem of waste gases but it went in waters and grounds. It was also a problem in dusts slags and activated carbon of filter processes. It became useful to divide between primary and secondary sources; the primary are formed in actuel processes and processes – the secondary are based on dioxins, which are brought into the environment on different ways becaming dangerous for human beings. -

Primary Sources

Waste-incinerators, heating of houses and motor vehicles were first tested and it was soon mentioned that their gases are harmful but a lot of different sources were soon detected and registered /1,11/.

13 The German law (17. BimSchV) prescribed a limit of 0,1 ng TE/m3 in the waste gas and this should be reached until 1996 – that means e.g. all waste incinerators needed special filters. In the thesis of R. Pütz /2/ a lot of problems in the first years of dioxin-research were discussed were shown. Special-waste incinerators with rotary kilns soon became clean and the wastes of clinics had to be burnt in special furnaces. The burning of natural gas, oil and hardcoal in houses were found not to be as harmful as first suggested, but burning of wood and special treated wood are still problematic. Since prohibiting (in Germany in 1992) of using Scavengar-containing leaded gasoline the problem seemed to be solved but the year by year increasing number of motor vehicles brought new problems. Industry was first spared out, for the ceramic industry e.g. brought results nearly to 0,1 ng TE/m3. Here are only some hints repeated /12/: Copper Recovery: Depending on the type of furnace and the input materials, operating conditions and gas cleaning systems used, PCDD/PCDF concentrations in the off-gases may vary considerable. Most of the results obtained from industrial scale facilities in Germany were in the range of 1 to 2 ng TEQ/m3. Fabric filters are normaly used for flue gas cleaning, a few plants are equipped with an afterburner. Aluminium Remelting Plants: Most processes for generation of secondary aluminium use a rotary kiln. Concentrations measured showed a wide range of emission values (0.15-13.4 ng TEQ/m3 for Al remelting plants; 0.02-21.5 as an average from 30 Al smelters). Very low levels were found in the flue gases of foundries (0.1 ng TEQ/m3). The arithmetic mean stands at about 4.4 ng TEQ/m3 and the total emissions from aluminium melting plants in Germany are estimated to be approximately 25 g TEQ per year. Single measurements from reprocessing of lead from accumulators (contamination almost unavoldable) gave dioxin concentrations from 0.02 to more than 1 ng TEQ/m3.

14 - Secondary Sources The slag of copper production e.g. at Marsberg showed such high contents, that this material was not any longer usable for playgrounds. Also dusts and acivited carbon of filters and slags of the non-ferrous industry was surprisingly high. - Dioxin in Iron and Steel-Industry In the following Fig. 5 the routes of the steelproduction are shown. In the world nearly 60,6% of steel is produced in the traditional route with blast furnace and the connected oxigen converter. 34,9% is produced by melting of scrap, which was before it became to scrap also was produced by the blast furnace/oxigenconverter route. Only 4,3% of the worldwide steelproduction went the way via sponge iron by the direct reduction route and the smelting-reduction route is only 0,2% /13/. On the right side of Fig. 5 scrap-melting is marked. The autothermic oxigen converter route needs colling scrap but the scrap amount is to large and therefore the allothermic route with scrap melting in a EAF is needed.

15

Fig. 5: Routes of Steel Production /14-16/

16 -

First Published Results

Before starting with results the paper about „sources of PCDD/PCDF and impact on the environment“ by Fiedler (1994) is mentioned /6/: The state of Northrhine Westfalia (Germany) has initiated a program to evaluate 42 priority industrial facilities with potentially relevant dioxin emissions to the air. The program includes analyses of gaseous emissions from remelting plantes and foundries (total of 28 plants), plants for wood combustion (5 plants), for melting, sintering, raw-iron and non-ferrous-raw material manufacturing, chipboard manufacture and manufacture of compounds using chemical processes with chlorine involved (wood preservatives, distillation of waste oil, bleaching of cotton and threads). So far, dioxin emission > 0.1 ng l-TEQ/m3 were found for most of the plants investigated. However, facilities with emissions > 1 ng l-TEQ/m3 were identified, too (Table 4).

Table 4: First results of the dioxin program in Nordrhine Westfalia – Plants with emissions more than 1 ng l-TEQ/m3 (mean value of three measurements) In detail more results of the iron and steel industry are given /2/: (The iron ore sintering will be discussed at the end of this chapter). Pig iron is produced in blast furnaces by reduction atmosphere, that means the possibility of formation of dioxins is small and therefore a few tests are done only at blast furnaces itself. The chance of dioxin formation seems to be possible in the blast furnace – cast house, but Table 5 shows low values /2/.

17 Facility/ Offgas cleaning

Capacity

Offgas flow [Nm³/h]

Blast furnace (cast house dedusting)/ Wet-EFilter Blast furnace (cast house dedusting)/ Baghouse Filter

600t/d

91.400

9000t/d

700.000

PCDD/F Concentration [ng TE/m³] 0,002 0,004 0,0015 0,0036 0,0022

Table 5: Dioxinemission at blast furnace – cast house Furthermore cowpers showed emissions of only 0.032 ng TE/m3 – see table 6. Facility/ Offgas cleaning

Capacity

Offgas flow [Nm³/h]

Blast furnace (cowper)/ N.N.

600t/d

70.000

Blast furnace (cowper)/ 1 seperator 2 whirler 2 scrubber

9000t/d

329.200

PCDD/F Concentration [ng TE/m³] 0,03 0,029 0,004 0,037 0,038 0,021

Table 6: Dioxin emission at blast furnace-cowper In the first route „blast furnace – O2-converter beside in the blast furnace and in the O2-converter there were no relevant dioxin contents measured. In the converters usually 20% scrap is charged as cooling material. Even in this case table 7 gives reasonable results. Facility/ Offgas cleaning

Charge

Comment

Offgas flow [Nm³/h]

Converter/ Baghousefilter

Pig Iron

Converter/ E- Filter

Scrap Iron

Primary Dedust

165.000

0,026 0,045 0,04

Converter/ Baghousefilter

Scrap Steel

Secondery dedust

912.068

0,024 0,042 0,063

570.000

Table 7: Some dioxin emissions at O2-converters

PCDD/F Concentration [ng TE/m³] 0,032 0,033 0,042

18 Electric arc furnaces showed different results. Especially scrap-preheating gase e.g. 9.2 ng TE/m3 see table 8. This kind of scrap preheating is since 1994 no longer allowed. Facility/ Off gas cleaning

Charge

Comment

Offgas flow [Nm³/h]

E- Arc Furnace/ Baghousefilter

60% Clean Scrap, 40% Dirty Scrap

without Preheating, with Preheating

68.000

E- Arc Furnace including e.g. Quenching

Shredder Scrap, Scrap Steel, Splinters

1.040.000

1.100.000

PCDD/F Concentration [ng TE/m³] 0,7 2,3 5,6 9,2 0,267 0,159 0,236 0,13 0,104

Table 8: Some dioxin-emissions at Electric-arc-furnaces Interesting was the fact, that scrap with impurities like oil containing grinding material or dirty oil-barrels were problematic.

19 4.

Iron Ore Sinter Process

- Definition This chapter will be not a course-book about iron ore sintering; only the main foundamentals will be given – especialy in connection with dioxin problems. The real treative are given e.g. in the lecture book about iron making at the RWTH Aachen /18/ an for e-learning /19/ and about iron ore sintering /20/. The main background was given e.g. by Cappel/Wendeborn /21/. Sintering may be defined as the agglomeration of fine mineral particles into a porous mass by incipient fusion caused by heat produced by combustion within the mass itself. In regard to the Ferrous Metallurgy the agglomeration of fine ferrous compounds, like fine ores as well as blast furnace dust (flue dust), remmants of the steel works, mill scale and dusts from electrostatic precipitators, is called the iron ore sintering process. Thereby the compounds are heated up, a melting is not taking place, but a partial liquefaction is fulfilled. On account of the melting below the surface, the liquefaction, just as the formation of slag a strengthening is obtained, the liquid phases are caked together with the down-cooling. The most important quality pretensions of sinter products are high resistance against mechnical stress under blast furnace reduction conditions, good reducibility, and uniformity of the size distribution as well as a high Fe-content of the product /18-21/. The iron-bearing constituents are iron ore concentrate, fine ores (fraction less than 810 mm, incl. about 70% > 0.2 mm), flue dust, recycled materials (mill scale precipitator dust, pyrites etc.). Hematite and magnetite ores can be used for sintering. Sinter process using magnetite ores requires lower (less) fuel consumption because of lower heat demand. Sintering using 100% finely pulverized concentrates in charge ore component is known. Share of recycled sinter fines makes up about 20-30% of sinter mixture /20/. Coke breeze is the most common solid fuel (fraction less than 3 mm), but coal and other carbonaceous materials are also used. The fuel should have low content of volatile matter, ash and sulphur, high calorific value and ignition temperature, low rate of fraction < 0.5 mm.

20 Limestone, burnt lime, dolomite or dunite or olivine (fraction less than 3 mm) is used as flux. Flux maintains not only a needed volume and chemical composition of slag in a blast furnace, an increase in the sinter reducibility but also (especially burnt lime) an increase in sinter production. Water (5-9% of sinter mixture) is needed for agglomerating. -

Sinter Strand

The schematic representation of a sinter strand is shown in Fig. 6:

Fig. 6: Sinter strand

Fig. 7: Sinter plant

21 Compared with a sinter plant it is obvious, that there are more facilities and equipments, which can influence the quality of sinter but also the composition of the waste gas: the materials and the delivering to the plant, the homogenization in blanching beds, transportation by belt conveyors to the bins, where flux, coke breeze and e.g. recycled sinter fines are added, conditioning with water in a mixing and pelletizing drum; furthermore the charging system, the ignition by an ignition hood, the sucking-system and the discharging – the crusher and the cooling system – see Fig. 7. -

Heat Transport

The sintering process is described as a non-stationary bed-reactor being flown through by the parallel-flow-process. Fig. 8 shows the most important thermal and chemical reactions.

Fig. 8: Thermal and chemical processes in the sinter bed

22 The lower layer of the sinter bed (G) is heated to 100°C by the hot process gas leaving the layers. This zone is followed by the drying zone (F). After the drying of the sinter mix dehydration (E) is taking place from 300 to 800°C, the expulsion of carbon dioxide and reduction follows (D). From 900°C starts the ignition of the fuel. The burning of the fuel heats up the sinter bed to 1250-1350°C. The range between the ignition of the fuel and the maximum temperature is called flame- and sintering zone (C). The maximum temperature depends on the composition othe sinter mix and the content of coke breeze. After the burning- and sintering zone the sinter is reoxydated (B) and cool by the gas stream (A). This ideal sinter-peak, which is discussed in literature very often, is influenced by different factors e.g. the changing of coke-breeze to charcoal: in this case a good sinter quality cannot be expected, for the optimal sinter temperature of 1350°C is not reached by charcoal – this has naturally an influence on the waste gas, too – see Fig. 9 /18,21/.

23

Fig. 9: Temperature with different fuels: charcoal (Holzkohle) and cokebreeze (Koks)

Fig. 10: Temperature-time by sintering of Labrador with 40% returned fines and 6,5% cokebreeze

24 This ideal sinter peak will appear after half of the sintertime e.g. after 10 min. of total 20 min. and near to the ignition it will be slim and will widen to the end of the sintertime in a sinter-pot and on a sinterstrand, see Fig. 10 /21/. In the mixture on the sinterstrand the reaction will run from the top (ignition) to the bottom of the sinterbed, see Fig. 11.

Fig. 11: Sinterreactiontemperature (1340°C) In the next figure – see Fig. 12 – it is shown that the waste gas temperature reaches at the end 350°C; the everage temperature of the waste gas is normally between 130°C to 180°C. Corrosponding to the operation mode, the sintermaterial especially to the additions the content of the waste gas may change; the highest content is normally N2, the rest 13,5% H2O, 13% O2, 5% CO2, 1-2% CO, some NOx and SOx. Fig. 12 shows that SO2 has a maximum of SOx at the middle of the sintermaschine length; it is explained that the SOx of the drying and burning zone is accumulated there and then decreases /18/.

25

Fig. 12: Temperatur and gas composition on a sinterstrand

-

Charged Materials

In the literature mainly the influence of the charged material was discussed in con-

Fig. 13: Influence of addition of fine material (Gichtstaub) on the decreasing efficiency

26 nection with the sinterquality, reducing of fuel and e.g. the influence of fines on the efficiency /22,23/. Intensive was discussed, how to remove lead, zink and alcalies at a sinterstrand. It was nearly not possible to vaporize these materials in a normal sinterprocess, only by adding of calciumchlorid considerable amounts could be removed /24/. An interesting possibility to solve the oil problem of mill-scale it was discussed and researched in 1985 by Thyssen in a double sinter process: the mill-scale was only added into the upper layer and the gasified oil was filtered in the second layer and burnt there /27/. From the viewpoint of using mill-scale in the sinter process it was in these days interesting, but an dioxin content was not measured. Four years later R. Bothe showed in his thesis that the amount of recycled material had an intensive influence on the hydrocarbons in the waste gas and on the burning problems of filters /26/. A foundamental research was carried out by M. Riedhammer on the influence of moisture on the sinterprocess /27/. There are two reasonable values, one to get a higher productivity and one to get the best sinter quality. This is interesting for the waste gas amount and concentration. A. Deja tested /28/ the preheating and prereduction of the sintermaterial to minimize the solid fuel content in the mixture. He could show very interesting low fuel contents but often combined with low sinterqualities /29/. F. Cappel who wrote already with Wendeborn the book „Sintering of Iron ores“ /21/ used the tests and results of Deja /28/ in the consideration of his thesis /30/. He did a lot of tests first parallel to the sinterstrand in Dünkirchen and then changing many parameters. Furthermore he developed a model to predict further tests but mainly to explain his results. In Fig. 14 one of his results of his tests is compared with his model. By these results he could predict the reactions in a sinter-bed even by recycling of waste gas from the strand, giving hints for the EOS (Emission Optimized Sinterprocess) of Lurgi /31/.

27

Fig. 14: Measured and calculated results: Temperature-Time of test 53 (Preheating time 38,6%, Gastemperature 600°C)

28 5.

Experiments in a Sinter Pan

X. Hong was the first one, who researched since 1989 in our department about dioxin /32-33/; he measured the influence of preheated scrap in an EAF and showed the 210 isomers and discussed e.g. their toxicity. In 1993 our department got by the State of Northrhine Westfalia (Germany) – MURL (Ministry of Environment) the researchproject: „Dioxin problems at metallurgical processes in the steel industry concerning the sintering of iron ores“. In many discussions with other researchers and members of the goverment details were discussed; first results were given in Brazil already in 1995 /3/. Our department got another research project to the above one from MURL: „Possibilities of the use of plastic waste in the iron- and steelindustry“ /34-37/. Some results were given in Brazil 1995, too /37/. It was explained that even by injecting of plastic until a special amount the formation of dioxin in different furnaces was not higher than 0.1 ng TE/m3. A further paper was given by K. Onaka in a Seminario International: „Sustainable Development Metallurgy of Iron and Steel“ in Belo Horizonte, Rio de Janeiro and Florianopolis in Brazil 2001 by comparing the results of our research and industry with results of the iron- and steel industry in Japan /38/: „Dioxin control technology in iron and steel industry“. He discussed as well results in EAF (Electrical Arc Furnaces) and iron ore sintering. At HKM (Hüttenwerke Krupp Mannesmann) A. Köfler researched and gave results of his company in the combination with the results at Aachen in his thesis /39/. At 26.-30.November 2006 a paper was given as a Keynote lecture in Osaka at the ICSTI ‚06 with the title: „Research based on international cooperation“ with iron ore sintering and dioxin as an example /40/. In the following chapter the result of these papers with the background of literature studies will be presented.

29 - Experimental Apparatus at Institute of Ferrous Metallurgy in Aachen The dioxin generation was investigated in our department in 1993 a sintering pan (Fig. 15), which had been used in several research programs before – see chapter 3. Added was further active-coal filter in the gas pipe to the blower before the gas went into the normal filter of the research lab. To measure the temperature in the sinterlayer 5 thermocuples are installed; O2, CO2, CO and CH4 were measured furthermore by a beame emission analysis (FID) the total C-content in the waste gas. The filter/cooling method was used take the gases and by the adsorption method the content was measured by the Gesellschaft für Arbeitsplatz und Umweltanalytik mbH (GfA).

Fig. 15: Sintering pan of the Institute of Ferrous Metallurgy To the base mixture which was used by industrial partner (with a raw mixture plus 4.1% cokebreeze and 24.3% returned fines) = SM I. Three different additions were given, see Table 9:

Table 9: Admixtures of sample sinter

30 - Results and Discussions of Experiments in a Sintering Pan The range of Dioxin concentrations is situated between 0.17 and 0.65 ng TEQ/m3 (TEQ: Toxic EQuivalents) with a tendency to raise from sinter mixture SM I to SM IV, Fig. 16. The average value of the Dioxin emissions from the assigned base mix (SM I) amounts to 0.185 ng TE/m3. Under the addition of 5% mill scale with a middle oil rate of 0.1% (SM II) the emission increases by only 22%. In the case of an additional admixture of 1% blast furnace dust (SM III) emission increasing rate is to be determined about further 75%. This results almost twice in relation to emission from the base mix. With the use of 5% mill scale with an oil rate of 0.34% (SM IV) the emission reaches to more than three times than the base value of SM I. Comparative PCDD/F emissions for the oil rate of mill scale and the addition of blast furnace dust could be shown through several lab tests.

Fig. 16: Dioxin emission in a sintering pan test The tests showed that by the sintering pan results are simular to results of a sinterstrand. Furthermore it was postulated out of these tests that an increasing C-total amount will show increasing PCCD/F-contents in the offgas.

31 6.

Measurements in Sintering Plants

In the same project with the sinterpan-tests, tests were done at the sinterstrand 3 of Krupp Hoesch Stahl AG together with our Institute at RWTH Aachen. Known were at that time different dioxin results see table. 10 /3/:

Table 10: PCDD/F-concentrations at German sinterstrands

Date of

Operator

County

measure

Table 11: PCDD/F-concentrations of sinterstrands in German neightbourcountries

12.06.1990 12.06.1990 13.06.1990 13.06.1990 10.10.1991 10.10.1991 10.10.1991 14.01.1992 16.01.1992 1994 1994 1994 1994

Concentration [ng TE/m³]

Hoogovens Hoogovens Hoogovens Hoogovens Voest-Alpine Voest-Alpine Voest-Alpine Arbed S.A. Arbed S.A. British Steel British Steel British Steel British Steel

Netherlands Netherlands Netherlands Netherlands Austria Austria Austria Luxemburg Luxemburg UK UK UK UK

3 2,5 3,4 3 2,52 1,79 2,47 0,85 2,08 0,6 1,6 3,4 1,7

32 These results of German Industry were single results (not repeated tests) out of plants with different operating modes, different materials and different additions. Such extreme values were not known in our neighbor countries, see table 11 /2/. In Fig. 17 the dioxin emissions are shown at Krupp-Hoesch AG. It is obvious that the extrem high emissions were stopped already at 1992 and in 1993 the values were normally not higher than 3ng TE/M3 /2/.

Fig. 17: Dioxinemission at Krupp-Hoesch These results were reached with primary measures, e.g. lower speed of the sintermachine and by this a lower productivity and e.g. by avoiding of mill scale with an oil content > 0,1%. -

Influence of Filter Systems

In the following two Figures 18 and 19 electrofilter and bagfilter are compared /2/. Though the two sinter strands were different even by changing from electrofilter to bagfilter it was not possible to overcome all problems of the dioxin emissions.

33

Fig. 18: Measured results with electro filter

Fig. 19: Measured results with fabric filter

34 -

Influence of Different Sintermaterials

At the same time tests were done with different coke-breeze-qualities and test with avoiding of the addition of blast furnace dusts, see Fig. 20.

Fig. 20: Different Sintermaterials -

Results of Dioxinemissions over the Length of the Sinter Strand

The following tests were done at the Hoesch (Dortmund) Sinter Strand (150 m 2) in cooperation of the measurement by LUA (Landesumweltamt NRW). Several different possibilities were checked e.g. without any additions like oil containing millscale and with millscale. Fig. 21 and 22 shows examples of the results e.g. with the bed heights 400 mm, the speed of the strand between 2.41 and 2.48 m/min and the production was between 31.2 and 31.5 t/m2d.

35 Fig. 21: Underpressure at windboxes

Fig. 22: Temperature at windboxes

The most interesting result is given in Fig. 23. At every second windbox the PCDD/Fconcentration was measured and the other were calculated. There is a continuous increase from windbox 3 to 11 and the main emission of Dioxins is measured in windbox 11. The less higher values in windbox 1 compared to windbox 3 can be due to the ignition zone. The decrease from windbox 11 to 13 is attributed to the final sintering operation. Approximately 3/5 of the exhaust gas stream can be classified as not critical, whereas the reamsining 2/5 need a special waste gas cleaning in order to decrease dioxin emissions.

Fig. 23: PCDD/F-concentration over length of sinter strand (measured and calculated)

36 The CO- and the NO-emission was nearly constant in nearly all compaigns. A remarkable correlation between the temperature and the PCDD/F-concentration is shown in Fig. 24. This can explain the dioxin behaviour in the sinterbed. It should be stressed that nearly half of the windboxes show less than 0.1 ng TE/m 3. The values of the addition e.g. of millscale or wastes can be compared with the results of the lab-tests.

Fig. 24: PCDD/F-concentration and temperature It is interesting that the maximum of dioxinemission and the temperature at the end of the sinterstrand does not correlate with the SO2 maximum, for this appears at the middle of the length – see Fig. 12 /18/. Also the theory of the presence of this SO2 maximum will not be same, for dioxin is not solutable in water. This SO2 maximum was explained that the SO2 is first absorbed by the water content in the lower part of sinterbed and then driven out, when the temperature reaches this area /18/. In 2001 also Kansai and co-authors showed this phenomenon in their research at sinter strands in the collaborative Japanese Research-Project (SDD-Project Japan), see Fig. 25 /41/.

37

Fig. 25: Changes in exhaust gas temperatures and relative concentrations of PCDD/Fs and other gases in windboxes with progressing of sintering

38 7. -

Proposals of Dioxin Minimizing by Technological Changes Air fine

By the author of this report a not published expertise was made about the development of the KVA-process of Voest-Alpine-Stahl (Donawitz/Austria). This continuously acting scrap melting process was based on the use of natural gas and oxygen – it was a flexible process of pure pig iron with coiling scrap (until 100% motorcar-scrap) /42/. The same dioxin problems as in an EAF were expected but in October of the same year it became obvious, that only by a large filter this aim could be reached /43/. Filter were developed e.g. by Voest Alpine-Industrieanlagen: Air fine to minimize the dust-out-put at electro-filter or at bagfilter to clean oven gases. By this way the amount of Dioxin could be minimized to 0,4 ngTE /39/. A problem by cleaning of sinter offgases by electric filters are the alkali containing aerosols, therefore by Air fine first the solid particles were minimized and then by a quenching and washing step difficult gases – even dioxins – could be treated. In the meantime VAI is developing a dry-typ gas cleaning process /44/. -

EOS

In the thesis of F. Cappel already 1977 /30/ many different ways of recycling of waste gas were discussed, see e.g. Fig 26.

39 Fig 26. Recycling of waste gases of the last wind boxes In Fig 14 measured and calculated preheatment treatment was shown and in the thesis discussed. While F. Cappel /30/ used these possibilities mainly to save energie, the combination with the results by Pütz /2/ gave the new EOS-Process /31/. In chapter 5 experiments in a sinter pan and at sinter plants about Dioxin emission were compared. In Fig. 27 the optimized sinter process (EOS) is shown /45/.

Fig. 27 Flow sheet of a sinter plant with EOS system Conventional sintering uses ambient air to transport heat within the sinter bed, requiring a high air flow rate. However, EOS takes advantage of the fact that only a part of the oxygen in the air is consumed for coke combustion. Therefore a part stream of the offgas is recycled via the hood, enriched with ambient air to an oxygen content of 13–14% and used as intake process air. This reduces off-gas volumes by about 40–50% without affecting the sintering process. The process was developed in 1994 by Outotec (the former Lurgi Metallurgy GmbH) and is presently applied at all three sintering strands of Corus Ijmuiden.

40 The EOS brings an almost 50% reduction of the waste gas volume, but also 10% reduction of the coke breeze. 75% of the Dioxins could be avoided /39/. -

LEEP

This Low-Emission-and-Energy-optimized-Sintering-Preocess (LEEP) was developed mainly by the doctor-thesis of A. Köfler /39/. He discussed the different possibilities of treating the NO-content or the desulphurization. Especially he mentioned the influence of carbon and CO and CU as catalyser on the PCDD/F formation. Before he started to explain his equipment at Hüttenwerke Krupp-Mannesmann he reported of the sinterplant No. 4 at Wakayama of Sumitomo Metals to recycle the hot waste gases of the whole sinterbed and at Yamata by Nippon Steel where some parts of the waste gases after ignition were brought back to the sinter layer. This procedure was mainly used to minimize the SO2-content. In the Köflers thesis Cu was tested under sinter strand conditions. From discussions and tests in different equipments it was known that Cu react at a catalyst. The starting value was between 0.958 and 1.017 ng TE/m3. The dioxin-emissions were lowered to 0.431 or 0.335 ng TE/m3 in the first step and then 0.248 and 0.265 were reached. This became possible for the Cu-content was lowered by 20% and once again by 20%. For this lowering the dusts of the roomcleaning filter and from the blast furnace were agglomerated with burned limestone and water. These agglomerates were then given into the sintermix. With this procedure it became possible that the Cu-containing particles remained in the sinter and were not transported into the sinter offgas and could not react as a catalyst. By this method it seemed to be possible to reach 0.5 ng TE/m3 but the company wanted to reach lower values. Therefore quenching tests were added. The windboxes 25 to 28 were selected, for it was known that this windbox showed the highest waste gas-temperature nearly 335°C without quenching. From pretests it was known that this windbox would show the highest dioxin emission. With the quenching the offgas-temperature was 150°C.

41 Fig. 28 shows the results, the lowering of the dioxin emission reached 30-50%.

Fig. 28: Results of the quench-tests in the windboxes The next step was the jet-injection of fine lignite coke particles (BKKS = Braun-KohleKoks-Staub), see Fig. 29 with following limitations: not too high amounts of coke breeze to avoid explosions and the waste gas temperature should be lower than 145°C. Some tests with this procedure were already done before by Thyssen and that knowledge was taken into consideration.

Fig. 29: Jetstream injection and –absorber

42

Fig. 30 shows the results; it is interesting that by this method 50% less dioxin emission was measured.

Fig. 30: Results of the injection- and adsorber-method -

Partly Offgas Recycling

Fig. 31 shows the possibility of recycling a special part of the off-gas.

Fig. 31: Partly off-gas recycling

43

This method was also checked, calculated and discussed by Köfler /39/. He found out that the PCDD/F-, the Sulfur- and the NOx-emission reached interesting low values. By Köfler also the influence on the efficiency and quality of sinter was checked and discussed. In Fig. 32 the recycling system at the sinter plants of HKM is shown.

Fig. 32 LEEP waste gas recycling process at HKM

-

Eposint

A waste gas recycling process has been developed by Voestalpine Stahl Linz and Siemens VAI. The “Environmentally Process Optimized Sintering” (Eposint) was developed with the knowledge of the Airfine process. In this process the gas is selectively recycled from the windboxes n the area of the high waste gas temperature see Fig. 33. Low SO2 concentrations were reached and Dioxions can effectively destroyed by the selective selection of the partial waste gas stream from the burn-trough zone. To get emissions a bag filter is installed after the electro-filter. This is called “Maximized Emission Reduction of Sintering” (Meros).

44

Fig. 33 Eposint waste gas recycling process at Voestalpine Stahl Linz

-

Bag filter

An End-of-pipe-solution for waste gas cleaning are bag filters. They have been developed by different companies. Fig. 34 shows the process diagram of the Rogesa Plant in Dillingen.

Fig.34 Bag filter technology at Rogesa

45 -

Injection of pulverized coke breeze

In a report by Prof. Philp /46/ tests were done and discussed to bring down the Dioxin emission of sinter strands; this is the state of the art. The aim was to bring down the PCDD/F concentration < 0,1ngTEQ/m². The demonstration was shown at the sinter strand 2 at TKS; the dates of the sinter strand were given, further more the dates of the sinter raw mix. The qualities of the ingnite coke breeze (BKKS=Braun-Kohle-Koks-Staub) was listed up. Fig. 35 shows the Bloek Diagramm /46/

Fig. 35 Waste gas cleaning with adsorption stage and catalytic converter

Results which were reached e.g.: -

it was possible to inject BKKS

-

increase of injected materials brings more efficiency

-

70% of Dioxin could be reduced

-

2,3,7,8-TCDD was reduced by 76%

-

Results were between 0,13 and 0,76 ngTEQ/m³

46 -

0,1 ngTEQ/m³ was not reached

Effect of Additives on the Dioxin Emission in a Sintering pan

Beside the interesting papers of the effect of metallic chlorides /47/ and the mechanism of dioxin-furans-formation at high temperatures /48/ the de novo formation characteristics of dioxins in the dry zone of iron ore sintering bed was studied /49/, where e.g. the following conclusions are valuable that the addition of CuCl2 and CuO to the sinter mixture led to a significant increase in the total about of dioxins. In particular, CuCl2 accelerated dioxin formation at a greater rate than CuO. The homologue distribution of PCDD/Fs shifted to higher versions and that the dioxin formation from the sinter mixture was influenced by temperature, presence of chlorine compounds, catalyst and carbonaceous materials in the sintering bed or gas. In the paper about the effect of additives it was shown that the sintering pan tests – like Pütz /2,3,7/ - see Fig. 15 and 16 – can give results, that can be used to explain results at sinter strands /50/. Fig. 36 shows the effect of additives in different series and the authors stated that the details had not been classified.

Fig. 36: Effect of additives on PCDD/Fs formation. (Anth: anthracite)

47 8.

Prediscussion of the Report Part I

In this report at first the literature about dioxin was taken in consideration, which was selected and discussed in the Phd-thesises at our University by X. Hong, R. Pütz, G. Schwanekamp and A. Köfler, furthermore the discussed results of their publications. Onaka (DAIDO-Steel, Japan), who researched in our University, gave interesting discussions about the Japanese research and publications. In chapter 1 „dioxin“ is introduced. Dioxins and furans can from 210 congeners. They consists of two „benzene-rings“ combined by two oxygen atoms = dioxins or by one oxygen atom = furans and they have Cl-atoms at different position. The most toxic one with 2,3,7,8 Cl-positions is called „Seveso poison“ with the highest „toxic equivalency factor“ = 1. This one has e.g. nearly no solubility in water. The dioxins are mainly formed in a middle temperature of 400°C to 800°C and destroyed by higher temperature, but they can be reformed again by “de novo synthesis“ by slowly cooling down. In chapter 2 a review is given and shown that after the „Seveso accident in Italy“ a lot of research started e.g. in Germany. In this report the research about iron-ore sintering is stressed – including results of electro-arc- and shaft-furnaces that means in iron metallurgy. Results e.g. with reactions as a poison to plants, animals and human beings are not discussed. In chapter 3 the iron ore sinter process is explained with its definition and the typical sinter strand. The heat transport with the moving of the „sinter-temperature-peak“ from the top of the sinterbed to the bottom. The importance of the sinter temperature of 1350°C is discussed and the quality of the offgas is explained. In chapter 4 experiments in a sintering pan in an apparatus at the Institute of Ferrous Metallurgy is shown. Results of electric-arc- and shaft-furnace were taken in consideration and the results were discussed with the partners at MURL and industry. Mill scale and blast furnace dust addition gave higher emissions of dioxins.

48 In chapter 5 results of industry at sinter plants were compared with results at KruppHoesch in a combined research between Aachen University and industry. Filters (electric and bag-) were tested and different sinter materials were used. Interesting results were found over the length of the sinter strand with a maximum of dioxin-emission at the end of the sinter strand parallel with the maximum of the offgas-temperature. Some years later in Japan by the SDD-Project were found and showed the rightness of the former results. In the last chapter 6 dioxin minimizing possibilities of different equipments were checked and discussed. First the Air fine process was introduced, but just a new way of this process was published with dry typ of gas cleaning. The „EOS (Emission optimized sintering)“ was shown and further test-campaigns with LEEP at HKM were added, e.g. Quenching- and Jet stream injection of active coke breeze. Step by step these ways were discussed. The partly off-gas recycling brought interesting low values. The clean part of the off-gas was given to the chimney but the off-gas with dioxin were returned into the hot zone of the sinter strand. At the end of this chapter once again tests in a sintering pan were discussed of the SDD-project in Japan. They showed e.g. the increase of dioxins by PVD- and by sinter strand dusts-addition. After these global views in the next chapter the Sinter plant and the possibilities of Taranto will be shown in short words. The first measurement results of Dioxin will be given and technologies and the used materials are mentioned. The following part will show the possibilities to minimize Dioxin emission without technological changes on the strand.

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/2/

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/29/

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/30/

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/35/

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/37/

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