Sustainable EAF steel production (GREENEAF).
Date: 2013-12-04
Institutions: Directorate-General for Research and Innovation
Subjects: chemical process, fossil fuel, furnace, iron and steel industry, metal waste, natural gas, research report

European Commission

Research Fund for Coal and Steel

Sustainable EAF steel production

(GREENEAF)

L. Bianco, G. Baracchini
Ferriere Nord
Zona Industriale Rivoli – 33010, Osoppo, ITALY
F. Cirilli
Centro Sviluppo Materiali
Via di Castel Romano 100, 00128 Rome, ITALY
A. Moriconi, E. Moriconi
Tecnocentro
Località Pentima Bassa, 21, 05100 Terni, ITALY
M. Marcos
Imperial College
South Kensington Campus, SW7 2AZ London, UNITED KINGDOM
T. Demus, T. Echterhof, H. Pfeifer, T. Demus
Rheinisch Westfälische Technische Hochschule Aachen
Templergraben 55, 52056 Aachen, GERMANY
C. Beiler
Deutsche Edelstahlwerke GmbH
Deutsche Edelstahlwerke, 101220, 57012 Siegen, GERMANY
T. Griessacher
Stahl- und Walzwerk Marienhütte Gmbh
Südbahnstrasse 11, 8020 Graz, AUSTRIA

Grant Agreement RFSR-CT-2009-00004 
1 July 2009 to 30 June 2012

Final report

Directorate-General for Research and Innovation

2013 

EUR 26208 EN

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Luxembourg: Publications Office of the European Union, 2013 

ISBN 978-92-79-33614-0 
doi:10.2777/44502 

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Table of contents

Executive summary .................................................................................................................................4

Scientific and technical description of results .......................................................................................15
1 ObJectives of the project ....................................................................................................................15

2 ComparIson of initially planned activities and work accomplished...................................................15

3 Description of activities and discussion .............................................................................................15
WP1 Biomass selection for EAF char production (Tecnocentro, CSM, IP)......................................15
WP2 Tailoring of biomass pyrolysis (TECNOCENTRO; IP; CSM) ...............................................20
WP3 Chemical and physical characterization of char produced by biomas pyrolysis (CSM, IP,
RWTH) ..............................................................................................................................................20
WP4 Definition of
TECNOCENTRO, IP) .......................................................................................................................42
WP5 Industrial experimentation (DEW, Ferriere Nord, CSM, RWTH, MH, Tecnocentro, IP)........67
WP6 Techno-economic evaluation and final report (Ferriere Nord, CSM, Tecnocentro, IP, RWTH,
DEW, MH) .......................................................................................................................................89

(DEW, FENO, CSM, RWTH, MU,

the EAF operating practices

Conclusions .........................................................................................................................................100

References ...........................................................................................................................................101

Exploitation and impact of the research results...................................................................................103
List of symbols and abbreviations.......................................................................................................104
List of Figures .....................................................................................................................................104
List of Tables.......................................................................................................................................109

Annex 1- Slag foaming........................................................................................................................112

ANNEX 2 - Calculation of CO2 emissions from DEW steelplant......................................................114

3EXECUTIVE SUMMARY

WP1 BIOMASS SELECTION FOR EAF CHAR PRODUCTION (TECNOCENTRO, CSM, IP)

WP is devoted to the analysis of availability of biomass in the area around the steel factories
participating to the project. In fact, in order to make the biomass utilization economically convenient
transportation costs must be reduced as much as possible.
The analysis of biomass availability has been carried out close to the steel plant of Ferriere Nord
(Italy), DEW (Germany) and MH (Austria). Following Table reports the amount of total biomass
amount close to the steel plants and the steel plant biomass demand.
In general, biomass is collected from agricultural residues, from forest residues, wood industry or can
be cultivated.
Within this activity some biomass species have been selected for characterization activities:
forest residues (including ligneous species as saw dust for pellets or pulp)
-
-
grapewine and corn stalk as agricultural residues
- mischantus and sorghum as biomass from cultivation

Following Table summarises the main vantages and disadvantages of different biomass specie

Biomass
Forest residues

Advantages
large amount available and well
distributed during year

Disadvantages
relatively high energy necessary
for collection and transportation

Corn and graspewines

large amount; low cost

larger ash content and nitrogen
other
(see
biomasses

analysis)

respect

Mischantus and sorghum

large amount available; present
both North
Germany; high energy ratio.
nitrogen and ash amount smaller
than residues form cultivations
Summary of main characteristics of different types of biomass.

Italy, Austria

in
and

Need of dedicated cultivation,
large productivity after second
year of
implantation; nitrogen
and ash amount larger than forest
residues

Samples of biomass of types described in Table 2 have been collected. The following characterization
activities have been carried out on selected biomass:

1. Physico-Chemical characterization

in terms of chemical composition, ash content, ash

composition and properties, heating value;

2. Thermogravimetric tests

Table below summarizes performed characterization activities on selected biomass

Data*
LHV* [kJ/kg]
Volatiles (%)
Ash (%)
C (%)
H (%)
N (%)
O (%)
S (%)
Cl (%)

Ligneous biomass (Forest residues)
20000
80
1.1
51.5
6.7
0.3
39.7
0.04
0.05

* Lower Heating Value

Corn straw
18000
76-81
5.5
47.3
5.4
0.8
43.2
0.05
0.2

grapewine
18900
78
3.9
46.2
5.5
1.3
37.7
0.03
0.05

mischanthus
19100
78
3.5
48.2
5.4
0.6
42.1
0.06
0.2

Characterization activities performed on selected biomass

4The performed analysis showed that the selected biomasses have very similar elemental analysis in
terms of C/H/O and similar volatile matter content. Biomasses heating value is also very similar. Main
differences can be found in minor elements (as N, S and Cl ) and ash amount.

WP2 TAILORING OF BIOMASS PYROLYSIS (TECNOCENTRO, CSM, IP)

WP3 CHEMICAL AND PHYSICAL CHARACTERIZATION OF CHAR PRODUCED BY
BIOMAS PYROLYSIS (IP, CSM, RWTH)

WP2 is devoted to the definition of the influence of the pyrolysis conditions in terms of temperature,
residence time, material size, atmosphere composition on char and biogas yields and characteristics.
WP3 is devoted to define the yield and the quality of the char produced in terms of chemical
impurities content and relevant physical characteristics, as a function of pyrolysis
composition,
conditions defined in WP2. Being the two WPs strongly connected, their activities are presented jointly
in this same paragraph. Pyrolysis products are charcoal, condensable vapours and syngas. The
percentages of formed products depends on pyrolysis heating rate, residence time and reaction
temperature. Moreover the characteristics of formed products (in terms of composition, porosity,
combustion behaviuour and so on) are a function of pyrolysis conditions.
The following characteristics of char and syngas have studied:

chemical composition and porosity

- Char/syngas yeld as a function of different pyrolysis conditions and starting biomas
-
- heating values of char as a function of different pyrolysis conditions and starting biomas
syngas composition and heating value as a function of different pyrolysis conditions
-
char reactivity
-
comparison of char reactivity with coal reactivity
-
- Char proximate analysis

Laboratory tests are carried out with:

(cid:120)

thermobalance, to follow weight variation as a function of time and temperature (TG tests),
using also different atmosphere and low heating rates (order of magnitude of 1-20 °C/min),

(cid:120) Wire Mash Reactor, for high heating rate,
(cid:120) Gray-King furnace, an apparatus used for testing coals according to the British Standard

method-BS1016-107.2.

According to the performed tests the starting biomass particle size does not affect the general yield in
terms of char, tar and syngas.
An important result is that, after 500°C, the char yield is almost stable, and this result does not depend
on the biomass type. Figure below reports Char yield as a percentage of the original biomass (dry basis)
as a function of temperature (°C) in experiments conducted in the Gray-King reactor.

Char
yield
(%)

100%

90%

80%

70%

60%

50%

40%

30%

20%

10%

0%

CS - CHAR db

SO- CHARdb

SW- CHAR db

Temperature (°C)

100

200

300

400

500

600

700

Char yield for three different biomasses (CS: ligneous biomas, SO cultivated biomass, SW: biomas from
residues)

Syngas compostion has been determined connecting a mass spectrometer As an example, following
curve compare char and syngas heating value as a function of pyrolysis temperature. Char heating

5values is measured, while syngas heating value is calculated from syngas composition measured with
mass spectrometer during TG test (Figure below).

Heating value of syngas and char as a function of pyrolysis temperature

The reactivity of the chars was assessed in a thermogravimetric apparatus by both isothermal and non-
isothermal methods. Below is reported result from non-isothermal determination. In this test, after an
initial step in an inert atmosphere, the gas is switched to air at the beginning of the temperature ramp
from 400 to 850ºC. As expected, the chars produced at higher temperatures present lower reactivities.
However, at the low end of the pyrolysis temperature range, there are marked differences between the
behaviour of the 300ºC char, which shows a high volatile content, and that of the chars produced
between 325-450ºC. There are as well significant differences between the latter and those chars
generated at 500-600 ºC, which present the same reactivity among themselves.

TGA non-isothermal char reactivity tests of beechwood chars produced in the Gray-King reactor.
Curves of fraction of remaining weight for the different chars and temperature as a function of time are
shown.

The tests performed by IP confirmed that char, gas and tar yeld are almost stable after 500°C.
A good compromise for pyrolysis temperature can be considered the value of 500°C. Validation of
these results has been done by Tecnocentro, a by a small scale pyrolysis apparatus test. The laboratory
system is composed by an horizontal electric furnace which works in nitrogen atmosphere. Scheme of
the apparatus is reported below.

6Legend:
A = Nitrogen;
B = Manual valves;
C = Pyrolyzer;
D = Electric furnace;
E = Tar collection filter;
F = Dehumidifiers;
G = Flowmeter;
H = Pump;
I = Gas bag;
L = Thermocouple

Scheme of laboratory pyrolysis furnace

and gas
Tests have been carried out with ligneous biomass and agricultural residues. Char, tar
percentage produced after different pyrolysis campaigns, were measured. Table 4 reports the amount of
formed products for different biomass at 500°C, for a fixed residence.

BIOMASS
Sorghum pellet
Grape raspe
Dried wood
Char and gas percentage produced after different pyrolysis campaigns

CHAR (% wt)
35.9
29.0
31.0

GAS (% wt)
52.8
49.0
51.0

TAR (% wt)
11.3
22.0
16.5

After laboratory tests pyrolysis campaigns were carried out on demonstrative plant to take char and
pyrogas samples in order to study their characteristics varying process parameters and define the
best condition for char production from biomass.
The effect of the main process parameters, such as different combination of rate of heating, time of
treatment and the rotation speed of pyrolysis reactor have been considerate.
The demonstrative pyrolysis plant can be fed with about 200 kg/h of fuel and the necessary heat energy
for pyrolysis reactions is supplied by a gas burner of the maximum power of 500 KW.
The photo below shows the pilot plant: pyrolysis reactor, gas cleaning system and the microturbine.

Enerpol pyrolysis plant (Tecnocentro)

During the tests on different kind of fuel, the pyrogas has been burnt in the torch and sampled; the tar,
which in biomass is in the percentage of 7-11% has been eliminated from the gas in the treatment
section and collected in the tank with cooling and washing water.
So, for each test and different biomass, the yields have been sampled, weighed and analyzed to
highlight the correlation between product characteristics and process parameters.

The main monitored and variable pyrolysis parameters are:

1. Pyrolysis temperature (optical pyrometer);

7Internal reactor pressure;

2. Gas temperature out from the reactor;
3. Gas pressure out from the reactor;
4.
5. Rotation speed of the reactor (residence time);
6. Feeding speed varying the rate of the feeding metering screw;
7. Chemical and physical properties of the feeding fuel;
8. Chemical - physical characteristics (density, elemental analysis, heavy metals), temperature and

mass balances of char and gas obtained;

The gas product is typically a mixture of carbon dioxide (9-55% by volume), carbon monoxide (16-
51%), hydrogen (2-43%), methane (4-11%) and small amounts of higher hydrocarbons.
Temperature affects char composition. Chars produced at higher temperatures having higher carbon
contents both total- and fixed-carbon; higher temperatures lead to lower char yeld in all pyrolysis
reactions.

Influence of temperature on pyrogas composition and on Higher Heating Value of pyrolysis yelds

Preliminary laboratory tests were carried out to have a first evaluation of char vs coal foaming
behaviour. The trials have been conducted using slag sampled from the DEW EAF right before slag
foaming. Foaming slag are carried into alumina crucible, filled with a mixture of pulverized char or coal
and put into a furnace at 1600°C. The foamy slag is increasing the slag volume and leads to a freezing
of slag to the inner crucible wall up to a height indicative of the maximum volume increase during the
trial. Figure below shows pictures of the crucibles after the slag foaming trials. Within these pictures the
foamy slag height reached during the trial is marked.

Foaming test with coal

Foaming test with char

Crucible after laboratory foaming tests

The achieved volume increases clearly show the general suitability of the char for slag foaming.

8WP4 DEFINITION OF THE EAF OPERATING PRACTICES (DEW, FENO, CSM, RWTH,
MU, TECNOCENTRO, IP)

Activities preparatory to industrial trials have been performed consisting in:

1. To perform test in pilot plant of RWTH
2. Analysis of EAF cycle of the steelmakers, to design an operating practice

The pilot plant tests at RWTH have been started with trials investigating the slag foaming capability of
the charcoal delivered by Tecnocentro and comparing it to conventionally used fossil coals.
Regarding the tests into the pilot EAF plant of RWTH two types of biochar have been tested in the
pilot plant as charge coal and as injection. Additionally tests with reference materials have been
performed to compare the results from biochar tests with the standard situation in the industrial mills.
As reference materials, anthracite coal and petrol coke presently used at DEW Siegen were used. The
different compositions have been analyzed and the results are shown in Table below.

[%]

Carbon
Ash
Volatiles
Humidity
Sulphur
Phosphor
Grain Size

Biochar from
grape seed (TC)1
77.5
9
7.7
5.6
0.3
0.5
<5 mm

Biochar from
wood residues2
60
21
13.5
5.2
0.06
0.4
<<1 mm

1: mean of 3 measurements; 2: mean of 24 measurements

Composition of different biochar and reference materials

Anthracite
(DEW)
86
11.1
2.6
-
0.3
-
6-12 mm

Petrol Coke
(DEW)
93
5.8
1
0.2
1
-
<1 mm

As a basis the reference trials have been performed using an amount of 1 kg anthracite coal on 50 kg of
scrap. Due to the lower heating value in comparison to the anthracite coal 1.6 kg of non-processed
biochar from Tecnocentro and from wood gasification plants were charged to compensate the
difference. Just before tapping at 1650°C, a melt sample was taken for chemical analysis to give
information about possible negative effects of biochar use. After tapping all output fractions have been
separated and the individual output masses were recorded. Figure below reports steel analysis after trial
tests, comparing coal, and two char from two providers.

Steel composition after pilot trials

9The evaluation of the pilot arc furnace trials shows no negative effects regarding the steel and slag
analysis. Differences occur in terms of the Ni and Mn content. These differences can be explained by
small fluctuations in the scrap composition and they are not addressed to pollution from char use.
The reference trial shows a higher carbon content than the two biochar trials. This would imply a better
carburization of the melt by the anthracite coal and would also be in agreement with the findings of the
off-gas analysis. Considering the sulphur content of the steel, the effect is evident of the lower sulphur
content of the biochar in relation to the reference materials. The steel produced by the biochar trials has
only about half the sulphur content in relation to the reference trial. Despite the higher phosphor
concentration in the different biochar on the other hand, the phosphor content in the steel is the same for
all trials. So the use of biochar instead of fossil coal shows no negative impact on steel composition in
the pilot trials. Also regarding the slag composition, these first preliminary results indicate no negative
influence of the use of biochar with higher ash content on the general slag composition.

WP5 INDUSTRIAL EXPERIMENTATION (DEW, FERRIERE NORD, CSM, RWTH, MH,
TECNOCENTRO, IP)

The use of char in EAF has been tested at industrial scale by the three industrial partners
participating to the GreenEAF project. The industrial partners involved in this project have different
EAF, which differs for size, capacity, and amount of chemical energy. Following Table reports the
main EAF characteristics. Char industrial testing with these three furnaces will exploit a wide range of
operational variability. Both char charging and injection have been tested. FENO uses coal charged and
injected for respectively bath carburization and foaming. DEW uses coal mainly for bath carburization:
coal is manly charged and injected in a small amount. DEW and MH uses coal for foaming: coal only
injected.

Charge
weight
(TLS)
140
130
40

Num.
buckets
/heat
3
2
3

Electrical
energy input
[kWh/TLS]
341
417,2
375

FENO
DEW
MH

CH4
[Nm3/TLS]

O2
[Nm3/TLS]

Coal lump
[kg/TLS]

6
0
7

42
21,8
45

4
10.7
0

Injected
Coal
[kg/TLS]
8
1,53
12

Power
on [min]

38
54
31

Tap
to tap
[min]
45
69
45

FENO: Ferriere Nord
DEW: Deutsche Edelstahlwerke GmbH
MH: Marienhütte Ges. m.b.h.

Main characteristics of the electric furnaces of the industrial partners participating to the project

Charged char tests
Substitution of charged coal with char has been tested by Ferriere Nord and DEW. Charged coal
can be needed to reach certain carbon levels in the steel depending on scrap qualities available. It can
also be used to substitute electrical energy by chemical energy when oxygen is used to decarburize the
melt and the carbon is burned to CO and CO2 respectively.

Ferriere Nord uses about 1 ton of charge coal per heat, while DEW about 1.4 tons of coal per
heat. The Electric furnace of Ferriere Nord is equipped also with the offgas online monitoring system
EFSOPTM.

The average of steel and slag analysis with char charged in 5 heats has been compared with the
average of 5 standard heats. As example Figure below reports the comparison of average values of steel
and slag analysis measured at DEW in standard and trials heats. The results from steel and slag analysis
show no significant differences.

Off gas analysis system (EFSOP analyzer) in Ferriere Nord has been used during tests. Measured

data have been compared with data of the production of CO/CO2/H2 during standard operations.

The main difficulty in char charging is related to high char reactivity. Significant powder
dispersion has been noticed during handling and charging operations and intense flame emissions were
observed during trials with char.

This problem has been solved with preliminary material briquetting. New industrial
tests
performed with charcoal briquettes have been performed and confirmed the absence of anomalous
flame emissions with briquetted material.

10Steel analysis

Slag analysis

Comparison of steel and slag analysis of standard and trials heat measured at DEW

O2/s*
0,39
0,16
Average Values of offgas compostion measured during industrial trials at Ferriere Nord

Char Trials
Standard Trials

CO2/s*
17,34
16,96

CO/s*
16,07
17,55

H2/s*
9,85
10,19

Injected char trials
Foaming trials were carried out by the three industrial partners. Slag foaming is a very complex
equilibria depending on slag properties (mainly viscosity and surface tension), amount of injected coal
(which affect the amount of gaseous species necessary to promote foaming) and also coal reactivity. So,
beside the energetic input, the foaming behavior is an important process aspect which must be taken
into account for industrial testing of char.

For a better control of foaming process Marienhütte developed together with VATRON GmbH
an Optical Foaming Slag Management System (OFSM). The slag height is detected by a camera
continuously. The camera is placed close to the slag door. Special image processing software calculates
a slag index to be used for the injection of the carbon amount required. Due to the real-time monitoring
of the slag level it is possible to adjust the C-contents by injection of the optimal quantity of carbon.
Following figure reports the images of three foaming tests with char produced by Tecnocentro.

Injection tests were carried out also by DEW and Ferriere Nord.

Results obtained by the three partners were partially satisfactory, in the sense that in some trials good
foaming behavior was observed, and in some trials no. These results indicate that injection system must
be improved promoting the penetration of char into the slag.

11Test C. No foaming

Test B. Poor foaming beavhiour

Test A . Good foaming beavhiour

Foaming tests recorded with Optical Foaming Slag Management System (OFSM installed at
Marienhütte

Environmental monitoring at stack was carried out both by FENO and DEW and confirmed that char
does not introduce any modification respect the historical plant trends.

Use of syngas in EAF

Due to the difficulty to produce syngas close to the steel plant for industrial trials, syngas
utilization into the EAF burners has been simulated trough CFD modeling. Due to complexity of syngas
composition the simulation of syngas industrial utilization has been carried out according to the
following criteria:

(cid:190) Definition of a quantitative criteria to compare natural gas burning with syngas burning
(cid:190) CFD calculation with natural gas burning to be used as reference situation
(cid:190) CFD calculation with the syngas and comparison with reference situation

Calculation was set considering a bidimensional calculation domain having diameter of 2500 mm
and length 6000 mm. The domain is surrounded on three sides by the furnace atmosphere (considered
composition of the atmosphere is taken from measurement of offgas analysis system of FENO) at
temperature of 1100°C. On one side (in which is present the burner in symmetric position) the
temperature is fixed at 100°C (considering the temperature of water cooled panels)

Quantitative criteria to compare the standard and syngas situation must be introduced. The

criteria selected to compare natural gas and syngas burning is the efficiency, defined as:

kW
(cid:152)

to
(cid:152)
(cid:152)
from

kW

the
(cid:152)
the
(cid:152)

scrap
burner
(cid:152)

The syngas composition used in the simulation has been measured during industrial char
production. Due to the heating value of the obtained syngas, syngas composition has been enriched with
methane up to obtain the value of 21 MJ/kg of heating value. This is the value which is compatible with
the maximum flow rates available on the steel plant of Ferriere Nord.

12Figures below report the temperatures of flames feed with natural gas and syngas and the

efficiency of the burners.

Calculated flame temperature in case of natural gas burning and syngas burning and comparison of
efficiency with syngas and natural gas.

The CFD calculation show that the shape of the flame of syngas is different, and the especially the
temperature is lower respect natural gas burning. The efficiency also is lower of values ranging from 8
to 15% .
To recover the gap of efficiency following actions are possible:

increase of amount of methane in the mix
increase burned size and syngas flow rate

(cid:120)
(cid:120)
(cid:120) modify burner geometry to increase combustion efficiency.

The design of new burner has been simulated and the increase of efficiency in about 10%.

WP6 TECHNO-ECONOMIC EVALUATION AND FINAL REPORT (FERRIERE NORD,
CSM, TECNOCENTRO, IP, RWTH, DEW, MH)

Charcoal is a wood product that is made by heating wood in absence of sufficient air for full
combustion to occur.
There is not a great deal of information available in literature on the cost of charcoal production.
Charcoal cost can be grouped into three main issues:

1. wood/raw material (including cost of harvesting and collection of biomass up to the pyrolysis

plant)

2. charcoal production
3. charcoal transport (to be intended as transportation from the pyrolysis plant to the steel factory)

where the first issue has the main weight.
The global cost of charcoal utilization can be decreased considering:

(cid:120)
(cid:120)

carbon tax
creation of local economy, optimising the process of biomass collection, transformation and
transportation close (as much as possible) to the steel plant.
Literature reports charcoal prices ranging from 160 to 400 (cid:188)/t of char [19,20].

General conclusions of the project

The global objective of the project is to investigate the partial or total substitution of coal and
natural gas with charcoal and syngas produced from pyrolysis of biomass. The char is used as injectable
powder or charged in the basket. The characteristics of char and syngas, and the related pyrolysis
process, are tailored in order to match the requirements for their utilization in EAF.

The tests performed (both pilot and industrial) showed that coal can be replaced by char, both for

charging and injection to promote foaming.

13In case of charging the following aspects should be deeply investigated:

(cid:190) char reactivity: char start burning during charging. Char reactivity depends on high surface
area, volatile content and powders dispersion during charging. Proposed solution is a char pre-
treatment with briquetting stage before charging;

(cid:190) slag foaming: some trials showed good foaming behaviour, other trials were not satisfactory.
Proposed solutions are improvement of injection system and utilization of additives togheter
with char powder to increase char/slag wettability and promote reaction of char with iron
oxide. The injection system must ensure char injection below the slag

Moreover, syngas utilization in EAF burners, instead of natural gas has been simulated by means of
CFD calculations. The used syngas composition was that arising from the pyrolysis tests. Syngas
utilization leads to a decrease of EAF efficiency.

Techno economic evaluation carried out considering char cost and CO2 emission leads to the conclusion
that:
(cid:120)

official market for biochar does not exist an which can be used in steel mills. Most part of
biochar production is still in pilot scale state. So the prices per ton of produced biochar are not
representative. Literature reports prices ranging from 160 to 400 (cid:188)/t of produced char.
Evaluation of Tecnocentro indicates a price of production in the range 200-250 (cid:188)/t. The local
availability of biomass is mandatory
exemplary price of 18 (cid:188) per ton of CO2 partially compensate actually higher price of charcoal.

(cid:120)

In the next few years the industrial scale production of different biochar qualities is expected and
according to this the development of a market and a market price.

In Addition to that increases of the prices for fossil coal are expected, too. In general the use of biochar
puts the electric steel mills in a position to avoid CO2 emissions which are relevant for the EU ETS like
the emissions from fossil carbon.

14SCIENTIFIC AND TECHNICAL DESCRIPTION OF RESULTS

1 OBJECTIVES OF THE PROJECT

The ECSC project “Sustainable EAF Steel Production – GREENEAF” has the objective to study
the EAF cycle in order to investigate the partial or total substitution of coal and natural gas with
charcoal and syngas produced from pyrolysis of biomass.

Generally speaking, in the electric furnace coal (and consequently char) can be used as injected

powder or charged into the basket. The syngas can be used for EAF burners.

The characteristics of char and syngas, and the related pyrolysis process, must be tailored in order

to match the requirements for their utilization in EAF.

The feasibility of coal substitution has been tested with industrial trial.

2 COMPARISON OF INITIALLY PLANNED ACTIVITIES AND WORK
ACCOMPLISHED

All project activities foreseen in the technical annex have been carried out without deviations.

3 DESCRIPTION OF ACTIVITIES AND DISCUSSION

WP1 BIOMASS SELECTION FOR EAF CHAR PRODUCTION (TECNOCENTRO, CSM, IP)

WP1 is devoted to the analysis of availability of biomass in the area around the steel factories
participating to the project.
In general, biomass is collected from agricultural residues, forest residues, wood industry or can be
cultivated.
These three species of biomass differ for:

• Amount
• Different expected characteristics of produced char in terms of size, shape, mechanical

characteristics and pollutants emissions

• Availability during the year
• Different energetic balance [3,4,7], considering the heating values and the energetic expense for

cultivation, collection and transportation.

In what follows,
the local situation in Friuli (Italy), North Rhine-Westfalia (Germany) and Styria
(Austria) has been analysed. In these three regions are located respectively the steel plant of Ferriere
Nord, Deutsche Edelstahlwerke and Marhienutte.

The situation in Friuli (Italy)
The steel plant of Ferriere Nord steel plant is located in the region of Friuli, in the North of Italy.
Table 1 reports the amount and types of available biomass, the corresponding energy potential and an
estimation of CO2 amount which can be saved.

15Biomass type

forest residues and ligneous species

agricultural residues

biomass from cultivations

tot

[t dry
mass/a]
284300

355100

300000

939400

Table 1

Friuli Biomass amount and potential energy availability [1,2,3]

The biomass amount necessary to replace coal has been estimated in 100000 t/year (see WP 4 for
details), so the amount of biomass available in the surrounding of the factory is largely enough. The
amounts of biomass ensures also that material is available within the year.

The situation in North Rhine-Westfalia (Germany)
locations Deutsche
To complete the information on biomass availability at
Edelstahlwerke (DEW) and RWTH provided data about the situation for the DEW plant in Siegen,
which is in the federal state of North Rhine-Westfalia (NRW) and the administrative district of
Arnsberg respectively.
The two types of biomass which are mainly available in this area are dendro mass (fast growing tree
species with short rotation) and agricultural residues like straw. Table 3 is showing the availability of
dendro mass in the Arnsberg district as well as in the state of NRW. Table 4 is presenting the
availability of straw in NRW and Germany.

the different plant

Arnsberg
[t dry mass/a]

Federal state NRW
[t dry mass/a]

Theoretical potential

Sustainably mobilizable potential total

Sustainably mobilizable potential solid
volume

Sustainably mobilizable
brushwood

potential

594,084

302,447

254,426

48,021

1,818,549

1,166,415

977,613

188,802

Table 2: Cultivated ligneous biomass (Dendro mass) availability in Arnsberg district and NRW [13]

Acreage [ha]

Straw total [twet mass/a]

Sustainably mobilizable potential for
energetic use [t/a]

Federal state NRW
[t dry mass/a]

630,000

2,600,000

600,000

Energy equivalent

2,400 GWh/a

Germany
[t dry mass/a]

8,100,000

36 – 43 Mill.

3,600,000

56.1 PJ/a

Table 3: Agricultural residues availability in NRW compared with availability in Germany [14]

In both cases sufficient potential is available to substitute the fossil fuel demand of the DEW plant in
Siegen.

16The situation in Styria (Austria)
Even if not directly involved in this WP, Stahl- und Walzwerk Marienhütte (MH) provided data about
local situation of biomass availability in Austria, in order to have a reference situation to be compared
with plant needs. Austria has a large amount of biomass availability, actually used for power generation
(see Figure 1, (a)). The potential on wood is about 31 million solid cubic meters per year, wherefrom
only 19 million are used at the moment. Most of this wood, with a still rising trend, is used for heat and
energy production in different forms. In Styria the annual amount of wood used for energy production is
about 1.2 million solid cubic meters (Steiermark Holzeinschlag, www.verwaltung.steiermark.at, Stand
21.1.2009).

(a)

geothermal energy 0.8 0%

heat pumpe 6.1 4%

solar heat 3.7 2%

other refuse 14.7 9%

waste 2.2 1%

waste liquor/Sludge of
paper industry 23.6 14%

biodiesel 0.2 0%

digester gas 0.7 0%

landfill 0.5 0%

straw 0,2 0%

woodpellets 2.9 2%

wind 1.3 1%

photvoltaics 0.0 0%

split logs 71.8 43%

woodchips 10.0 6%

(b)

]
a
/
M
D

,
t
[
s
e
i
t
i
c
a
p
a
C

,
d
n
a
m
e
D

200.000

180.000

160.000

140.000

120.000

100.000

80.000

60.000

40.000

20.000

-

industry wood off-cuts
(incl. bark) 17,3%

780.000 t,DM/a

Demand [t,DM/a]

Capacity Styria [t,DM/a]

Land requirements [ha]

122.616

115.000

56.000

27.800

24.849

3.000

-

25.000

20.000

15.000

10.000

5.000

-

]
a
h
[
t
n
e
m
e
r
i
u
q
e
r
d
n
a
L

Figure 1

(a): Gross consumption of renewable energy sources in Austria in the year 2003
(b): Biomass potential in Styria

Raw materials

Due to the fact, that wood is a typically expansive biomass also some potentials of low priced
biomasses were checked for the region Styria. One of these biomasses is strew from different origins,

17which has a potential of about 115000 t per year. The actually used part of strew can only be estimated.
One problem of strew is its seasonality, which would lead the high storage capacities.
In Styria also high amounts on corn are cultivated. This results in about 56000 t of cobs per year, which
are also one potential feedstock material for charcoal production. The quantity of biomass arising at
landscape conservation works is about 28000 t per year. In most cases this material is converted to
woodchips. Bark, which is very often a by-product in wood industry, has a potential of about 123000 t
per year. Also waste wood seems to be interesting for charcoal production. It accumulates in an amount
of approximately 25000 t/a.
Two examples for very special but also interesting biogenic feedstock materials are brewer grains and
sewage sludge with an occurring amount of 3000 t/a and 34000 t/a, respectively in Styria.
One additional option would also be the purchase of some agricultural areas and the cultivation of own
biomass in form of e.g. short rotation crops or wood. The typical crop yield for such plantations in
Styria is about 10 to 20 t/ha and year. This means, for the cultivation of reasonable amounts of biomass,
huge areas of several km² would be needed.
Figure 1(b) gives an overview of the arising amounts of different biomasses in Styria. Comparable, the
demand on injection coal at Marienhütte is about 5400 t per year, which gives a consumption of pure
carbon of about 5000 t per year for slag foaming. To cover this demand by charcoal, approximately
20000 t/a of feedstock biomass would be needed, if a carbonization yield of 30 % and a carbon content
of the charcoal of 80 % is taken as a base; this amount is largely available at the moment.

Main conclusions from the analysis carried out by all the partners are reported in Table 4, describing
synthetically the main advantages/disadvantages of considered biomasses.

Biomass
Forest residues

Corn and graspewines
(agricultural residues)

Mischantus and
sorghum (cultivated
biomass)

Advantages
large amount available and well
distributed during year
large amount; low cost

large amount available; present in
both North Italy, Austria and
Germany; high energy ratio.
nitrogen and ash amount smaller
than residues form cultivations

Disadvantages

relatively high energy necessary for
collection and transportation
larger ash content and nitrogen (see
analysis) respect other biomasses.
Seasonal
Need of dedicated cultivation, large
productivity after second year of
implantation; nitrogen and ash amount
larger than forest residues. Seasonal

Table 4

Main advantages/disadvantages of considered biomasses

Task 1.2 Characterization activities (Tecnocentro, CSM)

Physico-Chemical characterization in terms of chemical composition, ash content, ash composition and
properties, heating value have been carried out on the selected biomass. Results are presented in what
follows

Physico chemical characterization of biomass

Representative samples of biomasess have been collected by Industrial partners and Tecnocentro and
used for characterization activities and for further pyrolysis tests at lab scale..
Among the individuated categories of biomass (Table 5), the following representative samples were
collected:
(cid:120)
(cid:120) Corn straw and Grapewine (residues from cultivations)
(cid:120) Mischantus and sorghum (cultivated biomas)

Forest residues (with and without bark)

Following Table summarises performed characterization activities of CSM and Tecnocentro

18Data*

Forest
residues

Wood+bark

Bark

20000

18100

16200

Wood
without
bark
18500

Corn
straw

corn

grapewine mischanthus

Sorghum
pellet

18000

17500

18900

19100

18000

Lower
heating
value
(LHV)
[kJ/kg]
Volatiles
(%)
Ash (%)

80

1.1

C (%)

51.5

H (%)

N (%)

O (%)

S (%)

Cl (%)

6.7

0.3

39.7

0.04

0.05

82

0.8

47

6

0.3

44

85.0

5.5

51.0

-

0.16

76

3

47

5.4

0.4

40

0.05

0.06

0.02

-

-

-

76-81

5.5

47.3

5.4

0.8

43.2

0.05

0.2

76

3.5

45

6

1.8

43

0.12

0.08

78

3.9

46.2

5.5

1.3

37.7

0.03

0.05

78

3.5

48.2

5.4

0.6

42.1

0.06

0.2

81

6.8

43.7

5.73

1.07

<0.1

0.4

Table 5

Physico-chemical characterization of selected biomasses. Moisture content ranges
form 10-12 % in all the samples

Following Table reports the characterisation of biomass ashes, in term of oxide content and also
viscosity.
This data will be used to design the industrial tests. One representative example of ash for each category
of biomass has been considered.

[%]

SiO2
K2O
CaO
MgO
P2O5
Na2O
FeO
MnO
Al2O3

Forest
residues
5.6
38
22.87
17.35
14.98
1.1
0.42
0
0

corn

Grape wine

mischantus

1.4
42
11.02
9
28.5
0.5
1.3
0.2
1.06

22.03
31.2
20.1
8.52
16.19
0.7
0.54
0.1
0.1

71.7
14.56
7.56
2.69
2
0.9
0.5
0
0.93

Table 6

Biomass ashes composition

The performed analysis showed that the selected biomasses have very similar elemental analysis in
terms of C/H/O and similar volatile matter content. Biomasses heating value is also very similar.

Main differences can be found in minor elements (as N, S and Cl ) and ash amount. This means that the
possible effects on EAF process, influence on steel and slag composition and environment pollution
must be investigated and analysed in the industrial tests.

19Ashes composition is very different from the four types of biomass: mischantus has a very high silica
content, while the other biomass have a significant content of potassium oxide.
The effect on EAF slag composition and the subsequent effect of main slag physical properties (melting
behaviour and viscosity) will be evaluated in WP4.

WP2 TAILORING OF BIOMASS PYROLYSIS (TECNOCENTRO; IP; CSM)

WP3 CHEMICAL AND PHYSICAL CHARACTERIZATION OF CHAR PRODUCED BY
BIOMAS PYROLYSIS (CSM, IP, RWTH)

WP2 is devoted to the definition of the influence of the pyrolysis conditions in terms of temperature,
residence time, material size, atmosphere composition on char and biogas yields and characteristics.
WP3 is devoted to define the yield and the quality of the char produced in terms of chemical
composition,
impurities content and relevant physical characteristics, as a function of pyrolysis
conditions defined in WP2. Being the two WPs strongly connected, their activities are presented jointly
in this same paragraph.
In what follows the task activities are reported according to the following logical order:
1. Task 2.1: laboratory tests to define the pyrolysis kinetics of the selected biomass
2. Task 3.1: characterization of char and biogas
3. Task 3.2: process parameters
4. Task 2.2: definition of pyrolysis process parameters

Task 2.1: laboratory tests to define the pyrolysis kinetics of the selected biomass. (CSM, IP)

Laboratory tests have been carried out to determine:

-
-
-

pyrolysis kinetic
amount of char, biogas and tar produced under different pyrolysis conditions
the chemical composition of biogas

Tests are carried out with thermobalance (TG tests), with low heating rates (order of magnitude of 1-20
°C/min) and with wire mash reactor, for high heating rate and Gray-King furnace, an apparatus used for
testing coals according to the British Standard method-BS1016-107.2
Experimental tests have been carried out by CSM and Imperial College. Descriptions

TG tests (CSM)
Laboratory tests have been carried out using a termogravimetric apparatus (TG tests). Figure 2 reports
a scheme of the laboratory apparatus. It consists of a vertical electric furnace, with heating rate in the
range 1-20 °C/min, able to work under controlled Ar atmosphere. Sample is placed inside an allumina
crucible of 20 cm3, which does not interact with sample or gaseous atmosphere during experimental
test.
Sample is hang up to a balance, connected to a PC to continuously record weight variations during the
test. The furnace is equipped also with a mass spectrometer to analyse gas composition evolution during
test.

20Mass
spectrometer

Figure 2

Scheme of laboratory termogravimetric (TG) apparatus

Two types of tests have been carried out:

1. Tests under temperature gradient, to experimentally measure the characteristics temperature of
starting of reactions. All the four selected biomass have been tested. The used temperature
programme was: up to 900°C at 300°C/h, with continuous measurement of weight and gas
evolution

2. Tests at constant temperature: to obtain the kinetic of pyrolysis process. All the four biomasses
selected studied. Tested temperatures were: 400°C, 500°C and 600°C, and the Test duration
was up to constant weight. Weight loss and gas evolution continuously measured during TG
tests

Figure 3 reports an example of results from both type of tests.

From the analysis of the performed tests temperature of starting of pyrolysis, the temperature range of
higher pyrolysis velocity and the pyrolysis kinetic (expressed as the time, as a function of temperature,
of complete weight loss) have been measured. Table 7 reports the results of the both types of laboratory
tests. Example is shown in Figure 3.

Mischantus

graspewine

Comparison of weight evolution under temperature gradient
of grapewine and mischantus

Weight
mischantus

loss at

three test

temperature of biomass

from

Figure 3

Example of thermogravimetric tests under temperature gradient and constant
temperature

21biomass

Starting of
pyrolysis
(°C)

Max range
of dw/dt

Time for total
weight loss at
400°C (s)

Time for total
weight loss at
500°C (s)

for

Time
weight
600°C (s)

loss

total
at

Forest
residues

Corn

grapewines

Mischantus

210

200

190

200

430-510

400-480

420-500

400-470

800

800

800

800

620

600

610

600

310

300

320

280

Table 7Results of laboratory thermogravimetric tests

Pyrolysis process starts at about 200°C for all the biomass samples, but reaction kinetic increases at
temperature higher than 400°C; so the temperature of 400°C can be considered the minimum
temperature for the biomass pyrolysis process.
The effect of temperature is also well visible in Table 7. In fact, in columns 3, 4 and 5 time necessary to
complete pyrolysis (time for constant weight in TG test) is reported. Time to reach the final weight loss
decreases inversely with temperature.

Test at imperial College
Biomass pyrolysis tests have been carried out in a Gray-King reactor using different types of biomass.
Afterwards, char produced with these tests, together with chars received from project partners were then
assessed in a thermogravimetric analyser (TGA) in terms of their reactivities and proximate analysis.
Four samples of coal currently used in electric arc furnaces at Ferriere Nord were also analysed for
comparison. A wire mesh reactor has been used to provide a further characterisation of some of the
biomass-derived samples, in terms of their reactivity in comparison to that of coals industrially used.

A Gray-King furnace, which is an apparatus employed for testing coals according to the British
Standard method-BS1016-107.2, was adapted to be used as a pyrolysis laboratory scale reactor (Figure
4).
Basically, it consists of a 30cm long, 2cm internal diameter quartz tube reactor, which is inserted in a
furnace. 3-4g of sample is held by a wire mesh while a flow of gases removes the volatile matter
generated as the sample is heated. The heating rate is approximately 30ºC min-1 and, after the heating up
period, the sample is held at peak temperature for 15 minutes before the reactor is allowed to cool
down.
Condensable materials are trapped with liquid nitrogen. Most of the studies carried out in this reactor
focused on mischantus and beechwood (representing ligneous biomass) as raw materials, but other
feedstocks including corn stalks, sorghum and switchgrass have also been analysed.

Objectives of these tests were to determine char, gas and tar yields of different biomass species.

22Figure 4

Pyrolysis reactor based on a Gray King Furnace

Beechwood (ligneous biomas) was used as feedstock in pyrolysis experiments to determine the relative
amounts of char, tar and gas recovered under different pyrolysis temperatures, ranging from 300 to
900ºC. The char yield (Figure 5) was observed to decrease with temperature up to about 400ºC and
remain stable afterwards.
Tar and gas yields (not shown) also became stable after 400 ºC with values in the region of 50-60% and
20-30% of the original biomass, respectively. These trends in char yields seem common to all different
kinds of biomass studied, including miscanthus (Figure 6) and corn stalk (CS), sorghum (SO) and
switchgrass (SW) (Figure 7).
In all cases, char yields did not show much change with temperature above 400ºC and remained in the
region between 20-30%. It can be observed that as for the beechwood and miscanthus samples
discussed previously, the yield of char from these three biomass samples did not present significant
variations for temperatures above 500ºC. Variations in the particle size of the initial beechwood sample
did not significantly affect the yield of char in the three particle size ranges studied, 0.212-0.5 mm,
0.85-1.7mm and 2.057-3.15mm, as shown in Figure 5.

(cid:26)(cid:19)

(cid:25)(cid:19)

(cid:24)(cid:19)

(cid:23)(cid:19)

(cid:22)(cid:19)

(cid:21)(cid:19)

(cid:20)(cid:19)

(cid:12)
(cid:8)

(cid:87)
(cid:90)
(cid:11)

(cid:85)
(cid:68)
(cid:75)
(cid:70)

(cid:73)
(cid:82)

(cid:71)
(cid:79)
(cid:72)
(cid:76)
(cid:60)

(cid:19)

(cid:22)(cid:19)(cid:19)

Figure 5.

(cid:19)(cid:17)(cid:21)(cid:20)(cid:21)(cid:16)(cid:19)(cid:17)(cid:24)(cid:80)(cid:80)
(cid:19)(cid:17)(cid:27)(cid:24)(cid:16)(cid:20)(cid:17)(cid:26)(cid:80)(cid:80)
(cid:21)(cid:17)(cid:19)(cid:24)(cid:26)(cid:16)(cid:22)(cid:17)(cid:20)(cid:24)(cid:80)(cid:80)

(cid:23)(cid:19)(cid:19)

(cid:24)(cid:19)(cid:19)

(cid:25)(cid:19)(cid:19)
(cid:55)(cid:72)(cid:80)(cid:83)(cid:72)(cid:85)(cid:68)(cid:87)(cid:88)(cid:85)(cid:72) (cid:11)(cid:38)(cid:12)

(cid:26)(cid:19)(cid:19)

(cid:27)(cid:19)(cid:19)

(cid:28)(cid:19)(cid:19)

Char yields (as percentage of the original biomass in dry ash free basis) in the
pyrolysis of beechwood in a Gray-King reactor as a function of temperature for
three ranges of particle size.

23(cid:25)(cid:19)

(cid:24)(cid:19)

(cid:23)(cid:19)

(cid:22)(cid:19)

(cid:21)(cid:19)

(cid:20)(cid:19)

(cid:12)
(cid:8)

(cid:87)
(cid:90)
(cid:11)

(cid:71)
(cid:79)
(cid:72)
(cid:76)
(cid:60)

(cid:19)

(cid:22)(cid:19)(cid:19)

Figure 6.

100%

90%

80%

70%

60%

50%

40%

30%

20%

10%

0%

(cid:38)(cid:75)(cid:68)(cid:85)
(cid:55)(cid:68)(cid:85)
(cid:42)(cid:68)(cid:86)
(cid:38)(cid:75)(cid:68)(cid:85) (cid:16) (cid:36)(cid:89)(cid:72)(cid:85)(cid:68)(cid:74)(cid:72)
(cid:55)(cid:68)(cid:85) (cid:16) (cid:68)(cid:89)(cid:72)(cid:85)(cid:68)(cid:74)(cid:72)
(cid:42)(cid:68)(cid:86) (cid:16) (cid:36)(cid:89)(cid:72)(cid:85)(cid:68)(cid:74)(cid:72)

(cid:22)(cid:24)(cid:19)

(cid:23)(cid:19)(cid:19)

(cid:23)(cid:24)(cid:19)
(cid:24)(cid:19)(cid:19)
(cid:55)(cid:72)(cid:80)(cid:83)(cid:72)(cid:85)(cid:68)(cid:87)(cid:88)(cid:85)(cid:72) (cid:11)(cid:38)(cid:12)

(cid:24)(cid:24)(cid:19)

(cid:25)(cid:19)(cid:19)

(cid:25)(cid:24)(cid:19)

Char, gas and tar yields as a percentage of the original biomass (dry basis) in
pyrolysis of miscanthus (particle size range: 0.212-0.5 mm) in a Gray-King reactor
as a function of temperature.

CS - CHAR db

SO- CHARdb

SW- CHARdb

Temperature (°C)

100

200

300

400

500

600

700

Figure 7.

Char yield as a percentage of the original biomass (dry basis) as a function of
temperature (°C) in experiments conducted in the Gray-King reactor. Three
biomass samples were used: Corn Stalk (CS), Sorghum (SO) and Switchgrass
(SW).

Char yields were observed to drop with temperature up to 500°C, after which the variations with
increasing temperature were minor. Yields have been found to be similar across the range of biomass
studied for equivalent pyrolysis conditions, which is promising in terms of flexibility of feedstock to
supply electric arc furnaces. Particle size did not have a major effect on char yields for the range of
particle sizes studied. The pyrolysis operating conditions had a strong effect on char reactivity and the
volatile content of the chars. Reactivities similar to those of coals currently employed in electric arc
furnaces have been found.

24An important result is that, after 500°C, the char yield is almost stable, and this result does not depend
on the biomass type and on the size of biomass particles.

Task 3.1 characterization of char and biogas produced
Production of char at laboratory scale, as function of temperature and residence time has been carried
out.

CSM focused its attention to:

- Char chemical composition and porosity
- heating values as a function of different pyrolysis conditions
-

syngas composition and heating value

Imperial College focused its attention to:

char reactivity
comparison of char reactivity with coal reactivity

-
-
- Char proximate analysis.

RWTH and DEW focused its attention on:

- Char and ash chemical composition
- Microscopic investigation

The results of the whole series of characterization activities gives indications to set the industrial
pyrolysis process.

Char chemical compositition and porosity
Among the tests at various temperatures, no significant differences have been found in the char
chemical composition.
Table 8 reports, as representative example, the char characteristics after test at 500°C, with duration 700
s (complete weight loss).

C %
H%
N (%)
S (%)
P(%)
Ash (%)
LHV (kJ/kg)
Density (kg/m3)

corn
70
2
1.8
0.2

23
23000
280

grapewine
70-81
2
2
0.2-0.9
0.48
10-16
23000
270

Forest residues
75
3
0.3
0

mischanthus
73
2
1.2
0.1

3
27000
300

10
25000
270

Element(*)

Mass fraction

K

4.62

Ca

2.79

P

0.30

S

Cl

0.12

< LOD

Fe

0.21

Balance

91.93

Table 8

Char characteristics after test at 500°C, duration 700s, for the four biomasses
tested (carried out by CSM; RWTH, DEW).
(*) Grapeseed Ash chemical composition by DEW/RWTH

Porosity and density resulted slightly affected by the temperature test. Char porosity has been observed
to increase with increasing temperature, while density, as a consequence, decreases with temperature.
No quantitative indication as been given about these variations, because the measurement of both
quantities is affected by a large uncertainty.

25Moreover, char structure (qualitative evaluation) appears very brittle and with low mechanical
resistance (high porosity observed by OM), despite the starting biomass type and pyrolysis conditions.

Figure 8 reports the Optical image of char from grapewine, obtained at 500 and 600°C. The larger size
of pores in the sample treated at 600°C, respect the one treated at 500°C is visible.

Grapewine 500°C 15 min

Grapewine 600°C 15 min

Figure 8

Optical image of char sample from grapewine, after tests at 600 and 500°C

The important aspect to be remarked for all types of biomass, is the low value of density (see Table 7
above) which may cause problems during injection, causing large dispersion of char particles into
fumes instead penetrating into steel bath; in fact typical values of coal density are two or three times
higher.

Figures 9 to 12 show the initial grape seed char and the effects of processing the char in form light-
optical microscope images. Figure 10 shows the unprocessed char and the irregular form of the seeds is
visible. The grain size of the unprocessed char is in the range of 2-4 mm. Figure 11 shows the result of a
short processing of the char in a mortar. This result should be similar to the effect of transporting the
char mechanically for example in a screw conveyor or similar. The Figure shows on one hand
fragments of the char with sizes in the range of 0.5-1 mm and on the other hand a dust fraction which
might be problematic in a conveying system. Figure 12 shows the result of short milling of the grape
seed char. The resulting grain size is clearly below 50 (cid:80)m.

26Figure 9

Grain size distribution of char samples

Figure 10

Light-optical microscope image of unprocessed grape seed char (magnification
20x)

27Figure 11.

Light-optical microscope image of grape seed char after short processing in
mortar (magnification 200x)

Figure 12:

Light-optical microscope image of grape seed char after short milling
(magnification 200x)

Heating values
Table 9 reports the measured values of heating values of chars obtained from four different biomasses,
at three temperature. Heating values show increasing trend with temperature of pyrolysis. Obtained
results indicate that the heating value of the char is lower than coal but in any case comparable. Among
the different types of char, the one with highest heating value is, in according to literature obtained by

28ligneous biomass, even if (see WP 1), forest residues requires a relatively large energy expense for
collection and transportation.

LHV
(kJ/kg)
T=400°C

T=500°C

T=600°C

Forest
residues

25000

27000
28000

corn

23000

23000
25000

grapewine

Mischanthus

22000

23000
24000

25000

25000
26000

Table 9

Heating values of chars obtained from four different biomasses at
temperatures

three

Syngas composition
Gaseous evolution and composition has been measured in laboratory by mass spectrometer during
thermogravimetric (TG) tests. Details of TG tests are reported in previous paragraph. Tests under
temperature gradient have been used to characterise qualitatively the gas emission and to select a
suitable number of gaseous species, to be measured quantitatively during isothermal tests. Tests are
carried out under flowing Ar atmosphere. Figure 13 reports an example of gas concentration measured
by mass spectrometer and Ar normalised.

Figure 13.

Gas concentration measured by mass spectrometer and Ar normalised.

Table 10 reports the syngas composition, measured during mischantus pyrolysis. The syngas heating
value, reported in the Table, has been calculated by the heating values of the single species, multiplied
the molar ratio. The measurement of the gas evolution of the different considered biomass species did
not show significant differences in syngas composition and heating values.

29T=400°C
T=500°C
T=600°C

C2H6
10.0
9
9.0

C3H8
10.0
9
8.0

CH4
21
19
17

CO
21
24
27

CO2
23
21
19

H2
15
17
20

Calc. LHV
MJ/Nm3
27
26
24

Table 10

Composition (%) and LHV of char and syngas as a function of temperature, for
mischantus.

Figure 14 reports the heating values of syngas and char obtained in the same TG test. Depending from
the main objective of the pyrolysis, the process conditions can be optimised to have higher heating
value for char or syngas. If both products are required, a good compromise can be obtained at
temperature of 500°C.

Figure 14.

Heating values of syngas and char obtained in the same TG test

Char Reactivity Measurements
The reactivity of the beechwood chars was assessed in a TGA by both isothermal and non-isothermal
methods. The results from the non-isothermal determination are shown in Figure 15 along with the
temperature programme applied. Following an initial step in an inert atmosphere, the gas is switched to
air at the beginning of the temperature ramp from 400 to 850ºC. As expected, the chars that have been
exposed to higher temperatures present lower reactivities. However, at the low end of the pyrolysis
temperature range, there are marked differences between the behaviour of the 300ºC char, which shows
a high volatile content, and that of the chars produced between 325-450ºC. There are as well significant
differences between the latter and those chars generated at 500-600 ºC, which present the same
reactivity among themselves, while the 900ºC char is clearly less reactive.

30Figure 15.

TGA non-isothermal char reactivity tests of beechwood chars produced in the
Gray-King reactor. Curves of fraction of remaining weight for the different chars
and temperature as a function of time are shown.
W: measured weight; W0: starting weight

Proximate Analysis
Proximate analysis by TGA was performed on char samples in order to determine their remaining
volatile content after the pyrolysis process. There was a progression in the amount of fixed carbon in
the chars with the increase in pyrolysis temperature for both beechwood (Figure 16) and miscanthus
(Figure 17) chars.

In the case of miscanthus, the char produced at 600ºC showed a higher fraction of fixed carbon than
those obtained at lower temperatures, 350 and 450ºC. These two samples showed a similar amount of
volatiles, although the latter lost them more slowly (at higher temperatures).

The grapeseed char sample produced at Tecnocentro (Figure 18) had a fixed carbon content slightly
below 70%, which is not dissimilar from the fixed carbon content of beechwood pyrolysis char (65%)
produced at the same temperature (500ºC) in the Gray-King reactor. The grapeseed char also showed a
higer ash content than the chars derived from beechwood and miscanthus.

31Figure 16.

TGA proximate analysis of raw beechwood and beechwood chars produced in the
Gray-King reactor. Curves of fraction of remaining weight of the different chars
and temperature as a function of time are shown.

Figure 17.

TGA proximate analysis of raw miscanthus and miscanthus chars produced in the
Gray-King reactor. Curves of fraction of remaining weight of the different chars
and temperature as a function of time are shown.

32(cid:20)

(cid:19)(cid:17)(cid:28)

(cid:19)(cid:17)(cid:27)

(cid:19)(cid:17)(cid:26)

(cid:19)(cid:17)(cid:25)

(cid:19)(cid:17)(cid:24)

(cid:19)(cid:17)(cid:23)

(cid:19)(cid:17)(cid:22)

(cid:19)(cid:17)(cid:21)

(cid:19)(cid:17)(cid:20)

(cid:82)

(cid:58)

(cid:18)

(cid:58)

(cid:19)

(cid:19)

Figure 18.

(cid:42)(cid:85)(cid:68)(cid:83)(cid:72)(cid:86)(cid:72)(cid:72)(cid:71) (cid:38)(cid:75)(cid:68)(cid:85)
(cid:55)(cid:72)(cid:80)(cid:83)(cid:72)(cid:85)(cid:68)(cid:87)(cid:88)(cid:85)(cid:72)

(cid:20)(cid:19)(cid:19)(cid:19)

(cid:28)(cid:19)(cid:19)

(cid:27)(cid:19)(cid:19)

(cid:26)(cid:19)(cid:19)

(cid:25)(cid:19)(cid:19)

(cid:24)(cid:19)(cid:19)

(cid:23)(cid:19)(cid:19)

(cid:22)(cid:19)(cid:19)

(cid:21)(cid:19)(cid:19)

(cid:20)(cid:19)(cid:19)

(cid:19)

(cid:12)
(cid:38)
(cid:11)

(cid:72)
(cid:85)
(cid:88)
(cid:87)
(cid:68)
(cid:85)
(cid:72)
(cid:83)
(cid:80)
(cid:72)
(cid:55)

(cid:24)(cid:19)

(cid:20)(cid:19)(cid:19)

(cid:55)(cid:76)(cid:80)(cid:72) (cid:11)(cid:80)(cid:76)(cid:81)(cid:12)

(cid:20)(cid:24)(cid:19)

(cid:21)(cid:19)(cid:19)

TGA proximate analysis of grapeseed char produced at Tecnocentro. Curves of
fraction of remaining weight of the grapeseed char and temperature as a function
of time are shown.

In order to compare these results with the coal currently used in electric arc furnaces, four samples
supplied by Ferriere Nord have also been analysed. These comprise a metallurgical coke, two injected
coals of different particle sizes and an anthracite, which is loaded in the basket. With the exception of
the coke, the other three coals showed fixed carbon contents of nearly 90%. Their ash content was
higher than that of the coke. In all cases these coal samples were less volatile than the biomass-derived
chars, regardless of the conditions at which the latter were prepared.

)
C
°
(

e
r
u
t
a
r
e
p
m
e
T

Figure 19.

TGA proximate analysis of coal samples currently used at Ferriere Nord. Curves
of fraction of remaining weight of the grapeseed char (as percentage of initial
biomass, left axis) and temperature (ºC, right axis) as a function of time are
shown. Coal A: metallurgical coke; Coal B: injected coal (fine particles); Coal C:
injected coal (coarse particles); Coal D: anthracite loaded in the basket.

33Char reactivity tests (Wire Mesh Reactor Experiments)
A diagram of the reactor is shown in Figure 20. A full description of the reactor can found elsewhere
[Solid Fuels and Heavy Hydrocarbon Liquids, Kandiyoti, Herod and Bartle, Elsevier, 2006]. 5mg of
sample are kept as a monolayer on a wire mesh, which is folded and placed between two electrodes.
The sample is heated up by means of a current drawn between the electrodes and across the mesh while
a carrier gas, which may also be reactive, sweeps the evolving volatiles away. This configuration
suppresses any interactions between particles and between particles and evolving volatiles, and
therefore it enables single-particle behaviour to be determined under certain conditions of temperature,
heating rates and pressure.

Tar Trap
Tar Trap

Wire Mesh Sample
Wire Mesh Sample
Holder + Sample
Holder + Sample

Carrier Gas
Carrier Gas
Entry Port
Entry Port

Figure 20.

The atmospheric pressure wire mesh reactor.

In this study, experiments using this reactor have been carried out at atmospheric pressure, with a
heating rate of 1,000°C/s and peak temperature of 850°C. The holding time at peak temperature was
varied between 5 and 10 seconds. A CO2 atmosphere was used to make the occurrence of gasification
reactions possible to a certain extent. Two sets of experiments were performed at these conditions.
Firstly, the set of coals from Ferriere Nord were analysed (Figure 21). Similarly to the outcome of
TGA-based char reactivity experiments, the metallurgical coke showed very little conversion to
volatiles, remaining almost 100% of the initial sample as coke. On the other hand, the two injected
coals (both used in particle sizes between 106-150μm) had a significant release of volatiles, reaching
nearly 18% after 10 seconds at peak temperature.

Three char samples were also studied in the wire mesh reactor, the miscanthus and grapeseed chars
presented above, and a pumpkin seed char received from Marienhutte (Figure 22). At 5-second holding
time, the pumpkin seed char showed very little release of volatiles, while the other two samples were
more similar to the injected coals, with residual char in the range of 88-92%.

34Figure 21.

Char yield (as a percentage of initial sample weight in dry, ash free basis) as a
function of holding time in wire mesh reactor experiments with CO2 as carrier gas
at atmospheric pressure, heating rate of 1,000°C/s and peak temperature of
850°C. Coal A: metallurgical coke; Coal B: injected coal (fine particles); Coal C:
injected coal (coarse particles); Coal D: anthracite loaded in the basket.

Figure 22.

Char yield (as a percentage of initial sample weight in dry, ash free basis) as a
function of holding time in wire mesh reactor experiments with CO2 as carrier gas
at atmospheric pressure, heating rate of 1,000°C/s and peak temperature of 850°C.

According to these tests, char (obtained from the different biomasses types) is expected to have similar
reactivity behaviour inside the EAF.
In fact char produced at 500 and 600°C (see Figure 16) showed a similar weight loss trend of EAF coals
(see Figure 19, in which coal from FENO are used).

35Char from mischanthus and grape showed a reactivity beavhiour, in the wire mesh reactor (Figures 17
and 18), similar to EAF coal used in the MH steelplant.

Task 3.2 Definition of process parameters to optimize pyrolysis process (CSM, RWTH)

The industrial partners involved in the project use coal with different characteristics. The main
distinguish aspect is the amount of volatile matter. Table 11 reports the characteristics (provided by the
partners) of the coals currently used in the industrial practice.

charge anthracite

injection anthracite 1
injection anthracite 2

injection met. Coke
Blow carbon

Anthracite

Petrol carbon
Petrol carbon natural
Petrol carbon low S
Inj. Coal for foaming

FENO

DEW

MH

C %

> 80%
> 80%

> 80%

> 85%
> 96 %

> 90 %

> 97 %
> 98 %
> 98 %
99.7

S %

< 1.5%
< 1.5%

< 1.5%

< 2.5%
n. a.

n. a.

< 2 %
< 1 %
< 1 %
< 1.26 %

VM % ash kcal/kg

< 15%
< 20%

< 20%

< 20%
< 3 %

< 8 %

< 3 %
< 1 %
< 1 %
0.15

< 15%
< 20%

< 20%

< 20%
< 3 %

< 8 %

< 3 %
< 1 %
< 1 %
0.15

Table 11

Characteristics of coals currently used by industrial partners

For this reason, in order to define target figures for the process parameters of the pyrolysis process
RWTH did perform investigations regarding the requirements for carbon used in the EAF. The main
differences between charcoal and fossil carbon where also investigated.
Of the two possible applications of char, the use as blow carbon for slag foaming is the more
demanding application. The demands made by the steel plants regarding blow carbon are considerably
higher than for charge carbon. A literature review led to the factors shown in Figure 23 influencing the
foamy slag formation. Regarding quality requirements of the carbon source the important factors are the
reactivity of the carbon influencing the chemical reactions creating the gas phase. On the other hand the
ash content and its composition are influencing the slag phase and may change factors like slag
viscosity and surface tension. Especially changes of the basicity and of the P2O5 content are possible.

Figure 23:

Factors influencing the foamy slag formation

36Table 12 shows the main differences between carbon produced from biomass and fossil carbon
concerning its use in the EAF. Additional physical differences like grain size distributions can be
equalized by processing of the carbon.

Carbon content
Volatiles content
Ash content
Sulfur content
Chloride content
K2O content
CaO content
P2O5 content
Compressive strength [kgf/cm²]
Density [kg/m³]
Reactivity
Calorific value [MJ/kg]

Fossil carbon
> 80 %
1-3 %
~ 10 %
~ 0.5 %
n/a
~ 2 % of ash
~ 5 % of ash
~ 1 % of ash
10-80
550
lower
29-33

Carbon from biomass
lower – equal
higher
lower
lower
ppm range
up to 20 % of ash
up to 40 % of ash
up to 10 % of ash
130-160
180-350
higher
25-35

Table 12.

Characteristics of fossil carbon and charcoal [23,24]

Regarding its use in the EAF for example to foam the slag especially the carbon and volatiles content as
well as the reactivity is of interest. The usually higher amount of volatiles in charcoal may be able to
compensate for the often lower carbon content, which can also be seen by the higher reactivity of
charcoal. Regarding its use as charge carbon to add chemical energy to the EAF mainly its calorific
value is of interest which is usually similar for fossil carbon and charcoal.
Critical aspects of the use of charcoal in the EAF are the in relation to fossil carbon high concentrations
of chlorine, potassium, calcium and phosphor. Chlorine and potassium may be problematic regarding
corrosion within the off-gas dedusting system whereas the potassium, calcium and phosphor content
may influence the slag composition and characteristics in the EAF negatively.
The differences in compressive strength should not be so important regarding the use in the EAF but
may necessitate additional processing of the char like pelletizing or briquetting. The differences in
density on the other hand may lead to longer blowing times if a fixed mass has to be charged with a
given volume flow of gas. Moreover it has to be investigated whether the lower density has a negative
effect on penetration depth into the slag.

Regarding the pyrolysis process its process parameters should be optimized in order to achieve a high
carbon content and high reactivity respectively. On the other hand the amounts of alkali metals,
phosphor and chlorine should be as low as possible.

Task 2.2 Design of industrial pyrolysis tests

On the basis of preliminary laboratory activities industrial pyrolysis process has been designed.
According to coals characteristics reported in Table 9, different pyrolysis conditions can be used,
depending on the final char end user. A good compromise for pyrolysis temperature can be considered
the value of 500°C. According to CSM activity, this value is the best compromise for optimization of
char and syngas heating value.
The tests performed by IP confirmed that char, gas and tar yelds are almost stable after 500°C.
In case of pyrolysis process devoted to char production for char injection, the best temperature is
600°C, which allow to obtain a char with high heating values and low volatiles content, similar to used
coals.

Globally, the carried out work have two principal objectives:

37(cid:120) To study the range of variability of the pyrolysis process parameters and how these variations
affect yelds and properties of products. The effect of different feedstocks on the process is also
evaluated.
Secondly, it is to understand how this range of control of pyrolysis may affect the overall
energy and carbon balance of pyrolysis char and pyrogas systems, and so affect their industrial
utilization.

(cid:120)

Pyrolysis campaigns have been planned and implemented on laboratory and demonstrative scale that
could reproduce, with different limits, but with the advantages of small-scale tests, the transformation
process of the fuel gas, char and tar on industrial plant, taking into account the results obtained by the
partners in the previous WPs.

Pyrolysis is thermochemical
transformations which depend on thermodynamic parameters and
operating conditions that determine the characteristics of final products; those parameters influence the
choice of the industrial components plant. Three fractions are simultaneously present at the end of the
pyrolysis process (char, tar and syngas) and the amount and characteristics can be varied, changing the
process parameters governing the reactions of cracking, such as:

1.
2.
3.
4.

the temperature profile of the pyrolysis reactor;
the rate of heating of the material;
the residence time of material in the reactor;
the size of the pyrolyzed material;

Points (1), (2), and (3) are deeply investigated and results are shown below; point (4) has been largely
investigated by Imperial college, which found out that, in slow pyrolysis the grain size of starting
materials is not an influencing parameter.

Before making pyrolysis on demonstrative pyrolysis plant (named Enerpol) in Terni, a test system for
small-scale has been set up to increase knowledge about the process of pyrolysis of different kind of
materials and characterize the intermediate and final products of the pyrolysis process by simulating the
operating conditions at laboratory scale. Figure 24 shows the laboratory scale pyrolysis apparatus.

Legend:

A = Nitrogen;
B = Manual valves;
C = Pyrolyzer;
D = Electric furnace;
E = Tar collection filter;
F = Dehumidifiers;
G = Flowmeter;
H = Pump;
I = Gas bag;
L = Thermocouple

Figure 24

Scheme of the demonstrative plant used by Tecnocentro to design industrial
pyrolysis tests

This demonstrative apparatus represent the link of the laboratory apparatus (used by CSM and Imperial
College) and pilot plant which has been used for definite assessment, and industrial plant, which is used
for industrial char production

38Laboratory pyrolysis test have been useful to identify the char and gas percentage produced after
different pyrolysis campaigns, as showed in the following Table.

BIOMASS

CHAR (% wt)

GAS (% wt)

TAR (% wt)

Sorghum pellet

35.9

52.8

11.3

Grape raspe

Dried wood

Underbrush virgin
biomass

29

21

28

49

71

65

22

8

7

Table 13.

Char and gas percentage produced after different pyrolysis campaigns

After laboratory pyrolysis test on different kind of biomass, pyrolysis campaigns were carried out on
demonstrative plant to take char and pyrogas samples in order to study their characteristics varying
process parameters and define the best condition for char production from biomass.
The effect of the main process parameters, such as different combination of rate of heating, time of
treatment and the rotation speed of pyrolysis reactor have been considerated.
The demonstrative pyrolysis plant can be fed with about 200 kg/h of fuel and the necessary heat energy
for pyrolysis reactions is supplied by a gas burner of the maximum power of 500 KW.
Is it possible to vary the pyrolysis temperature (monitored continuously by a pyrometer) by means of
burner thermal power variation.
The photo below shows the pilot plant: pyrolysis reactor, gas cleaning system and the microturbine.

Figure 25

Enerpol pyrolysis plant (Tecnocentro)

The pyrolyzer rotation speed is variable by inverter. During the tests on different kind of fuel, the
pyrogas has been burnt in the torch and sampled; the tar, which in biomass is in the percentage of 7%-
11% (see Table 13) has been eliminated from the gas in the treatment section and collected in the tank
with cooling and washing water.
The char, conveyed by a screw, is usually discharged from the reactor at 500 ° C. The continuous
rotating movement of the reactor contribute to the degradation of biomass into powder.
The main monitored and variable pyrolysis parameters are:

39Internal reactor pressure;

Pyrolysis temperature (optical pyrometer);

(cid:120)
(cid:120) Gas temperature out from the reactor;
(cid:120) Gas pressure out from the reactor;
(cid:120)
(cid:120) Rotation speed of the reactor (residence time);
(cid:120)
(cid:120) Chemical and physical properties of the feeding fuel;
(cid:120) Chemical - physical characteristics (density, elemental analysis, heavy metals), temperature and

Feeding speed varying the rate of the feeding metering screw;

mass balances of char and gas obtained;

The main values of pyrolysis parameters during the tests have been:

Internal reactor depression: -2/ -3 mmH2O;

(cid:120) O2 content in the rotary kiln: 2-3 %;
(cid:120)
(cid:120) Biomass feeding to the reactor: 100 kg/h;
(cid:120)
(cid:120) Residence time for different tests: 30, 40, 50 min

Pyrolysis temperatures for the tests: 450°C, 550°C, 650°C;

During the tests, gas and char produced have been sampled to analyze the influence of process
parameters variation on their weight percentage and on their energy characteristics and chemical
composition.

The gas product is typically a mixture of carbon dioxide (9-55% by volume), carbon monoxide (16-
51%), hydrogen (2-43%), methane (4-11%) and small amounts of higher hydrocarbons. The gases are
usually present with nitrogen introduced to inert the pyrolysis equipment, this can be treated as a diluent
and ignored for material balancing but will affect the heating value of the syngas.

Gases analyses show high rates of nitrogen and oxygen, due to such infiltrations; additional calculations
are needed to verify the real mass and energy balances.
Figure 26 reports the chemical composition of syngas obtained with different starting biomasses

Figure 26

Syngas composition obtained during preliminary pyrolysis test at 550°C, with
rotating speed of 3 rpm

In agreement with laboratory tests performed by CSM and Imperial College (results described in task
3.1) syngas composition is dependent mainly on pyrolysis conditions than biomass types.

40Table 14 report
temperature of 600°C.

the detail of the syngas composition, obtained with sorghum, at

the pyrolysis

specie
H2
CH4
CO
CO2
O2
N2
C2H6
C3H8

[%vol]
6.5
7.6
21.7
23.6
6.6
31.8
0.7
0.6

Table 14.

Syngas composition, obtained with sorghum, at the pyrolysis temperature of
600°C.

This syngas composition, if normalised by nitrogen, is similar to what obtained in laboratory tests.
Table 15 reports char characteristics.

Char from
forest residues

Char from agric.
residues

C
H
S
N
O
Ash
HHV
(kcal/kg)
LHV
(kcal/kg)

39.12
1.87

1.30

55
2548.5

2548.1

75.06
1.84
<0.1
2.02
5.78
7.6
5450.7

5450.7

Table 15.

Char characteristics obtained with forest residues (underbrush) and grapewine.

Temperature also has an effect on char composition; chars produced at higher temperatures having
higher carbon contents both total- and fixed-carbon. Higher temperatures lead to lower char yield in all
pyrolysis reactions.

When temperature increasing it’s pointed out that:

•
•
•

Tar decreases
Pyrogas increases
Substantial stability of the char

With increasing residence time:
Tar decreases
Pyrogas increases

•
•
• Char decreases
• Char LHV increases with the residence time

41Feedstock humidity control is a parameter of great importance for optimizing the efficiency of the
process, because if the level increases, the heat necessary for pyrolysis of biomass is no longer
sufficient as used for evaporating the water in the fuel. For good process performances, fuel moisture
contents of 15-20% are typical. In all pyrolysis reactor, water is also a product and is usually collected
together with other condensable vapours in the liquid product.
Chars formed under low flow, high pressure conditions with consequent higher char yields also have
higher fixed-carbon yields.
As with the biomass feed, the char and liquid products have energy values roughly related to their
carbon contents.

For any given feedstock it is possible to vary the product distribution between char, liquid and gas,
within limits, by choice of process type and operating conditions. Higher char yields are obtained by
slow pyrolysis processes with lower temperatures and low flow rates; higher liquid yields arise from
fast pyrolysis processes, specific temperatures and high flow rates. The gas yield is not usually the
focus of slow or fast pyrolysis and is generally not actually measured but calculated by difference in
mass balance.
Similarly, for any given process and equipment set-up, different product distributions will arise from
different feedstocks depending on their composition. However, this should not be a major factor in
choice of feedstock for pyrolysis, as controllable operating conditions, such as temperature, generally
have a larger effect and could be changed to adjust product distributions. Choice of feedstock is more
likely to be dependent on factors such as availability, cost and sustainability considerations. Variation in
biomass feedstock, even if nominally a single source, is likely to be one of the main causes of
variability. The exact composition of a type of biomass will vary depending on many factors relating to
when, where and how it was grown, for instance the weather, soil type and agricultural regime.

Figures for carbon contents in nominally the same type of biomass may differ by as much as 10%
relative. The composition of a single supply of a particular biomass type should be more consistent but
is not likely to be truly homogenous, except at small scale, unless special provisions for mixing and
blending are made. Feedstock moisture content and particle size may vary within and between loads
and affect process yields.

Temperature control is also likely to be an important cause of variability, particularly for slow
pyrolysis. The lower heat fluxes and longer residence times of slow pyrolysis give scope for variation in
heating rate and peak temperature. Yields from traditional charcoal kilns are known to be affected by
weather conditions , due to the effect on temperature control and fuel-wood consumption.

As general conclusion, it can be stated that char yield is about 20% of weight of starting biomass, and
this value decreases with temperature; yield is almost constant at temperatures higher than 500°C.
Pyrolysis at temperatures higher than 500°C and longer residence time are necessary to obtain charcoal
with low values of volatile matter (suitable for charging); pyrolysis temperatures lower than 500°C
permit to obtain charcoal with higher volatile matter content, suitable for injection and foaming.
Regarding the amount of char, tar and syngas obtained after pyrolysis process, values are reported in
Table 13. Increases of temperature and residence time determines the reduction of Tar and increases of
syngas amount.

WP4 DEFINITION OF THE EAF OPERATING PRACTICES (DEW, FENO, CSM, RWTH,
MU, TECNOCENTRO, IP)

Task 4.1 EAF cycle Analysis (RWTH, Ferriere Nord, DEW and MH)

An analysis of the EAF cycle of the three steelmakers participating to the project has been carried out.
The analysis was aimed at:

collect data of amount of coal used
collect data about coal utilization (charge/injection)

-
-
- modification of current operating practices of coal utilization

42- Definition of burners working conditions (geometry, furnace atmosphere, burners powers, inlet

gas flow rate) to simulate biogas use

FENO EAF cycle analysis

FENO EAF is an AC furnace with capacity of 140 tons. The global energy consumption if of 80 Mwh.
Almost 50% of energy demand is provided by chemical energy, (coal and natural gas burning, and from
exothermic reactions oxidation of charge material as Fe, Si and Mn). Energy from coal represent
almost 17% of total energy demand of the furnace.
Coal and natural gas burning is managed through ten burners. Seven burner are natural gas fed (CH4)
and are installed in tangential position, and three are oxygen lance installed in radial position.

Figure 27 reports a general view of the EAF with the position of the installed burners.

Figure 27.

General view of the EAF with the position of the installed burners

Table 16 and 17 report the global energy input distribution of the furnace.

EAF Total energy input

total EAF energy input

electrical Energy

chemical Energy

80

42

38

Mwh

Mwh

Mwh

Table 16

Energy input of and chemical energy distribution of EAF of Ferriere Nord

43Chemical energy distribution

energy from carbon (pulv. + inject.)

natural gas energy

remaining chemical energy (Fe, Al, Si, Mn oxidation)

% of EAF energy input from carbon

13.4

8.7

13.8

16.8

Mwh

Mwh

Mwh

%

Table 17

Chemical energy distribution of EAF of Ferriere Nord

The amount of chemical energy which potentially can be replaced by biomass (charcoal charged and
injected and syngas burning) is 28% of the total EAF energy input.

An estimation of the amount of biomass yearly necessary to replace coal and natural gas has been
carried out and compared with regional amount of available biomass (described in WP1).
Table 18 reports the calculation of biomass necessary to replace coal; for this evaluation, average values
of heating values and pyrolysis char yield have been used.

Charcoal heating value (average value among measured
and literature data [3])
char per heat
% char from biomass pyrolysis (average value [3])
Calculated biomass per heat
average year steel production
biomass consumption per year

20.000

kJ/kg

2.000
20
8.066
1.2
100.000

kg
%
kg
Mt
t

Table 18

Mass Balances to estimate biomass necessary to replace coal in Electric Furnace of
Ferriere Nord.

According to the study of biomass availability it can be concluded that the amount of available biomass
is enough for Ferriere Nord EAF use.

According to the performed analysis syngas amount produced by pyrolysis is in the range 30-40%
respect the starting amount of biomass.
Considering that the current consumption of natural gas is 840 m3 per heat, which correspond to an
energy(cid:3)input(cid:3)of(cid:3)30,24(cid:194)104(cid:3)kJ(cid:3)per(cid:3)heat.(cid:3)The(cid:3)global(cid:3)energy(cid:3)input(cid:3)due(cid:3)to(cid:3)natural(cid:3)gas(cid:3)burning(cid:3)is(cid:3)3,024(cid:194)1011
kJ/year, with the productivity of FENO EAF.
If a relatively low value of heating value of syngas
(15.000kJ/kg, for a prudential evaluation) is considered, 20160 tons of syngas are theoretically
necessary to replace natural gas burning. Having estimated that 100.000 tons of biomass produces
30.000-40.000 tons of syngas, this amount is largely available

Design of industrial tests: char utilization in EAF
Coal is both charged in the bucket and injected. Both ways of utilisation have been tested in the
industrial tests. In the current operating practice, the amount of used coal is:
Charged
Injected
Steel and slag composition, offgas composition, oxygen and power consumption and gaseous emission
at stack (including dioxin monitoring) are monitored during industrial trials with char utilization and
compared with average current values.

4 kg/t (cid:198) 550 kg per heat
8 kg/t (cid:198) 1100 kg per heat

44The effects of char utilization on the process have been preliminarily analysed before making industrial
trials. The following aspects have been considered:

1. Effects of char ash on slag composition and on slag properties (viscosity and melting point)
2. Effects on steel composition
3. Effects on environmental pollution

Effects of char ash on slag composition and on slag properties (viscosity and melting point)

Table 19 reports the calculated amount of formed ashes due to char injection

corn
grapewine
Forest residues
mischanthus

kg charg. char
(per heat)
600
600
600
600

kg inject. char
(per heat)
1200
1200
1200
1200

kg of formed ash (per
heat)
414
432
54
180

Table 19.

Mass (kg) of formed ashes which derives from char charge and injection. Data
refers to single heat

Ashes dissolves into the slag and modifies its composition. The ash addition in case of forest residues
and mischanthus addition can be simply neglected, due to the low amount of ashes formed. In case of
ashes from corn and grapewine biomass, the modification of slag composition and the subsequent
modification on viscosity and melting behaviour (whim variation may affect EAF process) have been
evaluated with models available in literature. To calculate the variation of slag composition it has been
considered an average value of slag composition and a slag mass of 10 tons. Table 20 reports the
starting slag composition and the modification with ashes

Slag
[%]
39.6
4.1
13.4
0.1
0.1
6.1
3.2
29.1
1.0
0.4
0.0
0.0

slag+corn ash
[%]
39.3
4.1
13.3
1.2
0.1
6.1
3.5
29.3
0.9
0.4
1.7
0.0

slag+grapewine ash
[%]
37.8
3.9
13.7
1.8
0.1
5.9
3.7
28.9
0.9
0.4
2.8
0.0

FeO
MnO
SiO2
P2O5
S
Al2O3
MgO
CaO
Cr2O3
TiO2
K2O
Na2O

Table 20.

Starting slag composition and the modification with ashes

On the basis of the chemical composition of starting and modified slag, viscosity and melting behaviour
have been calculated with Urbain model [9] and with Thermocalc [26].
Figure 28 reports the viscosity of starting and modified slag.

45Figure 28

Viscosity of starting and modified slag. Viscosity is calculated with Urbain model
[9].

Slag viscosity remain practically constant after char ashes dissolution. The characterization of melting
behaviour calculated with ThermocalcTM did not show a significant modification respect the starting
composition.

(cid:120) Effect on steel composition

The presence of metal impurities inside char is of the same order of magnitude of coal. Moreover all
these metals are oxidized during injection and are entrapped by slag. Steel and slag samples will be
collected during industrial tests to verify that steel quality and slag characteristics are not affected by
char utilization.

(cid:120) Environmental pollution

Char utilization may affect environmental pollution for the following reasons:
1. presence of Cl (even if at low level) may affect dioxin formation
2.
3. presence of P and S in the slag may restrict further slag re-utilization

large amount of pulverised char in the EAF dust (due to low density of material)

An estimation of the amount of Cl in the fumes, considering the actual situation and the eventual
increase (min and max values are indicated) compared with optimal range of working defined by BATs
[10] indicates that char contribution to dioxin formation is low (see Table 21), and in any case is close
to the lower limit of the range defined by the BATs, considering both offgas and dust content (Best
Available Technologies).

46Chlorine added with char

Max

Min

Dust FENO (current situation)

Cl in char
[%]

0,2

0,05

Cl in EAF dust
[%]

1,5

char Kg/heat

Cl kg/heat

1600

1600

Dust kg/heat

1650

3,2

0,8

Cl in dust
kg/heat

24,75

BATs Clorine content in Off gas

HCl mg/t steel

t.steel/heat

Cl kg/heat

Max

Min

9600

800

120

120

1,15

0,10

BATs Clorine content in Dust

Cl % in Dust

Dust kg/heat

Cl kg/heat

Max

Min

Table 21.

1,5

4

1650

1650

24,75

66

Estimation of Cl presence into fumes and comparison with acceptability range of
BATs [10]

DEW EAF cycle analysis
At DEW coal is used in the EAF cycle in two ways. Blow carbon is used to foam the slag when
producing carbon steel qualities. Blow carbon is injected in order to foam the slag after melting down
the 2nd bucket. The carbon is lanced with air (carrier gas) in the layer between melt and slag. The slag
foaming procedure is used to shield the electric arc so that less energy is radiated onto the sidewalls of
the furnace and therefore to lessen energy losses and to improve the heat transfer from the arc into slag
and steel. Up to now there are no known foamable slags for the produced stainless steel grades.
Therefore the EAF in the steelworks Siegen utilise no blowing carbon for stainless steel grades.
Another way to use coal in the EAF cycle at DEW is to charge the coal together with the scrap in the
bucket. The coal used this way is also called charge coal at DEW. Charge coal can be needed to reach
certain carbon levels in the steel depending on scrap qualities available. It can also be used to replace
electrical energy by chemical energy when oxygen is used to decarburize the melt and the carbon is
burned to CO and CO2 respectively.
At the moment DEW is using fossil coal only. The characteristics of the used coal species are shown in
Table 22. The specific amounts of coal used at DEW are shown in Figure 29. According to this data
for the years 2006-2009 the mean amount of blow carbon used per ton of steel produced is about 3.1 kg.
The mean amount of charge carbon is 10.7 kg/tSteel.

47Blow carbon
Charge carbon

]
l
e
e
t
s
t
/
g
k
[

t
n
u
o
m
a

c
i
f
i
c
e
p
s

14

12

10

8

6

4

2

0

Figure 29.

Specific amounts of carbon used at DEW (2006-2009)

At DEW, per heat of carbon steel (140 t), are used on average 434 kg of blow carbon and 1498 kg of
charge carbon.
Based on the average carbon usage per heat and per ton of produced steel the annual demand for
biomass has been established for DEW. Taking the differences in carbon content into account and
assuming that there are no further differences in the quality of charcoal and fossil coal regarding
reactivity and therefore the ability to foam the slag the amounts of biochar and biomass needed have
been calculated. Table 22 reports the amount of biomass necessary to replace fossil carbon at DEW.

Annual carbon demand
CO2 emissions
Annual biochar demand
Average yield for biomass pyrolysis
Biomass demand

5000 - 8000 t/a
~ 18000 – 30000 t/a
6000 – 9600 t/a
20 %
30000 – 48000 t/a

Table 22: Annual carbon and biomass demand at DEW Siegen EAF

Within the scope of the cycle analysis at DEW also reference values for the foamy slag composition
have been established. These values will be used to investigate the influence of the charcoal and its
ashes on the composition of the EAF slag. Table 23 reports slag compositions and average values of the
slag composition for a series of heats at DEW.
The industrial trials planned at DEW will start with the partial to total substitution of fossil charge coal
with charcoal. Especially mass and energy balances will be used to investigate to influence of the
charcoal use on EAF operations.
In a further stage the substitution of blow carbon by charcoal was investigated. To prevent a negative
impact of possible problems like line clogging on the production, a redundant carbon blowing system
will be installed temporarily at the DEW EAF. The slag foaming capability of charcoal will be studied
qualitatively in comparison to fossil blow carbon.
The influence of char composition, especially the ash, on slag and steel composition will be investigated
for all trials by according analyses.

48Heat

FeOn
[%]

CaO
[%]

1

2

3

4

5

6

7

8

9

10

11

12

average

st. dev.

30,2

36,8

44,9

30,3

52,6

42,5

48,4

37,8

36,5

22,2

42,6

47,9

39,4

8,8

20,7

24,6

18,9

25,5

16,8

23,1

23,2

26,6

26,3

38,3

18,8

20,5

23,6

5,6

SiO2
[%]

13,4

12,8

8,5

12,0

10,0

8,5

7,0

8,8

10,7

15,0

13,5

7,4

10,6

2,7

MgO
[%]

MnO
[%]

Al2O3
[%]

Cr2O3
[%]

TiO2
[%]

8,8

7,8

6,9

8,4

7,1

8,0

5,4

8,7

9,7

8,0

7,4

6,9

7,8

1,1

6,3

7,0

5,3

5,9

3,5

4,3

4,2

5,4

6,0

5,0

6,5

4,2

5,3

1,1

3,5

3,6

4,0

4,9

3,5

4,7

3,9

3,9

4,2

6,3

5,3

3,3

4,2

0,9

2,7

3,8

4,1

5,5

1,3

3,7

2,9

4,4

2,8

2,1

3,6

5,1

3,5

1,2

2,0

0,6

0,7

0,8

1,0

1,2

0,8

0,8

1,0

1,0

1,0

0,5

1,0

0,4

S
[%]

0,2

2,5

-

-

-

-

-

-

-

-

-

-

-

-

Table 23.

Composition of foamy slag at DEW Siegen EAF

MH EAF cycle analysis

In case of Marienhutte steel plant, coal is injectd by a lance. So, beside the energetic input, the foaming
behavior is an important process aspect which must be taken into account for industrial testing of char.
Slag foaming is a very complex equilibria depending on slag properties (mainly viscosity and surface
tension), amount of injected coal (which affect the amount of gaseous species necessary to promote
foaming) and also coal reactivity. Comparison of coal and char reactivity (works carried out in WP3)
studied at laboratory scale indicated that a similar behaviour is expected.

For a better control of this process Marienhütte developed together with VATRON GmbH an optical
foaming slag management system (OFSM [24]). The slag height is detected by a camera continuously.
The camera is placed close to the slag door. A special image processing software calculates a slag index
to be used for the injection of the carbon amount required (Figure 30). Due to the real-time monitoring
of the slag level it is possible to adjust the C-contents by injection of the optimal quantity of carbon.

49Figure 30

Optical Foaming Slag Management (OFSM)

Due to the Optical Foaming Slag Management the overall efficiency of the melting process can be
increased significantly. Moreover a reduction of total carbon added could be achieved.
The OFSM was used for further assessment of the EAF cycle and for assessment of the charcoal
injected.

Task 4.2 Pilot plant tests

Before performing trials at the EAF pilot plant of RWTH, slag foaming capability of the charcoal
delivered by Tecnocentro and comparing it to conventionally used fossil coals has been carried out.
These trials have been conducted using EAF slag samples from the DEW and MH.
To determine the minimum amount of carbon needed to reduce the iron oxides in the slag, the slag has
been analysed using XRF. Table 24 shows the result of the XRF analysis of the slag of DEW. Table 25
shows the oxidic slag composition deducted from the XRF analysis and assuming that the balance
consists of oxygen. The amount of carbon needed for a stoichiometric reduction of the FeO and Fe2O3
in 100 g of slag has been determined to be about 14 g. Because of the lower carbon content of the char
this equates to 17.2 g of char.

Element

Fe

Ca Mn

Cr

Si

Mg

Al

Ti

S

P

Bal.

Mass fraction
[%]

25.71 16.65

3.80

1.25

0.83

0.38

0.35

0.15

0.12

0.04

50.38

Table 24: XRF analysis of the slag used for foaming trials at RWTH, with EAF slag from RWTH

Slag
composition

Mass fraction
[%]

CaO MnO Cr2O3 SiO2 Al2O3 MgO TiO2 P2O5

S

FeO Fe2O3

23.3

4.9

3.6

1.8

1.3

0.6

0.2

0.2

0.1

7.9

55.9

Table 25.

Oxides species composition derived from X ray analysis

50A defined amount of slag and carbon have been mixed and charged into alumina crucibles. The
crucibles have then been put into a furnace heated by a natural gas/oxygen burner. The furnace has been
heated to temperatures of up to 1600°C. Figure 31 shows a charged crucible und the crucibles inside the
furnace.

Figure 31:

Crucible filled with slag and carbon mixture (left) and crucibles in the furnace
(right) in lab experiment carried out by RWTH.

During the trial after the melting of the slag the formation of gas and the foaming of the slag can be
observed. The foamy slag is increasing the slag volume and leads to a freezing of slag to the inner
crucible wall up to a height indicative of the maximum volume increase during the trial. Figure 32 and
33 show pictures of the crucibles after the DEW slag foaming trials. Within these pictures the foamy
slag height reached during the trial is marked. Table 26 reports measured slag height in the crucible and
relative volume increase for the different trials.

Trial
Injection coal FENO
Injection coal DEW
Grape seed char 1
Grape seed char 2

Foamy slag height [mm]
50
76
98
82

Table 26:

Results of slag foaming trials

Volume increase [%]

250
378
491
421

The achieved volume increases show the general suitability of the char for slag foaming.

51Figure 32: Slag foaming with injection coal from FENO (left) and DEW (right)

Figure 33: Slag foaming trials with grape seed char

Similar experiment has been repeated with MH EAF slag, the same charcoal from Tecnocentro and
compared with char samples produced from a laboratory reactor and with petroleum coke. Especially
the influence of the volatile components on the slag foaming should be investigated. Also the reactivity
and the specific surface area are very important factors, which could influence the foaming of the slag.
For the reason, Table 27 gives an overview of these parameters of the tested materials. The reactivity
was measured with a TGA at 1300 °C under CO2 atmosphere, whereas the porosity and surface area
was measured with a gas sorption sampler using the BET-method.

52Calcined petroleum coke

Charcoal Tecnocentro

Charcoal 064/KO/07

Reactivity
[%/min]

Surface area
[m²/g]

Pore volume
[cm³/g]

1,51

3,28

6,96

2,34

165,75

327,69

0,002

0,069

0,135

Table 27 Reactivity, specific surface area and pore volume of the tested materials

It is obvious that charcoals have much higher porosity and therefore surface areas than petroleum coke,
which leads to their higher reactivity.
The investigations of the influence of these differences on the foaming behaviour were performed with
the so called “sessile drop test” as well as with some foaming test in small scale1.

The results of the “sessile drop tests” are illustrated in Figure 34, where some exemplary pictures are
picked out. These pictures are only a part of the whole video but visualize the sequence of the slag
foaming very clear. The first picture of each row gives the melting beginning of the slag which is at
about 1300 °C. The formation of a spherical form of the slag is obvious which indicates the non-
wettable character of carbon. The next pictures show the reaction of the FeO in the liquid slag with the
carbon of the substrate with increasing temperature. In dependence of the carbonaceous material the
intensity of the reaction differs, which results in varying CO bubble formation and therefore slag
foaming.
The calcined petroleum coke forms very rapidly a foamed slag due to a fast slag-carbon-reaction. This
foamy slag stays stable very a long time period. The specimen pulsates during this period due to the
permanent new CO bubble formation.
At the test with charcoal from Tecnocentro it can be seen, that at the beginning only a slightly foamed
slag specimen is formed which also collapses very fast. The CO bubble formation in combination with
slag foaming starts not before the slag is spread over the substrate by a strong reaction
Charcoal 064/KO/07 is, in contrast, absolutely unwettable. Here the liquid slag drop stays absolutely
unchanged and stable on the carbon substrate and does not react. Only a kind of explosion leads to a
changed situation. However, no slag foaming could be observed.
In conclusion, the “sessile drop test” represents a good tool to estimate the foaming behaviour of
different carbonaceous materials. Clear differences can be seen between the three tested materials.

1 The principle of the sessile drop test is illustrated in figure below. Here, a slag sample in cylindrical form is put
on a crucible filled with the carbonaceous material which should be tested. Both are put on a ceramic holder and
pushed in a furnace at 1500 °C under nitrogen atmosphere. There the slag liquefies and the FeO in the slag reacts
with the carbon below forming CO-bubbles which foam the slag. These reactions are recorded by a CCD-camera
and analyzed afterwards.

Scheme of a sessile drop test

53Whereas petroleum coke formed a well and stable foamed slag, the tested charcoals provided only bad
foaming results. The most evident difference is the varying wettability which, in case of charcoals,
prevents the reaction between FeO in the slag and the carbon and therefore the formation of CO
bubbles. The content of the volatile components in the carbonaceous material has in these trials
absolutely no influence on the slag foaming.

Slag on calcined petroleum coke

Slag on charcoal from Tecnocentro

Figure 34

Sequence of the slag-carbon-reaction with different carbonaceous materials as a
subject to the temperature (at the upper right corner in each picture)

Slag on charcoal 064/KO/07

To verify the results of the “sessile drop test” some additional foaming trials in a lab furnace were
performed. Due to the fact that the injection of carbon in a liquid slag in lab scale is far too complex, a
mixture of slag with 10 % carbon was produced. This mixture was then filled in a ceramic crucible and
put in a resistance heated furnace at 1400 °C. The furnace was flushed with nitrogen and monitored
with a camera from the top. The foaming of the slag was recorded by the camera and afterwards
checked by the slag height of the crucible (see Figure 35).
The best foaming performance shows, once again, petroleum coke. Here the slag even reaches the rim
of the crucible. The slag heights at the experiments with charcoals were very low.

Slag + calcined
petroleum coke

Slag + charcoal
from Tecnocentro

Slag + charcoal
064/KO/07

Figure 35

Comparison of the foaming height with different carbonaceous materials

54Some pictures of the video recording are shown in Figure 36. With these recordings especially the way
and the rate of the CO bubble formation could be investigated.
At the mixture with petroleum coke the bubble formation starts immediately after slag smelting and
stays constant over a long time period which leads to a perfect foamy slag. The bubbles rise to the slag
level and are obvious as dark points in the pictures.
In contrast, at the experiments with charcoal hardly any bubble formation is recognizable. Only some
but in this case very big bubbles were detectable. However, such big bubbles do not really foam the
slag. Once again, charcoals showed a worse performance.

Slag + calcined petroleum coke

Slag + charcoal from Tecnocentro

Figure 36

Pictures from the video recording of the slag foaming trials in a lab furnace; CO
bubbles (dark spot with arrow)

Slag + charcoal 064/KO/07

In conclusion, the small scale tests gave a good overview about the foaming behaviour of different
carbonaceous materials. In all trials petroleum coke delivered the better performance in case of slag
foaming and stability, whereas the slag foaming with charcoals was hardly recognizable in most cases.
The reason for this seems to be the different wettability of fossil coke and charcoal. Nevertheless, it has
to keep in mind that these small scale experiments can only give tendencies. It is nearly impossible to
reproduce the industrial process in lab scale due to the endless parameters. This is why in the next step
the foaming behaviour of charcoals is tested in industrial scale.

Pilot plant tests at RWTH Aachen
The pilot EAF tests were performed at the airtight pilot arc furnace of the department for industrial
furnaces and heat engineering (IOB). Figure 37 shows the furnace (left) and a schematic representation
of the pilot furnace (right). The water cooled furnace consists of a fixed top reactor and a moveable
crucible with a maximum capacity of about 200 kg of steel melt. It is possible to operate in AC-mode
with two electrodes or in DC-mode with one top electrode and an anode in the bottom of the crucible.
In AC-mode the maximum active power is 600 kW and in DC-mode it is 300 kW. The biochar and
reference material tests were performed in DC-mode. It is possible to take a sample of melt for

55chemical analysis and the actual melt-temperature. Through the three front windows the arc and the
bath level can be monitored during the melting phase.

Fig. 37. Pilot Arc Furnace (left) and schematic representation (right)

For determination of the off gas composition during the tests an off gas analysis system is installed. The
off gas sample and off gas temperature are taken directly at the reactor-room outlet. The analysis of the
exhaust gases was conducted with regard to CO, CO2 and H2 levels.
In the first experimental series RWTH Aachen tested two types of biochar in the pilot EAF plant as
charge coal and as injection coal. On one hand the biochar produced by Tecnocentro and on the other
hand waste products from wood gasification plants were tested.

Figure 38

Biochar from Tecnocentro (left); Biochar from wood gasification plants (right)

Additionally tests with reference materials have been performed to compare the results from biochar
tests with the standard situation in the industrial mills. As reference materials anthracite coal and petrol
coke which are presently used at DEW Siegen were used. The different compositions have been
analyzed and the results are shown in Table 28.

56[%]

Biochar from
grape seed (TC)1
81
Carbon
9
Ash
7.7
Volatiles
5.6
Humidity
0.3
Sulphur
0.5
Phosphor
<5 mm
Grain Size
1: mean of 3 measurements; 2: mean of 24 measurements

Biochar from
wood residues2
72.3
21
13.5
5.2
0.06
0.4
<<1 mm

Anthracite
(DEW)
86
11.1
2.6
-
0.3
-
6-12 mm

Petrol Coke
(DEW)
93
5.8
1
0.2
1
-
<1 mm

Table 28.

Composition of different biochar and reference materials

Due to the relatively high ash content of the biochar from wood gasification plants the ash composition
has been analyzed to get information about the possible influence on the slag composition. Figure 39
shows the results of the ash analysis.

rest

SiO2

P2O5

MnO

MgO

K2O

2,06

4,48

3,28

5,47

8,23

Fe2O3

2,17

CaO

Al2O3

3,82

35,76

34,73

0,00

10,00

20,00
[%]

30,00

40,00

Figure 39.

Results from ash analysis of biochar from wood gasification plants.

As a basis the reference trials have been performed using an amount of 1 kg anthracite coal on 50 kg of
scrap. Due to the lower heating value in comparison to the anthracite coal 1.6 kg of non-processed
biochar from Tecnocentro and from wood gasification plants were charged to compensate the
difference. Figure 40 illustrates the significant difference in density of the biochar fines (left) and the
anthracite coal (right).

Figure 40.

1.6 kg of biochar fines (left) and 1 kg of anthracite coal (right)

57Figure 41 (left) illustrates the process of lancing coal and oxygen through one of the front windows
directly into the slag using the IOB pilot lancing system (right) after reaching the liquid phase. While
lancing coal and oxygen by hand the furnace power had to be turned off.

Figure 41.

Lancing operation of coal and oxygen (left) and IOB pilot lancing system (right)

Just before tapping at 1650°C a melt sample was taken for chemical analysis to get information about
possible negative effects of biochar use. After tapping all output fractions have been separated and the
individual output masses were recorded. Table 29 gives an overview of the conducted trials in the pilot
plant.

Input [kg]

Scrap I

Scrap II

(cid:153)(cid:3)Scrap(cid:3)

Lime

1

50

2

50

3

50

50(cid:3)

50(cid:3)

50(cid:3)

Dolomite lime

0,5

1,5

Slag

(cid:153)Slag(cid:3)Former(cid:3)

0,5(cid:3)

1,5(cid:3)

Anthracite (DEW)

1

1

4

4(cid:3)

4

40

25

65(cid:3)

0,5

1,5

5

36

25

61(cid:3)

1,5

0,5

6

25

25

50(cid:3)

1,5

0,5

7

25

25

50(cid:3)

2

1,5

8

25

25

50(cid:3)

2

1,5

2(cid:3)

2(cid:3)

2(cid:3)

3,5(cid:3)

3,5(cid:3)

Biochar from wood gasification

1,6

1,6

1,6

1,6

1,6

TC biochar

Petrol Coke (DEW)

Biochar from wood gasification
as injection coal

(cid:153)Coal(cid:3)

Oxygen

1,6

0,10

1(cid:3)

1(cid:3)

1,6(cid:3)

1,7(cid:3)

1,6(cid:3)

1,7(cid:3)

1,85(cid:3)

1,75(cid:3)

0,10

0,25

0,15

1,23

1,1

0,3

1,71

2,89

0,29

0,31

Electrode Consumption

0,18

0,24

0,28

0,48

0,23

Table 29.

First conducted trials at pilot plant

58Results of first trials
The evaluation of the first pilot arc furnace trials shows no negative effects regarding the steel and slag
analysis. The comparison of the steel analysis of different trials is shown in Figure 42. Differences
occur in terms of the Ni and Mn content. These differences can be explained by small fluctuations in the
scrap composition. The reference trial shows a higher carbon content than the two biochar trials. This
would imply a better carburization of the melt by the anthracite coal and would also be in agreement
with the findings of the off-gas analysis. Considering the sulphur content of the steel, the effect of the
lower sulphur content of the biochar in relation to the reference materials can be seen. The steel
produced by the biochar trials has only about half the sulphur content in relation to the reference trial.
Despite the higher phosphor concentration in the different biochar on the other hand, the phosphor
content in the steel is the same for all trials. So the use of biochar instead of fossil coal shows no
negative impact on steel composition in the pilot trials.

Biochar from Tecnocentro
Biochar from wood gasification
Reference

]

%

[

0,1

0,09

0,08

0,07

0,06

0,05

0,04

0,03

0,02

0,01

0

Figure 42.

C

S
SI Mn
Steel composition after pilot trials

P

Cr Mo Ni

N

Al

In Figure 43 the slag composition for the trials is shown to investigate a possible influence of the
biochar ash content on slag chemistry. The striking differences between biochar from Tecnocentro and
the reference e. g. in the Fe2O3 or CaO content of the slag cannot be explained by the use of biochar,
since the biochar produced by Tecnocentro has similarly high ash content as the fossil anthracite coal.
Between biochar from wood gasification and the reference trial the difference in the ash content is
almost factor 2 (cf. Table1), but the slag compositions show only small differences. Further this issue
has to be investigated, but these first preliminary results indicate no negative influence of the use of
biochar with higher ash content on the general slag composition.

59Biochar from Tecnocentro

Biochar from wood gasification

Reference

80

70

60

50

]

%

[

40

30

20

10

0

Figure 43.

Al2O3

CaO
Slag compositions of pilot furnace trials

Fe2O3 MgO

MnO

SiO2

Agglomeration of biochar
Due to the handling problems using the biochar fines as charge coal in pilot scale at RWTH and
industrial tests at DEW agglomeration tests have been performed. The aim of the tests was to find
suitable binders and to establish the right blend to produce stable biochar agglomerates. At first some
tests have been carried out to agglomerate the biochar fines without binders. An agglomeration was not
possible (Fig. 44 a)). Also a blend using 30 % of molasses and 20 % of water did not provide stable
agglomerates (Fig. 44 b)). First stable agglomerates have been produced using 30 % of molasses and
15 % of water and a forge pressure of 100 MPa (Fig. 44 c)). These agglomerates had a green strength of
0.87 MPa and strength after 2 days of drying of 1.73 MPa.

a)

b)

c)

Figure 44: First agglomeration tests (a-c)

On this basis further tests have been performed to increase the strength of the biochar agglomerates.
Table 30 gives an overview of produced blends that have been tested.

60blend
no.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16

biochar [%] water [%]

85
78
71
65
80
73
66
60
75
68
61
55
70
63
56
50

5
5
5
5
10
10
10
10
15
15
15
15
20
20
20
20

molasses
[%]
10
17
24
30
10
17
24
30
10
17
24
30
10
17
24
30

green strength
[MPa]
-
-
-
-
-
-
-
1,16
0,78
1,27
1,73
0,92
0,69
1,16
1,30
-

fatigue strength
[MPa]
-
-
-
-
-
-
-
-
-
3,12
6,13
-
-
4,91
-
-

Fatigue strength measured after 3 days of drying

Table 30.

Produced and tested blends for agglomeration tests

Blend no. 11 showed the best performance and was elected to perform further pilot scale briquetting
tests. The comparison of most stable blends is shown in Figure 45.

green strength
strength after 3 days

]
a
P
M

[
h
t
g
n
e
r
t
S

6

5

4

3

2

1

0

8

9

10

11

12

13

14

15

blend

Figure 45.

Comparison of green strength and strength after 3 days of drying

Further an amount of about 30 kg of biochar briquettes was successfully produced on a pilot scale
double roll press. Figure 46 shows a briquette (left) for comparison a piece of anthracite coal from
DEW (right).

61Figure 46.

Biochar briquette (left) and anthracite coal (right)

For the use of the agglomerates to replace anthracite as charge coal it is important to know the bulk
behavior and the abrasion resistance. To compare the behavior of the agglomerates to the behavior of
the anthracite coal, tests in a vibrating sieve and drop tests have been performed. For vibrating sieve
tests 1 kg of biochar briquettes and anthracite have been tested for abrasion resistance. The results of
vibrating sieve tests (Figure 47) show nearly equal grain size distributions.

Biochar from wood gasification

anthracite

g
n
i
s
s
a
p

100%

90%

80%

70%

60%

50%

40%

30%

20%

10%

0%

(cid:148)(cid:3)6,3

6,3 - 10

10 - 16

grain size [mm]

> 16

Figure 47.

Grain size distributions (left) and mass fractions (right) after vibrating sieve tests

Additionally drop tests in a closed tube of 150 mm diameter and 2 meter length have been performed to
simulate transportation and charging behavior. Also the results of the drop test below show that there
are only minimal differences between biochar briquettes and anthracite coal.

Biochar from wood gasification
anthracite

g
n
i
s
s
a
p

100%

90%

80%

70%

60%

50%

40%

30%

20%

10%

0%

(cid:148)(cid:3)6,3

6,3 - 10

10 - 16

grain size [mm]

> 16

Figure 48.

Grain size distributions (left) and mass fractions (right) after drop tests

In summary it can be stated that the biochar could be briquetted successfully. The briquettes show good
strength and resistance behavior. The handling of the biochar briquettes in the same way as the

62anthracite coal in the steel mills should be possible. In addition, a better combustion behavior due to the
smaller surface area is expected in further trials.

In secondary trials the briquettes of the biochar from wood gasification were used as charge coal. The
composition of the biochar briquettes is shown in the following Table.

[%]

Carbon
Ash
Volatiles
Humidity
Sulphur
Phosphor
Grain Size

Biochar briquettes from
wood gasification (BCB)
55,9
21,6
23,6
7,7
0,09
0,317
6-12 mm

Table 31.

Chemical composition of biochar briquettes from wood gasification

The trials have been performed similar to the previous trials where the fines have been charged with the
scrap. An amount of 1.6 kg of briquettes was charged with scrap and slag formers in the crucible of the
pilot furnace. Figure 49 shows the crucible charged with the briquettes.

Figure 49.

Crucible of pilot furnace charged with a first scrap layer and biochar briquettes
(BCB)

The results of the steel analysis of the biocoal briquettes (BCB) trials is shown in Figure 50 compared
to the results of the reference coal (RC) steel analysis. Like the previous trials using the biochar fines
the steel analysis regarding the carbon content shows that the carburization of melt by the reference coal
is higher than using the agglomerates. Also the contents of phosphor and sulphur show the same
behaviour as in the previous trials and there is no discernible negative influence on the steel
composition from the higher phosphorus content of the agglomerates in comparison to the phosphorus
content of the reference anthracite coal from DEW (130 ppm) The very low silica content (<0.0015 %)
and other deviations can be explained by fluctuations in the scrap composition or by errors in the
measurement.

63]

%

[

BCB

RC

Biochar TC

Biochar from wood gasification

0,1

0,09

0,08

0,07

0,06

0,05

0,04

0,03

0,02

0,01

0

C

Si Mn

P

S

Cr Mo Ni

N

Al

Figure 50.

Steel compositions of BCB and RC trials

During the BCB trials a dislodging of the refractory of the crucible was observed. Considering the
significant higher Al2O3 and the MgO-content of the BCB slags, a dissolving of the dislodged refractory
could be the reason for this phenomenon. The wear layer of the crucible mainly consists of MgO and
when this wear layer is damaged the acid permanent lining (93 % Al2O3) reacts with the alkaline slag
and dissolves. Moreover there is no other explanation for the additional input of Al2O3 and MgO in this
case. Looking at the P2O5 content, it is obvious that the content is even lower by using the briquettes in
comparison to the reference material. Even the lower P2O5 level indicates that there must have been a
dilution effect caused by the refractory material dissolved in the slag. Because of the considerable
higher phosphorus content of the BCB a higher P2O5 content of the slag was expected. However the
results of the slag analysis in general show that there is no negative effect detectable by using the BCB.

BCB

RC

(a)

]

%

[

70

60

50

40

30

20

10

0

BCB

RC

(b)

]

%

[

0,50

0,45

0,40

0,35

0,30

0,25

0,20

0,15

0,10

0,05

0,00

Al2O3

CaO

Fe2O3

MgO

Mn3O4

SiO2

P2O5

Fig. 51: (a) Slag compositions of BCB and RC trials
(b) P2O5 content of BCB and RC slag

64Task 4.3 To evaluate the effects on the pollutants emission from the EAF

Effects of char on the formation of polluting species was investigated both in pilot trial and industrial
trials. Here are reported the results obtained with pilot plant. Results obtained with industrial tests are
reported in WP5.

Effects of pollutants emission from RWTH pilot plant
The effects of using biochar instead of fossil coal on pollutants emissions have been recorded during the
pilot plant tests and have been analyzed and evaluated. The results of evaluation are shown in the
following Figures. In Figure 52 the off gas composition of the reference trial is shown when coal from
DEW was used. Comparing Figure 52 with Figure 53, where the biochar from Tecnocentro was used, a
flatter curve of CO formation can be noticed using the coal from DEW. In addition the significantly
lower reactivity of the anthracite coal can be ratified. The reaction of oxygen with the carbon from
anthracite(cid:3)coal(cid:3)starts(cid:3)at(cid:3)a(cid:3)later(cid:3)point(cid:3)((cid:167)600(cid:3)s(cid:3)after(cid:3)power(cid:3)on)(cid:3)and(cid:3)extends(cid:3)over(cid:3)a(cid:3)period(cid:3)of(cid:3)about(cid:3)2100(cid:3)s(cid:3)
with a constant CO formation of about 4 to 5 vol.-% in the off-gas. The formation of CO in the trial
where(cid:3)the(cid:3)biochar(cid:3)from(cid:3)Tecnocentro(cid:3)was(cid:3)used(cid:3)already(cid:3)starts(cid:3)(cid:167)400(cid:3)s(cid:3)after(cid:3)power(cid:3)on(cid:3)and(cid:3)it(cid:3)largely(cid:3)ends(cid:3)
up(cid:3)after(cid:3)a(cid:3)period(cid:3)of(cid:3)(cid:167)1400(cid:3)s.(cid:3)(cid:3)

O2

CO

CO2

H2

25

20

]

%

-
l
o
V

[
2
O

15

10

5

0

25

20

15

10

5

0

0

600

1200

1800
Time [s]

2400

3000

3600

Figure 52

Off gas composition using anthracite coal

]

%

-
l
o
V

[
2
H

,
2
O
C

,

O
C

65O2

CO

CO2

H2

25

20

]

%

-
l
o
V

[
2
O

15

10

5

0

18

16

14

12

10

8

6

4

2

0

]

%

-
l
o
V

[

2
H

,
2
O
C

,

O
C

0

600

1200

1800

2400

3000

3600

Time [s]

Figure 53

Off gas composition using biochar from Tecnocentro

By using the biochar fines from wood gasification plants, the combustion starts directly after ignition of
the arc. The off gas composition (Figure 54) shows the highest formation rate and the shortest time
period to generate the main amount of CO.

O2

CO CO2 H2

25

20

]

%

-

l
o
V

[

2
O

15

10

5

0

25

20

15

10

5

0

]

%

-
l
o
V

[

2
H

,
2
O
C

,

O
C

Figure 54.

0

600

1800
Time [s]
Off gas composition using biochar from wood gasification plants

3000

2400

1200

In the evaluation of the off gas composition of secondary trials where the biochar briquettes were used
it was found that the use of briquetted biochar (BCB) has a positive influence on the combustion
behaviour. In comparison to Figure 54 the direct CO peak is missing and the reaction of oxygen and
coal starts at a later point. Generally it can be determined that the combustion behaviour of the
briquettes is closer to the combustion behaviour of the reference coal (Figure 52), excepting the higher
CO formation rate.

66O2

CO

CO2

]

%

-
l
o
V

[

2
O

25

20

15

10

5

0

0

600

1200

1800
Time [s]

2400

3000

Figure 55.

BCB: Off gas composition using biochar briquettes (BCB)

25

20

15

10

5

0
3600

]

%

-
l
o
V

[

2
O
C

,

O
C

In summary the results of the investigations regarding the pollutant emissions from biochar in
comparison to the fossil coal show that the combustion behaviour of the fines is completely different
from using the reference material. Because of the large surface scale of the fines it comes to a direct
combustion right after arc ignition. This may indicate problems by using the biochar fines in industrial
scale trials to replace charge carbon. There will be the danger of explosive combustion by charging the
bucket within the biochar together with scrap into the hot furnace. Only the briquetted char shows a
combustion behaviour which is comparable to the combustion behaviour of the anthracite.

WP5 INDUSTRIAL EXPERIMENTATION (DEW, FERRIERE NORD, CSM, RWTH, MH,
TECNOCENTRO, IP)

Task 5.1 Definition of the EAF operating practices
Char utilization into the EAF has been tested at industrial scale by the three industrial partners
participating to the GreenEaf project. The industrial partners involved in this project have different
EAF, which differs for size, capacity, amount of chemical energy. Following Table reports the main
EAF characteristics.

67Charge
weight
(TLS)

Num.
buckets
/heat

FENO
DEW
MH

140
130
40

3
2
3

FENO: Ferriere Nord
DEW: Deutsche Edelstahlwerke GmbH
MH: Marienhütte Ges. m. b. h.

Electrical
energy
input
kWh/TLS
341
417,2
375

CH4
Nm3/TLS

O2
Nm3/TLS

Coal
lump
kg/TLS

Injected
Coal
Kg/TLS

Power
on
(min)

Tap to
tap
(min)

6
0
7

42
21,8
45

4
10.7
0

8
1,53
12

38
54
31

45
69
45

Table 32. Main characteristics of the electric furnaces of the industrial partners participating to the project.

FENO EAF uses coal for both carburization and foaming; coal is both charged and injected.
DEW uses coal mainly for bath carburization: coal is manly charged and injected in a small amount.
MH uses coal for foaming: coal in only injected.

The results of the investigations on the use of biochar instead of fossil coal in the EAF steelmaking
process in comparison to reference material showed that in general there are no significant negative
impacts on the steel or slag compositions. Problems occurred regarding the handling of fine-grained
carbonaceous materials with a high specific surface in the presence of liquid steel and oxygen. First
tests showed the direct combustion of the highly reactive biochar fines right after arc ignition in the
pilot EAF.

In order to solve these problems, investigations on the agglomeration behaviour of biochar have been
made. The biochar was briquetted successful. A stable briquette from a fully biogenic blend has been
created with characteristics which are comparable to the characteristics of the anthracite coal that is
presently used in electric steel mills.
These biogenic briquettes have been used as charge carbon in the pilot EAF of the department for
industrial furnaces and heat engineering (IOB). The evaluation of the results of these trials regarding
steel, slag and off gas composition shows no negative impact on the slag and steel chemistry.
Concerning the off gas composition it could be shown that the combustion behaviour of the briquettes is
close to the combustion behaviour of the anthracite coal.

Char industrial testing with these three furnaces exploited a wide range of operational variability.
Moreover, the utilization of syngas in EAF has been simulated through CFD modeling.

Task 5.2 Industrial tests with char and biogas.

Industrial tests at FENO – charge trials
The Electric furnace of Ferriere Nord has a capacity of 120 t, with almost 50% of energy provided by
chemical reactions. Coal is used both as charge material in the bucket and bot as powder for slag
foaming. The furnace is equipped also with the offgas online monitoring system EFSOPTM. Both char
charging and injection have been tested.
Three industrial campaign were carried out:
first campaign: charge test
Second campaign: charge tests with preliminary char briquetting
Third campaing: Injection tests

-
-
-

In the charge test, five heats have been tested with char charging and compared with five subsequent
standard heats. Charging conditions and steel analysis at tapping are reported in Table 33.
In the first five consecutive heats, anthracite in the bottom of the first basket, has been partially or
completely replaced with CHAR. The material was loaded into the basket after two layers of fine
material using a scrap yard crane equipped with grabbers.
Off gas analysis system (EFSOP analyzer) has been used during tests. Measured data have been
compared with data of the production of CO/CO2/H2 during standard operations.

68Heat ID Grade Char/Coal C % x100 Mn % x100

4349
4350

4351
4352
4353

4354
4355
4356
4357
4358

Char+Coal

Fe50

Char

Average

Fe50

Coal

Average

14,00
14,60

14,60
14,30
14,90
14,48
14,90
14,60
14,40
14,40
13,70
14,40

62,60
65,60

64,60
65,70
65,70
64,84
63,60
61,00
65,00
63,80
66,80
64,04

Si % x100
11,60
11,70

P % x1000
14,10
11,90

S % x1000
20,10
16,70

14,30
13,70
12,70
12,80
12,80
13,70
14,40
13,80
14,50
13,84

15,50
16,30
15,50
14,66
14,50
14,30
11,50
13,80
19,20
14,66

18,40
21,60
13,70
18,10
16,60
18,70
27,70
17,40
14,40
18,96

Table 33

Trials and standard heats with steel analysis after EAF cycle (average values
measured during test heats are compared with average values of standard heats)

Table 34 shows the values of offgas composition measured.

4349
4350
4351
4352
4353
Average
4354
4355
4356
4357
4358
Average

CO/s*

17,61
12,83
16,79
16,69
16,42
16,07
19,01
16,57
16,54
17,65
17,98
17,55

CO2/s*
17,47
17,15
17,41
17,68
16,99
17,34
16,33
16,79
16,71
17,75
17,21
16,96

H2/s*
10,56
7,66
10,10
9,85
11,08
9,85
10,35
10,20
8,84
10,28
11,28
10,19

O2/s*
0,28
1,10
0,41
0,02
0,15
0,39
0,23
0,11
0,40
0,01
0,04
0,16

Table 34.

Values of offgas compostion measured during industrial trials at Ferriere Nord

The results achieved showed that:
1.
2.
3.

Difficulties occur in handling and loading in bucket due to material conditions (fine grain).
Combustion occurs during the charging of the bucket in EAF (fine grain).
Main process parameters (including steel/ slag analysis) are comparable with standard values.

The main difficulty in char charging is related to high char reactivity. Significant powder dispersion has
been noticed during handling and charging operations and intense flame emissions were caused during
trials with char.

Second industrial campaign
The main difficulty in char charging is related to high char reactivity. A possible countermeasure can be
to transform char into mechanically stable briquettes. Briquetting tests were performed both at
laboratory and semi-industrial scale, before performing industrial trials at EAF. The objective of the
laboratory activity was to define the best mix of materials in order to obtain briquettes with good
mechanical properties (able to resist to handling operations into a steel plant).
Satisfactory results were obtained with the following mix:

69- 90% char,
- 5% flour,
- 5% bentonite,
flour and bentonite being the binding agents.

Addition of ladle slag (in the range 10-15%) did not change briquettes properties. The briquettes were
characterized by drop tests (based on drops number from 50 cm on flat metallic surface).

After the laboratory activity a semi industrial activity has been carried out at Ferriere Nord. A semi-
industrial apparatus has been purposely set for briquettes production. Figure 56 shows a picture of the
apparatus used at FENO for briquetting tests.

Figure 56.

Semi industrial briquettes production

Five tests have been carried out using the same blend developed at laboratory scale. The material
mixing and the low grain size of the binding agents seem to be determinant in briquettes strengthening.
In tests no. 4 and 5, the EAF dust have been mixed with char to increase the density of the material and
to recover the powder. From a qualitative point of view, the addition of this powders seems to improve
the product stability. Briquettes have been characterized with drop tests from 1 m height. The presence
of powder fraction after drop formation was evaluated. Relevant data are shown in Table 35.

Test

N1

N2

N3*

N4*

N5*

Char/
%

90

90

90

85

85

Bent/%

5

5 (finer powder)

5 pure bent.

5 pure bent.

5 pure bent.

Flour/
%

Filter
dust/%

LF
slag/%

5

5

5

5

5

-

-

-

5

-

-

-

-

5

Drop test

negative

Partially positive

positive

Partially positive

Table 35.

Results of the briquetting tests at Ferriere Nord.

70Obtained results indicates that materials can be pressed into briquettes with good mechanical resistance.
In order to perform a long duration test (six heats), and to have enough material available in a short
time, briquetted material has been acquired from the market. A market research has been carried out in
order to acquire a charcoal having same physic chemical characteristics of one used in first campaign.
Another important characteristic which has been considered selecting the provider was the mechanical
stability of briquettes, measured with drop test carried out according to ISO 4700 (Table 36)

C
H
N
S
P
Cl
ash

volatile matter
Higher Heating* value
H2O
Drop test- Numb. Of drops
(ISO 4700)

Char Briquettes
%
55.1
2.1
0.7
0.052
0.099
0.084
19.3

260
20 MJ/kg
7

31

Wood residues
%
60

0.06
0.4

21

13.5
20 MJ/kg
5.2

Table 36.

Characteristics of char briquettes used in the second testing campaign at FENO,
compared with char used in this project

The testing campaign has been carried out charging 850 kg of char briquettes in the first bucket for six
heats. Subsequent six heats are carried out in standard mode and used as comparison.

In the trials heats the following parameters are monitored:

Steel and slag analysis at tapping
Slag analysis in subsequent ladle

(cid:120)
(cid:120)
(cid:120) Off gas composition
Power on time
(cid:120)
Productivity
(cid:120)
(cid:120) Gas analysis in the stack (including dioxin)

Results about gas analysis are reported in task 5.3
Tables 37 and 38 reports the results of industrial trials. The results are expressed as percentage variation
respect subsequent standard heats. Even if FeO variation may look as significant, it is in range usually
observed with coal practice.

FeO
+19.2%
(a)

CO
-2.9%
(b)

Table 37

MnO
-4,2%

SiO2
-14,9%

CaO
-8.2%

IB2

+17,8%

CO2
-4.8%

H2
+0.3%

(a) variation of slag composition
(b) Variation of offgas composition during industrial trials with char at FENO

71Steel prod. (t)

productivity (t/h)

Power On (min)

Electrical consumption (kwh/t)

-1,1%

-2,0%

+2,1%

+3,5%

Table 38

Variation of main production parameters recorded during industrial trials with
char at FENO

Char addition as substitute of charge coal did not modify steel and slag characteristics; also the main
process parameters did not show relevant deviation from standard situation.

The intense flame emissions during char charge in bucket, observed in first campaign tests disappeared
with performing a preliminary briquetting stage.

Third industrial campaing at FENO: injection tests
Pulverised char has been injected by a secondary lance modified for industrial tests. This lance is
currently used to spray refractory cement for furnace walls maintenance. Injection of 500 kg char was
made with a mass flow rate within the range 12(cid:121)16 kg/min.

The first results showed that the injected char did not penetrated inside the slag. In order to increase the
efficiency of the char penetration into the slag, two possible solutions were individuated:
- injection below the slag level;
- use of a double jet to improve the injection system (see Figure 54).
The double jet is achieved with one lance for oxygen and one lance for pulverized char with a carrier
gas. The jet penetration inside the slag can be calculated and it is mainly a function of lance distance
from the slag and gas velocity.
Calculation of jet penetration into the bath as a function of distance of lance from the bath and gas
velocity [23] has been carried out. The calculation takes as data input:
- distance to the bath: S0 (see Figure 57)
- coal/char flow rate
-(cid:3)angle:(cid:3)(cid:302)(cid:3)(see(cid:3)Figure(cid:3)54)(cid:3)
-(cid:3)jet(cid:3)angle:(cid:3)(cid:537)(cid:3)(see(cid:3)Figure(cid:3)54)(cid:3)
- carrier gas velocity
- slag density

(cid:3)(cid:3)
(cid:3)

(cid:3)
(cid:3)

(cid:3)
(cid:3)

(cid:3)
(cid:3)

72slag

steel

S0

(cid:302)

(cid:537)

(a) Injection below slag level

(b) double jet injection

Coal/char penetration into the slag

Carrier gas velocity

(c) results of calculation of jet penetration

Figure 57

Improvement of char injection: (a): installing a lance for under slag injection; (b)
using a double jet for slag penetration; (c) results of calculation of jet penetration

73Industrial tests at DEW – charge and injection trials
The biochar has been tested at DEW as charge coal and as injection coal.

Biochar as charge coal
The biochar fines from wood gasification plants were directly charged by the grabber into the scrap
buckets in big bags because of the low grain size. Figures below show the charging procedure. The
generation of dust caused by the damage of the big bags by sharp-edged scrap is enormous.

Figure 58.

Charging of biochar fines at DEW Siegen

Directly after charging the bucket into the furnace it came to an undesirable rapid combustion of the
biochar fines. For this Reason, it was only possible to replace the charge carbon from one charge
partially with the biochar fines. The Tables below show the feedstock quantities of the reference charge
(Table 39) and of the biochar charge (Table 40).

Feed

Scrap [kg]
Lime [kg]

Dolokalk [kg]

Anthracite [kg]

Biochar [kg]

Mass

141120
3520

1500

1320

0

Feed

Blow carbon [kg]
Sublimed sulfur [kg]

3
Oxygen [m
]
Spez. energy [kWh/t]

Heat duration [min]

Table 39.

Feedstock quantities of the reference charge

Feed

Scrap [kg]
Lime [kg]
Dolokalk [kg]
Anthracite [kg]
Biochar from wood
gasification [kg]

Mass

149100
3520
1400
800

720

Feed

Blow carbon [kg]
Sublimed sulfur [kg]
Oxygen [m3]
Spez. energy [kWh/t]

Heat duration [min]

Table 40.

Feedstock quantities of biochar charge

Mass

391
78

2930

421

55

Mass

388
105
3032
433

58

After evaluating the steel and slag analysis of the biochar and the reference charge the results have been
compared. Regarding Figure 59 there are no significant differences in the slag compositions that can be
referred to the use of biochar in the process. The basicity value of the reference slag is 2.63 and 2.93 is
the basicity value of biochar slag. The difference between these two values is small.

74Reference charge

Biochar charge

SiO2

MnO

MgO

Fe2O3

Cr2O3

CaO

Al2O3

0

10

20

30
[%]

40

50

60

Figure 59.

Slag analysis of reference and biochar charge (left) and basicity (right)

Considering the results from the steel analysis (Figure 60) there are also no significant differences.

Ni

Mo

Cr

S

P

Mn

SI

C

[%]

0

Reference
BC B

C
0,36
0,358

0,2

SI
0,56
0,55

0,4

Mn
1,05
1,08

0,6

0,8

P
0,008
0,008

S
0,023
0,021

Cr
0,16
0,14

1

Mo
0,03
0,02

1,2

Ni
0,1
0,08

Figure 60.

Steel analysis of reference and biochar charge

Industrial scale trials using biochar to replace charge coal have been performed with success.
In summary the industrial scale trials using biochar as charge coal showed no negative influences on
slag and steel compositions. The results regarding the off-gas evaluation will be discussed in task 5.3.
Problems occurred by the handling of the biochar fines (charging of buckets). Due to the very large
surface area the biochar fines combust directly by/after charging into the furnace. Using biochar fines as
charge coal seems not to be successful without a prior agglomeration step

Biochar as injection coal
For the industrial experiments of using biochar as injection coal DEW Siegen installed a secondary coal
injection system (Figure 61). The injection machine can directly be charged by big bags.

75Figure 61.

Secondary injection system for biochar fines

The following illustration shows the filling procedure of the injection system.

Figure 62

Charging the injection machine at DEW Siegen

Two trials have been performed using biochar fines as injection coal to foam the slag. The feedstocks of
the two charges are shown in Table 41.

Feed
Scrap [kg]
Lime [kg]
Dolokalk [kg]
Anthracite [kg]
BC B as blow carbon [kg]
Oxygen [m3]
Spez. energy [kwh/t]
Heat duration [min]
Feedstock of trial charges using biochar as injection coal

Charge 1
139920
3060
1300
2000
420
2867
407
52

Charge 2
145000
2020
600
180
440
2912
415
59

Table 41

76The foaming of slag using biochar fines from wood gasification plants was successful. The slag
compositions of the two trial charges have been analysed and evaluated. Regarding slag chemistry and
basicity no significant differences occur by using biochar instead of petrol coke to foam the slag.

rest

SiO2

MnO

MgO

Fe2O3

Cr2O3

CaO

Al2O3

0

Slag 2
Slag 1

Al2O3
3,56
5,07

10

CaO
23,7
30,6

20

[%]

30

Cr2O3
4,19
2,35

Fe2O3
46,2
37,9

MgO
4,77
5,56

MnO
7,2
5,92

40

SiO2
8,93
10,7

50

rest
1,45
1,9

Figure 63.

Slag composition of biochar trials

Regarding the basicity of the reference and the biochar trial Figure 64 shows that the difference is
marginal.

Figure 64.

Slag basicity of biochar trials

Industrial scale trials using biochar fines as injection carbon have been carried out successfully. The
results showed no negative influences on slag composition and basicity. Additionally the foaming of
slag could be achieved.
Problems appeared by the discharging of big bags into the injection system (Enormous dust emissions).
In addition problems came up by plugging of the fine material in the pneumatic conveying system.
Because of all these problems it came to delays in the logistics of the melting shop.

77Figure 65.

Problems occurring while using biochar fines as injection coal

MH industrial trials – injection trials

In order to evaluate the substitution of petroleum coke by charcoal as injection coal into the electric arc
furnace (EAF)
large-scale experiments were performed. Different carbon sources provided by
Tecnocentro were tested for their slag foaming ability.
The charcoal samples with different moisture contents were injected via the door lance manipulator.
The reference material was calcined petroleum coke used at Marienhuette as standard carbon for slag
foaming purpose.
The electric arc furnace has a diameter of 4700 mm, a height of 1870 mm and a capacity of around 40
tonnes. Additionally to the door lance the KT system (Köster Technology) is installed at the water-
cooled side wall panels near the "cold spots". The system combines three natural gas / oxygen-carbon
blocks, with burner function, lance function in the supersonic range and coal injection, distributed
evenly around the circumference.
The injection of carbon sources with compressed air for experimental purposes is possible only through
the door lance manipulator (see Figure 66). The injection started after melt down period of the scrap at
the beginning of the flat bath at a bath temperature of about 1540 °C. The carbon flow rate was about 20
kg/min. Compressed air was used at 6 bar for this application. The experimental evaluation and
documentation was done by the foaming slag management system OFSM (Optical Foaming Slag
Management), which determines the slag index. The slag index is a measure of the slag height.
Additionally, a video camera for visual assessment of foaming effect was installed. Furthermore, slag
samples were taken.

78Figure 66

Electric Arc Furnace and Injection Equipment at MH EAF.

The images of the video recording during the injection of three different char coals supplied by
Tecnocentro are illustrated in Figure 67. In the first field left the starting of the injection through the
door lance is shown, while the second and third Figure represents the injection itself. The last picture
right shows part of the slag foaming after the start of the KT-lances with petroleum coke. It can be seen
that with exception of the charcoal sample with the highest moisture content (50 %) any of the coals
tested even caused a foamy slag formation. Only with injection of calcined petroleum coke a slag
two minutes no
foaming and an overflow were achieved. Despite the injection time of about
improvements were observed. Only the wet charcoal led the slag to overflow the furnace wall. In
comparison, after the start of the KT system with petroleum coke a strong reaction deployed and the
slag immediately flow out of the furnace door. This shows evidence that the slags were foamable. The
corresponding slag analysis shows Table 42. The compositions are in typical ranges but without
particular correlation.

char

Sample C

B Tecnocentro

A Tecnocentro

FeO
[%]
25,45
34,45
38,53

Fe2O3 Al2O3 CaO
[%]
[%]
[%]
24,56
17,79
4,08
28,85
9,25
5,58
21,65
8,41
7,52

SiO2 MgO MnO Cr2O3
[%]
12,64
9,34
9,42

[%]
8,42
4,59
6,10

[%]
1,34
2,29
2,91

[%]
4,38
4,58
4,24

S
[%]
0,09
0,12
0,13

Table 42

Slag analysis after char injection tests at MH

79Test C Tecnocentro (dry)

Test B Tecnocentro (19 % H2O)

Test A Tecnocentro (50 % H2O)

Figure 67

video images of Injection tests with different char samples

The low bulk density of the charcoal samples had a negative effect on the flow rate and the higher
moisture contents led to blockages in the delivery system. After elimination of these technical
difficulties the injection experiments were carried out as planned. This was, as already mentioned, the
injection of char into the liquid slag through the door lance. The lance was submerged into the slag. The
KT-lances were not used during injection of char because petroleum coke injected via the KT-system
would falsify the test results. Only at the end of the refining period, the KT-lances were used to show
the differences between the slag formation caused either by char or by petroleum coke. The injection
procedure of test A with the wet char is illustrated in Figure 68 and 69.

5000

4500

4000

3500

3000

2500

2000

1500

1000

500

n
e
g
y
x
o

n
o

i
t
s
u
b
m
o
c
-
t
s
o
p

0

0

post-combustion oxygen [Nm³/h]
lancing [on/off]
biochar [kg/min]
burner [on/off]

power [on/off]
slag index [%]
carbon [kg/min]

200

180

160

140

120

100

80

60

40

20

0

e
k
o
c

l

o
r
t
e
p
;
x
e
d
n

i

g
a
l
s

;
r
a
h
c
o
b

i

5

10

15

20

25

30

35

Figure 68.

EAF cycle of injection Test A

minutes

80Figure 69.

Slag Index detected by the OFSM system

Figure 70 summarizes theoretical mechanism for slag foaming using char.

(cid:120)
(cid:120)
(cid:120)

CO formation by reduction of FeO
Volatiles
Moisture

The contribution of the CO bubbles formed by reduction of FeO to the slag foaming is called into
question.

Figure 70.

slag foaming mechanism using char

The result of the injection tests of charcoal in the EAF at MH shows that charcoal doesn´t cause or if
any a very slight foaming of the slag. The reason for this could be a low wettability of charcoal by the
liquid slag, which prevents a reaction of carbon with FeO of the slag to form enough CO bubbles. This

81was demonstrated by a sessile drop test. The low bulk density of the charcoal bears a risk of floating on
the slag layer, which reduces the penetration in the slag significantly. Only the experiment with moist
charcoal led to the formation of an acceptable slag foam. Here, the resulting water vapour at the high
temperatures > 1500 °C due to the water-shift equilibrium resulted in formation of high quantities of
gas which lead to slag foaming, but without effect on reducing FeO. This is of course undesirable. In
addition, high humidity in combination with liquid metal and / or slag bears the risk of explosive gas
formation.

Syngas utilization in EAF

Syngas produced during biomass pyrolysis can be used in EAF burners instead of natural gas. Due to
the difficulty to have pilot syngas production close to the steel plant, according to the technical annex
the syngas use has been simulated through CFD calculations. Considering the situation of FENO EAF,
the simulation has been designed according to the following steps:

i) Definition of a reference EAF situation with natural gas burners configurations.
ii) Definition of quantitative criteria to compare burner performances with natural gas and syngas.
iii) Definition of syngas characteristics and simulation with syngas burner feeding.
iv) Global evaluation about syngas utilization in EAF. Definition of a reference EAF situation with

actual burners configurations with natural gas.

i) Definition of a reference situation. CFD simulation has been carried out in order to set a reference
situation, to be compared with subsequent simulations with syngas. The reference situation consider the
the burners operating parameters and the EAF atmosphere
design of the current used burner,
composition . Figure 71 shows the burner geometry.

Figure 71.

Scheme of burner currently used at FENO steelplant

The calculation domain considers a cylinder with 2500 mm diameter and 6000 mm length. Atmosphere
composition is defined based on average values measured by EFSOP sensor. The burner is placed in
symmetric position in one side of the domain, as indicated in Figure 72, where boundary conditions are
also shown.

82burner

Figure 72.

Boundary conditions used for CFD calculations

Being the final objective of the calculations the syngas simulation, a detailed kinetic combustion model
has been chosen. This model includes 16 species and 42 reactions.

ii) Definition of quantitative criteria to compare burner performances with natural gas and
syngas.
Once the flow field and flame temperature has been calculated for the current process working
conditions, in order to simulate the EAF syngas utilization a quantitative criterion has been defined.
The criterion is based on the comparison of the burners efficiencies, calculated with natural gas and
with syngas. Such efficiency is defined as:

kW
(cid:152)

to
(cid:152)
(cid:152)
from

kW

the
(cid:152)
the
(cid:152)

scrap
burner
(cid:152)

Figure 73 reports the results of the calculations of the burner efficiency, for three different standard
working conditions (corresponding to three burner powers).

83Figure 73

Calculation of the burning efficiency, for the three working conditions with
natural gas.

The same calculation has been performed using syngas instead of natural gas.

iii) Definition of syngas characteristics and simulation with syngas burner feeding.

Syngas composition has been taken from the industrial trials of char production as follows:

Component
C3H8
C2H6
CH4
CO2
CO
O2
H2

%
0.9
0.7
4.1
35.1
20.6
7.1
0.5

Based on these data, the calculated syngas heating value is 7.15MJ/Nm3.

Due to the low value of such heating value it was necessary to increase gas flow rate in the burner.
In Ferriere Nord steelplant gas flow rates higher than 500Nm3/h are not available.

For this reason, syngas has been mixed with natural gas, in order to obtain the target heating value of 21
MJ/Nm3, to stay within the feeding steelplant constraints. The same CFD calculations have been then
carried out with syngas.

iv) Global evaluation about syngas utilization in EAF.

Figure 74 compares the flame temperature and the heat flux in case of syngas and natural gas. As a
result, the burner fed with syngas produces a flame with lower temperature respect natural gas and
lower heat flux on the scrap.

]

m
[
e
t
a
n
d
r
o
o
c
l

i

ia
d
a
r

1.2

1

0.8

0.6

0.4

0.2

0

0

syngas

NG

200

400

600

800

1000

heatflux [kW/m2]

Flame temperature during the sa me process condition
of a burner fed by natural gas and syngas

Heat flux on the scrap in front of the burner,in case
natural gas (NG) a nd syngas

Figure 74.

Comparison of flame temperature in case of natural gas and syngas burning.

84Comparing the performances of the burners in term of efficiency (Figure 75), it has been found that the
use of syngas determines a decreasing of efficiency of about 10%.

Figure 75.

Difference of efficiency of burner in case of natural gas (NG) and syngas

To recovery the efficiency lost by syngas utilization, different burner configurations have been
simulated. Figure 76 reports the results on a simulation showing the flame aspect and temperature in
case of feeding with syngas the current burner, a burner modified with swirl motion on oxygen and
swirl motion on oxygen and syngas.

No swirl

swirl O2

Swirl on O2 and syngas

Figure 76.

Flame aspect and temperature in case of feeding with syngas the current burner, a
burner modified with swirl motion on oxygen and swirl motion on oxygen and
syngas.

The calculation of efficiency in case of swirl motion did not a significant gain. Simulation show a larger
portion of scrap heated by burner improved with swirl, but the global increase of efficiency is small.
Summarising, the simulations showed a decreasing of efficiency of burner fed with syngas. In order to

85keep the plant productivity at the same level, it is necessary to enrich the mix of natural gas, or to
increases the gas flow rate. This calls for plant modifications.

Task 5.3 Evaluation of the variations of pollutants emissions from the plant.

Environemtal monitoring during industrial trials has been carried out at Ferriere Nord and DEW. MH
uses a smaller amount of char/ton of steel, respect the two other industrial partners, because carbon is
used only as foaming agent, and not as charge material for steel recarburization of energy input.

Ferriere Nord, beside the current off gas analysis carried out with patented online installed system
(EFSOP TM), performed extra analysis at the stack.

The results coming from stack analysis are compared with plant historical data.

Following species have been analysed.

Powders

(cid:120)
(cid:120) Metals (Pb, Cd, Cu, Zn, Cr, Cr(VI), V, Ni, Mn, Sn)
(cid:120) HCl
PAH
(cid:120)
PCDD/PCDF
(cid:120)

Below results of stack monitoring are reported and compared also with historical plant data:

Powders (mg/Nm3)
HCl (mg/Nm3)
Dioxin (ng/Nm3)
PAH (mg/Nm3)

measured
<0.5
<0.5
0.004
0.008

historical
<0.5
<0.5
0.005
0.002

The analysis at Ferriere Nord indicate that fumes chemical analysis is not modified by char utilization,
compared to average historical data.

Pollutant emissions and off gas temperature of biochar and reference trials at DEW have been
measured, analyzed and evaluated. The measurements were carried out in the exhaust system of the arc
furnace. Figure 77 shows a drawing of the exhaust system. The measuring point is marked. At this
position, there are openings in the pipe, which were used to install the measurement equipment.

86Figure 77.

Points of off gas measurement

In the opening a thermocouple type K (range 0-1000°C) for the measurement of the exhaust gas
temperature and a gas sampling probe was installed. From the gas sampling probe the exhaust gas was
filtered and was conducted in a gas analysis unit. The analysers are listed with their relevant technical
data in Table 43.

gas component
CO2
O2
CO

measuring principle

infrared radiation absorption

O2-para-magnetism
infrared radiation absorption

response delay
3 s -7 s

< 4 s

3 s - 7 s

measuring range
0 % - 20 %

0 % - 25 %

0 % - 2500 ppm

Table 43.

Technical data off gas analyzers

The continuously recorded data were analysed using the operating data of the electric arc furnace.

Reference Charge
The operating data of an exemplary reference charge is listed in Table 44. The measurement data of
temperature and gas composition is shown in the time course of the charge in Figure 78.

Material
charge time [s]
melting time [s]
tapping temp. [°C]
energy input [kWh]
specific energy input [kWh/t]
feedstock
scrap weight bucket I [kg]
scrap weight bucket II [kg]
injection coal [kg]
lime [kg]
SBLU [kg]
blow oxygen [m3]
output
tapped steel [kg]
slag weight [kg]

1.5231
4800
3300
1691
60660
421

82760
61180
391
3520
78
2930

139389
1862

Table 44.

Operating data of an exemplary reference charge

87]

%

[

2
O
C

,
2
O

25

20

15

10

5

0

O2

CO2

CO

Temp.

1st bucket

2nd bucket

1000

900

800

700

600

500

400

300

200

100

]

C
°
[

.

p
m
e
T
;
]

m
p
p
[

O
C

0

1000

2000

3000

4000

time [s]

0
5000

Figure 78.

Off gas composition of an exemplary reference charge

As expected for the measurement point, the exhaust temperature peaks at a maximum of 650°C. Also
expected and in agreement with previous measurements on this furnace, and this point the contents of
carbon monoxide in the exhaust gas are in a range up to 800 ppm. The CO2 content of the exhaust gas
varies in a range of about 0-10 vol -%.

Biochar charge
The operating data from the experimental operation with biochar as charge coal in the arc furnace is
listed in Table 45. The measurement data of temperature and gas composition are shown in the time
course of the charge in Figure 79. The temperature measurement shows temperature peaks up to 620°C
a very similar picture to the results from reference charge. Differences occur considering the measured
values for the CO content of exhaust gas. As for the reference batch, the CO content only from time to
time shows more than 500 ppm, for the biochar trials, especially during the melting of the second
bucket, significantly higher CO values of 500-1500 ppm in peaks and even up to full scale value of
2500 ppm have been measured.

material
charge duration [s]
melt duration [s]
tapping temp. [°C]
energy input [kWh]
specific energy input [kWh/t]
feedstock
scrap weight bucket I [kg]
scrap weight bucket II [kg]
injection coal [kg]
lime [kg]
SBLU [kg]
blow oxygen [m3]
output
slag weight [kg]
tapped steel [kg]

1.5231
4500
3480
1641
65180
433

80820
69680
388
3520
105
3032

not specified
not specified

Table 45.

Operating data of biochar charge

88O2

CO2

CO

Temp.

1st bucket

2nd bucket

25

20

15

]

%

[
2
O
C

,
2
O

10

5

0

3000

2500

2000

1500

1000

500

]

C
°
[

.

p
m
e
T
;
]

m
p
p
[

O
C

0

1000

2000

3000

4000

time [s]

0
5000

Figure 79.

Off gas composition of biochar charge

The Measurements at the electric arc furnace at DEW in Siegen have been performed successfully. Off-
gas data of both reference and biochar charges could have been recorded, evaluated and compared to
each other. The comparison of the data sets shows higher CO levels in the off-gas composition while
using biochar fines as charge coal.

As general conclusion from both monitoring activities at Ferriere Nord and DEW, the following
indications can be drawn:
- the CO increase in the second bucket observed with char utilization (20% in the off gas respect 16%)
is not a dramatic value which can be controlled optimising the operating practice and with a longer
industrial testing
- char does not contribute to dioxin formation or increase of powder dispersion into fumes.

From the environmental point of view char can be used as charge material in electric furnace

WP6 TECHNO-ECONOMIC EVALUATION AND FINAL REPORT (FERRIERE NORD,
CSM, TECNOCENTRO, IP, RWTH, DEW, MH)

Task 6.1: Techno economic evaluation of the project results

This project has exploited the possibility to use biomass products (char and syngas) in electric arc
furnaces, replacing fossil sources. Environmental benefits deriving from biomass utilization instead of
fossil fuels has been widely described in literature [1,2,3,22]. The main advantage derive from being
neutral respect CO2 emission.
the project showed that charcoal utilization is
Below techno-economic evaluations are reported;
technically feasible in shorter time respect syngas. For this reason most of considerations and
simulations are devoted to charcoal, even if economic aspect bond with syngas are taken into
considerations.

Charcoal is a wood product that is made by heating wood in absence of sufficient air for full
combustion to occur. Heating releases wood volatile compounds leaving behind a relatively light
weight and clean burning fuel that is 70-90% carbon. Tecno-economic evaluation of charcoal utilization
has to consider two aspects:

89- char costs
-cost savings from reduction of CO2 emission

There is not a great deal of information available in literature on the cost of charcoal production.
Schematic diagram [19] in Figure below shows the phases of char production; each step contributes to
the global char cost.

Figure 80

Schematic flowsheet of charcoal production

All the steps of production of Figure 80 can be grouped into three main issues:

1. wood/raw material (including cost of harvesting and collection of biomass up to the pyrolysis

plant)

2. charcoal production
3. charcoal transport (to be intended as transportation from the pyrolysis plant to the steel factory)

Figure 81 reports the contribution of these three various issues [19] to the global cost of charcoal.
According to this Figure, charcoal cost is estimated with an order of magnitude of 400 (cid:188)/t, but about
70% is due to the cost of biomass. Inside this cost is included cost for biomass production, cultivation
or collection and transportation to the pyrolysis plant. In Figure 81, with the term transportation is
intended only the delivery of produced charcoal from the production pyrolysis plant to the utilization l
plant.

90Figure 81. Contribution of stages to global charcoal cost.

In literature, smaller costs (in the order of magnitude of 160 (cid:188)/ton) are reported [22] for specific
situations with large amount of biomass available in the surroundings.

In order to get an idea about the economics of charcoal, case study of char production for MH steelplant
in Austria has been considered. Raw material prices and costs, investigations concerning costs for
transport as well as the conversion of biomass (including potentially drying) into charcoal have been
taken into account. Due to the fact, that the biomass market in most cases is not a typical market with
standardized products, it is impossible to get detailed and totally comparable prices for different
biomasses. This is why always price ranges dependent on quality, region etc. are referred. However, the
listed prices can change very quickly. Especially a big demand for certain biomasses can lead to a
radical price increase.

The only biomass which is a more or less standardized product with an existing trading is wood chips.
For bulk consumers the prices are in the range of 80-100 (cid:188)/t dry matter. However, also bark is very
often traded as biogenic energy source. The prices for bark are at about 25-40 (cid:188)/t dm and therefore still
attractive at the moment.
In case of strew the mentioned prices differ a lot. Realistically the price for strew is between 65 and 100
(cid:188)/t dm, but has to be fixed individually with the partners or farmers. The prices for cobs are similar in
the area of 43 to 89 (cid:188)/t dm. In general, the prices for agricultural products are a combination of
harvesting costs and collecting costs and are often declared as prices ex works.
The costs for waste wood also have a wide range depending on the degree of contamination. Untreated
waste wood realizes prices of up to 40 (cid:188)/t dm, whereas for contaminated waste wood you will even get
up to 30 (cid:188)/t dm for disposal. The problem in case of the utilization of waste wood is the legal situation.
The cost situation for short rotation crops including land purchasing, crop cultivation and harvesting
including chipping is about 110 (cid:188)/t dm.

To calculate the real charcoal costs, beside the costs for the feedstock material there are several other
things which have to be considered. E.g., the demand on biomass for every ton of charcoal is
approximately 4 tons. Further, charcoals typically have a carbon content of 80-85 %. This means, that
about 4 to 5 tons of biomass are needed to deliver the same carbon amount as with 1 ton of petroleum
coke. This is why in Table 46 the relative prices for petroleum coke as standard injection coal and those
of the comparable amount of several biomasses are listed.

91Material costs

Annual demand

Annual costs

Petroleum coke

Wood chips

Strew

Bark

Cobs

Waste wood

[%]

100

30

26,7

10

20

3,3

[t/a]

5400

24300

24300

24300

24300

24300

[%]

100

135

120

45

90

15

Table 46

Cost comparison of different feedstock for injection coal

It is obvious, that in most cases even the raw material price for the biomass is nearly the same or even
higher as the one for the standard injection coal, petroleum coke. Only really low priced biomass is an
economically attractive alternative to fossil coke. However, the availability of such biomasses is not the
best one. Nevertheless, additionally to the feedstock prices also transportation costs, storage costs
operating costs of the carbonization plant etc. have to be considered. Table 47 shows a rough estimation
for total costs of injection chars of different origin, which are between 220 and 580 (cid:188)/t and therefore up
to the double price of typical injection coals.

Raw material costs

Transport

Conversion costs

Storage and
handling

Total costs

[(cid:188)/t charcoal]

[(cid:188)/t biomass]

[(cid:188)/t charcoal]

[(cid:188)/t charcoal]

[(cid:188)/t]

Wood chips

Strew

Bark

Cobs

Waste wood
Table 47

405

360

135

270

10

20

15

20

150

150

150

150

10
Cost comparison of total costs for charcoals from different origins

150

45

15

15

15

15

15

580

545

315

455

220

The range of costs for charcoal production individuated is in agreement with what reported in literature
[19, 22]

Cost saving from reduction of CO2 emission
The economical evaluation about to biomass utilizations needs to consider also the advantage deriving
from the reduction of CO2 emissions.
The CO2 sources from the EAF process are shown in Figure 82. The main proportion of the total CO2
sources is provided by the injected/charged carbon. This calculation is tailored on the EAF of Ferriere
Nord, but the order of magnitude can be considered valid for most of EAFs.

92Figure 82

Percentage of CO2-sources of an EAF process

In oder to reduce the CO2 emission from the electric steel production, the main issue is to reduce the
coal consumption.

CO2 emissions are calculated with the mass balance approach that considers all the carbon entering and
leaving the installation.
The following formula is applicable for mass balance:

where:

EMmb
f
i
ADi

CCi

emissions from all source streams included on the mass balance [ton CO2];
factor for converting the molar mass of carbon to CO2. The value is 3.664 tonCO2/tonC;
index for the material or fuel under consideration;
activity data of the material or fuel under consideration. Ingoing materials or fuels are taken
into account as positive, outgoing are taken into account as negative.
the carbon content of the component under consideration;

Figure 83 represents CO2 emissions for Ferriere Nord SPA for year 2011, a total amount of 92.804 tons
of CO2 have been generated. The specific emissions were 78 Kg of CO2 / ton of steel produced by EAF.

93Figure 83.

CO2 emissions for Ferriere Nord SPA for year 2011. The specific emissions were
78 Kg of CO2 / ton of steel produced by EAF.

Figure 84 reports the scheme of CO2 emission from DEW Siegen.

94Figure 84.

DEW CO2 emission balance of a given year

Details of the calculations of the CO2 emissions for DEW steelplant are reported in Annex 2.

Once the CO2 emission is calculated, it is possible to estimate the advantages deriving from reduction of
CO2 emissions, and also make some hypothesis varying the amount of substitution, coal price, and
values of CO2 quotes.

In these calculations biomass is considered neutral respect the CO2 emission.
Figure 85 reports, for Ferriere Nord, global cost for CO2 emission from steel plant, in four cases:

1. Actual situation with fossil fuels
2. Substitution of charge coals
3. Substitution of injected coals
4. Substitution of syngas

For the calculation, three possible vaules of CO2 are considered:
10 (cid:188)/t, of the order of magnitude of current values
18 (cid:188)/t, a value higher
100 (cid:188)/t, the fine value, according to ETS, for missing EUA - European Union Allowances
(assumed as maximum value in the EU ETS market)

(cid:120)
(cid:120)
(cid:120)

95Cost of CO2 emissions

10 (cid:934)/ton CO2

18 (cid:934)/ton CO2

100 (cid:934)/ton CO2

(cid:934) 12.000.000

(cid:934) 10.000.000

(cid:934) 8.000.000

(cid:934) 6.000.000

(cid:934) 4.000.000

(cid:934) 2.000.000

(cid:934) -

Fossil sources

Total substitution of
carbon in charge with
biomass

Total substitution of
injected carbon with
biomass

Total substitution of
natural gas with syngas

Figure 85

Global cost for CO2 emission from steel plant (Ferriere Nord), in four cases:

1.Actual situation with fossil fuels
2.Substitution of charge coals
3.Substitution of injected coals
4.Substitution of syngas

Figure 86 reports the difference between the costs, calculated as a sum of supplying costs and CO2
emission costs, using only fossil carbons and using biomass as a total substitute for carbon in charge
and injection, in seven different market conditions.

(cid:934) 500.000

(cid:934) -

-(cid:934) 500.000

-(cid:934) 1.000.000

-(cid:934) 1.500.000

-(cid:934) 2.000.000

-(cid:934) 2.500.000

-(cid:934) 3.000.000

-(cid:934) 3.500.000

-(cid:934) 4.000.000

-(cid:934) 4.500.000

Figure 86

total substitution of carbon in charge with
biomass

total substitution of injected carbon with
biomass

10 (cid:934)/ton CO2
170(cid:934)/ton carbon
200(cid:934)/ton biomass

10 (cid:934)/ton CO2
350(cid:934)/ton carbon
200(cid:934)/ton biomass

10 (cid:934)/ton CO2
170(cid:934)/ton carbon
50(cid:934)/ton biomass

100 (cid:934)/ton CO2
170(cid:934)/ton carbon
200(cid:934)/ton biomass

10 (cid:934)/ton CO2
350(cid:934)/ton carbon
50(cid:934)/ton biomass

100 (cid:934)/ton CO2
350(cid:934)/ton carbon
200(cid:934)/ton biomass

100 (cid:934)/ton CO2
350(cid:934)/ton carbon
50(cid:934)/ton biomass

Difference between costs (supplying + CO2 emissions) using onlys fossil carbons
and using biomas as total substitute for carbon in charge and injection, in seven
different market conditions

96The actual market conditions indicates that globally a small global cost increases can be expected, but
realistic future scenario indicate that an economical convenience in biomass utilization can be foreseen.

The diagram in Figure 87, calculated for MH steel plant, shows a rough overview about the necessary
CO2-prices to make a usage of biomass in form of charcoal economically attractive for the production
of steel in an electric arc furnace, considering a value of 170 (cid:188)/ton for coal.
In the end, from the quantitative point of view, including the availability of biomass, and also the
qualitative point of view, almost entirely woody biomass like wood chips are eligible feedstock
materials for charcoal production. If this is the case, politically driven costs like CO2-taxes have to rise
to a level of about 50-100 (cid:188)/t to make these CO2-neutral alternatives also economically competitive.

Figure 87

Necessary CO2-price for economical biomass utilization in electric steel production
(calculated for MH steel plant)

Besides the increase of costs of CO2 certificates, the need to acquire CO2 quotes has been also
considered. For example, the DEW in Siegen has an annual allocation of 48,150 CO2 certificate.
Experience shows that, depending on the annual production output, more CO2 certificates would be
needed. This yields a missing quantity of about 10,000 CO2 certificates per year. In This case a partial
substitution may be enough to avoid increases of costs. Following table reports, the global reduction of
CO2, depending on the amount of coal substitution.

Depending on the substitution, it is possible to reduce the total CO2 emissions by 19 %.

Substitution
[%]
0
20
40
60
Table 48.

Operational CO2-Reduction
[%]
0
12
24
36

CO2-Reductions

Total Reduction
[%]
0
6
13
19

In order to calculate the monetary value of the CO2 certificate, the highest spot market prices for
emission allowances from 2008 to 2011 are being considered

97A price of 18 (cid:188) – 35 (cid:188) is assumed for the year 2013, this lies above the average price in the last 3 years
(16.40(cid:188)). The results of these calculations are summarized in Table 49. The case of non-substitution
with bio carbon yields additional cost of about 181,000 (cid:188) to 351,000 (cid:188). On the other hand, using 60%
substitution could yield additional revenue between 18,000(cid:188) and 37,000 (cid:188).

Substitution

[%]
0
20
40
60
Table 49.

(cid:153)CO2

[t]

58,192
54,493
50,794
47,096

allocated
certificates
[t]

(cid:168)CO2
certificates
[t]

18
(cid:188)

48,150
48,150
48,150
48,150

-10,042
-6,343
-2,644
1,054

-180,748
-114,173
-47,599
18,976

Additional cost in the third trading period

25
(cid:188)

-251,038
-158,574
-66,109
26,355

35
(cid:188)

-351,454
-222,003
-92,553
36,898

Figure 88 shows the price variation as a result of substitution. Positive results are yielded from 54%
Substitution.

Figure 88.

Price Variation

This techno economic evaluation on the basis of the data from DEW Siegen shows for an exemplary
price of 18 (cid:188) per ton of CO2 that the total savings for the steel plant by a replacement of 60 % of the
common anthracite coal by biochar would be about 11,000 (cid:188) per year. Assuming a price of 35 (cid:188) per ton
of CO2 that would mean even savings up to 388,000 (cid:188) per year.

These calculations are based on assumptions and the price for biochar is unaccounted. Up to now there
does not exist an official market for biochar which can be used in steel mills. Most part of biochar
production is still in pilot scale state. So the prices per ton of produced biochar are not representative.
Industrial scale production and the development of different production processes for different qualities
of biochar is currently under construction. In the next few years the industrial scale production of
different biochar qualities is expected and according to this the development of a market and a market
price.
However, rising prices for additional CO2 certificates are expected for the future. In Addition to that
increases of the prices for fossil coal are expected, too.

98Moreover, in these evaluations possible savings from syngas can be considered. These project showed
the problems arising with syngas utilization in electric arc furnaces. Syngas can be used as fuel for other
type of furnace, as re-heating furnaces, or can be used for power generation, directly inside the
pyrolysis plant.
Another by-product from pyrolysis which can be used to save cost from biomass utilization is tar. Tar
can be mixed with charcoal itself as binding agent for char briquettes production, or can be sold as
chemical.
Syngas and tar utilization would increase the economical advantages from charcoal practice.

In general the use of biochar puts the electric steel mills in a position to avoid CO2 emissions which are
relevant for the EU ETS like the emissions from fossil carbon. Therefore, depending on prices for
biochar and its processing, the use of biochar instead of fossil carbon should, apart from the positive
ecological effects, also have a positive effect on the economics of the electric steelmaking process.

99CONCLUSIONS
The global objective of the project is to investigate the partial or total substitution of coal and natural
gas with charcoal and biogas produced from pyrolysis of biomass. The char is used as injectable powder
or charged in the basket.
The characteristics of char and biogas, and the related pyrolysis process, are tailored in order to match
the requirements for their utilisation in EAF.

(cid:131) Optimization of pyrolysis process and production of char according to the indication obtained

from laboratory and pilot activities performed in the first half of the project.

(cid:131) Laboratory tests were carried out to study under controlled conditions char reactivity and slag

(cid:131)

(cid:131)

(cid:131)

foaming promoted by char
Pilot EAF tests before industrial tests revealed that steel and slag compostion are not altered by
coal substitution by char
Industrial tests have been performed replacing coal with char. Both char charging and injection
have been tested
Syngas utilization in EAF burners, instead of natural gas has been simulated by means of CFD
calculations. The used syngas composition is the one from pyrolysis tests (WP5).

The tests performed (both pilot and industrial) showed that coal can be replaced by char, both for
charging and injection to promote foaming.
In case of charging the following aspects should be deeply investigated:

(cid:120)

(cid:120)

char reactivity: char start burning during charging. Char reactivity depends on high surface
area, volatile content and powders dispersion during charging. Proposed solution is a char pre-
treatment with briquetting stage before charging;
slag foaming: some trials showed good foaming behaviour, other trials were not satisfactory.
Proposed solutions are improvement of injection system and utilization of additives togheter
with char powder to increase char/slag wettability and promote reaction of char with iron oxide.
The injection system must ensure char injection below the slag

Moreover, syngas utilization in EAF burners, instead of natural gas has been simulated by means of
CFD calculations. The used syngas composition was that arising from the pyrolysis tests. Syngas
utilization leads to a decrease of EAF efficiency.

Techno economic evaluation carried out considering char cost and CO2 emission leads to the conclusion
that:
(cid:120)

official market for biochar, which can be used in steel mills, does not still exist. Most part of
biochar production is still in pilot scale state. So the prices per ton of produced biochar are not
representative. Literature reports prices ranging from 160 to 400 (cid:188)/t of produced char.

(cid:120)

exemplary price of 18 (cid:188) per ton of CO2 partially compensate actually higher price of charcoal.

In the next few years the industrial scale production of different biochar qualities is expected and
according to this the development of a market and a market price.
However, rising prices for additional CO2 certificates are expected for the future. In Addition to that
increases of the prices for fossil coal are expected, too. In general the use of biochar puts the electric
steel mills in a position to avoid CO2 emissions which are relevant for the EU ETS like the emissions
from fossil carbon.

100REFERENCES

1. Ulcos ULCOS Periodic activity report – 5th year
2.

R. Teodoro da Costa and F. Mayrink Morais: Charcoal, renewable energy source for steelmaking
process. Rev. Met. Paris, N°5 (May 2006), pp. 203-209
Biomass sustainability La Revue de Métallurgie - CIT - Octobre 2009

3.
4. H. Pfeifer, M. Kirschen and J.P. Simoes, Thermodynamic Analysis of EAF Electrical Energy
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211–232
Cedric Briens, Jan Piskorz, Franco Berruti: Biomass Valorization for Fuel and Chemicals
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5.

6. G. Chen, J. Andries, Z. Luo, H. Spliethoff: Biomass pyrolysis/gasification for product gas
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7. Karin Ericsson_, Lars J. Nilsson: Assessment of the potential biomass supply in Europe using a

8.

9.

resource-focused approach. Biomass and Bionergy, 30 (2006) 1–15
E. Alakankas, A.Heikkinen, T. Lensu, P. Vesterinen: Biomass Fuel Trade in Europe, summary
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10.

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12. G. Fiorese, M.Gatto, G. Guariso; 14° conference of Italian society of ecology, October 2004
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improve chemical energy yield and performance of dedusting in airtight EAF. ECSC project 7210-
PR/328, Final Report. 2006
Improved EAF process control using on-line offgas analysis. 12RFCS-CT-2006-00004, project in
progress

15.

16. H. Goodfellow, D. Zuliani, M. Bianchi Ferri: Holistic Optimization(cid:140) of EAF Furnaces - Past,

Present and Future. 9th European Electric Steelmaking Conference, Krakow, Poland; May 2008

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pyrolysis through real case study”. Università La Sapienza di Roma, a.a. 2006/2007

18. Chen, J.-Y. (1988). A General Procedure for Constructing Reduced Reaction Mechanisms with

Given Independent Relations, Combust. Sci. Technol., 57, 89-94.

19. Chen J.-Y. (1997). Development of Reduced Mechanisms for Numerical Modelling of Turbulent

Combustion. CERMICS-ENPC Cite Descartes - Champus sur Marne, France 1997.

20 F. Magnussen: On the Structure of Turbulence and a Generalized Eddy Dissipation Concept for

Chemical Reaction in Turbulent Flow; 19th AIAA Meeting, St. Louis, 1981.

21 T. Norgate, D. Lanberg, Environmental and Economic Aspects of Charcoal Use in Steelmaking, ISIJ

International, vol 49 (2009), No. 4, pp 587-595

22 A. Fallot et al, Biomass sustainability, availability and productivity, la Revue de Metallurgie, CIT,

October 2009

23 DE CASTRO, L.-F.-A.; TAVARES, R.-P.: Charcoal blast furnaces process control, Proc. of
Association of Iron and Steel Technology Conference, Nashville, USA, September 2004, P. 1.459-
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24

LOVEL, R.-R.; VINING, K.-R.; DELL´AMICO, M.: The influence of fuel reactivity on iron
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Trondheim, Norway, 2007

10125

Krassnig, H.-J., H. Sommerauer, H. Fohringer, R. Krump und Ch. Koubek: Optische Detektion
und Regelung der Schaumschlackenhöhe am Elektrolichtbogenofen, Stahl und Eisen (2011),
Heft 10

26 Thermocalc

102EXPLOITATION AND IMPACT OF THE RESEARCH RESULTS

Application: the project results can be applied in all EAFs. Project results that coal substitution by char
is feasible: the steel, slag and furnace operating parameters are not modified significantly. Also the
absence of environmental increase of pollution due to char has been verified. The utilization of char as
charge material, on a routine basis needs industrial experimentation to optimize the operating practices.
The application as foaming agent (injection) needs also further experimentation to stabilize the foaming
process and modify the injection system and injection practice in general.

Advantages: char eliminate the dependency from fossil coal and reduces the CO2 emissions.

Patent: project results can not be transformed into a patent. The eventual modification of the injection
system may be protected by a patent, but further research activities is necessary and also subsequent
industrial validation is necessary

Publications: during the project have been produced five publications.

Other aspects: the possibility to use char form biomass to replace fossil coal is strongly related to the
local availability of biomass. The availability of biomass in the surrounding of the steel plant, and the
reduce of the CO2 emission increase the economicity of this technology.
Moreover the utilization and transformation of biomass into charcoal can generate new local
economies.

103LIST OF SYMBOLS AND ABBREVIATIONS
BCB
CSM
DEW
FENO
HHV
IP
LHV
MH
RC
RWTH
TG

biochar briquettes
Centro Sviluppo Materiali SpA - partner
Deutsche Edelstahlwerke GmbH, Deutsche Edelstahlwerke, - partner
Ferriere Nord - coordinator
higher heating value
Imperial College - partners
lower heating value
Stahl- und Walzwerk Marienhütte Ges. m. b. h.- partner
reference coal
Rheinisch Westfälische Technische Hochschule Aachen, - partner
termogravimetric apparatus

LIST OF FIGURES

Figure 1.

(a) Gross consumption of renewable energy sources in Austria in the year 2003
(b) Biomass potential in Styria

Figure 2.

Scheme of laboratory termogravimetric (TG) apparatus

Figure 3.

Example of
temperature

thermogravimetric tests under

temperature gradient and constant

Figure 4.

Pyrolysis reactor based on a Gray King Furnace

Figure 5.

Figure 6.

Figure 7.

Char yields (as percentage of the original biomass in dry ash free basis) in the pyrolysis
of beechwood in a Gray-King reactor as a function of temperature for three ranges of
particle size.

Char, gas and tar yields as a percentage of the original biomass (dry basis) in pyrolysis
of miscanthus (particle size range: 0.212-0.5 mm) in a Gray-King reactor as a function
of temperature.

Char yield as a percentage of the original biomass (dry basis) as a function of
temperature (°C) in experiments conducted in the Gray-King reactor. Three biomass
samples were used: Corn Stalk (CS), Sorghum (SO) and Switchgrass (SW).

Figure 8

Optical image of char sample from grapewine, after tests at 600 and 500°C

Figure 9

Grain size distribution of char samples

Figure 10

Light-optical microscope image of unprocessed grape seed char (magnification 20x)

Figure 11.

Light-optical microscope image of grape seed char after short processing in mortar
(magnification 200x)

Figure 12.

Light-optical microscope image of grape seed char after short milling (magnification
200x)

Figure 13.

Gas concentration measured by mass spectrometer and Ar normalised.

104Figure 14.

Heating values of syngas and char obtained in the same TG test

Figure 15.

Figure 16.

Figure 17.

Figure 18.

Figure 19.

TGA non-isothermal char reactivity tests of beechwood chars produced in the Gray-
King reactor. Curves of fraction of remaining weight for the different chars and
temperature as a function of time are shown.
W: measured weight; W0: starting weight

TGA proximate analysis of raw beechwood and beechwood chars produced in the
Gray-King reactor. Curves of fraction of remaining weight of the different chars and
temperature as a function of time are shown.

TGA proximate analysis of raw miscanthus and miscanthus chars produced in the
Gray-King reactor. Curves of fraction of remaining weight of the different chars and
temperature as a function of time are shown.

TGA proximate analysis of grapeseed char produced at Tecnocentro. Curves of fraction
of remaining weight of the grapeseed char and temperature as a function of time are
shown.

TGA proximate analysis of coal samples currently used at Ferriere Nord. Curves of
fraction of remaining weight of the grapeseed char (as percentage of initial biomass,
left axis) and temperature (ºC, right axis) as a function of time are shown. Coal A:
metallurgical coke; Coal B: injected coal (fine particles); Coal C: injected coal (coarse
particles); Coal D: anthracite loaded in the basket.

Figure 20.

The atmospheric pressure wire mesh reactor.

Figure 21.

Char yield (as a percentage of initial sample weight in dry, ash free basis) as a function
of holding time in wire mesh reactor experiments with CO2 as carrier gas at
atmospheric pressure, heating rate of 1,000°C/s and peak temperature of 850°C. Coal
A: metallurgical coke; Coal B: injected coal (fine particles); Coal C: injected coal
(coarse particles); Coal D: anthracite loaded in the basket.

Figure 22.

Char yield (as a percentage of initial sample weight in dry, ash free basis) as a function
of holding time in wire mesh reactor experiments with CO2 as carrier gas at atmospheric
pressure, heating rate of 1,000°C/s and peak temperature of 850°C.

Figure 23.

Factors influencing the foamy slag formation

Figure 24.

Scheme of the demonstrative plant used by Tecnocentro to design industrial pyrolysis
tests

Figure 25.

Enerpol pyrolysis plant (Tecnocentro)

Figure 26.

Syngas composition obtained during preliminary pyrolysis test at 550°C, with rotating
speed of 3 rpm

Figure 27.

General view of the EAF with the position of the installed burners

Figure 28.

Viscosity of starting and modified slag. Viscosity is calculated with Urbain model [9].

Figure 29.

Specific amounts of carbon used at DEW (2006-2009)

Figure 30.

Optical Foaming Slag Management (OFSM)

Figure 31.

Crucible filled with slag and carbon mixture (left) and crucibles in the furnace (right)

105Figure 32

Slag foaming with injection coal from FENO (left) and DEW (right)

Figure 33.

Slag foaming trials with grape seed char

Figure 34

Sequence of the slag-carbon-reaction with different carbonaceous materials as a subject
to the temperature (at the upper right corner in each picture)

Figure 35

Comparison of the foaming height with different carbonaceous materials

Figure 36

Pictures from the video recording of the slag foaming trials in a lab furnace; CO
bubbles (dark spot with arrow)

Figure 37.

Pilot Arc Furnace (left) and schematic representation (right)

Figure 38.

Biochar from Tecnocentro (left); Biochar from wood gasification plants (right)

Figure 39.

Results from ash analysis of biochar from wood gasification plants.

Figure 40.

1.6 kg of biochar fines (left) and 1 kg of anthracite coal (right)

Figure 41.

Lancing operation of coal and oxygen (left) and IOB pilot lancing system (right)

Figure 42.

Steel composition after pilot trials

Figure 43.

Slag compositions of pilot furnace trials

Figure 44.

First agglomeration tests (a-c)

Figure 45.

Comparison of green strength and strength after 3 days of drying

Figure 46.

Biochar briquette (left) and anthracite coal (right)

Figure 47.

Grain size distributions (left) and mass fractions (right) after vibrating sieve tests

Figure 48.

Grain size distributions (left) and mass fractions (right) after drop tests

Figure 49.

Crucible of pilot furnace charged with a first scrap layer and biochar briquettes (BCB)

Figure 50.

Steel compositions of BCB and RC trials

Figure 51

(a) Slag compositions of BCB and RC trials
(b) P2O5 content of BCB and RC slag

Figure 52.

Off gas composition using anthracite coal

Figure 53.

Off gas composition using biochar from Tecnocentro

Figure 54.

Off gas composition using biochar from wood gasification plants

Figure 55.

BCB Off gas composition using biochar briquettes (BCB)

Figure 56

Semi industrial briquettes production

Figure 57

Improvement of char injection: (a): installing a lance for under slag injection; (b) using
a double jet for slag penetration

106Figure 58.

Charging of biochar fines at DEW Siegen

Figure 59.

Slag analysis of reference and biochar charge (left) and basicity (right)

Figure 60.

Steel analysis of reference and biochar charge

Figure 61.

Secondary injection system for biochar fines

Figure 62.

Charging the injection machine at DEW Siegen

Figure 63.

Slag composition of biochar trials

Figure 64.

Slag basicity of biochar trials

Figure 65.

Problems occurring while using biochar fines as injection coal

Figure 66.

Electric Arc Furnace and Injection Equipment at MH EAF.

Figure 67.

Video images of Injection tests with different char samples

Figure 68.

EAF cycle of injection Test A

Figure 69.

Slag Index detected by the OFSM system

Figure 70.

slag foaming mechanism using char

Figure 71.

Scheme of burner currently used at FENO steelplant

Figure 72.

Boundary conditions used for CFD calculations

Figure 73.

Calculation of the burning efficiency, for the three working conditions with natural gas.

Figure 74.

Comparison of flame temperature in case of natural gas and syngas burning.

Figure 75.

Difference of efficiency of burner in case of natural gas (NG) and syngas

Figure 76.

Flame aspect and temperature in case of feeding with syngas the current burner, a
burner modified with swirl motion on oxygen and swirl motion on oxygen and syngas.

Figure 77.

Points of off gas measurement

Figure 78.

Off gas composition of an exemplary reference charge

Figure 79.

Off gas composition of biochar charge

Figure 80.

Schematic flowsheet of charcoal production

Figure 81.

Contribution of stages to global charcoal cost.

Figure 82.

Percentage of CO2-sources of an EAF process

Figure 83.

CO2 emissions for Ferriere Nord SPA for year 2011. The specific emissions were 78
Kg of CO2 / ton of steel produced by EAF.

Figure 84.

DEW CO2 emission balance of a given year

Figure 85

Global cost for CO2 emission from steel plant (Ferriere Nord), in four cases:

1071. Actual situation with fossil fuels
2. Substitution of charge coals

3.
4.

Substitution of injected coals
Substitution of syngas

Figure 86

Difference between costs (supplying + CO2 2missions) using onlys fossil carbons and
using biomas as total substitute for carbon in charge and injection, in seven different
market conditions

Figure 87

Necessary CO2-price for economical biomass utilization in electric steel production (calculated
for MH steel plant)

108LIST OF TABLES

Table 1

Friuli Biomass amount and potential energy availability [1,2,3]

Table 2.

Cultivated ligneous biomass (Dendro mass) availability in Arnsberg district and NRW
[13]

Table 3.

Agricultural residues availability in NRW compared with availability in Germany [14]

Table 4

Main advantages/disadvantages of considered biomasses

Table 5.

Physico-chemical characterization of selected biomasses. Moisture content ranges form
10-12 % in all the samples

Table 6.

Biomas ashes composition

Table 7

Results of laboratories thermogravimetric tests

Table 8.

Char characteristics after test at 500°C, duration 700s, for the four biomasses tested
(carried out by CSM; RWTH, DEW).
(*) Grapeseed Ash chemical composition by DEW/RWTH

Table 9.

Heating values of chars obtained from four different biomasses at three temperatures

Table 10.

Composition (%) and LHV of char and syngas as a function of temperature, for
mischantus.

Table 11.

Characteristics of coals currently used by industrial partners

Table 12.

Characteristics of fossil carbon and charcoal [23,24]

Table 13.

Char and gas percentage produced after different pyrolysis campaigns

Table 14.

Syngas composition, obtained with sorghum, at the pyrolysis temperature of 600°C.

Table 15.

Char characteristics obtained with forest residues (underbrush) and grapewine.

Table 16

Energy input of and chemical energy distribution of EAF of Ferriere Nord

Table 17

Chemical energy distribution of EAF of Ferriere Nord

Table 18

Table 19.

Mass Balances to estimate biomass necessary to replace coal in Electric Furnace of
Ferriere Nord.

Mass (kg) of formed ashes which derives from char charge and injection. Data refers to
single heat

Table 20.

Starting slag composition and the modification with ashes

Table 21.

Estimation of Cl presence into fumes and comparison with acceptability range of BATs
[10]

Table 22.

Annual carbon and biomass demand at DEW Siegen EAF

109Table 23.

Composition of foamy slag at DEW Siegen EAF

Table 24.

XRF analysis of the slag used for foaming trials

Table 25.

Oxides species composition derived from X ray analysis

Table 26.

Results of slag foaming trials

Table 27

Reactivity, specific surface area and pore volume of the tested materials

Table 28.

Composition of different biochar and reference materials

Table 29.

First conducted trials at pilot plant

Table 30.

Produced and tested blends for agglomeration tests

Table 31.

Chemical composition of biochar briquettes from wood gasification

Table 32.

Main characteristics of the electric furnaces of the industrial partners participating to the project.

Table 33

Trials and standard heats with steel analysis after EAF cycle (average values measured
during test heats are compared with average values of standard heats)

Table 34

Values of offgas compostion measured during industrial trials at Ferriere Nord

Table 35.

Results of the briquetting tests at Ferriere Nord.

Table 36

Table 37.

Table 38

Characteristics of char briquettes used in the second testing campaign at FENO,
compared with char used in this project

(a) Slag composition variation
(b) Variation of offgas composition during industrial trials with char at FENO

Variation of main production parameters recorded during industrial trials with char at
FENO

Table 39.

Feedstock quantities of the reference charge

Table 40.

Feedstock quantities of biochar charge

Table 41.

Feedstock of trial charges using biochar as injection coal

Table 42.

Slag analysis after char injection tests at MH

Table 43.

Technical data off gas analyzers

Table 44.

Operating data of an exemplary reference charge

Table 45.

Operating data of biochar charge

Table 46

Cost comparison of different feedstock for injection coal

110Table 47

Cost comparison of total costs for charcoals from different origins

Table 48.

CO2-Reductions

Table 49.

Additional cost in the third trading period

111ANNEX 1- SLAG FOAMING

By creating a foamy slag the following main benefits can be achieved: improvement of the heat
transfer, better arc stability, and protection of refractory material inside the furnace. Because of better
arc stability and less radiation losses, foaming slag practice leads to reductions in energy consumption,
electrode, consumption, noise level, and an increase in productivity. The foaming capability of the slag
depends on several parameters. The relationship of most important parameters is shown in Figure A1.

Figure A1

Parameters affecting the foaming capability [18]

The melting of scrap necessarily generates slag with a high level of silica from soil or sand inevitably
adhering to the scrap surface. Sulphur and phosphorus are usually present in the scrap as well. To
reduce their transfer to the steel it is necessary to employ a basic slag by adding lime and/or dolomite.
Good foaming capabilities can be achieved with a basicity CaO/SiO2 between 2 and 2.5.
Desulphurization and dephosphorization are the main metallurgical tasks for the slag. For example high
sulphur contents in the scrap/melt requires an higher amount of lime and carbon as well as higher
energy consumption and processing time. Slag is foamed by the rising of CO bubbles from the bath or
the generation of such bubbles directly in the slag. The generation scheme is illustrated in Figure A2.

112Figure A2

Process of elaboration of foamy slag [19]

During the initial foaming period the carbon content predominantly determines the process of
generation a foamy slag. This carbon content of the melt depends on the different scrap grades charged
to the furnace. To keep the C-content within the desired range for each single melt a constant mixture of
different scrap grades has to be obtained. According to the scrap mixture the necessary carbon is to be
injected or added as lump coke. In the second period carbon is injected in to the slag to reduce FeO and
to create CO bubbles leading to a further increase of the slag height.

113ANNEX 2
CALCULATION OF CO2 EMISSIONS FROM DEW STEELPLANT

According to Figure 80, the electrode and stock input are considered as operational (process related)
CO2 emission. The calculation of operational CO2 emissions of the electrodes is done according to
equation (1.1). The operational CO2 emission is the product of the annual electrode consumption, the
emission factor and reaction factor of the electrodes.

m

C, Electrodes
m

*conversion factor m(cid:32)

2CO ,Electrodes

(cid:32)

1400t*3.667

(cid:32)

2

CO ,Electrodes
5130t

(0.1)

For the process of steel production in the electric steel plant, the entire operational annual CO2 emission
on the raw material input, as well as a carbon balance for the input and output of carbon on scrap, steel
and other materials are calculated according to equation (7.4).

m

(cid:170)
(cid:172)

material input

m

2CO ,Output

(cid:32)

(cid:170)
(cid:172)

(cid:12)

(cid:16)

(cid:12)
(cid:11)
(cid:186)
* C % m * C % *conversion factor m
(cid:188)
503712 t* 1, 67% 408024 t* 0.34% *3.667

Stahl

(cid:32)

(cid:16)

(cid:11)
(cid:12)

(cid:11)

(cid:11)

(cid:12)

(cid:186)
(cid:188)

(0.2)

CO ,Output

2

(cid:32)

25739 t

The monthly material consumption is listed in Table below. The material input includes scrap, alloys,
coal and slag former. The material input yields an average of 1.67% for C-concentration value per year.
According to DEW, the average C- concentration value for produced steel is 0.34%.

January
February
March
April
May
June
July
August
September
October
November
December
Total

Material Input
[kg]
48,996,019
49,602,327
34,436,328
50,149,661
47,005,128
49,197,936
42,702,569
43,945,440
38,452,922
31,214,081
28,045,043
39,964,360
503,711,814

C in Input
[kg]
786,237
854,427
517,907
828,786
794,885
813,560
732,714
734,344
671,336
551,218
466,197
682,265
8,433,876

Portion
[%]
1.60%
1.72%
1.50%
1.65%
1.69%
1.65%
1.72%
1.67%
1.75%
1.77%
1.66%
1.71%
1.67%

C-concentration per batch

The annual energy related CO2 emissions of the combustion are the product of the fuel consumption,
the net calorific value, the calorific value related emission factor and the oxidation factor of the fuel.

(cid:11)

V

natural gas

(cid:12) (cid:11)
(cid:12) (cid:11)
* net calorific value * conversion factor

(cid:12)

m(cid:32)

CO , natural gas

2

(0.3)

114m

CO , natural gas

2

(cid:32)

(cid:11)
13498000 Nm * 10.121

(cid:12)

3

(cid:167)
(cid:168)
(cid:169)

kWh
3
Nm

(cid:183)
(cid:167)
* 0.2 kg
(cid:184) (cid:168)
(cid:185) (cid:169)

CO
2
kWh

(cid:183)
(cid:184)
(cid:185)

(cid:32)

27323 t

For the case of substitution the operational CO2 emissions and the total CO2 emissions are calculated on
the basis of the available process data: A production quantity of 60% carbon steel and 40% stainless
steel is considered in this example.

Carbon Steel:

503712 t* 1.67% * 100% 60% 408024 t* 0.34% *3.667* 60% 4347t

(cid:16)

(cid:16)

(cid:32)

(cid:11)

(cid:12) (cid:11)

(cid:11)

(cid:12)

(cid:12)

(cid:11)

(cid:12)

(cid:186)
(cid:188)

(cid:170)
(cid:172)

Stainless steel

(cid:170)
(cid:172)

(cid:11)
503712 t* 1.67% 408024 t* 0.34% *3.667*(40%) 10295 t

(cid:16)

(cid:32)

(cid:12)

(cid:11)

(cid:12)

(cid:186)
(cid:188)

The dependency of the balance of CO2 emissions is shown in table below.

Substitution

Structural
Steel
[t]
15,443
11,745
8,046
4,347

[%]
0
20
40
60
The balance of CO2 emissions

Stainless
steel
[t]
10,295
10,295
10,295
10,295

Electrodes(cid:3) (cid:153)(cid:3)

Natural(cid:3)gas(cid:3) (cid:153)CO2(cid:3)

[t]
5,130
5,130
5,130
5,130

[t]
30,869
27,170
23,471
19,773

[t]
27,323
27,323
27,323
27,323

[t]
58,192
54,493
50,794
47,096

115European Commission

EUR 26208 —  Sustainable EAF steel production (GREENEAF)

Luxembourg: Publications Office of the European Union

2013 — 115 pp. — 21 × 29.7 cm

ISBN 978-92-79-33614-0
doi:10.2777/44502

117