solutions for internal recycling of steelmaking dusts and

K1-MET ǀ 2020-11-13 ǀ 1

Johannes Rieger, K1-MET

2020-11-13

ESTEP workshop “Resi4Future”

Co-authors: Wolfgang Reiter (K1-MET), Harald Raupenstrauch (Montanuniversität Leoben), Laura Lohmeier, Hans-Werner Schröder (both TU Bergakademie Freiberg), Christoph Thaler (voestalpine Stahl)

Solutions for internal recycling of steelmaking dusts and sludges

K1-MET ǀ 2020-11-13 ǀ 2

(1) K1-MET in a glance

• Research on residue treatment and recycling solutions

(2) Treatment of BOF dust for internal recycling

• Project partners and methodology

(3) Treatment of DR dusts and sludges for internal recycling


• Process concept

(4) Summary and outlook

• Next steps in the process developments

Agenda

K1-MET ǀ 2020-11-13 ǀ 3

K1-MET in a glance

Research Areas

Four symbiotic areas:

➢ Area 1: Raw Materials and Recycling

• Endeavours the best possible utilisation of all resources and

searches for residue treatment and recycling solutions

➢ Area 2: Metallurgical Processes

• Unites the core topics of metallurgical process

developments.

➢ Area 3: Low Carbon Energy Systems

• Is dedicated to the developments of carbon-lean steal

production.

➢ Area 4: Simulation and Analyses

• Represents the enveloping area for numerical developments

and data analyses.

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K1-MET Research Area 1

Recycling of residues from primary steelmaking

Blast Furnace –

Basic Oxygen Furnace

MIDREX® Direct

Reduction Process

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(2) Treatment of BOF dust for internal recycling – RecoDust process




• Process concept



Agenda

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Treatment of BOF dust for internal recycling

RecoDust (Flash-Reactor)

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Small-scale lab trials [1]

- Conveying behaviour of BOF dust

Computational Fluid Dynamics [2]

- Gas-solid reaction kinetics

- Design studies for reactor and burner

Pilot plant operation [1]

(Flash-Reactor)

- BOF dust treatment

- Definition of process

parameters

RecoDust Process

Project partners and methodology

[1] Montanuniversität Leoben, Chair of Thermal Processing Technology

[2] K1-MET

Project

partners

K1-MET ǀ 2020-11-13 ǀ 8

Reduction/slaggingT ~ 1,700 °C

λ = 0.7

DosingT ~ 40 °C

Steps of the RecoDust process Way of BOF dust within the

RecoDust process

BOF dust

RecoDust Slag

(Iron)

Crude zinc

oxideCoolingT ~ 800 - 150 °C

Post-combustionT ~ 1,700 - 800 °C

λ = 1.4

Gas cleaningT < 250 °C

Bag filter

Clean gas

RecoDust process concept

Pilot plant at Montanuniversität Leoben

[1] Reiter, W. et al.: The

RecoDust process -

Upscale of a pilot plant,

Steel Research

International, published

online, 2020

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• Requirements of the dust input [1]

• Free flowing

• Grain size <1 mm

• Dry

• Product 1 → Crude zinc oxide ZnO [2]

• Zinc extraction >95 %

• Washing process to remove halides

• Product 2 → Fe-rich fraction (= RecoDust slag [1, 2])

• Hard material, not leachable

• Low Zn content (0.1-0.5 wt.-%);

Fe~50 wt.-% (= FeO + Fe2O3);

slag formers ~40 wt.-% (B2 ~3)

RecoDust process

Feed requirements and products

Typical composition of the crude ZnO product (left)

and the iron rich RecoDust slag product from the

RecoDust process (right, [2])

[1] Raupenstrauch, H. et al.: RecoDust - an efficient way of processing steel mill dusts, J Sustainable Metallurgy 5(3), 310-318

[2] Geier, B. et al.: RecoDust-process for the recycling of steel mill dusts, METEC & 2nd European Steel Technology and

Application Days (ESTAD), Düsseldorf, 2015

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Possible internal use of the RecoDust slag

• Sinter plant or BF (iron substitute material)

• Energy for slag grinding important for added-value

• Material hardness and abrasivity depend on slag granulation

• Crushing energy ~ 25 kWh/t (compare with ore ~ 1kWh/t)

• Extremely abrasive (1,600 - 2,000 acc. to LCPC test [3])

Grinding process needs to be optimized

• Combination of crushing and sieving steps

Iron-enriched product (RecoDust slag)

Comparison RecoDust vs. Waelz and possible internal use

Species

(extraction from

the composition)

RecoDust

slag [1]

Waelz

slag [2]

FeO [wt.-%] 37.0 45.0

Zn [wt.-%] <0.5 <5.0

MgO [wt.-%] ~4.0 <6.0

SiO2 [wt.-%] ~4.0 <10.0

CaO [wt.-%] ~19.0 <26.0

Cl [wt.-%] n.a. <0.1

• Some species not directly comparable (BOF dust used for RecoDust, EAF dust for Waelz)

• High separation degree of zinc and iron with RecoDust process

[1] Geier, B. et al.: METEC & 2nd European Steel Technology and Application Days (ESTAD), Düsseldorf (Germany), 2015

[2] Von Billerbeck, E. et al., book contribution „Treatment of electric steelmaking filter dusts with the Waelz process“, 2014

[3] Kurosch, T. et al.: 1st Canada-US Rock Mechanics Symposium, Vancouver, 2007

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• Process concept



Agenda

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Treatment of DR dusts and sludges for internal recycling

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MIDREX® residue briquetting

• Cold-bonded agglomeration of MIDREX® waste products for a reuse in the process

• Project partners beside K1-MET

• voestalpine Stahl

• TU Bergakademie Freiberg, Institute of Thermal-, Environmental- and Resources' Process Engineering

Methodology

Project partners and methodologyProject

partners

Abrasion

resistance R30

(100) [%]

Briquette strength measurements [1]

- Compressive and abrasive strength

[1] TU Bergakademie Freiberg, Institute of Thermal-, Environmental- and Resources' Process Engineering

Briquetting of MIDREX® residues [1]

- Hydraulic stamp press

- Screening of binder systems

Reducibility prediction (left) and

thermochemic stability (right) [1] +

low temperature disintegration tests

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• Screened oxide fines➔ Fine-grained residue from iron ore pellet feed (Fetot 67.2%, Femet 0%)

• Dried sludge➔ By-product from top gas cleaning (Fetot 74.0%, Femet 29.5%)

• HBI screened fines➔ Fine-grained residue fraction (Fetot 88.7%, Femet 74.9%)

Quality requirements for materials to be used in the MIDREX® process

• Composition, stability, and metallurgical properties must be within certain value ranges

• Composition: Fe~67%; 3-4% gangue (especially low contents on silicon, alumina)

• Stability: compressive strength >35 MPa (green strength), abrasive strength R30 (100) >85%

MIDREX® residue treatment concept

Iron bearing residue fractions & quality requirements

[1] Lohmeier et al.: Briquetting of fine-grained residues from iron and steel production using organic and inorganic binders,

Steel Research International, published online, 2020

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• Fe-carrier mixture (wt-%)

• 30% screened oxide fines / 40% dried sludge / 30% HBI & process residues (dust, fines)

• Tested binder systems: Organic (cellulose, starch) and inorganic (bentonite clay) materials

Test procedure

(1) Material mixing (Eirich-Mixer) with varying contents of binder and water

(2) Material preheating (60°C) and briquetting (hydraulic stamp press)

• Briquetting parameters: 140 MPa, pressing time 3s, pressing temperature 60°C

• Briquette dimensions: cylindric shape, 3 cm diameter, 1.5 cm height

(3) Briquette hardening under ambient air (1 day)

(4) Executed tests: compressive strength, abrasion resistance, shatter strength, apparent density, low-

temperature disintegration, reduction test

MIDREX® residue treatment concept

Case study



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Case study

Main results – Mechanical + metallurgical properties



Design of Experiments (DoE, [1])

+ Primary blend

* Binary blend

o Tertiary blend

x Additional runs

Results for bentonite (extraction from [1])

Compressive strength Abrasion resistance R30 (100)

Metallurgical properties

+ Small low-temperature disintegration tendency (positive)

- Slow reduction, 80% red. degree after 300 min (negative)

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• Test parameters

• Sample mass: 2,100 g (53 briquettes)

• Temperature: 820 °C

• Reduction agent: H2 (12 L/min gas flow)

• Similar oxygen content in the sample after

3h reduction test duration

Case study

Main results – Reduction test

B1, B2…Bentonite-bounded briquette samples, P2…Ore pellet sample

[1] TU Bergakademie Freiberg, Institute of Thermal-, Environmental- and Resources' Process Engineering

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• Process concept



Agenda

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• No complex dust-pretreatment necessary

• Small facility

• No further additives to be charged

• Use of gaseous reducing agents

• Variable input quality (treatment of EAF

dusts also possible)

• High dezincification rate (separation Zn-Fe)

• Processing of RecoDust slag important to

reach added-value (iron substitute)

The RecoDust process

A concept for increased circular economy

Life cylce in steel industry (voestalpine)

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• Mixture of different waste materials processable via

cold-bonded briquetting

• High mechanical strength reached for all tested

binders

• Optimal recipes for high briquette strengths

• Bentonite: Binder 3.0 - 5.5% / H2O 3.7 - 7.0%

• Starch: Binder 3.0 - 8.0% / H2O 3.0 - 4.0%

• Cellulose: Binder 3.0 - 5.5% / H2O 5.0 - 8.0%

• Small resistance for low-temperature disintegration

of organic-bounded briquettes

• Low reduction speed of bentonite-bounded

briquettes


A concept for increased circular economy

Life cylce in steel industry (voestalpine)

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Outlook

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RecoDust process

• Upscale of the pilot plant (300 kg/h ➔ 1,000 kg/h)

• Optimized dust feeding system

• Increased process and energy efficiency

• Optimized product properties


• Increased thermal stability and quantify effect of better

reducibility for organic-bounded briquettes

• Quantify optimum size of bentonite-bounded briquettes

• Impact on reducibility has to be proven

• Concept of continuous agglomeration

• Transfer of hydraulic stamp press to a roller press

Open challenges

Next steps in the research projects

K1-MET ǀ 2020-11-13 ǀ 23

Questions?Dr. Johannes Rieger

K1-MET

Franz-Josef-Strasse 18, Leoben 8700, Austria

T.: +43 / 3842 / 402-2280

M: +43 / 664 / 88 32 24 99

[email protected]

Dr. Christoph Thaler

voestalpine Stahl

voestalpine-Strasse 3, Linz 4020, Austria

T.: +43 / 50304 / 15-73316

M.: +43 / 664 / 61 572 34

[email protected]

Project partners

- Montanuniversität Leoben, Chair of Thermal Processing Technology (Austria)

- TU Bergakademie Freiberg, Institute of Thermal-, Environmental- and

Resources' Process Engineering (Germany)

The research program of the competence center

K1-MET is running within COMET - Competence

Center for Excellent Technologies and is funded by:

• The Federal Ministry for Climate Action,

Environment, Energy, Mobility, Innovation and

Technology

• The Federal Ministry for Digital and Economic

Affairs

• The provinces of Upper Austria, Tyrol and Styria

Beside the public funding from COMET, the

research projects are partially financed by industrial

partners. Continuous support is given by

Upper Austrian Research GmbH

solutions for internal recycling of steelmaking dusts and

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