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Energy Output Through EAF Off-Gas

–

Modelling the EAF Off-Gas System

VALEAF workshop, Aachen, 23.04.2015

Thomas Meier – RWTH Aachen

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20 – 40 % energy output from EAF melting process through off-gas

Off-Gas Energy Output

kWh/t %

carburizing agents 191 23,6

natural gas burner 50 6,2

chemical reactions 123 15,2

electrode consumption 28 3,4

ΔC steel 25 3,1

flue gas 169 20,7

vessel cooling 71 8,8

top cover cooling 37 4,6

slag 31 3,8

heat loss 69 8,5

balance difference 37 4,6

electric

energy

total energy input

useful

energy

(steel)

Source: Krüger, K.; Pfeifer, H.; Praxishandbuch Thermoprozesstechnik

169 21 %

41 %

Source: Yamazaki, M.; Sato, Y.;Seki, R.; AISTech (2011)

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Development of operating conditions to improve chemical energy yield and

performance of dedusting in airtight EAF [22973]

07.2002 – 06.2005: CSM, BFI, RWTH-IOB, ORI, GMH, TKN

Objectives:

New measurement techniques and operation conditions for airtight operation

Development of operation procedures to increase the use of chemical energy

Definition of operating conditions and plant configurations to obtain a controlled

amount of exhaust gas, dust production and polluting emissions

Results:

Airtightness was nearly achieved, but accurate process control is necessary

First development of dedusting system calculation model

Former RFCS Projects on Off-Gas Topics

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Improved EAF process control using online off-gas analysis – OFFGAS [25048]

07.2006 – 06.2009: RWTH-IOB, DEW, TKN, BFI, MH, CSM, ORI, Tenova, CRM

Objectives:

Increasing efficiency of oxygen injection and energy transfer to scrap and melt

Off-gas measurements at four industrial EAFs for basic model data

Process model development for optimized decarburisation, energy monitoring

system and optimized energy efficiency and post-combustion

Results:

Increase in EAF efficiency was obtained by using the EAF models

Further EAF dedusting system model development

Former RFCS Projects on Off-Gas Topics

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Increasing energy costs and statutory provisions or incentives leading to

increased offers and interest in process control through off-gas measurements

and waste heat recovery from EAF off-gas

Further investigation of off-gas related questions necessary

Optimising the EAF melting process and the EAF control

Prediction of waste heat recovery potential and its optimisation

Optimised plant design and operator assistance

Therefore:

Connection of EAF process simulation model with model of dedusting system

EAF and Dedusting System Modelling

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IOB EAF process model based on EAF model from Logar et al.

Deterministic model with fundamental thermodynamic/physical equations

for better adaptability to different EAFs

Process simulation for better understanding of energy and mass transfers in EAF

Model Input: mode of operation, EAF geometry

Process simulation with ordinary differential equations (ODEs)

Simulation results: temperatures, masses, heat flows, compositions

EAF Process Simulation Model

𝑑𝑄

𝑑𝑡= −𝐴𝜆

𝑑𝑇

𝑑𝑥

…

Output:

T, m, Q, …

Input:

operation data

EAF process

simulation model

Dedusting

system model

2CO + O2 2CO2

2H2 + O2 2H2O

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8 homogeneous phases with mass, temperature

1) Roof

2) Walls

3) Solid scrap

4) Liquid melt

5) Solid slag

6) Liquid slag

7) Electrodes

8) Gas phase

EAF Process Simulation Model

2

1

2

3

8

5

6

7

4

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Model structure and functioning

EAF Process Simulation Model

Data

module

Energy

distribution

module

Chemical

reaction

module

Input

mass

module

Thermal

and

mass

calculation

module

Calculated

results

𝑚𝑠𝑡𝑒𝑒𝑙

𝑐𝑠𝑡𝑒𝑒𝑙

𝑚𝑎𝑑𝑑𝑖𝑡𝑖𝑜𝑛𝑠

𝑐𝑎𝑑𝑑𝑖𝑡𝑖𝑜𝑛𝑠

𝑚𝑖𝑛𝑝𝑢𝑡

𝑇

𝑚

𝑇 𝑃

𝑃𝑎𝑟𝑐

𝑃𝑏𝑢𝑟𝑛𝑒𝑟

𝑃𝑐ℎ𝑒𝑚𝑖𝑐𝑎𝑙

𝑚

EAF Model

Melting

geometry

𝑚

𝑣𝑖𝑒𝑤 𝑓𝑎𝑐𝑡𝑜𝑟

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Simplified gas phase in EAF model from Logar et al. (CO, CO2, N2, O2)

Detailing gas phase calculations for improved dedusting system calculations

Further developments:

Variable melting geometry

Detailed heat radiation with complete view factor

calculation including gas radiation

Further gas components: H2, H2O, CH4

New phase: Electrode

Implementation of basic reaction mechanisms

(water gas shift reaction, Boudouard reaction,

post combustion)

EAF Model – Gas Phase

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0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 500 1000 1500 2000 2500 3000

Tem

pe

ratu

re [

°C]

Time [s]

T_liquid_melt

T_gas

T_solid_scrap

Temperatures

EAF Model – Results

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-60

-40

-20

0

20

40

60

80

100

120

140

160

180

0 500 1000 1500 2000 2500 3000Po

we

r [M

W]

Time [s]

P_electric

Q_solid_scrap

Q_liquid_melt

Q_water

Power and heat flows

EAF Model – Results

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Unsteady and nonlinear simulation of dedusting system in modular design

Water cooled pipe:

Input : EAF off-gas temperature, composition, volume flow rate (STP),

pipe and cooling system specifications

Fundamental thermodynamic calculations

(properties, mixing, post combustion, heat transfer coefficient, temperature)

Output: off-gas temperature, volume flow rate, composition,

heat flow to cooling

Usage for back calculation through neural network and measurements in non

critical sections possible

Dedusting System Model

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Model structure and functioning for water cooled pipe

Dedusting System Model

Temperature

Iterative

Calculation

Module

Properties Calculation Module

Amount of

Substance

Normal

Density Viscosity

Heat

Capacity Enthalpy

Mixing

Module

PC

Module

Heat Transfer

Module

Gas HTC

Module

(radiation,

convection)

Cooling

HTC

Module

PC : Post Combustion HTC: Heat Transfer Coefficient

Calculated

results

Dedusting

System Model

𝑄

𝑇

𝛼𝑐𝑜𝑜𝑙 𝑇 𝛼𝑟𝑎𝑑

Da

ta M

od

ule

Off-Gas Data

Cooling Data

Leak Air Data

Pipe Data 𝑇 𝛼𝑐𝑜𝑛

𝑇 𝑋𝑖 𝑇 𝑋𝑖

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Boundary conditions:

Input from EAF process model

Cooled pipe with post combustion

Length = 20 m; Diameter = 3.6 m

Cooling water: m = 150 kgs ; Tin = 27 °C

False air input: 2 x off-gas volume flow rate (STP) LAx2

4 x off-gas volume flow rate (STP) LAx4

Dedusting System Model – Results

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Temperatures

Dedusting System Model – Results

0

500

1000

1500

2000

2500

0 500 1000 1500 2000 2500 3000

Tem

pe

ratu

re [

°C]

Time [s]

T

T_EAF_off-gas T_PC_LAx2 T_Out_LAx2

T_PC_LAx4 T_Out_LAx4

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Heat flow to cooling

Dedusting System Model – Results

0

5

10

15

20

25

30

0 500 1000 1500 2000 2500 3000

He

at f

low

[M

W]

Time [s]

Qdot

Qdot_LAx2

Qdot_LAx4

LAx2:

7185 kWh

≙ 85 kWh/t

ø ≈ 9.62 MW

LAx4:

3937 kWh

≙ 46 kWh/t

ø ≈ 5.27 MW

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Exergetic investigation of CO and H2 post combustion in dedusting system

stoichiometric overstoichiometric

EAF Off-Gas – Average Exergy Flows

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High energy output through EAF off-gas

Optimisation potential:

Process control

Waste heat recovery through steam production

Cheap and fast estimation of waste heat recovery potential through models

Control of leak air input in dedusting system for increased steam production

Conclusion

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Further EAF process simulation model development:

Gas phase reactions via equilibrium with Gibbs energy minimisation

Model validation

Further dedusting system model development:

GUI for better usability

Steam generation

Model validation

Neural network utilisation for off-gas back calculation

Model interface between both models

Prospects

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Contact:

Thomas Meier

RWTH Aachen University

Department for Industrial Furnaces and Heat Engineering

Kopernikusstraße 10

52074 Aachen

Germany

meier@iob.rwth-aachen.de

www.iob.rwth-aachen.de