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Viscosity of partially crystalline slags Daniel Schwitalla, Arne Bronsch, Stefan Guhl

IEC - Freiberg

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Outline

1. Motivation

2. Slag preparation

3. Equipment and Demonstration

4. Modelling

5. Conclusion/Outlook

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Motivation

Heat conductivity

Viscosity

Surface tension

Form, size of boundary layer

Flow speed, Layer thickness

Temperature profileinfluence on other properties

process optimization based on models/database for physical property prediction

*IPP group - Dmitry Safronov - slag_submodel

*Internal source

Project: Virtual High Temperature Conversion

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Motivation

Approach: Create conditions close to full scale

gasifiers during measurement

Influence factors for viscosity: • Composition • Temperature • Oxygen Partial Pressure (FeO/Fe2O3) • T-History (cooling rate) • Shear Rate (newtonian/non-newtonian) • Crystallization Nuclei

Fully liquid (newtonian) slag

Partially liquid (non-newtonian) slag

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Slag preparation

Equilibrate slag in gas-atmosphere at desired T

for calculated po2

Ash coal according to DIN*

Slag ash in air at Tliq+100 K

XRF

Continue with viscosity/surface tension

measurement at specific po2

Calculate specific po2

for specific FeO-content Glass/HF-cleaning

procedure for reduced material strain

XRF

XRF

XRF

Optimizations: Reduced wear on material Reproducibility Optimum sample characterization

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Viscosimeters

Bähr Viscometer Anton Paar MCR 302 - T-range and pO2-range of full scale gasifiers

- Platinum measurement system - Calibrated with DGG standard float glass

- High frequency induction heater for fast heatup

- Small measurement system with low eccentricity for high shear rates

- Robust

- Standard resistive heating system (Tmax=1700 °C)

- Accurate control of gas atmosphere

- Torque-sensitive for low shear rates (10 -5 - 200 mNm)

020406080

100

1300 1350 1400 1450 1500 1550 1600 1650

visc

osity

[Pas

]

T [°C]

Ringtest of 4 viscosimeters

Ringtest validated with Siemens Fuel Gasification & Institute of Iron and Steel in Freiberg

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Viscosity measurement*

•Investigation of: • Thermal History (Cooling Rate) • Oxygen Partial Pressure; FeO/Fe2O3-Ratio

verified with Mößbauer spectroscopy • Shear Rate • Solid Volume Fraction

0

50

100

150

200

250

300

350

400

1150 1160 1170 1180 1190 1200 1210 1220 1230 1240 1250

Visc

osity

[Pas

]

T [°C]

-2 Kmin; air; 25 1/s

-10 Kmin; air; 25 1/s

-2 Kmin; red; 25 1/s

-2 Kmin; red; 50 1/s

-10 Kmin; air; 25 1/s

-2 Kmin; air; 25 1/s

-2 Kmin; red; 25 1/s

-2 Kmin; air; 25 1/s

*Data from Lusatian brown coal

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Solid volume fraction

• Intention: • Determine relationship between crystallization and viscosity • Fast and economical measurement of crystallization onset (Tcv)

• Procedure: • Copy conditions of viscosity measurement (atmosphere, cooling rate) • Drop sample into quenchpot freeze phase composition • subsequent analysis (XRD) for crystal species • Investigate crystallization for different cooling rates • DTA measurement for Crystallization onset at different cooling rates

Quench furnace

Air, CO, CO2, N2

PtRh-wire

Pt crucible & sample

Quenchpot with water

MoSi2-heater

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DTA vs viscosity measurements

DTA also reveals crystallization onset

-0.35

-0.3

-0.25

-0.2

-0.15

-0.1

-0.05

0

0

10

20

30

40

50

60

70

80

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100

1150 1200 1250 1300 1350 1400 1450

DTA

[µV]

visc

osity

[Pas

]

T [°C]

Lusatian slag under reducing conditions

-2 Kmin; red ; 12,5 1/s

DTA-curve

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Measurement evaluation*

-60-55-50-45-40-35-30

900 1000 1100 1200 1300 1400

DTA

[µV]

T in °C

Viscosity – CR=-2 K/min

-2K/min -1K/min

-60K/min

-20K/min

1280129013001310132013301340

0 20 40 60 80

T [°

C]

Cooling Rate [K/min]

DTA Tonset vs cooling rate

0.00.10.20.30.40.50.6

020406080

100

1270 1295 1320 1345 1370 1395

SVF

Visc

osity

[Pas

]

T [°C]

25 1/s 50 1/s

SVF - FactSage SVF - EXP

Supercooling can occur and lowers Tliq of slag FactSage calculations fail for accuracy DTA+Quench/XRD *internal source: partial results Master Thesis Tom Rosenhagen

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Modelling

• Database with 3781 slags and 5028 η(T) measurements from 77 authors in literature • Own measurements included:

• 41 samples • 199 measurements (various shear rates, atmospheres)

• 12 models for slag viscosity and Einstein-Roscoe Equation, link to FactSage for Solid Volume Fraction

• Application for prediction of η(T) for a given slag composition:

Slag Viscosity Toolbox*

Input: slag composition, T-range

search for “referenced slag system” in Database

test of implemented models with reference slag system

Output: prediction of slag viscosity with recommended model

*Duchesne MA, Bronsch AM, Hughes RW, Masset PJ. Slag viscosity modeling toolbox. Fuel 2013.

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Modelling

AALE – Average Absolute Logarithmic Error 𝜂 – effective viscosity 𝜂𝑙𝑙𝑙 – predicted viscosity value liquid phase 𝑎 – fitting factor for species

𝑓 – solid volume fraction in slag

*Duchesne MA, Bronsch AM, Hughes RW, Masset PJ. Slag viscosity modeling toolbox. Fuel 2012.

Input I. Slag composition and conditions

II. Viscosity measurements

IV. Fit a-factor for viscosity models by AALE-minimization

III. Viscosity Calculation [1]

Output V. Improved Model

𝜂 = 𝜂𝑙𝑙𝑙 ∙ 1 − 𝑎 ∙ 𝑓 −2,5 𝑎 = 𝑓(𝒔𝒔𝒔𝒔𝒔 𝒔𝒔𝒓𝒔; 𝒔𝒔𝒔𝒔𝒔𝒔𝒔)

Einstein-Roscoe-Equation **

**Roscoe R: The viscosity of suspensions of rigid spheres 1952

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Modelling Example

Classical Model

Classical Model + modified ER

model

Calculation of Solid Volume Fraction

with FACTSage™* or determine

experimentally

*currently modelled for solid fractions of anortite, hibonite, christobalite/tridymite

Outlook Expand range of a-factor

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50

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80

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100

1280 1300 1320 1340 1360 1380 1400

Visc

osity

[Pas

]

T [°C]

Lusatian brown coal measurement

25 1/s_-2 Kmin 50 1/s_-2 Kmin

0

10

20

30

40

50

60

70

80

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100

1280 1300 1320 1340 1360 1380 1400

Visc

osity

[Pas

]

T [°C]

Lusatian brown coal modelling

25 1/s_-2 Kmin Urbain Riboud Streeter

0.00

0.05

0.10

0.15

0.20

0.25

0

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40

60

80

100

120

140

160

180

200

1280 1300 1320 1340 1360 1380 1400

SVF

Visc

osity

[Pa

s]

T [°C]

Lusatian brown coal modelling

25 1/s_-2Kmin SVF

0.00

0.05

0.10

0.15

0.20

0.25

0

20

40

60

80

100

120

140

160

180

200

1280 1300 1320 1340 1360 1380 1400

SVF

Visc

osity

[Pa

s]

T [°C]

Lusatian brown coal modelling

25 1/s_-2Kmin Streeter+RE+a=f(SR;SVF) SVF

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Conclusion

Viscosity dependent on: • Temperature • Composition • Atmosphere • Shear rate • Thermal history

Simulating gasifier conditions during measurements delivers the most

valuable viscosity data for modelling

Database expansion ensures quick estimates over a wide range of compositions

Semiempirical approach (liquid phase model + Einstein Roscoe) accounts for crystallization/solid volume fraction

DTA + Quench/XRD measurements can determine Tcv and support systematic optimization of viscosity prediction/modelling

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Acknowledgement

TU Bergakademie Freiberg Institute of Energy Process Engineering and Chemical Engineering 09596 Freiberg - Germany Tel. +493731-39 4206 Fax +493731-39 4555 Email Daniel.Schwitalla@iec.tu-freiberg.de Web www.iec.tu-freiberg.de

This research has been funded by the Federal Ministry of Education and Research of Germany in the framework of Virtuhcon (Project Number 03Z2FN12).

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Lusatian slag

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Ma.

%

Lusatian - composition