ammonia preparation in the tailpipe: spray/wall ...€¦ · urea biuret cyanuric acid ammelide 1 2...

KIT – The Research University in the Helmholtz Association

KIT - Institute for Chemical Technology and Polymer Chemistry (ITCP)

www.kit.edu

Courtesy of Bosch

www.dieselforum.org

Ammonia preparation in the tailpipe: Spray/wall interaction and

deposit formation

M. Börnhorst, C. Kuntz, S. Tischer, O. Deutschmann

Cross-Cut Lean Exhaust Emissions Reduction Simulations (CLEERS) Workshop, Sept. 18-20, 2018, Ann Arbor

Institute for Chemical Technology and Polymer Chemistry2

Ammonia preparation in the tailpipe

Marion BörnhorstSept. 20, 2018

Injection of a 32.5 wt.-% urea solution

(AdBlue®) used as precursor for ammonia

Formation of liquid and solid deposits by

incomplete evaporation and urea conversion

Serious loss of NOx reduction efficiency

Diesel oxidation catalyst and

particel filter

Selective catalytic

reductionSource: BMW

ASCDOC & DPF SCR

AdBlue

injection

2 NH3 + NO + NO2 2 N2 + 3 H2O

(NH2)2CO (l) NH3 (g) + HNCO (g)

HNCO (g) + H2O (g) NH3 (g) + CO2 (g)

Robert Bosch GmbH

[1] Brack, W., Untersuchung der Ablagerungsbildung durch Harnstofffolgeprodukte im Abgasstrang, PhD thesis (2015), 1-175

Endoscopic records from a hot gas test rig [1]

Urea

thermolysis &

hydrolysis

SCR reaction

Ammonia slip

catalyst


Liquid and solid deposits in SCR systems

Marion Börnhorst

SCR

Spray:

pinj, Tinj, minj

Gas:

Tg, pg, ug

Liquid Film:

Af, hf, Tf

Wall:

Θ, Ra, Tw

Evaporation

Thermolysis &

Hydrolysis

Solid deposit

Drops:

ud, dd, Td

Sept. 20, 2018

Solid by-products:

Biuret

Triuret

Cyanuric acid

Ammelide

Ammeline


Outline

Urea decomposition

• Deposit formation at a hot gas test rig

• Deposit characterization

Kinetic modeling

• Kinetic measurements on urea decomposition

• DETCHEMMPTR model

Integration toCFD

• Coupling of kinetic model with StarCCM+ simulation



Laboratory test rig

Hot gas test rig with integrated urea dosing system

Marion Börnhorst

Vertical compressor

FlowmeterDiffusor Contraction

Control unit

Measuring section

UWS tank

Injection/measurement cell designed

for undisturbed flow and optical access

TABELLE

Parameter Unit Operating range

Gas flow L/min 50 - 3000

Gas velocity m/s 0.5 - 25

Reynolds number - 1200 - 50000

Gas temperature °C 100 – 350

Injection mass flow kg/h 0.03 – 5.3

Injection pressure bar 5

Injection angle ° 33

Sept. 20, 2018


Deposit formation in lab test benchInjection

Marion Börnhorst

OP: Tgas= 300°C, Vgas= 1200 L/min, ugas = 11 m/s,

murea = 1 g/min, 3 x 40 min injection

Film formation during

injection

Evaporation leaves solid

deposits

Dissolution of existing

deposits

Deposit build-up over time

Sept. 20, 2018


Deposit sampling

OP Tgas / °C Vgas / L/min ugas / m/s

1 150 866 8.0

2 190 916 8.5

3 280 1030 9.5

4 320 870 8.0

Marion Börnhorst

1 2

43

- Three injection periods of 40 min

- UWS mass flow of 1 g/min

Sept. 20, 2018


Deposit Characterization

Marion Börnhorst

High Performance Liquid Chromatography (HPLC)

Deposit composition

3D-Structure analysis

Surface profile of deposits

Thermogravimetric analysis (TGA)

Decomposition kinetics

Keyence LJ-V7200

Laser profile sensor

Sept. 20, 2018


Deposit analysis by HPLC

Method development for qualitative and quantitative deposit analysis based on

Koebel et al. (1995) and Bernhard et al. (2011)

Separation and quantification of components by adsorption potential

Na2HPO4 buffer as solvent and eluent

Anion exchange column

Photodiode-array detector (UV/VIS)

Ure

a

Biu

ret

Me

lam

ine

Am

me

line

Am

me

lid

Cya

nu

ric

acid

Method validation and calibration by

standard solutions

Strong pH sensitivity affects

measurement accuracy



TGA procedure

Thermogravimetric analysis of

decomposition kinetics

Grinded, representative sample of deposit

TG Setup: Netzsch STA 409, TASC 414/2

Initial sample mass of 15 – 20 mg

Gas flow of 100 ml/min synthetic air

Temperature programm: heating rate

of 2K/min, from 40 to 700°C


Sample

crucible


TGA of urea and by-product decomposition

Marion Börnhorst

0

20

40

60

80

100

50 100 150 200 250 300 350 400 450 500 550 600

sam

ple

mass [%

]

Temperature [°C]

0

20

40

60

80

100

50 100 150 200 250 300 350 400 450 500 550 600

sam

ple

mass [

%]

Temperature [°C]

Urea

Biuret

Cyanuric acid

Ammelide

1

2

3

Sept. 20, 2018


0

20

40

60

80

100

0 100 200 300 400 500 600 700

Mass lo

ss / %

Temperature / °C

OP 1

urea

Characterization of OP 1 deposit

Marion Börnhorst

Deposit volume cm³ 16.87

Max. height mm 19.25

Mean height mm 5.24

Substance Urea Biu Triu CyA Amd Amn Mel Rest

Portion

[wt.-%]

65.6 0.2 0 0 0 0 0 34.2

Sept. 20, 2018


1 150 866 8.0

Characterization of solid deposits from urea water solution injected into a hot gas test rig, Börnhorst et al. (2018)


0

20

40

60

80

100

0 100 200 300 400 500 600 700

Mass lo

ss / %

Temperature / °C

OP 2

urea




2 190 916 8.5


Max. height mm 0.80

Mean height mm 0.47


Portion

[wt.-%]

57.0 9.7 2.2 0.4 0 0 0 30.7




Marion Börnhorst

0

20

40

60

80

100

0 100 200 300 400 500 600 700

Mass lo

ss / %

Temperature / °C

OP3

cyanuric acid

OP3

Sept. 20, 2018


3 280 1030 9.5


Max. height mm 2.55

Mean height mm 0.57


Portion

[wt.-%]

19.4 2.3 0 53.1 5.8 0.9 0 18.5




Marion Börnhorst

0

20

40

60

80

100

0 100 200 300 400 500 600 700

mass l

oss /

%

Temperature / °C

OP4

cyanuric acid

OP4

Sept. 20, 2018


4 320 870 8.0


Max. height mm 2.46

Mean height mm 0.99


Portion

[wt.-%]

1.6 0 0 68.1 5.9 1.2 0 23,2



Deposit composition

Marion Börnhorst

0

20

40

60

80

100

50 100 150 200 250 300 350 400 450 500 550 600

sam

ple

mass [%

]

Temperature [°C]

Urea

Sept. 20, 2018

OP 1

OP 2OP 3

OP 4

Similar deposit composition for similar operating temperatures

Prediction of deposit composition by characteristic urea decomposition kinetics


DETCHEMMPTR

Multiple Phase Tank Reactor

0D batch type reactor model

Solves for species balances in multiple phases and heat balance

Homogeneous and inter-phase reactions

ni,g,Vg

ni,l,VlHomogeneous

Reactions

Inter-phase

Reactions

ni,aq,VaqHomogeneous

Reactions

ni,in

ni,s,Vs

Inter-phase

Reactions

Homogeneous

Reactions



Kinetic model

Marion Börnhorst

Consumption

Production

Water

Carbon dioxide

Isocyanic acid

Ammonia

Urea

Biuret

Triuret

Melamine

Ammeline

Ammelide

Cyanuric Acid

Sept. 20, 2018


Decomposition of urea in DETCHEMMPTR

Marion Börnhorst

100 200 300 400 500 600 7000

2

4

6

8

10 total

urea(l)

urea(s)

biu(l)

biu(s)

triu(l)

triu(s)

cya(s)

ammd(s)Mass / %

Temperature / °C

Validation of overall mass loss by experimental data

Evolution of different species in liquid and solid phase during decomposition

Sept. 20, 2018

mg


Simulation of chemical decomposition

Marion Börnhorst

urea biuret

cyanuric acid triuret

Sept. 20, 2018


CFD-Simulation of thermogravimetric

decomposition in StarCCM+

Mesh with ~30000 cells

Timestep of 20 ms

Segregated flow model

k-ε-turbulence model

Evaporation/condensation model

Rohsenow boiling model

Complex Chemistry CVODE model


MPTR algorithm C-code

Implementation by user coding


Coupling of DETCHEMMPTR with Star-CCM+

(l)

(aq)

(s)

User CodeMPTR

StarCCM+

Calculation of reaction rates in different phases (aq, l, s)and at interfaces

Calculation ofconcentrations in gas phase and liquid film, gas-liquid equilibrium, heat balance

(l)

(g)

ci, film, Tfilm, tri

Sept. 20, 2018 Marion Börnhorst


Simulation of by-product decomposition

Excellent agreement with simulation in

DETCHEMMPTR

Continuous improvement of kinetic model

for better agreement with experiments


biuret

cyanuric acid

triuret


Conclusion

Systematic study on deposit formation in a hot gas test rig

Characterization of derived solid deposits

Kinetic modeling of urea decomposition and simulation in DETCHEMMPTR

Integration of DETCHEMMPTR algorithm into a CFD simulation by user coding

Marion Börnhorst

Outlook

Comprehensive simulation of entire test rig

Flow field

Spray injection

Spray/wall interaction

Wall heat transfer

Liquid film formation and flow

Urea decomposition and by-product

formation

Sept. 20, 2018

KIT – The Research University in the Helmholtz Association

KIT - Institute for Chemical Technology and Polymer Chemistry (ITCP)

www.kit.edu

Courtesy of Bosch

www.dieselforum.org

Thank you for your attention.

Contact: [email protected]

We acknowledge financial support by

Research Association for

Combustion Engines

ammonia preparation in the tailpipe: spray/wall ...€¦ · urea biuret cyanuric acid ammelide 1 2...

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