Prof. Dr. techn. G. Scheffknecht

Institute of Combustion and Power Plant Technology

Fundamentals in Pilot plant

R&D activities

Operation, testing and analysis

Oxyfuel Combustion Capacity Building CourseWuhan, China 2015

Joerg Maier

joerg.maier@ifk.uni-stuttgart.de

Content

IFK oxy-fuel test facilities

Dedecated Investigations of IFK

NO formation and reduction

S behaviour

Corrosion, slagging and fouling

2

Gas supply and distribution

CO2O2

storage tanks

gas distribution

20kWth

0.5MWthothers

4

Concerned area of the major changes for the adaptation for the new burner design

Continuous gas emission measurements

Inflame Measurements•Gas emissions•Gas temperature•Heat Flux•Radiation etc.

Infrastructure

Sampling•Ash, HCL, SO3

Air/Flue gas

Air-Oxyfuel Test Facility (500kWth)

0

20

40

60

80

100

18:09 18:29 18:49 19:09Time

0

20

40

60

80

100

LA_OXY_1_20980-21450

O2 in vol.-%dry

CO2 in vol.-%dry

FGR flapposition in %

flap open

flap closed

5

Development of Low NOx Oxyfuel burner

Investigations at the 500 kW semi-technical test facility:

•Comparison of two different burner designs•Flame characterisation and ignition optimisation under recycled conditions•Optimum O2 injection method•Impact of recycle rate of flue gas on momentum ratio, flame stabilisation, internal recirculation•Staging at the oxyfuel combustion•Emission behavior

New burner designActual burner

secondary gas stream(optionally swirled)

primary gas streamand fuel

gas probe with nine drillings

secondary gas stream(optionally swirled)

primary gas streamand fuel

gas probe with nine drillings

Inflame Measurements•Gas emssions

•Gas temperature

Continuous gas emssion

measurements

Grathwohl, S., Maier, J., Scheffknecht, G., 2011. Testing and evaluation of advanced oxyfuel burner and firing concepts, 2011, OCC2 Yeppoon.

6

Vattenfall 30 MWth Oxyfuel Plant Schwarze Pumpe Oxyfuel Burner and Operation modes

Demonstration of Oxyfuel burner

Test program start in 2009

In flame measurements of flue gas species, and temperature

Measurement of radiative heat transfer

Measurement of emissions

Optimizing emissions, burnout, oxygen excess

CFD modelling

Ü 2

ECO 5

Ü 1

DS®-TBurner

ECO 4

ECO 3

ECO 2

ECO 1

HE OXY

Burn out-oxydant

Dry lignite firingPre-testing

Content

IFK oxy-fuel test facilities

Investigations

NO formation and reduction

S behaviour

Corrosion, slagging and fouling

7

Impurities: NOx – general

Conventional air firing (PF):NOX: NO is ~ 95%, NO2 is < ~5%

Oxy-fuel firing (PF):• Absence of atmospheric N2: - Increased dominance of fuel NOx

(thermal NOx can be disregarded)

- Reduced NOx emissions [mg/MJ]

Thermal NOX ~ 20% Prompt NOX <5%

J. Maier, Wuhan 2015

9

T1

T2

T3

T4

T5

• Vertical atmospheric

drop tube furnace.

• 250 x 20 cm

• Up to 50 kW

• 1 kg/h bitum. coal or 1.5

kg/h lignite.

• 5 elec.controlled heating

zones (800-1400°C)

• Oil cooled sampling

probe

Air-Oxyfuel Test Facility (20kWth)

10

NOx reduction potential during staged combustion

0

50

100

150

200

250

300

350

400

0.7 0.75 0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2

Burner Stoichiometry

NOx [

mg/

MJ]

Air_3 sec

Air_2 sec

27% Oxy_3 sec

27% Oxy_2 sec

Un-staged

Com

bustion

Parameters Optimum EffectBurner Stoichiometry 0.75-0.85 Oxygen deficiency,

encouraging formation of N2

Residence time in reduction zone 2-3 seconds Longer time available for conversion of NOx precursors to N2

Temperature Shift of coal-N towards gas phase

Klein Kopje Coal

11

Influence of fuel type on NOx reburning effect

0

20

40

60

80

100

120

20 25 30 35 40 45 50 55 60

Volatile Content of Coal [%waf]

Redu

ctio

n of

recy

cled

NO

[%] λ1=0.75 λ1=0.85 λ1=0.95 λ=1.15

N=1.67% N=1.42% N=0.97% N=0.65%

T 1= 3

sec

Oxy-Coal Combustion with 27% O2/73% CO2

Dhungel, Bhupesh Experimental Investigations on Combustion and Emission BehaviourDuring Oxy-Coal Combustion, Dissertation Universität Stuttgart, 2010

Impurities: NOx – Conclusions

Conventional NOx reduction can be applied to oxy-fuel systems:

99

8596

88

5950

95

4938

81

47

13

98

53

10091

72

39

92

798391

0

20

40

60

80

100

120

0.75 0.85 0.95 Unstaged

R

educ

tion

of re

cycl

ed N

O [%

]

Air_KK 27% O2_KK Air_LA 27% O2_LA Air_NG Oxy_NG

• Problem with SCR systems: catalytic SO3 generation (fouling, corrosion)

SCR-SO2/SO3 conversion rates similar to air-firing

• Primary NOx reduction efficiently

• Staged combustion prevent NOx accumulation

• Secondary NOx reduction (SCR): suitable for oxy-fuel operation, but may not be required

Recycling of 500 ppm NO3s in reducing zone

Air and oxy-fuel staging tests

Dhungel, Bhupesh Experimental Investigations on Combustion and Emission BehaviourDuring Oxy-Coal Combustion, Dissertation Universität Stuttgart, 2010

stoichiometry

Content

IFK oxy-fuel test facilities

Investigations

NO formation and reduction

S behaviour

Corrosion, slagging and fouling

13

Impurities SO2 – general (1/10)

• In oxy-fuel operation: SO2 concentrations approx. 3-5 times higher than in air-firing (concentrations up to 20000 ppm reported)

• SO2 emissions [mg/MJ] are reduced

CAUTION: NDIR and UV SO2 analyzers may be biased by CO2

• SO2 can be captured by (earth-)alkalis of the ash, e.g. CaCO3

14

24223 21 COCaSOOSOCaCO +↔++

422 21 CaSOOSOCaO ↔++

23 COCaOCaCO +↔Calzination & Desulphurization

Direct Desulphurization

Impurities SO2 – emission/capture (3/10)

15

• SO2 capture in ash dependent on temperature, residence timeand S-content of fuel

Graphics show simulation results

20

1.300 1.400Temperature [K]

1.5000

40

60

80

100 System desulphurizationefficiency [%]

Air,S=2wt.-%

Air,S=1wt.-%

O2/CO2,S=2wt.-%

O2/CO2,S=1wt.-%

20

0

40

60

80

100

2 4 6 8Residence time of particles [s]

Air,S=2wt.-%

O2/CO2,S=2wt.-%

System desulphurizationefficiency [%]

Liu, H.; Katagiri, S.; Okazaki, K.: Drastic Sox Removal and Influences of Various Factors in O2/CO2 Pulverized Coal Combustion System. Energy Fuels 2001, 15 (2), 403

• SO2 capture efficiencies in oxy-fuel (PF) can exceed values of air-firing (PF) by 10-25%

16

SO2 Reduction in the Flue-Gas Path

1. Increase in SO2 concentration lead to reach S-saturation of ash capture capacity.

2. SO2 capture efficiency decreases with decrease in stoichiometry at higher temperature (>1150°C)agrees with this result from X. Han. (PhD thesis- 2003, Modelling and simulation of SOx and NOx reduction Processes, University of Stuttgart, 2003)

y = -4E-05x2 + 0.2911x - 53.091

0

200

400

600

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Total SO2 [ppm]

Cap

ture

d S

O2

[ppm

]

Lausitz Coal, OF27

λ=1.15

2220

15

1112

6

20

15

97 8

21

0

5

10

15

20

25

1.15 0.95 0.75Burner Stoichiometry

Red

uctio

n of

SO

2 [%

]

LA_Oxy_0 LA_Oxy_3000 LA_Air_0 LA_Air_3000

Maier J., Al-Makhadmeh L., Scheffknecht G. 2009. Formation and Impact of Gases Sulfur components in an Oxyfuel Combustion Process. Proceedings AICHE Annual Meeting, 2009, 320e, Nashville TN, USA

Sulfat formation at higher furanceTemperatures

17

1100°C 1200°C

SO2:

850

ppm

a) b)

SO2:

625

0 pp

m

c) d)

Spörl, R., Paneru, M., Babat, S., Stein-Brzozowska, G., Ott, S., Maier, J., Scheffknecht, G., 2014c. Fly Ash and Deposit

Transformations in Air and Oxy-fuel Combustion, in: Proceedings of the 25th Impacts of Fuel Quality on Power Production Conference, 26-31/09/2014.

Impurities SO2 – implications

• Increased SO2 and H2O partial pressures impact high T corrosion: More pronounced corrosion possible in oxy-firing

Lab exposure of materials with ash deposit under oxy-fuel and air conditions

18

DM

V C

263

Inco

nel7

40

G. Stein-Brzozowska, D. M. Flórez, J. Maier, G. Scheffknecht, P. Huczkowski, L. Singheiser, W.J. Quadakkers, Fireside corrosion ofnickel base alloys in conventional and oxyfuel firing conditions, Poster at EFC Workshop: Beyond Single Oxidants, Sept. 2012, Frankfurt

30 µm

20 µm

Oxy-fuelFG

Air

FG

FG – flue gas

10 µm

10 µm

Impurities SO3 – general

• SO2 oxidation to SO3: Increased SO2 leads to SO3 increases

• SO2/SO3 conversion in oxy-firing enhanced by:

− Locally/globally increased O2 partial pressure

− Higher ash concentrations > higher availability of catalytic Fe2O3

− Temperature profile and residence time

• SO3 capture on alkaline/earth alkaline compounds enhanced by:

− Higher ash concentrations > higher availability of Ca, Mg, Na, K

− Temperature profile and residence time

19

Impurities SO3 – general

20

• Dominant parameter influencing SO3concentrations: SO2

• No clear trend in SO3/SO2 ratios, when switching from air to oxy: changes small and fuel dependent

• SO3/SO2 ratios in oxy-firing: 0.7 - 4%

• SO3/SO2 ratios in air-firing: 0.3 – 3.5%

Comparison of published data on SO3 formation

Spörl, R., Belo, L., Shah, K., Stanger, R., Maier, J., Wall, T., Experiments in a once-through furnacesimulating different extents of recycle gas cleaning in coal-fired oxy-fuel combustion: conversion of SO2 toSO3, 38th International Technical Conference on Clean Coal & Fuel Systems, Clearwater, Florida, USA, 2013

100 1000 10000

1

10

100

1

10

100

100 1000 10000

SO3

conc

entr

atio

n [p

pm]

SO2 concentration [ppm]

Coal A - IFKCoal B - IFKCoal C - IFKCoal A - IHICoal B - IHICoal C - IHIHard Coal - IFKLignite - IFKLignite - AlstomCanmet

= air, rest oxy

• Oxy-firing may increase due points by 20-40 K

• Selective H2SO4 condensation on cold surfaces corrosion

• Close to dew point: Effective H2SO4 capture on ash withremoval efficiencies of 40-65%in ESP/FF

• SO3 + H2O form H2SO4

• H2SO4 due points in flue gases: 95-160°C [f(SO3, H2O)]

Impurities SO2 – implications

21

Water content of flue gas [%-Vol.]

Aci

dde

w p

oint

tem

pera

ture

[°C

]

air

oxy-fuel

Scheffknecht G., Maier J.,Firing issues related to the oxyfuel process. VGBPowerTech; 88 (11); 91-97, 2008

Impurities SO2/SO3 – control

• Dry sorbent injection (e.g. Ca- or Na-based sorbents): Promising for highly reactive SO3

Application for SO2 limited (slower kinetics / high sorbent requirement)

• Wet flue gas desulfurization: Suitable for oxy-firing after modification

Oxy-firing: 99.8%-99.5% SO2 removal demonstrated at Schwarze Pumpe

Placement in- or outside recycle loop possible

• Caustic or Na2CO3 scrubber: Suitable for oxy-firing (e.g. Callide): limited to low S fuel and back-end

layout, due to caustic/Na2CO3 costs

• Other DeSOx processes for oxy-firing: Spray Drier Absorber (SDA), Circulating Dry Scrubber (CDS), Clean Energy Recuperator (CER)

23

Dhungel, B., 2010. Experimental investigations on combustion and emission behaviour during oxy-coal combustion. Dissertation, Stuttgart, Germany.Dhungel, B., Mönckert, P., Maier, J., Scheffknecht, G., 2007. Investigation of oxy-coal combustion in semi-technical test facilities. Third International Conference on Clean Coal Technologies for our Future-CCT, 2007, Cagliari.Paneru, M., Spörl, R., Stein-Brzozowska, G., Maier, J., Scheffknecht, G., 2013a. Behaviour of Deposit and Fly Ash under Oxyfuel Conditions. 3rd Oxy-Fuel Combustion Conference, 09-13/09/2013, Ponferrada, Spain.Scheffknecht, G., Al-Makhadmeh, L., Schnell, U., Maier, J., 2011. Oxy-fuel coal combustion - A review of the current state-of-the-art. International Journal of Greenhouse Gas Control 5 (1), 16–35.Maier J., Al-Makhadmeh L., Scheffknecht G. 2009. Formation and Impact of Gases Sulfur components in an OxyfuelCombustion Process. Proceedings AICHE Annual Meeting, 320e, Nashville TN, USA, 2009Spörl, R., Maier, J., Scheffknecht, G., 2013. Sulphur Oxide Emissions from Dust-fired Oxy-fuel Combustion of Coal. Energy Procedia 37 (0), 1435–1447. DOI: 10.1016/j.egypro.2013.06.019.Spörl, R., Paneru, M., Babat, S., Stein-Brzozowska, G., Ott, S., Maier, J., Scheffknecht, G., 2014c. Fly Ash and Deposit Transformations in Air and Oxy-fuel Combustion, in: Proceedings of the 25th Impacts of Fuel Quality on Power Production Conference, 26-31/09/2014.Spörl, R., Walker, J., Belo, L., Shah, K., Stanger, R., Maier, J., Wall, T., Scheffknecht, G., 2014d. SO3 Emissions and Removal by Ash in Coal-Fired Oxy-Fuel Combustion. Energy Fuels 28 (8), 5296–5306. DOI: 10.1021/ef500806p.Stein-Brzozowska, G., Díaz, H., Maier, J., Scheffknecht, G., 2013. Impact of oxy-fuel combustion on fly ash transformations and resulting corrosive behavior of alloys 310 and 617. Energy Procedia 37, 1462–1470. DOI: 10.1016/j.egypro.2013.06.021.Stein-Brzozowska, G., Norling, R., Viklund, P., Maier, J., Scheffknecht, G., 2014. Fireside Corrosion during OxyfuelCombustion Considering Various SO2 Contents. Energy Procedia 51, 234–246. DOI: 10.1016/j.egypro.2014.07.027.Grathwohl, S., Lemp, O., Schnell, U., Maier, J., Scheffknecht, G., 2010. Flexible Burner Concept for Oxyfuel Combustion.Proceedings AICHE Annual Meeting, 419f, Salt Lake City, Utah, USA, 2010Testing and evaluation of advanced oxyfuel burner and firing concepts, 2011, Yeppoon.Kull, R., Stein-Brzozowska, G., Theye, T., Maier, J., Scheffknecht, G., 2009. Corrosion of super-heater materials under oxy-fuel conditions. 1st IEA Oxyfuel Combustion Conference, 08-11/09/2009, Cottbus, Germany.Grathwohl, S., Maier, J., Scheffknecht, G., 2011. Testing and evaluation of advanced oxyfuel burner and firing concepts, 2011, Yeppoon.

References

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