Sulphur impacts during pulverised coal combustion …ieaghg.org/docs/General_Docs/TSB_Oxyfuel/01 - Terry Wall.pdf · Sulphur impacts during pulverised coal combustion ... Sulphur

Sulphur impacts during pulverised coal combustion in oxy-fuel technology for carbon capture and storage

Terry Wall and Rohan Stanger

Chemical Engineering, University of Newcastle, 2308, Australia

Outline

•General sulphur impacts•Pilot-Scale experiments•Sulphur Thermodynamics•Control and Mitigation

….. For pulverised coal fired oxy-fuel

Updated fromStanger, R and T Wall, Sulphur impacts during pulverised coal combustion in oxy-fuel technology for carbon capture and storage. Progress in Energy and Combustion Science,

2010. 37(1): p. 69-88

Sulphur Impacts in Oxy-fuel CCS

ESPSequestration

Site

Deep Geological Storage

Transport

(Pipeline, Truck, Ship)

CO2

Compression

Coal Handling

ASUO2

Combustion

Recycle

Higher H2S & COSSlagging & Fouling

SCR – SO3 formation

SNCR – NH4(SO3)2

Enhanced ESP – SO3 coating HEX – acid dew pointCooling - H2SO4

CO2 purity

H2SO4 corrosion

pH & porosity

FF

FF – SO3 competes for Hg sites

Process factors for SOx in Oxy-fuel: comparison with Air firing

• Higher Feed O2 and CO2 rather than N2% (to reproduce furnace heat transfer)– Lower volumetric flow– Longer residence times for gas and solids– Higher dust loading– Different thermal profile

• Flue Gas Recirculation – and N2 omission from oxidant– Higher SO2 concentration– Higher Acid Dew Point– Wet or dry recycle– Use/placement of FGD– Direct or Indirect FGC

• CO2/H2O atmosphere– Different thermal profile– Different diffusion rate– Higher Acid Dew Point (H2O0

Pilot Work with Oxy-fuel with recycle

• Chalmers, 100kW 2009• IFK, 20 & 500kW 2008• Callide/IHI, 1.2MW, 2005• CANMET, 300kW 2001• IHI, 1.2MW 1993-6• IFRF, 2.5MW, 1994

SO2 emissions

SO3 emissions

S balance

Fly ash capture

Conclusions• Higher SO2 concentration in oxy-fuel (ppm)

• Less SO2 “emitted” in oxy-fuel (mg/MJ)

• Sulphur balanced NOT CLOSED, ie S is “lost” (not accounted for)

• Sulphur in Ash + condensate cannot account for residual-S

Condensate

S BALANCES: Lost-S example

Fleig, D., K. Andersson, D. Kuhnemuth, F. Normann, F. Johnsson, and B. Leckner, The Sulphur Mass Balance in Oxy-fuel Combustion of Lignite- An Experimental Study, in IEA 1st Oxy-fuel Combustion Conference. 2009: Radisson Hotel, Cottbus, Germany.

Literature Conclusions about Lost-S

• “Although the mass balance of sulphur could not be closed completely, it is supposed ...... that the condensation of sulfate or sulfite in the duct where the gas temperature was low enough and the absorption of sulphur in ash resulted in the reduction of SO2 emissions from the stack on O2/recycled flue gas combustion”

Kiga, T., S. Takano, N. Kimura, K. Omata, M. Okawa, T. Mori, et al., Characteristics of pulverized-coal combustion in the system of oxygen/recycled flue gas combustion. Energy Conversion and Management, 1997. 38(Supplement 1): p. S129-S134.

• “it does not seem that the removal of SO2 through condensation is very significant..... ......the sulphur present in the ash cannot be the only explanation for the lower conversion of fuel-S into SO2”

Croiset, E. and K. V. Thambimuthu, NOx and SO2 emissions from O2/CO2 recycle coal combustion. Fuel, 2001. 80(14): p. 2117-2121.

• “Sulphur mass flow in in the ash is higher in oxy-fuel.... Sulphur mass flow in condenser water is low.... Clarify the gap in the mass balance.... Gap being Air 6-9%, OF35 dry 21-27%, OF43 wet 8-17%”

Fleig, D., K. Andersson, D. Kuhnemuth, F. Normann, F. Johnsson, and B. Leckner, The Sulphur Mass Balance in Oxy-fuel Combustionof Lignite- An Experimental Study, in IEA 1st Oxy-fuel Combustion Conference. 2009: Radisson Hotel, Cottbus, Germany.

IHI Pilot Plant for Callide/IHI tests

Air

FDF/GRF

PAF

Stack

IDF

Furnace

Pulverized coal

Electrical heater

Steam gas heater

Water spray tower

Electrical heater

Bag filter

Gas cooler

Gas cooler

Air heater

O2

Oxy-fuel combustion flowchart

Convective section

RadiativeSection

Sampling positions

Equal velocityaspiration sample

Air

FDF/GRF

PAF

Stack

IDF

Furnace

Pulverized coal

Electrical heater

Steam gas heater

Water spray tower

Electrical heater

Bag filter

Gas cooler

Gas cooler

Air heater

O2

Oxy-fuel combustion flowchart

Convective section

RadiativeSection

Sampling positions

Equal velocityaspiration sample

Air

FDF/GRF

PAF

Stack

IDF

Furnace

Pulverized coal

Electrical heater

Steam gas heater

Water spray tower

Electrical heater

Bag filter

Gas cooler

Gas cooler

Air heater

O2

Oxy-fuel combustion flowchart

Convective section

RadiativeSection

Sampling positions

Equal velocityaspiration sample

Air

FDF/GRF

PAF

Stack

IDF

Furnace

Pulverized coal

Electrical heater

Steam gas heater

Water spray tower

Electrical heater

Bag filter

Gas cooler

Gas cooler

Air heater

O2

Oxy-fuel combustion flowchart

Convective section

RadiativeSection

Sampling positions

Equal velocityaspiration sample

SO2/ SO3

Fly AshBottom Ash

Ash Deposits

~160°C~500°C

~800°C

Temperature of transport

lines ?

Direct FGC for primary

feed gas

0

100

200

300

400

500

0 0.2 0.4 0.6 0.8 1

Fuel-S, %

SO

2,

mg

/MJ

Pilot SO2 Results

Oxy-fuel concentration higher but produces LESS total SO2

Higher concentration acts as driver for secondary products

25-30% less

Example: Callide/IHI results

0

500

1000

1500

2000

2500

0 0.2 0.4 0.6 0.8 1

Fuel-S, % db

SO

2, p

pm

OXY

AIR

Pilot SO3 Results

Measured Oxy Fired

Measured Air Fired100

110

120

130

140

150

160

0 0.2 0.4 0.6 0.8 1Fuel-S, %

Aci

d D

ew P

oin

t, oC

Air Fired

Oxy Fired

SO3 estimate

SO3 measured

IHI/Callide Coal A-Air

IHI/Callide Coal A-Oxy

IHI/Callide Coal B-Air

IHI/Callide Coal B-Oxy

IHI/Callide Coal C-Air

IHI/Callide Coal C-Oxy

ANL-Air [17]

ANL-Oxy [17]

CANMET-Air [13,30]

CANMET-Oxy [13,30]

IVD Stuttgart-Air [31]

IVD Stuttgart-Oxy [31]

0

10

20

30

40

50

60

70

0 500 1000 1500 2000

SO2, ppm

SO

3, p

pm

AIR to OXY → 0.86%

HHV

1.94%

HHV

2.13%

HHV

Example: Callide/IHI results

∆Hloss

Fly Ash

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1

Fuel-S, %

S a

s S

O3,

%

AirOxy

Pilot Ash Results – Callide/IHI

Coal C

Little SO3 in Bottom Ash and Radiative Deposits for other coals

0

0.2

0.4

0.6

0.8

1

1.2

Bottom Ash Fly Ash DepositRadiative

DepositConvective

S a

s S

O3,

%

(ad

)

Air Fired

Oxy FiredCoal C

In-flame measurements

IVD - Stuttgart

0

2000

4000

6000

0 0.5 1 1.5 2 2.5

Distance from Burner [m]

SO

2, H

2S [p

pm]

0

6

12

18

24

30

O2

[vol

%]

SO2 H2S SO2+H2S O2

0

2000

4000

6000

0 0.5 1 1.5 2 2.5

Distance from Burner [m]

SO

2, H

2S [p

pm]

0

6

12

18

24

30

O2

[vol

%]

(SO2+H2S)max

(SO2+H2S)max

AIR-BLOWN COMBUSTION_LAUSITZ OF27_3000 COMBUSTION_LAUSITZ

Effects on corrosion in the boiler

Impacts of High S/High Cl coals on high temperature corrosion- a brief note

Robin Irons, E.ON

IEA 1st Oxyfuel Combustion Conference, Cottbus, 2009

Fuel-S 0.68 % daf Fuel-S 1.93 % daf

• Corrosion rate in oxy-fuel is an issue in Oxy-fuel USC development

• Boiler corrosion may dictate SOx control

Interaction of Fly Ash & SO2

Okazaki measurement/modelling of CaSO4decompositionIn-furnace desulphurisation with limestone – applicability to fly ash capture?

Increase of η due to inhibition of CaSO4 decomposition

Increase of η due to recirculation of flue gas

•

1170°C

1212°C

•High temperature limit for capture

Modelling Basis1.2 O2-Fuel ratio, 8s residence time

Ca/S = 5, 10µm limestone particle

Oxy with 0.84 recycle rate

1. Fixed Bed Reactor

→ Limestone sulphur capture kinetics & diffusivity

2. Drop Tube Furnace

→ CaSO4 decomposition vs SO2 concentration

3. Modelling

→ pore diffusion with shrinking core model

→ SO2 diffusion through calcined limestone

→ No direct sulphation

→ 4-6 increase in desulphurisation efficiency

Limestone Desulphurisation Experimentsperformed in drop-tube furnace

Mechanism of Highly Efficient In-Furnace Desulfurization by Limestone under O2/CO2 Coal Combustion AtmosphereChuanmin Chen, and, Changsui ZhaoIndustrial & Engineering Chemistry Research 2006 45 (14), 5078-5085

3000ppm SO2

1050°C3000ppm SO2

3s residence time

Direct Sulphation

Calcining inhibited by CO2

Indirect sulphation

Air

O2/CO2

BUT …. Calcium in fly ash is expected to be sintered, glassy & non-porous

Measurements of SO2 with Fly Ash

Fly Ash Capture in Oxy-fuel -IVD

Radiative (>1150°C) Convective (1150 → 450°C)

Patrick Monckert, Bhupesh Dhungel, Rene Kull, and Jorg Maier. Impact of Combustion Conditions on Emission formation (SO2, NOx) and Fly Ash. in 3rd MEETING of the OXY-FUEL COMBUSTION NETWORK 2008. Yokohama Symposia, Yokohama, Japan: IEA Greenhouse Gas R&D Programme.

3.17 0.83

3.96 1.28

1.03 0.90

2.98 0.38

Ca/S Fe/S

• No evidence of SO2 transformation in radiative section

• Convective SO2 transformation is coal specific

Catalytic Oxidation of SO2 to SO3

The Effect of Temperature & Fe2O3 in Fly Ash

Marier, P. and H. P. Dibbs, The catalytic conversion of SO2 to SO3 by fly ash and the capture of SO2 and SO3 by CaO and MgO. Thermochimica Acta, 1974. 8(1-2): p. 155-165.

Fly ash + temperature Fly ash + Fe2O3 mixtures

Co

nve

rsio

n o

f S

O2

to S

O3,

%

Mass Balance & Thermodynamics

0

1000

2000

3000

4000

0 0.2 0.4 0.6 0.8 1

Fuel-S, %

SO

2,

pp

m (d

ry)

Measured Air

Measured Oxy

Theoretical Mass Balance – Callide/IHI

Difference due to the formation

of secondary sulphur

products

0

1000

2000

3000

4000

0 0.2 0.4 0.6 0.8 1

Fuel-S, %

Th

eore

tical

SO

2, p

pm

Oxy - recycle with no gas treatment

Oxy - recycle with full gas treatment

Oxy - recycle with primary treatment only

Air Fired

Theoretical Mass Balance- Callide/IHI

Effect of Lower Flow Rate

Effect of Recycle

ASHY PRODUCTS- Thermodynamic shift in S-speciesSO

SO2

SO3

O2S(OH)2

Na2SO4 (slag)

K2SO4 (slag)

CaSO4 (slag)

Na2SO4 (salt)

K2SO4 (salt)

Na2SO4

MgSO4

CaSO4

K2SO4

Fe2(SO4)3

Temperature °C

Sol

ids

Liqu

ids

and

mol

ten

solu

tions

Gas

es

Air

com

bust

ion

1500 1400 1300 1200 1100 1000 900 800 700 600 500 400 300 200 100

H2SO4 (H2O)6

Oxy

-fue

l com

bust

ion

GASEOUS PRODUCTS- Sulphur Products & Effects

0.0

0.3

0.5

0.8

1.0

0 500 1000 1500

Temperature,oC

Eq

uili

bri

um

SO2H2SO4

SO3

Cooling Flue GasIn-flame reduction products

Acid dew point

Corrosion in compression

Convective Fouling

Fly Ash Capture

Kinetics “frozen” with cooling ???

0

1

2

3

4

5

6

7

8

9

10

0 500 1000 1500

Temperature, C

SO

2

SO

3 C

on

vers

ion

, %

OXY -

AIR -

↑

1200

IHI Pilot- 1.2 MWt

(Callide study)IVD Pilot- 0.5 MWt

(Maier et al )

Fuel-S Air Oxy

%, db ppm ppm

Coal A 0.24 2 7

Coal B 0.57 9 18

Coal C 0.88 3 11

SO3

SO2 Conversion to SO3

1000°C used to estimate SO3 conversion for acid dew point

(Okkes, Verhoff & Banchero methods)

Control Strategies

Mitigation Options

ESPSequestration

SiteTransport (pipeline, truck, etc)

Deep Geological Storage

Air Separation

Unit

Coal Handling

O2

N2

Recycled Flue Gas

CO2compression

Limestone

Low S Coal

Sulphur Scrubber

Soot Blowing

Sulphur Scrubber

Condenser/ Cooler

Sulphur removal in compression circuit

Control Strategies

• SO2 limited - low sulphur coals

• SO2 removed - FGD (85-98% capture)Limestone addition (<50% capture)High calcium coals (5-10% capture)Direct Cooling/Caustic wash (Linde, Air Liquide)In compression (Air Products)In purification

• Soot-blowers• Flue Gas above acid dew point• Corrosion resistant materials

Conclusions – Pilot-Scale Sulphur

• Higher SO2 in Oxy-fuel• Higher SO3 & acid dew point• Fly Ash & Bottom Ash appear to be unaffected in

limited current measurements tho’ theoretically this is expected

• Oxy-fuel Deposits higher in S

Conclusions- Sulphur Impacts

• Sulphur Impacts throughout oxy-fuel CCS• Oxy-fuel SO2 - higher conc (ppm), lower emissions

(mass/energy)• SO2 Concentration driver for S products• SO3 conversion ~thermodynamics 1000°C

Focussing questions…..SULFUR HAS MULTIPLE IMPACTS AND CONTROL OPTIONSTHERE IS LITTLE DATA, SOME OF WHICH DISAGREES WITH THEORYDATA• Can we be sure of data unless S balances?• Do we need to measure heterogeneously and homogeneously condensed S?

ACID DEW POINT (ADP)• No direct measurements, can we rely on ADP/SO3/H2O correlations?

ASH/DEPOSITS• Do we need to understand differences with air firing?

OPTIMUM S REMOVAL, WHERE/EXTENT?• POWER PLANT - Based on corrosion or ADP?• COMPRESSION - Based on transport and storage, and removal during

compression?• Is any FGD required?• Note that S removal is associated with gas drying/cooling

Thank you for your attention

Sulphur Impacts

Furnace corrosion, slagging

Convective Pass corrosion, fouling

SCR fouling, catalytic formation- SO3

ESP higher performance

Heat Exchange acid dew point

Compression H2SO4

CO2 Purity SO2

Transport corrosion, H2SO4

Storage Corrosion, injection (pH zone)

In-flame Sulphur Products

WITH RECYCLE

(~69% recycle, 28% O2 IN, 5% O2 OUT)

ONCE THROUGH

(O2/CO2 vs O2/N2)

(Thermodynamics at 1500°C)

0

1

2

3

4

5

6

7

8

9

10

0.8 0.9 1 1.1 1.2

Equivalence Ratio

OX

Y/A

IR

Co

nce

ntr

atio

n r

atio

SO2

SO3

H2S

COS

0

1

2

3

4

5

6

7

8

9

10

0.8 0.9 1 1.1 1.2

Equivalence Ratio

OX

Y/A

IR

Co

nce

ntr

atio

n R

atio

SO2

COS

H2SSO3

SO2 in Compression

For Aquifer Storage - 3% O2, 100ppm SO2, 50ppm H2O, CO2 balanceFor EOR Storage - 100ppm O2, 100ppm SO2, 500ppm H2O, CO2 balance

(Dynamis Project recommendations for Pre-combustion capture)

Low H2O Scenario – 50ppmHigh H2O Scenario – 500ppm

Limestone Addition

Tem

pera

ture

, °C

SO2, ppm

* Assumes max Ca/S = 2

Limestone Addition

* Assumes max Ca/S = 2

In-furnace measurements - IVD

Patrick Monckert, Bhupesh Dhungel, Rene Kull, and Jorg Maier. Impact of Combustion Conditions on Emission formation (SO2, NOx) and Fly Ash. in 3rd MEETING of the OXY-FUEL COMBUSTION NETWORK 2008. Yokohama Symposia, Yokohama, Japan: IEA Greenhouse Gas R&D Programme.