IMPACT OF OPERATING CONDITIONS ON SO2 CAPTURE

IN A SUPERCRITICAL CFB BOILER IN POLAND

Artur Blaszczuk, Rafał Kobylecki, Wojciech Nowak, Marcin Klajny, Szymon Jagodzik

18th Symposium on Fluidization and Particle Processing November 8 - 9, 2012, Sakai, Osaka, Japan

2

DEMONSTRATION PROJECT

FLEXI BURN CFB – Collaborative Project

Development of High-Efficiency CFB Technology to Provide Flexible Air/Oxy Operation for a Power Plant with CCS

RESEARCH INSTITUTES VTT Technical Research Centre of Finland CIUDEN Lappeenranta University of Technology (LUT) Czestochowa University of Technology (CzUT) Universidad de Zaragoza (UZ-LITEC)

PROJECT CONSORTIUM VTT (Coordynator) CIUDEN Foster Wheeler Energia Oy EDP Tauron Generation S.A., Lagisza Power Plant Praxair Siemens Energy ADEX UZ-LITEC LUT Czestochowa University of Technology Foster Wheeler Energia S.A. AICIA BUDGET : 11 190 163 €

3

DEMONSTRATION PROJECT

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SCHEDULE A PRESENTATION

Introduction Development of circulating fluidized bed technology SO2 capture inside a CFB furnace

CFB facility (large scale)

Operating range of the 1296 t/h CFB boiler, Characteristic solids samples (coal, limestone, ashes) Calcium balance

Results Effect of Ca/S molar ratio on SO2 capture, Utilization sorbent as a function of Ca/S molar ration, Sulfur dioxide levels versus of bed temperature, Effect of excess air ratio on SO2 emission.

Conclusions

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DEVELOPMENT OF CFB TECHNOLOGY

Fig. 1. The increase of the size of CFB boilers [1].

Main factors determinig the development of CFB technology:

• standarts of gaseous emissions (LCP Directive, IPPC directive);

• unlimited access to various types of fuels;

• strong competition in the field of new advanced energy technologies (i.e. clean coal technologies).

[1] Hotta A. : Foster Wheeler’s solutions for large scale CFB boiler technology. Features and operational performance of Lagisza 460Mwe CFB boiler. Proc. 20th International conference on Fluidized Bed Combustion, pp. 59-70, May 18-21, X’ian China, 2009

Modern CFB boilers characterized by:

• fuel flexibility,

• high efficiency (net efficiency near 45%),

• low emissions of pollutants.

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SO2 CAPTURE MECHANISM

CaCO3 CaO + CO2 – 183 kJ/ g mol Calcination

CaO + SO2 + 0.5·O2 CaSO4 + 486 kJ/g mol Sulfation

Fig. 2. Absorption of sulfur dioxide by sorbent [2].

[2] Basu P. : Combustion and Gasification in Fluidized Beds. Taylor&Francis Group, 2006

CaO + SO2 + 0.5·O2 CaSO4 + CO2 Direct sulfation

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KEY PARAMETERS FOR SO2 CAPTURE

fuel + sorbent

750 800 850 90050

60

70

80

90

100

SO

2 r

em

ova

l e

ffic

ien

cy,

[%]

Bed temperature, [oC]

Ca/S = 3.5

Ca/S = 2.5

Ca/S = 2.0

An important reason to optimized bed temperature !

Fig. 5 Topology of CFB boiler [3].

[3] source: Metso Power

Primary air to grid

Fig. 4 Effect of bed temperature on desulfurization efficiency [3].

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KEY PARAMETERS FOR SO2 CAPTURE

Important factors for desulfurization process in CFB boilers:

• bed temperature,

• Ca/S molar ratio,

• sorbent particle size distribution ,

• solids recirculation rate into CFB furnace

(bed inventory & ashes),

• efficiency of solids separator,

• bed hydrodynamic conditions (i.e. height bed),

• excess air ratio,

• utilization sorbent,

• sorbent residence time,

• sorbent reactivity index,

• fuel parameter (i.e. sulfur content).

Fig. 3 Effect of bed temperature on desulfurization efficiency for different particle size of limestone.

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SUPERCRITICAL CFB BOILER (LAGISZA POWER PLANT)

INTREXTM-RH II INTREXTM-SH IV

Water/Steam

Separator

Table 1. Design parameters of supercritical CFB boiler at Lagisza Power Plant.

Fig. 6 Schematic layout of utility supercritical CFB boiler – arrangement of superheaters (SH) and reheater (RH).

SH

II

SH III SH III Design parameters Unit Data

Capacity MWth 966

Net electrical efficiency % 44

Boiler type - OT - SC

Main steam flow kg/s 360

Main steam pressure MPa 27.5

Main steam temperature °C 560

Reheat steam flow kg/s 307

Reheat steam pressure MPa 5.5

Reheat steam temperature °C 580

Feed water temperature °C 289.7

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Furnace

10.6 m * 27.6 m

Height 48 m

Integrated

separators

INTREX™

superheaters

SUPERCRITICAL CFB BOILER (LAGISZA POWER PLANT)

BENSON Vertical Tube Technology

– Vertical Tube Furnace Walls

– Low mass flux design:

Low Pressure Drop

Self Compensating “Natural Circulation” Characteristic

Fig. 7. Siemens technology (rifled tube).

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EMISSION ( at 6% O2, dry flue gas) - (follows EU’s LCP directive)

SO2 mg/mn3 200

NOx (as NO2) mg/mn3 200

CO mg/mn3 200

Dust mg/mn3 30

Low Emissions

SUPERCRITICAL CFB BOILER (LAGISZA POWER PLANT)

Improved emissions

92% ~ 22 300 t/year reduction

71% ~ 4 700 t/year reduction

28% ~ 970 000 t/year reduction

SO2

NOx

CO

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EXPERIMENTAL CONDITIONS

Operating parameter Unit Range of variation

Superficial gas velocity, Uo m·s-1 2.92 - 5.25

Thermal velocity, Ut m·s-1 1.28 - 1.59

Minimum fluidization velocity, Umf m·s-1 0.00724 - 0.00773

Furnace temperature, Tb °C 762 - 860

Excess air ratio, - 1.21 - 1.69

Ca/S molar ratio - 1.43 - 7.44

Table 3. Operating range of the 1296 t/h CFB boiler during the tests.

Specification Unit Range of variation

Proximate analysis

LHV Qar MJ/kg 19.24 - 22.92

Ash Aar wt % 8.09 – 22.40

Moisture War wt % 11.81 - 18.47

Volatile Vdaf wt % 26.90 -30.37

Ultimate analysis

Carbon Cad wt % 52.00 - 57.00

Hydrogen Had wt % 3.86 - 4.74

Nitrogen Nad wt % 0.73 - 0.97

Oxygen Oad wt % 6.30 – 6.90

Sulphur Stad wt % 0.85 - 1.70

Table 4. Bituminous coal characteristic on performance tests.

Fig. 8. Particle size distribution of limestone at 1296t/h supercritical CFB boiler.

Superscripts: ad – air dried; ar – air dried; daf – dry ash-free Subscripts: t – total content

10 100 10000

10

20

30

40

50

60

70

80

90

100

Particle diameter, [m]

Cu

mu

lati

ve

dis

trib

uti

on

, [%

] experimetal data

approximation

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CHARACTERISTIC SOLIDS SAMPLES

X-ray fluorescence (XRF) spectrometry

Component Unit Value

CaO wt.% 54.85

CaCO3 wt.% 97.91

MgO wt.% 0.79

MgCO3 wt.% 1.65

Al2O3 wt.% 0.13

Fe2O3 wt.% 0.07

Na2O wt.% <0.05

K2O wt.% <0.05

Component Overall range, wt.%

Bottom ash Fly ash

SiO2 37.31-70.73 35.7-47.6

Al2O3 9.55-17.08 8.3-16.4

Fe2O3 3.86-5.79 5.39-8.28

CaO 2.91-17.70 14.3-23.7

MgO 0.29-4.32 0.59-4.3

Na2O 0.29-1.16 0.53-0.89

K2O 1.53-2.79 1.34-1.72

Table 5. Analysis of limestone on test runs.

Table 6. Elemental analysis of fly ash and bottom ash.

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CALCIUM BALANCE

Fig. 9. Solids mass flow at 1296t/h supercritical CFB boiler.

mCa in mCa out

mCa in = Ca limestone · mCaCO3 + Ca fuel · mfuel

mCa out = Ca FA · mfly ash + Ca BA · mbottom ash

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RESULTS

? Utilization rate of sorbent

(not available on-line),

Tb (available on-line)

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Ca/S molar ratio

Fig. 10. Effect of Ca/S molar ratio on desulfurization efficiency in a 1296t/h supercritical CFB boiler.

Fig. 11. Utilization sorbent as a function of Ca/S molar ratio in a 1296t/h supercritical CFB boiler.

1,8 2,0 2,2 2,4 2,6 2,8

0,25

0,30

0,35

0,40

0,45

0,50

0,55

0,60

experimental data

approximation

Uti

liza

tio

n r

ate

of

sorb

ent,

[-]

Ca/S molar ratio, [-]

0 1 2 3 4 5 6 7 8

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0

experimental data

approximation

Des

ulf

uri

zati

on

eff

icie

ncy

, [-

]

Ca/S molar ratio, [-]

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SULFUR DIOXIDE EMISSION

Fig. 12. Sulfur dioxide levels as a function of bed temperature within furnace chamber.

Fig. 13. Effect of excess air ratio on SO2 emission.

740 760 780 800 820 840 860 880

20

40

60

80

100

120

140

160

180

200

100% MCR load

80% MCR load

60% MCR load

40% MCR load

approximation

SO

2 e

mis

sio

n, [m

g/m

3 n]

Bed temperature, [oC]

Ca/S = 2.1

high level of sulfur content

in the fuel

1,1 1,2 1,3 1,4 1,5 1,6 1,7 1,8

20

40

60

80

100

120

140

160

180

200

experimental data

approximation

SO

2 e

mis

sio

n,

[mg

/m3 n]

Excess air ratio, [-]

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CONCLUSIONS

• Experimental studies in a large scale CFB boiler have shown that the SO2 capture was carried out at optimum temperature range.

• Ca/S molar ratio affects on SO2 removal efficiency, but only in the range of value Ca/S<3. Above this value the efficiency of sulfur dioxide capture was at the constant level equal to 99.8%

• Efficiency in the use of sorbent during all tests varied within the range 30% – 42%.

• In the case all unit loads concentration of SO2 in dry flue gas was lower than 200mg · mn-3

• Reduction of Ca/S molar ratio (approximately 27%) affected on the increase of sorbent utilization rate by about 53%.

Thank you for your attention