laboratory and pilot scale combustion experiments in high ... · – laboratory and pilot scale...

Development of 2nd generation oxyfuel CFB technology– laboratory and pilot scale combustion experiments inhigh oxygen concentration

VII Liekkipäivä, 30.1.2014, TampereHeidi Saastamoinen and Toni PikkarainenVTT Technical Research Centre of Finland

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Content

Introduction to O2Gen – projectExperimental work and preliminary results:

Bench scale BFBPilot scale CFB

What next

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O2GenOptimization of Oxygen-based CFBC Technology with CO2 capture

Project under EU 7th FPstarted 10/2012, duration 3 yearstotal budget 11.9 M€ (EU contribution 6.6 M€)

Consortium contains 11 partners4 companies and 7 research organisationsfrom Spain (5), Finland (3), France (1), Italy (1) and Poland (1)

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The project objective is to demonstrate the concept of the 2nd

generation oxyfuel combustion that reduce significantly (around50%) the overall efficiency penalty of CO2 capture into powerplants, from approximately 12 to 6 %-points.The efficiency improvements will be achieved by

the use of higher O2 concentrations in oxyfuel combustion reducingthe flue gas recirculation and energy penalty (also enabling boilersize reduction and thus cost reductions)integration of ASU (air separation unit) and CPU (CO2 processingunit) with the power plant reducing energy penaltiesmore efficient oxygen production, and CO2 purification andcompression steps

As a result, conceptual design for 600 MWe scale 2nd generationoxygen-fired CFB power plant will be created

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Motivation:Decrease the costs of CCS and making the way to towards competitivecommercialization of oxy-CFB based CCS technology


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Fluidised bed test facilitiesBench scale BFB and pilot scale CFB

http://www.vtt.fi/img/research/ene/combustion/VTT.html

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Fuel impulse testsObjectives and test matrix

Objectives in fuel impulse tests are to solve how high O2 concentrations

affect the

• char reactivity of coal

• emission (NO, CO, SO2) formation

Test Fraction, mm O2 feed (%) CO2 feed (%) T prim, (CO2+O2), Nl/min sec, (CO2+O2), Nl/minSpanish Anthracite 1 0.5-2 5 95 850 5 5Spanish Anthracite 2 0.5-2 15 85 850 5 5Spanish Anthracite 3 0.5-2 30 70 850 5 5Spanish Anthracite 4 0.5-2 50 50 850 5 5Spanish Anthracite 5 4-8 5 95 850 5 5Spanish Anthracite 6 4-8 15 85 850 5 5Spanish Anthracite 7 4-8 30 70 850 5 5Spanish Anthracite 8 4-8 50 50 850 5 5

Polish Bituminous coal 1 0.5-2 5 95 850 5 5Polish Bituminous coal 2 0.5-2 15 85 850 5 5Polish Bituminous coal 3 0.5-2 30 70 850 5 5Polish Bituminous coal 4 0.5-2 50 50 850 5 5Polish Bituminous coal 5 4-8 5 95 850 5 5Polish Bituminous coal 6 4-8 15 85 850 5 5Polish Bituminous coal 7 4-8 30 70 850 5 5Polish Bituminous coal 8 4-8 50 50 850 5 5

Gas composition for both prim and sec

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Bench scale fuel impulse tests: O2 responses

• When the oxygen concentration inprimary and secondary gasincreases combustion rateincreases

• Combustion of volatiles, chargasification and combustion occuralmost simultaneously in highoxygen combustion, whereas inlow concetrations and with largerparticles these phases separate

• Combustion of bituminous coaloccurs faster compared toanthracite due to higher volatilecontent of fuel

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Bench scale fuel impulse tests: Temperature, CO

• Peak temperature increases along with the increase in oxygen concentration• Char gasification in CO2 environment increases CO formation

• CO formation is controlled by feeding secondary gas• The less oxygen is fed

• the more CO forms• the longer CO forms

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Fuel impulse tests: Nitrogen emission formation

NO formation:• The rate of NO formation increases

along with the increase in oxygenfeed.

• Formation of NO strictly follows theincrease in temperature.

• There no significant change in totalamount of N released although therate of NO formation increases

• In 50% oxygen feed N2Oformation increases and NOformation decreases

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CFB-pilot testsAnthracite-petcoke blend

Test matrix with anthracite/petcoke blend contained 7 tests:Test 1: air reference, medium temperatureTest 2: oxyfuel 28% (ref. to 1st generation design), medium temperatureTests 3-5: oxyfuel 42% (ref. to 2nd generation design), 3 temperature levelsTest 6-7: Oxyfuel 42%, oxygen staging (prim. O2 share 60...80%)

Total feed gas flow and prim./sec. gas share (fluidisation conditions)were constantAlso Ca/S-ratio (limestone calcium to fuel sulphur ratio, mol/mol) waskept as constant as possible

Test Mode Fuel Limestone Fuel power Ca/S total Bed temp. Feed gas O2 Primary gas O2 Secondary gas O2 Primary gas# air/oxy blend type kW mol/mol ºC % wet % wet % wet share-%1 air 55 3.1 889 21 21 212 79 2.8 873 28 28 283 121 2.6 918 42 42 424 118 2.6 856 42 42 425 121 2.7 817 42 42 426 121 2.7 863 42 48 297 118 2.5 853 42 37 55A

nthr

acite

/Pet

coke

70/3

0w

-%

Est

rella

oxy 70

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CFB-pilot testsUnburned carbon (UBC) losses

In all tests UBC losses were low, <1.6 % of fuel LHVThe lowest UBC was measured from high temperature, high-O2 test 3, as expected

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Test 1 Test 2 Test 3 Test 4 Test 5 Test 6 Test 7

Air Oxy 28% Oxy 42% - highT

Oxy 42% -medium T

Oxy 42% - lowT

Oxy 42% - highprim. O2

Oxy 42% - lowprim. O2

Tem

pera

ture

[ºC]

UBC

[%LH

V]

UBC to fly ashUBC to bottom ashBed temperature

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CFB-pilot testsSO2 formation and capture – tests at medium temperature

Lower SO2 emissions and better sulphur capture in high-O2 oxyfuel conditions (at ~860ºC)Also at 28% oxyfuel conditions the sulphur capture was better than in air-firing

94 40 17 21 14

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2.82.6 2.7

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3135 38 37 39

94.6 97.6 99.0 98.7 99.1

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Test 1 Test 2 Test 4 Test 6 Test 7

Air Oxy 28% Oxy 42% Oxy 42% - highprim. O2


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O2

emis

sion

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utili

satio

n,S

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rete

ntio

n

Ca/

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talm

olar

ratio

SO2 emission [mg/MJ] Ca/S total [mol/mol]Calcium utilisation [%] SO2 retention [%]

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CFB-pilot testsSO2 formation and capture – high-O2 oxyfuel conditions

Clear effect of temperature (tests 3-5), temperatures >850ºC were favoredO2-staging had no significant effect (tests 4 and 6-7)

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856

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863853

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Test 3 Test 4 Test 5 Test 6 Test 7

Oxy 42% - high T Oxy 42% -medium T

Oxy 42% - low T Oxy 42% - highprim. O2


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on,C

aut

ilisa

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2re

tent

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Sto

talm

olar

ratio

SO2 emission [mg/MJ] Bed temperatureCalcium utilisation [%] SO2 retention [%]

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CFB-pilot testsSO2 formation and capture – calcination/carbonation

At low temperature and high CO2 partial pressure, CaCO3 is not calcined to CaO (direct sulfation to CaSO4)From the bottom ash analysis it can be seen that poor sulphur capture in test 5 was due to slow directsulfation of CaCO3 (main part remained as CaCO3)


Air Oxy 28% Oxy 42% -high T

Oxy 42% -medium T

Oxy 42% -low T

Oxy 42% -high prim. O2

Oxy 42% -low prim. O2

CaCO3 [%] 0.42 4.17 0.83 1.67 32.50 2.50 1.67CaO [%] 13.77 18.28 19.99 20.08 2.08 18.69 19.35CaSO4 [%] 15.64 23.38 25.12 27.84 19.08 24.99 26.22Ca utilisation 30.5 35.1 37.6 38.1 34.0 36.9 39.3

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Cal

cium

utili

satio

n[%

]

Mas

ssh

are

[%]Bottom ash

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CaCO3 – CaO equilibrium

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700 725 750 775 800 825 850 875 900 925 950 975

CO2

part

ialp

ress

ure

[atm

]

Temperature [°C]

Equilibrium curve according to Marion et al.

Test 1 Air

Test 2 Oxy 28%

Test 3 Oxy 42% - high T

Test 4 Oxy 42% - medium T

Test 5 Oxy 42% - low T

Test 6 Oxy 42% - high prim. O2

Test 7 Oxy 42% - low prim. O2

CaO

CaCO3

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CFB-pilot testsFormation of nitrogen oxides

NO and N2O emissions were clearly higher in air-firingIn high-O2 tests:

NO was higher and N2O lower than in 28% oxyfuel at comparable conditionsNO increased and N2O decreased with increasing temperatureO2-staging had relatively small effect on NO or N2O

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Air Oxy 28% Oxy 42% - highT

Oxy 42% -medium T

Oxy 42% - low T Oxy 42% - highprim. O2


Tem

pera

ture

[ºC]

Em

issi

ons

[mg/

MJ]

NO emission [mg/MJ] N2O emission [mg/MJ] Bed temperature

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Next

Second set of bench scale testsTemperature changes (750ºC & 950ºC) in high oxygenconcentration combustion

Model for bench scale combustor under developmentTarget: to obtain parametres for pyrolysis, char gasification, charcombustion and reactions of nitrogen speciesParticle model approach for bench scale results

Bench scale modelling results will be implemented to onedimensional CFB furnace model for pilot scale CFB

validation of the model with the data from air-firing and oxy-firingtests under widened operation range (O2 concentration 21...42 %)

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ACKNOWLEDGEMENT

The research leading to these results has received funding from theEuropean Union Seventh Framework Programme FP7/2012 under grantagreement no 295533.

Projects’ website:www.o2genproject.eu

More about VTT’s combustion research and services:http://www.vtt.fi/img/research/ene/combustion/VTT.html

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