oxyfuel combustion in bfb. experiences and simulations romeo.pdf · international energy agency ‐...

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Fluidized Bed Conversion

Ponferrada, November 2011

Oxyfuel combustion in BFB. Experiences and simulations

Luis M Romeo, Luis I Diez, Isabel Guedea, Irene Bolea Carlos Lupiañez, Pilar Lisbona, Yolanda Lara, Ana Martinez

CIRCE (Research Centre for Energy Resources and Consumption)

1




CIRCE

•

CIRCE

–

Non‐profit private organization, sponsored by the University of Zaragoza, the

Government of Aragón and Spanish industry

–

R&D in energy and thermal and electrical engineering, focus on efficiency and

renewable energy

–

Thermal division (~ 30 people):

•

Coal & biomass combustion, plant tests & monitoring, laboratory work, simulation,

CFD, conventional (PF) and advanced (FBC, IGCC, co‐firing) systems

•

CO2

capture: BFB Oxyfuel laboratory, Solid looping systems based on

CFB (mainly

Calcium looping) and studies about reduction of energy penalties

in CO2

capture

2




BFB Oxyfuel test rig

•

Test facility description–

90 kWt O2

/CO2

bubbling fluidized bed

–

2.5 m height, 20 cm i.d. FB water‐

cooled

–

2 x 200 litres hoppers for fuel feeding

(coal, sorbent, biomass)

–

CO2

/O2

mixer and flue gas

recirculation

–

Preheating of fluidising gas

–

Gas cleaning: settling chamber,

cyclone and fabric filter

–

Recycling ratio: from 0% to 60%

–

O2

in the mixture: from 20% to 60%

3




BFB Oxyfuel test rig

4

Preheating system/ Propane burner

Fuel feeder equipment

Air supply/ RFG

Gas supplyBubbling fluidized bed reactor

High efficiency cyclone

Heat exchangerFabric bag filter




Oxyfuel BFBC. Experimental

•

First tests

–

Fluidization problems and control (pressure) of flue gas recirculation

–

SINTERING

•

Only in oxyfuel, maximum temperatures around 1000ºC

•

Bed agglomeration. Broken in small pieces

•

Bed sintering. Harder and larger than agglomerate.

5


•

First tests

6

CaSO4Layer

O (15.2%)Ca (11.0%)Si (9.6%)K (3.0%)Al (4.5%)Fe (2.6%)

O (15.5%)Al (7.5%)Si (9.1%)Ca (9.4%)O (13.8%)

Si (21.2%)

2 mm

SEM3‐2

0

24

68

10

1214

16

O Na Mg Al Si S K Ca Ti Fe

SEM3‐1

02468

1012141618

O Na Mg Al Si S K Ca Ti Fe








7

Air Firing Ca/S= 2.5

CO2

/O2

= 65/35 –

60/40O2

= 3‐12% flue gases30 kW air 50‐70 kW oxy





8

Oxy FiringCa/S= 2.5CO2

/O2

= 65/35 –

60/40O2






•

SO2

emissions. Conclusions

–

As expected, in AF:

•

SO2

emissions increases with bed temperature (t > 830ºC)

•

Indirect sulfation

•

Sulfur capture remains around 90% with bed temp of 830‐860ºC

–

For OF

•

SO2

emissions are slightly higher than in AF

•

Sulfur capture remains near 90% with bed temperature of 860‐890ºC

•

Direct sulfation has been observed

•

Increasing bed temperature under OF conditions enhances SO2

capture, towards an

optimum temperature higher than in the case of air firing.

9





10

Air Firing

Oxy Firing

Ca/S= 2.5CO2

/O2

= 65/35 –

60/40O2






•

NOx emissions. Conclusions

–

As expected, in AF:

•

NOx concentration has showed a high dependence on O2

excess‐CO formed and coal

rank.

•

N‐fuel in lignite coal is lower than bituminous. This difference leads to lower NOx

emissions. Differences are shortened when expressed per energy unit

–

For OF

•

NOx concentration has showed a high dependence on O2

excess‐CO formed and

coal rank.

•

NOx concentrations has been clearly higher than under AF due to the large O2

concentration in comburent gas (35‐40% OF vs. 21% AF) and higher density of OF

exhaust gases

•

Differences are shortened when expressed per energy unit

11





•

Air in‐leakages in the facility during

oxy‐firing tests is detected: 7‐8 %, up to 15‐20% with RFG

•

NOx

concentrations are higher under

oxy‐firing conditions

•

CO2

concentrations in oxy‐firing cases are around 90% (d.b)

•

Combustion efficiencies are around 95 %

12

Romeo et al. 2011. Experimental Thermal and Fluid Science 35 (2011) 477–484





•

This ‘‘D‐shape’’

profile is explained by the increase of

heat rates due to char combustion located near the

splash zone

•

A different distribution of heat release in the

combustor, between the bed and the free‐board is

obtained with biomass: volatiles released from the

biomass are not completely burned in the dense‐solid

zone

13

Romeo et al. 2011. Experimental Thermal and Fluid Science 35 (2011) 477–484





•

Lower minimum fluidization velocities

values where detected under O2

/CO2

mixtures

•

The increase of the CO2

concentration in the

mixture brings along a increase of the bed

porosity

•

Pressure drop through the distributor change with

different gases blends: importance of the design

14

Guedea et al. /2011. Chemical Engineering Journal doi:10.1016/j.cej.2011.10.026





–

Low primary fragmentation was detected for both sort

of limestone

–

Oxy‐firing decreases primary fragmentation likely due

to the absence of calcination

–

Other parameters as particle size or SO2

concentration

do not seem to affect primary fragmentation

–

Limestone particle size distribution models under air‐

firing can be simplified to be used in oxy‐firing case

15

C. Lupiáñez et al. 2011. Fuel Processing Technology, 92, 1449–1456

PRIMARY FRAGMENTATION UNDER OXY‐FIRING CONDITIONSIn collaboration with Consiglio Nazionale delle Ricerche CNR,

and Università

di Napoli Federico II

Thermal shockGas releasing (steam and CO2

)Effective particle size Original particle size

Atmosphere compositionTemperatureLimestone




Oxyfuel BFBC‐CFBC. Simulation

16

O2

+CO2

denser

than O2

+ N2

Higher O2

concentration

More compact boilers↓

Less available area for water

wall heat exchanger

Higher particle combustion

temperature

Need of additional heat transfer for controlling bed temperature

More intensity in transfering heat to

the available water wallsHigher transfer in the External

Heat Exchanger

By increasing Gs




Oxyfuel BFBC‐CFBC. Simulation

•

1.5D large‐scale CFB simulation:

–

From air to oxy, boiler size may

reduce up to 35% and recoverable

heat in EHE increases 15 points

–

For certain boiler size: higher Gs

and thus, EHE heat transfer, allows

wider range of power loads.

–

EITHER increasing Gs OR cooling

solids further ‐> EHE is essential

–

Conventionally EHE consists of a

BFB but…how will it fluidized? ‐>

proper conditions for re‐

carbonation of CaO

17

Oxyfuel CFBC. Simulation

–

Solid looping systems

•


–

650ºC at carbonator, exothermic reaction

–

925ºC at calciner, pure CO2

•

Additional fuel input and O2

necessities

•

Four sources of high temperature heat

–

Many integration schemes with supercritical steam

power plants

•

Very competitive CO2

avoided cost, lower than 15

€/tCO2

–

Cheaper sorbents for low quality fuels (high ash

and sulphur content)

–

Expensive sorbents for high quality fuels (low ash

and natural gas)

18

Romeo et al. 2009. Chemical Engineering Journal, 147, 252–258

Romeo et al. 2008. Energy Conversion and Management 49, 2809–2814





–


Lisbona et al. 2010. Energy Fuels, 24, 728–736

19








CLC EXERGETIC ANALYSIS

•Coal Thermal input : 550 MWth

•Net power output: 279.8 MWe

–

High efficiency CLC with coal as fuel

(50.9%) (CO2

compression included)•

Steam turbine output, 119.8 (MWe

)•

Gas turbine output, 156.9 (MWe

)•

CO2

turbine output, 47.7 (MWe

)•

CO2

compression, 29.9 (MWe

)•

Net power output, 279.8 (MWe

)

–

Exergy efficiency was 64.2%•

The highest irreversibility was located in

the reactors (83.9 MW)

•

Lowest exergy efficiency in CO2

heat

exchangers (66.25%)

20

Guedea et al. 2011. International Journal of Energy and Environmental Engineering, 2, 35‐47




Conclusions. Future work

•

On‐going experimental tests in oxy BFB–

High oxygen concentration, sulphur in coal, temperatures

–

Recirculation and secondary comburent

–

Coals and co‐firing with biomass

•

The role of EHE. Recarbonation. Influence in design

•

Opportunities for energy penalty reduction in CO2

captures based on FB–

Oxyfuel combustion

–

Looping systems

–

Chemical looping combustion

21



Ponferrada, 29‐30 November 2011

Oxyfuel combustion in BFB. Experiences and simulations

Acknowledgements

R+D Spanish National Program from the Spanish Ministry of Science and Innovation (MICINN, Ministerio de Ciencia e

Innovación): projects ENE2005‐03286/ALT, ENE2008‐00440, ENE‐2009‐08246, CIT‐440000‐2009‐26.

Fundación CIUDEN is also acknowledged for the support to the oxyfuel rig development

22

http://www.micinn.es/portal/site/MICINN/menuitem.abd9b51cad64425c8674c210a14041a0/?vgnextoid=d9581f4368aef110VgnVCM1000001034e20aRCRD

oxyfuel combustion in bfb. experiences and simulations romeo.pdf · international energy agency ‐...

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