Design considerations for direct solid fuel chemical looping combustion … · 2013. 7. 25. ·...

Institute of Chemical EngineeringResearch Group Future Energy Technology

Prof. Hermann Hofbauer

Getreidemarkt 9/166 1060 Wien

www.vt.tuwien.ac.at

Design considerations for direct solid fuel chemical looping combustion systems

Tobias Pröll, Johannes Schmid, Christoph Pfeifer and Hermann Hofbauer

IEA GHG R&D ProgrammeHigh Temperature Solid Looping Cycles Network

2nd Network Meeting, Alkmaar, September 15-17, 2010


www.chemical‐looping.at 2T. Pröll

Outline

What is chemical looping combustion (CLC)?

CLC for gaseous fuels – status and limitations

CLC for solid fuels – challenges and approaches

Excursion: dual bed biomass gasification

Improved dual circulating fluidized bed design

Conclusion and outlook



Chemical looping combustion (CLC)

A new process for oxidizing fuels using metal oxides as oxygen carriers transporting oxygen from combustion air to fuel

No mixing of combustion air and fuel, combustion products (CO2 and H2O) not diluted by N2

Highly exothermal reactions in air reactor

Global heat release equal to that of direct combustion

Air reactor(AR)

Fuel reactor(FR)

MeOx

MeOx-1

Air

N2, (O2)CO2, (H2O)

Fuel

Cooling/ condensation

CO2

H2O

CLC shows unique potential for carbon capture because gas-gas separation is inherently avoided.

Global air/fuelratio > 1



Critical issues in CLC

Oxygen carrier particles• thermodynamic suitability• high reactivity• sufficient transport capacity• high mechanical stability• cyclic stability of reactivity and transport capacity

Reactor system• excellent gas-solids contact in both reactors• sufficient solids circulation rate



Dual fluidized bed systems

High in both reactors, no gas phase conversion without solids

Oxygen and heat transportChemical looping

High in the absorber/carbonator, low in the re-calciner (heat-driven)

CO2 (and heat) transportCarbonate looping for

CO2 capture

High in the reformer/carbonator, low in the re-calciner (heat-driven)

CO2 and heat transport, catalyst

Sorption enhanced reforming

Partially for tar reforming in the gas generatorHeat transport, catalyst(Biomass) gasification

Importance of gas–solid contactPurpose of solidsTechnology

Dual fluidized bed technologies apart from FCC

There is an ultimate requirement for good gas-solid contact in CLC systems



Dual circulating fluidized bed(DCFB) reactor system

• Global solids circulation is controlled by air reactor fluidization only (eg. air staging)

• Fuel reactor can be optimized towards fuel conversion

• Inherent stabilization of global solids hold up due to the direct hydraulic link between the reactors

• Low reactor volume compared to bubbling fluidized beds (i.e. low specific solids inventory)

• High potential for scale-upai

rrea

ctor

(AR

)

exhaustAR

fuel

reac

tor(

FR)

exhaustFR

air fuel

LS

LS

LS



CLC pilot plant



Status CLC for gaseuos fuels

140 kW DCFB pilot plant / NiO-based oxygen carrier:• CH4 conversion up to 99% • CO2 yield up to 96% based on total carbon in fuel• good fuel conversion in spite of the limited riser heights

Scale up to next size of about 10 MW possible

Immidiate application for industrial steam generation

Potential for power production limited because of competing gas turbine combined cycle technology

Two development targets for efficient power production• direct use of solid fuel – steam cycle application• pressurized operation for combined cycle application



CLC for solid fuels

There is a huge potential in CLC for coal

There is a lot of recent research on this topic

There are three main challenges associated with direct solid fuel introduction:

• decomposition and oxidation of volatile compounds• satisfactory conversion of char in the fuel reactor• selective removal of fuel ash from the system

Two of the challenges address fuel reactor design



Problem definition

Volatiles form bubbles and move quickly upwards lowcontact time to oxygen carrier

→ Force gas phase to pass dense regions before leavingthe system

Solids are well mixedimmediate loss of unreactedchar to air reactor

→ Try to obtain tubular reactorlike solids flow behavior or

→ Selectively separate carbonfrom oxygen carrier

airr

eact

or(A

R)

fuelreactor(FR)

LS

LS

airsteam

exhaustAR

exhaustFR

solid fuel



Theoretical consideration

Fuelreactor

MeOxMeOx

MeO(x-1)MeO(x-1)

CondensationDepleted airDepleted air

(to compression)(to compression)

Air reactorAir reactor

QAR.QAR.

global air ratio > 1global air ratio > 1CO2 + H2O CO2

H2O

Solid fuel

Air Steam

endoxidizer

devola-tizer

chargasifier



Early design proposal

from: Lewis W.K., Gilliland E.R. Production of pure carbon dioxide. U.S. Patent No. 2,665,972, 1954.



Early design proposal (2)

from: Lewis W.K., Gilliland E.R. Production of pure carbon dioxide. U.S. Patent No. 2,665,972, 1954.

solid fuel

If solid fuel is introducedbetween the "stages":

volatiles must pass through zones above

char is led along with bedmaterial through zonesbelow

Problems: too complicatedgeometry to be built at large scale, high pressure drop



Dual fluidized bedgasifier technology

producer gas flue gas

biomass

steam air

riser

gasifier

connecting chute

additional fuel

loop seal

producer gas flue gas

biomass

steam air

riser

gasifier

connecting chute

additional fuel

loop seal

additional fuel

loop seal

History:→Experience at Vienna

Univ. of Technol. since1993

→ 3rd generation of 100 kW (fuel power input) DFB gasifier pilot plantscurrently in operation

→ Large scale (8 MW fuelpower) plant for CHP generation in successfuloperation since 2001

→ 2nd unit in operation since2009 (10 MW)



Gasifier improvement efforts

char

com

bust

or

gasifier

ULS

LLS

air

fuel

exhaust gas

product gas

steam

char

com

bust

or

gasi

fier

ULS

LLS

air

fuel

steam

G-ILS

exhaust gas

product gas



New dual CFB design

Fuel reactor divided in verticalsections by areas of reducedcross section

Fast fluidization regime in thereduced cross section, bubbling to turbulent regime in the zones between

Consecutive dense zones

Gas-solid counter-currentflow behavior

Particle size separation

airr

eact

or(A

R)

exhaust AR

fuelreactor(FR)

exhaustFR

air steam

ULS

LLS

LS

solid fuel



Cold flow model testing



Local behavior

pressure, qualitative Solids density (1 – )



Conclusion/Outlook

Small geometrical change may be key to make dual bed systemssignificantly more efficient in fuel conversion

Erosion seems manageable, expected velocities 1 - 5 m/s

Significant acceleration effects around flow obstacles

Ongoing: investigation at three different cold flow models withvarious particles Determination of suitable operating regimes

Next step: 150-200 kW pilot unit (gasification and possibly CLC)

Contact:Tobias Pröll

[email protected]‐looping.at


Prof. Hermann Hofbauer

Getreidemarkt 9/166 1060 Wien

www.vt.tuwien.ac.at

Acknowledgement:

Financial support from the Austrian Government Climate and Energy Programmefor the research project NE-IF 821954 "G-volution" is greatfully acknowledged.

Design considerations for direct solid fuel chemical looping combustion … · 2013. 7. 25. ·...

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