METHODS TO REDUCE TARS PRODUCTION DURING THE GASIFICATION PROCES (Bibliography review)

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METHODS TO REDUCE TARS PRODUCTION DURING THE
GASIFICATION PROCES(Bibliography review)

• Jose Miguel Arostegui Ordorica
• Andrés Cabanillas Cabanillas
• CIEMAT. Madrid (Spain)

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OUTLINE

• - Tar definition, classification and dew point
• - Tars removal methods
• Primary methods
• Operation conditions
• Bed material
• Bibliography

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TAR DEFINITION
- The organics, produced under thermal or
partial-oxidation regimes (gasification) of any
organic material, and are generally assumed to be
largely aromatic. 1 - All organic contaminants
with a molecular weight larger than benzene 2.
Benzene is not considered to be a tar. - The
Achilles heel of biomass gasification as tars are
the major technical obstacle in the
implementation of this technology.
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TARS CLASSIFICATION
- Classification 2 I.- GC undetectable
tars. II.- Heterocyclic compounds. High water
solubility. III.- Aromatic components. IV.-
Light polyaromatic hydrocarbons (2-3 rings
PAHs) V.- Heavy polyaromatic hydrocarbons (?
4-rings PAHs) VI.- GC detectable, not
identified compounds. GC.-
Gas Chromatography)
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TARS CLASSIFICATION
Most relevant in water pollution
Most relevant in dew point
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Dew point of a mixture
The tar dew point is the temperature at which
the real total partial pressure of tar equals the
saturation pressure of tar . Mathematically, it
is that temperature at which
yi Mole fraction component i
in vapour phase xi
Mole fraction component i in liquid Ki
Vapour-liquid equilibrium ratio
yi/xi ? Pi Vapour
pressure component i P
Total pressure of mixture yv1,
yv2, Molar fractions of condensable gases
Pv1, Pv2, Vapour pressure of
condensable gases ygi Molar
fractions of incondensable gases
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Dew point of a mixture
Observations 1.- Iteration process with
temperatures ? ?1 Composition
of condensates at dew point 2.- The component
with a very low vapour pressure imposes the dew
point. 3.- http//www.thersites.nl/completemodel
.aspx
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Equilibrium tar concentrations vs dew points
Water
Updraft
FBG
Downdraft
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TARS REMOVAL METHODS

• To prevent or convert tars formed in the gasifier
• Selection of the operating conditions (P, T,
  ER)
• Bed additives/catalyst
• Gasifier design

Primary
Methods

• Chemical or physical treatment downstrem of
  process
• Thermal or catalytic cracking
• Mechanical methods cyclones, bag filters,
  particle
• separator, sand filters, ceramic filters,
  scrubbers,

Secondary
DRY WET
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CELULOSE DECOMPOSITION
Low heating
Fast heating
CO, CO2, H2, CH4 Char
TARS
Primary
Terc.
Secondary
T (low)
T (medium)
T (high)
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Primary methods Selection of the operating
conditions 3

• Temperature
• Influence Reduction and final composition
  of tars

T 1-2 rings
3-4
Tgt1100ºC to achieve high cleaning efficiency 13
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Primary methods Selection of the operating
conditions 1012
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Primary methods Selection of the operating
conditions 3
b) ER

• Equivalence ER??T. ER ? decreasing in Heating
  Value
• Increments in ER lead to a decreasing in total
  tars but the
  
  increasing in PAH and dew points

• Residence time ??Kinetic of water-shift,
  reforming, polymerisation and cracking
• If time ? Class 4-5 ? Class 2-3 ?

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Primary methods Selection of the operating
conditions 3
d) Ash Content. Negligible impact
e) Lignin ??Tar. No in composition but in
quantity

• f) Moisture content
• Decreasing of total tar 50 with the increment
  in moisture
• No decrease in water-soluble heterocyclic
  compounds (Class 2)

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Primary methods Selection of the operating
conditions 3
g) Use of Steam/O2, (from 0.7-1.2 ?85), CO2 h)
Black box model ?(conversion)
abTbedcTefd??eER
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Primary methods Raw materials in the bed

• Objectives Promotion of char gasification,
  changes in gas composition and reduction of tars
• Criteria for catalyst of condensable organic
  compounds 4
• The catalysts must be effective in removal of
  tars
• Distinction between thermal cracking and
  catalytic conversion
• If the desired product is syngas, the
  catalysts must be capable of reforming methane.

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Primary methods Raw materials in the bed

• (Promotion of char gasification, changes in gas
  composition and reduction of tars)
• Criteria for catalyst of condensable organic
  compounds 4
• The catalysts should provide a suitable syngas
  for the end process.
• The catalysts should be easily regenerated.
• The catalysts should be strong.
• The catalysts should be inexpensive.

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Primary methods Raw materials in the bed
Hydrocarbons may be reformed on catalyst
surface with either steam or carbon dioxide or
both (increasing LHV) Endothermic
reactions
T ? Reactions ?
P ?
Reactions ?
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General Observations Addition of active bed
materials
The following general observations can be made
with the addition of active bed material during
gasification 12
1.- A change in product gas distribution 2.- A
decrease in tar amount 3.- An increase in
hydrogen production 4.- A slight decrease in the
amount of CO and increase in the amount of
CO2 5.- An almost no variation in the amount of
CH4 6.- Problems regarding catalyst deactivation
and carryover of fines were severe
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Primary methods Raw materials in the bed

• - Limestone
• Limestone(25)Silica(75). To prevent
  agglomeration of bed.
• Limited value on removal tars. Class 2.
• Some increasing of HV.

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Primary methods Raw materials in the bed

• - Dolomites
• MgCO3.CaCO3 (variable composition from source
  to source)
• 30CaO, 21MgO, 45CO2, and SiO2, Fe2O3,
  Al2O3
• Different yields depending on the authors.
  
• It may used to reduce tars in primary
  catalyst, dry-mixed with biomass or in a
  downstream reactor. Mainly in secondary reactors
  (attrition).

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Primary methods Raw materials in the bed

• - Dolomites
• Cheap.
• Particle break and high fine production.
• Calcined more activation. Could decrease the
  amount of tar in 5 times 5.
• The elimination of tars is mostly due to
  steam and dry reforming reactions H2 ? and CO?).
  Tar removal depending of CO2 and H2O contents

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Primary methods Raw materials in the bed

• - Dolomites
• The water-soluble heterocyclic compounds can be
  easily converted by thermal treatment (900ºC)
• High activity than olivine. Mixtures calcined
  dolomiteolivine
• Dolomite (Activity associated to the
  specific surface)
• BET surface area 9.12 m2 g-1
  Dolomite
• 0.42
  Olivine
• No effects on dew points
  

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Conversion of different tar classes with calcined
dolomite as catalyst in a Secondary reactor 6
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Primary methods Raw materials in the bed

• - Olivine
• (Mg,Fe)2SiO4 .Variable composition from source
  to source.
• Lower efficiency than dolomite.
• Necessity of activation.
• It is not yet known if olivine itself has any
  catalytic activity.
• High melting point.
• No attrition. Material in bed or in secondary
  reactors.
• No porous. Low surface area.
• Fe(III) activity.

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Primary methods Raw materials in the bed

• - Olivine
• Activation with air at high temperature 7,8.
• Deactivation with the deposed char
  (Regeneration).
• Possibility to obtain M-olivine catalyst.
• H2O and CO2 have an enhancing and H2 has an
  inhibiting effect on naphthalene decomposition.
• Shoot formation in removal of heavy tars.
• Activation Treatment.
• Time ? Conversion ?
• Temperature ? Conversion ?

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Conversion of different tar classes with olivine
as catalyst in a secondary reactor 6
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Conversion of tars with different additives
(900ºC) 6

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Effect of olivine pretreatment on naphtalene
7,8
Effect of olivine pre-treatment on naphthalene
conversion. T 750900 ºC gas mixture H2O, Ar
Tt 900C (in air) t 1 h.
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Effect of pre-treatments on naphtalene 7,8
Effect of pre-treatment time on naphthalene
conversion. T 900 C gas mixture H2O, Ar Tt
900 C (in air) t 1, 5 and 10 h.
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Distribution of different tar compounds with 10
hours pre-treated olivine 3
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Primary methods Raw materials in the bed

• - Char
• Biomass char has a good catalytic activity for
  tar removal
• (Downdraft gasifiers. Low tars)
• Low cost and natural production inside
  gasifier
• Necessity of continuous char supply

DOWNDRAFT
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Effect of char on Phenol, T700ºC, ?0.3 s11
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Effect of char on Naphtalene, T900ºC, ?0.3 s
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Main technical implications of primary measures
3
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References

• 1.-Biomass Gasifier Tars Its Nature,
  Formation and Conversion. T.A. Milne and R.J.
  Evans NREL
• 2.-The novel OLGA technology for complete tar
  removal from biomass producer gas. Patrick C.A.
  Bergman, Sander V.B. van Paasen, and Harold
  Boerrigter ECN
• 3.- Primary measures to reduce tar formation in
  fluidized-bed biomass gasifiers. Final report SDE
  project P1999-012 (march 2004).
  ECN-TUE-TNO/MEP-UT
• 4.- Review of literature on catalyst for
  biomass gasification. D. Sutton, B. Kelleher,
  J.R.H. Ross. Fuel Processig Technology 73
  (2001)155-173
• 5.- Corella J, Herguido J, Gonzalez-Saiz J,
  Alday JF,Rodriguez-Trujillo JL. Fluidized bed
  steam gasification of biomass with dolomite and
  with a commercial FCC catalyst. In Bridgwater
  AV, Kuester JL, editors. Research in
  thermochemical biomass conversion. London
  Elsevier, 1988 p. 75465.
• 6.- Catalytic decomposition of biomass tars
  use of dolomite and untreated olivine. L. Devi et
  al. / Renewable Energy 30 (2005) 565587
• 7.- Catalytic removal of biomass tars Olivine
  as prospective in-bed catalyst for fluidized-bed
  biomass gasifiers. 2005 by Lopamudra Devi Thesis,
  Eindhoven
• 8.- Pretreated olivine as tar removal catalyst
  for biomass gasifiers investigation using
  naphthalene as model biomass tar. L. Devi et al.
  / Fuel Processing Technology 86 (2005) 707730
• 9.- A Review of the Literature on Catalytic
  Biomass Tar Destruction. Report December 2002
  NREL/TP-510-32815. D. Dayton
• 10.- Hallgren A. Improved technologies for the
  gasication of energy crops. Publishable Final
  Report (TPS AB), European Commission JOULE III
  Programme, Project no.JOR3-CT97-0125.
• 11.- Experimental comparison of biomass chars
  with other catalysts for tar reduction Z. Abu
  El-Rub a, E.A. Bramer, G. Brem (In Press)
• 12.- A review of the primary measures for tar
  elimination in biomass gasication processes.
  Lopamudra Devi, Krzysztof J. Ptasinski, Frans
  J.J.G. Janssen. Biomass and Bioenergy 24 (2003)
  125 140
• 13.- Catalytic conditioning of organic volatile
  products produced by peat pyrolysis David Sutton
  , , Brian Kelleher and Julian R. H Ross. Biomass
  and Bioenergy 23 (2002) 209 216

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Modifications in gasifier designs
product gas
flue gas
Vienna University of Technology
steam
steam
Gasification
Gasification
Combustion
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Modifications in gasifier designs
Asian Institute of Technology
Technical University of Denmark
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Modifications in gasifier designs
Moving-bed gasifier with internal recycle.
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Summary of properties and effectiveness of
nonmetallic catalysts used for tar destruction
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