Title: METHODS TO REDUCE TARS PRODUCTION DURING THE GASIFICATION PROCES (Bibliography review)
1METHODS TO REDUCE TARS PRODUCTION DURING THE
GASIFICATION PROCES(Bibliography review)
- Jose Miguel Arostegui Ordorica
- Andrés Cabanillas Cabanillas
- CIEMAT. Madrid (Spain)
2OUTLINE
- - Tar definition, classification and dew point
- - Tars removal methods
- Primary methods
- Operation conditions
- Bed material
- Bibliography
3TAR 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.
4 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)
5TARS CLASSIFICATION
Most relevant in water pollution
Most relevant in dew point
6Dew 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
7Dew 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
8Equilibrium tar concentrations vs dew points
Water
Updraft
FBG
Downdraft
9TARS 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
10CELULOSE DECOMPOSITION
Low heating
Fast heating
CO, CO2, H2, CH4 Char
TARS
Primary
Terc.
Secondary
T (low)
T (medium)
T (high)
11Primary 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
12Primary methods Selection of the operating
conditions 1012
13Primary 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 ?
14 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)
15Primary 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
16Primary 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.
17Primary 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.
18Primary 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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20General 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
21Primary 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.
22Primary 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).
23Primary 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
24Primary 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
25Conversion of different tar classes with calcined
dolomite as catalyst in a Secondary reactor 6
26Primary 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.
27Primary 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 ?
28Conversion of different tar classes with olivine
as catalyst in a secondary reactor 6
29Conversion of tars with different additives
(900ºC) 6
30Effect 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.
31Effect 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.
32Distribution of different tar compounds with 10
hours pre-treated olivine 3
33Primary 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
34Effect of char on Phenol, T700ºC, ?0.3 s11
35Effect of char on Naphtalene, T900ºC, ?0.3 s
11
36 Main technical implications of primary measures
3
37References
- 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 -
38Modifications in gasifier designs
product gas
flue gas
Vienna University of Technology
steam
steam
Gasification
Gasification
Combustion
39 Modifications in gasifier designs
Asian Institute of Technology
Technical University of Denmark
40 Modifications in gasifier designs
Moving-bed gasifier with internal recycle.
41 Summary of properties and effectiveness of
nonmetallic catalysts used for tar destruction
9
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