Corella 2008

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194 Int. J. Oil, Gas and Coal Technology, Vol. 1, Nos. 1/2, 2008

Copyright 2008 Inderscience Enterprises Ltd.

Biomass gasification with pure steam in fluidisedbed: 12 variables that affect the effectivenessof the biomass gasifier

Jos Corella,* Jos-Manuel Toledo andGregorio Molina

Department of Chemical Engineering,University Complutense of Madrid,Madrid 28040, SpainFax: +34-91-394-4164E-mail: [email protected]*Corresponding author

Abstract: Biomass gasification in fluidised bed with pure steam has alreadygenerated a 60 vol.%, dry basis, H

2rich gas that was increased to 7080 vol.%

H2 by using a CO

2 sorbent in the gasifier bed. A tar content as low as

0.25 g/Nm3 has also been reported when an active catalyst is used in thegasifier bed. Biomass gasification in fluidised bed with pure steam, therefore,has some potential interest for the production of a very rich in H

2 clean gas.

This work shows in detail 12 operational variables that have alreadydemonstrated a clear influence on the product distribution from the gasifier.Among all the products originating from the gasifier, this study concentrates onthe hydrogen and tar contents in the raw gasification gas.

Keywords:biomass; gasifier; hydrogen production; renewable energies;biomass gasification; steam gasification; hydrogen; fluidized bed.

Reference to this paper should be made as follows: Corella, J., Toledo, J-M.and Molina, G. (2008) Biomass gasification with pure steam in fluidisedbed: 12 variables that affect the effectiveness of the biomass gasifier,Int. J. Oil, Gas and Coal Technology, Vol. 1, Nos. 1/2, pp.194207.

Biographical notes:Jos Corella received a PhD in Chemical Engineering in1969. He is a full-time Professor of Chemical Engineering since May 1972.He started to work in fluidised beds in 1965 and in biomass gasification in1982. This means that he has more than 40 years of experience in fluidisationtechnologies and 25 years in advanced gasification of biomass. He haspublished around 200 papers. According to Webs of Science and/or

Knowledge

his Hirschs (h) index is 23.Jos-Manuel Toledo received a PhD in Chemical Engineering in 2003 and has10 years working experience on advanced gasification of biomass in fluidisedbed, and has published 22 papers. Even though he is a young person, hisHirschs (h) index is 7.

Gregorio Molina received an MS in Chemistry in 2003, and has 3 yearsworking experience on advanced gasification and catalytic hot gas cleaningwith monoliths.

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Biomass gasification with pure steam in fluidised bed 195

1 Introduction

Biomass gasification in fluidised bed is quite a well known process going back to themid-1980s when several institutions in the USA (PNL in Richland, WA,Battelle-Columbus, Universities of Arizona State, Missouri-Rolla and Kansas State, etc.)and in Spain, among other countries, published many papers on it. This process generatesan interesting H

2-rich, nitrogen free and medium heating value gasification gas. Biomass

contains on average only a 6 weight%of hydrogen and by itself would not be a valuableor interesting source of hydrogen. Nevertheless, some extra H

2 can be added to the

gasification gas from the molecule of H2O if this species is used as gasifying agent.

But to crack the molecule of H2O requires much energy and so the gasification with pure

steam becomes a highly endothermic process.To solve this problem, a possibly good solution could be to couple the endothermal

steam gasifier with an exothermal reactor where the char is combusted and to use a solidheat carrier between the two reactors, in a very similar way to FCC Units in oil refineries.This circulating system between two reactors, sometimes called Dual Fluidised Bed(DFB), already reached the demo scale in Burlington, Vermont, USA 10 years ago. Sincethis approach is complex and expensive, several research activities and plants based onthis concept were stopped in the 1990s or even more recently, as happened to theFERCOs plant in Burlington. Nevertheless, very recently there has been an explosionof interest in hydrogen as a non-contaminant source of energy. Consequently, there hasalso been a renewed interest in the biomass gasification with pure steam, as a process toproduce H

2. In fact, Aznar et al. (2006) have already obtained 140 g H

2/kg biomass daf

operation parameters that affect the gas is an interesting yield. For this reason, this studyis aimed at reviewing the design and operation parameters, which affect the gascomposition and gas quality in biomass gasification with pure steam. In this review, thekey component concerning gas composition will be the H

2-content and the key

component concerning gas quality will be the tar-contentin the gasification or producedraw gas.

It should be pointed out that this short review is only concerned with:

1 Gasification with pure steam. Only a few references to other gasifying agentswill be made due to their relevance for this study.

2 Papers published after the late 1980s. Papers before that date, although some ofwhich are relevant, such as those by Walawender and Fan in USA, were alreadyreviewed in Corella et al. (1991) and Herguido et al. (1992).

3 Gasification of biomass only in Bubbling Fluidised Beds (BFBs). Gasificationin DFBs, with and without simultaneous CO

2capture, has been recently

analysed in another work (Corella et al., 2007a and 2007b). Due to theirrelevance for this study, very few references (Fushimi et al., 2003; Pfeifer et al.,2004a,b) will be made to other types of gasifier.

4 Gasification at atmospheric pressure, or slightly above. The effect of the totalpressure on the product distribution at the gasifier exit is already known, but ithas not been studied yet.

We then show the design and operation variables which have already demonstrated inexperiments to affect the product distribution in biomass gasification in fluidised bedwith pure steam.

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196 J. Corella, J-M. Toledo and G. Molina

2 Variables that affect the product distribution

The variables discussed here are not ranked by importance because

1 all are important

2 most of them are interrelated

3 the key operation variable may be one or another depending on the values usedfor the remaining variables of operation.

These variables will be outlined briefly. For more details, the reader is kindly referred tothe papers discussing the relevant variable.

2.1 Temperature in the bed of the gasifier (Tb)

The effect of Tbon product distribution has been extensively studied, as given in Table 1,

and is well known today. From the point of view of low tar content, Tbshould be as high

as possible. Nevertheless, in biomass gasification with pure steam, it is not easy to reach750C, it is difficult to reach and work at 800C850C and it is very difficult to work inthe gasifier above 900C.

As Table 1 gives, and with a bed of silica sand, the highest H2-content obtained has

been 60 vol.%, dry basis (Corella et al., 1994, 2001). With in-bed additives and/orcatalysts, tar content as low as 0.9 (Wei et al., 2006, 2007) and 1.5 g/Nm 3(Pfeifer et al.,2004a,b) have been obtained in the gasification gas.

It has to be pointed out that Tbis not an independent variable in a BFB gasifier but it

depends on a lot of true independent variables such as the moisture of the biomass, theexternal energy provided to the gasifier, the Steam to Biomass (S/B) ratio, etc.

2.2 Steam to biomass fed ratio (S/B)

The S/B ratio [(kg H2O/h)/(kg biomass, as received, fed/h), dimensionless] is another

variable studied by many authors (see Table 1) and whose effect is well known. Therange most studied for the S/B ratio is between 0.20 and 2.0. At low (0.200.40) valuesfor S/B there could not be enough steam to fluidise the bed. At T

b = constant, on

increasing S/B the tar yield decreases and the product distribution from the gasifier isimproved. Nevertheless, it has also to be remembered that the steam flow rate has to beheated to the temperature of the bed (800C850C) and it consumes energy and costsmoney. Besides, by increasing the S/B ratio, the conversion of the H

2O in the gasifier

progressively decreases, which is an important fact and problem in this process. It has

already been reported (Gil et al., 1997; Puchner et al., 2005) how for (S/B) >1 the gas atthe gasifier exit contains more than 60 vol.%, wet basis, of unreacted H2O. In otherwords, as Pfeifer et al. (2004a) have reported, the conversion of the steam in the BFBgasifier (XH2O) is as low as 1.58.8%and 5.07.1%. Other authors (Fiorenza et al., 2007;van der Meijden et al., 2007; Xu, 2007), and ourselves, have also found H

2O conversions

in the gasifier less than 10%. This means that more than 90% of the steam used tofluidise the BFB gasifier is not used in it. Unreacted H

2O can be separated, by

condensation, from the raw gasification gas and recycled to the gasifier, but it must benoted that in this cooling, condensation and further recycling of the H

2O (with their

corresponding vaporisation and reheating till 800C850C) a lot of energy is lost

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(Pfeifer et al., 2006). The thermal efficiency of the overall gasification process becomes

very low because of the very low values for XH2O. This is a weakness of the gasificationwith pure steam which remains to be solved. Those working with this process shouldalways report detailed heat balances in the whole plant which often are missed inrelevant papers.

To conclude this point, values for (S/B) higher than 1.21.5 are not recommended.The most promising interval or range for (S/B) would be between 0.40 and 1.0, althoughvan der Meijden et al. (2007) reported that they were working well at S/B of 0.28.

Table 1 Effect of the temperature in the bed (Tb) and of the steam/biomass (S/B)

ratio in biomass gasification in fluidised bed with pure steam.

Variable Intervalstudied

Ref. H2content

Volume.%,

dry basis

Tar content

[g/Nm3

,

dry basis]

LHV[MJ/Nm

3,

dry basis]

XH2O

(%)

Tb(C) 570770 Singh et al.

(1986)3149 11.512.6

650820 Corella et al.(1991)

45 12.6


5060 70


5060 40

650800 Wei et al. (2006,2007)

40.7 1.567

650780 Herguido et al.(1992)

3557 2070 11.813.8

725900 Franco et al.(2003)

3545

750900 Pfeifer et al.(2004a,b)

4145 0.94.5 1.58.8*

750880 van der Meijdenet al. (2007)

1626 2443

S/B 0.402.6 Corella et al.(1991)

5060 70

(kg/kgd.a.f.)

0.401.5 Corella et al.(1994)

4560 40

0.201.2 Wei et al. (2006,2007)

3645 1.5

0.402.6 Herguido et al.

(1992)

5060 1060 1014

0.450.80 Franco et al.(2003)

2135

0.280.90 Pfeifer et al.(2004a,b and2006)

4145 57.1**

0.401.2 Wang et al.(in press)

2054 1114.7

*Figure 10 in Pfeifer et al. (2004a).

**Figure 9 in Pfeifer et al. (2004a).

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Table 2 Effect of the bed composition and of space time of the gas (g) in the bed


Ref. H2content

Vol.%, drybasis

Tarcontent

[g/Nm3

,

drybasis]

LHV

[MJ/Nm3,

dry basis]

XH2O

(%)

Bedcomposition.

Presence ofcatalysts or

FCC catalyst,

dolomite inbed

Corellaet al.(1988b)

4052 5.5 11.513.4

additives inthe bed ofthe gasifier

Olivine andimpregnatedolivines

Rapagnet al. (2000,2002)

4552 0.251.4

CaO Dalaiet al. (2003)

Limestone,olivine,dolomite

Weiet al. (2006,2007)

9.411.2

Co/MgO Tasakaet al. (2006,2007)

Two olivines Rauchet al. (2006)

3440 0.81.5 1213.5

Ni-olivine Pfeiferet al.(2004a,2006)

3845 1.2 4.47.2

Fe-impregnatedalumina

Matsuoka etal. (2006)

iron oxides Rosset al. (inpress)

Clay brick

Space timeof the gas inthe bed (s)

0.31.5 Corellaet al. (1991,2001)

48 40

0.72.7 Wei et al.(2006)

2550 0.754 127*

* These data are in Figure 13 of Wei et al. (2006). The gasifier used was a downdraftmoving bed (not a BFB).

2.3 Bed composition: presence of additives and/or catalysts in the bed of thegasifier

This variable has been studied by many authors, as indicated in Table 2. The pioneeringwork done in gasification with steam was made with silica sand as fluidising solid or bedmaterial. However, even in 1988 a study was published with the detailed effects of

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two additives to the gasifier bed, dolomites and commercial and in equilibrium (once

used in FCCUs) FCC catalysts (Corella et al., 1988b). Since then, many authors havestudied different catalysts to be used in the bed of the gasifier. Most of them showed verypositive results concerning gas composition and quality. Nevertheless, the followingfacts need mentioning:

1 Some of the proposed catalysts would be very expensive even more for aprocess like this one in which both feedstock and product (gas) are very cheapand the economic benefits are very low.

2 They do not yet succeed at commercial scale. This research has been mostlycarried out at small scale, with small amounts of catalysts.

3 The life of the catalyst is usually not reported.

4 Some heavy metals, as nickel, in the catalyst are transferred by erosion to theparticles of char in the bed, converting it into a contaminated residue which isnot easy (at least not cheap) to dispose of.

5 Many gasification tests were carried out at very low throughputs in the gasifier.Publications are still awaited on the performance of some proposed catalystsunder high, above 750 kg/h m2, throughputs, those of interest at commercialscale.

Leaving aside the nickel in olivine that has provided good results, but is expensive andmay transfer some nickel to the char too, the best results to date have been obtained witholivine. A tar content with olivine as low as 0.25 g/Nm3, dry basis, was reported byRapagn et al. (2002).

Unfortunately, there are very few quarries of olivine in Europe and the transport ofthe olivine to different countries could make this additive unacceptably expensive insome scenarios. So, for these authors and for many scenarios, the optimal or, at least, agood additive remains still to be found.

2.4 Space time of the gas (g) in the bed

This variable, often incorrectly called averaged or mean residence time of the gas, hasnot been much studied in an explicit way. The only two teams that have studied it aregiven in Table 2.

Based on the authors own experience, and in particular on the Corella et als modelfor BFB biomass gasifiers with pure steam (Corella et al., 2001), a value for gof 1.2 sec

is proposed. Higher values would increase the tar cracking in the bed (Corella et al.,1991, 2001) which is a positive or wanted effect. However, if the superficial gas velocityat the inlet of the bed (u

0) is typically 1.0 m/s, for g=1.20 sec, the total height of the bed

should be 1.2 m, which is a value often found in BFBs. Heights higher than 1.2 m arepossible as well but the pacross the bed would become high and perhaps unacceptable.If the pin a given BFB gasifier is not a problem, gcould be increased to values higherthan 1.2 sec.

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2.5 Space velocity for the biomass (WHSV) in the gasifier (h1

)

This variable can also be handled as the throughput (TR) of the gasifier. Given that theseimportant operation variables are not yet very popular, definitions are given below:

WHSV =Weight Hourly Space Velocity for the biomass, [kg biomass fed a.r./h]/[kg solids inventory in the BFB]

TR =kg biomass a.r. fed to the gasifier/hm2of cross sectional area of thegasifier (at the bed bottom if there is a troncoconical section)

Both variables are interrelated by the height and density of the bed of the gasifier.Although there are not many published data for these variables in fluidised bed gasifiersof biomass with pure steam, these authors consider, from their own experience, that agood value of reference for the throughput of these BFB gasifiers is 750 kg

biomass/hm2

. For a bed in a BFB of 1.2 m height and a density of 1200 kg/m3

, thisthroughput is equivalent to a WHSV for the biomass of 0.50 h 1. Notice that this value is26 times lower than those used in circulating fluidised bed biomass gasifiers operatedwith air (Sanz and Corella, 2006).

It should be pointed out that some studies carried out at small scale work, use verylow throughputs which means very soft conditions. Testing in-bed catalysts underthroughputs as low as 100150 kg/hm2 provide results which most probably could bevery far from those that would be obtained at commercial scale with TR 750 kg/hm2.

2.6 Temperature, volume, topology and hydrodynamics in the freeboard

Only a few authors, as given in Table 3, have studied the effect of the freeboard and of

the pipes and vessels located downstream from the fluidised bed in a gasifier operatedwith pure steam. If that volume above the bed is at a high temperature (above approx.600C), there would be some tar cracking and steam reforming in it, as demonstrated bySanz and Corella (2006). Consequently, the H

2-content, the tar-content, the LHV of the

produced gas and the overall conversion of the H2O in the gasification gas would change.

Some examples have been reported by Corella et al. (1989, 1991), Hoveland et al. (1985)and Fiorenza et al. (2007). The freeboard has, therefore, to be taken into account whenreporting or calculating the product distribution at the gasifier exit.

2.7 Type of biomass (feedstock)

The effects of the type of biomass used as feedstock are quite well known. Some authorswho have studied it are given in Table 3. It is known how:

The content in alkali (K and Na) species has a strong influence on

the reactivity of the biomass, which affects the throughput of the gasifier

on the melting of the ash (char) generated in the gasification and then in thepossible problems of agglomeration in the bed, walls and even gasdistributor plate (Corella et al., 2006).

A high content in alkalis in the biomass limits (lowers) the maximum allowablegasification temperature (Arvelakis et al., 2003; hman et al., 2003; Paisley, 2002),therefore increasing the tar and decreasing the H

2in the gasification produced gas

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The content in N-containing species in the biomass determines the NH3content

in the raw gasification gas. This may become a problem with some types ofbiomass.

The size and shape of the biomass may determine the type and location of thefeeding point.

Nevertheless, and as authors own opinion, if the gasifier has an optimal design andoperation, and for most types of biomass, this variable is not a key or determining factoron the H

2- and tar-contents in the raw gasification produced gas.

Table 3 Effect of the temperature at the freeboard and of type of biomass (feedstock)


Ref. H2content

[volume.%,

dry basis]

Tar content[g/Nm

3

,

dry basis]

LHV[MJ/Nm

3, dry

basis]Freeboard:

a) empty 400900C Corella et al.(1991)

55 10

Tbed

+83C Hovelandet al. (1985)

=2 to 10 =+0.2 2.0

b) withsilica sand(withthermalcrackingdownstreamfrom the

gasifier)

0.280.85

[kgsandh/Nm3]

Corella et al.(1991)

55 10

600900C Corella et al.(1989)

810

Type ofbiomass(feedstock)

Four differenttypes ofbiomass

Herguidoet al. (1992)

3560 1070 1014

Pine sawdustand legumestraw

Wei et al.(2007)

2741 14.366.6

Pine wood,holm-oak,eucalyptus

Franco et al.(2003)

41

Six different

types ofbiomass

Prasad et al.

(1988)

2042

2.8 Moisture of the biomass (feedstock)

In biomass gasification with pure steam, the detailed effect of the moisture content in thefeedstock has not, as far as these authors are aware, been published until now.Nevertheless, it is well known from biomass gasification with air how this moistureaffects the temperature of the bed of the gasifier, T

b(Sanz and Corella, 2006). Since this

Tbgreatly affects the H

2- and tar-contents, it can be said that the biomass moisture has an

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indirect effect on these top important results. It has to be added that the water content of

the feedstock clearly affects or influences the amount of auxiliary fuel that has to be usedin the overall gasification process as demonstrated recently by Murakami et al. (2007),having therefore, a clear influence on the chemical efficiency (Puchner et al., 2005) andthe economical feasibility of the overall gasification process.

Finally, it has to be remembered that to calculate the total [H2O/biomass] ratio, the

H2O entering with the biomass as its moisture has to be added to the H

2O used as

fluidising gas in the gasifier.

2.9 Type and location of the biomass feeding point

Already in 1988, it was demonstrated how the location of the feeding point to the gasifierinfluences the product distribution (Corella et al., 1988a). This is due to the different

heating rate of the biomass which depends on the location where it is fed. Some authorswho have studied the feed location are given in Table 4. If possible, the biomass shouldbe directly fed into the bed, and not from the top of the gasifier.

2.10 Bed design gasifier topology

Ross et al. (2007), for example, have found how some details concerning the design ofthe fluidised bed gasifier, such as the gas (steam) distributor plate, have an influence onthe product distribution.

The (u/umf

) ratio also has an effect on the yields of H2and tar. According to the well

known principles of Chemical Reaction Engineering, as the (u/umf

) ratio increases, thebubbling also increases and then the deviation from the ideal plug or piston flow.It therefore affects the yields of all products from the steam gasification of biomass.

Another interesting parameter is the slope or inclination of the gas (steam) distributorplate; a slope that is not zero in some gasifiers such as the one(s) in Austria (Pfeifer et al.,2004a,b, 2006). In this (these) gasifier(s), the biomass is fed directly into the bed. Thechar produced would go towards the upper zone of the bed because of its low density,according to the well known (Aznar et al., 1989) and important segregation in a fluidisedbed gasifier with a horizontal gas distributor plate (slope = 0). With an inclined gasdistributor plate there is a revolving circulation of the mixture of the solids in the bed.The revolving flow introduces both the charred biomass and the char towards the bottompart of the fluidised bed (This is the well known principle and/or technology in theJapanese EBARAs revolving fluidised beds). Such introduction of the charred biomassbenefits its further gasification in the bed and also the exit of the char at the bottom bedtowards the next combustor, as in the case of the DFB gasifier in Gssing, Austria.

Facing these two benefits by the inclined gas distributor plate, there is one simultaneousdrawback: The residence time or the space-time of the H

2O in the bed is quite different

from one side to another side of the gasifier. The H2O flow, where the height of the bed

is very low will have a small residence time (space-time) and its conversion will be low.Therefore, the averaged (across the diameter of the gasifier bed) or overall conversion ofthe H

2O in that gasifier will be low. In fact, Pfeifer et al. (2004b, 2006) have reported

very low H2O overall conversions, as given in Table 1, in their gasifier with an inclined

gas distributor plate.

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Table 4 Effect of the type and location of the biomass feeding point, of the gasifier topology

and of the circulating rate of bed material

Variable Interval studied Ref. H2content

[volume.

%, drybasis]

Tarcontent[g/Nm

3

,

dry basis]

LHV[MJ/Nm

3,

dry basis]

In-bedfrom the top

Corellaet al. (1988a)

3558 20150 11.613.0Type andlocation of thebiomass feedingpoint (derived:heating rate ofthe biomass)

1, 10 and100 K/s

Fushimi et al.(2003)

two locations ofthe feed

injection point

Ross et al.(in press)

Bed design orgasifiertopology

Cylindrical andconical basesections

Ross et al.(in press)

Circulating rateof bed material(C/B)

2040 Wei et al.(2006)

3742 24.2

530 Puchner et al.(2005)

7074 0.34.5

280 Corella et al.

(2006)1025 Hayashiet al. (2006)

40 van derMeijdenet al. (2007)

1030 Pfeifer et al.(2007)

6668 0.92.1

2.11 Simultaneous CO2capture

A promising new technology is appearing to gasify biomass (or coal) with pure steam ina BFB and with simultaneous CO

2 capture, for example, with CaO. This is generating

new DFB systems. Their description is beyond the scope of this study; besides, it is beingreviewed in a separate work (Corella et al., 2007a and 2007b). Nevertheless, this variablehas to be mentioned in this review here because it is already a proven method or way toincrease the H

2-content in the gasification gas to values above 70 vol.%, dry basis (Florin

and Harris, 2007), and to obtain very low tar content in the gasification gas. In thisDFB-based technology, a key parameter, as demonstrated by Corella et al. (2006) and byPfeifer et al. (2007), is the Circulation rate (C/B) ratio. This is defined as: [kg circulatingsolid (i.e. silica sand + CaO + olivine or other in-bed additive/catalyst + char)/h]/[kgbiomass a.r. fed to the gasifier/h]. It is dimensionless, and has to have a value above 10.

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Table 4 has some references and some interesting results concerning the gasification gas

generated when in the gasifier there is a simultaneous (in-bed) capture of CO2.

2.12 The experience of the operator of the BFB biomass gasifier

Last but not the least, the experience of the operator of the BFB biomass gasifier hasproved to have a clear, even important, influence on the product distribution at thegasifier exit. This variable is most often neither reported nor taken into account, but itreally affects the composition and tar content of the produced gas. This experience maybe considered as a 12th operating variable or may be considered only as the correctaddition of the previously reported eleven variables. The experience of the operator isnot a veritable non-subjective variable, but it affects the process results.

Corella et al. (1993) studied the influence of the operator on the product distribution.A gasification index (I

tar

) for a biomass gasifier with pure steam was defined as:

tar

(char yield)( tar yield)

(steam/biomass)=I

ThisItar

index is an evaluation of the quality of the gasification. A higher Itar

value meansa worse gasification. Corella et al. (1993) observed how this index, other experimentalconditions being the same, slowly decreased from experiment to experiment along theyears of performing gasification tests. This fact was attributed to the increasingexperience of the operator of that gasifier but this checking was then not welldisseminated.

The experience of the operator, as well as of the designer of the BFB gasifier,should always be taken into account to understand the results published by someresearchers.

3 Summary

In typical BFB biomass gasifiers a gasification gas with a H2-content as high as

60 vol.%, dry basis, and a tar content as low as 1.4 g/Nm3, dry basis, has already beenobtained. These two key data have been further improved to 7080 vol.%H2, dry basis,and to only 0.250.30 g tar/Nm3when:

1 the BFB gasifier is coupled to a combustor of the char generated in the gasifier

2 a CO2-sorbent (CaO) and a catalyst (to eliminate most of the tar generatedin-bed) are used in the bed

3 the circulating or cycling rate (C/B) ratio is high in a DFB.

Acknowledgement

This work was carried under project ref. ENE2006-15425 of the Spanish Ministry ofEducacin y Ciencia. The authors are grateful for the financial aid received for thiswork.

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