Bentzen, Jens Dall

Henriksen, Ulrik B.

Hindsgaul, Claus

A comparison of tar determination of particles from a down-draft gasifier using soxhlet extractions (with anisole, dichloromethane and acetone) and pyrolysis of the particles

Online Research Database In Technology

                       General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.  • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal   If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.     Downloaded from orbit.dtu.dk on: Dec 18, 2017Evaluation of Gravimetric Tar Determination in Particle SamplesHindsgaul, Claus; Henriksen, Ulrik Birk; Bentzen, Jens DallPublished in:Evaluation of Gravimetric Tar Determination in Particle SamplesPublication date:2000Document VersionEarly version, also known as pre-printLink back to DTU OrbitCitation (APA):Hindsgaul, C., Henriksen, U. B., & Bentzen, J. D. (2000). Evaluation of Gravimetric Tar Determination in ParticleSamples. In Evaluation of Gravimetric Tar Determination in Particle SamplesPublished by Kyritsis, S., Beenackers, A.A.C.M., Helm, P., Grassi, A., Chiaramonti, D. (eds) 2001,1st World Conference on Biomass for Energy and Industry. Proceedings of the Conferenceheld in Sevilla, Spain, 5-9 June 2000, London, James & James (Science Publishers) Ltd.1EVALUATION OF GRAVIMETRIC TAR DETERMINATIONS ON PARTICLE SAMPLESC. Hindsgaul*, U. Henriksen, J. Dall Bentzen**Technical University of Denmark, Dep. Energy Engineering, Building 403, DK-2800 Lyngby, Denmark*email: claush@et.dtu.dk** COWI Consulting Engineers and Planners AS, Parallelvej 15, DK-2800 Lyngby, DenmarkABSTRACT: In order to compare different methods for quantitative tar determinations in particles, paralleldeterminations were made on particle samples from three points in a low tar two-stage biomass gasifier fueled withwood chips. Extractions with anisole, acetone and dichloromethane showed that dichloromethane extracted thesmallest mass from the samples. Determination by pyrolysis of the particles resulted in higher mass losses than anyof the extractions.1. PURPOSE OF THE WORKMany different methods to determine the amount of "tar" inthe gas and particles from biomass gasifiers are in usetoday. "Tar" is a vaguely defined term for non-solid, oftensticky, organic compounds, which are produced e.g. bypyrolysis of biomass. Each tar determination method repre-sents its own operational definition of "tar". For example,the mass of the Soluble Organic Fraction (SOF) is oftenused as a tar measure. A wide range of solvents has beenused – each capable of dissolving a different range of "tar"substances.In order to compare numbers from different methods andevaluate their efficiencies, controlled parallel determinati-ons are needed.This work compared four different basic tar determinationmethods on particle samples from three sources in a low-tardowndraft biomass gasifier. No chemical characterisationwas made on the tars.2. EXTRACTION SOLVENTSIn 1979, Williams and Chock made a thorough evaluationof solvents for extracting SOF from diesel particles [1].They compiled a "solubility index" ranking ten solvents,most of which were binary mixtures, after their ability toextract mass from diesel particles (see Table 1). Theydefined their solubility index as the mass extracted with thetested solvent relative to the mass extracted by a benzene-ethanol mixture (4:1).Solvent Solubility indexDichloroethane-ethanol 1.12Benzene-ethanol 1.00Chloroform-ethanol 0.99Cyclohexane-ethanol 0.93Benzene-isopropanol 0.92Dichlormethane-ethanol 0.88Dichlorethane-isopropanol 0.85Cyclohexane-isopropanol 0.80Dichloromethane 0.66Dichlorethane 0.66Table 1: Extracted mass from diesel-soot by Soxhletextractions with benzene-ethanol as the basis [1].Table 1 indicates that dichloromethane is not the mosteffective solvent for diesel particles, although it is still thestandard solvent used for extracting such particles.When analysing tar from biomass gasifiers, dichloro-methane is by tradition in widespread use as the solvent.Acetone is sometimes preferred to dichloromethane, sincethe latter is both toxic and carcinogenic. Anisole has beenrecommended by Salzmann et al [3] as an excellent solventfor many tars.It was decided to compare acetone, dichloromethane andanisole as solvents for tar from the two-stage gasifier.3. EXPERIMENTAL WORKFour different gravimetric methods were applied todetermine the tar content in homogenous samples of solidparticulate from the two-stage gasifier:  Soxhlet extraction with acetone  Soxhlet extraction with dichloromethane  Soxhlet extraction with anisole  Pyrolysis at 600oC in N2 atmosphere  Series of extractions in successionThe particle samples were particles collected from threesources at the two-stage gasifier plant at The TechnicalUniversity of Denmark. Earlier investigations have shownthat the majority of the particle mass in the gas was sub-micron soot particles with a low content of tar [2]. Thethree sources of particles were:(1) In existing collection equipment in the hotproducer gas. These particles were already partlyextracted with acetone during collection.(2) Aquatic slurry from a fabric water filter, which fil-tered the scrubber water from the cooled producergas.(3) Particles from a cartridge gas filter used as part ofthe gas cleaning equipment.Published by Kyritsis, S., Beenackers, A.A.C.M., Helm, P., Grassi, A., Chiaramonti, D. (eds) 2001,1st World Conference on Biomass for Energy and Industry. Proceedings of the Conferenceheld in Sevilla, Spain, 5-9 June 2000, London, James & James (Science Publishers) Ltd.2PARTICLE SAMPLE SOURCESCoolerGasfromgasifier(700°C)ScrubberwaterWaterFilterGasfilter(2)(1)(3)ToengineScrubber 40°C50°CFigure 1: The origins of particle samples (1), (2) and (3)in the gasifier plant.Figure 1 shows a schematic presentation of the gascleaning system, from which the particles were collected. Atar sampling device took small gas samples in the gas atpoint (1). The small amounts of particles caught in itsprefilter were used as particle sample (1).After point (1), the gas passed a cyclone (not shown) andentered a cooler where the gas was cooled to approx. 50°C.Water was dispensed into the gas stream inside the venturiscrubber in order to collect most of the particles. In ademister (not shown), the scrubber water drops wereseparated from the gas stream. This scrubber water wascontinually filtered through a water filter. Particles fromthis filter were dried at 104°C and used as particle sample(2).The demisted gas was forced through a cartridge filtermade of impregnated paper. In this filter, the particle con-tents in the gas were reduced from 30-70 mg/m3 to lessthan 4 mg/m3. Particle sample (3) is particles collected inthis filter.Particles from each source were dried at 104oC for 26hours and divided into homogenous samples, to be used fordifferent tar determination methods.For Soxhlet extraction determinations, the samples (0,5-2grams) were wrapped in small fibre-filter packages. Themasses of the packages were determined before and afterthe extraction so that the amount of removed "tar" could bedetermined gravimetrically as the mass losses of thepackages.For pyrolysis determinations, 9-10 grams of particles wereplaced in an open ceramic container in an oven. Then theywere pyrolysed at 600oC in nitrogen atmosphere. The tarcontent was determined gravimetrically as with the Soxhletextractions. Four empty filter packages were extracted asblanks. Their masses were unchanged by the extractions.The extracted particle packages were later extracted usingother solvents in succession.4. RESULTSFigure 2 shows the results from the extraction and pyro-lysis determinations on particles from the three sources.Each number represents one single extraction, since nodouble determinations were made with the same method. Itshould be noted that very small amounts of particles fromsource (1) were available, which is why only two methodswere applied to this sample.DETERMINED TAR LEVELSFigure 2: Tar content (percent by mass) of the threeparticle sources determined by the four differentgravimetric methods.The results show a consistent order of determined tarcontent for all particle sources. For both of the pyrolysedsamples, the pyrolysis method showed a larger amount oftar than any of the extractions. The extraction solvents canbe consistently ordered by decreasing tar determination:anisole > acetone > dichloromethane.The excellent solvent properties of anisole may partly bedue to the fact that the Soxhlet extractions have to beperformed at the boiling point of the solvent. For anisole, itis 154oC, which is considerably higher than fordichloromethane (40oC) and acetone (56oC). The highertemperature can have brought more tar compounds intoliquid form and thus increased their mobility due to thetemperature alone. High temperatures are sometimesundesirable if chemical analyses are to be carried out onthe extract. Since all samples had been dried at 104oC, itwas assumed that the difference in boiling points betweenacetone and dichloromethane did not affect the results,since both were considerably lower than 104oC.Solvent Solubility indexPyrolysis* 1.2-3.9Anisole 1.00Acetone 0.8-0.9%Dichloromethane 0.6-0.7%Table 2: Solubility indices compiled from the resultsof samples (2) and (3) using anisole as the basis.*Pyrolysis is not a solvent, but the pyrolysis tardetermination method.Table 2 shows solubility indices for biomass tar compiledfrom the results for sample (2) and (3) in Figure 2. Notethat the basis is not the same, since data for benzene-ethanol were not available. The best solvent, anisole, waschosen as the basis. The results from sample (1) wereignored since it had been pre-extracted with acetone.The fact that the solubility index of dichloromethane inTable 2 is so similar to that in Table 1 is a coincidencesince both the particle source and the basis solvent aredifferent. Anyway, it shows that dichloromethane isneither the most effective solvent for particle samples-7%-6%-5%-4%-3%-2%-1%0%Hot gas (1) Water filter (2) Gas filter (3)Mass change of sampleAcetone DCM Anisole PyrolysisPublished by Kyritsis, S., Beenackers, A.A.C.M., Helm, P., Grassi, A., Chiaramonti, D. (eds) 2001,1st World Conference on Biomass for Energy and Industry. Proceedings of the Conferenceheld in Sevilla, Spain, 5-9 June 2000, London, James & James (Science Publishers) Ltd.3from diesel nor for the particles used for this investigation.On the contrary, acetone appeared to be a viable alterna-tive to dichloromethane, even when its toxicity was nottaken into account.Anisole seemed to be the most effective of the threesolvents. It was also far the most problematic to use in thelaboratory. The high boiling point made it hard toevaporate it from the particles before weighing them. Thecommercially available anisole quality was only of 99%purity, which will challenge most chemical analyses of theextracted material. As mentioned, the boiling point alsoforced an increased extraction temperature, which mayitself have affected the mobility of some tar compounds.SUCCESSIVE EXTRACTIONSFigure 3: Results of successive extractions withdifferent solvents.The successive extractions with different solvents did notgive very consistent results. Figure 2 shows the results ofthese extractions. Each package is represented by a set ofbars – one bar for each extraction from left to right. Thepatterns of the bars show which solvent was used.No sufficient explanation was found for the inconsistencybetween the samples. Most of the packages were partlyfrayed after the first extraction. This may have resulted inthe loss of small fragments of the surrounding filtermaterial. If so, it may have decreased the relative masses ofthe packages – especially for the small (1)-samples. Thisdoes not explain the fact that the (3)-samples had verystable masses during any of the second extractionscompared to the (2)-samples.5. CONCLUSIONSThe tar content of particle samples from a downdraftgasifier was determined by pyrolysis and extractions.Successive extractions with different solvents failed to giveconsistent results.It is remarkable that the most widely used solvent forextractions of combustion particulates – dichloromethane –extracted the smallest amount of solubles. This resultsuggests that other solvents — even the cheaper and lesstoxic acetone — can substitute dichloromethane as thesolvent for tars similar to those of the two-stage downdraftgasifier. Especially if it is wanted to extract a morecomplete range and fraction of the organic components.Pyrolysis resulted in the largest tar values. This couldindicate that none of the solvents extracted all of the tarcomponents.ACKNOWLEDGEMENTSThis work was financed by the Danish Energy Agency.REFERENCES[1] R. L. Williams and D. P. Chock, Characterisationof Diesel Particulate Exposure. Proceedings ofHealth Effects of Diesel Engine Emissions p.1-30.December 1979.[2] C. Hindsgaul et al, "Chemical and PhysicalCharacterization of Particles in Producer Gasfrom Wood Chips". Bioresource Technology 73 (2)(2000) pp.147-155.[3] R. Salzmann et al, Guideline for sampling andanalysis of tars, condensates and particulates frombiomass gasifiers. Technical report, ETHZ, ZurichNovember 1997.-6%-5%-4%-3%-2%-1%0%1%Extracted mass [%]AcetoneAnisoleDichloromethaneHot gas particles Water filter particles Gas filter particles

Evaluation of Gravimetric Tar Determination in Particle Samples

http://orbit.dtu.dk/ws/files/5409881/sevilla2000_v8-88.pdf

Evaluation of Gravimetric Tar Determination in Particle Samples

Abstract

Similar works

Full text

Available Versions

Online Research Database In Technology