Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: In recent times, governments around the world have placed increasing focus on cleaner
technologies and sustainable methods of power generation in an attempt to move away from
fossil fuel derived power, which is deemed unsustainable and unfriendly to the environment.
This trend has also been supported by the South African government, with clear intentions to
diversify the country’s power generation by including, among others, biomass as a renewable
resource for electricity generation. Woody biomass and associated forestry residues in
particular, could potentially be used as such a renewable resource when considering the large
amount of fast growing hardwood species cultivated in South Africa. Approximately 6.3
million ton of Eucalyptus grandis is sold annually for pulp production while a further 7
million ton of Eucalyptus species are sold as round wood. With these tree species reaching
commercial maturity within 7 – 9 years in the South African climate, there is real potential in
harnessing woody biomass as a renewable energy source. In this study, pyrolysis was
investigated as a method to condense and upgrade E.grandis into energy and chemical rich
products.
The pyrolysis of E.grandis is the study of the thermal degradation of the biomass, in the
absence of oxygen, to produce char and bio-oil. The thermal degradation behaviour of
E.grandis was studied using thermo-gravimetric analysis (TGA) at the Karlsruhe Institute of
Technology (KIT) in Germany and subsequently used to determine the isoconversional
kinetic constants for E.grandis and its main lignocellulosic components. Slow, Vacuum and
Fast Pyrolysis were investigated and optimised to maximise product yields and to identify the
key process variables affecting product quality. The Fast Pyrolysis of E.grandis was
investigated and compared on bench (KIT0.1 kg/h), laboratory (SU1 kg/h) and pilot plant scale
(KIT10 kg/h), using Fast Pyrolysis reactors at Stellenbosch University (SU) in South Africa and
at KIT in Germany. The Slow and Vacuum Pyrolysis of E.grandis was investigated and
compared using a packed bed reactor at Stellenbosch University.
The TGA revealed that biomass particle size had a negligible effect on the thermal
degradation behaviour of E.grandis at a heating rate set point of 50 °C/min. It was also
shown that increasing the furnace heating rates shifted the thermo-gravimetric (TG) and
differential thermo-gravimetric (DTG) curves towards higher temperatures while also increasing the maximum rate of volatilisation. Lignin resulted in the largest specific char
yield and also reacted across the widest temperature range of all the samples investigated.
The average activation energies found for the samples investigated were 177.8, 141.0, 106.2
and 170.4 kJ/mol for holocellulose, alpha-cellulose, Klason lignin and raw E.grandis,
respectively.
Bio-oil yield was optimised at 76 wt. % (daf) for the SU1 kg/h Fast Pyrolysis plant using an
average biomass particle size of 570 μm and a reactor temperature of 470 °C. Differences in
the respective condensation chains of the various Fast Pyrolysis reactor configurations
investigated resulted in higher gas and char yields for the KIT reactor configurations
compared to the SU1 kg/h Fast Pyrolysis plant.
Differences in the vapour residence time between Slow (>400 s) and Vacuum Pyrolysis (< 2
s) resulted in a higher liquid and lower char yield for Vacuum Pyrolysis. Local liquid yield
maxima of 41.1 and 64.4 wt. % daf were found for Slow and Vacuum Pyrolysis, respectively
(achieved at a reactor temperature of 450 °C and a heating rate of 17 °C/min). Even though
char yields were favoured at low reactor temperatures (269 – 300 °C), the higher heating
values of the char were favoured at high reactor temperatures (29 – 34 MJ/kg for 375 – 481
°C). Reactor temperature had the most significant effects on product yield and quality for
the respective Slow and Vacuum Pyrolysis experimental runs. The bio-oils yielded for SP
and VP were found to be rich in furfural and acetic acid. / AFRIKAANSE OPSOMMING: Regerings regoor die wêreld het in die afgelope tyd toenemende fokus geplaas op skoner
tegnologie en volhoubare metodes van kragopwekking in 'n poging om weg te beweeg van
fossielbrandstof gebasseerde energie, wat geag word as nie volhoubaar nie en skadelik vir die
omgewing. Hierdie tendens is ook ondersteun deur die Suid-Afrikaanse regering, met 'n
duidelike bedoeling om die land se kragopwekking te diversifiseer deur, onder andere,
biomassa as 'n hernubare bron vir die opwekking van elektrisiteit te gebruik. Houtagtige
biomassa en verwante bosbou afval in die besonder, kan potensieel gebruik word as so 'n
hernubare hulpbron, veral aangesien ‘n groot aantal vinnig groeiende hardehout spesies tans
in Suid-Afrika verbou word. Ongeveer 6,3 miljoen ton Eucalyptus grandis word jaarliks
verkoop vir pulp produksie, terwyl 'n verdere 7 miljoen ton van Eucalyptus spesies verkoop
word as paal hout. Met hierdie boom spesies wat kommersiële volwassenheid bereik binne 7
- 9 jaar in die Suid-Afrikaanse klimaat, is daar werklike potensiaal vir die benutting van
houtagtige biomassa as 'n hernubare energiebron. In hierdie studie is pirolise ondersoek as 'n
metode om E.grandis te kondenseer en op te gradeer na energie en chemikalie ryke produkte.
Die pirolise van E.grandis is die proses van termiese afbreking van die biomassa, in die
afwesigheid van suurstof, om houtskool en bio-olie te produseer. Die termiese
afbrekingsgedrag van E.grandis is bestudeer deur gebruik te maak van termo-gravimetriese
analise (TGA) by die Karlsruhe Instituut van Tegnologie in Duitsland en daarna gebruik om
die kinetiese konstantes vir die iso-omskakeling van E.grandis en sy hoof komponente te
bepaal. Stadige, Vakuum en Snel pirolise is ondersoek en geoptimiseer om produk
opbrengste te maksimeer en die sleutel proses veranderlikes wat die kwaliteit van die produk
beïnvloed te identifiseer. Die Snel Pirolise van E.grandis is ondersoek en vergelyk op bank-
(KIT0.1 kg / h), laboratorium- (SU1 kg / h) en proefaanlegskaal (KIT10 kg / h) deur gebruik te maak
van Snel pirolise reaktore by die Universiteit van Stellenbosch (US) in Suid-Afrika en die
Karlsruhe Instituut van Tegnologie (KIT) in Duitsland. Die Stadige en Vakuum Pirolise van
E.grandis is ondersoek en vergelyk met behulp van 'n gepakte bed reaktor aan die
Universiteit van Stellenbosch.
Die TGA studie het openbaar dat biomassa deeltjiegrootte 'n onbeduidende uitwerking op die
termiese afbrekingsgedrag van E.grandis het by 'n verhittings tempo van 50 ° C / min. Dit is ook bewys dat die verhoging van die oond verwarming tempo die termo-gravimetriese (TG)
en differensiële termo-gravimetriese (DTG) kurwes na hoër temperature verskuif, terwyl dit
ook die maksimum tempo van vervlugtiging laat toeneem het. Lignien het gelei tot die
grootste spesifieke houtskool opbrengs en het ook oor die wydste temperatuur interval
gereageer van al die monsters wat ondersoek is. Die gemiddelde aktiveringsenergieë vir die
monsters wat ondersoek is, was 177,8, 141,0, 106,2 en 170,4 kJ / mol, onderskeidelik vir
holosellulose, alpha-sellulose, Klason lignien en rou E.grandis.
Bio-olie opbrengs is geoptimeer teen 76 wt. % (DAF) vir die SU1 kg / h Snel Pirolise aanleg
met behulp van 'n gemiddelde biomassa deeltjiegrootte van 570 μm en 'n reaktor temperatuur
van 470 ° C. Verskille in die onderskeie kondensasie kettings van die verskillende Snel
Pirolise aanlegte wat ondersoek is, het gelei tot hoër gas- en houtskool opbrengste vir die KIT
reaktor konfigurasies in vergelyking met die SU1kg/h FP plant.
Verskille in die damp retensie tyd tussen Stadige (> 400 s) en Vakuum pirolise (<2 s) het
gelei tot 'n hoër vloeistof en laer houtskool opbrengs vir Vakuum Pirolise. Plaaslike vloeistof
opbrengs maksima van 41,1 en 64,4 wt. % (daf) is gevind vir Stadig en Vakuum pirolise
onderskeidelik, bereik by 'n reaktor temperatuur van 450 ° C en 'n verhittingstempo van 17 °
C / min. Selfs al is houtskool opbrengste bevoordeel by lae reaktor temperature (269 - 300 °
C), is die hoër warmte waardes van die houtskool bevoordeel deur hoë reaktor temperature
(29 - 34 MJ / kg vir 375 - 481 ° C). Reaktor temperatuur het die mees beduidende effek op
die produk opbrengs en kwaliteit vir die onderskeie Stadige Pirolise en Vakuum Pirolise
eksperimentele lopies gehad. Die bio-olies geproduseer tydens Stadige en Vakuum Pirolise
was ryk aan furfuraal en asynsuur.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/80179 |
| Date | 03 1900 |
| Creators | Joubert, Jan-Erns |
| Contributors | Knoetze, J. H., Carrier, M., Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | [213 p.] : ill. |
| Rights | Stellenbosch University |
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