Petersen, Abdul Muhaymin (2015-12)
ENGLISH ABSTRACT: Since the production of second-generation biofuel (SGB) from lignocellulosic plant biomass is only economically attractive if driven by government incentives, stakeholders are reluctant to commercialise the product despite its potential to mitigate global warming and socio-economic conditions. Integrating SGB processes with the facilities of biomass-based industries could reduce the production costs of SGB through pre-existing services and infrastructure. Integrating SGB, however, is technically viable only if available biomass residues are used effectively to co-produce fuel while maintaining the overall energy balance, financially viable only if it attracts private investment without governmental assistance and environmentally viable only if it reduces the carbon imprint of a fossil-intensive host industry.
In this dissertation, novel scenarios for integrating SGB with the South African raw sugar and the pulp and paper industries (RSI and P&PI, respectively) were explored. Focus was on ethanol production based on fermenting hemicellulose substrates, potentially available in both industries, and on SGB production through gasification-synthesis processes in the contextual representatives of these industries. This was accomplished through flow-sheet analysis in Aspen Plus® using process simulations constructed from protocols in published literature and experimental data.
In respect of RSI, integrating bioethanol production with electricity from sugarcane bagasse and harvesting residues were deemed both technically and economically viable and competitive against the exclusive generation of electricity. The necessity of Pinch Point Analysis was established through flow-sheet analysis, which had also shown the synergistic interaction of technologies in various processing stages, such as the variants in ethanol distillation technologies and heat and power production technologies. In respect of P&PI, represented by sulphite mills, ethanol production from spent sulphite liquor (SSL) pulping residue was deemed economically viable if the SSL fermentation substrate was concentrated. To attain net reduction of greenhouse gas emissions for the integrated ethanol-sulphite facility, it was essential to provide all process energy requirements from supplementary biomass sources rather than coal.
In respect of RSI, integrating methanol or Fischer-Tropsch syncrude via gasification synthesis was deemed not feasible at the current state of efficiency with which sugar mills are operating. In respect of P&PI, combining synthetic fuel production with bioethanol production at a sulphite mill improved economic potential, since disposal costs were negated through the use of waste biomass for synthesis processes and the yield of valuable products was enhanced on a small scale. In respect of both RSI and P&PI, however, integrating gasification-synthesis processes required the statistical optimisations of flow sheets to arrive at the optimum operating parameters for competing technologies for syngas production. In these contexts, syngas production based on optimised allothermal gasification had lower costs than optimised autothermal gasification.
To validate the process concepts developed in this thesis, it is firstly recommended that robust and recombinant microbial strains be readily available to ferment pentose-rich substrates, such as SSL and hemicellulose hydrolysates. Secondly, the effect of the chemical alteration of SSL on the recovery performance of process chemicals at sulphite mills should be examined and, thirdly, the catalytic gasification of biomass should be developed and demonstrated on pilot and pre-commercial scales.
AFRIKAANSE OPSOMMING: Aangesien die produksie van tweedegenerasie-biobrandstof (TGB) uit lignosellulosiese plantbiomassa slegs ekonomies aantreklik is indien dit deur staatsaansporings aangemoedig word, is belanghebbendes huiwerig om die produk te kommersialiseer, ondanks die potensiaal daarvan om aardverwarming teen te werk en sosio-ekonomiese omstandighede te verbeter. Die integrasie van TGB-prosesse by die fasiliteite van biomassagebaseerde nywerhede kan die produksiekoste van TGB verlaag deur voorafbestaande dienste en infrastruktuur. Die integrasie van TGB is egter slegs tegnies haalbaar indien die beskikbare biomassareste doeltreffend gebruik word vir die medeproduksie van brandstof terwyl die algehele energiebalans terselfdertyd gehandhaaf word; slegs finansieel haalbaar indien dit privaat belegging sonder staatshulp lok, en slegs omgewingshaalbaar indien dit die koolstofvoetspoor van ’n fossielintensiewe gasheernywerheid verklein.
Hierdie verhandeling verken nuwe scenario’s vir die integrasie van TGB by die Suid-Afrikaanse ru-suiker- en pulp-en-papierbedryf (RSB en P&PB onderskeidelik). Die klem val op etanolproduksie op grond van die fermentasie van hemisellulose-substrate, wat moontlik in albei nywerhede beskikbaar is, en op TGB-produksie deur vergassingsinteseprosesse in die kontekstuele verteenwoordigers van die twee nywerhede. Dít is gedoen met behulp van vloeikaartontleding in Aspen Plus®, wat gebruik gemaak het van prosessimulasies wat op grond van protokolle in gepubliseerde literatuur en eksperimentele data saamgestel is.
Wat RSB betref, blyk die integrasie van bio-etanolproduksie en elektrisiteit uit suikerrietbagasse en oesreste tegnies én ekonomies haalbaar te wees, sowel as mededingend vergeleke met die uitsluitlike opwekking van elektrisiteit. Die vloeikaartontleding het ’n behoefte aan knyppuntanalise uitgewys, wat ook gedui het op die sinergistiese wisselwerking tussen tegnologieë in verskillende verwerkingstadia, soos verskillende etanolsuiwering en hitte- en kragproduksie tegnologieë. Met betrekking tot P&PB, in soverre dit deur sulfietmeule in Suid-Afrika verteenwoordig word, word etanolproduksie uit gebruikte sulfietloog (GSL), synde ’n pulp-residu, as ekonomies haalbaar beskou indien die GSL-fermentasiesubstraat gekonsentreerd is. Om ’n netto vermindering in kweekhuisgasvrystellings vir die geïntegreerde etanolsulfietfasiliteit te verkry, moet daar met behulp van aanvullende biomassabronne eerder as steenkool in alle prosesenergievereistes voorsien word.
By RSB blyk die integrasie van metanol of Fischer-Tropsch- sintetiese ruolie (“syncrude”) via vergassingsintese nie teen die huidige bedryfsdoeltreffendheid van die suikermeule uitvoerbaar te wees nie. Vir P&PB toon die kombinasie van sintetiese brandstofproduksie en bio-etanolproduksie by ’n sulfietmeul ekonomiese potensiaal, aangesien wegdoeningskoste geneutraliseer word deur die gebruik van afvalbiomassa vir sinteseprosesse en die kleinskaalse verhoging in die lewering van waardevolle produkte. Tog vereis die integrasie van vergassingsinteseprosesse by RSB sowel as P&PB die statistiese optimalisering van vloeikaarte om die optimale bedryfsparameters van wedywerende tegnologieë vir singasproduksie te bepaal. In hierdie verband blyk singasproduksie met behulp van geoptimaliseerde allotermiese vergassing meer kostedoeltreffend as geoptimaliseerde outotermiese vergassing te wees.
Vir die bekragtiging van die proseskonsepte wat uit hierdie tesis spruit, word daar eerstens aanbeveel dat robuuste en rekombinante mikrobiese stamme geredelik beskikbaar moet wees om pentoseryke substrate, byvoorbeeld GSL en hemisellulose-hidrolisate, te fermenteer. Tweedens behoort die uitwerking van die chemiese wysiging van GSL op die herwinningsprestasie van proseschemikalieë by sulfietmeule ondersoek te word. Laastens word aanbeveel dat die katalitiese vergassing van biomassa op ’n proef- sowel as prekommersiële skaal ontwikkel en gedemonstreer word.
Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/97873
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