Systems approach in developing a model for sustainable production of bioenergy in Malawi
Chitawo, Maxon Lexon (2018-03)
ENGLISH SUMMARY: Bioenergy production from primary forest and rice residues can contribute to modern energy supply, such as electricity, liquid biofuels and gas, to rural communities in Malawi. These bioresources can be utilised for bioenergy production without alienating land from cultivation of other crops. However, sustainability of forest and rice residues-based bioenergy systems is complex owing to the dependency of availability of the residues on timber and rice production. Alterations in process operations in timber and rice production systems can cause variations in production and supply of the residues to a bioenergy conversion plant over time. For instance, forest management systems have evolved from sustainable yield management, which promotes clear cutting of mature forest stand to maximise the yield of wood products to sustainable forest management that promotes partial harvesting of mature forest stand to allow for ecosystem balance. Switching the harvesting regimes from clear cut to partial harvesting of mature forest stand, can influence variation in yield of forest residues in forest plantations over time. Variations are also evident in rice residues production and supply chains, emanating from seasonal production of rice and demand of the rice residues for competing uses. Stability in production and supply of the residues over a long time horizon can promote availability of the residues-based bioenergy systems and reliability of bioenergy supply to end use processes over time. Systems approach modelling based on systems thinking and system dynamics modelling methodology, was used in this study to develop a model for sustainable production of bioenergy (SAS-Biopro model). The model demonstrates state limiting processes to resilience of primary forest and rice residues supply chains for bioenergy production. Simulation results of the model show that variations in primary forest residues value chain over time result from variations in stocks of mature stand caused by over-exploitation for timber production, delayed replanting, high death (mortality) rate of replanted trees and underinvestment in plantations management. Results from scenario testing show that an integrated framework for forest plantations management and forest residues-based bioenergy production, can promote synchronised operation and management of the forest plantations and bioenergy production as a unit (whole) system. The framework entails setting an annual allowable cut for harvesting mature forest stand, synchronizing harvesting and replanting 100% of the annual allowable cut immediately after harvesting, reducing tree mortality fraction to less than 0.1, and sizing the scale of operation of bioenergy conversion plants based on the amount of residues generated from the annual allowable cut. The framework can promote stability of residues production and supply to bioenergy conversion plants. Similarly, modelling sustainability of rice residues-based bioenergy production has shown that a synergetic integration of bioenergy and rice production can simultaneously increase bioenergy and rice production over time. Thus, synergetic integration of bioenergy and rice production can promote stability, availability and reliability of rice (food) and rice residues supply for bioenergy production. This research has filled a significant gap in strategic information such as dynamics in residues-based bioresource flow and consumption rates that create a transient state, which can guide formulation of strategies for synchronising the scale of operation of the residues-based bioenergy conversion plants and operation processes in the primary systems that generate the residues. The research outputs provide innovative whole systems and synergetic integration, for production and deployment of residues-based bioenergy, to promote resilience of the residues supply chains to bioenergy conversion plants. These concepts can promote uptake and diffusion of small-scale bioenergy conversion technologies in primary systems that generate the residues. Matching the scale and rate of operation of the bioenergy conversion plants with the annual rate of production of the residues can provide opportunity for incremental uptake of small-scale residues-based bioenergy systems. Therefore, the concepts, although approached from the technology and process point of view, are flexible to respond to policy and societal changes in the value chain of bioenergy production. The concepts can be adopted in forest plantations and rice farms management systems to promote sustainability of bioenergy production from forest and rice residues.
AFRIKAANSE OPSOMMING: Die produksie van bio-energie uit primêre bos- en rys-afvalprodukte kan ’n bydrae lewer tot huidige energie-behoeftes soos met die verskaffing van elektrisiteit, vloeibare biobrandstowwe en gas aan landelike gemeenskappe in Malawi. Hierdie biobronne kan aangewend word vir bio-energie-produksie sonder om grond vir die verbouing van ander gewasse te vervreem. Die volhoubaarheid van bio-energie-stelsels gebaseer op bos- en rys-afvalprodukte is egter kompleks vanweë sy afhanklikheid van die beskikbaarheid van sodanige afvalprodukte. Oor tyd heen kan veranderings in proseswerksaamhede van hout- en rysproduksie-stelsels variasies in produksie en verskaffing van afvalprodukte aan bio-energie-verwerkingsaanlegte veroorsaak. Bosbestuurstelsels het byvoorbeeld ontwikkel uit volhoubare opbrengsbestuur, wat die kaalkap van volgroeide bosopstand bevorder om die opbrengs van houtprodukte vir volhoubare bosbestuur te maksimeer; hierdie bestuur laat toe dat gedeeltelike oes van volgroeide bosopstand bevorder word vir balans in die ekosisteem. Deur die oes-werkswyse te verander van kaalkap tot gedeeltelike oes van volgroeide bosopstand kan oor tyd heen opbrengsvariasie van bosafvalprodukte uit plantasies beïnvloed. Variasie is ook sigbaar in die produksie van rys-afvalprodukte en verskaffingskettings geassosieer met seisoenale produksie van rys en die kompeterende aanvraag na rysafvalprodukte. Oor ’n lang tydperk kan stabiliteit in produksie en verskaffing van afvalprodukte die beskikbaarheid van afvalprodukgebaseerde bio-energie-stelsels en die betroubaarheid van bio-energie-verskaffing aan eindgebruiksprosesse bevorder. Stelselbenaderingsmodellering gebaseer op stelseldenke en stelseldinamiese modelleringsmetodologie is in hierdie studie gebruik om ’n model (die SAS-Biopro-model) vir die volhoubare produksie van bio-energie te ontwikkel. Hierdie model demonstreer beperkings van prosesse deur die owerheid vir die lewensvatbaarheid van verskaffingskettings ten opsigte van primêre bos- en rysafvalprodukte vir bio-energie-produksie. Simulasie-uitslae van die model wys dat variasie in die primêre bosafvalprodukte-waardeketting oor tyd ontstaan as gevolg van variasie in onderstamme van volgroeide opstand veroorsaak deur oorbenutting vir houtproduksie, uitgestelde herplanting, hoë koers van vrekte onder herplantings en onderinvestering in plantasiebestuur. Uitslae van scenario-toetse wys dat ’n geïntegreerde raamwerk vir bosbestuur en bio-energie-produksie stabiliteit in die produksie en verskaffing van afvalprodukte aan ’n bio-energie-verwerkingsaanleg kan bevorder deur sinkronisasie van die oes van volgroeide bosopstand vir houtproduksie en herplant van die geoeste dele, die instelling van drempelwaardes vir die oes van volgroeide bosopstande per jaar, en die afparing van grootte en skaal van die bio-energie-verwerkingsaanleg se werksaamhede met afvalprodukte gegenereer uit die geoeste drempelwaardes as ’n volledige stelsel. Ingelyks, wys die modellering van die volhoubaarheid van rysafvalproduk-gebaseerde bio-energie-produksie dat ’n sinergistiese integrasie van bio-energie- en rys-produksie terselfdertyd beide met verloop van tyd kan verbeter. Dus kan die sinergistiese integrasie van bio-energie- en rysproduksie stabiliteit, beskikbaarheid en volhoubaarheid van rys (voedsel) sowel as rysafval vir bio-energie-produksie bevorder. Hierdie navorsing vul ’n beduidende gaping in strategiese inligting soos die dinamika van afvalgebaseerde bio-bronvloei en –verbruikerskoerse wat ’n kortstondige toestand veroorsaak en formulering van strategieë kan lei om die skaal van werksverrigting van afvalprodukgebaseerde bio-energie-verwerkingsaanlegte en prosesse in die primêre stelsels wat die afvalprodukte genereer te sinkroniseer. Die navorsingsuitsette verskaf innoverende volledige stelsels en sinergistiese integrasie vir produksie en aanwending van afvalprodukgebaseerde bio-energie, om lewensvatbaarheid van die afvalprodukverskaffingsketting vir bio-energie-verwerkingsaanlegte te bevorder. Sodanige konsepte kan die aanwending en verspreiding van kleinskaalse bio-energie-verwerkingstegnologieë bevorder in primêre stelsels wat die afvalprodukte genereer. Die afparing van skaal en werksverrigtingskoers van bio-energie-verwerkingsaanlegte met die jaarlikse produksiekoers van die afvalprodukte kan geleenthede verskaf vir toenemende aanwending van kleinskaalse afvalprodukgebaseerde bio-energiestelsels. Daarom is die konsepte buigsaam, alhoewel uit die tegnologie- en proses-oogpunt benader, om op veranderings in beleid en die samelewing te reageer in die waardeketting van bio-energieproduksie. Hierdie konsepte kan opgeneem word in bos- en ryslandbestuurstelsels om volhoubaarheid van bio-energieproduksie uit bos- en rysafvalprodukte te bevorder.
Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103540
Doctoral Degrees (Process Engineering) 
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