Comparative techno-economic assessment of sugarcane biorefineries producing glutamic acid, succinic acid, levulinic acid and xylitol from A-molasses and lignocellulosic biomass

Thesis (MEng)--Stellenbosch University, 2021.ENGLISH ABSTRACT: The financial sustainability of the South African sugar industry is currently threatened by difficult economic conditions, including external factors such as low sugar prices by new global competitors, and increased production costs. Because of these challenges, some of the sugar mills face potential closure in the future because they are no longer profitable. With this in mind, it has been proposed that sugar mills should valorise by-products to increase profitability. Molasses and lignocelluloses (bagasse and trash) biomasses are the two by-products of the sugar mill as the potential first-generation (1G) and second-generation (2G) feedstocks, respectively, for valorisation in a biorefinery context. These feedstocks are promising carbon sources for the prominent global bio-based economy, owing to their low cost, high content of the fermentable sugars, and relative abundance. The global demands, technological maturity, and potential to penetrate new markets support the section of the product of interest: glutamic acid (GA), levulinic acid (LA), succinic acid (SA), and xylitol for investigation in a biorefinery context as a way to diversify products in a sugar mill, thereby increasing revenues. An overall aim of this study was to determine if the profitability of sugarcane biorefineries producing GA, LA could be further improved from the previously attained profitable scenarios that utilised the second-generation (2G) feedstock (lignocelluloses), by further considering 1G feedstock (A-molasses). Considered as a cleaner raw material, 1G results in the elimination of the costly pretreatment and enzymatic hydrolysis processes. Furthermore, the integration of feedstocks (1G and 2G) was investigated to evaluate the economies of scale benefits through a sole production of GA, LA, and SA. Thereafter, multi-production of the aforementioned with xylitol was considered. Literature data were used to design and develop the process flow sheets for detailed AspenPlus® process simulation models considering feed capacities of 25.4 t/h A molasses and 113.5 t/h of lignocellulose. The generated mass and energy balances data were used for techno economic analysis for a yearly operation if 5000 hours. With reconfigurations on the sugar mill, 1G biorefineries can benefit from utilising the existing CHP facility or incorporating low-cost, low-pressure boiler in the 1G biorefineries. As a result, 1G biorefineries showed better economic performances than their 2G biorefinery counterpart. The integration of feedstocks in 1G2G designs showed the economies of scale benefits, compared to 1G-only scenarios. This was demonstrated by the decrease in minimum selling price (MSP) from $2950/t to $2102/t in 2G LA and 1G2G LA scenario, $2237/t to $1745/t in 2G SA and 1G2G SA, and $2969 to 2205 for 2G GA and 1G2G GA scenarios, respectively. Comparatively, multiproduct facilities achieved lower MSP than the sole product 1G2G configurations counterparts ($2205/t vs $1926/t for GA and $2600/t vs $1133/t for LA). Except 1G2G SA+Xylitol at $1745/t vs $1888/t. This can be accounted for by the reduction in sales for SA from when there was an upgrade from sole product to multiproduct. Since techno-economic evaluation alone does not fully justify the sustainability and competitiveness of the proposed biorefineries in the eyes of investors or decision-makers, a study on the Life cycle assessment considering the environmental and social impact of biorefineries could be further investigated.AFRIKAANSE OPSOMMING: Die finansiële volhoubaarheid van die Suid-Afrikaanse suikerindustrie word tans bedreig deur moeilike ekonomiese kondisies, insluitend eksterne faktore soos lae suikerpryse deur nuwe globale mededingers, en verhoogde produksiekostes. As gevolg van hierdie uitdagings, staar sommige van hierdie suikermeule potensiële sluitings in die toekoms in die gesig omdat hulle nie meer winsgewend is nie. Met hierdie in gedagte, is dit voorgestel dat suikermeule byprodukte moet valoriseer om winsgewendheid te verhoog. Molasse en lignosellulose (bagasse en afval) biomassa is die twee byprodukte van die suikermeule as die potensiële eerste-generasie (1G) en tweede-generasie (2G) voermateriale, onderskeidelik, vir valorisasie in ’n bioraffinadery-konteks. Hierdie voermateriale is belowende koolstofbronne vir die prominente globale bio-gebaseerde ekonomie, weens hul lae koste, hoë inhoud van die fermenteerbare suikers, en relatiewe volopheid. Die globale vereistes, tegnologiese rypheid, en potensiaal om nuwe markte te penetreer, ondersteun die deel van die produk in belang: glutamiensuur (GA), levuliniensuur (LA), suksiensuur (SA), en xilitol vir ondersoek in ’n bioraffinadery-konteks as ’n manier om produkte te diversifiseer in ’n suikermeul, en daardeur inkomste te verhoog. ’n Algehele doel van hierdie studie was om te bepaal of die winsgewendheid van suikerrietbioraffinaderye wat GA, LA produseer, verder kon verbeter uit winsgewende scenario’s wat voorheen verkry is deur die 2G-voermateriaal (lignosellulose) te gebruik, deur 1G-voermateriaal (A-molasse) verder te oorweeg. Oorweeg as ’n skoner rou-materiaal het 1G die eliminasie van die duursame voorbehandeling en ensimatiese prosesse tot gevolg. Verder, die integrasie van voermateriaal (1G en 2G) is ondersoek om die ekonomieë van skaal se voordele te evalueer deur ’n enkel-produksie van GA, LA en SA. Daarna is multi-produksie van die voorafgenoemde met xilitol oorweeg. Data uit literatuur is gebruik om die prosesvloeikaarte te ontwerp en ontwikkel vir gedetailleerde Aspen Plus®-prosessimulasiemodelle wat voerkapasiteite van 25.4 t/h A- molasse en 113.5 t/h lignosellulose oorweeg. Die gegenereerde massa- en energiebalanse se data is gebruik vir tegno-ekonomiese analise vir ’n jaarlikse bedryf van 5000 ure. Met hersamestellings op die suikermeule, kan 1G-bioraffinaderye voordeel trek deur die bestaande Gekombineerde hitte en krag (CHP) fasiliteite of die lae-koste, lae-druk ketel in die 1G-bioraffinaderye te inkorporeer. As ’n gevolg, het 1G-bioraffinaderye beter ekonomiese doeltreffendheid gewys as hul 2G-bioraffinadery eweknie. Die integrasie van voermateriaal in 1G2G-ontwerpe het die voordele van die ekonomieë van skaal gewys, in vergelyking met die 1G-alleenlik scenario’s. Hierdie is gedemonstreer deur die afname in (Minimum Verkoopprys) MSP van $2950/t tot $2102/t in 2G LA en 1G2G LA- scenario, $2237/t tot $1745/t in 2G SA en 1G2G SA, en $2643 tot $2794 vir 2G GA en 1G2G GA-scenario’s. In vergelyking het multi-produkfasiliteite laer MSPs teenoor die enkel-produk 1G2G-konfugirasies se eweknieë bereik ($2205/t vs. $1926/t vir GA en $2600/t vs. $1133/t vir LA). Buiten 1G2G SA+xilitol by $1745/t vs. $1888/t. Hierdie kan verduidelik word deur die reduksie in verkope vir SA vandat daar opgradering van enkel-produk tot multi-produk was. Aangesien tegno-ekonomiese evaluasie alleen nie die volhoubaarheid en mededingendheid van die voorgestelde bioraffinaderye ten volle regverdig in die oë van beleggers of besluitnemers nie, kan ’n studie op die lewensiklusassessering, wat die omgewings- en sosiale impak van bioraffinaderye oorweeg, verder ondersoek word.Master