Modelling and sustainability analysis of biorefineries using sugarcane lignocellulose to produce polyethylene, sorbitol, glucaric acid and levulinic acid at existing South African sugar mills

Thesis (PhD)--Stellenbosch University, 2021.ENGLISH ABSTRACT: The sugar industry in South Africa and the region has been plagued by factors including the low international sugar prices, reduced cane yields due to climate change and competition from new market entrants producing sweeteners. Therefore, to remain relevant and sustainable, this industry seeks to generate extra revenue by producing bio-based chemicals and bio-energy from part of the bagasse and brown leaves in biorefinery complexes, alongside sugar products. Using a rapid screening approach, bio-based chemicals polyethylene, sorbitol, glucaric acid and levulinic acid were shortlisted for possible production in such biorefineries (objective one). Conceptual biorefinery process flow diagrams were designed in Aspen Plus® v 8.6 producing the aforementioned chemicals with electricity cogeneration in combined heat and power plants, annexed to a conventional sugar mill (objective two), including a base case scenario that only produced electricity. This was followed by determining the techno-economic viability of the bio-energy self-sufficient biorefineries using developing countries’ economic parameters and a discounted cash flow rate of return methodology on real terms using a 9.7% hurdle rate that reflects South Africa’s and developing countries’ economic conditions (objective three). The internal rate of return (IRR), net present value (NPV) and minimum product selling price (MPSP) were indicators used to determine profitability. The most economically viable scenario coproduced levulinic acid, gamma valerolactone, furfural and electricity (LA-GVL-F-E) and attained a 23% IRR and US$253 million NPV at a 9.7$ 139 million. At present, most second generation bio-based chemicals cannot compete with first generation or fossil–based counterparts due to the large capital investment costs associated with processing lignocelluloses. A substantial premium is required on second-generation bio-based products if they are to compete with fossil-based or first generation products. In addition to economic viability, the overall sustainability of profitable biorefineries was assessed based on their environmental and social impacts (i.e. job creation) in objective four. For the environmental impact, a “cradle to factory gate” life cycle assessment in SimaPro® was used and the AWARE methodology applied for the water footprint. The most sustainable scenario produced glucaric acid via dilute acid pretreatment (Glucaric.DA) followed by LA-F-E. Objective five was a multi criteria decision assessment (MDCA) on profitable scenarios that ranked and scored the biorefineries based on equal and varied national sustainable (economic, environmental and social) representative weightings. When equal representative weightings of 33.33% were applied to the sustainability indicators, scenario LA-F-E attained the highest aggregate score followed by Glucaric.DA and Sorbitol.DA (chemicals produced via dilute acid pretreatment) and lastly, LA-GVL-F-E. The generated results can inform key sugar industry stakeholders of the most sustainable biorefineries for future feasibility studies. Therefore, potential exists at typical sugar mills for the sustainable valorisation of lignocelluloses for revenue generation and the advancement of a green economy. Future studies should investigate the sustainability of biorefineries utilising first and second generation feedstocks and also valorising part of the lignin to produce high-value chemicals.AFRIKAANSE OPSOMMING: Die suikerindustrie in Suid-Afrika en die streek word deur faktore geteister soos die lae internasionale suikerpryse, verlaagde rietopbrengs as gevolg van klimaatsverandering en kompetisie van nuwe markdeelnemers wat versoeters vervaardig. Daarom, om relevant en volhoubaar te bly, poog die industrie om ekstra inkomste te genereer deur bio-gebaseerde chemikalieë en bio-energie uit ’n gedeelte van die bagasse en bruin blare in bioraffinaderykompleks, saam met suikerprodukte, te produseer. Deur ’n vinnige siftingsbenadering, is bio-gebaseerde chemikalieë poliëtileen, sorbitol, suikersuur en levuliniensuur gekortlys vir moontlike produksie in sulke bioraffinaderye (doelwit 1). Konsepsuele bioraffinaderyprosesvloeidiagramme is ontwerp in Aspen Plus® v 8.6 wat die voorafgenoemde chemikalieë met elektrisiteitkogenerasie produseer in aanlegte wat hitte en krag kombineer, geannekseer aan ’n konvensionele suikermeul (doelwit 2), insluitend ’n basis scenario wat slegs elektrisiteit produseer. Dit is gevolg deur die bepaling van die tegno-ekonomiese uitvoerbaarheid van die bio-energie selfonderhoudende bioraffinaderye deur ontwikkelende lande se ekonomiese parameters te gebruik, en ’n korting op kontantvloeiopbrengsmetodologie op reële terme deur ’n 9.7% versperringskoers te gebruik wat Suid-Afrika en ontwikkelende lande se ekonomiese kondisies reflekteer (doelwit 3). Die interne opbrengskoers (IRR), netto huidige waarde (NPV) en minimum produkverkoopsprys (MPSP) was indikators wat gebruik is om winsgewendheid te bepaal. Die mees ekonomies uitvoerbare scenario het levuliniensuur, gamma valerolaktoon, furfuraal en elektrisiteit (LA-GVL-F-E) koproduseer en het ’n 23% IRR en US$253 miljoen NPV gehad by ’n 9.7$139 miljoen. Tans kan meeste tweede-generasie bio-gebaseerde chemikalieë nie met eerste generasie of fossiel-gebaseerde teenbeelde kompeteer nie as gevolg van die groot kapitaalbeleggingkostes geassosieer met prosessering van lignosellulose. ’n Aansienlike premie word vereis op tweede-generasie bio-gebaseerde produkte as hulle met fossiel-gebaseerde of eerste-generasie produkte wil kompeteer. Saam met ekonomiese uitvoerbaarheid, is die algehele volhoubaarheid van winsgewende bioraffinaderye geassesseer gebaseer op hul omgewings- en sosiale impak (i.e. werkskepping) in doelwit 4. Vir die omgewingsimpak is ’n lewenssiklusanalise van die “begin tot fabriekshek” in SimaPro® gebruik en die AWARE-metodologie toegepas vir die watervoetspoor. Die mees volhoubare scenario het suikersuur via verdunde suur voorbehandeling (Glucaric.DA) produseer, gevolg deur LA-F-E. Doelwit vyf was ’n multikriteriabesluitassessering (MDCA) op winsgewende scenario’s wat bioraffinaderye rangskik en punte gee gebaseer op gelyke en gevarieerde nasionale volhoubaarheid (ekonomies, omgewing, en sosiaal) verteenwoordigende gewigstoekennings. Toe gelyke verteenwoordigende gewigstoekennings van 33.33% toegepas is op die volhoubaarheidsindikators, het scenario LA-F-E die hoogste aggregaattelling behaal, gevolg deur Glucaric.DA en Sorbitol.DA (chemikalieë geproduseer via verdunde suur voorbehandeling), en laaste, LA-GVL-F-E. Die gegenereerde resultate kan sleutel suikerindustriebelanghebbers van die mees volhoubare bioraffinaderye inlig vir toekomstige uitvoerbaarheidstudies. Potensiaal bestaan daarom by tipiese suikermeule vir die volhoubare valorisasie van lignosellulose vir inkomstegenerasie en die bevordering van ’n groen ekonomie. Toekomstige studies moet die volhoubaarheid van bioraffinaderye wat eerste- en tweede-generasie toevoermateriale gebruik, ondersoek, en ook die valorisering van ʼn gedeelte van die lignien om hoë waarde chemikalieë te produseer.The financial assistance of the National Research Foundation (NRF) towards this research is hereby acknowledged. Opinions expressed and conclusions arrived at, are those of the author and are not necessarily attributed to the NRF

Gasificação direta de biomassa para produção de gás combustível

The excessive consumption of fossil fuels to satisfy the world necessities of energy and commodities led to the emission of large amounts of greenhouse gases in the last decades, contributing significantly to the greatest environmental threat of the 21st century: Climate Change. The answer to this man-made disaster is not simple and can only be made if distinct stakeholders and governments are brought to cooperate and work together. This is mandatory if we want to change our economy to one more sustainable and based in renewable materials, and whose energy is provided by the eternal nature energies (e.g., wind, solar). In this regard, biomass can have a main role as an adjustable and renewable feedstock that allows the replacement of fossil fuels in various applications, and the conversion by gasification allows the necessary flexibility for that purpose. In fact, fossil fuels are just biomass that underwent extreme pressures and heat for millions of years. Furthermore, biomass is a resource that, if not used or managed, increases wildfire risks. Consequently, we also have the obligation of valorizing and using this resource. In this work, it was obtained new scientific knowledge to support the development of direct (air) gasification of biomass in bubbling fluidized bed reactors to obtain a fuel gas with suitable properties to replace natural gas in industrial gas burners. This is the first step for the integration and development of gasification-based biorefineries, which will produce a diverse number of value-added products from biomass and compete with current petrochemical refineries in the future. In this regard, solutions for the improvement of the raw producer gas quality and process efficiency parameters were defined and analyzed. First, addition of superheated steam as primary measure allowed the increase of H2 concentration and H2/CO molar ratio in the producer gas without compromising the stability of the process. However, the measure mainly showed potential for the direct (air) gasification of high-density biomass (e.g., pellets), due to the necessity of having char accumulation in the reactor bottom bed for char-steam reforming reactions. Secondly, addition of refused derived fuel to the biomass feedstock led to enhanced gasification products, revealing itself as a highly promising strategy in terms of economic viability and environmental benefits of future gasification-based biorefineries, due to the high availability and low costs of wastes. Nevertheless, integrated techno economic and life cycle analyses must be performed to fully characterize the process. Thirdly, application of low-cost catalyst as primary measure revealed potential by allowing the improvement of the producer gas quality (e.g., H2 and CO concentration, lower heating value) and process efficiency parameters with distinct solid materials; particularly, the application of concrete, synthetic fayalite and wood pellets chars, showed promising results. Finally, the economic viability of the integration of direct (air) biomass gasification processes in the pulp and paper industry was also shown, despite still lacking interest to potential investors. In this context, the role of government policies and appropriate economic instruments are of major relevance to increase the implementation of these projects.O consumo excessivo de combustíveis fósseis para garantir as necessidades e interesses da sociedade conduziu à emissão de elevadas quantidades de gases com efeito de estufa nas últimas décadas, contribuindo significativamente para a maior ameaça ambiental do século XXI: Alterações Climáticas. A solução para este desastre de origem humana é de caráter complexo e só pode ser atingida através da cooperação de todos os governos e partes interessadas. Para isto, é obrigatória a criação de uma bioeconomia como base de um futuro mais sustentável, cujas necessidades energéticas e materiais sejam garantidas pelas eternas energias da natureza (e.g., vento, sol). Neste sentido, a biomassa pode ter um papel principal como uma matéria prima ajustável e renovável que permite a substituição de combustíveis fósseis num variado número de aplicações, e a sua conversão através da gasificação pode ser a chave para este propósito. Afinal, na prática, os combustíveis fósseis são apenas biomassa sujeita a elevada temperatura e pressão durante milhões de anos. Além do mais, a gestão eficaz da biomassa é fundamental para a redução dos riscos de incêndio florestal e, como tal, temos o dever de utilizar e valorizar este recurso. Neste trabalho, foi obtido novo conhecimento científico para suporte do desenvolvimento das tecnologias de gasificação direta (ar) de biomassa em leitos fluidizados borbulhantes para produção de gás combustível, com o objetivo da substituição de gás natural em queimadores industriais. Este é o primeiro passo para o desenvolvimento de biorrefinarias de gasificação, uma potencial futura indústria que irá providenciar um variado número de produtos de valor acrescentado através da biomassa e competir com a atual indústria petroquímica. Neste sentido, foram analisadas várias medidas para a melhoria da qualidade do gás produto bruto e dos parâmetros de eficiência do processo. Em primeiro, a adição de vapor sobreaquecido como medida primária permitiu o aumento da concentração de H2 e da razão molar H2/CO no gás produto sem comprometer a estabilidade do processo. No entanto, esta medida somente revelou potencial para a gasificação direta (ar) de biomassa de alta densidade (e.g., pellets) devido à necessidade da acumulação de carbonizados no leito do reator para a ocorrência de reações de reforma com vapor. Em segundo, a mistura de combustíveis derivados de resíduos e biomassa residual florestal permitiu a melhoria dos produtos de gasificação, constituindo desta forma uma estratégia bastante promissora a nível económico e ambiental, devido à elevada abundância e baixo custo dos resíduos urbanos. Contudo, devem ser efetuadas análises técnico-económicas e de ciclo de vida para a completa caraterização do processo. Em terceiro, a aplicação de catalisadores de baixo custo como medida primária demonstrou elevado potencial para a melhoria do gás produto (e.g., concentração de H2 e CO, poder calorífico inferior) e para o incremento dos parâmetros de eficiência do processo; em particular, a aplicação de betão, faialite sintética e carbonizados de pellets de madeira, demonstrou resultados promissores. Finalmente, foi demonstrada a viabilidade económica da integração do processo de gasificação direta (ar) de biomassa na indústria da pasta e papel, apesar dos parâmetros determinados não serem atrativos para potenciais investidores. Neste contexto, a intervenção dos governos e o desenvolvimento de instrumentos de apoio económico é de grande relevância para a implementação destes projetos.Este trabalho foi financiado pela The Navigator Company e por Fundos Nacionais através da Fundação para a Ciência e a Tecnologia (FCT).Programa Doutoral em Engenharia da Refinação, Petroquímica e Químic

Coal-fired high performance power generating system. Final report

As a result of the investigations carried out during Phase 1 of the Engineering Development of Coal-Fired High-Performance Power Generation Systems (Combustion 2000), the UTRC-led Combustion 2000 Team is recommending the development of an advanced high performance power generation system (HIPPS) whose high efficiency and minimal pollutant emissions will enable the US to use its abundant coal resources to satisfy current and future demand for electric power. The high efficiency of the power plant, which is the key to minimizing the environmental impact of coal, can only be achieved using a modern gas turbine system. Minimization of emissions can be achieved by combustor design, and advanced air pollution control devices. The commercial plant design described herein is a combined cycle using either a frame-type gas turbine or an intercooled aeroderivative with clean air as the working fluid. The air is heated by a coal-fired high temperature advanced furnace (HITAF). The best performance from the cycle is achieved by using a modern aeroderivative gas turbine, such as the intercooled FT4000. A simplified schematic is shown. In the UTRC HIPPS, the conversion efficiency for the heavy frame gas turbine version will be 47.4% (HHV) compared to the approximately 35% that is achieved in conventional coal-fired plants. This cycle is based on a gas turbine operating at turbine inlet temperatures approaching 2,500 F. Using an aeroderivative type gas turbine, efficiencies of over 49% could be realized in advanced cycle configuration (Humid Air Turbine, or HAT). Performance of these power plants is given in a table