Article by Rafael N Nakashima
International Journal of Exergy, 2020
Biomass conversion into either electricity or biofuels requires various energy intensive processe... more Biomass conversion into either electricity or biofuels requires various energy intensive processes that may drastically affect its technical and environmental competitiveness against their non-renewable counterparts. Therefore, in this paper, a comparative assessment between the total (cT) and non-renewable (cNR) unit exergy costs and specific CO2 emissions (cCO2) of the electricity, methane and hydrogen produced from sugarcane vinasse and bagasse is presented and compared with the conventional (fossil fuel-based) supply chains. As a result, the non-renewable unit exergy costs and specific CO2 emissions for the transportation service in all cases analysed are 3.1 to 4.7 times lower compared with conventional fossil fuels (e.g., diesel, gasoline, natural gas and hydrogen). Among the waste upgrade alternatives, methane production is able to maximise the exergy flow rate of products in the transformation stage (52.4-58.6 MW), while hydrogen and electricity production can substantially increase the transportation service in the end-use stage (51.7-52.1%) and the operational revenues (2,706-2,889 EUR/h).
Renewable Energy, Sep 30, 2020
The ethanol distillation produces large quantities of vinasse, a wastewater with high concentrati... more The ethanol distillation produces large quantities of vinasse, a wastewater with high concentrations of organic and inorganic substances that may cause environmental damages if incorrectly disposed. In this way, different alternatives are proposed to enhance the efficiency of vinasse disposal, such as the anaerobic digestion and concentration processes. However, the evaluation of the thermodynamic performance of those systems and their possible energy integration was seldom investigated. Thus, an exergy assessment and comparison of five different scenarios of vinasse disposal, including the vinasse fertirrigation, concentration and anaerobic digestion processes, is presented in this paper. The results indicate that, among the disposal alternatives, the highest exergy efficiency (20.1%) is attained by a system combining anaerobic digestion and vinasse concentration in series. In this case, the wastewater treatment plant produces the maximum amount of biogas, while the vinasse concentration still recovers water and reduce diesel consumption. Furthermore, the heat integration between the biogas power plant and vinasse concentration is able to increase the exergy efficiency of these processes (10-51%) and reduce 9-11% of steam consumption. In general, the major sources of exergy destruction in vinasse disposal alternatives are related with the exergy loss of organic substances in fertirrigation and irreversibilities in steam generation.
Journal of Power Technologies, Apr 2019
The upgrading of the biorefineries residues is a possible way to increase the overall process eff... more The upgrading of the biorefineries residues is a possible way to increase the overall process efficiency while attaining economical revenues from wastes that otherwise would be discarded. In this sense, anaerobic digestion and gasification represent
interesting alternatives to convert organic residues into biofuels, electricity or other bioproducts. However, few studies have explored energy integration possibilities between those options or evaluated various final product pathways. Thus, in this
work, various scenarios aimed at capitalizing the main residues of the sugarcane ethanol industry (vinasse and bagasse) are investigated. Two process layouts combining anaerobic digestion and gasification are proposed for each desired product
(methane, hydrogen or power). The highest exergy efficiency (48%) was obtained for the configuration focused on methane production and using a combined cycle, since it requires fewer resources and separation steps to convert feedstock into exportable products. On the other hand, exergy was primarily destroyed in vinasse disposal, since a significant fraction of its organic wastes are inert to anaerobic digestion, followed by the bagasse gasifier and utility systems, due to the irreversible reactions occurring in these processes. In short, this study points to some improvement opportunities and reinforces the advantages of the waste capitalization concept.
Conference papers by Rafael N Nakashima
32th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, ECOS 2019, 2019
The upgrade of sugarcane industry residues, such as vinasse and bagasse, has a notably potential ... more The upgrade of sugarcane industry residues, such as vinasse and bagasse, has a notably potential for large scale production of biofuels in Brazil. Despite this fact, the biomass conversion into either electricity or biofuels requires various energy intensive processes that may drastically affect its technical and environmental competitiveness against their non-renewable counterparts. Accordingly, the mapping of the generation of the process irreversibility and their associated atmospheric emissions may help, by issuing appropriate mitigation tasks, in the reduction of exergy consumption rates and environmental impact. Therefore, in this paper, a comparative assessment between the total (c_t) and non-renewable (c_nr) exergy costs and specific CO2 emissions (c_co2) of the electricity, methane and hydrogen produced from sugarcane vinasse and bagasse is presented and compared with the conventional (fossil fuel-based) supply chains. As a result, a strikingly high average renewable to non-renewable ratio ( c_r/c_nr ) of 15.2 is estimated for the biofuels derived from the waste upgrade plant. However, due to the larger number of process involved in the conversion of biomass resources, the total exergy costs of biofuels delivered vary from 2.6 to 2.2 times higher in comparison to those derived from fossil fuels. On the other hand, although hydrogen production from sugarcane wastes involves more processes, its unit exergy costs in the end-use stage (transportation service) were found to be the lowest among the studied biofuels, partially due to the higher efficiency of hydrogen-fueled transportation technologies. In general, the production of biofuels and electricity from sugarcane wastes can offer fuels with greatly reduced CO2 specific emissions and low non-renewable energy consumption shares.
Vinasse is the main liquid effluent of ethanol distillation and, when incorrectly disposed, can c... more Vinasse is the main liquid effluent of ethanol distillation and, when incorrectly disposed, can cause damages in water and soil resources. Since this effluent has a high concentration of organic compounds, anaerobic digestion is a possible solution to reduce vinasse chemical organic demand (COD) while producing biogas, an alternative fuel. However, this technology has some challenges related to biogas economical devaluation and high investments costs, which demands models to analyze this systems performance. Thus, the focus of this study was to develop a biogas production model, combining Matlab® and Aspen Plus®, to evaluate the anaerobic treatment efficiency by using exergy analysis. The results show that a significant quantity of exergy can be partially retrieved (44-52%) from vinasse with biogas production. In general, increases in hydraulic retention times (HRT) and COD concentrations tend to slightly increment anaerobic digestion efficiency, while high sulfates concentrations have the opposite effect. However, the biogas plant exergy efficiency tends to increase at lower HRT due to higher biogas production and lower portion of untreated vinasse. On average, the main sources of irreversibilities are the cooling system (45%) and the anaerobic reactor (48%). Moreover, the biogas plant performance throughout the year is considerably affected by ethanol production seasonality, start-up times and number of reactors.
Thesis by Rafael N Nakashima
O resíduo da primeira destilação do vinho, a vinhaça, destaca-se dentre os demais gerados na prod... more O resíduo da primeira destilação do vinho, a vinhaça, destaca-se dentre os demais gerados na produção de etanol de cana-de-açúcar pelo seu grande volume e alta concentração de substâncias orgânicas. O tratamento anaeróbio desse efluente pode melhorar suas características físico-química (e.g. pH e DQO) além de produzir um combustível alternativo ao gás natural, o biogás. No entanto, apesar dos possíveis ganhos energéticos e ambientais, essa tecnologia apresenta dificuldades em se tornar viável no setor sucroenergético. Tendo em vista esse cenário, este trabalho propõe uma nova análise termodinâmica, baseada no método exergético, do potencial da vinhaça e do biogás provindo de seu tratamento. Para isso, modelou-se a digestão anaeróbia da vinhaça por meio do ADM1 (Anaerobic Digestion Model No1) e atualizou-se o cálculo da exergia química deste efluente. Assim, os resultados obtidos indicam que o tratamento anaeróbio pode recuperar uma significativa parcela da exergia descartada com a vinhaça (44-52% de 189-1529 kJ/l), dependendo da degradabilidade e concentração do material orgânico, bem como o regime de operação do reator anaeróbio. Nota-se também, que apesar de a digestão anaeróbia ser mais eficiente com maiores tempos de retenção hidráulica, é preferível maximizar o volume de vinhaça tratada em detrimento da qualidade de conversão. Além disso, o desempenho anual da geração de biogás também é afetado pelo seu processo de partida e pela sazonalidade da produção de etanol. Por outro lado, a planta de biogás promove maiores reduções de exergia destruída em comparação com a fertirrigação e a concentração de vinhaça. Possíveis integrações térmicas entre a planta de biogás e a unidade de concentração de vinhaça foram propostas e analisadas, atingindo melhores eficiências exergéticas e reduzidas demandas térmicas. De forma geral, esse estudo demonstra a aplicação do método exergético na valorização de resíduos orgânicos por meio da produção de biogás.
Papers by Rafael N Nakashima
Journal of Power Technologies 99 (2) (2019) 104–114, 2019
The upgrading of the biorefineries residues is a possible way to increase the overall process eff... more The upgrading of the biorefineries residues is a possible way to increase the overall process efficiency while attaining economical revenues from wastes that otherwise would be discarded. In this sense, anaerobic digestion and gasification represent interesting alternatives to convert organic residues into biofuels, electricity or other bioproducts. However, few studies have explored energy integration possibilities between those options or evaluated various final product pathways. Thus, in this work, various scenarios aimed at capitalizing the main residues of the sugarcane ethanol industry (vinasse and bagasse) are investigated. Two process layouts combining anaerobic digestion and gasification are proposed for each desired product (methane, hydrogen or power). The highest exergy efficiency (48%) was obtained for the configuration focused on methane production and using a combined cycle, since it requires fewer resources and separation steps to convert feedstock into ex-portable products. On the other hand, exergy was primarily destroyed in vinasse disposal, since a significant fraction of its organic wastes are inert to anaerobic digestion, followed by the bagasse gasifier and utility systems, due to the irreversible reactions occurring in these processes. In short, this study points to some improvement opportunities and reinforces the advantages of the waste capitalization concept.
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Article by Rafael N Nakashima
interesting alternatives to convert organic residues into biofuels, electricity or other bioproducts. However, few studies have explored energy integration possibilities between those options or evaluated various final product pathways. Thus, in this
work, various scenarios aimed at capitalizing the main residues of the sugarcane ethanol industry (vinasse and bagasse) are investigated. Two process layouts combining anaerobic digestion and gasification are proposed for each desired product
(methane, hydrogen or power). The highest exergy efficiency (48%) was obtained for the configuration focused on methane production and using a combined cycle, since it requires fewer resources and separation steps to convert feedstock into exportable products. On the other hand, exergy was primarily destroyed in vinasse disposal, since a significant fraction of its organic wastes are inert to anaerobic digestion, followed by the bagasse gasifier and utility systems, due to the irreversible reactions occurring in these processes. In short, this study points to some improvement opportunities and reinforces the advantages of the waste capitalization concept.
Conference papers by Rafael N Nakashima
Thesis by Rafael N Nakashima
Papers by Rafael N Nakashima
interesting alternatives to convert organic residues into biofuels, electricity or other bioproducts. However, few studies have explored energy integration possibilities between those options or evaluated various final product pathways. Thus, in this
work, various scenarios aimed at capitalizing the main residues of the sugarcane ethanol industry (vinasse and bagasse) are investigated. Two process layouts combining anaerobic digestion and gasification are proposed for each desired product
(methane, hydrogen or power). The highest exergy efficiency (48%) was obtained for the configuration focused on methane production and using a combined cycle, since it requires fewer resources and separation steps to convert feedstock into exportable products. On the other hand, exergy was primarily destroyed in vinasse disposal, since a significant fraction of its organic wastes are inert to anaerobic digestion, followed by the bagasse gasifier and utility systems, due to the irreversible reactions occurring in these processes. In short, this study points to some improvement opportunities and reinforces the advantages of the waste capitalization concept.