• Energy Research

Fast microwave-assisted pyrolysis (fMAP) in the presence of a microwave absorbent (SiC) and catalyst (HZSM-5) was tested on a Chlorella sp. strain and on a Nannochloropsis strain. The liquid products were characterized, and the effects of temperature and catalyst:biomass ratio were analyzed. For Chlorella sp., a temperature of 550 °C, with no catalyst were the optimal conditions, resulting in a maximum bio-oil yield of 57 wt.%. For Nannochloropsis, a temperature of 500 °C, with 0.5 of catalyst ratio were shown to be the optimal condition, resulting in a maximum bio-oil yield of 59 wt.%. These results show that the use of microwave absorbents in fMAP increased bio-oil yields and quality, and it is a promising technology to improve the commercial application and economic outlook of microwave pyrolysis technology. Additionally, the use of a different catalyst needs to be considered to improve the bio-oil characteristics.

Goal: Hydrogen has shown increasing demand in oil refineries, due to the importance of its use as a sulfur capture element. As different oils and products require different amounts of hydrogen, their use optimally is an essential tool for refinery production scheduling. A comparison was made between the different approaches used in optimization via mathematical programming. Design / Methodology / Approach: One of the most used methods for hydrogen network optimization is through mathematical programming. Linear and non-linear models are discussed, positive aspects of each formulation and different initialization techniques for non-linear modeling were considered. Results: The optimization through the linear model was more satisfactory, taking into account the payback of the new proposed design, combined with the use of compressor rearrangement, which reduces the investment cost. Limitations of the investigation: The objective function chosen is based on the operational cost, but another approach to be considered would be the total annual cost. In addition, the parameters related to costs are obtained from the literature and may change over the years. Practical implications: The proposal is to discuss the main aspects of each model, showing which models more robust and easier to converge are capable of providing competitive results. Also, different initialization techniques that can be used in future works. Originality / Value: The main contribution is the relationship between hydrogen management and production scheduling and for that, a discussion is made about possible formulations. Linear model is sufficient to optimize the problem, due to its main characteristics discussed.

En este trabajo se propone un marco computacional para la síntesis de redes de intercambiadores de calor flexibles y controlables. Se proyecta que la síntesis funcione en un rango específico de variaciones esperadas en las temperaturas de entrada y los caudales de las corrientes de proceso utilizando un sistema de control descentralizado, de modo que el costo anual total que involucra el consumo de servicios públicos y la inversión se optimice simultáneamente. El marco se basa en una estrategia de dos etapas. Se realiza una etapa de diseño previa al análisis de operabilidad donde se eligen las variables de diseño. En la segunda etapa, las variables de control se ajustan durante la operación en las realizaciones de los parámetros inciertos. El marco produce un diseño de GALLINA, que está garantizado para operar con el sistema de control diseñado en diferentes condiciones, lo que garantiza los objetivos de temperatura de la corriente y una integración energética óptima. La aplicación del marco propuesto y su eficiencia computacional se ilustran con algunos ejemplos numéricos. Dans ce travail, un cadre de calcul est proposé pour la synthèse de réseaux d'échangeurs de chaleur flexibles et contrôlables. La synthèse devrait fonctionner sur une plage spécifiée de variations attendues des températures d'entrée et des débits des flux de processus à l'aide d'un système de contrôle décentralisé, de sorte que le coût annuel total impliquant la consommation de services publics et l'investissement soient optimisés simultanément. Le cadre est basé sur une stratégie en deux étapes. Une étape de conception est effectuée avant l'analyse d'opérabilité où les variables de conception sont choisies. Dans la deuxième étape, les variables de commande sont ajustées pendant le fonctionnement sur les réalisations des paramètres incertains. Le cadre donne une conception de POULE, qui est garantie de fonctionner avec le système de contrôle conçu dans des conditions variables assurant des objectifs de température de flux et une intégration optimale de l'énergie. L'application du cadre proposé et son efficacité de calcul sont illustrées par quelques exemples numériques. In this work a computational framework is proposed for the synthesis of flexible and controllable heat exchanger networks. The synthesis is projected to operate over a specified range of expected variations in the inlet temperatures and flowrates of the process streams using a decentralized control system, such that the total annual cost involving the utility consumption and the investment are optimized simultaneously. The framework is based on a two-stage strategy. A design stage is performed prior to the operability analysis where the design variables are chosen. In the second stage, the control variables are adjusted during operation on the realizations of the uncertain parameters. The framework yields a HEN design, which is guaranteed to operate with the designed control system under varying conditions ensuring stream temperature targets and optimal energy integration. The application of the proposed framework and its computational efficiency are illustrated with some numerical examples. في هذا العمل، يُقترح إطار حسابي لتوليف شبكات المبادلات الحرارية المرنة والقابلة للتحكم. من المتوقع أن يعمل التوليف على نطاق محدد من الاختلافات المتوقعة في درجات حرارة المدخل ومعدلات تدفق تدفقات العملية باستخدام نظام تحكم لامركزي، بحيث يتم تحسين التكلفة السنوية الإجمالية التي تنطوي على استهلاك المرافق والاستثمار في وقت واحد. يعتمد الإطار على استراتيجية من مرحلتين. يتم تنفيذ مرحلة التصميم قبل تحليل قابلية التشغيل حيث يتم اختيار متغيرات التصميم. في المرحلة الثانية، يتم ضبط متغيرات التحكم أثناء التشغيل على تحقيق المعلمات غير المؤكدة. ينتج عن الإطار تصميم دجاجة، وهو مضمون للعمل مع نظام التحكم المصمم في ظل ظروف مختلفة لضمان أهداف درجة حرارة التيار والتكامل الأمثل للطاقة. يتم توضيح تطبيق الإطار المقترح وكفاءته الحسابية مع بعض الأمثلة العددية.

Abstract In recent decades, environmental and economic issues have pushed the production of biofuels worldwide. In this scenario, ethanol is the most produced biofuel. Starch is a potential substrate for this purpose, but the extra cost needed to hydrolyze it into glucose is still a drawback. As an alternative for the expensive and energy demanding conventional hydrolysis process, the cold hydrolysis is being studied. In this process, granular starch degrading enzymes act directly on raw starch granules; therefore, this hydrolysis is carried out below gelatinization temperature. As a consequence, the energy requirement can be significantly reduced. In this work, the cold hydrolysis and fermentation of fresh sweet potato were experimentally studied. For that, it was employed the sweet potato strain BRS Cuia, whose carbohydrate level reaches 28.7%. It can be translated into a potential to produce 185 L t−1 ethanol, or equivalently 7400 L ha−1. The enzymes blend adopted for the hydrolysis stage was Stargen™ 002. The surface response method indicated 200 g L−1 of sweet potato and 45 GAU g−1 of sweet potato as the best balance between high glucose formation rate and low enzyme consume. The 1 h pretreatment that achieved the highest glucose concentration was at 52 °C in the presence of the enzymes blend. Finally, the study of the simultaneous hydrolysis and fermentation showed that the medium supplementation has no significant effect over the fermentation performance, while the pH control is beneficial, improving the ethanol production in 54%.

Hydrogen network management has economic appeal due to its importance in oil refineries. It has become genuinely relevant due to the restrictions of sulfur content in fuels, which need hydrogen to be removed. Mathematical programming can be used as a tool for optimizing hydrogen networks, and the efficient management of hydrogen within the refineries can be achieved through a material balance of the units that make up the hydrogen network. In this work, an optimization model Mixed-Integer Linear Programming (MILP) and Mixed-Integer Nonlinear Programming (MINLP) for hydrogen networks was applied to minimize the operating costs. The optimization model was developed in GAMS, and it was validated using a literature case study and a real case study from a Brazilian Refinery. The operation cost was reduced by 10% and 19.6% with MILP and 9.7% and 31.5% with MINLP, for example 1 and 2, respectively. Comparing the results, both achieve significant savings in operating costs. The MILP model, which is easier to solve, has proved to be an efficient tool for optimizing hydrogen networks. However, optimization via MINLP, although not guaranteeing the optimal solution, resulted in lower operating and capital costs. The design of the optimized hydrogen networks was also detailed, and other extra restrictions were imposed on the problem.

ABSTRACT Sweet potato is an attractive feedstock for ethanol production due to its high starch content and favorable agronomic characteristics. This paper proposes a simple equation to estimate the total reducing sugars (including glucose from starch) in sweet potatoes based on their moisture content (low cost and simple measurement). It allows the calculation of the ethanol production potential of a given sweet potato mash. According to the equation, the ethanol potential increases non-linearly with increasing concentrations of sweet potato mash in the fermenting medium (w/v), reaching a constant value for high concentrations (22 % of ethanol to 10 kg: L of a sweet potato with a moisture content of 66 %). Additionally, the ethanol yield potential is very sensitive to the sweet potato moisture, increasing linearly when the moisture decreases. We emphasize that the relations proposed in this paper can be used by other researchers, who can apply them to their specific cases.

Abstract Shochu is the most widely consumed spirit in Japan. In its manufacture is used koji, a solid fungus culture traditional of the Asian countries, but that makes the production process slow. Shochu can be produced from a variety of starchy sources, including sweet potato. About 7% of the world’s sweet potato production is wasted due to imperfections that make it unsuitable for consumption. However, this material can be used in ethanol production. Considering the high productivity of sweet potato in Brazil, an opportunity to add value to this raw material is perceived. An alternative process for the production of sweet potato distillate similar to shochu was proposed. Koji was replaced by a mixture of alpha-amylase and glucoamylase. Process time was reduced from 14 to only 1 day. Composition analyses were performed by HPLC and GC. The experimental yield of alcoholic fermentation using pectinase enzyme reached 67.31-73.65%, but methanol was above the limits of the legislation. Without the addition of pectinase, no methanol was formed. However, there was a decrease in yield (51.65-54.75%), due to the incomplete disintegration of sweet potatoes. The distillate produced and the commercial shochu presented the same absorption bands in FTIR analysis, identifying the similarity between them.

Recent developments in remote sensing are offering a promising opportunity to rethink conventional control strategies of wind turbines. With technologies such as LIDAR, the information about the incoming wind field - the main disturbance to the system - can be made available ahead of time. Feedforward control can be easily combined with traditional collective pitch feedback controllers and has been successfully tested on real systems. Nonlinear model predictive controllers adjusting both collective pitch and generator torque can further reduce structural loads in simulations but have higher computational times compared to feedforward or linear model predictive controller. This paper compares a linear and a commercial nonlinear model predictive controller to a baseline controller. On the one hand simulations show that both controller have significant improvements if used along with the preview of the rotor effective wind speed. On the other hand the nonlinear model predictive controller can achieve better results compared to the linear model close to the rated wind speed.