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This work aims to develop a stationary phenomenological model of an industrial steam reforming unit. Unlike the usual approach in literature, the combustion reactions at the furnace are described t...

Water hyacinth (WH, Eichhornia crassipes, ’Emboch’ in Ethiopia) is a highly disturbing class of invasive and noxious aquatic plants found worldwide in other water bodies and as such is a prime problem in Lake Tana. One approach to successfully control the rapid invasion of WH is to utilize it as a feedstock to produce high-valued commodities in a biorefinery framework. Preliminary life cycle analysis carried out in the study shows that WH biomass is a competitive feedstock for biorefinery systems with a unit cost at $ 24.40 per ton of dry matter. Based on the annual generation capacity of 0.71 million tons of dry mass in lake Tana and following the standard biorefinery process protocols, the predictions indicate that the economic potential of converting WH biomass into 38.8 billion liters of biomethane alone to be at $ 38.8 million, 74.2 million liters of bioethanol alone at $ 51.9 million, and o.52 million tons organic agro-fertilizer alone at $ 130.5/78.3 million as a partial substitute for Anhydrous Ammonia or Muriate of Potash (MOP) fertilizers. Hence the integrated WH management and utilization as a biorefinery feedstock ranks it among the world’s most competitive feedstocks with attractive socio-economic and environmental benefits.

Catalyzed chemical reactions inside tubular reactors play a key role in steam methane reforming process, as they define the temperature and composition profiles of the reformer and, consequently, its efficiency. Although the kinetic modeling of reforming reactions has already been widely discussed, studies that carry out the comparison between kinetic reform models are still scarce. In this context, this work aims to evaluate the influence of different kinetics on the stationary behavior of industrial reformer. The kinetic models of Singh and Saraf (1979), Numaguchi and Kikuchi (1988), Xu and Froment (1989a), and Hou and Hughes (2001) were analyzed and compared with each other. All models describe the reformer satisfactorily with relative deviations around 3.5% compared to experimental and literature data. The results show that the simplest kinetic models present advantages compared to traditional models, such as Xu and Froment (1989a), which is widely used without any prior analysis.

The techno-economic feasibility of three biogas utilization processes was assessed through computer simulations on commercial process simulator Aspen HYSYS: HPC (biogas to methanol), BioCH4 (biogas to biomethane) and CHP (biogas to heat & electricity). The last two processes are already used commercially with the aid of subsidy policies. The economic analysis indicates that, without these policies, none of these attain economic self-sustainability due to high overall manufacturing costs. The estimated minimum support cost (MSCs) were 108, 62 and 109 €/MWh for the HPC, BioCH4 and CHP processes, respectively. The model could explain currently practised government subsidies in Italy and Germany. It was seen that the newly proposed HPC process is economically comparable to the traditional CHP process. Therefore, the HPC process is a possible alternative to biogas usage. A support policy was proposed: 50, 66, 158 and 148 €/MWh for available heat, methane, electricity and methanol (respectively); the proposed energy policy results in a 10% OpEx rate of return for any of the processes, thus avoiding a disparity in the production of different products.

In this work (part of a series in which different biomass conversion routes are studied) a novel coupling between gasification and pyrolysis is described: by means of a design parameter (α) biomass is distributed between these two operations. In order to characterize the quality of the syngas produced, simulations are performed with a gasification / pyrolysis simulator, GASDS. Profiles were obtained for oxygen consumption, together with bio-char, syngas and steam production as a function of α. In a further work, an economic analysis shall define optimal design conditions.

Foi desenvolvido um modelo para representar uma torre de resfriamento operando em corrente cruzada a partir de balanços diferenciais de massa e energia. A utilização de uma função de ativação permitiu a unificação das formulações de gás saturado e insaturado, o que simplificou a forma final do sistema de equações resultantes e o seu processo de dedução. O modelo fez uso de expressões para a transferência de massa e energia que foram originadas a partir de analogias com o transporte de vapor e calor através de ar estagnado em um tubo vertical. O uso da expansão em séries de potência permitiu a criação de um sistema simplificado de equações, válido para baixos valores de umidade e baixas taxas de transferência de massa. Vários métodos numéricos foram propostos para a solução do sistema de equações diferenciais resultantes, dentre os quais estão o método de Euler, do Pontomédio, de BulirschStoer e o de Runge Kutta de 4ª ordem. Tais métodos foram usados na resolução do sistema de equações segundo o esquema proposto, o qual requereu a combinação de dois desses métodos: um para a direção principal e outro para a direção secundária. Neste esquema, cada uma das direções (principal e secundária) esteve associada a uma das fases (ar ou água) e a solução das equações da direção principal sempre precedeu a solução daquelas da direção secundária. As simulações foram realizadas através de scripts em Matlab® R2013b e foram utilizados os dados de BOUROUNI ET AL, GROBBELAAR ET AL E CORTINOVIS ET AL. Exceto para os dados fornecidos por BOUROUNI ET AL, os valores encontrados para os coeficientes de transferência de massa foram próximos daqueles reportados pelos autores. O valor reportado por BOUROUNI ET AL foi aproximadamente 45 vezes maior que o valor encontrado neste trabalho. Associase a tal discrepância o uso do método de Gauss Seidel por tais autores, o qual é um método de convergência lenta e baixa precisão. Os dados de CORTINOVIS ET AL são mais bem representados pelo modelo proposto nesse trabalho que aquele proposto por tais autores. Tal conclusão advém da grande concordância entre os resultados teóricos e experimentais relacionados com a correlação levantada para o coeficiente de transferência de massa. Utilizouse os dados de BOUROUNI ET AL para a realização de comparações entre os diferentes métodos numéricos. A combinação mais rápida e precisa foi aquela em que o método do Pontomédio e de Runge Kutta foram utilizados para a resolução das direções principal e secundária (respectivamente). O gás foi escolhido como componente principal e o domínio foi dividido em cinco intervalos na direção x e seis na direção y. Utilizouse a formulação exata do sistema de equações e a função de ativação degrau. O sistema de equações apresentado é particularmente desafiador devido à grande variação de temperaturas do líquido ao longo do domínio. A configuração escolhida, por ter conseguindo atingir alta precisão para tal sistema, não deve encontrar grandes dificuldades em apresentar bons resultados na resolução do sistema de equações de outras torres de resfriamento. A model was developed for the representation of a crossflow cooling tower through differential mass and energy balances. The use of activation functions allowed the unification of the saturated and insaturated gas formulations, thus enabling a simpler presentation of the system of equations and its development. The model used mass and energy transfer equations which were derived from analogies with the transport of steam and heat in a vertical tube through stagnant air. Power series expansions of the resulting equation system permitted the simplification of such system, one which is valid for low humidity values and low mass transfer rates. Several numerical methods were proposed for the solution of the resulting differential equation system, among which are Eulers method, the Midpoint method, BulirschStoers and the 4th order RungeKutta method. Such methods were used for solving the system of equations following the proposed scheme, which required the combination of two of these methods at a time: one for the main direction and another for the secondary direction. In this scheme each of the directions (main and secondary) were associated with one of the phases (air or water) and the solutions of the equations of the main direction always preceded those from the secondary direction. The simulations were run in scripts in Matlab® R2013b with the data of BOUROUNI ET AL, GROBBELAAR ET AL and CORTINOVIS ET AL. Except for the data acquired from BOUROUNI ET AL, the values found for the mass transfer coefficient were close to those reported by the other authors. The value reported by BOUROUNI ET AL was approximately 45 times greater than the one found in this work. Such discrepancy is attributed to the use of the GaussSeidel method by such authors, which is a slowconvergence, lowprecision method. The data from CORTINOVIS ET AL is better represented by the models proposed in this work than by the models proposed by such authors. Such conclusion is drawn from the close agreement between theoretical and experimental values of the mass transfer coefficient related to the correlation obtained. The data of BOUROUNI ET AL was used for the comparison of different numerical methods. The fastest, most precise configuration was the one in which the Midpoint and RungeKutta methods was used in the main and secondary direction (respectively). The gas was chosen as the main component and the dominium was divided in five intervals in the direction and six in the direction. The exact formulation of the system of equations was used, together with the step activation function. The presented system of equations is particularly challenging due to the great steepness of the liquid temperature profile through the dominium. After achieving a high precision for such a system, the chosen configuration shall not present difficulties in delivering good results when dealing with other cooling tower equation systems.