Silvio de Oliveira

Exergy analysis of petroleum separation processes in offshore platforms

This paper presents the exergy analysis of petroleum separation processes that take place in offshore platforms, in order to characterize the thermodynamic performance of these processes and identify possible ways of increasing the overall performance of the platform. In offshore platforms petroleum is separated into water, oil and gas. After the separation, water is sent back to the sea or reinjected into the reservoir, oil is pumped and gas is compressed and sent to the refineries. Gas-turbines and furnaces are employed to generate electricity, mechanical power and hot water that are utilized in the platform. These equipment consume part of the natural gas produced by the platform. The exergy analysis developed for the offshore platform evaluates the exergy efficiency and the exergy destroyed in each set of equipment (separators, pumps, compressors, furnaces and gas-turbines), as well as the overall platform performance. The importance of each set of equipment in the overall efficiency is quantified by the use of the factor f, defined as the relation between the consumed exergy in a particular set of equipment and the consumed exergy in the platform. This analysis is employed to evaluate the performance of a typical Brazilian offshore platform.

Exergy Analysis Applied to a Complete Flight Mission of a Commercial Aircraft

†‡ § The aeronautical industry has evolved to design extremely complex aircraft, with highl y integrated systems. Commonly used methods to design and later optimize are based on trade -off studies, which are faulty in evaluating new systems, as they present lack of information. Previous work s have shown the applicability of exergy analysis as a de cision making tool to aircraft systems design and optimization. Besides locating and quantifying the sources of entropy generation, exergy analysis can relate these irreversibities with fuel consumption, and thus with operational cost of a mission. Followi ng the methodology developed in recent works, this paper presents an exergy analysis of a complete flight mission of a conventional commercial aircraft. Such analysis allows the evaluation of exergy efficiency and exergy destroyed rate for the whole flight , as well as for each one of the flight phases (climbing, cruise, descent, holding and landing).

Uma visão das tendências e perspectivas em eletrocromismo: a busca de novos materiais e desenhos mais simples

Some aspects of electrochromism phenomena are presented in this review paper. A deep literature revision about the subject dealing with materials and device configurations developed in the last years, is presented. Great efforts of the scientific community have been done in this field. On the other hand, new electrochomic devices based on reversible deposition of metals are specially emphasized here. These devices present many advantages such as simple operation and construction and they have also shown high cycling rates. These factors make them suitable for application in display industry. In this way, many concepts used in the developement of electrodeposition baths are very useful for the improvement of these new devices; specially, all knowledge about the use of additives for modifying films microstructure and morfology.

More Electric Aircraft Analysis Using Exergy as a Design Comparison Tool

The more electric aircraft is an evolution of the aircraft industry to develop more efficient aircrafts in terms of fuel consumption and direct operational costs. One approach for a more electric aircraft is to substitute hydraulic and pneumatic power for electric power consumers: electric control surfaces actuators, cabin compressors for air conditioning and electric heaters for ice protection system. This paper describes the main characteristics of a more electric aircraft (MEA) and evaluates the exergy indexes for a complete flight cycle for the same aircraft. Previous works have shown the applicability of exergy analysis as a decision making tool to aircraft systems design and optimization. Such analysis allows the evaluation of exergy efficiency and exergy destroyed rate for the whole flight, as well as for each one of the flight phases.

Exergy, Exergy Costing, and Renewability Analysis of Energy Conversion Processes

This chapter introduces the foundations of the exergy, exergy production cost, and renewability analysis of energy conversion processes. Based on the concept of reversible work, the concept of exergy is derived and the exergy balance is presented as a combination of the energy and entropy balances. Some graphical representations are shown in which it is possible to determine or represent exergy and exergy balances. The exergy efficiency is introduced based on a general definition of efficiency, and the balance of cost is presented as an additional balance equation to be used in the performance analysis of energy systems. A brief discussion on cost partition criteria is presented to aid the analysis of the cost formation processes of the products of energy conversion processes. Finally, the renewability of energy conversion processes is analysed by means of a renewability exergy index that takes into account the type of inputs, renewable or fossil, the wastes, and the destroyed exergy of a given energy conversion process.

Exergy Method for Conception and Assessment of Aircraft Systems

A tendency of the commercial aeronautical industry is to develop more efficient aircraft in terms of fuel consumption and direct operational costs. Regarding fuel consumption, some strategies of the aeronautical industry are to use more efficient aerodynamics, lightweight materials, and more efficient engines and systems. The conventional turbo fan engine mainly provides electric power for cabin systems (lights, entertainment, and galleys) and avionics, hydraulic power for flight control systems, and bleed air for ice protection and environmental control systems. More efficient engines and different types of systems architectures, such as more electric systems, are a promise to reduce fuel consumption. In order to compare systems and engine architectures at the same basis, exergy analysis is the true thermodynamic approach that shall be used as a decision tool to aircraft systems and engine design and optimization. This chapter describes applications and a method based on exergy analysis for conception and assessment of aircraft systems. The method can support the design of the complete vehicle as a system and all of its subsystems in a common framework.

ON THE EXERGY DETERMINATION FOR PETROLEUM FRACTIONS AND SEPARATION PROCESSES EFFICIENCY

Petroleum separation processes are intensive in exergy use. However, only a very small fraction of the consumed exergy is converted into products. Due to the significant magnitude difference between consumed exergy and processed exergy, as well as to the unknown molecular structure of the involved streams, the calculation of specific exergy and of exergy efficiency is a delicate topic that involves significant uncertainties. Comparison and explanation of five different ways to perform exergy evaluation of petroleum separation processes are conducted. The indication of advantages and disadvantages of each formulation is presented. The chemical and physical exergy calculation for petroleum and its fractions are covered. An application is performed and the results are discussed.

THERMO-HYDRAULIC MODEL OF A TWIN-SCREW MULTIPHASE PUMP

The twin-screw multiphase pump has been studied as an alternative equipment to substitute the conventional system (fluid separation, liquid pumping and gas compression) in petroleum boosting. By “pumping” gas and liquid together, the multiphase pump could reduce production costs, particularly in deepwater activity. This paper presents a thermo-hydraulic model of a twin-screw multiphase pump developed to determine important parameters such as: volumetric efficiency, absorbed power, discharge conditions, heat transfer and pressure and temperature profiles. The continuous movement from suction to the discharge of pump chambers is divided in small discretive steps. This division allows the calculation of energy and mass balances for each screw chamber. At each step, it is possible to calculate mass and energy that enters and leaves one chamber. With this balance, pressure and temperature for the next step can be calculated. Differently from previous model, it considers not only water-air but also hydrocarbon mixtures (including petroleum heavy fractions) as working fluids. Besides, inclusion of screw rotation influence over peripheral backflow is not neglected as in previous models.Copyright

Compared exergy analysis of sugarcane bagasse sequential hydrolysis and fermentation and simultaneous saccharification and fermentation

This paper presents the compared exergy analysis of the enzymatic hydrolysis of sugarcane bagasse through Sequential Hydrolysis and Fermentation-SHF and Simultaneous Saccharification and Fermentation-SSF configurations to obtain lignocellulosic ethanol. Four pre-treatment processes were considered: Steam Explosion-SE, Organosolv, Liquid Hot Water-LHW, and a combined SE and LHW method. The pre-treatments analysed simultaneously with the SHF (Cases 1, 3, 5 and 7) and SSF (Cases 2, 4, 6 and 8) configurations were carried out for the overall system focus on the wine production. Processes simulations were performed by using Aspen Plus® to a plant with 500 t/h milling capacity. The results for SHF configurations in terms of exergy efficiency rate were 60.0% for case 1, 56.5% for case 3, 58.3% for case 5 and 59.4% for case 7. For SSF configurations, the exergy efficiency obtained in case 2, case 4, case 6 and case 8 were 62.4%, 58.3%, 60.3% and 61.5%, respectively.

Exergy and Renewability Analysis of Liquid Biofuels Production Routes

Liquid biofuels can be produced from a variety of feedstocks and processes. Ethanol and biodiesel production processes based on conventional raw materials are already commercial, but subject to further improvement and optimization. Biofuels production processes using lignocellulosic feedstocks are still in the demonstration phase and require further R&D to increase their production efficiency. Exergy analysis is a primary tool to assess the efficiency and renewability of biofuels production processes from an integrated point of view. In this chapter, an exergy-based comparative analysis of four biofuels production routes are described and discussed. The selected feedstocks are glucose and sugarcane syrups, the fruit and flower stalk of banana tree and palm oil. For each production route, the effect of process variables on the exergy efficiency and the renewability exergy index (presented in Chap. 2) are determined allowing the identification of possible ways to optimize the production of such biofuels. According to the values of the renewability exergy index, ethanol production process using sucrose, amilaceous, or lignocellulosic material cannot be considered renewable, while biodiesel production from palm oil can be considering renewable. The main reason for these conclusions is due to the irreversibilities that take place along the energy conversion processes of these biofuels production routes. These unexpected conclusions highlight that although renewable raw materials are used as feedstocks, the biofuel itself cannot be considered renewable due especially to the exergy destruction of its production process.