Environomic modeling and optimization of advanced combined cycle cogeneration power plants including CO2 separation options

EPFL, 1998
EPFL thesis

Abstract

Considering the economic importance of the electricity generation sector as well as its contribution to local, regional and global pollution, the development of new cost-effective and environmentally benign electricity generation and cogeneration systems is an essential task. In this context, combined cycle cogeneration power plants are among the most promising systems. The integration of gas turbines with a steam turbine cycle leads to complex systems and to an increasing number of technological options for their improvement. Faced with growing concerns about greenhouse gas emission, systems for CO2 separation become an additional option and compete with measures for efficiency improvement. The simultaneous consideration of economic and environmental concerns as well as the increasing system complexity and the growing number of options represent an important challenge to the engineer and require the development of new approaches and design tools. The present work contributes to the development of such an approach and its application to combined cycle cogeneration power plants and their advanced options. These options, such sequential combustion gas turbines, compressor intercooling of CO2 separation can improve performance with respect to efficiency and emissions, but require increased investment costs. These competing factors are united in a so-called environomic model which takes into account the costs of resources and capital investment, as well as the costs of pollution, and calculates a single criterion – the total cost of electricity production. The costs of pollution used in this work are based on economic studies from the literature. For internalization, a penalty factor allows the degree of pollution already present in the environment to be taken into account. Benefits due to the substitution of domestic furnaces through cogeneration are also considered. A so-called "superconfiguration" model allows the modeling of simultaneous changes in configuration and design. Uncertainties linked to thermodynamic performance and investment costs model are addressed through calibration by means of reference combined cycle power plants, as well as through a proposed method for directly taking them into account in the model. The influence of varying requirements such as the power plant size, operating time and emission limits can also be modeled, providing valuable information such as thermodynamic states, component performance and investment costs. The resulting optimization problem is of the non-linear, mixed integer type. The complex task of finding optimum solutions is accomplished by means of powerful optimization methods that allow searching of the entire solution space. In this work, a genetic algorithm was adapted to the requirements of the superconfiguration optimization, permitting the simultaneous optimization of configuration and design. Genetic algorithms work with populations instead of a single data point and rely on biological mechanisms such as mating, mutation and replacement, and provide multiple promising solutions. Reference cases with different electricity and heat demand as well as different annual operating time are optimized and analyzed in detail with respect to the solutions obtained. Based on these reference cases, sensitivity studies on the cost of pollution, as well as emission limits, show the influence of these factors on the combined cycle configuration and design, as well as on the cost structure of electricity, and demonstrate an application of the method.

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https://infoscience.epfl.ch/record/32268?ln=en

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EPFL, 1998
EPFL thesis

Abstract

Official source

https://infoscience.epfl.ch/record/32268?ln=en

About this result

Related concepts (24)

Related concepts

Related publications (45)

Related publications

Within the goal of reducing greenhouse gas emissions and supplying sustainable energy, complex integrated energy conversion systems have to be designed by taking into account thermodynamic, economic and environmental considerations simultaneously. The process performance highly depends on the quality of the process integration and on the energy conversion, in particular, on how the heat requirements are balanced and how the combined heat and power generation is integrated. In chemical processes, the heat requirements after heat recovery are typically satisfied by the energy conversion system, while for fuel and electricity producing processes, the requirements are balanced by waste and process streams available on-site. The optimal internal heat recovery and utility integration can be computed by applying heat cascade models that are solved by using mathematical programming techniques. The mass and energy balances of the process unit operations are therefore satisfied by the optimal energy conversion system integration without having to explicitly model the heat exchanger network. The presented thermo-economic optimization approach combines flowsheeting and process integration techniques with economic evaluation and life-cycle assessment in a multi-objective optimization framework. The advantage of including the process integration model in the design process is that the influence of the process design and operation is reflected on the thermo-environomic performance of an energy balanced system in which the heat supplied from energy resources is integrated. The methodology has been successfully applied to study CO2 capture concepts in power plants using natural gas, coal or biomass resources, to analyse thermo-chemical H2 production processes and to evaluate different biofuel processes producing Fischer-Tropsch fuel, methanol, dimethylether and H2 by biomass gasification. The potential performance improvement through process integration is revealed for each case. In particular, it is highlighted how the optimization of the combined cycle valorizing the excess heat and of heat pumping options improve the process efficiency by simultaneously maximizing the combined production of fuel, captured CO2, heat and power. This shows that this computer-aided process design strategy combining flowsheeting, energy integration, cost assessment and multi-objective optimization is a powerful tool to systematically generate different process options, assess trade-offs and reveal process improvements through process integration.

2013

As our awareness of the dangers of global climate change grows, the development of new renewable energy technologies is of primary importance in the effort to reduce emissions of carbon dioxide and other greenhouse gases. Rapid increases in the price of oil and worries about the stability and security of the extraction of fossil fuels have lead to renewed interest in the development of local energy sources, thereby reducing dependence on foreign sources. Amid the plethora of option available, one of the more promising solutions is the increased use of concentrating solar thermal power. Solar thermal power generation shows great potential for supplying the base electricity needs of numerous countries in the sun-belt regions, stretching from the tropics to the Mediterranean. This has lead to a recent renewal in the development of such systems, most notably with the construction of the PS10 and PS20 central receiver power plants in Spain. However, all currently existing solar thermal power plants have been based around the use of Rankine or steam turbine cycles, which are limited in the efficiencies they can achieve. In order to make better use of the Sun’s energy, higher efficiency cycles should be used. Recent developments in the field of high temperature solar receivers [13] have made it possible to imagine the use of solar thermal energy to drive gas turbine units, potentially allowing the use of combined cycle setups in solar thermal power plants. In order to evaluate the potential improvement in efficiency that can be achieved by using combined cycles in solar thermal power plants, a detailed simulation of such a setup will be performed. By taking into account the requirements of thermal energy storage and the design of the necessary heat exchangers, an objective evaluation of the performance of the combined cycle can be obtained. As a key element in the energy conversion process, particular attention will be given to the modelling and simulation of the high temperature receiver. Due to the highly variable nature of the solar flux, the performance of the receiver will be evaluated over a range of operating points. In order to obtain a detailed breakdown of the sources of losses and irreversibilities within the system, a complete exergy balance will be performed on the power plant. Combined with the standard energy balance, this analysis will allow identification of the key areas for improvement in the design of solar thermal power plants. Finally, in order to determine whether such a setup is economically viable, the construction, operation and maintenance costs will be evaluated in order to predict the levelised energy cost associated with electricity production in a combined cycle plant.

2008

The possibility of combining both the advantages of a solar tower thermal power plant and of a solar parabolic trough power plant could be interesting from an energetic point of view as well from an economic point of view. The preliminary study of this combination feasibility is the goal of this project. The study of the project viability consist first of all on the modeling of the trough system, the energy balance of the parabolic troughs will be established at first. Secondly, and choosing a perfect solar day simulating a day when the solar radiation is rather stable, with no cloudy periods along the day, the power available from the trough plant can be calculated. Once we have estimated the power that we can introduce into the cycle of the tower plant, the main issue consists on how and where it is better to use this energy in the cycle. Several possibilities seem to be interesting a priori, however a more detailed study of each one is to be done in order to get to the most economic and efficient layout. The work related to the tower thermal power plant will be done taking as starting point the master thesis of James Spelling, who did an incredible work in this field and whose work will be a valuable help to continue the research on the proposed concept in this project of combining two plants, tower and trough. The main advantage of the tower design compared to the parabolic trough design is the higher temperature. As it will be explained further, thermal energy at higher temperature can be converted more efficiently, the exergy efficiency is better. In terms of storage, the high temperature results in a cheaper and a more efficient storage system. Nevertheless, the set up of the field of heliostats is more complex than the set up of the parabolic trough lines even though the area for a trough plant must be previously flattened. The lower temperature level that entails an inconvenient itself for a parabolic trough power plant may become an advantage when combining both types of concentrating solar power plants. If the results are positive enough that it seems interesting to combine both types of power plants, another step forward will be done towards the use of the sun energy as a renewable source thus making it a more interesting choice for power generation. Sun potential has already shown as an important technology not only at the present time but also in the future. Commercial solar plants have already achieved levelized energy costs around 12-15 UScts/kWh, and the potential for cost reduction is expected to follow this trend even further, to costs as low as 5 UScts/kWh. In addition the taxes imposed for the non-green power should make even more interesting the use of concentrating solar power plants. The requirements of high beam normal radiation lead to a limited amount of suitable places where the implantation of this technology is possible. However many places exist on Earth where the conditions are perfectly adapted, we talk about regions such as United States (the country with more carbon dioxide emissions in the world), some regions in Mexico, North Africa, India, Australia, northeastern Brazil and some locations around the Mediterranean, especially in the south of Spain. The challenge is therefore set for a change in our energy production scheme.

2010

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