Multi-Criteria Optimization of an Advanced Combined Cycle Power Plant including CO2 Separation Options

This paper illustrates a methodology developed in order to facilitate the analysis of complex systems characterized by a large number of technical, economical and environmental parameters. Thermo-economic modeling of a natural gas combined cycle including monoethanolamine absorption CO2 separation option has been integrated within a multi-objective optimizer based on a genetic algorithm in order to characterize the economic and environmental potential of such complex systems within various contexts. A natural gas combined cycle project in a district of Germany is given as a case study. The results show the influences of the configuration and technical parameter changes on the evolution of electrical efficiency of the combined cycle plant as well as on those of its sub-systems, such as gas turbine cycle and steam cycle. The optimum integrations of such a complex system under different situations are revealed by the Pareto Optimal Frontier obtained through the multi-objective optimization process, which provides information on the relationship between power generation cost and CO2 emission performances. Such information is of direct relevance for policy makers to define coherent emission tax levels, or for utility owners or project investors to choose the appropriate emission levels to be reached by the new plant, or for power generation technology suppliers to identify the market potential of their products as well as the most appropriate design for a given power unit, under given policies and economic contexts.

Multi-objective optimization of an advanced combined cycle power plant including CO2 separation options

Meinrad Bürer, Daniel Favrat, Hongtao Li, François Maréchal

This paper illustrates a methodology developed to facilitate the analysis of complex systems characterized by a large number of technical, economical and environmental parameters. Thermo-economic modeling of a natural gas combined cycle including CO2 separation options has been coupled within a multi-objective evolutionary algorithm to characterize the economic and environmental performances of such complex systems within various contexts. The method has been applied to a case of power generation in Germany. The optimum options for system integration under different boundary conditions are revealed by the Pareto Optimal Frontiers. Results show the influence of the configuration and technical parameters on the electrical efficiencies of the Pareto optimal plants and their sub-systems. The results provide information on the relationship between power generation cost and CO2 emissions, and allow sensitivity analyses of important economical parameters like natural gas and electricity prices. Such a tool is of interest for power generation technology suppliers, for utility owners or for project investors, and for policy makers in the context of CO2 mitigation schemes including emission trading.

Elsevier2006

Environomic modeling and multi-objective optimisation of integrated energy systems for power and cogeneration

Hongtao Li

Current and future dynamics, of environmental legislations and trading market, of the fuel and electricity prices due to the market liberalization or resource shortages, and of the innovations of power/cogeneration technologies, impose great challenges on optimal design and operation evaluation of integrated energy systems. Developing new design tools for power and cogeneration technologies is therefore a key concern guiding the work presented in this thesis, which becomes the central problem that has been studied in this work. Based on 'Environomic Modeling', a decisive criteria decomposition and multi-objective optimization approach has been further developed based upon the previous work in the Laboratory for Industrial Energy Systems of the Swiss Federal Institute Technology of Lausanne. It has been implemented to evaluate the optimal design of integrated energy systems for power and/or cogeneration in the CO2 abatement context, or for solving the power load dispatching problems. By taking the specific investment cost versus the CO2 emission rate as the two objectives, the developed approach has been implemented to 'Typify' the environomic performance of natural gas combined cycle plants with market available gas turbines for both power and/or cogeneration applications, in the context of CO2 abatement. The dynamic exogenous parameters that impose difficulties in project-based evaluation, such as the fuel price, annual operating hours and interest rate, have been successfully treated through simple post optimization analysis from the derived 'Typification Map'. The developed methodology has also been used to study the potential of Clean Development Mechanism (CDM) defined in the Kyoto Protocol for the analyzed natural gas combined cycle (NGCC) projects in China, for both power alone and cogeneration applications. It is shown that in the latter case, a break-even Certified Emission Reduction (CER) price of 14.5 US

/tonCO2 to 16.5 US

/tonCO2 will be required to make NGCC plants able to compete with coal plants. When a NGCC plant is used for cogeneration, it is also shown that a reduced break-even CER price can be expected due to the profits from heat selling. Simultaneous optimization of CO2 emission rate or the annual total CO2 emissions, against the economic criteria of the project, e.g. cost of electricity or heating specific cost with sensitivity analyses for dealing with the dynamics of fuel and electricity prices have been applied to two project-based case studies. Those have even more complex superstructures including options of electricity importation or exportation. For the case of advanced natural gas combined cycle (NGCC) plants with a possible CO2 capture option, the obtained results provide information on the relationship between power generation cost and CO2 emission performance. This approach is intended for power/cogeneration technology suppliers, for utility owners or project investors, and for policy makers in the context of CO2 mitigation schemes including emission trading. One of the interesting results shows that a break-even value as high as 69 US

/ton has been identified for the CO2 tax or price of CO2 allowance that can bring a 400MW NGCC plant with CO2 capture into practice, due to the relatively high investment cost of CO2 capturing. For the case of an integrated heating plant, it is shown that the heating fuel specific consumption can be dramatically reduced down to 19.8 - 21.4 [kg coal.equ./GJ] with a significant reduction of associated emissions at a heating specific total cost of respectively 3.1 and 6.6 [US

/GJ]. These range performances are achieved whether power exportation is allowed or not, by implementing heat pump and/or cogeneration technologies. The 'Environomic modeling and multi-objective optimization' methodology has also been implemented for load dispatching for a given power generation system composed with power generation units associated with different fuel consumption, emission and cost performances. The obtained daily CO2 emissions versus daily power generation costs Pareto Optimal Frontiers (POFs) give the operator an increased flexibility and structured knowledge to take the decisions on the best power dispatching solution under different environmental regulation circumstances.

EPFL2006

Multicriteria Optimisation of Small Hybrid Solar Power System.

Daniel Favrat, El Hadj Malick Kane

A new concept of small hybrid solar power system (HSPS) has been successfully demonstrated in the context of a project called SPS (Solar Power System). This plant integrates two rows of solar collectors, two superposed Organic Rankine Cycles (ORC) each equipped with a scroll hermetic expander-generator and a heat engine. In operation with solar energy only, the heat is supplied by a thermal fluid (presently pressurized water) heated in the vacuum insulated focal tubes of sun following, flat concentrators made of series of thin plate mirrors (CEP). In hybrid mode additional heat is supplied by heat recovery from the exhaust gases of the engine in series with the solar network and by a separate network recovering heat from the cooling of the engine block at an intermediate temperature level. This paper presents the results of a multi-criteria optimization of a 22 kWe HSPS, including aspects such as energy performance, economic and financial analysis, and environemental aspects. The so called mini-maxi methodological approach with genetic algorithm is used considering three principal criteria such as the energy efficiency of the superposed ORCs, the minimal cost of the installation and the minimum emission of CO2 . Taking into account of the solar radiation time dependence, the elecricity supply variation and the change of configuration (night and day operation), the performance analysis is based essentially on the yearly energy simulation in which the off-design physical models of components are considered. A comparison of HSPS with pure fossil fuelled Plants (DEPU-Diesel Engine Power Unit) is reported for the same electrical power load curve, with an economic sensitivity analysis. Results show that the solar electricity costs are still high and depend considerably on the size of the Solar Field (the HSPS Levelized Electricity Cost with 5 to 16% of annual solar share is about 17% to 49% higher than a similar size Diesel Engine Power Unit). However, a reduction of CO2, emission up to 26% could be obtained when replacing the Diesel Engine Unit by a similar HSPS. Those hybrid solar thermal power systems may already be competitive if a tax of about 42 Swiss cts/kgCO2 would be considered.

2002