Lorena Giordano

A Genetic Algorithm for Optimizing Heat Recovery Steam Generators of Combined Cycle Power Plants

Improving performance of combined cycle power plants has been the target of numerous investigations. Most of the researchers have focused their attention on the heat recovery steam generator (HRSG), the connecting equipment between the gas turbine group and the steam section. On the other hand, almost all equipment in a combined cycle is a fairly standard design available from a manufacturer, while the HRSG is one of the few components that may be somewhat customized. In fact, the HRSG provides many different design options with respect to the layout of heat transfer sections and their operating parameters. The aim of this work is the development of a model for optimizing the main operating parameters of the heat recovery steam generator of a CCGT. The thermodynamic behaviour of the power plant has been simulated through the commercial software GateCycle, whereas the optimization has been carried out using a genetic algorithm. The objective function to be minimized is the cost of electricity, evaluated through a cash flow analysis in constant or in current dollars. Two CCGT power plant configurations, with one or three-pressure reheat HRSG, are simulated and optimized, evaluating the influence of fuel price variation on the optimal operating parameters of HRSG.Copyright

Feedwater Repowering of Coal Fired Power Plants: Effects of Steam Turbine Overloads on Energy and Economic Performance of the Integrated Power System

In recent years, the environmental concerns and the need to improve the competitiveness of existing coal-fired power plants have renewed the interest for the repowering option. Repowering techniques based on combustion turbines allow to increase thermodynamic performances of the steam power plant, as well as to reduce emissions of greenhouse gases, due to efficiency improvement and partial fuel-shift from coal to natural gas.This paper aims to evaluate performances of feedwater repowering of a coal fired power plant, considering various steam turbine overloads. Two types of analysis are here proposed. First, thermodynamic and environmental benefits of feedwater repowering are evaluated in terms of efficiency gain and CO2 emission reduction, with reference to the steam power plant only. Then, effects of the integration of a gas turbine into the existing coal fired power plant are highlighted. Different feedwater repowering options, varying the operating mode of the coal fired power plant, are compared from the energy, economic and environmental point of view. The attention is focused on performance parameters of the integrated steam-gas power plant, as well as on marginal indices defining the efficiency and unit cost of electricity of the additional power production.Copyright

Thermoeconomic Optimization of Heat Recovery Steam Generators: A Modular Approach to Define the Layout of Heat Exchange Sections

One of the most efficient energy conversion systems in state-of-the-art electricity generation technology are combined cycle gas turbines. As is well known, the heat recovery steam generator (HRSG) configuration has a major impact on the overall performance of a combined-cycle power plant. Thus providing a tool for optimizing design parameters and layout of a HRSG is an important issue.The present study focuses on HRSG optimization, employing an exergoeconomic methodology. This is based on the minimization of the total cost of HRSG, including capital costs of heat exchanger sections and operating costs related to exergy destruction. The decision variables of the proposed optimization method are the HRSG operating parameters, as well as the layout of the heat exchanger sections.To predict behavior and performance, the HRSG is regarded as a modular structure, i.e. as a set of elementary components, interacting through nodes affected by mass and energy flows. The modular approach proposed makes the optimization methodology particularly flexible, as the configuration of the HRSG can be identified defining an “interaction matrix” to characterize the mode of interaction of the elementary components.Copyright

Data supporting the validation of a simulation model for multi-component gas separation in polymeric membranes

The article describes data concerning the separation performances of polymeric hollow-fiber membranes. The data were obtained using a model for simulating gas separation, described in the research article entitled “Interplay of inlet temperature and humidity on energy penalty for CO2 post-combustion capture: rigorous analysis and simulation of a single stage gas permeation process” (L. Giordano, D. Roizard, R. Bounaceur, E. Favre, 2016) [1]. The data were used to validate the model by comparison with literature results. Considering a membrane system based on feed compression only, data from the model proposed and that from literature were compared with respect to the molar composition of permeate stream, the membrane area and specific energy requirement, varying the feed pressure and the CO2 separation degree.

CO2 post-combustion capture in coal-fired power plants integrated with solar systems

The majority of the Worlds primary energy consumption is still based on fossil fuels, representing the largest source of global CO2 emissions. According to the Intergovernmental Panel on Climate Change (IPCC), such emissions must be significantly reduced in order to avoid the dramatic consequences of global warming. A potential way to achieve this ambitious goal is represented by the implementation of CCS (Carbon Capture and Storage) technologies.However, the significant amount of energy required by the CCS systems still represents one the major barriers for their deployment. Focusing on post-combustion capture based on amine absorption, several interesting options have been investigated to compensate the energy losses due to solvent regeneration, also using renewable energy sources. One of the most promising is based on the use of concentrating solar power (CSP), providing a part of the energy requirement of the capture island.In this study the integration of a CSP system into a coal-fired power plant with CO2 postcombustion capture is investigated. Basically, a CSP system is used to support the heat requirement for amine regeneration, by producing saturated steam at low temperature. This allows to reduce or even eliminate the conventional steam extraction from the main power plant, affecting positively net power production and efficiency. The energy analysis of the whole system is carried out using the GateCycle software to simulate the coal-fired power plant and ChemCad platform for the CO2 capture process based on amine absorption.

Methane Steam Reforming and Metallic Membranes to Capture Carbon Dioxide in Gas Turbine Power Plants

Pre-combustion CO2 capture is regarded as a promising option to manage greenhouse gas emissions from power generation sector. In this regard, metallic membranes can provide a significant boost in power plants energy performances, due to their infinite hydrogen perm-selectivity and their ability to operate at high pressure and temperature. However, the properly integration of these devices still requires a deep investigation of power plant behavior, in order to detect the mutual interaction between system components, which may impose constraints on their operating conditions.This paper aims to investigate a chemically recuperated gas turbine (CRGT) with pre-combustion CO2 recovery based on hydrogen separation through a metallic membrane. At first, the steam reforming and membrane separation processes are investigated, in order to assess their sensitivity to the variation of the main operating parameters. Then, the CRGT power plant with CO2 capture is analyzed, highlighting the effect of system components interaction on energy and environmental performances. In addition, the study accomplishes a preliminary investigation of the system capability to produce an excess of hydrogen to be used as an energy carrier.Copyright

Hydrogen Production From Methane Steam Reforming With CO2 Capture Through Metallic Membranes

As an energy carrier, hydrogen has the potential to boost the transition toward a cleaner and sustainable energy infrastructure. In this context, steam methane reforming coupled with carbon capture through membrane separation is emerging as a potential route for hydrogen generation with a reduced carbon footprint. A potential way to improve the efficiency and reduce costs of the entire process is to integrate the hydrogen production system with a gas turbine power plant, using a fraction of waste heat exhausted to provide the heat and the steam required by the endothermic reforming reaction.The paper assesses the techno-economic performances of a small-scale hydrogen and electricity co-production system, integrating a syngas production section, a gas turbine and a membrane separation unit.The simulation study investigates two main configurations, depending on whether the gas turbine is fed by hydrogen or natural gas. For each configuration, energy and economic performance indices are evaluated varying the main plant operating parameters, i.e. the steam reforming temperature, the permeate sweep dilution, the membrane pressure ratio and the technology of gas turbine.Copyright

Enhancing Energy and Economic Performances of Combined Cycle Power Plants by Means of Gas-Cycle Regeneration

Efficiency improvement in the gas turbine sector has been mainly driven by increasing the turbine inlet temperature and compressor pressure ratio. For a fixed technology level, a further efficiency gain can be achieved through the utilization of waste thermal energy.Regeneration is an internal recovery technique that allows the reduction of heat input required at combustor, by preheating the air at compressor outlet. Under certain operating conditions, the temperature of exhaust gas leaving the regenerator is still enough high to allow the steam production via an heat recovery steam generator (HRSG).Regeneration in steam-gas power plants (CCGT) has the potential to enhance thermal efficiency, but reduces the margins for external recovery and then the bottoming steam cycle capacity. Moreover, the reduction of exhausts temperature at gas turbine outlet requires the reconsideration of HRSG operating parameters, in order to limit the increase of waste heat at the stack.The aim of this study is to explore the potential benefits that regeneration in the gas cycle gives on the whole steam-gas power plant. The extent of energy and economic performances improvement is evaluated, varying the gas turbine specifications and the layout and operating conditions of HRSG. Hence simple and regenerative configurations based on single and multi-pressure HRSG are compared, focusing on efficiency, specific CO2 emissions and unit cost of electricity (COE).© 2014 ASME

The Recovery of Exhaust Heat from Gas Turbines

Exhaust heat from gas turbines can be recovered externally or internally to the cycle itself [14]. Of the various technology options for external heat recovery, the combined gas–steam power plant is by far the most effective and commonly used worldwide. For internal heat recovery, conventional designs are based on thermodynamic regeneration and steam injection, while innovative solutions rely on humid air regeneration and steam reforming of fuel.