Roberto Carapellucci

Membrane systems for CO2 capture and their integration with gas turbine plants

Abstract The capture and sequestration of the CO2 emitted from fossil-fuelled power plants is gaining widespread interest for controlling anthropogenic emissions of greenhouse gases. Among technology options for CO2 capture, membrane-based gas separation systems are noteworthy owing to their low energy requirements, promising technology evolution and effective integration with power plants. This paper presents a mathematical model for membrane-based separation systems that is able to cover the most significant membrane types and configurations. This model has been integrated in a general simulation method for analysing and optimizing advanced energy conversion systems. Performance of these simulation tools is demonstrated by evaluating the influence of different operating conditions on the behaviour of pre-and post-combustion separation units, based on metallic or polymeric membranes. Finally, the feasibility of integrating a metallic membrane system into a chemically recuperated gas turbine (CRGT) power plant is explored, obtaining encouraging results for CO2 capture.

Power generation using dedicated woody crops: thermodynamics and economics of integrated plants

Biomass will continue to play a significant and probably increasing role in the worlds future energy mix, due to the strategic role it has for large availability, environmental concerns and technological advances. The raw biomass has a relatively high moisture content, requiring thermal drying processes in order to minimise stack losses.

Thermodynamic and Environmental Assessment of Integrated Gasification and Methanol Synthesis (IGMS) Energy Systems with CO2 removal

Environmental and technical concerns arise from the extensive utilization of the huge world coal reserves. They can nowadays be overcome only resorting to advanced energy conversion technologies. Integrated coal gasification and methanol synthesis power plants can perform a load-following service, by producing and storing liquid methanol, and reduce the carbon dioxide emissions, by removing CO2 and disposing it outside the atmosphere. In this paper, a comparative performance analysis among the different IGMS power plants has been carried out, by evaluating the influence of the coal gasification and methanol synthesis technologies on the main performance characteristics, such as the methanol production, the specific CO2 emissions and the overall efficiency.

Carbon dioxide removal via a membrane system in a natural gas combined-cycle plant

Abstract Gas separation using polymeric membranes is generally believed to be poorly suited for CO2 capture from gas turbine based power plants, because the high air-to-fuel ratios produce large amounts of exhaust gas containing strongly diluted CO2. The driving force for selective permeation is obtained by compressing the entire exhaust stream, resulting in a significant energy penalty. Additional energy is required for permeate compression, which is impaired by the other gases emitted with CO2. In spite of these difficulties, the present study is concerned with membrane systems, which the authors believe warrant further investigation. The attention was focused on natural gas combined cycles (NGCC), so as to have a starting point with high energy efficiency and low baseline emissions. To reduce the exhaust gases and to concentrate the CO2, the NGCC is fitted with a flue gas recirculation system, which has proven to leave plant performance substantially unaffected. The energy requirements for exhaust gas compression are reduced by introducing a heat exchanger between the compressed and residual exhaust gas and recovering heat from the latter. The membrane separator has been modeled using conservative data reported in the literature. Various configurations, such as multiple compression-expansion and multistage membrane units, are considered. Permeate compression is also modeled, so as to highlight the influence of permeate purity on this process. The results show a rather moderate performance penalty. A specific emission of 100 g CO2/kWh corresponds to 48 percent efficiency. Admittedly a CO2 separator for a power plant would be larger than any other membrane system designed for other purposes. However, the system appears technically feasible and would offer valuable benefits in terms of emissions.

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

Performance and emissions of CRGT power generation systems with reformed methanol

The performance of two different technological classes of chemically recuperated gas turbines (CRGT), with methanol used as primary fuel, has been evaluated. The analysis of the influence of the main CRGT parameters on the thermal matching between the flue gas and the reforming fuel in the reformer has been carried out. Emissions in lean premixed and nonpremixed combustors have been computed for various reformed methanol fuels of different compositions. This study shows that the CRGT could achieve thermodynamic performance superior to systems with conventional internal recovery and comparable with that of the more complex gas steam combined power plants. Furthermore, the levels of NO/sub x/ and N/sub 2/O, produced by the reformed fuels combustion, have been found to be considerably lower than for methane, while the CO emitted is roughly the same as in the case of conventional fuel.

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