Alessandro Franco

Combined cycle plant efficiency increase based on the optimization of the heat recovery steam generator operating parameters

Abstract At the present time combined cycle (CC) power plants allow to meet the growing energy demand with the least fuel consumption. Thus it is of great interest to define a strategy for the optimization of these systems, in order to get greater performances and efficiency from them. The purpose of the most part of the world manufactures involved in this sector is to reach overall thermal efficiency of 60% in the short term period, above all by improving the gas turbine inlet temperature. In the present work, it is shown how it could be possible to reach the same performances by best fitting the existing technology. In particular we point our attention to the optimization of the heat recovery steam generator (HRSG), as a first step in the analysis of the whole plant, according to a hierarchical strategy. We handle this problem adopting both a thermodynamic and a thermoeconomic objective function instead that with the usual pinch point method. Thermodynamic optimization has the purpose to diminish energy losses, expressed on exergy basis, while the aim of the thermoeconomic optimization is the minimization of a cost function, sum of the cost of exergy inefficiencies and the cost of the HRSG. Proposed methods have been applied to some HRSG configurations, including some present commercial plants. The results of the application of the thermoeconomic optimization leads to a meaningful increase of the thermal efficiency of the plant that approaches the 60%, obtained with and increases of the heat surface and a decrease of the pinch-points. The economic evaluations are referred to US dollars (

Thermoeconomic optimization of heat recovery steam generators operating parameters for combined plants

) even if the costs are referred to European scenario, assuming 1 US

On some perspectives for increasing the efficiency of combined cycle power plants

= 1.1 euro.

On the Optimum Thermal Design of Individual Longitudinal Fins with Rectangular Profile

The optimization of the heat recovery steam generator (HRSG) is particularly interesting for the combined plants design in order to maximise the work obtained in the vapour cycle. A detailed optimization of the HRSG is a very difficult problem, depending on several variables. The first step is represented by the optimization of the operating parameters. These are the number of pressure levels, the pressures, the mass flow ratio, and the inlet temperatures to the HRSG sections. The operating parameters can be determined by means both of a thermodynamic and of a thermoeconomic analysis, minimising a suitable objective function by analytical or numerical mathematical methods. In the paper, thermodynamic optimization is based on the minimization of exergy losses, while the thermoeconomic optimization is based on the minimization of the total HRSG cost, after the reduction to a common monetary base of the costs of exergy losses and of installation.

Thermodynamic and heat transfer analysis of LNG energy recovery for power production

Abstract The paper proposes an analysis of some possibilities to increase the combined cycle plant efficiency to values higher than the 60% without resorting to a new gas turbine technology. Optimization of heat recovery steam generator (HRSG) with the use of parallel sections and of limit subcritical conditions (up to 220 bar) is the key elements to obtain this result. The HRSG optimization is sufficient to obtain combined cycle plant efficiencies of the order of 60% while, joining HRSG optimization with the use of gas turbine reheat (postcombustion) and gas to gas recuperation can lead the efficiency of the whole plant to the limit value of 65%. Results are proposed with reference to a turbine inlet temperature of 1500 K, corresponding to those of usual commercial D–F series gas turbine.

Analysis of thermodynamic losses in ground source heat pumps and their influence on overall system performance

The optimum design of single longitudinal fins with constant thickness, considering different uniform heat transfer coefficients on the fin faces and on the tip, has been approached by means of an accurate mathematical method yielding the solution of constrained minimization (maximization) problems. Starting from the classical one-dimensional (1-D) model of the fin, the optimum design problem is reduced to a constrained optimization one by considering the limitations of the fin thermal convenience criterion, of the 1-D accuracy criterion, or of the geometric constraint on the primary surface of the fin array. The analysis, developed in dimensionless form, shows that the existence and the uniqueness of the solution are not ensured in any case, and the condition of the solution existence is often a consequence of the imposed constraints. A comparison between the results obtained and those achieved by applying to the fin optimization the half-thickness rule (HTR), based on the Harper and Brown approximation, has been carried out for some meaningful cases. Even if the HTR is usually satisfactory to design optimum fins, its uncritical use is very questionable.

The smart gas grid: state of the art and perspectives

An important option to transport the gas is to convert it into liquid natural gas (LNG) and convey it using insulated LNG tankers. At receiving terminals, the LNG is offloaded into storage tanks and then pumped at the required pressure and vaporized for final transmission to the pipeline. The LNG production process consumes a considerable amount of energy, while the cold availability, as also known as cold energy, has been stored in LNG. At a receiving terminal, LNG needs to be evaporated into gas at environmental temperature before fed into the gas distribution system. Seawater is commonly used for the regasification process of the LNG. In the present paper, after a general analysis of the perspectives of the various thermodynamic schemes proposed for power production from the regasification, a detailed analysis of enhanced direct expansion system is carried out in order to identify the upper level of the energy that can be recovered. The analysis outlines that power production typical of optimized ORC plant configurations (120 kJ/kg) can be obtained with direct expansion solutions.

Day-Ahead Hourly Forecasting of Power Generation From Photovoltaic Plants

The present work aims at identifying the relative influence of GSHP subsystems (viz. ground source, earth heat exchangers, heat pump unit, pumping devices) on the overall efficiency and the limits to which technological improvements should be pushed (because, beyond these limits, only minor benefits may be achieved). To this end, an analysis of thermodynamic losses is conducted for a case study, followed by a sensitivity analysis on the heat pump unit thermal performance. Primary energy consumptions of nine configurations with different combinations of ideal and real subsystems are compared. The completely ideal system is used as the reference to normalize energy consumptions and obtain a dimensionless efficiency parameter. The results show that – when a proper design methodology is employed – the performance of the borehole heat exchangers slightly affects the overall efficiency. On the contrary, the thermal response of the ground and the thermal and hydraulic performances of the heat pump unit are key factors. Finally, a sensitivity analysis is conducted by increasing the heating and cooling efficiencies of the heat pump device.

Theoretical analysis of screened heat pipes for medium and high temperature solar applications

The main objective of this paper is to illustrate the current state of the art of the newborn smart gas grid concept. We provide a detailed discussion of the envisaged features of the smart gas grid, giving attention to both the related academic literature and to the ongoing world-wide projects. In doing so, we also discuss the potentialities of rethinking the smart grid paradigm from the perspective of a whole energy system, that both encompasses the electrical and the gas grid, and identify some critical key aspects that must be handled while developing the new smart energy paradigm.

Concept for Modeling and Optimization of the Mixture Formation using Gasoline Direct Injection in Compact High Speed Engines

The ability to accurately forecast power generation from renewable sources is nowadays recognized as a fundamental skill to improve the operation of power systems. Despite the general interest of the power community in this topic, it is not always simple to compare different forecasting methodologies, and infer the impact of single components in providing accurate predictions. In this paper, we extensively compare simple forecasting methodologies with more sophisticated ones over 32 photovoltaic (PV) plants of different sizes and technology over a whole year. Also, we try to evaluate the impact of weather conditions and weather forecasts on the prediction of PV power generation.