Table of Contents
Regular Original Research Article
| Humid Air Turbine as a Primary Link PRIVATE of a Conventional Gas Turbine Set | |
| Jan T. Szargut | 49-55 | The effectiveness of the primary link of a conventional gas turbine set has been expressed by means of the incremental energy efficiency, defined as the ratio of the attained increase of power to the increase of chemical energy consumption. The calculations performed for the humid air turbine (HAT) applied as a primary link indicate a high effectiveness of the utilization of the additionally consumed fuel. The compression ratio in both parts of the considered gas turbine set has been optimized in order to attain maximum energy efficiency. |
| Second Law Analysis of the Earth System with a Radiative Model | |
| Sean Wright | 57-65 | Solar radiation provides the energy for many processes on Earth including processes that sustain living systems and circulation of the atmosphere and oceans. The Earth does not consume this energy; it is simply converted to outgoing thermal radiation. However, the entropy production rate of Earth causes energy degradation and the exergy destruction rate quantifies this degradation relative to a reference environment. The global entropy production rate also provides an additional constraint for comparison with atmospheric modeling results. In this paper a simplified expression for the global entropy production rate, associated with the absorbed portion of the solar flux, is presented based on a radiative model. The second purpose of this work is to investigate the exergetic analysis of the Earth. It is desirable to consider environment temperatures that are typical temperatures on Earth when comparing the total entropy production rate and irreversibility rate of the planet to those due to processes such as the global energy system; in other words, typical temperatures where these processes occur. However, multiplying the estimated global entropy production rate by an arbitrary environment temperature appears to result in irreversibility rates that violate the second law of thermodynamics. It is shown that the radiative interaction of the Earth with its surroundings can be theoretically modeled and tested in a laboratory environment showing that arbitrary environment temperature specifications should not cause these violations. These apparent violations are resolved through corrections to the energy, entropy and exergy calculations that are due to the specific character of radiative heat transfer. As a result, this analysis also provides an illustrative example of the implications of environment specifications on exergy analysis involving radiative heat transfer. |
| Exergy Efficiency Calculation of Energy Intensive Systems by Graphs | |
| V. Nikulshin, Chih Wu, V. Nikulshina | 67-74 | In the design and operation of energy intensive systems the problem of improving its efficiency is very important. The main way to solve this problem is thermodynamic analysis. This paper describes the general approach for calculating the exergy efficiency of complex energy intensive systems with arbitrary structure. A novel general equation of systems exergy efficiency is provided. An example of the method applied to a nuclear power plant analysis is given. |
| Zooming Procedure for the Thermoeconomic Diagnosis of Highly Complex Energy Systems | |
| Vittorio Verda, Luis M. Serra, Antonio Valero | 75-83 | Diagnosis techniques are usually adopted in energy systems to prevent anomalies that can cause, if not repaired, failures (Zaleta 1997). The aim of thermoeconomic diagnosis is different in that it is oriented to plant energy savings while the plant is in operation. In particular, it focuses on discovering reductions in system efficiency (detection of anomalies), locating where these inefficiencies have occurred, and understanding their causes. The solution of this problem is not banal, due to ‘collateral effects’. In fact, when the efficiency of a component decreases because of an anomaly, the efficiencies of the other components generally vary. Moreover, if some settings are not complied with, the control system intervenes and commands an adjustment, which changes the effects of the anomaly on the components. This paper proposes an approach particularly helpful for the diagnosis of complex energy systems. With this approach, the system is first divided into macro-components. A zooming strategy allows one to focus attention on a small part of the system. Then a detailed analysis of a few macro-components (the really malfunctioning ones) is conducted. Such an analysis is based on the principle of eliminating the contributions of the main collateral effects, i.e. the efficiencies of the components dependent on their operating conditions and control system interventions. In this paper, the procedure is presented and applied to a combined cycle, composed of two gas turbines, two HRSGs and a steam turbine. |
| A First Step Towards Unmanned Intelligent Process Management: A Procedure for the Diagnostics and Prognostics of Energy Conversion Plants | |
| T. Biagetti, Enrico Sciubba | 85-99 | This paper describes the conceptual development and the prototype implementation of an Expert System that deals with the prognosis and diagnosis of a significant subset of the operative faults of a cogeneration power plant. The expert system receives both raw and organised real-time information on the “instantaneous” (actually, averaged over 60-seconds intervals) plant operating conditions from a non-intelligent “plant interface” consisting of a standard plant data acquisition system and of a specific plant simulation software. This solution was adopted in view of possible future applications to industrial plants, where a low number of intrusive sensors is desirable: in this case, the simulator provides the missing data. The Inference Engine operates on the basis of a set of pre-defined rules that seek possible “faults chains” expressed as combinations of a pre-assigned number of continuously calculated performance indicators, like the air filter output pressure drop, the relative compressor, combustion and turbine efficiency decay with respect to their respective nameplate values, the compressor enthalpy gain and surge conditions, the pollutants concentration in flue gases, the relative pressure losses in both the primary and secondary water circuit, the TTD of the Heat Recovery Boiler, etc.: the complete list includes 29 indices. The rules establish whether a component’s behaviour is degraded by examining both the individual indicators and all of their relevant combinations. A graphic window displays a series of icons, one for each indicator, with a refresh rate of one real-time minute. The Expert System enables the user to determine in detail the instantaneous performance conditions. If performance deterioration is detected, it sends a message to the operator and provides some decision support via a customised graphic interface. The structure of the code is Object Oriented, and each component as well as each flux are represented as the instance of a class. Both the reasoning and the controlling actions are taken in the same O-O environment. The present paper presents the organization of an ES whose prototype version has been nicknamed PROMISE, from the Italian acronym for PROgnostic and Intelligent Monitoring Expert System, defines its goals and discusses both the results of the tests conducted so far and the implications for future applied research in this field. |
ISSN: 2146-1511