Thermoeconomic Diagnosis Research Articles

β-characterization by irreversibility analysis: A thermoeconomic diagnosis method

This paper presents a reconciliation methodology for the diagnosis of energy systems. The methodology is based on the characterization of irreversibilities in the components of an energy system. These irreversibilities can be attributed to malfunctions or dysfunctions. The characterization of irreversibilities as presented here makes possible to reconcile the Actual Operating Condition (AOC) versus the Reference Operating Condition (ROC) of the energy system in a real-time manner. The diagnosis methodology introduces a parameter β, which represents the total exergy or useful work of a component in terms of its inlet and output streams at either design (full-load) or off-design (partial-load) conditions. The methodology is applied to the diagnosis of an actual Natural Gas Combined Cycle (NGCC) power plant. Data for the model is obtained directly from the plant by monitoring its performance at every time; thus, a real-time thermodynamic diagnosis for the system is obtained. Results show that the methodology presented here is able to detect and quantify the deviations on the performance of the NGCC power plant during its real-time operation. Based on the detection and quantification of these deviations, the user is able to make recommendations to schedule maintenance on the components where the irreversibilities are present.

Assessing the Robustness of Thermoeconomic Diagnosis of Fouled Evaporators: Sensitivity Analysis of the Exergetic Performance of Direct Expansion Coils

Thermoeconomic diagnosis of refrigeration systems is a pioneering approach to the diagnosis of malfunctions, which has been recently proven to achieve good performances for the detection of specific faults. Being an exergy-based diagnostic technique, its performance is influenced by the trends of exergy functions in the “design” and “abnormal” conditions. In this paper the sensitivity of performance of thermoeconomic diagnosis in detecting a fouled direct expansion coil and quantifying the additional consumption it induces is investigated; this fault is critical due to the simultaneous air cooling and dehumidification occurring in the coil, that induce variations in both the chemical and thermal fractions of air exergy. The examined parameters are the temperature and humidity of inlet air, the humidity of reference state and the sensible/latent heat ratio (varied by considering different coil depths). The exergy analysis reveals that due to the more intense dehumidification occurring in presence of fouling, the exergy efficiency of the evaporator coil eventually increases. Once the diagnostic technique is based only on the thermal fraction of air exergy, the results suggest that the performance of the technique increases when inlet air has a lower absolute humidity, as evident from the “optimal performance” regions identified on a psychrometric chart.

Thermoeconomic Philosophy Applied to the Operating Analysis and Diagnosis of Energy Utility Systems

In this paper, the objectives of thermoeconomic diagnosis are presented. The paper is part of a project, started in 2001 and named TADEUS (Thermoeconomic Approach to the Diagnosis of Energy Utility Systems), aimed at integrating various experiences accumulated by a group of researchers working on thermoeconomic diagnostics, a field of research started by Antonio Valero and co-workers in 1990 and followed by various researchers all over the world. It is shown how, starting from the same basic set of ideas, researchers developed different approaches, each one having particular characteristics that are, nonetheless, complementary to each other.

Innovative thermoeconomic diagnosis of multiple faults in air conditioning units: Methodological improvements and increased reliability of results

Thermoeconomic faults diagnosis of air conditioning units is a pioneeristic approach to detect single or multiple faults and quantify their impact in terms of additional energy consumption. The poor reliability of conventional thermoeconomic approaches has been limiting the interest for practical applications of this technique. In this paper an improved thermoeconomic diagnosis is proposed and applied to a reference 120 kWc air-cooled air conditioning system; a simulator is used to evaluate thermodynamic data under normal and faulty conditions. Four faults are individually or simultaneously imposed: fouling at condenser and evaporator, refrigerant undercharge and compressor valve leakage. For setting up the diagnostic tool only a few numerical or experimental tests are required; the results testify the procedure to be sufficiently reliable both when heavy or light faults are considered. Also, the performance of the diagnostic procedure slightly improves when the effects of “system level” faults like refrigerant undercharge are preliminarily filtered.

Critical analysis of conventional thermoeconomic approaches to the diagnosis of multiple faults in air conditioning units: Capabilities, drawbacks and improvement directions. A case study for an air-cooled system with 120 kW capacity

Faults diagnosis in air conditioning systems is a crucial activity, since malfunctions may induce heavy degradation of performance. Among the available techniques, thermoeconomic diagnosis has played a marginal role due to the difficulties encountered when applying the methodology to refrigeration plants. In this paper a critical analysis on capabilities and limits of thermoeconomic diagnosis is proposed. The reference plant is a 120 kWc air-cooled air conditioning system; a simulator is used to evaluate thermodynamic data under normal and faulty conditions, setting up “virtual experiments” to simulate each fault. Five malfunctions are imposed, either individually or simultaneously: fouling at condenser and evaporator, refrigerant undercharge, compressor valve leakage and extra-superheating along suction line. From a qualitative viewpoint, the examined approach resulted efficient in identifying some faults, although false fault signals eventually emerged. Methodological improvements were suggested, to make thermoeconomic diagnosis capable of quantifying the additional energy consumption provoked by any specific fault.

Combining Diagnosis Methods for the Fouling on Flow Path of Steam Turbine

The fouling on flow path of steam turbine would lead to the changes of thermal parameters and significantly deteriorated efficiency. In this paper, a qualitative analysis of fouling on flow path based on measured parameters was described for the preliminary diagnosis, and the zooming thermoeconomic diagnosis model combined with the equivalent flow area diagnosis model was proposed to diagnose the specific location of fault. Then the flow performance of a 630 MW supercritical unit was analyzed, and the possible fouling stages were also discussed according to the thermoeconomic diagnosis and quantitative analysis. The result of diagnosis was consistent with the situation of uncovering cylinder, which indicated that though the actual system was complex, the coupling multiple faults of flow path could be diagnosed by combining the above diagnosis models.

Numerical model for thermoeconomic diagnosis in commercial transcritical/subcritical booster refrigeration systems

Transcritical/subcritical booster refrigeration systems are increasingly installed and used in Danish supermarkets. The systems operate in both transcritical and subcritical conditions dependent on the heat rejection performance and the ambient conditions. The plant consists of one refrigerant cycle supplying refrigerant for evaporators in both chilled and frozen display cases. In the paper, thermoeconomic theory is used to establish the cost of cooling at each individual temperature level based on operating costs.With a high amount of operating systems, faulty operation becomes an economic, and environmental, interest. A general solution for evaluation of these systems is considered, with the objective to reduce cost and power consumption of malfunctioning equipment in operation. An analysis of the use of thermoeconomic diagnosis methods is required, as these methods may prove applicable. To accommodate the analysis, a numerical model of a transcritical booster refrigeration plant is considered in this paper. Additionally the characteristic curves method is applied to the high pressure compressor unit of the refrigeration plant. The approach successfully determine whether an anomaly is intrinsic or induced in the component when no uncertainties are introduced in the steady state model.

Thermoeconomic diagnosis for improving the operation of energy intensive systems: Comparison of methods

The aim of thermoeconomic diagnosis of operating energy intensive systems is the determination of fuel consumption, the identification of the causes of its increment from design conditions and the quantification of the effect of each one of these causes. For this task, besides data acquisition and monitoring systems, a thermoeconomic diagnosis methodology is needed. After a review of methodologies, three of them are compared: quantitative causality analysis, linear regression and neural networks. These methods are based on thermodynamic indicators (more close to daily operation) instead of thermoeconomic parameters (which allow a homogeneous formulation); however, the first one is based on a thermodynamic description of the system, while the others are empirical. The comparison is based on the diagnosis of a 3 × 350 MW coal-fired-power plant for a time span of more than 6 years. Results show that quantitative causality analysis is able to quantify the effects of all variables while the others are only suitable for the most influential ones.

Hybrid Fuel Impact Reconciliation Method: An integral tool for thermoeconomic diagnosis

This paper proposes a method of thermoeconomic diagnosis based on the concepts of the fuel impact formula and the analytical reconciliation method. Such a method is able to detect, isolate and quantify individually the causes in terms of the additional fuel consumption, when internal malfunctions or control deviations occur. Commonly, any diagnosis method requires the definition of a Test State Condition (TEC), a Reference State Condition (REC), and a comparison technique. In the proposed method the technique is based on the reconciliation procedure, however the common factor consists in maintaining the overall production of a steady operating plant. This will determine the term-by-term fuel impact due to each malfunction. The results obtained allow a comparison between the methods mentioned earlier. The keys of the proposed method are the modification of the reference state, the integration of a modified fuel impact formula and the introduction of a filtering technique for the effects induced by the control and regulation system. In order to validate the mathematical model, this is applied to a combined cycle power plant. Comparisons between the proposed model and the results from the other two methods are studied. The diagnosis error was less than 0.2%.

Energy efficiency assessment and improvement in energy intensive systems through thermoeconomic diagnosis of the operation

Advanced monitoring techniques can play a key role in improving energy efficiency of operating energy intensive systems. In particular, thermoeconomic diagnosis aims at the determination of fuel consumption variation, the identification of causes of its increment from design conditions and the quantification of the effect of each one of these causes. A thermoeconomic diagnosis system installed in a coal-fired power plant has been used to analyse its operation during a time span of more than 6 years, quantifying the effects of variations in components (degradation, repairing and substitution), fuel quality, ambient conditions and operation strategy. The diagnosis method proposed (quantitative causality analysis) provides a precision of ±3% in addressing the source of inefficiency for about 70% of the cases.

Analysis for the Thermoeconomic Diagnosis of Energy Systems

Thermoeconomic diagnosis is aimed at the detection of malfunctioning components in energy systems and the quantification of additional fuel consumption caused by each malfunction. A formulation is proposed based on: i) the use of enthalpy, entropy and flow rate for the characterization of flows within a system; ii) the linearization of restrictions; and, iii) the application of standardized indicators for variations in components behavior, set-points and system product. The approach allows one to introduce the concepts of thermoeconomic analysis (irreversibility and cost) to describe the process of fuel impact formation, without losing the capability of describing accurately the physical behavior of the system. A simple example is developed to illustrate the ideas presented. This paper is an updated version of a paper published in the ECOS'08 proceedings.

Application of Quantitative Causality Analysis to the Quantification of Intrinsic and Induced Effects in the Thermoeconomic Diagnosis of a Coal-fired Power Plant

The aim of thermoeconomic diagnosis is to detect malfunctioning components in thermal systems and to quantify the additional fuel consumption caused by each these components. Thermoeconomics provides tools for this task such as malfunctions, malfunction costs and fuel impact formula, whose applicability to real examples may be difficult due to induced effects. On the other hand, the quantitative causality analysis is a diagnosis method based on a thermodynamic description of the system. In this paper, both approaches are integrated by applying the quantitative causality analysis to perform a systematic quantification of intrinsic and induced effects. The formulation is successfully applied to a coal-fired power plant. This paper is an updated version of a paper published in the ECOS'08 proceedings.

Quantitative Causality Analysis for the Diagnosis of Energy Systems

The aim of Thermoeconomic diagnosis is to identify malfunctioning components in energy systems and to quantify the impact on fuel consumption caused by each of them. The quantitative causality analysis is a method based on the linearization of the thermodynamic model of the system. The accuracy of the method is demonstrated by quantifying the error produced in the diagnosis of a large amount of points of a real example. Additionally, a formulation to combine this approach with thermoeconomic analysis has been developed. It allows to precisely quantify intrinsic and induced effects. Finally, the method is compared with two diagnosis approaches based on linear regression and neural networks.

Thermoeconomic analysis of a large industrial propane refrigeration cycle used in NGL recovery plant

In this paper a propane refrigeration cycle has been analyzed by thermoeconomic approach. This cycle is used for obtaining required refrigeration in a natural gas liquids (NGL) recovery plant. Most of the advanced methods in thermoeconomic diagnosis are examined on power plants. In this work thermoeconomic diagnosis is applied to NGL recovery plant. The impact of the component inefficiencies on the fuel plant consumption, and the effect of a component inefficiency (intrinsic malfunction) on the rest of the plant components (induced malfunctions and dysfunctions), are analyzed and quantified. The results show that thermoeconomics is not only a diagnostic tool, but also a useful tool for optimization, which can be applied to complex refrigeration processes in NGL recovery plants. Copyright © 2009 John Wiley & Sons, Ltd.

Control del Rendimiento y Diagnóstico Termoeconómico de Centrales Termoeléctricas

This paper outlines how thermoeconomic diagnosis helps plant personnel to detect possible malfunctions that affect the efficiency of a thermal power plant, to identify the components where these malfunctions have occurred and to calculate their impact on fuel consumption. Two methods of evaluating the contribution of the plant components to overall performance deviation are presented. The theoretical background on which both methods are based is given first, followed by a description of how the deviations caused by each component can be isolated in each method. The proposed methods have been applied to a thermal power plant allowing to diagnose the operation of the plant as well as to evaluate the validity of the performed analysis taking into account the uncertainties of the measured data.

Concepts on dynamic reference state, acceptable performance tests, and the equalized reconciliation method as a strategy for a reliable on-line thermoeconomic monitoring and diagnosis

The thermoeconomic diagnosis in operating power plants is more and more being demanded by the users of the same ones. Nevertheless, in spite of the efforts to unify the techniques or tactics of diagnosis, it seemed that we are even far from standardizing the analytical procedures to do it. Recently, a series of papers have been considered to compare different ways to solve a concrete problem to diagnose a power plants TADEUS part 1–7. In this paper, we look for to establish the minimum requirements that must fulfill the three fundamental aspects in an on-line thermoeconomic diagnosis and monitoring such as: Dynamic Reference Operating State, an Acceptable Performance Test State, and an Equalized Reconciliation Method. Where the Dynamic Reference Operating State, talks about to create a reference on the basis of the atmosphere conditions, fuel quality and present load of the plant in operation; in the Acceptable Operating State Test, we will describe to the minimum requirements of data acquisition and filtrate to have an acceptable tests and comparable with the reference; and an Equalized Reconciliation Method, talks about to the comparison of states (reference versus proves) to conditions of equal load and atmosphere, solved by a module of equation systems; respectively. An example of development and results applied to a plant of combined cycle 240 MW of third generation is presented.

Thermoeconomic diagnosis of a coal fired power plant

This paper presents a progressive separation procedure of the induced effects for power plant system diagnosis based on structural theory and symbolic thermoeconomics. The malfunction/dysfunction analysis and the fuel impact analysis of the structural theory as well as an improved induced malfunction evaluation method, which is composed of a progressive separation procedure, are applied to a 300 MW pulverized coal fired power plant located in Yiyang (Hunan Province, China). First, the dysfunctions induced by the malfunctions are separated by the malfunction/dysfunction analysis from the irreversibility increases in the components. The effects of the malfunctions on each component and the whole plant are also evaluated by using the fuel impact analysis, which are very useful for system maintenance and improvement. Then, the induced malfunctions generated by the inefficiencies in the other components are separated from the remaining irreversibility increases (i.e. malfunctions) by using the induced malfunction evaluation method proposed in this paper. This method enables evaluation of the induced malfunctions in thermoeconomic diagnosis applications. After separating the induced effects, the real anomalies can be quantified and localized. Nevertheless, the search for causality of the malfunctions is not equivalent to that for localization of these malfunctions. Hence, the capabilities and the limits of this approach to searching for the real causes of malfunctions are also discussed. The results show that thermoeconomics is a promising tool for the diagnosis of complex energy systems. This method also provides a great prospect for thermal power plant optimizations.

A Critical Review of the Thermoeconomic Diagnosis Methodologies for the Location of Causes of Malfunctions in Energy Systems

Thermoeconomic diagnosis procedures in the literature rely on the assumption that specific consumptions of resources in the components are the key to interpret the effects of malfunctions and then to trace a path towards the sources of anomalies. The main obstacle to a successful application of these approaches is represented by the actual interactions existing among components which cause a propagation of the alteration of component specific consumptions and therefore mask those effects that would allow a direct identification of the origin of malfunction. This paper presents an extensive discussion of potentialities and limits of diagnosis procedures proposed in the literature in distinguishing the effects induced by component interactions from those that are intrinsically generated by the anomaly, which is considered here as the main task to locate effectively causes of malfunctions in energy systems.

Accuracy level in thermoeconomic diagnosis of energy systems

This paper aims at analyzing the information that can be obtained by considering different accuracy levels in the thermoeconomic diagnosis problem. A progressive elimination of effects that impede a clear identification of anomalies causing performance degradation is performed. The analysis is applied to combined cycle plant.

Thermoeconomic Diagnosis: Zooming Strategy Applied to Highly Complex Energy Systems. Part 1: Detection and Localization of Anomalies*

This paper presents a summary of our most recent advances in Thermoeconomic Diagnosis, developed during the last three years, and how they can be integrated in a zooming strategy oriented toward the operational diagnosis of complex systems. In fact, this paper can be considered a continuation of the work presented at the International Conference ECOS’99 in which the concepts of malfunction (intrinsic and induced) and dysfunction were analyzed in detail. These concepts greatly facilitate and simplify the analysis, the understanding, and the quantification of how the presence of an anomaly, or malfunction, affects the behavior of the other plant devices and of the whole system. However, what remains unresolved is the so-called inverse problem of diagnosing, i.e., given two states of the plant (actual and reference operating conditions), find the causes of deviation of the actual conditions with respect to the reference conditions. The present paper tackles this problem and describes significant advances in addressing how to locate the actual causes of malfunctions, based on the application of procedures for filtering induced effects that hide the real causes of degradation. In this paper a progressive zooming thermoeconomic diagnosis procedure, which allows one to concentrate the analysis in an ever more specific zone is described and applied to a combined cycle. In an accompanying paper the accuracy of the diagnosis results is discussed, depending on choice of the thermoeconomic model.