Termodinámica

Applied Thermal Engineering 27 (2007) 457–466 www.elsevier.com/locate/apthermeng

Concept on thermoeconomic evaluation of steam turbines
A. Zaleta-Aguilar a, L. Correas-Uson b, J. Kubiak-Szyszka
a c

c,* ,

F.Z. Sierra-Espinosa

c

Department of Mechanical Engineering, University of Guanajuato Prolong, Tampico S/N, 36730 Salamanca, Gto, Mexico b Research Center for Power PlantEfficiency (CIRCE), Maria de Luna 3, 50015 Zaragoza, Spain Center for Research in Engineering and Applied Sciences (CIICAp), Av. Universidad No. 1001, 62210 Cuernavaca, Morelos, Mexico Received 21 June 2006; accepted 22 June 2006

Abstract Concepts of exergoeconomic audits and evaluation of steam turbines are presented. In the first part of the work, an analysis based on the first and second laws ofthermodynamics is applied to a power plant. The well-known procedures of ‘‘Exergy Cost Theory’’ and the ‘‘General Theory of Thermoeconomics’’ proposed by Valero et al. [V. Verda, L. Serra, A. Valero, Zooming procedure for the thermoeconomics diagnosis of highly complex energy systems, Int. J. Appl. Thermodyn. 6 (2) (2002) 75–83] are used. These methodologies allow the computation of exergy-cost andeconomic-cost of local products (P) and fuels (F) in each plant component (especially in steam turbines). The second part of the work consists of an evaluation and determination of the degree of entropy generation (DSg) and power loss (DW) in a steam turbine stage (nozzle-bucket), under the detection of specific malfunctions. As it is well known, steam turbines can develop intrinsic malfunctions such asroughness, seal and leak clearances, erosion, and sedimentation. The main objective of this work is to assess the exergy-cost (fuel impact cost) due to the intrinsic malfunctions in a steam turbine stage. Ó 2006 Elsevier Ltd. All rights reserved.
Keywords: Steam turbines; Thermoeconomic evaluation; Losses

1. Introduction Steam turbines in power plants are one of the most important componentsof the power generation process. Any malfunction occurring inside them will increase the overall heat losses. Currently, conventional procedures are implemented in power plants in order to maintain optimum performance in steam turbines, such as energy audits and on-line monitoring systems. The turbine efficiency monitoring procedures can be classified depending on whether the turbine is out of serviceor in operation, these are: (a) energy audits (for turbines out of service during an overhaul); (b) on-line monitoring and acceptance test (for turbines in service).
*

Corresponding author. Tel./fax: +52 777 329 7084. E-mail address: janusz@uaem.mx (J. Kubiak-Szyszka).

During an overhaul, a steam turbine energy audit is a good way to determine internal energy losses in stage componentslike the nozzle, the bucket, the seals, the end-packing, etc., which are particularly affected by solid particles, erosion, roughness and damage in the steam path. Reini et al. [1], compared three formulations used for thermoeconomic diagnostics based on the computation of losses of energy in components. A distinction is made between malfunction and miss function of these components. Torres et al. [2]also distinguish both kinds of failure to apply an advanced thermoeconomic theory developed to improve the diagnosis of faults. On the other hand, the on-line monitoring performance helps to account for the generated power, the efficiency and the fuel-impact cost due to malfunctions in the steam turbine section. Data of the most important variables of the process are obtained to conduct athermoeconomic analysis to find a sort of irreversibility level on which malfunctions are diagnosed [3]. The global heat rate in a process may be also used to detect effects like

1359-4311/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.applthermaleng.2006.06.018

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A. Zaleta-Aguilar et al. / Applied Thermal Engineering 27 (2007) 457–466

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