Exergy analysis of a thermal power plant with measured boiler and turbine losses

doi:10.1016/j.applthermaleng.2010.01.008

Applied Thermal Engineering

Volume 30, Issues 8–9, June 2010, Pages 970-976

https://doi.org/10.1016/j.applthermaleng.2010.01.008 Get rights and content

Abstract

In this paper, a thermodynamic analysis of a subcritical boiler–turbine generator is performed for a 32 MW coal-fired power plant. Both energy and exergy formulations are developed for the system. A parametric study is conducted for the plant under various operating conditions, including different operating pressures, temperatures and flow rates, in order to determine the parameters that maximize plant performance. The exergy loss distribution indicates that boiler and turbine irreversibilities yield the highest exergy losses in the power plant. In addition, an environmental impact and sustainability analysis are performed and presented, with respect to exergy losses within the system.

Introduction

The world energy needs rely heavily on fossil fuels for electricity generation. The majority of the world’s power generation is met by fossil fuels, particularly coal and natural gas. Despite the growth of renewable energy installations like wind and solar power, the heavy dependence on fossil fuels is expected to continue for decades. Despite the depletion of fossil fuel reserves and environmental concerns such as climate change, the growth in oil demand is expected to be 47.5% between 2003 and 2030, 91.6% for natural gas and 94.7% for coal [1]. Even though cleaner renewable sources of energy are being rapidly developed, their relative cost and current state of technology have not advanced to a stage where they can significantly reduce our dependence on fossil fuels. Therefore, given the continued reliance on fossil fuels for some time, it is important that fossil fuel plants reduce their environmental impact by operating more efficiently.

As energy analysis is based on the first law of thermodynamics, it has some inherent limitations like not accounting for properties of the system environment, or degradation of the energy quality through dissipative processes. An energy analysis does not characterize the irreversibility of processes within the system. In contrast, exergy analysis will characterize the work potential of a system. Exergy is the maximum work that can be obtained from the system, when its state is brought to the reference or “dead state” (standard atmospheric conditions). Exergy analysis is based on the second law of thermodynamics. This paper will examine a detailed exergy analysis of a thermal power plant, in order to assess the distribution of irreversibilities and losses, which contribute to loss of efficiency in system performance.

Past exergy studies have evaluated the performance of power plants, as a means to optimize the performance and turbine power output. Rosen [2] evaluated the performance of coal-fired and nuclear power plants via exergy analyses. Habib and Zubair [3] conducted a second law analysis of regenerative Rankine power plants with reheating. Dincer and Muslim [4] performed a thermodynamic analysis of reheat cycle power plants. Sengupta et al. [5] conducted an exergy analysis of a 210 MW thermal power plant. Rosen and Dincer [6] performed an exergoeconomic analysis of power plants that operate on various fuels. They investigated the relationship between capital costs and thermodynamic losses. Kwak et al. [7] presented an exergetic and thermo-economic analysis of power plants.

Unlike these past studies, this current paper presents an exergy analysis of a uniquely configured Rankine cycle operating in subcritical conditions. The generator power output is 32 MW. The boiler is a circulating fluidized bed combustion boiler with a capacity of 140 TPH of steam at 100% BMCR at the rated steam parameters. The power plant is designed to utilize an air cooled condenser to condense the exhaust steam.

The main objective of this paper is to perform a thermodynamic exergy analysis, using design data of an actual power plant under construction in India. It will compare the results of the analysis to demonstrate how exergy analysis can be valuable for improving the system performance. This paper will identify major sources of losses and exergy destruction in the power plant. It will provide ways and means to improve the system performance and reduce environment impact. Finally, it will perform a parametric study to determine how the system performance varies with different operating parameters.

Section snippets

Exergy formulation of power plant

The process flow diagram for the power plant is shown in Fig. 1. The process parameters for the power plant are shown in Table 1. The following thermodynamic analysis of the power plant will consider the balances of mass, energy, entropy and exergy. Unless otherwise specified, the changes in kinetic and potential energies will be neglected and steady state flow will be assumed. The process parameters and data are based on actual plant design data for a 32 MW power plant being installed by Tecpro

Results and discussion

Coal is the supply fuel of the power plant, with the following components: moisture = 25%, ash = 0.88%, hydrogen = 4.06%, nitrogen = 1.1%, sulphur = 0.075%, oxygen = 7.935%, carbon = 60.95%, GCV = 21,981.75 kJ/kg. Fig 2 shows that the reference temperature does not have an effect on the energy efficiency, but it affects the exergy efficiency. The performance of the system depends on the surroundings of the system. Table 5 further elucidates the effect of the reference temperature on exergy efficiency.

It can be

Conclusions

A second law analysis of a thermal power plant has been performed in this paper, along with a parametric study that considers the effects of various parameters like operating temperature and pressure on the system performance. The power plant’s energy efficiency is determined to be 30.12% for the gross generator output. The plant exergy efficiency for the system is 25.38% for the gross generator output. The maximum exergy destruction is found to occur in the boiler. As a result, efforts at

Acknowledgements

The authors are grateful to Tecpro Power Systems Limited, EPC Contractors of Power Plants, India, for providing technical design data of the power plant in this paper. Support from the Natural Sciences and Engineering Research Council of Canada (NSERC) is also acknowledged.

References (10)

S.K. Som et al.
Thermodynamic irreversibilities and exergy balance in combustion processes
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M.A. Rosen
Energy and exergy-based comparison of coal-fired and nuclear steam power plants
Exergy – International Journal
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M.A. Rosen et al.
Exergoeconomic analysis of power plants operating on various fuels
Applied Thermal Engineering
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H.Y. Kwak et al.
Exergetic and thermoeconomic analyses of power plants
Energy
(2003)
M.A. Rosen et al.
Role of exergy in increasing efficiency and sustainability and reducing environmental impact
Energy Policy
(2008)

There are more references available in the full text version of this article.

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Exergy analysis of a thermal power plant with measured boiler and turbine losses

Abstract

Introduction

Section snippets

Exergy formulation of power plant

Results and discussion

Conclusions

Acknowledgements

Science Direct Progress in Energy and Combustion Science

Exergy – International Journal

Applied Thermal Engineering

Energy

Energy Policy