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Publication Title | ENERGY AND EXERGY ANALYSIS OF A REHEAT REGENERATIVE VAPOR POWER CYCLE

Organic Rankine Cycle

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International Journal of Emerging Technology and Advanced EngineeringENERGY AND EXERGY ANALYSIS OF A REHEAT REGENERATIVE VAPOR POWER CYCLE

Volume 3, Special Issue 3: ICERTSD 2013, Feb 2013, pages 427-434

An ISO 9001:2008 certified Int. Journal, ISSN 2250-2459, available online at www.ijetae.com



ABSTRACT

M. Pandey 1+, T. K. Gogoi2 1B-Tech, Department of Mechanical Engineering

Tezpur University, Assam, India

2Associate Professor, Department of Mechanical Engineering Tezpur University, Assam, India

+Corresponding author email:mayank.pandey.tu@gmail.com

The present paper describes the energy and exergy analysis of a reheat regenerative vapor power cycle. The plant consists of one boiler feed pump, one supercritical boiler, two steam turbines with a reheater in between, two feed water heaters (one open and one closed) and a condenser. The energy and exergy balance study has been carried-out for each component of the plant. Energy efficiency, exergy efficiency and the irreversibility results obtained from the simulation has been presented in the form of graphs. The supercritical pressure is varied from 250 to 400 bar in a step of 50 bar and for each supercritical pressure the temperature has been changed from 500 to 800K. The parametric study reveals that the cycle energy and exergy efficiency increases with increase in pressure and temperature. This is due to reduced energetic and exergetic losses at increased pressure and temperature. While estimating the irreversibility and fractional exergy losses of various system components it is found that maximum irreversibility occurs in the boiler which accounts for 46-55% at 350 bar for the given temperature range. The fractional exergy loss in turbine, condenser, BFP, mixing chamber, OFWH and CFWH are found to 20-30%, 13-14%, 1.6 -2%, 0.37 – 0.64%, 1.6-2.8% and 1.25- 2.15% respectively at 350 bar inlet pressure and for the given temperature range. This combined study on energy and exergy analysis thus gives a better insight into the cycle operation with various system components and components requiring operational and design modifications for minimizing losses.

Keywords: Energy, Exergy, Irreversibility, Supercritical boiler, Rankine cycle.

1. INTRODUCTION

The work output is maximized when the process between the two specified states is executed in a reversible manner. A system delivers the maximum possible work as it undergoes a reversible process from the specified initial state to the state of its environment, that is, the dead state. The study of thermodynamic cycles applied to power stations is of great importance due to the increasing energy consumption, the opening of electricity markets and the rising environmental restrictions, specifically in the carbon dioxide emissions issue. Power plants that use steam as their working fluid work on the basis of Rankine cycle. The first stage in designing these power plants is the thermodynamic analysis process of the Rankine cycle. Also the second law analysis of these cycles reveals where the largest irreversibilities occur and what their magnitudes are. Now for evaluating second law efficiency of a thermodynamic cycle it‟s very important for us to know the concept of exergy.

Exergy is the maximum useful work that could be obtained from the system at a given state in a specified environment. Steam reheating is important in the case of a vapor power plant, because it increases the quality of steam at the turbine inlet which prevents the corrosion of turbine blades, and under certain conditions the thermal efficiency of the plant also increases. The effect of reheat alone on the thermal efficiency of the cycle is very small. Regeneration or the heating up of feedwater by steam extracted from the turbine has a marked effect on cycle efficiency. That‟s why both are equipped in the current analysis of supercritical rankine cycle.

The optimization of reheat regenerative thermal-power plants has been analyzed [1-2] for the subcritical pressure range. The exergetic analysis and optimization has been done for the supercritical rankine cycle [3]. Generalized Thermodynamic Analysis of Steam Power Cycle with „n‟ number of Feed Water Heaters has been analyzed.

Presented at International Conference on Energy Resources and Technologies for Sustainable Development, 07-09 February 2013, Howrah, India.

ICERTSD2013-15-218

© IJETAE2013

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