LOSSES IN A GAS TURBINE

Description

 

ABSTRACT

Gas turbines, like other prime movers, experience wear and tear over time, resulting in decreases in available power and efficiency which is known as losses. These loss events were then categorized based on the nature of the associated loss scenario. The study subsequently focused on the variables that could be monitored in real time to detect the abnormal turbine operating conditions, such as vibration characteristics, temperature, pressure, quality of working fluids, and material degradations. These groups of CM variables were then matched with detectable failures in each loss event and prioritized based on their effectiveness for failure detection and prevention. The detectable loss events and the associated loss values were used in this evaluation process. The study finally concluded with a summary of findings and path-forward actions.

Nomenclature

C = true chord length of airfoil

Cx = axial chord length of airfoil

Cx= axial chord length of airfoil

Cp= local total pressure loss coefficient, (Poi−Poe)/Poi

Cωs= streamwise vorticity coefficient

ELC= energy loss coefficient

H= enthalpy

H = flow passage height

Htc = heat transfer coefficient

IAL= integrated aerodynamic losses

K= ratio of specific heats

Me= exit local Mach number downstream of the airfoil

Me,ideal= ideal isentropic exit local Mach number downstream of the airfoil

Me∞= exit freestream Mach number downstream of the airfoil mass flow rate

P= airfoil passage effective pitch

Po= stagnation pressure

Poc= injectant stagnation pressure

Poe= exit local stagnation pressure

Poe= exit local stagnation pressure

Poe,m= mass-averaged exit stagnation pressure

Poe∞= exit freestream stagnation pressure

Poi= inlet local stagnation pressure

Poi= inlet local stagnation pressure

Poi,m= mass-averaged inlet stagnation pressure

Poi∞= inlet freestream stagnation pressure

Pse= exit local static pressure

Pse= exit local static pressure

Pse,m= mass-averaged exit static pressure

poe,A= area-averaged exit stagnation pressure

pse,A= area-averaged exit static pressure

PS= pressure side

Qe= exit local dynamic pressure

qe,m= mass-averaged exit dynamic pressure

R= gas constant

S= span spacing between adjacent airfoils

Se= local exit entropy

Si= local inlet entropy

SS= suction side

Te= exit absolute temperature

Tu= test section inlet longitudinal turbulence intensity level

U= local streamwise velocity

u∞= local streamwise freestream velocity

TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

CHAPTER ONE

INTRODUCTION

1.1      BACKGROUND OF THE PROJECT

• AIM OF THE PROJECT
• OBJECTIVE OF THE PROJECT
• SCOPE OF THE PROJECT

CHAPTER TWO

LITERATURE REVIEW

• OVERVIEW OF GAS TURBINE
• THEORY OF OPERATION
• OVERVIEW OF THE STUDY
• EARLY PAST INVESTIGATIONS
• REVIEW OF QUANTITATIVE AERODYNAMIC LOSS CHARACTERIZATION

CHAPTER THREE

• CATEGORIES OF GAS TURBINE LOSSES
• TURBINE LOSS DATA BY LOSS CATEGORIES
• COMPRESSOR LOSSES VERSUS TURBINE LOSSES

CHAPTER FOUR

• GAS TURBINE CONDITION MONITORING
• BLADE VIBRATION MONITORING
• ROTOR/CASE VIBRATION AND CLEARANCE MONITORING
• TEMPERATURE, PRESSURE, AND PERFORMANCE MONITORING
• FLUID QUALITY MONITORING
• MONITORING MATERIAL CRACKING OR DEGRADATION
• PRIORITIZATION OF CM

CHAPTER FIVE

• CONCLUSION
• REFERENCES

CHAPTER ONE

1.0                                                                              INTRODUCTION

1.1                                                                             BACKGROUND OF THE STUDY

Equipment losses contribute to a large portion of losses in higher hazard occupancies such as Power Gen. While the fleet of insured gas turbines has seen a steady growth over recent years, the reliability and availability of the gas turbines have been continuously challenged by more taxing loads, harsher environment, and over- stretched operations to meet rising power demand. Both operators and insurers of gas turbines have become increasingly concerned with the risk of turbine failures and associated losses. To help clients improve loss prevention and reduce exposure to the risks, the center for property risk solutions continues its efforts to understand turbine loss scenarios and failure mechanisms, and further, the risk mitigation methods based on effective monitoring of turbine condition variables.

Gas turbine loss events due to mechanical breakdown during a recent 10-year period at clients’ power generation plants were evaluated. While the true root causes of individual loss events may have been ambiguous in a number of cases, the study focused on the detection of the developing failure at an early stage through CM, so as to stop the failure progression or adjust the maintenance plan accordingly to mitigate the risk of equipment loss. Each of the reviewed loss events can be described as a loss scenario composed of a series of component failures. As a first step, these loss events were categorized based on the nature of their respective loss scenarios. Such categorization improves the understanding of major contributors of the turbine loss events. Second, the failures in each typical loss scenario of the categories led to the identification of appropriate condition variables that can be monitored to detect these failures. Relevant monitoring technologies were reviewed for each group of CM variables. Finally, evaluation and prioritization of the major types or groups of CM variables were performed based on the effectiveness of failure detection and prevention. The remainder of the paper is structured following the steps of the study outlined earlier.

1.2                                                                              AIM OF THE PROJECT

Gas turbines, like other prime movers, experience wear and tear over time, resulting in decreases in available power and efficiency which is known as losses. The aim of this work is to highlight and discussed those losses that affects the power and efficiency of a gas turbine.

1.3                                                                              OBJECTIVES OF THE PROJECT

The student involved shall discuss and monitored in real time to detect the abnormal turbine operating conditions, such as vibration characteristics, temperature, pressure, quality of working fluids and material degradations. These groups of condition monitoring variables were then matched with detectable failures in each loss event and prioritized based on their effectiveness for failure detection and prevention. The detectable loss events and the associated loss value were used in this evaluation process.

1.4                                                 SCOPE OF THE PROJECT

In-situ condition monitoring (CM) is a crucial element in protection and predictive maintenance of large rotating Power-Gen equipment such as gas turbines or steam turbines. In this work, selected gas turbine loss events occurring during a recent ten-year period at FM Global clients’ power generation plants were evaluated. For each loss event, a loss scenario or a chain of failures was outlined after investigating the available loss record. These loss events were then categorized based on the nature of the associated loss scenario.

CHAPTER TWO

2.0                                                    LITERATURE REVIEW

2.1                                            OVERVIEW OF GAS TURBINE

A gas turbine, also called a combustion turbine, is a type of continuous combustion, internal combustion engine. The main elements common to all gas turbine engines are:

1. An upstream rotating gas compressor;
2. A combustor;
3. A downstream turbine on the same shaft as the compressor.

A fourth component is often used to increase efficiency (on turboprops and turbofans), to convert power into mechanical or electric form (on turboshafts and electric generators), or to achieve greater thrust-to-weight ratio (on afterburning engines).

The basic operation of the gas turbine is a Brayton cycle with air as the working fluid. Atmospheric air flows through the compressor that brings it to higher pressure. Energy is then added by spraying fuel into the air and igniting it so the combustion generates a high-temperature flow. This high-temperature high-pressure gas enters a turbine, where it expands down to the exhaust pressure, producing a shaft work output in the process. The turbine shaft work is used to drive the compressor; the energy…