Self Activated Burner And Compare Various Combustion Chamber/Methodology

Description

ABSTRACT

Self-activated burner which involves combustion oscillations constitute an important problem for the development of modern burner combustion systems. Methods to avoid these oscillations by active instability control (AIC) to provide safe operations for the corresponding combustion system are the subject matter of this paper. In addition to applications of this technology for a land-based gas turbine, basic actuation possibilities, methods of measuring oscillation quantities and requirements to be met by control strategies are described.  Following this general section, the installation of AIC systems for gas turbines of the Siemens Vx4.3A family will be explained. This type of turbine features an annular combustion chamber with a total of 24 burners. In order to be able to damp combustion oscillations arising within this type of combustion chamber – appearing as azimuthal modes spreading along the circumference of the combustion chamber – every burner was fitted with a direct drive valve. This type of valve creates mass flow modulations within the pilot gas supply of the burner which are anti-cyclical to the oscillations characterising the heat release rate within the flame, thus extinguishing them. Input signals for the feedback control system are obtained by measuring sound pressures within the combustion chamber indirectly at the burner flanges. Finally, this type of gas turbine was fitted with a 12-channel controller and 12 sensors in order to allow a damping of the azimuthal modes excited around the circumference of its annular combustion chamber. Exploiting the symmetry characterising azimuthal modes, two actuators are driven by every feedback loop. In tests run on various type V94.3A gas turbines delivering up to 267 MW of electric power according to ISO, AIC systems were used to damp successfully a great variety of combustion oscillations for several burner variants and operating points. Thus, it was possible to obtain stable gas turbine operations over their full power ranges. In addition to the high AIC flexibility in damping various oscillation problems at different gas turbine operating points, this technology has proved to provide a high degree of fault tolerance and good long-term characteristics.

TABLE OF CONTENTS

COVER PAGE]

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

CHAPTER ONE

INTRODUCTION

1.1      BACKGROUND OF THE PROJECT

• AIM/OBJECTIVE OF THE PROJECT
• PURPOSE OF THE PROJECT

CHAPTER TWO

LITERATURE REVIEW

• REVIEW OF THE RELATED STUDIES
• BURNER AND COMBUSTION CHAMBER

CHAPTER THREE

METHODOLOGY

• INTRODUCTION
• ACTIVE CONTROL OF BURNER COMBUSTION
• POINTS OF ACTUATION AND ACTUATORS AVAILABLE
• REQUIREMENTS TO BE MET BY A CONTROLLER
• INSTALLING AIC ON SIEMENS TYPE VX4.3A LAND-BASED GAS TURBINES
• INSTABILITY PROBLEM

 

CHAPTER FOUR

RESULT ANALYSIS

• RESULTS
• BURNER CONFIGURATION A: ACTIVE CONTROL AT SWITCH-OVER
• 2 BURNER CONFIGURATION B: ACTIVE CONTROL AT LOAD CHANGE DURING PREMIXED OPERATION

CHAPTER FIVE

• CONCLUSION
• REFERENCES

CHAPTER ONE

1.0                                             INTRODUCTION

Primary development aims for all modern combustion systems are minimising pollutant emission values, enhancing efficiency and increasing power density in order to achieve design dimensions as compact as possible. This imposes strict operating limits for efficiency and power density; moreover, in order to achieve low NOx emissions, lean premixed combustion is favoured in most cases. One unwanted side-effect is the appearance of a special form of combustion instability, so-called self-excited combustion oscillations. For low thermal power combustion systems, these instabilities primarily lead to increased noise levels. For combustion systems delivering high heat release rates, such as process gas heaters, or for combustion systems working under pressure, such as gas turbines, the sound pressure generated will reach very high levels. Owing to the large surfaces of such systems, high mechanical loads on the combustion chamber as well as on upstream and downstream components will arise. Also the thermal load on the chamber walls will rise considerably. Depending on sound pressure amplitudes, components will fail sooner or later; thus, this kind of oscillation must be avoided by all means if those combustion systems are to be operated safely. In view of the high requirements to be met by up-to-date, highly optimised combustion systems and their low degree of flexibility as regards operating parameters, the scope available for avoiding oscillations by modifying burner operation is decreasing all the time. New methods to prevent oscillations will have to be found.

Basically, the possibilities available to prevent self-excited combustion oscillations can be subdivided into passive and active measures. For instance, increasing acoustical attenuation, acoustically detuning systems by design modifications, and operational modifications are considered passive measures.(1-4) By contrast, active measures imply creating an external feedback loop using an actuator to influence combustion oscillations so as to damp them down. With this type of “Active Instability Control” (AIC), the combustion system, properly speaking, does not have to be redesigned, and operations can continue as usual.

The basic idea to suppress combustion oscillations by an active feedback loop was published in a theoretical paper on rocket engines by Tsien as early as 1952.(5) However, it took until the eighties to convert this idea into a practical device. Various authors described successful tests based on laboratory- scaled burners with a thermal power of between 1 kW and 250 kW.(6-8) For all these publications, attenuation of combustion oscillations is achieved by anti-sound signals generated via loudspeakers. In addition to this method, other types of intervention and control strategies were researched for various combustion systems; however, all tests were performed at lab scales.(9-16) The first industrial-size application was realised by Seume et al. (17) in 1996 based on a land-based gas turbine delivering 160 MW of electrical power. For this gas turbine, active control was achieved by means of anti-cyclical fuel injection, with direct drive valves serving as actuators. This technique was then also extended to the largest type of this family of gas turbines, the V94.3A with an electric power output of 267 MW.(18, 19) Full scale tests on afterburners have been published by Moren et al. 20, and on a 67.5° sector of a liquid-fuelled lean premixed combustor by Hibsman et al. (21)

The way this technology was implemented and the problems encountered in doing so constitute the subject matter of chapters. To begin with, however, chapter one is on the introduction, chapter 2 review the necessary literature related to the study, the chapter three is on the methodology, the main possibilities for actuation, as well as the components available to do so, such as sensors and actuators. Moreover, practical requirements to be met by this technology will be illustrated. Results achieved with AIC are discussed in chapter 4. Chapter 5 deal with long-term experience and a short evaluation of the advantages offered by AIC as compared to passive measures.

1.2                                          BACKGROUND OF THE PROJECT

Burners are used in a wide variety of applications to heat water, heat homes, heat food and, more generally, to generate and use heat. In everyday life a wide variety of burners are used, including water heaters, stoves, ovens, environmental heaters, process heaters, fryers or others, etc., but not limited to these. One of the problems in common with all burners is that the residue tends to accumulate on the surfaces of the burners and associated parts.

There is usually little accumulation in areas of burners that get very hot, such as the combustion chamber. There are, in addition, many burners that themselves do not get very hot, such as a Venturi that combines fuel and air in a fuel / air mixture for combustion just outside the burner. However, surrounding parts, such as those that supply fuel and oxygen, are susceptible to accumulation of undesirable deposits. The problem is described in an article published by the American Gas Association (AGA) Labs in 1960, entitled “Minimizing Lint Stoppage of Atmospheric Gas Burner Ports”. The proposed solutions include filtering the inlet air and operating the burner at a temperature high enough so that the lint accumulation side of the burner inlet port is kept warm enough to incinerate the incoming lint when it reaches the port. See pages 9-10 of the AGA report.

For example, in a typical atmospheric Venturi burner that uses natural gas (mainly methane), a given volume of fuel may require as much as ten volumes of air for proper combustion. This means that a large volume of unfiltered air can pass through the Venturi, or other burner, and can mean that many air pollutants may have the opportunity to accumulate dirt, lint, or other undesirable residue.

Typical atmospheric burners, and even many forced draft burners, do not use filtered air. Therefore, a very large volume of air will pass through the burner and may include many impurities. For example, in home cooking or in a restaurant, the air may include very small amounts of lint, dust, particles, food vapors, oil vapors, grease vapors, and the like. Although the concentration of such contaminants is small, their cumulative effect over periods of time can be large. These contaminants can be deposited on the exterior and interior surfaces of a burner, such as the inlet pipe, the exterior of the burner, the interior of a Venturi, and the like.

An alert to owners and operators will recognize the need to clean these surfaces in order to keep the roads clear for fuel and air or oxygen. Naturally clean burners tend to operate with greater efficiency and will be more effective in transferring heat from the burner to the load or object (s) that is being heated. If the burner itself could be cleaned, this would relieve owners and operators of the need to stop heating operations to clean the burners. It would also be helpful to ensure that the burner operates at a high state of efficiency and, therefore, would at least potentially save energy and energy costs.

1.2                    AIM AND OBJECTIVE OF THE PROJECT

The main aim of this work is to discuss the self activated burner and compare various combustion chambers of the burner. At the end of this work, students involved shall be able:

1. To provide a method and a device for controlling the combustion of a burner which are capable of adapting the combustion parameters of the burner as a function of the characteristic features of the system and of the components used.
2. To provide a method and a device for controlling the combustion of a burner which take into consideration any variations over time of variable combustion parameters.

• To provide a method and a device for controlling the combustion of a burner which adapts itself to the variations over time of the combustion parameters.

1.3                                  PURPOSE OF THE STUDY

The purpose of the present invention is to provide a method and a device for controlling the combustion of a burner which overcome the aforementioned drawbacks.