I hope this book will serve as a reference text after it has accomplished its primary objective of introducing you to the broad subject of gas turbines. The book will be very useful as a textbook for undergraduate turbomachinery courses as well as for in-house company training programs related to the petrochemical, power generation and offshore industries. It is hoped that this book will serve as a reference text having fulfilled its primary objective of introducing the reader to the broad subject of gas turbines.
Special thanks go to the Texas A&M University Turbomachinery Symposium Advisory Committee and Dr. Simmang, chair of the Texas A&M University Department of Mechanical Engineering, who was instrumental in initiating the manuscript. The book will be very useful as a textbook for undergraduate courses in turbomachinery as well as for internal company training programs related to the petrochemical, power generation and offshore industries.
Their cooperation and patience made it easy to turn a rough manuscript into a finished book. The founding of Texas A&M University's Annual Turbomachinery Symposium can be counted among his major contributions to the field of turbomachinery.
Materials, Fuel Technology, and Fuel Systems
Auxiliary Components and Accessories
Installation, Operation, and Maintenance
Design: Theory and Practice
An Overview of Gas Turbines
Aviation engines have been leaders in most of the gas turbine technology. All this has changed in the last 10 years; spurred by the introduction of the "Aero-Derivative Gas Turbine", the industrial gas turbine has dramatically improved its performance in all operational aspects. The adiabatic efficiency of the compressors has also increased and efficiencies in the high 80s have been achieved.
Most of the velocity leaving the fan is converted to pressure energy in the diffuser. The air is finally returned to the end section of the intake manifold and exits to the intake gas turbine. Preheated combustion air is obtained by diverting part of the exhaust gas from the gas turbine.
The high pressure ratio in the compressor also causes the cooling air used in the first stages of the turbine to be very hot. Steam cooling is possible in new combined cycle power plants, which is the basis of most new high-performance gas turbines. The new gas will use steam as part of the cooling and power part of the cycle.
The use of pyrometers in the control of advanced gas turbines is being investigated.
Theoretical and
Actual Cycle Analysis
With these assumptions, the effect on ideal cycle efficiency as a function of pressure ratio for an ideal Brayton cycle operating between ambient temperature and firing temperature are given by the following relationship:. The advantage of a split shaft gas turbine is high torque at low speed. Gas turbine calculations are the same as shown for a simple cycle.
The work of the combined cycle is equal to the sum of the net work of the gas turbine and the work of the steam turbine. In a typical combination, the gas turbine produces about 60% of the power and the steam turbine about 40%. The steam turbine uses the energy of the exhaust gas of the gas turbine as input energy.
This increases the output of the steam turbine and thus the efficiency of the combined cycle. Combination of evaporative and refrigerated inlet systems—Using evaporative coolers to help the cooler system achieve lower inlet air temperatures. This mist then provides cooling when it evaporates in the air inlet duct of the gas turbine.
Steam injection into the gas turbine combustor using dual fuel nozzles. Turbine ignition temperature. The turbine flash temperature, the gas temperature measured at the inlet of the first stage nozzles, is limited to the design flash temperatures since an increase in flash temperatures would greatly reduce the life of the hot section of the turbine. In the case of the hot and humid compressed air injection system, the air must be saturated.
Surge control. Injection systems will all require major modifications to the control system to prevent injection until the units have reached full load and stabilized operation.
Compressor and Turbine
Performance Characteristics
The flow will be considered fully described if the magnitude, direction, and thermodynamic properties of the gas at every point in space are determined. Ideal flow in turbomachines exists when there is no heat transfer between the gas and its surroundings, and the entropy of the gas remains unchanged. -3) where ρV2/2gc is the dynamic pressure head indicating the velocity of the gas in motion.
Finally, using the definition of Mach number, the velocity of the gas flow can be calculated. The continuity equation is a mathematical formulation of the law of conservation of mass of a gas that is a continuum. The isentropic efficiency of the compressor can be written in terms of total enthalpy changes.
The isentropic efficiency of the turbine can be written in terms of the total enthalpy change. Flow coefficient is the flow rate capacity expressed in dimensionless form. The variation of the final results will depend on the scaling factor and the change in the fluid environment.
Common practice is to plot velocity lines as a function of given pressure and flow. In this map, constant aerodynamic velocity lines are functions of power and flow velocity. Below is a sample calculation of the techniques used to determine the performance of a gas turbine.
950 Btu/cu ft [(35,426 kJ/cu m)] and density 0.557) The air mass flow value was obtained by measuring the flow at the gas turbine inlet using an ion-gun velocimeter. This comment is not a criticism of the control package as it operates at a base exhaust temperature. This figure shows that below 50% of rated load, the combination cycle is not efficient.
Performance and
Mechanical Standards
The only task of the turbine part of the gasifier is to drive the gas turbine compressor. For most onshore applications, if the plant size exceeds 100 MW, the frame type is most suitable for a gas turbine. The type of fuel is one of the most important aspects when choosing a gas turbine.
This type of cycle affects the life of many of the hot section components in the gas turbine. This section covers some of the applicable API and ASME standards for the gas turbine and other various associated components. In conjunction with the API specifications, the following ASME codes also provide important data for proper gas turbine selection.
The standard is limited to a consideration of the basic gas turbine including the compressor, combustion system and turbine. The transmission is limited to the protective transmission of the electrical system used to protect the gas turbine station itself. The standards define terms used in the industry and describe the basic design of the unit.
Torsional criticals should be at least 10% off the first or second harmonic of the rotational frequency. Separate lubrication systems can be provided for different sections of the turbine and driven equipment. Cleaning the fuel system after a failed start is mandatory, even in manual operation mode.
The data is useful in further evaluation of the unit or can be used as baseline data. Critical speeds correspond to the natural frequencies of the gears and the rotor bearing support system. The overall physical length should be approximately 36 inches (914.4 mm) measured from the tip of the probe to the bottom of the probe.
Rotor Dynamics
The number of independent coordinates describing the system's motion is called the system's degrees of freedom. A single-degree-of-freedom system is one that requires a single independent coordinate to completely describe its vibrational configuration. Systems with two or more degrees of freedom vibrate in a complex manner where frequency and amplitude have no definite relationship.
Under these principal modes of vibration, each point in the system follows a particular pattern of common frequency. The simplest form of periodic motion is harmonic motion, which can be represented by sine or cosine functions. It is important to remember that harmonic motion is always periodic; however, periodic motion is not always harmonic.
Thus, one can determine the velocity and acceleration of this system by differentiating the equation with respect tot. If the mass is displaced from its original equilibrium position and released, the unbalanced force, the spring's recovery (−Kx), and acceleration are related through Newton's second law. The nature of the solution given by equation (5-9) depends on the nature of the roots,r1andr2.
If the motion is plotted as a function of time, the curve in Figure 5-7 is obtained. When the radical is zero and the roots are equal, the displacement decays most rapidly from its initial value as seen in Figure 5-8. If c2/4m2 < k/m, then the roots r1 and r2 are imaginary, and the solution is an oscillatory motion as shown in Figure 5-9.
So far, the study of vibrating systems has been limited to free vibrations, where there is no external input to the system. The external periodic force has a frequency ω that can vary independently of the system parameters. The equation of motion for this system can be obtained by any of the previously mentioned methods.
