Gas Turbine Handbook : Principles and Practices

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78 Gas Turbine Handbook: Principles and Practices Table 5-A. Control Functions (Mechanical Type) ———————————————————————————————— FUNCTION DESCRIPTION ———————————————————————————————— Sequencer •Start/Stop Gas Turbine Accessories •Load/Unload Gas Turbine ———————————————————————————————— Speed Control •Constant Time-Based Schedule ———————————————————————————————— Temperature •Exhaust Control (Average of Thermocouples), Control •Override Control at Loading & Acceleration ———————————————————————————————— Load Control •Manual-Hand Set (Using Speed Control Function) •Driven Equipment Feedback (Discharge Pressure, Flow, Megawatts) ———————————————————————————————— GT Compressor •Acceleration Schedule Surge Control Temperature Biased ———————————————————————————————— Driven Unit •Process Flow Output •Process Pressure •Megawatts ———————————————————————————————— While control system functions tend to overlap, they can be looked at as controlling three separate areas: Sequencing Control Routine Operation Control Protection Control Sequencing Control consists of the steps to Start, Load, Unload, and Stop the unit. Typical steps included in a normal start are: • Check that all permissives are made • Check that lube oil pumps are running
Gas Turbine Control 79 • Open the process compressor recycle valve (if applicable) • Actuate the gas turbine starter • Actuate the gas turbine starter time-out clock • Energize the ignition system • Actuate the ignition system time-out clock • Open the fuel valve to preset point • Stop the gas turbine starter when starter time-out clock expires • De-energize the ignition system when the time-out clock expires. When the start sequence is complete the gas turbine will have reached self-sustaining speed. At this time control can be, and usually is, handed over to the Routine Operation Controller. This controller will maintain stable operation until it receives an input (from the operator, or the process) to load the unit. Prior to initiating loading the unit, control is turned back over to the Sequence Controller to properly position inlet and discharge valves, electrical breakers, etc. On electric generator drives this is the point that the automatic synchronizer is activated to synchronize the unit to the electric grid. When these steps are completed, control is again turned back over to the Routine Operation Controller and the speed control governor, acceleration scheduler, temperature limit controller, and pressure limit controller all come into play. Controlling the gas turbine during steady state operation is a major function of the control system. However, while the control operates in this mode most of the time, it is the other modes of operation that are most critical. These are Starting, Stopping, Increasing Power and Decreasing Power. The direct result of varying fuel flow is higher or lower combustion temperatures. As fuel flow is increased, combustor heat and pressure increase and heat energy to the turbine is increased. Part of this increased energy is used by the compressor-turbine to increase speed which, in turn, causes the compressor to increase airflow and pressure. The remaining heat energy is used by the power extraction turbine to produce more shaft horsepower. This cycle continues until the desired shaft horsepower or preset parameter limit (temperature, speed, etc.) is reached. Similarly, to reduce shaft horsepower, the control starts by reducing fuel flow. The lower fuel flow reduces combustion heat and pressure and reduces the heat energy available to the compressorturbine. With less available energy the compressor-turbine slows
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Gas Turbine Handbook: Principles an
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Gas Turbine Handbook: Principles an
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Dedication This book is dedicated t
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Contents PREFACE ..................
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Chapter 13—BOROSCOPE INSPECTION .
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Preface to the Third Edition The ne
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Acknowledgments I wish to thank the
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Figure 2-3. Courtesy of United Tech
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5. Weather Hood Material __________
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Appendix C-6 Air/Oil Cooler Specifi
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9. Drive Requirements A. Hydraulic
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22. Packaging For Shipment Per Spec
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Parameters Units NH 3 CO H 2 CH 4 C
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.055 Parameters Units 1/0 .88/.12 .
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Koppers Foster Blue Coal Gas Winkle
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Gas Turbine Handbook : Principles and Practices

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