GEK111712 Control & Protection

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GEK111712 Control & Protection
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  g GEK 111712 June 2007  GE Energy    These instructions do not purport to cover all details or variations in equipment nor to provide for every  possible contingency to be met in connection with installation, operation or maintenance. Should further information be desired or should particular problems arise which are not covered sufficiently for the purchaser's  purposes the matter should be referred to the GE Company.  © 2007 General Electric Company   Control and Protection Articles DLN2.6+ Gas Fuel System  GEK 111712 Control and Protection Articles DLN2.6+ Gas Fuel System   2 The below will be found throughout this publication. It is important that the significance of each is thoroughly understood by those using this document. The definitions are as follows: NOTE Highlights an essential element of a procedure to assure correctness. CAUTION Indicates a potentially hazardous situation, which, if not avoided, could result in minor or moderate injury or equipment damage. WARNING INDICATES A POTENTIALLY HAZARDOUS SITUATION, WHICH, IF NOT AVOIDED, COULD RESULT IN DEATH OR SERIOUS INJURY ***DANGER*** INDICATES AN IMMINENTLY HAZARDOUS SITUATION, WHICH, IF NOT AVOIDED WILL RESULT IN DEATH OR SERIOUS INJURY.  Control and Protection Articles DLN2.6+ Gas Fuel System GEK 111712   3 TABLE OF CONTENTS I.   GENERAL.....................................................................................................................................................4   II.   EQUIPMENT.................................................................................................................................................4   A.   Gas Flow Measurement (96FM-1)............................................................................................................4   B.   Gas Fuel Auxiliary Stop Valve (VS4-1)...................................................................................................4   C.   Stop/Speed Ratio Valve (VSR-1)..............................................................................................................4   D.   Gas Fuel Control Valves (VGC-1, VGC-2, VGC-3, VGC-4)...................................................................5   E.   Gas Purge Block Valves (VA13-1, VA13-2, VA13-20, VA13-21, VA13-3, VA13-4, VA13-23, VA12-24).............................................................................................................................................................5   F.   Gas Purge Pressure Ratio Monitoring (96GN-1, 96GN-2, 96GN-3, 96GN-4).........................................5   III.   OPERATION.................................................................................................................................................5   A.   General......................................................................................................................................................5   B.   Pre-start Conditions...................................................................................................................................7   C.   Startup and Loading Operation.................................................................................................................8   IV.   CONTROL...................................................................................................................................................12   A.   P2 Pressure Control.................................................................................................................................12   B.   Gas Flow and Split Control.....................................................................................................................15   C.   Gas Fuel Temperature Compensation.....................................................................................................16   D.   Gas Purge Control...................................................................................................................................17   V.   PROTECTION............................................................................................................................................17   A.   P2 Pressure Control Protection and SRV Position Control Protection...................................................18   B.   Fuel Temperature and Modified Wobbe Index Protection......................................................................18   C.   Independent Flow Path Purge Protection................................................................................................19   LIST OF FIGURES Figure 1. DLN2.6+ Fuel Nozzle Arrangement.......................................................................................................6   Figure 2. Gas Fuel Leak Test Function Block Diagram.......................................................................................10   Figure 3. SRV P2 Pressure Control Algorithm Diagram.....................................................................................13   Figure 4. SRV Speed Ratio Valve Control Schematic.........................................................................................14   Figure 5. GCV Control Algorithm Diagram........................................................................................................15   Figure 6. GCV Control Schematic.......................................................................................................................16   LIST OF TABLES Table 1. DLN2.6+ Mode Staging Diagram............................................................................................................7   Table 2. Protective levels and actions for the Gas Fuel System – Gas Pressure..................................................18   Table 3. Independent Flow Path Purge Protection...............................................................................................20    GEK 111712 Control and Protection Articles DLN2.6+ Gas Fuel System   4 I.   GENERAL The Gas Fuel System's function is to provide accurate and repeatable gas fuel flow, and flow split control for a multi-stream fuel injection system DLN2.6+. It also provides safe and reliable isolation from the gas fuel source. This unit use preheated Gas Fuel @ 365 deg F. The DLN2.6+ control hardware and the control system are described in this document. See Appendix 1. Simplified Schematic of the Gas Fuel System and Gas Purge System. The Safer case ID for this System is EP-S-767. II.   EQUIPMENT The Gas Fuel System consists of a gas flow metering tube, a gas fuel section of the accessory module (or a separate gas fuel module for single shaft units), and the gas turbine on-base equipment. This section houses both the gas fuel system, and gas fuel purge system. A brief description of the system’s overall major components is described below. See Gas Fuel System Articles for further details. A.   Gas Flow Measurement (96FM-1) A mass flow transmitter, 96FM-1 and Gas fuel meter tube / orifice (MG2-1) are used to measure natural gas flow. The device, 96FM-1 operates on the principle of measuring delta pressure across the gas fuel meter orifice, static gas pressure and gas temperature. These measured parameters establish the mass flow when the flow area ratio (beta) is known (constant). Gas Fuel Flow is only used for monitoring, and display in the gas turbine controls. B.   Gas Fuel Auxiliary Stop Valve (VS4-1) The Auxiliary Stop Valve is a butterfly type isolation valve that provides the required ANSI Class VI shutoff of the gas fuel supply. This valve is only required for units with performance heating of the gas fuel. For units without performance heating, the Stop/Speed Ratio Valve (SRV) provides the required ANSI Class VI shutoff capability and the Auxiliary Stop Valve is not required. This valve is pneumatically actuated with a spring close actuator design for fail-safe operation. When the system is pressurized or not tripped, the solenoid operated pilot valve (20VS4-1) directs instrument air to the actuator of the aux. stop valve. The valve actuator acts against the valve spring causing the valve to open. During a trip event the solenoid valve (20VS4-1) is de-energized which vents the pressurized air in the Stop Valve actuator to atmosphere. The compressed spring causes the Fuel Gas Auxiliary Stop valve to close. This valve opens during the gas turbine ignition sequence when the turbine is started. C.   Stop/Speed Ratio Valve (VSR-1) The SRV is a V-notch type ball valve that serves two functions. First it operates as the primary stop valve, making it an integral part of the protection system. The SRV is tripped closed by the hydraulic trip system via the directional trip relay VH5-1. This valve is hydraulically actuated with a spring close actuator for fail-safe operation. An emergency trip or flame out on a normal shutdown will trip the valve to its closed position, isolating gas fuel to the turbine. Closing the SRV can be achieved in two ways: dumping the hydraulic trip oil to the SRV, or driving the SRV closed electrically using the servo valve 90SR-1 with the control systems SRV position control loop. The other function of the SRV is pressure regulation. The control system uses the SRV to regulate the pressure (P2) upstream of the Gas Control Valves. This function is described in further detail in Section IV - Control.
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