DRAWING/DOCUMENT STATUS A FOR REFERENCE 2006-04-10 First issue Steenmeyer DATE DESCRIPTION Bearb Coord Rev Liedtke Sudhoff Geprüft Checked APPD PROJECT : CAMAU 750MW COMBINED CYCLE POWER PLANT OWNER : OWNER’S ENGINEER : PETRO VIETNAM CPMB CONTRACTOR : CONTRACTOR’S ENGINEER : LILAMA CORPORATION FICHTNER SUBCONTRACTOR’S NAME : SUBCONTRACTOR’S SUPPLIER : s KING AG POWER GENERATION DRAWING TITLE : System Description Fuel Oil PKZ UAS Contents Code Ursprung/Original Reg No UNID Urspr.-PKZ-Nr Orig.-PC Ursprung-Nr./Original-No Projekt/Project gezeich Drawn bearb Coord geprüft Checked Abtlg Dept PKZ/PC Datum Date Name 06-04-10 STEENM 06-04-10 LIEDTKE 06-04-10 SUDHOFF P415 sgd s AG POWER GENERATION CA MAU CCPP VIT154 Maßstab Scale UA/DCC Type Inhaltskennzeichen Contents Code N/A A4 Benennung/Title System Description Fuel Oil Dienstst./Dept P415 XS00 MBN Zähl.-Nr Reg.-No Index/Rev UNID 423216811 355056 Version A Blatt-Nr./Page-No CM1-L1-M-MBN.08-355056 Erstellt mit/designed with of Ersatz für Supersedes Gas Turbine Description of Auxiliary System Fuel Supply System (Liquid) Fuel Oil System Refer also to: List of Control Settings (SREL) List of Measuring Instruments List of Electrical Loads Equipment List P+I Diagram, Fuel Oil Purge Water System Natural Gas System Fuel Change Over Hydraulic Oil System Pneumatic System 3.1-0210 3.1-0220 3.1-0230 3.1-0240 3.1-4010 3.1-4800 3.1-5000 3.1-5200 3.1-9000 3.1-9820 Settings, limits and measuring ranges of the items of equipment listed here are given in the List of Measuring Instruments, the List of Electrical Loads, the Equipment List and the List of Control Settings (SREL) This description only gives guideline values permissible in the upper output range (above approx 50% of rated power) In premix mode, the diffusion burners are used to produce small pilot flames that are required to stabilize the premix flames This means that both subsystems are activated in premix mode A large portion of this equipment, including the fuel oil filters, injection pump, as well as the emergency stop and control valves, are compactly arranged on the fuel oil package The fuel oil system is designed as leak-tight as possible Whenever possible and appropriate, the main components of the fuel oil system are described in the following in the order in which the fuel oil passes through them Components in the Supply Line The reproduction, transmission or use of this document or its content is not permitted without express written authority Offenders will be liable for damages All rights, including rights created by patent grant or registration of a utility model or design, are reserved Venting Overview The fuel oil system supplies the burners with fuel oil and controls the volume of fuel injected into the combustion chamber On shutdown, it ensures that the flow of fuel oil is quickly and reliably shut off Supply of fuel oil to the system must meet various requirements, i.e the fuel oil must have a certain pressure, temperature, and mass flow rate and be of a precisely defined quality The requisite booster pump and treatment system as well as the fuel oil tank are described elsewhere The fuel oil system branches downstream of the injection pump to form two subsystems, one for each of the two burner groups The diffusion burners and the premix burners The diffusion system comprises a supply line and return line since, for technical reasons, only a portion of the fuel oil supplied to the diffusion burners is actually injected into the combustion chambers The premix system only has a supply line, i.e all of the fuel oil entering the premix burners is also injected into the combustion chambers Class: RESTRICTED Startup and shutdown of the GT on fuel oil is always performed in diffusion mode The premix system is inactive during operation in diffusion mode Diffusion mode is possible over the entire output range of the gas turbine In the upper output range, pollutant emissions and thermal stresses on materials are significantly lower in premix mode than in diffusion mode At low output in premix mode, there is a marked increase in CO emissions (unfavorable fuel-air ratio) and the flames become unstable Premix mode is therefore only Siemens AG Power Generation A venting line is connected at the highest point of the fuel oil line upstream of the duplex filters (MBN11AT001 and MBN11AT002) Any air which may have collected during standstill to form large bubbles is fed into the auxiliary return line via orifice MBN11BP001 An additional venting device is located in the upper portion of the filter Any air present as small bubbles in the flowing fuel oil, which may rise in the filters (through which the fuel oil slowly flows), is discharged by way of this vent and likewise fed into the auxiliary return line via orifice MBN11BP002 Shutoff valves MBN11AA501 and MBN11AA502 in the filter vent lines are always open during operation of the GT Sight glass MBN11CF501 is installed in the vent line downstream of the two orifices Filter The fuel oil filters (MBN11AT001 and MBN11AT002) remove all matter from the fuel oil that could damage downstream components such as the injection pump, fuel oil nozzles, and turbine blades Since these filters have a very fine mesh, it is necessary to pass the as-delivered fuel oil through a prefilter (which may comprise several stages) Doing so avoids the need for frequent changeover of the fuel oil filter for cleaning This filter is a duplex filter If the pressure drop due to fouling exceeds a certain level, an alarm is annunciated on local display MBN11CP501 of differential pressure switch MBN11CP001; changeover to the other filter element must then be made manually It is absolutely imperative to ensure that this filter has already been filled with fuel oil using valve MBN11AA252 After draining a sufficient volume of fuel oil via the respective valve, MBN11AA401 or MBN11AA402, the fouled filter element 3.1-4000-0623/1 0206E-X Gas Turbine Description of Auxiliary System can be removed from the filter housing and cleaned Then the filter housing itself must be cleaned prior to reinsertion of the clean filter element Bladder Accumulator for Damping Pressure Surges Opening the emergency stop valves, starting up and shutting down the injection pump, but in particular, rapid closing of the emergency stop valves, induces sudden flow velocity changes in the fuel oil lines that can cause pressure surges of considerable amplitude Bladder accumulators MBN11BB001 and MBN11BB002 dampen these pressure peaks Injection Pump The reproduction, transmission or use of this document or its content is not permitted without express written authority Offenders will be liable for damages All rights, including rights created by patent grant or registration of a utility model or design, are reserved Injection pump MBN12AP001 boosts fuel oil pressure to the level required for atomization in the burners This pump is a centrifugal pump If at least two of the pressure measuring transducers MBN12CP101, MBN12CP102, MBN12CP103 signal that pressure upstream of the pump is too low (for example 1.5bar Fuel Oil Lines to the Combustion Chamber (Diffusion) Fuel oil from the diffusion burner supply line is distributed to the 24 burners via a manifold mounted directly on the combustion chamber Diffusion Burner Supply Line Emergency Stop Valve The purge water line, which supplies water for purging the manifold and the burners following the shutdown of the diffusion system, is connected at the highest point of the diffusion burner supply line upstream of the manifold (cf description “Purge Water System”) That portion of the diffusion burner supply line is shaped like a siphon This ensures that residual purge water or condensate from the seal air does not flow into the diffusion burner supply line after shutdown of the diffusion system If this occurred, the fuel oil would rise, pass through the manifold, and enter the burners, where it would be coked by the high material temperatures The fuel oil diffusion burner supply line emergency stop valve MBN14AA051 is used to enable or disenable the flow of fuel oil to the diffusion burners during startup and shutdown, and during changeover from fuel oil to natural gas operation and vice versa It is also closed in In addition to the diffusion burner supply line, the seal air line fitted with pneumatically-actuated seal air ball valve MBN34AA051 is also connected to the manifold The seal air ball valve opens after the diffusion system is shut down and purging is completed During operation on Diffusion System Components Class: RESTRICTED Diffusion Burner Supply Line Control Valve Siemens AG Power Generation 3.1-4000-0623/3 0206E-X Gas Turbine Description of Auxiliary System Class: RESTRICTED The reproduction, transmission or use of this document or its content is not permitted without express written authority Offenders will be liable for damages All rights, including rights created by patent grant or registration of a utility model or design, are reserved natural gas, cooled air from the gas turbine compressor outlet is fed into the manifold so that air flows through the fuel oil diffusion burners, preventing hot combustion gasses from the combustion chamber from egression into the fuel oil diffusion system To prevent coking due to the compressor outlet temperature of about 400°C, seal air is cooled between the compressor outlet and the seal air ball valve Pressurized seal air also passes through orifice MBN36BP001 into the return line manifold to help ensure that check valves MBN36AA201 through MBN36AA224, which close due to the weight of their disks, remain closed during natural gas operation This prevents the circulation of hot gas between the burners which would normally occur due to slight differences in pressure in the combustion chamber The diameter of the orifice is so small that only insignificant cross flows of fuel oil pass through during operation on fuel oil To prevent fuel oil from flowing from the manifold into the seal air line and from there to the compressor outlet (risk of ignition!) during operation on fuel oil (postulated defective seals in one of the seal air ball valves), a leakage oil line is provided to drain the space between the ball and valve body Solenoid valve MBN34AA002 is open during fuel oil operation, allowing any leakage oil to flow through orifice MBN34BP001 into leakage oil tank MBN60BB001 If the amount of leakage oil is so great that pressure upstream of this orifice exceeds a defined limit, the fuel oil system trips when at least two of the pressure switches MBN34CP001, MBN34CP002, MBN34CP003 operate The fuel oil returning from the diffusion burners flows through the branch lines into the return line manifold In the case of a fuel oil supply fault to one of the burners during operation on fuel oil operation (for example swirl chamber inlet slits clogged), the swing check valves prevent the high pressure of the fuel oil in the return line from causing fuel oil to pass from the return line manifold through the branch line of the defective burner and into the combustion chamber unswirled, where it could cause damage The return line to the fuel oil package has a connection to the purge water system When changing over from operation on NG to operation on FO, the return line from the fuel oil diffusion burners is filled with purge water prior to opening the return line ESV (see below) When the fuel oil system is shut down, air pockets which may form at the highest point of the return line are forced into the supply line via orifice MBN36BP001 This minimizes the amount of hot gas that could enter the return line in the first few seconds after opening the return line emergency stop valve Impermissible heating of the burners is prevented in this way Siemens AG Power Generation Fuel Supply System (Liquid) Fuel Oil System Diffusion Burner Return Line Emergency Stop Valve Return line emergency stop valve MBN52AA051 performs the same function in the fuel oil return line as the diffusion burner emergency stop valve MBN14AA051 in the supply line This valve is closed rapidly and reliably by spring force and opened hydraulically (cf description “Hydraulic Oil System”) If an “OPEN” command is issued to the diffusion burner supply line ESV, the return line ESV must open within a short time, otherwise the entire flow through the diffusion burner supply line would be injected into the combustion chamber and this is not permissible Fuel oil system trip is triggered if the return line ESV does not open within a short time Diffusion Burner Return Line Control Valve The task of the diffusion burner return line control valve MBN53AA151 is to regulate the return line flow This, in turn, determines the volume of fuel injected, which is the difference between the supply line flow and the return line flow The control valve is actuated hydraulically (cf description “Hydraulic Oil System”) It also functions as a leak-tight second shutoff element for the return line Whenever the return line emergency stop valve is closed, the associated control valve also closes Premix System Components Premix Burner Emergency Stop Valve Similar to the diffusion burner supply line emergency stop valve, the task of the premix burner emergency stop valve MBN23AA051 is to enable or disenable the supply of fuel oil to the premix burners Furthermore, it is closed in the event of faults requiring immediate shutdown of the gas turbine The emergency stop valve is opened hydraulically (cf description “Hydraulic Oil System”) It is closed very rapidly and reliably by spring force Premix Burner Supply Line Control Valve Like the diffusion burner supply line control valve, the premix burner control valve MBN23AA151 has two functions As a control valve, it regulates the amount of fuel oil supplied to the premix burners In addition, it also has a trip function, i.e spring force is used to very rapidly and reliably close this valve concurrent with the premix burner emergency stop valve when trip is triggered The control valve is actuated hydraulically (cf description “Hydraulic Oil System”) 3.1-4000-0623/4 0206E-X Gas Turbine Description of Auxiliary System Permanent-element Fuel Oil Filter (Premix) Despite filtering of the fuel oil, isolated instances of contamination may occur, particularly after an extended outage of the fuel oil system To protect the fuel oil burners against impermissible soiling, permanentelement, fine-mesh filter MBN41AT001 is installed upstream of the fuel oil premix burner manifold If the differential pressure at filter MBN41AT001 exceeds the setting of pressure transducer MBN41CP101 (for example >1.5bar), changeover is made from fuel oil premix mode to fuel oil diffusion mode In addition, the pretrip alarm “Differential pressure at fuel oil premix filter too high” is annunciated The reproduction, transmission or use of this document or its content is not permitted without express written authority Offenders will be liable for damages All rights, including rights created by patent grant or registration of a utility model or design, are reserved Fuel Oil Line to the Combustion Chamber (Premix) The premix burner supply line with purge water connection and the seal air line (equipped with pneumatically-actuated ball valve MBN44AA051) are identical, in terms of purpose and configuration, to the fuel oil diffusion burner supply line to the combustion chamber A drain line equipped with two drain valves MBN45AA401 and MBN45AA402 is connected to the lowest point of the premix burner manifold Their function is described in greater detail below (cf “Trip during Operation in Premix Mode”, and “Premix Burner Back Purge”) Burner Pressure Monitoring Proper burner function requires sufficient pressure at the burner inlet (diffusion, premix burner supply lines) to atomize the fuel oil Otherwise, unburned fuel oil could enter the combustion chamber (explosion hazard!) or hot combustion chamber gases could flow in the reverse direction into the burners and the fuel oil system Consequently, the differential pressure between the fuel oil supply line and the combustion chamber is monitored For reasons of simplicity, the compressor outlet pressure, which is only slightly higher, is used instead of the combustion chamber pressure This parameter is measured by pressure transducers MBA12CP101 and MBA12CP102 Class: RESTRICTED Pressure transducers MBN14CP101 and MBN14CP103 in the diffusion burner supply line and pressure transducers MBN23CP101 and MBN23CP102 in the premix burner supply line are provided for measuring fuel oil pressure at the burners Differential pressure is calculated by the I&C system from these instrument readings If pressure drops below a certain differential pressure limit (appr 10bar in the Siemens AG Power Generation Fuel Supply System (Liquid) Fuel Oil System diffusion burner supply line and 2bar in the premix burner supply line, 2-of-3 logic), either fuel oil system trip or premix system partial trip is triggered Pressure Relief of Diffusion and Premix Systems (Vented Oil Seal) When the GT is at standstill, there is a danger that a slight amount of leakage oil may enter the combustion chamber via the ESVs due to pressure prevailing in the supply line or to the tank back pressure in the return line An impermissibly large amount of oil could accumulate in the GT during a very lengthy outage To prevent this, the piping sections between the premix burner supply line valves (MBN23AA051, MBN23AA151), the diffusion burner supply line valves (MBN14AA051, MBN14AA151), and the diffusion burner return line valves (MBN52AA051 and MBN53AA151) is depressurized by opening solenoid valves MBN14AA501, MBN23AA501 and MBN52AA501 This diverts any oil leakages that occur into the leakage oil tank Very small diameter orifices installed in the relief lines (MBN23BP001, MBN14BP001, MBN52BP001) ensure that only an insignificant amount of oil can enter the leakage oil tank if a solenoid valve spuriously opens during fuel oil operation Leakage Oil Tank Leakage oil from the shutoff ball valves of the diffusion and premix burner seal air lines, the premix burner manifold drain line, the vented oil seal venting lines and from various drain lines is collected in the leakage oil tank MBN60BB001 This tank is provided with a venting line that opens to the atmosphere Leakage oil pump MBN60AP001 forwards oil leakages into the auxiliary return line It is automatically started up and shut down by level monitor MBN60CL001 Level switch MBN60CL002 annunciates “Leakage oil system faulted” if the leakage oil level exceeds a certain limit Burner Assembly The gas turbines 24 burner assemblies (MBM12AV001 through MBM12AV024) each comprise several individual burners In addition to the two fuel oil burners (diffusion burners and premix burners), the burner assemblies also include means for operation on natural gas (natural gas diffusion burner, natural gas premix burner, natural gas pilot burner) All burner assemblies are completely identical They are uniformly distributed around the circumference to achieve the most uniform possible temperature field in the annular combustion chamber 3.1-4000-0623/5 0206E-X Gas Turbine Description of Auxiliary System The reproduction, transmission or use of this document or its content is not permitted without express written authority Offenders will be liable for damages All rights, including rights created by patent grant or registration of a utility model or design, are reserved The fuel oil diffusion burners atomize the fuel oil so that it can burn completely in the combustion chamber The fuel oil fed through the diffusion burner supply line enters the swirl chamber of the diffusion burner nozzles where it is split into a partial flow that is injected into the combustion chamber and a partial flow that flows to the fuel oil return line The split is a function of the backpressure in the fuel oil return line, which in turn is determined by the lift of diffusion burner control valve MBN53AA151 With a widely opened control valve, return line pressure is low; consequently, a large volume of oil flows into the return line and only a small volume is injected A nearly closed control valve results in a high return line pressure Only a small volume of oil is returned and a correspondingly large volume of fuel oil is injected The amount of fuel oil entering the swirl chambers of the burner nozzles varies only slightly with the amount of fuel injected The injected jet of oil thus has a nearly constant turbulence, ensuring good atomization over the entire operating range A correspondingly large amount of oil is supplied to the burners even during startup Whereas the diffusion oil is injected directly into the combustion chamber via a central nozzle in the burner assembly, the premix oil is atomized using numerous small nozzles arranged in the primary air duct (diagonal swirler) of the burner assembly This thoroughly mixes the air and fuel prior to entry into the combustion chamber, hence the name premix combustion Startup, Fuel Oil Operation, Shutdown The sequence in which items of fuel oil system equipment are operated or actuated during startup, operation and shutdown is described below All of these processes are fully automatic Startup Class: RESTRICTED The booster pump system is started up with the gas turbine at standstill (or in turning gear mode) The diffusion burner supply line and return line control valves are actuated to their startup lift settings The startup equipment (generator and startup frequency converter) begins to accelerate the gas turbine If at least two of the pressure measuring transducers MBN12CP101, MBN12CP102, and MBN12CP103 upstream of the injection pump signal sufficient pressure, the injection pump is started when the gas turbine reaches a certain speed Since the emergency stop valves are still closed, the fuel oil delivered by the injection pump flows through the minimum flow line into the return line Fuel oil pressure downstream of the pump increases to its maximum Siemens AG Power Generation Fuel Supply System (Liquid) Fuel Oil System When the gas turbine has reached a speed of S.TURB.31 (for example 11% of rated speed), ignition gas is fed into the natural gas diffusion burners and ignited Thereafter the diffusion burner supply and return line emergency stop valves are simultaneously opened so that fuel oil flows through the diffusion burners and is ignited by the ignition flames Once a certain speed is exceeded, the ignition gas flow is shut off; the fuel oil diffusion flames burn stably on their own At a turbine speed of S.TURB.55 (for example 35% of rated speed), the volume of fuel oil injected is increased with a linear time function At turbine speeds above S.TURB.56 (for example 60% of rated speed), the slope of this time function becomes greater and the volume of fuel oil injected increases more rapidly When rated speed is reached, the speed controller assumes control of the diffusion burner control valve actuators The turbinegenerator is then synchronized with the electric power grid Diffusion Mode After synchronizing, the lift of the diffusion burner control valves and thereby the volume of fuel oil injected are set by the load controller Initially the gas turbine is operated in diffusion mode The diffusion burner supply line control valve is used to regulate the amount of fuel oil supplied in accordance with a stored characteristic as a function of the injection set point By so doing, the mass flow in the diffusion burner supply line is kept within a range favorable for the pumps and burners The diffusion burner return line control valve regulates the amount of fuel oil actually injected The changeover to premix mode can be made once output exceeds a certain level, for example 50% of base load Filling of the Fuel Oil Premix System The supply line downstream of the premix burner control valve could be empty after extended outages, major inspections and on initial startup of the fuel oil premix system Automatic filling of the premix burner supply line is required, if the gas turbine has not operated in fuel oil premix mode for the last 24 hours When filling is required, before the changeover from diffusion mode to premix mode the premix burner emergency stop valve opens, and the premix burner control valve is set to its minimum lift setting The fuel oil premix burner supply lines fill with fuel oil in the direction of the combustion chamber The gas turbine is monitored during this time “Fuel oil premix system trip during initial filling” is triggered if a power output increase of % and thus an 3.1-4000-0623/6 0206E-X Gas Turbine Description of Auxiliary System increased input of fuel into the combustion chamber is detected The gas turbine changes back into fuel oil diffusion mode (see below), the premix burner supply line is now completely filled with fuel oil and the gas turbine can now be changed over to fuel oil premix mode Changeover from Diffusion Mode to Premix Mode The reproduction, transmission or use of this document or its content is not permitted without express written authority Offenders will be liable for damages All rights, including rights created by patent grant or registration of a utility model or design, are reserved Once the conditions for changeover to premix mode operation have been satisfied, the premix burner seal air ball valve MBN44AA051 is closed and the premix burner control valve is actuated to its startup lift setting The premix burners must first be cooled with water to prevent the inflowing fuel oil from coking (the premix burner nozzles are surrounded by hot air supplied by the compressor at a temperature of approx 400°C) To this, the manifold is filled with water via the purge water line In the process, a small amount of water enters the combustion chamber via the lower burners As soon as the manifold is completely filled with water, the supply of purge water is shut off and the ESV opened The flow of oil initially forces the water through the premix burner nozzles, which cools these items After a brief transition period, all nozzles are supplied with oil and stable premix flames form The control valves for fuel supply to the premix and diffusion burners are then actuated such that although the total volume of oil injected remains constant, the premix fraction increases and the diffusion fraction decreases Changeover is completed when the diffusion burners only receive the minimum flow of fuel that is necessary for formation of the pilot flames Premix Mode In premix mode, the amount of fuel required for the desired output is controlled using the premix burner control valve, whereas the diffusion system supplies the minimum amount of fuel required for the pilot flames Class: RESTRICTED Changeover from Premix Mode to Diffusion Mode To change back to diffusion mode, the diffusion fraction is increased and the premix fraction decreased, initially maintaining a constant output A premix system trip is triggered shortly before the point at which stable premix flames are no longer possible The supply of purge water to the premix system is activated shortly before closing the premix burner ESV MBN23AA051 and the premix CV MBN23AA151 Pressure at the premix nozzles (produced by the purge water pump) still exists after trip This ensures that any oil remaining is displaced from the burners during the first seconds of the purge Siemens AG Power Generation Fuel Supply System (Liquid) Fuel Oil System operation, fully atomizes, and does not form an oil film on the burner parts which could cause coking After the purging operation has been completed, the manifold remains filled with purge water to the height of the outlet of the lowest burner The premix burner manifold drain valves MBN45AA401 and MBN45AA402, are opened briefly during the purging operation This also purges the premix burner manifold drain line with water, ensuring that during subsequent diffusion mode operation, no oil can reenter the premix burners from this line, which would cause clogging of the premix burner nozzles in the lowest burners Upon completion of purging, the premix burner seal air ball valve opens, i.e cooled air from the compressor outlet is supplied to the premix burners The gas turbine is now running in diffusion mode Shutdown First the output of the GT (which is operating in diffusion mode) is reduced The generator is disconnected from the grid at a very low positive output Fuel oil system trip is then triggered, i.e the diffusion burner emergency stop and control valves in the supply and return lines close and the injection pump is shut down The diffusion burners and their manifold are then purged with water With the return line ESV, and return line CV, the water forces the remaining fuel oil out of the supply lines into the return line The gas turbine coasts down without combustion until it reaches turning speed The fuel oil system is ready for the next startup Trip During Operation in Premix Mode If a fault makes it necessary to immediately shut down the GT during operation in premix mode, the premix and diffusion burner emergency stop and control valves are closed simultaneously and the injection pump is shut down During the subsequent purging operation, substantial amounts of oil still in the lines must be prevented from entering the combustion chamber This oil could undergo uncontrolled ignition on the hot walls or enter the exhaust system as unburned fuel oil mist Consequently, first the diffusion system alone is purged as described under “Shutdown” In doing so, most of the oil is forced into the return line At the same time, premix burner manifold drain valves MBN45AA401 and MBN45AA402 are opened, and the remaining (low) combustion chamber pressure forces the remaining oil from the premix burner manifold and the premix burners into the leakage oil tank The solenoid valves close after a defined delay 3.1-4000-0623/7 0206E-X Gas Turbine Description of Auxiliary System Once purging of the diffusion system has been completed, the premix system is purged by opening the premix purge water solenoid valve for a defined period Premix Burner Back Purge The reproduction, transmission or use of this document or its content is not permitted without express written authority Offenders will be liable for damages All rights, including rights created by patent grant or registration of a utility model or design, are reserved The premix burner back purging is to remove coke residuals from the fuel oil premix burner should they occur Obstructed premix burner nozzles cause unbalanced temperature loads upstream of the turbine blades The premix burner back purge sequence takes place prior to a switch over from fuel oil diffusion mode to fuel oil premix mode, therefore the gas turbine has to run for a certain time in fuel oil diffusion mode, so that the fuel oil premix burners are sufficiently hot Potential residues on the hot inner premix burner surface may first be detached by quenching with water For this purpose, the premix burners are filled with water via the premix purge water solenoid valves, as described above The premix seal air ball valve MBN44AA051 remains closed during the purging process After the quenching, the purge water valves are closed and the premix manifold drain valves MBN45AA401 and MBN45AA402 are opened Compressor discharge air now forces the detached coke residuals to leave the premix burners and the premix manifold into the fuel oil leakage tank MBN60BB001 The process is directly repeated one more time After this the premix burner system is filled with water for the third time, the premix emergency stop valve MBN23AA051 is opened, and the normal transfer to premix operation begins Correct operation of the premix burner back purge sequence is monitored by the temperature measuring point MBN45CT101A/B (duplex PT100 resistance temperature detector) A warning message is issued at high temperatures (> 100°C), excessive temperatures (> 150°C) leads to shutdown of the gas turbine in 2-of-2 evaluation and MBN45AA402, remains open when the premix burner back purge sequence is not active Upstream of the orifice MBN45BP001, the pressure is monitored via the pressure switch MBN45CP001 to detect a possible leak of the drain valves Fuel Changeover The following paragraph only gives a brief overview A detailed description of the fuel changeover from operation on natural gas to fuel oil is given in description “Fuel Change Over” To make the changeover from natural gas operation to fuel oil operation, the gas turbine must first be operated in natural gas premix mode Automatic changeover can be made to fuel oil diffusion mode when the gas turbine is operating in the requisite output window (approx 60% to 80%) Assuming that fuel oil premix mode and a specific output have been selected, automatic changeover to this mode and output can be initiated once changeover to operation on fuel oil in diffusion mode has been completed To make the changeover from fuel oil operation to natural gas operation, the gas turbine must first be operated in fuel oil diffusion mode Once the gas turbine is running in fuel oil diffusion mode in the requisite output window (approx 60% to 80%), the machine can be automatically changed over to natural gas premix mode Miscellaneous In addition to several optional measuring points, the following local pressure indicators are provided for maintenance and checking purposes: differential pressure across the fuel oil filter (MBN11CP501), pressure upstream of the injection pump (MBN12CP501), pressure downstream of the injection pump (MBN12CP502), and pressure in the diffusion return line (MBN52CP101) Valves are provided at various locations for draining piping and certain components of the fuel oil system These drain valves must remain closed whenever the gas turbine is running Class: RESTRICTED The solenoid valve MBN45AA501, which is installed between the premix manifold drain valves MBN45AA401 Fuel Supply System (Liquid) Fuel Oil System Siemens AG Power Generation 3.1-4000-0623/8 0206E-X ... trips Seal medium is pumped by the seal medium pump from storage tank MBN12BB010 into the bladder accumulator MBN12BB012 which is charged with nitrogen and perform buffer storage functions Seal... sections between the premix burner supply line valves (MBN23AA051, MBN23AA151), the diffusion burner supply line valves (MBN14AA051, MBN14AA151), and the diffusion burner return line valves (MBN52AA051... combustion chamber pressure This parameter is measured by pressure transducers MBA12CP101 and MBA12CP102 Class: RESTRICTED Pressure transducers MBN14CP101 and MBN14CP103 in the diffusion burner