dgsdes 800623 mbn9a a01 b 000

DRAWING/DOCUMENT STATUS

A

FOR REFERENCE

2006-04-10

First issue

Steenmeyer

DATE

DESCRIPTION

Bearb.
Coord.

Rev.

Liedtke

Sudhoff

Geprüft
Checked

APPD.

PROJECT :

CAMAU 1 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 1 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

0 of 8
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

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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

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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
<1bar), pump startup is prevented. If an additional limit

(for example <0.1bar) is violated during plant operation,
the pump is automatically shut down, causing the fuel oil
system to trip due to declining fuel oil pressure upstream
of the burners. This protective shutdown is necessary due
to the risk of pump cavitation associated with insufficient
intake pressure.
The pressure upstream of the pump can be read off
pressure gauge MBN12CP501; pressure gauge
MBN12CP502 indicates the pressure downstream of the
pump.
Bearing temperatures are monitored at all four
bearings of the pump and electric motor using dualelement temperature instruments (MBN12CT105 to
MBN12CT108). If both elements of any one of these
bearing temperature measuring points register excessive
temperature, the pump is shut down. If one element of a
given measuring point is faulted and the other signals
excessive temperature, this also triggers pump shutdown.
A pre-trip alarm is annunciated if both elements of a pair
are faulted.

Class: RESTRICTED

Seal Medium System for the Fuel Oil Injection
Pumps
The shaft of the fuel oil injection pump is equipped on
both the intake and discharge sides with a double
floating-ring shaft seal. The narrow space between the
floating-ring seals is pressurized with seal medium. The
seal medium pressure is greater than the fuel oil pressure
within the pump near the floating-ring seal, preventing the

Siemens AG
Power Generation

Fuel Supply System (Liquid)
Fuel Oil System

escape of fuel oil from the injection pump via the shaft
glands. A mixture of water and glycol is used as the seal
medium. If the floating-ring seal is damaged, seal
medium either escapes from or penetrates into the pump,
from where it is fed to the burners. Fuel oil cannot escape
to the surroundings, however.
Each floating-ring seal is connected with a heat
exchanger (MBN12AH001 and MBN12AH002). A helical
rib on the pump shaft circulates seal medium within the
respective floating-ring seal. The seal medium
temperature increases as it passes through the floatingring seal. This thermal energy is transferred to another
loop of cooling water by the heat exchangers. To ensure
that cooling water does not ingress into the seal medium,
the system pressure of the coolant loop must be lower
than that of the seal medium.
Temperature
switches
MBN12CT111
and
MBN12CT112 upstream of the heat exchangers monitor
the temperature of seal medium returning to the
respective heat exchanger. Supply and adjustment of
cooling water shall be provided in the feedline or

returnline of the coolant loop outside of the fuel oil
package.
Flowmeters MBN12CF111 and MBN12CF112 monitor
the respective seal medium circle for leaks. If the seal
medium flow exceeds a certain limit, the fuel oil injection
pump is shut down and the gas turbine 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
medium pump is started up when pressure switch
MBN12CP014 detects that pressure has dropped below a
previously-defined setting. When the requisite pressure
level has been restored, the pump is shut down. Release
for pump startup is given by level monitor MBN12CL011
in the storage tank MBN12BB010. Tank level can be
checked locally using sight glass MBN12CL511.
Pressure control valve MBN12AA161 ensures that
pressure does not drop below a certain level (e. g.
26 bar). If pressure declines, seal medium is allowed to
flow out of the bladder accumulator downstream of the
pressure control valve. The pressure that triggers supply
of medium from the accumulator is 2 bar higher than the
pressure that triggers shutdown of the fuel oil injection
pump. If pressure drops below the setting of two of the
three pressure switches (MBN12CP011/012/013), the
fuel oil pump is shut down and the gas turbine trips.

Temperature Monitoring
Due to the fact that the temperature level in the fuel oil

system increases, particularly at low fuel oil flow rates the

3.1-4000-0623/2
0206E-X


Gas Turbine
Description of Auxiliary System

fuel oil temperature is also measured by a resistance
thermometer MBN11CT101 at the fuel oil package inlet. If
the temperature in the fuel oil system is high (e. g. >
40°C), an alarm is annunciated.

Fuel Supply System (Liquid)
Fuel Oil System

the event of faults requiring immediate turbine shutdown
(for example over speed trip).
The emergency stop valve is opened hydraulically (cf.
description “Hydraulic Oil System”). It is closed very
rapidly and reliably by spring force.

Measurement of Pump Discharge Pressure
Pump discharge pressure is determined using
pressure transducers MBN13CP101, MBN13CP102, and
MBN13CP103. This measurement is required for various
open- and closed-loop control functions.

Minimum-flow Orifice and Shutoff Ball Valve in

the Bypass Line

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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

When the injection pump MBN12AP001 is running
and the emergency stop valves MBN14AA051 and
MBN23AA051 have closed, pneumatically-actuated ball
valve MBN12AA053 in the bypass line is opened by
spring force to direct the flow into the auxiliary return line.
Minimum-flow orifice MBN12BP004, which is installed
in the bypass line upstream of ball valve MBN12AA053,
is designed such that about 20% of the volumetric flow of
the injection pump operating point can be routed through
the bypass line when the ball valve is open.
After ESV MBN14AA051 has opened, this ball valve
is closed pneumatically by actuator MBX98AS007.
Spring force keeps the ball valve open when the gas
turbine is not running, because the supply of compressed
air is shut off.

Safety valve
Safety valve MBN13AA181 prevents pressure
downstream of the injection pump from reaching
impermissible levels.
Impermissible pressure increases can occur if highdensity fuel oil is used and / or if pump speed is
excessive, or if shutoff ball valve MBN12AA053 in the

minimum-flow line is spuriously closed when the
emergency stop valves MBN14AA051 and MBN23AA051
are closed. The safety valve opens at a pressure of
approx. 152bar.

The diffusion burner supply line control valve
MBN14AA151 has two functions. As a control valve, it
regulates the amount of fuel oil supplied to the diffusion
burners. This valve also has an emergency stop function,
i.e. when trip is triggered, it is closed very rapidly and
reliably by spring force, as is the diffusion burner supply
line emergency stop valve.
The control valve is actuated hydraulically (cf.
description “Hydraulic Oil System”).

Permanent-element Fuel Oil Filter (Diffusion)
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 MBN31AT001 is installed
upstream of the fuel oil diffusion burner manifold.
Controlled shutdown of the GT is initiated if the
differential pressure at filter MBN31AT001 exceeds the
setting of pressure transducer MBN31CP101, 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 2 % 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

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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 do
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

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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