Description
The main condensate system, as part of the steam generating cycle, is the section concerned with the circulation of boiler feed water from the atmospheric condenser via the observation tank and cascade/filter tank to the main feed pumps.
The drains from the steam services are normally led to the atmospheric condenser , which in turn drains to the observation tank and then to the cascade/filter tank. The level of the cascade tank is maintained by a float switch that operates a solenoid valve providing make up water from the storage tank. The condition of the condensate is monitored by a high salinity alarm.
The oil detecting alarm detects hydrocarbon contamination and the returns can be manually diverted to the waste oil tank. Any floating sediment can be drained through a scum line to the waste oil tank or the observation tank can be drained to the bilge holding tank. A weir in the observation tank outlet to the cascade tank prevents oil being carried over . The tank has a high and low level alarm.
Water from the cascade/filter tank provides the main feed pumps with a positive inlet head of pressure to the pump suctions.
The condensate outlet temperature from the atmospheric condenser should be maintained between 75°C and 90°C. This can be done by manipulating some of the drains to bypass the condenser and dischar ge directly to the cascade tank. A steam heating coil is provided in the cascade tank should extra heating be required.
Procedure for Preparing the Main Condensate System for Operation:
See illustrations 2.3.2a, 2.3.3a and 2.4.5a for valve positions mentioned below . a) Ensure that the pressure gauge and instrumentation valves are
open.
b) Fill the cascade tank from the distilled tank.
c) Check the correct operation of the level control valve.
d) Set up the valves as in the following table.
Position Description Valve
Open Outlet V alve from Atmospheric Condenser SL3 Closed Atmospheric Condenser Bypass V alves SL10, SL12
& SL13
Closed Observation T ank Drain V alve RL45
Open F.W. Make Up V alves to the Cascade T ank QG51
Open Run Down V alve from Distilled T ank QG24
Closed Observation T ank Scum V alve to Waste Oil T ank SL5
Open Outlet to Feed Pumps RL1
The feed pumps and boiler can now be put into operation.
Oil Contamination
If oil contamination occurs, divert the returns to the waste oil tank. Check the drain on the drain traps on all the steam services until the defective service is located, then isolate for repair .
After repair , flush the drain line of the defective service and clean drain trap.
Clean the observation tank and the oil content monitor probe.
2.3.2 Heating Drains Systems
Description
Condensate from the auxiliary steam services is returned to the cascade tank, through a seawater cooled atmospheric condenser and observation tank. The condensate is then returned to the feed water system. As there is a possibility of contamination from hydrocarbons from oil heating services, the drains are segregated and checked in the observation tanks before returning to the system.
All services can return to the cascade tank through the atmospheric condenser . In the interest of ef ficiency some drains can be fed directly to the observation tank or cascade tank to maintain the operating temperature. The condenser can be bypassed during maintenance, where oil heating drains are led to the observation tank and other services to the cascade tank.
Procedure for Preparing the Drains System for Operation
a) Ensure that the pressure gauges and instrumentation valves are open.
b) Set up the valves for the services required as in the following table:
Position Description Valve
Open Atmospheric Condenser Outlet V alve SL3
Open Drain V alve from Boiler Heating SL45
Open Drain V alve from Accommodation A.C. SL44 Open Drain V alve from Boiler F .O. and T ank Heating SL12
Open Drain V alve from Deck Seal SL48
Open Drain V alve from Car go Tank Heating SL1 Open Drain V alve from T ank Cleaning Heater SL07 Open Drain V alve from Purifier Heaters,
Double Bottom T anks and F .O. Storage T anks SL11 Open Drain Valve from M.E. F .O. and Auxiliary ServicesSL54 Open Atmospheric Condenser Cooling W ater Inlet V alveQA12 Open Atmospheric Condenser Cooling W ater Outlet V alveQA13 c) The various services can now be put into operation as required, by
opening the associated drain trap inlet and outlet valves.
Excessive temperature at the cascade tank would indicate a defective drain trap. Services should be isolated in turn until the defective trap is located.
P
Feed Water Cascade Tank
To Bilge Water Tank
To Bilge Water Tank From Atmospheric
Condenser
LAH
TI LAL SL5 LI
Main Feed Water Pump
13kg/cm2 Auxiliary Feed
Water Pump 11kg/cm2
P
P
PS P
No.2 No.1
P P
P P
No.2 No.1
From Chemical Dosing Station From Chemical
Dosing Station
Oil-Fired Boiler 25000 kg/h Exhaust Gas
Boiler 900 kg/h
Illustration 2.3.3a Boiler Feed Water System
Key
Feed Water
RL28
RL29
RL14
RL11 RL10
RL9 RL8 RL3 RL2
RL7
RL20
RL15 RL42
RL16
RL6
RL4
RL5
SL3
RL1
RL45
Fresh Water
2.3.3 Boiler Feed System
Description
The boiler feed system is the section of the steam generating plant which circulates feed water from the cascade tank into the steam drum of the boiler via the boiler feed water pumps and the feed water regulator.
The feed water flow is automatically controlled by the feed water regulating valve in proportion to the variation in water level in the steam drum.
Two boiler feed pumps take suction from the cascade tank and supply the boiler at a rate of 31m3/h at 13 kg/cm2. Each pump returns a small proportion of the discharge back to the cascade tank through an orifice, which prevents pump overheating when the feed water regulator is closed and when the boiler is on low load.
Feed water is supplied to the boiler through the feed water regulator. Feed water can also be supplied to the boiler using a separate auxiliary line, which can be used in an emergency. The standby feed pump will cut in on the failure of a running unit.
Two exhaust gas boiler feed pumps take suction from the cascade tank and supply the exhaust gas boiler at a rate of 1.35m3/h at 11 kg/cm2.
Boiler water chemical treatment is administered by injecting direct to the boiler drum using a chemical dosing unit.
Procedure for Preparing the Main Boiler Feed System for Operation:
a) Ensure pressure gauge and instrumentation valves are open.
b) Set up the valves as in the following table.
Position Description Valve
Open Feed Pump Suction Valve from Cascade Tank RL01 Open No.1 Boiler Feed Pump Suction Valve RL02 Open No.2 Boiler Feed Pump Suction Valve RL03 Open No.1 Boiler Feed Pump Recirculating Valve RL04 Open No.2 Boiler Feed Pump Recirculating Valve RL05 Open No.1 Boiler Feed Pump Main Feed Discharge Valve RL06 Open No.2 Boiler Feed Pump Main Feed Discharge Valve RL07 Open Crossover Between Main and Auxiliary Feed Line RL20
Open Feed Regulator Inlet Valve RL16
Open Main Feed Check Valve Closed Auxiliary Feed Check Valve
c) For initial start only, shut the discharge valve of the selected feed pump.
d) Start the pump and slowly open the discharge valve until the discharge line reaches working pressure.
e) Check the operation of feed check valve.
f) Fill boiler to working level.
g) Check the operation of the salinometer.
h) Switch the remaining pump to standby.
The boiler can now be brought into operation.
Procedure for Preparing the Exhaust Gas Boiler Feed System for Operation
a) Ensure that the pressure gauge and instrumentation valves are open.
b) Set up the valves as in the following table.
Position Description Valve
Open Feed Pump Suction Valve from Cascade Tank RL01 Open No.1 Exhaust Gas Boiler Feed Pump Suction Valve RL08 Open No.2 Exhaust Gas Boiler Feed Pump Suction Valve RL09 Open No.1 Exhaust Gas Boiler Feed Pump Discharge Valve RL10 Open No.2 Exhaust Gas Boiler Feed Pump Discharge Valve RL11 Open Boiler Feed Inlet Valve
c) For initial start only, shut the discharge valve of the selected feed pump.
d) Start the pump and slowly open the discharge valve until the discharge line reaches working pressure.
e) Switch the remaining pump to standby.
Oil-Fired Boiler 25000 kg/h Exhaust Gas
Boiler 900 kg/h
Illustration 2.3.4a Water Sampling and Treatment System
Key
Blowdown Line
Feed Water From
Domestic Fresh
Water Supply Sample Cooler
Sample Cooler
Sink
To Bilge To
Bilge
Sink
Chemical Dosing Station
From Main Feed Water Pump Chemical
Dosing Station
From Auxiliary Feed
Water Pump RL27
RL14
RL38 RL38
RL15
RL40 RL30
RL25
RL13 RL12 Fresh Water
2.3.4 Water Sampling and Treatment System
The main boiler and exhaust gas boiler are each provided with a sample cooler where a representative sample of the boiler water is obtained. The sample is tested on a daily basis using the chemical supplier's test kit.
Two chemical dosing units are provided, one for each system. They inject into the feed pump discharge lines using a metering pump which takes suction from the self contained chemical tank. The tank is charged with chemicals on a daily basis depending upon the results of the daily boiler water test and according to the manufacturer's instructions.
Boiler Water Testing Cabinet
Chemical Dosage Pump
TI
Illustration 2.4.1a Main and Auxiliary Sea Water Cooling Systems
QA11
To Inert Gas and Collection System
From Bilge Ballast and Fire System To Inert Gas and
Vapour Collection