An empirical study of the effects of technology on the Spanish banking
Chapter 4. An empirical study of the effects of technology on the Spanish banking sector
4.2. Classification of the effects of technology on banking
a) Check the level of the liquid in the tank. The pumps must not be started when the tank is dry. The cargo pump must be completely submerged in LNG.
b) Before starting the pump, select the automatic or manual mode from the IAS graphic display to open the pump discharge valve to about 22%. If the pump discharge valve is open less than 20%
the start up sequence will not operate. Conversely, starting the pump with the valve fully open when pumping liquid which has a high specific gravity, will overload the motor.
c) Start the cargo pump using the IAS by clicking on the START/
STOP icon in the graphic screen display to bring up the faceplate and clicking on the START soft key. The operator should keep a close watch on the discharge pressure and the motor current.
The current consumption should steady after the motor has been running for 3 seconds. During starting, while the discharge pipe is being filled, the current may be above the ammeter red line.
The current should not exceed the maximum rated current by more than 50% for more than 2 or 3 seconds when the tank is full. If the running current after this time is more than 150%
of the maximum rated current, stop the pump immediately and determine the cause of the high current, possibly a suction blockage.
d) When the pump discharge pipe is filled to the discharge valve, a substantial increase in the discharge pressure and a corresponding decrease in current should be observed.
e) Once the pump is operating normally, adjust the discharge valve to obtain the required flow or pressure. The operator should monitor the pump motor running current, taking care not to exceed the maximum current level.
(Note: When the pump is operating correctly, closing the pump discharge valve during operation will raise the head pressure and consequently reduce the running current.)
The cargo pumps may be restarted consecutively a maximum of 3 times. After the third time a 30 minute waiting period must be applied, then another 3 starts may be made. This procedure must be adhered to as heat build-up from the high starting current may not be carried away during stripping operations, which may be due to the lack of liquid flow when (and if) the pump does not prime, due to the extremely low level of LNG during stripping operations.
The pumps are started and stopped from the CCR via the IAS system. In an emergency all pumps will be stopped by activation of the Emergency Shut Down System trip.
Start
Illustration 4.3.1b Four Step Cargo Pump Start Sequence
No
Yes
Open tank filling valve Close branch valve
Open branch valve Close tank filling valve Open both discharge valves
25%
Issue: 1
Discharge of Cargo
Operating a pump at, or close to, its design flow level is in the best interests of the pump life span and operating performance. However, operating the pump at flow rates which are less than this cannot be avoided. This is especially the case when the shore receiving facility cannot accept the rated flow. However, it should be remembered that it is better to operate one pump at the design flow rather than two pumps running at 50% flow. The pump’s rated flow should only be exceeded during the starting period while the discharge valve is adjusted.
Stripping or Low Liquid Level Operation
As the end of a discharge approaches, the pump suction head will approach the NPSH for a given flow. At approximately 0.80 to 1 metre liquid level above the pump inlet bell, the NPSH for the rated capacity will be reached. When the amount of liquid falls to this level, the motor ammeter and the pump discharge pressure should be monitored continuously by the operator.
The low level alarm is triggered when the liquid level is about 1m above NPSH (at 2m sounding), the flow should be reduced by use of the throttling valve on the pump discharge side. If any fluctuations are observed on the motor ammeter or on the pump discharge pressure gauge during final pumping, the discharge flow rate should be further reduced until the readings stabilise. When the flow is throttled down to about 560m3/h the required NPSH will be about 10cm. This level represents the minimum level attainable by pumping.
CAUTION
It is of the utmost importance that the pumps are never allowed to run dry, even for short periods, as this will result in motor failure. A momentary loss of priming during cargo stripping should not be considered as running a pump dry. Up to 30 seconds of operation with dry suction but with fluid in the discharge pipe will not damage the pump or the motor.
When the liquid level reaches less than 1m above the pump inlet, avoid stopping the pump if at all possible until the cargo has been fully discharged.
If the shore facility is unable to accept the liquid for intermittent periods, it is preferable to keep the pump going and recirculate the liquid back into the tanks until the cargo discharge can be resumed and completed.
Points to Remember
• The operator should check the cargo liquid level before starting a pump and maintain at least 2kg/cm2 discharge pressure. This is to ensure the lubrication of the bearings on all pumps in cargo service.
• The operator should always open the discharge valve to 22%
open before staring a pump.
• The operator should always monitor the motor ammeter and the discharge pressure gauge.
• The operator should always try to run the pump at the design flow rate whenever possible.
• The operator should never run pumps dry.
• The operator should never blow hot air through a discharge line.
This may turn the impeller and rotor at high speed in the wrong direction, damaging the bearings.
• The operator should never operate the pump above the motor ammeter red line.
• The operator should never assume that all electrical interlocks and safety relays will continuously function correctly. The operator should be ready at all times for any eventuality.
• The operator should not allow sea water, water, steam or any cleaning agent containing water to come into contact with a pump or its cables and connections.
(Note: An insulation test of all the pumps should be carried out after leaving the loading port in order to establish that all pumps are operational and to allow time for the implementation of emergency procedures, should it be necessary.)
Pump Trips and Shutdowns
To protect the cargo pumps and the cargo tanks, the pumps will be shut down and a stop sequence activated if any of the following shutdown signals are activated:
• Low current: 23A for 10 seconds
• High current: 55A for 10 seconds (motor starter setting) 5 seconds on start-up
• Single phasing: 1 phase lost (motor starter setting)
• Low discharge pressure: 2kg/cm2 for 10 seconds
• Low low cargo pressure: <0.02kg/cm2
• ESDS low loop pressure: 3kg/cm2
• Low level in cargo tank: 0.37m
• ESDS activated
• Tripped and blocked from starter panel
Start Interlocks
The following conditions will prevent a remote start of the main cargo pump:
• The discharge valve: >20% open
• The discharge valve: <25% open
• Cargo tank filling valve: >95% open
• ESDS trips and shutdowns activated
• Cargo tank low level alarm: 2m
• Soft start unavailable
• Soft start blocked
• Power not available
Section 4.3.1 - Page 3 of 3
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Illustration 4.3.2a Stripping/Spray Pumps
Bearing Assembly
Shaft Power (kW) at 0.50 SPGR
Liquid : LNG
Specific Gravity : 0.5 Rated Flow : 50m3/h Rated Head : 145m Impeller Dia : 213mm
Pump Characteristic Curve Spray / Stripping Pump
Pump Model: 2EC-092
kWinput(kW),Current(Amperes),Efficiency&PowerFactor(%) Speed(rpm)
Shaft Power Output (kW) Representative Motor Performance Curve
22.4kW / 2P / 440V / 60Hz / Y250
Issue: 1
4.3.2 STRIPPING/SPRAY PUMPS
Maker: Ebara International Corporation
Type: 2EC-092
Capacity: Rated at 50m3/h at 145mth Min. continuous flow: 16.4m3/h
Motor rating: 440V 18kW Motor speed: 3,560 rpm Starting time: 1.2 seconds No. of stages: 2
No. of sets: 4 (1 per cargo tank)
The pumps are in principle similar to the main cargo pumps and a similar operating procedure should be used.
The spray pumps are intended for the cooldown of cargo tanks before loading after a ballast voyage.
The pumps are started and stopped from the CCR via the IAS system. In an emergency all pumps will be stopped by activation of the Emergency Shut Down System trip (ESDS).
The instances when these pumps can be used are:
• To cool down the liquid header prior to discharging.
• To cool the cargo tank during the ballast voyage prior to arrival at the loading terminal by discharging LNG to the spray nozzles in the tanks.
• To pump LNG from the tanks to the vaporisers (emergency case) when forced vaporisation of LNG to the boilers is required.
• To enable the tanks to be stripped as dry as possible for reasons such as a cargo tank entry.
Whenever possible, the stripping/spray pumps should be started early enough to avoid any possible starting problems due to very low tank levels (about 0.5m minimum).
Pump Trips and Shutdowns
The stripping/spray pumps will be stopped automatically should any of the following occur:
• Vapour header pressure below or equal to atmospheric pressure plus 0.3kPa (ESDS: Stage 1)
• Extremely high level in the cargo tank (99% volume)
• Activation of ship/shore pneumatic, fibre optic or electrical shutdown (ESDS: Stage 1)
• Motor single-phasing
• Low motor current
• High motor current (electrical overload)
• Low discharge pressure with time delay at starting
• Activation of ESDS stage 2
• Cargo tank level low low
• The end of a IAS cargo automatic sequence
Spray Pump Safety System
In addition to the above shutdowns, the spray pump safety system will stop the pumps and close the discharge valves if any of the following conditions occur:
• Low current: 15A for10 seconds
• High current: 35A for 5 seconds
• Low low cargo tank pressure: <0.02kg/cm2
• Low discharge pressure: 1.70kg/cm2 for 10 seconds
• ESD low loop pressure: 3.0kg/cm2
(Note: An insulation test of all pumps is to be carried out after leaving the loading port in order to establish that all pumps are operational and to allow time for the implementation of emergency procedures, should it be necessary.)
Start
Illustration 4.3.2b Spray Pump Start Sequence
No
Activate chime (10 sec) Run pump
Spray master opens Wait 5 seconds
Start control *1
*1 Discharge valve position controller mode : CAS
Return valve position controller mode : CAS
Spray pump Load controller mode : CAS
*1 Discharge valve position controller mode : AUTO
Spray header pressure controller mode : AUTO
Preset position discharge valve
Open spray return valve
Closed spray master valve
Set preset value of spray nozzle inlet pressure
to controller Set preset value of
pump load to
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0
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 25
NPSHR&Pumpdown(m) Head(m)&Efficiency(%) MinimumContinuousFlow(189m3/h) MaximumFlow(660m3/h) Power(kW)
Flow (m3/hr) Rated Flow : 550m3/h
Rated Head : 150m Specific Gravity : 0.5 Impeller Trim : 329mm
Calculated Pump Performance Curve Pump Model: 8ECR-12
Shaft Power At 0.5SG
NPSHR
Shaft Power Output (kW) Representative Motor Performance Curve
223.8kW / 2P / 440V / 60Hz / Y400
Illustration 4.3.3a Emergency Cargo Pump
Section 4.3.3 - Page 1 of 2
Issue: 1
4.3.3 EMERGENCY CARGO PUMP
Maker: Ebara International Corporation
Type: 8ECR-12
Capacity: Rated at 550m3/h at 150mth Min. continuous flow: 189m3/h
Motor rating: 440V 223.8kW Motor speed: 3,560 rpm
Starting method: Soft starter voltage variation system No. of stages: 1
No. of sets: 1 (Located in the deck store)
This pump well has a foot valve which is held in the closed position by highly loaded springs.
Should a failure of either one or both main cargo pumps in one tank require the use of the emergency pump, it is lowered into the emergency pump well after the well has been purged with nitrogen.
The weight of the emergency pump overcomes the compression of the springs to open the foot valve.
A small flow of nitrogen should be maintained whilst the pump is being installed. (See section 7.4 Emergency Cargo Pump Installation.)
(Note: Before undertaking this operation it is important to reduce the tank pressure to near to atmospheric pressure and to keep at this level throughout the entire operation.)
Electrical connections are made to the fixed junction box which is located adjacent to each pump well.
A dedicated starter is available with one circuit breaker which is located on No.2 cargo switchboard. A changeover selection switch is fitted on the same panel for whichever tank the emergency pump is placed.
All safety devices are transferred to the emergency pump when the circuit breaker is engaged, as they are the same for the main cargo pumps. The same starting procedures and schematic mimics are used as those for the main cargo pumps.
(Note: An insulation test of all pumps is to be carried out after leaving the loading port in order to establish that all pumps are operational and to allow time for the installation of the emergency cargo pump should it be necessary.)
Following installation into a cargo tank, it is most important that the emergency cargo pump is fully submerged in liquid LNG and remains in that condition for a minimum of one hour. This is in order that thermal stabilisation can take place. Only after this point can the pumps be started. Failure to do so may result in severe damage to the pump.
CAUTION
The emergency cargo pump must not be started or operated against a closed discharge valve, due to potential insufficient cooling, lubrication and excessive vibration.
CAUTION
The emergency cargo pump must only be operated between the minimum continuous capacity (195.7m3/h) and maximum capacity (550m3/h).
CAUTION
If there is a situation of a sustained rotor lock during starting, then a restart may only be initiated after a period of 30 minutes has elapsed with a total of two restarts allowed under this condition.
Emergency Pump Safety System
• Low current: 76A for 10 seconds
• High current: 320A for 0 seconds
• Low discharge pressure: 2kg/cm2 for 10 seconds
Section 4.3.3 - Page 2 of 2
4.4 Cargo Compressors
4.4.1 High Duty Compressor 4.4.2 Low Duty Compressor
Illustrations
4.4.1a High Duty Compressor
4.4.1b Screen Shot High Duty Compressor 4.4.2a Low Duty Compressor
4.4.2b Screen Shot Low Duty Compressor
4.4.2c Low Duty Compressor Alarm and Trip Set Point List
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Illustration 4.4.1a High Duty Compressor
A
ZLH ZLL LAL TAH TAL YAH YI YAHH
PDI
Surge Control by IAS
LNG Process
Ready to Start Auxiliary LO Pump
Remote Control Signal To Condensate System
Locked
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4.4 CARGO COMPRESSORS
4.4.1 HIGH DUTY COMPRESSORTwo high duty (HD) compressors are installed in the cargo machinery room for compressing the LNG vapour for return to shore during cargo loading, tank purging and tank warming up.
The HD compressors are driven by electric motors, installed in an electric motor room segregated from the compressor room by a gas tight bulkhead. The shaft penetrates the bulkhead through a gas tight shaft seal.
High Duty Compressors
Maker: Cryostar
No. of sets: 2
Model: CM 400/55
Type: Centrifugal, single stage, fixed speed with adjustable guide vanes
Mass flow: 46,200kg/h Suction volume: 30,000m3/h Inlet pressure: 1.06 bar absolute Outlet pressure: 1.96 bar absolute Inlet temperature: -140°C to -20°C Outlet temperature: -105°C to 70°C Shaft speed: 11,200 rpm Motor speed: 3,580 rpm Rated motor power: 850kW
The following conditions trip the HD compressors:
• ESD system
• Tank high level
• Low gas suction pressure
• High gas discharge temperature
• High bearing temperature
• Excessive rotor vibration
• Excessive shaft displacement
• Low LO pressure
• High high LO temperature
• High bulkhead gas seal temperature
• Low bulkhead gas seal pressure
• Low gas seal pressure
• Electrical power failure
Non-trip alarms are indicated on the IAS are as follows:
• Compressor discharge gas temperature
• Compressor LO filter differential pressure
• Compressor LO pressure
• Seal gas pressure
• Motor aft bearing temperature
• Motor forward bearing temperature
• Motor windings temperatures
The compressors are operated locally or from the cargo control room. The capacity of the compressor is controlled by the inlet guide vane opening, with the travel indication shown on the local and cargo control room panels.