COPS (Cargo Oil Pumps) Used On Oil Tankers

Categoy: Especial Articles
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17 November 2013

In the text the following items will be discussed:
1. General Information pertaining to pump specifications
2. Parts of the COP
3. How COP Works and Its Capabilities
4. Operation with the Pump
5. Points to Ponder While Operating the Pump

Cargo Oil Pump Components

1. General Information Pertaining to Cargo Oil Pump Specifications:

Cargo Oil Pump Steam Turbine

Manufacturer: HYUNDAI
Power: 1205 kW
Steam Consumption: 13495 KG/H
Steam Pressure: 14.4 KG
Speed: 7998/1510
Ratio: 5.29

COP Turbine & Gas Turbine Range

Steam Energy Plant

Steam Turbines

Cargo Oil Pump

Manufacturer: HYUNDAI
Model: ENV-120G
Pump Capacity: 2800M3/H
Suction Head: -5 MT
Discharge Pressure: 13 KG/CM2
SPEED: 1510 RPM
BHP at Sea Water: 1203.2 kW

Pump

2. Parts of the COP

Cargo oil pump consists of pump casing, impeller, impeller shaft, shaft seal and bulkhead stuffing box. Pump casing has the suction and discharge nozzles within its foundation. Impeller which is driven by impeller shaft is the section that creates suction and discharge ability in the pump. Impeller shaft is powered by the high speed steam turbine which is placed on the engine deck. The bulkhead stuffing box is used to seal the gas from the pump room to engine room. And shaft seals are provided in order to prevent the leakage of the liquid and the ingress of the air to the pump.

Closed impeller

Recessed Impeller

COP General View

3. How COP Works and Its Capabilities

COP is driven by a steam turbine which has to be fed by a boiler working at a steam pressure of 16 kg/cm². Pressurized steam that comes into the turbine force to rotate the impeller and impeller shaft. In other words, steam pressure is converted into the motion energy in the turbine and used as COP driving energy. In this way COP is able to turn and handle the liquids by centrifugal force. Pump is able to transfer 2800m³/h or 17611BBLS/h with a revolution of 1510 rpm. Suction head is-5meters. This is the distance from the center of the rotation in the pump to the suction bell-month. Total head is 28 meters with efficiency of 81%. Maximum discharge pressure is 13 bars. Maximum density for the liquid to be handled is 1025kg/m³ and minimum density is 0.7t/m³. The liquid to be pumped should have a minimum viscosity of 600 cSt.

Centrifugal Pump Cutaway

4. Operation with the Pump

Before having the pump running, all involved valves should be determined and set accordingly. All equipments should be checked carefully. COP must be fed by a tank or tanks through the suction valve. Duty officer ensures that the separator and the pump are full of liquid and the discharge valve is closed. The important point in filling the separator is the controlling the speed of the liquid in such a way that it does not damage the level indicators in the separator. This process which is called “priming” should be slow and smooth. After having done this COP turbine is ready for operation.

Duty engineer feeds pressurised steam to the turbine and makes the pump turn at the minimum speed (about 800RPM) and gives the control of the pump to the CCR (Cargo Control Room). According to manufacturer instructions pump should not be run no more than 3 minutes with a closed discharge valve. In 3 minutes COP reaches to nominal operating temperatures and its revolution becomes steady. From now on pump is ready for discharging. By opening the discharge valve 35% liquid transfer is started and at this moment discharge pressure gauge must be observed for any rapid fall. Then the manifold valve is ordered to open and flow of the cargo is observed closely by the watchman. If the revolution and the discharge pressure is steady then the speed of them pump may be increased gradually up to the required level which is determined by the receiving station capabilities.

While the pump is running suction valve must be fully open and the separator level must be high enough to provide sufficient liquid to pump and prevent any accumulation of air/vapour in the casing. In case of the liquid level is not high enough to prime the pump then pump casing, bearings, impellers, etc. start to heat up and if the pump is still kept running this will damage and collapse the pump severely. Due to this fact officer in charge should keep an eye on the separator level gauges, pump suction/discharge gauges and pump temperatures and log them hourly.

As the liquid level in tank gets low pump will experience some cavitations due to the vapour sucked from the cargo tank. And vapour tends to replace with the liquid being handled hence critically reducing the priming of the pump and so that increasing the temperature in the casing. In order to prevent gathering of vapour in the pump or separator an external device or some gas extraction system should be used. If the level of the liquid still becomes problem the pump should be set to minimum rpm and keep running for some time however after a while this will not be enough again and a shift to cargo oil stripping pump must be made after having stopped the main pump. Once the pump is stopped it should be left for a while to cool down and drain afterwards.

Parallel operation with the pumps requires due attention. The key point while running the pumps parallel is the discharge pressures. If the discharge pressures are not equal, then the higher pressure pump makes it difficult to pump for the lower pressure pump. Since the lower pressure pump cannot pump, it acts just as the discharge valve is closed and so that some build up of temperature occurs in the casing unless pump is shut down and keeps running. Increased temperature damages to internal components severely.

Operation with The Pump

5. Points to Ponder While Operating the Pump

The most critical point about the running of the COP is the control of the discharge valve. Discharge valve may be throttled in order to adjust the rate of flow but the pump must not be kept running against a closed valve. At the first stage of priming the pump with minimum speed may be operated against closed discharge valve however period of this process should not exceed 3 minutes. If the discharge valve is totally closed the liquid being handled stays in the pump casing more than 3 minutes it gets heated due to the high pressure created by impeller of the pump. Since the temperature impairs the oil inside the pump a possible collapse of the pump is highly probable. That is why priming period should be limited with 3 minutes.
If is necessary to adjust the discharging flow keep the discharge valve full and change the speed of the pump. Changing discharging valve position is not recommended because of loss of driving energy.
Duty officer should observe steam pressure, discharge pressure whilst increasing or decreasing the speed of the pump since the steam is the main source of power for the pump.
Emergency stop buttons should be tested prior to each operation. In case of an emergency pump should be able to stop by duty officer within a few seconds. On the other hand normal stopping procedure is to reduce the pump rpm to the minimum and ask to the duty engineer to stop the pump from the engine room which takes at least 5 minutes to stop it.
Vibration and the sound of the pump should be observed for any abnormality. Refer to Annexes for vibration and temperature limitations.
According to manufacturer instructions cargo oil pump should be lubricated with specified oils and inspected for wear and tear of the internal components.
The suction strainer should be kept clean as the presence of any residual will cause resistance in the suction line and will make pump impossible to produce adequate lift.