What is COPT?
Cargo Oil Pump Turbine (COPT) System is found on the Oil Tankers. It has two systems working together to collectively discharge the oil. One system is the driving force which gets the power from steam to drive the second system, the centrifugal pump system. Steam section has a turbine, which produces a tremendous force and gives a higher rate of discharge. They can be vertical or horizontal in design.
Working of COPT
COP is driven by a steam turbine, which gets a high pressure steam of 16kg/cm2 from a boiler. Generally, oil tankers have two auxiliary Boilers of nearly 16kg/cm2 working pressure capacity. This steam gives a tremendous force to the impeller and impeller shaft which produces a high suction force. In result of this good discharging rate can be achieved, which will ultimately save money for the Ship’s Owner by reducing port charges. According to the size and other specifications, COP can run at a speed of 2800m3/h with a revolution of 1510 rpm.
Critical Operations in COPT System
- Before Starting of pump: Ensure that the separator and pump are top up by liquid and discharge valve is closed. The main purpose of filling the separator is to control the speed of the liquid, so that level indicators are not damaged of the separator. This process is known as Priming and it should be slow and smooth always.
- During starting of the pump: Initially the speed of the pump to be kept minimum. And check for any abnormal sound from the turbine as well as a pump. According to manufacture’s instruction, pump should run for 3 minutes at this speed with closed discharged valve. Till this time, the turbine will attain the working temperature and will be ready for discharging.
- Opening of discharge valve: This is again a critical task to open the discharge valve. As if we open the valve fully can cause a surge in pressure and chances of pump trip is also there. Initially, 35% of the discharge valve are to be opened and observe the discharge pressure gauge for any rapid fall in pressure. If the revolution speed of the pump and pressure is steady, then increase the speed of the pump by increasing the flow from discharge valve.
- During operation of the pump: Ensure the separator is full with liquid in whole discharging process to avoid ingress of any air/vapour in casing. In case the suction valve and separator are not fully filled, can lead to heating up of the pump casing, impeller, etc. and if the pump still runs into this situation will lead to collapse and damage to the pump.
- Ending of discharge process: As the liquid level in the cargo tank gets low, the chances of cavitation increases. Changes of vapour ingress from tanks increases. To eliminate this situation vapour extraction system should be used. RPM is to be lowered and after sometime cargo level will be at that level that it will not be sucked by main cargo pumps. Then, stripping pump come into action. They are generally reciprocating pump which is also a steam driven.
- Parallel Operation: It is one of the most critical operation in cargo discharging. The discharge pressure is too critical in this case as if the discharge pressures are not equal, then the low pressure pump will act as the discharge valve is closed, due to which casing temperature increases.
Maintenance of COPT System
Cargo Oil Pump Turbine (COPT) Maintenance to be carried out before and during operation are: