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:
- Lube Oil System: Cleaning of L.O. should be done after every discharging depending upon the seawater cooling system or fresh water cooling system. For sea water cooling system, cleaning after every discharging to be carried out. Or if a fresh water cooling system is there, then after 3 to 4 discharging it can be done. While cleaning, always check the gaskets in the end covers. Try out to see there should not be any leakage from the end covers. L.O. Cooler outlet temperature of L.O. to be checked regularly.
- Drain the drain separator and piping after the finishing of cargo. Steam inside turbine is to be completely drained off to avoid corrosion or damage to turbine blades.
- Check for abnormal noise or vibrations when the turbines are started. Chances of slight misalignment can take place
- Oil Strainer must be cleaned regularly by the arrangement provided for them.
- Air in L.O. Cooler and strainer must be purged. Though, it is a closed system, but purging is to be done regularly.
- The Oil level from these places to be checked. Tank from dedicated gauge, governor for sight glass and gear coupling by oil leakage.
- All trip devices to be confirmed at every initial starting of the turbines. Every trip is to be checked by maker’s instruction. When testing the overspeed trip for the turbine, the pump must be disconnected in order to avoid dry running of mechanical seal fitted on the pump.
- Bearing temperature to be checked after every 4 hour interval when the turbines are running. If any abnormal rise occurs, take the appropriate action as soon as possible.
Alternatives to COPT
COPT system is more reliable than any other cargo discharging systems. Though the initial cost is high and operations are too critical to handle, but give a higher rate of discharge than any other system. Some other systems like FRAMO are also used in ships which works on the electrical supply. The driving force is an electrical motor due to which controlling of speed is easier than the COPT system. The speed control of the COPT is slow to respond than the FRAMO one as the boiler takes a long time to increase or decrease the production of steam. These factors affect the COPT system, but due to its robust operation capability gives it an upper position than FRAMO.