COPT = Cargo Oil Pump Turbine or Cargo Oil Pump & Turbine
It is a combination of 2 units i.e. Pump and Turbine. Pump is for pumping action and turbine is for driving the pump or driving the pump shaft. Normally we have motor for driving the pump but here turbine (steam turbine) drives the pump.
Steam turbine needs high pressure steam to get the desired rpm and thus we need high pressure boiler. Arrangement of the pump and turbine may be either horizontal or vertical.
COPT is used for discharging of cargo oil. It is generally used at oil tanker and product tankers. Its initial cost of installation is high but it is quite reliable and it reduces the port stay time significantly thus brings more benefit to company. There is alternative option also i.e. FRAMO Pump but it’s not beneficial for oil tanker than COPT.
COP (Cargo Oil Pump) is a centrifugal pump for handling huge quantity of oil. It has replaced reciprocating pumps. It requires less maintenance.
The pump and driver is connected with the flexible couplings trough an intermediate shaft and bulkhead stuffing box.
Components of COPT
Turbine casing: It contains turbine blades.
Turbine blades: These blades are responsible for energy conversion.
Volute casing: It contains the impeller of the pump.
Impeller: It’s a double entry impeller and
Pump Shaft: It’s a connection between turbine and pump. It transmits the motion to impeller.
Bearing: The rotating element is supported by ball bearing on both sides of pump casing.
Bulkhead stuffing box: It is used to seal the gas from pump to engine room.
Pump Stuffing Box Seal: The stuffing box is designed as to furnish mechanical seal exclusively. Therefore there is no leakage of the liquid pumped and no air leaks into the pump.
Other components are Condenser, L.O cooler, L.O sump tank, Governor etc.
Working of COPT
Boiler produces high pressure steam and it is forced to turbine blades. Here pressure energy of steam is converted to motion (kinetic) energy. Turbine rotates the pump shaft and thus impeller of the pump to take suction.
The main idea is to rotate the turbine blades. Generally oil tanker has 2 high pressure auxiliary boilers as COPT is driven by high pressure steam i.e. 16 kg/cm2 which provides a large force to the impeller shaft and as a result of which pump creates a suction force.
Checks before starting COPT:
Give some oil to mechanical seal.
Give a few turn to coupling with the turning bar and see if it turn normally.
Make sure the rotation direction of driver is correct.
Make sure the grease in bearing housing and the oil in coupling is within the limits.
Close the discharge valve completely and open the suction valve fully.
When the liquid level in the cargo tank is above the pump, the liquid flows in the pump casing by gravity, so open the air vent valve on the top of volute casing to draw the air in the pump and close it in when the liquid begins to flow out of it.
When the liquid level in the tank is below the pump, draw the air in the pump and suction through the gas vent on the volute casing by means of stripping pump or some other extracting device so that liquid can fill inside the pump. In this case keep the air vent valve closed so that no air can enter the pump casing.
Opening of 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.
As the level of the cargo tanks drops, suction pressure approaches the vapour pressure of the liquid and vapour develop in the suction line and pump starts to suck gas. In order to prevent this, vapour and gas coming into pump can be drawn through that vent by means of vacuum stripping or some other extracting device.
Never operate the pump for over 3 minutes with discharge valve fully closed. Most of the power will change into heat as a result of which temperature of the liquid inside the pump will rise causing seizure of interior parts of the pump.
When operating more than two pumps in parallel, be sure to keep the discharge pressure of each pump equal or else the low pressure pump will act to pump as discharge valve is closed and as a result of which temperature inside casing will rise.
Alarms and Trips in COPT
COPT system is very important as it discharges oil at very high rate. Failure of the system may lead to serious problem. There are following alarms to act during any problems:
Low L.O pressure
High L.O temperature
L.O Tank low level
High bearing temperature
Pump casing high temperature
There are some trips also for the safety of machinery and operation. Here is the some common trips in COPT system:
Low L.O pressure trip
High bearing temperature trip
Very high discharge pressure trip