Working principle

• Both are impulse/reaction turbines converting fluid energy (steam or exhaust gas) into shaft rotation. Cargo pump turbines are steam turbines (impulse or impulse-reaction) driving centrifugal cargo pumps on tankers; turbocharger turbines are exhaust-gas-driven turbines mounted on the main engine to drive an air compressor (blower).

Applications

• Cargo oil pump turbine: Drives a large centrifugal pump that discharges crude oil/ cargo. It runs on steam (from auxiliary boiler/exhaust gas boiler), typically at a fixed high speed available via reduction gearing to the pump shaft, and is reversible in some designs or uses a fixed rotation direction with the pump handling suction/discharge.
• Turbocharger turbine: Acts on the engine's exhaust gas to compress scavenge/charge air fed to the engine cylinders; it is an integral part of the engine's charging system and its speed varies continuously with engine load.

Design and operational differences

• Driving fluid: Cargo turbine uses dry saturated or superheated steam (constant supply pressure, ~7-17 bar); T/C uses variable-temperature exhaust gas (typically 250-500 C) from the engine.
• Speed: Cargo tur-bine runs at a relatively constant governed speed (around 2500-6000 rpm) driving via reduction gear; the T/C runs at 10,000-50,000 rpm, floating on engine load with no mechanical connection to a fixed load shaft.
• Mechanical connection: Cargo turbine has reduction gearing to a large low-speed pump; the T/C rotor is a single high-speed spindle with the compressor wheel on the same shaft.
• Blade design: Cargo turbine impulse blading for constant-pressure steam with power control; T/C has radial-flow compressor and axial-flow turbine blading optimised for the exhaust gas flow and for variable conditions.
• Control: Cargo turbine is controlled by steam throttle valves, governing to set the pump speed/ discharge pressure; the T/C is self-regulating matching its speed to the engine gas flow (with a waste gate/ by-pass on some designs to limit speed/boost at high load).
• Requirements: Cargo turbine must be robust in a cargo-pump room, withstand steam conditions, be smooth and reversible if required, and be capable of continuous heavy duty; the T/C must be highly efficient, compact, low inertia (rapid acceleration), heat-resistant, and oil-cooled to survive high speed and temperatures.

1. Throttle (steam admission) control: Varying the opening of the main/nominal stop and manoeuvring throttle valve admits more or less steam to the nozzles; more steam = more power and higher speed, less steam = lower speed. This is the primary method to set pump speed.
2. Nozzle group (nozzle control) valves: A set of independently operated nozzle valves admits steam to groups of nozzles in stages, giving efficient part-load control by adjusting the active nozzle area.
3. Governing valve on the reduction/gland or trip/ emergency overspeed: a speed governor adjusts steam admission automatically to hold a set speed as cargo discharge conditions (backpressure) change.
4. Reversing manoeuvring valve on reversible machines: Admits steam to the astern nozzle direction to reverse the rotation where pump is required to operate astern.
5. External variable-speed drive (where fitted, e.g. hydraulic coupling or VFD on turbo-generator pumps): adjusts pump speed. For conventional cargo turbines, throttle/nozzle governing is the method used.
6. By manipulating the discharge/ suction valve on the pump and the sea/cargo line so the pump operates on its curve - adjusting flow and hence required power, but the actual turbine speed is set by steam admission and governor.

Precision control of cargo operations is achieved because the turbine speed governs pump discharge pressure and flow; accurate throttle and nozzle settings together with the speed governor give stable control of cargo handling (loading, discharging, stripping and tank cleaning) at the required rates.

The vacuum condenser is part of the main condenser/ vacuum system serving the main cargo steam-turbine-driven pumps (and the turbine-alternator). Its role is to condense the exhaust steam from the turbines back to condensate (clean water) so it can be returned to the boiler and reused, maintaining a closed steam/condensate circuit. By creating a vacuum in the condenser (via eductor/hotwell vacuum or the air ejector), the backpressure on the turbine exhaust is lowered, which increases the turbine's efficiency and power output and reduces steam consumption. The condenser also protects the turbine from backpressure damage and recovers condensate, conserving water. It contributes to efficiency by enabling the turbines to develop the required power with less steam (better economy), and to safety by maintaining a proper steam/ condensate balance to the boiler, preventing the cargo operations from being interrupted by loss of vacuum or by contaminated/carry-over condensate, and preventing hot steam blow-through. The vacuum system (air ejector, eductor) removes air and incondensables to hold the vacuum.