TECHNICAL QUESTIONS & ANSWERS PART-10

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Q. Referring to the latest developments in Turbocharger application in marine diesel engines, write short notes on the following :-

a. Power turbine generators.

b. Hybrid turbochargers.

c. Electro-assist turbochargers.

Answer:-

The extreme slow steaming of ships has become the mainstream on the back of the recent energy-saving trend. Turbochargers (super chargers) for marine diesel engines are generally driven only by exhaust gas energy. Thus the industry has developed different turbo Systems for large turbocharger for marine diesel engines, and verified high energy saving advantages in the low-load operating range of the engine.

a). Power Turbine Generators:

1. It consist of an exhaust gas turbine installed in the exhaust gas bypass line on ME and a generator that converts power from turbine rotor shaft into electricity onboard a ship.

2. The increasing efficiency of Modern turbochargers means that there is a portion of unused exhaust gas energy available. The turbo compound system power turbine & generator (TCS-PTG) makes use of that excess exh gas energy.

3. The power turbine is inserted into the exh gas system parallel to the Turbocharger. Here it drives an electric generator via a reduction gear box from the main engine power

4. The TC performance and main engine output is not affected by the use pf PTG which can extract upto 5% of additional power from the ME Exh Gas.

5. Typically be larger as the power turbine unit typical is arranged several meters away from the ME in the E/R.

6. The power turbine, its reduction gear and generator are placed on a common bedplate.

7. The engine exhaust gas bypass valve will be closed at engine power lower than 40% MCR and the power turbine generator will be shut down.

8. Control v/v’s and fast acting emergency valves for emergency shutdowns are installed in the exhaust system to ensure reliable, safe operation

9. Payback period is as short as 2-3 years

10. this system leads to less funning hours of the DG hence saving in maintenance costs and reductions in emissions

b). Hybrid Turbo Chargers:

1. Exhaust gas energy is recovered to turn the compressor, which supplies scavenge air to the main engine and also generates electricity through an alternator attachment incorporated in the turbocharger known as hybrid turbocharger

2. The turbine and compressor does the heat energy recovery work and the alternator is used to generate electrical power without consuming any extra fuel as it is driven by the shaft power of the TC.

3. The alternator & compressor are connected by special designed flexible coupling

4. The alternator is fit at the centre part of the air intake silencer

5. The integrated generator driven by TC rotor shaft can produce upto 5% of main engine output.

6. While running on MCR the Hybrid TC system can generate enough power to take up full sea load of a normal size vessel.

7. The speed of the prime mover governs the voltage and frequency of the generator. An initial DC power is provided so that the required output voltage & frequency is used to supply stable electric power to main bus bar.

8. With only little increase in the dimensions, enough power can be generated from main engine operation.

9. The generator can function as a motor at low load operation to drive the turbocharger for maintaining scavenge air pressure of the ME. This can eliminate the need of Aux Blowers.

10. Fuel savings & reduction in emissions

11. Simple & compact design as there is no requirement for extra piping, valves etc as in PTG.

c). Electro – Assist Turbo Chargers

1. It is a TC which incorporates a compact electric motor with permanent magents directly attached to the rotor shaft and the stator is held in place by a support bracket attached to blower casing.

2. The motor assist the TC while running at low loads when the exh energy is less, hence there is no need to have a separate Aux Blower.

3. This provides optimization under slow steaming, improving the fuel combustion efficiency of the main engine and enabling the same or better performance than aux blower while consuming little power.

4. An electro assist TC saves approx 30% electric power consumption compared to conventional Aux. Blowers

5. Ideal for slow steaming , improved engine performance under partial and low loads

6. compact design as motor is directly attached to the TC

7. Separate Aux Blower not required

8. Suitable for retrofitting

Figure 6- Exploded view of electric-assist turbocharger
Figure 7- Drive shaft and coil installed on MET83MA turbocharger