Increasing efficiency of large engines

10 Jun 2011
TCS-PTG components

TCS-PTG components

MAN Diesel & Turbo recently presented its new efficiency technologies for large two-stroke engines, the WHR (waste heat recovery) systems, that include the TCS-PTG turbines, and are offered as an integrated system.

The company says that WHR exploits, among other things, exhaust-gas energy, and can be used in the production of electricity to cover a ship’s electrical needs. All ME- and MC- engine types in MAN Diesel & Turbo’s portfolio are suitable for WHR where, generally speaking, the greater the engine output, the greater the potential WHR offers and the quicker the economical return. As a result, WHR technology has traditionally been applied to container-ship and power-station applications.

MAN Diesel & Turbo offers total WHR system packages with exhaust boiler, steam and power turbine generator unit, PTO/PTI and power management. High-load optimisation is a major part of the WHR principle where a power turbine is placed in parallel with the main-engine turbochargers and/or steam turbine, using the heat from the exhaust gas after the turbochargers. Up to some 10% MCR power can be obtained with a full WHR system, which includes both power and steam turbines.

WHR options include:

  • power turbine stand-alone: PTG – power turbine generator
  • steam turbine stand-alone: STG – steam turbine generator
  • combined turbines: Steam turbine – power turbine

The company says that installation of a WHR system aboard a container ship requires a larger exhaust piping system to ensure an even exhaust-gas distribution within the exhaust boiler. The exhaust boiler itself requires a collector to control the exhaust flow velocity, velocity distribution and to collect the exhaust boiler washing water. For its exhaust boiler systems, MAN Diesel & Turbo recommends the installation of an exhaust bypass and bypass exhaust valves.

For WHR exhaust systems, MAN Diesel & Turbo recommends that shipyards use CFD to calculate and ensure an even exhaust gas velocity distribution into the exhaust boiler using guide vanes. This is important in securing a high WHR system efficiency. Back-pressure calculations for the exhaust system are necessary to ensure the correct functionality of the WHR system – the correct exhaust velocity up through the exhaust boilers ensures optimal functionality and minimises the risk of soot collection on the internal surfaces of the exhaust boiler. Engine data can be provided for exhaust systems with higher back pressures in cases where WHR systems and scrubber systems are combined, a situation that especially will arise in the case of new ships serving routes in SECA areas.

The TCS-PTG is the first of the new generation of power turbines based on MAN’s TCR/TCA turbines; based on a TCS-PTG system first patented as long ago as in 1957. The first two TCS-PTG18 units that have been assembled and tested in Germany and are bound for a power project in London.

The power turbine is inserted into the exhaust-gas system parallel to the turbocharger. It drives an electrical generator via a reduction gearbox and receives up to 12% of the exhaust-gas flow, diverted from the main-engine power.

MAN Diesel & Turbo claims more than 30 years’ expertise in the development, production and servicing of power-turbine applications, with some 50 references, mostly installed onboard ships. The company sees considerable potential for further TCS-PTG marine WHR applications as the recent increases in fuel prices have revived interests in systems that maximise overall system efficiency. MAN predicts that the ongoing CO2-debate and growing interest in environmental issues for newbuilding projects will make the power-turbine system an interesting option.

In a further development, MAN Diesel & Turbo has signed a cooperation agreement with Swedish energy and environmental technology company Opcon to exploit the possibilities arising from the merging of Opcon’s ‘Powerbox’ WHR technology with MAN Diesel & Turbo’s diesel engines for cutting fuel consumption and reducing emissions. The companies will examine how best to exploit the possibilities offered by re-using waste heat energy from low-temperature heat sources utilising the Opcon Powerbox technology.

The first system, with the Opcon Powerbox integrated with a two-stroke MAN B&W 8S60ME-C8 engine, is currently being installed on a newbuilding owned by Swedish shipping group Wallenius. Existing WHR units are targeted at high-temperature applications and large engines, but the Opcon system can be applied to smaller engines. It directly influences the performance of ships by reducing the amount of fossil fuels they consume during operation by 5-10%, while directly cutting carbon, NOx and sulphur emissions.

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