Partners harness waste heat and shaft energy

Deploying Wärtsilä's shaft generator control has increased the operational stability of MHI's waste heat recovery system Deploying Wärtsilä's shaft generator control has increased the operational stability of MHI's waste heat recovery system

Mitsubishi Heavy Industries and Wärtsilä are to jointly market a new energy solution that deploys both waste heat recovery (WHRS) and power take-off/in (PTO/PTI).

Ship operators are increasingly looking to tap waste heat energy (notably engine exhaust) and excess rotational energy from the propeller shaft as they seek to squeeze efficiency from their onboard plant. The IMO’s Energy Efficiency Design Index is a key regulatory driver for optimising power and propulsion on newbuild vessels.

The new system combines MHI Marine Machinery & Equipment’s waste heat recovery and energy saving power generation units with Wärtsilä’s shaft generator control technology. The result is more stable operation for the WHRS, which can now be used to drive the propeller shaft depending on main engine load and demand from the rest of the ship network.

At full main engine load, the surplus energy can be used to assist the ship's drive by being applied directly to the propeller shaft. At low load, the WHRS can be operated in parallel with a diesel generator set. Parallel operation with a shaft generator via PTO operation can also be implemented.

The design connects the WHRS generator to the DC link circuit of the PTO/PTI shaft generator, rather than directly into the mains. This allows operation of the WHRS at reduced speed, offering higher efficiency of the power-generating turbine system at part load and avoiding the need for speed regulation valves, which cause throttle or bypass losses.

The patented design connects the WHRS generator into the DC link circuit of the PTO/PTI shaft generator rather than directly into the mains. This allows operation of the WHRS at reduced speed to create higher efficiency of the turbine system at part load. In so doing, it avoids the necessity of speed regulation valves, which cause throttle or bypass losses.

MHI said that, in combination with its power turbine generator, the system could supply between 500-2,000kW of electricity, driven by gasses recovered from the main engine. It added that the cooperation with Wärtsilä would bring its WHRS technology – previously focused on large container ships - to a wider market.

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