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Stena Line seeking novel approaches to recover energy from exhaust gases from ship engines

Stena Line is seeking novel, cost-effective approaches to recover energy from exhaust gases from ship engines and to transform it into a more useful energy form (e.g., electricity to supply hotel loads on board the ship).

Stena Line said that it is especially interested in industrial-scale applications of thermoelectric generators (TEG) that use the temperature difference between the exhaust gas and the ambient air to directly transform waste heat into electricity. The company is also interested in efficient turbine systems that generate electricity from the kinetic energy from the massflow and velocity of the exhaust gases.

Currently, combustion engines onboard ships have an efficiency of 50% or less. If a ship consumes 10,000 tonnes of fuel in one year, then less than 5000 tonnes is transformed into “usable” energy. These energy losses are primarily radiant heat loss and the sensible heat of exhaust gases. About 30% of the total energy available is lost through the exhaust gases. Typically, the temperatures of the exhausts are in the region of 250-350 ˚C.

Ideally, Stena Line would like to convert a significant portion of this waste heat directly into electricity in a cost-effective manner.

Stena Line said that today there are different solutions for capturing the energy, including exhaust gas boiler that generate steam to drive a turbine and direct exhaust gas turbines. However, these are capital-intensive, energy-inefficient, and costly to maintain. As a result, interest in investment in these kinds of systems is limited in the marine industry.

Also, a 1MW engine produces a mass flow of about 7 tonnes/hour. Stena Line is also interested in approaches to transform a portion of the kinetic energy of this exhaust stream into electricity.

Criteria for proposals include:

  • Technical Viability. Solutions proposed must be based on sound scientific principles and have pilot scale data that demonstrate efficacy. Also, the associated equipment must be able to withstand the harsh environment inside an exhaust stack.

  • Scale-up Potential. Solutions proposed must have a clear pathway to be application on commercial ships within 1-2 years. Solutions already practiced in marine markets have higher value. The ideal partner would be able to lead the design and installation of full-scale systems.

  • Capital and Operating costs. Solutions would need to provide reasonable return on investment, consistent with the 30% energy losses experienced today. The return on investment assumptions for any proposed solution should include a full life-cycle analysis (including capital/installation costs, maintenance costs, installation time, etc.)

  • Ship Operations. Solutions should not impact the normal operation of the ship engine. The equipment space and weight must be able to be retrofitted onto existing vessels. Moreover, the equipment should not increase back pressure to the point it affects engine performance.

  • Ownership. Solutions covered by patents have higher value. At a minimum, proposed solutions must not be prohibited by other patents in the field.

  • Intellectual Property Requirements. None required when using exiting solutions; however, where Stena takes technology and creates a bespoke applied solution then patents and IP may need to be sought.

The company is looking for concise, non-confidential proposals. The proposal should describe the technical approach and should ideally include information on the technological readiness of the proposal, any proof of concept data, reference to any peer reviewed publications, and potential route to commercialization.

The companies comprising the Swedish-based Stena Sphere represent one of the largest private shipping groups in the world.



Nice idea; but, what about the gross ship emissions problem as a higher priority?

Thomas Pedersen

I must say I question the motives of this request, since neither of the 'ideas' make any thermodynamic sense at all.

TEG's have, what 1-3% efficiency (where the heat is lost at sink temperature), a factor of 10 lower steam generators.

'The kinetic energy of the exhaust gas'... Give me an F'in break!

If the exhaust gas is moving at an unreasonable high speed of 30 m/s (100 ft/s), its kinetic energy is 292 J/kg, whereas the energy potential is 110,000 J/kg (by cooling 100 K to avoid sulphuric acid condensation and/or clogging from heavy fuel pollutants). And this kinetic energy could be 95% recovered by reducing its speed to 5.4 m/s (18 ft/s).

Either some brainstorm was not filtered through someone who passes Thermodynamics 101, or they are pretending to do something about their emissions by throwing a hail Mary at 'some future development'.


The speed of the initial exhaust pulse during the blowdown phase is considerably higher than 30 m/s.

Marine diesels are already turbocharged.  A variable geometry turbocharger with an induction or switched reluctance generator could recover the available energy from this flow.  After that you'd need something like an organic rankine cycle engine to recover energy from the waste heat.  You'd want something with a turbine to minimize weight and size; piston expanders will work but they will be bulkier and less efficient.  Everything is either already patented or in the public domain.

TEGs are not in the running.

There are new regulations on the sulfur content of marine fuels.  Sulfuric acid condensation may not be an issue for much longer.

Thomas Pedersen

There is no space available to install equipment to utilize the exhaust impulse right out of the exhaust valve, which is why the effort is reduced to recover the kinetic energy as pressure ('gentle' slowdown) before the turbine of the turbo.

A multi-cylinder marine diesel has an exhaust receiver with the express purpose of reducing the pulsating nature of the exhaust and turn it into a steady flow in order to increase the aerodynamic efficiency of the turbo charger (which has too much inertia to utilize the pressure pulses).

Concerning sulfur content. Maybe you're right, but according to a refinery guy i heard, when I used to be in the 'utilize exhaust energy from marine diesels' business, it costs about the same to extract sulfur from heavy fuel oil (HFO) as it does to convert it to diesel + a pile of coke + a pile of elementary sulfur. And the latter combination has a much higher sales value. So right now, afaik, the strategy is to bunker HFO for ocean sailing and LGO (light gas oil - diesel) for near-shore sailing.

But even without the sulfur in the exhaust, HFO has so much sticky, unburnt 'stuff' (all the accumulated crap from the oil field through the refinery) that clogging is a high risk below temperatures where anything (sulfuric acid or organic compounds) can condense.

And, as refineries get more efficient in extracting all the valuable stuff, the remainder - HFO - gets worse. And the quality of the crude oil is also generally declining, because all the best oil was produced first.

Note: Diesel (LGO) generally costs about twice as much as HFO


Dynamic pressure increases as the square of speed; impulse energy doesn't have to affect turbine speed immediately to increase output, the gas just has to hit the turbine harder.

Lots of press releases posted here talk about dual-scroll turbochargers fed by split exhaust manifolds and how they increase turbocharger output, especially from impulse energy at low engine speed.  This suggests that several smaller turbochargers may recover more energy than one big one.  It would also reduce the total size of the exhaust collectors.

If there's an issue of space (the pics of diesel ship engine rooms look pretty spacious to me) printed-circuit heat exchangers are very compact.  So are CO2 turbines.  This suggests it's worth investigating.

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