The evolution continues

Our new class of ethylene carriers are the first HFO (Heavy Fuel Oil) fuelled TIER III* compliant ethylene carriers in the world. The vessel specification and detailed design is based on experience with our previous ECO design where we combine cost-effective means for minimizing the overall fuel consumption.
14. May 2019 // Andreas H Knudsen

The vessels are equipped with EGC (Exhaust Gas Cleaning) for HFO operations, which ensures a very cost effective operation. When HFO is used together with EGC, the result is a very environmental friendly solution. The waste from the cleaned exhaust is delivered ashore. The question is not which fuel to use, but how the fuel is used. Technically, high quality HFO is an excellent fuel, which again ensures low maintenance cost for the machinery. HFO has also the highest energy density of all available fuels, which again maximizes the cruising range and/or minimizes the overall CO2 foot-print from the cargo transported.

Up to now the exhaust gas cleaning has only been cost efficient in the SECA area (sulphur emission control areas), but from 2020 with the new IMO emission regulation (0.5 % sulphur), all vessels need either exhaust gas cleaning (scrubber) or they must operate on MGO or similar low-sulphur distillates. In the “well to wake” perspective, HFO operation gives approximately 10-15 % lower CO2 emissions than MGO operation.

The new vessels have a hybrid exhaust gas cleaning system combined with Solvang's low pressure EGR (Exhaust Gas Recirculation) system. This system has been developed on-board our own vessel Clipper Harald, where the NOx emission is reduced by almost 80 % when using low pressure EGR.  When combining exhaust gas cleaning and EGR we get a very cost efficient “all-in solution”, and compared to MGO operations, the savings are estimated to 5,000-6,000 USD per day.

The auxiliary engines are equipped with a catalyst for NOx reduction.

The main engine is a two-stroke HFO-fuelled diesel engine operating at 104 RPM with direct driven propeller. This gives an overall efficiency (engine to propeller) close to 50 %, which is higher than all other engine alternatives (including hybrid electric solutions etc). The vessel is optimized for both short- and long-haul trade, and the fuel capacity together with exhaust gas cleaning allows the vessel to sail more than 50 days without bunkering. Compared to our previous vessels, this is about 50 % increase in cruising range.

The vessels are furthermore fitted with “high-lift rudder” combined with integrated “Swirl Generator” which increases the propulsion efficiency. The high-lift rudder also ensures maximum low-speed manoeuverability which is an important safety feature. As a part of our newbuilding program the vessels will also undergo extensive model tests for establishing optimum trim condition under different load conditions.

The cargo plant is based on our experience (more than 40 year ethane/ethylene) and compared to previous generation the cargo plant gives about 15-20 % shorter cool-down time.

 

 

 

The figure above shows the fuel consumption together with NOx/SOx emissions for the new 21,000 cbm vessels compared to previous vessels. Set against the previous generations, the fuel consumption is reduced by almost 30 % measured as gram fuel / ton cargo per nautical mile, and with the corresponding reduction in CO2.

The NOx emission is reduced by more than 80 %. This is a combined effect of more efficient hull/propulsion (10 %) and larger cargo capacity (24 %). The Exhaust Gas Cleaning system reduces SOx emissions to almost zero, and soot with about 80-90 %.

Looking 40 years back, the fuel consumption is reduced by 55 %, NOx more than 90 % and SOx by 99%.

The vessels are also equipped with heat recovery on auxiliary engines for fuel savings (saving 1-2 tonnes of fuel per day at harbour).

In general, all systems on board are evaluated and designed in the most fuel-efficient way. This includes a thorough comparison to shore power in harbour mode and the use of battery as a means of reducing the fuel consumption and further optimising the power management on board. The results of this evaluation clearly favoured the EGC/EGR option.

 

 

Rating of different fuel and machine setups by emissions.

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