Don’t overlook auxiliary issues
Its worth noting that some auxiliaries see larger load steps while the propulsion engines are near idling, as they are often connected to pumps, cranes and other gear such as thrusters, says Tomas Aminoff of Wärtsilä.
This means that the auxiliary engines, and any associated equipment for emission control must be able to work over a large load range.
However, auxiliaries can be faced with a very variable picture. For example, some containerships have take into consideration a relatively high number of reefer plugs, pulling in a substantial power demand that can easily be 8MW in port and 12MW when manoeuvring with the bow thrusters.
But the biggest challenge, explains Mr Aminoff, is from legislation – and its not an even developmental field, “You are talking about different solutions for different areas and these things might change,” he says, referring obliquely to the ups and downs of the IMO/EU policy pull and push.
It’s worth noting here that switching between HFO and the distillate alternative has its own issues. With auxiliaries as well as main engines, there is a difficulty with changing over the fuel explains Michael Eggert of Lehmann & Michels – and there’s even more of a demand to cushion the impact. Firstly the changeover valve need to be controlled: different levels in the tanks can affect the flow and the traditional manual three-way kind might well let through too much at one time.
So, says Stephen Faircliffe of Aalborg Industries, the best solution is an electronic one, via parallel, twin lines. “Further, there’s a massive difference in lubricity, so it’s not worthwhile trying to move over from one to the other without modifications,” he says.
The need for cool
Mr Eggert explains that a control and automatic cooling system, such as the ControlMag, is even more necessary for auxiliaries running distillates than main engines: “Its not just on fuel change that issues occur, when you have a lower consumption, the temperature can rise very suddenly causing injector damage and resulting in a very expensive repair bill – so you need to keep the change below 2°C per minute.”
But given the difference in price of fuel as well as availability, many manufacturers are trying for ‘flexible’ engine solutions that don’t rely on distillates. “There are two very good solutions - gas or scrubbers with an SCR - that have received a lot of development work over the last 24 months,” says Mr Aminoff.
While you might not want to deal with the expense or space issues of retrofitting a scrubber system just for the auxiliaries, Mr Faircliffe does say that the treatment can be woven in with a main engine system, especially since the cleaning chamber can be remote from the engine room. Further, he adds “a freshwater-saltwater system like PureSOX gives more flexibility”.
Although the scrubbers are directly applied to sulphur and other particulates, the likely upcoming focus on NOx emissions means an SCR will be needed as well - and here the challenge is to get it to work with the cooler scrubber exhaust temperature. Most manufacturers work on a ‘wet’ or seawater system, which usually means reheating, although the benefit of a ‘dry’ (chemical) system is that the temperature remains high enough to be pushed through an SCR. And again, the more you add these kinds of gadgets, the more the back pressure increases, so the challenges also rise, explains Mr Aminoff: “At the same time manufacturers the world over have been making their engines more efficient, and more efficiency cuts down any margins you might have had to adjust and play with.”
Wärtsilä’s answer has been to tune the engines with higher exhaust gas temperatures in combination with low loads to allow a higher back-pressure; further, recent developments on both the engine and SCR catalyst material now allows the fitting of an SCR before – not after – the scrubber, even when using high sulphur fuels.
Regs add issues
Trying to predict legislation has also added complications. “Due to the development of ECAs we now have reason to believe that in future these will often be taken on as a pair – and this too has had to be taken into consideration with engine design,” says Mr Aminoff. You have to tune the whole thing together in order to know where you are.
” So phased retrofits or shopping around from several suppliers can be problematic.
For example, Norway has been very active in trying to clean up its act and many Norwegian operations have put in their vessels for SCR retrofitting so that they get some money back from the NOx fund. The drawback, explains Mr Aminoff, has been that in many cases the engine has not been tuned properly for SCR operations, and the SCRs haven’t been able to deal with the decreased volume of exhaust gases from the engine when it is operating on low loads. Thus, many operators have found their SCR to be ineffective during a remarkably large slice of the vessel’s operation.
However, Wärtsilä has, by tuning the engine and the SCR together, been able to develop an auxiliary package that works even when it’s down to as little as 10% of the nominal engine load.
The other prong to the auxiliary emission clean up act is gas.
Although the HFO part of the dual-fuel equation is slightly less efficient than single fuel engines, the gas side is actually more effective, explains Mr Aminoff. He goes on to say that dual fuel auxiliaries are under market pressure to become more capable: “Wärtsilä is now putting in more development hours on things like part-load operation,” he says, adding that all of them are now able to start and shut down in gas mode and able to idle with gas for up to eight hours. “These capabilities are needed because we see dual-fuel engines going into more and more new vessel types,” he adds. The change over from LNG to HFO is instant, although the change in the other direction is dependent on an 80% engine load or less.
Further, dual-fuel machinery actually offers lower CO2, NOx and SOx than cold ironing: this is because even assuming a zero emissions contribution from shore power, you have to add the diesel used while the ship is queuing, manoeuvring or berthing.
Although there have been a number of calculations predicting payback times, it must be said that the price of gas itself is difficult to forecast – and even difficult to pinpoint in the present, with Asian prices being very different from the cost in the US. However, with HFO prices on a steady rise, LNG has become increasingly attractive compared with HFO and LNG isn’t going to be anywhere near as expensive as MGO, the distillate version that the ECAs will require to get their sulphur down as low as 0.1% in just a couple of years.
But it does come down to the infrastructure – which is still in its infancy although there are several ongoing projects around the world. “For a start, the LNG should remain in liquid format from the import terminal to the ship in order to be truly viable - otherwise you are paying for compression of the fuel twice over,” says Mr Aminoff although some vessel types might benefit from removable gas tanks in form of containers or mounted on trucks.
This looks like meaning an expense on the quayside although the growing maturity of the infrastructure over time should make it more viable, but so will the distilling processes of MGO – what will happen is anyone’s guess.
However, in the US, the introduction of LNG from shale gas “has been a game changer”. Mr Aminoff points out that just one operation could push the market, giving it momentum. “Private operators with heavy industries are very dependent on sea transport – and will remain so,” he says.“I think when you talk about dual fuel, you are talking about a huge amount of development in a very short space of time – and much of it has been pulled by market interest,” Mr Aminoff concludes.
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