Shipping: an often overlooked source of sulfur emissions

Typically, when one thinks of curbing harmful emissions, things like wind turbines, solar panels, and hybrid vehicles are first to come to mind.  And this is not without due reason—power plants and automobiles are notorious for their consumption of fossil fuels, and efforts to make power generation and private transport “greener” have attained increasing public awareness and support.  In August of 2012, the Environmental Protection Agency (EPA) famously issued a new set of corporate average fuel economy (CAFE) standards that automakers selling in the United States must meet by the year 2025, which would effectively double the miles per gallon (MPG) rating that new cars on the road in the US must achieve [1].  In a similar vein, 2012 has been touted as “a bad year for the coal industry,” with 55 coal-burning power plants announcing their plans to close [2].  By all appearances, things are headed in the right direction in terms of curbing climate change-inducing emissions.

Despite all this, there remains a major source of pollution that has largely escaped public scrutiny: cargo ships.  Perhaps this is because the lack of day-to-day familiarity most people have with the shipping industry as compared to their more everyday experiences with filling up their car, paying their monthly electric bill, and so on.  There are many fewer people who see the enormous ships firsthand than who benefit from the steady flow of goods they bring from overseas—clothing, meat, electronics, toys, and much more.  Whatever the reason, maritime shipping has been and continues to be a significant and under-recognized source of pollution across the globe.

The primary cause for the increased level of pollution put out by these ships is their choice of fuel.  There are a number of different grades of fuel oils that are used in these ships’ engines, categorized by their viscosities.  The thinnest of these are comparable to what we know as diesel fuel on the common marketplace.  However, the thickest of these, IFO 380 and LS 380, have a kinematic viscosity of up to 380 centipoises at 50 degrees centigrade—about five times the viscosity of corn oil at room temperature [3], [4].  In fact, the fuel used on some of these big ships is so thick that it cannot even be pumped at room temperature—it needs to be heated to the boiling point of water before it can be piped into and used by the ships’ behemoth engines [3], [5].  These thick “residual fuels” are what is left over after all the lighter fuels (e.g. gasoline and diesel) are removed from crude oil in a refinery—this fuel is the literal bottom of the barrel.

Look how damn thick that is!

A jar of residual fuel oil. Photo credit: Wikipedia [3]

The greatest problem in using these thicker fuels comes from their increased sulfur content.  IFO fuels of varying viscosities are allowed a maximum sulfur content of 5% (with the actual average being around 2.67%); their lower sulfur LS fuel counterparts are allowed no more than 1.5% sulfur content [6].  Compare these to the EPA’s imposed limit of 30 ppm for gasoline—or, in the same units, 0.003% sulfur content [7].  The fuel that the ships use therefore contains 500 to 1667 times more sulfur per unit volume than does the gasoline that we are familiar filling our tanks with.  By one worst-case estimate, it would only take 16 of the largest type of ships to produce as much sulfur dioxide pollution as all of the cars on the road in the world in the year 2009 [8].  However, the price point of these residual fuels is significantly lower than their more refined counterparts’.  With IFO 380 costing only $649 per metric ton (and LS 380 costing $747 per metric ton) it can be difficult for major users to turn away from the cheap stuff [9].

It is probably folly to imagine that there is a simple way to solve the problem of maritime-generated air pollution.  After all, the infrastructure for fuel production and shipment is already very much in place.  Purifying the fuel by removing sulfur and other unwanted components would be costly to both the refineries and the customers buying the fuel.  Likewise, the monetary loss that would be incurred by replacing engines on these ships would be far from negligible, not to mention the increase in operating costs that would be caused by using pricier fuels.  As it stands, there is little incentive for ship owners and shipping companies to change the way that their fleets are powered.

On the bright side, there are currently a number of measures that are available to reduce the amount of emissions produced in the shipment of goods overseas.  The most charismatic of these is perhaps the “skysail,” a sort of parachute-shaped sail that can be attached to large ships that takes advantage of prevailing winds to provide additional locomotive power to large ships over long distances [10].  This solution is attractive to shipping companies because it is compatible with whatever other engine system is already installed.  The makers of this product estimate that its use could reduce ships’ fuel consumption by 10% – 35% per annum [11].  Even the lower end of this estimate would be considered a significant improvement over the current state of affairs.  However, considering how much more sulfur oxides are emitted by ships than by cars per gallon fuel burnt, this figure still seems inadequate in terms of the total reduction of pollution.  In order to truly reduce the amount of sulfur compounds released into the atmosphere, it is probable that restrictions will have to be placed on contaminant content within the fuel itself.  If this is not done, it seems unlikely that a real decrease in sulfur emissions from ships will be effected.















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3 responses to “Shipping: an often overlooked source of sulfur emissions

  1. I found your article very interesting and liked comparisons you have made, such as: “By one worst-case estimate, it would only take 16 of the largest type of ships to produce as much sulfur dioxide pollution as all of the cars on the road in the world in the year 2009” which enables the reader to compare and contrasts how much pollution is really being emitted by these ships.

    From an engineering point of view, I really, really liked how you discussed various technical aspects. The part I found interesting is when you discuss the cost of replacing the existing engines with newer engines that are more environment friendly. In addition to this, I liked how you discussed the viscosities of the fuels that these ships use.

    The solution you came up with is original and fool proof. After all, man kind has been using sails for centuries. It is hard to believe that such an important dilemma can be solved by such easy and simple solution. Two thumbs up!

    I am starting to realize how much problems sulfur creates. I am currently redesigning a heat exchanger for Chevron and the main problem is that the sulfur is depositing on the outside of the pipes due to too low operating temperatures.

    In my opinion, this world would be a better place without sulfur!

    Thanks for the interesting blog 😀

  2. This discussion is rich in detail and mostly-correct, but misses a few key points.

    First, I would disagree that the “greatest problem” with these fuels is their sulfur content – I would argue that CO2 has much greater environmental impact than any of the traditional “criteria” pollutants – especially since much (but not all) of the sulfur emitted by ships in the middle of the ocean falls out into the ocean rather than reaching land and causing the human-health impacts that drive these limits.

    Second, the IMO, via MARPOL Annex VI, has set sulfur content limits on marine fuels into the future – a stricter global cap still remains under discussion, but regional “Emissions Control Area” or “ECA” zones exist along some coastlines that reduce sulfur content so low it will drive operators to burn MDO – effectively road diesel – within 200 miles of shore. This will be in effect on the US West Coast in 2015.

    As for a proper response to this issue, you are correct to note that the refining industry is struggling to find ways to remove sulfur from these heavy fuels, but at present no economic solutions exist. Therefore, as noted above, industry may need to produce much more distillate in the near future than it does today – a significant challenge for refiners, and a loser for the climate (the net impact of producing all that distillate fuel is a ~2-3% increase in CO2 emissions per tonne).

    Finally, I am optimistic in the long term on kites and sails, but there are many more near-term energy-efficiency opportunities already being employed today: slow steaming (i.e. more ships moving slower – a net fuel burn reduction, effectively already mandated by the new EEDI); fluoropolymer hull coatings; weather-based voyage planning; hull cleaning; wake-improvement devices; vessel performance monitoring systems just to name a few.

  3. I agree improving the fuel quality in shipping vessel sounds like a great idea, but I am also unsure about the enforcement of higher quality fuels. With no international maritime police, enforcement of laws and regulations on the high seas is nearly impossible. Furthermore, ship owners often try to avoid vessel registration in countries with strict maritime laws, instead opting to register in countries with the cheapest or most lax laws. Known as a “flag of convenience”, this is why land-locked Mongolia has over 250 registered vessels [1] . As further example, in 2010 Panama ranked number one by number of registered tons with 300 million deadweight tons (DWT) followed by Liberia and the Marshall Islands with 150 million DWTs and 90 million DWTs, respectively. [2] For most measures, ships will only become more energy efficient when it is more economical.

    I think there are measures we can do to decrease vessel emissions while they are in port. As example, the Port of Long Beach has implemented the use of cold-ironing, a restriction that vessels must turn-off their engine and receive shore-side electrical power while docked. All power for cooling/heating, lighting, and etc is provided by the shore-side electrical grid instead of the vessel’s diesel generator [3]. I think that implementing the use of cold-ironing can greatly decrease the vessel pollution and can be enforced.




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