In order to reduce the greenhouse gasses which are produced by marine vessels burning high-sulphur fuels, and which currently contribute to global pollution, the International Maritime Organization (IMO), under the authority from the International Convention for the Prevention of Pollution from Ships (MARPOL) has set a maximum level of 0.5% sulphur content in the fuels used by these vessels. These limits come into effect on January 1, 2010. This is a marked reduction from the current 3.5% sulphur limit. The new limits, “IMO 2020,” will affect ships operating in any country that has adopted MARPOL.
Maritime transport emits around 940 million tonnes of CO2 annually and is responsible for about 2.5% of global greenhouse gas (GHG) emissions. Shipping emissions represent around 13% of the overall EU greenhouse gas emissions from the transport sector.
There are several important solutions suggested for the problem of reducing the pollution of the atmosphere as a result of burning high-content sulphur fuels. The first is to ban the consumption of the high-sulphur fuels by marine vessels and substitute for these fuels a range of advanced fuels which have a lower sulphur content. The second solution has been to install at the end of the combustion cycle of these high-sulphur fuels a mechanism which can “scrub” the combustion emissions which will reduce the volumes of high-volumes of sulphur compounds produced by the pyrolysis of high-sulphur fuels before they are released into the atmosphere.
In practice, however, there are advantages and disadvantages to each side of this simple choice. A regulated ship operator has four options:
• Use IMO-compliant fuel with a maximum sulphur content of 0.5 percent. The global shipping fleet now consumes about 4 million barrels per day (bpd) of high sulphur fuel oil, but about 3 million bpd of that demand will “disappear overnight” under the new IMO rules. The new demand is expected to shift to marine gasoil, a lower sulphur distillate fuel. This will generate at least 1.5 million bpd in extra demand for distillate in the next three years, pushing up total distillate demand growth for the period to 3.2 million bpd. These fuels are more expensive than the high-sulphur fuels. Gasoil now trades at a premium of about $250 a ton to fuel oil, but the forward curve forecasts this will balloon to $380 per ton by early 2020. Fuel accounts for about half a ship’s daily operating cost. Based on average fuel consumption of 20 to 80 tonnes a day (MT/day), a ship using cleaner fuel faces extra daily expenses of about $6,000 to $20,000. For example, a VLCC, one of the biggest oil tankers at sea, will pay 25 percent more for its fuel, or an extra $500,000 on top of normal bill of $2 million, for a typical 25-day voyage from the Middle East to Japan.[i] Early indications of prices for low-sulphur fuel oil 0.5% compliant with the IMO 2020 rule show that the new fuel costs about 30% more than the current, high-sulphur IFO380 fuel at Asian ports which have started selling it.
• Where IMO-compliant fuel is not available, ships can obtain a Fuel Oil Non-Availability Report, documenting unavailability. That report must be filed with the USCG Captain of the Port (not the EPA).
• Continue to burn high-sulphur fuel with a maximum sulphur content of 3.5 percent by installing a scrubber on the vessel’s exhaust system. Exhaust gas cleaning systems (scrubbers) provide one of the main compliance options for both existing ships and new buildings. There are several types of scrubbers available for shipowners. They need to choose a system for retrofit on their vessels which can be an open loop, closed loop or hybrid system. The introduction of scrubbers into the equation means that a shipowner must buy the scrubber system, await its delivery, arrange space at a facility for the installation of the scrubbers on the vessel and forgo the earnings on the use of the vessel as it is laid-up at the drydock awaiting the installation of the scrubbers. It has proved difficult for many owners to contract the fitting of scrubbers to their vessels as there are only a limited number of drydock facilities suitable for the installation of these scrubbers. In addition, the scrubber equipment alone can cost $1 million to $6 million, putting it out of reach of many operators. By 2020, about 2,000 ships could have scrubbers but this a “drop in the ocean”, given there are about 90,000 vessels in the global fleet, of which about 60,000 ply international routes [ii] Scrubbers can present their own issues of having to dispose of the removed sulphur.
• Use an acceptable alternative marine fuel, such as those identified by the IMO: battery power, biofuels, hydrogen fuel cells, and wind-assisted propulsion.
These regulations require that ship operators maintain onboard records that verify compliance. For example, bunker delivery notes and representative samples of fuel oil provided by fuel suppliers must be maintained onboard for a minimum of three years and 12 months, respectively. The records must also include a written fuel oil changeover procedure and a log recording changeover details. These records may be inspected, and the samples may be taken for verification to determine if the fuel oil used onboard meets the MARPOL sulphur standard.
What Are Marine Fuels?
Ever since the demise of coal-burning vessels, the fuels used by most of the industry has been a hydrocarbon fuel produced by the distillation of crude oil. Heavy fuels produced at the bottom of the barrel and the ‘cracked’ residuals were usually burned while at sea and marine diesel oil burned while in the port areas to reduce pollution and increase efficiency.
After this “straight-run “distillation”, the heavy fuel oil and the residuals at the bottom of the barrel are often transferred to a catalytic ‘cracking’ unit which reduces the heavy end of the barrel into lighter fractions of hydrocarbon bonding.
The heavier fuels that remain after all other useable fuel types have been drawn off are the residual fuels and are highly viscous. The fuels are used only in low and medium speed engines but require heating in order to reduce their viscosity allowing them to be pumped along the fuel system and injected into the combustion chamber. Such fuels have a higher energy content by volume but can also retain many more of the pollutants from the crude oil, especially sulphur. When refined using the catalytic cracking process there may also be catalytic or cat fines present. Cat fines are particles of aluminium and silicon oxides that are remnants of the catalyst used. They are hard and extremely abrasive and damaging to engines.[iii]
The term marine diesel oil (MDO) includes marine fuels that are composed of various blends of distillates, also called marine gasoil (MGO) and heavy fuel oil. Unlike diesel fuels on land that are used for cars and trucks, marine diesel oils are not a pure distillate but are blends with heavy fuel oil. Marine diesel is similar to automotive diesel fuel but has a higher density. Unlike heavy fuel oil (HFO), marine diesel oil does not have to be heated during storage. Marine diesel oil is sometimes also used synonymously with the term “intermediate fuel oil” (IFO). Marine gas oil (MGO) or ‘bunker fuel or bunker oil’ is any type of diesel which is used in seagoing vessels. The Marine Gas Oil (MGO) can be used in four-stroke machines and generator and can be produced with a low-sulphur percentage.
There are some low sulphur fuel oils (LSFO) available today although the quantities available are not high and there are some newer ultra-low sulphur fuel oils (ULSFO) sometimes referred to as hybrid fuels developed to meet the 2015 reduction to 0.1% in Emission Control Areas (‘ECA’). These are shipping zones: (a) U.S. exclusive economic zones where commercial vessels must meet the 0.5% sulphur limit; or (b) the North American ECA and the U.S. Caribbean ECA in which commercial ships must meet the 0.1 percent sulphur content for fuel.
There is a great difference in cost to the vessel owners by opting to use only acceptable fuels (LSFO), (ULSFO) or (VLSFO) as a response to the IMO2020 demands. There is an increasing amount of these LSFO fuels available and that is moderating the high premiums they demand and also spares the cost and delays of installing scrubbers as an alternative. The problem is that while the supply of these LSFOs may be growing and prices levelling out they may not be universally available in the world ports as the supply from different supplying refineries requires changes in the technologies of the refining processes.
There have been other types of fuel suggested for marine use including net-zero marine fuels like alcohol, biomethane and ammonia. Other processes produce fuels running on hydrogen. These are supplemented by improved batteries and fuel cells. By far the most promising has been the adaptation of vessels to use LNG or LPG as a fuel source; especially as many vessels are now plying the seas with LNG and LPG cargoes. There are several new LNG vessels capable of refilling other vessels with their LNG cargo (‘bunkering’). The cost, however, of retrofitting existing vessels to use LNG are prohibitively expensive but producing newbuilds with LNG propulsion systems seems to be the accepted way forward. The storage and use of LNG for propulsion requires a cryogenic capacity for the storage of LNG which makes it difficult to retrofit.
What Are Scrubbers?
Marine scrubbers are an economical and environmentally friendly solution to marine air pollution. Scrubbers or Exhaust Gas Cleaning Systems (EGCS) are used to remove particulate matter and harmful components, such as sulphur oxides (SOx) and nitrogen oxides (NOx) from the exhaust gasses generated as a result of combustion processes in marine engines to protect air and water quality.
Exhaust gas streams are passed inside the scrubber where an alkaline scrubbing material is present to neutralize the acidic nature of the exhaust gasses and remove any particulate matter from the exhaust. The used-up scrubbing material is then collected with wash water which may be stored or disposed of immediately as the effluent. The cleaned exhaust is passed out of the system and into the atmosphere. The scrubbing material is chosen such that specific impurities like SOx or NOx can be removed by suitable chemical reactions.
In an open loop scrubber seawater is used as the scrubbing and neutralising medium and no additional chemicals are required. The exhaust gas from the engine or boiler passes into the scrubber and is treated with seawater. The volume of seawater will depend upon engine size and power output, but a quite high pumping capability is required. The system is around 98% effective and even allowing for fuel oil with 3.5% sulphur should have no problem reaching the maximum 0.1% 2015 ECA level.
A closed loop scrubber works on similar principals to an open loop system but instead of seawater it uses fresh water treated with a chemical (usually sodium hydroxide but some systems others) as the scrubbing media. This converts the SOx from the exhaust gas stream into harmless sodium sulphate. Unlike the flow through method of open loop scrubbers, the wash water from a closed loop scrubber passes into a process tank where it is cleaned before being recirculated. The fresh water can either be carried in tanks or else produced on board if a freshwater generator is installed on the ship.[iv]
The hybrid system is a combination of both wet types that will operate as an open loop system where water conditions and discharge regulations allow and as a closed loop system at other times. Hybrid systems are proving to be the most popular because they can cope with every situation.
There is another system which has been introduced; the membrane scrubber in which the exhaust comes into direct contact with the scrubbing water in a spray or cascade system, where nanoporous ceramic membrane separation tubes are used to extract SOx from the engine exhaust.
The Membrane Scrubber consists of an array of ceramic tube membranes, suspended in the exhaust stream. A manifold system circulates the absorbent solution through the membrane tubes. Exhaust gases pass over the membranes where the SOx is dissolved into the absorbent solution. The ceramic tubes have temperature limits exceeding 800°C and the use of stainless steel ensures the acidic nature of the sulphur oxides does not corrode the membrane modules. Ionada, the maker of the system says one of the benefits of membrane scrubbing is the amount of effluent resulting from the system is significantly lower than typical closed loop scrubbers.
There is also a ‘dry’ system which employs pellets of hydrated lime to remove sulphur. An additional benefit is that the high temperature in the scrubber burns off any soot and oily residues. The lime pellets absorb sulphur and transform to gypsum. The dry system has a lower power consumption than wet systems as no pumps are required. However, the weight of the unit is much higher than wet systems.
Clean Fuels and the Environment
Whether one chooses to retrofit scrubbers to allow the continued use of higher sulphur fuels or if one chooses to use more expensive low sulphur fuels the price of transport will rise. There is a non-fuel solution to the problem of vessels in the port burning fuels on a continuous basis. Much of the pollution in the ports and along the adjacent coasts comes from the continuous release of SOx and NOx into the environment. The solution to this problem is for the port to provide to the vessels in the port and at the berths a constant supply of energy derived from non-carbon sources. Ports should erect energy supply sources from wind power, wave power, or analogous mechanisms which will supply the port facilities (vessels, cranes, grabs, pneumatic dischargers, portals, loaders, etc.) with a regular supply of energy from lines which can be accessed by these pieces of equipment. This will cut down the pollution risks dramatically and lower the burden of bunkering large supplies of fuels in the port and lowering the costs of port operations.
Perhaps this might become a priority for the IMO in addition to insisting on low-sulphur fuels.
[i] Libby George, Ahmad Ghaddar, "New rules on ship emissions herald sea change for oil market", Reuters 11/10/19
[iv] Malcolm Latarche, "How do scrubbers on ships really work",ShipInsight , 03 October 2017