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SOx emissions

Updated 11 Oct 2019

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Timeline: MARPOL Annex VI (SOx related)

  • 26 Sept 1997 – Annex VI formally adopted;
  • 19 May 2005 – Annex VI enters into force sulphur level in fuel set at – 4.5% global, 1.5% ECA;
  • 19 May 2006 – Baltic Sea SECA established;
  • 11 Aug 2007 – EU implements North Sea SECA prematurely;
  • 21 Nov 2007 – Official IMO date for North Sea SECA;
  • 17 Jul 2009 – MEPC approves proposed US/Canada ECA (SOx, NOx and PM);
  • 1 July 2010 – SOx 1.0% ECA;
  • 1 July 2011 – MEPC approves proposed US Caribbean ECA (SOx, NOx and PM);
  • 1 Jan 2012 – SOx 3.5% global;
  • 1 Aug 2012 – Implementation of US/Canada ECA;
  • 1 Jan 2014 – Implementation of US Caribbean ECA;
  • 1 Jan 2015 – SOx 0.1% ECA;
  • October 2016 – MEPC 70 Completes of review into availability of low-sulphur fuel;
  • 1 Jan 2020 – SOx 0.5% global limit.

IMO and local SOx regulation

As this guide is being completed, there are just weeks for shipowners to finalise what strategy they will adopt to meet the 2020 reduction on the global cap on permitted sulphur content in fuels. The reduction from a maximum of 3.5% sulphur to just 0.5% is aimed at dramatically cutting the level of SOx emissions attributable to the shipping industry.

Emissions of SOx are covered by the same MARPOL Annex VI as NOx but the rules and the timelines involved are quite different. As with NOx, individual states are free to impose different regulations on vessels entering their ports or waters and this has been done in several areas of the world, notably the EU and China and most recently by Norway.

The regulation of SOx began when Annex VI became effective in 2005. This was done in two ways. Firstly, the level of sulphur permitted in fuels was regulated according to a reducing level over a period of 15-20 years through to 2020 or 2025 (the later date was an option that was not taken up by the IMO which in 2016 settled for the earlier date).

Secondly, MARPOL Annex VI allows the designation of certain areas as emission control areas (ECAs) the first of which was the Baltic Sea which was designated as a SECA (sulphur emission control area) in 2005 with the rules applying from 2006. A second SECA – the North Sea SECA – was established the following year.

Seven years later the first of two ECAs in the Americas was established followed by another two years later. In these two ECAs, both NOx and SOx are controlled. These four regions are currently the only places were SOx is controlled by international regulation but there is talk of a new ECA being established in the Mediterranean and there are other places around the globe where local regulations exist. In these areas, the permitted level of sulphur allowed in fuels or the level of SOx emitted is significantly reduced.

EU SOx regulations
The basic EU legislation for regulating sulphur emissions from ships was Directive 1999/32/EC. This was amended by Directive 2005/33/EC, which designated the Baltic Sea, the North Sea and the English Channel as sulphur emission control areas (SECAs) approved and adopted by the IMO and limited the maximum sulphur content of the fuels used by ships operating in these sea areas to 1.5%. The same fuel standards also applied to passenger ships operating on regular service in EU waters outside of the controlled areas.

From 1 January 2010 when the 2005 directive came into force, as well as reinforcing the limits of sulphur for vessels operating in SECAs and limiting the sulphur content of fuels used ashore in the EU, it also introduced legislation governing the maximum sulphur content of fuels used by inland waterway vessels and ships at berth in ports that are part of the European Community. The limit for ships in ports was set at 0.1% sulphur, which is the maximum sulphur content of gas oil under ISO standards.

The rules permit some leeway in that they allow ‘sufficient time’ for the crew to complete any necessary fuel changeover operation as soon as possible after arrival at the berth and as late as possible before departure. Ships in port for periods of less than one hour or those that connect to shore electricity supplies are exempt from the requirement.

Considering the IMO timeline for sulphur levels, the EU is now only out of step in applying the 0.1% limit to ports outside of the two SECA zones.

Just as the EU was premature in imposing regulation in the two European SECAs, it has also done this in respect of reducing the global cap from 3.5% to 0.5%. Although the IMO only took that decision in 2016, EU Directive 2012/33/EU had already laid down a maximum sulphur content of 0.5% for fuel used outside the European ECAs in the territorial waters and exclusive economic zones of EU member countries for the year 2020.

Chinese regulation
China is another country that has imposed its own regulation with the Air Pollution Control (Marine Light Diesel) Regulation 01/04/2014. This introduced a new sulphur content cap of 0.05% for the locally-supplied marine light diesel (MLD).

In addition, Hong Kong’s Environmental Protection Department has required all ocean-going vessels to use low-sulphur fuel, defined in the new legislation as fuel with sulphur content not exceeding 0.5% by weight, when at berth in Hong Kong waters. All such ships must initiate fuel switch upon arrival at berth, complete the switch to low sulphur fuel within one hour, then use low sulphur fuel throughout the berthing period until one hour after departure.

On 4 December 2015, China announced the establishment of further ship ECAs in the Pearl River Delta, the Yangtze River Delta and the Bohai Bay rim area. The regulation applies to all merchant ships navigating, anchored or under operation in the waters of the control areas. With effect from 1 January 2016, ships were required to follow the current international conventions or local laws/regulations (whichever is stricter) on the emission control of SOx, particulates and NOx. If the port condition allows, ports within control areas may implement stricter requirements than current conventions and regulations, such as requiring use of fuel with 0.5% m/m sulphur content or below.

The implementation schedule for the Chinese requirements is:

  • 1 January 2016, some ports (if the port condition allows) within the control areas may implement the requirement for use of fuel with 0.5% m/m sulphur content or below when ships are alongside or at anchor. Note that this is for any port within the control area, not just the key/core ports;
  • 1 January 2017, key/core ports of control areas implement the requirements for use of fuel with 0.5% m/m sulphur content or below when ships are alongside or at anchor;
  • 1 January 2018, all ports within control areas shall implement requirements for use of fuel with 0.5% m/m sulphur content or below when ships are alongside or at anchor; and
  • 1 January 2019, ships entering into control areas shall use fuel with 0.5% m/m sulphur content or below.

It should be noted that following an assessment of the effects of the above actions China will possibly implement requirements for use of fuel with 0.1% m/m sulphur content or below after 31 December 2019. The requirements for ships at berth or at anchor are applicable from one hour after ships are berthed to one hour before departure. Ships may use other alternative measures to reduce emissions, such as shore power, clean energy systems or scrubbers.

2020 sulphur cap

As things stand, the only step in the MARPOL Annex VI timetable still to be taken is the final reduction in the global cap from 3.5% to 0.5% which will take place on 1 January 2020.

This will be a particularly expensive exercise for the shipping industry as none of the options for meeting the global cap are cheap. They include making use of expensive fuels or installing exhaust gas cleaning systems.

The price put on the IMO’s decision to reduce the global level of sulphur in fuels has been estimated at around $60Bn. This is based upon forecast premiums for compliant fuels or the capital cost of emission abatement technology more commonly known as scrubbers.

The regulations concerning SOx reduction in exhaust emissions is potentially the most expensive regulation that shipping has ever had to meet although the cost will inevitably be passed along the line, finally ending with consumers ashore. More to the point, the effect of SOx regulations are felt by almost every vessel afloat, regardless of age. This is because, unlike the NOx rules which apply to the engine rather than the ship, SOx rules fall on the ship itself.

It has also been suggested that the impact will also be felt outside of shipping because, instead of using residual fuels that few other industries can, ships will now be competing with shore users such as power producers, agriculture and road and rail transport for the limited quantity of distillate fuels that can be produced from crude oil.

Fuel choice options
MARPOL sets limits by mass for the sulphur content of fuels as the primary means for controlling SOx emissions from ships. Reducing SOx levels in exhaust emissions can come about in one of two ways. Either the sulphur level in fuel has to be reduced or abatement technology in the form of Exhaust Gas Cleaning systems – commonly referred to as scrubbers – have to be employed.

Unlike with NOx, there are no adjustments that engine manufacturers can make but the use of low sulphur fuel requires additional precautions that need to be taken in the choice of engine lubricants.

Because it is purely a product of the combustion process, SOx is only an issue for vessels burning residual fuels either in diesel engines or in boilers. Ships that operate purely on low-sulphur distillates, LNG or any of the newer gas fuels that do not contain sulphur are not affected by any of the regulations controlling SOx and are saved the additional expense of complying with the requirements of MARPOL beyond what effect the regulation has on the price of fuels.

Only ships fitted with dual-fuel engines can use LNG as an alternative to oil fuels. For all other vessels, the only fuels that allow compliance without some form of treatment are distillates. Almost all diesel engines can run on distillates without modification and indeed it is quite normal to do so when manoeuvring in ports in any case.

A potential alternative to distillates is methanol which can be used by some existing engines with modification. There are a small number of ships that have been successfully running on methanol for some years now and more will be delivered by the endof 2019. Methanol contains no sulphur so does not produce SOx although a small amount of pilot fuel – which can be HFO, MDO or MGO – is needed for ignition and these fuels may contain sulphur.

Methanol has the added virtue of being a liquid and can be stored and handled by most existing fuel systems on ships. There are however, a number of safety issues around its toxicity that means careful thought must be given to its use.

There are two factors that prevent owners from opting to run solely on distillate fuels: the first is price and the second is availability. Distillate typically cost between 50% and 100% more than residual fuels making them an expensive option when bunker fuel already accounts for between 30% and 50% of running costs. Availability is not a problem when the normal quantities of distillates used by ships are considered but increasing availability could be a huge problem. Before the 2020 changes were announced, only about 20% of all ship fuels were distillates the rest being HFO. Distillates for shipping compete with fuels for land use so increasing the quantity fivefold is a big ask.

Several economic analysts have forecast that the effect of the SOx regulation will extend to all areas of fuel use outside of shipping itself. This is because meeting the demand for distillate fuels will mean that refiners will either need to add desulphurisation plant to their refineries or to refine much more crude oil. While some desulphurisation capacity has been added the amount is considered well below that needed.

If refiners are obliged to process more crude this will inevitably mean that a lot of residual fuel will be unsellable so the price of all distillates will have to rise. Furthermore, the distillates used by the shipping industry are also used by other forms of transport and power production thus competition will increase between the different industries driving up prices.

Desulphurisation
One of the questions most commonly asked about fuels is whether the sulphur can be extracted from the fuel before use. This is possible in refineries, but it is an expensive process and the equipment is not available in all refineries. The refining sector is under no obligation to shipping to provide compliant fuels but operators must become compliant when the global cap comes into effect.

Small scale desulphurisation plant is in the process of being developed and could possibly become available before the 2020 date arrives or quite soon after. These systems may be too large for shipboard use but could be used by bunker suppliers or by co-operatives of operators producing and storing compliant fuel ashore for use as needed.

Exhaust gas cleaning
It was initially intended that the only means of compliance would be to use fuels that met the regulations but under pressure from ship operators it was agreed that abatement technology would also be permitted and in 2009, the MEPC.184(59) guidelines for Exhaust Gas Cleaning Systems (EGCS) were adopted. These guidelines enable a ship to achieve low-sulphur requirements by water-washing the exhaust gas stream prior to discharge to the atmosphere. The washwater used will become contaminated with oil, soot and other material which can be treated in a separator to allow some of the water to be discharged overboard and the residue stored on board. Each country party to Annex VI needs to ensure that its port and terminal facilities can accommodate residues from exhaust gas cleaning systems.

Long before SOx was considered an issue for the shipping industry it was being regulated around the globe in connection with the use of large diesel engines in power production and other shore-based industries. As a consequence, exhaust gas cleaning or scrubbing technology is already a long-established reality in shore-based situations cleaning up emissions from oil and coal-based power plants.

When fuel oil containing sulphur is burned in the presence of air, the sulphur in the fuel combines with oxygen to form sulphur oxides. In a scrubber, the sulphur oxides in the exhaust are removed from the exhaust gas which then passes out of the system.

The technology falls into two distinct basic categories – wet and dry. In shore-based scenarios, scrubbers not only remove SOx from exhaust gases but in doing so the by-products are used in the production of plasterboards for use in the construction industry.

Space limitations and power consumption of the scrubbing equipment are rarely factors to consider when used ashore but they are of much greater importance for ship operators so these profitable side effects will not be available.

The wording or MARPOL means that the decision whether to allow scrubbers to meet the emission requirements rests with flag states and, although none has yet declared against scrubbers, it is possible that their use may not be available to every vessel. Where scrubbers are allowed, MARPOL rules permit their use by setting equivalent emission limits in regulations 14.1 and 14.4 of ANNEX VI. These limits are expressed as a ratio of SO2 (ppm)/ CO2 (% v/v) and work out at approximately 43.3 for each 1% of sulphur content in the fuel. There are several makers of marine scrubbing systems, most of whom are members of a trade body known as the Exhaust Gas Cleaning Systems Association (EGCSA). Their products operate on similar lines to shore-based systems although the use of dry systems is limited to a choice of one or two.

While scrubbers can allow ships to continue to make use of lower cost fuels with high sulphur content, they do not suit every operating strategy. When the global sulphur cap was 3.5%, for a ship entering an ECA or any other area where sulphur is limited only on very few occasions, the capital outlay on a scrubber may not have been recouped in a reasonable period. However, when the global cap drops to 0.5%, a ship with a scrubber will be able to operate continuously on high-sulphur fuel which will likely fall in price compared to distillates and any ultra-low sulphur fuel that may be available.

All scrubber systems require a treatment bypass for when the ship is operating without the need to use the scrubber. This prevents damage to the scrubber and reduces maintenance. Care needs to be taken to ensure that the scrubber is not causing backpressure to the engine as this could be damaging and will affect NOx reduction systems.

Scrubbers are increasingly being fitted to newbuildings but the majority now in operation have been retrofits. The time for a retrofit is currently more than a typical scheduled drydocking, meaning that extra lost earning days add to the capital outlay. However, as experience with scrubber installation grows, so the time needed for installation is reducing. In some instances, times of 11-14 days are being quoted, although this pre-supposes that surveying the installation site, measuring and prefabricating the units has been done before hand.

The capital cost of scrubbers is currently high at between $500,000 to $5M depending upon maker and vessel size but that would conceivably reduce if volume sales materialise. Payback time for a scrubber depends upon three variables; the capital and installation cost of the system, annual fuel consumption and the price differential between distillate fuel and the normal fuel used on the vessel.

Take-up rates for scrubbers may be improved if flag states and others offered state aid or attractive financial deals. So far, aid has been limited to a small number of projects in Europe and some finance houses have begun offering schemes that assist with capital expenditure and which link repayments to savings made. Some shipowners have even gone so far as to take significant holdings in a scrubber manufacturer.

The number of ships fitted with scrubbers is growing and, with it, the number of scrubber manufacturers. At the time when the first commercial system was fitted in 2006, there were just a few organisations interested in the potential. Today the number of makers active in the field exceeds 20 and newcomers are appearing regularly.

At mid-October 2018, it was estimated that the number of ships fitted with scrubbers or with scrubbers on order was 1,850. Following a surge in announced orders through 2019, it is now expected that the number of ships with scrubbers on 1 January 2020 could exceed 3,300 and, taking into account newbuildings, could reach 5,000 in a short period after 2020.

Many of the ships involved are those belonging to owners that had previously rejected the idea of fitting a scrubber. There is however some resistance to their use from within and from outside the industry with some saying scrubbers are shifting pollution from the air to the sea. Some shipowners that disagree with this view have formed an alliance to promote scrubbers under the banner of the Clean Shipping Alliance 2020. Less than a year after its formation the organisation has a membership of 38 shipping companies with a combined fleet of over 3,000 vessels.

How scrubbers work

There are various types of scrubbers available on the market for marine use but so far none makes use of ground-breaking technology and draw on the technologies employed in shore-based industries. Scrubbers can either employ wet- or dry- scrubbing methods, but not both.

Wet scrubbing technology
In a wet scrubber, the sulphur oxides in the exhaust are passed through a water stream reacting with it to form sulphuric acid. In this way, they are removed from the exhaust gas which then passes out of the system. Sulphuric acid is highly corrosive but when diluted with sufficient alkaline seawater it is neutralised and the washwater can be discharged into the open sea after being treated in a separator to remove any sludge.

The alkalinity of seawater varies due to a number of reasons. In estuaries and close to land it may be brackish and closer to neutral and in some areas where underwater volcanic activity takes place the water may naturally be slightly acidic.

In the shipping sector, wet scrubbers are divided into two types: open loop and closed loop. These technologies were developed separately but are now often combined into a hybrid system that can employ the most appropriate technology depending upon prevailing circumstances. There is one type of wet scrubber that has been developed which combines wet scrubbing with membrane technology.

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 and to a lesser extent on the pH of the seawater but equates approximately to around 40m3 per MWh meaning 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.

An open loop system can work perfectly satisfactorily only when the seawater used for scrubbing has sufficient alkalinity. Fresh water and brackish water are not effective, neither is seawater at high ambient temperature. For this reason, an open loop scrubber is not considered as suitable technology for areas such as the Baltic where salinity levels are not high. MARPOL regulations require the washwater to be monitored before discharge to ensure that the pH value is not too low, which would indicate that it is still acidic.

A closed-loop scrubber works on similar principles 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 medium. This converts the SOx from the exhaust gas stream into harmless sodium sulphate. Unlike the flow-through method of open loop scrubbers, the washwater 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.

In order to prevent build-up of sodium sulphate in the system, a small amount of washwater is moved at regular intervals either over side or to a holding tank and new freshwater added. The volume of washwater required in a closed loop system is around half that of the open loop version but more tanks are required. These are a process or buffer tank in the circulation system, a holding tank where discharge to sea is prohibited and a storage tank able to have a controlled temperature between 20º and 50ºC for the sodium hydroxide which is usually used as a 50% aqueous solution. There must also be storage space for the dry sodium hydroxide.

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 were proving to be the most popular because they can cope with every situation but a surge of scrubber sales through 2019 appears to have favoured open-loop systems.

The wet systems are not the most compact pieces of equipment and would take up considerable space if it were necessary to install them in under deck machinery spaces. Fortunately, they can be installed in the funnel casing and can in some cases replace part of the conventional exhaust system.

Membrane option
At least one system maker has modified the technology to produce a membrane scrubber. Essentially the membrane scrubber is a wet scrubber but instead of the exhaust coming into direct contact with the scrubbing water in a spray or cascade system, nanoporous ceramic membrane separation tubes are used to extract SOx from the engine exhaust.

These tubes form an array that is suspended in the exhaust stream and 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 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. The absorbent solution discharge rate is much lower than existing closed loop scrubbers and allows the Membrane Scrubber to store the absorbed effluent onboard for discharge ashore.

If sodium hydroxide is used as the absorbent fluid, the effluent can be regenerated for reuse with a sulphuric acid by-product. Other absorbents such as potassium carbonate are converted into potassium sulphate which has a commercial value equal to the base absorbent making the system cost neutral in terms of consumables.

It is claimed that due to the smaller volume of discharge water and the reduced amount of exhaust gas contaminants that are absorbed, the discharge water cleaning is much simpler. Removing the exhaust contaminants generates a small amount of sludge that must be stored onboard as part of the vessel’s oily water. The amount of sludge generated is less than 0.05tonnes/MWh. In the system, seawater pumps provide cooling water to the heat exchanger to cool the circulating absorbent solution but no seawater is used for scrubbing the exhaust gases.

The membranes require periodic cleaning to remove soot fouling on the membrane outer surfaces. The frequency of cleaning is dependent on operating conditions of the engines and the membranes are cleaned by circulating the absorbent solution under pressure to ‘back wash’ the membranes. The cleaning solution sludge is sent to the general sludge tanks and the amount of sludge produced is said to be typical of an economiser cleaning.

Dry scrubbing technology
Dry scrubbing is used extensively in shore-based power plants and can produce valuable by-products. An additional benefit is that the high temperature in the scrubber burns off any soot and oily residues. The first dry scrubbers used for ships were large and did not have the advantage of being able to be housed within the stack. This system is potentially still available but an alternative has been developed by Andritz.

The first dry system employed pellets of hydrated lime to absorb sulphur, transforming them to gypsum. Although spent pellets need to remain on board for discharge at ports, they are not considered as waste because they can be used for fertiliser and to produce plasterboard among other things. 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.

The version developed by Andritz is quite different. In the process, sodium bicarbonate (NaHCO3), commonly known as baking soda, is injected as a dry powder into the existing exhaust pipe. Due to the prevailing high temperature and adequate residence time, the NaHCO3 particle is activated, which increases the reactive surface by many times. This activation is necessary for the NaHCO3 to react with the sulphur components.

Such a process requires a temperature of at least 150°C but if the temperature of the exhaust gas stream from the engines is higher than 250°C, a quench is connected upstream, which brings the exhaust gas to the desired temperature by means of evaporative cooling.

The dosed exhaust passes through a filter on which other particles such as soot and ash are also deposited in addition to the sodium bicarbonate. A filter cake builds up on the filter cloth, and this is where the decisive chemical reaction takes place. SO2 reacts with NaHCO3 to form Na2SO4 (sodium sulphate), which is also present as a powder.

After a defined period of time or due to the maximum allowed pressure loss, the dust filter is cleaned by means of a pulse-jet process. During operation, a short stream of air is introduced at high pressure into the bag filter, whereby the filter cake peels off and drops into a collecting funnel. From there, the product is carried off by compressed air and stored in a silo for disposal ashore.

Proving scrubber performance
Flag states that decide to permit scrubbers on board ships will need to ensure that operators can prove compliance. Under MARPOL Annex VI Regulation 4, there are two schemes allowed for a system to be permitted that mirror the requirements for NOx compliance. One demands that the performance of any scrubber is certified before use and, as with the NOx systems, providing it is always operated within approved parameters there is no need for continuous exhaust emission measurements on the ship.

Parameters that must be continuously recorded include scrubbing water pressure and flow rate at the scrubber inlet, exhaust pressure before the scrubber and the pressure drop, fuel oil combustion equipment load and exhaust gas temperature either side of the scrubber. A record of chemical consumption must also be maintained. Under the second scheme, the exhaust gas must be continuously monitored when the equipment is in use and there is no need for the system’s performance to be certified.

Under both schemes the condition of any washwater discharged to sea must be continuously monitored for acidity, turbidity and PAH (a measure of the harmful components of oil) and data logged against time and ship’s position. A test for nitrate content is also required at each renewal survey.

Washwater regulation
In May 2015 at MEPC 68 the meeting adopted amendments to the guidelines for exhaust gas cleaning systems which permits a calculation-based methodology for verification of washwater discharge criteria. The revision allows for calculation or modelling to verify the discharge of washwater pH at a point that is 4m from the point of discharge. This will be reviewed after two years and, if necessary, changes will made to the washwater discharge controls. However, any changes will apply only to new installations.

Wet scrubbers are good at removing particulate matter and soot which, although not currently regulated for specifically, are likely to be so in future. Typically, a scrubber will remove at least 500kg of particulate matter for every 100 tonnes of fuel oil burned and possibly more, depending on how much washwater is used.

These solids must be removed before the washwater is discharged overboard and to conserve space the system should have a separation phase included that removes as much of the water as possible before sending the sludge to be stored for later disposal ashore.

Despite being allowed under IMO regulation. scrubbers are a controversial solution to reducing SOx emissions and there have been objections to their use from inside and outside the shipping industry. Opponents claim that allowing scrubbers merely shifts the pollution potential from the atmosphere to the sea, but this is disputed by supporters of scrubbers. Open loop scrubbers are singled out as being the most polluting as the washwater is discharged direct to the sea. The argument is ongoing with both sides producing support for their position using scientific papers.

At the IMO, discussions are taking place within the MEPC and its PPR Sub-Committee. Most observers believe that the result will be a tightening of the guidelines and very likely the possibility that the guidelines will change from being voluntary to being mandated. Some form of monitoring equipment will then become compulsory and a small number of companies such as Rivertrace and Chelsea Technologies are already producing monitoring systems.

Rather than wait for the IMO and the scientific debate to be settled, some countries; notably Norway, Singapore and China, have introduced bans or restrictions on scrubber use in territorial waters.

Fuel-switching issues

For all ships operating on a fuel above the 0.1% sulphur allowed in ECAs and without a scrubber, a switch to distillates will be needed when entering an ECA. Switching fuels is something many operators calling at EU and ECA ports have become familiar with over the last few years but which may still be unfamiliar to crews operating mostly outside these areas.

More to the point, previous experience was gained on ships making use of conventional 3.5% sulphur HFO rather than the new compliant fuels that some suppliers are developing.

Switching fuels brings hazards such as the risk of fire because HFO needs to be heated for use and distillates do not. The high temperatures present in the fuel lines can cause low-flashpoint distillates to ignite, leading to loss of power and worse. The issue of loss of power during fuel switchovers is a well-known hazard and one that the USCG has issued a number of safety alerts over. It is recommended that, as part of the master-pilot information exchange, owners should discuss the vessel’s manoeuvring characteristics, including any change in RPM associated with ultra-low sulphur fuel oil. Shipowners should also determine if the use of ultra-low sulphur fuel oil necessitates amendments to the pilot card.

Exactly how the switchover process with the new generation of 2020 compliant fuels will need to change from the current procedures remains to be seen.

Under current circumstances, the switchover process can be long-winded and the various hazards need to be taken into account. In addition to the risk of fire, low-sulphur fuels may damage existing HFO pumps because of reduced fuel oil viscosity and lubricity leading to overheating and excessive wear. Fuel injection pumps can be similarly affected, necessitating their replacement by special equipment such as tungsten-carbide-coated pumps. Unless approved by the engine manufacturer, such changes may affect the engine’s compliance with NOx legislation.

When running on HFO, many components of the fuel system are either heated directly or will become hot because of the fuel temperature. MGO running through hot piping may vaporise, creating vapour locks that interrupt the fuel supply to the engine. During the changeover, rapid or uneven temperature change could cause thermal shock, creating uncontrolled clearance adaptation, which in turn may lead to sticking/scuffing of the fuel valves, pump plungers, suction valves and, in the worst-case scenario, total seizure of the pump.

To maintain an appropriate viscosity if MGO is used in an engine designed to run on HFO, a new cooler may have to be fitted; in some cases it may even be appropriate to install a chiller to remove heat through vapour-compression or an absorption refrigeration cycle.

Ships entering ECAs must have a defined written procedure on board to comply with MARPOL Annex VI Regulation 14. The rules also require that the following be recorded in the engine logbook:

  • volume of low-sulphur fuel oils in each tank;
  • date, time and position of vessel when changeover occurred before entering an ECA; and
  • date, time and position of the vessel when changeover took place after leaving it.

Several equipment-makers have developed devices intended to facilitate switchover for crews. Electronically-controlled engines may be easier to manage during switchover, but that is a side-effect of the technology. Devices designed with the changeover in mind include automatic switchover management systems and components for inclusion into the fuel treatment process. Some have the ability to log the data and even transmit it to a shore office. Where this feature is available, it may be used to counter claims about illegal use of fuels in ECAs.

Some devices also allow switching of fuels running at full load. These use sensors to detect if fuel temperature changes too rapidly, in which case the system freezes the position to protect the engine’s fuel injection system from thermal shock and sends an alarm. For safety, the fuel changeover process can also be stopped manually. In some is also possible to integrate a flow and density meter to calculate total fuel consumption.

Lubricants need to be matched to fuels in order to avoid excess corrosion or lacquering which are the extremes of mis-matching. Tribology – the science of interacting surfaces, friction, wear and lubrication – is an important part of engine and lubricant R&D. Attempts have been made by most lubricant makers to develop a universal lubricant for engines that can cope with all fuel types but universal acceptance of the products has so far been elusive.

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