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p30-34.qxd 09/05/2006 12:00 Page 3 TECHNOLOGY EMISSIONS Mixing versus segregating fuels The arrival of SECAs has caused the shipping industry to rethink ship design with reference to fuel tanks. DNV has outlined its thinking on the subject. Ships generally have two or more HFO storage tanks. SOLAS rules have required double day tanks for all fuel types used on board since July 1998. Some ships also have double HFO settling tanks to further reduce the risk of fuel incompatibility, and enhance settling. If the intention is to operate on different HFO qualities inside and outside SECAs, it is now beneficial to install (or retrofit) double HFO settling and service tanks for operational convenience, economy and safety. The benefits of double HFO systems compared with mixing fuels in the settling tank (or in the service tank if the settling tank is completely drained before changing to another fuel) are: • To facilitate verification of compliance with the Marpol Annex VI clause "…shall allow sufficient time for the fuel oil service system to be fully flushed of all fuels exceeding 1.5 % m/m sulphur content prior to entry into a SECA". • To avoid consuming expensive low sulphur HFO (LSHFO) during the mixing phase before entering and after exiting the SECA. • To avoid possible incompatibility problems. The benefits of double HFO systems compared with switching between HFO and LFO in the supply piping are: • To avoid the hazard of switching between completely different fuels at sea (especially in congested areas like the English Channel, or potentially rough areas like the North Sea or Bay of Biscay). • To simplify the switch-over procedure generally. Switching If double HFO systems are not provided and the ship does not have LSHFO available when entering a SECA, the only alternative will be to switch over all HFO engines to LFO at sea. In such a case the LFO temperature and the temperature change gradient need to be considered. For 2-stroke engines, a controlled temperature gradient is recommended, with a reduced engine load. For 4-stroke engines, the fuel changeover can generally be performed via the mixing tank at any load. Procedures and/or arrangements for switching from HFO to LFO may include fuel pre-heaters, fuel pipe trace heating, a 3-way valve in the suction line from the service tanks, redirecting the return fuel to the LFO service tank, LFO cooler, possible need to control engine load, and monitoring pressure difference of fuel filter (indication of incompatibility). Quoting DNV; "if gas oil is mixed in while the fuel temperature is still very high, there is a high probability of gassing in the fuel oil service system with subsequent loss of power" If the ship has only one HFO service and one HFO settling tank and assuming that it is possible to completely drain each of them with a transfer pump and that the operator deems it feasible to undertake even at sea, the switchover procedure may include the following phases: • Switching from HFO to LFO operation. • Stopping the separator. • Perhaps draining the bottom sludge to the sludge tank. • Draining the HFO service and HFO settling tanks completely with the transfer pump to a storage tank with the same fuel quality. • Filling the settling tank with the new quality. • Possibly changing the gravity disc of the separator. • Restarting the separator. • Filling up the service tank via the separator (at least partly to a safe level). • Switching over to this new fuel. Depending on the ship, this procedure may take around 15 hours if the service tank is filled up to 50% before being used. Fuel separators Until the mid -1980s, typical fuel separators were equipped with gravity discs, the purpose of which was to control the interface between the water and the fuel in the separator bowl. The gravity disc has to be selected according to prevailing parameters, including the fuel density. A new bunker delivery may require the gravity disc to be replaced. Finding a suitable disc sometimes takes a little time. From the mid-1980s, a new type of separator allowing water monitoring in the clean fuel outlet gradually became the dominating type installed on new ships. However, older type separators are still in operation on old ships. These old ships now find themselves in a new situation and could benefit from the fitting of newer fuel separators, in case the ship is alternating between HFO and LSHFO with different density. A difference in density is more likely if the LSHFO is based on blending at the refinery rather than on low sulphur crude oil. For newbuildings, it is beneficial to arrange double HFO settling and service tanks. The preferred minimum number of storage tanks is four, to permit the ship to bunker HFO and LSHFO in empty tanks at anytime, even if both fuel qualities are available in other tanks. Thus different bunker deliveries do not have to be mixed. Since January 2003, a new DNV voluntary class notation 'FUEL' has been available. The system design criteria of this class notation are suitable for ships, which due to their operational pattern, benefit from using two different HFO qualities. For existing ships with double HFO service tanks, SOLAS rules required double service tanks for all types of fuels used on board ships, the keel of which should have been laid on 1st July 1998, or later. These ships could dedicate one service tank permanently for HFO and the other for LSHFO. However, there are ships built with an 'equivalent' arrangement, where a LFO service tank of usable capacity has been approved as the second tank. If the ship has only one HFO settling tank, consideration could be given to installing another settling tank for complete segregation and proper functionality of that settling tank. For existing ships with single HFO service tanks, consideration could be given to installing another HFO service tank. If the ship has only one HFO settling tank, installing another settling tank would provide additional benefit Also for existing ships with single HFO service tanks, as an alternative to installing double tanks, a blending unit can be retrofitted. However, there is a risk of incompatibility. The unit is used to inject LFO (with low sulphur content) into the fuel booster system to reach the required sulphur content of 1.5%. LFO system layout The fuel system needs to be suitable to avoid too low LFO viscosities for generator engines in EU ports, also in warm conditions, even if the system has been designed for HFO. Heat is introduced into the system from the diesel engines and possibly from fuel separators and adjacent tanks. In some cases, a fuel cooler may be required. It may be prudent to review the fuel system thermal balance if and when larger amounts of LFO are beginning to be consumed in a continuous operating mode. This applies especially if LFO operation is foreseen also for the main engine operating in SECAs. Main engines are not affected by EU rule limiting the fuel used in ports. DNV has identified a range of technical challenges when operating HFO oil-fired boilers on low viscosity distillates. Double HFO settling and service tanks are also beneficial for this reason. TO TankerOperator May/June 2006 page 32
p30-34.qxd 09/05/2006 12:01 Page 4 TANKER Operator Marine fuels: ‘Avoiding bad bunkers’ Earlier this year, Razaghi Meyer released details of its latest INtegrity suite of applications, which was launched in 2005. Fuel quality is a serious and worsening problem. Approximately 14% of fuels analysed do not comply with the standards. The introduction of MARPOL and the current high cost of fuels mean that this is no longer a tenable situation. The true extent of the problem can only be guessed at, as not all fuels are analysed and some problems are not revealed by analysis, Razhagi Meyer claimed. Although designed to enable vessels and suppliers to demonstrate compliance with MARPOL 73/78 ANNEX VI regulation 18, an important benefit is the ability INtegrity applications give to suppliers and vessels alike to detect and avoid the supply of bad bunkers; bunkers which do not meet the standards, which do not comply with MARPOL, or which exhibit other problems not detected by the sample analysis. This particular regulation relates to the maximum permitted levels of sulphur allowed in marine fuels. INtegrity CMV and CEMS for vessels is designed to provide compliance monitoring and verification automatically and to provide a continuous emissions monitoring system, solutions which the current legislation lacks. Based around digital viscometers, the key to the compliance function is the 'fuel fingerprint' method developed for these applications by Razaghi Meyer. The INtegrity Application Suite has four key functions: • Enable suppliers to monitor and control quality, provide on spec fuels and demonstrate that capability to clients. • Prevents the bunkering of off-spec or improperly blended fuels. Even on a barge, the systems require virtually no maintenance. • Provides a monitoring system intended as an electronic log to demonstrate MARPOL compliance. • Protects engines from off spec fuels including fuels contaminated on board. For fuel suppliers INtegrity is a suite of applications developed around digital viscometers that is designed to support all bunker fuel supply methods including: • Batch blending. • Mechanical inline blending. • Meter inline blending. Whether in the refinery, in terminals or on board barges, these systems require virtually no maintenance and are ship friendly and user friendly. Using the INtegrity solution, suppliers can guarantee fuel quality to the client at the time of bunkering, Razhagi Meyer claimed. The supplier can also interdict the supply of off-spec fuels and can demonstrate to the client the quality of the fuel and confidence in the accuracy, efficiency and integrity of the supply chain right into the vessels bunkers. For vessel operators: INtegrity BIM, Integrity CMV and and INtegrity CEMS provide the vessel with protection against bunkering off spec fuels (BIN: Bunker Inlet Monitor) and provides a means to demonstrate compliance. It also provides protection at the engine against fuels that were off-spec when bunkered, or which have become off-spec while on board. What are good bunkers? The INtegrity suite of applications, for suppliers and vessels alike, detects in real time and will help to ensure that: • Fuel is free of entrained air. • The fuel or fuel component is homogenous. • The fuel is well mixed. • The fuel, nor any of its components are not a consolidation of different batches, co-mingled but not mixed and re-analysed. • That the density value used for the mass flow rate calculation is a true live value rather than a value derived from the component analysis. • That the fuel or fuel component has the properties described in the analysis or blend calculation (fuel fingerprint match) - thus validating the percentage mass of sulphur. Fuel quality is determined by the supplier through laboratory sample analysis; INtegrity validates the analysis and determines if the fuel being bunkered is the fuel described by the analysis. INtegrity does not measure sulphur, it measures a fuel fingerprint with which to validate a suppliers analysis and personnel on board the vessel can automatically identify and report which fuel is being consumed. It can then report the sulphur content as the value determined by analysis. Bad bunker recognition Razhagi Meyer can illustrate the commonly encountered bunker quality problems with data collected in actual bunkering operations displayed in Excel chart format. The company claimed that these illustrations demonstrate that most, if not all, common bunker quality problems are instantly visible, recognisable, understandable and above all actionable. Data collected and displayed in real time allows real time evaluation and decisions. It is no longer necessary to await the fuel sample analysis to know if the fuel is bad. Not up to standard fuels can be reject- Good bunker or Bad Bunker? Bunker Fuel Quality Assurance when you need it most - during bunkering! Don’t wait until it’s too late - Get INtegrity CMV : stop bad bunkers getting aboard your vessels and avoid expensive de-bunkering. Real Time Instant Recognition: Good and Bad in one Bunker Razaghi Meyer International 1 Lynwood House, 143 Blackborough Rd, Reigate, Surrey RH2 7DA, U.K. www.ViscoAnalyser.com ( +44 870 747 3477 e-mail info@ViscoAnalyser.com TankerOperator May/June 2006 page 33
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Navigation standards slammed - Tanker Operator

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