The Switch

31 Мар

Настоящая публикация посвящена очень актуальным вопросам, связанным с ужесточением требований к содержанию серы в топливе, которое используется на судах. Особое внимание авторы уделяют трудностям, связанным с переходом на топливо с низким содержанием серы, а также путям преодоления упомянутых трудностей.

This year shipping is taking a big step towards becoming greener, imitations on sulphur emissions (SOx) in Emission Control Areas (ECA) came into force on the 1st of January and have started to significantly reduce the industry’s footprint in terms of pollution.

When ships pass through or oper­ate non-stop in an ECA, their fuel oil is allowed to contain a maximum of 0.10% sulphur. Vessels powered with heavy fuel oils either need an exhaust gas cleaning system (a scrubber) or have to switch to ultra-low sulphur fuel oil (below 0.10%) before they enter an ECA.

Switching to Marine Gas Oil (MGO) is currently the most viable option for following the new threshold. This may appear to be simple task at first glance, but the fuel change-over procedure actually requires significant attention from crews in terms of operating as well as extensive preparation on-board a ship. The classification society DNV GL has produced guidelines to help the industry overcome the challenges associated with switching Heavy Fuel Oil (HFO) to MGO.

The difficulties

One parameter that needs to be taken into account is the fuels’ operating temperature. The operating temperature gradient between HFO and MGO is typically around 100°C can be up to 120°C. During the change-over procedure from hot HFO to cold MGO, the temperature of the injection equipment changes accordingly, creating potential hazards. Since the volume of the engine’s service system is relatively small, the change-over  may cause a rapid fall in temperature and  increase the risk of thermal shock to the injection components (thermal expansion or contraction may lead to “plunger sticking”), if not handled with care.

HFO and MGO also have very different consistencies. The main reason for this is their different chemical compo­sition as HFO contains molecules with much longer chains than MGO. This also causes the net calorific value of the distil­lates to be slightly larger than those of the residues (about 2-7%). Therefore, fuel systems need to account for the differ­ence in viscosity during operations. If the viscosity value is too low, there is a signif­icant risk of fuel pump failures as well as leakages in fuel pumps, engine mounted pumps and fuel handling pumps.

Cylinder lubrication is yet another factor that needs to be closely monitored. Decreas­ing the sulphur content of fuel has an impact on its acidity. The amount of alkalizing cylin­der oil therefore needs to be adjusted to avoid excessive engine wear or even damage.

During the change-over procedure HFO and MGO are mixed in all ratios. This bears the potential risk of incompat­ibility of residual fuel with ultra-low sul­phur distillates. Adding distillate fuels to residuals can cause the asphaltenes con­tained in the residual fuel to precipitate as heavy sludge clogging up the filters. In some cases, this may cut off the fuel sup­ply to the injection equipment completely and cause the engine to shut down. Tanks formerly used for HFO need to be cleaned thoroughly before switching to MGO, otherwise there is a risk of fuel contamination and failing to comply with the new and more stringent requirements.

The way out

These complications can be avoided by preparing detailed guidelines for the fuel change-over, training crews to take a meas-ured and careful approach to the procedure and by making informed decisions about the capabilities of a vessel. Carrying out compatibility tests for the respective fuels before they are bunkered is also advisable.

DNV GL has developed a ship-specific ‘Fuel Change-Over Calculator’ (FCO) to help ship-owners and operators determine the ideal parameters for their vessel’s fuel change-over. This new software can help to mitigate the risks associated with switching to MGO by providing owners and operators with the ideal parameters for the procedure.

Switching to MGO — currently the most viable option in order to follow the new threshold — requires significant attention from crews in terms of operating as well as extensive preparation on-board a ship.

The Calculator accounts for variables such as a vessel’s fuel system layout, any constraints on temperature and the vari­able sulphur content of fuels, as mixing occurs in the service system and can sig­nificantly reduce the risk of human error during the preparation of the change-over procedure. The software uses a complex numerical simulation that is more ac­curate than previous linear models and delivers insight into the optimised lead time for the change-over process, its costs and the maximum hourly consumption to meet constraints such as temperature.

This kind of data ensures a cost-efficient and reliable fuel change-over, aiding own­ers, operators and the crew in minimizing the risks by making data-driven decisions as well as helping to confirm compliance with the new Sulphur Directive when con­trolled by respective authorities.

Авторы: Jörg Lampe, Sophie Simon, Torsten Mundt

Источник: Baltic Transport Journal. – 2015. – January/February. – P. 25.