Methanol in fuel
Methanol onboard ships
Methanol is frequently carried onboard ships. Rules and guidelines for the carriage of methanol (and other, far more dangerous, substances) have existed for decades. However, the usage of methanol in shipboard machinery is somewhat exotic since it is forbidden, in principle (see Ch.3). Although the existing rules covering methanol is still tentative, there are some special features to it, worth to be noted.
As opposed to fuel oil, methanol can be carried in double bottom tanks since it is not considered harmful to the environment on a macroscopic level. (This does not mean that it is allowed to dispose methanol overboard as an operational procedure.) One special feature for methanol bunker tanks is that they need to be inerted, as opposed to conventional fuel oil tanks.
The SPIRETH project uses an independant transport tank container for bunker. The bunker tank is located on weather deck and is equipped with a drencher system for additional safety. Filling of the tank is done from tank truck.
For the Stena Germanica, a double bottom tank is proposed due to the significantly larger volumes of methanol needed.
A nitrogen supply system is needed, primarily for two purposes; inerting the bunker tank(s) and purging of (methanol) fuel system. The supply can be arranged from portable tanks or a generator system, whatever is more beneficial and practical. For the SPIRETH project, a portable solution was considered to be sufficiently economical but a generator system is proposed for Stena Germanica.
Fire- fighting system
A risk assessment approach has to be taken, according to SOLAS Ch. II-2 Reg. 17, to ensure that the proposed fire- fighting system provides equivalent safety for the methanol system as for a conventional fuel oil system. In principal, water- based extinguishing media are recommended due to methanol’s solubility properties in water. Carbon dioxide systems, as well. Nozzle design, flow requirements, and so forth, need to be specially considered and is subject for flag state approval.
For the SPIRETH project, both drencher and water- mist systems are used. Water-mist is proposed for Stena Germanica.
A dedicated compartment, separated from the engine room, is required for pressuring the supply fuel to the engine(s). The pump room shall be considered as a hazardous zone 1 area, unless quantitative statements are presented to prove otherwise, and require access through an airlock. Numerous safety requirements apply to this area, including means for fire- fighting, means for increased ventilation and gas detection, to mention a few.
Both the SPIRETH and Stena Germanica project have similar pump room design, although, for the Stena Scanrail it is combined with the OBATE plant (see Ch. 1.1.2).
Machinery spaces of category A
The methanol machinery space, whether it is for propulsion or power generation, shall be designed in a way that it is gas safe. This is accomplished with double- walled fuel piping. There shall be possibilities to purge the inner pipe and to monitor the annular space for hydrocarbons. The engine itself is subject to the same requirements as a conventional diesel engine, in principal, apart from some added features, such as crankcase gas detection.
The SPIRETH project uses conventional SCANIA diesel engines, modified for OBATE combustion. See Ch. 1.1.2 for further details. For the Stena Germanica, Wärtsilä proposes to use a common rail concept with pilot diesel. See Ch. 22.214.171.124 for further details