The shipping industry is actively seeking ways to reduce its environmental impact. The IMO’s ambitious emission reduction targets have spurred the development of new technologies and practices to make shipping more sustainable, according to Marine Insight.
About Methanol
Methanol is a simple organic alcohol compound that chemically is denoted as CH3OH. From the chemical point of view, it is purely a hydrocarbon-based organic substance composed of carbon, oxygen, and hydrogen at an elementary level.
Since it is a derivative of the hydrocarbon family, it has the innate potential of high combustibility, meaning it can easily be employed as a fuel for running propulsion systems at a tangible efficiency. Methanol can be produced using either of the following methods:
- Using biomass, that is, substances that can be traced back to having their sources on living beings. They include remains of plants and animals, bio-wastes, etc. that react under certain conditions to transform into organic residues chemically and subsequently gases that can be treated to form methanol compounds in liquid form.
- Using electricity to either: i) treat flue residue biologically derived gases, or ii) exploit captured hydrogen and carbon content from the atmosphere (using certain scientific and industrial methods), and perform electrolysis under certain physical conditions to produce raw gaseous mixtures that can be further processed to generate methanol.
- Derivatives and extracts from natural gas resources that are originally processed to produce other petroleum products like LNG, LPG, CNG, etc.
- Various carbon-based natural reserves like earth, coal, minerals, and so on.
Advantages and Disadvantages
From a pollution point of view, methanol as a marine fuel is highly advantageous in terms of significantly reducing emissions and release of noxious elements. While the largest reduction is in terms of reduction of carbon dioxide (CO2) and carbon monoxide (CO), other noxious gas emissions critically flagged by IMO and other international regulatory bodies across the globe like nitrogen oxides (NOx) and Sulphur oxides (SOx) are significantly curbed.
Some reports have stated that the use of methanol as fuel can reduce CO2 by almost 90-95%, NOx in the order of 60-80% (with IMO studies claiming a lifecycle or lifetime average reduction percentage of over 55%), and SOx from 90% to even close to 100% as compared to conventional fuels. Moreover, the release of particulate matter from emissions is almost nil.
While we already have big dividends when it comes to cutting down the numbers from an emission point of view, other added advantages also come into play. In terms of biodegradability, methanol, within allowable limits, takes less time to dissolve in water and dissociates back to elemental levels that do not cause much damage to marine ecosystems, unlike conventional fuels. This is again a satisfaction to another aspect of marine pollution, that is from fuel and oil spillage, covered by Annex I.
The disadvantages are also quite considerable. Firstly, methanol has a lower calorific value (22 MJ/Kg) as compared to other mainstream conventional fuels. This essentially means that methanol has a lower potential for combustion as compared to other fuels (like gasoline or petrol) for the same volume.
Conversely, this translates to the fact that for catering to the same level of engine service in terms of consumption and the mechanical work delivered (manifested as nautical distance traveled by vessels), more quantity of methanol is required as compared to any other conventional fuel.
Thus, methanol ships must have a provision for greater bunkering, and tankage for fuel storage can be maximized only till a certain volume, there is always a factor of constraint in terms of maximum range.
Along similar lines, a higher volume of fuel consumption also means a reduced energy efficiency index, something still contentious keeping in mind the international regulatory goals that promote all vessels of various ages to stringently adhere to certain acceptable standards for these indices.
Bunkering and Storage
The bunkering and storage of such methanol is the biggest challenge. Methanol is to be securely stored in dedicated tankage basically under two categories: Integral tanks or independent or portable tanks.
Integral tanks are those tanks that are a part of the ship’s structure itself whereas the portable or independent tanks are tanks that are not a part of the structure and can be removed or uninstalled as and when required. Independent tanks provide the advantage of having lesser effects on the ship structure, as a whole, in the event of a fire outbreak or fatal overheating levels as they are not directly connected to the ship’s structure. The design and construction of a tank space for methanol as a fuel is based on the following philosophies:
- Disposition and arrangement of tankage in the safest possible locations
- Safe insulation and protection are needed so that in the event of an explosion, leakage, or fire outbreak, the effects are well contained within the minimum spatial limits of the vessel.
- Ventilation, detection, and inerting are suited to minimize explosive effects to the lowest keeping in mind the low flashpoint of methanol.
- Sound structural strength and integrity of tanks to minimize external effects like forces and moments to the greatest extent.
- Maximum feasible capacity after optimizing the above as much higher tankage volume is required for methanol as compared to other conventional fuels.
According to various class rules for ships running on methanol (based on IMO requirements), no fuel tanks for methanol should be located anywhere in the vicinity of accommodation or crew spaces as well as critical areas like engine rooms or machinery spaces where there is a high risk of overheating, leading to significant probability for ignition of methanol.
The tanks for methanol are not to be located forward of the collision bulkhead or aft of the aft peak bulkhead. Moreover, IMO also requires that the minimum distance between the fuel tank boundary and the side shell or bottom shell plating should be 760 mm for keeping a safe margin in the event of a collision or any other structural damage. All methanol ships should be of double-bottom configuration as a bulk of the fuel is stored underneath.
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Source: Marine Insight
