What Are Methanol Ships?

Introduction 

The perpetual quest to reduce emissions and make the seas cleaner and greener has paved the way for the inception, development, and implementation of various technologies and practices over the years. 

These developments have accelerated at a greater pace in recent years, thanks to the ambitious new IMO GHG strategy that aims to reduce an overall index of marine emissions by at least 20% by 2030, 70% by 2040, and almost zero (net-zero) by 2050. (compared to 2008 baseline emission levels).

Alternate fuels have already gained significant prominence, and a crucial portion of the modern shipbuilding index has moved past the conventional fuel design philosophy to those reducing emissions. 

Over the past several years, methanol has gained a lot of significance as an alternate fuel supplanting conventional ones like diesel, HFO, or even complicated setups like LNG/LPG or hybrid. 

What is 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 that 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. 

The detailed description of each of these means is complicated and omitted from the scope of this article. 

Advantages and Disadvantages of Methanol

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. 

They include easier stowage, lesser maintenance, biodegradability, and of course, sustainability in terms of being produced from resources that do not face a threat of depletion (unlike conventional fuels that are produced from non-renewable fossil reserves).  

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. 

While we have weighed the significant advantages of methanol as a fuel, 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 travelled 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.  

Furthermore, methanol is also pricey and is available for ships as compared to diesel or HFO. 

Another critical aspect is that methanol has a very low flashpoint, 11 – 12 degrees centigrade. This accounts for very high risks of inflammability, and thus, methanol ships need to have special measures minimalizing the hazards associated with this substance. 

Design, Construction, and Technologies 

Methanol ships, from a basic design point of view, like hull form or structural strength, are like other cargo ships. 

However, the main differences stem from the following critical aspects of methanol as a fuel: 

• Bunkering of methanol in bulk quantities (arising from the large volume requirements) 
• Safe storage and handling of methanol owing to its dangerous nature of inflammability 
• Design for maximum safety considering worst-case scenarios like explosions and leakages. 
• Transfer and handling of methanol 
• Engine selection

The basic philosophy of design for methanol ships targets the following objectives: 

• Preserving the methanol at necessary temperatures and conditions during both bunkering and service/consumption, owing to its low flashpoint value.
• Prevention of any form of leakage or outflow of the methanol at any point in time. 
• In the event of any unwanted event like a fire outbreak or leakage, reducing the effects to a minimum. 

Since methanol with a very low flashpoint value is hazardous, methanol ships are designed and classified under the special ICG Code developed by IMO. Since 2017, all vessels, new buildings or retrofitted, using methanol as a fuel need to strictly adhere to the guidelines defined under this code, and individual classification societies have also detailed rules in line with the ICG’s framework. 

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. 

Regulations essentially underscore that all integrated fuel tanks should be bounded by cofferdams at all boundaries except when one of their boundaries is the side shell itself and it is well located below the waterline. 

Integrated tanks are structurally strengthened to very high levels to provide additional protection against high loading. 

Independent or portable tanks are either separately stowed in a separate storage hold compartment that has superior levels of insulative protection or can be kept on the open deck with adequate measures of temperature control. These tanks are to be necessarily surrounded by coamings. Overhead tanks are strongly connected to the deck with suitable structural members (as certified) and are of higher strength index, considering various worst-case scenarios of static and dynamic loading as well as external weather loading.               

Inerting, Detection, and Storage 

Inerting, detection, and venting is the next big challenge. All tanks should have a robust detection and venting system to detect and release potentially flammable built-up vapours of the methanol accumulated over time. The tanks should have a minimum number of two inlets and two outlets to prevent the build-up of pressure from the inflammable vapours over time. The inlets should be designed to let in maximum flow of inert gases at a positive pressure. 

The venting systems should be well controlled by pressure/vacuum relief valves as designated by the classification society. These valves are designed in such a way that in the event of a fire outbreak, there is no entry of flames into the fuel tankage that will be lethal. The outlet valves should be strictly designed such that the outflow relief pressure of flammable gases never goes below the atmospheric pressure plus some allowable margins. 

The outlet vent heads are at least more than 3 meters above the main deck or exposed deck as ratified by various class rules. 

Inerting is mainly done using an ample supply of nitrogen gas circulated through a dedicated system. Class rules also stipulate these inerting systems to have pressure controls and mentoring arrangements as suitable. Inerting systems should have proper shut-off valves to prevent the entry of flammable vapours into the supply line. 

The cofferdams surrounding integral tanks are also watertight with separate pumping systems for getting filled with water in the event of any leakage or overheating being detected.  

Piping 

Similarly to bunkering, the circulation of methanol to the engine for combustion should also have a well-protected system immune from any leakages or overheating that can lead to fast inflammation. 

The piping system for methanol is designed with extra redundancy using high-grade material as defined by appropriate class rules. The material grades should be quality tested considering worst-case mechanical and fatigue loading. Like tankage, the piping lines should have individual inerting and venting arrangements. Moreover, statutory regulations also require the piping systems to have a temperature control arrangement. 

The piping arrangement should be strictly separate from other piping systems and preferably within type-approved ducting. The piping arrangement should also not pass through any accommodation or service spaces. All lines should be fitted with suitable valves that can cut off supply in the event of any leakage or explosions. Detectors are present to sense any pressure build-up, leakage, or heating. 

You might also like to read:

• What is Carbon Offset Shipping?
• Introduction to Ammonia As A Potential Marine Fuel
• What is Green Ship Recycling?
• 14 Technologies to Make the Ultimate Green Ship
• The Urgent Need to Reduce Nitrogen Oxide (NOx) Emissions from Ships

About Author

Subhodeep is a Naval Architecture and Ocean Engineering graduate. Interested in the intricacies of marine structures and goal-based design aspects, he is dedicated to sharing and propagation of common technical knowledge within this sector, which, at this very moment, requires a turnabout to flourish back to its old glory.

Read More Articles By This Author >