Utilization of alternative fuels such as methanol has rapidly grown and seen as a viable alternative to heavy fuel oils/marine diesel oil due to several factors such as the properties, economic and environment circumstances and its business is becoming mature phase [1][2]. In addition to that benefits, the engine is successfully certified as IMO Tier3 compliant [3], using methanol, without the need of secondary exhaust gas treatment systems, such as selective catalyst reduction and/or exhaust gas recirculation, the engines are capable to burn MDO and low flash point fuels such as methanol with uninterrupted operation. Methanol as a fuel for ships is interesting for ship’s operators because methanol does not contain any Sulphur [4]. For ships operating in IMO emission control areas (ECA), methanol could be a feasible solution to meet the sulphur requirement [4]. Already in 2013, IMO has decided to adopt the Energy Efficiency Design Index (EEDI) as a mandatory instrument for ships built after January 2013 to limit CO₂ emissions. This will influence the engine market and technical solutions faster than we had anticipated at first. Here, alternative low carbon fuels, such as Methanol, will in the future be serious candidates to fuel oil in-order to lower EEDI. By nature, methanol generates less CO₂ emissions during combustion than fuel oils [4].

Over the past decade there has been a trend towards implementing progressively more stringent regulations aimed at reducing emissions that are harmful to human health and contribute to global warming. From the regulatory standpoint, marine methanol is a future-proof fuel that could comply with the most tightly specified emissions reduction legislation currently being considered. Methanol is characterised by having a low cetane number, and the self-ignition quality is therefore poor [5][6].

Methanol has been shipped globally, handled and used in a variety of applications for more than 100 years. From a health and safety perspective, the chemical and shipping industries have developed procedures to handle methanol safely [7]. There is ample experience in handling and transporting methanol as a chemical, both in tank trucks and bulk vessels. For example, methanol was the dominant bulk liquid handled in Finnish ports in 2008 and 2009 and is in general a very common chemical transported in ports around the Baltic Sea [8]. To cope with the demand of the methanol market with flexibility, this paper has newly and unique assessed and developed HAZID addresses all areas that need special consideration for the usage of the methanol fuel as low flashpoint fuel to become a global fuel choice.

The first version of the IGF Code addresses only LNG (methane). The IMO has been tasked to develop the second version of the Code, addressing methyl/ethyl alcohol and other low-flashpoint fules such as low flashpoint diesel, therefore according to SOLAS Reg. 1/5 and in order to comply with mandatory international regulations, IMO MSC./Circ.1455 alternative design and equivalent arrangements addressed on this study as an equivalent according to SOLAS 11/2, Reg.4.2.1 and SOLAS II-1. The flashpoint of methanol is below the minimum flashpoint for marine fuels specified in SOLAS. Methanol driven merchant vessels can be set into service via the alternative design approach covered by the IGF code. In this study, The IMO MSC./Circ.1455 alternative design and equivalent conditions have been met, and the alternative and/or equivalency was found feasible and suitable for its expected application. The goal of these alternative design and equivalent arrangement is to provide criteria for the arrangement and installation of machinery for propulsion and auxiliary purposes, using methanol as fuel, which will have an equivalent level of integrity in terms of safety, reliability and dependability as that which can be achieved with a new and comparable conventional oil-fuelled main and auxiliary engine. It is assumed that the vessel will run on methanol while performing cargo operations [9]-[15].

This analysis is the concept HAZID and based on by applying innovative thinking, maritime industrial experiences and the design concept of the vessel which is a typical methanol carrier operating between Korean port/Busan and Iranian Port/Bandar Abbas.

The vessel’s design data is shown in Table 1. The deadweight is about 38,000 tone on draught of 11.00m. Design speed (suitable service speed) is about 17 knots. Endurance for using gas fuel is set to 11,200 NM for one round trip between Iran/Bandar Abbas and Korea/Busan. In addition, endurance for emergency (using diesel oil) is estimated to be 5,600 NM.

The vessels slop tanks, or methanol fuel storage tank system will be filled from the cargo manifold. This design feature is an important aspect of the total fuel system, especially with respect to fuel contamination. The slop tanks, one on the starboard and one on the port side of the vessel, with a total capacity of about 2,500 m³, will be used as methanol fuel tanks. The slop tanks are placed according to Figure 1 general arrangement, methanol fuel tank arrangement and system.

Figure 1: 
General arrangement, methanol fuel tank arrangement and system

The fuel service tank, with a capacity of about 80 m³, is placed on the upper deck on the port side of the vessel as indicated Figure 1. The tank is protected towards the ship side by the methanol fuel supply room. Methanol is transferred by a submerged hydraulic pump from the slop tank to the service tank. All the connections to and from the service tank are shown in Figure 1.

The low flashpoint fuel supply system (LFSS) is locating in the methanol fuel supply room on the port side of the ship, towards the ship side at the same longitudinal location as the methanol service tank, as indicated in Figure 1, and including the supply unit, circulation unit and the fuel valve train. The supply and circulation units are locating in the methanol fuel supply room and constitute the LFSS. These units are designed, and include pumps, filters, and necessary safety systems.

The main engine uses temperature conditioned methanol at a fixed supply pressure and varying flow depending on the engine load. The LFSS will supply this fuel to the engine while complying with the requirements described regarding temperature, flow, pressure and ramp-up capabilities.

The fuel is taken from the service tank containing liquid fuel and boosted to a pressure close to the supply pressure, about 8.0 bar. The fuel is then circulated by the circulation pump, and the pressure is raised to the engine supply pressure, about 10.0 bar.

The delivery pressure must ensure that the fuel will stay liquid, and no cavitation will be generated at the temperatures to which the fuel is exposed until injection.

The flow of fuel in the circulation circuit should at all time be higher than the fuel consumption of the engine. A typical circulation factor is 2-3 times the fuel consumption. To ensure the fuel delivery temperature, a heater/cooler is placed in the circulation circuit. It is recommended to connect this through a secondary cooling circuit to the LT cooling system.

The methanol fuel system has its own draining system to handle spills as well as different emergency situations and in cases where the system needs emptying before switching over to fuel oil mode. The draining system is a combination between gravity draining and purging with nitrogen, which is an own system. Each unit described, such as the fuel valve train has its own delivery system of inert gas (Nitrogen) for purging.

The fuel valve train is designed and provided and connects the LFSS with the engine through a master fuel valve (MFV) arranged in a double block and bleed configuration. For purging purposes, the valve train is also connected to a nitrogen source. Typically, the valve train will be placed outside the engine room above the weather deck to avoid the need for double safety barriers. From the valve train, the fuel is fed to the engine in a double walled ventilated pipe through the engine room. The fuel valve train is locating in the methanol supply room. From the fuel valve train, the fuel is fed to the engine first in a single walled pipe on open deck and in a double walled ventilated pipe through the engine room. The supply piping from the fuel valve train to the main engine is shown schematically in Figure 1. The supply piping is divided into two main parts, namely above and below deck. The methanol fuel line on open deck is suited with single piping and with double piping below deck.

The ventilation system is totally dedicated ventilation system for the methanol fuel system. The dedicated ventilation system for the methanol fuel system consists of separate ventilation system for the cooling oil system, double wall piping, covering the main methanol supply and purge return lines below deck, with mechanical extraction ventilation with 30 air changes per hour. The nitrogen system is provided by a nitrogen generator in the inert gas delivery unit, with a minimum supply pressure of 10 bar. The delivery lines distribute the inert gas to all units in the methanol fuel system.

The engine is using temperature conditioned methanol at a fixed supply pressure and varying flow depending on the engine load. The LFSS supply this fuel to the engine while complying with the requirements described regarding temperature, flow, pressure and ramp-up capabilities. A different system layout could be chosen for this task. Purge return system (PRS) on methanol fuel engine is arranged because of the low flashpoint methanol fuel, there are a number of operation scenarios where the fuel piping will have to be emptied and inerted. For the methanol engines, the fuel piping on the engine and in the engine room is arranged so that the liquid fuel can purge it and thereby return it to the fuel service tank. After the methanol fuel has been returned to the service tank, full purging and inerting are conducted for the double wall piping system.

If methanol operation is expected to be stopped for a longer period, e.g. during short harbour stays, the procedure for switching to standby mode is used. However, the low flashpoint fuel supply system (LFSS) is switched off when the procedure finishes. Major servicing work involving lifting equipment over the supply lines is not recommended in this mode. The reason being that the supply lines in the engine room and on the engine are methanol filled. In a complete shutdown of the liquid gas system, all piping is emptied from methanol fuel and the low flashpoint fuel supply system (LFSS) and ventilation is turned off. Shut down philosophy and redundancy consideration has been given. In general engine shut down philosophy will comply with the international rules and regulations.

The Hazard Identification (HAZID) is a structured approach and exercises where documentation/drawings and a set of guidewords form basis for identifying hazards involved with an operation or the use of equipment and/or systems. HAZID’s are commonly used throughout the maritime industry for all types of safety and risk assessments [16]-[19].

Figure 2: 
The lifecycle of a vessel from construction strategy to scrapping [1]

Figure 2 shows vessel’s lifecycle. The focus for the HAZID assessment is the methanol fuel system and liquid gas engines (LGI) encompassing the following sequence of operations during the lifecycle of a vessel from construction strategy to scrapping:

• (1) Construction/installation including testing and sea trials.
• (2) Operations (Loading/offloading of cargo, voyage, bunkering, docking, maintenance, lay-up/Idle).
• (3) Decommissioning/scrapping

Safety of ship propulsion during voyage and maneuvering to avoid blackout has been taken in to account. The following hazard guidewords used as a basis for the Hazard Identification (HAZID) study [1]:

Fire or explosion hazard, fire/explosion – methanol initiated, fire/explosion – not methanol initiated, other hazards generated by materials and substances, leakage of methanol causing loss of structural integrity, mechanical hazards, electrical hazards, thermal hazards, hazards generated by malfunctions, collisions, dropped object, grounding, foundering, environmental hazards, pollution, occupational accidents, hazards generated by neglecting ergonomic principles, and hazards generated by erroneous human intervention [20].

For each hazard causes/treats/initiating events, consequences, and controls (preventive and mitigating) are identified and recorded in the HAZID findings and results, following bow tie hazard and effect model in Figure 3.

The diagram and model in Figure 3 is shaped like a bow-tie, creating a clear differentiation between proactive and reactive hazards and effects. The hazard and top event always appear together in the centre of the bow-tie diagram.

Figure 3: 
Bow tie hazard and effect model [21]

Over-pressurisation could be a cause of loss of containment/tank of a hydrocarbon carrying methanol fuel. Causes appear on the left-hand side of the bow-tie diagram. Causes should be independent of each other and should lead to the top event directly. Causes should not be failures of equipment as this is in fact a barrier failure.

A consequence results in loss or damage. It is common to think of consequences as impacting on people, the environment, assets, business and reputation. More safeguards/barriers are put in place to try and stop the top event from developing into the consequences. Consequences appear on the right hand side of the bow-tie diagram. Preventive barriers (also called safeguards) appear on the left of the diagram and are designed to prevent the top event from taking place. Mitigation barriers appear on the right of the diagram.

The main focus of HAZID study was the conceptual design of the methanol fuel system. The study considered the system starting from the pumping of liquid methanol from the methanol cargo tanks to fuel tanks and followed the liquid/gas through the system to the engines.

The fuel supply system for the concept vessel is evaluated with respect to as low as reasonably possible (ALARP). The ALARP principle is based on the concept of implementing risk reduction measures if their respective costs are not disproportionately high as compared to their attained benefits. This HAZID study will thus assist ensuring safety equivalency with comparable ships using conventional fuel.

One failure in a component is considered separately, and it is assumed that all other components work properly. Generally hidden failures are not considered. Hidden failures which may be caused by nonidentifiable malfunctions of a component are kept in consideration as far as possible. In addition are external influences, such as fire, collision, grounding or other impact damage affecting the methanol system, assessed separately.

External influences are thereby defined as a separate system, with sub-components such as fire, collision etc. The HAZID table is adapted to fit a system component with its functions, failures, effects, controls, causes and actions, which are not directly transferrable to fit the effect from external influences. A logical transformation of some of the columns in the HAZID study is therefore made and is presented in Table 2.

The analysis focussed on the identification of hazards caused by methanol leakages affecting the structural strength and the integrity of the vessel. The methanol fuel system is operating within its design limitations. Attention was given to single point failure and regular inspection and maintenance is stipulated. The methanol fuel system is operated by an experienced crew.

An assessment of the methanol fuel system was conducted systematically for normal operation (voyage) according to the following subsystems:

• (1) Manifold system (flanges, valves, piping on deck to inlet of methanol fuel storage tank, crossover connections, swing bends)
• (2) Methanol fuel storage tank system (submerged pumps, filters on line to methanol fuel service tank, Inlet valves to methanol fuel service tank)
• (3) Methanol fuel service tank system (methanol fuel service tank, inert gas inlet, drain to slop tank, engine purge return filters, low flashpoint fuel supply system, pressure and temperature indicators,)
• (4) Low flashpoint fuel supply system (pipe connection from methanol fuel service tank, inlet valve, filters, valves, pressure indicators, pump, mixing tube, heating exchangers, 3-way valve, cooling pump, piping system for water and glycol, fuel gas system connections)
• (5) Draining system for the methanol fuel supply room (safety relief valves, non-return valves, inert gas piping/valves)
• (6) Fuel valve train (all items on main fuel line, valves, methanol fuel system valves, inert gas system valves)
• (7) Supply piping to main engine (piping on open deck, piping below deck).
• (8) Drain system – purge return piping (general action suggested: consider separate safety relief line with no obstacles (e.g. non-return valves, etc.).
• (9) Ventilation system (dry air supply, valves, starting air system valves, ventilation fan, outer pipe, flow switches and gas detectors
• (10) Nitrogen system (N₂ generation, N₂ line, manual shutoff valves).
• (11) External influences (fire, collision or grounding, mechanical damage, blackout, opening of methanol fuel system for inspection/maintenance, loss of control air).

In general, for a safety analysis different operation conditions should be examined, to identify possible system weaknesses. For this analysis it was assumed during the HAZID study that all critical failures according to methanol leakage might occur during normal operation. There are two methanol fuel mode stop operations such as stop gas operation and stop for complete shutdown of liquid gas system.

It is assumed that during the start-up, shutdown procedure of these two operations or emergency shutdown (ESD), the risk for a leakage is equal or lower to the risk during normal operation. Only normal operation has therefore been considered during this HAZID study.

The identified hazards and failures have been summarized in Table 2.

Figure 4 classified and ranked main hazards and causes. Total 27 hazards have been identified on the subsystems of the methanol fuel system which ranked with respect to design (18), operation (5), materials/ equipment (2), impact and dropped objects (2).

Figure 4: 
Classifying and ranking main hazards and causes

The HAZID was carried out in two steps: first with the system as designed (initial rating) and in a second revised step taking the given recommendations under consideration to mitigate and reduce the HAZID and risk.

Total 15 recommendations with comprehensive summary in terms of design and operation proposed and made covering a wide range of design and operation topics with the division in high prioritization for follow-up. Several important gaps beyond mandatory regulations, standards, guidelines or of relevant organizations have been identified requiring for action under the recommendations below:

This study has concluded the system’s ability to operate safely and reliable during different predefined scenarios and potential events that proof and support to ensure a safe and reliable methanol fuel system. The study and evaluation can also conclude that there is no HSE (health, safety and environment) showstopper for construction/ conversion of conventional oil fuelled to dual fuelled using methanol which HAZID can also be mitigated and eliminated with sufficient design, engineering and operational controls that meet the required standards. The study is performed to ensure comprehensive identification of hazards. The conditions of IMO MSC. /Circ.1455 on alternative design and equivalent have been met which is no showstopper was identified and the alternative and equivalency was found feasible and suitable for its expected application.