6 Operational consequences

Natural gas for ship propulsion in Denmark

6.1 Experience using natural gas fuelled ships in Denmark

Natural gas can be used as a fuel for ships as CNG or LNG and both systems have been used as fuel for ship – although the global experience is limited so far.

6.1.1 CNG experiences

CNG is widely used as automotive fuel in many countries. The technology is well known and safety record is good. It appears that so far CNG has been used for short shuttle ferries, comparable e.g. to the Helsingør-Helsingborg crossing. Here the pressure vessels can be refilled frequently and the filling operation only takes a few minutes while he ferry is unloading/loading cars and passengers. The pressure vessels are e.g. stored on the weather deck to reducing risk and the engine has been retrofitted to use gas instead of diesel.

It seems logical that the first movers will not aim for long distance transport using CNG – but the reduces range of the ships using CNG when comparing to fuel oil or even LNG makes CNG a more obvious choice for short distances and frequent refilling.

Whereas CNG may still be an interesting option for smaller pleasure boats, LNG is clearly the preferred natural gas option for larger ships. One single RoRo ferry might annually consume more than 10,000 tonnes of LNG, or as much fuel as 10,000 standard passenger cars or 100-150 city buses.

Two other applications highlight benefits of natural gas operation.

For many years, the submarine and jungle rides at Disneyland have been powered by natural gas. The engines are cleaner and their emissions do not foul the water with an oily film or kill nearby plants, as other fuels have done.
In San Antonio, Texas, the party barges that carry over one million tourists per year along the San Antonio Riverwalk operate on natural gas, reducing both noise and air pollution. No major problems have been experienced with the vessels and the tourists' experience has been enhanced

The drive to use CNG for ship propulsion seems to be dominated by smaller players and aiming for retrofits and small scale operation. This is probably due to the existing large scale use of CNG for automotive propulsion. The global market however seems huge that many major cities have ferries crossing rivers and harbours contributing to local pollution of the air and sea.

6.1.2 LNG experiences

LNG carriers have used the boil off gas as fuel since the first ship was put into operation in 1964. Numerous LNG carriers have long and good experiences with natural gas as fuel for the propulsion machinery, mainly steam turbines.

Only one country has been identified as currently using LNG as bunker fuel: Norway. Norway has a total of eight ports where LNG bunkering takes place and approximately 20 ships have been identified.

However, many more countries seem eager to use LNG (and CNG) as alternative ships fuel. A demonstration project is expected to start operation of a LNG fuelled riverboat at the Yangtze River this year.

6.2 Regulator and legislation

In Denmark, the Maritime Authority (Søfartssyrelsen) has the responsibility for the shipping industry and framework conditions, the ship and its crew. In other words, the Danish Maritime Authority is responsible for the following:

The construction, equipment and operation of Danish ships (including safety, prevention of terrorism, safety of navigation, manning, occupational health and environmental protection) as well as port state control of foreign ships calling at Danish ports;
Ship registration;
The training, education, employment, health and social conditions of seafarers;
Shipping policy, maritime law as well as national and international industrial policy.

Harbours are regulated by the Ministry of Transportation (Transportministeriet) c.f. “Lov om havne”.

The construction of a LNG or CNG bunkering facilities will be governed by the relevant legislation (love og bekendtgørelser) e.g. Trykbeholderdirektivet (PED), ATEX, gasreglementet etc. and Dansih, European and international norms and standard e.g. ISO 28460 LNG – ship to shore interface”, ISO 1532 “Installation and equipment for liquefied natural gas - ship to shore interface”,

In Norway, the introduction of LNG powered ships has lead to an adaptation of the regulations set by the Norwegian Maritime Directorate (MD) in 2000. The main requirements for gas-fuelled ships are summarised below:

Generally by design reduce the risk of explosion; limiting area of gas in place, small engine rooms.
Redundancy of fuel storage, power generation, transmission and propellers.
Separation of engines in at least two engine rooms, separation of fuel supply.
Double piping of all gas pipes inside the ship.
If a fire or explosion should occur, the result should not harm the ship or endanger passenger’s life. And the ship should still be able to manoeuvre and get safely to port.
Detection of gas leakage in all areas where gas in place. Alarms of 20% Lower Explosion Limit (LEL), automatic shut down at 60% LEL based on voting 2 out of 3.

The International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC) will not be suitable related safety for other kind of ships than gas freighters. Some of the classification societies, however, have worked out requirements for the use of gas as fuel in ships based on this code. For instance, the Norwegian classification society, DNV, Rules for Classification of ships, has launched the rule proposal “Gas Fuelled Engine Installation” (DNV 1994). This means that in near future there will be classification rules to which you can design a gas-fuelled ship.

IMO has initiated work on developing provisions for gas-fuelled ships, following a Norwegian proposal. Draft Interim Guidelines covering gas-fuelled ships are in a process of continued work and review by the Subcommittee on Bulk Liquids and Gases (BLG). Intent of issuing such interim guidelines in 2009 has been expressed.

The IMO (www.imo.org), part of the United Nations system, provides the main organisational framework for addressing issues of air emissions from global shipping. The main legal framework for the purpose is the MARPOL (international convention for the prevention of pollution from ships), including its six annexes, which address different kinds of pollution from ships.

Annex VI of MARPOL concerns air emissions, and a revision has recently been adopted (October 2008) by IMO’s Maritime Environment Protection Committee, which comprise representatives of some 100 national governments. Though making no specific references to LNG, the changes can have important implications for the use of LNG in ships by setting requirements that can be met with LNG. The MARPOL Annex VI revisions are designed to bring significant reductions in emissions from ships of sulphur oxides, nitrogen oxides and particulates, taking effect in steps between 2010 and 2020.

6.3 Vessel safety

In its liquid form LNG is neither explosive, corrosive, nor toxic and CNG cannot “exist” in open air conditions. Natural gas is on the other hand both flammable and explosive and three factors should be observed:

LNG and CNG is cold when released (CNG due to large Joule Thompson cooling) and can thus have a higher density than air
Natural gas will only ignite at a temperature above 600°C
Natural gas will only ignite when mixed with air in the ration between 1:20-3:20 (5%-15%)

While the first factor increases risk for gas being trapped, the two other factors shows that natural gas is actually not that easy to ignite and that good design can overcome many risk factors. Indeed, existing CNG installation often uses CNG storage in open areas e.g. on the weather deck, since this reduces risk of ever having a flammable mixture of gas and air. This approach may, however, only be practical for smaller storage volumes e.g. for ferries, pleasure cruise boats, tugs and similar vessels. Large storage tanks may be difficult to place in the open and other factors may make this approach impossible.

In connection with the Fjord 1 ferry project DNV performed an extensive risk analysis (Brett 2006) on the dual fuel vessels. DNV concluded that the risk level for an LNG vessel is no greater than that of a diesel vessel.

6.4 Supply chain

6.4.1 CNG supply chain

CNG has the advantages in Denmark, that natural gas is already in widespread use and available in many urban areas. Bunkering facilities for e.g. cruise boats, tugs, ferries and similar can be established fairly quickly in any port where natural gas is already available. The facilities will e.g. consist of a high-pressure storage vessel (approximately 250 bar) and compressors that shall increase the pressure from the natural gas supply net (19-50 bar) up to 250 bar. The size of the vessel will depend on the vessels and operations. Existing facilities in e.g. Canada use a simple approach where the CNG system on the vessel is connected to the buffer vessel on the shore and pressure is simply allowed to equalise. This only lasts a few minutes and the final pressure is around 190 bar. A similar approach could be used in any Danish harbour where reducing emissions is a concern.

6.4.2 LNG supply chain

There are currently no LNG production or terminals in Denmark, so there are no existing facilities that could be used for LNG bunkering.

Some likely source of LNG is delivery by ship to the bunkering facilities from either European terminals or directly from the suppliers.

6.5 Bunkering operation

The bunkering operation consists of a number of steps, and they must be carried out within a small time window. The typical bunkering operation shall last less than 50 minutes and consist of the following steps (fuel oil):

Table 6‑1 Bunkering operation
Before bunkering	During bunkering	After bunkering
Checklist to receiving ship Connection link Connection hose Return of signed checklist Open manual valves Ready signal ship/sender	Pump start sequence Transfer sequence Pump stop sequence Transfer rate: 150 t/hr 30 minutes	Shut manual valves Purging cargo lines Disconnecting hose Inerting of cargo lines (receiver) Disconnection link Delivery cargo document Inerting cargo lines (sender)

This means that a natural gas bunkering operation should be completed within the same timeframe.

There are 13 terminals in Norway (March 2010). One LNG bunker facility is planned for in Göteborg, Sweden. This facility is intended as a ship-to-ship bunker operation. The Norwegian facilities use truck or smaller land based tank facilities.

6.5.1 LNG bunkering facilities

Pressurised above ground LNG vessels is preferred since these allow pump free transfer of LNG. The Fjord 1 bunkering station consists of two 500 m³ each LNG tanks.

Furthermore various concepts are used for transferring the LNG to the ships:

Permanents piping and loading arms
Truck to ship bunkering
Ship to ship (tanker or barge)

6.5.2 Truck to ship

In the case of the Fjord 1 LNG ferry in Norway truck bunkering has been chosen. Truck bunkering is convenient since the LNG storage does not have to be in the port. However, since the truck has limited capacity six truck loads are required for each bunkering operation if the LNG storage on the ferry (125 m³) is almost empty. In comparison a large cruise ship would require 40-50 truckloads when bunkering.

The Fjord 1 LNG bunkering station thus holds enough LNG for a total of 8 bunkering operations. The ship need refuelling every third night and thus requires replenishment weekly. The bunker operation lasts approximately 2 hours and takes place at night when the ships are not operating.

6.5.3 Ship to Ship

This concept is not in utilisation yet, but several parties have shown interest in the concept and both DNV and Excelerate (a company progressing the industry of deepwater LNG as well as regassification vessels) have shown proof of concept of the transfer of LNG from one vessel to another.

The ship-to-ship concept of bunkering LNG is likely to face the least opposition, as the “Not In My Backyard (NIMBY)” effect often expressed by inhabitants of coastal regions that opposes installation of LNG onshore is avoided.

6.6 Natural gas engines

Three options exist:

Use existing diesel engines
Dual fuel engines
Natural gas engines

6.6.1 Using diesel engines

Using existing diesel engines only seems relevant for retrofit projects. These are not so likely to occur for LNG projects due to other requirements for the fuel systems. Indeed, studies of existing ships in comparable services show little improvement with regards to emissions, except for particulates.

Diesel engines will run fine on natural gas – but the environmental benefits are not so obvious. Some methane will pass unburned through the engine (methane slip) contributing to the total greenhouse gas emissions. It will be required to mix an amount of diesel with the gas and the gas must be injected at a high-pressure.

6.6.2 Dual fuel systems

Dual-fuel (DF) engines run on gas with 1% diesel (gas mode) or alternatively on diesel (diesel mode); Combustion of gas and air mixture in Otto cycle, triggered by pilot diesel injection (gas mode), or alternatively combustion of diesel and air mixture in Diesel cycle (diesel mode); Low-pressure gas admission.

Figure 61 Dual fuel engine
Figure 6‑1 Dual fuel engine

6.6.3 Natural gas engines

Natural gas engines or spark-ignition gas (SG) engines run only on gas by combustion of gas and air mixture in an Otto cycle, triggered by spark plug ignition. The engines use low-pressure gas admission.

There are four main manufactures of technology that can be used for natural gas powered ships. These four engine manufactures includes Rolls-Royce, GE, Wärtsilä and MAN Diesel.

6.6.4 Summary of experiences

Using LNG and CNG for bunkering operations is not common in a global perspective – but the practice seems on the edge of catching on. Currently two issues seem to block further developments:

First movers dilemma
International regulation

Both CNG and LNG should be considered for Danish harbors, but the two storage principles seem to favor different segments of shipping.

CNG seems suited for a quick launch targeting smaller operations in Danish waters, e.g. minor ferries, tugs, cruise boats (e.g. excursion boats) and similar, where natural gas is readily available from the grid.

LNG would also be suited for the operations that CNG seems suited for, but LNG would in addition be suited for larger ships with a further action range. However, this requires that the ships are either suited for dual fuel or that bunkering is also possible in destination ports.

The technology is well known and experience using natural gas as ships fuel and CNG or LNG as storage also have reference projects.