**2. Liquified Natural Gas (LNG)**

In the management booklet of TarnTank, the significant information about LNG has been given. The information was given in the manual are listed below [3]:

LNG consists of methane (CH4) and other substances. It's form can be changed by cooling down to 162°C at atmospheric pressure. By converting the gas form into the liquid form, the volume is reduced 600 times compare to gas form. This reduction makes it easier to transport and store. Typically, LNG tanks contain three times the capacity of an equivalent volume of heavy fuel oil. LNG also contains small quantities of nitrogen, ethane, propane, butane, and some other trace components, with the proportions varying according to the source of the LNG and how long it has been ageing. Cryogenic hazards could occur due to LNG, since it has a low temperature. Natural gas has a flammability range of between about 5% and 15% by volume when mixed with air. As an example, 187°C is a flashpoint. 530°C is autoignition degree means that natural gas is not readily ignited by hot surfaces – unlike marine gas and fuel oil, which can be readily ignited by hot surfaces such as unlagged exhaust systems, a primary cause of engine room fires. After the operations, some LNG can be trapped in the transfer line. If this amount meets with heat ingress, some local pressures can occur, and this high coefficient of volumetric expansion can cause pipe bursts as shown in **Figure 1**. This burst leads to the release of natural gas.

70 Bar (g) is the critical limit for the pipe structure. After one hour of the line, pressure reached 70 Bar, rupture of the pipework or equipment is highly likely. "Thermal relief valves" are being used to maintain release trapped gas or liquid. The first LNG fuel oil ship started to operate in 2000. Statistics dated first March 2018 showed that the number of LNG powered vessels reached to 121 whereas 127 new ship started to be built by shipyards [4]. In general, in a new ship construction, the highest cost of the investment belongs to engine compartments. Engines need to be modified or wholly renewed according to the fuel oils planning to be used onboard

**Figure 1.** *Pipe burst due to the high coefficient of volumetric expansion.*

**Figure 2.** *Emission Decrements.*

the vessels. A few former companies find the solution to use the hybrid fuelpowered engine. For instance, the MT TarnTank, which is LNG powered vessel, fuel gas supply system is designed for both the gas-fuelled engine and conventional type fuel engine. LNG powered engines are one of the most widely used groups of alternative fuel oil engines in Nordic countries. As the emissions shown in **Figure 2**., liquefied natural gas is very clean source. The releasing of SOx is %99, NOx %97 less than heavy fuel oils whereas CO2 emission is high.

The energy density of liquefied natural gas is higher than heavy fuel oil. Despite its environment-friendly and efficacy, ship-owners suffer from several significant drawbacks: time loss to invest, spare parts, bunker supply, cost, educated crew to run this engine. By the help of IMO's regulations checklist shows the proper way for the bunkering operations of LNG. The main questions in the TarnTank Company checklist are about [3]; communication between the regulating authority, bunker deliverer and receiving vessel about safety and emergency response plans. Risk assessment forms are filled and discussed by each side, physical situation of the manifolds must be in operational range, LNG transfer profile (ratio/time) and vapour management schedule has been agreed upon, the receiving tank volume and temperature before bunkering must be within acceptable limits, temperature, pressure, methane number properties of the LNG must be acceptable, handling trapped volumes after an Emergency shutdown system for LNG bunkering – Electrostatic discharge (ESD) must be agreed upon, freeboards and the tidal and operational effects of the draft must be agreed, the ship must be ready for any shifting because of weather conditions, wavelength, wave height, wind speed, lightning is another critical point, the ships or other obstacles are essential in the Swinging Circle, cryogenic protection systems such as water curtains and insulated hose saddles must be compatible?, Safety zone should be established, Ship-Shore Connection box must be checked and ready to use. In the booklet, they call it as "Grounding and hose connection - a grounding cable from ship to quay must be connected and followed by bunker hose connection.", visual check must be done, stripping and purging, hoses must be drained before disconnection, disconnection of hoses and grounding.
