The purpose of the marine fuel gas system is to fill, store and vaporise LNG and to supply natural gas to engines on a ship. The system is designed for minimum heat in leakage to guarantee maximum holding time. The gas is fed to the engines using the tank pressure. Hence, no pumps are needed and the maintenance costs are low.
The system mainly includes:
- One or more LNG fuel tanks
- Water-heated vaporiser units for vaporisation of the LNG to gaseous natural gas
- Pressure build-up units for the increase of tank pressure
- Bunker stations
- Control system
- Piping for bunkering LNG and gas feed lines for supply of natural gas to the engines
Bunkering LNG to storage tanks
LNG is transported from a truck, bunker terminal or bunker ship to the storage tanks via the bunker station on the ship side. The bunker station is connected to the coldbox of the tank via bunker pipes. Depending on the existing conditions in the tank, the flow can be routed to the bottom or top of the tank. If the tank has a high pressure, LNG can be discharged at tank gas phase in order to recondense the gas phase and consequently lower the pressure.
For gas supply to the engines, LNG will be evaporated by the dedicated product vaporiser water-heated type (VAP). The capacity of the VAP unit can deliver gas to engines at the required power and temperature of about 10 – 40 °C depending on the water temperature supplied by the ship. The LNG supply to the vaporisers is ensured by the inner pressure of the storage tank. The pressure buildup unit (PBU) guarantees a constant pressure level. The vaporisers (VAP and PBU) are essential components for the operation of the ship; therefore, our systems are equipped with vaporisers of MAN Cryo design.
Coldbox (tank connection space)
The coldbox, which is attached to the tank, includes equipment such as VAP+PBU product vaporisers and pressure build-up vaporisers, valves, and instrument valves for controlling the LNG tank. The coldbox is insulated with A-60 insulation.
Vaccum-insulated C-type tank
The cryogenic LNG tank consists of two tanks, i.e. the inner vessel, which contains the liquid LNG, and the outer vessel, which is regarded as a second barrier. The annular space between the inner and outer vessels, which is filled with perlite, is vacuum evacuated. The tank is designed to prevent sloshing in the tank when operating in rough conditions and to ensure maximum holding time.
Ship control system
The LNG system is governed by a stand-alone control system. It includes a PLC and an OP panel installed in a cabinet. The control system receives signals from instruments and performs the desired activities depending on which mode of operation is chosen.
MAN Cryo LNG fuel gas systems are developed to your specific needs without any compromises regarding the well-known safety and quality standards of the formerly known Cryo AB. Our product portfolio includes horizontal as well as vertical LNG fuel gas systems and ranges from 20 m³ to 400 m³ or even larger in volume. It is designed for power levels of up to 50 MW.
All of the above will help you comply with stricter emission thresholds under the IMO emission regulations and under the European Maritime Directive.