Safe and controlled fuel changeovers with the push of a button
Do you operate in sulphur emission control areas?
If so, you know that the changeover process between high-sulphur content heavy fuel oil (HFO) and low-sulphur content fuels is complex and time-critical. Engine and fuel-system health are dependent on safe, controlled fuel changeovers.
Auramarine’s FuelSafeTM changeover system offers a cost-efficient, rapid method for enabling a vessel to use different fuel types and comply with sulphur emission control area (SECA) requirements. FuelSafeTM is ideal for both newbuilds and retrofits, so if you are thinking of making the switch, we have the solution for you.
Critical control of different fuel properties
The significantly different properties of HFO and low-sulphur content fuels pose a number of challenges that have to be successfully overcome to achieve a controlled, safe fuel changeover. HFO has a naturally high viscosity, while low-sulphur content marine diesel fuels (MDFs) such as marine gas oil (MGO), ultra-low sulphur fuels (ULSFO), light fuel oil (LFO) or diesel fuel oil (DFO) have a low viscosity.
The key is to manage and stabilise this viscosity by controlling fuel temperature through heating or cooling. Fuel in the system can have an initial temperature difference of up to 100°C. Temperatures have to be equalised, but to protect the system from thermal shock, it is essential to keep the temperature change rate to a maximum of 2°C/minute.
Engine and fuel-system health are dependent on a number of factors including:
- Injection pressure losses caused by too low a viscosity may result in difficulties during start-up and low-load operations.
- Too low a viscosity reduces the fuel’s effectiveness as a lubricant, which can result in fuel pumps sticking and working ineffectively.
- In addition to the engine, other machinery with moving parts in the fuel-circulation system has minimum viscosity requirements. For these parts, a low viscosity can also cause malfunctions due to lubrication issues.
- Interruptions in fuel supply during the changeover process can lead to reduced engine power or in the worst case scenario, total loss of propulsion, which could be hazardous for the vessel, its crew, passengers and cargo.
The changeover process requires three critical elements:
- The viscosity must not drop below 2cSt.
- The viscosity must not exceed the engine's maximum limits.
- Temperature change rate at the engine inlet must not exceed 2°C/minute.
Easy and safe to operate
FuelSafeTM combines the Auramarine fuel selector with our advanced cooler unit and heating system. Changeover is initiated at the push of a button, making the often challenging manual operation obsolete. Together all components control the fuel change by intelligently actuating the system valves and dynamically changing the temperature using the cooler unit and the external HFO heaters.
All steps are automatically controlled using continuous viscosity and temperature sensor feedback. With FuelSafeTM, there is no need for a vessel to reduce its speed during the fuel changeover process. It is suitable for various engine loads, fuel consumption rates and fuel system volumes.
FuelSafe is ideally delivered as part of a complete fuel supply system, but can also be supplied as separate components that can be integrated to the ship’s fuel system.
A standard delivery comprises:
- A fuel selector control panel with 7” touch-screen, mounted on a control cabinet door or supplied as an individual component
- Temperature sensors for feedback processes
- Main changeover valves; the number of valves and their sizes are project-specific and defined according to customer needs
- Feeder line cooler
- An Auramarine cooler unit (ACU), with cooling capacity control
For additional cooling needs, Auramarine modular chillers (AMC) are available.
Installation services, fuel system diagram updates, commissioning and turn-key packages are all available and support the easy integration of FuelSafeTM into your fuel supply system.
At the push of a button
Changeover from HFO to MDF
The changeover from HFO to marine diesel fuel (MDF) starts at the push of a button from the Auramarine fuel selector (AFS) panel, which is located in the control cabinet. This initiates the HFO/MDF changeover valve (V001) so that MDF also starts to flow into the system. The V001 is a pulse-control valve, which gradually controls the concentration of fuels entering the system until one fuel flows. The hot HFO and cold MDF start to mix slowly in the fuel supply system. At the same time, the FuelSafe™ system starts to lower the temperature of the HFO heaters at a maximum rate of 2°C/min.
The MDF concentration in the fuel supply system starts to rise at a rate depending on the engine load and volume of the fuel system. The larger the fuel consumption of the system, the faster the remaining HFO is consumed. When viscosity drops below the viscosity trigger level at the engine inlet, FuelSafe™ initiates the V111 valve, activating the Auramarine cooler unit (ACU). The ACU starts to actively cool the fuel with low temperature (LT) water by opening the closed water control valve. Finally, only MDF flows into the system. This starts a timer to activate the V002 valve initiating the heat exchanger, which cools the MDF if the engine is not consuming fuel. Eventually there is only MDF left circulating in the system. At this point, the required temperature and viscosity levels have been reached.
Changeover from MDF to HFO
The changeover from MDF to HFO also starts from the Auramarine fuel selector (AFS) panel. The V001 valve is initiated and HFO begins to flow into the system. At the same time the V002 valve activates the suction side of the feeder pumps. The ACU unit starts to close the LT-water cooling capacity valve and fuel temperature and viscosity start to rise. When the cooler control valve has closed fully, ACU cannot cool the fuel any further and indicates that it is time to direct the fuel towards the main fuel line by activating the V111 valve. At this point the HFO heaters start to heat the fuel temperature, keeping the change rate at the engine inlet at a maximum of 2°C/min. Finally, the V001 only allows HFO to flow into the system. Depending on fuel consumption rates, the engine eventually uses any MDF left in the system. The changeover is now complete and only HFO is circulating in the system.
Meeting multiple changeover parameters
Auramarine recommends that fuel oil consumption rates during changeover procedures are in the range of 33 to 100 percent of maximum fuel consumption. The lower the fuel consumption, the longer the changeover takes.
Operators should take into account the compatibility of different fuel oils by, for example, following compatibility test procedures defined in ASTM D7112.
Changeover time for the HFO/MDF changeover valve (V001) can be altered, but typically this should be between 30 to 80 minutes, depending on fuel system properties such as engine load.
Other changeover parameters, which must be specifically altered to meet the recommendations of various engine manufacturers, can also be met with Auramarine FuelSafeTM. For example, the maximum temperature change rate parameter can be set to 4°C/minute instead of the usual 2°C/minute, if required.