A new paper by Singapore-based Ascenz Solutions provides best practices for accurate monitoring of fuel bunkering of marine fuels using mass flow meter (MFM) systems. The fuel bunkering process is essential to all ships that rely on fuel oil for operation.
The use of MPA-approved Mass Flow Meters (MFM) for all Marine Fuel Oil (MFO) bunker delivery in the Port of Singapore was made mandatory in January 2017, while new bunkering standards using mass flow metering, specifically TR48 by Enterprise Singapore, have been introduced by MPA Singapore.
In order for flow meters to be able to accurately measure mass flows, pipelines need to be fully filled with single phase liquid.
In reality, this might not always be the case and this can cause inaccurate bunkering due to partially filled pipes and excessive aeration.
The presence of dead volume, the amount of fluid trapped between bunker tanker and receiving vessel which cannot be removed from within the pipelines can often lead to bunkering disputes caused by lack of understanding of the process.
Best practices to enhance accurate bunkering
-Meter installation and selection
Proper meter selection and installation procedures are critically important to ensure correct measurements. The whole process from meter selection includes choosing the right type of meters with marine approval standards, explosion proof certificates, and marine class approval certificates. Meter sizing is also important and is dependent on the operating flow rates and volumes required.
Further emphasis is given to the MFM system where proper installation plays a big role in obtaining reliable mass flow rate. The MFM system comprises the mass flow meter, its ancillary devices, pipelines and sealing points. The installation procedure includes careful pre-selection screening and site surveys, due to the different configurations of pipelines in each vessel.
Besides understanding the system drawings of the pipelines, the layout of pipes must be carefully considered as corners, bends and heads will influence the readings of the flow meters if the installation location is not optimal.
-Packing of meters
The process of filling up of pipelines with fluid is also commonly known as line packing. The entire process of bunkering is an ‘Empty-Full-Empty’ application, where at the beginning, most of the pipes are empty.
During the actual bunkering, full and partially full conditions are observed. At the end of the bunkering, the pipes need to be cleared to prevent possible spillage when disconnecting the bunker hose.
In order to avoid a partially filled pipe that contributes to inaccurate measurements of fuel flow during bunkering, it is important to ensure the bunker piping system is filled up as soon as the delivery process starts.
At the beginning of the delivery process, the bunker pipelines, which are above the liquid level in the storage tank, are almost always empty due to gravity flow, resulting in the bunker line that is usually empty unless in conditions where the pipe sections are at lower elevations compared to the fuel levels in the storage tank.
-Using plate fixtures
In cases where there are partially filled pipes, a plate fixture can be added to increase the accuracy of measurement of fluid flow. Careful selection of a suitable location for installation of the sensor and an investigation into the need of a device such as a plate fixture to manipulate the back pressure should be considered during installation of the flow meter system.
A plate fixture is introduced to improve accuracy of bunkering measurement by elevating fuel flow. To optimise measurement accuracy, a marine bunker measurement system may incorporate two level switches at both downstream and upstream sides of the sensor tubes of a mass flow meter.
The level switches will send a signal to activate the totalizers when fuel oil is present, and a signal is sent to deactivate totalizers when the flow stops. The addition of a plate fixture reduces false registering of fuel flow due to unbalanced partially filled sensor tubes.
System integrity ensures that the MFM system is set up and approved for bunkering operations and is secured against any interference before, during or after bunkering operations.
The entire system integrity includes the meter selection and installation, the acceptance test and the system monitoring during operations.
Each MFM system must be accompanied by approved documentation, equipment checks for mechanical, software, electrical and operational security. Where in doubt, authorities can be consulted, such as the National Weights and Measures Authorities or National Maritime Agencies.
Upon completion of installation, the MFM system is checked to ensure system security, where:
- Equipment shall be sealed against unauthorised adjustment, tampering or dismantling.
- Software shall be protected to guard against any unauthorised changes. Any changes made to the software must be otherwise authorised and documented.
- Data collected during the bunkering process such as the history of operations, batches and critical alarms are stored for a minimum of three months for references.
- Critical alarms shall be activated if there is power failure, equipment communication failure or meter and bunkering computer failure. The bunkering shall not proceed if any such critical alarm is found to be activated, and the implementing authority is notified immediately. System integrity of the entire installation and commissioning of the MFM system is scrutinised.
-Smart bunkering data monitoring
Data collected from the mass flow meters are gathered on a platform to be displayed allowing observation of mass flow during bunkering in real time. Typical data that are displayed are the bunker mass flow rate (t/h), density (kg/m3 ), the temperature (°C), drive gain (%), and totalising of the bunker fuel.
These data can be used to detect abnormalities that may occur during the bunkering process. For example, the presence of aeration can be detected when the drive gain shows a sudden spike.
Further information may be found herebelow: