30 to 70 per cent of overall ship operating costs are associated with fuel, according to agile maritime digitalisation company Ascenz. Inaccurate or unsafe bunkering practices can lead to costly and dangerous operations, with fires, oil overflow or spillages a risk. Accurate bunkering and effective monitoring is vital to ensure safe and correct operation as well as to make sure a vessel receives the correct quality and quantity of bunker fuel outlined in its bunker purchase contract.
In a new white paper published by Ascenz, ‘Reliable bunkering practices enhanced by new technologies’ bunkering inaccuracy and its risks and precautions are highlighted. When transferring fluid from a supply bunker vessel to a receiving vessel, some issues can arise, such as partially filled pipes, excessive aeration or dead volume, which results in inaccurate bunkering and bunkering disputes. In its latest white paper, Ascenz highlights some of the technological developments in bunkering monitoring that can often occur and why it is important to accurately measure bunkering.
Causes of inaccurate bunkering
The white paper states, “In order for flow meters to be able to accurately measure mass flows, pipelines need to be fully filled with single phase liquid.” However, one problem is partially filled pipes that is the result of a height difference between the bunker tanker and the receiving vessel. This can often be the result of a lack of understanding of the process, the white paper states. If similar measurement devices are installed on both the supply and receiving side, significant measurement variations can occur when comparing the bunkering fuel data from both ends. Partially filled pipes can lead to inaccuracy when measuring fuel flow though a pipe as the sensors “are not able to properly quantify the flow within the pipelines, such as the difficulty to maintain coil oscillation. Hence, the fuel meters on the bunker tanker may not be able to detect the presence of partially filled pipe conditions at the receiving end of the pipe unless the crew are informed otherwise.”
Another issue highlighted in the white paper is excessive aeration in pipes. Air can become trapped in the pipelines and not be flushed out due to the corners and bends in the pipelines. Air and gas in the same pipeline results in multiphase flow that negatively affects flow metre accuracy.
A third issue the white paper draws attention to is the existence of dead volume. This is the fluid that cannot be removed from within the pipelines. During the end of the bunkering process, residual fuel remains in the pipelines between two measurement points of supply bunker tanker and the receiving vessel. Fuel that has left the supply bunker tanker but not entered the receiving vessel causes a large difference between fuel transferred from supply side and that accounted for in the receiving vessel. This dead volume is causes by the long pipeline that the fluid must travel through between the supply and receiving side. It must be accounted for when comparing bunker notes to avoid misconception of inaccurate measurements between two flow metres. Dead volume can be estimated using a minimum measurable quantity (MMQ) calculation.
Best practices to enhance accurate bunkering
To enhance bunkering and avoid these issues, Ascenz suggests a number of precautions that can be taken. The first is proper metre installation. This includes selecting the right type of metre with marine approval standards, and the right metre size, which depends on flow rates and volumes. A Coriolis mass flow metre, which is certified by the Singapore Maritime and Port Authority (MPA) is the first step. According to Ascenz, correct installation including careful pre-selection screening and site surveys are important due to the different configurations of pipelines in each vessel. As well as understanding the system drawings of the pipelines, Ascenz recommends carefully considering the layout of pipes as corners, bends and heads will influence the readings of the flow meters if the installation location is not optimal.
Metre packing is another important factor outlined in the white paper. Filling up pipelines with fluid is known as line packing and is important to prevent partially filled pipes that can lead to inaccurate fuel flow measurements during bunkering. Pipes can become partially filled if the flow rate is not high enough or strict operating procedures are not followed. Good communication between the bunker supply vessel and the receiving vessel is essential to establish this maximum flow rate as quickly as possible without compromising safety.
Plate fixtures are recommended by Ascenz where partially filled pipes occur. These can increase the accuracy of fluid flow measurement. Plate fixture can be used to elevate fuel flow and increase the accuracy of bunkering measurement.
The white paper also highlights the importance of system integrity. This ensure making sure the mass flow metre (MFM) system is set up and approved for bunkering, as well as being secured against any interference before or after bunkering. This includes the metre election, installation, acceptance test and system monitoring. The white paper states that careful selection and scrutiny of the MFM system is essential to make sure equipment is sealed against unauthorised adjustment or tampering, software is protected and changes are authorised, data collected during bunkering is stored for a min of 3 months for reference and critical alarms are activated.
Smart bunkering data monitoring is another aspect covered in the white paper. Mass flow metre data from bunkering should be gathered and displayed to show mass flow rate, density, temperature, drive gain, and totalising of the bunker fuel, all of which can be used to detect bunkering abnormalities. Aeration, for example, can be detected and crews alerted to examine the cause of the issue. Data collection is important to provide a record of comparison against different bunkering processes. (See figure 1 – examples of reporting of bunkering operations showing proportion of specific bunkering activity.)
Correct certification of the MFM is essential to provide accountability and integrity of an installed system. There are two main certification procedures that provide the certification of the MFM for the bunkering process, according to the white paper. These are the European Union’s Measuring Instruments Directive (EU’s MID) and Singapore’s Technical Reference (TR) 48. This TR48 will be used to further develop the ISO 22192 (Bunkering of marine fuel using the Coriolis mass flow meter (MFM) system) and the development of ISO 21562 (Bunker fuel mass flow meters on receiving vessel – Requirements).
Ascenz also highlights the importance of smart bunkering, which includes visualising live data that allows the crew to be informed and aware of any changes in the bunkering activity. Smart bunkering systems can provide continuous data and help detect changes in operating conditions such as supply tank and cleaning of lines at end of delivery.
Ascenz offers a smart bunkering analysis module, where the bunkering activities are monitored under BunkerXchange HMI (BXHMI), which is a data logger and visualisation tool integrated within the Shipulse Platform. This allows operations and procurement staff to have automated analysis on each bunkering operation and on the overall performance and activity trends. Instant analysis of data will allow abnormalities to be detected and resolved quickly.
According to Ascenz, machine learning is increasingly being deployed for smart bunkering procedures, such as descriptive and predictive bunkering analysis. Data, automatic identification and classification of operations can be recognised throughout the entire bunkering process. Predictive bunkering allows the flow rate, density, and actual frequency to be modelled and compared to actual data set of bunkering process, with deviations highlighting safety breaches or malpractices.
The white paper can be downloaded here.