In this enlightening article from Veritas Petroleum Services (VPS), a renowned leader in the maritime sector and pioneers of the marine fuel testing industry, Wolf Rehder, Sales Manager, VPS Germany, sheds light on the paramount significance of precise VLSFO temperature management in safeguarding assets. The article delves into the challenges, repercussions, and effective solutions related to VLSFO fuel management, underscoring the crucial role of comprehending Wax Appearance Temperature (WAT) in maintaining seamless operations at sea.
Why Proper VLSFO Temperature Management Is Crucial to Safeguard Your Assets?
With the implementation of the IMO sulfur cap starting from January 1, 2020, the importance of precise fuel management has significantly escalated. Aboard vessels, one of the foremost challenges encountered involves maintaining the optimal temperature for Very Low Sulfur Fuel Oil (VLSFO) throughout the fuel system.
It has come to our attention that VLSFO can rapidly destabilize once it is on board a ship, with some of these fuels having a shelf life of less than three months. This destabilization process accelerates when the fuel is heated, leading to excessive sludge formation, resulting in issues such as filter and separator clogs.
VLSFOs are inherently more paraffinic than “conventional” High Sulfur Fuel Oils. If the fuel is not kept at a sufficient temperature, it may result in wax formation, adversely affecting separator operation and causing blockages in the fuel system, including filters. The traditional advice of storing fuels at 10°C above the pour point can sometimes be misleading for VLSFOs, as wax formation can initiate at temperatures higher than the pour point. Global statistics from VPS regarding Very Low Sulfur Fuel Oil indicate that the Wax Appearance Temperature (WAT) is approximately 20°C above the Pour Point.
Maintaining settling tank temperatures below the WAT can lead to wax precipitation in the tanks, potentially obstructing the suction line and diminishing heating efficiency if the wax coats the heating coils. Hence, knowing the precise WAT is indispensable for ensuring proper fuel management.
The WAT testing method, introduced by VPS in 2019, has proven invaluable for numerous ship owners and operators in overcoming this challenge.
The key is to maintain the fuel temperature as low as possible while ensuring it is high enough to meet the viscosity and WAT requirements. Prolonged heating of the fuel in storage tanks is discouraged, as it significantly deteriorates the fuel’s quality and accelerates aging.
However, heating the fuel to attain the appropriate purification temperature and injection viscosity is sometimes unavoidable, albeit for a relatively brief period. Assuming that the fuel leaving the purifier is promptly consumed, any damage is limited.
In the past, a separation temperature of 98°C was considered unalterable. However, with the advent of VLSFOs since 2020, we have observed a notable reduction in viscosity, necessitating lower separating temperatures at the purifiers.
In the diagram provided in Figure 1 above, we can observe that separator manufacturers typically provide recommendations for storage and separation temperatures based on the fuel’s viscosity. When the suggested separation temperature falls below the Wax Appearance Temperature (WAT), it can result in sludging or, in the worst-case scenario, complete blockage of the separator.
This issue becomes even more critical when dealing with fuels characterized by high cat-fine content and low viscosity. Heating a low-viscosity fuel above the WAT poses a significant challenge, as the viscosity drops to a level where the vessel’s fuel booster pumps are unable to generate sufficient pressure. This situation may lead to leaks and potentially result in vapor lock. When operational constraints prevent the vessel from elevating the temperature above the WAT, the fuel essentially becomes unusable.
Hence, a thorough understanding of the correct WAT is of paramount importance when working with VLSFO to ensure efficient and trouble-free operations.
Source VPS Veritas Petroleum Services