ABSTRACT

Sludging, purifier choking, and filter blocking have been one of the most serious operational concern for VLSFOs (Very Low Sulfur Fuel Oil). There are many reported cases where the VLSFO met ISO8217 specification limit for the sediment content (TSP & TSA) at the time of bunkering but became unstable within a matter of weeks.

Different chemical and physical properties of the VLSFOs (Very Low Sulfur Fuel Oil) have resulted in greater stability issues during long time storage. VLSFOs are more paraffinic and differ from HSFO (High Sulfur Fuel Oil) with respect to their structure and chemical composition. The degradation process is faster for VLSFOs when they are stored for a long time at elevated temperatures. The consequences of long-time storage results in fuel stability issues, filter choking, and purifier blocking causing problems during ship operations. As a result, determining and predicting the change in stability properties of VLSFOs during long term storage is essential to ship operations.

Determining the long-term storage stability of more than 100 VLSFOs showed that more than 50% of the VLSFOs which are stable on day 1 of testing, became unstable after 1-4 weeks of storage. We have developed a lab developed algorithm to predict the stability of VLSFO during long term storage over a period of up to 60 days for the fuels stored at a typical storage temperature of 50C. The protocol involves subjecting the fuel to various stresses and extensive testing over a period of 6 days.
Based on the new accelerated stability model, any VLSFO fuel can be categorized into one of the
following 3 groups:

Group 1: Based on the accelerated testing, the sediment content remained unchanged and will be less than 0.1% over period of 60 days.

Group 2: Based on the accelerated testing, the sediment content will be less than 0.1% up to 30 days. The sediment content will then increase and become greater than 0.1% over 60 days. There should be consideration given to use these fuels within 30 days.

Group 3: Based on the accelerated testing, The sediment content will be greater than 0.1% in less than 30 days. These fuels may need to be further evaluated for immediate usage, additive dosing etc. This paper focuses on the stability properties and predicting the stability properties during long term storage of VLSFOs and ways to lessen potential stability problems