Viswa Lab, in its recent technical update answers the question as how to prepare the tanks which contained high sulfur fuel so that they can receive VLSFO fuels with 0.50 % wt sulfur.
Sulfur content in VLSFO fuels should not exceed 0.50 % wt. Most ships currently use HSFO which can contain sulfur up to 3.50 % wt.
How to prepare the tanks for VLSFO fuels?
The expensive way to do it is to manually clean the tank. This is not necessary. There are at least two other ways to carry this out.
Use of additives
One is to use additives available in the market and flush out the tank after adding the additive.
This involves the additional cost of the additive.
Use of LSFO
The method many organizations are following is to take a low sulfur fuel or ultra low sulfur fuel, fill up the tank with this product and transfer it from one tank to another till all the high sulfur fuel in these tanks have mixed with the low sulfur fuel. The flushed oil can be used depending upon how much sulfur it contains after washing.
Factors to consider with HSFO
There are three factors to consider where the high sulfur fuel can pollute and raise the sulfur content in the low sulfur fuel used for flushing.
- The pipelines – We have seen that the quantity of high sulfur fuel in the pipelines by a rough calculation does not exceed 2 to 3 MT.
- The walls of the tanks ‐ High sulfur fuel will stick to the walls of the fuel tanks and this does not contribute to more than 2 MT of high sulfur fuel.
- Unpumpable ‐ The largest quantity of high sulfur fuel is the unpumpable quantity at the bottom of the tank. This quantity depends on if the tank is deep tank with tapered bottom or DB tank with a flat bottom. A Deep Tank with tapered bottom may not contain very high quantity of unpumpable fuel. However, a Double Bottomed tank with multiple compartments can contain 5 to 15 MT of unpumpable can be 5 to 15 MT high sulfur fuel.
Calculating sulphur content
It is possible to compute the total of this high sulfur fuels in relation to the quantity of flushing oil and calculate how much sulfur content will go up in the low sulfur flushing oil.
Viswa Lab says that one of its clients had 2 MT of fuel with 2.62% sulfur and added a 100 MT of a VLSFO with 0.48% sulfur. The sulfur content of this blend was 0.52% which would not meet the specification requirements. If the client had used 100 MT of fuel with 0.45% sulfur, the resulting blend would have a sulfur content below the 0.50% limit.
How to handle high sulphur present?
If the quantity of high sulfur fuel present in the unpumpable+tank+pipeline is high, this could be handled in two ways.
One is to start with ULSFO which will have less than 0.10 % sulfur and/or use a larger quantity of low sulfur fuel.
The final mix after flushing can be used as VLSFO provided the sulfur stays within the limit of 0.5 %. We do recommend checking the stability of this blend.
To assist with questions related to 2020 fuels Viswa has started an in‐house ‘Working Group’. You can reach us at wgfuels2020@theviswagroup.com
Please do not hesitate to contact us if you would like your VLSFO’s tested.
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Source: Viswa Group
