SUMMARY

Determining the ability of currently available skimmers to collect new types of diesel, including low sulphur marine gas oil, wide range diesel oil and hybrid fuel oils, is of great importance for preparedness against acute pollution. To be able to make operational assessments of which oil skimmers are best suited to a given situation, we must know how the skimmers work on these diesel and hybrid fuel oils. We have tested various oil skimmers in different oil types. Four different diesel and hybrid fuel oils have been tested: a marine gas oil, a wide range diesel oil and two hybrid fuel oils. Three oil skimmer types were tested. The types are with discs, brushes and adhesion belts. The tests are performed with natural seawater at water temperatures corresponding to winter temperature (0–2°C).

Capacity tests have been performed on MGO, HDME 50, ULSFO and WRG to find out how the oil skimmers work in these types of oil. The skimmers were first tested in a restricted basin with a thick layer of more than 20 cm of oil, so that pure oil and only small quantities of water were taken up. The skimmers and oils were then placed in a boom in the basin. A current was applied in the water, which caused a thickness of oil to build up around the skimmer. During our testing the operator ran the skimmers at optimum performance, so that maximum collection and efficiency were achieved.

The results gave us the answer that the selected skimmers work in MGO, HDME 50 and WRG. Which skimmer are chosen will vary depending on what is wanted. It is possible to increase the capacity of the skimmers, but this would have a negative effect on efficiency, since the total quantity taken up will be higher.

None of the skimmers worked well in ULSFO. This oil has a high point of solidification, which meant that the skimmers did not have a sufficient inflow of oil to work with.

INTRODUCTION

The Norwegian Coastal Administration has performed a contingency analysis for shipping in the areas around Svalbard and Jan Mayen. In this area, the greatest probability is the occurrence of spills of distillates, such as marine gas oil. The reasons for this are complex, but one important reason is the prohibition on the use of heavy fuel oil in the national parks around Svalbard. New requirements for lower sulphur content also mean that there is a trend along the Norwegian coast for vessels to change from bunker oil to lighter diesel oils. This is regulated in MARPOL convention appendix VI. An increase in shipping further north is also anticipated as possible new shipping routes open up in the future.

Several new types of fuel have come onto the market: low sulphur marine gas oil, wide range diesel oil and hybrid oils. We need to increase our knowledge about these types of oils and the Norwegian Coastal Administration has a current project aimed at finding out more about the physical, chemical and toxicological properties of diesel oils. Refer to posts from Silje Berger at the Norwegian Coastal Administration to IOSC 2017.

To be able to make operational assessments of which oil skimmers are best suited to a given situation, we must know how the skimmers work on these diesel and hybrid fuel oils. We have therefore started to test various oil skimmers in different diesel and hybrid fuel oils. The tests are being performed in the Norwegian Coastal Administration’s test facilities, the National Centre for Testing of Oil Spill Response Equipment. The oil skimmers being tested are types with discs, brushes and adhesion belts. The skimmers were chosen because these are the ones that NCA has and that we expected could work with low viscosity oils. The temperatures at each test are performed correspond to winter (0–2°C). We have also tested oils at water temperatures corresponding to Norwegian summer (10–15°C), to give us a reference of the efficiency of the skimmers in this condition. The summer results are not included in this paper.

METHOD

Test procedure for testing of oil skimmers at the National centre for testing of oil spill response equipment:

Capacity tests are completed to find out how the oil skimmers work in the selected diesel and hybrid fuel oils. The capacity tests show how much oil is skimmed per hour and an efficiency test have also been performed. The results show whether the skimmers work in accordance with requirements and expectations. The tests are performed by pumping oil into the saltwater basin. Two types of test were performed: one to test maximum capacity and one to test operational capacity.

  1. Test of the skimmer in a thick layer of oil when it is in a restricted basin. The skimmer is operated until maximum uptake has been achieved and is then run like this throughout the test.

  2. Test of the skimmer placed in a boom in the basin. A current of water collects the oil in the boom around the skimmer, simulating the boom been drawn through the water. The skimmer is ran for optimum performance in relation to oil thickness, i.e. there is a need for adjustment during the test as the oil layer becomes thinner. The test is ran until all the oil has been taken up.

Technical data of the basin of the National Centre for Testing of oil spill response equipment:

  • Length ................................................................................................30m

  • Width..................................................................................................7.0m

  • Depth (total)........................................................................................4.4m*

  • Depth above double bottom................................................................2.4m

  • Practical depth above double bottom..................................................1.7m

  • Water volume......................................................................................800m3

  • Water current speed (max)..................................................................4knots

  • Wave height (max)..............................................................................0.6m

Restricted test basin:

The basin is made of PVC tubing and the dimensions of the frame at the centre of the tubing are 3.65 × 3.65 metres. Thus with 2.5 m3 of oil the thickness is a little over 20 cm. The basin has a skirt that goes down a metre below water level.

Image 1.

Restricted test basin with disc skimmer

Image 1.

Restricted test basin with disc skimmer

Oil skimmers been tested:

  • Skimmers with discs and brushes

  • Adhesions belt skimmer

Oils been tested:

  • MGO - Marine gas oil 500 ppm

  • HDME 50 - Heavy Distillate Marine is a new category of marine fuel formulated to meet the Sulphur Emission Control Areas (SECA) limit.

  • ULSFO - Ultra-Low Sulphur Fuel Oil is to meet the Shipping industry’s demand for a 0.1%S maximum bunker fuel in advance of the SECA specification change.

  • WRG - Wide Range Diesel (MSD-WRG)

Test of skimmer in thick oil layer:

We used 2.5 m3 of oil, which were poured into the restricted basin. The skimmer was placed in an oil layer of more than 20 cm. The skimmers were tested without the influence of water or current. The operator ran the skimmers to optimum performance, so that maximum collection was achieved. The operations were based on the operators experience and knowledge and existing conditions.

Image 2.

Disc skimmer in thick WRG layer

Image 2.

Disc skimmer in thick WRG layer

Test of skimmers in boom with current in the water:

Tests were performed on three skimmers. For each test approximately 800 litres of oil were added to the basin. The disc and brush skimmers were tested by being placed in a boom in the basin, while the adhesion skimmer was suspended over the basin so that the belts were in the oil. A current of approximately 0.6–0.8 knots was applied in the water, which simulates the boom being drawn through the water. This causes a thickness of oil to build up around the skimmer. The skimmer was run for optimum performance and oil that was collected was sent to a collection tank. After 800 litres had been taken up, the skimmer was stopped and there was a 15 minute pause to allow the oil and water to settle. Any free water was drained out of the tank and the skimming capacity was calculated at 800 liters. There was still oil remaining in the boom, which we wished to take up. We began skimming again with the speed of the skimmer reduced so as to avoid taking up water. We continued until there was no oil in the basin and efficiency was calculated on the basis of the 800 litres we had put out divided into the total quantity taken up. Oil samples were also taken and these were analysed for density, water content and viscosity.

Image 3.

Brush skimmer in boom with current in the water

Image 3.

Brush skimmer in boom with current in the water

RESULTS

Test of skimmer in thick oil layer:

For tests on MGO 500 ppm, HDME 50 and WRG in the restricted basin, the disc and brush types achieved maximum capacity. The brush and disc delivered more to the reservoir than the pump could handle, meaning that it was the pump that limited the uptake. The adhesion belt worked in these oils, but here the limitation came from the adhesion belts, not the pump.

None of the skimmers worked well in ULSFO. With the disc and brush type, only oil in the immediate vicinity of the skimmer was taken up. The oil that was accessible was taken up effectively, and both discs and brushes had good adhesion. But ULSFO has a high point of solidification (+24 °C), so there was no inflow of oil towards the skimmer. A gap developed between skimmer and oil and when we lifted the skimmer from the basin we observed that the oil had been removed from where the skimmer had been. The adhesion skimmer did not function to the optimum either, but because the belts touched the oil in different places they took up the oil that was encountered. The adhesion belt skimmer was hanging from the crane, so it was also moved around the basin and the belts touched different parts of the oil slick. That`s way it took up oil.

Image 4.

Restricted basin with skimmers in ULSFO

Image 4.

Restricted basin with skimmers in ULSFO

Test results in restricted basin

Test results in restricted basin
Test results in restricted basin

Test of skimmers in boom with current in the water:

With the tests on MGO 500 ppm, HDME 50 and WRG in a boom, all the skimmers worked. When disc or brush skimmers are too low they shovel water into the reservoir, especially when the oil layer is thin. It is possible to increase the capacity of the skimmers, but this would have a negative effect on efficiency, since the total quantity taken up will be higher. Efficiency was calculated by dividing the quantity of oil introduced into the basin by the total amount taken up.

None of the skimmers worked well in ULSFO because they had no oil to work on. Because of the high point of solidification there was no inflow of oil towards the skimmers. With the disc and brush type, only oil in the immediate vicinity of the skimmer was taken up. The oil had an uneven thickness and it was not possible to measure it. Even with a current in the basin, the oil did not float in towards the skimmer and the floats acted as a barrier. The oil was so stiff that when we put the skimmer in the boom the oil slick did not change or break up. When the skimmer was run in the oil slick, a gap developed between the skimmer and the oil. When we lifted the skimmer from the basin we observed that the oil had been removed from where the skimmer had been. The oil was stiff and did not float together, so the hole were not filled. With the adhesion skimmer, the same thing happened as with the others, but because this skimmer operates while hanging in a crane it was moved around the basin so that the belts touched different parts of the oil slick. The adhesion skimmer therefore took up oil. The operator ran the skimmers for optimum performance in relation to oil thickness, which meant that the speed was reduced as the oil layer became thinner. The purpose of the optimum performance was to take up as much oil and as little water as possible.

Test results in basin with boom and current

Test results in basin with boom and current
Test results in basin with boom and current

CONCLUSION

When we tested the skimmers in MGO, HDME 50 and WRG all the skimmers worked well, but with different skimming capacities.

None of the skimmers worked well in ULSFO because they had no oil to work on, since the oil was so stiff. With the disc and brush type, only oil in the immediate vicinity of the skimmer was taken up. The adhesion skimmer was moved around the basin so that the belts touched different parts of the oil slick and the adhesion skimmer took up oil.

The results gave us the answer that the selected skimmers work in MGO, HDME 50 and WRG. Which skimmer is chosen will vary depending on what is wanted. It is possible to increase the capacity of the skimmers, but this would have a negative effect on efficiency, since the total quantity taken up will be higher. During our tests the operator ran the skimmers for optimum performance, so that maximum collection and efficiency were achieved.

Image 5.

The total capacity of three skimmers in four different types of oil.

Image 5.

The total capacity of three skimmers in four different types of oil.

Image 6.

Efficiency as a percentage of 800 litres in relation to total capacity taken up.

Image 6.

Efficiency as a percentage of 800 litres in relation to total capacity taken up.

The results enable us to choose the correct equipment for incidents with such diesel and hybrid fuel oils.

Image 7.

Adhesion belt skimmer taking up MGO

Image 7.

Adhesion belt skimmer taking up MGO

* The elements of the double bottom can be removed to create an opening of 4×7 metres so that the total depth of the basin can be made available.