|
Table 2 Ranges for oil properties and related slick
| Oil Class |
Target Visco sity |
Viscosity Range
(cP) |
Density
(kg/l) |
Slick Thickness
(mm)3) |
Recommended Current speed
(m/s) |
Slick length
(m) |
Comment |
| 1 2) |
10 |
5-20 |
0,85-
0,9 |
10mm |
|
|
Diesel, fresh crude, very light bunker |
| 2 |
200 |
170-230 |
0,9-
0,93 |
30mm |
0,18 |
6 |
Light Bunker |
| 50mm |
0,2 |
8 |
Light Bunker |
| 3 |
20.000 |
1.800-
2.200 |
0,92-
0,95 |
50mm |
0,18 |
8,2 |
Medium Bunker |
| 4 |
20.000 |
19.000
-21.000 |
0,95-
0,98 |
50mm |
0,18 |
6,2 |
Heavy Bunker |
| 5 |
20.000 |
19.000-
21.000 1) |
0,95-
0,98 |
50mm |
0,15 |
7 |
Emulsion of medium bunker |
| 6 2) |
50.000 |
40.000-
60.000 1) |
0,96-
0,99 |
100mm |
|
|
Emulsion of heavy bunker |
|
| 1) |
at shear rate 10 s-1 |
| 2) |
optional in the DNV certification program |
| 3) |
acceptable variation +/-10% |
The above table specifies the oil classes that should be used for testing. Classes 2-5 are the standard classes for testing in the DNV certification program. Class 1 and 6 are to be used for skimmers that are specifically designed for the recovery of such oils, i.e. very low and very high viscosity oils. The table specifies required slick thickness and suggests a current speed/ slick length combination that is likely to produce such conditions for testing. Note that other combinations of current and slick length may result in the same thickness (see Appendix 1). Minor deviations from the recommended settings may be acceptable to adapt to tank and skimmer dimensions.
Figure 1 Test facility arrangement
Appendix 1 - Guidelines for controlling oil slick thickness
The following provides guidelines for controlling the thickness of an oil layer contained in a boom. The method does not replace the need for in situ slick thickness measurements but is designed as a supplement to such measurements, since few methods are currently available for rapid and reliable slick thickness measuring.
The method is based on the following findings from studies of slick build-up in a boom (DNV, 2002):
| ・ |
The thickness of the slick in a boom is nearly uniform, with
the exception of some thinning at the slick's leading edge and very close to the
boom. This is proven through measurements in the viscosity range 200 to 10.000
cP and at current velocities above 0.15 m/s (DNV, 2002). For conditions outside
this range empirical data is not available.
|
| ・ |
There is a direct relationship between the slick length and
the slick thickness. The relationship is unique for each oil type
|
| ・ |
The slick thickness may be approximately controlled by controlling
the length of the slick |
The relationship between slick thickness and slick length (as determined by experiments) is given in the figures below, for 200 cP, 2000 cP and 10.000 cP bunker oil with density in the 0,93 to 0,95 range. These are meant as indications, and deviations may occur as a result of density variations.
In order to obtain a specified slick thickness the following steps should be followed:
| 1. |
Identify the viscosity of the test oil
|
| 2. |
From Figure 2 and 4 identify the combination of current and
slick length that will produce the desired slick thickness.
|
| 3. |
Identify the amount of oil to be preloaded in the tank. This
is calculated as slick length x slick thickness x tank width.
|
| 4. |
Start the current and adjust to the desired speed
|
| 5. |
Preload the test tank with the required oil quantity
|
| 6. |
Measure slick length and slick thickness. If found to deviate
from the desired thickness, adjust by either removing oil or increasing the oil
quantity.
|
| 7. |
When the desired thickness is achieved, measure the length
of the slick
|
| 8. |
If testing is to be carried out with waves, start the wave
generator and adjust to the desired setting. Notice any slick length reduction
as a result of the waves. Reduce the current velocity until the slick's leading
edge is at its original position.
|
| 9. |
Start the skimmer
|
| 10. |
Start the oil distribution system
|
| 11. |
Throughout testing, adjust the pumping rate of the oil distribution
system to maintain the location of the slick leading edge.
|
| 12. |
Verify that the slick thickness is maintained by measurements,
and adjust the slick length if required. |
| （拡大画面：65KB） |
 |
| （拡大画面：61KB） |
 |
| （拡大画面：63KB） |
 |
| Figure 2 |
Relationship between slick length and thickness for 200, 2000
and 10.000 cP oil |
| （拡大画面：70KB） |
 |
| Figure 3 |
Relationship between slick length and thickness for 10.000
cP w/o emulsion of bunker oil (at 10 s-1) |
|
