Bulk sorbents
AFNOR type A
These products do not have any particular shape of their own and are made up of particles without any links between them. Many such products are available on the market. They can be powders or short fibres, of mineral origin (treated substances: expanded perlite, vermiculite...), vegetable origin (non-treated substances: sawdust, peat...) or may be synthetic (polymers: polyurethane, polypropylene, polystyrene, epoxy...).
In
practice, the volume of sorbent needed isat least twice the volume
of pollutant to be recovered. Floating bulk sorbents can
therefore only be used to recover small amounts of oil,
especially when we consider the cost involved and the technical
and logistical difficulties linked to the products' properties
and their use. Furthermore, the spreading of these products
makes recovery difficult.
Bulk sorbents can be spread in several ways:
- manually (irregular spreading and only applicable to small amounts of pollution)
- using a hydro-ejector (e.g. foam hose)
- using an air projector.
Whatever the method chosen, all personnel must be protected (masks, glasses), due to the effect of the wind on the sorbent and the possibilty of irritation caused by the product.
Projection of sorbent using an air projector
After
spreading the sorbent on the oil, agglomerates are formed,
which may be more or less consistent depending on the type
of product, the type of oil and the sea state. For recovery
using nets, the mesh of the net must be smaller than the
average particle size of the sorbent.
Sorbents can even be used on viscous hydrocarbons (several
thousand cSt). However the sorption time depends on the
viscosity. In the case of high density pollutants, near
1 (for example, reverse emulsion of water on the surface),
contact between the oil and the sorbent is difficult to
obtain, because of the presence of a film of water on the
surface of the slick.
Last
update: 23/09/09