Cryogenics is an applying science which deals with low
temperatures. Ed this branch of engineering is of a great importance
in the field of sea preservation from different substances, which
are not friendly with sea environment. There are at least three
brunches, where low temperature engineering brings the greatest
help to support sea ecology when oil is digging out on the sea
shelf. The first item is a creation of sea oil digging platform on the
bases of water ice technology [1-3]. Water is a good and natural
friendly substance. When it is frozen down to an ice state, one
gets quite a solid and durable material, like concrete, if it is kept
at low temperatures. Generation of low temperatures at the sea oil
platform is not a hard problem even without electric energy supply.
So if a vertical metal tube is filled with water ice it turns into a
support column of the sea platform, strong and reliable. The bottom
of it is frozen down to the soil shelf with the help refrigeration unit.
This method reduces the time of constructing as well as simplifies
dismantling works with lowering costs when the period of platform
operating is over. The columns supporters do not remain where
they are installed, but are transported on the new place and can be
used many times.
The second item. Cryogenic fluids like nitrogen have the ability
to protect the platform communications from oil leakage through
forming of water ice cover on the spot where communication
tube gives oil leakage. The process of ice covering is developed
with a great rate and depends on the tube wall surface Ts, water
temperature Tw and heat transfer coefficient from water to the
surface αw.
At the first approach the growth rate of ice cover ξ´ can be
determinate by agnation
ρ – ice density, kg/m3
L – heat of phase changes (freezing of water into ice), Dj/kg
Tph – temperature of phase change, K
λ – heat conductivity of water ice at 0oC, W/(m·K)
τ – times, s
The third item. Oil digging platform is an object where
fire casualties may occur. Liquid nitrogen being preserved in a
cryogenic tank is an efficient fire extinguisher. Water ice formation
on the low temperature surface is also actual for underwater
works, connected with extraction of subjects from the sea bottom.
A lot of shell garbage pollute the marine environment. There are
a lot of metal barrels, some of them contain chemically dangerous
substances.
As they are in a long term location in a sea water the corrosion
has damaged the walls. The latter excludes a mechanical capturing
them for lifting to the sea surface and transporting for utilization
on the ashore. So, the low temperature engineering gives an
alternative to the mechanical method. New approach requires no
mechanical contacts with the subject. The procedure of contactless
capturing implies that heat insulated tube is moved out from
cryogenic tank and immersed at the subject depth. It is suspended
above the surface of the subject but without contacting it, the gap
is 50-100 mm. Then cryogenic fills the tube`s volume down to the
bottom, which looks like flat metal disk. Ice is formed on the surface
of the flat disk and gap between it and the shell surface is turned
into an ice bridge connecting both sides. Gradually ice is covering
the damaged shell and strengthen it. Then the heat insulated tube
with cryogenic tank are lifted from the depth of the sea water and
are carried to the shore. This method requires no manual efforts,
the works are implemented by a camera visualization.