Handbook of Solvents - George Wypych - ChemTech - Ventech!

14.26 Use of solvents in the shipbuilding 1031
lines will be shorter if the coating storage tanks are positioned close to the spray booths. The
transfer lines, that will need to be cleaned with solvent, will be longer if the coating tanks are
located away from the application area. When this is the case, the transfer lines typically
run underground at the facility and another representation than the one shown in Figure
14.26.1 will need to be used, to clearly identify the emission points and waste streams for
properly quantifying solvent losses. The latter may include a unit for recycling or reclaiming
solvents.
Spray gun cleaning procedures may be a once-through type with collection of spent
solvent in a container for disposal or reuse. Some facilities use commercial gun washers.
Because gun washers are enclosed and recirculate solvent, they can reduce the amount of
solvent lost by evaporation. In either case, the emissions are calculated as the difference between
the amount used and the amount recovered.
To calculate the emissions associated with cleaning a spray gun it is recommended
that a material balance around a “unit operation system” be considered. Several examples
are provided in the Alternative Control Techniques (ACT) document on industrial cleaning
solvents. 19
Several types of part cleaners are used at shipbuilding and ship repair facilities. The
types used in such facilities vary from the more simple sink and spray systems 20 to more
elaborate parts (machine) cleaners of the cold or vapor types. 4 Most of the parts cleaners in
shipyards are small — around 1.5 m x 1 m and 1 m deep - usually located in the machine
shops, not the paint rooms. Most of the parts are small components being cleaned prior to
being joined to other small parts into assemblies and sub-assemblies or being cleaned as
part of some type of repair operation. Most of parts cleaners used were basket-type design
with the parts loaded into a basket and dropped through the vapor zone several times to
clean off the oils and dirt. Some shipyards use contractors to come in and change out the
solvent on a routine schedule.
14.26.4.3 Maintenance cleaning of equipment items and components
Shipyards also undertake scheduled maintenance cleaning of many ship components such
as contacts and switches and equipment items such as bearings and packaging machines.
This is mostly done by hand-wiping the parts with organic solvents. These operations will
generally consume a relatively
small amount of the
overall volume of organic
solvents used for cleaning
in shipyards. Solvents are
also used in machine shop
areas and thus contribute to
the waste stream.
14.26.5 MARINE
COATINGS
There are several categories
of marine coatings that are
used to protect the surface
of a ship from the aggressive
marine environment
Figure 14.26.1 Schematic diagram of marine coating application equipment.