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3.Installation
The installation for hot dip galvanizing consists of
the heating system {galvanizing furnace)
the galvanizing kettle to hold the z1nc
- equipment for measuring and controlling the temperature (this
is normally an integral part of the galvanizing furnace)
The construction, the materials used, the manufacture and assembly of the heating system and the kettle as well as the
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3.1 Gas and oil heating systems
When using gas and oil the heat is supplied through burners mounted in the furnace walls. The number ,of burners depends on the fuel (gas or oil), the size of the kettle and the throughput.
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Heating systems for steel kettles:
Indirect heating over plates
The galvanizing kettle is protected against a direct contact of
as flames by fire plates. The energy efficiency is very poor.
- Forced circulation heating system
quality of the equipment for temperature measurement and control
To improve the energy efficiency the
hot gasses are blown
have an influence on the lifetime of the kettle. They also affect the costs and the efficiency of the galvanizing process.
Different heating systems have been developed to suit energy sources available i.e. gas {natural, town, propane, butane etc), electricity and oil. The installed heating system and its construction has a great influence on the lifetime of the kettle. The demand for a long kettle life, which is closely connected with the.reduction of unwanted dissolving of iron, has led to the development of heating systems with this as the principal aim. When carefully designed the available heat will be uniformly distributed over the kettle walls preventing hot spots and critical temperatures at the inside of the kettle walls.
Because it is not advisable to exceed the critical heat load on the kettle walls a uniform distribution of the heat over the whole heating surface is required for maximum utilisation of the zinc kettle area available. Earlier recommendations to distribute the heat unevenly over the heated surfaces are therefore not correct. The low.est part of the heated surface must be about
10.0 mm above the surface of the dross layer.
To achieve a longer kettle life the following requirements must be met by the galvanizing furnace:
- Uniform heat distribution
- minimising temperature differentials on the outside of the kettle
- The temperature at the inside of the kettle wall not exceeding
480 deg c
against the kettle walls by a fan mounted adjacent to the com-
bustion ch8mber.
- Rotating heating with self inducing injector burners.
Because no fan is used the energy and maintenance costs are low
for these ovens. The burners are mounted vertically and are
evenly distributed over the long sides of the kettle walls. The burned gasses leaving the jets induce part of the cooled waste gasses over a diffuser and the mixture is returned to the furnace chamber. The heat is mainly conducted to the upper part of the kettle walls.
High Velocity Furnaces
High velocity jet burners are mounted on diagonally qpposed
corners and fire along the furnace gallery surrounding the galvanizing kettle. The hot gases spin around the kettle resul ting in very uniform heat transfer rates, eliminating hot spots and further resulting in high thermal efficiency.
- Flat Flame Furnaces
The required uniform heating of the kettle is obtained by
radiation from a hot wall. The burners are mounted t the same
height opposite the long kettle walls. Depending on the type
of burners the gases leave the burner quarl at a high speed
and cling closely to the interior furnace walls by centrifugal
force heating the walls evenly. Direct contact with the kettle can be eliminated by placing a tile in front of the burner.