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Sulphur Systems - Sulphur Melting
January 16, 2003
Introduction
Sulphur Melters
Sulphur melters are either above ground
tanks or inground pits with steam coils for melting the sulphur. The tank or pit may be fitted with an agitator
which will increase the melting rate. Solid
sulphur is generally delivered from a storage hopper to the melting tank or pit by a
conveyor system. At this time lime may be
added to neutralize any acidity in the sulphur to minimize corrosion of equipment.
Each percent of water in the sulphur will
increase the heatload by approximately 20%. Moisture
may cause foaming in pit melters, which will decrease the capacity of the melter. Moisture is also undesirable because it will
accelerate corrosion.
Approximately 70
BTU are required to convert one pound of solid
sulphur at 60oF to liquid sulphur at a temperature of 280oF.
Melting Tanks
Melting tanks are generally plain carbon
steel lined with acid resistant brick. Tanks
should be equipped with an overflow to discharge any foam generated when the sulphur is
melted. A drain should be installed at the
low point of the tank.
Melting Pits
A melting pit are generally rectangular and
are made of reinforced concrete lined with acid resistant brick. Unlined concrete pits are unsatisfactory. The concrete solwly disintegrates because it is
attacked by sulphuric acid, small amounts which will be present in bulk sulphur. As a minimum requirement, the melting pit walls
should be brick lined at the liquid-air interface.
Melting pits are
generally covered with 1/4” carbon steel plates, suitably supported and reinforced. Corrosion of the underside of the covers will
occur making access to the top of the pit dangerous using the covers. If access to the top of the pits are required a
suitably designed platform and supported platform should be provided.
Provision should
be made to permit thermal expansion of the pit. Also,
the interior surface of the concrete will be hotter than the exterior surface which will
cause cracking of the concrete. Properly
placed reinforcing steel will minimize cracking of the concrete but it is not unusal to
find cracking in concrete melting pits.
Heating/Melting Coils
Melting coils
are usually fabricated of 1 1/2” or 2” schedule 80 steel pipe. They should be located below the minimum sulphur
level in order to reduce corrosion. The riser
pipes for steam and condensate should be protected in the region of variable liquid-air
interface to prolong their life. Coils may be
fabricated in trombone, helical and other shapes. The
use of finned tubes will increase surface area and enhance heat transfer.
With natural
convection melting and steam at 90 to 100 psig, overall coefficients of heat transfer of
approximately 25 BTU/h ft2 have been reported.
This is equivalent to approximately 7.5 ft2 or 15 lineal ft of 1
1/2” pipe per long ton of sulphur per day. Forced
convection increases the rate of heat transfer to approximately 80 BTU/h ft2 oF. A good practice is to double the calculated
required heating surface.
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