Sulphur Systems - Sulphur Melting
August 20, 2010

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 60^oF to liquid sulphur at a temperature of 280^oF.

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 ft^{2 o}F.  A good practice is to double the calculated required heating surface.