Durco Filters Molten Sulfur Filters


Molten Sulfur is commonly used to produce sulfuric acid (H2SO4). Sulfuric acid is typically used in manufacturing of fertilizer or in acid leach mining. The process of converting elemental sulfur to sulfuric acid begins with the burning of the sulfur to form SO2 gas. The SO2 is recovered and converted by catalyst step-wise from SO2 to H2SO4

Molten Sulfur Tech Brief
Durco Filters Molten Sulfur Pressure Leaf System
Click here to learn more about Durco Filters Pressure Leaf Units


During storage and handling, sulfur becomes contaminated with solids such as dirt and ash. This contamination quickly plugs sulfur burners, SO2 gas filters and catalyst beds. The burners need to be "rodded" regularly and long shutdowns are needed to clean the catalyst beds.


Our specially designed pressure leaf filters greatly reduce the maintenance costs in molten sulfur processing: Burner cleaning is reduced. Shutdowns are minimized and SO2 gas filters can be eliminated. Durco Filters incorporate exclusive features such as a full steam jacket (including the closing ring), proprietary filter leaves and devices for eliminating build-up of hardened sulfur. 

Superior Steam Jacket Beats a Bolt-on Design

Our welded steam jacket is far superior to a bolt-on dimple jacket.  In a bolted jacket, there is serious risk and probability of mastic deterioration, which leads to loss of heat transfer, thus causing significant risk that the molten sulfur will re-solidify in the tank.  That will result in expensive and time-consuming repairs and loss of production.  Our welded jacket includes the nozzles (up to the flange and even the closing ring, thus ensuring optimal heat transfer and elimination of cold-spots.

Durco Filters Technical and Filtration Data for Molten Sulfur Systems

Technical Data

  Application Clarification of either light or dark molten sulfur.
  Equipment Standard and customized engineered horizontal tank/vertical leaf filter with dry cake discharge and full-welded steam jacket.
  Materials of Construction Carbon Steel Vessel and Jacket, Stainless Internals and piping.
   Blowdown CO2 or Steam

Filtration Data

  Liquid Molten Sulfur (Molten Sulphur)
  Suspended Solids Dirt, ash and other solid contaminants
  Attainable Flow Rates Light Sulfur: 1 ton/Ft2/Day
Dark Sulfur: 1/2 ton/Ft2/Day
  Cycle Length (typical) Light Sulfur: 1 week
Dark Sulfur: 12 hours 
(Dependent on overall solids concentration)
  Filter Aid 20 lbs Diatomaceous Earth + 10 lbs Lime/100ft2 Filtration Area

Durco Filters Molten Sulfur Systems Features & BenefitsMolten-Sulfur-Filter-Frontal-Piping

  • Optional Overhead Frame: Eliminates sulfur deposits on the shell retraction rails and protects shell retraction mechanism. Also provides usable area under the rear section while onstream.
  • Quick Open Closure (QOC): Fast access to the internals during cake discharge. QOC fully steam jacketed.
    • Exclusive Durco Filters Safety Feature: An integral mechanical interlock on our QOC will not allow the filter to open under pressure.
  • Integral Teflon Scraper Plate: When the vessel is open, the scraper plate removes residual molten sulfur from the interior of the shell, eliminating buildup of hardened sulfur.
  • Optimum Leaf Spacing: Allows large cakes to be built, permits easy cleaning and prevents damage to leaf nest by discouraging bridging.
  • Proprietary Leaf Construction: Exclusive welded leaf construction provides higher throughput and greater strength than competitors' designs. It also insures cake break-up and prevents build-up on the filtrate manifold.
  • Full Steam Jacket: Maintains process temperature throughout the vessel - even extending to the nozzle area to prevent cooling. It also incorporates pressure relief valves on both the head and shell sections to allow safe operation at maximum steam pressure.
  • High-Speed Shell Retraction: A powerful stainless steel reversing chain drive opens the shell quickly. Quick opening is vital to prevent cake cooling during discharge. Stainless Steel components ensure long life in the corrosive environment.
  • Cake Deflectors: Located at both front and rear of leaf nest, these guides direct discharging cake into the cake container, preventing build-up inside the shell.

Click here to learn more about Durco Filters Pressure Leaf Units

Tubular Filters for Molten Sulfur

Molten Sulphur Tube Filter Installation
Molten Sulfur Tubular Backwash Filter

Although not used as often as our Pressure Leaf Filters, our line of Tubular Backwash Filters have also been used with great success in Molten Sulfur applications. The filters at left were designed for the following conditions:

  • 300gpm
  • 200 PSIG @ 320°F 
  • 150 micron removal @ 300ppm max
  • Continuous Operation Mode
  • External Backwash

They were supplied with a full automation package, steam jacketed and insulated, skid-mounted and ready for onsite hookup.

Click here to learn more about Durco Filters Tubular Backwash Systems


Durco Filters division of Ascension Industries incorporates over 130 years of filtration experience in every molten sulfur filtration system we build. Founded in 1933, Ascension Industries manufactures a broad line of self-cleaning Tubular Backwashing Filters, Pressure Leaf Filters, Pressure Nutsches, Filter Presses, and Sludge Dryers. Our Applications and Design Engineers know more about molten sulfur filtration than any other filtration manufacturer. We have improved process performance and eliminated costly maintenance for many sulfuric acid producers. Technologically advanced designs have made Durco Filters the premier choice for molten sulfur filtration.

Consult Durco Filters About Your Application Needs

Consult a Durco Filters Molten Sulfur Systems Engineer to arrange testing and analysis of your process stream and determine the optimum filtration technology for your particular operation.  You can call +1.716.693.9381, email This email address is being protected from spambots. You need JavaScript enabled to view it., or fill out one of ourFiltration Fast Track Form and one of our Application Engineers will get back to you right away.

Pressure Leaf Filters
Sludge Dryers
Tubular Backwash Filters
Pressure Nutsche
Filter Presses