Sulfur is a bright yellow, combustible, non-metallic element that occurs naturally and is found all over the globe. In its pure form, it is odorless; the smell usually associated with sulfur can be attributed to sulfur compounds.

Some of the earliest recorded references to sulfur are found in scripture passages that refer to sulfur as "brimstone" and associate sulfur with Divine Punishment. This contrasts to use of sulfur by other early civilizations as a balm for skin disorders such as psoriasis and ringworm.1

Sulfur is the primary source in the production of sulfuric acid, arguably the most widely-used chemical in the world. Sulfur is used in the manufacture of fertilizer, in oil refining, processing wastewater, mineral extraction, vulcanizing rubber and in the production of nylon. Sulfur is a component of gunpowder. It is also used in the paper-making process as a bleaching agent, and is used as an electrical insulator.

Sulfur is popular with mineral collectors due to its yellow color and crystalline shapes. The spelling of sulfur varies around the world, with "sulphur" predominant in the United Kingdom, Hong Kong, India, South Africa and Australia. However, many scientific societies including the IUPAC (International Union of Pure and Applied Chemistry) and the Royal Society of Chemistry Nomenclature Committee have adopted the spelling of "sulfur" in the 1990's and it is now considered the official spelling.2

Characteristics and Challenges:

Most grades of powdered or micronized sulfur have an average bulk density of 45 lb/cu ft (720.83 kg/cu m).3 In granular form, the average bulk density is closer to 70 lb/cu ft (1121.29 kg/cu m).

The main challenges to conveying sulfur are the corrosiveness of the element and
the risk of explosion and fire. Sulfur dust suspended in air ignites easily, and burns with explosive violence. Ignition can be caused by friction, static electricity, sparks, or heat. Toxic gases may form after combustion.4 Handlers are often faced with stringent regulations for the containment of sulfur during and after processing. The use of explosion protection devices may be necessary to help protect people and property both in and nearby the processing facility.

Sulfur can be abrasive as well as corrosive, so care must be taken to use equipment that can withstand prolonged exposure to sulfur. If the sulfur is being pneumatically conveyed into a processing system, the blower used to move this material through the air line must be sized to meet the demands of system. The use of 316 grade stainless steel is usually recommended for any equipment that is exposed to sulfur.

Some grades of sulfur can be non-free-flowing, so if the sulfur arrives at the processing facility in bulk bags, the frames used to discharge the bags should be equipped with additional accessories to reduce operator intervention when emptying the sulfur from the bag. This includes features such as spring-loaded frames that will stretch the bags as they empty and lighten, making them rigid and removing any pockets of sulfur cornered in the bags. Bag activating devices are usually effective in dislodging collections of sulfur, promoting a better flow. Some of these bag activating devices also serve as a dust-tight seal between the bulk bag and the receiving hopper.

After the bulk bag has been connected to the receiving hopper and the sulfur begins to flow, the air inside the hopper is forced out. Unless this displaced air passes through a filter, airborne dust particles can escape into the surrounding atmosphere, creating a potentially hazardous situation. A dust collector mounted on the discharger frame will contain the sulfur inside the conveyance system. Sulfur dust trapped in the filter media can be returned to the receiving

hopper by a pneumatic pulse through the filter.

If the sulfur is being added into the processing stream from smaller bags, a bag-breaking station with a dust hood, filtration devices and a pneumatic pulse cleaner is the recommended solution to support the manual unloading of the material. If empty bag disposal is an issue, a dust-tight bag compacting system may be necessary.

With its poor flowing characteristics, sulfur may tend to "rat hole" or bridge in hoppers, interrupting the proper flow of the material. Because of this, feed hoppers should be designed with proper geometry and may need to incorporate devices such as mechanical agitators, vibrators or air fluidizers to promote flow. A hopper grate above the receiving vessel will help to prevent the introduction of foreign objects and protects the operators from any moving equipment inside the hoppers.

If a flexible screw is being used to convey the sulfur, it is important to use a screw that matches sulfur's characteristics and other application requirements. Generally a screw with a wider, flatter surface than the standard-sized screw is necessary for this type of material.

Should your sulfur application feature the loading of material into bulk bags, the bag capacity will be maximized by use of a vibratory densification deck to level the sulfur as it fills the bag and by the application of load cells to attain the desired weight. Seals and other dust
containment devices will ensure a dust-tight operation.
Flexicon Applications:

Consultation with a Flexicon specialist will help you decide if a flexible screw or pneumatic solution best fits your sulfur application. Flexicon's expert design and engineering staff will weigh each parameter and recommend the best solution for you. Our product line of advanced flow promotion conveyors, high flow hoppers, deaeration/densification beds and a host of other components and accessories are proven performers that promote flow while reducing degradation, dusting and/or the separation of blends comprised of disparate particles.

Due to the sometimes unpredictable flow characteristics of sulfur, Flexicon-manufactured connectors and valves are recommended. Available in a wide array of options, these valves make the tying and untying of bulk bag spouts easy and reduces unwanted material flow, preventing uncontrolled bursts of sulfur into the hopper and conveying equipment and dust into the plant environment.

Upon request, Flexicon's test lab will simulate your sulfur handling applications before the system is installed in your plant.

1 The Sulphur Institute, Washington, DC
2 Nature Publishing Group
3 Source: Powder and Bulk. Com - Bulk Density Chart
4 Georgia Gulf Sulfur
Sources: Where noted. All other information courtesy of Flexicon Corporation.