IN THE KNOW
Sulfur Recovery 101
SULFUR BASICS
What is sulfur?
Sulfur is a nonmetallic chemical element with an atomic number of 16 and is a solid at ambient temperatures. Historically called brimstone, is estimated to be the tenth (10th) most abundant element in the universe and the fifth (5th) most abundant element on earth. The earth’s crust contains approximately 0.03 to 0.1% sulfur by weight.
What is sulfur used for?
Sulfur is primarily used to produce Sulfuric Acid (H2SO4), a precursor for many other manufacturing processes and fertilizer production. It is used to manufacture cellophane, batteries, as a vulcanizing agent for rubber, as a bleaching agent in paper production, and is a common element in pharmaceutical production. It is also an elemental macronutrient for all living organisms.
Sulfur vs Sulphur
The phonic spelling ‘Sulfur’ is the common spelling in North American English, while British English uses the ‘ph’ – Sulphur spelling. The French “soufre” entered English in the late 14th century, and both spellings have been used for many centuries.
What Is a Sulfur Recovery Unit?
A Sulfur Recovery Unit (SRU) converts H2S to elemental Sulfur (S). There are many processes to accomplish the conversion and they have varying product quality.
What Is a Thermal Oxidizer?
Thermal Oxidizers are air pollution control systems used in many processes to oxidize and decompose hazardous, flammable, and volatile organic compounds (VOCs) contained in the exhaust of many manufacturing and processing plants. Oxidizing and decomposing these compounds at high temperatures before they are released into the environment helps reduce smog and air pollution and, in some cases, eliminates fire hazards by preventing these compounds from accumulating at ground level.
How Does a Sulfur Recovery Unit Work?
The most common SRU configuration is the Modified Claus Process. One-third of the H2S in the incoming feed is combusted to SO2 in a Thermal Reactor with temperatures usually ranging from 1800-2400°F. The remaining two-thirds of the H2S combines with the SO2 in the Thermal Reactor and 50-60% is converted to sulfur (S). Thermal Reactor effluent enters a waste heat boiler and generates up to 600 psig steam. From there, the stream enters a sulfur condenser. Condensed liquid sulfur is separated from the process vapor stream and gravity flows to a sulfur pit or tank.
The Claus and Modified-Claus Reaction
The Claus process was first patented in 1883 by the German chemist Carl Friedrich Claus. His discovery, the Claus Reaction, is the basis for what has become the industry standard for sulfur recovery.
What is sour water?
Sour water is any water stream that contains H2S, CO2, or NH3 (ammonia). Gas plants typically don’t require sour water treatment because the volumes are small enough to be discharged to a plant sewer or removed by a tank truck.
How do amine units operate?
“Amine” in refinery and gas processing applications usually refers to a mixture of alkanolamines in water. The solution is basic and will absorb acidic compounds like H2S and CO2 and has been used extensively for H2S and CO2 removal in both liquid and gas process streams. H2S and CO2 absorbed in an amine solution can be removed (stripped) by increasing the temperature of the solution making amine an excellent regenerable acid gas solvent.
What Is Tail Gas?
Tail Gas, or SRU Tail Gas, is the final gas stream leaving a Sulfur Recovery Unit after most of the Hydrogen Sulfide (H2S) has been removed. A typical SRU operating at design conditions can remove between 95-97% of the incoming sulfur in the feed stream. Overall recovery efficiency depends on a variety of factors.
SULFUR PLANT OPERATIONS
What is debottlenecking?
Debottlenecking means improving the efficiency and / or throughput of a chemical process by identifying the limiting factors and eliminating them.
What are COS and CS2?
Carbonyl Sulfide (COS) and Carbon Disulfide (CS2) are produced by side reactions in the Thermal Reactor of a Sulfur Recovery Unit. COS and CS2 exist in relatively low concentrations in the process gas but can have a significant impact on sulfur recovery efficiency since they do not take part in the Claus reaction.
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