Goar, Allison & Associates
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> D'GAASS® Sulfur Degassing Process

D'GAASS Sulfur Degassing ProcessGoar, Allison & Associates' patented D'GAASS Sulfur Degassing Process is specifically designed to address your liquid sulfur degassing process requirements. The compact, simple D'GAASS process removes H2S and H2Sx from the liquid sulfur product produced from Claus sulfur recovery units, while greatly reducing odors and hazards associated with liquid sulfur. Our D'GAASS units may be supplied as shop fabricated modular units, providing an opportunity for additional cost savings as compared to standard field installation.

Key D'GAASS Advantages Include:

  • Ease of retrofit to an existing SRU
  • Low capital investment
  • Reliable, simple operation and low maintenance
  • Low air requirement and operating cost
  • No continuous catalyst or chemical use
  • Very small footprint for installation at any location between the sulfur pit and loading/forming
  • Pressurized sulfur product stream permits easy routing to storage, forming or loading
  • Pressurized overhead vapor stream may be routed to the SRU thermal stage or TGU burner resulting in no additional emissions
  • Better sulfur quality compared to degassing processes that use catalysts
  • Ability to degas to levels less than 10 ppmw H2S

These features have established D'GAASS as the leading technology for the degassing of liquid sulfur. Over 80 D'GAASS units have been licensed with a total capacity of over 40,000 long tons per day (LTPD).

Goar, Allison & Associates is ready to support your needs through all phases of your liquid sulfur degassing project, including:

  • Customized D'GAASS process design package developed to provide a basis for detailed process design;
  • Review and support, as required, of any detailed design package developed by client's EPC firm, including the design of modular units; and
  • Performing operator training, HAZOPS, start-up and operational support as needed after start-up.

For a list of installed and operating D'GAASS units or to learn more about our D'GAASS technology and how it can benefit your operation, please contact us. If you would like us to evaluate your current process for D'GAASS, please fill out and submit a D'GAASS Process Questionnaire.

> The D'GAASS Sulfur Degassing Process

D'GAASS Sulfur Degassing ProcessLiquid sulfur produced from a Claus SRU typically contains 200 to 350 ppmw H2S, partially dissolved and partly present in the form of polysulfides (H2Sx). If liquid sulfur is not degassed, H2S will be released during storage, loading and transport, and may create an explosive mixture of H2S in air. Un-degassed sulfur can also create a toxicity hazard as well as a noxious odor problem when H2S is released from the sulfur. Solid sulfur formed from un-degassed sulfur is more corrosive and friable; also as H2S is released from the solid sulfur, noxious odors are frequently a problem.

The D'GAASS Sulfur Degassing Process removes H2S and polysulfides (H2Sx) from liquid sulfur outside of the sulfur pit in a pressurized vertical vessel. The un-degassed sulfur is pumped from the sulfur rundown collection pit/tank to the vessel where it is intimately contacted counter-currently with pressurized process air across special fixed column internals. The contactor vessel may be located at any convenient location. Un-degassed sulfur and process air are the only feeds to the degassing contactor. Chemical catalysts are not required. For existing SRUs, the sulfur rundown pit/tank acts as the degassing unit feed tank. The installation of new sulfur feed pumps is the only modification required for an existing sulfur pit.

The D'GAASS process removes H2S and H2Sx through two mechanisms: 1) partial oxidation of the H2S and H2Sx to produce sulfur, and 2) stripping the balance of the H2S from the sulfur. The upward flow of air provides both agitation of the sulfur and stripping of H2S. At optimum conditions, the H2S content is reduced to less than 10 ppmw without the addition of a chemical catalyst to the sulfur feed. Other commercial processes operate at or near atmospheric pressure. Operation at elevated pressure and a controlled temperature accelerates the oxidation of H2S and H2Sx to sulfur and SO2. The SO2 can react with H2S via the Claus reaction to form additional sulfur. The degassed sulfur can be sent to sulfur storage, sulfur forming, or directly to loading without additional pumping.

The overhead vapor stream from the contactor vessel, which is pressurized air with low concentrations of H2S, SO2, and sulfur vapor, can be sent to the incinerator. Alternatively, the elevated D'GAASS operating pressure allows sending the overhead vapor stream to the SRU thermal stage, tail gas unit burner, or selective oxidation reactor such as SUPERCLAUS - thus eliminating the degassing unit as an SO2 emission source.

Major Process Advantages of the D'GAASS Process include:

– Degassing outside the sulfur pit

  • Limited or no modification to the existing pit
  • No internals in the pit
  • Reduced pit size for new units

– Process operates under pressure

  • Increased dissolved oxygen concentration and increased oxidation rate of H2S and H2Sx
  • Smaller equipment requirements
  • Installation in any convenient location
  • Reduced emissions with effluent gas routing to SRU reaction furnace
  • Transfer of degassed sulfur to storage, loading or forming without additional pumping

– Modular construction available

  • Reduces installation cost and field work
  • Minimizes production downtime

> D'GAASS Modular Units

D'GAASS Sulfur Degassing ProcessGoar, Allison & Associates can provide your D'GAASS process equipment in modular form, simplifying unit installation in the field and further reducing your capital cost. Goar, Allison & Associates can provide this service in two ways – through the full design and oversight of the unit fabrication on the customer's behalf or by selling the modular unit as a single equipment item.

The module contains the major D'GAASS unit controls, the contactor vessel, all interconnecting piping routed to the edge of the module, process instrumentation and controls, and electrical conduit routed to junction boxes at the edge of the module.

Goar, Allison & Associates' design team has experience in modular design as well as expertise in the unique requirements of D'GAASS units and will tailor our services to your specific needs.

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© 2019 by Goar, Allison & Associates, LLC. COPE and D'GAASS are registered service marks of Fluor Corporation.

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