THIOPAQ O&G Biodesulfurization System | Schlumberger

THIOPAQ O&G

Biodesulfurization system

Thiopaq oil and gas biodesulfurization system

Cost-effective, reliable, robust, and environmentally friendly solution for H₂S removal from natural gas

The THIOPAQ O&G biodesulfurization system uses nonhazardous, naturally occurring, and self-regulating bacteria to convert H2S in a produced gas stream to manageable solid elemental sulfur that can be used in a variety of agricultural applications or disposed of in a landfill. This addresses two goals: environmental stewardship and positive economics.

The process removes H2S from low-, medium-, and high-pressure streams in direct treat operations. It easily installs for indirect treating and runs downstream of amine, Claus, and membrane units for emissions cleanup and sulfur recovery. The THIOPAQ O&G system produces treated gas that meets a typical H2S outlet specification of 4 ppm or less.

Advantages

  • System requires significantly less chemicals compared with other competing technologies.
  • Nonsticky sulfur product results in easier operability, less downtime from clogging, more sulfur disposal options (agricultural and landfill), and less sulfur-handling equipment.
  • Nontoxic wastestreams are disposed of more easily compared with conventional sweetening processes.
  • Naturally occurring biological process is an environmentally friendly green technology.
  • Nontoxic process provides you with simple operation and low maintenance.
  • Environmental Technology Verification (ETV)—produced in association with the US Environmental Protection Agency (EPA)—enables easier regulatory compliance and approval.
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Continuous three-step process of absorption, conversion, and removal

The THIOPAQ O&G biodesulfurization system converts sour natural gas containing H2S into a sweetened gas stream. The process also includes extraction of elemental sulfur from the system.

H2S absorption by aqueous soda solution

To begin, a pH-controlled aqueous soda solution is sprayed into a contactor vessel containing plastic packing. The sour gas flows in a countercurrent direction within the vessel. The aqueous solution absorbs H2S from the natural gas stream, forming hydrogen sulfide ions (HS). The sweetened gas stream exits the contactor with as much as 99% of the H2S removed. The contactor is the only place where H2S is present in the process other than in some gas inlet scrubbing vessels that are required upstream to better clean the gas for improved H2S removal.

Conversion of hydrogen sulfide ions into elemental sulfur

The second part of the process is the conversion of the hydrogen sulfide ions that formed in the process solution. The conversion occurs when the solution is pumped into bioreactors where the haloalkaliphilic strains of the Thioalkalivibrio bacteria are stimulated by oxygen delivered by variable-speed air blowers. The bacteria oxidize and covert the sulfide ions into elemental sulfur. An enzyme is produced during the biological conversion that covers the sulfur particles, making them nonsticky or hydrophilic. This is unlike other liquid processes, which require chemicals for conversion and produce sticky or hydrophobic sulfur. Because sulfur particles are present throughout the process wherever the liquid solution exists, it follows that nonsticky sulfur particles lead to significantly less downtime for plant maintenance.

H2S removal technology selection
Sulfur load recovered for H2S and gas flow.
H2S removal technology selection
THIOPAQ biodesulfurization process flow diagram
THIOPAQ biodesulfurization process flow diagram.
THIOPAQ biodesulfurization process flow diagram

Automatic control and minimal operating requirements

The process liquid that is home to the bacteria is regulated by a programmable logic controller (PLC), which monitors pH, conductivity, temperature, oxygen demand, and many other parameters. Should any of these parameters fall outside its operational range due to changes in gas flow rates, total sulfur loading, or both, the PLC automatically adjusts the parameter to ensure that the bacteria continue their highly efficient conversion cycles.

The process system is approximately 95% efficient in regenerating. Compared with typical caustic scrubber systems, only modest amounts of caustic addition are required to maintain system alkalinity and pH for absorption. No heating equipment is used for regeneration and no catalyst is needed for conversions. This approach successfully reduces system cost. Small amounts of nutrients are added to the system to keep the bacteria in good health. After the one-time addition of bacteria to the system, the colony expands or contracts based on the feeding of H2S into the system. This enables the biological system to be self-regulating, supporting significant process turndown if conditions demand.

Removal of sulfur particles

The final step is the removal of the converted sulfur particles. Testing and experience have shown that compared with vacuum filters and filter presses, the decanting centrifuge is the most efficient and cost-effective method of removing sulfur particles. The supernatant liquid is returned to the system to minimize requirements for additional fluids.

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