CarbFix and SulFix - NCG Treatment Plant for a Geothermal Plant

The CarbFix and SulFix projects are part of the NCG (non-condensable gas) treatment plant at Hellisheidi Geothermal power plant designed by Mannvit. Mannvit lead the design and commissioning of the CO2 and H2S abatement plant at Hellisheidi Geothermal Power Plant. The owner of the power plant is Orka Náttúrunnar (ON) in Iceland. The abatement plant treats non-condensable gases (NCG) from the power plant. The plant separates hydrogen sulfide (H2S) and carbon dioxide (CO2) from other NCG gases. 

Project managers at ON have managed the project, whereas Mannvit has been in the lead of the design work and the commissioning of the abatement plant. Mannvit supervised and coordinated the design as well as the supervision of the construction and the installation. Mannvit's tasks included the design of a simulation model in which the functionality of the process design was verified, co-ordination and scoping of the individual parts of the terminal, and specification of components. Process design (P&ID) and design of the absorption column, which separates the gases, was handled by Mannvit as well as and so was the designing of steel piping and layout of equipment. 

Hellisheidi geothermal power plant - Hellisheiðarvirkjun

Operation of the NCG Treatment Plant

Operational testing of the first phase of the abatement plant began in spring 2014 and the re-injection of the hydrogen sulfide started at the same time. The plant was extended in 2016 where the plant capacity was doubled. The abatement plant is based on development and pilot projects based on scientific research at the Hellisheidi GPP going back to 2007. In the abatement plant, hydrogen sulfide and part of the carbon dioxide are separated from the non-condensable geothermal gases (NCG), which consisting mainly of three gases: carbon dioxide (CO2), hydrogen sulfide (H2S) and hydrogen (H2). Other gases such as nitrogen (N2), methane (CH4) and argon (Ar) are also part of the NCG gases but in small fraction. Up to 98% of the hydrogen sulfide and about 50% of the carbon dioxide are dissolved in condensate and re-injected deep into the bedrock at the plant site where H2S and CO2 mineralise.


Carbon Capture Confirmed

CarbFix is an R&D project carried out by Orka náttúrunnar (ON) along with other partners. The project goal is to imitate the natural fixing process of carbon dioxide (CO2) already observed in basaltic rocks in Icelandic geothermal fields. Recent studies of the drilling cores from the bedrock at the injection area of the CarbFix project strongly suggests that the theories of scientists are valid. The carbon dioxide binds with the basaltic rocks and by using this method, this main greenhouse gas is stored as a mineral in the ground for the foreseeable future. Studies show that 85-90% of carbon dioxide is captured this way within a year of re-injection.

Sulfix is another R&D project where this project has played a key role in reducing H2S from the power plant and complying with strict environmental regulations surrounding NCG emissions in Iceland in close proximity of urban areas.


  • Lead design and commissioning.
  • Supervision and coordination of design.
  • Construction supervision and installation.
  • Process design (P&ID) and design of the absorption column.
  • Steel piping design and equipment layout.
1000-2000 m. 
Injection depth
Injection of H2S
Carbon capture within a year

Mannvit has in many ways been a pioneer in dealing with Non-condensable gases (NCG) in geothermal utilization. NCGs have been dealt with in the Hellisheidi geothermal power plant in a new type of gas injection plant associated with the R&D projects named SulFix and CarbFix. Mannvit has played a key role as the technical engineering consultant for the plant owner and operator ON. The co-generation of power and heating, that takes place in Nesjavellir and Hellisheidi geothermal CHP plants, where Mannvit was the lead mechanical designer is also unique in many ways.


CarbFix and SulFix video by ON