NCG Treatment Plant for a Geothermal Plant

Mannvit leads the design and commissioning of a 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 sulphide (H2S) and carbon dioxide (CO2) form other NCG gases. After the first construction phase, the plant capacity was up-to one third of the hydrogen sulphide from the power plant but after extension about 60%.

Project managers at ON have managed the project, whereas Mannvit has been in the lead of the design work and the commissioning of the H2S 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. 

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 sulphide 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 sulphide 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 sulphide (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 sulphide 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.


  • 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.