Article - 12/01/2015

NCG Treatment Plant at Hellisheidi GPP

Orka náttúrunnar (ON) has taken over the management and operation of an exhaust treatment plant at the Hellisheidi Geothermal Power Plant (GPP). The treatment plant treats non-condensable gases (NCG) in the power plant exhaust. The treatment plant separates hydrogen sulphide (H2S) and carbon dioxide (CO2) from the exhaust and re-injects the gases deep into the bedrock at the plant site. The facility is expected to treat up-to one third of the hydrogen sulphide (H2S) emissions from the plant.

 

Geoscientists at ON have managed the project, whereas Mannvit has lead the design and the commissioning of the exhaust treatment plant. Mannvit supervised and coordinated the design as well as the supervision of the construction and the installation. 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 in the exhaust was handled by Mannvit as well as the  the steel piping design and layout of equipment.

 

Operation of the NCG Treatment Plant

Operational testing of the exhaust treatment plant began in the spring of 2014 and the re-injection of the hydrogen sulphide was started at the same time. Alignment of the exhaust treatment plant to the geothermal plant’s operation that was started in the second part of 2014 is now completed. The exhaust treatment plant is based on development and pilot projects based on scientific research at the Hellisheidi GPP going back to 2007. In the treatment plant, hydrogen sulphide and some carbon dioxide are separated from the non-condensable geothermal gases consisting mainly of three gases: carbon dioxide (CO2), hydrogen sulphide (H2S) and hydrogen (H2). Up to 98% of the hydrogen sulphide treated and about 50% of the carbon dioxide are dissolved in condensate from the power plant and re-injected one to two thousand meters down into the lava bedrock. Calculations show that about 1,000 tonnes of hydrogen sulphide have been re-injected into the strata since the operational testing began. According to ON & Reykjavik Energy’s project plan, the exhaust treatment plant will be operated at full load for one year before reassessing the performance of this new method.

 

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.

 

Next Demonstration Project

According to ON, the company is in the process of evaluating the construction of a steam stack close to the power plant, which would operate parallel to the exhaust treatment plant and the gas re-injection. Research on the meteorological conditions in the vicinity of the power plant indicates that the steam stack can ensure a better dispersion of emissions and thereby reduce atmospheric concentration of hydrogen sulfide, so that they will not exceed the regulatory atmospheric limits. The steam stack, along with related equipment, will be located at drilling platform #7, in the area above the steam separation unit #2 at the Hellisheidi Geothermal Power Plant. Gas that is not treated in the exhaust treatment plant will be directed through the steam stack. Trial operations of the steam stack are expected to start in the spring of 2015.