1. H2S Abatement and pH Modification Techniques for Scaling Inhibition at Hellisheiði Geothermal Plant
Michael L. Keller

2. H2S Health Effects Regulation 514/2010: 50 μg/m3 (.036 ppm)
Concentration (ppm)
Symptoms/Effects
Typical background concentrations
Odor threshold. Odor becomes more offensive at 3-5 ppm. Above 30 ppm, odor described as sweet or sickeningly sweet.
2-5
Prolonged exposure may cause nausea, tearing of the eyes, headaches or loss of sleep. Bronchial constriction in some asthma patients. 20
Possible fatigue, loss of appetite, headache, irritability, poor memory, dizziness.
50-100
Slight conjunctivitis ("gas eye") and respiratory tract irritation after 1 hour. May cause digestive upset and loss of appetite.
100
Coughing, eye irritation, loss of smell after 2-15 minutes (olfactory fatigue). Altered breathing, drowsiness after minutes. Throat irritation after 1 hour. Gradual increase in severity of symptoms over several hours. Death may occur after 48 hours.
Loss of smell (olfactory fatigue or paralysis).
Marked conjunctivitis and respiratory tract irritation after 1 hour. Pulmonary edema may occur from prolonged exposure.
Staggering, collapse in 5 minutes. Serious damage to the eyes in 30 minutes. Death after minutes.
Rapid unconsciousness, "knockdown" or immediate collapse within 1 to 2 breaths, breathing stops, death within minutes.
Nearly instant death
Regulation 514/2010: 50 μg/m3 (.036 ppm)

3. H2S Emissions

4. Silica Scaling 1) Reduction of Fluid Flow: Production wells,
Flash Vessels,
Brine Lines,
Heat Exchangers,
Re-injection Systems
2) Reduced Heat Transfer
in heat exchangers
3) Loss of Injectivity

5. pH Modification HCl or H2SO4 used to prevent silica scaling
First investigated and developed in the 1980s to mitigate silica scaling (Darrell Gallup)
Utilized at plants in the US and New Zealand
(pH mod experiments have been conducted in Iceland)
Sigfusson and Gunnarsson - Scaling prevention experiments
in the Hellisheiði power plant, Iceland (2011).

6. Hellisheiði NCG Emissions
Two processes are capable of converting H2S into
acidic compounds suitable for pH modification

7. Incineration Unit

8. Wet Sulfuric Acid Process (WSA)
Developed by Haldor Topsøe in the late 1980s
Utilized in over 100 plants around the world
+0.52 MW per 45 MW turbine or +3.5 MW with 100% of H2S stream

9. Wet Sulfuric Acid Process (WSA)
+ 9,988 tonnes H2SO4 Per 45 MW turbine
or 67,250 tonnes for entire H2S stream

10. Purified CO2 Stream 58,580 tonnes/year from Hellisheiði Possible Uses:
Methane production
Methanol production
Food Grade CO2
Geo Greenhouses
or Re-Injected with Carbfix
* Production of a purified CO2 stream requires the stoichiometric
combustion of oxygen to prevent a combined N2 and CO2 stream.

11. Re-Injection Well Stimulation
Geothermal boreholes are multi-million dollar assets
pH modification can greatly reduce the loss of injectivity in re-injection wells.
For example: the SOCO field lost injectivity 8x
slower after utilizing a pH modification system.

12. Value of:
extra electricity produced,
avoided scaling rehabilitation costs,
reduced plant downtime,
extended lifetime of re-injection wells,
sulfuric acid produced (WSA),
& purified CO2 stream. VS
Cost of:
capital &
operational costs

13. Programming and Analysis
H2S incinerator to be designed using EES.
WSA process to be designed using ChemCad.

14. H2S Abatement and pH Modification Techniques for Scaling Inhibition at Hellisheiði Geothermal Plant
Michael L. Keller
Thank you