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1876-6102 © 2017 The Authors. Published by Elsevier Ltd.Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.

The 15th International Symposium on District Heating and Cooling

Assessing the feasibility of using the heat demand-outdoor temperature function for a long-term district heat demand forecast

I. Andrića,b,c*, A. Pinaa, P. Ferrãoa, J. Fournierb., B. Lacarrièrec, O. Le Correc

aIN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, PortugalbVeolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France

cDépartement Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France

Abstract

District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heatsales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors.The results showed that when only weather change is considered, the margin of error could be acceptable for some applications(the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.

© 2017 The Authors. Published by Elsevier Ltd.Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.

Keywords: Heat demand; Forecast; Climate change

Energy Procedia 146 (2018) 135–145

1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved.Selection and peer-review under responsibility of the publication committee of the International Carbon Conference 2018.10.1016/j.egypro.2018.07.018

10.1016/j.egypro.2018.07.018 1876-6102

Copyright © 2018 Elsevier Ltd. All rights reserved.Selection and peer-review under responsibility of the publication committee of the International Carbon Conference 2018.

Available online at www.sciencedirect.com

ScienceDirect

Energy Procedia 00 (2018) 000–000 www.elsevier.com/locate/procedia

1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the publication committee of the International Carbon Conference 2018.

International Carbon Conference 2018, ICC 2018, 10–14 September 2018, Reykjavik, Iceland

Reducing emissions of carbon dioxide and hydrogen sulphide at Hellisheidi power plant in 2014-2017 and the role of CarbFix in

achieving the 2040 Iceland climate goals Bergur Sigfússona,*, Magnús Þór Arnarsonb, Sandra Ósk Snæbjörnsdóttira,

Marta Rós Karlsdóttirb, Edda Sif Aradóttira, Ingvi Gunnarssona aReykjavik Energy, Bæjarháls 9, 110 Reykjavík, Iceland

bON Power, Bæjarháls 9, 110 Reykjavík, Iceland

Abstract

The CarbFix gas injection method was developed to mitigate the gas emissions associated with geothermal utilization at Hellisheidi power plant. Pilot injections started in 2012 and the first industrial scale injection took place in 2014. The process was scaled up in 2016, and again in 2017. In 2017 about 10,000 tonnes of CO2 and 5,000 tonnes of H2S were injected back into the geothermal reservoir, corresponding to 34% and 68% of the annual emissions from the plant. The gases react with basaltic subsurface rocks to form stable minerals for safe, long-term storage of the injected gases. Copyright © 2018 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the publication committee of the International Carbon Conference 2018.

Keywords: CO2 capture; H2S capture; CCS; basaltic storage; mineralization; CarbFix2

1. Introduction

Geothermal energy is regarded as both clean and sustainable energy source. However, geothermal power plants emit some gases that have environmental impact; these are mostly carbon dioxide (CO2), which is the most abundant greenhouse gas and contributes to global warming, and hydrogen sulfide (H2S), which has a local effect due to its corrosive nature, odor, and toxicity in high concentrations. These gases are of magmatic origin. The amount of CO2

* Corresponding author. Tel.: +354 516 6100. E-mail address: [email protected]

Available online at www.sciencedirect.com

ScienceDirect

Energy Procedia 00 (2018) 000–000 www.elsevier.com/locate/procedia

1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the publication committee of the International Carbon Conference 2018.

International Carbon Conference 2018, ICC 2018, 10–14 September 2018, Reykjavik, Iceland

Reducing emissions of carbon dioxide and hydrogen sulphide at Hellisheidi power plant in 2014-2017 and the role of CarbFix in

achieving the 2040 Iceland climate goals Bergur Sigfússona,*, Magnús Þór Arnarsonb, Sandra Ósk Snæbjörnsdóttira,

Marta Rós Karlsdóttirb, Edda Sif Aradóttira, Ingvi Gunnarssona aReykjavik Energy, Bæjarháls 9, 110 Reykjavík, Iceland

bON Power, Bæjarháls 9, 110 Reykjavík, Iceland

Abstract

The CarbFix gas injection method was developed to mitigate the gas emissions associated with geothermal utilization at Hellisheidi power plant. Pilot injections started in 2012 and the first industrial scale injection took place in 2014. The process was scaled up in 2016, and again in 2017. In 2017 about 10,000 tonnes of CO2 and 5,000 tonnes of H2S were injected back into the geothermal reservoir, corresponding to 34% and 68% of the annual emissions from the plant. The gases react with basaltic subsurface rocks to form stable minerals for safe, long-term storage of the injected gases. Copyright © 2018 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the publication committee of the International Carbon Conference 2018.

Keywords: CO2 capture; H2S capture; CCS; basaltic storage; mineralization; CarbFix2

1. Introduction

Geothermal energy is regarded as both clean and sustainable energy source. However, geothermal power plants emit some gases that have environmental impact; these are mostly carbon dioxide (CO2), which is the most abundant greenhouse gas and contributes to global warming, and hydrogen sulfide (H2S), which has a local effect due to its corrosive nature, odor, and toxicity in high concentrations. These gases are of magmatic origin. The amount of CO2

* Corresponding author. Tel.: +354 516 6100. E-mail address: [email protected]

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136 Bergur Sigfússon et al. / Energy Procedia 146 (2018) 135–1452 Author name / Energy Procedia 00 (2018) 000–000

emitted during geothermal utilization is estimated to be up to 5% of CO2 emissions from a fossil-fuel-burning power plant of a comparable size [1].

The Hellisheidi co-generation power plant was commissioned in 2006. The plant is located in SW-Iceland, about 30 km east of Reykjavík. It has 303 MWe of electric production capacity, and 133 MWth of thermal capacity serving the local district heating system. During its production history, about 417,000 tonnes of CO2 and about 114,000 tonnes of H2S have been produced from the geothermal reservoir. Since 2007, Reykjavík Energy has in cooperation with the University of Iceland, CNRS in Toulouse, France, Columbia University in New York, USA, and several other universities and institutes, developed methods to mitigate these CO2 and H2S emissions as a part of the CarbFix and CarbFix2 projects.

The CarbFix project is an EU funded combined industrial and academic research project centered on the Hellisheidi power plant. The project developed methods and technology for the permanent mineral storage of CO2 and CO2-H2S gas mixtures in basalts. The injection of CO2 into young basaltic formations provides significant advantages, including great storage potential and permanent storage, by combining the injected CO2 with metals contained in the basalts to form stable carbonate minerals. The same method has been utilized for the mineral storage of H2S in the Hellisheidi field. In 2012, two pilot-scale injections were carried out in Hellisheidi where 175 tons of CO2 and 73 tons of a gas mixture consisting of 75% CO2 and 25% H2S from the Hellisheidi power plant were injected, respectively [2]. Extensive geochemical monitoring was carried out prior to, during, and after both injections, which revealed the rapid mineralization of the injected gases: Over 95% of the injected CO2 was mineralized in less than two years [3], and the bulk of the injected H2S was mineralized within four months from injection [4].

Following the success of the two pilot scale injections, the CarbFix method was scaled up as part of the CarbFix2 project starting in June 2014, and is on-going as an integral part of the operations at the Hellisheidi power plant. The gases are captured at the power plant, dissolved in condensate, and injected at about 700 m depth at the Húsmúli injection site in the northern part of the Hellisheidi field, where they react with the basaltic bedrock to form stable minerals for safe and secure storage [5, 6]. Here we report on the gas capture method that has been deployed since the scale-up, the amount of gases that have been injected and mineralized, the storage potential estimate of the Hellisheidi field, and how the CarbFix method could contribute to achieving the 2040 climate goals.

2. Gas emissions and gas capture

2.1. Gas flow from the geothermal reservoir

The Hellisheidi power plant is fed by about 35 production wells discharging fluids having a wide flow rate and composition range. The two-phase discharged fluids are separated, and the steam with most of the Non-Condensable Gases (NCG, approximately 0.5 % of the steam mass) is then fed into the seven turbines of the power plant. Steam flow into each turbine is measured continuously by an orifice plate meter, and daily averages are calculated and stored in the power plant database. The chemical composition of the steam is measured every three months. The daily gas flow is calculated by multiplying the annual mean gas concentration with daily steam mass flow of each turbine. In addition to these measurements, venting of steam from the steam collection system is estimated and discharge from wells during testing and maintenance is monitored (~1% of total gas flow from the reservoir). Fig. 1 shows the daily mass flow of CO2 and H2S entering the turbines at the plant. The mass flow has decreased from approximately 120 tonnes/day CO2 and 29 tonnes/day H2S in early 2014 to 100 tonnes/day CO2 and 25 tonnes/day H2S at the end of 2017. The lowered mass flow has been attributed to degassing of the geothermal reservoir during production, and is also a result of different wells feeding the power plant over time.

2.2. Gas capture in the power plant

Gas is captured through two main processes at Hellisheidi; dissolved in condensate at liquid ring vacuum pumps, and through the CarbFix capture process. The NCGs are extracted from the condensers at the plant with the aid of liquid ring vacuum pumps. Condensate is fed into the pumps by centrifugal acceleration to form a series of seals between impeller vanes, which form compression chambers. The condensate reacts with the NCGs and new condensate is continuously fed to the pumps. The volume flow of condensate, now termed seal water to distinguish it

Bergur Sigfússon et al. / Energy Procedia 146 (2018) 135–145 137 Author name / Energy Procedia 00 (2018) 000–000 3

from other condensate, is measured using a Siemens, type Sitrans FUS Sonokit 1 - Track. The seal water, now with elevated dissolved CO2 and H2S levels (mean concentration of 890 and 565 mg/l for CO2 and H2S) is fed in a closed circuit towards the re-injection wells of the power plant. The chemical composition of the seal water is measured every three months. The daily gas flow is calculated by multiplying the annual mean gas concentration with daily condensate volume flow. The annual flow of gaseous CO2 and H2S from vacuum pumps that is either vented to cooling towers or captured by the CarbFix process (discussed below) is approximately 33,000 and 8,000 tonnes/year, respectively.

Fig. 1. CO2 (green) and H2S (red) mass flow from the Hellisheidi geothermal reservoir for the years 2014 - 2017.

The majority of the gas from the turbines is diverted to a specific capture and re-injection process applying the CarbFix technology. A detailed description of the CarbFix capture and re-injection process is provided in Gunnarsson et al. [5]. Briefly, NCG streams from condensers are compressed into a 12 m absorption column with 6 meter packing under controlled pressure, temperature and water and gas flow rates where CO2 and H2S are dissolved into condensate water from the power plant. Other les soluble gaseous species, most notably H2, Ar and N2 are vented from the column. A Siemens, type Sitrans FUS Sonokit 1 - Track flow meter, Endress and Hauser, type Cerabar M pressure gauge, and a Endress and Hauser, type Omnigrad temperature probe are used to measure, in 10 minute intervals, which are then stored in the power plant database. The concentration of CO2 and H2S in the gas-charged condensate leaving the absorption column is measured every three months. The capture plant can be operated with zero, one or two parallel gas compressors resulting in three different chemistries of the fluid. The operational hours of the compressors are monitored. Fig. 2 shows the condensate flow from the capture plant from 2014 to 2017. No gas was captured during commission, and in summer 2014 on compressor started operation. In 2016, an additional compressor was installed and the flow rate of condensate through the absorption column increased. The hiatus in plant operation in September 2017 was due to work being done near the capture plant requiring complete shutoff of the capture plant. The daily gas injection was thus calculated by multiplying the weighed mean concentration of the day with the total flow of each day.

Fig. 3 shows the mean daily concentration of gas-charged condensate resulting from different daily operation times of the compressors for the years 2014-2017. A sharp increase in concentration occurred in July 2016 when the capacity of the capture plant was increased by the addition of the second compressor.

138 Bergur Sigfússon et al. / Energy Procedia 146 (2018) 135–145

4 Author name / Energy Procedia 00 (2018) 000–000

Fig. 2. Condensate flow from the CarbFix capture plant for the years 2014 - 2017. Blue lines indicate periods when no gas was being captured, green lines indicate periods when one compressor was in operation, and red lines indicate periods when two compressors were operated.

Fig. 3. Mean daily concentration of CO2 (green) and H2S (red) in the gas-charged condensate exiting the CarbFix capture plant in 2014 – 2017.

2.3. Re-injected gas from the Hellisheidi power plant

All gas that is captured in the liquid ring vacuum pumps extracting NCGs from the power plant condensers is mixed dissolved in the vacuum pump seal water into the main piping network feeding the re-injection zones. In addition, two of the 13 re-injection wells connected to the power plant have been retrofitted to receive the gas-charged condensate from the CarbFix capture plant; wells HN-14 and HN-16, which are cased with carbon steel to 690 m and 660 m respectively, were retrofitted with stainless steel pipe to 750 m depth. In both wells, separator water flows on the outside of the stainless steel pipe. Therefore, the gas-charged condensate, which is acidic and corrosive, has no contact


with the carbon steel casing [5]. The flow rate is monitored both at the capture plant and at the well-head, as well as the flow rate of separator water into the two re-injection wells. Well HN-16 has received most of the gas-charged water. The exception is the period between 15.07.2015 to 15.03.2016 when the gas-charged water was injected into well HN-14. Fig. 4 shows the water flow into wells HN-14 and HN-16 and Fig. 5 shows the gas flux into the same wells over this time period.

Fig. 4. Flow rate of separator water (blue) and condensate water (red) of variable gas concentrations into wells HN-14 (a) and HN-16 (b)

during 2014 - 2017.

a)

b)


Fig. 5. Dissolved flux of CO2 (green) and H2S (red) into wells HN-14 (a) and HN-16 (b) during 2014 – 2017.

2.4. Emissions from the Hellisheidi power plant

The daily emissions from the Hellisheidi power plant are calculated by subtracting the captured and re-injected gas (section 2.2) from the gas flux measured into the geothermal turbines (section 2.1). Fig. 6 shows that the daily CO2

a)

b)


emissions reduced from 120 tonnes/day to 60 tonnes/day and H2S daily emissions reduced from 29 tonnes/day in early 2014 to 5 tonnes/day in end of year 2017.

Fig. 6. Daily emissions of CO2 (green) and H2S (red) from the Hellisheidi power plant during the years 2014 – 2017.

Continuous efforts have been made to reduce the NCG emissions from the Hellisheidi power plant. These efforts,

in addition to decreased gas discharge from the geothermal reservoir have steadily decreased the share of emitted gases to the atmosphere. Fig. 7 shows the daily contribution of the CarbFix capture plant and the vacuum pump seal water towards injecting NCGs into the reservoir, back to where it originally came from. The remaining portion of the gas emitted to the atmosphere. The shift in seal water injection in 2015 is due to connection of seal water pipes into the power plant re-injection system instead of releasing the water into shallow boreholes. The inlet in Fig. 7 shows these values aggregated on annual basis. The injected portion of gases increased from 0 to 34% for the CO2, and 0 to 68% for the H2S from 2014 to 2017 (see Table 1). The system is still being optimized and it is anticipated that unscheduled maintenance stops will decrease significantly during the year 2018, resulting in higher proportions of CO2 and H2S injected.

Table 1. The amount of CO2 and H2S (tonnes/yr) produced out if the Hellisheidi field, emitted and injected in 2014-2017. CO2

(tonnes/yr) Flow through power plant

Venting of steam

Well testing

Total flow

Dissolved in seal water

Injected Emitted % injected

% emitted

2013 43300 400 1200 44900 Not measured 0 44900 0 100 2014 42400 400 200 43000 1700 2400 38900 10 90 2015 38300 400 200 38900 1900 3900 33100 15 85 2016 34200 400 0 34600 1800 6700 26100 25 75 2017 35200 400 0 35600 1900 10200 23500 34 66 H2S

(tonnes/yr)

2013 11900 100 400 12400 Not measured 0 12400 0 100 2014 10800 100 0 10900 1100 1300 8500 22 78 2015 9600 100 0 9700 1100 2200 6400 34 66 2016 8300 100 0 8400 1100 3400 3900 54 46 2017 8800 100 0 8900 1100 4900 2900 68 32


Fig. 7. Fate of CO2 (bottom) and H2S (top) from the Hellisheidi power plant in 2014-2017. The red and dark green represent CO2 and H2S re-injected through the CarbFix process. The orange and light green represent CO2 and H2S re-injection with seal water from vacuum pumps. Blue area represents emissions to the atmosphere.

3. Storage potential estimates of the CarbFix2 injection site

In nature, mineralization of CO2 in basalts occurs in well documented settings, including the upper oceanic crust, surface weathering, and geothermal alteration. A significant amount of CO2 is already naturally stored within the active geothermal areas in Iceland, which receive CO2 fluxes from cooling magma intrusions. The CarbFix and CarbFix2 projects imitate and accelerate this natural storage process. The gas-charged fluid is injected into the reservoir at the Húsmúli injection site in the northern part of the Hellisheidi field [6], where it reacts with the basaltic reservoir rocks to form stable minerals for safe and long-term storage of the injected gases.


Two key factors are essential for the success of this mineral storage method: 1) Sufficient permeability and/or active porosity, providing flow paths for efficient injection of the gas-charged

fluid, and mineral surfaces for geochemical reactions to occur, and 2) Conditions favorable for the efficient formation of C and S-bearing minerals. Studies on mineral storage of CO2 and H2S are still at an early stage. There have however been few attempts made

to evaluate how much CO2 can be stored within basaltic rocks. Wiese et al. [7] measured to CO2 bound in carbonate minerals in drill cuttings from geothermal areas in Iceland and estimated that the Hellisheidi geothermal reservoir contains about 1,600 Mt of naturally bound CO2. The overall pattern of distribution with depth shows a large range, from 0-300 kgCO2/m3 (Fig. 8), but demonstrates the potential for basalts to store large amounts of carbon. The most feasible formations for mineral storage of CO2 and H2S are fresh and reactive rocks, where faults and fractures are still open and pore space has not been filled with secondary minerals.

Fig. 8. a) Aerial photo showing the location of the plant, the injection site, and the cross-section shown in b) Cross section from E to W, modified from Wiese et al. [7], showing the spatial distribution of CO2 bound in calcite within the Hellisheidi field.

The study concluded that about 30-40 GtCO2 are already naturally stored in carbonate minerals within the bedrock of active geothermal areas in Iceland. This amount equals the global annual anthropogenic emissions of CO2 in 2017 [8], and underscores the large storage potential for CO2 in fresh and unaltered basalts. This agrees with other storage potential estimates using the petro-physical properties of basalts [e.g. 9-12], natural analogues [e.g. 7, 13], and reactive transport modelling [e.g. 14]. These estimates, when applied to the Hellisheidi field (80 km2) reveal a storage potential ranging from 50-5,200 MtCO2 for Hellisheidi. The storage potential of H2S has been less studied, but using estimates from Přikryl et al. [15], the potential is calculated in the range of 2,6 MtH2S.

The different scenarios for these storage estimate calculations are listed in Table 2. Even though the results reveal a large range of this theoretical storage potential based on the different calculations, which also underlines the uncertainties of these estimates, they all point towards this large storage potential, which is partly confirmed by direct measurements of the amount of CO2 bound in the Hellisheidi reservoir rocks [7]. The results indicate that the storage potential of the reservoir is not a limiting factor for the on-going operations; it would take roughly 400 years to reach the lowest estimated storage potential if all CO2 produced out of the geothermal reservoir was re-injected, using the total flow of CO2 in 2017 (Table 1).

The consequences of altered bedrock, due to hydrothermal alteration, should be considered, since this could potentially affect the storage capacity due to limited pore space and less reactive rocks. Pre-existing carbonates and sulfides in the system should also be accounted for potential large-scale injection of CO2 and H2S. On the other hand, injection of CO2 and H2S into the highly altered rocks in Hellisheidi has been ongoing since 2014 without any major complications. More extensive studies, including reactive transport modelling, water-gas-rock interaction experiments

b)


on hydrothermally altered basalts, and extensive characterization of the petro-physical properties of the reservoir rocks are needed to better constrain these storage potential estimates.

Table 2. Storage potential estimates for CO2 and H2S in basaltic rocks applied to the Hellisheidi field (80 km2). # Source Short description Storage potential at Hellisheidi (MtCO2) 1 Gislason et al., 2010 [9]

0.5 km thick storage formation – 10% porosity 10% of which eventually will be filled with calcite

477

2 Anthonssen et al., 2013 [10] 0.5 km thick storage formation – 5% porosity, 10% of which eventually will be filled with calcite

239

3 Goldberg et al., 2010 [11] 0.1 km thick storage formation (one-sixth of the uppermost 600 m of the basin), 10% porosity, 100% of which eventually will be filled with calcite

955

4 McGrail et al., 2006 [12] Interflow thickness of 10 m, average porosity of 15% and 10 available interflow zones at the uppermost 1000 m; 100 m thick storage formation.

48

5 Snæbjörnsdóttir et al., 2014 [13] Minimum average at Reykjanes geothermal area; 18.8 kg CO2/m3. Applied to 1000 m thick segment. Maximum average at Krafla geothermal area; 48.7 kg CO2/m3. Applied to 1000 m thick segment.

1,504-3,900

6 Aradóttir et al., 2012 [14] Reactive transport modelling of pilot scale injection (1,200 tonnes CO2) at CarbFix1 site in Hellisheidi; 5,000 tonnes/km2 Reaction path modelling of full scale injection (400,000 tonnes CO2) at CarbFix1 site in Hellisheidi; 35,000 tonnes/km2)

400-2,800

7 Wiese et al., 2008 [7] Natural sequestration of CO2; 65 Mt/km2 5,200 8 Přikryl et al., 2018 [15] Reactive transport modelling of a system with

10% porosity, flow of 8.9 m/day and H2S concentration of the injection fluid entering the reservoir of ∼30 mmol/kg. The modeled porous medium with area of 0.001 km2 had the potential of sequestrating 32 t of H2S. This

2.6 MtH2S

4. Conclusions and final remarks

Injection of CO2 and H2S from the Hellisheidi Plant has been on-going since summer 2014, and the amount of injected gases has been gradually increasing each year of the operation. In 2017 about 10,000 tonnes of CO2 and about 5,000 tonnes of H2S were dissolved in condensate and injected into well HN-16 at the Húsmúli injection site in the northern part of the Hellisheidi field.

Few attempts have been made to estimate the storage potential of CO2 in basalts, which all reveal a large potential. Preliminary estimation on the theoretical storage capacity has been done, underscoring the large potential of basaltic rocks; the Hellisheidi reservoir has been estimated to be up 5.8 GtCO2 and up to 2.6 GtH2S. The total emission of CO2 in Iceland in 2016 accounted for 4.7 MtCO2 without land use, land use change, and forestry (LULUCF) [16] or less than 1% of the estimated storage potential of CO2 within the Hellisheidi reservoir. The total emissions of H2S in connection with the utilization of geothermal energy in Iceland was a total of about 19,000 tonnes H2S in 2016, which is orders of magnitude less than the estimated storage potential.

Iceland has committed to mitigate climate change under both the Kyoto Protocol and the Paris Agreement. In 2016, emissions from Hellisheidi would have accounted for 1.3% of Iceland’s GHG emissions without the CarbFix reinjection (emissions without LULUCF and those covered by the European emission trading scheme (EU ETS)) [16]. Current reinjection of CO2 with the CarbFix method reduced the countries emissions by 0.4% points, and has the future potential of reducing it by 1.3% in total should there be full reinjection of all CO2 produced from the geothermal reservoir. The CarbFix method could easily be applied elsewhere in Iceland, where emissions from point sources such


as aluminum smelters which account for about 30% of the CO2 emissions, could be injected and mineralized for safe and long-term storage of the otherwise emitted CO2.

Acknowledgements

We acknowledge funding from the European Commission through the projects CarbFix (EC coordinated action 283148), CarbFix2 (European Union’s Horizon 2020 research and innovation program under grant number 764760), and S4CE (European Union’s Horizon 2020 research and innovation program under grant number 764810), Nordic fund 11029-NORDICCS; and the Icelandic GEORG Geothermal Research fund (09-02-001). We thank our friends in the CarbFix group and our colleagues at Reykjavik Energy and ON Power for their contribution to this work.

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