Experimental techniques used for corrosion testing in dense phase CO2 with flue gas impurities

Arne Dugstad, Malgorzata Halseid and Bjrn Morland

Institute for Energy Technology P.O. Box 40, NO-2027 Kjeller

Norway

ABSTRACT There are no recognized standards for corrosion testing in dense phase CO2 with impurities. The main experimental challenge is impurity control. The concentration of water and other impurities (SOx, NOx, O2, H2S, CO, amines, glycols) is very small and the impurities are therefore consumed fast if they take part in the corrosion process or other bulk phase reactions. In order to predict corrosion and solid formation in CO2 transport it is important to understand and quantify the reactions taking place. It is especially important if a network system is considered in which CO2 with different specifications are mingled. The paper discusses experimental techniques and the functionality and capability of a new dynamic test system that allows continuous impurity renewal and concentration control. Key words: CCS, transport of CO2, dense phase CO2, impurities

INTRODUCTION

Dense phase CO2 (liquid and supercritical CO2) has been transported for many years,1,2 but there is limited knowledge about corrosion and bulk phase reactions when the CO2 contains flue gas impurities like SOx, NOx, O2 and CO in addition to H2O and H2S. A number of CO2 specifications and recommendations have been published, 2,3,4 but there are presently no consensuses on the operation window for safe transport. The main reason for the uncertainty is lack of field experience and laboratory data. Based on field experiences5-7 and laboratory experiments9,12-16 it is reasonable to conclude that the corrosion rate is insignificant when the water content is below the solubility limit for the pure CO2-H2O system. However, interactions between impurities might lead to the formation of corrosive phases and solids although the water content is far below the solubility limit in pure CO2.8-11,13,16 -29 In the presence

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Paper No.

4383

2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

of H2O, NO2 or/and SO2 different acids can precipitate, and elemental sulfur can form if H2S and O2 are present. Corrosion and reduced injectivity might be issues if elemental sulfur is deposited on the pipe wall or transported to the reservoir. Highly corrosive environment and demanding experimental conditions (high pressure and continuous dosing and monitoring of impurities) will limit the type and availability of equipment that can be used for laboratory testing. Test systems with means for continuous dosage of impurities under high pressure are required as the concentrations of impurities are very low and can be quickly consumed.34,35 The consumption rate of the impurities needs to be monitored and that requires state of the art analytical instrumentation that can measure small quantities of impurities in the presence of reactive impurities (H2S, SOx and NOx) that limit the type of instruments that can be used. Lack of impurity control in published experimental studies can explain large differences in the reported corrosion rates even for simple systems with dense phase CO2 and small amount of water where no corrosion is expected.19,36 The present paper discusses experimental challenges, describes two test systems with impurity control and gives some examples of results obtained in these systems.

REACTIONS BETWEEN IMPURITIES AND THE NEED FOR IMPURITY CONTROL Acid formation Experiments have shown that precipitation of acids can occur when the dense phase CO2 contains small amounts of H2O, O2 and SO2 or NO2. The actual reaction route has not been determined. When both NO2 and SO2 are present, the lead chamber reaction might occur where NO2 catalyzes the oxidation of SO2 to form sulfuric acid.10

NO2 + SO2 + H2O NO + H2SO4 (fast) (1)

2 NO + O2 2 NO2 (2) 2 NO2 + H2O HNO2 + HNO3 (slower) (3)

Aqueous phases with low pH will cause corrosion of the steel and if the acidic phase is transported to the reservoir it might cause dissolution of minerals and precipitation of sulfates which could influence storage capacity and injectivity. The solubility of H2SO4 in CO2 is very low (high boiling point) due to the hydrogen bonding. Sulfuric acid is hygroscopic and will further attract water. It has very slow diffusivity in dense phase CO231 and corrosion caused by H2SO4 is rather localized.25,32 Nitric acid on the other hand diffuses quickly through dense phase CO231 and can cause general corrosion.27,32 Elemental sulfur formation Corrosion and reduced injectivity might be issues if elemental sulfur is deposited on the pipe wall or transported to the reservoir. It is not reported any problems in existing CO2 transport pipelines where small amounts of H2S is present,1 but in-house experiments show that elemental sulfur can form when impurities such as H2S, SO2, NO2, and O2 are present. Possible sulfur formation reactions are shown below:

2 H2S+ 3 O2 2 SO2 + 2 H2O (4)

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2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

2 H2S + SO2 3/x Sx + 2 H2O (Claus process) (5) 2 H2S + O2 2/x Sx + 2 H2O (6)

Formation of elemental sulfur can also involve high oxidation state of metal33:

8 H2S + 16 Mn+ S8 + 16 H+ + 16 M(n1)+ (7) The picture in Figure 1 shows the autoclave wall after an experiment in dense phase CO2 with less than 0.07 mol % total impurities (NO2, SO2, H2O, H2S, and O2). Energy dispersive X-ray spectroscopy (EDS) analysis confirmed formation of elemental sulfur. Sulfur formation is somewhat unpredictable and the triggering mechanism is not clear.

Figure 1: Autoclave wall covered with elemental sulfur. Experiment performed in rocking autoclave with dense phase CO2 (25 C, 10 MPa) containing 99.93 mol% CO2 and 0.07%

impurities (NO2, SO2, H2O, H2S, and O2)

TEST EQUIPMENT WITH IMPURITY CONTROL Rocking autoclaves with continuous dosing/analyzing of impurities An outline of a rocking autoclave where the impurity concentrations can be measured and adjusted during the exposure is shown in Figure 2 and a photo of the test system is seen in Figure 3. Long (1-2 m) and slim (ID 20-30 mm) 50 MPa autoclaves are connected to an impurity feeding and analyzer system. Cylindrical test specimens are mounted on small cylindrical racks (Figure 3) that slide from one end to the other when the autoclave rotates. This gives good mixing and disturbed flow around the test specimen. The rack geometry and weight determine the maximum flow velocity. The shear stress experienced by the steel surface varies with the rotation speed and whether the flow is turbulent or laminar. The shear stress range for the long autoclaves is usually 0-10 Pa under turbulent conditions. The benefit of the rotating autoclave compared to fixed autoclaves and loops are: easy and relatively cheap to operate, simple geometry, few dead ends where impurities that form a water rich phase can be trapped.

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2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

Three separate feeding lines from three independent impurity dosing units can be connected to one end of the autoclave and an analyzing unit to the opposite end. The system can be used both for continuous and batch-wise injection.

Figure 2: Rocking autoclave with impurity feeding lines and venting lines for CO2 composition analyses

Figure 3: 1 m long autoclaves rotated in a thermal cabinet. The test specimen is mounted in a

specimen rack that slides from one end to the other when the autoclave rotates

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2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

It is important to avoid pressure fluctuations in the system. This can give uneven dosing from the three feeding lines and lead to undesired partitioning of impurities between liquid and gaseous CO213,30 and formation of corrosive phases. Many combinations of impurities cannot be premixed as the impurities react with each other. Therefore the test system needs several reservoir autoclaves from which impurities in diluted form (diluted with CO2) can be injected in the rocking autoclave: One main line that can feed the rocking autoclave continuously with CO2 containing the target

concentration of water. The water concentration is controlled with a cryo-system. Two or more lines (depending on number of impurities) made of accurate back pressure pumps and

piston autoclaves containing premixed CO2 with various impurities. When the rocking autoclave is fed continuously with CO2 and impurities the excess CO2 must also be vented/drained continuously. Comparing the composition in the vented CO2 and the feed makes it possible to: identify reactions that consume impurities (in the absence of corrosion specimens) measure the impurity concentrations at which separate corrosive aqueous phases are formed measure reaction rate of impurities by varying the impurity feed rate measure corrosion rates and identify corrosion mechanisms (when comparing H2 concentration) Phase separation must be avoided in order to obtain representative samples and correct measurements of impurity concentrations. The sampling line and the pressure reduction valves are therefore heated in order to avoid water drop out on cold spots. There is no analyzing system that can measure all actual impurities, and four separate analyzers are used. These are: Tunable Diode Laser System (TDLS) for water measurements Non-dispersive, infrared, ultraviolet, visible (NDIR/UV/VIS) photometer for NOx and SOx analysis Gas chromatograph (GC) for H2S and O2 Zirconium oxide sensor for O2 analysis when H2S, SOx and NOx are not present

Figure 4 : Dosing of SO2 into the rocking autoclave, 25 C and 10 MPa

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2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

Figure 4 shows how the concentration of H2O and SO2 in the vented gas changed during continuous injection of SO2 into the autoclave that contained CO2 with 420 ppmv H2O before SO2 injection started. The measured concentration of SO2 and H2O matches the theoretical dilution lines very well until the pressure varies slightly (< 0.2 MPa) after about 30 hours. The good match indicates that no reaction took place between the impurities in the present experiment. Dense Phase Impurity Loop with continuous dosing/analyzing of impurities The described rocking autoclave is simple to operate, but a loop system with bypass is better suited for some types of studies. With a flow loop it is possible to study the effect of shear stress systematically, reaction kinetics can be studied by shutting test sections in and out and a flow loop gives more flexibility when it comes to test sections and specimen geometries. A dedicated Dense Phase Impurity Loop (DPI-loop) has been constructed recently. An outline and a picture of the loop are shown in Figure 5. The test system has three main modules: Module 1: A 3 liter reaction loop where CO2 and impurities are circulated. The main components of

the loop are the circulation pump, coriolis flow meter, sampling/venting port and test section. All components are made in alloy N10276. The maximum operating pressure is 55 MPa and the temperature range 4-50 C. The inner diameter of the piping is 12 mm. The diameter in the test section can be varied from 8-30 mm giving an expected flow velocity of up to 6 m/s. The loop volume is kept small in order to rapidly record changes in the CO2 composition when impurity reactions take place.

Module 2: System for accurate feeding of CO2 and impurities into the loop. The feeding system is the same as described for the rocking autoclave.

Module 3: The analyzing system is the same as described for the rocking autoclave. The DPI-loop will not be used for corrosion testing only, but also for solid formation studies, bulk phase reactions and testing of soft materials and coatings.

Figure 5: Picture and outline of the Dense Phase Impurity Loop

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2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

EXPERIMENT PERFORMED IN THE ROCKING AUTOCLAVE

The rocking autoclave has been used to test the CO2 specification shown in Table 1. A steel specimen was mounted on the torpedo seen in Figure 3 and exposed at 25 C and 10 MPa for 10 days. The autoclave was rotated 180 degrees 3 times per minute. The autoclave was filled with pure CO2 before the impurities were added gradually through the feeding lines. The impurity concentrations in the vented CO2 that were routed to the analyzer were much lower (see last row in Table 1) than in the feed showing that the impurities reacted and formed separate phases. No NO was fed to the autoclave, but significant amounts were measured in the vented CO2.

Table 1 The concentrations of impurities in CO2

H2O ppmv

H2S ppmv

NO2 ppmv

NO ppmv

SO2 ppmv

O2 ppmv

Feed 122 130 96 0 69 275 Vented CO2

Figure 6: Photography and Scanning Electron Microscope (SEM) image of the corrosion film

deposited on the carbon steel sample. EDS analysis indicated presence of S, O and Fe on the specimen surface

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2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

Figure 7: Picture of elemental sulfur formed in the experiment. Indication paper show very low

pH of formed aqueous phase

CONCLUSIONS

The results confirm that reactions between impurities can occur at ppm level (< 100 ppmv) giving elemental sulfur or acidic aqueous phases that can cause corrosion. Impurity control is a challenge in experiments with dense phase CO2. When the impurities react giving corrosion, solid corrosion products and other type of solids (sulfur) the impurities are consumed and must be replenished. Therefore laboratory tests should be performed at conditions resembling real CO2 transport conditions e.g. in a loop system with continuous flow of CO2 with impurities. Precise high pressure dosing systems and analytical instrumentation are needed in order to dose and control impurity concentrations on the ppm level.

ACKNOWLEDGEMENTS The new loop is built within the Kjeller Dense Phase CO2 JIP and the authors would like to acknowledge CLIMIT, Gassco, Shell, Total, Statoil, and Institute for Energy Technology for their financial and technical support. The authors would also like to acknowledge Gassco for supporting the experiments that were discussed in the paper.

REFERENCES

1 A. Oosterkamp J. Ramsen State-of-the-Art Overview of CO2 Pipeline Transport with relevance to

offshore pipelines Open Polytec report: POL-O-2007-138-A 2 IPCC IPCC Special Report on Carbon Dioxide Capture and Storage. Prepared by Working

Group III of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, (2005) p. 442

3 E. De Visser, C Hendriks, M Barrio, MJ Mlnvik, G de Koeijer, S. Liljemark, YL Gallo, Dynamis CO2 quality recommendations, Int. J. Greenhouse Gas Control 2 (2008) 478

9

2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

4 IEAGHG Int. Oxy-Combustion Network, Yokohama, Japan, 5-6 March, 2008 5 T.E. Gill, Canyon Reef Carriers, Inc. CO2 Pipeline: Description and 12 Years of Operation,

ASME Energy-Source Technol. Conf, Pipeline Eng. Symp., p. 59, 1985. 6 J.M. West, Design and Operation of a Supercritical CO2 Pipeline-Compression System Sacroc

Unit, Scurry County, Texas, SPE Paper no. 4804, 1974. 7 L.E. Newton, SACROC CO2 Project Corrosion Problems and Solutions, CORROSION/84,

Paper no. 67, NACE International, 1984. 8 Y.-S. Choi, S. Nei, Effect of impurities on the corrosion behavior of carbon steel in supercritical

CO2 water environments, CORROSION/2010, Paper No. 10196, NACE International, Houston, 2010

9 A. Dugstad, B. Morland, S. Clausen, Transport of dense phase CO2 in C-steel pipelines- when is corrosion an issue, CORROSION/2011, Paper No. 11070, NACE International, Houston, 2012

10 B. Paschke, A. Kather, Corrosion of pipeline and compressor materials due to impurities in separated CO2 from fossil-fuelled power plants, Energy Procedia 23 (2012) 207

11 I.S. Cole, P. Corrigan, S. Sim, N. Birbilis, Corrosion of pipelines used for CO2 transport in CCS : Is it a real problem?, Int. J. Greenhouse Gas Control, 5 (2011) 749

12 W.A. Propp, T.E. Carleson, C.M. Wai, P.R. Taylor, K.W. Daehling, S. Huang, M. Abdel-Latif, Corrosion in Supercritical Fluids, US Department of Energy report DE96014006, Washington DC, 1996.

13 A. Dugstad, B. Morland, S. Clausen, Corrosion of Transport Pipelines for CO2 effect of water ingress, Energy Procedia, 4 (2011) 3063

14 F.W. Schremp, G.R. Roberson, Effect of Supercritical Carbon Dioxide on Construction Materials, SPE Paper no. 4667 (1973)

15 F.W. Schremp, G.R. Roberson, Effect of Supercritical Carbon Dioxide on Construction Materials, Soc. Petr. Eng. J., 15 (1975) 227

16 B. P. McGrail, H. T. Schaef, V.-A. Glezakou, L. X. Dang, A. T. Owen, Water Reactivity in the Liquid and Supercritical CO2 Phase: Has Half the Story Been Neglected?, Energy Procedia 1 (2009) 3415

17 R. Thodla, F. Ayello, N. Sridhar, Materials performance in supercritical CO2 environments, CORROSION/2009, Paper No. 9255, NACE International, Houston, 2009

18 F. Ayello, K. Evans, R. Thodla, and N. Sridhar, Effect of impurities on corrosion of steel in supercritical CO2, CORROSION/2010, Paper No. 10193, NACE International, Houston, 2010

19 Y.-S. Choi, S. Nei, Effect of impurities on the corrosion behavior of carbon steel in supercritical CO2 water environments, CORROSION/2010, Paper No. 10196, NACE International, Houston, 2010

20 Dugstad, M. Halseid, B. Morland Corrosion in dense phase CO2 pipelines state of the art, EuroCorr 2011, Stockholm, Paper No 4954

21 H. El Alami, Ch. Augustin, B. Orlans, J-J Servier Carbon capture and storage projects: material integrity for CO2 injection and storage, EuroCorr 2011, Stockholm, Paper No 4741

22 Y.Xiang, Z. Wang, Ch. Xu, Ch. Zhou, Z. Li, W. Ni Impact of SO2 concentration on the corrosion rate of X70 steel and iron in water-saturated supercritical CO2 mixed with SO2 J. Supecritical Fluids, 58 (2011) 286

23 Y.-S. Choi, S. Nesic, D. Young, Effect of impurities on the corrosion behavior of CO2 transmission pipeline steel in supercritical CO2-water environment` Environ. Sci.Technol., 44 (2010) 9233

24 Y.S. Choi, S.Nesic, Effect of water on the corrosion behavior of carbon steel in supercritical CO2 phase with impurities` CORROSION/2011, Paper No. 11377, NACE International, Houston, 2011

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2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

25 F. Farales, Y.S. Choi, S. Nesic, Effects of CO2 phase change, SO2 content and flow on the corrosion of CO2 transmission pipeline steel, CORROSION/2012, Paper No. C2012-0001322, NACE International, Houston, 2012

26 A. Dugstad, M. Halseid, B. Morland, A.O. Sivertsen, Corrosion in dense phase CO2 with small amounts of SO2, NO2 and water, EuroCorr 2012, Istanbul

27 B. Paschke, A. Kather, Corrosion of pipeline and compressor materials due to impurities in separated CO2 from fossil-fuelled power plants, Energy Procedia 23 (2012) 207

28 J. Collier, C. Shi, S. Papavinasam, P. Liu, J. Li, J-P. Gravel, Effect of impurities on the corrosion performance of steels in supercritical carbon dioxide: Optimization of experimental procedure, CORROSION/2013, Paper No. 2357, NACE International, Houston, 2013

29 Y. Xiang, Z. Wang, Z. Li, W.D. Ni, Effect of exposure time on the corrosion rates of X70 steel in supercritical CO2/SO2/O2/H2O environments, Corrosion, 69 (2013) 251

30 A. Dugstad, M. Halseid, B. Morland, A.O. Sivertsen, Corrosion in dense phase CO2 the impact of depressurisation and accumulation of impurities, Energy Procedia, 37 (2013) 3057

31 A.S. Ruhl, A. Kranzmann, Corrosion in supercritical CO2 by diffusion of flue gas acids and water, J. Supercritical Fluids, 68 (2012) 81

32 A. Dugstad, M. Halseid, B. Morland Effect of SO2 and NO2 on corrosion and solid formation in dense phase CO2 pipelines, Energy Procedia, 37 (2013) 2877

33 H. Fang, D. Young and S. Nei Corrosion of mild steel in the presence of elemental sulfur, CORROSION/2008, Paper No. 08637, NACE International, Houston, 2008

34 O. Yevtushenko, R. Bler., I. Carrillo-Salgado, Corrosion stability of piping steels in a circulating supercritical impure CO2 environment, CORROSION/2013, Paper No. 2372, NACE International, Houston, 2013

35 K. Patchigolla, J.E. Oakey, Design overview of high pressure dense phase CO2 pipeline transport in flow mode, Energy Procedia 37 (2013) 3123

36 S. Sim, I.S. Cole, F. Bocher, P. Corrigan, R.P. Gamage, N. Ukwattage, N. Birbilis, Investigating the effect of salt and acid impurities in supercritical CO2 as relevant to the corrosion of carbon capture and storage pipelines, International Journal of Greenhouse Gas Control, 17 (2013) 534

37 National Energy Technology Laboratory (NETL) Quality Guidelines for Energy System Studies, CO2 impurity design Parameters, DOE/NETL-341/011212, 2012

38 Q. Zhang, I.G. Dalla Lana, K.T. Chuang, H. Wang, Reactions between hydrogen sulphide and sulphuric acid: a novel process for sulphur removal and recovery, Ind. Eng. Chem. Res., 39 (2000) 2505

39 H. Fang, D. Young, S. Nei, Elemental sulfur corrosion of mild steel at high concentrations of sodium chloride, CORROSION/2009, Paper No. 2592, NACE International, Houston, 2009

40 Y. Song, A. Palencsr, G. Svenningsen, J. Kvarekvl and T. Hemmingsen, Effect of O2 and Temperature on Sour Corrosion, CORROSION/2011, Paper No. 11077, NACE International, Houston, 2011

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2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.