Scholarly article on topic 'Effect of water and nitrogen impurities on CO2 pipeline transport for geological storage'

Effect of water and nitrogen impurities on CO2 pipeline transport for geological storage Academic research paper on "Mechanical engineering"

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{"Carbon dioxide capture and storage(CCS)" / "Marine geological storage" / "N2 impurity" / "Equation of state" / "Two-phase flow"}

Abstract of research paper on Mechanical engineering, author of scientific article — Cheol Huh, Seong-Gil Kang, Mang-Ik Cho, Jong-Hwa Baek

Abstract Carbon dioxide capture and storage (CCS) technology is regarded as one of the most promising emission reduction options for the mitigation of climate change and global warming. The technology of CCS involves a process of capturing CO2 from industrial and energy-related sources (such as a power plant), transporting it from its sources to the storage sites, and storing it in the geological structures for long-term isolation from the atmosphere. Although the technologies for capture and storage of CO2 have been globally investigated and verified, the development of transport infrastructure is still in the initial stage except some typical cases. Especially, the effect of impurities on transport and injection is not clearly resolved yet. Up to now, process design researches for CO2 transport and storage have been carried out mainly on pure CO2 cases. Unfortunately the real captured CO2 mixture contains many impurities such as N2, O2, Ar, H2O, SOx, H2S. Some impurities can change the thermodynamic properties and then significantly affect the compression, purification, transport and injection processes. Among them, N2 can affect the CO2 transport process by its low boiling point. In other words, a small amount of nitrogen can make change flow conditions from single phase flow to two-phase flow. And a small amount of water in CO2 stream can trigger the clogging problem due to formation of hydrate. In this paper, a numerical evaluation of process design model was carried out. We compared and analyzed the relevant equations of state for CO2-N2 mixture. To quantitatively evaluate the predictive accuracy of the equation of the state, we compared numerical calculation results with reference experimental data. In addition, optimum binary parameters to consider the interaction of CO2 and N2 molecules were suggested based on the mean absolute percent error. With regard to CO2-H2O mixture transport, the hydrate formation possibility was analyzed based on the hypothetical scenario in republic of Korea. To understand the physical behavior of CO2-imputities mixture, experimental investigations are necessary. We made an experimental facility which is consist of high pressure compression module, liquefaction module, mixing module, cooling module and transport test section. The flow behavior such as single phase and twophase pressure drop of CO2-N2 mixture pipeline transport was experimentally analyzed. Based on this experimental data, we may suggest some design guideline for CO2 pipeline transport.

Academic research paper on topic "Effect of water and nitrogen impurities on CO2 pipeline transport for geological storage"

 Available online at www.sciencedirect.com

W ScienceDirect Energy

Ij&JEHL Procedia

ELSEVIER Energy Procedia 4 (22011) 2214-2221 www.elsevier.com/locate/procedia

GHGT-10

Effect of Water and Nitrogen Impurities on C02 Pipeline Transport

for Geological Storage

Cheol Huha1*, Seong-Gil Kanga, Mang-Ik Choa, Jong-Hwa Baeka

aMarine Safety & Pollution Response Research Department, Maritime & Ocean Engineering Research Institute, KORDI, Sinseong-ro 104, Yuseong-

gu, Daejeon, 305-343, Republic of Korea

Abstract

Carbon dioxide capture and storage (CCS) technology is regarded as one of the most promising emission reduction options for the mitigation of climate change and global warming. The technology of CCS involves a process of capturing C02 from industrial and energy-related sources (such as a power plant), transporting it from its sources to the storage sites, and storing it in the geological structures for long-term isolation from the atmosphere. Although the technologies for capture and storage of C02 have been globally investigated and verified, the development of transport infrastructure is still in the initial stage except some typical cases. Especially, the effect of impurities on transport and injection is not clearly resolved yet. Up to now, process design researches for C02 transport and storage have been carried out mainly on pure C02 cases. Unfortunately the real captured C02 mixture contains many impurities such as N2, 02, Ar, H20, S0x, H2S. Some impurities can change the thermodynamic properties and then significantly affect the compression, purification, transport and injection processes. Among them, N2 can affect the C02 transport process by its low boiling point. In other words, a small amount of nitrogen can make change flow conditions from single phase flow to two-phase flow. And a small amount of water in C02 stream can trigger the clogging problem due to formation of hydrate. In this paper, a numerical evaluation of process design model was carried out. We compared and analyzed the relevant equations of state for C02-N2 mixture. To quantitatively evaluate the predictive accuracy of the equation of the state, we compared numerical calculation results with reference experimental data. In addition, optimum binary parameters to consider the interaction of C02 and N2 molecules were suggested based on the mean absolute percent error. With regard to C02-H20 mixture transport, the hydrate formation possibility was analyzed based on the hypothetical scenario in republic of Korea. To understand the physical behavior of C02-imputities mixture, experimental investigations are necessary. We made an experimental facility which is consist of high pressure compression module, liquefaction module, mixing module, cooling module and transport test section. The flow behavior such as single phase and two-phase pressure drop of C02-N2 mixture pipeline transport was experimentally analyzed. Based on this experimental data, we may suggest some design guideline for C02 pipeline transport. © 2011 Published by Elsevier Ltd.

"Keywords: Carbon dioxide Capture and Storage(CCS), Marine geological storage, N2 impurity, Equation of State, Two-phase Flow"

1. Introduction

To response climate change, Carbon dioxide Capture and Storage (CCS) is one of key player in greenhouse gas reduction portfolio [1]. The technology of CCS is three stage process involving a process of capturing C02 from industrial and power generating sources (such as a power plant), transporting it from its sources to the storage sites, and storing it in the geological structures for long-term isolation from the atmosphere. Although C02 capture and storage technologies have been globally investigated and verified, the development of transport and injection process is still in

* Corresponding author. Tel.: +82-42-866-3622; fax: +82-42-866-3624. E-mail address: chuh@moeri.re.kr.

doi:10.1016/j.egypro.2011.02.109

the initial stage except some typical cases. Especially, the effect of impurities on transport and injection is not clearly resolved yet.

A CO2 purity issue in CCS application can be a big obstacle in respect of not only technical viewpoint but also public acceptance. In this paper, the effect of water and nitrogen impurity on the CO2 pipeline transport process was studied with numerical and experimental methods. With regard to water impurity, the hydrate formation possibility was analyzed in the offshore pipeline conditions. And nitrogen can affect the CO2 transport process by its low boiling point. We evaluated the predictive accuracy of the equation of the state for the CO2-N2 mixture and drew optimum binary parameters based on the quantitative comparison with calculation and experiment. To understand the physical behavior of CO2-imputities mixture flow, we made an experimental facility which is consist of high pressure compression module, liquefaction module, mixing module, cooling module and transport test section. The flow behavior such as single phase and two-phase pressure drop of CO2-N2 mixture pipeline transport was experimentally analyzed.

2. CCS application in Republic of Korea

In Korea, most of the largest CO2 emission sources such as fossil power plant and industrial plants are located along the coastal area, as shown in Fig. 1. Generally, geological CO2 storage can be carried out in oil/gas reservoir, saline aquifer and coal bed [2]. Unfortunately, there is no enough oil/gas reservoir and coal bed in Republic of Korea. With regard to saline aquifer, there are not enough onshore storage sites to store a huge amount of CO2 on the Korean Peninsula. Furthermore, it is necessary to resolve the public acceptance in the case of onshore geological storage. We have therefore focused our research on sub-seabed geological storage in the ocean region, especially for saline aquifer. In Korea, one of the largest emission sources is the POSCO steel-making plant. The daily emission rate of the steel-making plant in the city of Pohang is about 70,000 tons per day. The CO2 emitted in the steel-making process can be captured by an ammonia absorption process or a pressure swing adsorption process depending on the characteristics of the steel-making processes. The candidate storage site is offshore saline aquifer near by the Donhae-1 gas reservoir, which is located in the south-east offshore area of the Korea peninsula. The priority scenario covering whole CCS chain including capture, transport and storage is analyzed [3]. The emission source is steel-making plant, the transport method is onshore/offshore pipeline and the storage site is saline aquifer in Ulleung basin. A conceptual schematic of the CO2 transport and storage process is that the captured and preprocessed CO2 is transported from Pohang through the onshore pipeline and the offshore pipeline, as shown in Fig. 1.

In onshore and offshore pipeline transport design, it is necessary to consider not only delivery performance but also safety issues. Among them, CO2 purity issue can be a big problem because small amount of impurities make it possible to severe change thermodynamic properties of the CO2 stream and then affect downstream processes such as transport, injection and storage. To obtain reliable and optimum transport design conditions, designers of transport systems should consider the effect of the impurities. In this paper, the effect of water and nitrogen impurity was analyzed based on the numerical and experimental simulations.

Figure 1 C02 transport scenario for CCS application in Republic of Korea [3].

3. Effect of water impurity

Offshore pipeline will be installed in the seabed by virtue of technical and economical considerations. And the operating conditions of the seabed C02 transport pipeline are high pressure and low temperature. High pressure transport makes C02 as subcooled liquid or supercritical state to maintain higher density conditions. This high density

transport conditions enhance the pipeline transport performance. Due to the low seawater temperature in the seabed, generally around 4 °C, the temperature of transported C02 decrease along the flow direction as shown in Fig. 2. The captured C02 flow from right-hand-side to left-hand-side in Fig. 2 and the pipeline inlet conditions of the transported C02 are shown in the legend. In calculating the heat transfer of C02 inside the pipeline, we used a constant environmental temperature condition for the onshore pipeline transport region. On the other hand, the temperature variation with depth was considered in the offshore pipeline transport region because there is a temperature change with depth in the seawater. Any topographical variations in the offshore transport region were carefully considered because it changes the density of transported C02 due to the hydrostatic forces. But we assumed there was no topographical variation in the onshore transport region. In other words, the horizontal pipe flow condition was used in the onshore pipeline transport calculation.

In this paper, we analyzed the winter season (February) and summer season (August) transport process design cases considering the seawater temperature variation conditions. Except the surface condition, seawater temperature of summer season is lower than that of winter season due to the current of seawater in the transport and storage site area.

-Hydrate w/o inhibition -----Hydrate w/ inhibition

-T-25°C, 130 bar (Feb.)

—v— 25°C, 130 bar (Aug.)

—25°C, 160 bar (Feb.) —a— 25°C, 160 bar (Aug.)

Temperature (°C)

Figure 2 Hydrate formation conditions in onshore and offshore C02 pipeline transport conditions.

Due to the high pressure and low temperature conditions in offshore C02 pipeline, there is a possibility to form a hydrate which is a physical structure formed by trapping water molecule of C02. Figure 2 shows the hydrate formation conditions and C02 behavior during the pipeline transport. The hydrate formation conditions represented by hydrate stabilization curve (solid line in Fig. 2) were calculated in 99% (mole fraction basis) C02 and 1% water mixture using CSMGem [4]. Both 130 bar and 160 bar transport conditions suffer from the possibility of hydrate formation. The hydrate formation can make it possible to trigger the pipeline plugging problem. 0nce the hydrate forms and plugging starts, it is very difficult to dissociate the hydrate and remove the plug in the harsh seabed environment.

To avoid the hydrate formation, small inhibitor such as methanol, glycol, etc can be used. In this calculations, small amount (1 mole %) of Mono-ethylene Glycol (MEG) was added in the C02 stream. The hydrate stabilization curve moved to low temperature region in the Fig. 2. By adding the inhibitor, about 20 °C of thermal margin can be obtained. This makes sure hydrate free C02 transport.

4. Effect of nitrogen impurity

4.1. Equation of state for C02-N2 mixture

For the design of a reliable C02 transport and storage system, it is necessary to perform a numerical process simulation by using a thermodynamic equation of state (EOS). Before the construction of expensive transport and storage system, numerical process simulations can verify the design of the sequestration system. Up to now, process design for this C02 marine geological storage has been carried out mainly on pure C02. Unfortunately the captured C02 mixture contains many impurities such as N2, 02, Ar, H20, S0x, H2S, depending on the fuel characteristics and capture process. A small amount of impurities can change the thermodynamic properties and then significantly affect the compression, purification and transport processes. Li and Yan [5] studied the C02-N2 mixture Vapor Liquid Equilibrium (VLE) properties using Redlich-Kwong (RK) [6], Soave-Redlich-Kwong (SRK) [7], Peng-Robinson (PR) [8], Patel-Teja (PT), and 3P1T E0Ss. In this paper, we analyze the predictive capability of E0S for C02-N2 mixture including PR, Peng-Robinson-Boston-Mathias (PRBM) [9], Redlich-Kwong-Soave (RKS) [6, 7], and SRK. To evaluate

the predictive accuracy of the EOS, we compared the numerical calculation results with experimental VLE data of Dorau et al.[10], Arai et al.[11], and Muirbrook and Prausnitz[12],

Numerical calculations of VLE data using EOS were carried out by varying the mole fraction of N2 impurity and binary parameter kjj. The binary parameter, ky models the interaction between the carbon dioxide molecules and the nitrogen molecules in EOSs. Fig. 3 compares the results of each calculation and measured experimental data for the four types of EOS: namely, (a) the PR, (b) the PRBM, (c) the RKS, and (d) the SRK. All EOSs well predicted the dew point pressure for given mole fraction variations. On the other hand, there are large variations in predictive capabilities for bubble point pressure. Similarly with previous researches [3, 5], the prediction error increase as the concentration of impurity increase or the absolute value of binary parameter kij increase. Generally, the nitrogen concentration of the captured CO2 mixture from the power plant and steel-making plant is lower than 15%. It is reliable to use the above EOSs.

Experiment

■ Dorau el. at (bubble)

□ Dorau el. at (dew)

• Arai el. at (bubble)

O Arai el. at (dew)

A Muirbrook el. at (bubble)

A Muirbrook el. at (dew)

Liquid phase

fc 120- A 0 • ▲ fc 120-

Q -.A O X \ q .

0 100- 0100-

D 52 80- Two-phase D ' 52 80-

Gas phase

-Experiment -----

■ Dorau el. at (bubble)

□ Dorau el. at (dew) Liquidphase

• Arai el. at (bubble)

O Arai el. at (dew) %

A Muirbrook el. at (bubble)

A Muirbrook el. at (dew)

AO • A

O a ' '\ \ \

Two-phase

Calculation --------4------

k.- -0.2------ (bubble) ------ (dewT^---

k.= -0.1 ......... (bubble) ......... (dew) ___

k.- -0.0- (bubble) - (dew)

k- 0.1 -........ (bubble) ------- (dew) Gas phase

k= 0.2 -------- (bubble) --------- (dew)

Mole fraction of C02

(a) PR

-Experiment -----

■ Dorau el. at (bubble)

□ Dorau el. at (dew) Liquid phase

• Arai el. at (bubble)

O Arai el. at (dew)

A Muirbrook el. at (bubble)

A Muirbrook el. at (dew)

. AO • A

Two-phase

Calculation

k= -0.2 ------ (bubble) ------ (dewT®-—-

k = -0.1 ......... (bubble) ......... (dew) -----s--->J

k = -0.0 - (bubble) - (dew)

k = 0.1 ------ (bubble) -....... (dew) Gas phase

k = 0.2 —...... (bubble) ........- (dew)

Mole fraction of C02

(c) RKS

Mole fraction of C02 (b) PRBM

Experiment

■ Dorau el. at (bubble) □ Dorau el. at (dew)

■ Arai el. at (bubble)

O Arai el. at (dew) -A Muirbrook el. at (bubble) A Muirbrook el. at (dew)

Liquid phase

<5 120-

o 100- □

=3 IgAo

CO 80-

Two-phase

Calculation

k=-0.2 ------ (bubble) ...... (dew)

1 ......... (bubble) ......... (dew)

0 - (bubble) - (dew)

1 ------- (bubble) --------- (dew)

= 0.2 -......- (bubble) ......— (dew)

Mole fraction of C02 (d) SRK

Fig.3 Comparison of CO2-N2 mixture VLE calculation and experimental data at 0°C [3]

To carry out more reliable CCS process design, it is necessary to obtain and use more accurate binary parameters for the different molecular interactions. To obtain the optimized binary parameter based on the quantitative analysis, we quantified the prediction accuracy of EOS with mean absolute percent error (MAPE) defined as below equation. The subscript 'exp' means the experimental data and 'cal' means the calculation value. And N represents the total number of data.

MAPE = - yl^kl^ x100%

^ Pexp

Fig. 4 shows the results of MAPE for each calculation with the four types of EOS: namely, (a) the PR, (b) the PRBM, (c) the RKS, and (d) the SRK. The PR EOS shows maximum 9.1% error for whole range of the binary parameter and minimum error 5.7% was estimated at ky=-0.02. The PRBM EOS shows maximum 8.8% error for whole range of the binary parameter and minimum error 5.0% was estimated at ky=-0.06. The RKS EOS shows maximum 40.0% error as the binary parameter increase and minimum error 5.3% was estimated at ky=-0.02. Finally, the SRK EOS shows maximum 18.6% error for whole range of the binary parameter and minimum error 4.7% was estimated at ky=-0.02.

Binary parameter k..

(a) PR

—■—Total

—•— Bubble point

a Dew point

k =-0.02

Binary parameter k..

(c) RKS '

15 20 <

—■—Total —•— Bubble point Dew point

k.=-0.06

-0.2 -0.1 0.0 0.1 0.2

Binary parameter k..

(b) PRBM

—■- Total —•— Bubble point * Dew point

k.=-0.02

Binary parameter k..

(d) SRK

Fig.4 Comparison of C02-N2 mixture binary parameter kij at OX [3]

4.2. Experiment of C02-N2 mixture flow

The experimental apparatus consisted of four major subsystems: a working fluid C02 flow system, impurity N2 flow system, a flow visualization system, and a data acquisition system. Figure 5 shows a schematic diagram of the flow loop, which was configured to supply subcooled liquid or supercritical C02 to the test section. C02 and N2 are supplied to the experimental apparatus as gas state using evaporator, respectively. Gaseous C02 and N2 are compressed to high pressure with separate compressor. To reduce pulsating flow, dampers are installed at outlet of the compressors. Compressed C02 gas is liquefied in the condenser with external cooling source, chiller. The liquefied C02 is gathered in the receiver and flow rate is controlled and measured with metering valve and mass flow meter, respectively. The flow rate of N2 gas is also controlled and measured with metering valve and mass flow meter, respectively. Compressed N2 gas is added in the downstream of the C02 metering valve. Before reaching the test section, temperature of the C02-N2 mixture is controlled by chilling bath.

The test section consists of horizontal double pipe heat exchanger and inlet/outlet instrument devices. The C02-N2 mixture is entered inner circular tube which has 3.8 mm inner diameter, 1.24 mm thickness, and 6 m length. In annular flow passage, cooling fluid such as ethylene glycol entered to simulate seabed environmental conditions. As shown in Fig. 6, the whole test section is insulated to reduce heat loss or gain. Two absolute pressure transducers and resistance temperature sensors (RTD) were installed to measure the inlet and outlet pressures and temperatures. A differential pressure transducer was installed between the inlet and outlet of the test section to measure the pressure drop across the test section. The heat losses from the test section to the outside were neglected based on the measured inlet/outlet temperature. Discharged C02-N2 mixture passed through high pressure view cell with same inner diameter as test inner tube to observe real-time flow behavior. A CCD camera with a microscope was installed in front of view cell to provide flow patterns. After the test section, the pressure of the C02-N2 mixture is reduced.

The experimental test were performed for the mass flux of 4O7-4O9 kg/m2s, inlet temperature of 21 X, and inlet pressure of 7O, 85, 12O bar conditions. The components of the test flow system were adjusted to yield the desired mass flux, inlet pressure, and inlet temperature. During the experiment, N2 mass flow rate was slightly controlled with maintaining the total mass flow rate as 17.2 kg/hr. However, the maintaining of the exact same total mass flow rate was impossible due to the uncertainties of metering valve's mechanical accuracy. Therefore, the measured pressure drops across the pipeline test section were normalized with total mass flow rate to remove the effect of mass flow rate. After

the flow became stable, temperature, pressure and differential pressure are measured, and flow visualization carried out, simultaneously.

OUT DOOR

Figure 5 Experimental apparatus of C02-N2 mixture flow.

Figure 6 Test section of C02-N2 mixture flow.

The experimental test were performed for the mass flux of 407-409 kg/m2s, inlet temperature of 21 °C, and inlet pressure of 70, 85, 120 bar conditions. Prior to conducting a test, the C02-N2 mixture flowed with enough time. The components of the test flow system were adjusted to yield the desired mass flux, inlet pressure, and inlet temperature. During the experiment, N2 mass flow rate was slightly controlled with maintaining the total mass flow rate as 17.2 kg/hr. However, the maintaining of the exact same total mass flow rate was impossible due to the uncertainties of metering valve's mechanical accuracy. Therefore, the measured pressure drops across the pipeline test section were normalized with total mass flow rate to remove the effect of mass flow rate. After the flow became stable, temperature, pressure and differential pressure are measured, and flow visualization carried out, simultaneously.

Figure 7 shows the C02-N2 mixture flow behavior at 70 bar and 21 °C inlet condition. N2 mass fraction was controlled from 0 to 9.35 %. The pressure drop increase as the N2 impurity increase, as show in Fig. 7(a). But the gradient of pressure drop show a little bit different behavior according to the N2 impurity fraction. From 0 to 1.44 %, the C02-N2 mixture flow show single phase behavior as liquid state and gradual pressure drop gradient. On the other hand, two-phase and gaseous C02-N2 mixture flow show more steep pressure drop gradient. The C02-N2 mixture flow show two-phase behavior from 2.08 to 4.55 %, and single phase gaseous behavior from 5.25 to 9.35 %. As shown in Fig. 7(b), pure C02 at 70 bar and 21 °C inlet condition is nearly saturated liquid state. But C02-N2 mixture flow change from single phase flow to two-phase flow as N2 impurity increase to 4.55 %. Figure 8 shows the C02-N2 mixture flow behavior at 85 bar and 21 °C inlet condition. N2 mass fraction was controlled from 0 to 8.93 %. The pressure drops severely increase as the N2 impurity increase, as show in Figs. 8(a). From 8.42 to 8.93 %, the C02-N2 mixture flow show more steep pressure drop gradient. This means that gaseous single phase flow shows more pressure drop compared with two-phase flow at 85 bar conditions. In 85 bar and 21 °C inlet conditions, most of the C02-N2 mixture flow except 8.65 and 8.93 % cases show two-phase flow conditions, as shown in Fig. 8(b).

N2 fraction (mass%) Density(kg/m3)

(a) pressure drop per mass flow (b) temperature-density conditions

Figure 7 Pressure dropper mass flow and temperature-density conditions of C02-N2 mixture flow experiment at 70 bar.

N2 fraction (mass%) (a) pressure drop per mass flow

-N2 0.0 %

• 1 ---N24.795 %

• \ .....N29.013 %

■ \ O Exp (85 bar)

'■ /V Ns •/ N A S / ' __ // * ^ t '• ' . 1 .' 1 •' \ ' ' ' ' ' • ^ \ \ * \ \ * \ \ \ \ >> \ \ \ \ ■ vx \ \

200 400 600 801

Density(kg/m3) (b) temperature-density conditions

Figure 8 Pressure dropper mass flow and temperature-density conditions of C02-N2 mixture flow experiment at 85 bar.

N2 fraction (mass%) (a) pressure drop per mass flow

-N2 0.0 %

---N 4.795% \ \ \

• \ \

.....N2 9.013 % ■ \ \

0 Exp (120bar) 1 N \

X v \ '. \ \ \

/ • v \

/ \ 0 \

t N \\ \

• ■ \ A \

i ; It-' 1 .' *• -X A \ *• n A \ 'x A \ ■ \ \\ \ v \ \ \

200 400 600 80

Density(kg/m3) (b) temperature-density conditions

Figure 9 Pressure dropper mass flow and temperature-density conditions of C02-N2 mixture flow experiment at 120 bar.

Figure 9 shows the C02-N2 mixture flow behavior at 120 bar and 21 °C inlet condition. N2 mass fraction was controlled from 0 to 9.01 %. The pressure drops linearly increase as the N2 impurity increase, as show in Fig. 9(a). The C02-N2 mixture flow show liquid single phase flow from 4.8 to 6.57 %. On the other hand, the C02-N2 mixture flow shows supercritical single phase flow from 7.84 to 9.01 %. But the gradient of pressure drop show similar behavior, irrespective of flow state. The flow patterns of the C02-N2 mixture flow are shown in Fig. 10.

(a) N2 3.23 % at 70 bar

(b) N2 8.42 % at 85 bar

(c) N2 8.93 % at 85 bar

(d) N2 6.57 % at 120 bar

(e) N2 9.01 % at 120 bar

Figure 10 Flow patterns of CO2-N2 mixture flow experiment.

5. Conclusion

The effect of water and nitrogen impurity on the CO2 pipeline transport process was studied with numerical and experimental methods. In the offshore pipeline, the hydrate formation possibility due to existence of water in high pressure and low temperature conditions was analyzed. With regard to N2 impurity, we evaluated the predictive accuracy of the equation of the state for the CO2-N2 mixture and drew optimum binary parameters based on the quantitative comparison with calculation and experiment. Finally, we made an experimental facility to understand the physical behavior of CO2-imputities mixture flow behavior. As N2 impurity increases the CO2-N2 mixture shows different flow patterns and pressure drop behavior. The supercritical CO2-N2 mixture flow shows similar pressure drop gradient with liquid single phase flow due to the higher density in 120 bar conditions. On the other hand, two-phase flow of CO2-N2 mixture shows larger pressure drops in 70 bar conditions. Therefore, the N2 impurity should be maintained below 5 % in low pressure transport conditions.

Acknowledgements

This work was conducted on behalf of the Ministry of Land, Transport and Maritime Affairs (MLTM) of Korean government under their "Development of Technology for CO2 Marine Geological Storage" program.

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