Scholarly article on topic 'Feasibility Study on CO2 Micro-Bubble Storage (CMS)'

Feasibility Study on CO2 Micro-Bubble Storage (CMS) Academic research paper on "Materials engineering"

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Abstract of research paper on Materials engineering, author of scientific article — Kenichiro Suzuki, Hideaki Miida, Hiroshi Wada, Shigeo Horikawa, Takeyuki Ebi, et al.

Abstract Among many different portfolios in the CCS technology, this paper presents the feasibility of a system that stores CO2 by injection in the gas phase and dissolution at shallower depths. There involved dissolution characteristics of CO2 in the form of microbubbles, existence of potential storage sites in Japan, conceptual overview of a storage system for model geology and its storage potential, and regulatory issues and economic side of the system. From the results of this feasibility study, CMS system could well be feasible technically and economically.

Academic research paper on topic "Feasibility Study on CO2 Micro-Bubble Storage (CMS)"

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Energy Procedia 37 (2013) 6002- 6009

GHGT-11

Feasibility Study on CO2 Micro-Bubble Storage (CMS)

Kenichiro Suzukia*,Hideaki Miidab, Hiroshi Wadab, Shigeo Horikawac, Takeyuki Ebid, Kaoru Inabae

a Obayashi Corporation, 4-640 Shimokiyoto, Kiyose-City Tokyo,204-8558 Japan b Engineering Advancement Association of Japan (ENAA), 3-18-19 Toranomonn, Minato-ku Tokyo,105-0001 Japan c Suncoh Consultants Co. Ltd. ,1-8-9 Kameido, Koutou-ku Tokyo,136-8522 Japan d Kajima Corporation, 6-5-11 Akasaka, Minato-ku Tokyo,107-8348 Japan _e Takenaka Corporation, 1-5-1 Ootsuka, Inba-City Tiba, 270-1395 Japan_

Abstract

Among many different portfolios in the CCS technology, this paper presents the feasibility of a system that stores CO2 by injection in the gas phase and dissolution at shallower depths. There involved dissolution characteristics of CO2 in the form of microbubbles, existence of potential storage sites in Japan, conceptual overview of a storage system for model geology and its storage potential, and regulatory issues and economic side of the system. From the results of this feasibility study, CMS system could well be feasible technically and economically.

© 2013 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of GHGT

Keywords; Feasibility Study; CO2 micro-bubble; Small scale dipersed storage

1. Introduction

Carbon dioxide capture and storage (CCS) plays an essential role in reducing global greenhouse gas (GHG) emissions. As part of a portfolio of low-carbon technologies, CCS is needed to stabilize atmospheric greenhouse gas concentrations. Among many different portfolios in the CCS technology, Koide & Xue (2009) [1] proposed a microbubble storage system (CMS) as an economic leak-free option. In the system, gas/supercritical/liquid phase CO2 is injected into ground in the form of microbubbles.

* Corresponding Author. Tel.: +81 424 95 1015; fax: +81 424 95 0909. E-mail address: suzuki.kenichiro@obayashi.co.jp.

1876-6102 © 2013 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of GHGT doi:10.1016/j.egypro.2013.06.528

This paper, highlighting on the economic side of CMS, presents the feasibility of a system that stores CO2 by injection on the gas phase and dissolution at shallower depths. Especially, CMS is effective for smaller emission sources such as hydrogen production plants in oil refinery or chemical plants to develop a small but more effective storage scheme in distributed locations to minimize storage and transportation costs. The storage unit designed in CMS is composed of an injection well of CO2 at the center and four circumferential wells for pumping up underground water to be used to dissolve CO2. CO2 is stored in such a way that groundwater is replaced with CO2 dissolved water. It is expected that the options for the storage site selection will increase, since the structural trapping that rely on low permeability and strength of caprock may not necessarily be required. The system would contribute economically, because the transportation cost can be minimized by the CO2 storage in small amounts directly below or in the vicinity of the plant, and because the drilling cost can be reduced by the storage at shallower depths. It also possesses an advantage to control the extent of the storage area with the use of water pumping wells that may be used later as observation wells for a long-term storage management. In the series of feasibility study, dissolution characteristics of CO2 by microbubbles, existence of potential storage sites in Japan, conceptual overview of a storage system for model geology and its storage potential [2], design summary of a storage unit [3] and the effect of various operational conditions through site-scale simulation of the behavior of CO2 in CMS using TOUGH2 with ECO2N option [4] and regulatory issues and economic side of the system [2] were comprehensively examined. The present paper is summarized from the concept to some awaiting solutions.

2. Concept of CMS system

2.1. Concept of CMS system

Basic concept of CMS is a replacement of underground water by CO2 dissolved underground water. CO2 is dissolved immediately by creating CO2 micro-bubble by blowing gaseous CO2 with the underground water pumped up in the injection well, and then the CO2 dissolved underground water flows into storage layers (Figure 1). The storage unit designed in CMS shown in figure 2 is composed of an injection well of CO2 at the centre and four circumferential wells for pumping up underground water to be used to dissolve CO2. CO2 is stored in such a way that groundwater is replaced with CO2 dissolved water in the volume surrounded by the circumferential wells.

In case the total CO2 emission from sources, such as hydrogen production plants in oil refinery, is small in volume and high in purity, no CO2 capture is required, and all the emission volume may be directly stored. However locally distributed small-scale CCS will need a potential storage area in the vicinity of the plant for reduction of transportation cost by approximating sink to source, as having mentioned above.

In Table-1, the characteristics and requirements of some geological storage concepts were summarized. CO2 dissolved water is slightly heavier than underground water and then it migrate planarly according to hydraulic gradient and reach to the bottom layer (See [4]). Therefore the presence of caprock as sealing layer would not be necessary condition for CMS system but safety condition. It is therefore possible to store CO2 safely at shallower depths, as long as underground water is not domestically used.

2.2. Characteristics of Micro-bubble

Microbubbles have various unique chemical and physical characteristics in contrast to bubbles on the order of several tens of microns. The micro-bubbles make their rise velocity very low and, therefore, they are easily improved the dissolution rate of gas within the bubbles. Furthermore, it is hard to join each micro-bubble and to increase its size since the gas-water interface of micro-bubble negatively charged. Therefore, little buoyancy acts caprock layer.

CO2 gas/CO2 dissolution

Monitoring

Oil Refinery Hydrogen production factories

PumpingWell

Clearance

Compressor

Injection Well

^ Pump Pumping Well

Fig. 1. Concept of CO2 microbubble Storage System (CMS) and a storage unit

Effective layer thickness

Injection Well Pumping Well

Storage Area

Fig. 2. Concept of a storage unit Table 1. Storage concepts and requirements for geology

CMS system

Phase of CO2 and Gas microbubble Liquid microbubble Supercritical CO2

storage concept Dissolution Emulsion Replacement

Target of storage Small-Middle scale distributed Local Storage Middle position Large-scale Centralized Storage

Depth of Storage -300m —500m -570m ~ -800m ~

Geological structure Aquifer Aquifer Anticline and deep saline aquifer

Storage layer Sufficiently Porous and Permeable Sufficiently Porous and Permeable Sufficiently Porous and Permeable

Geology Presence of impermeable caprock Not necessary (For safety ) Not necessary (For safety ) Necessary

Mechanical requirements for caprock Low Strength Middle Strength High Strength

Especially, remarkable characteristics are high solubility in liquid; self pressurized effect, resolution into liquid by pressure and crush, electrification and so on. These characteristics are caused by very small diameter of micro-bubble. Then, these characteristics depend on diameter.

When the dissolution rate of gas to liquid is considered, two-film model can be generally used. From two-film theory, in case of gas which dissolves slightly such as CO2, the diffusion in liquid film determines the rate of gas dissolution. When CO2 dissolves in water, gaseous CO2 becomes aqueous CO2(aq), and some of associates with water molecules to form carbonic acid, H2CO3. Actually CO2(aq) is at 25°C about 600 times more abundant than H2CO3, but to facilitate calculations a convention is adopted in which the two species are summed up as H2CO3*. The overall reaction becomes then: CO2+H2O->H2CO3* where H2CO3*=CO2(aq)+H2CO3. Describing C and Cs as the concentration of H2CO3* in water and the concentration under atmospheric pressure of it, respectively, reaction rate in liquid film is [5]:

dCdt^Cs-C (1)

where the coefficient of velocity K is theoretically shown as the following equation:

k _ dco2 a K ~ 8 V

where Dco2 is the liquid film dispersion coefficient as 2xl0~5 cm2/s, 5 is a thickness of liquid film as 40|um at no stirring condition, A is specific contact area between gas/liquid, and V is a volume of water. Substituting C=Co at t=0 and C=C at t=t into equation (1), then we obtain:

C = Cs — Cs - C0 exp -Kt (3)

This equation shows the variation of concentration of H2CO3* with time. Using this equation, theoretical dissolution rate is calculated and shown in Figure 3. Assuming the uniform distribution of average diameter of microbubble 100 |um that has inner pressure 29kPa expected by Young-Laplace equation, which derives conservative results as compared with results under atmospheric pressure, the effectiveness of microbubble for the dissolution is represented as their specific area (A/V in the coefficient K) and the density of them. In Figure 4, experimental results of CO2 microbubble dissolution is quoted from Miyazawa et.al [6]. These shows that gaseous CO2 by microbubbles could be dissolved in water more rapidly than the case using bubble with millimeter order diameter. These demonstrated that it is feasible to dissolve rapidly with smaller and/or denser of microbubbles.

Here, let us consider the possibility of subsurface gas separation by the difference in solubility to investigate a further cost-down method. A flue gas is composed by CO2, N2, O2, and a very small quantity of NOx and SOx. The solubility of CO2 is about 60 and 30 times as high as N2 and O2, respectively. A vent could be installed at the upper part of storage layer to take insoluble gas micro-bubbles out. However, the quantitative explanation for the possibility such regulation of vent pressure and the residence time of insoluble gas microbubble has not been discussed yet.

£ 1000

-A/V=0.03 (100/ml) -A/V=0.05 (160/ml) A/V=0.3(1000/ml)

0 200 400 600 800 1000 1200 1400 Elapsed time (min)

. 1000

Stoppage of CO2 injection operation at 250 min

X Deionized water

>/W__M¿ ^ 7K '

• Groundwater

"-SlOHlf-*--*-*

Deionized water(Bubbling)

200 400 600 300 100fl 1200 1400 Elapsed time(min)

Fig. 3. Theoretical dissolution rate of CO2 microbubbles Fig. 4 Experimental Results of CO2 microbubbles after

Miyazawa et.al. [6]

3. Possible Storage Sites in Japan

Taking the requirements in Table 1 of CMS system into consideration, the following geological conditions have been specified as examination criteria:

1) Presence of highly permeable porous reservoir (e.g., sandstone) and impermeable layer of low porosity as a caprock (e.g., mudstone) in the sedimentary basin;

2) Distribution of Neogene to Quaternary Pleistocene sedimentary rocks at depths between -300 and -500 m.

3) Presence of sealing layer as a caprock for greater safety;

There are a number of sedimentary basins containing the Neogene to the Quaternary Pleistocene sedimentary rocks in the coastal areas of Japan. 11 sedimentary basins, including Sothern of Hokkaido, Japan Sea near the coast of Akita, Tokyo Bay, Ise Bay, Osaka bay, Northern and southern Kyushu and the southern part of Okinawa Island, are selected as probable promising areas by the existence of sedimentary basins and emission sources. Their characteristics were explained in detail by Shidahara et.al. [2].

4. Evaluation of Potential and Possible Storage Capacity

4.1. Possible quantity of storage

Among these basins, feasibility of the CMS units was tested at two locations (A, B) selected from a type of emission sources and above geological property, and at depths between 300 and 500m (only at vicinity of plant in the case of B), storage potentials of 2.4, and 150Mt-CO2 were estimated. Possible quantity of storage is estimated by the following equation:

Possible Quantity of Storage = RcxA*hx(px [co2] (4)

where Rc: Reduction coefficient depending on accuracy of geological survey (We here used 0.25 on the regional scale survey phase and 1.0 on the site-scale detailed survey phase.);

A: Area of storage formation (m2);

h: Sum of layer thickness to store CO2 of the targeted formation (m);

cp: Average porosity of storage layers in the targeted formation;

[CO2]: concentration of CO2 (t/m3H2O).

CO2 concentration is calculated as saturation solubility that is obtained for the referred water chemistry, thermal gradient and pressure in the geochemical calculation using Phreeqc [7].

The sections of the sites A and B of the above mentioned areas were shown in figure 5. The section (a) shows the formation of site A, where the targeted formation distributes the area about 450 km2. In the site A, possible quantity of storage is expected 150 Mt-CO2 from equation (4). There are a lot of kinds of emission source around this area. The section (b) shows the formation of site B, sandstone layers which are targeted for storing CO2 are distributed under the on- and offshore area at and near to the oil refinery plant. Storage area was able to be set in the area which is in the range of around 8 km2. Sandstone layer of thickness around 100m in the range of 300m to 500m in depth was selected as the storage formation (b). Under conditions that average porosity q> is 0.3 and concentration of CO2 is 0.04 t/m3H2O, possible quantity of storage of 2.4Mt-C02 was calculated [2].

4.2. Storage potential of injection and pumping system

The design flow of CMS system is explained in detail by Hitomi et.al. [3]. After selecting possible site, solubility of CO2 to the groundwater will be expected and possible water volume to dissolve will be estimated. And then a unit of injection/pumping wells will be designed. Above hypothetical model sites were then defined according to the conditions of geology and emission sources in interest, and the properties of CO2 such as saturation solubility were obtained for the referred water chemistry, thermal gradient and pressure in the geochemical calculation using Phreeqc [7]. As a result it was found that solubility would be 4 to 5 % by weight, and that an injection of 200,000 to 250,000 tons of CO2 dissolved water would be necessary to store 10,000 ton of CO2 annually. It may be noted that the saturation value is conservatively estimated, since the characterization of microbubble is not adequate at this time. Considering further ionization, saturation would be higher, leading to increase in storage quantity.

For the injection method and the targeted depth defined above, a unit of an injection well and four water pumping wells was modeled, and a storage potential and the injection/pumping-up conditions were studied in the well hydraulics theory. Water required to produce10,000 tones of CO2 solution per year is pumped up from the storage reservoir through the water pumping wells. If the injection pressure is not too large so it would not impose damage onto reservoir and caprock, and balancing the injection/pumping amounts, the calculated injection pressure is equivalent to a water column of 100m. The storage capacity

Fig. 5. (a) Section of the Model A(a) and the Model B(b) in Plan

may be given by the pore volume of rock in a storage unit, and it can be increased by making the distance between the injection and water pumping wells larger. For a distance of 200m, the storage capacity is 150,000 t-CO2, which is 15 years of storage for an annual injection amount of 10,000 t-CO2 [3]. This system may be advantageous in a sense that the storage amount can be controlled by adjusting the amount of pumping water, even when there is underground water flow, or the reservoir permeability is heterogeneous.

The bottom clay layer is effective for preventing the injected CO2-saturated water from leaking. The plume has not reached the aquitard while it reached the withdrawing wells. The CO2 mass fraction around the plume head is lower than the injected water because of the mechanical dispersion [4].

5. Cost of Storage

Cost evaluation of the CMS storage system was carried out, taking construction cost of the storage unit facilities into account. Basic storage unit is comprised of 1-500m long injection well, 4-500m long circumferential wells, CO2 and underground water transportation pipelines, compressor for micro-bubble generation on the ground, pumps on the ground and so on. The distance between the injection well and a circumferential well, viz., the unit radius is set at 200m.

Under these conditions, storage cost excluding separation/capture cost was estimated to be about JPY 4,600/t-C02 to 6,100/t-C02. In trial calculation of CMS, drilling cost including well logging, monitoring cost, maintenance cost and transportation cost were calculated and added up. They were calculated in the 2 cases, where one is with an annual injection rate of 10,000 t-C02 per year and the other is with an annual injection rate of 20,000 t-C02 per year. Although equipment cost of large scale centralized CCS is cheaper than CMS because there is scale effect, that of CMS will become equal or cheaper than large scale centralized CCS when transportation cost is considered. Therefore this value indicates that the CMS storage cost could be lower compared with the estimated storage cost for large scale emission sources.

Furthermore, the C02 reduction effect by CMS was compared with the reduction effect by the large-scale concentrated CCS and by generation of the renewable energy on a basis of a cost test calculation result of CMS. C02 reduction effect of CMS is higher than solar power generation, micro hydro power generation and biomass generation, and is less than geothermal generation and wind power generation. But this comparison depends on the selling of generation unit price of the renewable energy.

6. Environmental impact assessment

CO2 is a gas, which once dissolved into water produces as weak acid: carbonic acid as mentioned above. This substance reacts immediately with alkalis such as caustic soda, sodium carbonate and dissolved lime, turning them into neutral carbonates and bicarbonate salts.

Rocks with high amounts of calcium, such as limestone, are effective in reducing the acidity of water as it infiltrates, but other rock types are not. If acid precipitation is not buffered, metals such as copper, lead, iron and magnesium found in storage layer rocks may dissolve into groundwater supplies. In Japan, CMS will be regulated by water pollution control Law and Environmental Quality Standards for Groundwater Pollution etc. if C02 dissolved water were injected in the layer where the underground water is not domestically used. Then pumping wells arranged around the injection well will become observation wells that monitor the migration of CO2 and other constituents dissolved in the underground water, which is the one of advantage of CMS system.

7. Conclusions

In the feasibility study, dissolution characteristics of CO2 by microbubbles, existence of potential storage sites in Japan, conceptual overview of a storage system for model geology and its storage potential, and regulatory issues and economic side of the system were examined. From the results of this feasibility study, the following conclusions may be drawn:

1) Gaseous CO2 by microbubbles could be dissolved in water rapidly. But there are still some unexplained points such as the ratio of residual bubbles.

2) There are potential storage sites with adequate storage amount in the coastal areas of Japan. The storage potentials of two model sites at depths between 300 and 500m were estimated to be 2.4, and 150 Mt-CO2, respectively.

3) CO2 dissolved water with a solubility of 4% to 5 % weight can be injected at a pressure of about 1 MPa with an injection rate of 10,000 t-CO2 per year per a injection well without damage on the storage and sealing layers. This is stored in the reservoir stably since CO2 dissolved water is slightly heavier than underground water.

4) The system is economically feasible provided the cost is kept low by small scale storage in a locally distributed style in the vicinity of emission areas.

Acknowledgements

This study received a subsidy of Keirin by JKA Foundation has been enforced by General ENAA Foundation. We write it down here and show gratitude.

References

[1] Koide, H. and Xue, Z.: Carbon microbubbles sequestration: a novel technology for stable underground emplacement of greenhouse gases into wide variety of saline aquifers, fractured rocks and tight reservoirs, GHGT-9, pp.3655-3662, 2009

[2]Shidahara, T., Okumura, T, Miida, H., Shimoyama, M., Matsushita, N., Yamamoto, T., Sasakura, T., and Ogawa, T.: Storage potential and economic feasibility for CO2 microbubble storage (CMS) in Japan, GHGT-11, 2012

[3]Hitomi, T., Shidahara, T., Yamaura M, Tozawa, M., Tagami, Suzuki, K., and Wada, H.: Numerical analysis of storage potentials for CO2 micro-bubble storage (CMS), GHGT-11, 2012

[4]Miyoshi, S, Shidahara, T., Miida, H., Wada, H., Inaba, K., and Yamaura M.: Numerical Study on Field-scale Behavior of Carbon in CO2 Micro Bubble Storage (CMS), GHGT-11, 2012

[5] Aoki, T., Igarashi, T., Iio, Y., and Nishio, H.: pH reduction of alkaline seepage from a tunnel by dissolution of atmospheric carbon dioxide (in Japanese), Journal of Japan Society of Engineering Geology Vol.51, No.5 pp.220 - 228 (2010)

[6] Miyazawa, D., Ioka, S., Kiyama, T., Takahashi, M., and Ishijima, Y.: Laboratory Experiments Based on CO2 Microbubble Sequestration-Characteristics of CO2 Dissolution by CO2 Microbubbles- (in Japanese), Journal of MMIJ Vol.127 p.189 - 193 (2011)

[7] Parkhurst, D. and Appelo, C.A.J.: Use's guide to PHREEQC (version 2)—A computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations, U. S. Geological Survey, Water Resources Investigations 99-4259, 326p, 1999