• Energy Research

Captured CO2 is in a subcritical state, whereas CO2 deep underground is in a supercritical state because of the high geothermal heat and pressure. The properties of CO2 can change rapidly at the critical point and in the near-critical region during the transportation and injection process. This study aims to identify the instabilities in the CO2 flow in these regions, along with the causes and effects, during the transportation and injection process, and propose relevant design specifications. Thus, the critical points and near-critical region of CO2 flow were numerically analyzed. The unstable region is presented in terms of temperature and pressure ranges, and the changes in the CO2 properties in this region were analyzed. In the unstable region, the sudden change in density was similar to the density wave oscillation of a two-phase flow. The CO2 stability map we obtained and the stability map of supercritical water show similar trends. Flow instability was also found to occur in standard CO2 transportation pipelines. We demonstrate that flow instability in CO2 transportation and injection systems can be avoided by maintaining the proposed conditions.

Abstract The thermal efficiency of a reheating furnace was predicted by considering radiative heat transfer to the slabs and the furnace wall. The entire furnace was divided into fourteen sub-zones, and each sub-zone was assumed to be homogeneous in temperature distribution with one medium temperature and wall temperature, which were computed on the basis of the overall heat balance for all of the sub-zones. The thermal energy inflow, thermal energy outflow, heat generation by fuel combustion, heat loss by the skid system, and heat loss by radiation through the boundary of each sub-zone were considered to give the two temperatures of each sub-zone. The radiative heat transfer was solved by the FVM radiation method, and a blocked-off procedure was applied to the treatment of the slabs. The temperature field of a slab was calculated by solving the transient heat conduction equation with the boundary condition of impinging radiation heat flux from the hot combustion gas and furnace wall. Additionally, the slab heating characteristics and thermal behavior of the furnace were analyzed for various fuel feed conditions.

Abstract This study proposed ship-based carbon capture and storage (CCS) chains with different CO 2 liquefaction pressures and compared them in terms of life cycle cost (LCC) to determine the optimal pressure. Seven liquefaction pressures were suggested between the triple point (5.18 bar, −56.6 °C) and the critical point (73.8 bar, 31.1 °C) of CO 2 with increments of 10 bar, and the chain was divided into five modules: a liquefaction system, storage tanks, a CO 2 carrier, storage tanks in the intermediate terminal and a pumping system. LCC, including capital expenditure (CAPEX) and operational expenditure (OPEX), was used to estimate the CAPEX and OPEX of the five systems of the chain with each of the seven liquefaction pressures. The results showed that the optimal liquefaction pressure was 15 bar (−27 °C), which had an appropriate pressure, temperature, and density. As the liquefaction pressure increased, the costs of the liquefaction and pumping system decreased, and the costs of the storage tanks and CO 2 carrier increased. The cost of the liquefaction system was the largest contributor to the LCC, whereas the pumping system accounted for the smallest part. Sensitivity analysis was performed because this study was carried out in an early design stage with data subject to some uncertainty. The results of the sensitivity analysis showed that the optimal pressure was 15 bar without regard to the disposal amount, the distance from source to sink, the uncertainty of an employed methodology, and unit electricity cost.

AbstractThe objective of the present study is to gain a fundamental understanding on CO2 behavior during the seepage from the geologic carbon sequestration site. To elucidate the seepage behavior in the marine sediment, CO2 bubble dynamics in partially saturated porous media was studied. Force balance on a CO2 bubble in porous media was calculated by considering buoyancy force, surface tension effect and drag force. To consider the effect of porosity, permeability and wetting fluid saturation on ascent of CO2 in porous media, a new surface tension force model was studied. Based on the calculation results, the bubble rising velocity showed strong dependency on porosity and grain diameter. But there was negligible permeability effect. The developed model showed different calculation results with correction factor of force balance. There is no agreement in previous researches whether the escaped CO2 bubble from the marine sediment can be released to the atmosphere or not. To understand the CO2 bubble behavior in the water column, we calculated the dissolution of CO2 bubble in sea water. A molecular diffusion and a convective mass transfer of CO2 bubble were calculated by considering offshore environmental conditions during the dissolution. Based on the calculation results, the bubble dissolution rate showed strong dependency on the initial bubble diameter and bubble rising velocity.

AbstractCarbon dioxide capture and storage (CCS) technology is arising as one of the key technology for reducing emission of global warming gas and mitigating climate change. Especially the impurity effect on the CO2 transportation is important, cause with small amount of impurity, specific volume, boiling point and critical temperature of CO2 might possibly change tremendously, and along with that problems such as formation of hydrate and pipe clogging, etc are possible. Moreover the real captured CO2 mixture might contain impurities such as N2, O2, H2O, SOx, H2S. 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. To understand the thermo physical behavior of CO2-N2 mixture, experimental investigations are essential. In this study, we designed and built an experimental apparatus for simulating CO2–N2 mixture pipe-line transportation which consists of 4 parts with high pressure compression module, liquefaction module, mixing module, cooling module and transport test section. The transportation test section consists with 2 parts, one for horizontal pipe-line test section made by a horizontal tube and the other for long-pipe test section which composed of horizontal tubes and bended U-tubes. The steady flow experiment was tested on the horizontal pipeline test section to evaluate pressure drop behavior of CO2-N2 mixture in horizontal flow. Test condition was 70, 85, 100 and 120bar with varying N2 impurity composition. With increasing N2 impurity ratio, pressure drop, fluid phase, pressure, and temperature change was acquired and compared the value with calculated by single phase and two-phase model. The unsteady conditions such as severe variations of temperature, pressure and phases can be encountered during shut in, blow down of CO2 transport and injection systems. So designed at built unsteady flow experimental apparatus and conducted unsteady test with pure CO2.

AbstractIn line with the fact that carbon dioxide capture and storage (CCS) technology has been regarded as one of the most promising option to mitigate the climate change and global warming, we have started a 10-year R&D project on CO2 storage in marine geological structure. We carried out relevant studies, which cover the initial survey of potentially suitable marine geological structure for CO2 storage site, monitoring of the stored CO2 behavior, basic design for CO2 transport and storage process including onshore/offshore plant and assessment of potential environmental risk related to CO2 leakage in storage site. The purpose of this paper is to introduce and review the latest progress on the development of technologies for CO2 storage in marine geological structure and its perspective application in republic of Korea. At current stage, sub-seabed geological storage at ocean region is technically more feasible and economically attractive CO2 disposal option. Therefore, we try to capture CO2 from major point sources (eg., steel making industry and power plant) and transport CO2 for long-term storage into the marine geological structure in coastal area around the Korean Peninsula.We developed Korean technology roadmap for CO2 storage in marine geological structure and carried out collaborative basic and detail researches to demonstrate the feasibility of CO2 storage with national research institute and university groups. By using the results of the present researches, we can contribute to understanding not only how commercial scale (about 1 Mt CO2) deployment of CO2 storage in the marine geological structure of East Sea, Korea, is realized but also how more reliable and safe CCS is achieved.

AbstractThis study developed an economic evaluation model for CCS (Carbon Capture and Storage) chain where pipelines and ships were expected to come into play in transporting CO2 from power plants to offshore storage sites. In case of ship-based transportation, several alternatives with various operating conditions were feasible, demanding optimization of the transportation mode. The economic evaluation model was based on the LCC (Life Cycle Cost) methodology where the operational availability of equipment and systems were taken into consideration in addition to the capital and operating expenditure. The economic evaluation model was applied to the LCC estimation of two cases. The LCC results showed that the governing factor was the OPEX, dominantly affected by the liquefaction system.

In this study, the basic configuration and operation concept of a CO2 terminal were identified by conducting a system engineering process. The performance goal of a CO2 terminal was determined by requirement analysis. Then, functions and timelines were derived by functional analysis to meet the performance goal. Equipment to perform the functions were defined and finally, a process flow block diagram of the CO2 terminal was acquired. The CO2 terminal in this study consisted of three parts. First, the CO2 loading/unloading part is responsible for liquid CO2 unloading from the carrier and loading vapor CO2 onto the carrier. Secondly, the liquid CO2 transmission part extracts liquid CO2 from the storage tanks and increases the pressure until it satisfies the offshore pipeline transportation condition. The vapor-treatment part collects boil-off gas, generates vapor CO2, and charges the storage tanks with vapor CO2 to control the pressure of the storage tanks that discharge liquid CO2. Finally, the study results were compared with a liquefied natural gas (LNG) terminal. The biggest difference between the CO2 terminal in this study and the LNG terminal is that a vaporizer is essential in the CO2 terminal due to the smaller storage capacity of the CO2 terminal and, therefore, the lower amount of boil-off gas.