Techno-Economic Assessment of CO2 Transport for Carbon Capture and Storage

Abstract

The continuous rise of CO2 emissions is a major cause of global climate change. Carbon capture and storage (CCS) is widely seen as a practical technology for reducing CO2 emissions. CCS is essential if global temperature increase should be limited below two degrees Celsius. CCS mainly consists of capturing CO2 from large emitting sources and its transportation to a sequestration site where it can be stored safely for a long period of time. Transport links the capture and storage part, so it is a critical component that should not be overlooked.

This research is motivated by the fact that when CCS is to be deployed in full scale, very large quantities of CO2 will have to be transported from the source to the storage sites. Therefore, this study is focused to investigate the various CO2 transportation options, technically and economically. Large-scale deployment of CCS will require the development of new infrastructure to transport the captured CO2 from various sources to the appropriate CO2 storage sites. Land based transport of CO2 can be done using pipelines, tanker trucks and/or trains. However, this study is limited to the pipeline and ship transportation of CO2 at different thermodynamic conditions. The work is divided in four parts, namely dehydration, CO2 pipeline transport, CO2 liquefaction for ship transport and CO2 terminal design.

a. Dehydration It is necessary to remove water from the captured CO2 stream prior to the transportation. Low moisture content is critical in prevention of both corrosion and hydrate formation. The selected dehydration process must be reliable while minimizing the operational issues and ensuring process safety. In this study, traditional glycol process has been simulated to analyze the factors that affect the water removal from the captured CO2 stream. Using the standard glycol process can easily achieve moisture content of approximately 50 ppmv in the dehydrated CO2 stream.

b. Pipeline Transport Currently pipelines are the most economical way of transporting large quantities of CO2 in the supercritical phase. However, there is a need to compare CO2 transportation at different thermodynamic operating conditions. A plausible workflow model has been developed that can calculate operational parameters for the CO2 transportation based on the input variables. This model is useful for performing an economic analysis to check the feasibility of a project. The model is applied to South Korean case to transport captured CO2 from the power plants to an offshore storage site. Three different sets of temperature-pressure inlet conditions are studied for the CO2 pipeline transport. Temperature = -20 ?C

Pressure = 6.50 MPa

Liquid phase Temperature = 5 ?C

Pressure = 9.30 MPa

Liquid phase Temperature = 40 ?C

Pressure = 15.00 MPa

Supercritical phase The transport cost for Korean case varies from 10.9 to 15.5 US$/tCO2 depending on the specific scenario.

c. CO2 Liquefaction for Ship Transport Liquefaction is a vital component in ship transportation. A state-of-the-art CO2 liquefaction processes have been designed by taking CO2 capture facilities into account. The proposed processes require lower liquefaction energy compared to other processes found in the literature. Different scenarios have been studied in order to explore the effect of thermodynamic conditions on the economics of CO2 transport. The considered scenarios are categorized on the basis of liquefaction plant location as: (i) the capture site, liquefaction plant and shipping terminal are located close to each other

(ii) the capture site and liquefaction plant are far from shipping terminal

(iii) the capture site is far from liquefaction plant and shipping terminal. The liquefaction energy of 97.3 and 71.89 per kWh tonne of CO2 is required for post-combustion and pre-combustion facilities, respectively. The basic liquefaction and intermediate storage cost for a post-combustion source varies between 7.00 $ and 7.30 $ per tonne of CO2 and, a basic cost of 5.28 $ to 5.55 $ per tonne of CO2 is incurred for a pre-combustion source facility.

d. CO2 Terminal Design CO2 terminal acts as a connecting link between CO2 liquefaction and the shipping section. Due to the discrete nature of the process, there are number of operational modes which cannot be analyzed using steady-state simulation. Hence, the study is performed using the dynamic simulation for different operational modes of CO2 terminal. Four scenarios have been developed to define the operational strategy of the terminal: loading case, holding case, unloading case, and emergency shutdown. The results show that boil-off gas (BOG) generation within the CO2 terminal depends on storage tank size operating pressure, ambient conditions, insulation thickness, and the filling level of the vessel.