Carbon Capture and Storage from a Point Source
Six significant criteria affecting implementation costs particularly staff training.
The emissions of carbon dioxide from industry can be captured before it enters the atmosphere. Fossil fuel, often coal and oil, burns and the carbon bonds with oxygen and forms carbon dioxide gas. It is at this point that carbon dioxide can be separated and captured, but it is an expensive process.
Liu, Yüksel & Dinçer (2020) conducted an analysis of the criteria for efficient use of Carbon capture and storage CCS technologies and determined 6 criteria affecting the cost and uptake of the technology.
These are:
- organizational factors, the training of employees, and personnel efficiencies;
- technical factors, the engineering improvements, and technological infrastructure;
- the market factors, the benchmarking of the opposition’s actions and performance, and the socio-demographic competencies, meaning the public’s environmental awareness and their sensitivity to the environment.
The authors determined the training and education of staff or the employment of trained personnel, both leading to personnel efficiencies, to be of the most important factors in the lowering of costs in the implementation of CCS technology.
CCS technology is one way to reduce the amount of carbon dioxide CO2 entering the atmosphere, along with reduced energy consumption and use of fuels with shorter carbon chains. Storage involves injecting the captured CO2 into deep geological formations (Raza et al., 2019).
CCS was first proposed in 1977 and since then many demonstration or pilot projects have been built, with 3 large scale projects started in 2016 and 2017. These are:
In Japan the Tomakomai CCS Demonstration projects captures CO2 from a hydrogen production plant and injects it into an in-shore deep geological formation.
The Illinois Industrial is a large-scale bioenergy plant which, starting in 2017, injects CO2 into a deep saline formation, at up to 1 million tons per annum.
In Texas, in 2017, the Petra Nova CCS Project has the capacity to capture 1.4Mtpa, and is the world’s largest CCS project.
The CCS process involves capturing CO2 from power plants, industrial processes and natural gas wells, then piping the gas to suitable geological formation for injecting and retention for thousands of years, without seeping back to the surface.
Capture and separation of CO2 from a point source such as a power station has four main technical options, post-combustion, pre-combustion, oxy-fueling and capturing from an industrial process, such as, from an oil refinery or from ammonia production.
Post-combustion technology is generally only used for exhaust gases with a low concentration of CO2, 4 to 14% volume per volume. Different technologies have been used: absorption using carbonate solutions or other alkaline absorbents, adsorbtion (adhesion to the surface) using zeolites , cryogenic distillation (separation by low temperatures) and membrane distillation.
Membrane distillation, using thin semipermeable membranes have been used where there is a high flow, high CO2 concentration or in remote locations.
In pre-combustion the fuel is converted by oxygen or steam to achieve a mixture of H2 and CO2. Upon combustion the products are CO2 and H2O, these can be separated by condensing the water. The separated CO2 is at high concentration and can be sent for storage.
Carbon dioxide can occur in several states, gas, liquid, solid and supercritical, that is, between a liquid and a gas.
In storage it is pumped to depths of lower than 800metres, the increasing pressure changes CO2 to a supercritical fluid. In this state it can pour into the surrounding porous solid materials.
The increased density of this state also reduces the CO2 buoyancy helping to retain it within the geological formation.
Increasing temperatures will drive CO2 to a more gaseous state, so cold, deep sedimentary basins are more suitable for storage.
The mechanisms that keep CO2 in deep geological formations after injection are:
The fluid flow of CO2 in the porous material it is injected into and the pressure that holds it in that state.
Fluid flow as a result of natural hydraulic gradients; an example of natural hydraulic gradient is ground water that is at a higher elevation in a nearby hill will push ground water to the surface in a valley.
Contamination with methane, if storing in disused gas reservoirs, causing the CO2 to be less dense and more buoyant.
Transport of C02 is often by pipeline for storage in deep geological formation or pressurized road transport vessels for industrial use. Impurities need to be removed before injection and these are often nitrogen, oxygen and argon, all to reduce the volume, and removal of moisture to reduce corrosion of equipment. Mostly CO2 is transported in the supercritical form, compressed to 900 kilograms per cubic metre.
Storage sites are determined by regional suitability, and are selected from sedimentary basins which had oil and gas reserves, deep sandstone and carbonate aquifers, coal beds and salt beds. Active and depleted oil and gas reserves and deep aquifers have been found to be the most suitable CO2 storage sites.
Storage capacity in depleted gas and oil reserves is often calculated numerically by using recovered volumes. Assessment of saline aquifers is much more difficult.
CO2 can only be injected into the storage geological formation at a certain rate, termed the injectivity, without cracking the overlying rock. Injectivity can be monitored and adjusted by measuring pressure and temperature inside the injection well.
Trapping is a key storage mechanism holding the CO2 in place and can be structural as in the rock over a mined salt cavern, or by the pressure and temperature at depth, or by dissolving in a brine liquid.
Containment is by existing caprock over the storage site and monitoring must be conducted during and after the injection. Time lapse seismic measurements are an effective approach to ongoing monitoring of potential movement of the stored CO2 (Raza et al., 2019).
Carbon capture and storage technology is another tool that we can use to achieve our goal of zero greenhouse gas emissions by 2050, together with use of sustainable energy generation such as wind and solar, reduce energy consumption and use of fuels with shorter carbon chains.
References:
Abdulla, A., Hanna, R., Schell, K. R., Babacan, O., & Victor, D. G. (2020). Explaining successful and failed investments in US carbon capture and storage using empirical and expert assessments. Environmental Research Letters, 16(1), 014036.
Durand, B. (2005). Carbon dioxide capture and storage.
Liu, H., Yüksel, S., & Dinçer, H. (2020). Analyzing the criteria of efficient carbon capture and separation technologies for sustainable clean energy usage. Energies, 13(10), 2592.
Raza, A., Gholami, R., Rezaee, R., Rasouli, V., & Rabiei, M. (2019). Significant aspects of carbon capture and storage–A review. Petroleum, 5(4), 335–340.
