Speaker
Description
As the International Maritime Organization (IMO) is gradually strengthening regulations on greenhouse gas emissions from ships, the shipping industry is considering Carbon Capture and Storage (CCS) technology as a mid-term decarbonization strategy. A representative CCS technology with high readiness and proven onshore performance is the amine absorption-based capture technology. However, its high energy consumption leads to high Operational Expenditure (OPEX) and reduces the net CO2 reduction efficiency due to additional CO2 emissions from energy consumption.
The applicability of CCS technology in ships decreases as energy consumption increases. Ships produce all the necessary energy through generators or Aux. boilers, so higher energy consumption leads to an increase in the fuel supply system's Capex and CO2 storage tank capacity due to additional CO2 emissions, leading to higher cargo loss.
Therefore, for the amine absorption-based CCS technology to be applied to ships, energy saving is a priority, and two improvement strategies have been applied in this regard. One is the optimization of amine absorbent for ship exhaust gases, and the other is the utilization of available waste energy on ships.
Ship exhaust gases have lower CO2 concentrations and higher oxygen concentrations than onshore, making it necessary to apply absorbents with high oxidative stability and fast CO2 absorption rates. This allows for the use of less absorbent for the same amount of CO2 removal, leading to a reduction in energy consumption of over 30% for regenerating the absorbent.
Available waste energy on ships includes waste heat from exhaust gases and, in some cases, cold energy generated when LNG is vaporized for propulsion. Waste heat from exhaust gases can be used as heat energy for regenerating the absorbent, and the regenerated energy can be saved by over 50% compared to the existing system. However, to prevent abrupt thermal degradation of the absorbent, an indirect heat exchange system using steam as a heat transfer medium has to be designed, and an Aux. boiler-linked system has also been designed to supplement insufficient energy due to varying waste heat depending on the season or operating time.
When using LNG as a propulsion fuel, the cold energy generated during LNG vaporization can be used as cooling energy required for CO2 liquefaction, resulting in over 20% energy savings. The cold energy generated during LNG vaporization can sufficiently cool CO2 below -164 degrees Celsius for liquefaction, but cooling CO2 at too low temperatures may lead to the formation of solid hydrates. Therefore, an indirect heat exchange system using a separate refrigerant has been designed.
The application of the three energy-saving measures leads to a reduction in OPEX of over 50% compared to the technology, while improving the net CO2 reduction efficiency by over 45%. As a result, the applicability of amine absorption-based CCS technology in ships is significantly enhanced
References
[1] International Maritime Organization(IMO), Guidelines on the Method of Calculation of the Attained Energy Efficiency Index (EEDI) for New Ships. Resolution MEPC308(73), 2018
[2] Feenstra, M., Monteiro, J., Akker, J.T., Abu-Zahra, M.R.M., Gilling, E., & Goetheer, E., Ship-based Carbon Capture Onboard of Diesel or LNG-fuelled Ships, International Journal of Greenhouse Gas Control, 85, 1–10, 2019
[3] F. Vega, A. Sanna, B. Navarrete, M.M. Maroto-Valer, V. Cortés, Degradation of amine-based solvents in CO2 capture process by chemical absorption, Greenhouse Gases: Science and Technology, vol. 4, no. 6, pp. 707-733, 2014
| Keywords | Onboard carbon capture storage, CCS, Amine absorption |
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