Abstract:
The shipping industry needs to be decarbonised to below its 2008 levels by 2050
according to the initial strategy set target proposed by the International Maritime
Organisation. With fossil fuels having a huge role in the energy space and in
particular, the maritime industry, it is paramount that measures to meet this
challenge are considered. Carbon capture utilisation and storage is the only
technology with the potential to transform fossil utilisation sources into low carbon
sources, although their use is not yet established in the shipping industry.
Therefore, this research is aimed at evaluating different operational modes and
conditions for a ship energy system (manoeuvring, sailing and hotelling)
retrofitted with a post combustion capture system. To meet this aim, process
models of the ship energy system, capture and liquefaction system were
developed in Aspen Plus and benchmarked against literature data available in
the public domain. This was done considering ship types powered by both heavy
fuel oil and liquefied natural gas at different power requirements (9.8MWe,
7.7MWe, 6MWe and 5MWe).
Ship operating worldwide have been required to use fuels with a lower sulfur
content as compared to the former situation where sulfur contents of 3.5% were
not uncommon. This requirement has been adopted since January 2020. Many
researchers have explored sulfuric emissions reduction whilst neglecting carbon
emissions. In this research, this issue was resolved by the applicability of a
solvent with a multi component handling capacity. Aqueous ammonia was used
as the solvent at varying concentrations (<10wt%) and conditions for the powered
ship types.
A comparison was made between the two fuel systems with regards to the
process, economic and weight analysis. It was found out that the heavy fuel oil
case resulted in about 12% higher carbon emissions than that of the liquefied
natural gas case. The cost of capture was used as the economic index in this
study, and about 40% higher was obtained for the heavy fuel oil case compared
to that of the LNG. This outcome was traced to the absence of sulfuric emissions
in addition to the lower fuel cost. The impact on the ship infrastructure was also
investigated in terms of the weight incurred, this was found to be 480 and 356
tonnes for the heavy fuel oil and liquefied natural gas case respectively. The
weight accounted for was the installed weight (the solvent and liquid inventory
included).
Importantly, in ensuring that the ship gets to its required destination, an additional
1MWe was added and this was estimated to be enough for the capture and
liquefaction system in all the cases considered. The waste heat recovered from
the flue gas served as a thermal source for the solvent regeneration, thereby
minimizing power demand needed from the ship energy system. About 70% of
the carbon emissions was captured from the flue gas without additional thermal
source. Therefore, this research study revealed that carbon capture technologies
has the capacity to significantly reduce carbon emissions on a shipping
infrastructure taken into consideration additional power demand and related
impacts.