1. Shipping and CO2 mitigation A systems perspective
N. Mac Dowell and N. Shah
Centre for Process Systems Engineering, Department of Chemical Engineering, Imperial College London

2. Outline Extent of problem Future emissions
Environmental impact of shipping
Current mitigation options
Next generation technologies

3. Extent of problem Global shipping is a major contributor
3 – 3.3% of total global emissions
More than aviation
In 2003, cumulative emissions were more than 1 billion tonnes!

4. Extent of problem 6th largest emitter in the world
Projected to triple by 2050
If unregulated, global shipping could account for 12 – 18% of total global emissions by 2050

5. Future emissions
Shipping transport has historically increased at a rate greater than global GDP growth
In light of emission reduction targets, this represents a potentially very large contribution to total global emissions

6. Future emissions
Future emission levels under no, low, medium and high emission reduction scenarios
Each of the growth futures has two scenarios corresponding to different global development pathways

7. Environmental impact of shipping
International shipping exerts an influence similar to that of aviation
SOx emissions exert a negative radiative forcing (RF)
Increasing requirements to mitigate SOx emissions from shipping
Increased warming effect associated with residual CO2 emissions, if these are not mitigated in line with the SOx emissions.

8. Current mitigation options
Four fundamental options for emission reduction
Increased efficiency
Advanced fuels
Different power sources
Emission reduction technologies

9. Current mitigation options: Increased Efficiency
Optimisation of propeller design
Astute selection of propeller has a non-negligible effect on propulsive efficiency: 5 – 10%
This is a relatively easy and cost effective measure to retrofit
Ships can be in service for a long time – propeller could be changed in line with service and fuel costs

10. Current mitigation options: Increased Efficiency
Optimisation of hull/bow design
Many designs available
Bow and hull design is an ongoing activity
The “beak bow” is designed to reduce wave added resistance

11. Current mitigation options: Advanced fuels
Liquefied natural gas (LNG)
Very attractive, near term option
LNG has a high H-to-C ratio when compared to marine diesel oil (MDO)
Low specific CO2 emissions (kg CO2/kg Fuel)
LNG is clean burning – essentially no SOx, NOx or PM

12. Current mitigation options: Advanced fuels
Liquefied natural gas (LNG)
Using LNG will result in increased CH4 emissions
GWPCH4 = 30xGWPCO2
Energy density of LNG ~ 55% that of MDO
Actual volume requirement is 3x that of MDO
Must be stored on board at pressure
Ready availability of LNG at bunkering ports not guaranteed

13. Current mitigation options: Advanced fuels
Biofuels
First-generation biofuels produced from sugar/starch/vegetable oil or animal fats
Can be readily used in marine diesel engines with minimal engine adaption
Blending biofuel with MDO is also a possibility
Potential technical problems include stability, biological growth (biofouling), wax formation

14. Current mitigation options: Advanced fuels
Biofuels
Net carbon intensity of biofuels is not straight-forward
Depends on how the original biomass is obtained and transformed from biomass to biofuel, i.e., biorefinery design and operation must be environmentally benign
Note that NOx intensity of biofuel can be 7 – 10% higher than that of MDO

15. Current mitigation options: Advanced fuels
Biofuels
First generation biofuels can compete with food crops
Second generation biofuels are produced from energy crops, and industry waste
More sustainable source of fuel
Process is not yet optimised at scale

16. Current mitigation options: Different power sources
Solar
Current technology is sufficient to meet only a fraction of the power requirements of a tanker.
Solar power is intermittent, thus an appropriate –backup power source would be required.
Present-day cost levels and efficiency place solar power towards the lower end of the cost-effectiveness list

17. Current mitigation options: Different power sources
Wind
Wind technology can be added to current vessels with large reductions in fuel consumption
Fuel savings from 5 – 20% possible
Kites are particularly interesting, with savings of up to 35% possible
Drawbacks with the kite systems include complex launch, recovery and control systems.

18. Current mitigation options: Different power sources
Wind
Sails impose bending moments on the hull, which can cause ships to list.
Strength issues could result in a need for masts to run down to the keel
Mast and rigging could have significant impacts on cargo handling
Nevertheless, sail assisted power does seem to be an interesting opportunity for fuel saving in the medium and long term picture

19. Next generation technologies: Chemical conversion
Removing CO2 from exhaust gases is not considered feasible…?
Technical/operational strategies considered previously can reduce CO2 intensity by as much as 60%!
How to address the remaining 40%?

20. Next generation technologies: Chemical conversion
Conventional chemical conversion method:
Contact the exhaust gas with a sorbent
CO2 is physically/chemically absorbed into the sorbent
The sorbent is then regenerated, CO2 is recovered, and stored
Regenerated sorbent is then reused

21. Next generation technologies: Chemical conversion
Challenges associated with chemical conversion
Exhaust gas flowrate
30 – 40 m3s-1
13.9 gCO2.tonne-1.km-1
Composition
5 vol% CO2
13 vol% O2
1500 ppm NOx
600 ppm SOx
Very dilute in CO2
Oxidative degradation a concern

22. Next generation technologies: Chemical conversion
These technologies are used in submarines for air scrubbing
Even more dilute in CO2
Completely closed system
Captured CO2 is vented   

23. Next generation technologies: Chemical conversion
Challenges associated with chemical conversion on ships
Space
– where to house the equipment?
– where to store solvents?
– where to store captured CO2?
Energy
– solvent circulation
– solvent regeneration

24. Next generation technologies: Chemical conversion
Ammonia based capture
Reaction: NH3(l) + CO2(g) + H2O(l) NH4HCO3(s)
High absorption capacity
No degradation problems
Saleable reaction products: (NH4)2SO4 and NH4NO3
Very volatile!
Operate the process at low temperature
Ocean provides a useful heat sink

25. Next generation technologies: Chemical conversion
On-board storage of captured CO2
NH3-based process
Store (NH4)2SO4 and NH4NO3 as solids
Need to have large inventory of NH3 on board
Interesting optimisation problem!

26. Next generation technologies: Chemical conversion
On-board storage of captured CO2
Use CO2 as a C1 building block
Copolymerisation of CO2 and cyclohexene to produce polycarbonates and polyurethanes
This reaction proceeds at low P and T
Easier to offload solid material than compressed fluids at port

27. Conclusions No single measure – no silver bullet!
Ship superstructure important to solution
Aggregated effect of all measures is significant
Future fuel prices are important towards cost-effective emission reduction
GHG emission reduction by ~ 30 – 60% feasible
Chemical conversion can lead to further reductions