Monday, December 26, 2011

Assessing the potential of hybrid energy technology to reduce exhaust emissions from global shipping
Abstract: The combination of a prime mover and an energy storage device for reduction of fuel consumption has successfully been used in automotive industry. The shipping industry has utilised this for conventional submarines. The potential of a load levelling strategy through use of a hybrid battery–diesel–electric propulsion system is investigated. The goal is to reduce exhaust gas emissions by reducing fuel oil consumption through consideration of a re-engineered ship propulsion system. This work is based on operational data for a shipping fleet containing all types of bulk carriers. The engine loading and the energy requirements are calculated, and sizing of suitable propulsion and the battery storage system are proposed. The changes in overall emissions are estimated and the potential for fuel savings identified. The efficiency of the system depends on the storage medium type, the availability of energy and the displacement characteristics of the examined vessels. These results for the global fleet indicate that savings depending on storage system, vessel condition and vessel type could be up to 0.32 million tonnes in NOx, 0.07 million tonnes in SOx and 4.1 million tonnes in CO2. These represent a maximum 14% of reduction in dry bulk sector and 1.8% of world's fleet emissions.

► Global shipping makes a significant contribution to CO2, SOx and NOx emissions.
► We examine noon reports from a fleet of bulk carriers to identify the amount engine is operating off design.
► A hybrid propulsion system is proposed that uses multiple diesel–electric generators and battery storage.
► Analysis indicates hybrid may give an attractive rate of return as well as emissions savings in emissions.
► Implementation will require review of class society regulations.

Approximately 80% of world trade by volume is carried by sea (UNCTAD, 2008). In 2007 it is estimated that international shipping was responsible for approximately 870 million tonnes of CO2 emissions, or 2.7% of global anthropogenic CO2 emissions (IMO, 2009). Domestic shipping and fishing activity bring these totals to 1,050 million tonnes of CO2, or 3.3% of global anthropogenic CO2 emissions. Despite the undoubted CO2 efficiency of shipping in terms of grammes of CO2 emitted per tonne-km, it is recognised within the maritime sector that reductions in these totals must be made (IMO, 2009). Shipping is responsible for a greater percentage share of NOx (∼37%) and SOx (∼28%) emissions (AEA Energy & Environment, 2008) and recent legislation is aimed at reducing these emissions through the introduction of emission control areas and requirements on newly built marine diesel engines (MARPOL, 2005).
Costs per kilowatt hour for batteries range from $90 for lead acid to $110 for Sodium/nickel chloride to $300 for Vanadium–Bromine to $600 for Lithium Ion.
The principal disadvantage of Lithium Ion batteries in this application is their large cost which exceeds 600$/kWh. Lead acid batteries appear to be a more economic solution. However, the low material resistance in the marine environment, corrosive failures and the short life period of 400 complete charges and discharges, make them more expensive in the life cycle of the ship. Lead acid batteries suffer from a quick voltage drop and in a long period of storage from self-discharging.
The main engine cost is approximately 250 $/kW. However, the typical cost of diesel generator engines is significantly higher than the main engine. A typical price per kW of diesel generators is 350 $/kW (Fragkopoulos, 2007). Although the initial cost of such engines is higher, the advantage of prefabrication and the modular application of the machinery components, leads to saving in construction man-hours in shortening the whole construction time of the vessel. Thus, potentially the total construction costs are reduced (Gertsos et al., 2006) although this is not investigated further here. Furthermore, cost difference exists due to the installation of electric motors, cabling and other components of the electrical installation. An overall 6% increase in machinery cost will be assumed as the cost of the electrical components. The machinery cost is taken to be 30% of the total cost of the ship (Papanikolaou, 1994). Thus the extra machinery cost represents a 2% increase in the overall price of the vessel. The market value of the vessels is taken according to the current market state (Cotzias Shipping Group, 2010). Concerning the fuel price market, an average value for the year is taken equal to 520 $/tonne (Petromedia LTD, n.d.). However, the trend of fuel prices shows that its price is likely to be increased in future years. As a result, a rate of price increase of 10% each year is assumed. It is further assumed that after 25 years, the storage system can be sold for 10% of the original cost.
For an initial evaluation of the economics of the hybrid concept the dynamic index of Internal Return Rate (IRR) is adopted.... Two scenarios are evaluated.  Scenario 1 is an all electric ship concept.  Scenario 2 involves the use of a conventional two-stroke main engine with a PTO/PTI system.  Ranges of Internal Rates of Return of storage and diesel generators investments for two scenarios follow:
  • Handysize 8 MW Sodium Nickel-Chloride (11.5 - >100)
  • Handysize 8 MW Vanadium Bromine (2.0 - 25.1)
  • Handymax 8 MW Sodium Nickel-Chloride (0 - 0) 
  • Handymax 8 MW Vanadium Bromine (0 - 0)
  • Panamax 15 MW Sodium Nickel-Chloride (20.0 - >100)
  • Panamaz 15 MW Vanadium Bromine (1.4 - 16.6)
  • Post-Panamax 5 MW Sodium Nickel-Chloride (71.7 - >100)
  • Post-Panamax 5 MW Vanadium Bromine (33.0 - >100)
  • Capesize 4 MW Sodium Nickel-Chloride (0 - 61.6)
  • Capesize 4 MW Vanadium Bromine (0 27.6)
The value is >100% because in Handysize, Panamax, Post-Panamax, the payback period is 8, 19, 3 and 1 years, respectively, instead of 25 in other cases.
The study has shown that installing hybrid power technology on-board dry bulk ships can save fuel up to 1.27 million USD (at the price of 520$/tonne) per vessel and per year, assuming that the 60% of the time ship sails in laden and 40% in ballast condition. This value depends as well on the ship's dimensions, the storage medium adopted and the demand for energy availability. The emission reduction is achieved primarily through reducing the consumption of fuel and further reductions could be achieved by optimisation of the combustion process or the operation of other engine components. The combination of a hybrid energy storage and the flexibility that offers in the coupling with the propulsor, along with other possible improvements in hydrodynamics based improvement in ship energy efficiency should allow a step improvement in overall efficiency of ship propulsion systems (estimated between 2% and 10%) although this requires further systematic design studies.

by Eleftherios K. Dedes, Dominic A. Hudson and Stephen R. Turnock; all of Fluid Structure Interactions Research Group, School of Engineering Sciences, University of Southampton, Southampton S017 1BJ, UK
Energy Policy via Elsevier Science Direct
Volume 40; January, 2012; Pages 204-218
Special Issue: Strategic Choices for Renewable Energy Investment
Keywords: Hybrid electric propulsion for ships; Emission reduction; Fuel consumption reduction

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