To keep the global warming of the Earth to a minimum, the greenhouse gas emissions need to be reduced. Van Oord aims to be carbon neutral by 2050; therefore, Van Oord is exploring alternative fuels. Ammonia is a promising option to use as a fuel due to the forty times lower well-to-wake emissions than MGO when it is produced with green energy. There is no carbon content in ammonia. Furthermore, the expected cost of using ammonia as a fuel is lower than other competitive 'green' fuels, such as hydrogen or methanol, due to the lower storage or fuel fabrication cost of ammonia. The goal of this research is to determine if and when it is economically viable to use ammonia as a fuel to decarbonize a trailing suction hopper dredger (TSHD). This is expressed in cost per dredged material [€/m^3].
Ammonia needs to be handled, stored and consumed taking into account safety precautions to have a safe operable ship. Additionally, ammonia has poor combustion characteristics, and therefore a promoter such as hydrogen (7-11%) or MGO (40-60%) is necessary to initiate the combustion. Additionally, internal combustion engines (ICE) using ammonia as a fuel are expected to have a low transient load capability. Therefore, if there is no MGO present, the dynamic loading capability of the ICE with the load variation of the dredging process is a challenge. The same challenge applies for a Solid oxide fuel cell (SOFC), where the SOFC does hardly have transient load capabilities.
A TSHD currently has an ICE capable of dynamic loading, and the main reasons for this transient load is the change in propulsion power, which is dependent on the friction of the draghead and the sailing speed of the vessel. Furthermore, a sudden change in mixture density in the dredging tube during dredging will result in a sudden transient load. To cope with these transient loads, the energy supply on board of a TSHD must have transient load capabilities.
A fuel consumption model has been developed to compare five drive train configurations for the dredging project Kustlijnzorg with an operational profile of 30 days with respect to the original drivetrain. The total power demand [kW] and the transient load [kW/s] was included on a boolean way in this model. When the power demand or the transient load was too high then the model would stop. By means of this model, the main particulars of the engines, fuel cells and batteries regarding power and energy were determined. The output of this model was the amount of fuel consumed during 30 days. This fuel consumption model was validated with another project.
The Construction Industry Research and Information Association (CIRIA) has developed a method to valuate a TSHD. With this CIRIA methods, the value of a conventional TSHD is determined and compared with the value of the ammonia driven configurations. The value of a new vessel that operates on ammonia can be estimated with the help of a sustainability factor. It is found that the weekly cost of the vessel is mainly dependent on; the value of the vessel, which is dependent on the installed power and cost of technology, the fuel consumption, the cost of fuel and the carbon tax.
Currently, it is not economically feasible to use ammonia as a fuel to decarbonize a TSHD. So, not with an ICE or SOFC. However, when green ammonia is used in combination with a SOFC, then a TSHD can be fully decarbonized. In order to make ammonia an economically feasible option for a TSHD, the price of MGO and carbon has to increase, or the price of the SOFC and ammonia (grey and green) has to decrease significantly.
Currently it is unclear if the carbon tax in the future applies to tank-to-wake (TTW) or well-to-wake (WTW) emissions. If the WTW emissions are taxed, then grey ammonia is never a better choice than MGO in terms of cost. Which is also the case when considering the CO2 equivalent emissions.
To conclude, it is currently not economically feasible to decarbonize a TSHD using ammonia as a fuel based on the cost per dredged material [€/m^3]. The limited transient load capabilities of drive train configurations on ammonia, need a battery or MGO to cope with the transient load of a TSHD. Future progress in the technology or developments in the reduction of transient loads could make ammonia as a fuel for a TSHD a better option. Finally, future developments in the price of: carbon, ammonia and MGO can make it economically feasible to decarbonize a TSHD.