This chapter explores the critical role of fuels for marine propulsion. Maritime shipping is vital for international trade and is often considered a relatively energy-efficient mode of transport. Yet, maritime shipping is heavily dependent on fossil fuels and contributes approximately 3% of annual global greenhouse gas emissions. This chapter discusses the different fuels used in maritime shipping and examines transitions toward alternative fuels, such as biofuels, electrofuels, and hydrogen. The chapter also highlights the role of policy and infrastructural needs for scaling-up transitions to low- and zero-carbon energy sources in the maritime shipping industry.

Demand for biofuels will likely increase, driven by intensifying obligations to decarbonize aviation and maritime sectors. Sustainable biomass is a finite resource, and the forest harvesting level is a topic of ongoing discussions, in relation to biodiversity preservation and the short-term role of forests as carbon sinks. State-of-the-art technologies for converting lignocellulosic feedstock into transportation biofuels achieves a carbon utilization rate ranging from 25% to 50%. Mature technologies like second-generation ethanol and gasification-based processes tend to fall toward the lower end of this spectrum. This study explores how electrification can enhance the carbon efficiency of biorefinery concepts and investigates its impact on energy, economics and greenhouse gas emissions. Results show that electrification increases carbon efficiency from 28% to 123% for gasification processes, from 28% to 45% for second-generation ethanol, and from 50% to 65% for direct liquefaction processes. Biofuels are produced to a cost range 60–140 EUR/MWh-biofuel, depending on the chosen technology pathway, feedstock and electricity prices. Notably, production in electrified biorefineries proves cost-competitive when compared to pure electrofuel (E-fuels) tracks. Depending on the selected technology pathway and the extent of electrification, a reduction in GHG emissions ranging from 75% to 98% is achievable, particularly when powered by a low-carbon electricity mix.

The per capita municipal solid waste (MSW) generation per day in Ghana is estimated to be 0.47 kg/person/day, which translates to over 14,000 tonnes of solid waste generation daily. The disposal and management of this amount of solid waste has been challenging worldwide, and in Ghana, this is evident with the creation of unsanitary dumping sites scattered across most communities in the country, especially urban communities. The indiscriminate disposal of solid waste in Ghana is known to cause flooding, the pollution of water bodies, and the spread of diseases. The purpose of this review is to highlight the prospects of waste incineration with energy recovery as a waste-to-energy (WtE) technology which has contributed immensely to the disposal and management of MSW in nations worldwide (especially developed ones). The review indicates that waste incineration with energy recovery is a matured waste-to-energy technology in developed nations, and there are currently about 492 waste incineration plants in operation in the EU, over 77 in operation in about 25 states in the USA, and about 1900 in operation in Japan. Waste incineration with energy recovery is also gradually gaining prominence in developing nations like China, Brazil, Bangladesh, Nigeria, Indonesia, and Pakistan. The adoption of waste incineration with energy technology can reduce Ghana’s overdependence on fossil fuels as primary sources of energy. It is, however, recommended that a techno-economic assessment of proposed waste incineration facilities is performed considering the MSW generated in Ghana. Additionally, it is also recommended that the possibility of incorporating the use of artificial intelligence technology into the management of MSW in Ghana be investigated.

The use of waste incineration with energy recovery is a matured waste-to-energy (WtE) technology. Waste incineration can reduce the volume and mass of municipal solid waste significantly. However, the generation of high volumes of polluting flue gases is one of the major drawbacks of this technology. Acidic gases are constituents in the flue gas stream which are deemed detrimental to the environment. The wet flue gas desulphurization (FGD) method is widely employed to clean acidic gases from flue gas streams, due to its high efficiency. A major setback of the wet FGD technology is the production of wastewater, which must be treated before reuse or release into the environment. Treating the wastewater from the wet FGD presents challenges owing to the high level of contamination of heavy metals and other constituents. Membrane distillation (MD) offers several advantages in this regard, owing to the capture of low-grade heat to drive the process. In this study the wet FGD method is adopted for use in a proposed waste incineration plant located in Ghana. Through a mass and energy flow analysis it was found that MD was well matched to treat the 20 m(3)/h of wastewater generated during operation. Thermal performance of the MD system was assessed together with two parametric studies. The thermal efficiency, gained output ratio, and specific energy consumption for the optimized MD system simulated was found to be 64.9%, 2.34 and 966 kWh/m(3), respectively, with a total thermal energy demand of 978.6 kW.

In combined heat and power (CHP) plants, reverse osmosis (RO) based flue gas condensate treatment processes have shown several intrinsic problems including bio-fouling and higher electrical energy demand. In contrast, novel membrane separation techniques can operate at reduced electricity demand, provide better separation efficiency and are not prone to bio-fouling. As shown in our previous studies, membrane distillation (MD) has proven itself as a promising technique for such applications. MD is a thermally driven separation process where district heating (DH) can be considered as a viable heat source to comply with its required thermal energy demand. In the present study, a DH driven MD process is presented and evaluated. Performance model of MD system was first developed in MATLAB, based on previously performed experiments where semi-commercial air gap membrane distillation (AGMD) module was considered. This empirical model was then employed to design DH driven MD system in Aspen Plus for flue gas condensate cleaning at industrial scale. Furthermore, in order to evaluate the potential of the technology, feasibility study of the proposed system was performed. Results show the techno-economic viability of the presented DH integrated MD system. The estimated unit flue gas condensate treatment cost is found as low as 2.38 $/m³.

A novel integrated renewable-based energy system for production of synthetic diesel is proposed and simulated in this study. This system merges solid oxide electrolyser (SOE), entrained gasification (EG) and Fischer-Tropsch (FT) technologies. Two case scenarios are considered here. In the first case, the electrolyser unite produce syngas through co-electrolysis of steam and carbon dioxide, while in the second case only steam is electrolyzed. The effects of SOEC and EG operating pressure and temperatures on the system performance in each case are investigated and compared. It is shown that the operating condition of electrolyser subsystem has a more considerable effect on the performance of the integrated system as compared to the gasification subsystem. Also waste heat recovery results in about 43 and 2 percentage point increase in energy and exergy efficiency, respectively. It is also shown that internal recovering of oxygen has the best effect on the system performance.

In this study, a novel integrated system for production of advanced synthetic diesel is proposed and analyzed from thermodynamic, economic, and environmental perspectives. This system consists of a solid oxide electrolyzer, entrained gasification, a Fischer Tropsch reactor (FT), and upgrading processes. Eleven different combinations of precursor syngas production through steam and CO, co-electrolysis and biomass gasification are investigated. Results show that an increasing share of produced syngas in the electrolyzer unit results in higher system efficiencies, emission savings, and levelized cost of FT diesel. Moreover, different options of heat and mass :flow recovery are considered. It is concluded that recovery of produced medium pressure steam in the system is highly beneficial and recommended. Besides, it is shown that while oxygen recovery is the best choice of mass recovery, hydrogen recovery for internal use has adverse effect on the system performance.

Production of synthetic hydrocarbon fuels as a means for renewable energy storage has gained attention recently. Integration of solid oxide co-electrolysis of steam and carbon dioxide with the Fischer-Tropsch process to transform renewable electricity into Fischer-Tropsch diesel is one of the promising suggested pathways. However, considering the intermittency of produced renewable electricity such integration will have a low capacity factor. Besides, locating a reliable source of carbon dioxide near the installed integrated system may prove to be difficult. A novel integration for production of Fischer-Tropsch diesel from various renewable sources is suggested in this study. The proposed integrated system includes solid oxide electrolysis, entrained gasification, Fischer-Tropsch process and an upgrading system. Gasification is assumed to have a continuous operation which increases capacity factor of the integrated system. Carbon dioxide supplied via gasification of biomass provides a reliable source for on-site co-electrolysis. Technical capabilities of the proposed integrated system examined by investigating performance in relation with electricity, and diesel demand of four different European cities. Results show that the proposed system is capable of supplying Fischer-Tropsch diesel of between 0.9-32% of the annual diesel demand for road transportation respective to the location of installation, with a high emission savings (around 100%). Cost of produced diesel is not competitive with conventional diesel for all cases, even when all the other by-products were assumed to be sold to the market.

A pressurized solid oxide electrolyser (SOE) system for syngas production is analyzed. The system is modeled and analyzed considering energy and exergy aspects. The main consideration is to quantify the effect of operating pressure on the system performance when syngas is used for synthetic diesel production. At elevated pressures methanation reaction within the electrolyser causes internal production of methane from syngas. The results show that methane fraction increase from almost zero percent to 14% at 25 bar. Since methane is not a favorable outcome of this system, elevated pressure has adverse effect on the total system performance and consequently system efficiency drops by about 20% points by increasing the electrolyser operating pressure from atmospheric to 25 bar. This effect also results in higher levelized cost of syngas at elevated pressures. Effects of other operating parameters like temperature and utilization factor on the syngas production rate and system performance are also explored. In addition, relative irreversibility of each component is estimated. It is concluded that the solid oxide electrolyser has the highest relative irreversibility amongst other system components which can be minimized by changing operating temperature. At last but not least, levelized cost of produced syngas is estimated.