Comparative feasibility study of combined cycles for marine power system in a large container ship considering energy efficiency design index (EEDI)

This study investigates an appropriate combined cycle as the electric propulsion system in a large container ship. A gas turbine combined cycle and molten carbonate fuel cell-steam turbine cycle are considered; the gas turbine uses LNG or hythane fuels. Because it is difficult to choose an appropriate propulsion system from only one perspective, comprehensive and unbiased analyses refer to the system performance, eco-efficiency, and economic feasibility for three configurations. An LNG-fueled COGES (combined gas turbine and steam integrated electric drive system) seems to be a promising alternative with regards to economic feasibility as well as a greenhouse gas regulation. The following alternative is the molten carbonate fuel cell-steam turbine cycle. A hythane-fueled COGES has a relatively low economic feasibility but will be the sole propulsion system if the regulation of greenhouse gas emission from shipping is stringent. On the other hand, the carbon taxation and implementation of an incentive for hydrogen fuel may facilitate a greener shipping environment; the additional eco-friendly policy for the shipping industry needs to be provided, shortly soon.     

Experimental and numerical study of oxidant effect on hythane combustion

This paper reports on the experimental and numerical results of the hythane diffusion flame enriched by oxygen, realized in a coaxial burner characterized by a central jet of hythane injection with an internal diameter of d_fuel = 6 mm and an annular jet of oxidant injection with a diameter of d_ox = 18 mm. For velocity measurements, the Particle Image Velocimetry (PIV) technology is used. The numerical study is based on the K-ω-SST Turbulent Model and the Eddy Dissipation Model (EDM) for combustion. Firstly, a comparative study is carried out between experimental and numerical simulation of the flow dynamics in the hythane/Air + O₂ flame. Secondly, the numerical results show that the oxygen enrichment increases the temperature of the hythane flame and minimizes the formation of harmful gases into the environment.     

Extraction of hydrogen from a lean mixture with methane by metal hydride

Hydrogen/methane mixtures draw attention due to the idea of the injection of hydrogen into natural gas networks and biological production of biohythane by one- and two-step anaerobic fermentation/digestion methods. It is hard to extract hydrogen from dilute mixtures with methane by traditional separation processes, since hydrogen is the minor component with low partial pressure. Metal hydrides selectively absorb hydrogen and offer an opportunity to overcome the limitations of traditional separation methods. In the present paper, we present experimental results on the separation of a dilute mixture of hydrogen (10%) with methane in a flow-through metal hydride reactor with inlet mixture pressure of 0.95 MPa by the LaNi_4.8Mn_0.3Fe_0.1 intermetallic compound. Hydrogen was separated in one step with roundtrip (absorption/desorption) recovery of 74%. An exergetic analysis of the metal hydride separation of a binary mixture containing hydrogen was implemented and equations for hydrogen recovery and exergy efficiency of separation are obtained. Thermodynamic analysis shows that the exergy efficiency of the metal hydride purification has a clear maximum at hydrogen concentrations around 5–20%. The advantage of metal hydride purification is the absorption of the minor fraction from the feed, thus it is preferable for dilute mixtures and could be feasible for practical applications. With the use of low potential or waste heat to drive the reaction, it is possible to increase the efficiency of hydrogen purification by metal hydrides. The maximum exergy efficiency is 61% for 0.8 MPa outlet pressure, taking into account the quality of involved heat flows.     

Effect of ammonia concentration on hythane (H2 and CH4) production in two-phase anaerobic digestion

Co-production of hydrogen and methane by two-phase anaerobic digestion (AD) may offer a sustainable solution for the centralized treatment of food waste (FW), while ammonia accumulation is potentially encountered. A mesophilic two-phase AD was investigated for hydrogen and methane production from FW at varying ammonia concentrations. The process achieved a hydrogen yield of 47.7 mL/g VS and a methane yield of 335 mL/g VS by optimizing the organic loading rate (OLR) and recirculation ratio. Total ammonia nitrogen (TAN) concentration of 4044 mg/L corresponded to a threshold in the hydrogen reactor, above which ammonia would initiate inhibition of hydrogenogenesis and acidogenesis. Methane yield was recovered in the methane reactor after acute inhibiting effects of TAN below 5800 mg/L, while TAN above 6200 mg/L caused chronic inhibition of methanogens. Adjusting hydraulic retention time (HRT) and recirculation ratio in hydrogen and methane reactors reduced TAN to 960 and 2105 mg/L respectively, resulting in successful recovery was achieved in the hydrogen reactor but not in the methane reactor. The two-phase AD for methane and hydrogen production can be a promising solution for ammonia accumulation in AD from FW.     

Effects of hydrogen addition and Carbone dioxide dilution on the velocity field in non reacting and reacting flows

The evolution of anti-pollution standards and the optimization of combustion efficiency push the development of new fuels with high energy efficiency. It is necessary to develop new alternative fuel to improve the efficiency of conventional systems, reduce emissions (NO_x, SO_x, soot particles) and recover for its materials. A new fuel called bio-hythane, a mixture of natural gas up to 20% hydrogen and up to 50% Carbone dioxide, from the recovery of the waste from households and agriculture, via suitable digesters provides a source of renewable energy and usable, is a very interesting solution to improve emission standards and optimization of the combustion chambers.     

Effect of hythane enrichment on performance,emission and combustion characteristics of an ci engine

Although compression ignition engines have high torque output and thermal efficiency, they emit lots of NO_x and smoke emissions. Moreover, total number and percentage of compression ignition engine powered vehicles in road vehicles have been increasing recent years which is called as dieselisation in EEA term reports. Dieselisation is really hazardous for human life and environment. Therefore, some governments in Europe take action to forbid using diesel engine powered vehicles in city centers. Hydrogen and methane mixture which is named as hythane can be an alternative to restrict this negative situation. For this reason, 90% methane and 10% hydrogen gas mixture was used as additional fuel in diesel engine. According to obtained results, smoke emission was decreased 95.44% at the rate of 50% gaseous fuel at 2100 rpm engine speed. However, increase of THC, CO and NO_x emissions with hythane addition weren't prevented. Using hythane in conventional diesel engines as dual operation mode will be solution to diminish dieselisation problem in near feature.     

Techno-economic assessment of low-carbon hydrogen export from Western Canada to Eastern Canada,the USA,the Asia-Pacific,and Europe

The use of low-carbon hydrogen is being considered to help decarbonize several jurisdictions around the world. There may be opportunities for energy-exporting countries to supply energy-importing countries with a secure source of low-carbon hydrogen. The study objective is to assess the delivered cost of gaseous hydrogen export from Canada (a fossil-resource rich country) to the Asia-Pacific, Europe, and inland destinations in North America. There is a data gap on the feasibility of inter-continental export of hydrogen from an energy-producing jurisdiction to energy-consuming jurisdictions. This study is aimed at addressing this gap and includes an assessment of opportunities across the Pacific Ocean and the Atlantic Ocean, based on fundamental engineering-based models. Techno-economics were used to determine the delivered cost of hydrogen to these destinations. The modelling considers energy, material, and capacity-sizing requirements for a five-stage supply chain comprising hydrogen production with carbon capture and storage, hydrogen pipeline transportation, liquefaction, shipping, and regasification at the destinations. The results show that the delivered cost of hydrogen to inland destinations in North America is between CAD$4.81/kg and CAD$6.03/kg_, to the Asia-Pacific from CAD$6.65/kg to CAD$6.99/kg, and at least CAD$8.14/kg for exports to Europe. Delivering hydrogen by blending in existing long-distance natural gas pipelines reduced the delivered cost to inland destinations by 17%. Exporting ammonia to the Asia-Pacific provides cost savings of 28% compared to shipping liquified hydrogen. The developed information may be helpful to policymakers in government and the industry in making informed decisions about international trade of low-carbon hydrogen in both energy-exporting and energy-importing jurisdictions, globally.     

Sustainable biohythane production from algal bloom biomass through two-stage fermentation: Impacts of the physicochemical characteristics and fermentation performance

Algal bloom biomass, sourced from a freshwater lake in Chongqing, was pre-treated by hydrothermal pre-treatments with or without acid/alkali catalysts, and subsequently used as a substrate for sustainable biohythane production via fermentation. Fourier transform infrared (FTIR) spectroscopy analyses suggested hydrothermal acid/alkali pre-treatments significantly changed peak intensities of chemical compositions in algal bloom biomass. Derivative thermogravimetric (DTG) analyses showed more macromolecular substances hydrolysed after hydrothermal acid/alkali pre-treatments. When bloom algae were pre-treated with 1% HCl at 140 °C for 10 min, an optimal specific hydrogen yield (SHY) of 39.4 mL/g volatile solid (VS) was obtained, which is 38.2% higher than raw biomass. However, a 34.4% decrease in SHY occurred under hydrothermal pre-treatment with 1% NaOH due to the enhancement of Maillard reaction. When using the effluents in methane fermentation, specific methane yields (SMYs) were 177.1–276.8 mL/g VS. Two-stage process effectively reduced the total fermentation time by 22.7% compared with single-stage fermentation.     

Can the addition of hydrogen to natural gas reduce the explosion risk?

One of the main benefits sought by including hydrogen in the alternative fuels mix is emissions reduction - eventually by 100%. However, in the near term, there is a very significant cost differential between fossil fuels and hydrogen. Hythane (a blend of hydrogen and natural gas) can act as a viable next step on the path to an ultimate hydrogen economy as a fuel blend consisting of 8-30% hydrogen in methane can reduce emissions while not requiring significant changes in existing infrastructure.This work seeks to evaluate whether hythane may be safer than both hydrogen and methane under certain conditions. This is due to the fact hythane combines the positive safety properties of hydrogen (strong buoyancy, high diffusivity) and methane (much lower flame speeds and narrower flammability limits as compared to hydrogen). For this purpose, several different mixture compositions (e.g. 8%, 20% and 30% hydrogen) are considered. The evaluation of (a) dispersion characteristics (which are more positive than for methane), (b) combustion characteristics (which are closer to methane than hydrogen), and (c) Combined dispersion + explosion risk is performed. This risk is expected to be comparable to that of pure methane, possibly lower in some situations, and definitely lower than for pure hydrogen.The work is performed using the CFD software FLACS that has been well-validated for safety studies of both natural gas/methane and hydrogen systems. The first part of the work will involve validating the flame speeds and flammability limits predicted by FLACS against values available in literature. The next part of the work involves validating the overpressures predicted by the CFD tool for combustion of premixed mixtures of methane and hydrogen with air against available experimental data. In the end, practical systems such as vehicular tunnels, garages, etc. is used to demonstrate positive safety benefits of hythane with comparisons to similar simulations for both hydrogen and methane.     

Comparative life cycle assessment of hydrogen-fuelled passenger cars

In order to achieve gradual but timely decarbonisation of the transport sector, it is essential to evaluate which types of vehicles provide a suitable environmental performance while allowing the use of hydrogen as a fuel. This work compares the environmental life-cycle performance of three different passenger cars fuelled by hydrogen: a fuel cell electric vehicle, an internal combustion engine car, and a hybrid electric vehicle. Besides, two vehicles that use hydrogen in a mixture with natural gas or gasoline were considered. In all cases, hydrogen produced by wind power electrolysis was assumed. The resultant life-cycle profiles were benchmarked against those of a compressed natural gas car and a hybrid electric vehicle fed with natural gas. Vehicle infrastructure was identified as the main source of environmental burdens. Nevertheless, the three pure hydrogen vehicles were all found to be excellent decarbonisation solutions, whereas vehicles that use hydrogen mixed with natural gas or gasoline represent good opportunities to encourage the use of hydrogen in the short term while reducing emissions compared to ordinary vehicles.