The presence of >1ppm concentrations of hydrogen sulfide (H2S) in biogas can pose a challenge for the implementation of off-grid biogas-SOFC energy systems in rural Uganda. This study investigated the potential of biochars made from cow dung (CB), jackfruit tree leaves (LB) and jackfruit tree branches (TB) to remove H2S from biogas to below the 1 ppm threshold and compared the findings to the use of commercially available activated carbon (AC). The surface area, pore structure, particle size, trace-metal content, pH and alkalinity were characterized and their influence on the H2S adsorption capacity was qualitatively evaluated. Furthermore, a Central Composite Design (CCD) was used to determine the influence of the gas hourly space velocity (GHSV) and inlet H2S concentration on the H2S adsorption capacity. AC was observed to exhibit the highest H2S adsorption capacity, followed by CB, LB and TB, in that order. The specific surface area (SSA) and micropore volume were argued to be the determining factors to explain the differences in H2S adsorption capacity. Furthermore, the GHSV and inlet H2S concentration were both found to be negatively correlated to the H2S adsorption capacity. The interaction effect between both parameters was observed to be insignificant and no optimum was found by the response surface analysis. The comparison of the research findings with similar studies highlighted the complexity involved in comparing the H2S adsorption capacities of biochars between studies. It is therefore suggested that a reference benchmark breakthrough test should be created and used by future studies. Ultimately, the insights of this study may contribute to the implementation of cost-effective biogas-SOFC systems in rural Uganda. ... Read more

The interest in alternative fuels in the maritime sector is growing due to increasing concerns of the effect of harmful emissions. Hydrogen in combination with a fuel cell has a high potential to be a more environmental friendly solution than the commonly used fossil fuel systems. However, the use of hydrogen encounters problems looking at the fuel storage density, safety and the operating profile of a vessel. Hydrogen storage in a material, such as sodium borohydride, has the potential to overcome or mitigate these problems.
The goal of this research is to provide an insight in the technical feasibility of this technology for the maritime industry. Therefore, the following research question will be answered: How does a technical design of a power train using sodium borohydride as hydrogen storage material on-board of vessels perform in terms of power and energy density and in a transient load? There are three important elements in this system: the sodium borohydride, water and the spent-fuel. The hydrogen in sodium borohydride can be released in a reaction with water, resulting in a hydrogen gas and liquid spent-fuel. The energy and power density is determined using the weights and volumes of these separate elements. Both the least, and most compact configurations are considered to determine the operating range of this technology. A model is made and measurements are done on the power demand of the `Stad Amsterdam' to investigate the performance of the system on dynamic behaviour. The most slow components, such as the mix-chamber, fuel cell and the battery system, are dynamically modelled to identify the critical elements in the design.
In the first configuration, all fuels are stored in separate tanks and all the water needed for the process is stored on-board. This results in a low volumetric energy and power density. To improve the density of the system multiple concepts are considered: a concentrated or dry fuel, a volume-exchange tank, on-board water generation and a filtered spent-fuel. Implementing these concepts results in a compact configuration which is more competitive with diesel systems and other alternative fuels. The hydrogen buffer in the mix chamber, the fuel cell and the battery systems are the most important elements influencing the performance of the system in a transient load. A more constant behaviour can be expected by making use of multiple mix chambers. The safety on-board of the vessel still needs attention, especially around the places containing hydrogen gas and where hydrochloric acid is present. It can be concluded that this technology has a high potential for many types of applications in the maritime industry. It will be technically feasible to implement such a system on-board of a vessel. The harmful emissions in this industry can be decreased significantly using this system. Cost and safety of the system are a challenge and, therefore, further research has to be done to realise the implementation of these systems on-board of vessels. ... Read more

Global warming, caused by the excessive release of greenhouse gases due to the use of fossil fuels, is the main reason why a switch to renewable energy sources is becoming a necessity. A renewable energy source with a high potential to contribute to the energy needs worldwide is biomass. Biomass can be used for the production of electricity and heat or for the production of chemicals for a wide range of applications.

The overall challenge for the thermal conversion of biomass is the development of robust and efficient technologies to process biomass with a high conversion efficiency into a useful and clean product. Biomass pyrolysis has great potential to convert a wide range of biomass species into various products.

In this project, the decomposition characteristics of two high-potential biomass feedstocks, Miscanthus and Ulva, were investigated. The grass species Miscanthus has been in the spotlight as a potential biomass feedstock due to its rapid growth, high biomass yield potential and high calorific value. There is a growing interest in the seaweed species Ulva as a potential biomass feedstock due to its rapid growth and due to the fact its use may lead to a reduction of ecological problems (Ulva is a major sea pollutant).

Decomposition characteristics of Miscanthus and Ulva at slow heating rates were investigated with a thermogravimetric analyser. Proximate analysis results and mass loss rate graphs were obtained. The shapes (peaks) of the mass loss rate graphs were linked to the different biomass components present in Miscanthus and Ulva.

For the decomposition at fast heating rates pyrolysis experiments were carried out in a Pyroprobe reactor. The solid, liquid and gaseous product yields were analysed for different final pyrolysis temperatures. The compositions of the gas fractions were analysed using a micro gas chromatograph. The influences of pyrolysis temperature and biomass feedstock composition on the product yields and compositions were linked to different pyrolysis mechanisms

In order to determine the role of different biomass components in the pyrolysis process, the decomposition of the biomass feedstocks and pyrolysis kinetics are further investigated by modelling the mass loss rates of Miscanthus and Ulva during slow pyrolysis obtained from thermogravimetric analysis. For this purpose, the independent parallel reaction (IPR) model was used.

The experimental and modelling results obtained in this study for Miscanthus and Ulva help characterising the two biomass species. Based on the decomposition rates, product yields and gas compositions, a better understanding of the pyrolysis reaction mechanisms of the different constituents of Miscanthus and Ulva is gathered. This is a contribution to the knowledge required to optimise thermal conversion processes for different biomass species. ... Read more