The CFD modeling based on the two-fluid model (TFM) was used on studying the novel indirectly heated bubbling fluidized bed steam reformer (IHBFB-SR). This is a collaborative project between Petrogas and TU Delft for testing the advance’s reactor configuration, which indirectly supplies the heat via radiant burner on the center toward the surrounding bed, thereby improving heat transfer efficiency and reduced the losses. The present work aimed to observe the hydrodynamic and heat transfer of the reactor by first employing air as the fluidizing gas and corundum (Geldart B size) as the bed material. The minimum fluidization condition, bubbles development, and voidage profile are the main objectives for the hydrodynamic simulation. In the heat transfer study, the effect of radiative heat transfer, bubbles and voidage profiles, and different radiative models (P1 and DO) on the heat transfer mechanism were examined. The 2D and 3D models were built, and three drag models: Gidaspow, adjusted Syamlal, and EMMS/Bubbling was employed. The simulation results were then compared to the experimental data obtained, such as minimum fluidization flowrate, pressure drop, bed expansion, and temperature profile on a specific flow rate.

Initially, a grid independency test was conducted using five different grid sizes. It is concluded that the appropriate grid size for simulating the IHBFB-SR with a bed material particle size of 0.496 mm should be at least 7.5 mm or 15 times the corundum particle size. The present research used 2.5 mm or five times dp. The minimum fluidization obtained was in the range of 14-16 kg/h based on both 2D and 3D simulation. Nonetheless, if primarily refers to the 3D model results, the minimum fluidization condition should lie around 14 kg/h. Three drag models have also been compared. It was found that the adjusted Syamlal gives the closest result compared to the experimental data. Nevertheless, the drag modification, based only on minimum fluidization conditions like modified Syamlal, tends to overpredict the drag coefficient on the entire range of solid volume fraction. There are also no significant differences in the bubbles or voidage profiles among those three drag models. Adjusted Syamlal has a slightly larger bubble while Gidaspow and EMMS bubbling has a bit smaller one. The expected better result of using the EMMS bubbling drag model does not appear to have a considerable impact on the case of Geldart B or larger particles. There was also an underprediction of pressure drop and bed expansion on the simulation. Two major factors were the absence of proper particle shape representation through a sphericity factor and the lack of precise simulation of particle size distribution. Only a perfect rounded sphere of corundum with a sphericity factor of one and one uniform size of the particle was assumed.

In the case of heat transfer simulation, bubbles and voidage effect firstly studied. It was found that the increase of the bubbles frequency and size, as represented on the voidage profile, would improve the heat transfer process indicated by the increase of the heat flux. The bubbles’ occurrence on the bed plays a critical role in the mass transfer’s improvement from and to the vicinity of the radiant burner wall, thus increasing heat transfer. In contrast with the voidage, the increase of superficial gas velocity does not directly influence the heat flux. It was also proved that the radiative heat transfer improved the overall heat flux in this bubbling fluidized bed reactor by about 16.11 %. Though it appears small, this contribution fits the range of other proven works, with a similar operating environment and particle size used. There are two different radiative models performed in the simulation: first-order spherical harmonics method (P1) and discrete ordinate method (DO). Both models presented a similar trend, with P1, has a slightly higher magnitude. However, the P1 model shows a peculiar result of having a strange lower temperature lower on the bottom part of the bed. On the contrary, that is not the case for the DO, which is well known for its accuracy but a higher computational cost demand. It is then concluded that for the present setup, the DO model could perform better. Lastly, the overall heat transfer process was investigated. Since no specific experimental data available for validating the heat transfer properties, only the final steady temperature values of five different thermocouples were used. Comparing these two, it was found that the present model did not give satisfactory results due to overprediction of air temperature above the bed and underprediction of bed temperature at the same time. Some improvements are required, as will be presented in the recommendations section.

Presently, the majority of the worlds energy supply is dependent on fossil fuels. As these fuels area limited resource and have significant negative side effects, the way humanity uses these is unsustainable and other sources of energy have to be found. One of these sustainable energy sources is plant-derived biomass. However, biomass cannot be efficiently used in its natural form and needs to be converted to other products through processes such as pyrolysis and gasification. Pyrolysis will be the focus of this thesis, as fast pyrolysis of Miscanthus is studied for the BRISK 2 project at Process & Energy (TU Delft). However, the current setup used for pyrolysis research does not provide a complete mass-closure of the experiments, with only 80% of the total mass accounted for in the char, tar and gaseous yields. In order to improve this closure, four different methods were developed and investigated during this thesis. All of the pyrolysis experiments were performed in a Pyroprobe 5200. The pyrolysis parameters were comparable to fast pyrolysis, with a high heating rate of 600°C/s, a low residence time of 10 s and a Final Pyrolysis Temperature between 600°C and 1000°C. The objective of the first adjustment was to improve the purge flow stability, reduce the amount of blockages in the system and increase the accuracy of the experiments. The flow meter, controlling the purge flow, was replaced with a mass-flow controller and a tube in the setup was simplified and shortened. No further blockages were observed and the total mass-closure improved on average by 7.85 wt% over the temperature range of 600-1000°C, with an increase at every temperature. The second considered element was the homogeneity of the biomass. Two biomass feedstocks were investigated, the first feedstock consisted of inhomogeneous pellets grinded down to a size less than 80μm, while the second type was homogenized biomass of a size of less than 200μm. Both biomass types performed comparably to each other and better than the previous data collected with the setup. At 600°C the inhomogeneous biomass performed better, while at 700°C the homogeneous biomass gave a higher yield. The last two experimental series both focused on gravimetrically measuring the tars collected in the condenser of the setup, which was not gravimetrically measured before. The first of these methods removed the condenser in favour of a direct capture in a quartz trap. This gave a maximum yield increase of 1.14 wt% at 700°C. However, concerns of contaminating the gas mixture with tars arose, therefore this method was not investigated at higher temperatures. In the second technique, the 2ml of isopropanol in the condenser was evaporated from a glass Petri dish, leaving the tars behind. This method was explored over a larger temperature range (600-1000°C), yet only provided a maximum increase of 1.5 wt% at 1000°C, while giving significant fluctuations between experiments. Thus proving that neither of these methods is a suitable way of gravimetrically measuring the condenser.

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.