Development of a spatially and timely resolved CFD model of a steam sterilizer to predict the load temperature and the theoretical inactivation of bacteria based on sterilization parameters

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Multi-scale modelling of fluidized bed biomass gasification using a 1D particle model coupled to CFD

For many fluidized bed applications, the particle movement inside the reactor is accompanied by reactions at the particle scale. The current study presents for the first time in literature a multi-scale modelling approach coupling a one-dimensional volumetric particle model with the dense discrete phase model (DDPM) of ANSYS Fluent via user defined functions. To validate the developed modelling approach, the current study uses experimental data of pressure drop, temperature and gas composition obtained with a lab-scale bubbling fluidized bed biomass gasifier. Therefore, a particle model developed previously for pyrolysis was modified implementing a heat transfer model valid for fluidized bed conditions as well as kinetics for char gasification taken from literature. The kinetic theory of granular flow is used to describe particle¿particle interactions allowing for feasible calculation times at the reactor level whereas an optimized solver is employed to guarantee a fast solution at the particle level. A newly developed initialization routine uses an initial bed of reacting particles at different states of conversion calculated previously with a standalone version of the particle model. This allows to start the simulation at conditions very close to stable operation of the reactor. A coupled multi-scale simulation of over 30 s of process time employing 300.000 inert bed parcels and about 25.000 reacting fuel parcels showed good agreement with experimental data at a feasible calculation time. Furthermore, the developed approach allows for an in-depth analysis of the processes inside the reactor allowing to track individual reacting particles while resolving gradients inside the particle.This project has received funding from European Union's Horizon 2020 Research and Innovation Programme under grant agreement number 731101 (BRISK II). Furthermore, the financial support of the COMET Module project BIO-LOOP (Austrian Research Promotion Agency - FFG - Project Number 872189) funded by the federal government of Austria and the federal province Styria is gratefully acknowledged. The authors want to thank Mario Blehrmühlhuber for conducting cold-flow simulations and evaluating the applicability of the DDPM for the developed model. We further want to thank Markus Braun for his helpful hints when using the DDPM and Simon Schneiderbauer for his advice regarding the coupling strategy.Publicad

Analysis of Heating Effects and Deformations for a STAF Panel with a Coupled CFD and FEM Simulation Method

Conventional sandwich panels are one of the cheapest and easiest solutions for forming the thermal building envelope of industrial buildings. They are pre-fabricated façade elements, of which millions of square metres have been produced and mounted every year. There is great potential to reduce the consumption of fossil fuels and CO2 emissions through the solar thermal activation of such a sandwich panel. In the course of the research project ABS-Network SIAT 125, a Solar Thermal Activated Façade (STAF) panel was designed which is to be optimised both thermally and structurally. This study shows a first version of a so-called ‘one way coupled’ thermal and structural analysis of a conventional sandwich panel compared to the STAF panel. For this purpose, the numerical methods of Computational Fluid Dynamics (CFD) and Finite Element Method (FEM) are used  together in one simulation environment. Furthermore, results from an outdoor test facility are presented where a first version of a STAF panel is tested under real climate conditions. The CFD model was positively evaluated by comparing measured and computed temperatures

Evaluation of heat transfer models at various fluidization velocities for biomass pyrolysis conducted in a bubbling fluidized bed

Four different models for heat transfer to the particles immersed in a fluidized bed were evaluated and implemented into an existing single particle model. Pyrolysis experiments have been conducted using a fluidized bed installed on a balance at different temperatures and fluidization velocities using softwood pellets. Using a heat transfer model applicable for fluidized beds, the single particle model was able to predict the experimental results of mass loss obtained in this study as well as experimental data from literature with a reasonable accuracy. A good agreement between experimental and modeling results was found for different reactor temperatures and configurations as well as different biomass types, particle sizes ¿ in the typical range of pellets - and fluidization velocities when they were higher than U/Umf=1.5. However, significant deviations were found for fluidization velocities close to minimum fluidization. Heat transfer models which consider the influence of fluidization velocity show a better agreement in this case although differences are still present.This project has received funding from European Union's Horizon 2020 Research and Innovation Programmeunder grant agreement number 731101 (BRISK II)

Effect of bed material density on the performance of steam gasification of biomass in bubbling fluidized beds

Steam gasification of lignocellulosic biomass in a bubbling fluidized bed reactor was analyzed by means of the composition of the producer gas, including tars, and temperature distribution in the reactor. The catalytic and sorbent effect of sepiolite particles was studied by comparison of the tars generated with those produced in a bed of olivine, widely used in biomass gasification applications. Sepiolite has a lower particle density, which influences the forces acting on fuel and char particles and leads to a more homogeneous distribution of them in the dense bed during the gasification process. Fluidized beds of sepiolite particles contribute to increase the heating value of the producer gas and its hydrogen content compared to gasification under the same operating conditions in olivine beds. Furthermore, the tar yield is around 25% lower when gasifying in sepiolite beds, reducing the requirement of secondary methods for tars removal. Long-term gasification tests were also conducted in a sepiolite bed to evaluate the mitigation of the sorbent/catalytic effect of sepiolite with time.This project has received funding from European Union’s Horizon 2020 Research and Innovation Programme under grant agreement number 731101 (BRISK II)

Low-temperature HS removal for solid oxide fuel cell application with metal oxide adsorbents

The desulfurization of biogas is essential for the successful operation of solid oxide fuel cells. H 2 S is one of the main components in biogas. In order to feed a solid oxide fuel cell, the contaminated gas has to be reduced to a certain degree. In this work, different parameters onto the desulfurization performance of commercially available desulfurization adsorbents were investigated. The experiments were carried out using a custom made lab-scale unit. Synthetic biogas was passed through the sorbent bed and the outlet H 2 S concentration was measured. Experimental runs in a fixed bed reactor were conducted to monitor H 2 S removal efficiency of a zinc oxide adsorbent, an adsorbent based on a mixture of manganese and copper oxide and a zeolite adsorbent. H 2 S removal efficiency was monitored under various operating conditions such as different temperatures, space velocities and inlet concentrations. This work provides useful data for adsorption tower design and process optimization

Thermal treatment of raw and pre-treated wastes from the paper industry

In this study, the thermal treatment of two types of waste from the paper industry was investigated, paper mill sludge and sewage sludge from biological wastewater treatment plants. Hydrothermal carbonisation (HTC) and torrefaction were investigated as sustainable alternatives for solid biofuel production. Untreated samples and samples chemically pre-treated with alcoholic vinegar were subjected to torrefaction at 350 °C in N2 atmosphere, and the exhaust gases were analysed. HTC was performed at 250 °C with a residence time of 4 h. The feedstocks and the biochars produced were characterised by different analytical methods, and the effects of pre-treatment on fuel properties were studied. Both processes, HTC and torrefaction, showed inspiring results in the production of biofuels from paper industry wastes under the tested experimental conditions. A positive influence of pre-treatment on fuel properties (higher heating value, carbon content) of the obtained char was observed, and changes in the gas phase during torrefaction were observed

Adsorptive hydrogen chloride and combined hydrogen chloride–hydrogen sulphide removal from biogas for solid oxide fuel cell application

In order to reduce the toxic effect on solid oxide fuel cells performance caused by biogas contaminated with hydrogen chloride and hydrogen sulphide, the purification of biogas is essential. Adsorptive gas purification is a highly auspicious technology to provide pollution-free biogas for solid oxide fuel cell-based power units. In this work the authors examined the influence of different parameters onto the adsorption capacity of three commercially available sorbents. Experimental runs in a laboratory glass downflow fixed-bed reactor were carried out to analyse the adsorption capacity of a potassium carbonate impregnated activated carbon and two sorbents based on a mixture of aluminium oxide and silicon dioxide. Hydrogen chloride removal was accomplished with the impregnated activated carbon and metal oxide-based sorbents. Hydrogen chloride adsorption capacity was analysed under space velocities 8000 and 16,000 h −1 . In addition, the effect of a hydrogen chloride inlet concentration of 100 and 1000 ppmv was investigated. Furthermore, pellets in the size of 3–4 mm in diameter were crushed into a fraction between 500 and 1000 µm to investigate the influence of particle size on hydrogen chloride adsorption capacity. Additionally, the combined adsorption of hydrogen chloride and hydrogen sulphide was realized using the impregnated activated carbon. The experimental runs and the results obtained in this work provide useful data for designing an adsorption reactor to clean up biogas and optimizing the process

Towards a wastewater energy recovery system: The utilization of humidified ammonia by a solid oxide fuel cell stack

This study presents the results of investigations on performance and durability of an ammonia-supplied MK352 solid oxide fuel cell stack with electrolyte supported cells and chromium based interconnects. The performance evaluation revealed no significant differences between ammonia and equivalent hydrogen/nitrogen gases as fuel, which was a result of the excellent ammonia conversion rates up to 99.99%. When using high ammonia flow rates, temperature measurements inside the stack revealed a temperature drop due to the endothermic ammonia decomposition of up to 18.8 K, which proceeded preferentially at the fuel inlet region. An 1000 h durability test with humidified ammonia in 80% fuel utilization condition was performed, which resulted in a stack performance degradation rate of about 1.1%/1000 h. Tests with hydrogen/nitrogen fueled reference stacks revealed similar degradation rates during the initial 1000 h. Post-mortem analyses by scanning electron microscopy and energy-dispersive X-ray spectroscopy revealed no significant micro-structural deterioration of the functional layers of the anode, but nitriding effects on the nickel contact meshes and chromium nitrides were found in the material structure of the interconnects. Also, an oxide layer was found between interconnect and contact meshes at the anode, which appears to be the main cause of the performance degradation