Design of a novel cyclonic gasifying unit for biomass gasification using CFD tools

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2017 (EL)
Design of a novel cyclonic gasifying unit for biomass gasification using CFD tools (EN)

Nanousis, Dimos (EN)

School of Science and Technology, MSc in Energy Systems (EL)
Heracleous, Eleni (EN)
Skevis, George (EN)
Martinopoulos, Georgios (EN)
Dergiades, Theologos (EN)

Waste is something that is discarded. Waste can be classified by chemical characteristics, biological parameters or by their origin. It can be derived from food, or various sec-tors of human activity, even from vehicle or electrical usage. Organic waste derives from agriculture, horticulture, forestry, hunting and fishing, food preparation and processing. Europe follows the path of reuse or recycle and getting away from landfilling and burning which are even nowadays the major treatment methods for waste. And although some countries decreased the amount of waste they produce, some others increased it and the numbers of waste produced remain more or less the same. Municipal waste was produced more in the past. Better handling of waste is needed to reduce the amount of waste produced or gain from its treatment, for example in energy, electricity or new jobs. Europe strives to implement rules and follow the path of combination of the energy sec-tor with the environment and the economy. Organic waste in Europe tends to be used for energy production, heat, electricity, me-thane rich gas or compost and not landfilling. Landfilling is the major treatment method for waste in Europe but other technologies like gasification or combustion, energy or heat retrieval method are gaining ground and there is plenty of space for them to develop and become profitable. Gasification is a promising process that transforms a solid or liquid material into a partially oxidized gas, called “syngas”. It is a little tricky because it depends on many parameters, but with proper handling can have many advantages. Waste to Energy (WtE) is defined the usage of energy present in waste. Lately the thermal process of waste gains ground. Combustion, gasification, pyrolysis and not incineration and landfill. The most common transformation techniques are: fuel bed (stationary, moving, circulating), fluidized bed and entrained flow. Those techniques can be applied in some machinery, equipment and technologies, like grate firing, fluidized bed, rotary furnace, gasifiers and pyrolysers. They differ in principles and in handling of various substances included in the processes. Inorganic material cause problems, the cleaning procedures are expensive, ashes also interfere with the procedures. Cyclones catch many of these undesired impurities. Gasification handles solid or liquid materials and transforms them in gas/vapor phase and a solid phase. The gas phase is called “syngas”. The solid phase is called “char”. The outcome is the partial oxidation of the carbon included at the feeding material. The whole try has to do with the usage of biomass in energy applications and getting away from fossil fuels, which are harmful to the environment. It is an endothermic procedure and the oxidization of the biomass is made through allo-thermal and auto-thermal phas-es. The main steps are: 1. Oxidation, 2. Drying, 3. Pyrolysis, 4. Reduction. Another step is tar decomposition. The most common used gasification reactors are: 1. Entrained flow reactor, 2. Fixed bed, 3. Fluidized bed, 4. Rotary kiln reactor, 5. Plasma reactor. Some other gasification technologies are high temperature air gasification, high temperature steam gasification, solar driven gasification with multiple advantages. For cyclonic gasification the cyclones are essential. Cyclones isolate small parts of mater from gases or liquids, they use centrifugal forces of a vortex to isolate them. The design criterions of a cyclone are very important. These are: The temperature of the flow field in the cyclone, the particle separation, the pressure drop, the cyclone efficiency, how cyclones operate in high temperatures, the parameters that play a key role in gasifier operation, which are: 1. Turndown analogy, 2. Efficiency, 3. Conversion amount and the last criterion the gasification process in the cyclone. Computational Fluid Dynamics (CFD) is a modern method of research which follows the basic rules of the conservation laws of mass, momentum and energy. They are ex-pressed by partial differential equations. Many tests were run with CFD and geometry, turbulence, efficiency and velocity profiles are the sectors more important to consider them. The Lagrangian framework was selected, in which the particles are followed one at a time. The description of the gasifier was made by detailed analysis of the gasifier geometry and images of it, the mesh and mesh metrics, and also providing the Reynolds number. The configuration of the model follows, first with the description of the configuration of a cold/isothermal flow with air only and providing its results, and second with the description of the configuration of a cold/isothermal flow with particles, solid (wood) and liquid (kerosene) and also providing its results. A comparison of the models with solid (wood) and liquid (kerosene) particles is also provided. Lastly a comparison of the flows with and without particles is made and pressure, velocity and wall shear are tested. (EN)



Διεθνές Πανεπιστήμιο της Ελλάδος (EL)
International Hellenic University (EN)



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