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A stationary SOFC system utilizing gas from a biomass updraft gasifier is under development within the project “HiEffBioPower” by MAWERA, BIOS, Bosal, AVL, Calida Cleantech, Fraunhofer IKTS, Wuppertal Institute and University Utrecht (European Union Horizon2020 No. 727330). The system is based on Mk352-CFY-stack with Chromium based (CFY) interconnects and electrolyte supported cells. These stacks are robust, redox stable and demonstrated low degradation rates. The stacks are arranged to modules of eight 30-cell stacks and are electrically connected in series. The stack module was pre-tested at the test rig at IKTS and showed performance in accordance with system requirements. Stationary power points were measured to compare the behaviour of the stack module with the system tests at MAWERA. AVL designed and installed the overall SOFC system (heat exchangers, stack, catalytic afterburner, process control and visualisation) with a nominal capacity of 6 kWel. After shipping all parts of the SOFC system to MAWERA in Hard (AT), the coupling of the biomass gasifier, the gas cleaning unit and the SOFC system was conducted. The system is operated by an automated process control. The highest efforts needed the novel gas cleaning unit, consisting of a high temperature filter, a desulphurisation unit as well as a novel catalytic gas reforming stage developed by BIOS. The biomass gasifier has been operated with wood chips of different quality. The high tar contents of the product gas make a tar cracking essential to reach a high calorific value of the gas for the SOFC system. The novel gas cleaning system shows good performance and reaches the defined SOFC requirements. The SOFC system developed and operated by AVL reached stable conditions for several days. The operating results of the stack module at lab conditions and at the real system are in a good agreement. The SOFC stack module performance in terms of cell voltages, stack temperature distribution and fuel utilization under biomass reformate fuel will be shown and supported by several simulation to get an overall energy balance. Examples of optimization for several components by CFD simulation and component tests will be given.

To examine relevant combustion characteristics of biomass fuels in grate combustion systems, a specially designed lab-scale reactor was developed. On the basis of tests performed with this reactor,...

This paper presents a one-dimensional steady state mathematical model for the simulation of a small scale fixed-bed gasifier. The model is based on a set of differential equations describing the entire gasification process of softwood pellets and is solved by a two step iterative method. The main features of the model are: homogeneous and heterogeneous combustion and gasification reactions, one-step global pyrolysis kinetics and drying, heat and mass transfer in the solid and gas phases as well as between phases, heat loss, particle movement and shrinkage within the bed. The pyrolysis model has been improved by partially cracking primary tar into lighter gases according to experimental data. The model is used to simulate a laboratory scale fixed-bed updraft gasifier. Good agreement is achieved between prediction and measurements for the axial temperature profiles and the composition of the producer gas. Moreover, results are presented for different air to fuel ratios and varying power inputs. The gasification process is improved by increasing the power input of the gasifier as a result of higher temperatures. Furthermore, a higher air to fuel ratio lowers the efficiency of the gasification process.

Inorganic elements and compounds in biomass fuels influence the combustion process and the composition of the ashes produced. Consequently, knowledge about the material fluxes of inorganic elements and compounds during biomass combustion for different kinds of biofuels and their influencing variables is of great importance. The results gained will especially influence the future design and control of biomass furnaces and boilers in order to prevent slagging, fouling and corrosion and to assist in the definition of quality requirements for biofuels as well as the possibilities of a sustainable ash utilization. For this reason, comprehensive test runs were carried out in several biomass combustion plants equipped with different combustion technologies and using various biomass fuels (wood chips, bark, straw and cereals). During continuous observation periods of at least two days, samples of the biomass and the different ash fractions were taken and analysed. Furthermore, the most important operating data of the plants were recorded. The results of the material balances for inorganic elements showed that the concentrations of environmentally relevant heavy metals (especially Cd and Zn) in biomass ashes increase with decreasing precipitation temperature and particle size. This effect is independent of the biofuel used. Consequently, a major requirement for a sustainable ash utilization is a fractionated heavy metal separation, distinguishing between different fly-ash fractions and taking the temperature of fly-ash precipitation into consideration for new furnace technologies. Research has also shown that straw and cereals, as well as their ashes, contain significantly lower amounts of heavy metals than woody biofuels and wood ashes. The same principles pointed out for environmentally relevant heavy metals are also valid for K, Na, Cl and S. The high concentrations of these elements in the filter fly-ash as well as in the boiler fly-ash are of great relevance for reactions that can take place in the boiler section where the flue gas is subjected to a considerable temperature gradient which is accompanied by chemical reactions, phase transitions and precipitation processes that can support or initiate fouling and corrosion. These effects are of special importance for biofuels that are rich in alkali metals and Cl such as straw and cereals.

Previous research has shown that the natural cycle of minerals within the process of energy production from biomass is disturbed by deposition of heavy metals on the forest ecosystem. By separating a side stream rich in heavy metals (filter fly-ash) it should be possible to recycle the major part of the ashes produced (usable ash – a mixture of bottom ash and cyclone fly-ash). The aims of technological development are to reduce heavy-metal concentrations in the usable ash and to upgrade them in the filter fly-ash by implementing primary measures during the combustion process. In the first phase of the present research project large-scale tests were carried out in a state-of-the-art biomass combustion plant. The results have shown that some variables have a significant influence on the Cd and Zn fluxes. These variables include the reducing potential of the gaseous phase around the ash particles, the temperature of ash precipitation in an oxidizing atmosphere and the size of the ash particles at temperatures below 800 °C. Based on these results a new combustion technology with integrated fractionated heavy-metal separation was developed. In order to achieve reducing conditions in the primary combustion zone an "air staging" technology was implemented. Part of the flyash is precipitated at high temperatures in a relaxation zone in the secondary combustion chamber and in a high-temperature cyclone placed before the boiler. The filter fly-ash rich in heavy metals is efficiently precipitated in a flue-gas condensation unit followed by an aerosol electrostatic filter. The new combustion technology was realized in a biomass district heating plant in Austria. The results of test runs carried out at the new plant show a high fractionation potential of Cd and Zn under reducing conditions. On an average the bottom ash produced in the new plant contains 27 times less Cd and 5 times less Zn than the respective ash fraction generated by state-of-the-art plants. In hot-precipitated flyashes the levels of Cd are 5 to 15 times lower than in fly ashes generated in multicyclones, whereas the fractionation potential of Zn is low. Furthermore, the amount of filter fly-ash with high heavy metal content increased due to the lower precipitation efficiency of the hot cyclone as compared to multi-cyclones. Therefore, hot cyclones are considered not efficient enough for fractionated heavy metal separation. Future research and development will especially focus on the high fractionation potential for volatile heavy metals under reducing conditions.

Previous research has shown that the elementary cycle of nature within the process of biomass combustion is disturbed by deposition of heavy metals on the forest ecosystem caused by environmental pollution. By separating a heavy metal rich side stream (filter fly-ash) it should be possible to recycle the major part of the ashes produced (usable ash). Consequently, the aims of technological development are to reduce the heavy metal concentrations in the usable ash and to upgrade them in the filter fly-ash. In order to find out the necessary requirements for a fractionated heavy metal separation, 11 large-scale tests in an Austrian biomass district heating plant were carried out. In addition, the influence of the specific surface of the ash particles on the heavy metal precipitation was examined by sieving experiments. The results showed that above 800 °C the temperature is the most important influencing variable for the condensation/desublimation of Zn, Cd and Pb. The reduction potential for these heavy metals and their compounds in fly ashes precipitated at high temperatures is considerable. Below 600 °C, the concentrations of these heavy metals increase with decreasing particle size. Consequently, at low temperatures the surface of the particles represents the dominating influencing variable. The low amounts of volatile heavy metals in the bottom ashes show that a reducing atmosphere around the ash particles also seems to play an important role

von Prof. Cantzler

Unter „Synchronismus“ oder „Gleichlauf“ versteht man den Zustand dauernder Frequenzubereinstimmung zweier oder mehrerer, periodisch sich wiederholender Vorgange. So sind zwei rotierende Achsen dann miteinander synchron, wenn ihre Drehzahlen ubereinstimmen; sie konnen sich dabei nur noch in ihrer gegenseitigen Bewegungsphase um einen konstanten Betrag unterscheiden.