Wood pellet combustion units are a comfortable, full automatic and low emission solution for the provision of space heating in small scale applications. The requirement of an auxiliary energy source for the heat supply and distribution however results in a dependence on the electrical grid. The goal of this work is thereby to eliminate this dependence and to meet the auxiliary energy demand through the independent production of electrical energy. The thermoelectric power production method was chosen from a number of technology variations so as to guarantee the silent and maintenance free production of direct current that can be implemented in cellars and space heaters. The first development step was the implementation of a Prototype with a fuel heat input of 10 kW and a nominal electrical power of 200 W. The central point of the implementation was the integration of a thermo-generator in a pellet combustion unit and the subsequent evaluation of the system concept. The integrated system implemented in the prototype confirms the feasibility of the combination of these technologies. The electrical efficiency of the thermo-generator was found to be in accordance with the target value of 4%, corresponding to a produced nominal electric power of 200 W.

Holzpellets werden in zunehmendem Maße aus Hackschnitzel hergestellt. Es ist davon auszugehen, dass diese Veränderung der Rohstoffbasis zu erhöhten Aschegehalten im Brennstoff führt und zu Schwierigkeiten bei der Nutzung führen kann. Die vorliegende Arbeit kommt zum Schluss, dass moderate Anteile (< 5%) sauberer Rinde zu keinen wesentlichen Verschlackungen führen. Bei Verunreinigung oder / und sehr hohen Rindenanteilen ist mit
Verschlackungsproblemen jedenfalls zu rechnen.

In the presented work the fuel quality and basic data about production processes of wood pellets from
all over Europe are investigated. For this purpose pellets producers were interviewed and fuel samples were analysed. Information from 91 companies was evaluated, covering about 50% of the European pellets production capacity, and pellets samples of 51 companies from 18 different countries were examined. It was found, that the raw material for pellets production is mainly taken from local resources. 75% of the plants process soft wood, whereas the use of hard wood is more common in Eastern Europe, Italy, Spain and France. Regarding the fuel properties of the pellets, differences were mainly found with regard to ash content and mechanical durability. In spite of these strong variations, almost all samples fulfilled the requirements according to the respective quality standard declared, and a clear correlation of valid standards and available pellets qualities was observed.

Thermal treatment of residues and waste is an important issue with increasing demand. In this work two pathways of thermal waste treatment, incineration and gasification, are compared. For this purpose literature on both technologies has been reviewed and the state-of-art technology for waste incineration and gasification is presented. The comparison highlights the strengths and weaknesses of both technologies and identifies future potentials.

More and more waste is generated every year, which has to be disposed. There is a legal obligation to treat waste before it can be landfilled in the European Union. Thus, thermal waste treatment is a very important issue.
In this work two pathways of thermal waste treatment, incineration and gasification, are compared. For this purpose, literature on both technologies has been reviewed and the stateof‐art technology for waste incineration and gasification is presented. The comparison highlights the strengths and weaknesses of both technologies and identifies future potentials. In Europe waste incineration is the state‐of‐the‐art technology ensuring destruction of the pollutants and allowing recovery of the energy content of the waste. A waste incineration plant consists of a furnace, where the waste is incinerated and the chemically bonded energy of the waste is discharged as heat. The hot flue gases pass the heat to the water in the heating surfaces of the steam generator. The energy of the waste can be used for the generation of hot water, steam of electrical power. Then the flue gas has to be cleaned in the air pollution control system. Dust is precipitated, HCl and HF is removed in an acid scrubber and SO2 in an alkaline scrubber. A catalytic reaction destroys dioxins and furans and reduces the emissions of NOx. Due to waste incineration the volume of the residues, which have to be landfilled, is
reduced by 90%. The second pathway of thermal waste treatment is waste gasification, where solid carbonaceous materials are converted into combustible gases by reaction with gasification agents. Due to gas production, not only the energy content of the waste can be recovered but the product range is extended. The producer gas can be converted into heat and power in a conventional steam boiler but also combusted in gas engines or turbines with higher efficiencies. In a combined cycle plant the hot exhaust gas of the turbine can be used in a heat recovery steam generator to increase the efficiency even more. After further cleaning the producer gas is also a suitable feedstock for synthesis of liquid fuels, synthetic natural gas and other chemicals.
Waste gasification processes have been developed in the past, but the plants have been shut down because of economic reasons and/or technical problems. However, important research has been done in the field of biomass gasification and thus gasification technology has been improved markedly. The fluidised bed gasifier in Güssing is one of the most successful examples; this technology is about to be commercialised. Considering these developments, there is definitely interesting potential for waste gasification now and the design of a new waste gasification process based on the findings in biomass gasification will be the scope of future research work.

The global warming, the increasing CO2 emission, the combustion of and dependency on fossil
fuels, as well as the high-energy price have resulted in an increasing demand in renewable energy
sources. Biomass, as a renewable energy source, has the potential to contribute to the future energy
mix in various ways. In thermo-chemical biomass conversion processes, especially gasification and pyrolysis, the tar content and its composition is a major subject. Due to the various processes examined at VUT, this
work picks up the opportunity to compare the different tar amounts and compositions at different
temperatures and process parameters. The tar content and composition in the producer gas of steam
gasification of straw and wood as well as the tar yields of low temperature pyrolysis of straw are
displayed in the following work. Gasification experiments were carried out in a 100 kW dual fluidized bed steam gasifier at a temperature range of 700° C to 870° C. Pyrolysis experiments were conducted in a rotary kiln
reactor at temperatures between 600° C and 630° C. For better understanding of tar formation during thermo-chemical conversion of biomass the tar content and composition in the producer gas was analyzed with a gas chromatograph coupled with a mass spectrometer. Main observation was that at higher temperatures the tar composition is shifted to higher molecular tars as poly aromatic hydrocarbons (PAH). Key tar components at lower temperatures (pyrolysis) are phenols. These results give the opportunity to analyse tar formation in different thermochemical conversion steps, therefore, for the future a better understanding of tar formation in large scale facility’s should be gained. This means lower tar content in the producer gas for gasification processes and an achievement of required pyrolysis oil yields for pyrolysis.

This paper focusses on the elaboration of the potential of the waste sector to contribute to the provision of 100% renewable energy systems. Waste is an abundant and locally available ressource and in many cases it is (at least partially) of biogenic origin, therefore pursuing political goals in waste management by energetic utilization of waste contributes towards achieving political goals in the energy as well as climate policy, too. However, it is shown based on the example of Austria that looking at energy systems on a national or international scale the waste sector is only able to contribute very little to the provision of the overall energy needed. It is different if one looks at specific energy systems in industrial sectors or on individual industrial sites. Here one must aknowledge that the energetic utilization of waste can have a high impact towards establishing renewable energy systems. Exemplarily this is shown by discussing the Austrian pulp & paper as well as the cement industry sector.

Heterogeneous wastes, which cannot be material-recycled easily are used for energetic utilization. Certain quality criteria need to be met in this context, addressing especially the chlorine content due to the product quality as well as to environmental and safety issues. In regard of current issues in climate policy concerning emission trading, also an increased biogenic content in these waste fractions is desirable. Therefore, experiments with a sensor-based sorting technology at pilot scale as well as large scale have been conducted to analyse the technical feasibility of this technology for its application on heterogeneous wastes to gain products with desired material and quality criteria. The results of pilot scale experiments show that the sensor-based sorting technology is generally technically feasible to gain waste fractions with the required characteristics, if the technology was adjusted to the specific waste stream. Due to restrictions during the large scale experiment a number of further issues need to be addressed in
further experiments to allow for a concluding evaluation of that treatment concept.