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.

This paper briefly discusses the relevance of small-scale biomass combustion systems for European renewable energy policy. Moreover, the state-of-the-art of modern small-scale biomass combustion systems is presented. The different technologies are reviewed regarding emissions and efficiency for different biomass. On-going developments and innovative approaches are presented and discussed.

Straw, Miscanthus, maize, and horse manure were reviewed in terms of fuel characteristics. They were tested in existing boilers, and the particulate and gaseous emissions were monitored. The ash was analyzed for the presence of sintered material. All the fuels showed problems with ash lumping and slag formation. Different boiler technologies showed different operational performances. Maize and horse manure are problematic fuels regarding NO_x and particulate emissions. Miscanthus was the best fuel tested. Due to the big variation of fuel properties and therefore combustion behavior of agricultural biomass, further R&D is required to adapt the existing boilers for these fuels.

Experimental data on the release of NO_x precursors from solid biomass fuels during thermal conversion are necessary to study N release in general and to supply reliable data for the purpose of packed bed and gas phase conversion model development and validation. In this work the release of NO_x precursors was studied at a lab-scale pot furnace (batch reactor) by taking measurements during the conversion process of solid biomass in a packed bed. The investigations were carried out with relevant woody biomass fuels, which cover a broad range of fuel N contents: sawdust, bark, waste wood and MDF board. The most important NO_x precursor detected above the fuel bed under fuel rich conditions was NH₃, while HCN was almost insignificant with the exception of sawdust. NO was detected mainly under air rich conditions. Furthermore, the experimental data were utilised to derive release functions for the relevant NO_x precursors NO, NH₃ and HCN. The release functions were implemented in an in-house empirical packed bed combustion model, which serves as a basis for a subsequent CFD N species gas phase calculation. © 2007 Elsevier Ltd. All rights reserved.

For an appropriate operation of a heat exchanger it is very helpful to know its dynamic behaviour. To this a simple sufficient accurate nonlinear model for the description of the dynamic behaviour is derived on the basis of a gas tube heat exchanger. Due to the general approach used for the derivation the model could be adaptet easily for other types of heat exchangers. The presented model can be used to estimate not measured physical values, to monitor the deposit formation in the heat exchanger and as a basis for the design of a model based control strategy. © Oldenbourg Wissenschaftsverlag.

The availability of energy is important to our every day lives. Biomass-fuelled heating systems are comfortable and reach an efficiency form over 90 %. With a thermoelectric generator (TEG) it’s possible to convert a part of the heat directly into electrical power and so become self sufficient from electicity. The purpose of this thesis was to optimise an existing prototype of a combined heat and power (CHP) plant based on a pellet heating system and a thermoelectric generator. Balancing the energy flows, especially the losses, was also part of the thesis.
Tests with the prototype were done. Some with the originial prototype, some with additional insulation and some with preheating the combustion air. To examine the part load behaviour, tests were done at 10, 7 and 4 kW fuelheat input.
By insulating the TEG the performance rose from 153 W to 174 W. The insulation and the preheating of the combustion air from room temperature to 350 degree lead to an power output from 194 watt. All at 10 kW fuellheat input. Finally the following conclusions can be drawn: For the series product it is recommended to optimize the insulation of the TEG. As the preheating of the combustion air didn’t lead to the expected effects it should be left out.

This paper presents one part of the results of a project dealing with straw pellets combustion in small
scale combustion systems. Whereas the other part of the work investigates gaseous and particulate emissions, this part focuses on the results of experiments to determine corrosion of refractory material. Three different types of straw
pellets are combusted in a prototype of a 15 kW residential heating boiler. The fuel samples are natural wheat straw,
wheat straw with alumina based additive and wheat straw with a mixture of calcium-/magnesium carbonate based
additive. Combustion experiments are performed under different operating conditions of the test boiler. Three
different types of refractory material are used as combustion chamber material. The refractory materials are different
mixtures of alumina, silica, zirconia and silicium-carbide. The degree of deterioration of these materials is
investigated for temperatures between 700 and 1300 deg C in the presence of slag formed during combustion of the
straw samples and the influence of the fuel additives on corrosion effects is analysed.

The primary energy consumption world-wide is rising constantly. Therefore it is necessary to open up renewable resources for energy production. Besides wood, the application of agricultural resources and residuals for energy production is possible, also within the range of small scale combustion units. These fuels still pose a challenge, concerning gaseous and particulate emissions. This work examines the application of straw pellets in a small scale combustion unit. Gaseous and particulate emissions, as well as the separation eciency of a secondary heat exchanger with scrubber were investigated. Compared with wood-like fuels a strong slagging of the combustion chamber could be determined. Gaseous emissions as NO_x, SO₂ and HCl, as well as the emission of particles were clearly higher than with combustions of wood. The gaseous emissions were below the considered limit value for other biogenous fuels after Art. 15 a B-VG 2007 [1]. The burnout of the gaseous phase, which can be evaluated by the emission of CO, was always good and comparable with the combustion of wood.
Using a secondary heat exchanger with scrubber (Hydrocube R of the company Schräder ) particulate emissions could be reduced by 20%. Element analysis of the particulate emissions as well as particle size measurements showed that primarily large particles were separated. A retrot of the Hydrocube R by an ionizing electrode increased the degree of separation on 60%. Besides the separation of particles, the Hydrocube R also reduced gaseous emissions like SO₂ and HCl. The absorption of these components in the condensate phase caused a decrease of the pH value. Low ph value increased the corrosion of the Hydrocube R , what could be detected by rising concentrations on Fe, Ni and Cr in the condensate.