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.

A cell agglomeration algorithm is proposed to mitigate the computational cost of incorporating detailed chemical kinetics in multi-dimensional Computational Fluid Dynamics (CFD) simulations. Cells that are close in species and energy composition space are agglomerated before calling the reaction integrator, substantially reducing the number of chemistry integrations. The algorithm is generalized and applicable to any reacting flow configuration, and the accuracy is fully controllable. A dynamic hash table is used to efficiently bin cells into high dimensional hyper-cubes in composition space. The method is applied to four different CFD simulations and the speed-up and incurred error are assessed for a range of agglomeration tolerances and table dimensions. The proposed approach exhibits up to an order of magnitude speed-up with a relatively moderate decrease in accuracy.

The project BioHeatLABEL aims at the derivation of eco-design criteria for small scale biomass
combustion systems. It is a mirror project to the on-going European preparatory study for solid fuel small combustion installations. The presented paper gives an overview of the on-going work. It presents the applied methodologies so far. Sales and performance data as well as prices are collected for the existing stock as well as for new products. Six Base Cases are defined to best possibly represent market relevant product categories. These Base Cases are (1) log wood boilers with natural draught, (2) log wood boilers with forced draught, (3) wood chips boilers, (4) wood pellets boilers, (5) log wood stoves, and (6) wood pellets stoves. For these product categories the bills of production materials as well as for packaging are collected and information about the end-of-life behaviour is retrieved. Based on the above, preliminary life cycle assessment calculations are performed using the tool EuP EcoReport. The usability of this tool for a sound, reliable and representative life cycle assessment is discussed. Finally, an outlook on the further work is given.

Driven by increasing energy and raw material prices as well as changes in the legal framework the state of the art in the European Union has changed from waste management to resource management over the past 15 years. This has led to a higher appreciation of the resource “waste” as a secondary raw material as well as an energy resource. In this context the importance of effective waste processing in order to allow quality specific routing of waste streams has become very important. On the one hand material recycling requires a high purity of the waste material to be recycled. The prices to be achieved for the recycling material are highly dependend on the purity of the recyclables. The economic viability of treatment concepts very much depends on the rate of recovery of the recycling product. On the other hand the portion of waste that is thermally treated has increased and still is on the rise. Furthermore extensive efforts on the usage of waste fractions as Solid Recovered Fuels (SRF) in alternative thermal treatment processes with higher energy recovery are being undertaken. Alternative thermal treatment
processes have special demands on the quality of the waste streams to be treated due to process and product quality reasons as well as ecological concerns. Sophisticated waste pre-treatment concepts ensure compliance with required quality standards of wastes to be recycled or utilized energetically. In spite of that waste pre-treatment - in sometimes complex processes - the problem of disposal of the remaining residual waste fraction has to be solved, as the disposal of the residuals in compliance with the regulatory framework causes high expenses for the waste treatment plant operator. The first part of this manuscript focusses on the legal framework prompting the implementation of new waste processing technologies allowing an effective routing of waste fractions by material specific splitting of the over all waste stream. Most relevant in that respect are the EU Waste Framework Directive as well as the EU Landfill Directive and the EU Packaging Directive. Climate
policy and respective regulations are also influencing waste management practice. Additionally economic aspects for destination-process specific routing of waste streams are being addressed. In the second part of this manuscript the set-up of test runs as well as the results obtained and experiences gained based on the test runs are being reported. One test set-up aims at removing highcaloric waste components from waste streams of Mechanical-Biological Treatment (MBT) facilities in order to maximize the quantity of waste that can be landfilled. A second test set up deals with the processing of commercial plastic waste containing different types of polymers in order to gain pure recyclables. As the economic value of waste plastic depends on the purity in terms of individual polymers it is very important to separate individual polymers from mixed plastic waste. Near-Infrared
(NIR) sensor based sorting allows a separation of different types of plastics. The results of test runs are explained in terms of quality and yield of product gained as well as economical aspects. Although the prices for recyclables have fallen during the last months as a result of the financial and economical crisis leading to a decrease in the demand of recyclables it is assumed that gaining high quality waste fractions from mixed wastes for material recyling as well as energy recovery will become more important in the long run.

The global warming, the increasing CO2 emission, the combustion and dependency on fossil fuels, as well as the high-energy prices 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 many countries. In this thesis the so-called low temperature or slow pyrolysis is chosen to convert biomass into energy rich products. Pyrolysis is a process to convert biomass directly into solid, liquid and gaseous products by thermal decomposition in absence of oxygen. The goal of the pilot plant Dürnrohr is to generate a combustible gas to substitute fossil fuels in the thermal power plant Dürnrohr. The complete process consists of individual steps. First of all the biomass is pyrolysed and pyrolysis gas and pyrolysis char are produced. The obtained pyrolysis gas is combusted in a fluidized bed combustion chamber implemented as afterburner. The following step is fluidized bed combustion of
the intermediate-stored pyrolysis char. Due to the use of different biomasses and adjustment of the individual steps, the process should be optimized for the application for the power plant Dürnrohr. One major point of the production of the pyrolysis gas is the amount of tar. The tar amount was analyzed during pyrolysis operation to find out how much tar is produced at which process settings with a main focus on the temperature. The gravimetric
analysis included gravimetric tar, dust, entrained char, water content and ph-value, as well as the GC/MS tars of the pyrolysis gas. All these data was sampled, analyzed and evaluated as well as discussed.