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.

In this study, we investigated the emissions, including odor, from log wood stoves, burning wood types indigenous to mid-European countries such as Austria, Czech Republic, Hungary, Slovak Republic, Slovenia, Switzerland, as well as Baden-Württemberg and Bavaria (Germany) and South Tyrol (Italy). The investigations were performed with a modern, certified, 8 kW, manually fired log wood stove, and the results were compared to emissions from a modern 9 kW pellet stove. The examined wood types were deciduous species: black locust, black poplar, European hornbeam, European beech, pedunculate oak (also known as “common oak”), sessile oak, turkey oak and conifers: Austrian black pine, European larch, Norway spruce, Scots pine, silver fir, as well as hardwood briquettes. In addition, “garden biomass” such as pine cones, pine needles and dry leaves were burnt in the log wood stove. The pellet stove was fired with softwood pellets.

The composite average emission rates for log wood and briquettes were 2030 mg MJ⁻¹ for CO; 89 mg MJ⁻¹ for NO_x, 311 mg MJ⁻¹ for C_xH_y, 67 mg MJ⁻¹ for particulate matter PM₁₀ and average odor concentration was at 2430 OU m⁻³. CO, C_xH_y and PM₁₀ emissions from pellets combustion were lower by factors of 10, 13 and 3, while considering NO_x – comparable to the log wood emissions. Odor from pellets combustion was not detectable. CxHy and PM10 emissions from garden biomass (needles and leaves) burning were 10 times higher than for log wood, while CO and NO_x rise only slightly. Odor levels ranged from not detectable (pellets) to around 19,000 OU m⁻³ (dry leaves). The odor concentration correlated with CO, C_xH_y and PM₁₀. For log wood combustion average odor ranged from 536 OU m⁻³ for hornbeam to 5217 OU m⁻³ for fir, indicating a considerable influence of the wood type on odor concentration.

urpose: Decreasing energy demand due to improved building standards requires the development of new biomass combustion technologies to be able to provide individual biomass heating solutions. The purpose of this paper is, therefore, the development of a pellet water heating stove with minimal emission at high thermal efficiency. Design/methodology/approach: The single components of a 10 kW water heating pellet stove are analysed and partly redesigned considering the latest scientific findings and experimental know-how in combustion engineering. The outcome of this development is a 12 kW prototype which is subsequently down-scaled to a 6 kW prototype. Finally, the results of the development are evaluated by testing of an accredited institute. Findings: Based on an existing pellet water heating stove, the total excess air ratio was reduced, a strict air staging was implemented and the fuel supply was homogenized. All three measures improved the operating performance regarding emissions and thermal efficiency. The evaluation of the development process showed that the CO emissions are reduced by over 90 per cent during full load and by 30-60 per cent during minimum load conditions. Emissions of particulate matter are reduced by 70 per cent and the thermal efficiency increased to 95 per cent. Originality/value: The result represents a new state of technology in this sector for minimal emissions and maximal thermal efficiency, which surpasses the directives of the Eco label "UZ37" in Austria and "Blauer Engel" in Germany, which are amongst the most stringent performance requirements in the European Union. Hence this design possesses a high potential as heating solution for low and passive energy houses. © Emerald Group Publishing Limited.

An active condensation system for the heat recovery of biomass boilers is evaluated. The active condensation system utilizes the flue gas enthalpy exiting the boiler by combining a quench and a compression heat pump. The system is modelled by mass and energy balances. This study evaluates the operating costs, primary energy efficiency and greenhouse gas emissions on an Austrian data basis for four test cases. Two pellet boilers (10kW and 100kW) and two wood chip boilers (100kW and 10MW) are considered. The economic analysis shows a decrease in operating costs between 2% and 13%. Meanwhile the primary energy efficiency is increased by 3-21%. The greenhouse gas emissions in CO2 equivalents are calculated to 15.3-27.9kg MWh-1 based on an Austrian electricity mix. The payback time is evaluated on a net present value (NPV) method, showing a payback time of 2-12 years for the 10MW wood chip test case. © 2014 Elsevier Ltd.

The results of experimental work to investigate the effects of air staging on emissions from energy crop combustion in small scale applications are presented. Five different biomass fuels (wood, willow, miscanthus, tall fescue and cocksfoot) were combusted in a small scale (35 kW) biomass boiler and three different tests looking at the effects of (1) air ratio in the primary combustion chamber (primary air ratio), (2) temperature in the primary combustion chamber, and (3) overall excess air ratio, on NO_x and particulate emissions were conducted. It was shown that by varying the primary air ratio, NO_x emission reductions of between 15% (wood) and 30% (Miscanthus) and PM₁ reductions of between 16% (cocksfoot) and 26% (wood) were possible. For all fuels, both NO_x and particulate emissions were minimised at a primary air ratio of 0.8. Particulate emissions from miscanthus increased with increasing temperature in the primary combustion chamber, NO_x emissions from Miscanthus and from willow also increased with temperature. Overall excess air ratio has no effect on emissions as no significant differences were found for any of the fuels. Emissions of particulates and oxides of nitrogen from a wide range of biomass feedstocks can be minimised by optimising the primary air ratio and by maintaining a temperature in the primary combustion chamber of approximately 900 °C.

Nowadays dynamic building simulation is an essential tool for the design of heating systems for residential buildings. The simulation of buildings heated by biomass systems, first of all needs detailed boiler models, capable of simulating the boiler both as a stand-alone appliance and as a system component. This paper presents the calibration and validation of a boiler model by means of laboratory tests. The chosen model, i.e. TRNSYS "Type 869", has been validated for two commercially available pellet boilers of 6 and 12. kW nominal capacities. Two test methods have been applied: the first is a steady state test at nominal load and the second is a load cycle test including stationary operation at different loads as well as transient operation. The load cycle test is representative of the boiler operation in the field and characterises the boiler's stationary and dynamic behaviour. The model had been calibrated based on laboratory data registered during stationary operation at different loads and afterwards it was validated by simulating both the stationary and the dynamic tests. Selected parameters for the validation were the heat transfer rates to water and the water temperature profiles inside the boiler and at the boiler outlet. Modelling results showed better agreement with experimental data during stationary operation rather than during dynamic operation. Heat transfer rates to water were predicted with a maximum deviation of 10% during the stationary operation, and a maximum deviation of 30% during the dynamic load cycle. However, for both operational regimes the fuel consumption was predicted within a 10% deviation from the experimental values. © 2014 Elsevier Ltd.

This study investigates the general concept of reduced firebed temperatures in residential wood pellet boilers. Residential wood pellet boiler development is more and more concerned with inorganic aerosols characterized by a temperature-dependent release from the firebed. Hence, different concepts are applied aiming to reduce firebed temperatures. Unfortunately, these concepts influence not only firebed temperatures, but also other important parameters like air flow rates which may cause unwanted side effects with respect to combustion quality or efficiency. Thus, a new approach was developed solely affecting firebed temperature by implementing a water-based firebed cooling in a 12 kW underfeed pellet boiler. The effectiveness of the cooling was monitored by comprehensive temperature measurement in the firebed. The cooling capacity ranged from 0.4 kW to 0.5 kW resulted in a significant decrease of firebed temperatures. Gaseous emissions remain stable showing no significant changes in major components (O₂, CO₂, NO_x). Furthermore, CO emissions were even reduced significantly by the activated cooling, which was supposedly caused by a stabilized devolatilization due to the firebed cooling. Moreover, the temperature-dependent release of aerosol forming elements was influenced at activated firebed cooling, which is proved by a decrease of 17 wt% of dust (Total Suspended Particles; TSP). At the same time the gaseous emissions of HCl increase, supposedly by a reduced potassium release from the firebed to the gas phase and a subsequently different particle formation. The general concept of reduced firebed temperatures proved to be successful decreasing overall aerosol emissions without impacting combustion quality.

High-temperature corrosion in biomass fired boilers is still an insufficiently explored phenomenon which causes unscheduled plant shutdowns and hence, economical problems. To investigate the high-temperature corrosion and deposit formation behaviour of superheater tube bundles, online corrosion probe as well as deposit probe measurements have been carried out in a specially designed fixed bed/drop tube reactor in order to simulate a superheater boiler tube under well-controlled conditions. The investigated boiler steel 13CrMo4-5 is commonly used as steel for superheater tube bundles in biomass fired boilers. Forest wood chips and quality sorted waste wood (A1-A2 according to German standards) as relevant fuels have been selected to investigate the influence on the deposit formation and corrosion behaviour. The following influencing parameter variations have been performed during the test campaigns: flue gas temperature between 650 and 880°C, steel temperature between 450 and 550°C and flue gas velocity between 2 and 8 m/s. One focus of the work presented is the detailed investigation of the structure and the chemical composition of the deposits formed as well as of the corrosion products. A further goal of the work presented was the development of an empirical model which can be used within CFD simulations of flow and heat transfer to calculate and evaluate the local corrosion potential of biomass fired plants already at the planning stage. The corrosion probe measurements show a clear dependency on the parameters investigated and the empirical function developed reproduces the measured corrosion behaviour sufficiently accurate. Since the additional calculation time within the CFD simulation is negligible the model represents a helpful tool for plant designers to estimate whether high-temperature corrosion is of relevance for a certain plant or not, when using fuels with similar compositions and the steel 13CrMo4-5. © 2014 Elsevier Ltd. All rights reserved.

The interest in experimental data regarding thermal fuel decomposition as well as the release behavior of ash-forming elements of biomass fuels for modeling and simulation purposes is continuously increasing. On the basis of combustion experiments with lab-scale reactors and single-particle reactors, integral release data regarding ash-forming vapors can be obtained, whereby the release is calculated on the basis of analysis data of the fuel and the ash residues. At the moment, almost no time-resolved release data of ash-forming elements from single particles exist. Therefore, a single-particle reactor was designed, which has been coupled to an inductively coupled plasma mass spectrometer (ICP-MS). This reactor can be used for targeted experiments in a temperature range of 250–1050 °C under inert, reducing, and oxidizing conditions. With this reactor, it is possible to simultaneously determine the surface and center temperatures of a biomass particle, weight loss of the particle, and flue gas composition. The reactor has been coupled to an ICP-MS through a gas stream that is sufficiently diluted with Ar. First performance tests with pure salts (KCl, NaCl, (NH₄)₂SO₄, ZnCl₂, and PbCl₂) proved that relevant volatile ash-forming elements can be detected with the ICP-MS. For a further validation of the received signals, combustion tests with Miscanthus pellets have been carried out, whereby the controlled interruption of the experiments has also been investigated. These tests prove that with this system the simultaneous time-resolved determination of S, Cl, K, Na, Zn, and Pb is possible whereby the Cl signal can only be used with restrictions. On the basis of the determined release of ash-forming elements for the entire combustion experiment, a quantification/calibration of the measured intensities has been carried out. The data gained from these tests will provide deeper insights into release processes as well as form a relevant basis for release model development.

In modern buildings with tight shells, often room-independent air supply is required for proper operation of biomass stoves. One possibility to arrange this supply is to use a double-wall chimney with flue gas leaving through the pipe and fresh air entering through the annular gap. A one-dimensional quasi-static model based on balance equations has been developed and compared with experimental data. Inclusion of leak air is crucial for reproduction of the experimental results. © 2014, Springer-Verlag Berlin Heidelberg.

Biochar is the product of biomass pyrolysis and gasification. One of the possible application of this product is certainly in agronomic sector, as soil amendment. However biochar use in Italy is subordinated to insert this product in fertilizer list, which biochar could be commercialized with. The aim of this paper is to know the biochar from gasification process (using an Imbert downdraft prototype), in particular investigating its potentiality as soil amendment in terms of European and Italian regulations and in terms of physical and chemical characterizations.

Wood pellets have been reported to emit toxic gaseous emissions during transport and storage. Carbon monoxide (CO) emission, due to the high toxicity of the gas and the possibility of it being present at high levels, is the most imminent threat to be considered before entering a pellet storage facility. For small-scale (<30 tons storage capacity) residential pellet storage facilities, ventilation, preferably natural ventilation utilizing already existing openings, has become the most favored solution to overcome the problem of high CO concentrations. However, there is little knowledge on the ventilation rates that can be reached and thus on the effectiveness of such measures. The aim of the study was to investigate ventilation rates for a specific small-scale pellet storage system depending on characteristic temperature differences. Furthermore, the influence of the implementation of a chimney and the influence of cross-ventilation on the ventilation rates were investigated. The air exchange rates observed in the experiments ranged between close to zero and up to 8 m³h^-1, depending largely on the existing temperature differences and the existence of cross-ventilation. The results demonstrate that implementing natural ventilation is a possible measure to enhance safety from CO emissions, but not one without limitations. © 2014 © The Author 2014. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.

Nowadays prefabricated houses are becoming increasingly popular, thanks to their low cost and high energy performance. Heating systems installed in these houses should be carefully designed and controlled, to ensure sufficient thermal comfort while maintaining low fuel consumptions. This study presents the simulation of different system configurations and control strategies for a pre-fabricated house, located in Lower Austria. The house is heated by a 6 kW pellet boiler directly connected to a floor heating system, in a configuration without buffer storage tank. Using the TRNSYS simulation suite, a coupled simulation of the house and its heating and hot water supply system was set up, calibrated and validated with reference to monitoring data. As monitoring data evidenced that the control strategy of the heating system is not ideal to maintain a comfortable indoor temperature during the whole day, two improved strategies were simulated over the heating season and evaluated in terms of thermal comfort, pellet consumption and boiler’s efficiency. Moreover, to better understand the influence of the system configuration, simulations have been repeated considering another heat distribution system (radiators instead of floor heating). Results show that the radiators’ network, if adequately controlled, reduces by 85% the total discomfort time. In addition, the pellet boiler mainly operates in load modulation regime, leading to lower pellet supply rates and therefore to lower pellet consumptions (18% less than floor heating). However, the lower operational loads and frequent ignitions result in a slightly lower efficiency of the pellet boiler (4% less than the configuration with floor heating.

Biochars produced from pelletized grape vine (GV) and sunflower husk (SFH) agricultural residues were studied by pyrolysis in a batch reactor at 400 and 500 °C. Chemical and physical evolution of the biomass under pyrolysis conditions was determined and the products were characterized, including the main gaseous organic components. Results showed a decrease in solid biochar yield with increasing temperature. Biochar is defined as a “porous carbonaceous solid” produced by thermochemical conversion of organic materials in an oxygen depleted atmosphere, which has physiochemical properties suitable for the safe and long-term storage of carbon in the environment and, potentially, soil improvement. The aim of this work is to improve the knowledge and acceptability of alternative use of the biochar gained from agro-forestry biomass residuals, such as grape vine and sunflower husks, by means of modern chemical and physical characterization tools.

Ash related problems such as slagging, fouling, and high temperature corrosion in biomass fired boilers are still insufficiently explored due to the complexity of the underlying processes. High temperature corrosion of low alloy steels like 13CrMo4-5 has already been investigated in plants firing chemically untreated wood chips. In this earlier work it has been suggested that the oxidation of the steel is the dominating mechanism in the material temperature range between 450 and 550 °C. Unfortunately the exponential dependence of the material degradation on the flue gas temperature also found within this work cannot be explained with the proposed corrosion mechanism. To determine the dominating corrosion mechanism, additionally test runs have been carried out in a specially designed drop tube reactor. To investigate the time-dependent corrosion behavior of 13CrMo4-5, a newly developed mass loss probe was applied under several constant parameter setups. In addition to these measurements, the time-dependent oxidation of 13CrMo4-5 under air was investigated in a muffle furnace. To gain relevant information regarding the corrosion mechanism prevailing, the deposits as well as the corrosion products have been examined subsequently to the test runs by means of scanning electron microscopy and energy dispersive X-ray analyses. With the experimental data gained it could be shown that the dominating corrosion mechanism strongly depends on the conditions prevailing (e.g., steel temperature, flue gas temperature, and velocity) and can either be the oxidation of the steel by gaseous O₂ and H₂O or a combination of oxidation and active Cl-induced oxidation.

The crucial point in inorganic particle formation from biomass combustion is the temperature-dependent release of inorganic compounds, especially potassium (K). Currently, common wood fuels comprise of a comparatively low amount of K, but the increased usage of wood energy requires new feedstocks in the future. Potentially new feedstocks, such as short rotation coppice (SRC), fuels from agriculture (e.g., straw), or wood from broad-leafed trees of low rotation, contain usually high ash contents and/or high K concentrations. Apparently, these feedstocks will cause increased inorganic particle emissions from biomass combustion processes. The principle of a decreased firebed temperature as a primary measure aiming at a retention of K in the ashes of the firebed is a common approach for particle emission reduction and was investigated in several previous studies. The present study describes the usage of an ash-rich fuel from SRC pellets made from willow in a residential pellet boiler modified with an unique prototype of direct water-based firebed cooling. This test setup enables the study of the isolated impact of decreased firebed temperatures and its influence on the combustion process and emissions as well. A statistically significant effect of the firebed cooling on temperatures below the burner plate as on gaseous HCl and SO₂ was found. The high ash content of the used fuel limited the effectiveness of the applied direct firebed cooling in residential biomass combustion. The accumulation of a thick and thermal insulating ash layer above the burner plate decreased the heat transfer, limited the cooling efficiency, and revealed deviations from the expected particle formation process.

To gain better insight into inorganic element release processes, test runs with a specially designed single particle reactor connected with an inductively coupled plasma mass spectrometer (ICP-MS) have been performed. Relevant combustion related parameters such as mass loss during thermal degradation, temperature development of the particle (surface and center), and composition of released gases were recorded. By coupling the reactor to an ICP-MS, time-resolved release profiles of relevant aerosol forming elements (S, Cl, K, Na, Zn, and Pb) were determined. Targeted and controlled interruptions of the experiments (quenching) after a certain time were performed to validate reactor performance and reliability of the measurements. Test runs with softwood and straw pellets (8 mm in diameter and about 20 mm in length) were performed at reactor temperatures of 700, 850, and 1000 °C under oxidizing conditions (5.6 or 4.2 vol % O₂). These test runs have revealed that the release ratios of volatile and semivolatile ash forming elements (S, Cl, K, Na, Zn, and Pb) generally increase as reactor temperatures rise. Moreover, regarding straw, higher Si and Al contents influence the release behavior of K, Na, Zn, and Pb. For K, existing release mechanisms proposed in the literature have been confirmed, and for Na it has been suggested that release mechanisms similar to K prevail. Especially during the starting phase of the experiment, a distinct temperature gradient exists from the surface to the center of the particle. Thus, different conversion phases occur in parallel in different layers of the particle, which has to be considered during the interpretation of the time-resolved release profiles of the main inorganic elements. Furthermore, transport limitations due to the occurrence of molten phases (especially for straw at reactor temperatures of 1000 °C) were obvious and could be directly derived from the online recorded release profiles. The targeted interruption of the ongoing decomposition process (quenching) provided an indication of the validity of the release profiles for S, K, Na, Zn, and Pb. Additionally, these experiments delivered valuable information regarding possible release mechanisms.

The phenomenon of off-gassing from wood pellets during storage has been the cause of several, in some cases fatal, accidents due to toxic atmospheres in storages. To optimize safety measures the nature of the responsible processes needs to be clarified. In this study the impact of O₂ availability, which is a decisive factor for the presumed oxidation of fatty acids, is pointed out. Off-gassing rates of CO, CO₂, VOC, and CH₄ of pellets at relatively constant O₂ levels of approximately 35%, 20%, and <1% over a period of 20 d at approximately 295 K were investigated. For this purpose 7 kg of spruce pellets was stored under simulated ventilation of the atmosphere in a 31 L tank. Gas concentrations were determined every 24 h by GC-FID/TCD. Compared to the mean emission rates at 35% O₂ of CO (0.22 mg kg^–1pellets_d.b. in 24 h) and CO₂ (0.76 mg kg^–1pellets_d.b. in 24 h) the lowest O₂ concentration of <1% resulted in a significant reduction of off-gassing rates of 40% for both gases. In contrast the release rates of VOCs and also CH₄ decreased with the higher O₂ concentration (0.035 to 0.025 mg kg^–1pellets_d.b. in 24 h; 0.0085 to 0.0061 mg kg^–1pellets_d.b. in 24 h), presumably, because of increased onward reactions to CO and CO₂. Since off-gassing was not prevented by the lack of O₂ (<1% O₂-trial) it is assumed that the O₂ required for the reactions originated from the biomass itself. During the storage of pellets at 20% O_2, emission rates of CO (0.18 mg kg^–1pellets_d.b. in 24 h) and CO₂ (0.79 mg kg^–1pellets_d.b. in 24 h) at the start decreased by more than 20% and those for VOCs (0.032 mg kg^–1pellets_d.b. in 24 h) by almost 30% after 3 weeks. It can be assumed that in ventilated storages the reactivity and thus a potential risk from off-gases from wood pellets decreases considerably in only a few weeks. The effects of aging, in terms of declining reactivity at relatively constant tank conditions, on off-gassing rates could be clarified for the first time. A realistic development of the decline of reactivity of the material itself could be determined.

Wood pellets have been used in domestic heating appliances for three decades. However, because the share of renewable energy for heating will likely rise over the next several years, alternative biomass fuels, such as short-rotation coppice or energy crops, will be utilized. We tested particulate emissions from the combustion of standard softwood pellets and three alternative pellets (poplar, Miscanthus sp., and wheat straw) for their ability to induce inflammatory, cytotoxic, and genotoxic responses in a mouse macrophage cell line. Our results showed clear differences in the chemical composition of the emissions, which was reflected in the toxicological effects. Standard softwood and straw pellet combustion resulted in the lowest PM₁ mass emissions. Miscanthus sp. and poplar combustion emissions were approximately three times higher. Emissions from the herbaceous biomass pellets contained higher amounts of chloride and organic carbon than the emissions from standard softwood pellet combustion. Additionally, the emissions of the poplar pellet combustion contained the highest concentration of metals. The emissions from the biomass alternatives caused significantly higher genotoxicity than the emissions from the standard softwood pellets. Moreover, straw pellet emissions caused higher inflammation than the other samples. Regarding cytotoxicity, the differences between the samples were smaller. Relative toxicity was generally highest for the poplar and Miscanthus sp. samples, as their emission factors were much higher. Thus, in addition to possible technical problems, alternative pellet materials may cause higher emissions and toxicity. The long-term use of alternative fuels in residential-scale appliances will require technological developments in both burners and filtration.

Detailed reaction schemes and experimental data for the online release of pyrolysis volatiles are required to gain a more fundamental understanding of biomass pyrolysis, which would in turn allow the process to be controlled in a more precise way and the development of more targeted applications. A detailed online characterisation of pyrolysis products has been conducted in single particle experiments with spruce pellets at different temperatures, obtaining a good closure of the elemental mass balances. The yields and online release of CO, CO₂, H₂O, CH₄, other light hydrocarbons and total organic condensable species, as well as char yield and composition, can be predicted with a reasonable accuracy with the application of a single particle model, coupled with a detailed pyrolysis scheme, and a simple one-step scheme for tar cracking. In order to achieve it, improvements have been conducted in the pyrolysis scheme, mainly concerning the release of light hydrocarbons and char yield and composition. Deviations are still present in the different groups in which organic condensable species can be classified.

This study presents combustion behavior and emission results obtained for different fuels: poultry litter (PL) and its char (PLC), scrap tires (ST) and its char (STC) and blends of char/lignite (PLC/LIG and STC/LIG). The combustion parameters and emissions were investigated via a non-isothermal thermogravimetric method and experiments in a lab-scale reactor. Fuel indexes were used for the prediction of high temperature corrosion risks and slagging potentials of the fuels used. The addition of chars to lignite caused a lowering of the combustion reactivity (anti-synergistic effect). There was a linear correlation between the NO_x emissions and the N content of the fuel. The form of S and the concentrations of alkali metals in the fuel had a strong effect on the extent of SO₂ emissions. The use of PL and PLC in blends reduced SO₂ emissions and sulphur compounds in the fly ash. The 2S/Cl ratio in the fuel showed that only PLC and STC/PLC would show a risk of corrosion during combustion. The ratio of basic to acidic oxides in fuel indicated that ST, STC and STC/LIG have low slagging potential. The molar (Si + P + K)/(Ca + Mg) ratio, which was used for PL, PLC and PLC containing blends, showed that the ash melting temperatures of these fuels would be higher than 1000 °C.

The CO/CO₂ release ratio obtained during char combustion of single biomass particles has been analysed in this work experimentally and by modelling. Experiments have been conducted with spruce, straw and Miscanthus pellets at different temperatures. Furthermore, these experiments have been modelled with a single particle model coupled with a CFD model of the single particle reactor. The results show that the CO/CO₂ ratio strongly depends on the feedstock, being lower for spruce than for straw or Miscanthus. Furthermore, the most commonly employed correlations for this ratio in literature are not adequate, as they either under- or over-predict it.

Firewood roomheaters are popular, widespread and important for reaching European CO₂ emission targets. Since they contribute significantly to local air pollution, they have to be optimized towards minimal emission release, especially in real-life operation. Draught conditions and user behavior, particularly the ignition technique, significantly affect the emission and efficiency performance of firewood roomheaters. This study assessed the effects of the respective parameters experimentally. The results revealed a clear correlation between draught conditions and thermal efficiency. Increased draught conditions up to 48 Pa significantly decreased thermal efficiency by 6%–11% absolutely. However, for gaseous emissions no clear trend was observed. Accordingly, CO and OGC emissions increased at higher draught conditions for one tested roomheater by 30% and 60%, but decreased for two other tested roomheaters by 13%–45%. For PM emissions no effect of increased draught conditions was evident. Top-down ignition technique did not lead to a significant decrease of PM emissions compared to bottom-up ignition. In contrast, bottom-up ignition led to best thermal efficiencies. The use of either spruce or beech as kindling material revealed no significant relevance for the ignition performance.

This study analyses the emission factors of two firewood room heaters under testing conditions which emulate real life operation. A 6.5 kW stove with low heat storage capacity and high leakage rate (stove A) is compared with an 8 kW air-tight stove with high heat storage capacity (stove B). Thermal efficiency, carbon monoxide (CO) and organic gaseous compound (OGC) emissions, as well as the thermal heat losses (THL) during cool down phase were investigated in a series of laboratory tests. Furthermore, the influence of closing the air supply dampers at the end of the heating cycle was evaluated. Test results for the whole test cycle (including cool down phase) showed that stove A had CO emissions of 2633 mg/MJ_Output and OGC emissions of 203 mg/MJ_Output, while stove B had CO emissions of 2408 mg/MJ_Output and OGC emissions of 109 mg/MJ_Output, when air dampers were closed. It was also found that user behaviour has a critical influence on the stoves’ performance. Closing the air supply dampers at the end of the stove operation improved the efficiency by up to 5.0 percentage points. Furthermore, the duration of the cool down phase increased, as well as CO and OGC emissions decreased. As a matter of fact, measures to improve the user behaviour as for example user trainings and accurate manuals are of major importance in order to decrease emissions and increase efficiency of domestic heating appliances. Moreover, real life emission factors of other technologies should be established in order to develop a database which can be applied in air quality dispersion models.

Wood pellet combustion for heating is increasing in importance in Europe. However, the most commonly used heating appliances such as wood pellet stoves are responsible for emissions which could negatively affect human health. The emissions quality of pellet stoves is influenced by pellet properties and combustion phase characteristics. The goal of this study is to investigate the influence of pellet length on the performance of pellets stoves under real life operation conditions. Three softwood pellet samples were produced, differing only in length. Combustion tests with two different types of pellet stoves were performed in steady and non-steady combustion phases. Gaseous and particulate emissions as well as fuel mass flow were measured. Results show a reduced fuel mass flow (up to 36%) into the combustion chamber for long pellets compared to short pellets. The results of the combustion tests show a considerable influence of pellet length on the performance of both pellet stoves. For example, carbon monoxide emissions and particulate emissions of one stove in nominal load operation increased for long pellets compared to short pellets from 185 mg/m³ to 882 mg/m³, and from 27 mg/m³ to 37 mg/m³ respectively. Results also show a considerable influence of the combustion phase on the emissions level.

The energetic utilization of alternative fuels (short rotation coppice, miscanthus), agricultural by-products (straw, corn cobs) or biomass residues (nut shells, coffee grounds) becomes of increasing interest. Due to variations in fuel properties – and the ash content in particular – biomass fuels considerably influence the conditions in the combustion zone and especially in the fuel bed. Usually, state-of-the-art combustion appliances are optimized for a particular fuel quality and typically approved only for utilization of standardized wood pellets or wood chips. Research activities within the GrateAdvance project focus on fuel flexible grate technologies being capable of adapting conditions in the combustion zone by a systematic and targeted adjustment of grate parameters in order to minimize emissions and slagging problems, thus setting the basis for a new generation of biomass technologies. Moreover, a novel control concept will ensure optimal combustion conditions for any biomass fuel, and specifically adjust to relevant fuel properties.

Toxicological characterisation of combustion emissions in vitro are often conducted with macrophage cell lines, and the majority of these experiments are based on responses measured at 24 h after the exposure. The aim of this study was to investigate how significant role time course plays on toxicological endpoints that are commonly measured in vitro. The RAW264.7 macrophage cell line was exposed to PM₁ samples (150 μg/ml) from biomass combustion devices representing old and modern combustion technologies for 2, 4, 8, 12, 24 and 32 h. After the exposure, cellular metabolic activity, cell membrane integrity, cellular DNA content, DNA damage and production of inflammatory markers were assessed. The present study revealed major differences in the time courses of the responses, statistical differences between the studied samples mostly limiting to differences between modern and old technology samples. Early stage responses consisted of disturbances in metabolic activity and cell membrane integrity. Middle time points revealed increases in chemokine production, whereas late-phase responses exhibited mostly increased DNA-damage, decreased membrane integrity and apoptotic activity. Altogether, these results implicate that the time point of measurement has to be considered carefully, when the toxicity of emission particles is characterised in in vitro study set-ups.

Glycerol is a co-product compound of biodiesel production with an interesting heating value. In this work pyrolysis kinetic parameters for a pellet made with a mass fraction of 90% sawdust and a mass fraction of 10% glycerol are derived through thermogravimetric analysis. A new parallel reaction scheme with four components (cellulose, hemicellulose, lignin and glycerol) is adopted and the kinetic triplet for each component is derived using a model fitting approach applied to this particular kind of pellet. The isoconversional method Kissinger-Akahira-Sunose is employed both to provide initial values for model fitting simulations and to check final results. Results show that activation energies and pre-exponential factors are respectively: 149.7 kJ mol⁻¹ and 1.98*10¹¹ s⁻¹ for hemicellulose, 230.1 kJ mol⁻¹ and 1.84*10¹⁷ s⁻¹ for cellulose, 154.3 kJ mol⁻¹ and 5.14*10⁹ s⁻¹ for lignin, 74.5 kJ mol⁻¹ and 2.17*10⁵ s⁻¹ for glycerol with a first reaction order for all components, except for lignin (n = 2.6). Through evolved gas analysis it was demonstrated that the thermal degradation of glycerol contained in the pellet can increase hydrogen content in pyrolysis gases.

Several methods for identifying the phenomena of self-heating and off-gassing during production, transportation and storage of wood pellets have been developed in recent years. Research focused on the exploration of the underlying mechanisms, influencing factors or the quantification of self-heating or off-gassing tendencies. The present study aims at identifying a clear correlation between self-heating and off-gassing. Thus, different methods for determining self-heating and off-gassing potentials of wood pellets are compared. Therefore, eleven wood pellet batches from the European market were analyzed. For this investigation, three methods for the determination of self-heating, like isothermal calorimetry, oxi-press and thermogravimetric analysis, and four methods for off-gassing, like volatile organic compound (VOC) emissions measurements, gas phase analysis of stored pellets in a closed container by offline and by glass flask method and determination of fatty and resin acids content, were performed. Results were ranked according to the self-heating and off-gassing tendency providing a common overview of the analyzed pellets batches. Relations between different methods were investigated by Spearman’s correlation coefficient. Evaluation of the results revealed an equal suitability of offline and glass flask methods to predict off-gassing tendency and indicated a very significant correlation with isothermal calorimetry for the identification of self-heating tendency. The thermogravimetric analysis as well as the fatty and resin acids determination proved to be insufficient for the exclusive assessment of self-heating and off-gassing tendency, respectively.

There is a need to reduce NO_x emissions, which can only be achieved through a detailed understanding of the mechanisms for their formation and reduction. In this work the release of the NO_x precursors, NH₃ and HCN, for different fuels is experimentally analysed and modelled in typical fixed-bed combustion conditions. It is shown that NH₃ and HCN are released during the main devolatilization phase and the NH₃/HCN ratio increases for fuels with a higher nitrogen content. A simplified two-steps model for their release is presented. The model can predict with a reasonable accuracy the release for fuels with a low nitrogen content, however deviations are present for fuels with a high nitrogen content, which probably arise due to a reduction of NH₃ and HCN taking place already in the bed.

n the course of this study the direct utilization of ammonia in different types of solid oxide fuel cells (SOFCs), such as anode- and electrolyte-supported SOFC, is investigated. Experiments in low fuel utilization, exhibited excellent performance of ammonia in SOFCs, although the power outputs of equivalent hydrogen/nitrogen fuels were not attained due to the incomplete endothermic ammonia decomposition. Next, the single cells were operated under high fuel utilization conditions and methane was added to the humidified ammonia stream, where they showed excellent ammonia- and methane conversions. The stability of the cells used was proven over a period of at least 48 hours with a variety of fuel mixtures. Post mortem scanning electron microscopy analysis of the anode micro-structures indicated nitriding effects of nickel, as microscopic pores and enlargements of the metallic parts occurred. Finally, a long-term test over 1,000 hours was carried out using a ten-layer stack consisting of electrolyte-supported cells.

Several studies pointed out that emission release is related to the concentration of particular elements in the fuel. Fuel indexes were developed to predict emissions of biomass combustion based on the elemental composition of the fuel. This study focuses on emissions of different biomass combustion technologies for domestic heating. Based on combustion tests with a wide range of fuel qualities we validated fuel indexes from the literature. We calculated the values for predicting total suspended particulate (TSP) matter and nitrogen oxide (NO_x) emission of 39 biomass-derived fuels. Combustion tests conducted in 10 different small-scale appliances provided experimental data. The combustion technologies had a nominal load between 6 and 140 kW_th. We measured TSP and NO_x emissions during the stable phases of the experiments. The evaluation considered 529 combustion test intervals. All tested indexes for predicting the TSP corresponded well to the measured values. The correlation analysis confirmed that these indexes are associated with each other and are basically dominated by the concentration of potassium. The results regarding NO_x emissions confirm previous findings from the literature by showing the typical nonlinear relation between nitrogen content of the fuel and NO_x in the flue gas. Overall the comparison of the fuel indexes with the practical data indicated also an influence of the combustion technologies.

Several methods are available to predict the combustion behavior of fuels. Fuel indexes have been developed either for specific fuel types (e.g., coal, biomass) or their utilization in combustion technology (fluidized bed, grate systems). This study deals with the validation of fuel indexes for biomass fuels utilized in small-scale appliances for residential heating. Laboratory analysis data of 33 biomass-derived fuels were used for determining indexes for predicting slag formation tendencies. Indexes were selected that have been reported and previously applied in the literature. They vary in terms of their derivation: ratio or concentration of specific components that are relevant for ash chemistry, temperature-based indexes, and empirical correlations. Combustion tests with 9 different small-scale appliances were conducted to gain experimental data. The appliances had a nominal load between 6 kW_th and 140 kW_th. After each experiment, the fraction of fuel ash that formed slag was quantified. Because of several boiler–fuel combinations in total, data from 90 combustion experiments were available for evaluation. The comparison of the quantified slag with the calculated slagging indexes showed that the applicability was strongly dependent on the (chemical) background of the respective index. Also, the fuel composition (e.g., fuels rich in calcium, silicon or phosphorus) plays an important role. Thus, available indexes are not applicable without restrictions and require a closer look on fuel properties and possible ash transformation mechanisms. Overall, the comparison of the fuel indexes with practical data (slag formation) also indicated an influence of the combustion technologies and operation conditions. The comparison of indexes that predict particulate matter and nitrogen oxide emissions with data measured during combustion experiments was evaluated as well. These results will be described in the second part of the present work.

Coupling biomass gasification with high temperature Solid Oxide Fuel Cells (SOFCs) is a promising solution to increase the share of renewables and reduce emissions. The quality of the producer gas used can, however, significantly impact the SOFC durability and reliability. The great challenge is to ensure undisturbed operation of such system and to find a trade-off between optimal SOFC operating temperature and system thermal integration, which may limit the overall efficiency. Thus, this study focuses on experimental investigation of commercial SOFC single cells of industrial size fueled with different representative producer gas compositions of industrial relevance at two relevant operating temperatures. The extensive experimental and numerical analyses performed showed that feeding SOFC with a producer gas from a downdraft gasifier, with hot gas cleaning, at an operating temperature of 750 °C represents the most favorable setting, considering system integration and the highest fuel utilization. Additionally, a 120 h long-term test was carried out, showing that a long-term operation is possible under stated operating conditions. Local degradation took place, which can be detected at an early stage using appropriate online-monitoring tools.

Fluidized bed gasification of sewage sludge is a promising method for its valorisation due to the fuel flexibility of the process. The main drawbacks are the impurities present in the producer gas, with a high tar content, and its low calorific value. In this study, sewage sludge and wood mixtures are gasified in a fluidized bed. A tar cracking reactor is used to reduce the amount of tars and to increase the calorific value of the producer gas. Sewage sludge char is employed for tar cracking with a real producer gas, showing the feasibility of the process with a tar conversion of about 80% at the beginning. The test was conducted for several hours and tar deactivation was observed, which lead to a decrease of tar conversion to about 35% after 5 hours. Reactivating the char with steam increases again the tar conversion up to 84%, however, the subsequent deactivation was found to be faster compared to the one for fresh char. First tests using char from the gasification process in the tar cracking unit also show promising results.

The reduction of greenhouse gas emission is an important issue for steel industry. One possibility is to use biomass-based reducing agents, also called bioreducers, to replace a least partly the fossil reducer agents. To produce bioreducer we treated woody biomass in a lab-scale muffle furnace, we performed grinding experiments with a ball mill, we analyzed the particle size distribution with laser diffraction and we used a rotating device, the revolution powder analyzer, for flow behavior investigations. Our preliminary results show that treatment temperatures >250 oC bring adequate increased calorific value and improved grindability. For a certain treatment temperature the particle size distribution and as well the flow behavior shows similarities to lignite.

The efficient and flexible conversion of solid biomass into energetic products will be an essential part of a future renewable, independent and reliable energy providing system. The main objective of the project Bio-CCHP is the development of a novel tri-generation system, including biomass gasification, gas cleaning, a Solid Oxide Fuel Cell (SOFC) and a cooling machine with the aim to produce electricity, heat and cold (CCHP), maximizing the efficiency and flexibility of the system. However, the employment of biomass derived product gas as fuel gas for SOFC is facing new challenges for gas quality assurance. For the evaluation of required dry high temperature gas cleaning processes the applied methods of gas characterization have to be accurate and reliable. Therefore, a comprehensive evaluation of analytical methods for the detection of SOFC harmful compounds is conducted within the ongoing project. First results of online and offline sampling and analysis methods employed at air- and steam-operated gasifiers are shown in this paper.

Chemical looping combustion is a highly efficient CO2 separation technology without direct contact between combustion air and fuel. A metal oxide is used as an oxygen carrier in dual fluidized beds to generate clean CO2. The use of biomass is the focus of current research because of the possibility of negative CO2 emissions and the utilization of biogenic carbon. The most commonly proposed OC are natural ores and residues, but complete combustion has not yet been achieved. In this work, the direct utilization of CLC exhaust gas for methane synthesis as an alternative route was investigated, where the gas components CO, CH4 and H2 are not disadvantageous but benefit the reactions in a methanation step. The whole process chain, the coupling of an 80 kWth pilot plant with gas cleaning and a 10 kW fluidized bed methanation unit were for this purpose established. As OC, ilmenite enhanced with limestone was used, combusting bark pellets in autothermal operation at over 1000 °C reaching high combustion efficiencies of up to 91.7%. The fuel reactor exhaust gas was mixed with hydrogen in the methanation reactor at 360 °C and converted with a methane yield of up to 97.3%. The study showed especially high carbon utilization efficiencies of 97% compared to competitor technologies. Based on the experimental results, a scale-up concept study showed the high potential of the combination of the technologies concerning the total efficiency and the adaptability to grid injection.

Wastewater contains high amounts of unused energy in the form of dissolved ammonia, which can easily be converted into gaseous humidified ammonia via membrane distillation, thus providing a potential fuel for solid oxide fuel cells. This study presents comprehensive investigations of the use of humidified ammonia as the primary fuel component in high-fuel utilization conditions. For these investigations, large planar anode- and electrolyte-supported solid oxide single cells were operated at the respective appropriate temperatures, 800°C and 850°C. Fueled with ammonia, both cells exhibited excellent ammonia conversion ( > 99.5%) in addition to excellent performance output and fuel utilization. In 100 h stability tests performed at 80% fuel utilization, the cells exhibited stable performance, despite scanning electron microscopy analyzes revealing partial impairments to the nickel parts of both cells due to the formation and subsequent decomposition of nickel nitride. This study also demonstrates that methane is a perfect additional fuel component for humidified ammonia streams, as steam supports the internal reforming of methane. Alternating and direct current as well as electrochemical impedance measurements with a variety of ammonia/steam/methane/nitrogen fuel mixtures were used to evaluate the performance potential of the cells, and proved their stability over 48 h in highly polarized conditions.

The increasing demand for wood pellets on the market, which is caused by their excellent combustion properties, inspires the production as well as the utilization of alternative biomass pellets as fuel. However, the emission of volatile organic compounds gives pellet materials a distinct odor or off-odor, which is directly perceived by the end user. Thus, there is an urgent need for knowledge about the emitted volatile organic compounds and their potential formation pathways as well as their contributions to odor properties of the pellets. In this study, pellets made of biomass energy crops (i.e., straw or miscanthus), byproducts from the food industry (i.e., rapeseed, grapevine, or DDGS (dried distillers grains with solubles from beer production)), or eucalyptus, as well as torrefied pinewood and torrefied sprucewood were investigated with respect to the emitted volatile compounds and their possible impact on the pellet odor. Headspace solid-phase microextraction in combination with gas chromatography–mass spectrometry was used to enrich, separate, and identify the compounds. Techniques used in sensory science were applied to obtain information about the odor properties of the samples. A total of 59 volatile compounds (acids, aldehydes and ketones, alcohols, terpenes, heterocyclic compounds, and phenolic compounds) were identified with different compound ratios in the investigated materials. The use of multivariate statistical data analysis provided deep insight into product–compound interrelation. For pellets produced from bioenergy crops, as well as from byproducts from the food industry, the sensory properties of the pellets reflected the odor properties of the raw material. With respect to the volatiles from torrefied pellets, those volatiles that are formed during the torrefaction procedure dominate the odor of the torrefied pellets covering the genuine odor of the utilized wood. The results of this work serve as a substantiated basis for future production of pellets from alternative raw materials.

Pellet boilers and pellet stoves are widely used for heat production. But in most cases, only specific wood pellets with a low ash content are approved due to the increased risk of slagging and limited deashing capacity. The ash fusion test (AFT), according to prCEN/TS 15370-1, is currently the only standard method for the prediction of slagging. This method is not feasible for all biomass fuel types, since sometimes the characteristic temperatures cannot be determined or the characteristic shapes do not occur for temperature determination. Furthermore, the method is costly and requires complex instrumental infrastructure. Hence, a demand for more expressive or more rapid methods to characterize slag formation potential of fuels is often claimed. Based on a literature study, four such laboratory test methods were chosen, partly adapted, and then experimentally investigated. These methods included thermal treatment of the fuel itself or the ashes of the fuel and were the rapid slag test, CIEMAT, the slag analyzer, and the newly developed pellet ash and slag sieving assessment (PASSA) method. Method performance was practically assessed using 14 different biomass fuel pellets, which were mainly from different assortments of wood, but also herbaceous or other nonwoody fuels. The results from the tests with these four alternative methods were evaluated by comparing to both results from standard AFT and results from full-scale combustion tests performed over a maximum of 24 h. Seven different pellet boilers were assessed, of which one boiler was used to apply all 14 test fuels. According to the granulometric ash analysis (i.e., the ratio of >1 mm-fraction toward total ash formed), the sensitivity of the new test methods to depict slagging phenomena at a suitable level of differentiation was assessed. Satisfactory conformity of the boiler ash assessment (reference) was found for both, the slag analyzer and the PASSA method. The latter may, in particular, be seen as a promising and relatively simple low-input procedure, which can provide more real-life oriented test results for fixed-bed combustion. The standardized AFT could, however, not sufficiently predict the degree of slag actually formed in the reference boiler, particularly when only wood fuels are regarded.

Biomass combustion is a major contributor to ambient air pollution. Thus, knowing the real-life emissions of biomass heating systems is crucial. Within the project Clean Air by biomass a field measurement campaign was conducted. 15 biomass heating appliances were tested in households at the end user according to their usual operation. Emission factors for gaseous and particulate emissions, as well as for the genotoxic and carcinogenic substance benzo(a)pyrene, were evaluated and compared to current proposed European and Austrian emission factors used for emission inventories. Moreover, the shares of particles and benzo(a)pyrene in hot and cooled flue gas were determined. Results showed a high variability of emissions in the field. Highest values and ranges occurred for room heaters (TSPtotal: 226 mg/MJ). Biomass boilers showed clearly lower emission factors (TSPtotal: 184 mg/MJ) in the field than room heaters and also than the proposed European and Austrian emission factors, in many cases. Emission factors for tiled stoves showed a similar trend (TSPtotal: 67 mg/MJ). The share of condensable particles in the flue gas was remarkable. Especially benzo(a)pyrene was found mostly in the condensable fraction of the particles.

Biomass combustion is a major contributor to ambient air pollution. Thus, knowing the real-life emissions of biomass heating systems is crucial. Within the project Clean Air by biomass a field measurement campaign was conducted. 15 biomass heating appliances were tested in households at the end user according to their usual operation. Emission factors for gaseous and particulate emissions, as well as for the genotoxic and carcinogenic substance benzo(a)pyrene, were evaluated and compared to current proposed European and Austrian emission factors used for emission inventories. Moreover, the shares of particles and benzo(a)pyrene in hot and cooled flue gas were determined. Results showed a high variability of emissions in the field. Highest values and ranges occurred for room heaters (TSPtotal: 226 mg/MJ). Biomass boilers showed clearly lower emission factors (TSPtotal: 184 mg/MJ) in the field than room heaters and also than the proposed European and Austrian emission factors, in many cases. Emission factors for tiled stoves showed a similar trend (TSPtotal: 67 mg/MJ). The share of condensable particles in the flue gas was remarkable. Especially benzo(a)pyrene was found mostly in the condensable fraction of the particles.

The incineration of waste wood is very often associated with ash-related problems (deposits, slagging and corrosion). This leads to short maintenance intervals, which result in significant power generation losses and high downtime costs. To avoid these problems, additives can be used, with particularly cost-effective additives being of great interest. Based on pre-evaluations, the addition of 2% gypsum and 3% coal fly ash was recommended, since an improved ash melting behaviour and reduced risk for high-temperature corrosion can be expected with addition of gypsum and coal fly ash. These additives with the recommended mixing rates were then investigated in a large-scale plant. Extensive investigations were carried out without additive (as a reference), and with the additives focusing on dust formation (aerosols and total dust), deposit formation and the corrosion behaviour of superheaters. These investigations were accompanied by fuel and ash analyses (grate, cyclone and filter). The addition of additives increased the amount of total dust in the flue gas up to 195% and 262% for gypsum and coal fly ash respectively. The chemical analysis of the total dust showed an enrichment of refectory species like Al for coal fly ash and Ca and Mg for gypsum which can positively influence the slagging behaviour. Aerosol measurements showed that the addition of coal fly ash minimised the amount of fine particulate matter, as less alkali metals (K and Na) were released into the gas phase. Gypsum addition increases the SO2 concentrations in the gas phase due to the decomposition of gypsum, as in the combustion chamber about 900°C are present. Due to the preferred sulphation reactions (binding of S to alkali metals) less Cl is bound to alkali metals and therefore the Cl concentrations in the aerosols were lower compared to the reference case. This effect was also found in the deposits sampled at the position of the superheater. Based on the chemical composition of deposits the molar 2S/Cl ratios were determined, which can be used to predict the risk for high temperature corrosion. The analysis data showed that an improvement concerning the high temperature corrosion risk is possible by adding coal fly ash, whereas a significant improvement in case of gypsum additions seems very likely. The measurements carried out so far showed the influence (built-up rate, chemical composition etc.) of the additive application on ash fractions, deposits and dusts. By taking a closer look at the change in chemical compositions of dusts and deposits, additives with an appropriate additivation ratio can be suggested. In case of coal fly ash 3% and in case of gypsum 1% additive related to dry fuel seems to be adequate additive ratios to positively influence the risk of high temperature corrosion and reduce the slagging behaviour.

Natural draft wood log stoves for residential bioheat production are very popular due to the low fuel costs, the ecological aspect of a renewable energy source and the visual appeal of the flame. However, they have rather high pollutant emissions, specially of unburnt products. The description of large wood logs conversion in stoves needs to be improved to allow a process optimization which can reduce these emissions. The transient conversion of a single wood log in a stove is experimentally investigated with test runs quenching the log after defined time intervals and measuring the flue gas composition and temperatures in the log and stove. The experiments have been described with a volumetric single particle model, which predicts with good accuracy the log conversion until a time of around 30 min, when pyrolysis is almost ending. At that point, log fragmentation takes place and smaller fragments are detached from the log falling onto the bed of embers. Despite the increase in external surface area, char oxidation takes place at a moderate rate. This last stage of wood log conversion in a stove is the most challenging to model. Finally, preliminary recommendations are provided for reducing CO emissions in wood log stoves.

A broad range of different biomass combustion appliances dedicated to domestic heating is available on the market. Depending on the technology the impact of varying properties of biomass fuels on slag formation and emission release may vary. Aspects as the design of the grate section and the selection of individual boiler components as well as operational settings determine the applicability of biomass fuels. Apart from fuel properties also the fuel load on the grate, residence time, air distribution and geometry of grate and combustion chamber affect the degree of slag formation and emission release. Technology indexes determined by means of constructional measures enable a systematic comparison and – in a further step – an assessment of combustion appliances. In this work specific technology indexes were specified and applied to compare technological aspects, which will prospectively allow investigating the technological influence on the combustion performance.

Third party testing of direct heating appliances fueled with pellets has been established in many countries worldwide. The main goals are ensuring operation safety and a minimum level of performance of the products prior to market implementation. This kind of approval procedure for new products requires testing standards, certified testing bodies and a legal framework defining minimum requirements for specified performance parameters which are assessed in the respective standards.

While the overall targets are quite similar for all countries having set-up such procedures, the practical implementation of these targets in the national/international testing standards is remarkably different. This applies to both, the way of operating the appliance during the testing and the measurements performed during the testing.

Furthermore several industries were requested recently to modify their product standards towards more realistic operating conditions. The most famous example is car industry, but this request may also apply to biomass heating systems.

The aim of this paper is to test the applicability of upgraded agricultural biomass feedstock such as torrefied sunflower husks during combustion in small and medium heating applications. Sunflower husk is formed in large quantities at enterprises producing sunflower oil and can be used as biofuel. However, big problems arise due to the low bulk density of husks and the rapid growth of ash deposits on the heating surfaces of boilers. In order to solve these problems, it was proposed to produce pellets from husks, and to subject these pellets to torrefaction. After torrefaction, net calorific value was increased by 29% while the risk of high temperature corrosion of boilers was reduced. Signs of ash softening neither occurred in combustion of raw nor in combustion of torrefied sunflower husk pellets. High aerosol emissions, already present in raw sunflower husk pellets, could not be mitigated by torrefaction. First combustion results at medium scale furnaces indicated that sunflower husk pellets (both raw and torrefied) in a commercial boiler < 400 kW, operated in a mode with low primary zone temperatures (< 850 °C), meet current emission limits. Regarding the future upcoming emission limits according to the European Medium Combustion Plant Directive, additional measures are required in order to comply with the dust limits.

During the last years biomass evolved into one of the most important energy sources in Central Europe. Depending on the atmosphere, different types of thermochemical processes can be differentiated: pyrolysis, gasification and combustion, whereas pyrolysis operates without any oxygen in the atmosphere, combustion with the highest ratio of oxygen. Depending on the conversion technology and conversion conditions, different products can be generated: heat, cooling power and electrical power, liquid, gaseous and solid products, such as hydrogen, FT-fuels and biochar.
This work focuses on the valorisation of solid side products of gasification based biomass CHP-systems to increase ecologic and economic benefit. Depending on the conversion process of biomass into producer gas this solid residue consists mainly of ash or of so called biochar with high carbon content. Increasing the amount of biochar leads to a decrease of producer gas, but, with the high market potential of biochar, the economic benefits increase. According to its characteristics (e.g. purity, surface structure) different applications can be addressed and therefore different prices can be achieved. Therefore, extended research on biochar treatment processes and related reaction kinetics of biochar is from crucial importance for the development and optimisation of downstream upgrading processes in order to reach the desired quality of the biochar. In the past, such considerations of utilising side products, like biochar, have not been in the centre of attention during the design phase of gasification reactors. Therefore, the establishment of a finishing-treatment of biochar extracted from a gasification process is under investigation. The focus of this paper lies on the reaction kinetics of biochar activation itself and not the primary material (biomass). In order to derivate correlations between reaction kinetics and atmosphere compositions as well as temperature, experimental test runs are conducted with a Thermogravimetric Analyser (TGA) including a steam furnace, which enables studies of mass and energy changes under defined absolute humidity. To produce applicable and reliable data, the limitations of the TGA-test-setup are evaluated with examinations on variations of sample mass, bulk density, particle size distribution and the gas flow. On this basis the test design is defined with certain specifications on the sample preparation and a constant flow velocity. The investigated biochar taken out the gasification process is dried, milled and sieved for the TGA-tests. The main part is devoted to conduct a detailed investigation changing the content of moisture (H2O) and carbon dioxide (CO2) as well as the temperature. The tests are operated at a temperature range between 700 and 1000°C, H2O-concentrations from 0 to 80 vol% and CO2-concentrations also in the range of 0 to 80 vol%. These systematic experimental variations provide the basis for a model of the reaction kinetics of biochar under different boundary conditions. The data is to be evaluated via the generic model including temperature and the partial pressures of CO2 and H2O. Afterwards it will be matched with conventional models (e.g. Arrhenius plot, linear regression models) to determine their suitability. One of those models was used in the paper of Ollero et al, where the influence of CO2 on the reaction kinetics of olive residue was investigated. 1First results show that the reaction rate of biochar is much lower than the one of olive residue. Effects of treatment conditions on the surface properties are investigated by taking out the treated samples after a defined treatment period at a defined mass loss and subsequent surface analysis (BET, pore size/volume distribution) of the samples. In first BET surface analysis, the treatments of biochar with vapour lead to a surface of approximately 1000m²/g whereas the original sample has a BET surface lower than 150m²/g. This finding leads to the question how the reaction kinetics of a treatment process influences the surface change. The obtained data is taken as basis for developing an upgrading process for biochar to a high value product of the gasification process. In order to prove the suitability of TGA-tests for identifying optimised treatment conditions, further research shall demonstrate the correlation of the lab-scale TGA-results with experiences of pilot scale tests.
 

The large variations found in literature for the activation energy values of main biomass compounds (cellulose, hemicellulose and lignin) in pyrolysis TGA raise concerns regarding the reliability of both the experimental and the modelling side of the performed works. In this work, an international round robin has been conducted by 7 partners who performed TGA pyrolysis experiments of pure cellulose and beech wood at several heating rates. Deviations of around 20 – 30 kJ/mol were obtained in the activation energies of cellulose, hemicellulose and conversions up to 0.9 with beech wood when considering all experiments. The following method was employed to derive reliable kinetics: to first ensure that pure cellulose pyrolysis experiments from literature can be accurately reproduced, and then to conduct experiments at different heating rates and evaluate them with isoconversional methods to detect experiments that are outliers and to validate the reliability of the derived kinetics and employed reaction models with a fitting routine. The deviations in the activation energy values for the cases that followed this method, after disregarding other cases, were of 10 kJ/mol or lower, except for lignin and very high conversions. This method is therefore proposed in order to improve the consistency of data acquisition and kinetic analysis of TGA for biomass pyrolysis in literature, reducing the reported variability.

A deeper understanding and quantification on the influence of inorganic species on the pyrolysis process, combined with the presence of heterogeneous secondary reactions, is pursued in this study. Both chemical controlled and transport limited regimes are considered. The former is achieved in a thermogravimetric analyser (TGA) with fine milled biomass in the mg range, while the latter is investigated in a particle level reactor with spherical particles of different sizes. To account for the influence of inorganics, wood particles were washed and doped with KCl aqueous solutions, resulting in K concentrations in the final wood of around 0.5% and 5% on dry basis. Gas species and condensable volatiles were measured online with Fourier transform infrared (FTIR) spectroscopy and a non-dispersive infrared (NDIR) gas analyzer. The removal of inorganic species delayed the pyrolysis reaction to higher temperatures and lowered char yields. The addition of inorganics (K) shifted the devolatilization process to lower temperatures, increased char and water yields, and reduced CO production among others. Higher heating rates and temperatures resulted in lower char, water, and light condensable yields, but significantly higher CH4 and other light hydrocarbons, as well as CO. The increase in these yields can be attributed, at least in part, to the gas phase cracking reactions of the produced volatiles. Larger particle size increased the formation of char, CH4 and other light hydrocarbons, and light condensables for low and high pyrolysis temperatures, while reduced the release of CO2 and H2O. This novel data set allows to quantify the influence of each parameter and can be used as basis for the development of detailed pyrolysis models which can include both the influence of inorganics and transport limitations when coupled into particle models.

Combustion of waste wood can cause slagging, fouling and corrosion which lead to boiler failure, affecting the energy efficiency and the lifetime of the power plant. Additivation with mineral and sulfur containing additives during waste wood combustion could potentially reduce these problems. This study aims at understanding the environmental impacts of using additives to improve the operational performance of waste wood combustion. The environmental profiles of four energy plants (producing heat and/or power), located in different European countries (Poland, Austria, Sweden and Germany), were investigated through a consequential life cycle assessment (LCA). The four energy plants are all fueled by waste wood and/or residues. This analysis explored the influences of applying different additives strategies in the four power plants, different wood fuel mixes and resulting direct emissions, to the total life cycle environmental impacts of heat and power generated. The impacts on climate change, acidification, particulate matter, freshwater eutrophication, human toxicity and cumulative energy demand were calculated, considering 1 GJ of exergy as functional unit. Primary data for the operation without additives were collected from the power plant operators, and emission data for the additives scenarios were collected from onsite measurements. A sensitivity analysis was conducted on the expected increase of energy efficiency. The analysis indicated that the use of gypsum waste, halloysite and coal fly ash decreases the environmental impacts of heat and electricity produced (average of 12% decrease in all impacts studied, and a maximum decrease of 121%). The decrease of impacts is mainly a consequence of the increase of energy generation that avoids the use of more polluting marginal technologies. However, impacts on acidification may increase (up to 120% increase) under the absence of appropriate flue gas cleaning systems. Halloysite was the additive presenting the highest benefits.

The reduction of greenhouse gas emissions is an important issue for iron and steel industry. One possibility is to use biomass-based reducing agents, also called bioreducers, to replace at least partly the fossil reducer agents. In a first step woody biomass was treated in a lab-scale muffle furnace and afterwards ground with a ball mill. The powder characteristics were investigated in respect to the flow behavior. For a certain treatment temperature the particle size distribution and as well the flow behavior shows similarities to lignite. The next stage was to identify relations between powder characteristics and its fluidization behavior. A fluidization device was assembled and used to determine the minimum fluidization gas velocity for various bioreducer powders.

This publication focuses on the experimental investigation of a novel small-scale fuel flexible biomass combustion technology with a fixed-bed employing a low oxygen concentration. It was obtained through a low primary air ratio and the additional supply of recirculated flue gas. The plant was operated with spruce wood chips, which contained three different mass fractions of water, and miscanthus pellets. All relevant components of the released gas above the fixed-bed were measured, as well as the 3D bed temperature distribution. The balances confirmed a high experimental data consistency. Therefore, it was possible to determine the location of the four different conversion zones inside the fixed-bed: drying, pyrolysis, char gasification and char oxidation. The reduction of CO2 to CO in the char reduction zone worked efficiently across the entire grate area. Furthermore, the results showed that the water mass fraction of the fuel did not influence the dry product gas composition, but significantly affected the location for the release of pyrolysis products such as tars. It was found that the low oxygen concentration in the fixed-bed combined with flue gas recirculation was an effective method to reduce bed temperatures and therefore its inorganic emissions while significantly increasing feedstock flexibility. The investigations provided fundamental findings on the conversion and release behavior of the new technology under real operating conditions and are very useful for further experimental work and CFD simulations targeting the reduction of PM and NOX emissions.

Four different models for heat transfer to the particles immersed in a fluidized bed were evaluated and implemented into an existing single particle model. Pyrolysis experiments have been conducted using a fluidized bed installed on a balance at different temperatures and fluidization velocities using softwood pellets. Using a heat transfer model applicable for fluidized beds, the single particle model was able to predict the experimental results of mass loss obtained in this study as well as experimental data from literature with a reasonable accuracy. A good agreement between experimental and modeling results was found for different reactor temperatures and configurations as well as different biomass types, particle sizes – in the typical range of pellets - and fluidization velocities when they were higher than . However, significant deviations were found for fluidization velocities close to minimum fluidization. Heat transfer models which consider the influence of fluidization velocity show a better agreement in this case although differences are still present.

The release of potassium during biomass combustion leads to several problems as the emissions of particle matter or formation of deposits. K release is mainly described in literature in a qualitative way and this work aims to develop a simplified model to quantitatively describe it at different stages. The proposed model has 4 reactions and 5 solid species, describing K release in 3 steps; during pyrolysis, KCl evaporation and carbonate dissociation. This release model is coupled into a single particle model and successfully validated with experiments conducted in a single particle reactor with spruce, straw and Miscanthus pellets at different temperatures. The model employs same kinetic parameters for the reactions in all cases, while different product compositions of the reactions are employed for each fuel, which is attributed to differences in composition. The proposed model correctly predicts the online release at different stages during conversion as well as the final release for each case.