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.

Diffusion coefficients of various solutes in supercritical water, which were either measured or retrieved from Molecular Dynamics simulations, were reviewed. Diffusion coefficients of molecules relevant for supercritical water processes were calculated with correlations reported in the literature and compared to the values of reference data. For conditions well above the critical point of water the simple Stokes-Einstein equation predicts the diffusion coefficients with an accuracy better than 20%. For conditions near the critical point the Wilke-Chang correlation gives the most accurate results. Diffusion coefficients for typical molecules occurring in supercritical water processes such as O2, N2, CO, CO2, or CH4 are estimated to be in the range of 60 · 10⁻⁹ m²/s at 673 K and 30 MPa. For H2, for which no experimental data are available, much higher diffusion coefficients in the range of 250 · 10⁻⁹ m²/s seem plausible. The data set of binary diffusion coefficients in supercritical water, either determined experimentally or by Molecular Dynamics simulations, should be extended significantly to include more solutes, as well as higher temperatures and pressures.
 

In order to evaluate the combustion behaviour of new biomass feedstocks such as short rotation coppice (poplar wood chips), fuels from agriculture (wheat straw pellets) and biomass residues (maize spindle grits), comprehensive test runs investigating both particulate matter (PM) and gaseous emissions were performed. A commercially available small-scale biomass boiler, especially designed to enable high fuel flexibility, was used for this evaluation. The combustion behaviour was determined for various boiler load conditions and primary air ratios while maintaining a constant total air ratio. Based on wet chemical analyses of the fuels, fuel indexes were calculated to deliver primary information on the combustion behaviour to be expected. During the test runs appropriate operating conditions were determined for these new biomass feedstocks in order to optimise combustion parameters and to minimise PM and gaseous emissions as well as to inhibit ash related problems (slagging, ash deposit formation and corrosion). The optimisation of operating conditions by primary measures showed a big potential for a stable boiler operation combined with reduced emissions. The findings provide the basis for a further development of combustion systems as well as control systems for the combustion of new biomass feedstocks.

Most of the hydrogen produced is derived from fossil fuels. Bioenergy2020+ and TU Wien have been working on hydrogen production from biomass since 2009. A pilot plant for hydrogen production from lignocellulosic feedstock was installed onsite using a fluidized bed biomass gasifier in Güssing, Austria. In this work, the behavior of impurities over the gas conditioning stage was investigated. Stable CO conversion and hydration of sulfur components could be observed. Ammonia, benzene, toluene, xylene (BTX) and sulfur reduction could be measured after the biodiesel scrubber. The results show the possibility of using a commercial Fe/Cr-based CO shift catalyst in impurity-rich gas applications. In addition to hydrogen production, the gas treatment setup seems to also be a promising method for adjusting the H₂ to CO ratio for synthesis gas applications.

Steam gasification of solid biomass in dual fluidized bed systems is a suitable technology for the production of chemicals, fuels for transportation, electricity, and district heating. Interaction between biomass ash and bed material leads to the development of Ca-rich bed particle layers. Furthermore, incomplete decomposition of biomass leads to the formation of tar components; among these are stable intermediate products such as 1H-indene and stable gaseous hydrocarbons such as methane. In this work, the influence of bed particle layers on the conversion of intermediate products such as 1H-indene and methane via steam reforming was investigated by conducting experiments in a lab-scale test rig. Satisfying conversion of 1H-indene into gaseous molecules (e.g., CO, CO2, H2) was achieved with used, layered olivine, whereas fresh olivine showed significantly poorer performance. Since steam reforming was connected to the water-gas-shift reaction for the tested hydrocarbons, investigations regarding carbon monoxide conversion in the presence of steam were conducted as well. Furthermore, a comparison of the influence of fresh and used bed material concerning the conversion of methane is presented, showing that methane is not affected by the bed material, independent of the presence of particle layers.
 

The influence of heterogeneous secondary reactions on char oxidation reactivity, which can take place during slow pyrolysis processes in a woody biomass particle, is analyzed in this study. To this end, the oxidative behavior of primary char produced in a thermobalance with initial wood masses of a few milligrams is compared to the behavior of char produced under conditions enhancing secondary reactions, i.e., large particle and bed sizes in fixed-bed reactors. The influence of the maximum conversion temperature, heating rate, and catalytic effect of inorganics is also studied to compare the effect of each parameter. Results show that a significant reduction in reactivity takes place when char is produced under conditions enhancing these secondary reactions during pyrolysis. The effect is of similar order as the effect as a result of thermal annealing at 900 °C or the catalytic effect of alkali and alkaline earth metals. Therefore, the presence of heterogeneous secondary reactions during pyrolysis should be taken into account in studies addressing biomass char reactivity. Furthermore, it is shown that the reduction of reactivity as a result of secondary reactions is related to neither the loss of oxygen-containing functional groups nor the potential blocking of pores, specially micropores, resulting from the formation of this secondary char. The explanation may, therefore, lie on the deactivation or blocking of active sites by the secondary char.

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.

This paper treats the mixing and movement of char in a dual fluidized bed (DFB) biomass gasification plant. In these plants such measurements are troublesome to perform, and so a cold flow model has been developed to investigate this topic. This cold flow model allows simulating the fluidization behaviour of the gasification reactor in the DFB plant in Güssing, Austria. The recirculation of the bed material is also possible, and can be easily controlled with a rotary valve. In the cold flow model, bronze is used as the bed material and polyethylene as the char. It is possible to take samples during operation to investigate the char concentration in the bed material recirculation stream. Experiments have shown that the char shows a flotsam behaviour since it is of low density. Furthermore, the investigations have shown that higher fluidization rates and higher bed material recirculation rates enhance the char mixing and increase the char concentration in the recirculation stream. It was found that doubling the overall char concentration in the system does not lead to a doubling of the char concentration in the bed material recirculation stream. Furthermore, the influence of the bed height in the gasification reactor was investigated. It was found that higher bed heights lead to lower char concentrations in the recirculation stream. These initial investigations revealed that much is still unknown about DFB plants, but the knowledge of the behaviour of the different types of particles in the bubbling bed of the gasification reactor helps to further improve and develop the DFB technology.

The integration of solar thermal plants into district heating grids requires advanced control strategies in order to utilize the full potential in terms of efficiency and least operating effort. State-of-the-art control strategies cannot completely fulfil this since they are not able to consider the physical characteristics of the different components, nor do they take information on future conditions and requirements into account properly. A promising attempt for improvement is the application of model-based control strategies together with practicable forecasting methods for both the solar yield as well as the heat demand. This contribution will present the results of several projects performed on the development of suitable mathematical models, forecasting methods and control strategies relevant for the integration of solar thermal plants into district heating grids.

Primary devolatilization and the exothermic heterogeneous secondary charring of the primary volatiles need to be described in a consistent manner in order to correctly predict the heat of reaction of biomass pyrolysis. Detailed reaction schemes can currently predict mass loss and product composition of biomass pyrolysis with good accuracy, but have a weakness in the description of the heat of reaction. In this work it is shown for the first time that including secondary charring reactions a detailed reaction scheme can predict the evolution of the heat of pyrolysis for different conditions. The enthalpy of reaction is calculated for each reaction as the difference between the net calorific value of reactants and products. The presented model is able to describe the heat evolution in micro-TGA-DSC experiments conducted without a lid, where pyrolysis is endothermic, and with a lid, where secondary reactions are enhanced and the global heat of reaction shifts to exothermic. Furthermore, when it is coupled to a particle model, it correctly describes single particle pyrolysis experiments conducted with beech spheres where there is a remarkably exothermic peak in the centre temperature.

The use of renewable-energy-based heat producers within district heating grids is getting more and more popular. In order to benefit from the advantages and compensate for the different disadvantages of the various types of heat producers powered by renewable energy sources like biomass, solar energy or waste heat, a combination of these systems could be favoured over using, for example, only one main biomass-based boiler. Furthermore , in many cases, the additional use of buffer storages is necessary to fully benefit from the use of these kinds of heat producers. A major challenge with such multi-producer heating grids is the cost optimal management of all heat producers and buffer storages. Therefore , a high-level control strategy is necessary, which is able to plan ahead the use of slowly reacting and/or weather dependent heat producers while minimizing operational costs and pollutant emissions. This article shows the development of a linear model predictive controller (MPC) for a district heating grid with several (renewable) decentralized heat producers and heat storages. In order to provide the MPC with the required forecast of the future heat demand, an adaptive load forecasting method has been designed. Additionally, in order to be able to incorporate solar panels, the MPC needs to have a forecast of their possible future heat output. Therefore, a physically motivated solar yield forecasting method has been designed. The required prediction models for the MPC were represented by so-called mixed logical dynamical (MLD) system models. MLD system models combine the modelling power of discrete state system models (finite state machines) and discrete time system models by the extension of the regular linear state-space system model approach with integer and continuous auxiliary variables and linear inequality constraints. The occurrence of both integer and continuous variables within the resulting optimization problem of the MPC leads to a mixed-integer linear program (MILP), which can be solved efficiently using modern MILP solvers. The resulting control strategy is tested in a thermo-hydraulic simulation environment of an actual small-scale multi-producer district heating grid consisting of a medium-scale wood chip boiler with buffer storage, a solar collector with buffer storage and a high temperature heat pump, an oil boiler and 25 heat consumers. Additionally, a state observer was designed and connected with the MPC in order to detect control errors and to incorporate feedback from the heat producers and the buffer storages. The simulations have indicated that the designed MPC and the state observer work properly. Therefore, these elements have been implemented on-site on the actual heating grid, with the first test run scheduled for October 2017.
Modellprädiktive Regelung eines solar-und biomassebasierten Fernwärmenetzes | Request PDF. Available from: https://www.researchgate.net/publication/321314304_Modellpradiktive_Regelung_eines_solar-und_biomassebasierten_Fernwarmenetzes [accessed Feb 21 2018].

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.

In this paper, the performance of a water gas shift unit processing product gas from a commercial dual fluidised bed biomass steam gasification plant is studied. The experiments were carried out during a partial load operation of the gasification plant. In order to investigate a water gas shift process, a water gas shift unit, located at the site of the gasification plant in Oberwart, Austria, was used. The water gas shift unit consisted of three reactors in series filled with a commercial Fe'Cr-based catalyst and was operated with tar-rich product gas. No performance decrease of the water gas shift unit was observed during the partial load operation of the gasification plant. Furthermore, a CO conversion of 92% and a GCMS tar reduction of about 30% were reached. In addition, it was found that partial load operation of the gasification plant did not negatively affect the performance of the water gas shift unit.

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.

Adsorptive on-board desulfurization units require a high desulfurization and regeneration performance for a wide range of fuels to keep them small and ensure long maintenance intervals. A novel thermal regeneration strategy was investigated in this work, fulfilling all requirements for in situ on-board regeneration. In this strategy, a temperature-controlled flow rate (TCFR) of air was used to control the temperature inside the adsorber. With this dynamic approach, the regeneration time was reduced significantly in comparison to other thermal regeneration strategies. The novel regeneration strategy was tested using Ag–Al₂O₃ as an adsorbent to desulfurize a benzothiophen (BT)-enriched road diesel (300 ppmw of total sulfur). A commercial diesel containing fatty acid methyl ester (FAME) was used to evaluate the fuel flexibility regarding desulfurization and regeneration performance. In the case of 6.63 wt % FAME and 300 ppmw of sulfur, the breakthrough adsorption capacity of sulfur decreased from 1.04 to 0.17 mg/g. In TCFR regeneration experiments, the breakthrough adsorption capacity was restored to over 94% in the case of both fuels. Thereby, the Brunauer–Emmett–Teller (BET) surface area of the regenerated adsorbent decreased by only 1.5%, and negligible carbon deposits were detected.

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.

The dual fluidized bed (DFB) steam gasification technology of biomass was developed at Vienna University of Technology and is well-established for transforming biomass into a product gas which can be used for further applications. The DFB steam gasification reactor consists of a gasification chamber (bubbling bed, fluidized with steam) and a combustion chamber (turbulent bed, fluidized with air). Biomass is fed into the gasification chamber and gets in contact with the bed material, typically Olivine, at about 840°C. The released volatiles leave the gasification reactor as product gas. A part of the solid residue, called char, flows with the bed material via a chute to the combustion chamber where it is burnt with air. The bed material is heated up, separated from the flue gas stream in a cyclone and flows back to the gasification reactor via a loop seal where it provides the heat for devolatilization and drying of the biomass. The movement of the char is crucial since a sufficient amount has to flow to the combustion chamber and burn to provide enough energy for bed material heat-up. Up to now little is known about the char concentration in the bed material recirculation stream (or short recirculation stream) and its influencing variables. Therefore, a cold flow model, operated with ambient air, was constructed to study the influence of various parameters on the char concentration in the recirculation stream. Bronze is used as bed material since is matches closest to the scaling criteria. The char is also scaled; polyethylene is used as model char.

The cold flow model, see Figure 1 for the flowsheet, consists of a “gasification chamber” which corresponds to the gasification chamber in the hot plant and is as well operated as a bubbling bed. Via a chute the recirculation stream moves to a rotary valve which enables to set a fixed recirculation rate and make it independent from the following pneumatic conveying. Then, gas and solids are separated in a cyclone and the recirculation stream finally flows back to the gasification chamber. After the loop seal samples are taken for investigation of the model char concentration in the recirculation stream. In the present study the influence of fluidization rate in the gasification chamber, bed material recirculation rate and model char mass in the system on the char concentration in the recirculation stream are investigated. It was found that the model char particles show a flotsam behavior. Higher fluidization rates increase the model char concentration in the recirculation stream because of better mixing, whereas the bed material recirculation rate has only little influence. Doubling and tripling the overall char mass in the system did not lead to a doubling or tripling model char concentration in the recirculation stream. The present observations are helping to better understand the ongoing phenomena inside of the dual fluidized bed gasification reactor and provide knowledge to further optimize it.

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.

In this paper, the activity of a cobalt/molybdenum (Co/Mo) commercial catalyst for the Water Gas Shift Reaction for hydrogen production was investigated in a three fixed-bed reactor pilot plant using a tar-rich synthesis gas from a full-scale biomass gasification plant as feed-stream. A parametric variation study was carried out to assess CO conversion (X_CO) and selectivity for the water gas shift reaction as a function of the operating temperature (T) in the range 300–450 °C. The effects of four dry gas hourly space velocities (GHSV), Case A-Case D, two steam to dry synthesis gas ratios (H₂O/SG), 56% v/v and 67% v/v, and a H₂S concentration in the range 100–220 ppm_v,db were investigated: the highest CO conversion (∼95%) was observed in the base case (Case A GHSV) at 67% v/v H₂O/SG, and 450 °C, the lower the operating temperature the lower the CO concentration, the lower the gas hourly space velocity the higher the CO conversion and the higher the H₂O/SG the higher the CO conversion. The effect of H₂S variation on CO conversion was also studied, keeping the operating temperature constant (≈365 °C) and using the Case D GHSV: CO conversion increased as the H₂S concentration increased and X_CO ≈ 40%. Selectivity was not influenced by the parameters investigated. Finally, the effect of the catalyst on tar removal was studied and a CO conversion close to 85% was found.

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.

Utilization of biomass as feedstock in dual fluidized bed steam gasification is a promising technology for the substitution of fossil energy carriers. Experience from industrial scale power plants showed an alteration of the olivine bed material due to interaction with biomass ash components. This change results mainly in the formation of Ca-rich layers on the bed particles. In this paper, a mechanism for layer formation is proposed and compared to the better understood mechanism for layer formation on quartz bed particles. Olivine bed material was sampled at an industrial scale power plant before the start of operation and at pre-defined times after the operation had commenced. Therefore, time dependent layer formation in industrial-scale conditions could be investigated. The proposed mechanism suggests that the interaction between wood biomass ash and olivine bed particles is based on a solid-solid substitution reaction, where Ca2+ is incorporated into the crystal structure. As a consequence Fe2+/3+ and Mg2+ ions are expelled as oxides. This substitution results in the formation of cracks in the particle layer due to a volume expansion in the crystal structure once Ca2+ is incorporated. The results of this work are compared to relevant published results including those related to quartz bed particles.
 

Conceptual solution of production of pure renewable hydrogen from wood gas or product derived from the commercial biomass steam gasification plant Güssing, Austria was carried out. The proposed process of product gas upgrading consisted of tree basic operations: (I) catalyzed water-gas shift (WGS) reaction, (II) gas drying and cleaning in a wet scrubber and (III) hydrogen purification by pressure swing adsorption. The tail gas or adsorbate can be used like fuel for gas engine for electrical energy production or like a boiler fuel for hot water-heat production.