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.

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.

This paper presents the virtual biomass grate furnace, which comprises of comprehensive CFD models of all relevant processes for the simulation of biomass grate furnaces. The models consist of a 3D packed bed model, a gas phase combustion model for laminar to highly turbulent flows and a model to account for the influence of the flue gas streaks arising from the fuel bed in the freeboard. The simulation results of a 20 kW underfeed stoker furnace show that the overall CFD model is able to provide valuable insight on the processes occurring in the packed bed and freeboard and their interactions.

The use of biomass as feedstock for gasification is a promising way of producing not only electricity and heat but also fuels for transportation and synthetic chemicals. Dual fluid bed steam gasification has proven to be suitable for this purpose. Olivine is currently the most commonly used bed material in this process due to its good agglomeration performance and its catalytic effectiveness in the reduction of biomass tars. However as olivine contains heavy metals such as nickel and chromium no further usage of the nutrient-rich ash is possible and additional operational costs arise due to necessary disposal of the ash fractions. This paper investigates possible alternative bed materials and their suitability for dual fluid bed gasification systems focusing on the behavior of the naturally occurring minerals olivine, quartz and K-feldspar in terms of agglomeration and fractionation at typical temperatures. To this end samples of bed materials with layer formation on their particles were collected at the industrial biomass combined heat and power (CHP) plant in Senden, Germany, which uses olivine as the bed material and woody biomass as feedstock. The low cost logging residue feedstock contains mineral impurities such as quartz and K-feldspar which become mixed into the fluidized bed during operation. Using experimental analysis and thermochemical it was found that the layers on olivine and K-feldspar showed a significantly lower agglomeration tendency than quartz. Significant fractionation of particles or their layers could be detected for olivine and quartz, whereas K-feldspar layers were characterized by a higher stability. High catalytic activity is predicted for all three minerals once Ca-rich particle layers are fully developed. However quartz may be less active during the build-up of the layers due to lower amounts of Ca in the initial layer formation.
 

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.

The study investigates for the first time the possibility of using carbon rich paper recovery sludge, and nitrogen rich meat processing industry waste as cultivation medium for the production of high value enzymes needed in the respective industries. The complex cellulose rich deinking sludge was able to support the growth of many industrially relevant enzyme producing microorganisms (Bacillus licheniformis, Candida cylindracea, Aspergillus oryzae, Trichoderma reesei) and of recombinant enzyme producers (Escherichia coli and Pichia pastoris). Further detailed studies with Trichoderma reesei as model organism demonstrated that the organism was able to grow optimally in the presence of 40gL-1 paper sludge as carbon source and 67.5 gL-1 pasteurised blood as nitrogen source substituted in Mandels medium. Under these conditions cellulase activities up to 28.1 nkat FPU were achieved. Anyhow, to achieve these results pretreatment of both waste streams is inevitable. In summary, this study provides the practical basis for a valorisation systems of paper industry waste to produce valuable enzymes to be used on-site in paper processing or for other purposes.

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.

Anaerobic digestion offers a good opportunity to degrade residues from breweries to biogas. To improve the anaerobic degradation process thermal pretreatment of brewers' spent grains (BSG) offers the opportunity to increase degradation rate and biogas yield. Aim of the work is to show the influence of the thermal pretreatment of BSG to anaerobic digestion. BSG were pretreated at different temperature levels from 100 to 200°C. The biogas production of thermally pretreated BSG lies between 30 and 40% higher than for untreated reference. The temperature of the pretreatment process has a significant influence on the degradation rate or gas yield, respectively. Up to a temperature of 160°C, the biogas yield rises. Temperatures over 160°C result in a slower degradation and decreasing biogas yield. Substrate with and without pretreatment gave a daily biogas yield of 430 and 389 Nm³ × kg^-1 VS, respectively. Batch analysis of the biochemical methane potential gives a total methane yield of 409.8 Nm3 CH₄ × kg^-1 VS of untreated brewers' spent grains and 467.6 Nm3 CH₄ × kg^-1 VS of the pretreated samples. For pretreatment energy balance estimation has been carried out. Without any heat recovery demand is higher than the energy surplus resulting from pretreatment of BSG. With energy recovery by heat exchanger the net energy yield could be increased to 38.87 kWh × kg^-1 FM or 8.81%. © 2015 American Institute of Chemical Engineers Environ Prog.

To gain reliable data for the development of an empirical model for the prediction of the local high temperature corrosion potential in biomass fired boilers, online corrosion probe measurements have been carried out. The measurements have been performed 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. Within the test runs the flue gas temperature at the corrosion probe has been varied between 625 °C and 880 °C, while the steel temperature has been varied between 450 °C and 550 °C to simulate typical current and future live steam temperatures of biomass fired steam boilers. To investigate the dependence on the flue gas velocity, variations from 2 m·s⁻¹ to 8 m·s⁻¹ have been considered. The empirical model developed fits the measured data sufficiently well. Therefore, the model has been applied within a Computational Fluid Dynamics (CFD) simulation of flue gas flow and heat transfer to estimate the local corrosion potential of a wood chips fired 38 MW steam boiler. Additionally to the actual state analysis two further simulations have been carried out to investigate the influence of enhanced steam temperatures and a change of the flow direction of the final superheater tube bundle from parallel to counter-flow on the local corrosion potential.

The direct combustion of the biomass is the most advanced and mature technology in the field of energetic biomass utilisation. The legislations on the amount of emitted pollutants and the plant efficiency of biomass combustion systems are continually being restricted. Therefore constant improvement of the plant efficiency and emission reduction is required Numerical modelling is gaining increasing importance for the development of biomass combustion technologies. In this paper an overview about the numerical modelling efforts deal with the most relevant phenomena in biomass grate firing systems is given. The numerical modelling results in a deeper understanding of the underlying processes in biomass combustion plants. Therefore, it leads to a faster and safer procedure of development of a new technology.

Biomass boilers used for residential heating and hot water supply are typically combined with a buffer storage and solar collectors. However, the annual utilization rates typically achieved with such systems are far below those theoretically possible, which is mainly because of the often poor quality of both the individual control of the components as well as the high-level control of the entire system. The control strategies typically applied consist of simple decou-pled control circuits with linear controllers, which cannot deal with the mostly nonlinear and coupled behaviour of the components and thus do not ensure their reasonable interaction. The most appropriate approach to address these challenges is the application of model-based control techniques. Within the paper an overview of mathematical models suitable for control purposes, a simple to implement load forecasting method as well as control strate-gies for both the individual components and the entire system are presented. Future chal-lenges for a practical implementation of this novel approach are discussed in the outlook sec-tion.

Industrial waste streams from brewing industries and distilleries provide a valuable but largely unused alternative substrate for biogas production by anaerobic digestion. High sulfur loads in the feed caused by acidic pretreatment to enhance bioavailability are responsible for H₂S formation during anaerobic digestion. Microbiological oxidation of H₂S provides an elegant technique to remove this toxic gas compound. Moreover, it allows for recovery of sulfuric acid, the final product of aerobic sulfide oxidation, as demonstrated in this study. Two-stage anaerobic digestion of brewer’s spent grains, the major byproduct in the brewing industry, allows for the release of up to 78% of total H₂S formed in the first pre-acidification stage. Desulfurization of such pre-acidification gas in continuous acidic biofiltration with immobilized sulfur-oxidizing bacteria resulted in a maximum H₂S elimination capacity of 473 g m^–3 h^–1 at an empty bed retention time of 91 s. Complete H₂S removal was achieved at inlet concentrations of up to 6363 ppm. The process was shown to be very robust, and even after an interruption of H₂S feeding for 10 days, excellent removal efficiency was immediately restored. A maximum sulfate production rate of 0.14 g L^–1 h^–1 was achieved, and a peak concentration of 4.18 g/L sulfuric acid was reached. Further experiments addressed the reduction of fresh water and chemicals to minimize process expenses. It was proven that up to 50% of mineral medium that is required in large amounts during microbiological desulfurization can be replaced by the liquid fraction of the digestate. The conducted study demonstrates the viability of microbial sulfur recovery with theoretical recovery rates of up to 44%.