Robert Scharler - Academia.edu (original) (raw)

Papers by Robert Scharler

Renewable Energy, 2020

Wood log stoves are a common residential heating technology that produce comparably high pollutan... more Wood log stoves are a common residential heating technology that produce comparably high pollutant emissions. Within this work, a detailed CFD model for transient wood log combustion in stoves was developed, as a basis for its optimization. A single particle conversion model previously developed by the authors for the combustion of thermally thick biomass particles, i.e. wood logs, was linked with CFD models for flow and turbulence, heat transfer and gas combustion. The submodels were selected based on a sensitivity analysis and combined into an overall stove model, which was then validated by simulations of experiments with a typical wood log stove, including emission measurements. The comparison with experimental results shows a good accuracy regarding flue gas temperature as well as CO 2 and O 2 flue gas concentrations. Moreover, the characteristic behaviour of CO emissions could be described, with higher emissions during the ignition and burnout phases. A reasonable accuracy is obtained for CO emissions except for the ignition phase, which can be attributed to model simplifications and the stochastic nature of

European Biomass Conference and Exhibition Proceedings, 2017

In this work a novel reaction mechanism for gas phase reactions has been developed to predict the... more In this work a novel reaction mechanism for gas phase reactions has been developed to predict the formation of aromatic compounds from the pyrolysis products of woody biomass particles. The aromatic compounds are important for being main soot precursors as well as their toxic properties. The developed gas phase mechanism is validated with experimental data from literature as well as experimental data performed with a single particle reactor for three different pyrolysis temperatures, namely 550, 800 and 1000°C. A good agreement is achieved between model results and experimental data for the total yield of each main family of aromatic hydrocarbons, i.e. phenolics, BTXs and PAHs.

Biomass Conversion and Biorefinery, Apr 16, 2020

Solid oxide fuel cells represent a promising technology to increase the electrical efficiency of ... more Solid oxide fuel cells represent a promising technology to increase the electrical efficiency of biomass-based combined-heat-power systems in comparison to state-of-the-art gas engines, additionally providing high temperature heat. To identify favorable fuel gas compositions for an efficient coupling with gasifiers at low degradation risk is of major importance to ensure stability, reliability, and durability of the systems used, thus increasing attractiveness of electricity production from biomass. Therefore, this study presents a comprehensive analysis on the influence of main gas components from biomass gasification on the performance and efficiency of a cell relevant for real application. An industrial-size electrolyte supported single cell with nickel/gadolinium-doped ceria anode was selected showing high potential for gasifier-solid oxide fuel cell systems. Beneficial gas component ratios enhancing the power output and electric efficiency are proposed based on the experimental study performed. Furthermore, the degradation stability of a SOFC fueled with a synthetic product gas representing steam gasification of woody biomass was investigated. After 500 h of operation under load at a steam-to-carbon ratio of 2.25 in the fuel gas, no performance or anode degradation could be detected.

Renewable Energy, Oct 1, 2023

Solid oxide fuel cells (SOFC) represent a promising technology to increase the electrical efficie... more Solid oxide fuel cells (SOFC) represent a promising technology to increase the electrical efficiency of biomass-based combined-heat-power systems in comparison to state-of-the-art gas engines, additionally providing high temperature heat. To identify favorable gas compositions and operating conditions for an efficient coupling with gasifiers at low degradation risk is of major importance to ensure stability, reliability and durability of the systems used. Therefore, this study presents a comprehensive analysis on the influence of main gas components on the performance of an industrial-size SOFC relevant for the use with product gases from biomass gasification. Recommendations for concentrations of H2O, CO, CH4 and CO2 in a H2+N2 gas mixture for enhancing cell performance are presented. Moreover, the degradation stability of a loaded cell fueled with a modeled steam-gasifier product gas is investigated showing no performance- or substrate degradation.Austrian Ministry for Transport, Innovation and Technology (bmvit)1011121

Energy Conversion and Management, Jun 1, 2023

Energy Procedia, Feb 1, 2019

District heating networks are commonly addressed in the literature as one of the most effective s... more District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.

The presented grate firing system is a patented small scale screw burner, which is designed for h... more The presented grate firing system is a patented small scale screw burner, which is designed for high fuel flexibility. This work focuses on the numerical modelling of the boiler via CFD simulations. The in-house developed CFD models use an Euler – Lagrange approach to predict the thermal degradation of the fuel particles and the subsequent gas-phase reactions. The CFD models are validated with experimental data from a representative measurement campaign where the boiler is operated with softwood pellets and the composition of the flue gas is measured in the primary and secondary combustion zone as well as the boiler outlet. The simulation results agree well with the data acquired in the measurement campaigns.

To optimize the combustion of biomass grate furnaces a sensitivity analysis is carried out by mea... more To optimize the combustion of biomass grate furnaces a sensitivity analysis is carried out by means of CFD simulation. The methodical procedure consists of a 3D packed bed biomass combustion model, which describes the most essential characteristics of the thermal conversion of biomass particles, such as the detailed consideration of drying, pyrolysis and char oxidation in parallel processes. Within the sensitivity analysis the following parameters have been investigated: distribution of false air, residence time of fuel on the grate and distribution of recirculated flue gas and primary air below the grate. To evaluate the influence of the varied parameters on the combustion process the focus lied on the position of the thermal conversion of the biomass and the CO at the outlet of the simulation domain. The results of the sensitivity analysis show a shift of the thermal conversion towards the grate end for increased false air as well as for reduced momentum of primary air/recirculated flue gas mixture. An increase of the fuel residence time leads to a shift of the thermal conversion towards the fuel inlet. Consequently a large region of the primary combustion zone is not used due to earlier release of CO inside the fuel bed.

Air pollution is the world's largest single environmental health risk. Globally, 3.8 million ... more Air pollution is the world's largest single environmental health risk. Globally, 3.8 million deaths were attributable to household air pollution in 2016, almost all in low- and middle-income countries. This is mainly due to cooking with solid biomass in substandard traditional stoves, as 2,700 million people (38 % of world population) rely on this method. These traditional processes produce very high emissions of unburnt products as CO, volatile organic compounds (VOC), polycyclic aromatic hydrocarbons (PAH), and soot, which lead to several health problems. One possible solution to address this situation is to re-engineer the employed devices and methods, with concepts such as the top-lit updraft gasifier (TLUD). In this work, a TLUD-based cook stove employed in Uganda is further optimized in order to reduce its emissions. The conducted simple modification increases the residence time of the flue gas in sufficiently high temperatures for combustion (> 700 - 750 °C). In this way, the CO emissions are reduced from 8.5 to 2.2 gCO/MJdel. The obtained 75 % reduction in CO emissions can be therefore achieved with simple measures. These concepts can then lead to significant health improvements for biomass cook stove users.

Renewable Energy, 2019

Energy Procedia, 2019

Fuel Processing Technology, 2020

The catalytic conversion of biomass-derived tars over char during long tests (over 6 hours) is st... more The catalytic conversion of biomass-derived tars over char during long tests (over 6 hours) is studied. The syngas is generated in a steam-blown fluidized-bed gasifier employing wood pellets and conducted to a second tubular reactor where non-activated char particles are fluidized. The gasifier operated at 750 °C whereas the temperature of the secondary reactor was varied between 750 °C and 875 °C. The evolution of the tar conversion, gas composition and internal structure of the used catalysts were studied. At 750 °C, the initial catalytic activity of the char was low and deactivation occurs rapidly. However, as the reactor temperature increased, the catalytic activity of the char improved significantly. At 875 °C, the initial conversion of tar was above 70 % and over 64 % after 5 h of operation. Moreover, the conversion of the heaviest tars was above 80 % during the entire test. At this temperature, the decrease in tar conversion is attributed to the consumption of the char by steam gasification since its catalytic activity increased during of the test. In these conditions the char bed with an initial weight of 32 g converted approximately 12 g of tars (benzene not included) after 5 h of operation. 1-Introduction Gasification is a thermo-chemical route for conversion of solid fuels, such as biomass and wastes, into a syngas that can be used in a variety of applications [1,2]. Fluidized bed (FB) gasification has several advantages over that in fixed/moving bed or entrained-flow for distributed energy production [3]. However, in all types of FB gasifiers the process temperature must be kept relatively low to prevent agglomeration and sintering of bed material. The low temperature results in incomplete carbon conversion and a high concentration of heavy tars in the gas. The condensation of heavy tars in downstream equipment is the main bottleneck for the use of the syngas in any application where the gas needs to be cooled down. During the last decades, different methods have been developed to reduce the tar concentration in the gas based on physical separation (wet/physical methods) or reforming/cracking of the tar in the hot gas. Wet methods have been tested using water [4,5] or organic solvents [6], and have been reported to be technically efficient. However, this way to clean the gas seems to be too complex and expensive for small or medium-size plants [1]. The reforming/cracking of tar using metallic catalysts (mainly Ni-based) in a downstream vessel is also efficient [7,8] but the presence of certain contaminants in the syngas causes their rapid deactivation. The fast

bios-bioenergy.at

... Alexander Weissinger1, Ingwald Obernberger1, 2, Robert Scharler1 1 Institute of Chemical Engi... more ... Alexander Weissinger1, Ingwald Obernberger1, 2, Robert Scharler1 1 Institute of Chemical Engineering Fundamentals and Plant Engineering, Graz University ... grate by investigating the ash and moisture content of samples taken from different positions at the grate as described ...