Determining the influence of material structure and sizing on the comminution behaviour of carbon fibres

Mit der stetig wachsenden Nachfrage nach Carbonfasern (CF) und carbonfaserverstärkten Kunststoffen (CFK) steigt die Menge der CFK-Abfälle, die am Ende ihrer Lebensdauer verwertet werden müssen. Die Kenntnis der Abhängigkeiten des Zerkleinerungsverhaltens von CF von ihren mechanischen Eigenschaften, unter Berücksichtigung der möglichen Erzeugung und Freisetzung von lungengängigen Faserfragmenten (WHO-Fasern) während der Zerkleinerung, ist essentiell für alle optionalen Verwertungsverfahren. Zu diesem Zweck wurde eine Auswertungsroutine entwickelt, die aus einer Probenvorbereitung der gemahlenen CF, der Bilderzeugung durch optische Digitalmikroskopie, der automatischen Bildanalyse und der Datennachbearbeitung besteht. In dieser Studie wurden drei verschiedene CF auf Basis von Polyacrylnitril und eine auf Basis von Mesophasenpech in einer Planetenkugelmühle bei ausgewählten spezifischen Energieeinträgen unter Variation der Drehzahl und der Mahldauer zerkleinert und das Zerkleinerungsverhalten mit den mechanischen Fasereigenschaften (Zugfestigkeit, Elastizitätsmodul) verglichen. In einer weiteren Versuchsreihe wurden dieselben CF vor der mechanischen Zerkleinerung pyrolysiert, um den Einfluss der Schlichte auf das Zerkleinerungsverhalten der CF zu bestimmen. Die Versuche zeigten, dass der Einfluss der Schlichte auf das Zerkleinerungsverhalten von CF deutlich größer ist als der der Zugfestigkeit und des Elastizitätsmoduls. Zu erwähnen ist, dass bei allen Zerkleinerungsversuchen lungengängige Faserfragmente entstanden sind, was im Hinblick auf die Gesundheitsgefährdung bei der mechanischen Behandlung von CF zu berücksichtigen ist

Extremgruppenvalidierung von LAMBDA-neu

Ziel der vorliegenden Diplomarbeit war es, das psychologisch-diagnostische Verfahren LAMBDA-neu mittels Extremgruppen zu validieren. Zu diesem Zweck wurden zwei Extremgruppen identifiziert: „Lernende“ Wissenschaften, diese Extremgruppe setzte sich aus acht StudentInnen der Medizin und Rechtswissenschaften zusammen, und „Verstehende“ Wissenschaften, hierzu zählten acht StudentInnen der Mathematik, Chemie und Informatik. Diesen beiden Gruppen wurden in Einzeltestungen die Verfahren LAMBDA-neu und Syllogismen 2010 vorgegeben. Die anschließende Auswertung mit dem Computerprogramm CADEMO TRIQ, mit dem ein sequentieller Dreieckstest gerechnet wurde, zeigte, dass bei allen zuvor aufgestellten Hypothesen die Nullhypothese zum Tragen kam. Aufgrund dieser Ergebnisse kann gesagt werden, dass die angestrebte Extremgruppenvalidierung von LAMBDA-neu nicht gelungen ist.The aim of the following study was an extreme group validation of the psychological diagnostic test LAMBDA-neu. For this purpose two groups were specified: “Lernende” sciences and “Verstehende” sciences. “Lernende” sciences means, that the students in this group learn primarly by memorizing and the students in the group “Verstehende” sciences use appreciation as their overriding learning strategy. Eight medicine and law students as well as eight mathematics, chemistry and informatics students were tested with LAMBDA-neu and the psychological diagnostic test Syllogismen 2010. The following analyses with CADEMO TRIQ, which compute a sequential triangular test, conclude that the extreme group validation of LAMBDA-neu was not successful

Thermal Stability and Material Balance of Nanomaterials in Waste Incineration

Nanostructured materials are widely used to improve the properties of consumer products such as tires, cosmetics, light weight equipment etc. Due to their complex composition these products are hardly recycled and thermal treatment is preferred. In this study we investigated the thermal stability and material balance of nanostructured metal oxides in flames and in an industrial waste incinerator. We studied the size distribution of nanostructured metal oxides (CeO₂, TiO₂, SiO₂) in a flame reactor and in a heated reaction tube. In the premixed ethylene/air flame, nano-structured CeO₂ partly evaporates forming a new particle mode. This is probably due to chemical reactions in the flame. In addition sintering of agglomerates takes place in the flame. In the electrically heated reaction tube however only sintering of the agglomerated nanomaterials is observed. Ceria has a low background in waste incinerators and is therefore a suitable tracer for investigating the fate of nanostructured materials. Low concentrations of Ceria were introduced by a two-phase nozzle into the post-combustion zone of a waste incinerator. By the incineration of coal dust in a burning chamber the Ceria nanoparticles are mainly found in the size range of the fly ash (1 – 10 µm) because of agglomeration. With gas as a fuel less agglomeration was observed and the Ceria nanoparticles were in the particle size range below 1 µm

Waste incineration of Polytetrafluoroethylene (PTFE) to evaluate potential formation of per- and Poly-Fluorinated Alkyl Substances (PFAS) in flue gas

n recent years, concerns over some per- and polyfluorinated alkyl substances (PFAS) have grown steadily. PFAS are a large group of chemical substances with widely differing properties. While one class of PFAS, fluoropolymers, have been demonstrated to meet the OECD criteria for polymers of low concern during the in use phase of their lifecycle, questions remain regarding waste handling at the end of useful life for products containing fluoropolymers. To show that polytetrafluoroethylene (PTFE) can be almost fully transformed into fluorine (F) (as hydrofluoric acid (HF)) and to study the possible generation of low molecular weight per- and polyfluorinated alkyl substances (PFAS), PTFE combustion under typical waste incineration conditions at the BRENDA (German acronym for “Brennkammer mit Dampfkessel”) pilot plant at Karlsruhe Institute of Technology (KIT) was investigated. Results indicate that, within procedural quantitation limits, no statistically significant evidence was found that the PFAS studied were created during the incineration of PTFE. Therefore, municipal incineration of PTFE using best available technologies (BAT) is not a significant source of the studied PFAS and should be considered an acceptable form of waste treatment

Oscillating Combustion - Primary Measure to Reduce Nitrogen Oxide in a Grate Furnace - Experiments and Simulations

The emission from industries and the mobility sector is under strong legal regulations in many countries worldwide. In Germany, the amendment to the 17th BlmSchV (Federal pollution control ordinance), which has been in force for waste incineration plants since 2013, has given rise to a new limit for nitrogen oxides of 150 mg/m3 as the daily mean level from 2019 on. A similar focus is on biomass-fired plants. According to the MCP (medium combustion plant) guideline of the EU, as a consequence, existing plants are required to either increase their consumption of ammonia water for nitrogen oxide reduction (SNCR process) or back fit SCR catalysts as secondary measures, which is a costly procedure. This paper presents a novel two-stage process in which an oscillating supply of secondary air allows nitrogen oxides to be reduced by approx. 50% at a good burnout level, which may obviate the need for secondary measures. Besides experimental investigations in a fixed bed reactor, CFD simulations confirm a high potential for reduction of nitrogen oxides. Together with the company POLZENITH, this process is under development for scale-up in a biomass incineration plant as a next step

Analysis of Oscillating Combustion for NOx-Reduction in Pulverized Fuel Boilers

Thermal power plants in different fields are regularly adapted to the state-of-the-art emissions standards, applying “The Best Available Techniques Reference”. Since 2016 in the power plant area new, more stringent limits for power plant units with a thermal output of more than 300 MW operated with black coal are valid. Usually, in order to reach the new limits e.g., for NOX emissions, downstream reduction processes (Selective Non-Catalytic Reduction, SNCR or Selective Catalytic eduction) are applied, which use of operating resources (essentially ammonia water) thereby increase. By the means of an xperimentally validated process, by which pulverized fuel is fed by oscillation through a swirl burner into a pilot ombustion chamber with a thermal output of 2.5 MW, nitrogen oxides can be reduced without further activities, for nstance from 450 mg/mN3 in non-oscillation operation mode (0 Hz) to 280 mg/mN3 in oscillation operation mode (3.5 Hz), normalized to an O2–content of 6% each. These findings were patented in EP3084300. Particularly promising are the experiments which utilize oscillation of a large portion of the burn out air instead of the fuel in order to minimize the fatigue of the pulverized fuel oscillator, amongst others. Thereby, the nitrogen conversion rate, which describes the ratio of NOX to fuel nitrogen, including thermal NOX can be reduced from 26% for non-oscillation operation mode down to 6%. The present findings show that fuel oscillation alone is not sufficient to achieve nitrogen oxides concentrations below the legislative values. Therefore, a combination of different primary (and secondary) measures is required. This paper presents the experimental results for oscillating coal-dust firing. Furthermore, an expert model based on a multivariate regression is developed to evaluate the experimental results