Mathematical Modeling and Experimental Investigation of the Pyrolysis of Waste in Rotary Kilns

Für die Optimierung eines bereits bestehenden Prozesses, z.B. im Hinblick auf den maximal möglichen Durchsatz bei gleich bleibender Qualität der Pyrolyseprodukte oder für die Einstellung der Betriebsparameter bei einem unbekannten Einsatzstoff, kann ein mathematisches Modell eine erste Abschätzung für die Einstellung betrieblicher Parameter, wie z.B. Temperaturprofile im Gas und Feststoff, geben. Darüber hinaus kann man mit einem Modell für neu zu konzipierende Anlagen konstruktive Parameter ermitteln oder überprüfen. In dem hier dargestellten vereinfachten Modellansatz werden u. a. die Umsatzvorgänge für ein Partikelkollektiv mit Hilfe von Summenparametern aus Untersuchungen an einer Thermowaage und ergänzend im Drehrohr ermittelt. Das Prozessmodell basiert auf einem Reaktormodell, das das Verweilzeitverhalten des Einsatzstoffes im Reaktor beschreibt und einem Basismodell, bestehend aus Massen- und Energiebilanzen für Solid und Gas sowie Ansätzen zur Trocknung und zum Umsatz. Im Hinblick auf die Verfügbarkeit von stoffspezifischen Daten von Abfällen sind insbesondere zur Berechnung des Verweilzeitverhaltens und des Umsatzes im Heißbetrieb vereinfachende Ansätze durch die Bildung von Summenparametern hilfreich. Das Prozessmodell wurde schrittweise validiert: Zunächst wurde in Kaltversuchen ein Summenparameter, der u.a. die unbekannten Reibungsverhältnisse im Drehrohr berücksichtigt, durch Vergleich von Experiment und Rechnung für Sand ermittelt. Für heterogene Abfallgemische kann dieser Materialfaktor zwar für Kaltversuche bestimmt werden (soweit dies für Abfälle möglich ist), im Heißbetrieb ändern sich jedoch alle wesentlichen Stoffparameter wie Partikeldurchmesser, Schüttdichte und Schüttwinkel sowie die Reibungsverhältnisse. Für diesen Fall wird der Materialfaktor zu Eins gesetzt und die wesentlichen Stoffgrößen umsatzabhängig modelliert. Dazu ist die Kenntnis der Schüttdichten, statischen Schüttwinkel und mittleren Partikeldurchmesser vom Abfall und Koks aus dem Abfall notwendig. Die mit diesen Stoffdaten berechnete Verweilzeit wurde in einem Heißversuch bei der Pyrolyse von Brennstoff aus Müll- (BRAM) Pellets mit einem Fehler von ca. 20 % erreicht. Das Basismodell wurde zunächst ohne Umsatz an Messergebnisse mit Sand im Drehrohr unter Variation von Temperaturen und Massenstrom angepasst bevor mit diesem Modell die Pyrolyse von einem homogenen Einsatzstoff (Polyethylen mit Sand) im Drehrohr berechnet wurde. Hier konnte bereits gezeigt werden, dass mit diesem vereinfachten Modellansatz gute Ergebnisse beim Vergleich von Modell und Experiment erzielt werden können. Im nächsten Schritt wurde der Sand angefeuchtet, um die Teilmodelle der Trocknung unterhalb und bei Siedetemperatur zu validieren. Die Mess- und Modellierungsergebnisse stimmen gut miteinander überein. Für ein Abfallgemisch aus BRAM-Pellets konnte der Verlauf der Solidtemperaturen unter der Berücksichtigung variabler Stoffwerte des Solids und eines Verschmutzungsfaktors, der den Belag des Drehrohres mit anklebendem Pellets bis zur Verkokung berücksichtigt, gut wiedergegeben werden. Die Gastemperaturen können in erster Näherung ausreichend genau durch das mathematische Modell beschrieben werden. Mit diesem vereinfachten mathematischen Modellansatz steht nun ein Hilfsmittel zur Auslegung und Optimierung von indirekt beheizten Drehrohren zur Verfügung, um bei einem neuen Einsatzstoff mit Daten aus experimentellen Basisuntersuchungen, die Temperaturverläufe im Feststoff und Gas sowie die Gaszusammensetzung in Abhängigkeit der wesentlichen Einflussgrößen abzuschätzen.Pyrolysis processes are used in the field of the thermal treatment of waste e.g. as a process unit in combination with a gasification or combustion unit realized in the RT21 process in Japan from Mitsui. Furthermore, pyrolysis processes are used for specially prepared waste fractions as a thermal pre-treatment unit, e.g. before a power station in the Con-Therm process in Germany or in the steel and cement industry. In principle there is also the possibility to use pyrolysis for the direct recycling of materials such as Plexiglass or plastics reinforced with carbon fibres. Rotary kilns are often used in the field of pyrolysis. The lumpy starting material is mixed due to the rotation of the rotary kiln. The energy for the pyrolysis can be given to the starting material indirectly, e.g. through radiant tubes from an external heater, to the rotary kiln wall or directly through a hot gas flow. The starting material is converted through the steps of drying, release and conversion of volatile components to a pyrolysis coke and pyrolysis gas. To optimize existing plants or to design new ones, mathematical models are important tools to minimize the experimental effort. In order to be able to describe the pyrolysis process in a rotary kiln using a mathematical model, the transport of the solid and the specific conversion processes dependent upon the construction parameters such as diameter and length of the rotary kiln as well as operating parameters such as angle of inclination, rotational frequency, throughput and course of the temperature over the length in the rotary kiln must be described. For process models which describe such processes in a reactor, it can usually be distinguished between a reactor model and a so-called basic model. The behavior of the solid in the reactor (residence time behavior) is described using the reactor model and the material and heat transfer as well as the conversion process with the help of the basic model. The mathematical model was evaluated for homogeneous materials (sand and polyethylene) as well as for mixed wastes. For both a good accordance between the experimental and mathematically determined data could be reached. With this simplified mathematical model and experimental data it is possible to show the dependency of the temperature profiles of the solid and gas phase and the gas species distribution of the main influencing parameters in for the practice suitable way for homogenous and heterogenous materials. To design a new rotary kiln for pyrolysis processes in industrial scale for a special input material, in general several investigations in a pilot scale plant are necessary. Based on these material and operational information (e.g. static bottoming angle and bulk density of the input material and its char, the pyrolytic gas composition etc.) a scale-up to the industrial plant and optimizing calculations could be done with the help of the mathematical model to estimate e.g. the maximum feed, a potential staging of the wall temperatures and the average residence time

Charakterizace paliv z biomasy v IPFR reaktoru

Combustion of fossil fuels is one of the most important source of energy. However low carbon politics and environmental commitments, affects developing combustion and co – combustion technologies. Utilization of biomass fuels can be answer for new challenges, although more research on effective utilization of these fuels are needed. Nowadays, combustion of biomass fuels, especially straw, causes many technical problems, mainly slagging formation, fouling of heat exchangers inside combustion chamber and insufficient fuel burnout. This paper focuses on analysis of biomass combustion. Better knowledge of behavior during biomass combustion may help to optimization of PF (Pulverized Fuel) boiler of and avoid some technical problems. The results of investigation shows that temperature and oxygen concentration in reactor play significant role in process of devolatilization and char burnout. For instance during char burnout experiments at temperature 850⁰C at 14% oxygen concentration after 200 ms more than 80% of mass loss were achieved. Compared to 700⁰C at 14% oxygen concentration this same level of mass loss were completed after 500 ms. Experiments performed on Isothermal Plug Flow Reactor (IPFR) at Institute of Energy Process Engineering and Fuel Technology (IEVB) at TU Clausthal were a part of project between IEVB and the Karlsruhe Institute of Technology (KIT) in Germany.Spalování fosilních paliv je jedním z nejdůležitějších zdrojů energie. Nicméně nízkouhlíková politika a environmentální závazky ovlivňují vývoj spalovacích a spolu-spalovacích technologií. Využívání paliv z biomasy může být odpovědí na nové výzvy, i když je zapotřebí více výzkumu o efektivním využití těchto paliv. V současné době spalování paliv z biomasy, zejména slámy, způsobuje řadu technických problémů, zejména tvorbu strusky, zanášení výměníků tepla uvnitř spalovací komory a nedostatečné vyhoření paliva. Tento příspěvek se zaměřuje na analýzu spalováníbiomasy. Lepší znalost chování procesů při spalování biomasy může přispět k optimalizaci návrhu práškového kotle a vyhnout se tím technickým problémům. Výsledky výzkumu ukazují, že teplota a koncentrace kyslíku v reaktoru hrají významnou roli v procesu tvorby prchavé hořlaviny a vyhoření tuhého zbytku. Například během experimentů s vyhořelým tuhým zbytkem při teplotě 850 ° C při 14% koncentraci kyslíku po 200 ms bylo dosaženo více než 80% úbytku hmotnosti. Ve srovnání se 700 ° C při 14% koncentraci kyslíku byla stejná úroveň úbytku hmotnosti dosažena po 500 ms. Experimenty provedené na izotermickém reaktoru (IPFR) v Institutu energetických procesů a technologií paliv (IEVB) na TU Clausthal byly součástí projektu mezi IEVB a „Karlsruhe Institute of Technology (KIT)“ v Německu

Methods for the evaluation of waste treatment processes

Decision makers for waste management are confronted with the problem of selecting the most economic, environmental, and socially acceptable waste treatment process. This paper elucidates evaluation methods for waste treatment processes for the comparison of ecological and economic aspects such as material flow analysis, statistical entropy analysis, energetic and exergetic assessment, cumulative energy demand, and life cycle assessment. The work is based on the VDI guideline 3925. A comparison of two thermal waste treatment plants with different process designs and energy recovery systems was performed with the described evaluation methods. The results are mainly influenced by the type of energy recovery, where the waste-to-energy plant providing district heat and process steam emerged to be beneficial in most aspects. Material recovery options from waste incineration were evaluated according to sustainability targets, such as saving of resources and environmental protection

Two- and Three-Dimensional Benchmarks for Particle Detection from an Industrial Rotary Kiln Combustion Chamber Based on Light-Field-Camera Recording

This paper describes a benchmark dataset for the detection of fuel particles in 2D and 3D image data in a rotary kiln combustion chamber. The specific challenges of detecting the small particles under demanding environmental conditions allows for the performance of existing and new particle detection techniques to be evaluated. The data set includes a classification of burning and non-burning particles, which can be in the air but also on the rotary kiln wall. The light-field camera used for data generation offers the potential to develop and objectively evaluate new advanced particle detection methods due to the additional 3D information. Besides explanations of the data set and the contained ground truth, an evaluation procedure of the particle detection based on the ground truth and results for an own particle detection procedure for the data set are presented

On the Development Concept for a New 718-Type Superalloy with Improved Temperature Capability

The superalloy 718 stands out for its excellent manufacturability and strength at ambient temperature. However, its application temperature is limited to about 650 °C due to the instability of the γ’’ precipitates. Here, we provide an in-depth account of an alloy development concept, allowing for the design of superalloys with 718-type properties, yet with a significantly improved microstructural stability. The article begins with a detailed discussion on how the microstructural and chemical composition must be altered to achieve this objective. Then, model alloys were used to explore and validate the outlined strategy. Finally, it is shown how these considerations ultimately led to a new 718-type superalloy with far more improved microstructural stability— namely, VDM Alloy 780. The introduction of a large amount of Co as a substitute for Fe (and partially Ni) is the most important element of our alloy development concept in terms of chemical composition. The most important microstructural feature is the introduction of low solvus temperature, high misfit γ´-strengthening, replacing γ´´-hardening

Hybrid Models for Efficient Control, Optimization, and Monitoring of Thermo-Chemical Processes and Plants

This paper describes a procedure and an IT product that combine numerical models, expert knowledge, and data-based models through artificial intelligence (AI)-based hybrid models to enable the integrated control, optimization, and monitoring of processes and plants. The working principle of the hybrid model is demonstrated by NOx reduction through guided oscillating combustion at the pulverized fuel boiler pilot incineration plant at the Institute for Technical Chemistry, Karlsruhe Institute of Technology. The presented example refers to coal firing, but the approach can be easily applied to any other type of nitrogen-containing solid fuel. The need for a reduction in operation and maintenance costs for biomass-fired plants is huge, especially in the frame of emission reductions and, in the case of Germany, the potential loss of funding as a result of the Renewable Energy Law (Erneuerbare-Energien-Gesetz) for plants older than 20 years. Other social aspects, such as the departure of experienced personnel may be another reason for the increasing demand for data mining and the use of artificial intelligence (AI)

3D Refuse-derived Fuel Particle Tracking-by-Detection Using a Plenoptic Camera System

Multiple particle tracking-by-detection is a widely investigated issue in image processing. The paper presents approaches to detecting and tracking various refuse-derived fuel particles in a industrial environment using a plenoptic camera system, which is able to yield 2D gray value information and 3D point clouds with noticeable fluctuations. The presented approaches, including an innovative combined detection method and a post-processing framework for multiple particle tracking, aim at making the most of the acquired 2D and 3D information to deal with the fluctuations of the measuring system. The proposed novel detection method fuses the captured 2D gray value information and 3D point clouds, which is superior to applying single information. Subsequently, the particles are tracked by the linear Kalman filter and 2.5D global nearest neighbor (GNN) and joint probabilistic data association (JPDA) approach, respectively. As a result of several inaccurate detection results caused by the measuring system, the initial tracking results contain faulty and incomplete tracklets that entail a post-processing process. The developed post-processing approach based merely on particle motion similarity benefits a precise tracking performance by eliminating faulty tracklets, deleting outliers, connecting tracklets, and fusing trajectories. The proposed approaches are quantitatively assessed with manuelly labeled ground truth datasets to prove their availability and adequacy as well. The presented combined detection method provides the highest F 1 -score, and the proposed post-processing framework enhances the tracking performance significantly with regard to several recommended evaluation indices

Use of Low-quality Biogenic Fuels in a Decentralized Biomass Boiler for Thermal Energy Generation

The KIT generate heat with three hot water tube boilers and a combined heat and power unit. Their operation is based on natural gas. Alternatively, light fuel oil can be used in the hot water tube boilers. For the future the KIT has to achieve climate protection goals and for that to consider about alternative heat generation. This could be the operation of a biomass boiler, which is operated with wood chips or wood pellets. The Institute of Technical Chemistry (ITC) and Facility Management (FM) of KIT in cooperation with medium-sized enterprises now plans to integrate a decentralized biomass boiler into the existing heat supply network of KIT Campus North. The goal for the decentralized biomass boiler is to operate with low-quality biogenic fuel. Within the framework of preliminary studies, the biogenic fuels shall be characterized according to their combustion properties. To enhance sustainability, reduce the consumption of resources and increase economic efficiency, the studies are to focus on the use of waste materials. In addition, the waste flows at KIT and the suited waste shall be identified. The considered materials are lop, sieve residues or other previous identified waste. When planning such a project, legal and licensing-relevant aspects and their consequenses have to be considered. Then, the requirements to be met by the selected fuels will be listed and experimental tests at the “KLEAA” test facility of ITC will be reported. This test facility is a fixed bed reactor used for the characterization of burnout of solid fuels. Studies are aimed at identifying and assessing alternative fuels for future use in biomass boilers. Furthermore side effects such as corrosion, slagging, and emissions shall be taken into account. Depending on the achieved intermediate data the insert of additives to reduce the side effects will be tested. The project findings will be verified in an experimental facility later on. In the proposed paper first results of the preliminary investigations shall be presented

Methods for the Evaluation of Waste Treatment Processes

Decision makers for waste management are confronted with the problem of selecting the most economic, environmental, and socially acceptable waste treatment process. This paper elucidates evaluation methods for waste treatment processes for the comparison of ecological and economic aspects such as material flow analysis, statistical entropy analysis, energetic and exergetic assessment, cumulative energy demand, and life cycle assessment. The work is based on the VDI guideline 3925. A comparison of two thermal waste treatment plants with different process designs and energy recovery systems was performed with the described evaluation methods. The results are mainly influenced by the type of energy recovery, where the waste-to-energy plant providing district heat and process steam emerged to be beneficial in most aspects. Material recovery options from waste incineration were evaluated according to sustainability targets, such as saving of resources and environmental protection