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TY  - THES
AU  - Schenke, Lukas
TI  - Entwicklung eines Kugelrosts zur Verbrennung von Biomassepellets aus Weizenstroh in Kleinfeuerungsanlagen
PB  - Rheinisch-Westfälische Technische Hochschule Aachen
VL  - Dissertation
CY  - Aachen
M1  - RWTH-2020-06934
SP  - 1 Online-Ressource (141 Seiten) : Illustrationen, Diagramme
PY  - 2020
N1  - Veröffentlicht auf dem Publikationsserver der RWTH Aachen University
N1  - Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020
AB  - The energetic use of biomass is an important component of the energy supply from renewable energies. A considerable energetic utilization potential of agricultural grain straw currently remains unused in the Federal Republic of Germany. However, grain straw is produced regionally in very different quantities, of which varying straw masses are available for energetic utilization due to competing utilization paths. In order to avoid long transport distances, decentralized energetic utilization in small-scale furnaces is an option. The incineration of straw poses great challenges for the plant technology. Chemical elements contained in the fuel, such as potassium, ensure low ash melting temperatures. At normal combustion temperatures, the ash melts or sinters, resulting in plant malfunctions and shutdowns. By washing out the straw with water (leaching), such problematic constituents can be reduced. In combination with additives, which are added to the straw during pelleting, ash melting can be prevented. However, sintering of the ash cannot be completely avoided, which is why the pellet ash remains as an ash body in geometric pellet form without combustion bed movement or stoking. It cannot be transported away through the grate slots. This problem was tackled by developing a continuously operated ball grate system for moving the firing bed or the pellet ash. A mixer was integrated on the grate plate in a drop shaft furnace with burner pot and a grate plate provided with grate slots. Balls were poured onto the mixer or grate plate. The mixer causes a ball movement and thus a moderate firing bed movement, whereby the ash slowly sinks through the ball bed, is partially crushed and transported away with the help of the mixer through grate slots. The basic principle of the developed ball grate system was first tested in cold tests. As was to be expected, the straw pellets were transported through the moving ball bed into deeper layers of the bed. Due to the cold tests, the particularly relevant influencing parameters mixer speed and ball diameter could already be estimated as start parameters of the combustion tests. Combustion tests with the integrated ball grate system were carried out in a drop firing system with a nominal heat output of 65 kW. The aim was to investigate the influences of mixer speed, ball diameter, ball material and pouring height on the functionality and efficiency of the system. For this purpose, temperatures, air mass flows and exhaust gas concentrations were continuously recorded during the tests. After the tests, the remaining ash in the burner pot could be gravimetrically recorded, the balls and the grate system examined for material-related changes and the ash removed analyzed as a measure of the ash burnout with regard to the annealing loss. Wheat straw was used as the test material and leached after harvesting, dried and pelletized as an additive with the addition of lime hydrate. In the first experiments without balls and with a single ball layer a too high temperature stress of the mixer could be determined. The shaft of the mixer deformed, blocking the system. A multi-layer pouring height of 60 mm ensured sufficient heat shielding of the mixer from the firing bed. V2A stainless steel was determined to be the most suitable ball material. Other material types were susceptible to corrosion, temperature or adhesion due to a too rough surface. High mixer speeds of 4.82 min-1 resulted in excessive carbon monoxide emissions, some of which significantly exceeded the legal limit of 400 mg/m3. The most suitable parameters were ultimately a mixer speed of 0.84 min-1, a pouring height of 59 mm with V2A stainless steel balls with a diameter of 15 mm and a primary air number between 0.7 and 0.8.A long-term test consisting of five separate individual tests was carried out with these parameters. After the tests, highly different results were obtained with regard to ash removal from the burner pot. In three of the five tests, all ash was almost completely removed and no adhesion or deposits on the balls could be detected. In two experiments, however, 12 
LB  - PUB:(DE-HGF)11
DO  - DOI:10.18154/RWTH-2020-06934
UR  - https://publications.rwth-aachen.de/record/793453
ER  -