Search

Der vorliegende Beitrag zeigt Untersuchungsergebnisse eines in Kooperation zwischen der TU Chemnitz und der Universität Paderborn durchgeführten AiF-IGF Vorhabens zum Warmgasstumpfschweißen. Die inhaltlichen Schwerpunkte lagen einerseits auf Analysen zum Einfluss des Werkzeugdesigns auf das Erwärm- und Schweißverhalten sowie andererseits auf Untersuchungen zum Einfluss des Prozessgases (Luft vs. Stickstoff) und den im Vergleich erreichbaren Nahteigenschaften. Im Rahmen des Projektes konnte gezeigt werden, dass insbesondere die verwendete Düsengeometrie einen signifikanten Einfluss auf das Erwärmverhalten ausübt und sich dieses direkt in den Schweißnahteigenschaften widerspiegelt. Bei der richtigen Auswahl und Einstellung des Schweiß-Setups können sowohl mit Luft als auch mit Stickstoff hohe und vergleichbare Schweißnahteigenschaften erreicht werden.

Ill., graph. Darst.

Oxycoal processes are promising power plant concepts which would allow easy CO2 removal from the exhaust products. These processes are based on the combustion of coal with recirculated flue gas that has been enriched in oxygen. To ensure the energy efficiency the oxygen may be provided by a high temperature oxygen membrane. Because of the high partial pressure of CO2 in the flue gas, the hot gas chemistry and ash behaviour of the system change in comparison to conventional air blown systems. The aim of the present work was to examine the effects of these changes concerning the condensation and stability of alkali metal containing ash and slag phases. The results led to an evaluation of the fouling and corrosion potential that is given by these phases. Thermodynamic modelling calculations have been made to characterise the alkali containing ash and slag phases that condensate in the process at different combustion conditions, as well as to investigate the interaction between these phases and nickel base alloys of a future power plant. Experimental investigations with conditions of an oxycoal process demonstrated the release of alkali metals, chlorine and sulphur during coal combustion, the sorption of the alkali metals on solid alumosilicates, the condensation of ashes and the interaction between these ashes and materials of filter candles. The results of the experiments complement and generally affirm the results of the modelling calculations. It has been shown that the stability of alkali metal containing sulphates, chlorides and carbonates is depending on one hand on the oxygen content of the combustion gas, on the other hand on the silicon and aluminium content of the coal. According to the lambda-value and the used type of coal a certain risk of sulphate or carbonate induced hot corrosion has to be considered for metal materials, especially nickel base alloys. Further on, it has been found out, that by the use of coals, which are poor in silicon and aluminium, the formation of alkali metal containing ashes and solid or liquid slag may cause malfunction or even the destruction of filter candles. Finally the investigations show that an effective hot flue gas cleaning concerning the alkali metals is a requirement to protect the high temperature oxygen membrane from fouling and corrosion, if the membrane operates at the same or slightly lower temperature as the gas cleaning. Results reveal that the use of solid alumosilicates as sorbent is a feasible option for this purpose.

High porous alumina fiber structures appear promising for hot gas filtration in particular for diesel particulate traps. For this purpose, however, a method is required for manufacturing of stable shapes resistant to the blow-out by the gas flow. The sol-gel-process was expected to be the best suited method for fiber bonding to provide the required stability.The main tasks of the development-work were a uniform isotropie fiber-distribution, the adaptation of the sol-gel-process to the application, and the deliberate synthesis of the gel-derived alumina bonding phase.The appropriate fibrous structure was obtained by a repeated filtration of sol/fiber suspensions. The properties of the ceramic binder were adapted by concentrating the sol and/or adding aluminas or aluminium hydroxides.Testing of prototypes with optimized structures has shown, however, that the stability of the structure decreased after thermal load. The thermal fatigue of x-A12O3 is assumed to be responsible for this failure.