Är det möjligt att använda SCR-rening av rökgaserna vid inblandning av avfall i biobränslet?
Waste appears to be a low-cost fuel compared to biofuel. This Masters thesis was conducted for Vattenfall Utveckling AB and deals with how waste in the fuel affects the performance of a SCR-catalyst. Different mechanisms of deactivation were surveyed, focusing on the poisoning mechanism. A literature study was carried out, which was used as a reference when analysing the results.Small samples (9x2x2 cm, 64 pieces) cut out from a full-scale unused honeycomb catalyst were exposed up to 1500h in two different combustion plants, Johannes in Gävle (co-combustion) and Högdalen in Stockholm (waste-combustion). The activity was measured mainly at 300°C but also at 250, 350, 375 and 400°C. SEM/EDS-analysis (about 20 samples) and wet chemical analysis (about 20 samples + 2 fly-ash samples) was then performed on the samples. A sample from each boiler was sent for BETanalysis.The results from the analysis above were compared to earlier studies conducted on bio-fuel plants in order to investigate what might have deactivated the catalyst samples. Also a small multivariate data analysis (MVDA) was performed. The results from the study show that the catalyst samples exposed in Johannes have slightly less than 60 % of the activity left after 1500h, for Högdalen only 20 % of the activity remains after 1500h. For Johannes when only firing biofuel the corresponding figure is 74 % and in a coal-fired boiler just over 80 % of the activity remains after 1500h. For catalysts with a higher initial activity the deactivation rate is slower. The main mechanism of deactivation is poisoning from alkali metals. In Johannes the poisoning is mainly due to water-soluble potassium. In Högdalen water-soluble potassium, sodium and acid soluble lead causes the deactivation. Potassium stands for just over half of the poisoning effect, sodium just over 1/3 and lead for less than 1/6. SEM/EDS-analysis shows that the potassium content is about 3 times higher the first centimetre from the inlet, than the rest of the sample. The difference in potassiumconcentration between the surface and the walls of the catalyst is rather small. The concentration of lead on the other hand was found to be constant along the catalyst, but the concentration on the surface is much higher than in the walls. Erosion, sintering and plugging have not been studied in detail. Erosion tends to be a bigger problem in Johannes than in Högdalen, probably due to the texture of the fly ash. It does not seem to be any risk of sintering where the test-bench was exposed. For Johannes plugging was estimated to affect around 25 % of the channels in the samples after 1000h of exposure. Solely exposure for fly ash wasn?t found to affect the activity significantly.