Ash interactions with oxygen carriers Glödskal and LD-slag in biomass-CLC
Examensarbete för masterexamen
Innovative sustainable energy engineering, MSc
Chemical-looping combustion (CLC) is a novel combustion technology where fuel is converted in the absence of air. The process is carried out in two ﬂuidized bed reactors, one in which a metal oxide (oxygen carrier) is oxidized by air and one in which fuel is converted to combustion products through reaction with the oxidized oxygencarrier. Thecombustionproductsarethusinherentlyseparatedfromairand CO2 can be separated for carbon capture and storage without large energy penalties. Much of the current work with implementing conventional scale CLC aims at evaluatingtheperformanceandeconomicviabilityofdiﬀerentoxygencarriers. CLC of biomass is of interest for sustainability reasons and evaluating if oxygen carriers are suitable for biomass-CLC includes ensuring that the material can perform well also in the presence of biomass ashes. Glödskal and LD-slag are two low cost steel industry by-products that have shown desirable fuel conversion properties in CLC, and their interactions with some common potassium ash components (KCl, K2CO3, K2SO4 and KH2PO4) in reducing atmosphere have been investigated in this study. Glödskal consists mainly of Fe and Fe oxides and traces of other metals and oil residuesfromtheprocess. ThemaincomponentsofLD-slagisCa-oxidesandoxides of Fe, Si, Mg and Mn. LD-slag also contains lower concentrations of Al, Ti and V. Utilizing low cost waste materials is beneﬁcial both for economic and sustainable reasons. The materials have been mixed with potassium salt to obtain a mixture with 4wt% potassium content. The mixtures have been reduced in a glass quartz reactor for 8 hours in 850°C. The reduced samples have been analyzed in SEM with EDS.ThemixtureshavealsobeentestedinThermogravimetricanalysis. Itwasseen that all the salts except for KH2PO4 had positive eﬀect on the porosity of Glödskal. K2CO3 increased the reduciton rate of Glödskal. KH2PO4 caused agglomeration of Glödskal which had a negative impact on the reactivity. The agglomeration is due to formation of a K-P-Fe component. Some accumulation of K was seen in both Glödskal and LD-slag after reduction in the presence of K2SO4. With K2CO3 and K2SO4 K accumulated in LD-slag together with vanadium. K2CO3 deactivated LDslag. KH2PO4 reacted with Ca in LD-slag and formed a K-P-Ca component which caused some agglomeration but didn’t aﬀect the reduction rate.
Kemi , Kemiteknik , Chemical Sciences , Chemical Engineering