Study of the interaction between a Mn ore and alkali chlorides in chemical looping combustion.

• Four alkalis are compared for the interaction with a Mn ore oxygen carrier in CLC. • Potassium salts result in earlier onset of defluidization than sodium. • Carbonate alkalis (Na and K) derived defluidization is more permanent than chloride. • Sodium retention in the oxygen carrier is double that for potassium. Chemical looping combustion (CLC) is a novel technology for heat and power generation with inherent CO 2 capture. Using biomass in CLC (bio-CLC), negative CO 2 emissions can be attained. Biomass usually contains high content of alkalis (mainly K and Na) which can be problematic in the process, such as potential alkali-bed interaction, and this is the focus of current work. This work uses charcoal with and without the impregnation with alkali chlorides, KCl and NaCl. The results are compared to previous data from samples impregnated with K 2 CO 3 and Na 2 CO 3. A low-alkali braunite manganese ore is used as bed material to study the oxygen carrier interaction with the alkalis in cyclic experiments at 950 °C in a quartz batch fluidized-bed reactor. As compared to charcoal without alkali impregnation, the impregnation with KCl, NaCl, K 2 CO 3 , and Na 2 CO 3 can improve the rate of gasification by a factor of 4, 3, 10, 8, respectively. Partial-defluidization of the braunite particles was found with all the alkali-fuels, although the extent differed, e.g., K 2 CO 3 and KCl resulted in earlier onset of defluidization than Na 2 CO 3 and NaCl. Further, indications of partial defluidization were earlier and more permanent with the carbonates than the chlorides. Partial agglomeration with soft agglomerates of the bed was observed, while hard agglomerations were never seen. Accumulation of K, Na, Si, and Ca was found in the agglomerates after cycles with K 2 CO 3 -charcoal and Na 2 CO 3 -charcoal, while little K and Na was detected in the bridges between particles after the KCl and NaCl cycles. A significant fraction of the alkali added was found in the oxygen carrier, with 80% or more being retained for the Na salts, and around 40% for the K salts. There was no clear difference between chlorides and carbonates with respect to retention. The fresh and used braunite have very similar reactivity with CH 4 and H 2 , whereas some decrease in reactivity is noticed with CO. [ABSTRACT FROM AUTHOR]