Reduction Kinetics of Foreign-Ion-Promoted Ilmenite Using Carbon Monoxide (CO) for Chemical Looping Combustion

Abstract

In a previous work by our group, a new kind of ilmenite oxygen carrier, namely, natural ilmenite particles impregnated with foreign ions (K+, Na+, or Ca2+), was reported as having a promoted reactivity. The objective of this work was to investigate the detailed reduction kinetics of the new foreign-ion-promoted ilmenite carrier. Ilmenite particles impregnated with different types of foreign ions, including K+, Na+, and Ca2+, at different loading ratios were investigated by thermogravimetric analysis (TGA) using CO as the reducing gas. The samples tested by TGA for kinetics included the initial ilmenite particles and particles extracted from the fluidized-bed reactor after 40, 70, or 100 continuous redox cycles, as was done in the previous work. The obtained kinetic parameters were applied for the design of a chemical-looping combustion (CLC) reactor. The findings confirmed that the impregnation of foreign ions can promote the reduction rate of ilmenite. The kinetic data obtained by TGA indicated that the 15 wt % K+-promoted ilmenite showed a ∼6.85 times faster reactivity than the activated raw ilmenite after 40 cycles in the fluidized bed. Even when the number of cycles was increased to 100, the modified ilmenite still maintained a much higher reduction rate than the activated raw ilmenite. Although the reduction rate of the 15 wt % K+-promoted ilmenite decreased as the CO concentration decreased, it still remained higher than the reactivity of the activated raw ilmenite. A theoretical calculation with the kinetic parameters indicated that the required minimum solids inventory of the fuel reactor was 1670 kg/MWth for the 15 wt % K+ promoted ilmenite, which was approximately one-seventh that required for the activated raw ilmenite (11436 kg/MWth).

Chemical-Looping Combustion and Gasification of Coals and Oxygen Carrier Development: A Brief Review

“…To study the impact of oxygen concentration on reaction rates, the O2 concentration was selected between 0-9 vol % for reduction and 1.5-21 vol % for oxidation. The reaction rate is presented in Equation (36): , (36) where Co2 is the O2 concentration at each time and Co2,eq is the O2 concentration at equilibrium. Equations 35 and 36 are also valid for oxidation reactions.…”

“…In general, natural minerals usually have lower reactivity than synthetic oxygen carriers. Research on improving natural mineral reactivity with the addition of metal oxides or alkali and alkaline metals (K+, Na+, or Ca+) has been reported [35][36][37][38].…”

Characteristics of hematite and fly ash during chemical looping combustion of sewage sludge

“…Those compounds act as catalysts which can not only enhance pyrolysis and gasification [32], but also promote the reactivity of hematite. Bao et al found that the addition of foreign ions (K + , Na + or Ca 2+ ) could significantly promote the reduction rate of ilmenite [21,22]. Additionally, the consumption of CO and H 2 , which has an inhibiting effect on steam gasification, can increase the fuel conversion rate [33].…”

“…Besides, Ksepko [19] reports that sludge ash can be effectively used as a low-cost, valuable oxygen carrier in CLC process. In addition, it should be mentioned that a large amount of Ca is presented in sludge ash [20], which has been shown to be an efficient additive in oxygen carrier to promote the reactivity of carrier and catalyze gasification process [21,22]. Thus, the interaction between sludge ash and oxygen carrier cannot be ignored.…”

The performance of Fe2O3-CaO Oxygen Carriers and the Interaction of Iron Oxides with CaO during Chemical Looping Combustion and H2 production

“…Calcium oxide has well known interactions with iron oxide and the thermodynamics of the Ca-Fe-O system are available in the literature. CaO is cheap and more recent work by Bao et al [10] has shown that addition of foreign ions such as Ca 2+ , Na + and K + enhanced the reactivity of Ilemenite (an iron based mineral -FeTiO3) in looping reactions. Since CaO is often used as a fluxing agent in steel making, it might be expected that it's addition to the iron oxide might worsen sintering.…”