Hydrogen with purity higher than 90% was produced continuously by sorption-enhanced steam methane reforming reactions in two parallel fixed-bed reactors operated in a cyclic manner. The process involved sorption-enhanced steam methane reforming reactions and a sorbent regeneration reaction. First, through addition of a CO2 sorbent into a reforming reactor, the reactions of reforming, water−gas shift, and CO2 sorption were combined, and more CH4 was expected to convert H2 in one reactor. Second, regeneration of the sorbent was carried out in the other reactor. The hydrogen production and sorbent regeneration processes were carried out simultaneously in the two fixed-bed reactors, operated in a cyclic manner by switching a methane/steam feed and an Ar-containing feed between the two reactors at a fixed feed switchover time. The critical value of the feed switchover time for achieving the production of higher concentrations of hydrogen was investigated and analyzed.

Experimental results performed with a fluidized-bed reactor supported the feasibility of the three processes including direct reduction of iron oxide by char, H2 production by the steam−iron process, and the oxidation of Fe3O4 resulting from the steam−iron process to the original Fe2O3 by air. Chars resulting from a Chinese lignite loaded with K2CO3 were used successfully as a reducing material, leading to the reduction of Fe2O3 to FeO and Fe for the steam−iron process, which was confirmed by both the off-gases concentrations and X-ray diffractometer analysis. The reduction of Fe2O3 by K-10-char at 1073 K is desirable from the perspective of the carbon conversion rate and high concentration of CO2. The carbon in char was completely converted to CO2 when the mass ratio of Fe2O3/K-10-char was increased to 10/0.3. The oxidation rate of K-10-char by Fe2O3 without a gasifying agent was comparable to the K-10-char steam gasification rate. The fractions of FeO and Fe in the reduced residue were 43 and 57%, respectively, in the case of 3 g of Fe2O3 and 0.5 g of K-10-char, which was verified by the total H2 yield equaling 1000 mL/g K-10-char from the steam−iron process. The time that it took to achieve complete oxidation of Fe3O4 to Fe2O3 by air with an 8.7% O2 concentration at 1073 K was about 15 min.

The feasibility of the reduction of oxygen carrier Fe 2 O 3 in chemical-looping combustion using solid fuel (lignite) provided a gasifying agent like steam was introduced into the reactor was investigated with a fixedbed reactor. The X-ray diffractometer and scanning electron microscope were used for the characterization of the Fe 2 O 3 and its reduction residue. Results strongly supported the feasibility of Fe 2 O 3 reduction by lignite and obtaining pure CO 2 from the off-gases. Fe 2 O 3 can be fully converted to Fe 3 O 4 by pyrolysis and gasification intermediates primarily H 2 and CO, which was confirmed by both the off-gas concentrations and X-ray diffractometer analysis. A 0.75 g portion of Fe 2 O 3 can be completely reduced to Fe 3 O 4 by the volatile matter released from 0.1 g coal, and Fe 2 O 3 can be fully reduced to Fe 3 O 4 by steam char gasification products provided that the molar ratio of carbon in char to Fe 2 O 3 is 1:6. The purity of CO 2 in the outlet gases was higher than 85% when Fe 2 O 3 was reduced by intermediate products during coal pyrolysis, and the purity of CO 2 in the off-gases was higher than 95% when Fe 2 O 3 was reduced by intermediate products resulting from steam char gasification, making CO 2 sequestration disposal desirable for high purity CO 2 . The char gasification reaction rate was slow compared with the reactivity of the iron oxide with the char gasified intermediates, indicating that char gasification was the rate-limiting step in the reduction process. In the steam char gasification process, the times it took to reach 90% carbon conversion for K-10-char and Ca-10-char were 15 and 30 min, respectively, at 1123 K, but the time for the raw char was 50 min at 1173 K.

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