Chemical Looping Hydrogen Generation Using Potassium-Modified Iron Ore as an Oxygen Carrier

Abstract

Chemical looping hydrogen generation (CLHG) consists of an oxidation process, a reduction process, and a hydrogen generation process. Achieving deep reduction of the oxygen carrier is the challenge for the CLHG process. In this paper, experiments on CLHG using K-modified iron ore as an oxygen carrier and CO as a fuel were carried out in a laboratoryscale fluidized bed reactor. A high temperature improved the reduction reactivity. However, at the same reduction condition, a higher temperature did not improve the hydrogen generation process, which means that a higher temperature mainly benefited the reduction process and then elevated hydrogen generation in a CLHG process. Adding KNO 3 improved the rate of reduction and hydrogen generation. With the KNO 3 loading in iron ore increasing from 0 to 10%, not only the carbon conversion but also the hydrogen production was accelerated. A high KNO 3 loading in iron ore can also maintain longer reaction time. The 10% Kmodified iron ore could decrease carbon deposition. The scanning electron microscopy analysis and the cycling experiments indicated that adding K could keep the porous structure of the oxygen carrier and the K-modified iron ore was a stable catalyst in the CLHG process.

Inhibition of carbon deposition using iron ore modified by K and Cu in chemical looping hydrogen generation

“…As discussed above, the carbon deposition was significantly suppressed by introducing potassium and copper to modify iron ore. The similar effect was also observed when iron‐based oxygen carrier was modified by copper or potassium separately . It was the first work to investigate the property of carbon deposition based on iron ore co‐decorated by potassium and copper, and the condition was different from most of the previous researches .…”

“…These Fe‐Cu‐K solid solutions would be formed during the calcining process. There were few studies considering the property of K 4 CuO 3 , but many researches had reported that K 2 Fe 4 O 7 and CuFe 2 O 4 were active phases to improve the reactivity and deepen reduction of iron oxides . (3) Additionally, the migration of potassium and copper made the oxygen carrier particle more porous, and it was beneficial to enhance the reduction rate .…”

“…During the deep reduction, 6% CO is introduced as fuel gas to produce FeO and Fe which are considered as the effective constituent for hydrogen production (R2‐R4). The reduction period lasts for 60 minutes which had been demonstrated to obtain a deep reduction with a relatively high reaction rate . After that, the reduced particles are exposed to the oxidation atmosphere with steam (0.5 g/min) to generate hydrogen (R5, R6) for 30 minutes.…”

“…Kang et al has reported that the carbide and graphite formation were inhibited effectively for CuFe 2 O 4 , as compared with Fe 3 O 4 . Furthermore, alkali metal K has already been employed to modify the natural ores as promoter of reactivity and inhibitor of carbon deposition . Gu et al had pointed out that K 2 CO 3 ‐decroated iron ore accelerated the reaction rate in the CLC.…”

“…Gu et al had pointed out that K 2 CO 3 ‐decroated iron ore accelerated the reaction rate in the CLC. Liu et al had also investigated the performance of K‐modified iron ore and found that adding KNO 3 improved the reduction rate and the hydrogen yield, as well as suppressed the carbon deposition in CLHG process.…”