Study on the Interaction of the Fe-Based Oxygen Carrier with Ashes
Danyan Cheng, Qirun Yong, Yongchun Zhao, Bengen Gong, Junying Zhang
Abstract
Oxygen carriers (OCs) are the key factor in chemical looping combustion (CLC), a promising and efficient technology for converting coal and biomass into pure carbon dioxide and high concentrations of hydrogen. However, existing CLC techniques cannot completely separate OCs and ash, which could affect the performance of the OCs through the interaction with the ash-forming mineral matter at a high temperature. In this work, the effect of solid–solid carbothermal reactions on the Fe-based OC was systematically examined via changes in the carbon content and temperature. Furthermore, the CLC of the Fe-based OC was simulated by a fixed bed reactor, with oxidizing and reducing gases switched constantly. The results indicated that the added amount of biomass carbon had a significant influence on the Fe-based OC. Under highly reducing conditions, the reduction between Fe 2 O 3 and C took precedence and inhibited the reaction between Fe 2 O 3 and minerals. Under weakly reducing conditions, the reactions between Fe 2 O 3 and minerals were promoted. In the looping experiment of the Fe-based OC and ash, a small amount of ash could promote the reduction of Fe 2 O 3 . When ash accumulated, some foreign ions (Ca 2+, K +, and Na + ) in the ash interacted with the aluminosilicate to form compounds with lower melting points, covering the surface of Fe 2 O 3 particles to hinder the reaction. Increasing the cycle temperature not only accelerated the reaction of Fe 2 O 3 but also promoted the formation of large particles, such as (Fe 2 SiO 4 ) x ·(Fe 3 O 4 ) 1– x and CaMgSi 2 O 6, which aggravated sintering and decreased the oxygen-releasing performance of the OC.