Reduction behavior and growth kinetics of metallic iron in slag bath of BGL coal gasifier

Abstract

The appearance of metallic iron reduced by residual char leads to the serious blockage and unpredictable shut-down of coal gasifiers, especially in moving bed slagging gasifiers. To prevent blockage, the reduction and growth characteristics of metallic iron are required to understand. In this study, slag mixed char and metallic iron from an industrial British Gas-Lurgi (BGL) coal gasifier was separated and analyzed to the properties of metallic iron formation process under gasification conditions. Results showed the relative carbon content (α) had the strongest effect on the content and average particle size of iron at α = 1.2 in this work. The reduction was weakened by poor mass transfer of reduction reaction when α > 1.2. The endothermic reduction reaction was promoted by the increase in high temperature. The iron precipitation and particle growth can be divided into rapid increase and stable stage with the increase of reduction time, corresponding to the reduction and accumulation of iron. The growth model of the metallic iron in slag under gasification condition was established as D = 4.439 × 10^10 × t^(1/1.190) × exp^(−340.716 × 10^3/RT) (t ≤ 900 s) and D = 4.277 × 10^14 × t^(1/3.580) × exp^(−412.253 × 10^3/RT) (t > 900 s, R2 = 0.9868). The growth model of metallic iron in slag can provide guidance for slag tapping operation of fixed-bed slagging gasifier during iron-rich coal gasification.