CaO-based sorption-enhanced steam gasification of biomass for high purity H2 production: a modeling approach

In this study, a detailed simulation model of steam-only gasification of pine sawdust with limestone for in situ CO₂ capture and simultaneous tar elimination is developed using the ASPEN plus simulator. The predicted results were compared with the experimental data available in the literature, and a good agreement was found. After validating the model, a parametric study was performed to investigate the influence of operational conditions on the product gas composition and the gasification characteristics. In order to evaluate the reactivity of carbonation reaction in terms of tar destruction and CO₂ absorption, two parameters named CO₂ capture ratio (CCR) and tar cracking ratio (TCR) are also defined. According to the predicted results, higher temperature and introducing more sorbent particles are favorable for promoting the H₂ production and tar elimination; however, enhancing H₂ production and tar conversion is marginal above CaO/biomass ratio (C/B) of 1.5. The addition of steam not only increased H₂ content and H₂ yield by promoting water–gas shift reaction but also apparently enhanced tar reforming/cracking and char conversion. The predictions also showed that the limestone can play the role of both CO₂ absorber and tar converter at low temperature (T < 800 °C); however, it only acts as a catalyst for tar conversion at high temperature (T > 800 °C). For C/B > 1.5, CCR showed a slight increase, implying that less CO₂ was captured as the C/B increased from 1.5 to 2.0.