Comprehensive investigation on the gasification reactivity of pyrolysis residue derived from Ca-rich petrochemical sludge: Roles of microstructure characteristics and calcium evolution

Abstract

Pyrolysis-gasification coupling process is an effective technology that can realize the thorough reutilization and clean disposal of petrochemical sludge. However, pyrolysis residue of petrochemical sludge (PRPS) produced at different temperatures possesses obviously different structure properties, which profoundly impacts the subsequent gasification. This study reveals the effect of pyrolysis degree of PRPS on the CO2 gasification reactivity by evaluating the micromorphology, pore property, existed form of calcium mineral and carbon structural characteristics. Results demonstrate that micromorphology development of the PRPSs with diverse pyrolysis degree (PRPS prepared at 500–900 °C) has three main stages, namely, the emergence of macropores and fissures (500–600 °C), the pore development (700–800 °C), and the pore jam (900 °C). The optimal PRPS was obtained at 800 °C-pyrolysis (800-PRPS) as the maximal specific surface area and desorption pores volume were observed. In addition, Raman analysis indicated that the 800-PRPS has the best carbon activity as well. By further increasing pyrolysis temperature to 900 °C, the carbon disordering, defect, and active sites of the PRPS decreased. Moreover, results of non-isothermal PRPS-CO2 reaction indicated that the basic calcium compound carbonation, gasification, calcium carbonate decomposition regimes were involved. Compared with 800–900 PRPSs, 500–700 PRPSs were more vulnerable in the lower gasification temperature owing to the more char matrix remain. In addition, owing to the occurrence of the carbonation reaction, the calcium carbonate product layer was formed and might affect the early-age gasification.