Experimental assessments of pyrolytic and fluid-dynamic interactions between pretreated residual biomasses and fluidized beds made up of oxygen carriers for chemical looping gasification

Abstract

Oxygen carriers (OCs) and wheat straw pellets (raw or pretreated by combinations of torrefaction, CaCO3-addition, water-washing) were experimentally investigated for Chemical Looping Gasification (CLG) in the Horizon2020 project CLARA (Chemical Looping gAsification foR sustAinable production of biofuels, grant agreement n.817841). Laboratory-scale experiments included: (i) pellet devolatilizations (700 °C-900 °C) in bubbling fluidized beds made of OCs or sand; (ii) study of pressure fluctuations within OC fluidized beds (700–1000 °C) containing 10 vol% of ashes from investigated pellets, to assess OC/ash interactions and fluidization quality. Those two campaigns – performed at relevant process conditions for CLG – allowed straightforwardly screening and selecting the most eligible biomasses and OCs for future CLG demonstrations in fluidized beds at higher scales. Gas yield, H2/CO molar ratio, and carbon conversion increased as the devolatilization temperature increased from 700 °C to 900°C. Untreated and pretreated wheat straw pellets showed different pyrolytic behaviors. Analyses of pressure fluctuations and characterizations of spent beds (scanning electron microscopy, particle size distribution) suggested that biomass pretreatments limit agglomeration phenomena, depending on OCs nature (e.g., mechanical strength, composition). Ilmenite was the most mechanically and chemically stable OC. Among investigated materials, pretreated wheat straw pellets and ilmenite emerged as the most promising for future CLG demonstrations.