Biomass Char Direct Chemical Looping Gasification Using NiO-Modified Iron Ore as an Oxygen Carrier

Abstract

Chemical looping gasification (CLG) is considered as a novel gasification technology because gas-phase oxygen of the gasifying medium can be replaced by lattice oxygen of the oxygen carrier. The gasifying mediums (e.g., pure O 2 and steam) used as the oxygen source can apparently improve the char conversion in traditionally biomass gasification. Similarly, the objective of this study is to investigate char CLG with the oxygen carrier as an individual oxygen source. A NiO-modified iron ore oxygen carrier was prepared by the impregnation method coupled with ultrasonic treatment. The characteristics of the oxygen carrier were analyzed by an X-ray diffractometer (XRD) and H 2 temperature-programmed reduction (H 2 -TPR). The formation of spinel-type nickel iron oxide NiFe 2 O 4 can evidently enhance the reactivity of the oxygen carrier. The reduction of the oxygen carrier by biomass char was investigated using thermogravimetric analysis (TGA) together with a fixed-bed reactor under an inert atmosphere. TGA tests show that the reactivity of the oxygen carrier increased with the increase of NiO loading. An optimal mass ratio of char/oxygen carrier is determined at 4:6 with the aim of obtaining a maximum reaction rate. The presence of spinel-type nickel iron oxide NiFe 2 O 4 apparently improved the reaction rate of char gasification. The fixed-bed gasification results show that CO was generated faster than other components because carbon was partially oxidized and H 2 was quickly consumed by the lattice oxygen [O] of the oxygen carrier. A relatively high carbon conversion of 55.56% was obtained in the char CLG, in comparison to that of char pyrolysis (5.52%). The lattice oxygen [O] of the oxygen carrier was fully consumed by biomass char. Moreover, biomass char was catalytically pyrolyzed becausee the deep reduction products (metallic iron and nickel) can act as catalysts for char pyrolysis. XRD analysis shows that the oxygen carrier was deeply reduced into Fe (Ni) alloy and Fe 3 C species during the reduction stage of char CLG. However, the regenerated oxygen carrier after oxidation can be recycled for char CLG on the basis of XRD and scanning electron microscopy (SEM) analyses.

Process Control Strategies in Chemical Looping Gasification—A Novel Process for the Production of Biofuels Allowing for Net Negative CO2 Emissions

“…A similar gasification concept allowing for decent fuel conversions, without requiring an ASU is the chemical looping gasification (CLG) process, where biomass gasification is also carried out in two separate reactors (see Figure 1) [15,[19][20][21][22]. Just as the related chemical looping combustion (CLC) process, CLG is realized using two coupled fluidized bed reactors, in order to attain good heat and mass transport characteristics [21,23,24].…”

Negative CO2 emissions through the use of biofuels in chemical looping technology: A review

“…The first works at laboratory scale appeared in 2013, and the efforts for the development of this technology have been increasing since then, particularly in China. There are laboratory-scale works, mainly based on thermogravimetric data or batch fluidized beds, analysing the use of different oxygen carriers based on nickel [255,256] copper oxide [224,257,258], iron oxide (both natural iron ore, synthetic and waste materials) [259][260][261][262][263][264][265][266][267][268], copperiron [269,270] and nickel-iron [271,272]. The different forms of biomass used in those studies vary from woody biomass, pine sawdust and rice straw to biomass char and microalgae.…”

Chemical looping hydrogen production with modified iron ore as oxygen carriers using biomass pyrolysis gas as fuel

“…Intensive references demonstrated that the presence of a spinel structure improved the reduction kinetics and enhanced the reducibility of Fe 2 O 3 . 14,[41][42][43][44] In the reduced samples, the unmodied iron ore was mainly reduced into FeO and Fe 3 O 4 ; the CuO-iron ore was reduced into Cu, FeO and Fe; the NiO-iron ore was reduced into Ni, FeO, (Ni, Fe) and Fe; while the CeO 2 -iron ore was reduced into FeO, CeFeO 3 and Fe. The reduction of Fe 2 O 3 to Fe 3 O 4 did not contribute to the production of hydrogen in the oxidation step.…”