Fluidized Bed Gasification of Torrefied and Raw Grassy Biomass (Miscanthus × gigantenus). The Effect of Operating Conditions on Process Performance

Abstract

Torrefaction is suggested to be an effective method to reduce the cost of biomass provision and improve the fuel properties. In this study, both raw and torrefied Miscanthus × giganteus (M×G) were gasified in an externally heated air-blown bubbling fluidized bed (BFB) gasifier using olivine as the bed material. The effects of equivalence ratio (ER) (0.18–0.32) and bed temperature (660–850 °C) on the gasification performance were investigated. Torrefied M×G has higher energy density primarily due to a higher ratio of lignin to cellulose and hemicellulose; it has lower bulk density, smaller particle diameter and lower reactivity than the original biomass. These properties affect its performance during gasification. The cold gas efficiency was on average 12% lower for torrefied than for raw M×G for the range of operating conditions studied. Within the same temperature range the carbon conversion was about 10% higher for raw than for torrefied biomass. The hydrogen conversion was higher for torrefied M×G since gasification of this feedstock results in higher yields of methane and ethane and lower yields of unreacted process water. The carbon loss with char elutriated from the gasifier for torrefied M×G was significantly higher than that of raw (5% vs 3%) and was driven by physical properties of torrefied M×G. The results obtained suggest that chemical composition expressed as lignin to cellulose and hemicellulose ratio has a pronounced effect on carbon conversion efficiency and tar production.

Kinetics and Performance of Raw and Torrefied Biomass in a Continuous Bubbling Fluidized Bed Gasifier

“…This was expected because the gasification of torrefied biomass produced more CH 4 gas compared to AROK thus promoting R8. The hydrogen conversion into dry gas was higher for torrefied biomass since the gasification of this feedstock results in higher yield of CH 4 and C 2 H 6 [50]. This is in an agreement with Taba et al [51], who stated that the biomass having low contents of volatile matter is more suitable for significant H 2 production.…”

The Synergy Effect of Ni-M (M = Mo, Fe, Co, Mn or Cr) Bicomponent Catalysts on Partial Methanation Coupling with Water Gas Shift under Low H2/CO Conditions

“…In addition, despite the comparable CO 2 growth rate and CO conversion at high water content (1.0-1.5 H 2 O/CO) for both catalysts, 15Ni-3Mn presents better CH 4 selectivity than 15Ni-3Cr, implying that the Mn species is more competent than Cr as the second component in the Ni-M bicomponent catalyst since the former is more efficient in converting CO to CH 4 .…”

“…Judging from the peak temperatures in the TPR profiles and referring to relevant reported literature, the reducible NiO species could be sorted into three categories: (1) α-type, free nickel oxide species [30] or bulk NiO [28], which interact weakly with the support; (2) β-type, Ni-rich phases, which have medium interaction with the support; (3) γ-type, Al-rich phases, which interact strongly with the support. In Figure 3A, for 15Ni-3Mo and 15Ni-3Fe, there is no distinct reduction peak ascribed to the NiMoO 4 and NiFe 2 O 4 spinel structure. Given their relatively high reduction temperature (NiMoO 4 : higher than 500 • C [31]; and NiFe 2 O 4 : 402-715 • C [32]), their reduction process may be overlapped by that of NiO.…”

“…Biomass gas generated by means of gasification from organic materials, such as agricultural and forestry residues, which exist abundantly in rural places, might be one potential solution to the problem of central gas supply [1]. However, due to assorted biomass resources, as well as gasification conditions and agents [2][3][4][5][6], the H 2 /CO ratio of acquired biomass gas varies greatly, and particularly, low H 2 /CO ratio biomass gas (H 2 /CO < 1) cannot be applied directly by urban residents because of its dreadful toxicity and relatively low heating value. Hence, from the standpoint of safety and efficiency, a series of requisite processing technologies has to be employed in order to eliminate the above two drawbacks before it is transported through a pipeline to downstream users.…”

“…As is well known, water gas shift (WGS) (Equation (1)) is highly efficient to adjust the H 2 /CO ratio by converting CO with H 2 O to CO 2 and H 2 [7]. In addition, methanation (Equation (2)) as one type of CO hydrogenation reaction is capable of reducing CO content and in the meantime generating CH 4 that is of high heating value and innocuity. Therefore, a proper connection of these two methods could be theoretically feasible to upgrade low H 2 /CO ratio biomass gas into urban gas.…”