Biomass Gasification Behavior in an Entrained Flow Reactor: Gas Product Distribution and Soot Formation

Abstract

Biomass gasification and pyrolysis were studied in a laboratory-scale atmospheric pressure entrained flow reactor. Effects of operating parameters and biomass types on the syngas composition were investigated. In general, the carbon conversion during biomass gasification was higher than 90% at the optimal conditions of 1400°C with steam addition. The biomass carbon that was not converted to gas in the gasification process only appeared as soot particles in the syngas in all of the experiments, except for the two experiments performed at 1000°C, where a very small amount of char was also left. In comparison to pyrolysis, lower yields of soot, H 2 , and CO were produced during gasification. The yield of soot could be reduced by a longer residence time, larger feeder air flow, lower oxygen concentration, higher excess air ratio, higher steam/carbon ratio, and higher reactor temperature. Changes in residence time, feeder air flow, and oxygen concentration did not show a noticeable influence on H 2 and CO yields. Increasing the excess air ratio decreased both the H 2 and CO yields; increasing the steam/carbon ratio increased the H 2 yield but decreased the CO yield; and increasing the reactor temperature increased both the H 2 and CO yields. Wood, straw, and dried lignin had similar gasification behavior, except with regard to soot formation. The soot yield was lowest during straw gasification possibly because of its high potassium content.

Influence of H 2 O, CO 2 and O 2 addition on biomass gasification in entrained flow reactor conditions: Experiments and modelling

“…This could be explained by two opposite phenomena: the tar yield decreases when temperature increases because of cracking reactions, whereas soot production increases with temperature. Indeed, previous works show that tar contents are very low above 1000°C [7,10] while soot production is significant at 1000°C and above [4]. The presence of steam or CO 2 leads to a decreasing amount of carbon in tar and soot, certainly because of soot precursors consumption, which is discussed in more details in Section 4.1.3.…”

“…Experimental ones are generally performed with lab-scale reactors which allow reproducing some important EFR characteristics as temperature, heat flux, residence time and particle size: the Drop Tube Reactor (DTR). Only few studies have dealt with woody biomass pyrolysis in a DTR above 1000°C [3][4][5][6]. Woody biomass gasification has been studied at high temperature (T > 1000°C) in presence of oxygen [4,7,8] and/or in presence of steam [4,7,[9][10][11] or in presence of carbon dioxide [11].…”

“…These models, which include simple reaction schemes, generally allow predicting the syngas composition with a good accuracy for the main gases (CO, H 2 , CO 2 , CH 4 , H 2 O) but are unable to predict tar and soot production. On the other hand, detailed chemical schemes based on elementary reactions are able to predict the production of minor products [15,16] and are very useful to better understand the mechanisms leading to undesirable products like soot or tars.…”

High temperature thermochemical processing of biomass and methane for high conversion and selectivity to H2-enriched syngas

“…4 that methane yield does not seem to be correlated with biomass type, only temperature, indicating that discussion of the two conversion pathways may be decoupled for the purposes of this study. The reaction processes in biomass gasification are complex and numerous and can generally be categorized according to the following groupings: biomass [53][54][55][56]. Soot is also formed when polyaromatic species released during biomass pyrolysis combine and nucleate solid particulates [54,[57][58][59].…”

“…The reaction processes in biomass gasification are complex and numerous and can generally be categorized according to the following groupings: biomass [53][54][55][56]. Soot is also formed when polyaromatic species released during biomass pyrolysis combine and nucleate solid particulates [54,[57][58][59]. While C 2 H 2 is a precursor to PAHs, the yield of PAHs during biomass devolatilization has been shown to increase with increasing temperature and may increase the total yield of soot in gasification systems [57,60,61].…”