Co-gasification of Biomass with Coal and Oil Sand Coke in a Drop Tube Furnace^†

Abstract

The present paper is aimed at investigating the co-gasification of biomass with coal and oil sand fluid coke. Chars were obtained from individual fuels and blends with different blend ratios of coal, oil sand coke, and biomass in a drop tube furnace at different temperatures. The chars were then gasified in a thermogravimetric analyzer (TGA) under CO 2 atmosphere to determine their reactivity. Results showed that the effect of the blending ratio of biomass to other fuels on the reactivity of the co-pyrolyzed chars is more pronounced on chars prepared at low temperatures and the effect becomes less significant as the pyrolysis temperature increases. The increased reactivity at a higher biomass blending ratio is due to the presence of synergetic effects originating from the interaction of the two fuels. Scanning electron microscopy images showed differences in shapes and particle size distribution of char particles from biomass and coal/coke. These also showed the agglomeration of coal and coke chars with biomass char particles at high temperatures. The agglomeration may be the reason for the non-additive behavior of the blends. The chars were also analyzed for the particle size distribution using a laser diffraction Mastersizer instrument and surface area with the Brunauer-Emmett-Teller (BET) technique. BET analysis showed an increase in the surface area with an increasing temperature from 700 to 1400°C for biomass and coal, but the trend for coke was inversely related to the temperature.

A Review of Thermal Co-Conversion of Coal and Biomass/Waste

“…These observations are in accordance with Zhang et al [59]; they pyrolyzed blends of Dayan coal (lignite) and legume straw in a free fall reactor under atmospheric pressure at temperatures ranging from 773 K to 973 K with nitrogen as the carrier gas. Their investigation revealed that synergy was pronounced at lower temperatures (around 873 K) but reduced as temperature increased and was less pronounced around 993 K. Gao et al [116] made a similar observation. Park et al [64] also noted as Oney et al [115] as well as Gao et al [116], that synergy was more pronounced at higher biomass blending ratio (around 70%).…”

“…Their investigation revealed that synergy was pronounced at lower temperatures (around 873 K) but reduced as temperature increased and was less pronounced around 993 K. Gao et al [116] made a similar observation. Park et al [64] also noted as Oney et al [115] as well as Gao et al [116], that synergy was more pronounced at higher biomass blending ratio (around 70%). Ulloa et al [117] conducted co-pyrolysis of blends of subbituminous (Bitsch Coal), bituminous (Lemington coal) coals, with Radiata Pine sawdust in a TGA under nitrogen at different heating rates (10, 30 and 50 K/min) to a maximum temperature of 1473 K. Their experiment depicted interaction between biomass and the two coals at temperatures higher than 673 K and up to 1473 K. Their explanation of the interaction was that the synergy between devolatilization of biomass and lignin (which spans from 673 K to 1173 K) coincides with that of coal.…”

“…Those authors favoring interaction between coal and biomass have suggested that free radicals formation and hydrogen transfer from biomass to coal could be the key explanation behind this phenomenon. Temperature dependence of the synergy has also been mentioned, with prominent synergy at lower temperature up to an optimum above which no synergy is noticeable [95,116,303,304].…”

“…While extensive studies have been conducted on free radicals release during coal pyrolysis [115][116][117][118][119][120][121][122][123][124], such studies involving direct in situ observation of radicals released during biomass or biomass components (cellulose, hemicelluloses and lignin) pyrolysis are lacking. Understanding the mechanism of free radicals release during biomass/biomass components pyrolysis can pave the way to improvements in the modeling of coal and biomass blends during co-pyrolysis/co-gasification, and the synergistic effect between coal and biomass; therefore, providing an insight to the prediction of co-conversion of coal and biomass.…”

Comparison of kinetic models for isothermal CO2 gasification of coal char-biomass char blended char

“…Moreover, Fig. 3(b) reveals that gasification peak value (R m ) of the BC/CC blended char occurred relatively earlier than CC or BC probably due to the synergetic effect of the BC/CC blended char [9]. Fig.…”