Transformation of char carbon during bubbling fluidized bed gasification of biomass

Timmer, Kevin; Brown, Robert C.

doi:10.1016/j.fuel.2019.01.039

Cited by 16 publications

(7 citation statements)

References 57 publications

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“…The effect of ER on the CO yield depends to some extent on the operating conditions; for ER below 0.2, the CO yield increases with ER, and in some cases, it also increases when raising the ER from 0.20 to 0.25–0.26, provided the temperature is low enough. This can be related to an increase in char conversion as ER increases . Varying ER does not seem to significantly affect the yields of CH 4 and C 2 H 4 in agreement with some previous observations ,, using conventional bed materials such as sand and bauxite, although the use of olivine as a bed material has shown a decrease in CH 4 yield with ER …”

Section: Results and Discussionsupporting

confidence: 90%

Comparison of Six Different Biomass Residues in a Pilot-Scale Fluidized Bed Gasifier

et al. 2019

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The gasification behavior of six different biomass species (four forest pruning residues including Pinus pinaster, Pinyon pine, Eucalyptus, and white poplar as well as two types of garden prunings) has been investigated in a pilot fluidized bed gasifier to experimentally quantify (i) the yields of pyrolytic gas released from the fuel particle in the absence of oxygen; (ii) the effect of oxygen on the gas yields and the significance of the secondary reactions (gasification of char and reforming/cracking of gas species) during gasification with air; and (iii) the effect of fuel throughput on gasification performance. Continuous steady-state experiments were conducted using air at temperatures 800, 850, and 900 °C, equivalence ratios (ER) in the range of 0.16–0.32, and throughputs between 245 and 426 kg/h/m2, as well as semicontinuous (batch of fuel in a continuous gas stream) devolatilization experiments with N2 (ER = 0). Although significant quantitative differences in the gas yields, char conversion, gas heating value, and gasification efficiency were found for different fuels, the trends with changing temperature and ER followed similar characteristics. P. pinaster gave the best results, showing cold gas efficiencies of up to 70% at 900 °C, while white poplar and garden prunings performed considerably worse. The effect of throughput was analyzed for three out of six fuels, and it was observed to be small for P. pinaster and garden prunings, whereas it was significant for white poplar as a result of the lower bulk density of white poplar compared to the other fuels. The results conclude about gas composition and process efficiency expected from different biomass residues in fluidized bed gasifiers and provide fundamental data to validate a theoretical model, currently under development, to scale up the process.

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Section: Results and Discussionsupporting

confidence: 90%

Comparison of Six Different Biomass Residues in a Pilot-Scale Fluidized Bed Gasifier

et al. 2019

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“…Ideal mixing of the fuel particles, the bed material, and the gas phase promotes excellent heat transfer in a fluidized bed. The efficiency of the gasification process is determined by the conversion rate of biomass (to the product gas) [2]. The conversion of solid biomass into producer gas is a complex thermochemical process that occurs in several steps.…”

Section: Introductionmentioning

confidence: 99%

A CPFD model to investigate the influence of feeding positions in a gasification reactor

Jaiswal¹,

Furuvik²,

Thapa³

et al. 2020

Int. J. EQ

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The efficiency of a gasification process is directly related to the rate of biomass conversion into product gas. The rate of fuel conversion depends on the interaction of fuel with the bed material, the gasifying agent, and the residence time of fuel particles. The interactions and the residence time depend on the fuel feeding positions along the height of the reactor. Thus, the fuel feeding position in a gasification reactor is an important parameter that influences the efficiency of the gasification process; longer residence time of the fuel particles in the bed enables efficient carbon conversion and less tar formation. In this work, in-bed and on-bed feed positions of the fuel particles have been investigated using a computational particle fluid dynamics (CPFD) model. The model is developed and validated against experimental data obtained from a bubbling fluidized bed gasification reactor. Experiments were carried out in a 20 kW pilot scale bubbling fluidized bed gasification reactor. Wood pellets of 3-30 mm length and 5 mm diameter are fed into the reactor at a mass flow rate of 2.4 kg/h. The molar flow rate of the producer gas, which typically consists of CH 4 , CO, CO 2 , and H 2 for both the in-bed and on-bed cases, is calculated by the CPFD model. The results show that CO and CH 4 concentrations increase in the product gas when the biomass is fed at the location near to the bottom of the bed, while CO 2 and H 2 increase in the case of on-bed feed. The fuel particles segregate, followed by partial combustion of the smaller fuel particles on the bed surface in the case of on-bed feed. The total mass of the bed including unreacted char is higher for on-bed feed, indicating that the char is consumed slowly. The CPFD model can predict the product gas compositions, the fuel conversion, changes in the bed hydrodynamics, and the product gas yield at different feeding positions of the fuel particles. Thus, the model can be useful for design purposes.

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“…The increase in ER slightly increased the yield of CO (Figure a) but showed a higher and apparent increase in the CO 2 yield (Figure b) due to the greater char oxidation. , Figure a and b show that the addition of steam to the gasification agent decreased the CO, it increased the CO 2 yields. Steam shifts the WGS reaction toward the production of CO 2 and H 2 .…”

Section: Resultsmentioning

confidence: 85%

Distribution of Inorganics and Trace Elements during Waste Gasification in a Bench-Scale Fluidized Bed

et al. 2021

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The gasification of refuse-derived fuel (RDF) in a fluidized bed gasifier followed by a high-temperature filter was investigated in a bench-scale plant. The tests were performed at a fixed reactor (bed and freeboard) temperature of 850 °C and filter temperatures of 450 and 550 °C using air–N2 and air–steam mixtures as gasification agents with equivalence ratios (ER) in the range of 0.24–0.32 and sand and sand/dolomite mixtures as bed material. The influence of these parameters on the gasification performance was studied with the primary objective of understanding the fate of fuel–N, fuel–S, fuel–Cl, and the distribution of fuel–trace elements into the gas and ash streams (both filter and bottom ashes). It was found that steam addition, besides increasing the yield of H2, promoted the yields of NH3, H2S, and tars. The catalytic effect of dolomite on decreasing tar production was not observed in our experiments. Fuel–N and fuel–S were mainly converted into ammonia (≥40%) and H2S (≥20%). Most of fuel–Cl was measured in the filter ash, whereas only a minor fraction of the fuel-S was detected in this solid fraction, especially at low temperature. The distribution of trace elements into the filter and bottom ashes was consistent with their inherent volatile behavior, although precise quantification was difficult due to the heterogeneity of the fuel. Preliminary assessment of utilization/disposal options of the filter and bottom ashes generated was made by studying the enrichment factor.

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Transformation of char carbon during bubbling fluidized bed gasification of biomass

Cited by 16 publications

References 57 publications

Comparison of Six Different Biomass Residues in a Pilot-Scale Fluidized Bed Gasifier

Comparison of Six Different Biomass Residues in a Pilot-Scale Fluidized Bed Gasifier

A CPFD model to investigate the influence of feeding positions in a gasification reactor

Distribution of Inorganics and Trace Elements during Waste Gasification in a Bench-Scale Fluidized Bed

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