Investigation of competitive tar reforming using activated char as catalyst

Buentello-Montoya, D.A.; Zhang, Xiaolei; Marques, Simão

doi:10.1016/j.egypro.2019.01.216

Cited by 17 publications

(15 citation statements)

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“…In the two tar samples taken at 750 °C the conversion of benzene was negative indicating a slight increase in the benzene concentration with respect to the reference test without char. This result, in agreement with previous work [32], could be explained by the enhancement of cleavage of alkyl and polyaromatic tars into smaller compounds, such as benzene, over the surface of the char.…”

Section: 1-tar Evolutionsupporting

confidence: 93%

“…The use of simulated (and simplified) syngas as surrogate syngas is convenient when a careful control of experimental conditions is necessary to isolate processes and investigate detailed aspects of mechanisms of conversion. However, the use of real pyrolysis/gasification gas containing dozens/hundreds of different compounds is more useful to verify the activity of char in a real gasification process since the competition between different tar compounds for the active sites can influence their conversion [32]. Matsuhara et al [15] studied the conversion of a coal pyrolysis gas over a fixed bed of char produced by pyrolysing the same coal.…”

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confidence: 99%

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Tar conversion of biomass syngas in a downstream char bed

Fuentes-Cano

Berg

Dieguez-Alonso

et al. 2020

Fuel Processing Technology

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The catalytic conversion of biomass-derived tars over char during long tests (over 6 hours) is studied. The syngas is generated in a steam-blown fluidized-bed gasifier employing wood pellets and conducted to a second tubular reactor where non-activated char particles are fluidized. The gasifier operated at 750 °C whereas the temperature of the secondary reactor was varied between 750 °C and 875 °C. The evolution of the tar conversion, gas composition and internal structure of the used catalysts were studied. At 750 °C, the initial catalytic activity of the char was low and deactivation occurs rapidly. However, as the reactor temperature increased, the catalytic activity of the char improved significantly. At 875 °C, the initial conversion of tar was above 70 % and over 64 % after 5 h of operation. Moreover, the conversion of the heaviest tars was above 80 % during the entire test. At this temperature, the decrease in tar conversion is attributed to the consumption of the char by steam gasification since its catalytic activity increased during of the test. In these conditions the char bed with an initial weight of 32 g converted approximately 12 g of tars (benzene not included) after 5 h of operation. 1-IntroductionGasification is a thermo-chemical route for conversion of solid fuels, such as biomass and wastes, into a syngas that can be used in a variety of applications [1,2]. Fluidized bed (FB) gasification has several advantages over that in fixed/moving bed or entrained-flow for distributed energy production [3]. However, in all types of FB gasifiers the process temperature must be kept relatively low to prevent agglomeration and sintering of bed material. The low temperature results in incomplete carbon conversion and a high concentration of heavy tars in the gas. The condensation of heavy tars in downstream equipment is the main bottleneck for the use of the syngas in any application where the gas needs to be cooled down.

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Section: 1-tar Evolutionsupporting

confidence: 93%

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confidence: 99%

Tar conversion of biomass syngas in a downstream char bed

Fuentes-Cano

Berg

Dieguez-Alonso

et al. 2020

Fuel Processing Technology

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“…The two-stage reactor was simulated under different operation conditions to determine the effect of thermophysical parameters in the process. 31 . The amount of steam injected for reforming was not varied because studies have shown that it has a little effect in the reforming of tar 13,41,42 , and is thereby set at a constant value of 10% of the total gas volume in the reforming stage.…”

Section: Resultsmentioning

confidence: 99%

“…Reforming model. Validation of the kinetic mechanism for tar reforming was done by reproducing experiments documented elsewhere31 . Briefly, simulated syngas with a mixture of benzene, toluene and naphthalene was injected into a drop tube furnace containing a bed of either char or activated char as and subject to reforming at 650, and °C and residence time of approximately 0.5 seconds.…”

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confidence: 99%

An Energy and Exergy Analysis of Biomass Gasification Integrated with a Char-Catalytic Tar Reforming System

Buentello-Montoya

Zhang

2019

Energy Fuels

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Adequate tar removal is a recurrent challenge for biomass gasification. Materials such as char and activated char are promising catalysts for tar reforming because of their activity, inexpensiveness and constant production during gasification. Although the behaviour of char and activated char as catalyst has been previously studied, an evaluation of the thermodynamic efficiencies of the tar reforming process using char as a catalyst still lacking. This work analyses the performance of a two-stage system, where gasification is followed by tar reforming using char catalysts. For the study, a model based in a combination of equilibrium thermodynamics and chemical kinetics was developed. The first stage, where gasification occurs, was simulated with a thermodynamic equilibrium model. Gasification equilibrium models available in literature only predict the fractions of H 2 , CO, CO 2 and CH 4 ; the model developed for this work also predicts the formation of three model tar with different characteristics (benzene, toluene and naphthalene), providing information on the stability of formed tar. The second stage, simulated using kinetics from literature, consists on reforming the tar with catalysts made of residual char. The effects of the reactor temperature, equivalence ratio, and residence time were assessed via the gas quality, based on the gas lower heating value and tar concentration, and process efficiency, based on the energy and exergy efficiencies. Results showed that using char or activated char catalysts increases the heating value of the gas while reducing its tar concentration. Moreover, the process benefits thermodynamically (i.e. less exergy is destroyed) from low gasification temperatures and high reforming temperatures. Simulations indicate that a tarless gas with a lower heating value of more than 8 MJ/Nm 3 can be produced from gasification at 1023K with an equivalence ratio of 0.15 and subsequent reforming at 1123K with a residence time in the catalyst bed of 1 second.

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“…Most of the tar cracking catalysts studied in tandem with plasma are nickel or noble-metal supported catalysts. Traditional tar cracking catalysts such as dolomite [74,75,76], olivine [77,78,79], K 2 CO 3 [80,81], CaO [82,83,84], iron oxides [85] and chars [86,87,88] are yet to be explored. Indeed most of the catalysts found in many tar removal reviews [13,38,57,58] have been unexplored in tandem with plasma.…”

Section: Cold Plasmas In Hybrid Units: Secondary Refining Unitsmentioning

confidence: 99%

The role of plasma in syngas tar cracking

Rueda

Helsen

2019

Biomass Conv. Bioref.

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Gasification of biomass and municipal solid waste is a technology that has been proposed as a dualpurpose solution for mitigating environmental impacts as well as for producing syngas, a very useful intermediary product for energy valorization and organic synthesis. However the presence of pollutants, notably tar, hamper this raw syngas (producer syngas) to be used in high-efficient energy applications such as jet engines, fuel cells or in Fischer-Tropsch synthesis, limiting its economic value. For reducing tar a lot of scientific and technical effort has been devoted. In this paper, the state-of-the-art of plasma tar removal from syngas is done, focusing on the use of plasma in tandem with existing technologies, underlining its advantages and the remaining challenges. The most promising ways to get a syngas with very low tar levels using plasma seem to be: (i) tandem tar cleaning techniques (e.g. secondary plasma enhanced catalytic unit) and (ii) secondary thermal plasma cracking units. Keywords tar cracking • plasma • syngas cleaning 1 IntroductionThe conversion of carbon-rich raw materials such as biomass and Municipal Solid Waste(MSW) into syngas has been proposed as the perfect solution for decreasing the amount of waste and byproducts discarded while obtaining a syngas that can be used for organic

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Investigation of competitive tar reforming using activated char as catalyst

Cited by 17 publications

References 1 publication

Tar conversion of biomass syngas in a downstream char bed

Tar conversion of biomass syngas in a downstream char bed

An Energy and Exergy Analysis of Biomass Gasification Integrated with a Char-Catalytic Tar Reforming System

The role of plasma in syngas tar cracking

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