Indirectly heated biomass gasification using a latent heat ballast — 1: experimental evaluations

Pletka, Ryan; Brown, Robert C.; Smeenk, J.L.

doi:10.1016/s0961-9534(00)00088-x

Cited by 29 publications

(11 citation statements)

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“…[1][2][3] Pyrolysis refers to the air-free thermal decomposition, forming some combination of gases, liquids, and/or solid ("char"). Approaches for biomass conversion that involve pyrolysis include fast pyrolysis, [4][5][6][7][8][9] gasification, [10][11][12][13][14] and catalytic fast pyrolysis. 15,16 Pyrolysis is typically classified in terms of heating rate and temperature.…”

Section: Introductionmentioning

confidence: 99%

Kinetics and Mechanism of Cellulose Pyrolysis

et al. 2009

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In this paper we report the kinetics and chemistry of cellulose pyrolysis using both a Pyroprobe reactor and a thermogravimetric analyzer mass spectrometer (TGA-MS). We have identified more than 90% of the products from cellulose pyrolysis in a Pyroprobe reactor with a liquid nitrogen trap. The first step in the cellulose pyrolysis is the depolymerization of solid cellulose to form levoglucosan (LGA; 6,8-dioxabicyclo[3.2.1]octane-2,3,4-triol).LGA can undergo dehydration and isomerization reactions to form other anhydrosugars including levoglucosenone (LGO; 6,8-dioxabicyclo[3.2.1]oct-2-en-4-one), 1,4:3,6-dianhydro--D-glucopyranose (DGP) and 1,6-anhydro--D-glucofuranose (AGF; 2,8-dioxabicyclo[3.2.1]octane-4,6,7-triol). The anhydrosugars can react further to form furans, such as furfural (furan-2-carbaldehyde) and hydroxymethylfurfural (HMF; 5-(hydroxymethyl)furan-2-carbaldehyde) by dehydration reactions or hydroxyacetone (1-hydroxypropan-2-one), glycolaldehyde (2-hydroxyacetaldehyde), and glyceraldehyde (2,3-dihydroxypropanal) by fragmentation and retroaldol condensation reactions. Carbon monoxide and carbon dioxide are formed from decarbonylation and decarboxylation reactions. Char is formed from polymerization of the pyrolysis products. The pyrolytic conversion of cellulose was fitted to two different reaction models. The first model (Model I) combined the first-order kinetic model with a thermal-lag model that assumed the temperature difference between the thermocouple and specimen in TGA to be directly proportional to the heating rate. The second model (Model II) combined the first-order kinetic model with an energy balance that took into account the heat transfer at the sample boundary including the heat flow by endothermic pyrolysis reaction. Both models were able to adequately fit the empirical data. The kinetic parameters obtained from both models were similar. Cellulose pyrolysis had an activation energy of 198 kJ mol . Model I is computationally easier, however Model II is physically more realistic. Importantly, our results indicate that the intrinsic kinetics for cellulose pyrolysis are not a function of heating rate. During the pyrolysis of cellulose a thermal temperature gradient between the cellulose and heater can occur due to the endothermic pyrolysis reaction. A faster heating rate can magnify the thermal-lag, which leads kinetic derivations to artificial outcomes.

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Section: Introductionmentioning

confidence: 99%

Kinetics and Mechanism of Cellulose Pyrolysis

et al. 2009

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“…Alternately, a flow-of-heat carrier such as CO 2 can be employed. Various indirect-heating means have been used in gasifiers previously [37][38][39], and a fluidized-bed configuration should enhance the heat transfer.…”

Section: Process Simulationmentioning

confidence: 99%

Clean combustion of solid fuels

2008

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“…Depending on the hydrodynamic properties of reactors, gasifiers can be fixed or moving beds, bubbling or circulating fluidized beds, spouted beds, rotary kilns, or some combination of these types. Gasifiers may be directly heated (most gasifiers), or indirectly heated, usually employing molten salt designs (Pletka et al, 2001).…”

Section: Gasification For Energy Use Of Biomassmentioning

confidence: 99%

04/02017 Biomass gasification in a circulating fluidized bed

2004

Fuel and Energy Abstracts

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This work is devoted to the experimental study of biomass gasification in a pilot-scale circulating fluidized bed, and development of an equilibrium model of the process based on Gibbs free-energy minimization. Biomass gasification has considerable potential for reducing greenhouse gas emissions. In the present study, six types of sawdust were gasified in a pilotscale air-blown circulating fluidized bed gasifier to produce low-calorific-value gases. The pilot gasifier employs a riser 6.5 m high and 0.1 m in diameter, a high-temperature cyclone for solids recycle and a ceramic fibre filter unit for gas cleaning. The riser temperature was maintained at 970-1120 K (700-850°C), while the sawdust feed rate varied from 16-45 kg/h, corresponding to a superficial gas velocity of 4-10 m/s. It was found that gas composition and heating value depended heavily on the air or O/C ratio, and to a lesser extent on operating temperature. The higher heating value of the product gas decreased from 5.6 to 2.1 MJ/Nm 3 as the stoichiometric air ratio increased from 0.22 to 0.54. The gas heating value was increased by increasing the overall suspension density in the riser. Fly ash re-injection and steam injection led to increases in gas heating value for the same Q/C molar ratio. Tar yield from biomass gasification was found to decrease drastically from 15 to 0.54 g/Nin 3 as the average suspension temperature increased from 970 to 1090 K. Elevating the operating temperature provides the simplest solution for tar removal in the absence of any catalyst. Secondary air had only a very limited effect on tar removal with the total air ratio maintained constant. A nickel-based, catalyst proved to be effective in reducing the tar yield and in adjusting the gas composition. Ill The cold gas efficiency decreased with increasing air ratio (or O/C molar ratio), though the carbon conversion increased. The cold gas efficiency provides a better criterion for evaluating the gasification process than the carbon conversion. Experimental data showed that the gasification efficiency can be maximized within an optimum range of air ratio (a = 0.30-0.35, or O/C = 1.5-1.7), while keeping the tar yield acceptably low. A non-stoichiometric equilibrium model based on Gibbs free energy minimization was developed for biomass gasification. Five elements (C, H, O, N and S) and 44 species were considered in the model. Both pure equilibrium and situations where kinetic factors cause a partial approach to equilibrium are considered. The equilibrium model predicts that the product gas composition from gasification of woody biomass (e.g. sawdust) depends primarily on the air ratio. An air ratio of 0.2-0.3 is predicted to be most favourable for producing CO-rich gas, while temperatures of 1200-1400 K and an air ratio of 0.15-0.25 are predicted to be optimum for H 2 production. The predicted cold gas efficiency reached a maximum at an air ratio of about 0.25. The model successfully predicts the onset of carbon formation in a C-H-O-dominated system when the relative abundan...

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Indirectly heated biomass gasification using a latent heat ballast — 1: experimental evaluations

Cited by 29 publications

References 2 publications

Kinetics and Mechanism of Cellulose Pyrolysis

Kinetics and Mechanism of Cellulose Pyrolysis

Clean combustion of solid fuels

04/02017 Biomass gasification in a circulating fluidized bed

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