Coal and biomass char reactivities in gasification and combustion environments

Tilghman, Matthew B.; Mitchell, Reginald E.

doi:10.1016/j.combustflame.2015.05.009

Cited by 54 publications

(52 citation statements)

References 67 publications

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“…The Arrhenius parameters for the rate coefficients shown in the table were obtained for the char of Wyodak Coal, a sub-bituminous coal from Wyoming, using data obtained in a thermogravimetric analyzer. The experimental procedure and least squares process used to determine kinetic and thermochemical parameters in the reaction mechanism are described by Tilghman and Mitchell [12]. All parameters are reasonable and supportable -all activation energies are in expected ranges.…”

Section: Model Descriptionmentioning

confidence: 99%

“…Rate coefficients for the reverse reactions are determined from the forward rate coefficients and the equilibrium constants, which are calculated from the heats of formation and the absolute entropies of the species involved in the reactions. The enthalpies and absolute entropies of the adsorbed species were determined in the work by Tilghman and Mitchell [12]. They show that the absolute entropy of an adsorbed species can be found by…”

Section: Nrmentioning

confidence: 99%

“…when S gas,i is the absolute entropy of the gas phase species and the coefficients A 1 and A 2 are given in Table 2. Although a slight temperature dependence on the heats of formation of adsorbed species was noted (more so for C(CO)), constant values were recommended by Tilghman and Mitchell [12], as given in Table 2. Table 2: Parameters for absolute entropy, S ad,i = S gas,i (A 1 T c + A 2 ) − 3.3R, together with the heat of formation for adsorbed species i on Wyodak coal char.…”

Section: Nrmentioning

confidence: 99%

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A comprehensive model for char particle conversion in environments containing O2 and CO2

Haugen

Mitchell

Tilghman

2015

Combustion and Flame

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In this work, conversion of char is studied in a simulation code that includes a simplified heterogeneous adsorption-desorption reaction mechanism for char chemical reactivity and uses GRI-Mech 3.0 as the chemical kinetic mechanism that describes the impact of homogeneous reactions. Besides sub-models for the consequences of chemical reactions, a mode of char particle conversion sub-model is included that describes how particle size and apparent density vary with mass loss as well as a radiation sub-model that describes the radiant exchange of energy between the char particle and surrounding particles and walls. The code is transient and zero dimensional in space, and designed to be used both as a stand-alone gasification/combustion code and as a sub-model for heterogeneous reactions of solid particles in a CFD code.

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Section: Model Descriptionmentioning

confidence: 99%

Section: Nrmentioning

confidence: 99%

Section: Nrmentioning

confidence: 99%

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A comprehensive model for char particle conversion in environments containing O2 and CO2

Haugen

Mitchell

Tilghman

2015

Combustion and Flame

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“…This reduces the total gasification carbon transformation and the disposal of the semi‐char is a problem. Effectively re‐burning semi‐char has become a promising way to improve overall conversion efficiency of coal gasification, use the residual carbon in the semi‐char, and reduce waste pollution . Meanwhile, high‐temperature steam produced from the semi‐char combustion boiler can be used as the gasification agent in the gasifier, promoting the total carbon conversion and gasification efficiency.…”

Section: Introductionmentioning

confidence: 99%

“…Effectively re-burning semi-char has become a promising way to improve overall conversion efficiency of coal gasification, use the residual carbon in the semi-char, and reduce waste pollution. [9][10][11] Meanwhile, high-temperature steam produced from the semi-char combustion boiler can be used as the gasification agent in the gasifier, promoting the total carbon conversion and gasification efficiency. Through coal gasification and waste combustion, the step use of coal can be realized.…”

Section: Introductionmentioning

confidence: 99%

Combustion characteristics of ultrafine gasified semi‐char in circulating fluidized bed

Ren

Shu

2016

Can J Chem Eng

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Coal fluidized bed gasification generates large amounts of semi‐char, which has a high carbon content. Effectively re‐burning semi‐char has become a promising way to improve overall conversion efficiency of coal gasification and use the residue carbon in the semi‐char. However, due to the ultrafine particle size (mean particle size ≈ tens of microns), nearly zero volatile content, and the graphitization structure of the semi‐char, the fluidization and combustion organization of semi‐char in a circulating fluidized bed (CFB) is difficult, leading to poor self‐sustained combustion stability and low combustion efficiency. The physicochemical properties of the semi‐char from an industrial CFB gasifier were studied. The combustion characteristics and activation energy of the semi‐char were tested using thermogravimetric analysis. The occurrence of sulphur and nitrogen in the semi‐char and fly ash after combustion were characterized with X‐ray photoelectron spectroscopy (XPS). A re‐burning experiment was carried out in a 5 t/day CFB pilot facility. The key is to build a balance between sufficient residence time to burnout and a proper fluidization velocity for bed material cycle. The effects of residence time, preheating temperature, and the ratio of preheating air to fuel on the combustion efficiency and pollutant emission was studied. The balance between the preheating time and residence time in the furnace was discussed. Results show that it can reach stable combustion in a specially designed CFB furnace without auxiliary fuel and the combustion efficiency can be higher than 98 %.

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