Pore development and combustion behavior of gasified semi-char in a drop tube furnace

Kelebopile, Leungo; Sun, Rui; Wang, Hui; Zhang, Xin; Wu, Shaohua

doi:10.1016/j.fuproc.2013.01.017

Cited by 23 publications

(13 citation statements)

References 48 publications

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“…At a reaction temperature this relation however involves correlations in two regions separated by the pore size that is 10 times the mean free path of O 2 , 10 λ, i.e., free diffusion in pores (and fractures) of larger than 10 λ in size with the coefficient approximately D O 2 and restrictive diffusion in pores of smaller than 10 λ in size with a coefficient D 1 , which is smaller than D O 2 . Previous study [36] suggested that D 1 is proportional to the porosity as shown in Equation 14, where ε 1 is porosity of the pores with diameters less than 10 λ and τ is tortuosity of pores generally within 2 to 6 [37].…”

Section: Effective Diffusion Coefficient With Temperature and Ash Laymentioning

confidence: 99%

Estimation of Effective Diffusion Coefficient of O2 in Ash Layer in Underground Coal Gasification by Thermogravimetric Apparatus

Lin

Liu

2018

Energies

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Underground coal gasification (UCG) proceeds generally in the presence of an ash layer on coal (or char) surface. The ash layer increases the mass transfer resistance of O 2 to the gasification surface, which may become the limiting step of whole process. This paper studies O 2 diffusion in ash layer formed on cylindrical char samples using a specially designed one-dimension setup in a thermogravimetric apparatus (TGA). The effective internal diffusion coefficient (D e) is found to increase with an increase in ash layer thickness, due to an increase in median pore diameter. Methods are established to correlate D e with operating conditions and to estimate the role of internal diffusion resistance in overall mass transfer resistance.

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Section: Effective Diffusion Coefficient With Temperature and Ash Laymentioning

confidence: 99%

Estimation of Effective Diffusion Coefficient of O2 in Ash Layer in Underground Coal Gasification by Thermogravimetric Apparatus

Lin

Liu

2018

Energies

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“…Further burnout experiments in a drop-tube furnace were conducted, and the results indicated that higher temperature and oxygen are needed to attain a high carbon conversion ratio for CGFA utilization. 17 reactivity and extremely low volatile content of CGFA limits its direct use as a primary fuel. The preheating flameless novel combustion concept of CGFA was tested, and stable flame distribution can be established.…”

Section: Introductionmentioning

confidence: 99%

Combustibility and Cofiring of Coal Gasification Fine Ash with High Carbon Content in a Full-scale Pulverized Coal Furnace

et al. 2020

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Coal gasification fine ash (CGFA) having a high carbon content is produced in large quantity as a byproduct from coal gasifiers in China. CGFA is usually disposed of by landfill as a solid waste, which is not only detrimental to environment but also a loss of an enormous energy that renders the process inefficient. Therefore, it is crucial to make use of the high carbon content in the CGFA with an economic and environmentally friendly method. In this study, the ignition and burnout behavior of CGFA were investigated via a thermogravimetric analyzer (TGA), flat-flame burner (FFB), and drop-tube furnace (DTF). Further, the cofiring of CGFA was numerically studied in a tangentially fired pulverized coal boiler burning anthracite with various cofiring ratios (0%, 10%, 20%, and 30%). The TGA results show the similar oxidation reactivity, oxidation kinetics, and ignition behavior of CGFA with the anthracite. In the FFB atmosphere with practical heating rates, the CGFA and anthracite are both heterogeneously ignited with an ignition time of 8.1 and 7.6 ms, respectively. The particle size significantly affected the ignition time of CGFA, as the particle size decreased from 125 to 135 μm to 45−63 μm and the ignition time of CGFA decreased from 10.1 to 5.6 ms. The burnout test in DTF indicates that the promising burnout performance in a pulverized coal furnace required a crucial oxygen concentration >10%, and the CFD simulation results coincided well with the experimental data from DTF. The CFD modeling results of the full-scale furnace show that the cofiring of CGFA is feasible in the pulverized coal furnace burning anthracite. Compared with the mode of pure anthracite combustion, under the cofiring mode with 10−30% CGFA as the energy input, the central maximum temperature of the main combustion zone increases by 50−90 °C, resulting in the slightly improved burnout for both anthracite and CGFA.

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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%

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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Pore development and combustion behavior of gasified semi-char in a drop tube furnace

Cited by 23 publications

References 48 publications

Estimation of Effective Diffusion Coefficient of O2 in Ash Layer in Underground Coal Gasification by Thermogravimetric Apparatus

Estimation of Effective Diffusion Coefficient of O2 in Ash Layer in Underground Coal Gasification by Thermogravimetric Apparatus

Combustibility and Cofiring of Coal Gasification Fine Ash with High Carbon Content in a Full-scale Pulverized Coal Furnace

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

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