scholarly journals Modeling of Effects of Volatile Matter Cloud on Heterogeneous Ignition of Single Coal Particles.

2000 ◽  
Vol 33 (1) ◽  
pp. 49-56 ◽  
Author(s):  
Hassan Katalambula ◽  
Jun-ichiro Hayashi ◽  
Kunihiro Kitano ◽  
Tadatoshi Chiba
Keyword(s):  
Volatile Matter ◽  
Heterogeneous Ignition ◽  
Coal Particles

Group Ignition of a Cloud of Coal Particles

1991 ◽  
Vol 113 (3) ◽  
pp. 677-687 ◽  
Author(s):  
W. Ryan ◽  
K. Annamalai
Keyword(s):  
Initial Conditions ◽  
Numerical Study ◽  
Ignition Time ◽  
Volatile Matter ◽  
Combustion Model ◽  
Ambient Conditions ◽  
Experimental Conditions ◽  
Coal Particles ◽  
Group Combustion ◽  
Ignition Characteristics

Ignition of an isolated single coal particle is known to occur either heterogeneously or homogeneously. While single-particle studies may be useful for dilute coal sprays, their application to burners is limited since ignition occurs in the vicinity of the burners where the spray is dense. Rather than considering an isolated particle, one must consider a collection of particles in order to determine the change in ignition characteristics resulting from particle interactions. Thus, group combustion models have been developed essentially to predict the ignition and combustion characteristics of a larger number of interacting drops/particles. This paper presents results of the ignition characteristics of a spherical cloud of uniformly distributed coal particles in quiescent surroundings using a simple group combustion model. For the conditions studied, the results are as follows: (1) Ignition is heterogeneous if the cloud is dilute and homogeneous if the cloud is dense under the same ambient conditions; (2) there is a minimum ignition time for a given set of initial conditions corresponding to a certain cloud denseness; (3) ignition time is less sensitive to the denseness of the cloud at higher ambient temperatures; and (4) decreased proximate volatile matter can result in either increased or decreased ignition time depending on the cloud denseness (ignition mode). Qualitative comparisons to experimental data are given; however, these comparisons should be approached with caution since the experimental conditions and geometries may be vastly different than those used in the numerical study presented here.

scholarly journals Beneficiation and Physiochemical Characterization of Coal Deposits in Achibo-Sombo Area, South-Western Ethiopia

2021 ◽  
Author(s):  
Temam Usman ◽  
Samuel Abicho ◽  
Daniel Meshesha ◽  
Getachew Adam Workneh
Keyword(s):  
Coal Sample ◽  
Calorific Value ◽  
Volatile Matter ◽  
Crystal Structure Analysis ◽  
Fixed Carbon ◽  
Coal Deposits ◽  
Treated Sample ◽  
Coal Particles ◽  
Coal Grade ◽  
Froth Floatation

Abstract This study was conducted to upgrade the quality of Achibo-Sombo coal deposits by physiochemical beneficiation methods particularly by using froth floatation technique to minimize the ash and sulfur content from coal particles. During the floatation test, proximate, ultimate, calorific value, functional groups, surface morphology and crystal structure analysis of Achibo-Sombo coal was carried out through different methods. The moisture content of a raw sample and treated sample is found in the range of 11.81 to 20.27% and 8.12 to 14.02 % respectively. The volatile matter is ranging from 22.74 to 34.85 % for raw coal and 21.92 to 30.64 % for treated coal samples. The ash content of the raw coal sample is ranging from 22.47 to 36.58 % which became in the range 7.49 to 13.62 % after treatment. The fixed carbon is also changed from 23.85–38.31% of raw sample to 44.47–55.87 % for treated coal samples. The calorific value of a raw sample is found in the ranges of 5838.46 Btu/lb. to 9531.29 Btu/lb. whereas for treated coal samples it is found in the ranges of 9438.12 Btu/lb. to 11756.63 Btu/lb. The sulfur and nitrogen contents of the raw coal sample which were ranged from 0.57 to 1.9 % − 1.22 to 1.44 % are reduced to 0.25 to 0.41% -0.52 to 0.92% respectively after treatment. Generally, the Achibo-Sombo raw coal is falling under the coal grade of lignite B to sub-bituminous B whereas the treated coal sample is grouped under sub-bituminous C to high volatile bituminous C. Accordingly, the results obtained indicate that the Achibo coal streams are upgraded relatively with better calorific value and fixed carbon and with lowest ash contents as compared to samples collected from other sites.

A Review of Combustion of Single Coal Particles in Fluidized Beds

1985 ◽  
Vol 9 (3) ◽  
pp. 142-150
Author(s):  
Prabir Basu
Keyword(s):  
Mass Transfer ◽  
Fluidized Beds ◽  
Heterogeneous Reaction ◽  
Mass Transfer Rate ◽  
Volatile Matter ◽  
Carbon Surface ◽  
Bed Temperature ◽  
Coal Particles ◽  
Order Of Magnitude ◽  
And Performance

The state of the art of the theory of the process of combustion of single coal particles in fluidized beds is reviewed. The process of combustion of coal is divided into two stages: devolatilisation, and burning of the char. The devolatilisation and the subsequent combustion of the volatile matter takes an order of magnitude less time than that for burning of the char. Therefore, the burning of char dominates the characteristics and performance of the combustor. Generally, the combustion of char is found to be controlled by the mass transfer to and reaction on the external surface if the area of pores in the char is less than 0.3 × 106m2/m3. Existing information suggests that in a fluidized bed oxygen diffuses to the carbon surface and it enters into heterogeneous reaction with carbon producing mainly CO. The carbon monoxide burns to CO2 in a diffusion flame surrounding the char particle. The surface temperature of the char, which is always higher than the bed temperature, is found to increase with decreasing size of the char, but it may start decreasing again if the site of CO oxidation moves away from the char surface for very small char particles. The mass transfer rate to the char particles may be calculated by considering the radial variation of local voidages, but this effect is significant only in limited cases.

scholarly journals Combustion peculiarities of coal-methane-air mixtures in a recuperative burner

2018 ◽  
Vol 243 ◽  
pp. 00007
Author(s):  
Leonid Minkov ◽  
Kseniya Moiseeva
Keyword(s):  
Carbon Dioxide ◽  
Carbon Monoxide ◽  
Water Vapor ◽  
Reaction Zone ◽  
Volatile Matter ◽  
Oxidation Reactions ◽  
Volatile Substances ◽  
Fine Coal ◽  
Coal Particles ◽  
Roll Type

Numerical modeling of the combustion of a lean methane-air mixture containing fine coal particles entering the “Swiss-roll” type recuperative burner is considered. The mathematical model is constructed under the following assumptions: the flow field is two-dimensional; the gas mixture is an ideal incompressible gas consisting of oxygen, methane, coal volatile substances, carbon monoxide, carbon dioxide, water vapor, hydrogen and nitrogen. In the gas phase four oxidation reactions, in which methane, volatile matter of coal, carbon monoxide, hydrogen participate and the reaction of carbon dioxide decomposition take place. On the surface of the coal particle, there are three oxidation reactions involving oxygen, carbon dioxide and water vapor, resulting in the formation of carbon monoxide. It is assumed that coal contains 8% of ash, 12.9% of volatile substances and 79.1% of carbon. It is shown that for a two percent methane-air mixture the reaction zone shifts toward the center of the burner as the feed rate of the mixture increases. An increase in the content of coal particles leads to a shift of the reaction zone into the inlet part of the burner, and the heat release in the burner increases.

Pyrolysis and Ignition Characteristics of Pulverized Coal Particles

2000 ◽  
Vol 123 (1) ◽  
pp. 32-38 ◽  
Author(s):  
Masayuki Taniguchi ◽  
Hirofumi Okazaki ◽  
Hironobu Kobayashi ◽  
Shigeru Azuhata ◽  
Hiroshi Miyadera ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Fine Particles ◽  
Early Stage ◽  
Radiant Heat ◽  
Volatile Matter ◽  
Combustible Mixture ◽  
Radiant Heat Transfer ◽  
Coal Particles ◽  
Intermediate Size ◽  
Ignition Characteristics

Pyrolysis and ignition characteristics of pulverized coals were examined under similar burning conditions to those of industrial burners. In the early stage, fine particles (less than 37 μm) were mainly pyrolyzed by convective heat transfer from surrounding gas. The coals ignited when pyrolyzed volatile matter mixed with surrounding air and formed a combustible mixture. Pyrolysis of large particles was delayed, but accelerated after ignition by radiant heat transfer from coal flames. The effects of radiant heat transfer were strong for intermediate-size particles (37–74 μm). Ignition temperature was examined analytically by using a modified distributed activation energy model for pyrolysis. The calculated results agreed with experimental ones obtained from both laboratory-scale and semi-industrial-scale burners.

The ignition of clouds of particles in shock-heated oxygen

1967 ◽  
Vol 300 (1460) ◽  
pp. 62-77 ◽  
Keyword(s):  
Radiant Heat ◽  
Volatile Matter ◽  
Radiant Heat Transfer ◽  
Ignition Process ◽  
Particle Ignition ◽  
Ignition Delay Times ◽  
Complex Process ◽  
Coal Particles ◽  
Delay Times ◽  
The Times

The ignition of clouds of coal particles in shock-heated oxygen has been studied. The requisite gas temperatures and pressures for ignition have been measured and have been related to particle ignition temperatures which are dependent on the volatile content of the coal and are in close agreement with the temperatures at which the particles lose volatile matter at an appreciable rate. Ignition delay times for various coals of different size ranges have been measured at oxygen pressures of 1.5 to 30 atm and temperatures of 700 to 1600°K. The experimental results indicate that the influence on the delays of the radiant heat transfer from a previously established flame at the shock-reflecting face is small. Some evidence that ignition is a surface catalysed process is presented. A mechanism for the ignition process is proposed. This relates the ignition delays with the times required to heat the particles solely by conduction to the appropriate particle ignition temperature. This theory is shown to describe the experimental delays satisfactorily. In testing it, similar experiments on completely volatile particles (anthracene) and non-volatile particles (graphite) have been carried out. Ignition of anthracene occurs when the particles approach their boiling point. Ignition of small graphite particles is a more complex process in which the first stage is the heating of the particles by conduction to a temperature just below that of the shock-heated gas. This is followed by a period in which heating due to chemical reaction overtakes heating by conduction.

Heat Transfer From a Molten Phase to an Immersed Coal Particle During Devolatilization

1993 ◽  
Vol 115 (3) ◽  
pp. 717-723 ◽  
Author(s):  
R. H. Hurt ◽  
T. H. Fletcher ◽  
R. S. Sampaio
Keyword(s):  
Heat Transfer ◽  
Coal Gasification ◽  
Volatile Matter ◽  
Molten Carbonate ◽  
Transfer Coefficients ◽  
X Ray ◽  
Heat Transfer Coefficients ◽  
Coal Particles ◽  
Bath Smelting ◽  
Molten Phase

In several developmental and commercial processes, coal particles come into direct contact with a high-temperature molten phase. These processes include molten carbonate coal gasification and bath smelting for the production of iron. Recently, real-time X-ray fluoroscopic images have been published that show volatile matter evolving rapidly from coal particles immersed in molten phases, displacing the surrounding melt and producing a periodic cycle of formation, rise, and detachment of gas cavities. The present work makes use of these observations to develop a model of heat transfer from the melt to particles undergoing gas evolution. The model is developed for the general case and applied to predict melt-particle heat transfer coefficients under conditions relevant to bath smelting processes. The model shows that the presence of the gas film can actually increase the overall heat transfer rate under certain conditions.

Soot Volume Fractions in Volatile Matter Envelope Flames of Bituminous Coal Particles in Air and Oxy-Fuel Combustion

2013 ◽  
Author(s):  
Reza Khatami ◽  
Yiannis A. Levendis
Keyword(s):  
Bituminous Coal ◽  
Volume Fraction ◽  
Soot Volume Fraction ◽  
Volatile Matter ◽  
Fuel Combustion ◽  
High Speed Photography ◽  
Drop Tube ◽  
Volume Fractions ◽  
Coal Particles ◽  
Shell Forming

This work calculated volume fractions of soot in volatile matter envelope flames which form around burning single particles of bituminous coal. Both conventional combustion in air and simulated oxy-fuel combustion, with oxygen mole fractions in the range of 20–40% in CO2, were studied. Particles of 75–90 μm were injected in a bench-scale, transparent drop-tube furnace (DTF), at wall temperatures of 1400K. Upon ignition, optical pyrometry and high-speed photography were implemented to optically diagnose the burning particles. The method of Timothy et al[1] was applied to determine the instantaneous spatially-average soot volume fraction in these envelop flames. Results showed that soot shell forming around the particle was thicker and more luminous in air than the shell forming at the same O2 concentration in CO2. The soot volume fraction was decreased when N2 in air was replaced by CO2. Average soot volume fraction in the envelope flames in air was in the order of 7×10−5, whereas it was in the range 3.5×10−5 – 5.0×10−5 in oxy-fuel atmospheres.

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