Coal Ignition Research Articles

SHORT COMMUNICATION Effect of Prior Ultraviolet Irradiation on Thermal Decomposition and Ignition of Coal

Abstract Prior ultraviolet irradiation of coal results in catalysing the subsequent thermal decomposition and ignition of coal. Mechanically, it is shown that ultraviolet radiation brings about the catalysis by acting on the inorganic components of coal.

Thermal decomposition and ignition of coal

A study of the thermal decomposition and ignition of coal as functions of pelletizing pressure and dwell time has revealed that: (1) ignition and thermal behaviour are related to the apparent density of the pelletized coal; (2) for a given apparent density of pelletized coal, the ignition temperature is related to the rate constants of thermal decomposition. Isothermal decomposition in air at 550 °C has been shown to fit the Avrami-Erofeev equation for three-dimensional growth of nuclei.

A lowering of the coal ignition temperature at mechanical impact

A lowering of the coal ignition temperature at mechanical impact

Direct observations of devolatilizing pulverized coal particles in a combustion environment

Direct observations of the early stages of combustion of size-graded (≈100μm) pulverized coal particles are reported. The particles are introduced on the centerline, of a high temperature, transparent, laminar flow reactor fed by a gas fueled, premixed flat flame. Photographs of particle emission, high magnification shadowgraphs of burning particles, and micrographs of partially burnt captured material have been obtained. The ignition of both bituminous coal and lignite subjected to rapid heating (≈105K/sec) by hot combustion products is characterized by, bright diffuse emission attributed to burning of ejected volatile matter. After approximately 5 msec this emission ceases, and incandescence attributed to heterogeneous char oxidation is observed. Shadowgraphs and micrographs of burning bituminous coal indicate that, coincident with ignition, ejected volatile matter forms a condensed phase surrounding the particle. The condensed phase is evidently a soot-like material resulting from pyrolytic cracking of hydrocarbons in the volatile matter. Viscous drag forces cause the condensed material to be swept into laminar wake structures which eventually separate from the particles. Under oxidizing conditions this condensed volatile matter is oxidized during the early stages of char burning, while under reducing conditions it persists throughout the flow reactor. Although burning lignite appears similar to bituminous coal in emission, shadowgraphic and micrographic observations, indicate that a condensed phase is not formed during devolatilization. Nor are, changes in particle size or shape observed during the earliest stages of combustion. These observations are consistent with previous results which showed that bituminous coal volatiles contain large fractions of soot producing heavy hydrocarbons, while lignite volatiles are largely composed of CO, CO2, H2, H2O and light hydrocarbons. The observations are also consistent with differences in the pore structure and swelling properties of the two coasl.

Shock tube techniques in the study of pulverized coal ignition and burnout

The extension of shock tube techniques to the study of ignition and burnout of pulverized coal is examined. Nonintrusive optical techniques for characterizing the particle size distribution and the particle temperature as a function of time during burnout are described. Comparison of surface oxidation rates of soot particles and several bituminous coals obtained in the shock tube are in excellent agreement with the higher temperature results found in other apparatus. Because of the wide but controllable ranges of total pressures, oxygen parital pressures, particle temperatures, and coal loadings obtainable, the shock tube offers an additional instrument for the study of solid particle ignition and reactivity under conditions comparable to those found in mine explosions and anticipated in high intensity combustors.

Ignition of Pulverized Coal with Arc Heated Air

C powerplant practice, with suspension fired boilers, involves consumption of large quantities of premium fuel to accomplish ignition of pulverized coal. A new approach to coal ignition is described. A vortex stabilized electric arc heater was attached to a full-scale commercial pulverized coal burner. A continuous arc heated air jet was used as an ignition source. The equipment was operated in a powerplant where ignition of coal was demonstrated. Ignition was accomplished with igniter input power levels which are lower than conventional practice by a factor of six. Cost of an igniter system for a large commercial size coal burner was estimated; the arc igniter appears to be economically viable and competitive with conventional practice.

Critical Regimes of Coal Ignition

In a normal operation of the coal fired power plant, critical regimes exist where the particles cannot be ignited either in the gas mode or in the heterogeneous mode due to excessive heat loss. Following thermal theories of ignition, sufficient conditions for the extinction sizes for quenching gas phase combustion are presented along with critical limits for the gas phase and heterogeneous ignition of coal particles. Universal plots are given to present the critical parameters of both modes of ignition in terms of known physico-chemical data of any coal/char particle. Quantitative results for the critical size and oxygen concentration of brown coal particles estimated from the plots are found to check with the iterative numerical results carried out elsewhere. Such sizes and oxygen concentrations may serve as ignitability indices of different coal particles.

Single pulse shock tube studies of pulverized coal ignition

The ignition behavior of sized samples of pulverized coal has been studied using a modified single pulse shock tube. Ignition delays and particle temperature history were recorded optically while batch samples of evolved gases were sampled prior to and after ignition and analyzed by gas chromatography. Significant pre-ignition pyrolysis in the form of low molecular weight hydrocarbons was detected in all samples tested. Although the ignition delay of two similarly sized samples (Illinois no. 6 and Pittsburgh Seam) were substantially different, the volatile compositions were similar with the Pittsburgh having a somewhat higher yield at all conditions studied. Activation energies, determined from surface oxidation rate data, were used to successfully model the temperature dependence of the ignition delay of both smaller coals (number mean diameter 3.3 μ m for Pittsburgh and 4.1 μ m for Illinois no. 6). This heterogeneous theory failed for the larger Pittsburgh coal (14.9 μ m mean number diameter) as it consistently overpredicted the ignition delay. Inasmuch as the oxidation of pre-ignition hydrocarbons prior to ignition of the solid phase was observed only for the large Pittsburgh coal, the discrepency can be explained plausibly on the basis of the gas phase volatiles participating in the ignition of the larger particles.

Critical volumes for spontaneous ignition of dry and wet coals

Critical volumes for spontaneous ignition of dry and wet coals

The thermal theory of induction periodsand ignition delays

Coal spontaneous combustion is an inherent problem in coal mines throughout the world. The analysis of stationary-states, including stable point and critical point, is an effective method to judge its ignition tendency. A lower critical point temperature means that it is more likely to cause fire. In the past, due to the limitation of mathematical methods, the consumption and distribution of oxygen concentration are usually neglected. In order to accurately analyze coal ignition tendency, this paper takes coal bulk as a porous system and develops an improved model by a combination of oxygen species and energy equation. The model is solved for stationary-states of the system. Qualitative analysis of the stationary-states gives a mechanism explanation for the reason why coal spontaneous ignition is hard to be extinguished and indicates that the temperature of initial endpoint and that of internal site can be uniquely determined from each other. It further points out a trend that the location of critical point moves inward as the inlet air velocity increases, which correlates well with simulation results of the existing literatures. Then, for stationary-states, calculation results of Killoch 6015 coal are obtained. Quantitative analysis of them finds a trend that the temperature of critical point rises rapidly after its slow increase. At last, a velocity range, in which the possibility of fire is extremely high, is presented by simulation computation, e.g., the range of Killoch 6015 coal is determined as 8 × 10− 5–3 × 10− 3 m/s when the critical ignition temperature is set as 150 °C.

LXXXVI.—The oxidation and ignition of coal

The first page of this article is displayed as the abstract.

Spontaneous Ignition of Coal

Spontaneous Ignition of Coal

Spontaneous ignition of coal

Spontaneous ignition of coal

Spontaneous Ignition of Coal

Spontaneous Ignition of Coal

Remarks on the different modes of applying power for locomotive purposes

Oxy-steam combustion is a potential new-generation option for CO2 capture and storage. The ignition and combustion characteristics of single coal and biomass particles were investigated in a flow tube reactor in O2/N2 and O2/H2O at various oxygen concentrations. The ignition and combustion processes were recorded using a CCD camera, and the two-color pyrometry was used to estimate the volatile flame temperature and char combustion temperature. In O2/N2 and O2/H2O, coal ignites heterogeneously at <O2> = 21–50%. In O2/N2, biomass ignites homogeneously at <O2> = 21–30%, while it ignites heterogeneously at <O2> = 40–50%. In O2/H2O, biomass ignites homogeneously at <O2> = 21–50%. With increasing oxygen concentration, the ignition delay time, volatile burnout time and char burnout time are decreased, and the volatile flame temperature and char combustion temperature are increased. At a certain oxygen concentration in both atmospheres, the ignition delay time, volatile burnout time and char burnout time of biomass are shorter than those of coal. Moreover, biomass has a higher volatile flame temperature but a lower char combustion temperature than coal. The ignition delay time, volatile burnout time and char burnout time in O2/H2O are lower than those in O2/N2 for coal and biomass. The presence of H2O can improve the combustion rates of coal and biomass. The volatile flame shows a lower temperature in O2/H2O than in O2/N2 at <O2> = 21–50%. The char combustion shows a lower temperature in O2/H2O than in O2/N2 at <O2> = 21–30%, while this behavior is switched at <O2> = 40–50%. The results contribute to the understanding of the ignition and combustion characteristics of coal and biomass in oxy-steam combustion.