Spontaneous ignition of soils: a multi-step reaction scheme to simulate self-heating ignition of smouldering peat fires

2021 ◽  
Author(s):  
Han Yuan ◽  
Francesco Restuccia ◽  
Guillermo Rein
Keyword(s):  
Reaction Scheme ◽  
Spontaneous Ignition ◽  
Self Heating ◽  
Peat Fires

scholarly journals Effect of wood biomass components on self-heating

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Nozomi Miyawaki ◽  
Takashi Fukushima ◽  
Takafumi Mizuno ◽  
Miyao Inoue ◽  
Kenji Takisawa
Keyword(s):  
Moisture Content ◽  
Inductively Coupled Plasma ◽  
Optical Emission ◽  
Chemical Oxidation ◽  
Spontaneous Ignition ◽  
Emission Spectrometry ◽  
Inductively Coupled ◽  
Self Heating ◽  
Inorganic Substances ◽  
Before And After

AbstractBiomass may ignite due to biological oxidation and chemical oxidation. If this phenomenon (spontaneous ignition) is controlled, it would be possible to produce biochar at a lower cost without the need for an external heat resource. We investigated if self-heating could be controlled by using sawdust and bark chips. When sawdust and bark chips were used under controlled conditions, the bark chips temperature increased to the torrefaction temperature. The ash content of bark chips was ~ 2%d.b. higher than that of sawdust; consequently, the inorganic substances contained in the bark chips might affect the self-heating. Self-heating was suppressed when inorganic substances were removed by washing with water. Therefore, the inorganic substances in the biomass might have affected self-heating. The inorganic element contents of the bark chips were measured by inductively coupled plasma optical emission spectrometry before and after washing. The potassium content of the bark chips was reduced remarkably by washing, and there was a possible influence of potassium on self-heating. Finally, the effect of moisture content on self-heating was investigated to obtain stable reactivity. Thus, at a moisture content of 40%w.b., a steady self-heating behavior may be realized.

scholarly journals Efficacy and Risk of Aeration to Prevent Self-heating Powder Bed from Spontaneous Ignition.

1993 ◽  
Vol 30 (7) ◽  
pp. 483-489 ◽  
Author(s):  
Yoji NAKAJIMA ◽  
Satoru FURUSAWA ◽  
Hua LIANG ◽  
Tatsuo TANAKA
Keyword(s):  
Spontaneous Ignition ◽  
Powder Bed ◽  
Self Heating

scholarly journals Self-Heating of Biochar during Postproduction Storage by O2 Chemisorption at Low Temperatures

Energies ◽  
2022 ◽  
Vol 15 (1) ◽  
pp. 380
Author(s):  
Aekjuthon Phounglamcheik ◽  
Nils Johnson ◽  
Norbert Kienzl ◽  
Christoph Strasser ◽  
Kentaro Umeki
Keyword(s):  
Low Temperatures ◽  
Pilot Scale ◽  
Thermal Runaway ◽  
Spontaneous Ignition ◽  
Transient Model ◽  
Thermogravimetric Analyzer ◽  
Self Heating ◽  
O2 Adsorption ◽  
Insight Into ◽  
Good Agreement

Biochar is attracting attention as an alternative carbon/fuel source to coal in the process industry and energy sector. However, it is prone to self-heating and often leads to spontaneous ignition and thermal runaway during storage, resulting in production loss and health risks. This study investigates biochar self-heating upon its contact with O2 at low temperatures, i.e., 50–300 °C. First, kinetic parameters of O2 adsorption and CO2 release were measured in a thermogravimetric analyzer using biochar produced from a pilot-scale pyrolysis process. Then, specific heat capacity and heat of reactions were measured in a differential scanning calorimeter. Finally, a one-dimensional transient model was developed to simulate self-heating in containers and gain insight into the influences of major parameters. The model showed a good agreement with experimental measurement in a closed metal container. It was observed that char temperature slowly increased from the initial temperature due to heat released during O2 adsorption. Thermal runaway, i.e., self-ignition, was observed in some cases even at the initial biochar temperature of ca. 200 °C. However, if O2 is not permeable through the container materials, the temperature starts decreasing after the consumption of O2 in the container. The simulation model was also applied to examine important factors related to self-heating. The results suggested that self-heating can be somewhat mitigated by decreasing the void fraction, reducing storage volume, and lowering the initial char temperature. This study demonstrated a robust way to estimate the cooling demands required in the biochar production process.

Thermal effects accompanying spontaneous ignition in gases. IV. The decomposition of diethyl peroxide in a cylindrical vessel and the effect of diluents on self-heating

1971 ◽  
Vol 325 (1561) ◽  
pp. 175-196 ◽  
Keyword(s):  
Thermal Conductivity ◽  
Critical Temperature ◽  
Stationary State ◽  
Temperature Rise ◽  
Cylindrical Vessel ◽  
Spontaneous Ignition ◽  
Spherical Vessel ◽  
Average Value ◽  
Self Heating ◽  
Rate Of Dissipation

The investigation (see parts I to III) of the spontaneous ignition of gaseous diethyl peroxide as a thermal explosion is concluded by a series of experiments mainly in a cylindrical vessel, and including diluted mixtures. A very fine thermocouple (25 µ m diameter) has been used to probe the temperature distributions between the axis and the wall both in systems reacting subcritically and in systems on the verge of ignition. A multijunction thermocouple has also been employed to obtain instantaneous readings of distributed temperature in a spherical vessel. It is found that self heating is always present. In accordance with a conductive theory of heat losses, temperatures are not uniform throughout the reactant, but depend on the fractional distance ( z = r / r 0 ) from the vessel axis, being greatest at the axis and least at the walls. For the cylinder, the form of the profiles expected in a stationary state is ( T - T a )/( RT a 2 / E ) = 2 ln (1 + G )/(1 + Gz 2 ) and good agreement is found between theory and experiment. (The significance of G is discussed in the text.) This agreement, the symmetry of the profiles, and the absence of any temperature step at the walls confirm the absence of convection at the pressures concerned. A critical centre temperature rise exists above which ignition is inevitable. The greatest value of this increment is 23.3 K ; for simple theory, the predicted value is 19 K (1.39 RT a 2 / E ). Any temperature dependence of this critical increment lies beyond the discrimination of the present apparatus. Similar agreement is found between ‘measured’ and theoretically expected values for Frank-Kamenetskii’s δ . At criticality, the measured values average 2.25 against a theoretical value (uncorrected for finite vessel size or finite reaction rate) of 2 exactly. ‘Measured’ values for δ in subcritical systems are also in satisfactory accord with expectation. Other ‘indirect’ tests of thermal theory are also satisfied. Thus the curvature of the critical pressure limit (boundary on the p — T diagram between explosive and slow reaction) exactly corresponds to the activation energy measured in isothermal decomposition. Similar temperature-position profiles are found in diluted mixtures below criticality, and although critical explosion pressures depend on the degree of dilution, the critical temperature rise for ignition does not. The average value found is 19.0 K. Nor does the critical temperature gradient at the vessel boundary vary from the value ( — 2 exactly) predicted for any dilution of vessel geometry. There are the same influences on criticality as in the spherical vessel: in accord with stationary state conductive theory, thermal conductivity is the principal factor but its influence is distorted to varying degrees, first by the occurrence of dynamic heating accompanying gas entry, secondly by the rate of dissipation of this heating, which is governed by the thermal diffusivity, and thirdly by the departures from stationary state behaviour largely governed by the specific heat of the diluent. These influences explain an otherwise erratic dependence of critical ignition pressures on thermal conductivity.

Efficacy and risk of aeration to prevent self-heating powder bed from spontaneous ignition

1995 ◽  
Vol 6 (1) ◽  
pp. 63-77 ◽  
Author(s):  
Yoji Nakajima ◽  
Satoru Furusawa ◽  
Hua Liang ◽  
Tatsuo Tanaka
Keyword(s):  
Spontaneous Ignition ◽  
Powder Bed ◽  
Self Heating

Thermal effects accompanying spontaneous ignitions in gases III. The explosive decomposition of diethyl peroxide

1970 ◽  
Vol 316 (1525) ◽  
pp. 255-268 ◽  
Keyword(s):  
Isothermal Kinetics ◽  
Critical Conditions ◽  
Spontaneous Ignition ◽  
Explosive Decomposition ◽  
Self Heating ◽  
Thermal Theory ◽  
Principal Influence ◽  
Straight Line ◽  
Temperature Position ◽  
Critical Ignition

An extensive quantitative test of the application of thermal theory of the spontaneous ignition of diethyl peroxide has been carried out, and both indirect aspects and direct temperature measurements in systems on the verge of ignition have been studied. The principal conclusions may be stated as follows. (i) Ignition is always preceded by self heating. Temperatures are greatest at the vessel centre and in accordance with the postulates of Frank–Kamenetskii there is no detectable excess at the walls. (ii) Temperature-position profiles differ significantly from parabolae being less steep at the walls and more curved at the centre. (iii) Stable decomposition is impossible once the centre temperature exceeds 20 °C (i. e. close to 1.61 RT 2 0 / E ) or the wall-gradient a value greater than 2 RT 2 0 / Er 0 . (iv) The 'experimental ’ value for δ around the explosion boundary derived from fifteen sets of measurements of p cr , T cr together with new values for Q, λ and ‘ isothermal’ values for k, A , and E is 4.0. Agreement with theory is good and if a correction is made to allow for reactant consumption, the discrepancy is insignificant. (v) A graph of R ln p cr / T 3 against 1/ T gives a straight line with slope (35 kcal (147 kJ) mol -1 ) in good agreement with expectations (34 kcal (143 kJ) mol -1 ), based on isothermal kinetics. (vi) Inert diluents exert their principal influence on critical conditions by their effect (here measured experimentally) on thermal conductivity, but because mixtures with diluents undergo more self-heating on admission to an evacuated vessel than does the pure peroxide there are deviations from simple proportionality between p cr and λ. (vii) The critical ignition temperature and the critical wall gradient are unaffected by dilution. The experiments carried out represent the fullest test to date of thermal theory. They have been made possible by the use of very fine (13 μ m) thermocouples as temperature measuring devices.

Sign in / Sign up

Export Citation Format

Share Document