J.C. Jones

Kinetic parameters of oxidation of bituminous coals from heat-release rate measurements

Arrhenius parameters of oxidation of two Scottish bituminous coals were determined from heat-release rate measurements at laboratory oven temperatures. When the heat release rate expression so obtained was applied at stockpiling temperatures (∼300 K), one coal was shown to have a significantly greater propensity to spontaneous combustion than the other.

Kinetic parameters of oxidation of coals by heat-release measurement and their relevance to self-heating tests

From heat-release rates made in oven heating experiments, kinetic parameters of oxidation of a number of bituminous coals are determined. Calculations are performed to determine the critical ambient temperature for ignition of each coal in a 3 m shipping hold, and rates of heat release at that temperature are calculated for each coal. These are found to be the same for each coal and it is suggested that this can provide a criterion for an alternative approach to assessing self-heating hazards with such materials.

Continuity of kinetics between sub- and supercritical regimes in the oxidation of a high-volatile solid substrate

Peat samples were subjected to oven experiments spanning a considerable temperature range, some resulting in ignition and some in failure to ignite. Heat release rates for the two display a temperature dependence describable by a single pair of Arrhenius parameters in spite of significantly greater volatiles release in some experiments than in others. Applicability of the Frank-Kamenetskii treatment to such materials is discussed in the light of these findings.

Swelling of a German brown coal in acetone-water and methanol-water mixtures

Samples of a German brown coal were treated with acetone-water and methanol-water mixtures of different compositions and the consequent coal swelling was measured. Owing to the very high solubility parameter of pure water, these mixtures have higher solubility parameters than binary organic solvent mixtures commonly used in such experiments. The results are interpretated on the basis that matching of coal and solvent solubility parameters maximizes swelling, although note is also taken of supplementary effects including those accompanying entry of solvent into the coal pores.

A means of obtaining a full kinetic rate expression for the oxidation of a solid substrate from a single criticality data point

Abstract A method whereby kinetic rate parameters for the oxidation of a material such as powdered coal or shredded wood can be obtained from a single criticality data point—determined, for example, from oven heating tests with a 10-cm cubic gauze container—is developed theoretically and applied to two bituminous coals.

On the role of times to ignition in the thermal safety of transportation of bituminous coals

Abstract Previously presented results for the oxidation kinetics and hence the spontaneous combustion propensity of six Scottish bituminous coals are reappraised in terms of ignition times, an aspect not considered previously. All six coals could be considered unsafe to ship according to safety criteria based on the spontaneous combustion propensity, but at least two of them have ignition times so long that no incident would be expected on an export voyage. The test for assessing spontaneous combustion propensity does not alone appear to be an adequate criterion for safety in transport.

Temperature uncertainties in oven heating tests for propensity to spontaneous combustion

Abstract Formal analysis of heat transfer within an air oven is carried out and it is concluded that in heating tests for spontaneous combustion using such ovens radiation effects preclude determination of critical ignition temperatures to better than about ±1 K.

Evidence from microcalorimetry for irreversible chemisorption of oxygen in a low-rank coal

Abstract Air-dried 60 mg samples of a German brown coal were examined using a microcalorimeter at temperatures in the range 30–55°C. Heat release rates in the range ∼ 1–25 μW were recorded, and an irreversible effect was observed whereby once the sample had experienced a temperature of ∼42°C, previously obtained results at lower temperatures could not be repeated. This is believed to be due to chemisorption.

Indirect evidence of relatively high thermal conductivities in powdered activated carbons

Abstract From ignition experiments, indirect estimates of the thermal conductivities of two commercial powdered activated carbons are made. The values are much higher than expected and indicate that existing literature estimates of the thermal conductivities of such materials might not be broadly applicable.