Analysis on the Governing Reactions in Coal Oxidation at Temperatures up to 400°C

Abstract

The present study aims to further understanding of the principal reactions that occur during coal oxidation at moderate temperatures. Mass change and heat evolution of a sample were monitored by thermo-gravimetric analysis coupled with differential thermal analysis (TGA/DTA). Gaseous and solid products were traced using online or in situ Fourier transform infrared spectroscopy (FTIR). Measurements were conducted by heating the samples up to 400˚C, with the O 2 concentration in the reaction medium set at 0, 10, 21, and 40 vol%, respectively. It was observed that the mass increase of a sample between 150˚C and ~275˚C was a result of the accumulation of C=O containing species in the coal structure, whereas substantial mass loss and heat evolution of a sample at ~400˚C can be attributed to the significant involvement of the direct "burn-off" reaction. Enrichment of O 2 in the reaction medium leads to the acceleration in oxygen chemisorption, formation and decomposition of the solid oxygenated complexes, as well as the "burn-off" reaction. With the temperature increasing, the oxidation process governed by oxygen chemisorption gradually shifts to that by significant decomposition reactions, and eventually to that by the direct "burn-off" reaction. Temperature boundaries of these stages can be determined using parameters defined based on a set of TG/DTA data. Shift in the governing reactions is essentially due to the diverse requirements of reactants of the reactions and their energy barriers to be overcome. In engineering practice, the phenomena of self-heating and spontaneous combustion of coal correspond to chemisorption and the direct "burn-off" reaction, respectively.

Functionalization of sewage sludge char by partial oxidation with molecular oxygen to enhance its adsorptive properties

“…All the TG/DTG profiles are available in the Supplementary Information (Figure S1). Zhan et al (2014) reported TG results for coal oxidation in dynamic runs up to 400 C and a similar trend for the mass change was observed. In that study, the sample mass under oxidation conditions increased up to 275 C and then decreased by increasing temperature.…”

“…In that study, the sample mass under oxidation conditions increased up to 275 C and then decreased by increasing temperature. The oxidation mechanism might be described as two parallel steps (Su et al, 2017): (1) char is directly oxidized to volatile products (CO 2 , CO and H 2 O) or (2) it initially reacts to form intermediate surface species, which subsequently either continue to react to gases or alternatively are stabilized as functionalized groups (hydroxyl and phenolic (eOH), carbonyl (eCO), carboxyl (eCOOH) and ether (CeOeC) linkages (Zhan et al, 2014)). The mass gain during oxidation is attributed to oxygen uptake and the formation of solid oxygenated complexes (Zhan et al, 2014).…”

Ilgin Li̇nyi̇t İşletmesi̇nde Kömürün Kendi̇li̇ği̇nden Yanmasi Ve Ri̇sk Anali̇zi̇

“…Bazı kömürlerin kendiliğinden yanmaya çok yatkın olduğu ve bazılarının ise olmadığı, hatta bazı damaların tavanının yandığı fakat tabanının yanmadığı olaylar bilinmektedir. Bunun nedeni, kömürde oksidasyonu başlatan temel parametrenin henüz tam olarak tespit edilememesidir [13], [14]. Kömürde oksidasyon ve kendiliğinden yanmaya etki eden faktörleri iki ana başlık altında toplamak mümkündür.…”

Spontaneous combustion coal parameters for the Crossing-Point Temperature (CPT) method in a Temperature–Programmed System (TPS)

“…In [26][27][28], researchers examined the role of flow dynamics on the spontaneous combustion within an open stockpile using CFD simulations. In addition, other researchers have also studied the oxidation process and gaseous products under oxygen-lean conditions at low temperatures [29][30][31]. Note that the process of coal spontaneous combustion consists of oxygen absorption, mass weight gain/loss, oxidation, burn-off and finally coal combustion at high temperatures (>400 o C).…”

“…Note that the process of coal spontaneous combustion consists of oxygen absorption, mass weight gain/loss, oxidation, burn-off and finally coal combustion at high temperatures (>400 o C). Zhan et al [31] proposed four stages of coal oxidation, namely water evaporation, oxygen chemisorption, significant decomposition reaction reactions and burn-off reaction, taking place up to 400 o C as determined by a TG/DTA data. Wang [21] brought forward three stages as slow oxidation stage (< 70 o C) , accelerated oxidation stage (> 140 o C) and middle stage between them at low temperature coal oxidation .…”