Combustion Tendency Research Articles

A Comprehensive Study of Effect of Maceral Content on Tendency of Spontaneous Coal Combustion Occurrence

Coal mining has many serious hazards, and the spontaneous combustion phenomenon is one of them. Many factors can influence the tendency for occurrence of this phenomenon. The maceral content is one of the coal inherent characteristics, which has a crucial aspect in the occurrence of this process. Until now, this parameter has not been discussed in a comprehensive study by the scientists. Thus a final conclusion about the effect of maceral content on spontaneous coal combustion is required. Maceral content is directly affected by the growth of coalification and origin of coal formation. This study aimed at developing a new statistical model for predicting the spontaneous coal combustion tendency based on the maceral content. In this work, firstly, 51 coal samples with a variety of maceral contents were collected for training data of the overall underground coal fields in Iran, and the Crossing Point Temperature (CPT) test was carried out on each coal sample. Then the method of regression analysis was used for modeling and predicting the spontaneous coal combustion tendency. For validation and testing, 11 coal samples of another coalfield were collected, the CPT test was carried out on each one of them, and the results obtained were compared using the regression equation. Validation of the developed model was checked by the F test. By examining the experimental results and comparing the CPT test values, it was found that with increase in the vitrinite and liptinite contents and decrease in the inertinite content, the coal samples displayed a higher tendency for spontaneous combustion. The results also showed that the spontaneous combustion tendency could be reliably predicted using the proposed model.

Evaluation effect of macerals petrographic and pyrite contents on spontaneous coal combustion in Tabas Parvadeh and Eastern Alborz coal mines in Iran

ABSTRACT Among the fossil fuels, coal is the most widely used one all over the world for different purposes and is a stable source of energy. Coal mining has serious hazards such as spontaneous combustion. Many factors can influence the tendency for occurrence of this phenomenon in coal mines and coal storages, one of which is the petrographic characteristics (maceral and pyrite contents). The petrographic characteristics are directly affected by the growth of coalification and origin of coal forming. In this research work, firstly, the maceral and pyrite contents in coal samples were identified in two various mines in Iran (Tabas Parvadeh and Eastern Alborz coal mines). Then the spontaneous coal combustion propensity of each sample was measured using the Crossing Point Temperature (CPT) test method. The aim for carrying out this research work was to measure the effect of the maceral and pyrite contents on the grade of spontaneous coal combustion propensity. It was found that the pyrite contents and the vitrinite, liptinite, and inertinite mean levels in the Tabas Parvadeh and Eastern Alborz coal mines were (2.08%, 53.30%, 9.91%, 34.71%) and (1.14%, 53.06%, 6.39%, 39.41%), respectively. The mean CPT value was 148.43ºC in the Tabas Parvadeh coal mines and 175.86ºC in the Eastern Alborz coal mines. By examining the results of the experiments and comparing the CPT values, it was found that with an increase in the liptinite and pyrite contents and a decrease in the inertinite content, the Tabas Parvadeh coal mines tend to have more tendency for spontaneous coal combustion in comparison with the Eastern Alborz coal mines.

Oxygen consumption and chemisorption in low-temperature oxidation of sub-bituminous pulverized coal

ABSTRACTStudying the effect of oxygen in coal oxidation is very important for understanding and controlling coal spontaneous combustion. However, the oxygen effect is not very easy to determine clearly due to the large effect of heat source on coal oxidation in temperature rising experiments. Here, focused on sub-bituminous coal, the oxygen effect was separated from coal oxidation by continuously measuring FTIR spectra of coal with respect to varying temperatures and under oxygen and nitrogen. The active groups’ real-time changes of coal oxidation, thermal treatment and oxygen effect were measured. The carboxylic ester and carboxyl units are the main functional groups that increase with temperatures increasing under oxygen and nitrogen, while the other functional groups decrease in quantity. The oxygen effect promoted the consumption of aliphatic hydrocarbons and hydroxyl groups and also promoted the formation of oxygen-containing groups (except hydroxyl). Four characteristic temperature stages involved in the oxygen effect and their key functional groups were identified. Simultaneously, the relationship of oxygen consumption and chemisorption in oxygen effect was analyzed. The starting temperature of oxygen chemisorption is between 50 and 60°C. The maximum contribution of oxygen effect was observed in methyl and methylene groups. These results are important for chemical control of coal spontaneous combustion. The oxidation of aliphatic hydrocarbon should be controlled before oxygen chemisorption. The value of oxygen consumption between 70 and 80°C can be measured accurately due to the constant chemisorption rate, which help to identify the tendency for spontaneous combustion. These results will help in better understanding of the reaction mechanism of coal oxidation, especially the oxygen effect.

Study on the Filtering Purification of AZ91 Magnesium Alloy

High quality magnesium casting depends significantly on the purification of its alloy melt. However, it is very difficult to obtain high-quality magnesium alloy melt due to its high reactivity and its tendency of combustion. The fluxing processing, a traditional purification method for magnesium melt, not only bears the risk of flux inclusions but also is facing more and more environmental pressure today. Therefore, the effective substitutes for fluxing processing, such as physical filtering method, are paid more attention recently. In this paper, the effects of technological conditions including the pore size of stainless steel mesh and the filtering temperature on the purification degree of AZ91 alloy melt were investigated in the mesh filtering processing, in which 2 wt.% calcium was added into the melt in order to obtaining ignition-proof property. The results indicated that mesh filtering processing could improve the purification degree markedly, and the purification degree increased with the increase of filtering temperature properly or the decreased of pore size of mesh. However, too high filtering temperature would lead to the increasing of the tendency of oxidation and combustion, and too small pore size would decrease the filtering ability of mesh which would lead to the interrupting of purification operation.

Alternate materials choices—some challenges to the increased use of Ti alloys

Ti alloys are used in a variety of high-performance applications. Properties that lead to the selection of Ti alloys include modulus, chemical inertness, density, static strength, fatigue strength and damage tolerance (fracture toughness and fatigue crack growth). The reasons that Ti alloys are selected for a wide range of products have been widely discussed. Reasons for not selecting Ti alloys have been less widely discussed, and are the focus of this paper. This paper describes examples where alternate materials have been chosen in lieu of Ti alloys. The reason for these choices include elevated temperature creep strength, the tendency for combustion, raw material cost and article manufacturing cost. Specific examples of aircraft engine and aircraft components will be described and the reasoning behind the selection of alternate materials will be outlined. The paper concludes by suggesting factors that could re-balance the decision making process in favor of Ti alloys.