Thermal Conductivity Of Coal Research Articles

Dynamic response characteristics of water–gas–coal in freezing process of gas-bearing coal under water infiltration condition

Rock cross-cut coal uncovering (RCCU) is susceptible to coal and gas outburst incidents, greatly impeding the safe extraction and miner safety. Freezing coal at low temperatures can enhance its mechanical properties and encourage gas adsorption. For the practical application of this method to prevent coal and gas outburst, water needs to be injected into the coal seam. However, the mutual dynamic response of the water–gas–coal combination during low-temperature freezing has not been sufficiently investigated, seriously restricting its application in disaster prevention. Therefore, this study investigates these characteristics using a low-temperature freezing experimental setup that was built for gas-bearing coal under conditions of water infiltration. The findings indicated that under low-gas-pressure conditions, the coal samples exhibited a larger degree of pore wettability. The improved Aronofsky index model was used to explain the relationship between the gas replacement quantity and time. Time required for the coal temperature to reach equilibrium showed a positive correlation with freezing temperature and gas pressure, respectively. As freezing temperature and gas pressure rise, respectively, freezing coal's thermal conductivity falls. The longitudinal strain of freezing coal rises with the drop in gas pressure and freezing temperature, respectively. Low-temperature freezing was conducive to the transformation of micropores and small pores into mesopores, macropores, and fractures. Based on these results, a collaborative measure of borehole methane drainage, coal seam water injection, and low freezing coal to prevent coal and gas outburst was proposed. The study lays a theoretical foundation for preventing coal and gas outbursts during RCCU.

Thermogravimetric and thermal properties analysis of bituminous coal from coalfield fire area

This paper combined the thermogravimetry TG209F1 Libra with Netzsch LFA 457 to study the thermogravimetric behaviours from 25°C-650°C and measured thermal properties from 25°C-300°C for bituminous coals taken from Wuda coalfield. The characteristic temperatures and different stages of reaction were determined using thermogravimetry (TG-DTG). The thermal diffusivity of the bituminous coal decreases with increasing temperature (from 0.11 ± 0.03 mm2 × s−1 to 0.078 + 0.02 mm2 × s−1, depending on the material). Moreover, the specific heat capacity of coal samples presented closely a linear increase with increasing temperature up to 300°C, thermal conductivity of coal appeared a cubic polynomial growth (0.117 - 0.175 W / (m × K)). It might happen because that the thermal expansion plays a more important role than the release of gases and volatile on the quantity of pores. [Received: April 1, 2015; Accepted: September 20, 2015]

Effects of low molecular weight compounds in coal on the characteristics of its spontaneous combustion

Low molecular weight compounds (LMWCs) account for 10–23 % of total coal mass. However, their role in coal's spontaneous combustion has not been well understood. In this paper, we first experimentally tested the effects of LMWCs on coal's oxygen consumption as well as heat release and transfer, and analyzed the components of LMWCs in coal, then we measured the oxidation characteristics of main active groups of LMWCs using model compounds method and last presented the mechanisms of LMWCs affecting coal spontaneous combustion. Raw coal with low metamorphic grade had greater oxygen consumption rate and the heat release intensity than the extracted residual coal, while the extracted residual coal of anthracite coal at the higher temperature had higher oxygen consumption rate and the heat release intensity than the raw coal. LMWCs could increase coal's thermal conductivity, lower coal's specific heat capacity, and shorten coal's self‐igniting period. Extraction of LMWCs could increase total pore volume and specific surface area of low rank coals. The extracted LMWCs had far greater, even one hundred more times higher, oxygen consumption rates than raw coal. Taken together, LMWCs could significantly promote the spontaneous combustion of low rank coal. Addition of substances that could dissolve LMWCs or inhibit their oxidation during water or cement injecting can significantly prevent spontaneous combustion of LMWCs‐rich coal mines.

Numerical Simulation and Evaluation of Cavity Growth in In Situ Coal Gasification

A 3D CFD model of the UCG process is developed and evaluated on a small-scale coal block with the dimensions of 3 × 1.5 × 2 cm. The results are discussed in detail and compared with the experimental data available. It was observed that the process reaches a steady sate condition after 4000 s of the process and remains in this condition until 8300 s, when drying and pyrolysis of the whole block is finished. The rate of cavity growth and the temperature at the outlet increased right after this period. Comprehensive sensitivity analysis indicated that the coal thermal conductivity has a major effect on the UCG process. Initial permeability of the seam also had strong influence on the growth rate and shape of the cavity. The higher coal permeability led to faster growth of the cavity and resulted in a much wider cavity. Lower oxygen flow rates at the inlet led to a more bulbous cavity shape, whereas at higher flow rates, the cavity became elongated in the direction of the production well. Increasing the inlet...

Energy conservation in the Earth's crust and climate change

Among various matters which make up the earth's crust, the thermal conductivity of coal, oil, and oil-gas, which are formed over a long period of geological time, is extremely low. This is significant to prevent transferring the internal heat of the earth to the thermal insulation of the surface, cooling the surface of the earth, stimulating biological evolution, and maintaining natural ecological balance as well. Fossil energy is thermal insulating layer in the earth's crust. Just like the function of the thermal isolation of subcutaneous fatty tissue under the dermis of human skin, it keeps the internal heat within the organism so it won't be transferred to the skin's surface and be lost maintaining body temperature at low temperatures. Coal, oil, oil-gas, and fat belong to the same hydrocarbons, and the functions of their thermal insulation are exactly the same. That is to say, coal, oil, and oil-gas are just like the earth's “subcutaneous fatty tissue” and objectively formed the insulation protection on earth's surface. This paper argues that the human large-scale extraction of fossil energy leads to damage of the earth's crust heat-resistant sealing, increasing terrestrial heat flow, or the heat flow as it is called, transferring the internal heat of the earth to Earth's surface excessively, and causing geotemperature and sea temperature to rise, thus giving rise to global warming. The reason for climate warming is not due to the expansion of greenhouse gases but to the wide exploitation of fossil energy, which destroyed the heat insulation of the earth's crust, making more heat from the interior of the earth be released to the atmosphere. Based on the energy conservation principle, the measurement of the increase of the average global temperature that was caused by the increase of terrestrial heat flow since the Industrial Revolution is consistent with practical data. Implications: This paper illustrates “pathogenesis” of climate change using medical knowledge. The mathematical verification is based on the principle of energy conservation. The central idea or clou in this paper is that fossil energy is a thermal insulating layer in the earth's crust, the thermal insulating layer was destroyed after human large-scale mining of fossil energy, and the internal heat of the earth was excessively released to the surface so as to cause climate change.

Measurement and Analysis of Thermal Conductivity of Rocks in the Tarim Basin, Northwest China

Abstract:As a parameter that describes heat transmission properties of rocks, thermal conductivity is indispensable for studying the thermal regime of sedimentary basins, and retrieving high‐quality data of thermal conductivity is the basis for geothermal related studies. The optical scanning method is used here to measure the thermal conductivity of 745 drill‐core samples from the Tarim basin, the largest intermontane basin with abundant hydrocarbon potential in China, and water saturation correction is made for clastic rock samples that are of variable porosity. All the measured values, combined with previously published data in this area, are integrated to discuss the distribution characteristics and major controlling factors that affect the thermal conductivity of rocks in the basin. Our results show that the values of thermal conductivity of rocks generally range from 1.500 to 3.000 W/m·K with a mean of 2.304 W/m·K. Thermal conductivity differs considerably between lithological types: the value of a coal sample is found to be the lowest as being only 0.249 W/m·K, while the values for salt rock samples are the highest with a mean of 4.620 W/m·K. Additionally, it is also found that the thermal conductivity of the same or similar lithologic types shows considerable differences, suggesting that thermal conductivity cannot be used for distinguishing the rock types. The thermal conductivity values of mudstone and sandstone generally increase with increasing burial depth and geological age of the formation, reflecting the effect of porosity of rocks on thermal conductivity. In general, the mineral composition, fabric and porosity of rocks are the main factors that affect the thermal conductivity. The research also reveals that the obvious contrast in thermal conductivity of coal and salt rock with other common sedimentary rocks can induce subsurface temperature anomalies in the overlying and underlying formations, which can modify the thermal evolution and maturity of the source rocks concerned. This finding is very important for oil and gas resources assessment and exploration and needs further study in detail. The results reported here are representative of the latest and most complete dataset of thermal conductivity of rocks in the Tarim basin, and will provide a solid foundation for geothermal studies in future.

One‐dimensional model of the physico‐chemical processes occurring inside a burning coal surface

AbstractA one‐dimensional model has been developed to account for the physicochemical processes occurring inside a burning wet coal surface. The model considers the vaporization of coal moisture and the existence of a moving evaporation front, pyrolysis and char/gas reactions in the hot zone, molecular diffusion and Darcy flow through the dry porous coal, transpiration cooling effect of the water vapor and pyrolysis gases, temperature‐dependent reaction kinetics and coal thermal conductivity, and variable porousity of the coal due to pyrolysis and char/gas reactions.The model and associated assumptions have been verified with experimental data from the combustion and drying of coal. The results also show that the model prediction of the heat transferred from the coal surface into the coal is much higher than that calculated by the simple heat conduction equation.The fraction of the water in the coal that reacts with char is shown as a function of the linear burn velocity and the surface temperature. In addition, the effect of variations in coal moisture and the thermal conductivity on the thickness of the dry zone are also shwon.