| As the coal industry to continue to promote the work of production capacity,many coal-producing provinces itself coal production can not meet demand,the need to transfer a large amount of coal.The state arranges central budget investment of 1 billion yuan per year to support the construction of reserve facilities.Development and Reform Commission is clearly given the national coal reserve capacity construction goals,the need to form the equivalent of 15% of annual coal consumption in the country,about600 million tons of coal reserve capacity.However,in the process of coal reserve construction,the problem of natural coal fires is very serious.The spontaneous combustion of coal will produce a large amount of harmful gases and also cause the quality of coal to decline.Therefore,analyzing the heat transfer mechanism of coal storage in coal yard and establishing the early warning system of spontaneous combustion of coal in storage is a key issue to be solved.In this study,lignite,long-flame coal and coking coal are used as research objects.Firstly,we build a coal spontaneous combustion warning model and obtain the oxygen consumption rate and oxidation kinetic parameters of coal spontaneous combustion based on the programmed warming-gas chromatography experiment.Then,through small coal pile and L-shaped porous channel experiments,we obtained the temperature field distribution law of the heat source at different temperatures and burial depths;finally,we constructed a coal pile spontaneous combustion early warning system to predict the fire area and the development of spontaneous combustion by simulating the spontaneous combustion area of coal pile,guiding the installation position of monitoring equipment,integrating the early warning indexes and analyzing the monitoring data of monitoring equipment with software.The conclusions obtained from the study are as follows:The sign gas change patterns of lignite,long-flame coal,and coking coal at 6%,10%,14%,17%,and air atmosphere were determined by programmed temperature rise-gas chromatography experiments.At the reaction temperature below 110°C,the marker gas generation and oxygen atmosphere were less correlated.After the temperature exceeded 110℃,the warning gas curves were gradually arranged from top to bottom according to the size of oxygen supply concentration.The temperature exceeds 140 ℃,and various metamorphic degree coals reach the spontaneous combustion point one after another.The auto-ignition temperature point of lignite is179℃ and the auto-ignition critical oxygen concentration is 10%;the auto-ignition temperature point of long-flame coal is 172℃ and the auto-ignition critical oxygen concentration is 14%;the auto-ignition critical temperature of coking coal is 304℃ and the auto-ignition critical oxygen concentration is 17%.The early warning critical indexes of lignite,long-flame coal and coking coal were also established.The oxygen consumption rate as well as kinetic parameters of coals with different degrees of metamorphism were also fitted according to the reaction temperature and oxygen atmosphere segments.It is determined experimentally by loose coal pile that the heat source has a strong influence in the area within the range of 0～25cm of the coal pile;the area within the range of 25～35cm,the influence of the heat source on the temperature in this range begins to gradually weaken;the area larger than 35 cm,the temperature is little influenced by the heat source,and even no influence under the condition of lower heat source intensity.In addition,the ultimate heat transfer distance in the vertical direction is always greater than that in the horizontal direction,and the difference is 13.09 cm at120°C,15.19 cm at 180°C and 16.04 cm at 240°C.The change trend is a curve of gradually decreasing growth rate.The effect of the porous chimney effect on the fresh air flow rate was calculated based on the expression of Darcy’s law and Bernoulli’s equation.It is found that the growth rate is more rapid in the range of chimney height from 0 to 1.5m,and then the growth rate of air flow rate decreases gradually with the increase of the fire source depth.And when the coal pile permeability is too small or even below 1×10-7,the effect of chimney effect almost disappears.The qualitative analysis confirms that air flow rate is the main factor of the chimney effect.The increase of air flow rate will not only promote the accelerated warming of coal by intensifying the oxidation reaction of coal.It also enhances the convective heat dissipation of the coal and inhibits the heating up and spontaneous combustion of the coal.The curve of average combustion rate increases gradually with the increase of chimney height.This indicates that as the chimney effect intensifies,its strengthening effect on convective heat dissipation is weaker than its strengthening effect on combustion,and therefore the chimney effect has an overall characteristic of promoting combustion.A coal spontaneous combustion early warning system was built to monitor the coal storage area and to conduct a holistic analysis of coal spontaneous combustion early warning data.The system collects data through beam pipe sampling devices and fiber optic temperature measurement terminals,and records and analyzes the data in real time through software.Simulation of oxidative spontaneous combustion of coal piles is also performed based on field conditions.The model of coal pile spontaneous combustion was constructed based on the kinetic parameters of coal body measured by programmed temperature rise and gas chromatography through Fluent 2021 R2 software.The monitoring location of the natural warning system was determined to be in the range of2 m height from the ground on the windward side of the coal pile and 0.25-0.75 m depth from the coal pile surface.For the 33 days monitored by the software,there were 12 days of gray warning and 21 days of blue warning,and the trends of monitoring data and fiber optic temperature measurement data were basically similar.There are 78 figures,19 tables and 98 references in this thesis. |
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