Study On Smoldering Of Weathered Coal And Its Gas Generation

Smoldering is a flameless,self-sustaining slow combustion,mostly in an oxygen-poor environment.There are a large amount of broken coal under the coal mine to form a porous medium space,and a little oxygen is provided under the condition of air leakage,so as to achieve the required conditions for smoldering.Underground coal fires have become a major issue that endangers our country’s energy strategy security and ecologically harmonious development.Underground coal fires will not only directly burn non-renewable coal resources,but also indirectly cause dozens of times the resources to be unexploited,and affect the safety of coal mine production and pollute the environment.Coal fire combustion mainly originates from the spontaneous combustion of crushed coal.The oxygen-poor environment in the combustion area and the spatial characteristics of coal itself determine that coal fire combustion is mainly in a smoldering state.With thermal stress cracks and combustion cavity collapse cracks as air leakage channels,and the fire pressure between the high-temperature fire area and the ground surface as the air leakage power,the spread of coal smoldering leads to the characteristics of continuous and slow burning of coal fires,and the management of coal fires In essence,it is to block the spread of coal smoldering.At present,many scholars at home and abroad have carried out smoldering experiments on combustible materials such as coal,peat,polyurethane foam,and fiber ropes around the characteristics of smoldering.They studied the characteristics of smoldering spread under different conditions,such as moisture content,inorganic content,and oxygen supply.However,there are few studies on the development and propagation characteristics of smoldering under different air supply and moisture in the oxygen-lean combustion space of weathered coal.In this paper,by designing and building a similar experimental platform for coal fire smoldering simulation,it explores the law of temperature change,maximum reaction temperature and total cathode of coal burning time,under different air supply and raw material moisture content during coal smoldering in vertical and horizontal directions.The study of gas generated by the smoldering of weathered coal can provide theoretical guidance for coal fire control.The main research conclusions of this paper are as follows:（1）Pyrolysis experiment of weathered coal.Using thermogravimetric analyzer,under nitrogen atmosphere,air atmosphere and different oxygen concentration atmosphere,control different heating rate to explore the influence of atmosphere and heating rate on the pyrolysis of weathered coal,and obtain the composition of weathered coal.The weight loss reaction of weathered coal can be divided into three stages.The first stage is the stage of water evaporation,carboxyl decarboxylation and gas desorption.The second stage is pyrolysis of organic matter,which generates a large amount of volatilization.The third stage is the stage ofdecomposition of inorganic substances or the secondary pyrolysis of weathered coal,which produces some phenolic substances.The weathered coal in the second stage loses more mass in the air atmosphere than in the nitrogen atmosphere,and the weight loss rate is fast and lasts for a long time.With the increase of oxygen concentration,the stronger the pyrolysis reaction,the greater the weight loss rate.（2）Experimental research on smoldering of weathered coal in vertical direction.By studying the vertical forward and reverse,the weathered coal smoldering temperature of different air supply and different moisture changes with time,it can be known that the temperature maintains T1>T2>T3>T4 during the heating process of vertical forward smoldering.The coal body is prone to collapse in the later stage.The oxidation wave of vertical and reverse smoldering will spread from the top of the reactor to the bottom,and then from the bottom to the top,resulting in a second temperature increase,and the second temperature increase reaction is more intense.Compared with vertical forward smoldering,the smoldering reaction is more severe.Larger air volume and appropriate amount of moisture are conducive to the smoldering reaction in the vertical direction.（3）Experimental research on smoldering of weathered coal in the horizontal direction.By studying the horizontal forward and reverse,weathered coal smoldering temperature of different air supply and different moisture changes with time,it can be known that the horizontal forward smoldering temperature curve is gentle,and the temperature remains T1>T2>T3>T4 during the process.The horizontal reverse smoldering ignition process has the characteristics of reverse smoldering,that is,oxidation propagates from the top to the bottom,and then forms an oxidation front at the bottom and propagates to the top.The smoldering reaction in the reverse horizontal direction is more severe than the smoldering reaction in the horizontal forward direction.The influence of air volume on forward smoldering is greater than the influence on reverse smoldering,and the influence of moisture content on the horizontal forward direction is greater than the influence on the vertical forward direction.（4）Research on the gas produced by the smoldering of weathered coal.During the smoldering process of weathered coal,CO,CO₂,Cx Hy and a small amount of SO₂,NO and NO₂are mainly generated.During the process of smoldering heating,the production of CO and CO₂increases,and the greater the air volume,the greater the production of CO and CO₂.Under the level of positive smoldering,with the increase of water content,the output of CO and CO₂first increases and then decreases.