Study On Temperature Control Inflation Inhibitor For Coal Spontaneous Combustion

Spontaneous combustion of coal is a serious threat to the production safety of the coal industry.Once a fire accident is triggered,it will cause a large number of casualties,property losses,environmental pollution and waste of resources.Through the research on the mechanism and characteristics of coal oxidation,experts at home and abroad have put forward many prevention and control technologies of coal spontaneous combustion.However,the commonly used inhibition methods have the problems of easy evaporation to lose effect,poor stability and short inhibiting time.The"heat release technology of temperature controlled coating inhibitor"proposed by Jiang Shuguang’s team has successfully overcome these problems.Nevertheless,due to the limitations of phase change materials as coating,temperature sensitive coating inhibitor has some disadvantages,such as small capacity,low strength,complex process and large amount of combustible materials.In this project,the action mode of the inhibitor release triggered by the melting of the phase change material coating after heating is replaced by the action mode of the internal reaction triggered by the melting of the phase change material coating after heating,the reaction product increases the internal pressure,and the pressure triggers the release of the inhibitor solution.While retaining the advantages of the original technology of water retention and oxygen isolation,the capacity of a single inhibitor can be arbitrarily adjusted the production process can be simplified,and the strength requirement and combustible substance proportion can be reduced.The temperature controlled inflation inhibitor of oxidation of coal developed in this project includes three parts:temperature control ball,inhibitor solution to be reacted and outer package.The inhibitor solution to be reacted is saturated Na HCO₃solution.The temperature control ball is composed of skeleton ball,inhibitor powder to be reacted and phase change material coating.The inhibitor powder to be reacted is Al₂（SO₄）₃bonded ball.When the temperature of the inhibitor reaches the critical temperature of coal oxidation,the temperature control balls phase change material coating melts and exposes Al₂（SO₄）₃inside.Then Na HCO₃solution reacts with Al₂（SO₄）₃to produce CO₂,which causes the pressure to rise inside the outer package to rise.When the gas pressure reaches a certain level,the completely reacted inhibitor solution is released.First of all,through the goaf simulation experiment platform and numerical simulation calculation,the influence of coal seam thickness,ventilation wind speed and other factors on coal seam surface temperature is studied when the coal seam reaches the critical temperature.It is confirmed that there is a temperature difference between the trigger temperature of the coal seam surface where the inhibitor is located and the highest temperature the oxidized coal.The thickness of coal seam has the most obvious influence on the temperature difference,which change in the range of5cm-11cm,the surface temperature of coal seam above the heat source decreases by4.6℃-10.2℃;the effective action capacity of inhibitor solution was analyzed through the research with soil moisture sensor,that is,the depth and range of the coal seam to which the inhibitor solution released at a single position on the coal seam surface can diffuse.For the area with a radius r=33cm,the thickness of coal seam is5cm,8cm and 11cm,the amount of inhibitor solution required is about 1000ml,3200ml and 4100ml respectively.Change the moisture content and ventilation conditions of the coal sample.The evaporation rate of the inhibitor solution at the critical temperature,that is,the acting time of the inhibitor solution,is the most appropriate when the moisture content of coal sample is 20%,which is about 36h.The change of wind speed only has obvious influence on the positions of air inlet and outlet.From the above-mentioned tests,we understand the trigger temperature of the temperature controlled inflation inhibitor that used for oxidation of coal,single inhibitor solution capacity and other issues that need to be applicable to the remaining coal samples in goaf,and they provide the basis for the next design of the composition structure.According to the new mode of action and the new requirements of effective inhibitor,the temperature controlled inflation inhibitor is designed and the effect of each structure part is optimized.This experiment explores the influence of gas pressure and temperature produced by the reaction of different weights of Al₂（SO₄）₃with saturated Na HCO₃solution,and the effect of Na HCO₃decomposition on the gas pressure.The damage pressure of outer package should be selected between 0.3MPa and 1.3MPa;the influence of the number of holes in the skeleton ball on the reaction of Na HCO₃solution with Al₂（SO₄）₃was studied,the results show that the reaction speed tends to be the same as that of direct contact when the skeleton ball has 8 holes of 3.3mm;The low temperature resistance and the adhesion properties of phase change materials were improved by compounding.The proportion of phase change materials was 82%58#Paraffin,10%microcrystalline wax and 8%polyisobutylene additive;the skeleton ball was changed as a convex point surface ball to increase the surface adhesion and significantly reduce the coating thickness to about 0.3～0.5mm;the surfactant suitable for Na HCO₃solution and Al₂（SO₄）₃reaction was explored,and Decyl Glucoside was selected as the surface active additives of the to be reacted inhibitor solution,which increase foaming capacity about 500%and foaming time about 5h,and the volume ratio of 2%is selected for adding proportion,which increases the release form of the gas-liquid foam;Set up a special pressure releasing opening for the outer packing to avoid premature pressure relief and ensure that the release rate of the inhibitor is above 96%.Foam generating spacers are added to increase the gas-liquid foam ratio from 20%to 260%after the inhibitor release.Finally,the temperature tracking adiabatic system was used to complete the contrast experiment of coal oxidation temperature rising with or without the temperature control inflation inhibitor.This experiment was to verify the inhibitory effect of the temperature control inflation inhibitor after the complete reaction on the oxidation of coal samples.The results of coal oxidation temperature change show that adding a completely reacted inhibitor solution at the critical temperature can effectively control the coal temperature to continue to rise.The gas monitoring shows that the concentration of CO decreases sharply after the inhibitor solution is added,while the concentration of CO₂increased sharply after adding inhibitor solution and then decreased sharply.It is verified that the inhibition effect of the inhibitor solution is that the inhibitor solution infiltrates the coal sample and CO₂fills the coal sample gap to complete the oxygen isolation of the coal sample.The data of temperature,CO and CO₂all verify the inhibitory effect of the temperature controlled inflation inhibitor on coal oxidation.The paper consists of 85 figures,21tables and 121references.