| Microwave coal breaking technology is a promising new method for enhancing the permeability of coal seams.Under the action of microwave radiation,polar minerals in the coal body absorb microwave and generate a rapid thermal effect,causing local temperature differences in the coal body,generating thermal stress,causing damage to the microstructure of the coal body,crack expansion,and increasing the permeability of the coal body.It can be seen that the size of the microwave absorbing ability of coal will directly affect the microwave coal breaking and transparency enhancement effect.However,due to the limited microwave absorbing ability of raw coal,it is necessary to increase the content of its polar minerals to improve the microwave coal breaking effect.Therefore,this thesis proposes a new idea of"improving the microwave absorbing ability of coal by injecting a solution containing a high dielectric water soluble solid wave absorbing agent into coal,thereby enhancing the microwave coal breaking and enhancing the transparency".Using the independently developed microwave coal breaking experimental device,the feasibility and implementation effects of high dielectric water soluble solid wave absorbing agents such as acetamide,potassium ferrate,and sodium bromide to enhance the microwave coal breaking and enhancing the transparency have been explored,and the following research results have been achieved:（1）The evolution law of functional group content of raw coal,microwave absorbent solution leached coal,and microwave absorbent solution leached coal after collaborative treatment with microwave radiation were analyzed,and the molecular structure evolution law of the coal containing microwave absorbent under microwave radiation was revealed.The results show that under microwave radiation,the content of functional groups such as hydroxyl,aliphatic hydrocarbons,and oxygen-containing functional groups in coal can be significantly reduced by microwave absorbing agents,while the amount of aromatic hydrocarbons can be significantly increased,with both decreasing or increasing by more than 35%.The change in the content of functional groups caused by microwave absorbing agent leaching is only about 4%.The increase in the amount of aromatic hydrocarbons in the coal body and the accelerated water removal will result in the collapse of micropores under pressure,reducing the adsorption area of the coal body.At the same time,the decrease in the content of hydroxyl,aliphatic hydrocarbons,and oxygen-containing functional groups in coal can not only lead to a decrease in the hydrophilic water level and adsorption sites on the surface of coal pores,reducing the adsorption ability of coal to gas,but also cause the continuous generation of fatty small molecule gases in the coal body,thereby breaking through closed pores,and promoting pore connectivity in the coal body.（2）The differences in the fracture structure of coal after microwave radiation and after microwave radiation synergistic treatment with absorbent solution leaching were analyzed,and the evolution law of pore fracture structure of coal containing absorbent under microwave radiation was revealed.The results show that under microwave radiation,microwave absorbers can significantly increase the number of small holes,medium and large holes,as well as the increase of coal fractal dimension,the number of pore throats,the length of pore throats,the number of fractures,and the maximum width of fractures;The growth rate of pore and fissure volume in coal after microwave radiation and solution leaching is between 140%and 325%,and the CT permeability is between 5.19e-06 and 5.30e-05.However,the growth rate of pore and fissure volume in coal after microwave radiation is only 85%,indicating that microwave radiation can strengthen and promote the development of isolated pores into connected pores in coal and improve pore connectivity.（3）The surface temperature distribution and structural damage of coal containing microwave absorber under microwave radiation were analyzed quantitatively.The results show that the leaching action of the wave absorbing agent itself can cause damage to the coal structure,but its damage degree is relatively weak;Under microwave radiation,microwave absorbing agents can significantly increase the maximum surface temperature of coal,increase the local temperature difference,and significantly increase the area and number of high-temperature areas,resulting in a significant increase in the number and width of cracks on the surface of coal,thereby enhancing the microwave coal breaking effect.Acetylamine at 60 g/L has the strongest strengthening ability for the microwave coal breaking effect.（4）The mechanism of enhancing microwave coal breaking and enhancing transparency by using high dielectric water soluble wave absorbers lies in:on the one hand,due to the leaching effect,the wave absorbers penetrate into the interior of the coal body,dissolve soluble molecules in the coal body,promote the regeneration and expansion of pores in the coal body,form local structural weak areas,and form a"primary damage"to the microstructure of the coal body caused by the solution leaching of the wave absorbers;On the other hand,due to the increase in the content of strong absorbing substances in the coal body by microwave absorbing agents,the coal body’s microwave absorbing ability is enhanced,and the microwave heating efficiency is improved.This is manifested by the general increase in the surface temperature of the coal body and the significant increase in the area of the high-temperature region,resulting in higher thermal stress,aggravating the destruction of the coal body,causing the rapid expansion and connectivity of the coal body’s pore cracks,increasing the permeability of the coal body,and forming a"secondary damage"to the microstructure of the coal body,Among them,"secondary damage"plays a major role in enhancing microwave coal breaking and transparency by microwave absorbing agents.The thesis has 71 figures,14 tables and 134 references,Published 2 articles... |
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