Influence Of Magnetic Nanoparticles On Adsorption/Desorption Characteristics Of Particulate Coal Methane

It is a relatively new research direction of fracturing fluid at present to modify fracturing fluid raw materials through nanotechnology so as to improve various properties of fracturing fluid.Therefore,on the basis of the previous research on the modification of coal seam fracturing fluid by nano materials,this paper studies the modification experiment of coal seam by Fe₃O₄nanoparticles（S）,and explores the influence of Fe₃O₄ nanoparticles on the adsorption and desorption of coal seam.Based on the combination of experiments and theoretical analysis,this paper takes the coal samples of Pingmei No.4 Mine（PD）,Anyang Main Coking Coal Mine（AY）and Shanxi Runhong Mine（JC）as the research objects,and conducts the experimental research on the influence of drying and Hengshui granular coal containing different proportions S on methane adsorption-desorption under different adsorption equilibrium pressures.According to the experimental data,the adsorption amount,desorption amount and desorption speed of S to dry and Hengshui granular coal methane are calculated.In addition,the relationship between experimental desorption speed and time was obtained by origin fitting,and the variation law of fitting coefficient with S mass percent for dry and Hengshui granular coal with different proportions of S under different adsorption equilibrium pressures was analyzed and compared.The data changes of adsorption and desorption,specific surface area,pore volume and pore diameter of coal samples with different S contents were measured by liquid nitrogen method.The change rule of pore structure of coal after S addition was explained by the theories of two-phase transition of adsorption layer,coverage rate,adsorption substrate,laminar flow and turbulent flow in pores,etc.The adsorption amount data of S to methane under the same adsorption equilibrium pressure was measured by gas experimental instruments.Combined with the adsorption amount data of S,the effect of water and the previous theory,the influence law of S on the adsorption and desorption of dry coal methane and Hengshui granular coal methane was explained.（1）Experimental study on the effect of S on methane adsorption/desorption of dry granular coal:in terms of adsorption amount,under the adsorption equilibrium pressure of 0.5MPa,the order of isothermal adsorption amount of the three dry coal samples to methane before adding S is JC>AY>PD.After mixing with mass percentages of（2%,4%,6%）S respectively,the methane adsorption amount increased by the largest percentage,43%～168%,compared with that before adding S.Followed by AY,up 29%～110%.However,the adsorption percentage of JC dry coal sample decreased by 9%～18%before mixing 4%S,and increased by 40.12%after mixing 6%S,Under other adsorption equilibrium pressures,the same change rule is also obtained.In terms of desorption amount,under the adsorption equilibrium pressure of 0.5MPa,the cumulative desorption amount of PD and AY dry coal samples after adding 2%S is increased by 0%～19%in the first 15 minutes and 120minutes than after adding（4%,6%）S,while the cumulative desorption amount of JC dry coal samples after adding 2%S is decreased by 0%～7%in the first 15 minutes and120 minutes than after adding（4%,6%）S.In addition,after adding（2%and 4%）S to the three dry coal samples respectively,the order of change in percentage of methane cumulative desorption in the first 15 minutes and 120 minutes is PD>AY>JC,while after adding 6%S,the order of change in percentage of methane cumulative desorption in the first 15 minutes and 120 minutes is AY>JC>PD,AY>PD>JC,respectively.Under other adsorption equilibrium pressures,the same change rule is also obtained.In terms of initial desorption velocity,under the adsorption equilibrium pressure of 0.5MPa,the initial desorption velocity of PD dried coal samples after adding（2%and 4%）S respectively is increased by 0%～18%compared with that before adding S,and the initial desorption velocity after adding 6%S is decreased by28.17%compared with that before adding S.After adding（2%,4%,6%）S to AY dry coal samples respectively,the initial methane desorption speed is reduced by 0%～6%compared with that before adding S.After JC dry coal samples are added with（2%,4%,6%）S respectively,the initial methane desorption speed is also reduced by0%～15%and the decrease is gradually reduced.Under other adsorption equilibrium pressures,the same change rule is also obtained.（2）Experimental study on the influence of S on methane adsorption/desorption of balanced water particle coal:In terms of adsorption capacity,the percentage change of methane cumulative adsorption capacity after adding（2%,4%,6%）S to the three kinds of balanced water coal samples is 0%～15%larger than that when they are dried under the adsorption equilibrium pressure of 0.5MPa.In terms of desorption amount,under the adsorption equilibrium pressure of 0.5MPa,the percentage change of methane cumulative desorption amount in the first 15 minutes and 120 minutes after the three equilibrium water coal samples are added（2%,4%,6%）S respectively is0%～17%smaller than that when they are dried.In terms of initial desorption speed,under the adsorption equilibrium pressure of 0.5MPa,the percentage change of fitting a value after adding（2%,4%,6%）S of the three equilibrium water coal samples respectively is 0%～1%smaller than that when they are dried.（3）By measuring the influence of s on the pore structure of coal through the pore surface area and pore diameter analyzer,it can be seen that the liquid nitrogen adsorption/desorption amount,specific surface area,pore volume and pore diameter of coal have changed correspondingly.from this,we can get the coverage rate of different proportions S on the surface of the three kinds of coal substrates and the order between them is PD>AY>JC.the lattice structure of adsorbate in the adsorption system depends on the coverage rate and the temperature of the adsorption substrate.