| As a typical clean energy,coalbed methane with the main co mponent methane(CH4)is expected to be used as an alternative energ y for coal to a certain extent,thereby mit igat ing and eventually so lving environmental po llut io n issues caused by the large-scale use of fossil energy such as coals.Data show that gas-bear ing coa l seams in China are o f low per meabilit y(<1×10-3?m2),low resource abundance(<1.5×108 m3/km2),and large bur ial depth(>600 m).As a result,the coalbed methane explorat ion and product ion in China is relat ively slow.Therefore,aiming to enhance coalbed methane recover y,it is o f great significance to modifiy the phys ica l and chemical properties o f coals to improve the per meabilit y.This dissertation use s the controlled microwave fie ld radiat ion techno logy to enhance coalbed methane recover y.Co mbined wit h exper imental research and theoretical analys is,this paper focuses on the effects of microwave radiatio n power on the pore structure and chemical propert y of coals and it s effect on the adsorptio n/desorption capabilit y o f CH4.The main contents and conclusio ns der ived fro m this dissertation ar e summar ized as fo llo ws.(1)Based on a co ntrolled microwave fie ld radiat ion plat for m,the influences o f microwave radiat io n on the physical and chemical properties,mainly inc luding pore structure and sur face funct ional groups,related to the coal adsorption properties were studied.Results show that controlled microwave field radiat io n wit h radiat io n power range o f 1600-2400 W can change the pore structure parameters,pore shape,pore surface co mplexit y,and sur face funct ional group contents of coal.Specifically:1)The microwave field radiat io n can change the coal pore structure mainly due to the fo llowing factors.First ly,microwave has select ive heat ing character ist ics,whic h cause ther mal stresses to for m wit hin the coals.Different inorganic minera l compo nents in the coals exhibit different microwave absorption capabilit ies.Thus,the generated ther mal stress will cause fractures at different mineral inter faces,and it is expected that new pores and fr actures will be for med.Secondly,microwave radiat io n will also cause the precipitatio n o f vo lat ile matters of coal,the deco mposit io n of funct io nal groups,and the precipitat ion of deco mposit ion products of macro mo lecular organic matter,thereby changing the pore structure of the coals.2)For low-rank coals,Zhaotong(ZT)and Tianji(TJ),with the increasing microwave radiat io n power,the micropore specific sur face area of the coals first decreases and then increases,while the high-rank coals including Datong(DT),Fumin(FM),and Yangquan(YQ)show the opposite trends.The pore specific sur face area of the Buliangou(BLG)coal shows a decreasing trend.The meso/macropore specific sur face area and pore vo lume of ZT,TJ,DT,FM and YQ decreases wit h the elevated microwave radiat ion power.3)The microwave field radiat io n enchances the complexit y o f pores in low-and medium-rank coals.T herefore,the effect o f microwave radiat ion on the pore structure of low-and medium-rank coals is not conducive to CH4 desorption.On the contrar y,the microwave radiat ion reduces the complexit y o f the pore sur face o f high-rank coals and improve the smoothness o f the pore sur face of coals,which is conducive to the desorption,diffusio n and flow of CH4.4)The pore shape o f medium-and high-rank coals after microwave fie ld radiat io n are prone to be cylinder,which is beneficial to impro ve pore connect ivit y.5)Microwave fie ld radiat ion deco mposes carboxyl groups and macro mo lecular organic co mpounds within the coals,thereby pro moting the development of coa l pore structure.In addit io n,the microwave field radiat ion causes pyrro le nitrogen in coals to undergo ring cracking and release,or be converted to pyr idine nitrogen in coals.(2)Based on an exper imental plat for m fo r determining t he amount of fluid adsorption/desorption using vo lumetr ic method,and the effect of microwave radiat io n on the statics of CH4 adsorption/desorption o f different rank coals wa s studied.Results indicate that:1)the Ono-Kondo lattice model(denoted as the OK lattice model)can well descr ibe the adsorptio n equilibr ium o f CH4 on coal samples before and after microwave radiat io n.2)The controlled microwave field radiat io n changes CH4 adsorption per for mance o f co al samples.Specifically,the adsorption capacit y o f ZT,TJ,BLG and YQ coal samples increases after the microwave radiat io n with power of 2000 W,while DT,FM coal samples show an opposite trend.3)The influence of microwave radiat ion on CH4 adsorption capabilit y o f coals is mainly caused by t he co mbined effect of the change in the microporous structure and oxygen-containing funct ional groups o f coals after the radiat io n.However,the microporous structure is the main factor determining CH4 adsorptio n capabilit y o f coals.4)Compared wit h the raw sample,the area of CH4 adsorption/desorptio n hysteresis loops of coal samples(except for YQ coal)after controlled microwave field radiat ion significant ly reduces and near ly clo ses.Thus,the microwave field radiat io n is beneficia l to enhance CH4 desorption fro m coals.(3)An exper imental plat for m for determining the amount of adsorption/desorption by vo lumetr ic method was used to study the effect of microwave radiat ion on the adsorption kinetics of CH4 on var ious rank coals.Result s show that:1)the bidisperse model can well descr ibe the adsorption kinet ics of CH4on coal samples before and after microwave radiat io n.2)The micropore effect ive diffusio n coefficients of ZT,TJ,BLG and DT coals on CH4 after microwave field radiat io n increase.The micropore effect ive diffusio n coefficients of high-rank coals FM and YQ on CH4 decrease.3)The meso/macropore effect ive diffusio n coefficient s of TJ,DT,and YQ coals on CH4 increase after the microwave radiat ion,and the meso/macropore effect ive diffusio n coeffic ients o f ZT,BLG,and FM coals decrease.4)The change o f the micropore effect ive diffusio n coefficient of CH4 is mainly due to the alterations of the oxygen-co ntaining funct ional groups in coal samples after the microwave field radiat ion.However,the change of the meso/macropore effect ive diffusio n coefficients of CH4 is controlled by the meso/macropore volume and sur face funct ional groups of coal sample.In summar y,the controlled microwave field radiatio n alter s the pore structure and sur face chemical properties o f coals,thereby affect ing the equilibr ium and kinetics behaviors o f CH4 adsorption/desorption on coals.Thus,it is expected to enhance the coalbed methane CH4 recover y.The results of this dissertatio n cannot only improve and make up for the lack of exist ing CBM product ion techno logy in China,but also provide so me novel ideas for scient ists and engineer s engaged in unconvent ional natural gas product ion. |
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