Experimental Study On The Influence Of Heating Rate And Temperature On The Physical And Mechanical Properties Of Secondary Carbonized CBS

The coal and coal-bed methane resources of China has excellent endowment and great potential,and fossil energy is an important strategic resource that cannot be replaced in a quite long period of time in our country,which is related to the stable and healthy development of the national economy and the living and working of the people in China.Therefore,in order to ensure the safe mining of coal resources,research on disaster prevention and control in the direction of coal and coal-bed methane has always been a hot spot for scholars to choose.At present,the laboratory's research on the prevention and control of coal and gas outbursts and other coal mine disasters is mostly based on large and medium-scale similar simulation or physical simulation experiments.Small pieces of raw coal specimens(RCS)are brought back from the mining area,and coal briquette specimens(CBS)is prepared to replace RCS experimenting after grinding.However,in this process,the physical and mechanical properties of CBS and RCS are likely to be very different,which affects the reliability of coal mine disaster simulation test results,and it is difficult to guide coal mine safety production.To this end,this paper uses the self-developed briquette hot press forming equipment to investigate the the physical and chemical properties,adsorption analysis characteristics,mechanical properties and seepage characteristics of the second carbonized briquette hot press forming specimens under different heating rates,different carbonization temperatures and other briquette preparation conditions.The physical and mechanical properties of secondary carbonized CBS,such as seepage flow,reveal the law that the physical and mechanical properties of secondary carbonized CBS change with the change of heating rate,carbonization temperature and other conditions,in order to further improve the basic data of secondary carbonized hot-pressed coal research.Further in-depth research on sub-carbonized briquette and the use of briquette instead of RCS experiments provide support.The specific research work and test results are as follows:(1)Using the Horsfield theory in powder science research as the carrier,through the analysis and calculation of hexagonal tight packing structure and hexagonal tight packing characteristics of reducing ball,it is concluded that when the coarse grain is set as 20?40 mesh,the particle size ratio is 20?40:60?80:100?120,the variance S₁²=0.000812;when the coarse grain is set as 40?60 mesh,the particle size ratio is40?60:100?120:180?200,variance S₂²=0.000004.According to the analysis of variance,due to variance S₂²<<S₁²,the second particle size matching is better,so the second matching method is chosen.According to the ball volume formula,the volumes of40?60,100?120 and 180?200 mesh pulverized coal particles were 0.16146mm³,0.01033mm³ and 0.00207mm³ respectively.The relative number of the first three balls in the table of reducing ball accumulation characteristics was 1,1,2,and the particle size composition of briquette was calculated as follows:40?60 mesh:100?120 mesh:180?200 mesh=0.16146×1:01033×1:00207×2=91.77:5.87:2.35.(2)Organize the existing research results of RCS similar materials,analyze the advantages and disadvantages of different binders,and finally choose the organic binder of sodium humate,and determine the material ratio scheme as pulverized coal:sodium humate:water=92:1.6:6.4,in which the concentration of sodium humate aqueous solution is 20%.(3)The physical and mechanical properties of the CBS prepared at different heating rates have certain differences,but the differences are small.With the increasing of heating rate,the density and mechanical strength of secondary CBS first increased and then decreased.The stability of microcrystals and the response strength of functional groups were firstly enhanced and then weakened.The proportion of micropores first increased and then decreased,while the proportion of macropores first decreased and then increased.In the triaxial seepage test,the principal stress difference increases first and then decreases,and the initial permeability decreases first and then increases.The adsorption analytical isotherm test shows that most of the pores in the specimen are slit pores,and the hysteresis ring decreases first and then increases,and the regularity of the pore structure increases first and then decreases.In general,the physical and mechanical properties of secondary carbonized briquette are better when the heating rate is 5?/min.(4)The physical and mechanical properties of secondary CBS prepared at different carbonization temperatures and between secondary CBS and cold-pressed RCS have great differences.As the carbonization temperature increases,the density and uniaxial compressive strength of specimens of secondary carbonization hot pressing CBS first increase and then decrease,and the uniaxial compressive strength of specimens of secondary carbonization hot pressing CBS is close to that of raw coal at 300?carbonization temperature.The microcrystalline stability and the response strength of functional groups of hot-pressed CBS and RCS are different,and the microcrystalline stability and molecular structure strength of briquette are the most similar to those of raw coal at 300?and 450?carbonization temperature.Compared with RCS,hot?pressed CBS has more uniform pore size distribution,less micropore proportion,and smaller specific surface area.With the increase of carbonization temperature,the average pore size and specific surface area of secondary hot?pressed CBS decrease first and then increase,and the pore size and specific surface area are relatively minimum at300?carbonization temperature.Under the condition of triaxial compression,the permeability of the specimen decreases first and then increases with the increase of axial compression,and the initial and minimum permeability increase with the increase of carbonization temperature.The hysteresis loop of secondary CBS decreases first and then increases,and the mesopores in the specimens are the least when the temperature is300?and 450?.(5)The second type coking coal way material preparation to a certain extent,improved the physical and mechanical properties of coal,increasing the molecular structure of microcrystalline stability and strength,improve the secondary type coking coal and RCS in the aspects of strength and pore structure similarity,shows that secondary carbonization hot-pressing is an important way of similar material preparation.