二次炭化型煤成型装置及型煤制作方法

Thermal forming method and device for secondary carbonized briquette coal

针对煤与瓦斯突出事故研究中物理模拟实验所需型煤材料具有强度低、渗透性高等特性,自主研制了二次炭化型煤热压成型装置和型煤制作新方法。该装置主要由电液伺服加载控制系统、加热炉体及密封系统、真空及气氛保护系统、炉体电控系统、水冷系统和石墨模具、碳钢模具等6个部分组成,其最大轴压为200 kN、最高温度为1200℃、炉膛温度均匀性为±6℃、升温速率为±0.01~10℃、炉膛使用真空度≤10 Pa、炉膛工作室尺寸为φ240 mm×260 mm(直径×高),石墨模具和碳钢模具均可制备尺寸分别为φ25 mm×50 mm和φ50 mm×100 mm(直径×高)的圆柱体型煤试件。该热压成型装置具有如下特点:①系统采用计算机控制自动加荷载,实现力、位移的闭环控制;②炉膛尺寸设计紧凑、炉内温度均匀性好,能实现热压、无压、真空和气氛保护烧结等;③模具耐高温、热膨胀系数低,组装、拆卸均方便,可成型多种类、多数量热压型煤。并利用该装置进行了不同炭化温度的型煤试件的制作,其中煤粉颗粒配比采用致密堆积理论优化后其粒径为0.250~0.425,0.125~0.150,0.075~0.083 mm,配比为91.775.872.35。基于所开展的单轴压缩荷载作用下的力学特性试验、三轴压缩荷载作用下的渗流特性试验等,通过对比分析热压型煤的密度、单轴抗压强度、泊松比、弹性模量、初始渗透率和最小渗透率等,揭示了不同温度下型煤强度增加与渗透性降低的影响机制。其中密度变化率呈先增后减再增的趋势;单轴抗压强度和弹性模量呈现先增后减,泊松比则为先减后增的趋势;初始渗透率及最小渗透率均呈不断增大的趋势,综合考虑热压型煤的密度、强度和渗透率等,确定了二次炭化型煤制作中最佳炭化温度为300℃,从而优化了型煤与原煤之间的相似性,提高了煤与瓦斯突出物理模拟实验研究真实还原性。

Based on the low strength and high permeability of briquette coal(BC)used in coal and gas outburst physical simulations for coal mine disasters,a self-developed thermal forming method and device for secondary carbonized briquette coal under vacuum conditions was introduced.The thermal forming device is composed of a servo-controlled loading system,heating furnace,vacuum and atmosphere protection system,electric control system,water-cooling system,graphite molds,and carbon steel molds.The maximum pressure of this device is 200 kN and the highest sintering temperature is 1200℃.The vacuum working temperature uniformity,heating rate,and vacuum are±6℃,0.01-10℃/min,and≤10 Pa,respectively.The internal dimensions of the furnace body is 240 mm×260 mm(diameter×height),respectively.Cylindrical BC specimens with sizes of φ25 mm×50 mm and φ50 mm×100 mm(diameter×height)can be formed by using graphite and carbon steel molds.The thermal forming device has the following characteristics:①The closed-loop control of force and displacement is achieved by automatic loading with a computer.②The furnace size design is compact,the temperature is uniform in the furnace,and the furnace can be adjusted to achieve hot-pressing sintering,non-pressing sintering,vacuum sintering,and atmosphere protection sintering.③The mold has high-temperature resistance,corrosion resistance,good thermal stability,low thermal expansion coefficient,so many kinds of briquette coals can be formed by the device.Using the thermal forming device,several groups of briquette coal specimens with different heating temperatures were made.Based on the packing density theory,the optimal ratio of the 0.250-0.425,0.125-0.150,0.075-0.083 mm particle sizes is 91.775.872.35.Then a series of uniaxial compression tests and triaxial compression seepage tests on these briquette coal specimens were carried out.The density,uniaxial compressive strength,Poisson’s ratio,elastic modulus,the effect of the initial permeability and minimum permeability were analyzed,and the mechanism of changes in the strength and permeability of these specimens was revealed.The rate of the change of and density of the BC first increases,then decreases,and then increases again.The mechanical parameters(strength and elastic modulus)first increase and then decrease,whereas the Poisson’s ratio first decreases and then increases.Both the initial and minimum permeability increase.Considering the density,strength,and permeability of BC,the optimal heating temperature,at which the similarity between the BC and raw coal(RC)is the highest,was determined as 300℃.It strengthens the bonds between raw coal and briquette coal and helpful for the similar simulation study of coal and gas outburst.