玉米秸秆与烟煤混燃过程灰熔融特性试验研究

Experimental study on ash melting characteristics of mixed combustion of corn stalk and bituminous coal

生物质与煤混燃对助力我国减煤降碳战略,节约煤炭资源,发展利用生物质能源具有重要意义。但是,生物质与煤混燃反应过程中混燃灰熔融作用机制复杂。为探讨不同热转化条件对生物质与烟煤混燃灰熔融特性的影响,利用灰熔点测定仪、扫描电子显微镜-能量分析仪(SEM-EDS)、X射线荧光衍射仪(XRD)等设备系统研究生物质质量分数、灰化温度及停留时间对混燃灰的熔融温度、矿物成分、晶相结构以及微观形貌的影响。结果表明,添加玉米秸秆可使混燃灰熔点先降低再升高,其中,在玉米秸秆质量分数为75%时混燃灰熔点最低。混燃灰中生成的钠长石(Na_(2)Si_(2)O_(5))、钾长石(Al_(2)O_(3)K_(2)OSiO_(2))、铁尖晶石(FeAl_(2)O_(4))和白榴石(KAlSi_(2)O_(6))等硅铝酸盐是使混燃灰熔点降低的重要因素,K、Fe、Ca元素在促进混燃灰熔融方面起显著作用。此外,玉米秸秆质量分数为25%时混燃灰开始出现熔融现象,因此在实际应用中玉米秸秆的质量分数应低于25%。改变灰化温度和停留时间对混燃灰熔融温度影响不显著,混燃灰软化温度(Softening Temperature,ST)、半球温度(Hemispherical Temperature,HT)和流动温度(Flow Temperature,FT)都基本保持不变,但二者机理稍有不同,本质区别在于矿物质种类是否发生变化。

To study the melting characteristics of cornstalk and bituminous coal blended combustion ash,this paper carried out combustion experiments with different mixing mass fractions,different ashing temperatures,and different residence times.The changes in melting temperature,mineral crystal phase,micro-morphology,and element composition of mixed combustion ash in different experiments were analyzed using an ash melting point tester,a scanning electron microscope-energy analyzer(SEM-EDS) and a X-ray fluorescence diffractometer(XRD),and the internal mechanism of the change of experimental data was discussed.First of all,the addition of YM causes the melting temperature of the mixed combustion ash to decrease first and then increase.When the mass fraction of YM is less than 75%,the melting temperature of the mixed combustion ash decreases,the internal debris decreases,and the melting bonding phenomenon continues to intensify.At this time,the XRD results show that the mineral composition of the mixed combustion ash has changed,the high melting point substances such as quartz and aluminum phosphate decreases,and a lot of silicate minerals containing K,Fe,and Ca elements are generated,which have a low melting point.This is the internal reason why the melting point of the mixed combustion ash is reduced and the ash begins to melt.When the mass fraction of YM is greater than 75%,the melting temperature of the mixed combustion ash has a small increase,which is presumably related to the high SiO_(2) content of YM.The high content of YM brings some free SiO_(2),which improves the ash melting point.It is worth mentioning that slight melting occurs when the mass fraction of YM is 25%,so it is recommended that the mass fraction of YM should be controlled within 25% at 1 000℃ in practical application.Secondly,the change in ashing temperature and residence time has little effect on the melting temperature of mixed combustion ash.The softening temperature(ST),hemispherical temperature(HT),and flow temperature(FT) are almost unchanged,but their mechanisms are slightly different,mainly reflected in the change of internal mineral species.