高温气化条件下Na_2O对煤灰中矿物质演化行为的影响

Effect of Na_2O on mineral transformation of coal ash under high temperature gasification condition

利用XRD和FT-IR考察了高温弱还原气氛下Na_2O对两种硅铝含量不同的煤灰中矿物质组成的影响,揭示了Na_2O影响煤灰熔融特性的本质。通过Fact Sage计算了高温下矿物质反应的ΔG,探讨了Na_2O影响煤灰中矿物质组成的机理。结果表明,Na_2O对煤灰矿物质组成的影响与原煤灰的硅铝含量密切相关。硅铝总含量82.89%的煤灰,Na_2O含量为5%-20%时,钠长石和霞石的生成是煤灰熔融温度降低的主要原因;当Na_2O含量大于20%时,导致煤灰熔融温度降低的原因是霞石的生成。硅铝总含量47.85%的煤灰,Na_2O含量小于10%时,没有含钠矿物质生成;当Na_2O含量大于10%时,主要生成菱硅钙钠石、青金石和含钠的硅铝酸盐矿物,导致煤灰熔融温度降低。Fact Sage计算表明生成含Na矿物质反应的ΔG较小,其在高温下更容易发生。

In order to reveal the mechanism of Na2O influence on ash fusion temperatures（ AFTs）,effect of Na2O on mineral transformation of two coal ashes with different SiO2＋ Al2O3 levels were investigated by XRD and FT-IR under reducing atmosphere at high temperature. Thermodynamic software package Fact Sage was used to calculate the ΔG of reactions between minerals to reveal the mechanism of Na2O influence on mineral transformation. It is found that the effect of Na2O on mineral compositions depends on SiO2＋Al2O3levels of coal ash. For ash with 82.89% SiO2＋Al2O3while Na2O content is 5%-20%,albite and nepheline are formed,leading to a decrease of AFTs. However,only nepheline is formed when Na2O content is higher than 20%. For ash with47.85% SiO2＋Al2O3,when Na2O content is less than 10%,no Na-containing mineral is observed. When Na2O content is higher than 10%,Na-containing minerals such as combeite,lazurite and sodium aluminium oxide are formed,resulting in a decrease of AFTs. Furthermore,Fact Sage results reveal that Na-containing mineral is easily formed at high temperature due to lowΔG of the reactions.