煤气化是发展煤基大宗化学品及清洁燃料的关键技术,也是实现双碳目标的重要途径。准东高钠煤中碱金属钠含量高,气化过程中碱金属钠释放造成严重的灰释放问题,因此,探究准东高钠煤在气化过程中灰沉积、结渣机理及煤灰流动性对准东煤的清洁高效利用具有重要意义。鉴于此,综述了近年来气化过程中高钠煤的灰化学研究最新进展。总结了煤中钠的赋存形态及含量,阐明了气化过程中钠的迁移转化机制及钠释放导致气化炉受热面造成的灰沉积、结渣问题。由于高钠煤中钠释放主要受气化温度的影响,因此成灰温度不宜高于500℃。气化过程中易生成熔点低的含钠矿物质,降低高钠煤煤灰熔融温度。高钠煤中钙、铁含量高时,煤灰中钙长石及钙铝黄长石在高温下生成低温共晶体、Fe2+与煤中矿物质反应形成低熔点尖晶石均是加剧煤灰熔融的重要原因。同时,热转化过程中气氛对高钠煤中矿物演化具有一定影响。高钠煤灰的熔融区间窄,熔融速率快,表明高钠煤灰流动性强,由于Na+的离子势较低,O2-被Si4+夺取,导致桥氧键断裂成非桥氧键,熔渣网格结构解聚,黏度降低,其熔融机理符合“熔融-溶解”机理。降温过程中晶体的析出对黏度的影响至关重要。Na2O的引入降低了熔渣析晶体温度,改变晶体类型,同时降低熔渣的黏滞活化能及结晶能力。

Coal gasification is a key technology to develop coal based bulk chemicals and clean fuels, and also an important way to achievethe goal of carbon neutrality. High sodium content and its volatilization of Zhundong coal during gasification lead to serious ash-releaseproblems. Therefore, it is of great significance to clarify the ash deposition and slagging mechanism and ash fluidity duringZhundong coal gasification for the clean and efficient utilization of high-sodium coal. Given this, the research progress on the ash chemis⁃try of high-sodium coal during gasification process was reviewed. The forms and content of sodium in coal were summarized. The migrationand transformation mechanisms of sodium in gasification and the ash deposition problem caused by sodium release on the heating surface ofthe gasifier were clarified. The ashing temperature is set at 500 ℃ because the sodium release in high sodium coal is mainly affected bythe gasification temperature. Low melting point sodium-containing minerals are easily generated during the gasification process, reducingthe ash melting temperature of high sodium coal ash. When the content of calcium and iron in high sodium coal is high, the formation oflow-temperature eutectic of anorthite and gehlenite in coal ash at high temperature, and the formation of low melting point spinel by Fe2+reacting with minerals in coal are important reasons for reducing coal ash melting temperature. Meanwhile, the atmosphere has a certain in⁃fluence on the minerals evolution of high-sodium coal during thermal conversion. The melting rate of high-sodium coal is fast,and the av⁃erage melting temperature is low, indicating that the ash has a strong fluidity. The Na2O can provide O2- and break the bridge oxygenbonds, causing the slag to depolymerize and reducing the viscosity value. The slag grid structure depolymerizes, the viscosity is reduced.The melting mechanism confirms the melting-dissolution mechanism. The precipitation of crystals in the slag during cooling has a crucialimpact on the viscosity. The introduction of Na2O reduces the crystallization temperature of slag and changes the crystal type. At the sametime, the viscosity activation energy and crystallization ability of the slag are reduced.

0 引言

1 准东高钠煤的煤质特性

   1.1 煤中钠的赋存形态

   1.2 气化过程中钠的迁移转化机制

   1.3 高钠煤煤灰中钠含量

2 高钠煤的灰沉积特性

3 高钠煤灰的熔融特性

   3.1 高钠煤成灰温度选择

   3.2 矿物质演化对煤灰熔融温度的影响

   3.3 气化过程中高钠煤灰熔融过程及机理分析

   3.4 高钠煤灰熔融温度预测

4 高钠煤灰的黏温特性

   4.1 钠对熔渣黏温特性的影响

   4.2 钠对煤灰网格结构的影响

   4.3 钠对熔渣结晶行为的影响

5 结语及展望