The variety regulation and mechanism of high silica and alumina coal ash fusion temperature caused by Ca-Fe binary flux under different atmosphere

doi:10.11949/0438-1157.20220844

Abstract

Abstract:

The high ash fusion temperature (AFT) of ZGE coal is easy to cause the blockage of the slag discharging of the liquid slag tapping gasifier. It is necessary to add flux to reduce the AFT. Thus, the effects of CaO/Fe₂O₃ (Ca/Fe) additives on AFT of ZGE coal ash were measured by the AFT analyzer. The synergetic fluxing mechanism of Ca-Fe binary addition in argon atmosphere and mild reducing atmosphere was studied by combination of thermomechanical analysis (TMA), thermogravimetric and differential scanning calorimetry (TG-DSC), XRD and thermodynamic software FactSage. The results showed that the AFT decreases first and then increases with growing Ca/Fe ratio in both weak reduction and argon atmosphere, and the AFT is the lowest when Ca/Fe=1/1, but the AFT in mild reducing atmosphere is lower than in argon atmosphere. The corresponding shrinkage degrees of coal ash with different Ca-Fe additives at deformation temperature (DT), softening temperature (ST), hemispherical temperature (HT) and flow temperature (FT) are quite different, and the melting temperature range under argon atmosphere (the shrinkage rate of the ash column in DT—FT) is significantly higher than that under weak reducing atmosphere. Nevertheless, the shrinkage curves can be divided into three parts no matter in mild reducing atmosphere or in argon atmosphere, and the shrinkage degree in the first and the second stage under mild reducing atmosphere is larger than that in argon atmosphere. The further investigation demonstrated that the first shrinkage is caused by the solid sintering induced by chemical reactions among components, the shrinkage in the second stage was related to the liquid sintering caused by initial slag, and the third shrinkage determined the value of AFT. The mineral transition displayed that the minerals in ash existed as exclusive anorthite or mullite owns high AFT, but the eutectics can be formed between them under appropriate condition to decrease AFT. Moreover, Fe²⁺ facilitated to form eutectics. The formation temperature of the eutectic in the weak reducing atmosphere is lower than that in the argon atmosphere.

Key words: Ca-Fe binary flux, high silica and alumina coal ash, ash fusion temperature, fusion process, fluxing mechanism

摘要：

准格尔高硅铝煤灰熔融温度（AFT）高，易引发液态排渣气化炉排渣口堵塞问题，需添加助熔剂降低AFT。利用灰熔融温度测试仪研究了不同质量比CaO/Fe₂O₃（Ca/Fe）助剂的助熔效果，结合热机械分析仪、热重-示差扫描量热仪、XRD以及热力学计算对比分析了氩气气氛与弱还原气氛下Ca-Fe协同助熔机理。研究发现，弱还原与氩气气氛下，AFT均随Ca/Fe增加先降低后升高，在Ca/Fe=1/1时AFT最低，但弱还原气氛下Ca-Fe的助熔效果优于氩气气氛。不同Ca-Fe助剂煤灰在变形温度（DT）、软化温度（ST）、半球温度（HT）和流动温度（FT）时对应的收缩程度差异较大，并且氩气气氛下熔融温度范围（DT~FT）内灰柱的收缩速率显著高于弱还原气氛下的收缩速率。氩气与弱还原气氛下煤灰的收缩过程均可分为三个阶段，且其收缩程度依次递增，但弱还原气氛下第一、二阶段收缩程度较氩气气氛下高。进一步研究表明第一阶段的收缩主要以化学反应引起的固相烧结为主，第二阶段以初始液相形成的液相烧结为主，而第三阶段的收缩行为最终决定煤灰的AFT。高温矿物演化行为显示莫来石和钙长石单独存在时AFT很高，但两者可以与含铁组分形成低共熔物降低AFT，并且Fe²⁺可以促进低共熔物的形成，促使弱还原气氛下低共熔物的生成温度低于氩气气氛下的。

关键词: Ca-Fe助剂, 高硅铝煤灰, 灰熔融温度, 熔融过程, 助熔机理

CLC Number:

TQ 53

Wenju SHI, Jin BAI, Lingxue KONG, Jingpei CAO, Wen LI. The variety regulation and mechanism of high silica and alumina coal ash fusion temperature caused by Ca-Fe binary flux under different atmosphere[J]. CIESC Journal, 2022, 73(10): 4638-4647.

石文举, 白进, 孔令学, 曹景沛, 李文. 不同气氛下Ca-Fe二元助剂改变高硅铝煤灰熔融温度的规律和机制[J]. 化工学报, 2022, 73(10): 4638-4647.

Figures/Tables 10

Table 1 Chemical compositions of ZGE coal ash

组成	含量/%
SiO₂	49.18
Al₂O₃	41.01
Fe₂O₃	2.34
CaO	3.23
MgO	0.32
SO₃	0.43
TiO₂	1.20
K₂O	0.42
Na₂O	0.20
P₂O₅	0.16

Fig.1 XRD patterns of samples

Fig.2 The variation of contents of main mineral species in ZGE coal ash during heating process

Fig.3 The influence of Ca-Fe binary flux on AFT of ZGE coal ash

Fig.4 Shrinkage curves of ZGE coal ash with different Ca-Fe binary flux

Fig.5 Shrinkage degree of ZGE coal ash with different Ca-Fe binary flux at DT, ST, HT and FT

Fig.6 TG-DSC combined with TMA curves of ZGE coal ash with different Ca-Fe binary flux

Fig.7 TG-DSC curves of pure Fe2O3 during heating process

Fig.8 Mineral transition of ZGE coal ash with different Ca-Fe binary flux under argon atmosphere

Fig.9 Mineral transition of ZGE coal ash with different Ca-Fe binary flux under mild reducing atmosphere

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