气氛及硅铝添加剂对高碱煤灰成分转化特性的影响

Effects of atmosphere and Si/Al additives on component transformation in high-alkali coal ash

高碱煤在燃烧过程中极易出现严重的积灰结渣问题,同时富氧燃烧是一种有利于CO_(2)减排的燃烧技术,然而关于富氧燃烧气氛对高碱煤灰组分演化行为的影响机理尚不明晰,且以往研究在利用FactSage计算煤灰的转化特性时往往采用高温灰成分作为研究基准,无法准确研究在低温下煤中无机物的转化行为。基于高碱煤等离子低温灰的成分特性,通过FactSage模拟研究了富氧燃烧中灰成分的演化行为,同时对气相中元素的分布规律,O_(2)体积分数对灰中物质组成的影响及硅铝添加剂对灰演变行为的影响进行了探索。研究结果表明:当温度为600℃时,O_(2)/CO_(2)气氛更有利于Cl的挥发。气相中的氯化物及硫酸盐类可能在低温下凝结在灰颗粒表面,从而加剧高碱煤的积灰结渣问题。五彩湾煤灰中的Ca,Na,Al氧化物在200℃就发生反应生成Na_(2)Ca_(3)Al_(16)O_(28),且随着温度的升高Na_(2)Ca_(3)Al_(16)O_(28)逐渐消失,可能生成复杂的低温共熔体。富氧气氛下O_(2)体积分数变化对五彩湾煤灰组分转化没有显著影响。富氧气氛中高浓度的CO_(2)会促进灰中物质的碳酸化,出现较多的Ca_(5)Si_(2)O_(7)(CO_(3))_(2)和CaMg(CO_(3))_(2),但对Na_(2)SO_(4),CaSO_(4)等硫酸盐的影响较弱。硅铝添加剂的加入会降低反应产物中的CaCO_(3)含量,但对CaSO_(4)的赋存影响较小。

Serious ash-related issues could occur during the combustion of high-alkali coal.Oxy-fuel combustion is a promising combustion technology to deal with the emission reduction of CO_(2).However,the influence mechanism of oxy-fuel atmosphere on the transformation of high-alkali coal ash is far away from enough.In addition,the previous study mainly adopted the high-temperature ash composition as the research benchmark,which was difficult to explore the inorganic substances behaviors at low temperature.This study explored the impacts of combustion atmosphere,oxygen content,and additives on the transformation of ash components via FactSage software on the basis of the low-temperature ash composition,also including the element distribution in gas phase.The results showed that the oxy-fuel condition benefited the vaporization of chlorine at 600℃.The chlorides and sulfates in the gas phase could condense on the ash particle surface to worsen the fouling and slagging.The oxides of sodium,calcium and aluminum reacted each other to form Na_(2)Ca_(3)Al_(16)O_(28) at 200℃and the Na_(2)Ca_(3)Al_(16)O_(28) was absent with the increasing temperature,which could be put down to the formation of low-temperature eutectic.The oxygen content had little influence on the ash transformation of Wucaiwan coal.The high content of CO_(2) could accelerate the carbonation of ash to generate Ca_(5)Si_(2)O_(7)(CO_(3))_(2) and CaMg(CO_(3))_(2),but had little influence on the sulfates.In addition,the addition of Al_(2)O_(3) and SiO_(2) could reduce the content of CaCO_(3) in the ash but exerted little effect on CaSO_(4).