高钠煤灰烧结特性研究进展

中国新疆准东煤具有储量巨大、开采成本低、挥发分高、硫含量低等特点,是优质的动力用煤。但准东煤钠含量高,燃烧利用时易在受热面上形成烧结性积灰,产生严重的结渣,极大限制了高钠煤的开发利用。因此,要实现高钠煤的清洁高效利用,需充分认识高钠煤灰的烧结特性。总结了高钠煤积灰结渣机理,概述了高钠煤灰烧结机制,探讨了二者之间的内在关联。高钠煤在燃烧过程中,煤中碱金属(主要为钠)释放并以Na_2SO_4、NaCl及Na的形式存在于烟气中,与受热面接触并于其上冷凝形成黏性内白层,内白层捕获飞灰颗粒后反应生成低熔点化合物,其烧结温度降低,使锅炉受热面上发生沾污增强型的"沾污烧结"过程。高钠煤灰的烧结过程包含固相烧结、液相烧结和气相烧结3种方式,对煤灰烧结过程的影响因素包括反应温度、化学组成、煤灰粒径、反应气氛、添加剂种类、锅炉设计和锅炉运行工况等。其中添加剂按氧化物种类可分为碱性氧化物和酸性氧化物,一般情况下碱性氧化物可以降低煤灰烧结温度,酸性氧化物可提高煤灰烧结温度。未来对于提高高钠煤灰烧结温度的研究方向可从新型添加剂出发,找到既能固定烟气中的钠,又能与灰渣中的低熔点含钠矿物质反应生成高熔点化合物的单一或混合成分的添加剂。同时,关于钠蒸气对积灰结渣在微观层面上的动态特性的影响机制也需进一步研究。概述了煤灰烧结温度的测量方法,热导率分析法、压力测量法、热机械分析法、筛分法和压降法,其中压降法是目前为止测量烧结温度较为准确的方法。介绍了上海理工大学碳基燃料洁净转化实验室在高钠煤灰烧结特性方面的研究方向,以期为解决燃用高钠煤锅炉积灰结渣问题提供参考。

Research progress on sintering characteristics of high sodium coal ash

Zhundong coal in Xinjiang with the characteristics of huge reserves,low mining cost,high volatile yield and low sulfur content,is a high-quality power coal.However,due to high sodium content of Zhundong coal,ash sintering and depositing easily occur on the heating surface during its combustion process,resulting in the serious ash deposits and slagging,which greatly limits the development and utilization of the high sodium coal.Thus,to realize the clean and efficient utilization of high sodium coal,it is necessary to fully understand the sintering characteristics of high sodium coal ash.In this paper,the research progress on the ash depositing and slagging mechanism and ash sintering behavior of high sodium coal was summarized.Furthermore,the inherent relationship between the sintering characteristic and the fouling and slagging behavior of the high sodium coal ash was explored.During the combustion process,alkali metals(mainly sodium)in coal is released into flue gas in the forms of Na 2 SO 4,NaCl and Na,which contact with the heating surface and condenses onto it to form viscous inner white layer.The fly ash particles in the flue gas can be captured by the inner white layer and reacts to form low melting point compounds,and thus,the sintering temperature decreases,and the contamination-enhanced"contamination sintering"process on the heating surface of the boiler is promoted and accelerated.The sintering process of high sodium coal ash includes:solid state sintering,liquid phase sintering and gas phase sintering.The influencing factors on the sintering process of the coal ash include reaction temperature,ash composition,ash particle size,reaction atmosphere,additives,boiler design and boiler operating conditions,etc.The additives can be divided into basic oxides and acidic oxides according to the types of oxides.Basic oxides can reduce the sintering temperature of the coal ash,and acidic oxides can increase the sintering temperature of the coal ash to some extent.The future research focuses on the development of new and low-cost additives consisting of single or mixed compound,which can fix sodium matters in the flue gas or react with low-melting sodium-containing minerals in the ash to increase the sintering temperature of high sodium coal ash.Moreover,the influence mechanism of sodium vapor on the dynamic depositing and slagging characteristics should be further studied from the micro-level.The methods for the sintering temperature measurement of coal ash are also introduced,including thermal conductivity analysis method,pressure measurement method,thermomechanical analysis method,sieving method and pressure drop method.Among them,the pressure drop method is relatively accurate for the sintering temperature measurement so far.Laboratory for Clean Conversion of Carbon-based Fuels,USST has engaged in the research on the sintering and slagging characteristics of high-sodium coal ash,in order to provide some guiding meaning for the coal combustion and utilization process.