高碱金属燃料灰结渣特性表征方法

Characterization of slagging about high alkali metal fuel ash

由于准东煤和生物质等碱金属含量高,其燃烧用于发电供热易造成锅炉受热面沾污结渣,成为锅炉安全稳定长周期运行的技术瓶颈。灰的熔融特征参数是指导锅炉设计和运行的重要依据,实际工程应用中,普遍采用GB/T 219—2008《煤灰熔融性的测定方法》测定4个特征温度来描述灰熔融过程的变化,从而判断灰的沾污结渣特性。然而该方法制灰过程中碱金属挥发,导致测量结果明显高于实际值,对锅炉设计运行无指导意义。总结不同灰化终温下碱/碱土金属的释放规律:准东煤550℃时,Na析出约20%~50%,815℃时,析出在30%~80%;生物质中K在400℃时开始析出,到800℃时,K几乎全部析出。在此基础上,进一步分析了国标法制灰后熔点的测量方法,尽管采用低温灰样,在制灰过程中抑制了碱金属的挥发,但在后续加热测量熔点的过程中仍会引起碱金属的释放,进而明确了国标法不适用于高碱金属燃料灰熔融特性的测定。为此,针对高碱金属燃料,提出一种低温灰化后,用压差法测定灰初试烧结温度的测量方法,并在压差法试验装置上进行测量,达初始烧结温度前,样品室压降随温度升高而增大,满足达西定律,一旦出现烧结时,样品体积收缩,样品室两端压降迅速降低,则压降变化的拐点为燃料的初始烧结温度,也是灰熔融团聚的最低温度。采用低温灰化仪制得稻壳灰,并在试验台上开展初步试验,测得其初始烧结温度为695℃,与工业上实际结渣温度吻合较好,而国标法测得软化温度高达1500℃以上,远高于稻壳实际结渣温度,初步表明,该试验方法可准确表征高碱金属燃料结渣特性,为工业应用提供参考。

Due to the high alkali metal in the Zhundong coal and biomass,it will cause slagging of the heating surfaces in boiler during combustion which influences the long-time safe operation of the boiler.The ash fusibility temperature is used to guide the boiler design and operation.On the project,the GB/T 219-2008 Determination of fusibility of coal ash is used to measure the four characteristic temperatures to describe the varation of ash fusion.So as to judge the characteristics of slagging.However,the measured value is so higher than actual value evidently because of the release of alkali metal that failue to guide the boiler operation.In order to acquire accurate datas,the release characteristic of alkali metal are summarized.The 20%-50%of Na releases at 550℃and to 815℃,the releases arrive to 30%-80%in Zhundong coal.From 400℃to 800℃,the K releases almost completely.The GB method is further analyized,the production process of low temperature ash decrease the release of alkali metel,but still release during the measurement.So the GB method is unsuitable for characterization of fusibility about high alkali metal fuel ash.Aimed to high alkali metal fuel,the measure method is proposed which adopted the low temperature ash to determine the initial sintering temperature by pressure-drop method.Before the sintering,the pressure-drop in the chamber increase with the increase of temperature which adapt to dacy′s low.When the sintering occurs,the ash will shrink,the pressure-drop will decrese quickly.Usually,the temperature of break point is the initial sintering temperature,also is the minimum temperature of ash fusion and agglomeration.The low temperature asher is used to produce low temperature rice husk ash and determine the initial sintering temperature that is 695℃which is close to the value in engineering.But the result of GB method is 1500℃above,which is higher than actual slagging temperature.Preliminary suggest that the pressure-drop method could be used to judge the slagging of high alkali metal fuel and guide industrial application.