生物质模型化合物碱金属的释放及碱金属对灰熔融特性的影响

发布时间：2017-12-28 05:01

本文关键词：生物质模型化合物碱金属的释放及碱金属对灰熔融特性的影响　出处：《华北电力大学(北京)》2017年博士论文　论文类型：学位论文

【摘要】：煤和生物质是我国火力发电的主要燃料。燃料中碱金属钾和钠的存在,能够造成锅炉的积灰、结渣和腐蚀等一系列问题,严重影响锅炉的经济、安全运行。生物质中碱金属钾的含量较高而钠的含量较低,煤中碱金属的含量普遍较低,但高钠煤(如准东煤)中钠的含量较高。因此,根据生物质和煤燃料特性的不同,论文主要研究生物质中碱金属钾的释放规律,以及碱金属钠和钾对灰熔融特性的影响规律。通过实验探究了负载KCl的纤维素、木聚糖、木质素、果胶和松木在热解过程中Cl和K的释放和迁移规律以及CH_3Cl的生成机理。研究发现,部分KCl中的K以有机K的形式转移到了有机物中,并在更高的温度下得到释放。负载KCl的松木、木质素和果胶由于含有碳环上的甲氧基官能团,能在热解中产生大量的CH_3Cl,CH_3Cl主要在低温下(200-350℃)生成,因而能够被高温和高升温速率所抑制。利用智能灰熔融仪研究了合成灰中Na_2O的含量对灰熔融温度的影响。实验表明,当灰分中Na_2O的含量低于3%时,提高Na_2O的含量能够降低合成灰的初始变形温度,但对软化温度、半球温度和流动温度影响较小;当灰分中Na_2O的含量在3-10%范围内时,提高Na_2O的含量能够使合成灰的4个特征温度全部降低。利用FactSage 7.0软件包计算了随着灰分中Na_2O含量升高和温度升高的过程中矿物质的变化趋势。热力学分析表明,钠长石、霞石的产生是提高Na_2O的含量能够降低灰熔融温度的原因,含钠矿物质的产生替代了熔点更高的含钙矿物质(如钙长石),同时与含钙矿物质发生低温共熔,从而降低灰的熔融温度。研究了不同成分合成灰中K_2O的含量对灰熔融温度的影响。实验表明,对于CaO含量较低(0-5%)的煤灰,适量增加K_2O的含量(0-5%)有助于降低灰分的初始变形温度、软化温度和半球温度,但对流动温度几乎没有影响;对于CaO含量较高(20-25%)的煤灰,适量增加K_2O的含量(0-5%)能够使灰的4个特征温度全部降低;对于生物质灰,当K_2O的含量低于30%时,增加K_2O的含量有助于降低灰熔融温度,继续增加K_2O的含量(至50%)则对灰熔融温度几乎没有影响。经过热力学计算分析可知,K_2O对灰熔融温度的降低作用与含钾矿物质钾长石、白榴石的产生相关,含钾矿物质能与其他矿物质发生低温共熔,降低灰熔融温度。研究了煤灰中不同氧化物的含量对灰熔融温度的影响。向煤灰中分别添加Na_2O、MgO、SO_3和CaO来探究它们对灰熔融特性的影响规律。研究表明,提高Na_2O的含量(0-5.5%)能够降低煤灰的熔融温度,这与在合成灰中得到的结论相吻合;提高SO3的含量(6.5-13%)能够升高煤灰的熔融温度;提高MgO的含量(3-9%)对煤灰的熔融温度起到先降低后升高的作用;提高CaO的含量(13-47%)对煤灰的熔融温度起到先降低后升高的作用。
[Abstract]:Coal and biomass are the main fuel for thermal power generation in China. The existence of alkali metal potassium and sodium in fuel can cause a series of problems, such as ash accumulation, slagging and corrosion of the boiler, which seriously affect the economic and safe operation of the boiler. Alkali metal in the biomass was higher and the content of sodium with low content of alkali metal in coal is generally low, but high sodium coal (such as coal) were higher in sodium. Therefore, according to the different characteristics of biomass and coal fuel, the paper mainly studies the release rule of alkali metal potassium in biomass, and the influence rule of alkali metal sodium and potassium on ash fusion characteristics. The release and migration of Cl and K in the pyrolysis process of cellulose, xylan, lignin, pectin and pine wood loaded with KCl and the formation mechanism of CH_3Cl were investigated through experiments. It was found that the K in part of KCl was transferred into organic matter in the form of organic K and released at a higher temperature. KCl loaded pine, lignin and pectin, which contain methoxy functional groups on the carbon ring, can produce a lot of CH_3Cl in pyrolysis. CH_3Cl is mainly generated at low temperature (200-350 degrees), and therefore can be inhibited by high temperature and high heating rate. The effect of the content of Na_2O in the synthetic ash on the ash melting temperature was studied by an intelligent ash melting instrument. Experiments show that when the content of ash in Na_2O is lower than 3%, improve the content of Na_2O can reduce the initial deformation temperature of synthetic ash, but has little effect on softening temperature, Hemisphere temperature and flow temperature; when the ash content in Na_2O in the range of 3-10%, improve the content of Na_2O can make the 4 characteristic temperature of synthetic ash all decreased. The FactSage 7 software package was used to calculate the mineral changes in the process of increasing the content of Na_2O and increasing the temperature in ash. The thermodynamic analysis shows that sodium feldspar, nepheline is produced to improve the content of Na_2O can reduce the ash melting temperature, sodium mineral substitute the higher melting temperature of calcium minerals (such as calcium feldspar), simultaneous eutectic with calcium containing minerals, thereby reducing the melting temperature of ash. The effect of the content of K_2O in different synthetic ashes on the melting temperature of the ash was studied. Experiments show that for low CaO content (0-5%) of the ash, the amount of the increase of the content of K_2O (0-5%) helps to reduce the ash content of the initial deformation temperature, softening temperature and Hemisphere temperature, but almost no effect on the flow temperature; with high content of CaO (20-25%) the amount of fly ash, the content of K_2O increased (0-5% 4) can make the characteristic temperature of ash for biomass ash, all decreased; when the content of K_2O is lower than 30%, the increase of the content of K_2O is helpful to reduce the ash melting temperature, the increase of K_2O content (up to 50%) of the ash melting temperature has little influence. Through thermodynamic calculation and analysis, it is known that the reduction of K_2O to ash fusion temperature is related to the production of potassium bearing minerals, potassium feldspar and garnet. Potassium containing minerals can co occur with other minerals at low temperature and reduce the ash fusion temperature. The influence of the content of different oxides in coal ash on the melting temperature of ash was studied. Na_2O, MgO, SO_3 and CaO were added to the coal ash to investigate their influence on the ash melting characteristics. Research shows that improve the content of Na_2O (0-5.5%) can reduce the melting temperature of ash, which is consistent with the conclusions obtained in the synthesis of ash; improve the content of SO3 (6.5-13%) can increase the melting temperature of ash; improve the content of MgO (3-9%) on the ash melting temperature has decreased first and then increased; improve the content of CaO (13-47%) on the ash melting temperature plays the role of first decreased and then increased.
【学位授予单位】：华北电力大学(北京)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TK6

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