【作者】 孙宇；

【导师】 王永征；

【作者基本信息】 山东大学 ， 动力工程（专业学位）， 2020， 硕士

【摘要】 生物质作为能源具有来源广泛、绿色可再生的特点,是化石能源的理想替代品。当前,生物质直燃技术在可再生能源利用领域已经逐渐成熟并初具规模。但是生物质燃料中通常钾、钠、钙等碱金属、碱土金属元素和氯元素的含量较高,这些元素尤其是钾元素含量过高,会导致燃烧时生物质锅炉出现如高温过热器表面积灰、炉内结渣、设备腐蚀等一系列问题,严重影响了生物质锅炉运行的安全性和经济性。本文针对这些问题,从生物质沉积灰特性层面研究了造成生物质锅炉受热面积灰、结渣和腐蚀的机理,在此基础上提出使用硅铝添加剂作为生物质燃料的抗结渣腐蚀添加剂,并深入研究和探讨了硅铝添加剂的作用效果及添加剂配比;进一步提出了使用调制粉煤灰作为添加剂的方案,并通过试验探讨了粉煤灰调制硅铝添加剂的作用效果。选用小麦和棉花秸秆两种生物质燃料,对生物质灰的形貌特征和物相组成特征进行了分析。试验发现两种生物质随着温度的升高,成灰率逐渐减少,表面收缩结渣现象更加严重。小麦秸秆灰中钾、硅、氯元素含量很高,随着燃烧温度的提高,灰中的KCl会逐渐以气态形式释放,进而造成锅炉内换热表面的氯腐蚀;棉花秸秆灰中含量最高的元素为钾、钙、镁,灰中的钾浓度高达225.55mg/g,导致灰的熔点很低,在800℃以上的高温出现CaO、MgO晶相,是结渣熔融体的主要成分。利用SiO2和Al2O3配制硅铝添加剂以模拟粉煤灰添加剂的主要作用成分,通过试验研究探讨了硅铝基添加剂抑制结渣、腐蚀问题的作用效果和作用原理。使用硅铝添加剂后的小麦秸秆灰和棉花秸秆灰中固定了更多的钾,小麦秸秆灰的固钾量由57.29mg提高至150mg以上,有效减少了气相中的KCl;棉花秸秆灰的钾浓度则从225.55mg/g降低至100mg/g以下,减轻了结渣。两种生物质在添加剂硅铝比为3:2时,有最佳的固钾能力;小麦秸秆最佳的添加剂使用量为15%,棉花秸秆最佳的添加剂使用量为10%。使用硅铝添加剂后两种生物质灰中的KC1均得以降低,更多的钾被固定在灰中,棉花秸秆灰中形成结渣的碱土金属氧化物CaO、MgO等也明显减少。添加剂使灰中的钾、钙等金属元素反应转化为硅铝酸盐类物质,性质稳定,熔点较高,释放的气态钾化合物减少,能够有效减轻结渣和腐蚀。在对硅铝添加剂的研究基础上,提出了调制粉煤灰添加剂的配制方法和最佳添加比,并通过试验验证了调制粉煤灰添加剂的作用效果。在试验选用的粉煤灰中加入质量分数为4.8%的Al2O3粉末,可以得到硅铝比为3:2的调制粉煤灰添加剂。通过试验得出,小麦秸秆使用调制粉煤灰添加剂的最佳添加比为17%,棉花秸秆的最佳添加比为15%,此时两者固钾量分别为154.03mg和82.82mg,与硅铝添加剂类似。从形貌特征上看,在两种添加剂的作用下灰的质地更加松散细腻,几乎没有粘连结块,结渣问题得到了有效改善,两种生物质灰颗粒的尺寸明显减小,颗粒间的团聚也大大减轻。使用硅铝添加剂的灰样颗粒细小松散,使用调制粉煤灰添加剂的灰样颗粒大多为球状。使用调制粉煤灰添加剂后,小麦秸秆灰中钾的浓度、KCl含量明显下降,在添加剂的作用下,KCl转化为KAlSi3O8等熔点高、性质稳定的硅铝酸盐,其作用效果与硅铝添加剂的作用效果相似;棉花秸秆灰中主要成分完全变为硅铝酸盐类物质,引起结渣、腐蚀问题的CaO、MgO、KCl等成分在灰中已经几乎不存在,反应更加彻底,使用调制粉煤灰添加剂的效果更佳。更多还原

【Abstract】 Biomass as a source of energy has the characteristics of wide sources and diverse uses,and is an ideal substitute for fossil energy.At present,biomass direct combustion technology has gradually matured and taken shape in the field of renewable energy utilization.However,the content of alkali metals,alkaline earth metal elements such as potassium,sodium and calcium and chlorine in biomass fuel is usually high.The content of potassium is very high,which will cause a series of problems of biomass boiler at high-temperature superheater surface during combustion,such as slagging in the furnace and equipment corrosion.These problems will seriously affect the safety and economy of biomass boiler operation.In view of these problems,this paper studies the mechanism of ash slagging and corrosion of biomass boiler heating surface from the perspective of biomass deposit ash characteristics.Basis on this,it is proposed to use silicon aluminum additives as anti-slagging corrosion additives for biomass fuels,and in-depth research and discussion on the effect of silicon aluminum additive and additive ratio;further proposed the use of modulated fly ash as an additive program,and through experiments to explore the effect of fly ash modulation of silicon aluminum additive.Two types of biomass fuels,wheat straw and cotton straw,were used to analyze the morphological characteristics and phase composition characteristics of biomass ash.The experiment found that as the temperature increased,the ash formation rate gradually decreased,and the phenomenon of surface shrinkage and slagging became more serious.The content of potassium,silicon and chlorine in wheat straw ash is very high.As the combustion temperature increases,the KC1 in the ash will be gradually released in gaseous,which will cause chlorine corrosion of the heat exchange surface in the boiler;the potassium concentration in the ash is as high as 225.55 mg/g,which results in a very low melting point of the ash.CaO and MgO crystal phases appear at high temperatures above 800℃ and are the main components of the slag melt.Using SiO2 and Al2O3 to prepare silicon-aluminum additives to simulate the main action components of fly ash additives,the influences and principles of silicon-aluminum-based additives to suppress slagging and corrosion problems were discussed through experimental research.After using the silicon aluminum additive,more potassium was fixed in the wheat straw ash and cotton straw ash.The amount of potassium fixed in the wheat straw ash was increased from 57.29mg to more than 150mg,which effectively reduced the KCl in the gas phase;the potassium concentration of the cotton straw ash Then reduced from 225.55mg/g to below 100mg/g,which reducing slagging.The two kinds of biomass have the best potassium fixation capacity when the additive silicon-aluminum ratio is 3:2;the best additive usage of wheat straw is 15%,and the best additive usage of cotton straw is 10%.After using silicon aluminum additive,the KC1 in both biomass ash is reduced,more potassium is fixed in the ash,and the slag-forming alkaline earth metal oxides CaO,MgO,etc.in the cotton straw ash are also significantly reduced.The additive converts potassium,calcium,and other metal elements in the ash into aluminosilicates with stable properties,high melting point,and less gaseous potassium compounds released,which can effectively reduce slagging and corrosion.On the basis of the research on silicon aluminum additives,the preparation method and the optimal addition ratio of the modified fly ash additive are proposed,and the effect of the adjusted fly ash additive is verified through experiments.By adding Al2O3 powder with a mass fraction of 4.8%to the fly ash selected in the experiment,a modulated fly ash additive with a silicon to aluminum ratio of 3:2 can be obtained.According to the test,the best addition ratio of wheat straw using modified fly ash additives is 17%,and the best addition ratio of cotton straw is 15%.The two potassium fixation amounts are 154.03mg and 82.82mg respectively,which are similar with silicon aluminum additive.From the morphological characteristics,under the action of the two additives,the texture of the ash is more loose and delicate,and there are almost no sticking blocks.The problem of slagging has been effectively improved.The size of the two biomass ash particles is significantly reduced.Reunion is also greatly reduced.The ash-like particles using silicon aluminum additives are fine and loose,and the ash-like particles using the modulated fly ash additives are mostly spherical.After using the prepared fly ash additive,the potassium concentration and KCl content in the wheat straw ash decreased significantly.Under the action of the additive,KCl was converted into aluminosilicates with high melting point and stable properties,such as KAlSi3O8,which are similar with the ash with silicon aluminum additive;the main components in the cotton straw ash are completely changed to aluminosilicates,and the CaO,MgO,KCl and other components that cause slagging and corrosion problems are almost non-existent in the ash,and the reaction is more thorough.So the effect of coal ash additives is better.更多还原