【作者】 李琳娜；

【导师】 吕清刚；

【作者基本信息】 中国科学院研究生院（工程热物理研究所） ， 热能工程， 2014， 博士

【摘要】 流化床燃烧技术由于其燃料适应性广、燃烧效率高及污染物排放少等优点,是大规模高效利用生物质最有前途的技术之一。秸秆资源在我国生物质资源中占有重要地位,然而由于秸秆中碱金属含量较高,在流化床燃烧过程中,易引发结焦、床料粘结、积灰及腐蚀,其中最突出的是床料粘结导致流化失败的问题。解决秸秆流化床燃烧过程中碱金属引发的粘结问题,对于秸秆的利用具有很高的实用价值。本论文提出利用城市污水污泥(以下简称污泥)与秸秆混烧解决秸秆流化床燃烧过程中粘结问题的新思路。主要研究了污泥与秸秆混烧特性；探索了污泥对秸秆流化床燃烧过程中粘结问题的影响；阐明了污泥中磷元素对秸秆中碱金属元素迁移转化行为的影响以及与碱金属间的反应机理；最终掌握利用污泥控制秸秆流化床燃烧粘结的方法。利用热重-质谱联用技术(TG-MS)对秸秆与污泥混烧特性以及气体产物释放规律进行研究。研究结果表明：秸秆、污泥单独燃烧及秸秆与污泥混烧的失重过程主要分成两个阶段：挥发分的析出和燃烧及固定碳的燃烧。对于秸秆与污泥混合燃料,挥发分析出阶段主要受秸秆燃烧控制,碳燃烧阶段主要受污泥燃烧控制,污泥的掺混降低了秸秆燃烧的综合燃烧特性,但有利于降低秸秆燃烧过程中CO2、NH3、 HCN和NO气体析出峰的离子强度。采用立管炉实验系统,研究了污泥对秸秆燃烧过程中碱金属迁移转化特性。研究结果表明,污泥对秸秆中碱金属具有捕集作用,形成了高熔点的硅铝酸盐KAlSi2O6、KA1Si3O8和磷酸盐Ca9MgK(PO4)7。以三种磷酸盐(磷酸二氢铵NH4H2PO4、磷酸二氢钙Ca(H2PO4)2·H2O、磷酸钙Ca3(PO4)2)为富磷添加剂与麦秆混烧,研究了混烧过程中碱金属的迁移转化规律以及含磷添加剂与碱金属的反应机理。研究结果表明：三种富磷添加剂与麦秆混烧提高了碱金属在底灰中的固留率,抑制了碱金属以气态形式析出；有利于抑制低熔点碱金属盐的生成以及低温共熔现象的发生；NH4H2PO4和Ca(H2PO4)2·H2O与麦秆中的碱金属反应主要生成CaK2P2O7; Ca3(PO4)2与麦秆中的碱金属反应主要生成Ca10K(P04)7. Ca10Na(PO4)7和Ca5(PO4)3Cl。选择Ca3(PO4)2为污泥中磷的模型化合物,深入研究污泥与麦秆混烧过程中P与碱金属的反应机理。Ca3(PO4)2与KCl在温度高于800℃时生成Ca10K(PO4)7和Ca5(PO4)3Cl,此反应揭示了污泥麦秆混烧过程中磷酸钾盐的生成机理。利用5kW鼓泡流化床实验装置,研究污泥对麦秆流化床燃烧粘结失流特性的影响。研究结果表明,污泥的掺混可以降低麦秆燃烧过程粘结趋势延长失流时间。污泥灰对碱金属具有捕集作用,使碱金属生成高熔点的硅铝酸盐KA1Si3O8、 KAlSi2O6和磷酸盐Ca9MgK(PO4)7,抑制了碱金属元素与石英砂床料之间的反应,从而有效抑制麦秆燃烧时粘结失流问题的发生。通过污泥中磷的模型化合物Ca3(PO4)2与麦秆混烧研究污泥中磷对麦秆燃烧粘结失流特性的影响,实验结果证明了污泥中P对麦秆燃烧粘结失流的抑制作用。随着床层温度升高,需要增加Ca3(PO4)2的掺混量以抑制粘结失流发生。基于Gibbs自由能最小化法,利用FactSage6.1热力学平衡软件计算了秸秆与污泥混烧过程中碱金属的平衡分布,为利用污泥控制碱金属问题提供了理论基础。计算结果表明,秸秆中K和Na的化学形态分布有很大的不同。随着燃烧温度的升高,K更易以熔融态和气态形式存在；与玉米秆相比,麦秆在燃烧时碱金属分布中熔融态和气态的摩尔百分比更大；与秸秆相比,污泥中的碱金属主要以固态或者熔融态存在；秸秆与污泥混烧会改变秸秆中碱金属的分布,掺混质量比对秸秆与污泥混合物在不同温度下对K化学形态分布的影响较大,对Na化学形态分布影响较小；污泥有助于改善秸秆单独燃烧时碱金属的分布,有利于高熔点硅铝酸盐KA1Si2O6生成,减少气态KC1的释放。更多还原

【Abstract】 Due to the advantages of wide fuel flexibility, high combustion efficiency, and low pollutant emission, fluidized bed combustion technology has been one of the most promising technologies for efficient and large-scale utilization of biomass. Straws play an important role in biomass resources in China, but the content of alkali metals is relatively high, which will cause several problems such as slagging, bed agglomeration, deposition and corrosion during fluidized-bed combustion. Among these problems, bed agglomeration is more severe, because it can lead to defluidization. It is practically valuable for the energy-oriented utilization of straws to solve the agglomeration initiated by alkali metals during straw fluidized bed combustion.In this thesis, a new method is proposed to deal with the agglomeration by co-combusting straw and municipal sewage sludge. The co-combustion characteristics of straw/municipal sewage sludge blends are researched. The influence of municipal sewage sludge addition to straw on agglomeration characteristics during fluidized bed combustion is investigated. The effect of phosphorus in sewage sludge on the behavior of alkali metals in straw and the phosphorus-potassium reaction mechanism are explored. The ultimate objective of this thesis is to master the method of inhibiting agglomeration during straw fluidized bed combustion with municipal sewage sludge addition.The combustion characteristics and gas products distribution during co-combustion of straw and municipal sewage sludge (sludge for short) were investigated by thermogravimetry-mass spectroscopy(TG-MS). The results show that there are two weight loss steps for combusting straws and municipal sewage sludge separately, and their co-combusting:the volatile releasing and burning, and the fixed carbon burning. For the blends, the stage of the volatile releasing and burning is controlled by the straw, while the stage of the fixed carbon burning is controlled by the sewage sludge. Adding sewage sludge to the straw decreases the combustion performance of straw, but is helpful to lower the emission peaks of CO2, NH3, HCN, and NO. The behavior of alkali metals during co-combustion of municipal sewage sludge with straw was explored in a vertical tubular furnace reactor. The results indicate that adding sewage sludge to the straws enhances the retention of alkali metals retention in ash due to the formation of high melting point compounds such as potassium aluminosilicates (KA1Si2O6and KAlSi3O8) and alkali phosphates Ca9MgK(PO4)7. Chemical reaction mechanisms between alkali metals and three kinds of phosphorous-rich additives are studied to investigate the effect of phosphorus on the behavior of alkali metals during wheat straw combustion. The selected phosphrous-rich additives are ammonium dihydrogen phosphate (NH4H2PO4), monocalcium phosphate (Ca(H2PO4)2·H2O) and calcium phosphate (Ca3(PO4)2). The results results demonstrate that a certain amount of phosphorous-rich additives is positive for capturing alkali metals, restraining the volatilization of alkali metals and inhibiting the sintering of wheat straw ash. The reaction between NH4H2PO4or Ca(H2PO4)2·H2O and potassium metals in wheat straw forms CaK2P2O7, and that between Ca3(PO4)2and potassium metals produces Ca10K(P04)7,Ca10Na(P04)7and Ca5(PO4)3Cl. Calcium phosphate (Ca3(PO4)2) is selected as a model compound of phosphorus in municipal sewage sludge ash to study the reaction mechanism between phosphorus and alkali metals during co-combustion of wheat straw and municipal sewage sludge. The reaction between Ca3(PO4)2and KC1produces Ca10K(PO4)7and Ca5(PO4)3Cl at about800℃and higher temperature, revealing the mechanism of potassium phosphate formation during the co-combustion of sewage sludge and wheat straw.The influence of sewage sludge addition on the agglomeration characteristics during wheat straw combustion was investigated in a5kW bubble fluidized bed. The results reveal that the sewage sludge addition decreases the agglomeration tendency and can extend the defluidization time during wheat straw combustion. Adding sewage sludge to wheat straw leads to the formation of potassium aluminosilicates (KAlSi2O6and KAlSi3O8) and alkali phosphates Ca9MgK(PO4)7in the bottom ash, which will reduces the amount of K available for the reaction with the quartz bed material grains, and effectively restrains the reaction between the alkali and quartz sands, thus preventing the agglomeration. The influence of phosphorus in sewage sludge on the agglomeration characteristics during straw combustion in fluidized bed was explored using the model compound of phosphorus Ca3(PO4)2. The results proves that the phosphorus in sewage sludge can decrease the agglomeration tendency. The higher the temperature is, the more Ca3(PO4)2will be needed.Based on Gibbs free energy minimization, the equilibrium analysis software FactSage6.1was used to simulate thermodynamics state of the transformation behavior of alkali during co-combustion of straws and municipal sewage sludge. The results show that the distribution of K and Na in straws is in different chemical forms. As the temperature increases, K exists in the form of molten and gaseous. Compared with corn stalk, the alkali metals in wheat straw are mainly in the molten and gaseous state. Compared with straw, the alkali metals in sewage sludge are mainly in the solid and molten state. The addition of sewage sludge to straws will change the distribution of alkali metals, and the blending mass ratio has greater effect on the distribution of K than Na. The addition of sewage sludge would help improve the distribution of the alkali metals in straw, due to the generation of a refractory aluminosilicate KAlSi2O6and reduction in the release of gaseous KC1.更多还原