煤粉燃烧细颗粒物生成、演化与沉积特性实验研究

发布时间：2018-03-27 17:17

本文选题：煤粉燃烧　切入点：细颗粒物排放　出处：《清华大学》2014年博士论文

【摘要】：和石油天然气等化石燃料不同，煤炭特有的无机矿物质成分使得其在燃烧气化利用过程中面临更多挑战。如在煤粉燃烧过程中，部分无机矿物质通过蒸发-凝结-团聚等机制形成细颗粒物，污染大气环境；其余绝大部分矿物质成分通过破碎-熔融脱落-聚并等机制形成飞灰粗颗粒，在炉膛内部和尾部烟道中沉积在对流换热器管路表面，恶化传热特性进而降低电厂效率。因此，研究煤粉燃烧过程中无机矿物质的演化特性十分重要。本文基于这样的背景研究了我国几种典型动力用煤燃烧过程中细颗粒物的生成、演化与沉积特性。首先，通过高温一维炉细颗粒物采样试验研究了不同煤阶煤种细颗粒物排放特性的差别。结果显示低阶高钠准东煤生成的超细颗粒数量明显多于高阶烟煤。进一步的形貌和成分分析表明低阶煤中富含的水溶态和离子可交换态矿物成分是亚微米颗粒的主要来源，而内在矿物质通过还原反应形成的易挥发亚氧化物/金属单质是高阶烟煤亚微米颗粒的主要来源。采用特征时间分析的方法探讨了易挥发矿物蒸气在炉内的演化特性，其中矿物蒸气均相成核/异相凝结作用贯穿炉内燃烧全过程，而微米级颗粒间的碰撞-聚并作用概率很低。低阶准东煤燃烧过程中金属蒸气向颗粒表面异相沉积主要受扩散机制控制，而高阶神华烟则更多受到表面化学反应的影响使得矿物蒸气更容易在微米级颗粒表面沉积。其次，本文基于一维炉积灰试验探讨了积灰形成机理。试验结果表明准东煤积灰倾向性明显高于其它燃料，甚至高于草本生物质燃料。微观形貌观察显示准东煤粘性积灰内层生成量较多，而且很多飞灰粗颗粒表面沾有大量粘性细颗粒物，这些现象都表明准东煤积灰具有较高的粘结特性。离散动力学计算表明积灰内层大大增加了飞灰粗颗粒与积灰管壁碰撞过程中的能量耗散，，进而增强了积灰管的捕集效率。此外，输运理论定量计算显示高钠准东煤的积灰内层形成量比高阶神华烟煤要多，因此准东煤飞灰更容易被积灰管捕集形成更高的积灰倾向性。最后，比较研究了富氧和常规两种不同燃烧气氛下细颗粒物排放特性和积灰特性的差异。一维炉试验结果表明真实烟气循环富氧条件下炉内细颗粒物浓度明显高于常规燃烧，而理论计算显示富氧条件下单位质量灰分生成的亚微米颗粒反而略低于常规工况，因此烟气循环携带的细颗粒物才是浓度增加的主要来源。此外高流速引起的高撞击效率是常规条件下积灰速率高于富氧条件的主要原因。
[Abstract]:Unlike fossil fuels such as oil and natural gas, coal's unique inorganic minerals make it more challenging in the process of combustion and gasification, such as in pulverized coal combustion. Some inorganic minerals form fine particles by evaporation-condensation agglomeration, which pollute the atmospheric environment, and most of the other minerals form fly ash coarse particles through the mechanism of crushing, melting, shedding and coalescence. Deposition on the surface of the convective heat exchanger pipe in the furnace and the tail flue, which deteriorates the heat transfer characteristics and reduces the efficiency of the power plant. It is very important to study the evolution characteristics of inorganic minerals during pulverized coal combustion. Based on this background, the generation, evolution and deposition characteristics of fine particles in the combustion process of several typical power coal in China are studied in this paper. First, The difference of emission characteristics of fine particles from different rank coal was studied by sampling test of fine particles in one dimensional furnace at high temperature. The results showed that the quantity of ultrafine particles produced by low-rank high-sodium coal was obviously higher than that of high-order bituminous coal, and the further shape of coal was more than that of high-order bituminous coal. The analysis of appearance and composition shows that the water-soluble and ion-exchangeable mineral components in low-rank coal are the main sources of submicron particles. The main source of high-order bituminous coal submicron particles is the volatile oxide / metal single mass formed by the reduction reaction of internal minerals. The evolution characteristics of volatile mineral vapor in the furnace are discussed by the method of characteristic time analysis. Among them, the homogeneous nucleation / heterogeneous condensation of mineral vapor runs through the whole process of combustion in the furnace. However, the probability of collision-aggregation interaction between micron particles is very low. The heterogeneous deposition of metal vapor to particle surface is mainly controlled by diffusion mechanism. Higher order Shenhua smoke is more affected by surface chemical reaction, which makes mineral vapor deposit on micron particle surface more easily. Secondly, based on one-dimensional furnace ash deposition test, the formation mechanism of ash deposit is discussed, and the results show that the tendency of coal ash deposition in Jindong coal is obviously higher than that of other fuels. Even higher than herbaceous biomass fuel, the microscopic observation showed that the amount of cohesive ash deposits in the inner layer of Jindong coal was more, and many coarse particles of fly ash had a large amount of fine particles. All these phenomena indicate that the ash deposit of Jindong coal has a high bonding property. The discrete dynamic calculation shows that the inner layer of ash deposit greatly increases the energy dissipation during the collision between coarse particles of fly ash and the wall of ash deposit pipe. In addition, the transport theory quantitative calculation shows that the formation amount of ash deposit inner layer of high sodium Zhundong coal is more than that of high order Shenhua bituminous coal, so the fly ash of Jindong coal is easier to be captured by ash deposit tube to form a higher tendency of ash accumulation. Finally, the characteristics of fine particulate matter emission and ash deposition in oxygen-enriched and conventional combustion atmospheres are compared. The results of one-dimensional furnace test show that the concentration of fine particulate matter in the furnace is obviously higher than that in conventional combustion under the condition of real flue gas circulation and oxygen-enrichment. The theoretical calculation shows that the sub-micron particles produced by ash per unit mass under oxygen-enriched conditions are slightly lower than those under normal conditions. In addition, the high impact efficiency caused by high velocity of flow is the main reason that the ash deposition rate is higher than that under the condition of oxygen enrichment.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM621.2

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