【作者】 韦迎春；

【导师】 钱觉时；

【作者基本信息】 重庆大学 ， 材料科学与工程， 2014， 博士

【摘要】 循环流化床燃煤技术其将燃烧和固硫两个过程合二为一，是一种先进的清洁燃煤技术，但因循环流化床燃煤副产物即循环流化床燃煤固硫灰渣（以下简称固硫灰渣）中含有的固硫产物无水石膏和游离氧化钙会产生明显的体积膨胀等原因，制约了固硫灰渣的处置与利用，导致该技术的推广应用受到严重影响。蒸压养护是一种成熟应用于CaO-SiO2-Al2O3-CaSO4-H2O五元体系硅酸盐制品生产的湿热养护工艺，水化生成强度高、体积稳定的托贝莫来石（C5Si6H4）、C-S-H（B）等水化产物；固硫灰渣的矿物组成属于该五元体系，但该典型五元体系蒸压硅酸盐制品的组成中CaSO4的含量一般不超过5%，CaSO4多为二水石膏和硬石膏，而固硫灰渣中的石膏为Ⅱ型无水石膏，含量在10-30%（以SO3计）。因此，研究蒸压养护是否像典型的CaO-SiO2-Al2O3-CaSO4-H2O五元体系的一样促进固硫灰渣水化、抑制其制品的膨胀、改善固硫灰渣制品的体积稳定性具有理论价值和实际应用需求。通过研究不同蒸压制度对固硫灰渣制品的水化、强度发展和体积稳定性的影响，并与常压养护进行对比。结果显示蒸压养护对固硫灰渣膨胀抑制作用主要取决于蒸压后固硫灰渣水化产物的种类及数量、水化产物的结构和制品的强度；蒸压养护后的固硫灰渣（或掺水泥）水化产物中没有钙矾石生成，生成大量托贝莫来石生成，且水化产物结晶更完善，制品强度是自然条件养护下试件的2~3倍，28d抗压强度达到25MPa。蒸压养护的升温速率、恒温温度和恒温时间、降温速率等参数显著影响制品的水化产物和强度，恒温温度较低、恒温时间过短会导致钙矾石、二水石膏存在。相对于常温养护，合适的蒸压养护能显著抑制固硫灰渣中无水石膏水化反应生产二水石膏、与其他物质反应生成钙矾石而引起的体积膨胀，特别是固硫灰渣制品水养条件下的体积膨胀，经过蒸压养护后的试件水养下的线性膨胀率只有未经蒸压养护试件的10%左右，且蒸压养护后水养时的体积膨胀主要发生在14d前，之后随龄期变化很小，有利于固硫灰渣蒸压制品的后期体积稳定性。对蒸压养护后固硫灰渣制品的XRD分析能确定无水石膏的存在，而SEM未发现柱状形态的无水石膏晶体，EDS面扫描也未显示硫元素分布情况。通过计算化学的方法及分子动力学的理论计算表明每个托贝莫来石晶格能容纳4个SO42-，且得到能量降低更稳定的晶体结构，由此可推断SO42-可进入托贝莫来石的晶体结构，体系前后能量计算结果说明SO42-进入托贝莫来石体系后，降低了体系的能量，使体系更为稳定。结合在早期的石灰-粉煤灰蒸压制品的研究得出的SO42-能促使C-S-H(B)转换为托贝莫来石，并进入托贝莫来石的晶格中的结论，可以推断固硫灰渣蒸压养护条件下无水石膏能促使C-S-H(B)转换为托贝莫来石，并进入托贝莫来石的晶格，形成更为稳定的托贝莫来石，在蒸压养护中固硫灰渣的无水石膏促进托贝莫来石的生成，提高制品的强度和体积稳定性。由于固硫灰渣组成相对复杂，研究选择与固硫灰渣中无水石膏晶体结构相同、性质相似的模拟石膏作为研究对象，并以无水石膏作为对比，研究了蒸压养护对其溶解性、稳定性和水化反应活性影响。结果表明蒸压后的天然硬石膏和模拟石膏的其矿物组成没有改变，但最强衍射峰和高级次衍射线峰高均明显上升，完整性升高，蒸压后硬石膏的稳定性提高，衍射线峰高上升表明晶粒度变大；SEM观察结果显示蒸压养护后的物质出现明显的团聚和颗粒增大现象，是导致溶解度降低的重要原因之一；蒸压使其水化反应生成二水石膏和与其他物质反应生成钙矾石的水化反应能力降低。蒸压养护使无水石膏的稳定性增加、在水中溶解速度降低、生成二水石膏和钙矾石的水化反应能力减弱，利用固硫灰渣来配制蒸压制品时，不能采用完全纯固硫灰渣，保证配合比中足够的钙极其必要。生产固硫灰渣蒸压制品时，合理的工艺参数应为：压制成型时水固比在0.15~0.20，成型压力为25MPa，静停时间为24h，尤其是压制成型时更应适当延长静停时间；压制成型的固硫灰渣蒸压制品的耐久性高于浇注成型，且固硫灰渣蒸压制品的抗冻性和抗碳化能力都是随着固硫灰渣掺量的增加而下降，在固硫灰渣中掺加5%以上的水泥熟料时可以显著改善其耐久性。完成年产3000万标准砖的固硫灰渣蒸压砖生产线的工艺设计和生产调试。采用压制成型，固硫灰（磨细固硫渣）：水泥在80:20~90:10，水固比在0.15~0.20，胶砂比为1:2，成型压力为25MPa，静停时间为24h，蒸压制度为升温2h、恒温6h（恒温压力13大气压）、降温2h，生产的蒸压砖性能符合GB11945-1999《蒸压灰砂砖》和JC239-91《粉煤灰砖》中M25、M10蒸压砖的要求，制品体积稳定性良好。总之，蒸压养护加速了固硫灰渣水化反应，改变水化生成物，生成强度高、体积稳定的托贝莫来石（C5Si6H4）、C-S-H（B）等水化产物；蒸压养护降低固硫灰渣中石膏水化反应活性，残留的无水石膏较为稳定；两者共同作用改善了固硫灰渣蒸压制品的体积稳定性。更多还原

【Abstract】 Circulating fluidized bed coal combustion is an advanced and clean coaltechnology, which combined combustion with sulphur-fix together. However, the factthat the anhydrite and free lime contained in circulating fluidized bed coal by products,namely circulating fluidized bed sulphur-fixed coal ashes(referred to as FBC ashes) hasa significant volume expansion in the process of hydration, limits the disposition andapplication of FBC ashes, thus the popularization and application of this technology areseriously affected. Autoclaved curing is a mature Wet-heat curing technology used inproducing silicate products with CaO-SiO2-Al2O3-CaSO4-H2O system, Hydrationproducts such as tobermorite (C5Si6H4,、C-S-H(B))with high strength and volumestability can be gained. Minerals in FBC ashes belong to theCaO-SiO2-Al2O3-CaSO4-H2O system, but the content of CaSO4in the typical system isusually less than5%, and CaSO4are dihydrate gypsum and anhydrite in the majoritysituations, FBC ashes contains II-CaSO4with a content of10%~30%(Calculated bySO3). In such case, the research on whether autoclaved curing can promote hydration,inhibit expansion and improve products volume stability like the typicalCaO-SiO2-Al2O3-CaSO4-H2O systemis of important theoretical and practical value.By studying the influence of different autoclaved systems on hydration, strengthdevelopment and volume stability of FBC ashes, and comparison with specimens curedin normal atmospheric pressure curing, the results shows that autoclaved curing caninhibit the volume expansion caused by anhydrite in FBC ashes, which mainly dependson the types and quantity of hydration products, the structure of hydration products andthe strength of the products after autoclaved curing；After the autoclaved curing, thestrength of FBC（or FBC ashes-clinker）products is2~3times than that of the specimenscured under natural conditions, with28-daycompressive strength reaching25MPa, andno ettringite forming in hydration products. However, tobermorite does form, andhydrates crystalline better. The parameters such as the heating rate, constant temperature,and time, and cooling rate for autoclaved curing have significant impact on the strengthand hydration products. With lower constant temperature and shorter holding time,ettringite and gypsum will be easily gained. Compared to room temperature curing,autoclaved curing can significantly inhibit volume expansion caused by anhydrite inFBC ashes, especially the volume expansion of FBC ashes products under water curing;The results show that the linear expansion of the specimen under water curing after autoclaved curing is only about10%that of the specimen without autoclaved curing,and the volume expansion under water condition after autoclaved curing occurs mainlybefore14d, with small changes afterwards, which is in favor of the late volume stabilityof FBC ashes autoclaved products.The XRD images of FBC ashes and slags production after autoclaved curing canprove the existence of anhydrite, but columnar crystal of anhydrite can’t be found inSEM images, and the distribution of sulfur can’t be found by EDS either. Thecalculation through chemical method and the theory of molecular dynamics shows thateach tobermorite lattice can accommodate four SO42-, and get more stable crystalstructure with lower energy, which can infer that SO42-can enter the crystal structure oftobermorite, The calculation of energy of system shows that SO42-enter crystal structureof tobermorite，resulting in lowing the energy of system and making the crystal structuremore stable. Combininng the conclusion obtained in the early research of lime-fly ashautoclaved products that SO42-can promote C-S-H (B) convertion into tobermorite andenter tobermorite lattice, it can be inferred that the anhydrite in FBC ashes underautoclaved curing conditions can promote C-S-H (B) convertion into tobermorite andenter tobermorite lattice to form a more stable tobermorite. Therefore, the anhydrites inFBC ashes improve the formation of tobermorite, increase the strength of autoclavedproducts and volume stability.Due to the complex composition of FBC ashes, the present research selectssimulate anhydrite with the crystal structure and properties similar to those of theanhydrite in FBC ashes as the research objects, with comparison with natural anhydrite.The research focuses on the influence of autoclaved curing on the solubility andstability and hydration reactivity of the two kinds of anhydrite.The XRD results ofnatural anhydrite and simulate anhydrite after autoclaved curing show that mineralcomposition of both has no change, but the height of the strongest diffraction peak andthe senior secondary diffraction peak significantly increases after autoclaved curing.They also tend to be complete. The stability of anhydrite after autoclaved curing hasbeen improved; Diffraction peaks rising indicates larger grain size. SEM results showthat the substance after autoclaved curing shows obvious phenomenon of agglomerationand particle increasing, which is one of the important causes of reducing solubility. AndTG results indicate that the thermal stability of anhydrite gets better; autoclaved curingdiminishes hydration capacity, which makes it able to convert to gypsum and react withothers to generate ettringite. And autoclaved curing can also help increase the stability and decrease dissolution rate of anhydrite in water, and hydration capacity of generatinggypsum and ettringite diminishes. When FBC ashes are used to produce autoclavedproducts, pure FBC ashes are not recommended, and enough calcium in the mixproportion is extremely necessary. In the process of producing FBC ashes autoclavedproducts, reasonable parameters should be as follows: water-solid ratio reaches0.15to0.20when pressing, molding pressure is25MPa, and static time is more than24hourswhich should be appropriately extended especially when pressing; the durability ofpressed FBC ashes autoclaved products is higher than that of the casted ones, and frostand carbonation resistance of FBC ashes autoclaved products decline with FBC ashescontent increasing. The durability can be significantly improved when FBC ashes aremixed with more than5%cement clinker. The process design and method of productionof FBC ashes autoclaved brick production line with an annual capacity of30million hasbeen built according to following conditions and parameters: using compressionmolding, the ratio of FBC ashes (pulverized sulfur residue): cement at80:20to90:10,water-solid ratio being0.15to0.20,25MPa molding pressure, and more than24hoursstatic time. The basic properties of autoclaved bricks meet the requirement of M25,M10autoclaved bricks in GB11945-1999"autoclaved lime sand brick" and JC239-91"fly ash bricks", and the stability of production is good enough.In a word, autoclaved curing promotes the hydration reaction of FBC ashes,changes hydration products, and forms tobermorite with high strength and volumestability(C5Si6H4), C-S-H（B）and so on. In addition, autoclaved curing reduces thehydration activity of anhydrite in FBC ashes, the rest anhydrous gypsum is stable. Bothimprove the volume stability of FBC ashes autoclaved products.更多还原