固硫灰渣水化浆体中钙矾石稳定性

流化床燃煤固硫灰渣(简称固硫灰渣)含有大量烧粘土质矿物,还含有较多f-CaO和无水石膏,因此固硫灰渣水化浆体中含有一定量的钙矾石.用X射线衍射和化学分析方法研究钙矾石含量随水化龄期的变化规律,并以此反映其稳定性.结果显示:在标准养护条件下,钙矾石含量从1 d至28 d水化龄期呈逐渐增长趋势,但在28 d龄期后则显著减少.研究表明固硫灰渣水化浆体中的钙矾石是不稳定的,在一定龄期后会出现明显分解现象.     

流化床燃煤固硫灰渣自硬机理的研究

流化床燃煤固硫灰渣是一种比较特殊的燃煤灰渣,主要特征之一为其明显自硬性,这种特性对其资源化利用有比较大的影响.通过对来源不同的7种流化床灰渣自硬性进行研究,结果显示,经固硫的灰渣具有明显的自硬性,而未经固硫的灰渣则自硬性不明显.采用化学方法确定了固硫灰渣中存在有一定量的C2S和C3A.结果显示,除可溶解的硬石膏与活性Al2O3、游离CaO反应生成钙矾石外,固硫灰渣中的C2S和C3A是其具有自硬性的主要来源.     

流化床燃煤固硫灰渣微观结构研究

分别用X射线衍射、红外光谱和扫描电镜研究固硫灰渣矿物组成、硅酸盐阴离子聚合度和颗粒形貌。并与煤粉炉粉煤灰进行对比。结果表明：与粉煤灰不同，固硫灰渣基本不舍莫来石；固硫灰渣[SiO4]和[AlO6]聚合度均低于粉煤灰；固硫灰渣的颗粒形貌极其不规则且疏松多孔。研究发现，固硫剂和生成温度对固硫灰渣微观结构影响很大。     

蒸压养护下粉煤灰和固硫渣性能差异研究

固硫渣与粉煤灰成分和性能有所不同,因此固硫渣加气混凝土与粉煤灰加气混凝土性能可能存在一定差异。调节粉煤灰和固硫渣比例制备蒸压加气混凝土,研究其强度、干密度和干缩等性能,并用XRD研究其水化矿物组成。结果显示,由粉煤灰和固硫灰渣混合而成的燃煤灰渣加气混凝土蒸压产物中有托贝莫来石生成;固硫渣加气混凝土的干密度、抗压强度均高于粉煤灰加气混凝土,且前者干缩性能优于后者。研究表明,用固硫渣代替粉煤灰制作蒸压加气混凝土是可行的。     

流化床燃煤固硫灰渣的特性

流化床燃煤固硫灰渣(固硫灰渣)是一类特殊的燃煤灰渣.用11种来源不同的固硫灰渣,研究了需水性、自硬性和膨胀性.结果显示:同硫灰渣因为颗粒表面疏松多孔,具有非常强的吸水性,标准稠度需水量达到粉煤灰的2倍;固硫灰和固硫渣具有明显的自硬性,28d净浆抗压强度可达到10MPa;固硫灰渣具有明显膨胀特性,这种不良的安定性主要来自固硫组分.     

固硫灰渣的活性评定与现行标准的适应性研究

循环流化床固硫灰渣在矿物组成、化学成分等方面与煤粉炉粉煤灰存在显著区别,两者活性来源也不相同。现行标准中的火山灰活性评定方法主要针对的是低硫火山灰,而固硫灰渣中硫含量较高(以SO3计可高达10%以上),现行标准是否适合用来评价固硫灰渣活性存在疑问。对固硫灰渣与现行标准中的两种火山灰活性评定方法的适应性进行了研究,结果显示:"水泥胶砂28 d抗压强度比试验"不适合用来评定硫含量较高的火山灰质材料的活性;准确测定固硫灰渣的活性需改进现行试验方法。     

固硫灰渣的微观结构与火山灰反应特性

用X射线衍射、红外光谱和扫描电镜研究流化床燃煤固硫灰渣(简称固硫灰渣)的微观结构.用化学反应动力学方法研究固硫灰渣的火山灰反应特性,并与粉煤灰进行对比.阐述了固硫灰渣的微观结构与其火山灰反应特性之间的关系.结果表明:固硫灰渣与粉煤灰矿物组成差异较大,主要体现在它不含莫来石.固硫灰渣中[SiO4]和[AlO6]聚合度均低于粉煤灰的.固硫灰渣颗粒表面比粉煤灰的疏松.固硫灰渣的火山灰反应速率常数明显高于粉煤灰的,而表观活化能相反.固硫灰渣火山灰反应活性明显高于粉煤灰的,反应阻力也较小,这是由其微观结构所决定的.     

燃煤灰渣中无定形物质差异研究

粉煤灰、沸腾炉渣和固硫灰渣中的无定形物质性质有明显差异。分别用扫描电镜和化学分析方法研究无定形物质微观形态和含量，并用“28d抗压强度比方法”反映其对燃煤灰渣一普通硅酸盐水泥系统强度贡献。结果表明：粉煤灰中无定形物质结构比较规则致密，而沸腾炉渣和固硫灰渣则比较疏松且不规则；沸腾炉渣中无定形物质含量明显高于粉煤灰，由于含有一定量结晶矿物，固硫灰渣中无定形物质含量低于沸腾炉渣；沸腾炉渣和固硫灰渣中无定形物质活性明显高于粉煤灰。     

流化床燃煤固硫灰渣水硬性机理研究

经固硫的流化床燃煤灰渣有明显的早期水硬性,甚至可在与水混合几小时后即凝结硬化,而未经固硫的灰渣则不明显。本文采用X射线衍射、红外光谱和化学方法对固硫灰渣早期水硬性机理进行研究,结果表明:固硫灰渣基本不含水泥熟料成分,矿物主要以无定形态存在;固硫灰渣中[SiO4]及[AlO6]的聚合程度均低于未经固硫的流化床灰渣及粉煤灰;进一步的化学测定结果证实,固硫灰渣早期水硬性主要来源于一定数量水化性能较快的无定形矿物组分。     

固硫灰渣的基本特性及其作水泥混合材的关键问题研究进展

固硫灰渣是循环流化床燃煤技术的主要副产物,如何高效、清洁地利用这一类固体废弃物是一个亟待解决的问题。本文根据近年来国内外对固硫灰渣的研究成果,从化学组成、矿物组成、微观结构、典型特性等方面综述了固硫灰渣的主要特征。相较于粉煤灰等其他燃煤副产物,固硫灰渣中存在游离氧化钙、硫酸钙和无定形铝硅酸盐物质,且颗粒疏松多孔,这导致其具有明显的火山灰活性、自硬性和水化膨胀性等特性。同时本文分析了固硫灰渣作为水泥混合材使用时需要注意的几个关键问题。结果表明,固硫灰渣特殊的组成、微结构和性质导致其作为水泥混合材使用时,必须考虑使用合适的激发剂提高灰渣活性,调整养护工艺、用水量等条件提高制品的安定性,并以添加减水剂等方式控制水泥制浆中的需水量,提高水泥石强度。这为有效实现固硫灰渣的建材资源化利用提供一定指导。     

流化床燃煤固硫灰渣体积稳定性及影响因素研究

采用检测固硫灰渣净浆试件线性膨胀率方法表征其体积稳定性,并对影响因素进行分析。结果显示:固硫灰渣净浆试件的线性膨胀率在14～28d龄期前迅速增加,而后增长幅度明显变缓;固硫灰的膨胀特性明显低于固硫渣;固硫灰渣体积稳定性主要决定于游离氧化钙(CaO)含量而非三氧化硫(SO3)含量。     

流化床燃煤固硫灰渣膨胀控制因素研究

分别用线性膨胀率和XRD研究固硫灰渣净浆试件的膨胀特性和固硫灰渣水化产物随龄期变化趋势,并在结合二者试验结果的基础上对膨胀控制因素进行探讨。结果显示:固硫灰渣净浆试件的线性膨胀率在14～28 d前增加迅速,而后趋于平缓。试验表明,固硫灰渣的膨胀特性可分为两个阶段:14～28 d前主要受钙矾石量所控制,而随后龄期则主要受二水石膏量所控制。     

红外光谱分析淮南煤灰中矿物组成

选取淮南矿区HN115与HN119两种煤样,在氧化性气氛下,制成815℃煤灰。利用红外光谱研究了其矿物质组成以及煤中添加不同比例助熔剂CA后矿物组成的变化。结果表明:淮南煤灰中,矿物质组成为石英、硬石膏、方解石、高岭土和赤铁矿,其中硬石膏和方解石含量较低。煤中添加助熔剂CA后,煤灰中硬石膏含量增加,并且随着助熔剂CA量的不断增加,方解石含量在不断减少,硬石膏含量在不断增加。     

Calcium sulphide in FBC boilers and its fate using liquid water reactivation

CaSO₄ and CaS are the only sulphur compounds found in solid residues from the sulphation process in FBC boilers. Early results indicated very high levels of CaS in ashes from small-scale FBC pilot plant combustors. However, these results were due to the presence of high levels of char carbon in standpipes and cyclones. In commercial-scale FBC boilers, CaS concentrations are normally less than 0.1% although levels of up to 0.6% are seen in some ashes. Sometimes elevated CaS concentrations are found in deposits in CFBC boilers firing high levels of petroleum coke (although this is unusual), and in ashes from stripper coolers. In both cases, this can be minimized by proper design. CaS can also be deliberately introduced into FBC boilers with the char from a topping cycle gasifier. Test work using hydration in a similar manner to a reactivation strategy has been shown to be ineffective for sulphide destruction when used directly with char from a topping cycle gasifier. Instead it is recommended that reactivation be used on ashes from the CFBC boiler receiving the sulphided char residues. This guarantees overall high sorbent utilization and the effective elimination of sulphides in the ashes finally discharged from the CFBC boiler.     

Speciation of mercury in fly ashes by temperature programmed decomposition

Mercury (Hg) is a toxic trace element which is emitted mostly in gas phase during coal combustion, although some Hg compounds may be retained in the fly ashes depending on the characteristics of the ashes and process conditions. To improve the retention of Hg in the fly ashes a good knowledge of the capture mechanism and Hg species present in the fly ashes is essential. The temperature programmed decomposition technique was chosen to identify the Hg species present in fly ashes obtained from two Pulverized Coal Combustion (PCC) plants and a Fluidized Bed Combustion (FBC) plant. The fly ashes were then used as Hg sorbents in a simulated flue gas of coal combustion and gasification. The Hg compounds found in the fly ash from the FBC plant after elemental mercury retention were mainly HgCl₂ and HgSO₄. The Hg species present in the two fly ashes from the two PCC plants were HgCl₂ and Hg⁰. The Hg species formed in the coal gasification atmosphere was HgS for all three fly ashes. The only Hg compound identified in the fly ashes after the retention of mercury chloride was HgCl₂.     

Sintering characteristics of low-rank coal ashes

The electrical resistance and compressive strength were measured to gain a better understanding of the sintering characteristics of low-rank coal ashes involved in deposit formation in combustion systems. Low-rank coal ashes were prepared by the standard ASTM ashing procedures at 750°C and then separated into three different particle size fractions. The sinter point determined by the electrical resistance method decreased with decreasing particle size at three different particle size fractions of each coal ash. The compressive strength lest was made as a function of temperature in the range 750–950°C. At a given sintering temperature, strength of the sintered ash was inversely proportional to particle size. For any given particle size of each coal ash, the strength increased with increasing sintering temperature. X-ray diffraction of the sintered coal ashes showed that, as sintering temperature increased, there was an inverse relationship between sinter strength and the amount of anhydrite in the sintered ash, and a direct relationship between strength and the amount of hauyne.