| At present, coal-fired power plant in China’s power industry still occupy a dominant position. With the use of lignite, high calcium fly ash emissions in China were obvious increasing in recent years, which also caused a series of environmental pollution. At this stage the use of fly ash (especially high calcium fly ash) as additives for absorbent in flue gas desulfurization to control SO2emission in coal-fired power plant is an important content of the comprehensive control of environment pollution in our country. Because of the high calcium fly ash contains a certain amount of water hardness minerals, thus it not only has the characteristics of volcanic ash in low calcium fly ash, but also has certain self hardening. Because of its special self-hardening characteristics, it is more used to as a special mineral admixtures for building structure and highway backfill material. In this paper, first, field emission scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffraction were used to carry out a preliminary study on the nature of the high calcium fly ash of Xiaolongtan power plant in Yunnan. At same time, the chemical composition and phase transformation of high calcium ash were analyzed to reveal the evolutionary mechanisms of a variety of calcium-based composition, to provide theoretical references for the rational use of high calcium fly ash.High calcium fly ash was defined by most domestic researchers according to the CaO content in the fly ash. If CaO content in the fly ash was less than10%, called the low calcium fly ash, known as the ordinary fly ash; If CaO content in the fly ash is more than10%, called high calcium fly ash. Because of the high calcium fly ash has a higher vitreous content than the ordinary fly ash, and contains a small amount of clinker minerals, so the activity of high calcium fly ash is higher than the ordinary fly ash. The properties of the ordinary fly ash as additives in desulfurization sorbent were studied and analyzed by some research institutions, but it was not universal in commercial operation. The high calcium fly ash has a special volcanic ash activity. It was suited to desulphurization additive, but the investigation about that was not too much. The phase composition of high calcium fly ash was analyzed in this paper. It was known that there were more calcium compound in the high calcium fly ash, combination of CaO with a variety of minerals crystalline phase, trace amounts of CaCO3, Ca(OH)2and the combination of silicate, even CaCl also existed in the high-calcium fly ash. In addition, there was a relatively large difference in the external micro-structure between high calcium fly ash and ordinary fly ash.Secondly, parameters in CaO slaking process and parameters in the high calcium fly ash/Ca(OH)2hydration conditions were studied and analyzed in the thesis. First, specific surface area and particles characteristics of pure CaO slaking product were measured and analyzed in different stirring rate. Then the optimal stirring rate under the experimental conditions was obtained. Pure CaO slaking product and high calcium fly ash were used to make hydration test under the condition of four factors and four levels. The experimental result showed that high calcium fly ash/Ca(OH)2hydration was affected by specific surface area, pore volume and pore diameter of hydration product. The extent of the characteristic impact of these parameters in hydration product was hydration time, mass ratio of high calcium fly ash/Ca(OH)2, water-solid ratio, stirring intensity in turn. And the optimizing parameters were obtained in the experimental condition. Finally, the desulfurization reaction mechanism was theoretically analyzed in mathematic model. |
PDF Full Text Request