Experimental Study Of Molten Ash Lignite Mix

Owing to its location of plateau, the amount of lignite reserves is abundant in Yunnan. The lignite has the characteristics of low calorific value, high moisture and high volatiles. The lignite ash in Yunnan posses a low melting temperature, which can cause slagging on the heating surface of furnace in boiler and influence the economy and safety of boiler operation. So the study for fusion characteristics of lignite ash plays a significant role.The lignite ash from Xiaolongtan (XLT ash) and Xianfeng (XF ash) were selected as an investigating object.TGA, XRD and ash fusion temperature determination meter were used to research the fusibility of single ash. It indicated that there was a difference in fusibility of two ashes due to the difference between mineral composition and thermal activity of minerals in ash samples. In order to further explore the factors which impact the fusibility of lignite ash, some experiments were carried out in different ways. For example, XF ash was mixed with XLT ash in different proportions; Alkaline metal oxides (CaO) and residual carbon were added into these samples in different proportions. And these samples were put in the different reaction atmosphere. The experimental results showed that:(1) With the increasing of proportion of XF ash in mixed ash, mineral composition and phase transition have been changed greatly. And the fusion temperature of samples was increasing gradually;(2) when the alkaline metal oxides (CaO) was added into these two samples with different proportion, the fusion temperature of XLT ash firstly tend to increase with adding of alkaline metal oxides, and then decrease, and increase again later. When the adding content (part) of CaO increases to6%, the fusion temperature of XLT ash reaches to the maximum. In addition, the fusion temperature of XF ash firstly tends to increase with the adding of CaO. That result was consistent with the study carried out based on the comparison with different SiO2/Al2O3;(3) Two samples were put in different reaction atmosphere. The ash fusion temperature which is measured in oxidizing atmosphere is50℃higher than that in reducing atmosphere;(4)when different proportions of residual carbon were added into these two samples, the ash fusion temperature of these two samples tend to increase firstly, and then decrease and increase again slowly. The ash fusion temperature of these two samples reached to the maximum respectively when adding ratio of residual carbon for XLT ash comes to2%and4%for XF.To find out the experimental factors which influence the ash fusion temperature of XLT lignite ash, the softwares of orthogonal design and response surface optimization were used to analyze the factors which influence the ash fusion temperature of ash. The result showed:(1) A orthogonal table based on three factors and two levels was created, which is used to calculate the related factors by orthogonal software. The calculation result showed that the effect caused by residual carbon on the ash fusion temperature of lignite ash was less than the amount of adding of XF ash and CaO, so this factor can be ignored. Therefore, an optimal experimental condition can be obtained based on this calculation, which was that the amount of adding of XF ash was40%and CaO was6%. At this situation, the ash fusion temperature of mixed ash is1184℃.(2) orthogonal calculation was carried out by response surface optimization which is based on three factors and three level. A result can be inferred from response surface chart, which is the amount of adding of XF ash possess a remarkably influence on the ash fusion temperature. The optimal experimental condition can be obtained based on this calculation, which is the amount of adding of XF ash was40%, CaO was6%and residual coal was6%. At this situation, the fusion temperature of mixed ash was1178℃. According to calculation, we can conclude that these two ways are consistent with the factors related to the influence on the ash fusion temperature.In order to further explore the impact of ash composition on the fusion temperature, the35data of lignite and mixed ash was selected which can be more close to the actual fusion temperature of lignite ash. Software called SPSS was used to carry out the analysis on statistic regression. Based on this analysis, a polynomial regression model which was related to the composition and fusiontemperature of ash can be obtained. And then the composition of XLT and XF lignite ash were put in the model to do verification. Finally a polynomial equation between composition of lignite ash and fusion temperature is obtained.