The Melting Characteristics During Co-combustion Of Coal With Different Sludge

With the development of the national economy, the disposal of sewage sludge is becoming a pressing problem. As the incineration of sludge has the advantages of reduction, harmless and recycling, it attracts more and more attention. The sludge has high water content and low calorific value, it is hard to be incinerated stably, so generally it is burned with coal or other auxiliary fuel. However, the sludge has a high ash content and its composition is complicated, which may cause serious slagging problems and threat to the safety and normal operation of the boiler. To solve the problems above, a kind of bituminous coal used in coalfired power plant, 3 kinds of different sludge(2 kinds of industrial sludge and one kind of municipal sludge) were used to study the melting and mineral transformation characteristics of the co-combustion of coal with different sludge.When the sludge is added to the coal, the ash fusion temperatures of the mixed samples show a non-linear relationship with the proportion of sludge, when the coal is mixed with industrial sludge, with the increase of mixed ratio, the ash fusion temperature increased first and then decreased; when the coal is mixed with municipal sludge, the ash fusion temperature drop slightly at 10 wt.% of municipal sludge and no significant change has been observed. The results of the mineral analysis show that the eutectic of iron composition, anorthite and diopside can decrease the ash fusion point of the samples, and the monomer iron oxide, merwinite, spinel and mullite can improve the ash fusion point of the samples. The thermo analysis of the samples shows that the minerals which cause the weight loss during the heating process include kaolinite, aliphatic sulfur, pyrite, ferric sulfate, calcite and calcium sulfate, when the coal is blended with industrial sludge the experimental value of heat absorption curves are obviously higher than the calculated value curves, which indicated obvious lowtemperature eutectic phenomenon; when the coal is mixed with municipal sludge the experimental value of heat absorption curves showed no obvious difference with the calculated value of heat absorption curves. The micromorphology of the samples changes much when the sludge is added to the coal.The method of adding additives to the blended samples of coal and sludge can effectively promote the melting characteristics of the samples, the reason that adding kaolinite can improve the ash fusion temperature is that the disappearance of dioposide and the generation of mullite; and when the blended samples were added with calcite, the ash fusion temperature goes down first and then goes up with the increase of calcite, the main reason for decreasing of ash fusion temperature at first is that the wallastonite and anorthite can form eutectic, and the reason for increasing of ash fusion temperature is that the generation of large amount of gehlenite.