The Experimental Study On The Co-Combustion And Co-Pyrolysis Of Sewage Sludge And Coal And Its Incineration Residues Analysis

Sewage sludge has become a serious environmental problem besetting each country. Because of its advantage of energy recovery and resources recycle, combustion (incineration) and pyrolysis has become two promising disposal methods, which have received wide application in the developed countries. With rapid development of the economy, the treatment and disposal of sewage sludge have been paid attention to by more and more peoples in China. Therefore, how to ensure efficient and clean combustion (incineration) of sewage sludge becomes an emergent subject which needs further research.In this dissertation, the pyrolysis of sewage sludge was systematically investigated under different atmospheres of nitrogen and oxygen in the thermogravimetry which can obtain the kinetic parameters by means of a mathematical model, different heating rates being used. The characteristics of samples were detected by calorimeter, proximate analyzer, and the SEM and XRD techniques were used to identify the morphology and mineralogy characteristics of the ash residue respectively.The surface area and dry temperature of sludge have important influence on dry characteristics. As the surface area of sludge increases, the dry pace becomes fast, dry time shortened, at the same time its shrink influence change well too, the overheated dry demonstrates better influence than the saturation one.The thermogravimetric characteristics of sewage sludge were studied under non-isothermal heating in nitrogen media. The thermogracimetric process can be described as a gas-solid reaction equation, da/dτ=AeE/RT(1-α)n.The apparent kinetics parameters of sewage sludge were calculated using Coats-Redfen integral method and they fitted well with experimental values. Mathematical models of sewage sludge were obtained to describe the pyrolytic decomposition kinetics mechanics in different temperature regions.The combustion characteristics indexes at difference heating rates were obtained by experiments of sewage sludge which were carried out in oxidative atmosphere. Two or three different behaviors were observed when comparing the combustion curves with the corresponding pyrolysis curves. Sludge have a combustion curve that is close to the corresponding pyrolysis curve in the 20-330℃temperature range and then show a slower decay at 330-450℃, but at 450-550℃temperature range strong decay at probably as a consequence of the combustion of the car formed. The facts, the higher burnout ratio of sludge in oxidative atmosphere, indicated that the oxygen accelerates the decomposition rate in comparison to the pyrolysis.An experimental investigation on the combustion characteristics of the blends of Lanba's coal and Changsha's sewage sludge is conducted by TG dynamic runs at 20℃/min in the temperature range 20～1200℃. The investigation reveals that the curve of blend basically locates between the curves of sewage sludge and coal. Although the sludge-coal blends show an intermediate behavior between sludge and coal, the sewage sludge and coal have basically maintained their respective devolatilisation characteristic, and devolatilisation releasing process can be considered as total devolatilisation of two parent samples. In a way, the ignition and burnout behaviors of blends samples are better than the parent samples. This showed that the co-combustion of coal and sludge (their blends) were feasible, if the weight percentage of sludge in the blend can be controlled properly. A comprehensive discrimination index S'is being suggested, which reflects the combustion and burn-out properties. The Arrhenius activation energy corresponding to the co-combustion of the blends was evaluated by non-isothermal kinetic analysis.Slagging characteristics of sludge-coal blends is one of the main factors which influence the safety and economy of incineration boiler. The sintered ash of sludge-coal blends, after having been incinerated in a high temperature furnace at different temperatures, have been studied by scanning electron microscopy (SEM), energy dispersive X-ray microanalysis (EDX) and X-ray diffractometry (XRD). The results showed that the melting temperature of the ash decreases with the increase the content of sludge ash in blended ash. At the same time, appearances of blended ash is gradually close the sludge ash, in which in situ visual observation and SEM morphology indicate that fusion occurs for the residue. X-ray diffractometer analysis shows that the crystalline material will presented with the sintered temperature increasing. Energy dispersive X-ray microanalysis results show that the content of atriums and kaliums reduce with the sintered temperature increasing, due to the vaporizations of alkali metal. The fact, there are few content of heavy metals in sewage sludge, indicated that there is significant difference between industrial sludge and sewage sludge. X-ray diffractometer crystallization phase results show that quartz, hematite and calcium silicide form in the residue of sludge-coal blends, whereas mullite will be presented in few residue at higher temperature.