| Sewage sludge hazare-free treatment and recycling has been a topic issue in recent years. Sludge treatment for synthetic fuel was regarded as an effective disposal technology of pollution eliminating, volume reducing and energy reusing to deal with the sludge problems. After analyzing the characteristic of sludge sampled from a typical middle scale sewage treatment plant in Three Gorges reservoir area and the situation in sludge treatment and disposal, some ideals,which synthesizing the sludge to fuel and the ash used as building material,were put forward. Some experiments researching on sludge synthetic fuel combustion characteristic,ratio and technics were conducted. The main conclusions were drawn as follows.①The sample dry sludge was with high volatile matter and low fixed carbon characteristic, which the volatile matter was 46.45%, the ash was 49.00%, fixed carbon was 1.56% and water was 2.99%. The characteristic of coal used in the experiment was with high fixed carbon and low ash. The energy in sludge and coal were 9373 kJ/kg and 26440 kJ/kg respectively. The energy in sludge was about 35% of that of coal,it could be used as fuel.②Experiments on combustion characteristic of sewage excess sludge and the mixtures with coal of different mixing ratio by Thermo Gravimetry Analysis (TGA) were carried out. Some parameters, such as the process of burning, ignition temperature, burning-out characteristic, complex combustion characteristic index, dynamics characteristic and so on were analyzed. The influencing factors of co-combustion characteristic with different mixing ratio were researched, and the dynamics equation of co-combustion was solved. The result showed that during the burning process of the mixed samples, the coal and the sludge don't have effect on each other, preserving their own combustion characteristic. The ignition temperature of volatile matter is lower than that of the fixed carbon, so compared with the coal burning separately, the mixed samples reach their ignition and burn-out temperature earlier but violence degree and the complex combustion performance decreased. In the process of the mixed sample burning, the sludge content in the mixed samples is low (about 20% ~30%), the complex characteristics, for example the ignition and burn-out temperature, are prior to those of the two matters burning separately. Except for that, the decreasing rates of the complex combustion performance are 6.42%~7.17%. The co-combustion of the samples mixed with sludge and coal obeyed combustion dynamics rules. It can be described with different first-order reaction equations in different temperature ranges.③The sludge synthetic fuel was made in the special die and the prescription was ensured with orthogonal design. Make sure the significance of the influencing factors in the fuel experiment, check out the optimal sludge synthetic fuel significance. During the influencing factors of strength, the order was pressure,water content and the diameter. The optimal significance of sludge synthetic fuel was like that, in which the pressure is 30 MPa, the content of water is 15%, the mixing ratio of sludge and coal is 20%, the diameter of it is 25mm, the content of clay is 5% and the content of calcium hydroxide is 5%. The heat value of this kind of sludge synthetic fuel is 19117 kJ/kg and the ignition temperature is 380℃, which satisfied the heat value of common coal fuel.④After comparing the cost of sludge synthetic fuel and the one of landfill, the results showed that: the technology of sludge synthetic fuel reduced the cost of excess sludge treatment about 74%, it was with a good economic benefit. Besides, the technology of sludge synthetic fuel reduced secondary pollution of harmful substances in sludge and utilized the energy in the sludge effectively. It was with a good environmental benefit and social benefit.
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