Processing Property Of Sludge As Alternative Fuel For Cement Industry

Sludge generated during wastewater treatment has been seen as a problematic but unavoidable by-product. The disposal of sludge is becoming acute progressively owing to the surging production and the increasing restrictive policies concerning re-use. If not handled properly, serious secondary pollution will form for the large capacity, instability, corruption, odor, toxicity and harm of sludge. Choosing sludge as research object, this paper systematically studies the sludge drying process. Based on the comparative study between physicochemical properties of both the coal used for cement industry and the dried sludge and their combustion characteristics, this paper, also in accordance with the requirements of cement industry for fuel, investigates a reasonable process for sludge used as a kind of alternative fuel which provides theory basis for sludge used as alternative fuel in cement industry.The drying process of sludge was studied by measuring the moisture content and observing the morphology and the volume of sludge. The higher the drying temperature and the lower the sludge thickness, the better the drying characteristics of sludge can be obtained. There are no significant differences in drying characteristics between different types of sludge. As some organic components volatilize during the drying process, the drying temperature should be reduced greatly, which is recommended below 100℃. In addition, due to the huge volume contraction of sludge, extending drying time and improving stirring speed can effectively prevent sludge from agglomeration and compaction.Analysis on odor components of sludge by gas chromatography-mass spectrometry shows that there is a great difference between the odor components generated during the drying process because sludge properties vary in different regions. Gas chromatography-mass spectrometry is an effective method to analyze odor components of sludge.Physicochemical properties of coal and dried sludge were studied by some modern testing methods. Fineness and liquidity of dried sludge can reach the requirements of cement industry by controlling the sludge drying process reasonably. Proximate analysis and elemental analysis results have a big gap between dried sludge and coal, the net calorific value of dried sludge is about 8MJ to 12MJ. The coal and the dried sludge vary widely in the proximate analysis and elemental analysis results. Mineral composition of sludge requires further study. Chemical composition of sludge ash and coal ash is similar. Sludge can be used as alternative fuel for cement industry from this aspect.Simultaneous thermogravimetric analysis was applied to study the combustion characteristics of coal and dried sludge. According to the experimental curves obtained from thermal analysis, combustion processes were analyzed. Assuming different reaction models, the mechanism and kinetics of the combustion reaction were discussed by Coats-Redfern method. The combustion of dried sludge has the advantage over coal in some aspects--its combustion is mainly in the low temperature stage, besides, its ignition temperature and activation energy are also low. Thus, sludge can partly replace coal used as cement industry fuel.According to the requirements of cement industry for fuel, dried sludge can be used as alternative fuel for cement industry. When dried sludge fuel is used in cement industry, the moisture content is suggested from 10% to 30% and mixing ratio should not be too high. Providing the same heat, actual flue gas volume of dried sludge is higher than coal, but amount of CO2 is almost equal to each other.