| Wstewater sludge (sludge hereafter) generated during wastewater treatment is a special mixture with complex compositions. Sludge is essentially the aggregation of the microorganism zooglea and absorbed organic and inorganic matter. Aside from large amounts of water, numerous hazardous substances, including refractory organics, parasites, pathogenic microorganisms, heavy metals, and volatile matter are present in sludge. It has a high content of organic substances, which are easy to corrupt and stink. If the sludge is discharged to the environment without proper treatment and disposal, the water, soil and air will be seriously polluted, and the local ecological environment will be destroyed. Coal water slurry (CWS) is a clean fuel which can substitute petroleum, and it is also the necessary supply material for texaco gasification technology. In the study, the sludge was taken as carbon-containing substance and blended with coal powder to synergistically prepare slurry fuel, which can be used either as boiler fuel or as gasification material. The environmental problems caused by sludge discharge are solved, and at the same time the benefits of sludge recycling are achieved.Sludge were used to prepare coal sludge slurry (CSS) or petroleum coke sludge slurry (PCSS) synergistically with coal or petroleum coke. The slurrying concentration, rheology, thixotropy and stability of these slurry samples were studied systemly and deeply. After adding sludge into conventional CWS or PCSS, the slurry viscosity increased evidently, and a more sludge addition led to a more reduce in the maximum slurrying concentration (SCmax). With increasing the sludge mixing proportion, the CSSs or PCSSs showed shtronger "shear-thinning" pseudoplastic behavior and increasing thixotropy. The stability of the slurry was improved after adding sludge. Adding more sludge into slurry resulted in lower water seperation ratio (WSR) and better stability.Various pretreatment methods including alkali, ultrasonic and combined alkali-ultrasonic treatment was used to modify the sludge. The sludge flocs were hydrolyzed and the refractory macromolecular organic materials were disrupted into soluble ones to a certain extent, then the interstitial and cellular water in the sludge was released and water holding capacity of the sludge was decreased. Therefore, the co-slurrying ability of sludge and coal was improved greatly. The optimum dosage of CaO for improving the co-slurrying ability was10%～15%of the raw sludge. The specific energy input should be not more than40kJ/g dry sludge when the ultrasonic was used to improve the co-slurrying ability. Combined alkali-ultrasonic method had a more significant effect in improving the co-slurrying ability of sludge and coal than solo-alkali and solo-ultrasonic. The main objectives of CSS technology are to dispose of sludge at a large-scale level and to solve environmental problems caused by sludge. The slurryability of sludge was improved significantly by pretreatment, and thus, more environmental and economic benefits could be realized.Dynamics of ultrasonic cavitation bubbles was computed using Matlab. Results showed that with increasing ultrasonic pressure, the resonant initial radius of the bubble decreased, the maximum radius that bubble reached increased, and the maximum impact-velocity of the bubble wall increased. With increasing the ultrasonic frequency, the maxium radius that bubble reached decreased, and the maximum impact-velocity of the bubble wall decreased. It was indicated that higher ultrasonic pressure and lower ultrasonic frequency resulted in more significant cavitation, i.e., more strong impacting action due to bubble collapsing. After pretreated with ultrasonic of higher pressure or lower frequency, the sludge can easily be made into CSSs of lower viscosity. Experimental results indicated that higher pressure or lower frequency increased the improving effects of ultrasonic on the slurryability of the sludge. The experimental results were consistent with dynamics computations.Highly concentrated organic wastewater, sludge, and petroleum coke were mixed to prepare petroleum coke slurry (PCS). The sludge provided the necessary microorganisms, and the organic wastewater provided the carbon and nitrogen sources for fermentation. During the storage of this slurry, biogas was generated because of fermentation. Biogas bubbles bonded with petroleum coke particles and formed gas-solid combos. The lifting and steric hindrance effects of biogas effectively prevented petroleum coke particles from settling and coagulating, thus enhancing PCS storage stability. Structure strength theoretical model of the slurry system was established. Results showed that before storage, the five sludge-containing PCS samples had similar energy dissipation Wm at approximately2.31×105J/kg to2.38×105J/kg. After7of storage, the Wm of the slurries made from high-concentration starch wastewater (18000mg/L COD) increased to2.77×105J/kg. The increased structure strength are contributive to the improvement of slurry stability.Industrial wasteliquid was mixed with coal to prepare coal slurry fuel, and pilot-scale combustion test of the coal slurry fuel was performed. The flame temperature of the coal-wasteliquid-slurry (CWLS) was higher than that of CWS in the early combustion zone, suggesting that the wasteliquid facilitated the release and ignition of the volatiles. The SO2and NOx emissions of the CWLS were less than those of CWS because of the sulfur and nitrogen retention or catalytic retention effects of the alkaline metal ions in the wasteliquid. However, the alkaline metals in the wasteliquid increased the slagging tendency. Proper decrease in the operating load improved the slagging status of the heating surfaces. Pilot-scale combustion test showed that, it is feasible in slurrying and combustion performances for the slurry fuel prepared by mixing industrial wasteliquid and coal. |
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