| This article carried out a survey of several advanced domestic cement enterprises and hangzhou surrounding cement enterprises, the results show that advanced domestic cement enterprises in sludge treatment have abundant funds, advanced technology and facilities are more perfect, however around Hangzhou, only a small number of large cement enterprises mixes very little sludge in cement production, some companies don’t accept for the use of sewage sludge in cement production process.We studied the adding calcium material half drying system about the third phase of the sludge of Hangzhou qige sewage treatment plant. The fundamentals of lime treatment for dewatered sludge and main factors which affect the treatment process are introduced in this work. According to the results, higher effective calcium oxide content in lime contributes to faster heating rate of the semi-dry system and better effects of semi-dry process. Sludge at the moisture content of45%-55%after the semi-dry process can be well balled while that at the moisture content of35%can easily get collapsed and has hard surface. Mechanical design parameters are determined by experiments. The optimum stirring time is5-10mins when well stirred and the stirring rate should be slow. Heat preservation jacket is needed for the machine and the water vapour, which is produced by heating, should be exhausted in time.The cement raw meal formula provided by Hangzhou tai mao sheng yuan cement co., LTD was worked as control group. Sludge was mixed with dosage of0.0%,0.5%,1.0%,1.5%,2.5%,3.0%of the weight of control group respectively. The results show that free calcium oxide decreases with the increase of sludge dosage. When the sludge was not been mixed, free calcium oxide content is0.60%, and decreases to0.16%when Sludge dosage is3%. The addition of sludge to cement raw meal to some extent improve the burnability.3days compressive strength of cement clinker with sludge dosage less than1%is essentially the same as the control group. When the sludge dosage is more than1.0%, three days compressive strength decreases. The28days compressive strength increases with the increase of sludge dosage before the dosage is1%, which is the maximum, and then decreases. The clinker with1.5%sludge dosage and the control group roughly have the same28days compressive strength.Fixed modulus (KH=0.90±0.01, SM=2.5～2.9, IM=1.70±0.1), and replaced shale with Sludge entirely in raw cement formula calculation, the results show that clinker compressive strength is too low. The reason why not conducive to the clinker burning may be that sandstone provides the main SiO2, and the SiO2is crystalline. So the method is not workable.With modulus (KH=0.89, SM=2.42, IM=1.70), we studied the influence of different amount of sludge on cement raw meal sintering, mineral composition, compression strength and leaching value of heavy metal element, by working out cement raw meal formulas through substituting shale with sludge in different percentages. The results indicate that free calcium oxide decreases first and then increases as the sludge increases, while compression strength have a opposite result. Free calcium oxide is the lowest when the sludge dosage reaches2.56%, when 28days compression strength reaches its maximum which is1.37times as large as the cement clinker without sludge. The XRD and SEM test results also show that the composition of clinker and mineral structure remains unchanged when shale replaced by sludge. When the sludge proportion is12.18%, free calcium oxide and compression strength are nearly the same as the cement clinker without sludge, and leaching value of heavy metals could satisfy the concentration limits of hazard ingredients in the lixivium. |
PDF Full Text Request