Research On Disposal Of Typical Waste Sludge By Cement Rotary Kiln Co-Processing

It is well known that the sludges have complicated characteristics and the production of sludge increase annually. The traditional methods of treating sludge (landfill, incineration and land use, etc) are not suitable for sustainable use because of some shortages (large in land use, secondary pollution risk and small treatment capacity). At the same time, the cement rotary kiln co-processing waste technology has aroused wide attention in the field of solid waste disposal due to its large treatment capacity, high degree volume reduction and harmlessness. Sludges that have complicated characteristics are solid wastes and also resources placed in wrong place. So we studied the feasibility of cement rotary kiln co-processing technology with disposing three typical sludges.First, the municipal sewage sludge was chosen as the alternative raw material in cement clinker production. According to the results of sludge content and mixing methods (in-mixed and out-mixed) in clinker production, we found that the raw material burnability was barely influenced, but the cement quality varied dramatically depending on different mixing methods. The in-mixed ratio of sludge in raw material can be up to 30%, while the out-mixed ratio of sludge only can be 15%. The compressive and flexural strength for 28 d (long-term strength) of those cement production can reach the quality standard of P.O 42.5. Thus, the low early-term strength became the limitative factor of improving municipal sewage sludge ratio in raw material. The determined heavy metal leaching concentrations in all those cement productions were below the limitation of GB 30760-2014 standard.Secondly, the oil sludge was chosen as alternative fuel in cement clinker production. The cement test results showed that the mixing content (14%) and methods (in-mixed and out-mixed) of oil sludge in raw material had no influence on burnability. The f-CaO content in clinker decreased with the increasing temperature. At the same time, the addition of oil sludge in raw material had no negative impact on the cement quality, but only prolonged the initial setting time. However, all the quality indexes could meet the request of national standard (GB 175-2007) as well as the P.O 42.5 quality standard. Considering the release concentration of VOCs during calcination, oil sludge was suggested to be added at high temperture point.Finally, the tannery sludge was chosen as heavy metal sludge to be disposed by cement rotary kiln co-processing technology. The tannery sludge content (0.7%) with different adding points (low, middle and high temperature points) had no obvious influence on the cement quality, and all the quality indexes can meet the request of national standard (GB 175-2007) as well as P.O 42.5 quality standard. During the calcination process, the solidification ratios of heavy metals in clinker were closely related to the melting and boiling point of heavy metals. For the heavy metals with high melting and boiling point (Cr, Cu), the solidification ratios could reach to 90% which had no relationship with adding point of tannery sludge. Regarding to the heavy metal with low melting and boiling point (Pb), the solidification ratio was below 50% and decreased with the increasing temperature of adding point of tannery sludge. When the adding content of tannery sludge was up to 0.5%, together with employing high temperature adding point, the heavy metal (Cr) leaching concentration of these cement production have risk of exceeding the standard limitation(GB/T 30810-2014).