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To solve the problem of high flow resistance of wet sludge pipeline, a rotary viscometer and a small self-made water film viscosity reduction device were used to explore the effects of the rheological properties of wet sludge, water-sludge ratio (WSR), wet sludge moisture content, wet sludge flow rate and water film temperature on water film viscosity reduction of wet sludge pipeline. The results show that the stress-time curve of wet sludge mainly goes through four stages, i.e. linear sharp increase stage, nonlinear increase stage, peak stage and gradual decrease stage. With the decrease of water content, the dynamic yield stress of wet sludge increases significantly. The greater the WSR, the more obvious the wet sludge pipeline viscosity reduction effect. When the WSR is 0.05, the viscosity reduction efficiency reaches 71.6% when the moisture content of wet sludge is 82.4% and the flow rate is 42.4 mL/min. When the WSR is 0.03, the turning point of viscosity reduction efficiency appears under these conditions. With the increase of wet sludge flow rate, the pipe shear stress and water film viscosity reduction amplitude increase, but the pipe shear stress increases more significantly, so the viscosity reduction rate decreases with the increase of wet sludge flow rate. Increasing water film temperature can improve the wet sludge viscosity reduction effect, and the lower the wet sludge moisture content, the more significant the improvement effect. Compared with water film at 18.5 °, the viscosity reduction of 70% wet sludge moisture content at 60.0 ° and WSR of 0.03 increases by 31.3%. [ABSTRACT FROM AUTHOR]

A method of waste heat recovery and utilization was explored by incorporating a heat recovery system into an existing industrial-scale sludge drying system with handling capacity of 440 kg dry solid (DS) per hour. The recovered heat was used to preheat sewage sludge (and carrier gas) to lower sludge viscosity and flowing resistance during sludge transportation in pipeline, as well as the heat consumption during drying. 5.3% decrease of heat consumption in drying, 48% decrease of sludge flowing resistance, and 15% decrease of spraying water consumption in spray tower were fulfilled. Theoretical modeling of heating and flowing behavior of sewage sludge in pipeline, and cooling behavior of hot wet air in a type-III spiral plate heat exchanger were also conducted. The results showed that wall slip phenomenon occurred between sludge and inner surface of sludge pipe during sludge flowing process, which had marked influence on sludge preheating in pipeline. [ABSTRACT FROM AUTHOR]