| An active sludge process is the preferred method for treating urban sewage with high efficiency and low energy consumption. However, the large quantities of sludge produced in the treatment process can be a great burden for the sewage treatment plant. Currently, there are two methods to dispose sewage sludge. One is decentralized the treatment, another is centralized treatment. Latter one, whose area requirements is smaller and pollution is light, has been an ideal choice to dispose sewage sludge. Practice has proved that sewage sludge truck conveying has higher cost, lower delivery efficient and severe pollution. Alternatively, sewage sludge pipeline transport with lower operation cost, automation control and hygiene has become the best choice. This purpose of paper is to guarantee the safe and reliable operation of sludge pipeline through studying resistance characteristics of transport of urban sludge pipeline and optimization of the design parameters.The rheological properties of sludge with the mass concentration2.38%,3.94%and5.39%were determined. The results showed that it has obvious shear thinning characteristics. When the shear rate is large enough, the limiting viscosity is stable. When the temperature T=293K, the limiting viscosity of three kinds of concentration of sludge is2.60mPa s，3.21mPa s and5.95mPa s, respectively; when the temperature T=298K, the limiting viscosity of three kinds of concentration of sludge is2.45mPa s,2.91mPa s and5.78mPa s, respectively; when the temperature T=303K, the limiting viscosity of three kinds of concentration of slugged is2.32mPa s,2.78mPa s and3.69mPa s, respectively. All these suggested that the limiting viscosity increases with the elevation of sludge concentration, and decreases with the increase of temperature. Sludge rheological curve is in agreement with the Bingham model, which exhibits Bingham pseudo plastic rheological characteristics.Based on the rheological properties of sludge, Turian-Yuan heterogeneous model was used to predict the flow resistance of urban sludge in pipeline, and to correct the parameters through the test data. The sludge volume concentrations CV index parameter m1and sludge particle settlement coefficient CD index m2are corrected as0.887and-0.162, respectively. The improved Turian-Yuan heterogeneous resistance model can be expressed as20.694i.8870.1621.2m io0.551C0v C (v s Dbility and accuracy of gD)() i0. The sta improved Turian-Yuan heterogeneous resistance model prediction has been verified by the actual data. The improved Turian-Yuan heterogeneous resistance model meets the accuracy requires, meanwhile, error source of the improved model wasanalyzed. The relationship between the main parameters of pipeline prototype and physical model was deduced based on the similarity theory, and the flow parameters of pipeline prototype was obtained based on the results of the experiment on the physical model. Then the resistance simulation results from this method were compared to those from the improved Turian-Yuan model, which further verified theaccuracy and safety of the improved Turian-Yuan model. The mathematical model for total annualized cost of the sludge transport system was set up, and sludge concentration and transport velocity were chosen as the two key parameters of the complex nonlinear sludge pipeline transport system cost model, and then the two parameters were carried out using a genetic algorithm which is adaptive and allows parallel computing and global optimization. The results of the calculation example showed that the optimal values of sludge concentration Cw, transport velocity v and pipeline diameter D were2.32%,1.10m/s and300mm, respectively under the conditions of sludge quantity Q=0.226~0.045m3/s (sludge concentration Cw=0.8~4.0%) and transport length L=4.5103m.The total annualized cost W was528,300RMB under this scheme. The analysis results of composition of total annualized cost of the sludge pipeline transport system showed that the total annualized cost was composed of annualized construction cost and annual operating cost, and the latter cost takes up the major proportion in the selected optimization scheme. Therefore, reducing the conveying velocity which meets the constrained velocity can be helpful to control the sharp increasing of annual operating cost and then helpful to decrease the total annualized cost. At the same time, the sludge concentration can be divided into several partitions, and the optimization scheme is then selected for each partition based on the bias of the specific total annualized cost. The results showed that in the third partition, the reference value W0’(300)=1.77E-06and reached the minimum value when Cw=2.32%, which met the optimization results in the example. |
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