| The vacuum drainage system is a potentially and extensively practical engineering technology. However, the researches on the basic theories, the design principles, and the calculation methods for vacuum drainage systems have been not enough yet, There are no design specifications or criteria for vacuum drainage system yet at present in our country. Based on the analysis of the design of the vacuum drainage system, this dissertation conducted deep investigation in the key technologies including the head loss calculation model of air-sewage multi-phase flow in vacuum drainpipes, the optimization design and calculation technique for the system in order to improve the reliability and economy performance of the system.Characteristics of the sewage and the transport process of the sewage in vacuum pipelines were briefly analyzed, and the complex gas-liquid-solid mixture in piplines was predigested into two different type of gas-liquid two-phase flow: (a) air and mixed Newton liquid gas-liquid two-phase flow; (b) air and mixed Non-Newton liquid gas-liquid two-phase flow. Based on it, the important research on the characteristics of the air and mixed Newton liquid gas-liquid two-phase flow in vacuum pipelines was done. Based on the Separated Flow Model and the Lockhart-Martinelli formula, the correlation for the estimation of the multiphase frictional head loss in the vacuum drainpipe was deduced, and the frictional head loss has a direct ratio of 1.75 times exponent of the sewage flow; and its inverse ratio is 4.75 exponents to the inner diameter of the sewer. Finally, the comparison of the results of the deduced formula with the experimental data in the dissertation and the results of the traditional formula for the frictional head loss of vacuum sewers in popular was conducted. It was shown that the deduced formula was well available for predicting the frictional pressure drop for multiphase flow in vacuum pipelines.Based on the formula of the frictional head loss established beforehand, the maximal design flow of vacuum sewers with different diameter was deduced. Then based on the return flow conditions of two-phase flow theory, the minimum air flow rate for sewage lifting at different pipe diameter was calculated to be 20-45m/s. this dissertation discussed deeply those basic technique parameters reflecting the transportation capacity such as design flow, vacuum head, air-to-liquid ratios, head loss, and maximal collection radius.Based on it, the relation between the collection capacity of the vacuum station and the power of vacuum pump was set up. After the factors such as the topography, sewer diameter, and design flow and press loss affecting the transportation distance of the vacuum system were analyzed, the maximum collection radius of the vacuum sewer system was taken for 2500.Based on the above model of predicting the frictional head loss in vacuum sewers, the conjunction matrix of the vacuum sewer network, and improved genetic algorithm, the optimization design and calculation approach for large and middle vacuum sewers network was established in order to design and calculate the design flow, pipe diameter, head loss and node vacuum head. And the methods for designing and calculating the parameters of the vacuum station were established perfectly, and the methods for selecting the type of vacuum station pump station and vacuum reservoir vessel were discussed.Firstly, to increase the velocity and the precision of calculating the sewers network, this dissertation used the frictional head loss model and the conjunction matrix of vacuum sewers network to construct the expressions for the hydraulic parameters such as the design flow, head losses of each sewers and vacuum head of the nodes.Secondly, this dissertation proposes a mathematical model and improved genetic algorithms that are very suitable for solving pipe diameter optimization of the vacuum drainage pipe network. The engineering cost is regarded as target function, while the least vacuum head of each node and the flux equilibrium of each node are respectively constraint conditions. Then, genetic algorithm is chosen to optimize the diameter of pipe networks, and some effective measures on selection operator, crossover operator, mutation operator and some parameters setting are taken in order to obtain high and right convergence probability. Moreover, the number of available diameter for each design pipes was decreased from 7 into 3, so that the search range of the improved genetic algorithms was decreased. Based on the research, the computation process for pipe diameter optimization of the vacuum drainage pipe network is also presented.Thirdly, based on the mass conservation equation of gas, the formula for the volume of vacuum reservoir tank was deduced. The minimum volume of the vacuum reservoir tank shall be calculated taking account of the maximum start frequency of the vacuum genetrators and forwarding pumps and the range of operational pressure. This reservoir capacity shall be provided by the sewage collection vessels and the available vacuum sewer capacity. Then the merit and shortcoming of three types of familiar vacuum generators, vacuum head available to sewage collection vessel and the maximal head loss of pipelines analyzed, the approach for selecting the vacuum generator types was proposed: when the maximal headloss of vacuum main in the system is less than 4 m of water column, water ring vacuum generators were selected; and when maximal headloss of vacuum main in the system is higher than 4 m of water column, mechanical vane vacuum generators or rotary lobe vacuum generators were selected. Then vacuum generator type is selected in the light of vacuum generator capacity. The system evacuation time, which is defined as the time period between the vacuum generator start and stop, shall be between 1 and 3 minutes. If greater than 3 minutes the capacity of the vacuum generators shall be increased.Fourthly, this paper took an engineering design calculation of vacuum sewers system of 2000 doors for instance. In the initialization condition that the length of pipework, the individual number and the number of lift were same, the approach of optimization design calculation and the traditional design calculation approach were applied separately to calculate design flow, pipe diameter and headloss of each design pipes, and each nodes in the vacuum system. The above results were used to design and calculate the parameters of vacuum station equipment. The result shows that the optimization design and calculation approach can apply to vacuum sewers network efficiently. In comparison with the traditional design approach, optimal pipe diameter combination determined by the relatively novel algorithm is much better, and good economic benefits can be reached.Based on the above researches, related successful experience of foreign country, the experimental research of our scientific research group, and the research production of the paper, the draft edition"Design Criterion for Vacuum Sewerage Systems"(appendix B)has been written. The design criterion contains General design requirements, Design of gas-liquid dynamics, Design of vacuum pipeline, vacuum station and collection chamber, Installation, Testion and verification.
|
PDF Full Text Request