| The pump plays a very important role in the water supply project, and supports pressure energy for the media of water supply project. Whether the pump can start or stop normally affects whether the water supply pipes and water supply systems can operate safely. Therefore, the pump work as follows is necessary.When the pump stops in normal circumstances, the water supply system which contains pump export of water hammer with the butterfly valve protection, the butterfly valve should be closed firstly, close the valve completely or to a very small angle (less than6°in general), then the pump was off. If the accidents (e.g. power outages and so on) occur in the open butterfly valve, the pump stops when the valve opens, the case is known as non-normal shutdown. Such case lead to strong broken water hammer, furthermore, resulted in strong destructive burst pipes accidents. Otherwise, when the pump stops in exceptional circumstances, water hammer can disconnect the water immediately and quickly to limit the drying speed and the unit upside down, to prevent the vicious water hammer pressure fluctuations, which is the most striking contradiction of the water hammer protection. Substantial theoretical and experimental researches suggest that two-stage slow closing valve adjustment mode can be used commonly and further improve the protective effect of Water hammer. The time and angle of turning off the pump fast or slowly is the important input factors of two-stage slow closing valves, have a significant impact on the pressure tube.This thesis includes:(1) Based on previous studies, we simply derive the calculation principles and formulas, and study the boundary conditions in the project instance, therefore establish the appropriate model of water hammer;(2) Analysis to calculate the pump normal operation, the outlet two-phase slow closing the butterfly valve flow characteristics and resistance characteristics, including the opening of the valve, drag coefficient, pressure loss, shut down the law as well as the relationships between them;(3) We analysis the water flow and pipeline characteristics within export pine when pump work normally and the outlet of a two-stage butterfly valve close to a certain angle. Meanwhile, we start to calculate the time when valve closed to a certain angle, and calculate the changes of pressure and velocity in the pipeline section with the time according to the characteristic line, when the special accidents occur. Therefore, with the method of computer iteration, we calculate each moment in the pipe under pressure and flow simulation calculation, and we develop the closure rule in the butterfly valve protection of Zhang-Feng Reservoir water supply system;(4) According to the above theoretical analysis and simulation, we model the accident of Hydraulic transition process, Analog Zhang-Feng Reservoir Water Supply Project;(5) To calculate the simulation of hydraulic transition process under the normal case of downtime Zhang-Feng Reservoir Water Supply Project, and develop suitable water hammer protection measure. Meanwhile, normal shutdown of the situation and try to run the simulation of accident conditions the results of comparative analysis, analysis of Zhang-Feng burst pipes cause of the accident, and propose appropriate solutions and protective measures;(6) We developed pumping station hydraulic transition process numerical simulation system which a simple interface, easy operation, fully functional and reliable, via using Visual Basic6.0programming language, and SQL Server2000database.In this thesis, we get the three main results in the following by analysis:(1) Given the state calculation of Seven Slope pump Station of Zhang-Feng Reservoir Water Supply Project, the locations of the pump and hydraulic factors have been determined, the range of the operating of steady state has been worked out, making the pumps to try to keep the high efficiency zone running.(2) We developed the safe and correct two-stage pump outlet slow closing the butterfly valve closing law, with the hydraulic transition process calculations of Seven Slope pumping station, Zhang-Feng Reservoir Water Supply Project, to ensure the pipe pressure with a reasonable range.(3) Based on the above mentioned, and with calculation and analysis, the results indicate that two reasons caused Zhang-Feng Reservoir water supply system tube rupture. On the one hand, there are some defects in the pump automation control program automatically shut down the program and its control flow diagram. On the other hand, the manufacturer of pump outlet hydraulic control butterfly valve modify the valve closure rule without theoretical support and professional guidance, resulted in the butterfly valve to lose the protective effect of water hammer, caused piping water pressure too large. The accident of burst pipes occurred because of both above factors.Through the analysis and research of this paper, we got the reason why the pipeline accident happened, and proposed the corresponding solution and protective measures. This provide some references for the next similar water supply project of design, construction and operation management of the security guarantee. |
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