Water Hammer Analysis and Protection of the First Water Filling of a Pumping Water Conveyance Project. Ru Dong * 1,2,3

Transcription

1 Water Hammer Analysis and Protection of the First Water Filling of a Pumping Water Conveyance Project Ru Dong * 1,2,3 1. School of civil engineering, Yulin University, Yulin,Shaanxi, , China 2. The City's Water Distribution and Pollution Control Research Center of Yulin University. Yulin, Shaanxi , China 3. Shaanxi Key Laboratory of Ecological Restoration in Northern Shaanxi Mining Area. Yulin, Shaanxi , China Abstract: Taking a special long-distance, low-rise, multi-fluctuation and large-diameter pipeline as an example. The water hammer analysis and protection were carried out to study the first water filling condition, pump starting condition, pump restarting and pump operating condition during the initial water flow of pumping water supply project. The results show that the exhaust and other protective measures are not taken, The entire pipeline system water column interruptions and trigger a larger water hammer to close the pressure, must take the exhaust and a negative pressure water injection Pressure relief of the two-way surge tank in order to make the pipeline safe operation, the results of similar projects can provide a reference. Key words: pump pressure water conveyance project; initial water filling; water hammer breaking; bridging boosting protection. 1. Introduction The pump pressure water pipeline through the first process is a continuous process of dynamic hydraulic transient, and pipe flow is containing water, gas multiphase flow [1].Initial water filling pipeline, because the pipeline gas if the gas is stored for a long time, the water filling process cannot be discharged, will produce sustained pressure oscillation, a certain amount of gas accumulation occurred suddenly, quickly cut the pipe section with water, can easily occur in the water column, water hammer [2],stop production. The new pump pressure water pipeline first filling, maintenance or outage after start again, adjust the operating conditions, suddenly stop pumping again after the start of the situation of the start pump or stop pump water hammer are generally gas type broken water hammer. Theoretical analysis shows that the pressure produced by the broken water hammer can rise to several MPa, which is enough to destroy the general water pipeline [3].Therefore, this paper combined with the engineering example of a long distance pipeline with large diameter and low lift many ups and downs and stable operation conditions, process for water filling pump start condition, stop the pump after the pump condition of water hammer analysis, combined with the water pipeline and pumping station specific situation, put forward a reasonable protection scheme [4]. 2. Project overview A long distance low lift many ups and downs of large diameter water pipeline project. The system diagram is shown below [5]: 2.1 Pipeline situation Figure 1 Engineering system diagram The starting point of the project A (0+000) for water intake pump house, ending with E 4# waterworks (31+750), B (12+700),along the way in C (14+800),D (15+450) from three lines respectively to 1#,2#,3# water purification plant. The water pipe material for PCCP tube, the AC segment was two DN1800 water supply pipe with groove laying, CD segment for a DN1800 water supply pipe, DE section of DN1600 pipe for emergency branch, the total length of the full range of AE single 31750m [6]. The transmission pipe elevation trend line shown in Figure 2. Figure 2 Trend chart of water pipeline 2.2 Water pressure conditions Table 1 Emergency conditions, the water distribution point of the flow, outlet pressure (67.56*10 4 m 3 /d) Water distribution point flow(10 4 m 3 /d) Outlet pressure(m) Journal of Residuals Science & Technology, Vol. 13, No. 8,

2 Pump station Water purification plant# Water purification plant# Water purification plant# Water purification plant# Water pump information Table 2 Water pump basic information Parameter name Company parameter values Parameter name Company parameter values Model of water pump KQSN700-M14/639 Runaway speed r.p.m 1800 Rated flow m 3 /h 4700 Operating point efficiency % 88 Rated head MPa 42 Shaft power Kw Rated speed r.p.m 990 Motor power Kw Analysis and protection of water - filled water hammer in pumping water transfer project 3.1 Necessity of water hammer analysis Pipeline design of this project a large amount of water, there are many points in the middle of the water points, pipe diameter, pipeline ups and downs, is a large water conservancy project, where the water pipeline safety is very important. Theoretical analysis shows that the pressure rise of water hammer can reach several megapascals, which is enough to destroy the general water pipelines. If the explosion in the event of an accident, not only a great repair costs, but also extend the water test time, affecting the realization of water supply goals. Therefore, strengthening the analysis and protection of water hammer broken water pipe is an important means to ensure pipeline safety. Therefore, this paper combined with the project examples to consider the stability of the pipeline flow, unsteady flow of various conditions, combined with the height of the pipeline, distance, layout, pipe flow and pipe attachments of various operating performance and other factors Water hammer pump analysis, prediction of the possibility of water hammer pump and its harm, put forward a reasonable method of protection. 3.2Water hammer computer analysis parameters By using the characteristic line method, a water hammer analysis was carried out on the trunk main line AE of a long-distance, multi-fluctuating, large-diameter water main pipeline. On the way, the three points of B,C and D were the water discharge ports, and the pipes were changed in several ways. According to the actual situation of the pipeline Preparation of water hammer computer program, the relevant parameters are as follows: Water hammer wave speed: pipe for the cast iron pipe, a approximate take 1000m / s: Pump exit slow closing check valve with two stages of speed off: fast off 10s off 60,the total clearance 120s.The main trunk line of the project is 31750m long and the water hammer phase is μ = 2L / a = 63.5s. Therefore, 120s closed valve does not produce direct water hammer. Calculate Duration: T=1000s. 3.3 Water hammer analysis Water hammer analysis for steady operation of pipelines in various flow From Figure 2,the trend of water pipelines can be seen, the water pipeline ups and downs vary greatly, and the pipeline in the post-section there are several high elevation in the normal operation of the pipeline can guarantee any point does not appear negative pressure, But also to ensure the safety of piping system an important condition. The system uses variable frequency pump and non-variable frequency pump to adjust the use of the maximum operating conditions for the use of six pumps at the same time, based on pump characteristics and pipeline characteristics of the intersection curve, and water calculation, Stable running at different flow rates without interruption measures Water pressure lines Figure 3: Journal of Residuals Science & Technology, Vol. 13, No. 8,

3 Figure 3 Steady operation under different flow rates without pressure Figure 3 shows, in the three ~ six pumps stable operation, there was no negative pressure in the pipeline, but in the two pumps running at the same time, the high point of the pipeline station there have been negative. Therefore, under normal operating conditions, when the two pumps are running at different flow rates, the pressure should be taken at the end to ensure that there is no negative pressure at the high point (station no ).The pipeline can be operated safely and stably Analysis and calculation of water hammer in start - up pump As the length of the pipe, head low, large diameter, and more ups and downs, changes in flow, there may be water column interrupt phenomenon. Therefore, must analyze the initial test pipeline water, water repairs, and suddenly stop the pump and so on again after the start of the pump will produce water shut-off to close the water hammer, and the corresponding protective measures. 1)The first trial water cut off water hammer calculation The first test water to open the three water pumps for water filling, do not take any protective measures, the pressure curve shown in Figure 4 the first trial of water when the water hammer step-up curve: Figure 4 The initial test water without protective measures water hammer step-up curve Journal of Residuals Science & Technology, Vol. 13, No. 8,

4 Figure 5 The first test water when there are protective measures against water hammer step-up curve Figure 4 shows that the initial test of water does not take protective measures, that is not exhaust, this time the pipeline does not flow and exhaust control, the pipeline due to poor exhaust or water filling speed is higher than the exhaust gas pressure generated by airbag shock And gas blocking, etc, water lines across the pipeline interrupt, the occurrence of water shut-off to close. The maximum pressure of the pipeline is increased by 350m water column, the pressure of most pipe sections is above 150m water column, far exceeding the pipe pressure value. Figure 5 shows, after taking exhaust and pressure protection measures (see 2.4 water hammer protective measures analysis) pipeline line across the water column did not interrupt the pipeline across the line pressure stability between 20 ~ 60m water column in the pipeline to allow pressure range (Pipe pressure value of 0.6MP a),pipeline operation safe and stable. 2) Stop pump again after the start of the water pump when the water hammer calculation If the pipeline suddenly stopped after the pump start again, not to control the flow, do not exhaust the gas to increase the flow of water hammer breaking the pipeline pressure rise curve as shown in Figure 6 stop pump again after the start of the pump without protective measures Water hammer curve: Figure 6 Stop pump again after the start of the pump without protective measures water hammer curve Figure 7 Stop pump again after the pump has protective measures to break water hammer curve Can be seen from Figure 6, stop pump and then start the pump again, do not take protective measures, the same line of water lines across the line interrupt, the occurrence of water hammer bridging. Pipeline maximum pressure increased 380m water column, most of the pressure in the 200m above the water column, far more than pipe pressure value. Figure 7 shows that after taking exhaust and voltage protection measures, the pipeline did not occur Journal of Residuals Science & Technology, Vol. 13, No. 8,

5 across the water column interruption, the pipeline pressure across the board in the 20 ~ 60m water column between the pressure in the pipeline to allow the range (pipe pressure value of 0.6 MP a), pipeline operation safe and stable. 3.4 Analysis of Water Hammer Protection Measures First, the installation of slow-closing check valve at the pump outlet, slow closed check valve for the speed of two-stage closure; Second, according to the relevant specifications of about 1km to install an exhaust valve, combined with the ups and downs along the project and more comprehensive to determine the location of the pipeline exhaust valve installation point as follows: From the above water hammer analysis can be seen in the absence of protective measures, across the board at different times there are water column interruptions, and caused a high cut-off to close the water hammer boost. Moreover, the water hammer calculation program analysis only at the pump outlet installed slow closing check valve and along the installation of buffer exhaust valve does not completely eliminate the water hammer boost, as shown in Figure 8, it must further take anti-flow Water hammer protective measures. Figure 8 Slow closed check valve + buffer exhaust valve protection measures when the water hammer curve Finally, in the pump outlet 50m and the pile , , , Office are installed four box-type two-way surge tank, box-type two-way surge tank with over-pressure discharge, when the negative pressure in the pipeline, the box-type two-way surge tank through the tank of water, the water quickly to the pipeline to prevent the water column interrupt, causing water hammer to close up pressure. The most difficult to protect the speed boost type water hammer, such as balloon vibration water hammer, gas-type water-breaking hammer, shut the water hammer, pump water hammer, box-type two-way surge tank can direct action, waterproof hammer effect. As shown in Figure 9 for the use of slow closing check valve method, exhaust valve and box-type combination of two-way surge tank under the water hammer curve, no water line across the pipeline interruption,60m between the water column, within the allowable pressure in the pipeline (pipe pressure value of 0.6MP a), pipeline operation safe and stable. Figure 9 Slow closing check valve + buffer exhaust valve + box-type two-way surge tank protection measures when the water hammer curve 4 In conclusion For the long distance, low head, large diameter, and more ups and downs of the water pipeline, in order to ensure the initial safe water, to avoid the occurrence of water hammer, water-filled conditions must be detailed water hammer analysis, Water hammer analysis results show that the pipeline does not take protective measures, due to poor ventilation and the occurrence of water shut-off to close the water hammer, water hammer boost is high enough to undermine the entire pipeline system, Therefore, the exhaust pipe is particularly important, followed by easy to produce water for the hammer to close the Journal of Residuals Science & Technology, Vol. 13, No. 8,

6 pipeline, as well as to take anti-water hammer to stop measures, such as a negative pressure water, two-way pressure relief over pressure he or box-type two-way surge tank, etc.to protect the water pipeline safety all-pass water, to avoid accidents. Reference [1]Du Y.Zh,Chen Y,Ch,,Li.The Harbin Mopanshan water project water test. Water supply and drainage, 2009, 35(10), pp [2]Yang Yusi.Technical specification for long distance water supply pipe (canal) works of urban water supply. Beijing: China Planning Pres, [3] M.L. Diao, Ch. Y.Wang,J.LGao,J.H.Liu.Research on the optimization of the initial water gravity flow scheme of long distance pipeline. China Water supply and drainage, 2013, 29(9), pp [4] Ohba T, Kaneko K. Initial filling mechanism of predominant water adsorption on hydrophobic slit-shaped carbon nanopores. Journal of Physics: Conference Series. 2009, pp [5] Volynchikov A N, É. G. Gaziev. Analysis of Vertical Displacements of the Concrete Dam at the Boguchany HPP During Initial Reservoir Filling. Power Technology and Engineering, 2015, 48(5), pp [6] Liu A, Liu Y, Xiang H, et al. MIMO B-MAC Interference Network Optimization Under Rate Constraints by Polite Water-Filling and Duality. IEEE Transactions on Signal Processing, 2011, 59(1), pp Journal of Residuals Science & Technology, Vol. 13, No. 8,