Planning and Design of Nanhu Integrated Management Sludge Pump Reactor Transportation Engineering Liu Chunyan (Guangxi Water Conservancy and Electric Power Survey and Design Institute, Nanning 530023, Guangxi, China) Introduced the main design of the implementation of dredging treatment of Nanhu silt using 8-stage pump station single-pump pump relay transmission Parameters, piping design, piping and pump selection, piping connections, and issues to be aware of during operation.
Sludge; pump relay transport; design of each pump H ~ Q operating conditions are within the single-stage slurry pump performance range. However, due to the difference in abrasion between pumps, there may be a difference in the H~Q characteristics of each pump, which may cause slurry overflow in the feed tank. Multiple feed tanks should be built under normal operating conditions. The suction head of each pump is close to atmospheric pressure. The discharge head is approximately equal to the single-stage head; it is easy to generate water hammer when the pump is started and suddenly stopped. It is necessary to build multiple pump stations. The power supply and control devices for the pump stations are expensive to install and maintain. However, low-pressure piping can be used. Lower cost. And can use centrifugal seal Liu Chunyan (1971 -) female, Nanning, Guangxi, Guangxi Water Conservancy and Electric Power Survey Design and Research Institute of engineers, mainly engaged in hydropower hydraulic machinery design work.
Nanhu Lake is located in the eastern part of Nanning City, from the south end of Zitou and Guangxi Medical University to the north end of Longdong, and has a total length of 3.8km, a lake width of 250~380m, and an lake area of ​​1.076km2. The whole lake is divided into upper and middle sections by the Scenic Bridge and Nanhu Bridge. In the next three parts, the lake can be discharged into the bamboo raft by the east gate. Due to the injecting of rainwater and domestic sewage for many years, the decomposition and sedimentation of aquatic organisms, the lake water becomes cloudy and odors are emitted, seriously affecting the quality of life of the surrounding residents, and Nanhu Park and even the entire Nanning city have to implement dredging treatment for Nanhu Lake. The sludge with a total volume of 8.43 million m3 of undisturbed soil was discharged to a sludge field far from urban areas.
The main technical process of dredging construction is: water barrier lake water pumping lake total relay lake lake pumping station pipeline relay pumping lake pumping station pipeline relaying old wushi sludge field.
1 Main design parameters 1.1 Design flow The total dredging volume of Nanhu Lake is about 843,000m3, and the density of natural sludge wet soil is not more than 1390kg/m3. The volume ratio of sludge to water is 1:3 considering the volume concentration of sludge. : Cv = 25%, specific gravity of slurry: 1.3 Performance of Centrifugal Slurry Pump Under the same flow rate and speed, the ratio Hr of pumped slurry head and pumped clean water head is calculated according to different recommended formulas: Hr= 0.985, Hr = 0.915, calculated from the slurry density Hr = 0.911, taking into account a comprehensive consideration Hr = 0.915. Typical slurry pump operating range, under normal circumstances, at the same flow and speed, pumping slurry efficiency and pumping The ratio of clean water efficiency is the ratio of Er to head ratio Hr, and ErHr is equal to 0.2. 2 Pump Relay Conveying to Mud Pipe Design 2.1 Selection of Centrifugal Slurry Pump Selection Centrifugal slurry pump is used to achieve slurry long-distance transport. There are three kinds of layout methods. One is the slurry pump relay in the middle of the feed pool; the other is the slurry pump directly connected in the pipeline; and the third is the centrifugal slurry pump in series arrangement. The comparison of the three arrangements is shown in Table 1. Table 1 The arrangement of the pump stations for different schemes and the requirements There is a solution for the 2 in the middle of the scheme 1 directly in the tube scheme 3: The slurry of the slurry pump relayed on the centrifugal pool The slurry pump is arranged in series and multiple pumps are arranged in one pumping station. Equipment installation, maintenance, operation and management are convenient. With the increase of the allowable pressure of high pressure centrifugal slurry pump. This arrangement is more and more widely adopted. The higher pressure required for the design of the piping requires the use of higher pressure grade pipes. It is bound to increase investment in the selection of centrifugal slurry pump layout must be adapted to the actual project, combined with the construction unit's existing equipment and construction preparation, pipeline hydraulic loss distribution, pipeline allowable pressure, pump suction height, pump pressure level After comprehensive analysis of several aspects, the slurry pump scheme that directly relayed on the pipeline was finally selected.
2.2 Pipe Selection The current standard pressure pipe working pressure can reach 2MPa or more; ductile iron casing centrifugal slurry pump allowable pressure of 2.1MPa high-density polyethylene plastic pipe nominal working pressure is 0. 1.6MPa and other 6 levels. However, with the increase in pressure levels, its wall thickness continues to increase, and the cost continues to increase. Large diameter, O.MPa pressure grade polyethylene plastic pipe (PE pipe) both can meet the requirements of use, PE pipe has the characteristics of abrasion resistance, impact resistance, small flow resistance, long life, light weight, easy construction In the same nominal diameter, the steel tube has the advantages of large area for the passage, excellent welding processability, and much lower price. Therefore, the steel tube was finally selected for the project.
2. Pump selection pump head analysis. According to the optimized construction organization design scheme, when Shanghu Pulp slurry pump is relayed, 8 centrifugal slurry pumps are used, the average lift of single-stage pump is 36.7m; 7 single-stage pumps for relay transmission in Zhonghu slurry The average lift is 36.7m; the average lift of the 6 single-stage pumps for the relay transmission of the lake slurry is 36.9m. The designed single-stage pump has a lift of 37m. Although the slurry of this project is a high-concentration, low-resistance slurry, considering the reliability of pump operation, the AH pump can be applied to high-concentration strong abrasive slurry.
Performance parameters selection. According to the hydraulic calculation results, the required design flow and design head of each single-stage pump in each pump station of this project are: 390L/s 37m According to the flow and head primaries 12/10ST-AH type water pump, the performance curve of this type of pump clear water (ie Mans slurry pump water performance curve "), the maximum speed of 800rpm, the general choice of speed should be about 3/4 of the maximum speed, the project according to the head and flow requirements, select the standard speed of 675rpm, the speed of the slurry pump The Q curve corresponds to the highest efficiency point flow rate of 418. For high concentration low abrasive slurry, the design flow rate should be selected within the range of 40% to 100% of the maximum efficiency point flow rate. The project design flow rate of 390!7s meets this requirement.
Pump motor configuration. Calculated pumping slurry shaft power is 212. 1kW, supporting motor power considerations richness coefficient 1.1 should not be less than 233kW The actual use of slurry pump supporting motor power during construction is 245kWL pump cavitation operation requirements. According to "Worman's Slurry Pump Clear Water Performance Curve", the scum pump must have a bleed margin not less than 6m. After calculation, the minimum liquid level of the feed pool (Lake District pump pool) must not be lower than the height of the pump installation centerline. 1m can ensure that no cavitation pump operation of the slurry pump, so as to avoid vibration, noise generated by the pump, even lead to a sharp drop in head, flow, and efficiency.
For ease of operation, no vacuum is required during start-up and a bottom valve with a large local resistance loss is installed. The height of the centerline of the pump installation center should be less than 0.5m below the start level of the feed pump slurry pump. It is convenient for slurry feeding and the water inlet. Should be set at the bottom of the feed tank.
Feed pool set requirements. The effective volume of the inlet basin (ie the feed pool) is estimated to be about 120m3 at a working flow of not less than 5min. In addition, in order to prevent the overflow of the slurry from polluting the surrounding environment, an overflow port and diversion facilities should be provided. 2. Water hammer analysis is common and dangerous The phenomenon of water hammer is the water hammer phenomenon caused by sudden shutdown of the pump unit. If a check valve is installed in the pipeline, it may also cause a serious accident with an explosive water pipe. In order to reduce the hydraulic losses in the pipeline and prevent the generation of huge water hammers, it is necessary to cancel the check valve in the long pipeline. The transient abnormal operation caused by the sudden stoppage of the pump can be divided into three stages, namely, forward positive flow (ie, pump condition), forward reverse flow (ie, braking condition), and reverse reverse flow (ie, hydraulic turbine operation condition). According to the calculation of the longest pipe feeding the lake slurry, the rated lift of the 1W10ST-AH centrifugal slurry pump is 37m, the rated flow is Q = 0.39m3/s, the efficiency is 79.5%, and the rated speed n 8 type motor (N= 250kW 〖,n=730r/min)Motor moment of inertia 15.5kgm2, calculate the maximum pump pressure wave 7%H positive, the pump maximum reversal speed is 123%ne, the pressure pipe maximum step-down wave is 6.7%H positive, Basically meet the pump station design specification requirements. Taking into account the possibility of negative pressure and pipeline exhausting in some pipe sections, a DN50P2-10 dual port exhaust valve is installed at each high point of the horizontal pipe. This valve can quickly eliminate the gas in the pipe and negative pressure can be found in the pipe. The gas is quickly drawn into the pipeline to prevent it from being damaged by the vacuum.
The maximum pressure of the pipeline appears at the outlet of the slurry pump at the 4th station of the external force of the lake. Consider the maximum boost pressure of 7%. The maximum head of the pipeline is 56.9m. The pressure capacity of the pipeline and its accessories is designed at >0.6MPa.
2. Pipeline connection method and withstand voltage test require pipeline connection method. Spiral welded steel pipe is used in this project. The connection between the steel pipe and the inlet and outlet of the water pump should be connected with a flexible pipe with shock-absorbing function and a low cost hose connection (the length of the connecting hose should be not less than 1m). After the pipelines are laid, strict pressure resistance test must be carried out. The pipeline test is completed before the concrete is poured. The entire system should pass the test before it can be put into production. The test shall be performed on the entire piping system or part of the piping system in accordance with the relevant requirements. The test pressure shall not be less than 0. 9MPa The piping system shall be maintained for 30 minutes after filling. If any water leakage or other defects are found, the contractor shall carry out Repair or replace, and re-tight test until it is qualified.
2. Equipment operation precautions When the pump starts, it should start from the first stage to the last stage step by step. When the pump is turned off, it is turned off from the last stage to the first stage.
When the pump is started, the outlet valves of the relay pumps at all levels should be in the 1/4 opening state. After the pumps are started step by step, they are opened step by step until they are fully opened. Each pump station is prohibited from running when the valve is closed.
When the water pump is turned off, it is shut down from the last stage to the first stage step by step, and the valve opening of the pump stations at various levels is gradually reduced to reduce the flow, reduce the water hammer pressure and the reverse rotation speed of the water pump, and protect the water pump. After the pump is completely shut off, slowly close the pump outlet valve.
The gate valve used with the exhaust valve is a normally open valve. It is closed when the exhaust valve is replaced or overhauled.
Pipeline segmenting valve is normally open, only closed when the pipeline is overhauled, normally closed valve operation is prohibited.
3 Conclusion The construction of the comprehensive management dredging project of Nanhu Lake has been completed. According to the implementation of the project, the following points are summarized: In the case that the construction of the dam at the old Wushi silt yard has not been completed and passed the acceptance check, blindly let the sludge transport The pipeline construction unit entered the site and began dredging. The result was just pumping for a period of time. Due to a problem in the dam, the silt transportation had to be temporarily stopped. During the construction period, the flood water level in the torrential rain lake rose and the transportation had to stop. After the rain stopped, the water was pumped again and again and again, the actual construction period exceeded the design construction period by more than two times, resulting in a relatively large waste. This reminds us that we must pay attention to the construction organization and everything should be done according to scientific procedures.
In accordance with the optimized construction organization design scheme, when Shanghu slurry slurry pump is relayed, 8 sets of centrifugal slurry pumps are used, and the single-stage pump (turning to page 75) is more serious and uneven in terms of the gate groove construction. In the case of the gate, the height of the gate steel block was cut from the design value of 88 mm to 80 mm, and at the same time, the top elevation of the gate was blocked to meet the installation requirements.
After the flood season in 2001, the speed slowed with slight vibration when the gate opened and closed through the threshold. After inspection, it was found that the top seal was severely deformed. The bottom of the top seal was upturned to about 85 mm, the top part was retracted to about 65 mm, and the local bending was uneven. The participants of the project conducted a field study on this phenomenon, and believed that the reason was that the height of the top sealing pad was too large during the initial installation, and the water pressure plate at the top was not continuous, and the pressing force of the bolt installation was not uniform, resulting in the gate opening and closing. After the watertight contact with the door sill, local force causes deformation of the top waterstop device. The author put forward the processing advice: Before replacing the water seal, carefully check the size of the door slot, and determine the height of the water seal according to the measured size.
Replace the water seal according to the status of the door groove. When replacing the water seal, ensure that the surface of the water seal is flat and securely installed.
The top water seal pressure plate is changed from a font type to a double-warp pattern to prevent the water seal from turning over.
A limit sleeve is added on both sides of the connecting shaft of each pull rod and the lug to ensure equal force on both sides of the lug.
After processing, the gate has been operating well so far.
5 Conclusion With the emphasis and strengthening of urban flood control and coastal development, two-way retaining gates will be more and more widely used. Summarizing the technical characteristics of the bidirectional retaining gate is a very significant thing. Through the whole process of design, manufacture, installation and commissioning of the Xiexiu flood barrier, the author has come up with some rough understanding: It should be in the process of hydraulic layout. Fully demonstrate the feasibility of setting up a two-way retaining gate, clarifying the inspection conditions and operating conditions of the gate, and ensuring the safe operation of the gate.
Two-way retaining gates require high precision for the installation and installation of door leaves and doorways. Therefore, in the design of the gate structure, the structure should be as simple as possible and easy to make and install to ensure that the door leaves have sufficient rigidity.
Since the direction of the water pressure in the bidirectional retaining gate changes, there must be a special time period during which the water level difference between the front and the back of the gate is very small. In order to ensure that the gate does not leak during this special period, the water stop rubber must always maintain a certain amount of pre-compression.
Strictly control the installation dimensions and accuracy of the components of the door leaf and the door slot, and do a full record of the data in the process to provide the basis for follow-up work.
The operation and management personnel should be familiar with the operating conditions of the gate, and observations should be strengthened in the meantime. Pay attention to the working conditions of the supporting walk structure and the water seal structure. Those that do not meet the requirements for use should be promptly repaired or replaced.
(Editor: Liu Zhengzhan) (Continued from page 72) Average lift is 36.7m. Only 6 pump stations are actually used. There are two reasons for the analysis: One is the design calculation, the slurry volume ratio of sludge to water is 1:3 considered, but the construction process using high-pressure water flow excavation silt, simply can not effectively control the water slurry ratio, silt and water The actual volume ratio is arbitrarily large, the proportion of mud is greatly reduced, resulting in a surplus of the pump lift; another reason is that according to the construction preparation conditions and requirements of the successful bid winner, the Y400X 20.6 high-density polyethylene plastic pipe is used for design calculation. According to the calculation, the Y600 spiral welded steel pipe is used in actual construction, the flow area is increased, and the head requirement is reduced. The pump station setting is not adjusted accordingly. If the adjustment is made in time, the cost can be further reduced.
During construction, the entire sludge transportation pipeline runs along the South Lake side of the Ming Dynasty and crosses the city's two major arterial roads and rapid loop roads. At the time of trial operation, the projectiles emerged at the gates of the Xihu Pumping Station and Changhu Road in the civil service area of ​​Nanning City. There is a problem with the tubing connection flange seal. The flooding caused pollution to the exterior wall of the old people's activity center on the lake side, flowerbeds, and gates of the civil servants' area. Fortunately, there was no pollution along the street, and only cleaning work was done to remedy the situation. No major economic losses were caused. After replacing the seals, the construction unit wrapped nylon cloth around each flange of the pipeline that is located in the densely populated urban area to prevent possible pollution caused by the re-emergence of the projectile. Practice has shown that this measure is effective and cost-effective, and that similar preventive measures can be taken in advance in the construction of similar municipal projects.
(Editor: Liu Zhengzhan)
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