Theoretical study on optimizing pipeline layout of water supply network?

Water supply pipe network system is a water delivery system composed of pipelines, pumping stations, water towers and regulating valves. Through the reasonable design and operation management of the system, a large amount of engineering investment can be saved and the economic benefit of the water plant can be improved. However, the problem of pipe network is very complicated, and the layout of pipe network, the volume of regulating tank and the working condition of pumping station will all affect the technical and economic indicators. Before the technical and economic calculation, the pipe network layout must be completed in advance.

2. Optimal layout of urban water supply network

2. 1 pipe network layout

In the past, in the construction of municipal water supply system, the construction of water supply network was arbitrary. With the continuous improvement of urban planning, road construction and management are gradually standardized. Some grades of roads clearly stipulate that excavation is not allowed for several years after completion, which requires that pipeline laying must be planned and planned accurately. In addition, with the enhancement of enterprise benefit control consciousness, pipe network planning has been paid more and more attention, and has gradually become an important part of water supply planning.

The planning and alignment of water supply network is the initial stage of network design, and the rationality of its layout is directly related to the rationality of water supply operation and the setting of pump head, which also has great influence on project investment and management and maintenance. Pipeline network planning and layout is an important part of pipeline system planning. The investment of pipe network engineering is huge, generally accounting for 60% ~ 80% of the total investment of pipeline system. The pipeline is buried underground, so it is difficult to expose the problems such as waste of funds and unreasonable water supply, and there are many hidden dangers. Therefore, in order to completely eliminate these unreasonable factors, reasonable planning and optimization design must be carried out in the planning and design stage of the pipe network, and the current situation, short-term and long-term hydraulic simulation check of the system must be carried out to achieve the purpose of design optimization. The layout of urban water supply pipe network shall meet the following basic requirements:

① It should conform to the requirements of the overall urban planning, and the possibility of building water supply system by stages should be considered when the pipe network is arranged, and sufficient development space should be left;

(2) the pipe network should be arranged in the whole water supply area, so that users can have enough water and water pressure technically;

(3) The layout of pipe network must ensure the safety and reliability of water supply, and when the local pipe network fails, the water cut-off range should be minimized;

④ Try to lay pipelines in the shortest distance to reduce the cost of pipe network and water supply and energy.

For cities with relatively flat terrain, the planning and layout of pipe network is relatively simple. However, for cities with large topographic differences, it will be more difficult to adjust the ring network if unified water supply is adopted. Because the ground elevation difference of each part of the pipe network is too large, it is easy to cause high pressure in the low area, pipe explosion and pipe damage. In high areas, the pressure in the pipe network will be insufficient, and even water cannot be supplied to the most unfavorable points. If district water supply is adopted, it will involve how to delimit the boundaries of districts and how to coordinate the water quantity between districts, which is difficult to adjust, which is also a problem to be considered in the layout of water supply network. For cities with a long history of water supply development, when considering the preparation of pipe network planning, urban pipe network can be divided into two parts: new urban pipe network and old urban pipe network reconstruction.

2.2 pipe network alignment

The line shape of the pipe network depends on the urban layout, the topography of the water supply area, the location of water sources and regulating pools, the distribution of blocks and users (especially large users), and the location of rivers, railways and bridges. Therefore, the key points to be considered in pipe network alignment are as follows:

1) water pipe alignment:

(1) The line is short, the water supply is safe, the cost is economical, and it should be laid along the highway as far as possible, occupying less farmland and not fertile land.

② Avoid crossing obstacles such as railways, highways, rivers, swamps and valleys as much as possible.

(3) The direction of water pipes should be consistent with the water flow direction of secondary pumping stations to pools, water towers and large users.

(4) Water pipes should make full use of the topographic conditions as much as possible, and give priority to gravity flow.

(5) the water supply project shall not be interrupted, and there shall be two or more water pipes.

⑥ The water pipe should have a certain slope, and an exhaust valve should be set at the height of the water pipe, and a drain valve should be set at the lower part.

⑦ The combination of distance and stage should be considered in the selection of water pipes.

2) Main routes:

① The location of water source and water tower should be considered in the layout of main pipeline to meet the requirements of urban road network planning, and it should be laid along the original road and planned road.

(2) The supervisor shall be arranged in a higher position as far as possible to ensure that the water distribution pipes of nearby users have enough pressure and increase the water supply safety of the pipeline.

(3) According to the situation of the block, the distance between the main pipes is 500 ~ 800 meters, and the main pipes are provided with crossing pipes at regular intervals, with the distance of about 800 ~ 1000 meters ... Its function is to ensure water supply when some valves are closed.

(4) give full consideration to the setting of water distribution pipe on the main pipe, and leave the interface. The layout of the main pipeline should also consider the future development and be built by stages. Auxiliary equipment, such as gate valves (for water regulation and maintenance) and fire hydrants, should be installed on the pipeline. ⑤ The scope of water supply area should be determined according to the planning principle, and pipelines should be distributed reasonably in the whole water supply area, especially in high, far and local water shortage areas.

2.3 Reconstruction and expansion of pipe network pipeline layout

The comparison of pipeline layout schemes is the key to optimize the design of reconstruction and expansion pipe network. The layout of pipe network reconstruction and expansion should make full use of the original pipelines and add new pipelines, mainly focusing on the transformation of pipe network. Seize the opportunity of pipe network reconstruction and expansion, rebuild and expand the low-pressure water-deficient area step by step, add new pipes or increase the diameter of the original pipes, and replace the pipe sections that have been in disrepair for a long time or whose sections have been obviously reduced, so as to improve the water supply efficiency and enhance the safety and reliability of pipe network operation. According to the plan, combined with the actual situation that there are many kinds of pipelines buried under the original pipe network, the following points should be considered in the pipeline layout during the reconstruction and expansion of the pipe network: the road where the original pipeline is located should be included in the reconstruction planning scope or there are planned roads in the parallel direction nearby, and the pipeline should be laid along the planned roads; The road where the original pipeline is located remains unchanged, but it is allowed to add pipelines, which is set to add pipelines along the road where the original pipeline is located; There is no planned road and no new pipeline is allowed, so we have to consider dismantling the original pipeline and building a new large-diameter pipeline; For the expanded pipe network, the pipeline should be laid along the planned road to meet the layout requirements of the new pipe network. In short, the transformation of water supply network should be carried out in accordance with the following principles:

(1) Abandon the old pipeline with serious leakage and replace it with a new one;

② Pipelines with better pressure resistance and corrosion resistance shall be adopted as far as possible in the pipeline network reconstruction to reduce pipeline accidents;

(3) The transformation of pipe network should be beneficial to reduce the operation cost and avoid secondary pollution to water quality;

(4) The laying of the new pipeline should be consistent with the original pipeline as far as possible, so as to reduce the cost of survey and construction and facilitate the connection with the existing pipeline section;

⑤ The laying of new pipelines should be consistent with the trend of street reconstruction;

⑥ Consider the organic combination of long-term and short-term pipe networks.

2.4 pipe network graphics simplification

Properly simplify the newly-built water supply network, keep the main pipeline, and omit some minor pipelines with little influence of hydraulic conditions, so that the simplified network can basically reflect the actual water consumption, ensure the user's water consumption and water pressure, and make the urban water distribution system run optimally. However, improper simplification of the pipe network will increase the difference between the calculated results and the actual water consumption, resulting in low pressure in some water supply areas and high pressure in some water supply areas, and even waste of investment and operation. In order to prevent the pressure in a certain area of urban pipe network from being too high or too low, and make the investment and operation of the whole system reach the best state, it is necessary to simplify the pipes in the pipe network reasonably. Therefore, the simplification of pipe network graphics is to simplify the pipeline on the premise of ensuring that the calculation results are close to the actual situation. The pipe network simplification method is as follows:

① The principle of pipeline omission is that under normal circumstances, the diameter of pipeline is directly proportional to the role of pipeline in water supply and distribution and the influence of hydraulic conditions. According to the distribution of water consumption population and water consumption standard in the pipe network, the branch pipes or pipelines that do not affect the hydraulic calculation of the pipe network are gradually dismantled, but the influence degree of pipelines on the pipe network work (such as small connecting pipes between trunk lines) needs to be judged manually. ), and calculation errors will inevitably occur, especially for small diameter pipes forming rings. After omitting a pipeline (without sharing flow) in the pipeline network, strictly speaking, it will affect the hydraulic conditions of the whole pipeline network, and it will have the greatest impact on the hydraulic conditions of the pipelines around the omitted pipeline. The influence of pipeline omission on head loss is related to the location, diameter and length of pipeline, the number of pipelines to be omitted and the flow in surrounding pipelines. However, if the end of the branch pipe is used by large users, and it is prone to fire, especially at the end of the branch pipe, such pipes cannot be easily omitted. The reason is to check whether the pipe diameter and pump can meet the requirements of flow and water pressure during fire fighting.

② In theory, accurate calculation results can be obtained by merging pipelines. In the water supply network of large and medium-sized cities, the pipeline can be simplified by 30%. The closer the distance between the two pipelines is, the smaller the head loss caused by the merger will be. In addition, the merging and pipeline omission of parallel pipelines need to consider the processing of its surrounding pipelines.

(3) When the number of decomposable pipe networks is small and connected by two pipes at most, if the flow direction and flow velocity of the pipes are easy to determine, the connected pipes can be disconnected and one pipe network can be decomposed into two independent pipe networks, which can be calculated separately. However, most pipe networks in China are arranged in a ring shape, and a water supply area is connected with external pipe networks in many places. This method is generally difficult to achieve.

(4) For cities with large water supply scale, there are more than one water supply pipeline under many municipal roads, which are usually located on both sides of the road and connected with each other through crossing pipelines. The diameter of these crossing pipes is usually the same as or similar to that of the main pipe, and the length is small, which has little influence on the hydraulic conditions of the pipes on both sides of the road, and the hydraulic parameters at both ends of the crossing pipes are basically the same, so this kind of pipe section can be regarded as one section.

3. Concluding remarks

Pipeline network planning and layout is an important part of pipeline system planning. Buried in the ground, pipelines are easy to expose problems such as waste of funds and unreasonable water supply, and there are many hidden dangers. Therefore, in order to completely eliminate these unreasonable factors, reasonable planning and optimization design must be carried out in the planning and design stage of the pipe network, and the current situation, short-term and long-term hydraulic simulation check of the system must be carried out to achieve the purpose of design optimization.

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