Pipeline design and equipment selection of the compressed air supply system of the water plant You Ding Peng should discuss the piping system process design of the compressed air supply system of the water plant and the problems that should be paid attention to in the air cleaning and pipeline equipment selection work. And provide some examples to illustrate the relevant principles and opinions.
0 Preface At present, with the improvement of people's living and industrial development level, urban water supply standards are becoming stricter. However, some old water plants with outdated equipment and backward technology in the towns have been unable to adapt to new production needs.
Therefore, many new water plants with advanced technology and high degree of automation in the production process have emerged. At the same time, a considerable number of water companies have improved their water supply capacity or quality of water supply by performing various technological changes in their processes or controls on their old water plants.
Under the new development situation, the advanced gas-water backwash homogeneous filter media filter water filtration process is widely used in major new water plants. Some of the old water plants have also adopted this water filtration process through the technological transformation of the filter tank.
Gas water backwash homogeneous filter media filter water filtration process needs to be equipped with the following process valves: 1 filter to water valve 2 filter drain valve 3 filter water filter valve 4 filter back flush valve 5 filter back flush valve 6 filter gas, water distribution channel vent valve 7 recoil blower outlet valve 8 recoil pump outlet valve.
For the above valves that should be equipped for this process, many technicians consider the use of pneumatic valves. Because of the comparison of electric valves, pneumatic valves have the following advantages: (1) quick and reliable opening and closing action (2) for use with electrical position controllers The position-controlled pneumatic valve (such as the water filter valve) has high position control precision, good control linearity, large opening vibration damping (3) simple structure, no over-torque of the electric valve, and large current and other fatigue. The requirements for the use environment are relatively low and easy to maintain.
Because of the above advantages, pneumatic valves have been widely used in water plants with new water filtration processes.
However, the main factors determining the quality of pneumatic valves include two aspects. The first is the quality of the valve itself, and the other is the quality of its use environment and gas supply. For the former aspect, many water companies or water plants pay more attention to equipment selection and installation. However, the latter factor to be considered, especially the quality level of the gas source, is easier to ignore. Combining with the design of the compressed air supply system of water plants and the practice of equipment selection in recent years, I will discuss the process design of the piping system for compressed air supply system and the work of air cleaning and pipeline equipment selection. There are several issues that should be noted. This article only explores the pipeline part of the compressed air supply system. There are many specific issues related to the compressor, which will not be discussed.
1 Pipeline system flow design should pay attention to the problem When the pneumatic system works, the content of water, solid impurities in the compressed air, oil lubrication from the compressor lubrication system or the special gas source oil mist generation system is An important factor in determining whether a system can work properly. Therefore, the compressed air used in special pneumatic equipment (such as pneumatic valves, electric position controllers, etc.) used in water plants must be equipped with drying, purification and decompression systems to optimize the quality of the gas, and also pay attention to the gas supply pipeline. Whether the process is reasonable and efficient.
For most water plants, the drying, purification and decompression system of compressed air should include the following basic steps: 1 air tank 2 dry section 3 decompression section 4 filter section 5 oil mist separation section.
In the engineering design stage, the above basic links can generally be arranged in the following order: compressor air tank drying section decompression section filter section follow-up pipeline oil mist separation section for the convenience of the following description, named this layout order is the way A. Foshan This layout sequence was adopted in the engineering design of two sets of independent compressed air supply systems in the two workshops and three workshops of Shiwan Water Plant.
Another process is to arrange the drying section and the position of the gas storage tank. The compressed air is dried before entering the gas storage tank.
Name this layout order as mode B.
Some water plants (such as Huizhou Jiangbei Water Plant) have selected compressors with dryers. If it is confirmed that the relative humidity of the outlet compressed air reaches the system requirements, the above-mentioned layout sequence can also be deducted from the dedicated drying section. In this case, it also became the way B.
In the production practice, the two layout sequences have their own advantages and disadvantages, and the results are compared.
Mode content mode Drying effect Compared with mode B, compared with mode A, the poor degreasing effect is better than mode B, compared with mode A, the poor dry energy consumption (in the cooling dryer Example) Small gas storage tank maintenance workload size Dry section Maintenance workload Small compressed air supply system Drying equipment drying capacity refers to its ability to reduce the relative humidity of compressed air, dried under the same pressure and temperature The smaller the relative humidity value of the treated compressed air, the better the drying ability of the system.
For the dryers equipped with the compressed air supply system of the water plant, the cooling dryer is more commonly used, and the effect is better.
Under certain supply pressures and related working conditions, the drying effect and energy consumption of the cooling dryer are directly related to the temperature difference between the inlet and outlet. The difference between the temperature of the cooling dryer inlet and the dew point of the exhaust gas is greater. , the higher the drying cost). In the mode A, the gas storage tank can cool the high temperature compressed air discharged from the compressor and separate part of the condensed water and the condensed oil, thereby reducing the load of the dryer, optimizing the working condition of the dryer and saving energy. Therefore, in the engineering design work, generally consider the choice method A.
In order to reduce the drainage and drainage maintenance of the gas storage tank, a bottom automatic/manual double-acting liquid discharge device may be added to the gas storage tank.
The decompression section is an indispensable part of the compressed air supply system. Its main functions are as follows: (1) The pressure of the cooled compressed air is adjusted to stabilize the pressure at a certain amplitude and reach the supply pressure of the pneumatic equipment. Claim.
(2) Under the premise of meeting the gas supply pressure requirements of the pneumatic equipment of the water plant, reduce the delivery pressure of the compressed air, reduce the burden on the subsequent pipeline, and reduce the leakage caused by the micropores or the connection seal of the pipeline.
The special filter section and oil mist separation section in the compressed air supply system are necessary for further dedusting and degreasing treatment of the cooled and dried compressed air. In the process layout sequence, these two links must be placed after the gas storage tank and the drying section. Otherwise, the high-temperature compressed air that has just been discharged from the compressor without cooling and drying will bring excess load to these two links, and Accelerate the fatigue of their work.
For pneumatic equipment with high control accuracy (such as electric position controller), in the case of economic permission, it is best to add a primary filter to the inlet of the gas supply near the equipment (the filter pore size of the filter must comply with The requirements of the protection equipment) further optimize the quality of the gas supply to reduce the probability of failure of the capillary control air pipe by the metal, plastic or seal debris brought by the gas supply pipe.
Some pneumatic equipment requires a certain amount of lubricating oil mist in the compressed air supply. We have to set up a gas supply branch for them and install an oil mister. Pneumatic equipment selection in water plants generally tends to use maintenance-free, non-lubricated pneumatic valves and other pneumatic components.
In the engineering design of the compressed air supply system of the water plant, it is also necessary to pay attention to the parallel interconnection problem of each air treatment equipment. For equipment with short maintenance intervals and high maintenance rates, online spare equipment or jumper piping must be set up. To effectively reduce the impact on plant production caused by equipment failure or equipment maintenance.
In summary, take the compressed air pipeline system flow (main part of the main road) of the second workshop of Shiwan Water Plant in Figure 1 as a concrete example for reference.
2 Problems to be paid attention to in the selection of equipment In order to make the working conditions of the pneumatic system of the water plant meet the requirements and further optimization, it is necessary to improve the quality level of the gas supply source. In order to do this, in addition to fully considering the process and process rationality in engineering design, it is necessary to put a good technology in the equipment selection work. The quality of the equipment selection directly affects the quality of the pneumatic equipment in the water plant.
2.1 Problems to be paid attention to in the selection of gas storage tanks The role of the gas storage tanks in the process of compressed air supply pipelines is to effectively buffer the unloading of the compressor unit, reduce the number of actions of the compressor pressure control electromechanical components and the compression will be compressed. The compressed air discharged from the machine is cooled to separate most of the condensed water and oil, which reduces the load of the subsequent cooling dryer and saves energy.
When selecting the gas tank, we should pay special attention to two aspects: 2.1.1 Specifications (1) The maximum operating pressure of the gas tank should be greater than 25 of the upper limit of the normal operating pressure range.
The gas storage tank of the compressed air supply system in the second workshop of Shiwan Water Plant is designed to use a pressure range of 0.55 to 0.70 M Pa, and finally a gas storage tank with a maximum operating pressure of 1.00 M Pa is selected.
(2) The guaranteed pressure resistance of the gas storage tank should be greater than 30 of its maximum working pressure, which is due to the safety of use.
The guaranteed pressure of the compressed air supply system in the second workshop of Shiwan Water Plant is 1.50 MPa.
(3) The capacity of the gas storage tank should not be too small. For example, when two gas storage tanks are installed in parallel, the capacity of the gas storage tank can be relatively small.
Compressed air supply system in the second workshop of Shiwan Water Plant Two capacity of the gas storage tanks in parallel are 1.0 m. 2.1.2 Accessories/standard equipment (1) must be equipped with safety valve, manual or manual/automatic drainage The gas storage tank of the device and the pressure gauge connection port is convenient for the safe operation and daily maintenance of the gas storage tank.
(2) The set pressure of the safety valve should not be higher than the maximum use pressure of the gas tank. The pressure gauge should be 1.5 to 2.0 times the upper limit of the pressure range and should be greater than the maximum pressure of the gas tank. The reason for this choice is the consideration of safety and measurement accuracy.
2.2 Problems to be paid attention to in the selection of cooling dryers (1) For the selection of cooling dryers (only mode A is considered here), the selection of the rated flow rate must be considered in conjunction with the possible instantaneous maximum air consumption of the pneumatic system of the water plant. Generally, the following formula can be adopted: the rated flow rate of the cooling dryer = the possible instantaneous state of the pneumatic system. The possible instantaneous instantaneous maximum air consumption of the pneumatic system of the Shiwan Water Plant II workshop is 350 L/min. We have selected the rated flow rate of 660 L. /min cooling dryer.
(2) The maximum operating pressure of the cooling dryer should be greater than the upper limit of the normal operating pressure range. 25. The maximum operating pressure of the cooling air dryer of the compressed air supply system in the second workshop of Shiwan Waterworks is 1.00 MPa.
2.3 Problems to be paid attention to in the decompression selection mode For the compressed air supply system of the water plant, it is advisable to use a pressure reducing valve for the decompression section.
(1) The maximum operating pressure of the pressure reducing valve should be greater than 25 of the upper limit of the normal operating pressure range.
(2) The pressure resistance of the pressure reducing valve should be greater than 30 of its maximum working pressure, which is due to safety considerations.
(3) The rated flow of the pressure reducing valve must be greater than twice the maximum instantaneous maximum air consumption of the pneumatic system, and the larger the better. This is advantageous for the stabilization of the supply pressure.
(4) The pressure regulating range of the pressure reducing valve must be selected according to the requirements of the air supply pressure, and must have good stability accuracy near the stable point of the air supply pressure.
(5) The pressure reducing valve must be equipped with a pressure gauge. The pressure gauge range should be 1.5 to 2.0 times the upper limit of the pressure range used, and should be greater than the maximum operating pressure of the pressure reducing valve. The reason for this choice is the consideration of safety and measurement accuracy.
The parameters of the compressed air supply system pressure reducing valve in the second workshop of Shiwan Water Plant.
Specifications parameter value maximum use pressure / MPa to ensure pressure / MPa rated flow / L / min pressure range / MPa pressure gauge range / MPa 2.4 filter section and oil mist separation section should pay attention to the problem due to compressed air in the two Before the purification process, it has flowed through compressed air storage and drying equipment such as gas storage tanks and cooling dryers. Most of the condensed water, condensed oil and solid dust particles have been effectively removed, but the suspended solid dust particles and oil mist are also It is impossible to meet the requirements of the gas supply purification of the pneumatic equipment of the water plant, especially the pneumatic equipment with high control precision (such as electric position controller). It is necessary to set up the two purification steps to further perform dust removal and degreasing treatment of the compressed air.
In the equipment selection, the following problems should be noted: (1) Pay attention to the size of the filter aperture. It is forbidden to filter the pore size larger than the minimum suspended solid dust particle size and the suspended oil droplet size requirement of the pneumatic equipment of the water plant. .
(2) As for the selection of parameters such as pressure resistance, maximum working pressure and rated flow rate, it is similar to the selection clause of the pressure reducing valve.
The parameters of the compressed air supply system filter in the second workshop of Shiwan Water Plant are shown in Table 3.
The parameters of the oil mist separator of the compressed air supply system in the second workshop of Shiwan Water Plant are shown in Table 4.
Specification parameter value Maximum use pressure / MPa Guaranteed pressure resistance / MPa rated flow / L / min Filter aperture / μm specification Parameter value Maximum use pressure / MPa Guaranteed pressure resistance / MPa minimum pressure / MPa rated flow / L / min filter aperture / Mm drainage mode automatic drainage (pressure loss normally open) The electrical position controller of each filter valve in the second workshop of Shiwan Water Plant requires that the suspended solid dust particle size in compressed air is not more than 25μm, and the suspended oil droplet size is not more than 2μm.
Therefore, the above selection of filters and oil mist separators is satisfactory. The selection of filters and oil mist separators for subsequent pipes is similar to the above.
2.5 Problems in the selection of compressed air supply pipe and pipe fittings The compressed air supply pipe of the water plant is generally composed of metal pipes, plastic hoses and corresponding pipe fittings.
For the selection of pipes and fittings, the following points should be noted: (1) For the selection of the diameter and pressure rating of pipes and fittings, it is necessary to combine the relevant supply pressure, supply flow, safety margin, etc. of the compressed air supply piping. Specific design data to consider.
(2) The material of the pipe and fittings must be selected in conjunction with the estimated service life of the compressed air supply pipe, the allowable deformation, and other factors (such as engineering expenses, ease of installation, etc.).
(3) For the pipeline valve used in the compressed air supply pipeline, it is recommended to use a copper alloy ball valve or a stainless steel ball valve because it is required to have good durability, easy maintenance, and rapid switching.
The three gas workshops of the Shiwan Water Plant are supplied with the following pipes and fittings: ordinary galvanized welded steel pipe galvanized malleable iron pipe fittings copper alloy ball valve PU (polyurethane) plastic hose copper internal structure self-sealing plastic hose quick connector .
The selection method of the compressed air supply pipe pipe and the pipe fitting has the advantages of saving engineering expenditure and installation workload. The disadvantage is that the main pipe of the pipe is a common galvanized welded steel pipe and a galvanized malleable cast iron pipe joint. During use, a certain amount of rust dust is generated, which increases the working load of each filter in the pipeline, and It is also easier to control the air circuit blockage faults of pneumatic equipment (such as electric position controllers) with high control precision.
Since the compressed air supply system of the third workshop of Shiwan Waterworks has been put into use since April 1998, two electrical position controllers have been in control of the air circuit blockage due to this reason.
The gas supply pipeline of the compressed air supply system of the second workshop of Shiwan Water Plant adopts the following pipes and fittings: welded stainless steel pipe stainless steel pipe joints stainless steel ball valve PU (polyurethane) plastic hose stainless steel inner structure self-sealing plastic hose quick connector.
The selection method of the compressed air supply pipe pipe and the pipe fitting has the advantages that the pipe is relatively durable, and can effectively solve the additional equipment maintenance and repair amount brought by the three-station compressed air supply system. The disadvantage is increased engineering costs and installation effort.
In the work of equipment selection, in order to save engineering expenses and future maintenance and maintenance costs, under the premise of meeting the selection conditions of the system design, it is not appropriate to adopt excessive margin for the parameters of the above various equipments.
3 Conclusions As more and more water plants (including newly built or retrofitted old ones) use gas-water backwashing homogeneous filter media filter water filtration process, pneumatic valve supply gas source quality level The quality of the high and low, compressed air supply system will gradually be valued by the engineering and maintenance technicians of each water plant. In addition to strict control of the system flow design of the compressed air supply system, we must pay attention to the preparation of clean air and the selection of pipeline equipment. Only in this way can we ensure and optimize the quality conditions of the gas supply source of the pneumatic valve of the water plant, and effectively reduce the maintenance and maintenance workload and maintenance cost of the pneumatic equipment.
1 Deppert W Stoll K. Low-cost integrated automation of pneumatic technology. Li Baoren translated. Beijing: Mechanical Industry Press, 1999 2 Sun Ziqiang. Production process automation and instrumentation. Shanghai: East China University of Science and Technology Press, 3 Shanghai Hardware Machinery Company. Practical Hardware Manual (Fourth Edition). Shanghai: Shanghai Science and Technology Press, 1991 4 Yan Yushi, Fan Yuchu. Water Supply Engineering (third edition). Beijing: China Building Industry Press, Author's Office of Communications: 528000 Foshan City Water Supply Corporation Automation Working Group, No. 16 Tongji West Road, Foshan City Discussion on the rigorous inspection of the drainage pipelines between China and Germany. Tang Jianguo, Lin Jiemei, mainly on the pipelines of China's current regulations. The rigor test requirements are compared with the corresponding German standards. The new German inspection methods are introduced and the views on some of the problems in the pipeline rigor inspection are explained.
1 Necessity of inspection of the tightness of the drainage pipe After the completion of construction, overhaul and remediation, the drainage pipe shall be inspected or tested before being delivered for use. This is the main content of the completion acceptance. If the drainage pipe is not tight, the following adverse effects will occur: 1 The sewage will seep through the pipeline and the tightness of the well, polluting the soil and groundwater. 2 Rainwater and sewage will seep through the pipeline and the tightness of the well, causing erosion on the soil and causing the ground. Collapse 3 In the high groundwater area, groundwater will penetrate into the pipeline through pipelines and tightly-noted wells, increasing the displacement. 4 Plant roots will grow in pipelines, wells and even in pipelines, which will hinder the pipeline's water transport capacity.
It is precisely because of the tightness of the drainage pipe that the above-mentioned hazards exist. In addition to the rigorous inspection before the completion acceptance, the rigorous inspection is carried out regularly during the operation. Early detection and elimination of the imperfect defects are to ensure the safe operation and avoidance of the drainage system. Prerequisites that pose a hazard to the environment.
2 Methods of strict inspection The drainage pipelines (sewage, rainwater, rainwater and sewage combined pipelines) mostly adopt the pressureless gravity flow conveying method, in accordance with the provisions of China's "Water Supply and Drainage Pipeline Engineering Construction and Acceptance Specifications" (GB5026897) (referred to as the specification) The rigor test should be carried out using the closed water method. The methods and requirements for the closed water test are specified in this specification.
German non-pressure gravity flow drainage pipe tightness inspection methods are: hydraulic pressure test, air pressure test, irrigation test, optical inspection (when the pipeline is below the groundwater level), leakage inspection.
The German water pressure test is actually similar to the closed water test method in China. Since the test head is tested to the top of the well, there is actually a certain water pressure, which is different from the irrigation method (water level to the top of the pipe). It is called hydraulic pressure inspection. Germany's German industrial standard DIN EN1610 (referred to as the standard, which has replaced the old standard DIN4033) issued in 1997 provides detailed regulations for hydraulic and barometric inspections, which are applicable to the tightness inspection of newly laid pipes.
The comparison to be asked.
According to the German standard DIN EN1610, the pipe tightness inspection can be carried out by hydraulic pressure or pneumatic method. The main advantage of the barometric inspection is that the time required for the inspection is short, and the entire inspection process takes only 30 minutes. The cost is low and there is no need to test the water source and the discharge location. The requirements for air pressure inspection are detailed. This barometric inspection is also suitable for the rigor of the pipeline during operation. Another form of barometric inspection is the vacuum method, which has proven to be more suitable for large diameter pipes using vacuum.
In Germany, it is allowed to use the irrigation method to check the tightness of the pipeline, that is, from the inspection well to the top of the pipe. If after 15 minutes, there is no obvious (visible) drop in the water level at the initial inspection of the inspection section, then the pipeline is considered to be Strict. The advantage of this type of inspection is that the water in the pipeline can be used for rigorous inspection without pre-filling time. According to relevant German standards, this method is applicable to the inspection of the tightness of pipes with a pipe diameter below 500 mm.
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