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When designing the steam pipeline in the chemical plant, in order to ensure the quality and efficiency of the design, the pipe diameter should be reasonably selected, and the layout of the pipeline should also meet the requirements of stress. In addition, attention should be paid to other details to avoid the phenomenon of water hammer.
01、Design of steam pipeline
Many different pipelines are set in the chemical plant, which are generally arranged outside the plant or along the plant, and supported in the air with supports to form a pipe gallery. The configuration of pipe rack has specific requirements. Generally, the process material pipes are arranged on the first floor and the first floor pipe rack, the utility pipes are arranged on the third floor, and the instrument cable tray plate is arranged on the fourth floor. The steam pipeline is arranged on the third floor.
In order to facilitate the setting of π shaped compensator, the general steam pipeline should be arranged on the front side of the pipe gallery. Under the condition of high temperature, the steam pipeline will expand. At this time, π compensator can be used to absorb the thermal expansion of the pipeline. As the bellows expansion joint is expensive and its service life is not long, it is generally not used for absorption when the steam pipeline is thermally expanded. When determining the installation position of the compensator, we must first strictly analyze the pipeline so that the compensator can be centrally set. The pipes with high temperature and large compensation are generally set on the outside, while the pipes with low temperature and small compensation are set on the inside. The π shaped compensator is generally set in the middle. In addition, the guide frame shall be set on both sides of the compensator, and the distance between the guide frame and the compensator shall be determined according to the stress of the pipeline. When calculating the thrust of the support and the stress of the steam pipeline, the stress of the whole steam pipeline shall be calculated. Generally, multi-layer pipe gallery is set in chemical plants, while steam pipeline is set on the upper layer of multi-layer pipe gallery, so that the low-temperature pipeline and liquid hydrocarbon pipeline are not adjacent. On the same floor, steam pipes and electronic instrument cables can be arranged at the same time, but the spacing between them shall not be less than 200mm. The steam pipe can also be arranged at the lower layer of the electronic instrument cable, but the interval shall not be less than 500mm.
2、Design of steam pipeline drainage facilities
In general, the special drainage is set in the steam pipeline in the warm-up stage. Since a large amount of condensate will be generated when driving, special drainage facilities should also be set up. The setting of drainage facilities shall be selected according to the grade of steam pressure.
Under normal conditions, the ultra-high pressure pipeline will not produce condensate, and there is no condensate pipeline with corresponding specifications set on the ultra-high pressure steam pipeline, so the drainage facilities are generally not set on the ultra-high pressure pipeline. The ultra-high pressure pipeline has the characteristics of thick pipe wall, difficult opening and high pressure, so the liquid separation package is generally not set. Under normal circumstances, generally, condensate will not be generated in high-pressure, medium pressure and low-pressure pipelines. However, in order to prevent a large amount of condensate from being generated in the steam pipeline in the warm-up stage or start-up stage, drainage facilities such as drain valve and liquid drum shall be set on these steam pipelines.
When setting the liquid discharge facilities of the steam pipeline, the liquid separation package should be set at the end of the steam main pipe. The spacing between the liquid separation packages on the steam main pipe is also specified. If it is saturated, the spacing between the liquid separation packages in the device is 80mm. If it is overheated, the interval of the liquid separation drum shall be 160mm. If it is in the downhill state, the interval of the liquid separation package outside the unit should be 300mkm. If it is in the downhill state, the interval of the liquid separation package outside the unit should be 200mm. The steam water separator is generally set when the saturated steam main pipe enters the device, and should be set near the boundary of the device side. In addition, regular drainage measures shall be set at the lower part of the water separator. If the superheated steam main pipe enters the device, there is no need to set a water separator. The steam vent pipe shall be directly discharged to the atmosphere, so a drain hole shall be opened, and a DN15 pipe shall be connected at the lower end of the steam vent pipe and at the appropriate places such as drainage ditch and funnel. Guide and load-bearing supports shall also be set on the steam vent pipe. Because the steam flooding pipeline is often discharged or connected, it should be led to the main operation area or where there are not many operators.
3、Design of steam branch pipe
A steam branch pipe is set at the top of the steam main pipe. Generally, a shut-off valve is set on the steam branch pipe. In order to avoid liquid storage, the shut-off valve should be set on the horizontal pipe close to the main pipe. Some steam pipelines have strict requirements for steam consumption, so the steam branch pipe cannot be connected to this steam pipeline, and the branch pipe cannot be connected from the π compensator of the steam pipeline. If the branch pipe is connected to the main pipe at both ends of π compensator, the branch pipe shall not be affected by the displacement of steam main pipe. During thermal expansion, the main steam pipe will produce the displacement of the outlet point of the branch pipe, and the branch pipe will not bear too much pressure or displacement. Under normal circumstances, when the branch pipe is connected to the main steam pipe, the two valve group is used. However, in order to make the leakage be found at any time, the two valve group cannot be used to lead from the branch steam pipe or main steam pipe to other process pipes, but three valve group should be set. According to different conditions, the setting of drainage, such as drain valve or drain valve, should be set at the low point of steam branch pipe. When setting drainage facilities on the official road, it should be set according to the different grade pressure on the pipe gallery.
4、Design of steam condensate pipeline
Generally, steam pipes and steam condensate pipes are arranged on the same floor on the pipe gallery. In order to prevent water hammer, π shaped compensator can be set on the steam condensate pipe. The π line compensator should be set in the horizontal direction, or the riser should be designed as an inclined section.
Condensate from steam traps with different pressures should be connected to their respective recovery header. When the nominal diameter of the branch pipe is not less than 50mm, it can be directly connected to the top of the steam condensate recovery main pipe. The printing plate adopts flange connection as the drain valve and is set in the recovery system of steam condensate. There should be no bag on the pipe at the inlet of the drain valve. If the drain valve is lower than the main steam condensate recovery pipe, a check valve should also be set behind the drain valve. When setting the check valve, it should be set on the horizontal pipeline, close to the main steam condensate pipe. The check valve should also be connected with flange, which can facilitate the purging and disassembly of steam pipeline.
5、Key points needing attention in steam pipeline design
1. Reasonable selection of pipe diameter
The pipe diameter shall be selected according to the steam demand. When the pipe diameter is too large, it will increase investment, increase heat loss and increase condensate. When the pipe diameter is too small, it will cause the pressure at the steam use point and insufficient steam flow, and finally lead to water hammer and erosion. Therefore, when selecting the pipe diameter, it should not be too large or too small.
2. stress requirements
When arranging pipelines, we must meet the requirements of stress and strictly calculate the stress. The setting of π shaped compensator on the pipeline, the thrust of the fixed point of the compensator and the piping of the steam pipeline connected with the equipment should meet the requirements of stress. This operation can improve the efficiency of design work.
3. Avoid water hammer
When the high-speed flowing water shot touches the installation parts, equipment or valves of the pipeline, it will produce certain vibration and noise, which is the so-called water hammer phenomenon. In order to avoid the phenomenon of water hammer, pay attention to the setting of drainage system. On the other hand, when connecting the branch pipe to take steam, it should be above the main pipe. The pipeline shall not use too many branch pipes, necking bends, etc. In order to prevent local sinking of the pipeline, the setting of pipeline support must be reasonable. The filter screen of the filter should be installed horizontally. Attention should be paid to the above details, so as to avoid the phenomenon of water hammer and improve the quality and efficiency of steam pipeline design in chemical plant.
There are many strict requirements for the setting of steam pipeline in chemical plant. In addition, we should pay attention to many details, so as to ensure the scientific and reasonable design, improve the working efficiency of steam pipeline and ensure the normal function of steam pipeline.