When designing steam piping in a chemical plant, in order to ensure the quality and efficiency of the design, the pipe diameter should also be reasonably selected, and the piping should be arranged to meet the requirements of the stress, in addition to paying attention to a number of other details to avoid the phenomenon of water hammer.
01
Design of steam piping
Many different pipelines are set up in the chemical plant, generally arranged outside the plant or along the plant, supported in the air with a bracket, becoming a pipe corridor. There are specific requirements for the configuration of the pipe corridor, generally the process material pipes are arranged in the first layer and the first layer of the corridor, the utility piping is arranged in the third layer, and the instrumentation cable trough plate is arranged in the fourth layer. Among them, the steam pipes are arranged in the third layer.
In order to facilitate the setting of π-shaped compensator, generally the steam pipeline should be arranged on the side of the corridor. At high temperatures, the steam pipes will expand, and the π-compensator can be used to absorb the thermal expansion of the pipes. Because bellows expansion joints are more expensive and do not have a long service life, they are generally not used to absorb the thermal expansion of steam pipes. When determining the installation position of the compensator, the pipeline should first be analysed strictly so that the compensator can be set centrally. The pipelines with high temperature and large compensation capacity are usually set up on the outside, while the pipelines with low temperature and small compensation capacity are set up on the inside. pi-shaped compensators are usually set up in the middle, and guiding frames are set up on both sides of the compensators to determine the distance between the guiding frames and the compensators according to the stress of the pipelines. When calculating the thrust of the bracket and the stress of the steam piping, the stress of the entire steam piping is calculated. Generally, there are multi-layer pipe galleries in chemical plants, and steam pipes are installed in the upper layer of multi-layer pipe galleries, so that cryogenic pipes and liquid hydrocarbon pipes are not adjacent to each other. On the same layer, steam piping and electronic instrumentation cables can be arranged simultaneously, but to ensure that the interval between the two is not less than 200 mm, or steam piping can be arranged in the electronic instrumentation cables in the lower layer, but the interval is not less than 500 mm.
02
Steam piping liquid discharge facilities design
In general, the special liquid discharge is set in the steam pipe in the warming stage. In the driving time because it will produce a large amount of condensate, so it is also necessary to set up special liquid discharge facilities. The setting of the drain facility is selected according to the steam pressure level.
UHP piping does not produce condensate under normal conditions, and there is no condensate piping of the corresponding specifications on UHP steam piping, so there are generally no hydrophobic facilities installed on UHP piping. UHP piping is characterised by thick walls, difficult openings, and high pressures, so generally there are no liquid separation packages installed either. Under normal circumstances, condensate is not normally generated in high-, medium- and low-pressure piping. However, in order to prevent a large amount of condensate from being generated in steam piping during the warm-up or start-up phases, it is necessary to install trapping facilities such as drain valves and liquid separation packages on these steam piping.
When installing steam piping, a manifold should be installed at the end of the steam main, and the interval between manifolds on the steam main is also subject to certain regulations: if in a saturated state, the interval between manifolds inside the unit is 80 mkm; if in a state of overheating, the interval between manifolds should be 160 mkm; if in a state of downhill, the interval between manifolds outside the unit should be 300 mkm; if in a state of downhill, the interval between manifolds outside the unit should be 300 mkm; if in a state of overheating, the interval between manifolds should be 160 mkm. In the case of a downhill condition, the interval between the manifolds outside the unit should be 300 mkm, and in the case of a downhill condition, the interval between the manifolds outside the unit should be 200 mkm. The steam separator is normally installed near the boundary of the side of the unit when the saturated steam main enters the unit. In addition, the lower part of the distributor should be equipped with a measure for frequent dewatering. If a superheated steam main enters the unit, there is no need to install a water separator. A drain hole should be provided at the lower end of the steam vent pipe for the steam vent pipe to be discharged directly to the atmosphere, and a DN 15 pipe should be connected to the drain, funnel, etc., wherever appropriate. Guiding and load-bearing brackets should also be set up on the steam vent pipe. Because the flooded steam pipe is often discharged or connected to discharge, it should be led to the main operating area or to a place where there are not too many operators.
03
Design of Steam Branch Pipes
Steam mains are set up at the top of the steam branch, generally set up with a shut-off valve in the steam branch, in order to avoid liquid storage, the shut-off valve should be set in the horizontal piping, close to the main. Some steam piping requirements are more stringent than others, so steam branch pipes should not be connected to such piping, and branch pipes should not be connected to the π-compensator of the steam piping. If the branch pipe is connected to the main pipe at both ends of the π-compensator, the branch pipe should not be affected by the displacement of the steam main. In the case of thermal expansion, the steam main will cause displacement at the branch connection point, and the branch will not be subjected to excessive pressure or displacement. Normally, a two-valve manifold is used when the branch is connected to the steam main, but in order to allow leaks to be readily detected, the two-valve manifold should not be used to connect to other process piping from the steam branch or the steam main, but rather a three-valve manifold should be installed. Depending on the situation, traps, such as drain valves or traps, should be installed at the low point of the steam branch pipe. When installing traps on the pipeline, the pressure should be set according to the different levels of pressure in the pipeline corridor.
04
Design of Steam Condensate Piping
Generally, steam piping and steam condensate piping are arranged on the same level on the pipe corridor. In order to prevent water hammer, a π-shaped compensator can be set up on the steam condensate piping. This π-row compensator is to be set in a horizontal direction, or the riser is designed as an inclined section.
Condensate from steam traps with different pressures should be connected to their respective recovery mains. When the nominal diameter of the standpipe is not less than 50 mm, it can be connected directly to the top of the steam condensate recovery main. The printing plate selects a flange connection as the trap set in the steam condensate recovery system, and should not have a bag shape on the piping at the inlet of the trap. If the trap is lower than the steam condensate recovery main, a check valve should also be set behind the trap. When installing check valves, they should be installed on horizontal piping, near the steam condensate main. A flange connection should also be used for the check valve so that the steam piping can be easily blown out to remove the check valve.
05
Points to note when designing steam piping
1 Reasonable selection of pipe diameter
When choosing the pipe diameter, according to the demand for steam. When the pipe diameter is too large, it will increase the investment, increase the heat loss, and also increase the condensate. When the pipe diameter is too small, it will cause the pressure of the steam use point, the steam flow is insufficient, and finally make the phenomenon of water hammer and erosion. Therefore, when selecting the pipe diameter, not too large or too small.
2 Stress requirements
When arranging the pipeline, it must meet the requirements of stress and strictly carry out the calculation of stress. The setting of π-shaped compensator on the pipeline, the thrust of the compensator fixed point and the piping of the steam pipeline connected to the equipment should meet the requirements of stress, so that the efficiency of the design work can be improved.
3 to avoid water hammer phenomenon
When the high-speed flow of water particles touch the pipeline installation, equipment or valves, will produce a certain amount of vibration and noise, which is known as the water hammer phenomenon. In order to avoid the phenomenon of water hammer, pay attention to the setup of the hydrophobic system, in addition to the sub ah connecting the branch pipe to take the steam, to be above the main pipe. The pipeline can not use too many branch pipes, shrinkage bends, etc.. In order to make the phenomenon of local sinking of the pipeline does not occur, set the pipeline support settings must be reasonable. The filter screen should be installed horizontally. All these details should be paid attention to so that the phenomenon of water hammer can be avoided and the quality and efficiency of steam piping design in chemical plants can be improved.
Summary
Chemical plant steam piping setup is a lot of strict requirements, but also pay attention to a lot of details, so as to ensure that the design is scientific and reasonable, improve the efficiency of the steam piping, when the steam piping function properly.
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