Steam Pipelines in Chemical Plants

Steam pipelines in chemical plants

Design of steam pipelines

Many different pipelines are set up in chemical plants, generally arranged outside the plant or along the plant, supported in the air by brackets, and become pipe corridors. There are specific requirements for the configuration of pipe corridors. Generally, process material pipes are arranged on the first floor and the first floor of the pipe corridor, public engineering pipes are arranged on the third floor, and instrument cable troughs are arranged on the fourth floor. Among them, steam pipelines are arranged on the third floor.

In order to facilitate the setting of π-type compensators, steam pipelines should generally be arranged on one side of the pipe corridor. Under high temperature conditions, steam pipelines will expand. At this time, π-type compensators can be used to absorb the thermal expansion of the pipeline. Since the bellows expansion joint is relatively expensive and has a short service life, it is generally not used to absorb the thermal expansion of the steam pipeline. When determining the installation location of the compensator, the pipeline must first be strictly analyzed so that the compensator can be set up in a centralized manner. The pipelines set on the outside are generally those with higher temperatures and larger compensation amounts, while the pipelines set on the inside are those with lower temperatures and smaller compensation amounts. The π-shaped compensator is generally set in the middle position, and the guide frame should be set on both sides of the compensator. The distance between the guide frame and the compensator is determined according to the stress of the pipeline. When calculating the thrust of the bracket and the stress of the steam pipeline, the stress of the entire steam pipeline should be calculated. Generally, multi-layer pipe corridors are set in chemical plants, and steam pipelines are set on the upper layer of the multi-layer pipe corridor, so that the low-temperature pipeline and the liquid hydrocarbon pipeline are not adjacent. On the same layer, steam pipelines and electronic instrument cables can be arranged at the same time, but the interval between the two must not be less than 200mm. The steam pipeline can also be arranged on the lower layer of the electronic instrument cable, but the interval cannot be less than 500mm.

Design of steam pipeline drainage facilities

Generally, special drainage is set in the steam pipeline in the warm-up stage. Because a large amount of condensate will be generated during driving, special drainage facilities must also be set up. The setting of drainage facilities should be selected according to the different levels of steam pressure.

Under normal circumstances, ultra-high pressure pipelines will not produce condensate, and there is no condensate pipeline of corresponding specifications set on the ultra-high pressure steam official road, so drainage facilities are generally not set on the ultra-high pressure official road. Ultra-high pressure pipelines have the characteristics of thick pipe wall, difficult to open holes, and high pressure, so liquid separators are generally not set. Under normal circumstances, condensate will not be produced in high-pressure, medium-pressure and low-pressure pipelines. However, in order to prevent a large amount of condensate from being produced in the steam pipeline during the warm-up stage or the start-up stage, drainage facilities such as drain valves and liquid separators should be set on these steam pipelines.

When setting up the drainage facilities of the steam pipeline, the liquid separator should be set at the end of the steam main pipe. There are also certain regulations on the spacing between the liquid separators on the steam main pipe. If it is in a saturated state, the spacing of the liquid separators in the device is 80mm. If it is in an overheated state, the spacing of the liquid separators should be 160mm. If it is in a downslope state, the spacing of the liquid separators outside the device should be 300mkm, and if it is in a reverse slope state, the spacing of the liquid separators outside the device 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, measures for regular drainage should be set at the bottom of the water separator. If the steam entering the device is a superheated steam main pipe, there is no need to set up a water distributor. Because the steam vent pipe is directly discharged to the atmosphere, a drain hole should be opened at the lower end of the steam vent pipe, and a DN15 pipe should be connected to a suitable place such as a drain ditch or funnel. A guide and load-bearing bracket should also be set on the steam vent pipe. Because the steam pipeline is often discharged or connected to discharge, it should be led to the main operation area or a place where there are not many operators.

Design of steam branch pipe

A steam branch pipe is set on 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 pipes have strict steam requirements, so steam branches cannot be connected to such steam pipes, and branches cannot be connected from the π-shaped compensator of the steam pipe. If the branch pipe is connected to the main pipes at both ends of the π-shaped compensator, the branch pipe should not be affected by the displacement of the steam main pipe. During thermal expansion, the steam main pipe will produce displacement of the branch pipe connection point, and the branch pipe will not be subjected to excessive pressure or displacement. Under normal circumstances, when the branch pipe is connected to the steam main pipe, a two-valve group is used. However, in order to make the leakage detectable at any time, the two-valve group cannot be used to lead from the steam branch pipe or steam main pipe to other process pipes, but a three-valve group should be set. According to different situations, the setting of the drain, such as the drain valve or the steam trap, should be set at the low point of the steam branch pipe. When setting the drain facilities on the official road, it should be based on the different pressure levels on the pipe gallery.

Design of steam condensate pipeline

Generally, steam pipes and steam condensate pipes are arranged on the same floor of the pipe gallery. In order to prevent water hammer, a π-shaped compensator can be set on the steam condensate pipe. This π-shaped compensator should be set in a horizontal direction, or the riser should be designed as an inclined section.

Condensate comes out of steam traps with different pressures and should be connected to their respective recovery mains. 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 uses flange connection as the steam trap to be set in the steam condensate recovery system, and there should be no bag shape on the pipe at the entrance of the steam trap. If the steam trap is lower than the steam condensate recovery main pipe, a check valve should also be set behind the steam trap. When setting the check valve, it should be set on the horizontal pipe, close to the steam condensate main pipe. The check valve should also be connected with a flange, which can facilitate the steam pipeline purge and disassembly of the check valve.

Key points to pay attention to when designing steam pipelines

1. Reasonable selection of pipe diameter

When selecting the pipe diameter, it should be based on the demand for steam. When the pipe diameter is too large, it will increase investment, increase heat loss, and also increase condensate. When the pipe diameter is too small, it will cause pressure at the steam use point, insufficient steam flow, and finally cause water hammer and erosion. Therefore, when choosing the pipe diameter, it should not be too large or too small.

2. Stress requirements

When arranging the pipeline, it must meet the stress requirements and strictly calculate the stress. The setting of the π-shaped compensator on the pipeline, the thrust of the compensator fixing point, and the piping of the steam pipeline connected to the equipment must meet the stress requirements, so that the efficiency of the design work can be improved.

3. Avoid water hammer phenomenon

When the high-speed flowing water ball hits 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, attention should be paid to the setting of the drainage system. In addition, when connecting the branch pipe to take steam, it should be above the main pipeline. The pipeline cannot use too many branch pipes, shrinking bends, etc. In order to prevent the phenomenon of local sinking of the pipeline, the setting of the pipeline support must be reasonable. The filter screen should be installed horizontally. All of the above details should be paid attention to, so as to avoid the phenomenon of water hammer and improve the quality and efficiency of the steam pipeline design in the chemical plant.

In summary, there are many strict requirements for the setting of steam pipelines in chemical plants. In addition, many details should be paid attention to, so as to ensure that the design is scientific and reasonable, improve the working efficiency of the steam pipeline, and make the steam pipeline play a normal role.