Design of steam pipeline in petrochemical plant

Design of steam pipeline in petrochemical plant

With the continuous improvement of China’s economic level, China’s petrochemical industry has made great achievements. In the whole chemical industry, petrochemical plant plays a very important role, and steam pipeline, as an important part of petrochemical plant, also plays an important role. Steam pipeline mainly includes steam pipeline and steam condensate pipeline. Through the reasonable design of piping in steam pipeline, the economy of steam pipeline can be improved. Safety, environmental protection and energy conservation are of great significance to the development of the whole petrochemical industry.

Design of steam pipeline

Many different pipelines are set in chemical plant, which are generally arranged outside the plant or along the plant. They are supported in the air with brackets to form a pipe gallery. The configuration of the pipe gallery has specific requirements. Generally, the process material pipes are arranged on the first floor and the first floor of the pipe gallery, the utility pipes are arranged on the third floor, and the instrument cable tray is arranged on the fourth floor. The steam pipeline is arranged on the third floor.
In order to facilitate the installation of π compensator, the steam pipe should be arranged on the front side of the pipe gallery. In the case of high temperature, the steam pipeline will expand. At this time, the π compensator can be used to absorb the thermal expansion of the pipeline. Because the price of bellows expansion joint is relatively 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, the first step is to analyze the pipeline strictly so that the compensator can be set centrally. Generally, the pipes with high temperature and large compensation are set on the outside, while the pipes with low temperature and small compensation are set on the inside. π compensator is generally set in the middle position, in addition, guide frame should be set on both sides of the compensator, and the distance between guide frame and compensator should be determined according to the stress of the pipeline. When calculating the thrust of support and the stress of steam pipe, the stress of the whole steam pipe should be calculated. Generally, multi-layer pipe gallery is set in chemical plant, while steam pipeline is set in the upper layer of multi-layer pipe gallery, so that low temperature pipeline and liquid hydrocarbon pipeline are not adjacent. On the same floor, steam pipe and electronic instrument cable can be arranged at the same time, but the interval 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.

The 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 produced during driving, special drainage facilities shall also be set. The setting of drainage facilities shall be selected according to the different levels of steam pressure.
Under normal conditions, the ultra-high pressure pipeline will not produce condensate, and there is no corresponding specification of condensate pipeline set on the ultra-high pressure steam channel, so generally, there is no drainage facilities on the ultra-high pressure channel. Ultra high pressure pipeline has the characteristics of pipe wall thickness, not easy to open holes, large pressure, etc., so it is generally not equipped with a sub liquid package. Under normal conditions, generally, 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 or start-up phase, drain valves, subcontractors and other drainage facilities should be set on these steam pipelines.
When setting the drainage facilities of the steam pipeline, the subcontracting shall be set at the end of the steam main pipe, and the spacing between the subcontracting on the steam main pipe is also specified. If it is in the saturated state, the spacing between the subcontracting in the device is 80mm. If it is overheated, the interval of the subcontracting shall be 160mm. If it is in the state of slope, the interval of liquid subcontracting outside the unit shall be 300mkm; if it is in the state of slope inversion, the interval of liquid subcontracting outside the unit shall be 200mm. Generally, the steam separator is set near the boundary of the device side when the saturated steam main enters the device. In addition, regular drainage measures shall be set at the lower part of the water separator. If the main pipe of superheated steam enters the device, the water separator is not required. The steam vent pipe shall be directly discharged to the atmosphere, so a drain hole shall be opened at the lower end of the steam vent pipe, and a DN15 pipe shall be connected at a suitable place such as drainage ditch and funnel. Guide and bearing brackets shall also be provided on the steam vent pipe. Because of the frequent discharge or connection discharge of the flood steam pipeline, it should be led to the main operation area or the place without too many operators.

Design of steam branch pipe

The top of the main steam pipe is provided with a steam branch pipe, and generally a shut-off valve is provided 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 requirements for steam use, so it is not possible to connect the steam branch pipe to the steam pipe, and the branch pipe can not be connected to the π – shaped compensator of the steam pipe. 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 main steam pipe. During the thermal expansion, the main steam pipe will produce the displacement at the outlet of the branch pipe, and the branch pipe will not bear too much pressure or displacement. In general, when the branch pipe is connected to the main steam pipe, the two valve manifold is used. However, in order to make the leakage situation be found at any time, the two valve manifold cannot be used to lead out from the steam branch pipe or the main steam pipe to other process pipes, but the three valve manifold should be set. According to different situations, the setting of drainage, such as drain valve, should be set at the low point of the steam branch pipe, when the drainage facilities are set on the official road, it should be based on the different level of pressure 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, π type compensator can be set on the steam condensate pipe. The π – row compensator should be set in horizontal direction, or the riser should be designed as inclined section.
Condensate from steam traps of different pressures should be connected to their respective recovery mains. When the nominal diameter of the branch pipe is not less than 50 mm, it can be directly connected to the top of the main steam condensate recovery pipe. Flange connection is selected as the drain valve to be set in the recovery system of steam condensate, and 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 shall also be flanged, so that it is convenient for steam pipeline purging and disassembling.

Key points to be paid attention to in the design of steam pipeline

1. Reasonable selection of pipe diameter
When selecting pipe diameter, it should be based on the demand of steam. When the pipe diameter is too large, the investment will be increased, the heat loss will be increased, and the condensate will also be increased. When the pipe diameter is too small, it will cause the pressure of the steam point of use, insufficient steam flow, and finally water hammer and erosion. Therefore, when selecting pipe diameter, it should not be too large or too small.
2. Stress requirements
When arranging pipelines, it is necessary to meet the requirements of stress and strictly calculate the stress. The setting of π compensator on the pipeline, the thrust of the fixed point of the compensator and the piping of the steam pipeline connected with the equipment shall meet the requirements of the stress, so that the efficiency of the design work can be improved.
3. Avoid water hammer
When the high-speed flowing water ball 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. In addition, when connecting the branch pipe to take steam, it should be above the main pipe. Too many branch pipes, contraction bends, etc. shall not be used for pipes. In order to prevent the local sinking of pipeline, the setting of pipeline support must be reasonable. The filter screen should be installed horizontally. All the above details should be noted, so as to avoid water hammer and improve the quality and efficiency of steam pipeline design in chemical plant.

Summary

There are a lot of strict requirements for the setting of steam pipes in chemical plant. In addition, attention should be paid to many details, so as to ensure the scientific and reasonable design, improve the working efficiency of steam pipes, and play a normal role in steam pipes.

Source: China Stainless Steel Pipeline Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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