Design of Protective Pipes for Steam Pipes in Chemical Process Units (Part One)
Abstract: common design points in chemical process design are introduced, including the design of reducers, elbows, valves, and connections. The protective pipe of steam pipelines of chemical process units was designed and studied. The steam pipeline was arranged and drainage facilities were proposed. The design of steam branch pipes and steam condensate pipes provides a certain reference for the design of chemical process equipment.
One of the necessary items in the petrochemical production process is the design of protective pipes of steam pipes, which has an important impact on the operational safety and quality improvement of chemical plants. It is required to adopt unified planning and layout to design the relevant values and items in the steam pipeline system; make adjustments based on the actual situation in the actual steam pipeline's transportation, and select the corresponding conveying pressure and pipe diameters in combination with the design process of steam pipes' protective pipes. Make the protective pipe's design and process equipment fully unified.
1. Common design points in chemical process design
1.1 The design of reducers
The reducer has an important influence on the protective pipe's design, and its design is required to be optimized. The concentric reducer and eccentric reducer are common reducers. In the process of selecting the reducer, it is required to combine the actual protective piping requirements for the unit's steam design to choose the best form. You can design and select the corresponding protective piping design data on the pipe gallery. Flat-bottomed eccentric reducers are more common in design. If concentric reducers are used, they will increase the difficulty of the later stage of the construction, and the pipeline system on the steam pipe gallery is likely to be unstable during use.
1.2 The design of elbows
The important link of the protective pipe connection is the elbow, which is prone to some problems in the design process, such as the failure of the protective pipe's connection. Therefore, it is required to actively take a variety of effective measures in the process of the protective pipe's connection. Improve the drawing in combination with the actual situation or add elbows to effectively connect the protective pipe. However, in the specific design process, simply adding elbows and the design being not good easily occur, and this will lead to greater running resistance during the operation of the elbow, which may cause welding seams or leakages and certain risks.
1.3 The design of valves
One of the important links in the protective pipe's design is the valve's design. Different valves have great differences based on uses. In order to ensure safety during use, it is required to select the most suitable valve. In the case of conveying different media, the corresponding operation mode and pipe grade should be selected.
2. Research on the design of protective pipes of steam pipelines for chemical process equipment
2.1 Fixing the steam pipeline up
Because of the influence of factors such as external temperature, internal pressure in the pipe and steam temperature, a large amount of thermal expansion may occur inside the steam pipeline in operation. However, thermal expansion is difficult to be fully released in the pipeline in operation, it may affect the bracket, pipe and related pipe devices to a large extent. In the design process of traditional steam pipelines, bellows and natural compensation are generally used to prevent pressure absorption to deal with expansion caused by heat and contraction caused by cold that occur when the pipeline is in operation. The following design method of the 1000kt/a ethylene device is mainly adopted, and the relevant layout of the steam pipeline is shown in Table 1.
Table 1 Relevant layouts of steam pipelines in chemical process units
One of the necessary items in the petrochemical production process is the design of protective pipes of steam pipes, which has an important impact on the operational safety and quality improvement of chemical plants. It is required to adopt unified planning and layout to design the relevant values and items in the steam pipeline system; make adjustments based on the actual situation in the actual steam pipeline's transportation, and select the corresponding conveying pressure and pipe diameters in combination with the design process of steam pipes' protective pipes. Make the protective pipe's design and process equipment fully unified.
1. Common design points in chemical process design
1.1 The design of reducers
The reducer has an important influence on the protective pipe's design, and its design is required to be optimized. The concentric reducer and eccentric reducer are common reducers. In the process of selecting the reducer, it is required to combine the actual protective piping requirements for the unit's steam design to choose the best form. You can design and select the corresponding protective piping design data on the pipe gallery. Flat-bottomed eccentric reducers are more common in design. If concentric reducers are used, they will increase the difficulty of the later stage of the construction, and the pipeline system on the steam pipe gallery is likely to be unstable during use.
1.2 The design of elbows
The important link of the protective pipe connection is the elbow, which is prone to some problems in the design process, such as the failure of the protective pipe's connection. Therefore, it is required to actively take a variety of effective measures in the process of the protective pipe's connection. Improve the drawing in combination with the actual situation or add elbows to effectively connect the protective pipe. However, in the specific design process, simply adding elbows and the design being not good easily occur, and this will lead to greater running resistance during the operation of the elbow, which may cause welding seams or leakages and certain risks.
1.3 The design of valves
One of the important links in the protective pipe's design is the valve's design. Different valves have great differences based on uses. In order to ensure safety during use, it is required to select the most suitable valve. In the case of conveying different media, the corresponding operation mode and pipe grade should be selected.
2. Research on the design of protective pipes of steam pipelines for chemical process equipment
2.1 Fixing the steam pipeline up
Because of the influence of factors such as external temperature, internal pressure in the pipe and steam temperature, a large amount of thermal expansion may occur inside the steam pipeline in operation. However, thermal expansion is difficult to be fully released in the pipeline in operation, it may affect the bracket, pipe and related pipe devices to a large extent. In the design process of traditional steam pipelines, bellows and natural compensation are generally used to prevent pressure absorption to deal with expansion caused by heat and contraction caused by cold that occur when the pipeline is in operation. The following design method of the 1000kt/a ethylene device is mainly adopted, and the relevant layout of the steam pipeline is shown in Table 1.
Table 1 Relevant layouts of steam pipelines in chemical process units
| Items | 2 longitudinal pipe gallery (4-layer pipe gallery) |
3 horizontal pipe gallery (4-layer pipe gallery) |
Layers of pipe gallery |
| 1 000kt/a ethylene devices | EL10.000 | EL8.500 | The first and second layers: processing material pipeline |
| 1 000kt/a ethylene devices | EL7.000 |
EL5.500 |
The first and second layers: processing material pipeline |
| 1 000kt/a ethylene devices | EL13.000 | EL11.500 | The third layer: pipelines for public works |
| 1 000kt/a ethylene devices |
EL16.000 |
EL14.500 | The fourth layer: electrical and flaring pipelines as well as instrument cable trough panels |
Table 2 Diameter design of drain pipes of steam pipelines
| Sizes of steam pipes DN | Sizes of drain pipes DN | Separating bags DN |
| 100 | 20 | 80 |
| 150 | 20 | 100 |
| 200 | 20 | 100 |
| ≥250 | 25 | 150 |
Steam with four different pressure ratings is designed for the 1000kt/a ethylene device in order to meet various operational needs. The first one is the pressure with low ratings of 0.6MPa and 0.4MPa. Steam pipes with diameters between DN15mm and DN800mm are designed, which have operating temperatures of 200 to 545℃. The second one is the pressure with medium ratings, including 1MPa, 1.6MPa and 2MPa. The third one is the high pressure, and the fourth is super high pressure greater than or equal to 13MPa.
To ensure the smooth operation of the ultra-high steam pipeline, an "II" type compensator is installed in the system at intervals of 50m, and such an "II" type compensator is also installed in the operation of low-pressure, medium-pressure and high-pressure steam pipelines. It is installed at intervals of 100m, 100m, and 80m respectively (see Table 2).
