Dilution steam generation system of ethylene plant

Abstract

This utility model relates to a dilution steam generation system for an ethylene plant, comprising: a steam generator, whose first inlet is connected to a medium-pressure steam pipeline, its second inlet is connected to a process water pipeline, its first outlet is connected to a medium-pressure condensate pipeline, and its second outlet is connected to a dilution steam pipeline; a medium-pressure condensate tank, whose inlet is connected to the medium-pressure condensate pipeline; a non-condensable steam discharge pipeline is provided at the top of the medium-pressure condensate tank, and a flow-limiting orifice plate is provided on the non-condensable steam discharge pipeline; the bottom outlet of the medium-pressure condensate tank is also connected to a low-pressure condensate conveying pipeline for conveying low-pressure condensate; and a straight pipe section located after the flow-limiting orifice plate and connected to the non-condensable steam discharge pipeline, and a return pipeline, the end of which is provided with a detachable and replaceable blind end; the return pipeline is connected to the low-pressure condensate conveying pipeline. The advantage is that it can effectively improve the system downtime problem caused by leakage from the non-condensable steam discharge line.

Description

Technical Field

[0001] This utility model relates to the field of ethylene plant technology, and in particular to a dilution steam generation system for an ethylene plant. Background Technology

[0002] The dilution steam generation system in an ethylene plant typically uses medium-pressure steam (1.1 MPa, 250°C) as the heat source to heat the process water after it has been stripped of acidic substances and some hydrocarbons in a process water stripping tower. The system includes a dilution steam generator. The medium-pressure steam heats the process water in the generator, producing medium-pressure condensate (1.1 MPa, 150°C), which is then transported to the low-pressure condensate system. The process water, heated by the medium-pressure steam, becomes the diluent for the cracking furnace feedstock. The medium-pressure condensate system includes a medium-pressure condensate tank, with a non-condensable steam discharge line on the top to discharge non-condensable steam generated during production, thereby improving the heat exchange efficiency between the medium-pressure steam and the process water.

[0003] In existing technologies, flow-limiting orifice plates are typically installed on pipelines where non-condensable steam is discharged from medium-pressure condensate. After the medium-pressure condensate flows through the flow-limiting orifice plate, it undergoes partial vaporization, becoming a two-phase flow. The presence of this two-phase flow causes scouring of the pipeline downstream of the orifice plate. Over time, this thinning of the pipeline leads to leakage, and in severe cases, it can cause the entire dilution steam generation system or ethylene plant to shut down, resulting in significant economic losses and environmental pollution.

[0004] Therefore, the existing dilution steam generation system of ethylene plants still needs further improvement. Utility Model Content

[0005] The technical problem to be solved by this utility model is to provide a dilution steam generation system for ethylene plants that can effectively improve the system shutdown problem caused by non-condensable steam discharge line flushing and leakage, in light of the current state of the technology.

[0006] The technical solution adopted by this utility model to solve the above-mentioned technical problems is as follows: a dilution steam generation system for an ethylene plant, comprising:

[0007] A steam generator includes a first inlet, a second inlet, a first outlet, and a second outlet. The first inlet is connected to a medium-pressure steam pipeline for conveying medium-pressure steam, the second inlet is connected to a process water pipeline for conveying process water, the first outlet is connected to a medium-pressure condensate pipeline for conveying medium-pressure condensate, and the second outlet is connected to a dilution steam pipeline for conveying dilution steam.

[0008] A medium-pressure condensate tank, the inlet of which is connected to the medium-pressure condensate pipeline;

[0009] The top of the medium-pressure condensate tank is equipped with a non-condensable steam discharge pipeline, which is provided with a flow-limiting orifice plate. The bottom outlet of the medium-pressure condensate tank is also connected to a low-pressure condensate delivery pipeline for conveying low-pressure condensate. The tank also includes a straight pipe section located behind the flow-limiting orifice plate and connected to the non-condensable steam discharge pipeline, as well as a return pipeline. The end of the straight pipe section is provided with a detachable and replaceable blind end. The return pipeline is connected to the low-pressure condensate delivery pipeline.

[0010] The aforementioned "removable and replaceable blind end" can be understood as a cover plate at the end of a closed pipe, which can be removed via a flange or threaded connection. For example, a blind flange can be fastened with bolts.

[0011] To facilitate the isolation and replacement of the blind end of the straight pipe section, a control valve is also installed on the straight pipe section.

[0012] To simplify operation and reduce costs, the control valve is a manual valve as an improvement. Manual valves have a simple structure, low failure rate, and can maintain a fixed opening degree for a long time under stable operating conditions, reducing the investment and maintenance requirements of the automatic control system.

[0013] As an improvement, the length of the straight pipe section is in the range of 10cm-50cm.

[0014] As an improvement, the return pipeline is arranged at an angle to the straight pipe section. This structural design allows the condensate to flow smoothly into the return pipeline, avoiding eddies or secondary gas entrainment caused by sharp bends, thus improving separation efficiency.

[0015] In order to concentrate the pipeline section that is easily scoured by two-phase flow after the flow restrictor plate as much as possible in the straight pipe section, as an improvement, the return pipeline is perpendicular to the straight pipe section, and the straight pipe section and the section of non-condensable steam discharge pipeline where the flow restrictor plate is located are on the same straight line.

[0016] To ensure operational safety and isolate the system during online maintenance of the flow-limiting orifice plate or straight pipe section, as an improvement, a shut-off valve is installed on the non-condensable steam discharge pipeline upstream of the flow-limiting orifice plate.

[0017] Compared with existing technologies, the advantages of this invention are as follows: This invention adds a straight pipe section and a detachable blind end after the flow-limiting orifice plate. The straight pipe section provides a stable buffer space for the vaporized two-phase flow after the orifice plate, significantly reducing fluid velocity and turbulence intensity, and greatly mitigating the direct and severe scouring of the pipe wall. The blind end, acting as a "sacrificial section" to withstand residual scouring, is designed to be detachable and replaceable. In the event of thinning, it can be replaced individually without replacing the entire pipeline or shutting down the system, effectively solving the problem of unplanned shutdowns caused by leaks at this point. The buffering effect of the straight pipe section significantly reduces the continuous scouring of the subsequent main pipeline by the fluid, extending the service life of the entire non-condensable steam discharge pipeline. The replaceable blind end design minimizes maintenance costs; only periodic inspection or replacement of a small section of the blind end is required, avoiding the huge economic losses caused by expensive main pipeline replacement or prolonged system shutdowns. Attached Figure Description

[0018] Figure 1 This is a flowchart of the dilution steam generation system of an ethylene plant according to an embodiment of the present invention. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0020] In the specification and claims of this utility model, terms indicating direction, such as "front," "rear," "upper," "lower," "left," "right," "side," "top," and "bottom," are used to describe various exemplary structural parts and elements of this utility model. However, the use of these terms is merely for the purpose of explanation and is based on the exemplary orientations shown in the accompanying drawings. Since the embodiments disclosed in this utility model can be arranged in different orientations, these terms indicating direction are for illustrative purposes only and should not be regarded as limitations. For example, "upper" and "lower" are not necessarily limited to directions opposite to or consistent with the direction of gravity.

[0021] Figure 1 This illustration shows a preferred embodiment of the ethylene plant dilution steam generation system of this invention. The ethylene plant dilution steam generation system includes a steam generator 10, a medium-pressure condensate tank 20, a medium-pressure steam pipeline 11, a medium-pressure condensate pipeline 13, a dilution steam pipeline 14, a process water pipeline 12, a low-pressure condensate delivery pipeline, and a non-condensable steam discharge pipeline 21, etc.

[0022] The steam generator 10 has a first inlet, a first outlet, a second inlet, and a second outlet. The first inlet of the steam generator 10 is connected to a medium-pressure steam pipeline 11 with a pressure of 1.1 MPa and a temperature of 250°C. The second inlet is connected to a process water pipeline 12 from a process water stripping tower (not shown in the figure). The process water enters the steam generator 10 after acidic substances and hydrocarbons have been removed by the stripping tower. The first outlet of the steam generator 10 is connected to a medium-pressure condensate pipeline 13 (outputting condensate at 1.1 MPa and 150°C), and the second outlet is connected to a dilution steam pipeline 14 that supplies steam to the cracking furnace.

[0023] The inlet of the medium-pressure condensate tank 20 is connected to the end of the medium-pressure condensate pipeline 13, and the bottom outlet is connected to the low-pressure condensate delivery pipeline 23 (delivered to the low-pressure condensate system). The non-condensable steam discharge pipeline 21 is connected to the top of the medium-pressure condensate tank 20, and a shut-off valve 27, a flow-limiting orifice plate 22, and a straight pipe section 24 with a detachable blind end are installed sequentially on it. The shut-off valve 27 is located at the upstream end of the non-condensable steam discharge pipeline 21 and is used for system isolation. The flow-limiting orifice plate 22 is located downstream of the shut-off valve 27 and is used to throttle and control the amount of non-condensable steam discharged. A straight pipe section 24 (length range 10cm-50cm) is connected to the discharge pipeline downstream of the flow-limiting orifice plate 22. This straight pipe section 24 is aligned with the pipeline containing the flow-limiting orifice plate 22, and its end is connected to a detachable blind flange (as a blind end).

[0024] A non-condensable steam discharge pipeline 21 has an interface on the side of a section of pipeline (or a straight pipe section 24) located after the flow restrictor plate, connecting to a return pipeline 25. The return pipeline 25 is perpendicular to the straight pipe section 24 (the included angle can also be between 75° and 105°) and slopes downwards to connect to the low-pressure condensate delivery pipeline 23 (the connection point is located downstream of the medium-pressure condensate tank 20).

[0025] A control valve 26, preferably a manual gate valve (but also an automatic valve), is installed on the straight pipe section 24 near its connection with the main pipeline to isolate the straight pipe section 24.

[0026] The workflow of the ethylene unit dilution steam generation system in this embodiment is as follows:

[0027] Normal operation: The shut-off valve 27 and the manual gate valve are fully open. Non-condensable vapors in the medium-pressure condensate tank 20, carrying a small amount of saturated water, are throttled and depressurized by the flow-limiting orifice plate 22, causing some of the liquid to flash vaporize and form a two-phase flow. The two-phase flow enters the straight pipe section 24, where the velocity decreases significantly. It is then smoothly introduced into the low-pressure condensate delivery pipeline 23 via the vertically connected return pipeline 25, preventing liquid accumulation.

[0028] Maintenance procedure: When thinning of the blind end due to erosion is detected, close the stop valve 27 and the manual gate valve on the straight pipe section 24 to isolate the area of ​​the straight pipe section 24. Remove and replace the blind flange.

Claims

1. A dilution steam generation system for an ethylene plant, comprising: The steam generator (10) includes a first inlet, a second inlet, a first outlet and a second outlet. The first inlet is connected to a medium-pressure steam pipeline (11) for conveying medium-pressure steam, the second inlet is connected to a process water pipeline (12) for conveying process water, the first outlet is connected to a medium-pressure condensate pipeline (13) for conveying medium-pressure condensate, and the second outlet is connected to a dilution steam pipeline (14) for conveying dilution steam. Medium-pressure condensate tank (20), the inlet of which is connected to the medium-pressure condensate pipeline (13); The medium-pressure condensate tank (20) is characterized by having a non-condensable steam discharge pipeline (21) at the top, a flow-limiting orifice plate (22) on the non-condensable steam discharge pipeline (21), and a low-pressure condensate conveying pipeline (23) for conveying low-pressure condensate at the bottom outlet of the medium-pressure condensate tank (20). It also includes a straight pipe section (24) located behind the flow-limiting orifice plate and connected to the non-condensable steam discharge pipeline (21) and a return pipeline (25). The end of the straight pipe section (24) is provided with a detachable and replaceable blind end, and the return pipeline (25) is connected to the low-pressure condensate conveying pipeline (23).

2. The dilution steam generation system of an ethylene plant of claim 1, wherein: The straight pipe section (24) is also equipped with a control valve (26).

3. The dilution steam generation system of an ethylene plant of claim 2, wherein: The control valve (26) is a manual valve.

4. The dilution steam generation system of an ethylene plant of claim 1, wherein: The length of the straight pipe section (24) ranges from 10cm to 50cm.

5. The dilution steam generation system of an ethylene plant of claim 1, wherein: The return line (25) is arranged at an angle to the straight pipe section (24).

6. The dilution steam generation system of an ethylene plant of claim 4, wherein: The return pipeline (25) is perpendicular to the straight pipe section (24), and the straight pipe section (24) and the section of non-condensable steam discharge pipeline (21) where the flow limiting orifice plate (22) is located are on the same straight line.

7. The dilution steam generation system of an ethylene plant according to any one of claims 1 to 6, characterized in that: A shut-off valve (27) is provided on the non-condensable steam discharge pipeline (21) upstream of the flow-limiting orifice plate (22).

Images