Ethylene plant cracking gas large valve purge system

Abstract

The utility model relates to a kind of pyrolysis gas large valve purging system for ethylene device, including pyrolysis gas large valve, the pyrolysis gas large valve includes the valve body with valve cavity, the top of valve body is equipped with the purging steam import for being connected with purging steam pipeline, the bottom of valve body is equipped with the purging steam export for being connected with steam return pipeline, valve body has first side and second side opposite to each other, the first side of valve body corresponds with the medium inlet, the second side of valve body corresponds with the medium outlet, the purging steam import of the top of valve body has two, the two purging steam imports are respectively adjacent first side and second side of valve body and are arranged, the purging steam export of the bottom of valve body has two, the two purging steam exports are respectively adjacent first side and second side of valve body and are arranged.Advantage is that: it can effectively reduce the dead area in valve cavity for anti-coking steam purging.

Description

Technical Field

[0001] This utility model relates to the field of ethylene plant technology, and in particular to a pyrolysis gas purging system for ethylene plants. Background Technology

[0002] In the process of ethylene plants: ethane and propane are used as raw materials and reacted in a tubular cracking furnace at a high temperature of 840-860°C to produce cracked gases such as hydrogen, methane, ethylene, and propylene. Secondary reactions often occur during the cracking reaction, such as olefin polymerization, cyclization, and condensation, which are converted into coke; and hydrocarbon decomposition to produce carbon.

[0003] The pyrolysis gas main valve is located between the outlet of the corresponding quench cooler of the pyrolysis furnace and the main pyrolysis gas pipe. It serves as a shut-off valve between the individual furnace and the overall system and is situated on the main product output pipeline. A commonly used pyrolysis gas main valve is a parallel double-gate valve. The medium is pyrolysis gas containing coke powder. The valve is equipped with a steam purging flange, allowing continuous purging of the valve chamber. The purging pressure is set 0.5 bar higher than the actual process pressure to create an airlock within the valve chamber. This prevents coke powder from being carried into the valve chamber during operation, which could lead to long-term coking inside the valve chamber and obstruction of the opening and closing action.

[0004] The current purging scheme involves top-side single-sided purging for steam intake and bottom-side single-sided purging for steam exhaust. During the opening and closing phases of the cracked gas valve, the valve plate contracts and moves upwards. The valve plate moves within the guide plate, resulting in small gaps on both sides. Upon opening, the sealing surface opens, disrupting the purging steam balance within the valve cavity for a short time, inevitably introducing fine coke powder from the medium into the valve cavity. This introduced coke powder can be removed through a steam purging process, with steam entering from the top of the valve cavity and removing the remaining coke powder from the bottom. However, the current purging process has a dead zone in the valve cavity (e.g.,...). Figure 1 (Area A shown in the diagram). Coke dust within the dead zone tends to accumulate over time in the gap between the valve plate and the guide plate. Furthermore, the coke particles produced by ethane and propane cracking are relatively hard, easily causing wear on the guide plate surface and forming scratch channels. This accelerates the entry of coke dust into the valve cavity, leading to valve obstruction in minor cases and, in severe cases, coking inside the valve cavity. Since this cracked gas valve cannot be disassembled during ethylene plant operation, valve malfunctions may prevent operation, potentially causing ethylene plant shutdowns and impacting production. Actual valve disassembly and inspection revealed that coking in the inner cavity of many valves was unilateral, with scratches on one side of the guide plate, all located in the purging dead zone, consistent with the existing purging pipeline setup. Therefore, effectively reducing the dead zone within the valve cavity during anti-coking steam purging has become a pressing technical problem for those skilled in the art. Utility Model Content

[0005] The technical problem to be solved by this utility model is to provide a pyrolysis gas large valve purging system for ethylene plants that can effectively reduce the dead zone in the valve cavity during anti-coking steam purging, 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 cracked gas main valve purging system for an ethylene plant, including a cracked gas main valve, the cracked gas main valve including a valve body with a valve cavity, the valve body having a medium inlet and a medium outlet facing each other, the top of the valve body is provided with a purging steam inlet for connecting to a purging steam pipeline, the bottom of the valve body is provided with a purging steam outlet for connecting to a steam return pipeline, and both the purging steam inlet and the purging steam outlet are connected to the valve cavity;

[0007] The valve body has a first side and a second side that are opposite to each other. The first side of the valve body corresponds to the medium inlet, and the second side of the valve body corresponds to the medium outlet. There are two purge steam inlets at the top of the valve body, which are respectively located near the first side and the second side of the valve body. There are two purge steam outlets at the bottom of the valve body, which are respectively located near the first side and the second side of the valve body.

[0008] As an improvement, the purge steam inlet and purge steam outlet arranged diagonally on the valve body are used as a set of steam inlets and outlets for coordinated use, and the two sets of steam inlets and outlets are used alternately.

[0009] The aforementioned diagonal arrangement can be understood as a combination in which the purge steam inlet and purge steam outlet are diagonally related in spatial position (such as the top inlet on the front side of the valve body + the bottom outlet on the rear side as a group).

[0010] The above structural design allows for alternating purging paths, preventing coke powder from accumulating in fixed locations and improving cleaning capabilities.

[0011] In order to flexibly control the start-up, shutdown and pressure of different purging paths, the purging steam pipeline is connected to two purging steam inlets through two first branches, and each of the two first branches is equipped with a first control valve. The steam return pipeline is connected to two purging steam outlets through two second branches, and each of the two second branches is equipped with a second control valve.

[0012] As an improvement, the outlet end of the steam return pipeline is connected to a corresponding pipeline located downstream of the medium outlet of the valve body. This structural design, due to the overall closed nature of the system, prevents external contaminants from entering, thus ensuring the purity of the pyrolysis gas.

[0013] As an improvement, an exhaust control valve and an orifice plate are sequentially installed on the steam return pipeline. The orifice plate's flow restriction and the exhaust valve's pressure regulation work together to maintain a constant purging pressure.

[0014] As an improvement, a drain pipe for blowdown is also connected to the steam return pipeline near the purge steam outlet, and this drain pipe is equipped with a drain valve. This structural design allows for the periodic removal of deposited coke dust, preventing pipeline blockage. Blowdown cleaning can be performed without shutting down the furnace, reducing maintenance costs and making maintenance more convenient.

[0015] As an improvement, the purging steam pipeline is also equipped with a pressure reducing valve, a safety valve, and a pressure gauge. The pressure gauge displays data in real time, and the pressure reducing valve automatically stabilizes the pressure. The safety valve releases pressure to prevent pipe rupture and ensures system safety.

[0016] Compared with the prior art, the advantages of this utility model are as follows: This utility model adds two purge steam inlets and outlets at the top and bottom of the valve body of the cracked gas large valve, respectively, and positions them adjacent to the front and rear sides of the valve body (i.e., the first and second sides). This design allows the purge steam to evenly cover the entire valve cavity, eliminating the dead zone caused by the original single-sided purge (as described in the background art). Figure 1 (as shown in the area), thus effectively preventing the accumulation of coke powder in the gap between the valve plate and the guide plate. On the one hand, this effectively reduces the introduction of coke powder, avoids coking and valve actuation blockage, and extends the service life of the valve; on the other hand, it reduces the risk of one-sided wear and scratches on the guide plate, maintaining the valve's sealing performance; in particular, by enhancing the comprehensiveness of purging, it ensures the steam balance of the valve at the moment of opening and closing, improves operational reliability, avoids ethylene unit shutdowns caused by valve failure, and ensures production continuity and safety. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a pyrolysis gas large valve purging system in the prior art;

[0018] Figure 2 This is a schematic diagram of the structure of the pyrolysis gas large valve purging system 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 2This invention illustrates a preferred embodiment of the pyrolysis gas purging system for an ethylene plant according to the present invention. The pyrolysis gas purging system for an ethylene plant in this embodiment includes a valve body 10 of a pyrolysis gas purging valve. A valve cavity 100 is formed inside the valve body 10, with a medium inlet 111 and a medium outlet 112 at its front and rear ends, respectively. Two purging steam inlets 121 are symmetrically arranged at the top of the valve body 10: a first purging steam inlet 121 is adjacent to the front side of the valve body 10 (corresponding to the medium inlet 111), and a second purging steam inlet 121 is adjacent to the rear side of the valve body 10 (corresponding to the medium outlet 112). Two purging steam outlets 122 are symmetrically arranged at the bottom of the valve body 10: a first purging steam outlet 122 is adjacent to the front side, and a second purging steam outlet 122 is adjacent to the rear side.

[0022] The purging steam line 21 is connected to the top inlet via two parallel first branches 211, each branch equipped with an independent first control valve 22 (such as a shut-off valve). The steam return line 31 is connected to the bottom outlet via two parallel second branches 311, each branch equipped with an independent second control valve 32. The end of the steam return line 31 is connected to the cracked gas line downstream of the medium outlet 112 of the valve body 10, forming a closed loop.

[0023] The operation process of the pyrolysis gas purging system for the ethylene plant in this embodiment is as follows:

[0024] Alternating purging mode: Open the front top inlet control valve and the rear bottom outlet control valve, allowing steam to flow through valve chamber 100 along the "front top → rear bottom" path. Periodically switch the purging steam inlet and outlet, opening the rear top inlet control valve and the front bottom outlet control valve, allowing steam to flow through valve chamber 100 along the "rear top → front bottom" path. When switching, first open both first control valves 22 at the two purging steam inlets simultaneously, then switch the two second control valves 32 at the purging steam outlet 122. After the two second control valves 32 at the purging steam outlet 122 have switched, close one of the corresponding first control valves 22 at each of the two purging steam inlets, leaving the diagonal valves fully open.

[0025] In this embodiment, a pressure regulating unit is added to the steam return pipeline 31, and an exhaust control valve 33 and a flow-limiting orifice plate 34 are installed sequentially along the steam flow direction. The orifice diameter of the orifice plate 34 is calculated and determined according to the purging pressure requirement (maintaining the purging pressure higher than the process pressure).

[0026] Upstream of the purging steam pipeline 21, a pressure reducing valve 23, a safety valve 24, and a pressure gauge 25 are installed. The pressure gauge 25 can display data in real time, and the pressure reducing valve 23 automatically stabilizes the pressure. The safety valve 24 releases pressure to prevent pipe rupture and ensures system safety.

[0027] In this embodiment, a drain pipe 35 is connected to the lowest point of the pipe near each purge steam outlet 122 on the steam return pipeline 31. The drain pipe 35 is equipped with a high-pressure drain valve 351 (such as a ball valve). The drain operation procedure can be as follows: close the control valve of the currently running purge path, open the drain valve 351 to discharge for 5-10 seconds, and switch to another purge path to resume operation.

[0028] In this embodiment, two purge steam inlets 121 and outlets are added to the top and bottom of the valve body 10 of the cracked gas valve, respectively, and are positioned adjacent to the front and rear sides (i.e., the first and second sides) of the valve body 10. This design allows the purge steam to uniformly cover the entire valve cavity 100, eliminating the dead zone caused by the original single-sided purge (as described in the background art). Figure 1 (as shown in the area), thus effectively preventing the accumulation of coke powder in the gap between the valve plate and the guide plate. On the one hand, this effectively reduces the introduction of coke powder, avoids coking and valve actuation blockage, and extends the service life of the valve; on the other hand, it reduces the risk of one-sided wear and scratches on the guide plate, maintaining the valve's sealing performance; in particular, by enhancing the comprehensiveness of purging, it ensures the steam balance of the valve at the moment of opening and closing, improves operational reliability, avoids ethylene unit shutdowns caused by valve failure, and ensures production continuity and safety.

Claims

1. A pyrolysis gas purging system for an ethylene plant, comprising a pyrolysis gas purging valve, the pyrolysis gas purging valve comprising a valve body (10) having a valve cavity (100), the valve body (10) having a medium inlet (111) and a medium outlet (112) opposite to each other, the top of the valve body (10) having a purging steam inlet (121) for connecting to a purging steam pipeline (21), the bottom of the valve body (10) having a purging steam outlet (122) for connecting to a steam return pipeline (31), the purging steam inlet (121) and the purging steam outlet (122) being connected to the valve cavity (100); Its features are: The valve body (10) has a first side and a second side that are opposite to each other. The first side of the valve body (10) corresponds to the medium inlet (111), and the second side of the valve body (10) corresponds to the medium outlet (112). There are two purge steam inlets (121) at the top of the valve body (10), which are respectively located near the first side and the second side of the valve body (10). There are two purge steam outlets (122) at the bottom of the valve body (10), which are respectively located near the first side and the second side of the valve body (10).

2. The pyrolysis gas purging system for an ethylene plant according to claim 1, characterized in that: The purge steam inlet and purge steam outlet (122) arranged diagonally on the valve body (10) serve as a set of steam inlets and outlets for use in conjunction with each other, and the two sets of steam inlets and outlets are used alternately.

3. The pyrolysis gas purging system for an ethylene plant according to claim 2, characterized in that: The purge steam pipeline (21) is connected to two purge steam inlets (121) via two first branches (211), and each of the two first branches (211) is equipped with a first control valve (22). The steam return pipeline (31) is connected to two purge steam outlets (122) via two second branches (311), and each of the two second branches (311) is equipped with a second control valve (32).

4. The pyrolysis gas purging system for an ethylene plant according to claim 1, characterized in that: The outlet end of the steam return line (31) is connected to the corresponding line located downstream of the medium outlet (112) of the valve body (10).

5. The pyrolysis gas purging system for an ethylene plant according to claim 4, characterized in that: The steam return pipeline (31) is provided with an exhaust control valve (33) and an orifice plate (34) in sequence.

6. The pyrolysis gas purging system for an ethylene plant according to claim 4, characterized in that: The steam return pipeline (31) is also connected to a sewage discharge pipeline (35) near the purging steam outlet (122), and a sewage discharge valve (351) is provided on the sewage discharge pipeline (35).

7. The pyrolysis gas main valve purging system for an ethylene plant according to any one of claims 1 to 6, characterized in that: The purging steam pipeline (21) is also equipped with a pressure reducing valve (23), a safety valve (24), and a pressure gauge (25).

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