An oil discharge system for a double-disc valve of cracking furnace cracking gas

Abstract

An oil drainage system for a cracking furnace cracking gas double-disc valve comprises a cracking gas valve, a coke prevention steam return line for the cracking gas valve, and an oil drainage system; the cracking gas valve is a double-disc valve; and the oil drainage system is characterized in that the oil drainage system is arranged on the coke prevention steam return line drawn from the bottom of the valve box of the cracking gas valve; the oil drainage system is arranged as a vertical downward oil drainage line, the lower end of which is directly connected to the cracking gas main pipe below; when the valve of the cracking gas valve is opened, the coke prevention steam return line simultaneously opens the oil drainage line; when the valve of the cracking gas valve is closed, the oil drainage line is simultaneously closed. The present invention ensures that accumulated materials in the valve box of the cracking gas double-disc valve are promptly and effectively drained and sealed, and solves the problem of easy clogging of the coke prevention steam return line.

Description

Technical Field

[0001] The present invention relates to the technical field of petrochemical industry, and in particular provides an oil discharge system for a cracking furnace cracking gas double-disc valve, which is used on a coke-proof steam return line of a cracking gas large valve. Background Art

[0002] The cracking gas switching valve, installed on the cracking gas pipeline at the cracking furnace outlet, includes cracking gas valve 1 and char gas valve 6, and serves as the sole connection between the cracking furnace and the quenching system. Since the cracking furnace needs to cut out the char after a single cycle, the cracking furnace valves must be switched. The cracking gas valve must be fully closed while the char gas valve is fully opened to allow industrial air to flow in for charring. The key is to ensure that the cracking gas valves are fully closed and leak-free. The incoming industrial air contains a large amount of oxygen, and even after high-temperature combustion with the coke, it still has a high oxygen content, with the oxygen content increasing further in the later stages of charring. Preventing oxygen-containing char gas from entering the rear system and potentially causing an explosion is crucial, as fully closed sealing of the cracking gas valves is crucial. Furthermore, it is also crucial to prevent the rear system medium from leaking back and mixing with the oxygen-containing, high-temperature char gas, potentially creating a combustion and explosion hazard.

[0003] For this reason, many cracking furnace cracking gas valves and coke burning valves are equipped with double-disc valves, which have the following features: 1. High temperature resistance: up to 600°C; 2. Erosion resistance: resistant to the erosion of coke particles; 3. Anti-coking: prevents coke particles from entering the valve cavity; 4. Double seal: equipped with two seals to ensure the sealing effect; 5. Purge steam: equipped with purge steam to achieve auxiliary sealing.

[0004] The cracking gas switching valve is important for process control. At the same time, because the medium contains tar generated by high-temperature cracking, the difficulty in switching the cracking gas valve has always been a hot issue in the ethylene industry. Therefore, the cracking gas switching valve is a key part of the maintenance of major ethylene plants.

[0005] Double gate valve structure:

[0006] The parallel double-disc valve features two independent gates mounted on a disc carrier, which precisely slots between two guide plates. The center section of the disc, comprised of two wedges and a freely movable ball, provides a parallel force on the disc to the seat, strengthening the seal. When closing the valve, it has two stop positions. Once the disc reaches the seat, the sealing surfaces are not tightly seated, and the stem needs to move downward a few millimeters. The wedges and freely movable ball push the disc outward, tightening the seal. When opening, the stem pulls the wedges and freely movable ball upward, causing the disc to retract inward, loosening the sealing surface and preventing friction.

[0007] Because oil coke can easily enter the valve box and form coke when the double-disc valve is not fully opened or closed during operation, which increases the difficulty of maintenance, a special anti-coking steam system is set up for protection. The steam has the dual functions of purging to prevent tar accumulation and sealing the valve box.

[0008] Problems in using the anti-scorch steam system:

[0009] The anti-coking steam return line of the cracking furnace's cracking gas valve is designed to meet pressure differential control. The return line is equipped with a flow-limiting orifice and potential difference. Therefore, liquid accumulation in the pipeline and blockage of the flow-limiting orifice can cause the return line to be blocked. In the return line blockage, tar in the valve box of the cracking gas double-disc valve cannot be blown away in time, and eventually accumulates into coke blockage, which is more difficult to blow clean and affects the valve opening and closing.

[0010] See also Figure 1 The figure shows the on-site piping layout for the cracking gas valve. The anti-scorch steam return line 2 is designed to exit from the bottom of the cracking gas valve 1, through a vertically extending pipe extending over 2 meters, before being throttled by a flow restriction orifice 5. It then passes through a 50-cm vertically extending pipe, where it bends back into the cracking gas pipeline behind the valve. The design concept is to create a pressure differential through the throttling in the vertically extending pipe, ensuring that the pressure in the valve housing X is higher than the pressure in the cracking gas pipeline. This prevents cracking gas from leaking back into the valve housing X, especially when the valve is closed, and prevents the risk of backflow from the downstream system. However, the vertically extending pipe has significant resistance, causing steam condensation and accumulation within the pipe to form a water seal. This creates a risk of anti-scorch steam leaking through the sealing gap in the housing into the cracking gas pipeline. Consequently, the driving force generated by the anti-scorch steam pressure in housing X is insufficient to break the water seal within the pipeline, resulting in a blockage in the anti-scorch steam return line.

[0011] When the purge steam system's return line is blocked under pressure differential control, the amount of purge steam entering is equivalent to the amount of steam leaking from the valve box sealing surface into the cracked gas pipeline. High pressure differentials can cause even greater damage to the sealing surface. The double-disc valve structure relies on the expansion ring to form a seal when fully open. The greater the pressure differential, the more severe the scouring and leakage of steam from the sealing surface into the cracked gas pipeline.

[0012] The tar accumulated in the cracking gas valve box cannot be drained in time. When the cracking furnace valve needs to be switched, the cracking gas valve is fully closed and the charring valve is fully opened. The oil accumulated in the valve box will leak from the valve box sealing surface to the charring tank system, causing environmental pollution and even safety hazards such as fire and explosion.

[0013] For this purpose, a discharge line is usually set under the double gate valve box, and the accumulated tar in the valve box is discharged by regularly operating the gate valve switch on the discharge line. However, there are the following disadvantages:

[0014] 1) Regularly discharging the valve box accumulation cannot be effectively discharged.

[0015] Typically, the discharge line is terminated at a drum, resulting in high risk and labor-intensive on-site discharge operations. Some designs connect the discharge line to an underground slop tank with very low pressure. Because the slop tank is interconnected with numerous systems, discharge from these other systems can cause significant pressure fluctuations in the discharge line, potentially backflowing into the cracked gas valve box. The high risk of cross-operation between multiple slop tanks makes long-term discharge impossible.

[0016] 2) Regular discharge can easily cause blockage.

[0017] Since the discharge medium is tar, regular discharge means intermittent flow, which is prone to blockage when the valve box and pipeline are not flowing, causing the discharge line to be blocked. Summary of the Invention

[0018] In view of the above problems, the present invention provides an oil drainage system for a cracking furnace cracking gas double-disc valve, which aims to ensure that the accumulated matter in the valve box of the cracking gas double-disc valve is effectively discharged and solve the technical problem of easy blockage of the anti-coking steam return line.

[0019] The technical solutions of the present invention are as follows:

[0020] An oil drainage system for a cracking furnace cracking gas double-disc valve comprises a cracking gas valve, a coke prevention steam return line for the cracking gas valve, and an oil drainage system; the cracking gas valve is a double-disc valve; the oil drainage system is arranged on the coke prevention steam return line extending from the bottom of the valve box of the cracking gas valve; the oil drainage system is arranged as a vertical downward oil drainage line, the lower end of which is directly connected to a cracking gas main pipe below;

[0021] When the valve of the cracked gas valve is opened, the anti-coking steam return line opens the oil discharge line synchronously; when the valve of the cracked gas valve is closed, the oil discharge line is closed synchronously.

[0022] Two valves are provided on the oil discharge line, including a first valve and a second manual valve. The first valve provided on the oil discharge line adopts a solenoid valve, and an interlock signal is provided to control the switch of the solenoid valve. The solenoid valve corresponds to the switch signal of the cracked gas valve. When the cracked gas valve fully opens, the first valve solenoid valve is triggered to open; when the cracked gas valve fully closes, the first valve solenoid valve is triggered to close.

[0023] The second manual valve provided on the oil discharge line is a gate valve. The gate valve is manually opened when the first valve solenoid valve is opened; and the gate valve is manually closed when the first valve solenoid valve is closed.

[0024] A one-way valve and a flow-limiting orifice are also provided on the oil discharge line; the one-way valve is located at the end of the oil discharge line, and the flow-limiting orifice is located between the first valve and the second manual valve.

[0025] The oil discharge line (3) is located below the valve box of the cracked gas valve (1) and forms a height difference therewith.

[0026] The oil discharge line is arranged at the position where the anti-scorch steam return line is led out from the bottom of the cracking gas valve box, that is, it is led out from the pipeline at the bottom of the anti-scorch steam return line.

[0027] A discharge line is led out from the head end of the bottom pipeline to connect to the low-pressure dirty oil tank E, the oil discharge line is led out from the middle part, and the discharge guide F is led out from the end; a valve switch is set on the discharge line.

[0028] The oil discharge line is connected in sequence from the head end to the tail end with a first valve, a flow limiting orifice plate, a second manual valve, and a one-way valve.

[0029] The nominal diameter of the oil discharge line pipeline is DN50 to DN75 mm.

[0030] The oil discharge line is provided with a steam heating pipeline with a nominal diameter of DN20mm on the outer wall of the pipeline and the outer walls of the solenoid valve, flow limiting orifice flange, gate valve and check valve. The steam pipeline is parallel to the pipeline of the oil discharge line and adheres to the wall. The steam travels back and forth in two trips to form a loop heating pipeline to prevent condensation from clogging the pipeline.

[0031] The key point of the present invention is to modify the oil discharge line and add a set of cracked gas double gate valve oil discharge system. The process flow and operation method are as follows:

[0032] 1) Take the DN50~DN75 oil discharge line and let it go as vertically as possible directly into the cracking gas main pipe below.

[0033] 2) The oil discharge line is provided with a DN20mm steam tracing pipeline on the pipe wall and valve body to prevent condensation from clogging the pipeline;

[0034] 3) The return line opens the oil drain line when the cracked gas valve is open, and closes the oil drain line when the valve is closed. This ensures an effective pressure differential between the valve box steam and the cracked gas pipeline when the cracked gas valve is closed. Therefore, the first valve is designed to be a solenoid valve, and an interlock control solenoid valve switch is set. In response to the cracked gas valve switch signal, when the cracked gas valve fully opens, the solenoid valve of the first oil drain line opens, and the second manual valve opens manually. When the cracked gas valve fully closes, the solenoid valve of the first valve in the modified line closes, and the second valve closes manually.

[0035] The beneficial effects of the present invention are as follows: 1. When the cracking gas valve is in the open state, the valve of the oil discharge line of the modified oil discharge system is opened; when the cracking gas valve is closed, the oil discharge line of the modified oil discharge system is closed. The oil of the oil discharge line of the modified oil discharge system is discharged downward directly into the cracking gas main pipe below; after the valve of the oil discharge line of the modified oil discharge system is opened, the pressure of the valve box of the cracking gas valve is reduced, which will cause the pressure difference controlled by the purge steam to be insufficient, and the sealing effect of the purge steam is reduced. However, even if there is no sealing effect, the risk of internal leakage can be eliminated, because there is no worry about internal leakage due to poor sealing when the cracking gas valve is open. Even if the sealing pressure difference cannot be formed, the cracking gas entrains oil coke and enters the box X from the seal, and the drainage of the oil discharge line of the modified oil discharge system is unobstructed. The thrust formed by the potential difference and the effect of the purge steam can timely discharge the tar in the box X into the cracking gas main pipe below, reducing the accumulation of tar in the cracking gas valve box X. At the same time, the anti-coke steam return line will not produce liquid accumulation to form a water seal.

[0036] 2. The cracking furnace valve is switched. The cracking gas valve is completely closed while the coke valve is fully opened, and then industrial air is introduced for coke burning. It is necessary to ensure that the cracking gas valve is completely closed without internal leakage. The modification plan adopts interlock valve control. The first valve of the oil discharge line adopts a solenoid valve, which corresponds to the valve switch signal of the cracking gas valve. When the cracking gas valve fully closes, the solenoid valve of the first valve of the modification line is closed, and the second manual valve is manually closed. With this solution, after closing the oil discharge line, the anti-coking steam forms a sealed pressure difference control between the valve box and the cracking gas pipeline under the action of the resistance of the anti-coking steam return line, preventing the risk of low-pressure cracking gas leaking into the valve box and finally leaking back from the double-disc valve inlet seal.

[0037] It ensures timely and effective discharge of accumulated materials in the valve box of the cracking gas double-disc valve and the sealing effect, and solves the problem of easy blockage of the anti-coking steam return line. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram of the anti-coking steam flow of the cracking gas valve in the prior art.

[0039] Figure 2 This is a schematic diagram of the anti-coking steam flow of the coke gas valve in the prior art.

[0040] Figure 3 This is a schematic diagram of the oil discharge line modified on the cracking gas large valve anti-coking steam return line of the present invention;

[0041] Description of the accompanying figures

[0042] Cracked gas valve 1, cracked gas valve anti-coking steam return line 2, anti-coking steam inlet 21, anti-coking steam outlet 22, coke particle discharge port 23, oil discharge line 3, first valve 31, second manual valve 32, one-way valve 33, cracked gas pipeline 4, lower cracked gas main pipe 41, flow limiting orifice 5, cracked gas A, anti-coking steam B, pressure indicator C, cracking furnace outlet D, low-pressure waste oil tank E, discharge drain F, cracked gas valve box X;

[0043] Burnt gas valve 6, burnt gas valve anti-scorch steam return line 7, burnt gas M. DETAILED DESCRIPTION

[0044] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings;

[0045] See also Figure 3 The figure shows a schematic diagram of the modified oil drain line on the anti-coking steam return line of the cracking gas valve according to the present invention. The oil drain system of a cracking furnace cracking gas double-disc valve according to the present invention comprises a cracking gas valve 1, an anti-coking steam return line 2 for the cracking gas valve, and an oil drain system. The cracking gas valve is a double-disc valve. The oil drain system is arranged on the anti-coking steam return line 2 extending from the bottom of the valve box of the cracking gas valve 1. The oil drain system is arranged as a vertical downward oil drain line 3, the lower end of which is directly connected to the cracking gas main pipe 41 below.

[0046] When the valve of the cracked gas valve 1 is opened, the anti-coking steam return line 2 opens the oil discharge line 3 synchronously; when the valve of the cracked gas valve 1 is closed, the oil discharge line 3 is closed synchronously.

[0047] Two valves are provided on the oil discharge line 3, including a first valve 31 and a second manual valve 32. The first valve 31 provided on the oil discharge line 3 is a solenoid valve, and an interlock signal is provided to control the switch of the solenoid valve. The solenoid valve corresponds to the switch signal of the cracked gas valve 1. When the valve fully open signal of the cracked gas valve 1 is issued, the solenoid valve of the first valve 31 is triggered to open; when the valve fully close signal of the cracked gas valve 1 is issued, the solenoid valve of the first valve 31 is triggered to close.

[0048] The second manual valve 32 provided on the oil discharge line 3 is a gate valve. The gate valve is manually opened when the solenoid valve of the first valve 31 is open; and the gate valve is manually closed when the solenoid valve of the first valve 31 is closed.

[0049] The oil discharge line 3 is further provided with a one-way valve 33 and a flow-limiting orifice 5 ; the one-way valve 33 is located at the end of the oil discharge line 3 , and the flow-limiting orifice 5 is located between the first valve 31 and the second manual valve 32 .

[0050] The oil discharge line 3 is located below the valve box of the cracked gas valve 1 and forms a height difference therewith.

[0051] The oil discharge line 3 is arranged at the position where the anti-scorch steam return line is led out from the bottom of the cracking gas valve box, that is, it is led out from the pipeline at the bottom of the anti-scorch steam return line.

[0052] A discharge line is led out from the head end of the bottom pipeline to connect to the low-pressure dirty oil tank E to discharge coke tar, the oil discharge line 3 is led out from the middle part, and the discharge guide F is led out from the end; a valve switch is set on the discharge line.

[0053] The oil discharge line 3 is connected to a first valve 31 , a flow limiting orifice 5 , a second manual valve 32 , and a one-way valve 33 in sequence from the head end to the tail end.

[0054] The nominal diameter of the oil discharge line 3 is DN50-DN75mm.

[0055] The oil drain line 3 is equipped with a steam heating line with a nominal diameter of DN20mm, located along the outer wall of the pipeline and the outer walls of the solenoid valve 31, the flange of the flow-restricting orifice 5, the gate valve 32, and the check valve 33. This steam line runs parallel to the wall of the oil drain line 3, with steam flowing back and forth in a loop to prevent condensation and blockage. Steam line heating is a conventional technique, and steam heating is typically done against the wall. The oil drain line is a 2-inch or 3-inch pipeline. A small DN20mm nominal diameter pipeline is attached to the outer surface of this pipeline to pass steam. This pipeline is arranged parallel to the oil drain line, with steam flowing in and out of the pipeline to form a loop. The outer surface is then wrapped with insulation material and then aluminum foil.

[0056] The workflow of the present invention is briefly described as follows:

[0057] When the cracking furnace is in operation, the raw materials are put into the cracking furnace for high-temperature cracking reaction. The high-temperature cracked gas at the cracking furnace outlet D enters the cracking gas pipeline 4 through the cracking gas valve 1, and then the cracking gases from multiple furnaces are collected into the cracking gas main pipe 41 to the downstream separation system.

[0058] When the cracking furnace is in the coking condition, the cracking furnace is in the process of high temperature coking by introducing industrial air. The high temperature coking gas M at the cracking furnace outlet D enters the coking tank and is discharged to the atmosphere through the coking gas valve 6. Figure 2 shown.

[0059] Figure 3Only the valve box of the cracking gas valve 1, the anti-scorch steam inlet line B, the anti-scorch steam return line 2, and the low-pressure waste oil tank E and drain drain F on the anti-scorch steam return line are marked. The return injection point of the anti-scorch steam return line 2 is on the cracking gas pipeline behind the cracking gas valve, and all of these connections are based on existing technology. The valve box of the scorch burn valve, the anti-scorch steam inlet line and the anti-scorch steam return line, as well as the low-pressure waste oil tank and drain drain on the anti-scorch steam return line, follow this connection method and are not marked in the figure. The difference is that the anti-scorch steam return injection point is on the cracking gas pipeline before the scorch burn valve 6, and all of these connections are based on existing technology.

[0060] The oil discharge line 3 in the figure represents the modified and added cracked gas valve oil discharge system. The process design utilizes a solenoid valve as the first valve 31, with an interlocking mechanism to control its on / off. In response to the on / off signal from cracked gas valve 1, the solenoid valve 31 in the oil discharge line opens when the cracked gas valve 1 fully opens, and the second manual valve 32 opens manually. The solenoid valve 31 in the modified line closes when the cracked gas valve 1 fully closes, and the second manual valve 32 closes manually. The interlocking mechanism is conventional and will not be further described.

[0061] Working principle of the present invention:

[0062] Since there is no concern about internal leakage due to poor sealing when the cracking gas valve 1 is open, there is no need to form a sealing pressure difference between the valve box and the cracking gas pipeline. When the cracking gas valve is fully open, the cracking gas carries oil coke and enters the box body X through the sealed gap. The modification adds an oil discharge system to the oil discharge line to keep it open and unobstructed. The thrust generated by the high and low head difference and the effect of the purge steam can timely discharge the tar in the box body X into the lower cracking gas main pipe below, reducing the accumulation of tar in the cracking gas valve box body X. The purpose of the modification is to rely on the thrust generated by the high and low head difference and the effect of the purge steam to continuously discharge the liquid to the lower cracking gas main pipe when the cracking gas valve is fully open. Generally, in the prior art, the lower cracking gas main pipe has a minimum head difference of 4 meters below the cracking gas valve box body X. At the same time, the anti-coking steam return line will not produce liquid accumulation to form a water seal. When the large valve of the cracking gas is fully closed, after the oil discharge line of the modified and added oil discharge system is closed, the anti-coking steam forms a sealed pressure difference control between the valve box and the cracking gas pipeline under the action of the resistance of the anti-coking steam return line, preventing the risk of low-pressure cracking gas from leaking into the valve box and finally leaking back from the double gate valve inlet seal.

[0063] The cracking furnace switching valve is a key equipment of the cracking furnace. At present, the large cracking furnace switching valves all adopt imported double-disc valves (representative brands: Zimmermann&&Jansen, FRIATEC (DGV)). The price of the cracking gas valve with a nominal diameter of DN1200 is about 5 million yuan / unit. Domestic brands have been gradually developed and applied in recent years. Therefore, the present invention is very important for studying the technical transformation of the cracking furnace switching valve to facilitate maintenance.

Claims

1. An oil drainage system for a cracking furnace cracking gas double-disc valve, comprising a cracking gas valve, a coke prevention steam return line for the cracking gas valve, and an oil drainage system; the cracking gas valve is a double-disc valve; and is characterized in that: The oil drainage system is arranged on the anti-coking steam return line (2) drawn out from the bottom of the valve box of the cracked gas valve (1); the oil drainage system is arranged as an oil drainage line (3) in a vertical downward direction, the lower end of which is directly connected to the cracked gas main pipe (41) below; When the valve of the cracked gas valve (1) is opened, the oil discharge line (3) is opened synchronously; when the valve of the cracked gas valve (1) is closed, the oil discharge line (3) is closed synchronously; Two valves are provided on the oil discharge line (3), including a first valve (31) and a second manual valve (32); the first valve (31) provided on the oil discharge line (3) is a solenoid valve, and an interlocking signal is provided to control the switch of the solenoid valve, and the solenoid valve corresponds to the switch signal of the cracking gas valve; when the cracking gas valve fully opens, the first valve is triggered to open; when the cracking gas valve fully closes, the first valve is triggered to close; The second manual valve (32) provided on the oil discharge line (3) is a gate valve, and the gate valve is manually opened when the first valve is opened; and the gate valve is manually closed when the first valve is closed; A one-way valve (33) and a flow-limiting orifice (5) are also provided on the oil discharge line (3); the one-way valve (33) is located at the end of the oil discharge line (3), and the flow-limiting orifice (5) is located between the first valve (31) and the second manual valve (32); The oil discharge line (3) is provided with a steam heating pipeline on the outer wall of the pipeline and the outer wall of the first valve (31), the flow limiting orifice (5) flange, the second hand valve (32), and the one-way valve (33). The nominal diameter of the steam heating pipeline is DN20mm. The steam heating pipeline is parallel to the pipeline wall of the oil discharge line (3). The steam goes back and forth twice to form a loop heating pipeline to prevent condensation from clogging the pipeline.

2. The oil discharge system of the double-disc valve for cracking gas in a cracking furnace according to claim 1, characterized in that: The oil discharge line (3) is arranged at the position where the anti-coking steam return line is led out from the bottom of the cracking gas valve box, that is, it is led out from the pipeline at the bottom of the anti-coking steam return line.

3. The oil discharge system of the double-disc valve for cracking gas in a cracking furnace according to claim 2, characterized in that: A discharge line is led out from the head end of the bottom pipeline to connect to the low-pressure dirty oil tank E, the oil discharge line (3) is led out from the middle part, and the discharge guide F is led out from the end part; a valve switch is set on the discharge line.

4. The oil discharge system of the double-disc valve for cracking gas in a cracking furnace according to claim 3, characterized in that: The oil discharge line (3) is connected in sequence from the head end to the tail end with a first valve (31), a flow limiting orifice (5), a second manual valve (32), and a one-way valve (33).

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