Automatic liquid level control system and pressure reduction equipment applying same

Abstract

The utility model discloses an automatic liquid level control system and decompression equipment applying the same, the automatic liquid level control system is used for a decompression device and comprises a liquid seal device, a liquid level sensing mechanism and a tower bottom product pump, a liquid inlet pipeline of the liquid seal device is communicated with the side wall of a tower body of the decompression device, and a liquid outlet pipeline of the liquid level sensing mechanism is communicated with the tower bottom product pump. A liquid outlet pipeline of the liquid sealing device is communicated with a liquid outlet pipeline of the pressure reducing device, the tower bottom product pump is communicated with the liquid outlet pipeline of the liquid sealing device and the liquid outlet pipeline of the pressure reducing device, and the tower bottom product pump is also connected with the liquid level sensing mechanism to realize pressure balance. According to the automatic liquid level control system, the liquid level sensing mechanism is adopted to control the rotating speed of the product extraction pump, so that the net positive suction head of the tower bottom product pump is counteracted, the stability of liquid drainage of the tower bottom product pump in a pressure reduction state is improved, and the problem that the product pump is damaged due to small height difference between a pressure reduction device and the tower bottom product pump is solved. And the phenomenon that a product pump at the bottom of the tower does not discharge liquid or the liquid discharge is unstable due to insufficient feeding pressure heads is avoided.

Description

Technical Field

[0001] The utility model belongs to the technical field of pressure reducing devices, and in particular relates to a liquid level automatic control system and pressure reducing equipment using the same. Background Art

[0002] Atmospheric and vacuum distillation units are essential equipment used in oil refineries and chemical plants, primarily in the crude oil fraction separation process, known as fractional distillation or rectification. Both atmospheric and vacuum distillation are physical processes. Crude oil is heated in a fractionating tower and separated into fractions, or distillates, based on their boiling points. During crude oil processing, vacuum distillation reduces the external pressure, thereby lowering the critical temperature of the saturated vapor pressure of the fractions, allowing the products to vaporize and separate at lower temperatures. Proper and stable operation of the vacuum tower requires a stable vacuum level, which significantly impacts the vapor and liquid phase loads throughout the tower, as well as its smooth operation.

[0003] Since the vacuum distillation tower operates under vacuum conditions, if the liquid level at the bottom of the tower is not high enough, it will not be able to provide sufficient priming pressure head for the shutdown bottom pump to start the pump operation. During operation, the temperature rise of the tower kettle will also cause the viscosity of the material in the tower kettle to decrease, causing cavitation in the pump. Cavitation will cause the liquid output of the tower bottom pump to be unstable and even damage the pump body, and will also affect the stability of the vacuum degree. In order to provide sufficient priming pressure head, it is necessary to increase the height of the vacuum tower when installing it, and use a skirt-type support at the bottom of the tower, that is, a skirt seat. The height of the skirt seat mainly ensures that the height difference between the tower bottom product outlet and the pump inlet is greater than the cavitation margin of the tower bottom pump to prevent the tower bottom pump from being evacuated.

[0004] However, during equipment installation, the vacuum distillation tower is generally connected to other equipment. If the skirt height is increased too much, the difficulty and cost of equipment installation will increase. The manufacturing of auxiliary equipment will be more difficult, which will also cause material waste. The difficulty of maintenance and safety requirements will also be further increased. Utility Model Content

[0005] In view of this, the purpose of the present invention is to provide an automatic liquid level control system that can offset the cavitation head of the pump, so that the pump can stably discharge liquid, and can also achieve continuous and stable control of the liquid level.

[0006] The purpose of the utility model is also to provide a pressure reducing device using the above-mentioned liquid level automatic control system.

[0007] In order to achieve the above-mentioned purpose, the technical solution of the present utility model is implemented as follows: a liquid level automatic control system is used for a pressure reducing device, including a liquid sealing device, a liquid level sensing mechanism and a tower bottom product pump, the liquid inlet pipeline of the liquid sealing device is connected to the side wall of the tower body of the pressure reducing tower in the pressure reducing device, the liquid outlet pipeline of the liquid sealing device is connected to the liquid outlet pipeline of the pressure reducing tower in the pressure reducing device, the tower bottom product pump is connected to the liquid outlet pipeline of the liquid sealing device and the liquid outlet pipeline of the pressure reducing tower in the pressure reducing device, and the tower bottom product pump is also connected to the liquid level sensing mechanism to achieve pressure balance.

[0008] Preferably, the liquid level sensing mechanism includes a liquid level component, a sensing component and a control component. The liquid level component is arranged below the pressure reducing tower in the pressure reducing device, the sensing component is arranged on the liquid level component, and the control component is connected to the sensing component.

[0009] Preferably, the control assembly is connected to the bottom product pump.

[0010] Preferably, the liquid level component is a magnetic float liquid level gauge; and the sensing component is a sensor for sensing liquid level signals.

[0011] Preferably, the liquid sealing device is a liquid sealing tank, the pipeline above the liquid sealing tank is connected to the liquid outlet of the pressure reducing tower in the pressure reducing device; the pipeline below the liquid sealing tank is connected to the bottom of the pressure reducing device.

[0012] Preferably, valves are provided on both the liquid inlet pipeline and the liquid outlet pipeline of the liquid seal tank; and a pressure gauge is also provided on the pipeline of the tower bottom product pump.

[0013] Another technical solution of the present invention is achieved as follows: a liquid level automatic control pressure reducing device comprises a pressure reducing device and the above-mentioned liquid level automatic control system, wherein the liquid level automatic control system is arranged on the pressure reducing device.

[0014] Preferably, the pressure reducing device includes a pressure reducing tower, a heat exchanger, and a product storage assembly. The pressure reducing tower is connected to the product storage assembly through the heat exchanger, and the liquid inlet and outlet pipelines of the liquid seal device in the liquid level automatic control system are both connected to the pressure reducing tower.

[0015] Preferably, the pressure reducing device further comprises a vacuum buffer, wherein the vacuum buffer is in communication with the heat exchanger and the product storage assembly.

[0016] Preferably, the product storage assembly includes at least two product storage tanks, and the two product storage tanks are connected to the heat exchanger and the vacuum buffer in a parallel manner.

[0017] Compared with existing technologies, the present invention's automatic liquid level control system achieves automatic liquid level control by using a liquid level sensor to control the rotational speed of the product extraction pump. Furthermore, a liquid seal device is installed at the front end of the tower bottom product pump. This not only offsets the cavitation margin of the tower bottom product pump and improves the stability of the tower bottom product pump's discharge under reduced pressure, but also avoids the phenomenon of the tower bottom product pump failing to discharge or having unstable discharge due to insufficient feed pressure head due to the small height difference between the pressure reducing device and the tower bottom product pump. Furthermore, in high-temperature system environments, a heat exchanger can be used outside the liquid seal device to reduce the temperature of the discharge medium, thereby increasing its viscosity and significantly offsetting pump cavitation. This effectively protects the internal components of the tower bottom product pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a process flow chart of a liquid level automatic control system provided by an embodiment of the utility model.

[0019] In the figure, 1. liquid sealing device, 2. liquid level sensing mechanism, 3. tower bottom product pump, 4. pressure reducing device, 41. pressure reducing tower, 42. heat exchanger, 43. product storage component, 44. vacuum buffer, 5. pressure gauge. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0021] In the description of the present invention, it should be clarified that the terms "vertical", "transverse", "longitudinal", "front", "rear", "left", "right", "up", "down", "horizontal", etc. indicating orientation or positional relationships are based on the orientation or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and do not mean that the devices or components referred to must have a specific orientation or position. Therefore, they cannot be understood as limitations on the present invention. In the description of the present invention, it should be noted that, unless otherwise clearly stipulated and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0022] Example 1

[0023] Embodiment 1 of the present invention provides a liquid level automatic control system for a pressure reducing device 4, comprising a liquid sealing device 1, a liquid level sensing mechanism 2, and a tower bottom product pump 3. The liquid inlet pipeline of the liquid sealing device 1 is connected to the side wall of the tower body of the pressure reducing tower 41 in the pressure reducing device 4, the liquid outlet pipeline of the liquid sealing device 1 is connected to the liquid outlet pipeline of the pressure reducing tower 41 in the pressure reducing device 4, the tower bottom product pump 3 is connected to the liquid outlet pipeline of the liquid sealing device 1 and the liquid outlet pipeline of the pressure reducing tower 41 in the pressure reducing device 4, and the tower bottom product pump 3 is also connected to the liquid level sensing mechanism 2 to achieve pressure balance.

[0024] After adopting the above solution, automatic liquid level control is achieved by using the liquid level sensor mechanism 2 to control the rotation speed of the product extraction pump. At the same time, the liquid seal device 1 is added to the front end of the tower bottom product pump 3. This not only offsets the cavitation margin of the tower bottom product pump 3 and improves the stability of the tower bottom product pump 3's discharge under reduced pressure, but also avoids the phenomenon of the tower bottom product pump 3 not discharging liquid or discharging liquid unstably due to the small height difference between the pressure reducing device 1 and the tower bottom product pump 3 and insufficient feed pressure head. At the same time, in a high-temperature system environment, the heat exchange device outside the liquid seal device can reduce the temperature of the discharge medium, resulting in an increase in viscosity, greatly offsetting the pump's cavitation. At the same time, it effectively protects the internal components of the tower bottom product pump.

[0025] See also Figure 1 In the specific implementation process of the embodiment of the present invention, the liquid level sensing mechanism 2 includes a liquid level component 21, a sensor component 22 and a control component 23. The liquid level component 21 is arranged below the pressure reducing tower 41 in the pressure reducing device 4, the sensor component 22 is arranged on the liquid level component 21, and the control component 23 is connected to the sensor component 22.

[0026] Specifically, the pressure reducing device 1 (preferably a pressure reducing tower) is used for the vacuum fractionation of crude oil or oil products, wherein the oil products are mixed hydrocarbon oil products of C5-C9 fraction, C10-C14 fraction and C14-C18 fraction synthesized by Fischer-Tropsch synthesis, and the bottom of the pressure reducing tower 41 in the pressure reducing device 4 is connected to the liquid sealing device 14.

[0027] See also Figure 1 In the specific implementation process of the embodiment of the present utility model, the control component 23 is connected to the bottom product pump 3.

[0028] See also Figure 1 In the specific implementation process of the embodiment of the present invention, the liquid level component 22 is a magnetic float liquid level gauge; the sensor component 22 is a sensor for sensing the liquid level signal; the sensor signal is transmitted to the control component 23, and the control component 23 controls the speed of the bottom product pump 3.

[0029] Specifically, the magnetic float level gauge can set four liquid level node values ​​according to the liquid level process index range of the pressure reducing tower 41 in the pressure reducing device, namely low value, high value, low-low value and high-high value; the sensor transmits the liquid level value signal to the control component 23, and the control component 23 controls the speed of the bottom product pump 3 through the signal.

[0030] See also Figure 1 In the specific implementation process of the embodiment of the present invention, the liquid sealing device 1 is a liquid sealing tank, and the pipeline above the liquid sealing tank is connected to the liquid outlet of the pressure reducing tower 41 in the pressure reducing device 4; the pipeline below the liquid sealing tank is connected to the bottom of the pressure reducing tower 41.

[0031] Specifically, the top (liquid) pipeline of the liquid seal tank is connected to the bottom liquid outlet of the vacuum tower 41, the bottom outlet of the liquid seal tank is connected to the inlet of the bottom product pump 3, the overall horizontal position of the liquid seal tank is lower than the bottom outlet of the vacuum tower 41, and the top pipeline of the liquid seal tank is connected to the gas phase part of the bottom of the vacuum tower 41. When the vacuum tower 41 is in operation, the liquid seal tank should be continuously in a full liquid state.

[0032] See also Figure 1 In the specific implementation process of the embodiment of the present invention, valves are provided on the upper pipeline and the lower pipeline of the liquid seal tank.

[0033] Specifically, the liquid seal tank needs to be in a full liquid state before starting the bottom product pump 3. By switching the valves on the upper and lower pipelines of the liquid seal tank to normal pressure, the pump cavity can be filled with material. After the bottom product pump 3 is stable, the liquid seal tank is cut into the vacuum tower pipeline through the valve to connect with the tower kettle.

[0034] See also Figure 1 In the specific implementation process of the embodiment of the present utility model, a pressure gauge 5 is also provided on the pipeline of the bottom product pump 3.

[0035] Example 2

[0036] The present invention also provides a liquid level automatic control pressure reducing device according to embodiment 2. Figure 1 , including a pressure reducing device 4 and the liquid level automatic control system described in Example 1, and the liquid level automatic control system is arranged on the pressure reducing device 4.

[0037] See also Figure 1 In the specific implementation process of the embodiment of the present invention, the pressure reducing device 4 includes a pressure reducing tower 41, a heat exchanger 42, and a product storage assembly 43. The pressure reducing tower 41 is connected to the product storage assembly 43 through the heat exchanger 42, and the liquid inlet pipeline and the liquid outlet pipeline of the liquid sealing device 1 in the liquid level automatic control system are both connected to the pressure reducing tower 41.

[0038] See also Figure 1 In the specific implementation process of the embodiment of the present invention, the decompression device 4 further includes a vacuum buffer 44 , and the vacuum buffer 44 is connected to the heat exchanger 42 and the product storage assembly 43 .

[0039] See also Figure 1 In the specific implementation process of the embodiment of the present invention, the product storage component 43 includes at least two product storage tanks, and the two product storage tanks are connected to the heat exchanger 42 and the vacuum buffer 44 in a parallel manner. Specifically, the bottom product pump 3 extracts the heavy phase product after oil separation from the bottom of the liquid seal tank, and the inlet of the bottom product pump 3 is connected to the bottom of the liquid seal tank; when the liquid level changes at the node value, the control component 23 changes the speed of the bottom product pump 3. When the vacuum tower liquid level is lower than the low value, the speed of the bottom product pump 3 is reduced. When the vacuum tower liquid level is lower than the low-low value, the speed of the bottom product pump 3 is reduced again. When the vacuum tower liquid level is higher than the high value, the speed of the bottom product pump 3 is increased. When the vacuum tower liquid level is higher than the high-high value, the speed of the bottom product pump 3 is increased again.

[0040] Specifically, during actual operation, the speed setting value of the bottom product pump 3 within a certain node range can be manually changed according to specific circumstances.

[0041] See also Figure 1 In the specific implementation process of the embodiment of the present invention, the vacuum tower 41 is not limited to the vacuum fractionation tower. A tower or device that uses a pump to discharge liquid under a reduced pressure environment will have an impact on the stability of the discharge due to the cavitation margin under certain conditions. Therefore, the tower or device with the above problem can be included in the embodiment of the present invention. In the embodiment of the present invention, taking a laboratory small vacuum tower demonstration device as an example, the C5-C9 fraction, C10-C14 fraction and C14-C18 fraction mixed hydrocarbon oil products synthesized by Fischer-Tropsch synthesis are subjected to vacuum fractionation, and the vacuum fractionation operation is preferably performed at a vacuum degree of 1.0-20.0 kPa. The original height of the vacuum tower 41 was 5.4 m above the ground. Due to the installation of a crane above the laboratory, the height of the vacuum tower was reduced to 3.2 m. The top reflux mode of the vacuum tower 41 is internal reflux, and the feed load is preferably 2.0-6.0 L / h. The top heat exchanger 42 (preferably a heat exchanger) and the top tank are connected to the vacuum system with pipelines.

[0042] After inputting the set value, the controller automatically adjusts the speed of the bottom product pump 3 by receiving the sensor signal, controls the size of the output flow of the bottom product pump 3, and realizes automatic adjustment of the liquid level; when the vacuum tower liquid level is a high value, the speed value range of the bottom product pump 3 is set to 4000~6000r / min, when the vacuum tower liquid level is a high value, the speed value range of the bottom product pump 3 is set to 2000~4000r / min, when the vacuum tower liquid level is a low value, the speed value range of the bottom product pump 3 is set to 1000~2000r / min, when the vacuum tower liquid level is a low value, the speed value range of the bottom product pump 3 is set to 200~1000r / min.

[0043] An embodiment of the present utility model further provides a pressure reducing device, comprising the above-mentioned automatic liquid level control system.

[0044] The following are specific embodiments

[0045] Example 1

[0046] The C5 to C9 produced after the fractionation of the Fischer-Tropsch synthetic oil are taken as raw materials for vacuum distillation. C5 to C7 are distilled from the bottom of the vacuum tower 41, and C8 to C9 are produced from the kettle. The system pressure is set to 20.0 kPa. At this time, the top distillate temperature and the bottom outlet temperature are 53°C and 74°C respectively, and the liquid seal tank outlet temperature is 30 to 35°C. After starting the bottom product pump 3, the vacuum system is cut in, and the raw material feed rate is set to 6.0 L / h. After the operating conditions stabilize, the pressure of the vacuum tower is stabilized at 19.8 to 20.4 Pa. When the speed of the bottom product pump 3 is 4000 r / min, the outlet pressure of the bottom product pump 3 is 0.28 to 0.32 MPa. When the speed of the bottom product pump 3 is 1000 r / min, the outlet pressure of the bottom product pump 3 is 0.12 to 0.16. MPa.

[0047] Example 2

[0048] The C10 to C14 produced after the Fischer-Tropsch synthetic oil is fractionated and subjected to vacuum distillation. C10 to C12 is distilled from the bottom of the vacuum tower 41, and C13 to C14 is produced from the kettle. The system pressure is set to 7.0 kPa, and full reflux is used to achieve the expected separation effect between the top and bottom products. At this time, the top distillate temperature and the bottom outlet temperature are 128°C and 146°C respectively, and the liquid seal tank outlet temperature is 78 to 84°C. After starting the bottom product pump 3, the vacuum system is cut into, and the raw material feed rate is set to 4.2 L / h. After the operating conditions stabilize, the pressure of the vacuum tower is stabilized at 6.6 to 7.4 Pa. When the speed of the bottom product pump 3 is 4000 r / min, the outlet pressure of the bottom product pump 3 is 0.30 to 0.36 MPa. When the speed of the bottom product pump 3 is 1000 r / min, the outlet pressure of the bottom product pump 3 is 0.15 to 0.22. MPa.

[0049] Example 3

[0050] The C14 to C18 produced after the Fischer-Tropsch synthetic oil is split and subjected to vacuum fractionation. C14 to C16 is distilled from the bottom of the vacuum tower 41, and C17 to C18 is produced from the bottom of the tower. The system pressure is set to 3.0 kpa, and full reflux is used to achieve the expected separation effect of the top and bottom products. At this time, the top distillate temperature and the bottom outlet temperature are 166°C and 182°C respectively. The outer wall of the liquid seal tank is air-cooled to dissipate heat, so that the outlet temperature of the liquid seal tank is maintained at 45 to 140°C. If the temperature is too low, the substances in the pipeline will be discharged. The material will coagulate and clog, and too high a pressure will damage the gear pump. After starting the bottom product pump 3, cut into the vacuum system and set the raw material feed rate to 2.4L / h. After the working conditions stabilize, the pressure of the pressure reducing tower is stabilized at 3.0~3.8kPa. When the speed of the bottom product pump 3 is 4000r / min, the outlet pressure of the bottom product pump 3 is 0.24~0.28mpa. When the speed of the bottom product pump 3 is 1000r / min, the outlet pressure of the bottom product pump 3 is 0.12~0.18.mpa.

[0051] Comparative Example 1

[0052] Consistent with the operating parameters of any of Examples 1, 2, or 3, if the vacuum system is connected after the bottom product pump 3 is started, and after a period of operation, the secondary valve is opened to allow the material at the bottom of the vacuum tower 11 to be directly connected to the inlet of the bottom product pump 3, and the valves before and after the liquid seal tank are completely closed, eliminating the role of the liquid seal tank in this area, the outlet pressure of the bottom product pump 3 will fluctuate, and the outlet flow rate cannot be maintained stable. After a period of time, the liquid level of the vacuum tower 11 rises, and the controller adjusts the pump speed to increase, but the outlet pressure and flow rate of the bottom product pump 3 still cannot be stabilized. In addition, the turbulent flow of the medium in the pump cavity of the bottom product pump 3 causes the pump body temperature to gradually increase, forcing the pump to stop, ultimately resulting in unqualified product results.

[0053] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A liquid level automatic control system for a pressure reducing device (4), characterized in that: The invention comprises a liquid sealing device (1), a liquid level sensing mechanism (2) and a tower bottom product pump (3); the liquid inlet pipeline of the liquid sealing device (1) is connected to the tower body side wall of the pressure reducing tower (41) in the pressure reducing device (4); the liquid outlet pipeline of the liquid sealing device (1) is connected to the liquid outlet pipeline of the pressure reducing tower (41) in the pressure reducing device (4); the tower bottom product pump (3) is connected to the liquid outlet pipeline of the liquid sealing device (1) and the liquid outlet pipeline of the pressure reducing tower (41) in the pressure reducing device (4); and the tower bottom product pump (3) is also connected to the liquid level sensing mechanism (2) to achieve pressure balance.

2. The liquid level automatic control system according to claim 1, characterized in that: The liquid level sensing mechanism (2) comprises a liquid level component (21), a sensing component (22) and a control component (23); the liquid level component (21) is arranged below a pressure reducing tower (41) in the pressure reducing device (4); the sensing component (22) is arranged on the liquid level component (21); and the control component (23) is connected to the sensing component (22).

3. The liquid level automatic control system according to claim 2, characterized in that: The control component (23) is connected to the bottom product pump (3).

4. A liquid level automatic control system according to claim 2 or 3, characterized in that: The liquid level component (21) is a magnetic float liquid level gauge; the sensor component (22) is a sensor for sensing liquid level signals.

5. A liquid level automatic control system according to any one of claims 1 to 3, characterized in that: The liquid sealing device (1) is a liquid sealing tank, and the pipeline above the liquid sealing tank is connected to the liquid outlet of the pressure reducing tower (41) in the pressure reducing device (4); the pipeline below the liquid sealing tank is connected to the bottom of the pressure reducing device (4).

6. The liquid level automatic control system according to claim 5, characterized in that: Valves are provided on the liquid inlet pipeline and the liquid outlet pipeline of the liquid seal tank; and a pressure gauge (5) is also provided on the pipeline of the tower bottom product pump (3).

7. A liquid level automatic control pressure reducing device, characterized in that: It comprises a pressure reducing device (4) and the liquid level automatic control system according to any one of claims 1 to 6, wherein the liquid level automatic control system is arranged on the pressure reducing device (4).

8. The liquid level automatic control and pressure reducing device according to claim 7, characterized in that: The decompression device (4) comprises a decompression tower (41), a heat exchanger (42), and a product storage assembly (43); the decompression tower (41) is connected to the product storage assembly (43) via the heat exchanger (42); and the liquid inlet pipeline and the liquid outlet pipeline of the liquid sealing device (1) in the liquid level automatic control system are both connected to the decompression tower (41).

9. The liquid level automatic control and pressure reducing device according to claim 8, characterized in that: The decompression device (4) further comprises a vacuum buffer (44), wherein the vacuum buffer (44) is in communication with the heat exchanger (42) and the product storage assembly (43).

10. The liquid level automatic control and pressure reducing device according to claim 9, characterized in that: The product storage assembly (43) includes at least two product storage tanks, and the two product storage tanks are connected to the heat exchanger (42) and the vacuum buffer (44) in a parallel manner.

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