A device and method for recovering residual liquid cooling capacity of a synthesis gas CO cryogenic separation system

Abstract

The present invention discloses a device and method for recovering the coldness of residual liquid in a synthesis gas CO cryogenic separation system, and belongs to the field of chemical process. When the synthesis gas CO cryogenic separation system is shut down and drained, the temperature can reach -190°C due to the large amount of low-temperature residual liquid stored in the cold box. The conventional treatment method is to send the low-temperature residual liquid to the flare gas heater through ambient gasification, and discharge it as room-temperature flare gas after heat exchange with saturated steam. When the amount of low-temperature residual liquid is large, this method takes a long time to vaporize the low-temperature residual liquid; or nitrogen is used to cool and gasify the low-temperature residual liquid to produce low-temperature flare gas, which is then sent to the flare gas heater for heat exchange. This method increases nitrogen loss, increases the load of the flare gas heater, makes its equipment size larger, and increases cost. The present invention utilizes the high-grade low-temperature coldness of the low-temperature residual liquid in the CO cryogenic separation system to convert room-temperature nitrogen into liquid nitrogen for storage and recovery, thereby reducing nitrogen loss, reducing 0.5MPaG steam loss, and reducing flare gas emissions.

Description

Technical Field

[0001] The present invention belongs to the field of utilizing and converting high-grade cold in low-temperature residual liquid into liquid nitrogen, and specifically relates to a residual liquid cold recovery device and method for a synthesis gas CO deep cold separation system, which can recover liquid nitrogen and reheat the residual liquid at a very low cost. Background Art

[0002] Synthetic Gas (synthetic gas) is primarily composed of a combination of various gases, including hydrogen and carbon monoxide, as well as carbon dioxide, water vapor, nitrogen, and methane. Synthetic gas is a product produced by coal gas or natural gas conversion. It is also a feedstock in various chemical processes, such as methanol synthesis, ammonia synthesis, ethylene glycol synthesis, acetic acid synthesis, polyglycolic acid, and dimethylformamide. Before entering various devices, syngas requires separation and processing, and the separation methods and technologies used vary significantly depending on the situation.

[0003] As a major technical means of syngas separation, CO cryogenic separation has the advantages of large-scale scalability, small footprint, low unit energy consumption, simple operation, and a mature and stable system. By using cryogenic separation technology and performing specific operations based on the actual composition of the feed gas, good separation effects can be achieved.

[0004] CO2 cryogenic separation units typically require a large amount of liquid to be discharged during shutdown, and the temperature of the discharged liquid can reach around -190°C. This liquid must be vaporized and then reheated to room temperature using a flare gas heater to prevent room-temperature flaring. Due to the large liquid storage capacity of the distillation tower within the CO2 cryogenic separation unit, the amount of liquid discharged during shutdown is relatively large. Air convection heat exchange through the walls of the residual liquid buffer tank is difficult to meet this requirement, and conventional air-temperature vaporizers have the disadvantage of occupying a large space. Therefore, a small, low-cost, and simple-to-control, efficient recovery device is urgently needed. Summary of the Invention

[0005] The present invention aims to overcome the deficiencies of the prior art and to provide a device and method for recovering residual liquid cold from a synthesis gas CO cryogenic separation system. The device has the characteristics of small equipment, low investment cost, simple and effective control, and can achieve the purpose of vaporizing and discharging residual liquid while recovering cold to produce liquid nitrogen.

[0006] The specific technical solutions adopted in the present invention are as follows:

[0007] In a first aspect, the present invention provides a residual liquid cooling capacity recovery device for a synthesis gas CO cryogenic separation system, comprising a residual liquid buffer vaporizer, a flare gas heater, a liquid level control valve, and a liquid nitrogen tank truck;

[0008] The residual liquid buffer vaporizer comprises a nitrogen inlet pipe box, a liquid nitrogen outlet pipe box, a nitrogen inlet tube sheet, a shell, a core tube, a wound tube bundle and a liquid nitrogen outlet tube sheet;

[0009] The inlet at the top of the shell is connected to the nitrogen inlet pipe box via a nitrogen inlet tube sheet, and the outlet at the bottom is connected to the liquid nitrogen outlet pipe box via a liquid nitrogen outlet tube sheet. The shell, nitrogen inlet tube sheet, and liquid nitrogen outlet tube sheet together form a hollow, enclosed structure.

[0010] Inside the shell, a central core tube is located between the nitrogen inlet and liquid nitrogen outlet tube sheets. A coiled tubing bundle is axially secured to the core tube. The top and bottom of the coiled tubing bundle are connected to the nitrogen inlet and liquid nitrogen outlet manifolds, respectively. The coiled tubing bundle contains several heat exchange tubes for inter-wall heat exchange between the nitrogen and cryogenic residual liquid sides. The liquid nitrogen outlet manifold is connected to a liquid nitrogen tank truck via a pipeline equipped with a level control valve.

[0011] The side walls of the shell are respectively provided with a low-temperature residual liquid inlet and a low-temperature flare gas outlet, which are connected to the inlet of the flare gas heater. The flare gas heater includes a heat exchanger for heat exchange between the low-temperature flare gas side and the saturated steam side.

[0012] Preferably, the liquid level control valve is provided with a liquid level gauge for controlling the liquid level in the liquid nitrogen outlet pipe box.

[0013] Preferably, the sealing connection between the upper end and the lower end of the wound tube bundle and the nitrogen inlet tube sheet and the liquid nitrogen outlet tube sheet is achieved by welding.

[0014] Preferably, the upper end and the lower end of the central core tube are connected to the nitrogen inlet tube sheet and the liquid nitrogen outlet tube sheet by expansion welding.

[0015] In a second aspect, the present invention provides a method for recovering the residual liquid cooling capacity of a synthesis gas CO cryogenic separation system using the recovery device described in the first aspect, which is specifically as follows:

[0016] S1: The cryogenic residual liquid at the outlet of the CO cryogenic separation unit's cold box is introduced into the shell through the cryogenic residual liquid inlet. Room-temperature nitrogen is introduced into the nitrogen inlet manifold and evenly distributed through the nitrogen inlet tubesheet to the individual heat exchange tubes of the spiral wound tube bundle. The spiral wound tube bundle contains several heat exchange tubes, which perform inter-wall heat exchange between the nitrogen and cryogenic residual liquid sides. The room-temperature nitrogen vaporizes the cryogenic residual liquid to produce low-temperature flare gas. This room-temperature nitrogen is then liquefied through the spiral wound tube bundle to produce liquid nitrogen. This liquid nitrogen is condensed and collected in the liquid nitrogen outlet manifold.

[0017] S2: The low-temperature flare gas is discharged through the low-temperature flare gas outlet to the refrigerant inlet of the flare gas heater, while the saturated steam is introduced into the heat medium inlet of the flare gas heater. The low-temperature flare gas and saturated steam undergo heat exchange through heat exchangers within the flare gas heater. The low-temperature flare gas is reheated to ambient temperature flare gas, and the saturated steam condenses into steam condensate. The ambient temperature flare gas is discharged into the flare pipeline through the refrigerant outlet of the flare gas heater, while the steam condensate is discharged to the outside through the heat medium outlet of the flare gas heater.

[0018] S3: The liquid nitrogen in the liquid nitrogen outlet pipe box is delivered to the liquid nitrogen tank truck through a pipeline provided with a liquid level control valve.

[0019] Preferably, the pressure of the low-temperature residual liquid in S1 is 0.05 to 0.15 MPaG, and the temperature is -190°C to -185°C.

[0020] Preferably, the nitrogen pressure at room temperature in S1 is 0.4-0.7 MPaG.

[0021] Preferably, the temperature of the low-temperature flare gas in S1 is -190°C to -185°C.

[0022] Preferably, the temperature of the liquid nitrogen in S1 is -179.1°C to -172.7°C.

[0023] Preferably, the pressure of the saturated steam in S2 is 0.5 MPaG, the temperature is 159°C, and the temperature of the normal temperature flare gas in S2 is 20°C.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The present invention can convert the high-quality cold energy in the low-temperature residual liquid in the cold box of the CO deep-cold separation device into liquid nitrogen for utilization;

[0026] (2) The present invention adopts a smaller flare gas heater device size, reducing the 0.5MPaG saturated steam consumption by about 55%, which can save industrial costs, and the use of a smaller flare gas heater device can reduce the flare gas discharge volume. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of a residual liquid cooling capacity recovery device for a synthesis gas CO cryogenic separation system;

[0028] Figure 2 Schematic diagram of the vaporizer for residual liquid buffer;

[0029] Figure numerals: residual liquid buffer vaporizer 1, flare gas heater 2, liquid level control valve 3, liquid nitrogen tank truck 4, nitrogen inlet pipe box 5, liquid nitrogen outlet pipe box 6, nitrogen inlet tube sheet 7, shell 8, core tube 9, wound tube bundle 10, liquid nitrogen outlet tube sheet 11. DETAILED DESCRIPTION

[0030] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention may be combined accordingly, provided that there is no conflict between them.

[0031] like Figure 1 The figure shows a schematic diagram of a residual liquid cooling capacity recovery device for a synthesis gas CO cryogenic separation system, as follows:

[0032] The residual liquid buffer vaporizer 1 includes a nitrogen inlet pipe box 5, a liquid nitrogen outlet pipe box 6, a nitrogen inlet tube sheet 7, a shell 8, a core tube 9, a wound tube bundle 10 and a liquid nitrogen outlet tube sheet 11. Figure 2 As shown, the residual liquid buffer vaporizer 1 is placed vertically, which is convenient for the heat exchange of the wound tube bundle 10 and makes the flow more sufficient.

[0033] The residual liquid buffer vaporizer 1 includes a nitrogen inlet pipe box 5, a liquid nitrogen outlet pipe box 6, a nitrogen inlet tube plate 7, a shell 8, a core tube 9, a wound tube bundle 10 and a liquid nitrogen outlet tube plate 11.

[0034] Specifically, the inlet at the top of the housing 8 is connected to the nitrogen inlet manifold 5 via a nitrogen inlet tube sheet 7, while the outlet at the bottom is connected to the liquid nitrogen outlet manifold 6 via a liquid nitrogen outlet tube sheet 11. The nitrogen inlet tube sheet 7 separates the nitrogen side (inside the tubes) from the low-temperature residual liquid side (outside the tubes), and the liquid nitrogen outlet manifold 6 collects and buffers condensed liquid nitrogen.

[0035] Located within the shell 8, a central core tube 9 is installed between the nitrogen inlet tube sheet 7 and the liquid nitrogen outlet tube sheet 11. Since the wound tube bundle 10 is a flexible heat exchange pipeline, to ensure more efficient and uniform heat exchange between the low-temperature residual liquid and the room-temperature nitrogen, the wound tube bundle 10 is wound layer by layer, using the central core tube 9 as a base support. In practical applications, as a preferred embodiment of the present invention, the central core tube 9 can be connected to the nitrogen inlet tube sheet 7 and the liquid nitrogen outlet tube sheet 11 by expansion welding.

[0036] The top and bottom of the coiled tube bundle 10 are connected to the nitrogen inlet manifold 5 and the liquid nitrogen outlet manifold 6, respectively. The coiled tube bundle 10 contains several heat exchange tubes for inter-wall heat exchange between the nitrogen and cryogenic residual liquid sides. The upper and lower ends of the coiled tube bundle 10 are sealed to the nitrogen inlet tube sheet 7 and the liquid nitrogen outlet tube sheet 11, respectively. This allows nitrogen to flow from the nitrogen inlet manifold 5 through the nitrogen inlet tube sheet 7 into the heat exchange tubes within the coiled tube bundle 10. After heat exchange and condensation, nitrogen is collected in the liquid nitrogen outlet manifold 6 via the nitrogen inlet tube sheet 7 below. In practical applications, as a preferred embodiment of the present invention, welding can be used as the sealing connection method.

[0037] The liquid nitrogen outlet manifold 6 is connected to a liquid nitrogen tanker 4 via a pipeline equipped with a liquid level control valve 3. In practical applications, as a preferred embodiment of the present invention, a liquid level gauge can also be installed on the liquid level control valve 3 to control the level control valve. Liquid nitrogen tankers are convenient for transportation and can be used in other process equipment requiring liquid nitrogen.

[0038] The side walls of the shell 8 are provided with a low-temperature residual liquid inlet and a low-temperature flare gas outlet. The low-temperature residual liquid inlet is connected to the outlet of the CO cryogenic separation unit cold box and is used to receive low-temperature residual liquid from the CO cryogenic separation unit cold box. The lower space within the shell 8 is used to store the low-temperature residual liquid. When the CO cryogenic separation unit is shut down and drained, the liquid storage volume in the cold box is relatively large, with a temperature of up to -190°C. The high-grade low-temperature cooling capacity of this low-temperature residual liquid can be used to convert room-temperature nitrogen into liquid nitrogen for storage and recovery.

[0039] The low-temperature flare gas outlet is connected to the inlet of the flare gas heater 2. The flare gas heater 2 contains a heat exchanger for realizing heat exchange between the low-temperature flare gas side and the saturated steam side.

[0040] The specific method for recovering the cold capacity of the residual liquid in a synthesis gas CO cryogenic separation system provided by the present invention is as follows:

[0041] (1) The low-temperature raffinate C at the outlet of the CO cryogenic separation device cold box is introduced into the low-temperature raffinate inlet of the raffinate buffer vaporizer 1. The low-temperature raffinate C has a pressure of 0.05 to 0.15 MPaG and a temperature of approximately -190°C to -185°C. Room-temperature nitrogen A at a pressure of 0.4 to 0.7 MPaG is introduced into the nitrogen inlet pipe box 5. The room-temperature nitrogen is evenly distributed to each heat exchange tube of the wound tube bundle 10 through the nitrogen inlet tube sheet 7. The multiple heat exchange tubes contained in the wound tube bundle 10 perform inter-wall heat exchange between the nitrogen side and the low-temperature raffinate side. The room-temperature nitrogen A vaporizes the low-temperature raffinate C into low-temperature flare gas D at -190°C to -185°C. At the same time, the room-temperature nitrogen A is heat-exchanged through the wound tube bundle 10 to obtain liquid nitrogen H at a temperature of -179.1°C to -172.7°C. The liquid nitrogen H is collected in the liquid nitrogen outlet pipe box 6.

[0042] (2) The low-temperature flare gas D is discharged to the refrigerant inlet of the flare gas heater 2 through the low-temperature flare gas outlet, and the saturated steam is introduced into the heat medium inlet of the flare gas heater 2. The pressure of the saturated steam F is 0.5 MPaG and the temperature is 159°C. The low-temperature flare gas D and the saturated steam F are heat exchanged through the heat exchanger in the flare gas heater 2. The low-temperature flare gas D is reheated to the room-temperature flare gas E, and the saturated steam F is condensed to steam condensate G. The room-temperature flare gas E is discharged to the flare pipeline through the refrigerant outlet of the flare gas heater 2, and the steam condensate G is discharged to the outside through the heat medium outlet of the flare gas heater 2.

[0043] (3) The liquid nitrogen H in the liquid nitrogen outlet pipe box 6 is delivered to the liquid nitrogen tank truck 4 for filling through a pipeline provided with a liquid level control valve 3.

[0044] The residual liquid buffer vaporizer device provided by the present invention is simple and effective. It quickly vaporizes and discharges low-temperature residual liquid while producing liquid nitrogen that meets production needs for utilization. At the same time, the device itself adopts a wound tube bundle to adapt to large temperature differences and has the functions of residual liquid storage, residual liquid vaporization, and nitrogen liquefaction.

[0045] The embodiment described above is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Persons skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent substitution or equivalent transformation falls within the scope of protection of the present invention.

Claims

1. A device for recovering residual liquid cooling capacity of a synthesis gas CO cryogenic separation system, characterized in that: It comprises a residual liquid buffer vaporizer (1), a flare gas heater (2), a liquid level control valve (3) and a liquid nitrogen tank truck (4); The residual liquid buffer vaporizer (1) comprises a nitrogen inlet pipe box (5), a liquid nitrogen outlet pipe box (6), a nitrogen inlet tube sheet (7), a shell (8), a core tube (9), a wound tube bundle (10) and a liquid nitrogen outlet tube sheet (11); The inlet end of the top of the shell (8) is connected to the nitrogen inlet pipe box (5) through the nitrogen inlet tube sheet (7), and the outlet end of the bottom is connected to the liquid nitrogen outlet pipe box (6) through the liquid nitrogen outlet tube sheet (11). The shell (8), the nitrogen inlet tube sheet (7) and the liquid nitrogen outlet tube sheet (11) together constitute a hollow closed structure. A central core tube (9) is provided inside the shell (8) between the nitrogen inlet tube sheet (7) and the liquid nitrogen outlet tube sheet (11). A winding tube bundle (10) is fixed axially on the central core tube (9). The top and bottom of the winding tube bundle (10) are respectively connected to the nitrogen inlet pipe box (5) and the liquid nitrogen outlet pipe box (6). The winding tube bundle (10) includes a plurality of heat exchange tubes for realizing inter-wall heat exchange between the nitrogen side and the low-temperature residual liquid side. The liquid nitrogen outlet pipe box (6) is connected to the liquid nitrogen tank car (4) through a pipeline provided with a liquid level control valve (3). The side walls of the shell (8) are respectively provided with a low-temperature residual liquid inlet and a low-temperature flare gas outlet, and the low-temperature flare gas outlet is connected to the inlet of the flare gas heater (2); the flare gas heater (2) contains a heat exchanger for heat exchange between the low-temperature flare gas side and the saturated steam side.

2. The device for recovering residual liquid cooling energy of a synthesis gas CO cryogenic separation system according to claim 1, characterized in that: The liquid level control valve (3) is provided with a liquid level meter for controlling the liquid level in the liquid nitrogen outlet pipe box (6).

3. The device for recovering residual liquid cooling energy of a synthesis gas CO cryogenic separation system according to claim 1, characterized in that: The upper and lower ends of the wound tube bundle (10) are sealed and connected to the nitrogen inlet tube sheet (7) and the liquid nitrogen outlet tube sheet (11) by welding.

4. The device for recovering residual liquid cooling energy of a synthesis gas CO cryogenic separation system according to claim 1, characterized in that: The upper end and the lower end of the central core tube (9) are connected to the nitrogen inlet tube plate (7) and the liquid nitrogen outlet tube plate (11) by expansion welding.

5. A method for recovering cold energy from residual liquid in a synthesis gas CO cryogenic separation system using the recovery device according to any one of claims 1 to 4, characterized in that: The details are as follows: S1: The low-temperature residual liquid at the outlet of the cold box of the CO deep-cold separation device is introduced into the interior of the shell (8) through the low-temperature residual liquid inlet; normal-temperature nitrogen is introduced into the nitrogen inlet pipe box (5), and the normal-temperature nitrogen is evenly distributed to each heat exchange tube of the wound tube bundle (10) through the nitrogen inlet tube plate (7); the plurality of heat exchange tubes contained in the wound tube bundle (10) perform inter-wall heat exchange between the nitrogen side and the low-temperature residual liquid side, and the normal-temperature nitrogen vaporizes the low-temperature residual liquid to obtain low-temperature flare gas; the normal-temperature nitrogen is liquefied through the heat exchange of the wound tube bundle (10) to obtain liquid nitrogen; the liquid nitrogen is condensed and collected in the liquid nitrogen outlet pipe box (6); S2: The low-temperature flare gas is discharged to the refrigerant inlet of the flare gas heater (2) through the low-temperature flare gas outlet, and the saturated steam is introduced into the heat medium inlet of the flare gas heater (2); the low-temperature flare gas and the saturated steam are heat-exchanged through the heat exchanger in the flare gas heater (2), the low-temperature flare gas is reheated to the room-temperature flare gas, and the saturated steam is condensed to steam condensate; the room-temperature flare gas is discharged to the flare pipeline through the refrigerant outlet of the flare gas heater (2), and the steam condensate is discharged to the outside through the heat medium outlet of the flare gas heater (2); S3: The liquid nitrogen in the liquid nitrogen outlet pipe box (6) is delivered to the liquid nitrogen tank truck (4) through a pipeline provided with a liquid level control valve (3).

6. The method for recovering cold energy of residual liquid in the synthesis gas CO cryogenic separation system of the recovery device according to claim 5, characterized in that: The pressure of the low-temperature residual liquid described in S1 is 0.05 to 0.15 MPaG, and the temperature is -190°C to -185°C.

7. The method for recovering cold energy of residual liquid in the synthesis gas CO cryogenic separation system of the recovery device according to claim 5, characterized in that: The nitrogen pressure at room temperature described in S1 is 0.4 to 0.7 MPaG.

8. The method for recovering cold energy of residual liquid in the synthesis gas CO cryogenic separation system of the recovery device according to claim 5, characterized in that: The temperature of the low-temperature flare gas described in S1 is -190°C to -185°C.

9. The method for recovering cold energy of residual liquid in the synthesis gas CO cryogenic separation system of the recovery device according to claim 5, characterized in that: The temperature of the liquid nitrogen described in S1 is -179.1°C to -172.7°C.

10. The method for recovering cold energy of residual liquid in a synthesis gas CO cryogenic separation system of a recovery device according to claim 5, characterized in that: The pressure of the saturated steam described in S2 is 0.5 MPaG and the temperature is 159°C; the temperature of the normal temperature flare gas described in S2 is 20°C.

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