A low-temperature methanol washing carbon dioxide flash distillation preparation system

Abstract

The utility model relates to the field of gas purification and resource recovery technology in coal chemical industry and refining integration, concretely is a kind of carbon dioxide flash evaporation system for preparation of low-temperature methanol washing, including hydrogen sulfide concentration tower, middle pressure flash tank, carbon dioxide flash tank and heat exchanger.Hydrogen sulfide concentration tower top is equipped with gas phase export, for discharging tail gas;Bottom is equipped with liquid phase export, for discharging sulfur-containing methanol-rich.The bottom liquid phase export of middle pressure flash tank is divided into middle pressure liquid phase first outlet pipeline and middle pressure liquid phase second outlet pipeline, and the middle pressure liquid phase first outlet pipeline is connected to the inlet of hydrogen sulfide concentration tower, and the middle pressure liquid phase second outlet pipeline is connected to the inlet of carbon dioxide flash tank.The bottom liquid phase export of carbon dioxide flash tank is connected to the middle pressure liquid phase first outlet pipeline.It solves the problems of insufficient carbon dioxide raw material gas supply, low resource utilization and easy disturbance of main device in the prior art.

Description

Technical Field

[0001] This utility model relates to the field of gas purification and resource recovery technology in coal chemical and refining integration, specifically a flash evaporation system for producing high-purity carbon dioxide feed gas in a low-temperature methanol washing process. Background Technology

[0002] In large-scale coal-to-hydrogen and integrated refining and chemical plants, low-temperature methanol washing is a core process for removing acidic components such as H2S, COS, and carbon dioxide (CO2) from crude coal gas. The high-concentration carbon dioxide produced as a byproduct during operation is a high-quality feedstock for food-grade liquid carbon dioxide and new material processing plants. Currently, the industry generally faces the following problems: traditional low-temperature methanol washing plants often have a single series equipped with a carbon dioxide flash evaporation system, while another series lacks independent flash evaporation facilities. Medium-pressure carbon-rich methanol directly enters the hydrogen sulfide concentration tower, and carbon dioxide is emitted with the tail gas, resulting in low resource utilization. With the commissioning of downstream new material projects and the increasing demand for food-grade carbon dioxide, there is a significant supply gap for carbon dioxide feedstock gas. Conventional modification methods are prone to problems such as low-temperature freezing blockage, excessive sulfur content, and disruption of the main unit's purification and regeneration systems. Therefore, a process system is needed that does not affect the operation of the main unit, can increase production, and allows for switching of carbon dioxide feedstock gas. Utility Model Content

[0003] In view of the deficiencies of the prior art, this utility model provides a low-temperature methanol washing carbon dioxide flash evaporation production system. To achieve the above objectives, the present invention provides a low-temperature methanol washing carbon dioxide flash evaporation production system, comprising a hydrogen sulfide concentration tower, a medium-pressure flash tank, a carbon dioxide flash tank, and a heat exchanger. The hydrogen sulfide concentration tower has a gas phase outlet at the top for discharging tail gas and a liquid phase outlet at the bottom for discharging sulfur-rich methanol. The liquid phase outlet at the bottom of the medium-pressure flash tank is divided into a first medium-pressure liquid phase outlet pipeline and a second medium-pressure liquid phase outlet pipeline. The first medium-pressure liquid phase outlet pipeline is connected to the inlet of the hydrogen sulfide concentration tower, and the second medium-pressure liquid phase outlet pipeline is connected to the inlet of the carbon dioxide flash tank. The liquid phase outlet at the bottom of the carbon dioxide flash tank is connected to the first medium-pressure liquid phase outlet pipeline. The tube-side inlet of the heat exchanger is connected to the gas phase outlet at the top of the carbon dioxide flash tank, and the tube-side outlet is connected to the carbon dioxide feed gas pipeline; the shell-side inlet of the heat exchanger is connected to the hot-state shift gas pipeline, and the shell-side outlet is connected to the cold-state shift gas pipeline.

[0004] Through the above setup, the system adds an independent carbon dioxide flash evaporation and product gas reheating and delivery process in parallel along the flow from the medium-pressure flash tank to the hydrogen sulfide concentration tower. The flow path of the carbon-rich methanol can be selected as needed: when carbon dioxide feed gas is required, the carbon-rich methanol enters the carbon dioxide flash tank through the second outlet pipeline of the medium-pressure liquid phase. The high-purity carbon dioxide released is reheated by the heat exchanger and then delivered through the carbon dioxide feed gas pipeline. The flashed carbon-rich methanol flows from the bottom liquid phase outlet of the carbon dioxide flash tank into the first outlet pipeline of the medium-pressure liquid phase, and then into the hydrogen sulfide concentration tower. Gas-liquid separation is completed in the hydrogen sulfide concentration tower. The top gas phase outlet discharges tail gas, and the bottom liquid phase outlet discharges sulfur-containing carbon-rich methanol for downstream regeneration. The purification and regeneration cycle of the main unit remains completely undisturbed. The heat exchanger uses the hot-state shift gas as the reheat heat source, and the cold-state shift gas after heat exchange is delivered through the cold-state shift gas pipeline, achieving comprehensive heat utilization.

[0005] Furthermore, a switch valve A and a regulating valve A are sequentially installed on the first outlet pipeline of the medium-pressure liquid phase; a switch valve B is installed on the second outlet pipeline of the medium-pressure liquid phase. With this configuration, the carbon-rich methanol discharged from the bottom of the medium-pressure flash tank can be selectively directed to either the hydrogen sulfide concentration tower or the carbon dioxide flash tank according to process requirements, and flow distribution and switching control can be achieved through the switch valves and regulating valves.

[0006] Furthermore, a variable frequency methanol-rich pump and a level regulating valve B are sequentially installed on the liquid phase outlet pipeline at the bottom of the carbon dioxide flash tank. The outlet of level regulating valve B is connected downstream of regulating valve A on the first outlet pipeline of the medium-pressure liquid phase. With this configuration, the flash-distilled methanol-rich pump is pressurized and then flows into the main pipeline leading to the hydrogen sulfide concentration tower, and the return flow is precisely controlled by level regulating valve B.

[0007] Furthermore, the switching valve B and the level regulating valve B form a level-flow cascade control loop, used to control the liquid level in the carbon dioxide flash tank and the flow rate of rich methanol returning to the hydrogen sulfide concentration tower. This cascade control maintains a stable liquid level in the carbon dioxide flash tank during flash evaporation, while ensuring a stable flow rate of rich methanol entering the hydrogen sulfide concentration tower, thus avoiding disturbances to the main unit.

[0008] Furthermore, a methanol spraying line is installed on the hot-state shift gas pipeline. Since the temperature of the carbon dioxide feed gas in the heat exchanger tube side is low, it can easily cause moisture in the shell-side shift gas to freeze and clog. With the methanol spraying line installed, methanol can be injected into the shift gas according to the temperature, lowering the water vapor dew point and effectively preventing freezing and blockage in the heat exchanger shell side.

[0009] Furthermore, the operating pressure of the carbon dioxide flash evaporator is controlled at 0.25~0.35MPa, and the operating temperature is controlled at -60~-40℃. Within this operating window, the carbon dioxide flash evaporator can achieve both a high carbon dioxide desorption rate and a low methanol vapor entrainment, ensuring the purity of the carbon dioxide product gas while reducing methanol loss.

[0010] Furthermore, as a preferred embodiment, the operating pressure of the carbon dioxide flash evaporator is 0.31 MPa, and the operating temperature is -50°C. Operating under these preferred parameters, the system can produce high-quality carbon dioxide feed gas with a purity ≥98.5%, H2S ≤0.5 ppm, and methanol ≤150 ppm, fully meeting the feed requirements for food-grade carbon dioxide and new material devices.

[0011] Furthermore, the switching valve A and regulating valve A, together with the switching valve B and level regulating valve B, form a parallel switchable dual-flow system. In the event of a fault, switching valve B and level regulating valve B are closed within 3 seconds, while switching valve A and regulating valve A are opened, achieving a seamless switchback to the original flow. Through this dual-flow design, when the carbon dioxide flash evaporation system experiences equipment failure or process fluctuations, the system can automatically switch back to the original direct flow in a very short time, with no flow interruption throughout, ensuring that the methanol circulation and purification regeneration of the main unit are unaffected.

[0012] The beneficial effects of this utility model are: (1) Increased production and increased efficiency: The second series can add 24,000 Nm³ of carbon dioxide feedstock gas. 3 / h, increasing the annual production of liquid carbon dioxide by approximately 240,000 tons, resulting in an annual economic benefit of approximately 48 million yuan; safe and stable: does not disturb the main unit, can be switched off from the system at any time, and can be put into operation at any time, with no freezing, no sulfur exceeding the standard, and no environmental risks; (2) Reliable switching: Dual-process design, fault switching time <3 seconds, no flow interruption, and no impact on methanol circulation; (3) High versatility: It is applicable to the retrofitting of various low-temperature methanol washing units, with low investment, short construction period and quick results; (4) Low carbon and environmental protection: reduce carbon dioxide emissions from exhaust gas and achieve efficient use of resources. Attached Figure Description

[0013] Figure 1 This is a process flow diagram of the present invention; In the diagram: 100, medium-pressure flash tank; 110, first outlet pipeline of medium-pressure liquid phase; 111, on / off valve A; 112, regulating valve A; 120, second outlet pipeline of medium-pressure liquid phase; 121, on / off valve B. 200. Carbon dioxide flash evaporator; 210. Carbon dioxide vapor phase outlet pipeline; 220. Carbon dioxide liquid phase outlet pipeline; 221. Variable frequency methanol-rich pump; 222. Liquid level regulating valve B. 300. Heat exchanger 400. Hydrogen sulfide concentration tower 500. Carbon-rich methanol pipeline. 600. Thermal shift gas pipeline; 610. Methanol spray pipeline. 700. Carbon dioxide feedstock pipeline. 800. Cold-state change gas pipeline. Detailed Implementation

[0014] To make the above-mentioned objects, features, and advantages of this utility model more apparent and understandable, the specific embodiments of this utility model will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a full understanding of this utility model. However, this utility model can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this utility model. Therefore, this utility model is not limited to the specific embodiments disclosed below.

[0015] like Figure 1 As shown in the figure, one embodiment of the present invention provides a low-temperature methanol washing carbon dioxide flash evaporation production system, including a medium-pressure flash tank 100, a carbon dioxide flash tank 200, a heat exchanger 300, a hydrogen sulfide concentration tower 400, and related pipelines and valves.

[0016] The feed inlet of the medium-pressure flash tank 100 is connected to the carbon-rich methanol pipeline 500. The liquid phase outlet at the bottom of the medium-pressure flash tank 100 is divided into a first medium-pressure liquid phase outlet pipeline 110 and a second medium-pressure liquid phase outlet pipeline 120. The first medium-pressure liquid phase outlet pipeline 110 is equipped with a switch valve A111 and a regulating valve A112, and its end is connected to the inlet of the hydrogen sulfide concentration tower 400. The second medium-pressure liquid phase outlet pipeline 120 is equipped with a switch valve B121, and its end is connected to the inlet of the carbon dioxide flash tank 200.

[0017] The carbon dioxide flash evaporator 200 has a gas phase outlet at the top, which is connected to the tube-side inlet of the heat exchanger 300 via a pipeline. The tube-side outlet of the heat exchanger 300 is connected to the carbon dioxide feed gas pipeline 700 for external delivery of the reheated carbon dioxide feed gas. The shell-side inlet of the heat exchanger 300 is connected to the hot-state shift gas pipeline 600, which is equipped with a methanol spray pipeline 610; the shell-side outlet of the heat exchanger 300 is connected to the cold-state shift gas pipeline 800 for delivery of the heat-exchanged cold-state shift gas out of the boundary area or back to the shift system.

[0018] The bottom of the carbon dioxide flash tank 200 is equipped with a liquid phase outlet. A variable frequency rich methanol pump 221 and a liquid level regulating valve B222 are installed in sequence on the outlet pipeline. The outlet of the liquid level regulating valve B222 is connected to the downstream of the regulating valve A112 on the first medium-pressure liquid phase outlet pipeline 110, so that the rich methanol after flashing flows into the main pipeline to the hydrogen sulfide concentration tower 400.

[0019] The hydrogen sulfide concentration tower 400 has a gas phase outlet at the top, which is connected to the tail gas pipeline for discharging tail gas; and a liquid phase outlet at the bottom, which is connected to the sulfur-rich methanol pipeline for discharging sulfur-rich methanol to the downstream regeneration system.

[0020] The switching valve B121 and the level regulating valve B222 form a level-flow cascade control loop, which is used to control the level of the carbon dioxide flash tank 200 and the flow rate of the rich methanol returning to the hydrogen sulfide concentration tower 400.

[0021] In this embodiment, the operating pressure of the carbon dioxide flash evaporator 200 is maintained at 0.31 MPa, the operating temperature at -50°C, and the methanol-rich processing capacity is 288 m³. 3 / h, with a maximum output of 24,000 Nm³. 3 The carbon dioxide feed gas has a purity of ≥98.65%, H2S ≤0.5ppm, and methanol ≤150ppm, meeting the feed requirements for food-grade carbon dioxide and new material equipment.

[0022] When carbon dioxide feedstock is not required, switch valve B121 and level regulating valve B222 are closed, carbon dioxide flash tank 200 and heat exchanger 300 are shut down, and no hot-state change gas or sprayed methanol is introduced; carbon-rich methanol is directly introduced from medium-pressure flash tank 100 into hydrogen sulfide concentration tower 400 through switch valve A111 and regulating valve A112 on medium-pressure liquid phase first outlet pipeline 110. Tail gas is discharged from the top of the tower, and sulfur-containing rich methanol is discharged from the bottom of the tower, maintaining the original process operation.

[0023] When carbon dioxide feedstock is needed, switch valve A111 and regulating valve A112 are closed, and switch valve B121 is opened. Carbon-rich methanol enters the carbon dioxide flash tank 200 for flash evaporation via the second outlet pipeline 120 of the medium-pressure liquid phase. The flashed carbon dioxide is reheated in the tube side of heat exchanger 300 and then sent out via the carbon dioxide feedstock pipeline 700. Hot shift gas is introduced into the shell side of heat exchanger 300 as a heat source, and simultaneously, spray methanol from the spray methanol pipeline 610 is activated according to the temperature to prevent freezing in the shell side of the heat exchanger. The cooled shift gas after heat exchange is sent out via the cooled shift gas pipeline 800. The flash-enriched methanol is pressurized by the variable frequency methanol pump 221 at the bottom of the carbon dioxide flash tank 200, and after the flow rate is regulated by the level regulating valve B222, it flows into the first outlet pipeline 110 of the medium-pressure liquid phase and finally enters the hydrogen sulfide concentration tower 400. The hydrogen sulfide concentration tower 400 normally discharges tail gas from the top gas phase outlet and normally discharges sulfur-rich methanol from the bottom liquid phase outlet, and the purification and regeneration of the main unit are completely unaffected.

[0024] When the carbon dioxide flash evaporation system malfunctions or experiences process fluctuations, the parallel switchable dual-flow system consisting of switch valve A111, regulating valve A112, switch valve B121, and level regulating valve B222 comes into play: the control system quickly and synchronously closes switch valve B121 and level regulating valve B222, and quickly opens switch valve A111 and regulating valve A112, with a switching response time of less than 3 seconds. Carbon-rich methanol resumes direct flow from the medium-pressure liquid phase first outlet pipeline 110 into the hydrogen sulfide concentration tower 400. The entire switching process is uninterrupted, and methanol circulation, tail gas, and sulfur-containing rich methanol discharge remain stable. The carbon dioxide flash evaporation system can be restarted after the anomaly is resolved.

[0025] Actual operation has verified that this parallel switchable system can enable the low-temperature methanol washing series, which originally did not produce carbon dioxide, to stably produce qualified carbon dioxide feed gas, increasing the annual production of liquid carbon dioxide by about 240,000 tons. At the same time, it realizes the recovery of the cooling capacity of the conversion gas, resulting in significant economic benefits. The entire transformation does not change the original tower structure, has no risk of freezing blockage or excessive sulfur, is safe and reliable, and has great promotional value.

[0026] This invention provides a low-temperature methanol washing carbon dioxide flash evaporation production system, solving the problems of insufficient carbon dioxide feed gas supply and low resource utilization in existing technologies. It adds an independent carbon dioxide flash evaporation system to the medium-pressure flash evaporation zone of existing low-temperature methanol washing units, forming a parallel, switchable dual-flow system without altering the original tower structure or disturbing the main unit's purification and regeneration processes. The system includes a medium-pressure flash tank, a carbon dioxide flash tank, a heat exchanger, a variable frequency methanol-rich pump, a hydrogen sulfide concentration tower, and switching valves. The liquid phase at the bottom of the medium-pressure flash tank is split into two paths: one path flows through the original process to the hydrogen sulfide concentration tower, and the other path flows into the newly added carbon dioxide flash tank. The carbon dioxide obtained from flash evaporation is reheated by the heat exchanger and then sent out. The methanol-rich system after flash evaporation returns to the hydrogen sulfide concentration tower. The heat exchanger uses hot-state change gas as a heat source and is equipped with methanol spray to prevent low-temperature freezing and blockage. The system employs cascade control of liquid level and flow rate, allowing seamless switching back to the original process within 3 seconds in case of failure.

[0027] Process parameters: CO2 flash tank operating pressure 0.31 MPa, operating temperature -50℃, methanol-rich flow rate 288 m³ / h 3 / h, maximum carbon dioxide feedstock production is 24,000 Nm³. 3 / h, carbon dioxide purity ≥98.65%.

[0028] Differences from existing technologies: The addition of an independent carbon dioxide flash evaporation system enables the second series, which originally did not produce carbon dioxide, to stably produce qualified carbon dioxide feed gas; the methanol-rich gas after flash evaporation is returned to the regeneration system without changing the original process or affecting the purification and regeneration effect; a spray methanol antifreeze structure is set up to solve the problem of freezing blockage in low-temperature heat exchange; the delivered carbon dioxide has high purity and extremely low sulfur content, which can simultaneously meet the requirements of food-grade CO2 and new material equipment.

[0029] In the description of this utility model, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this utility model and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model.

[0030] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this utility model, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0031] In this utility model, unless otherwise explicitly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0032] In this utility model, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0033] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

Claims

1. A low-temperature methanol washing carbon dioxide flash evaporation production system, characterized in that: include The hydrogen sulfide concentration tower (400) has a gas phase outlet at the top for discharging tail gas and a liquid phase outlet at the bottom for discharging sulfur-rich methanol. The medium-pressure flash tank (100) has a bottom liquid phase outlet divided into a medium-pressure liquid phase first outlet pipeline (110) and a medium-pressure liquid phase second outlet pipeline (120). The medium-pressure liquid phase first outlet pipeline (110) is connected to the inlet of the hydrogen sulfide concentration tower (400), and the medium-pressure liquid phase second outlet pipeline (120) is connected to the inlet of the carbon dioxide flash tank (200). The bottom liquid phase outlet of the carbon dioxide flash tank (200) is connected to the medium-pressure liquid phase first outlet pipeline (110). The heat exchanger (300) has its tube-side inlet connected to the gas phase outlet at the top of the carbon dioxide flash tank (200), and its tube-side outlet connected to the carbon dioxide feed gas pipeline (700); the shell-side inlet of the heat exchanger (300) is connected to the hot-state shift gas pipeline (600), and the shell-side outlet is connected to the cold-state shift gas pipeline (800).

2. The low-temperature methanol washing carbon dioxide flash evaporation production system according to claim 1, characterized in that: The medium-pressure liquid phase first outlet pipeline (110) is provided with a switch valve A (111) and a regulating valve A (112) in sequence; the medium-pressure liquid phase second outlet pipeline (120) is provided with a switch valve B (121).

3. The low-temperature methanol washing carbon dioxide flash evaporation production system according to claim 2, characterized in that: The bottom liquid phase outlet pipeline of the carbon dioxide flash tank (200) is equipped with a variable frequency rich methanol pump (221) and a liquid level regulating valve B (222). The outlet of the liquid level regulating valve B (222) is connected to the downstream of the regulating valve A (112) on the medium pressure liquid phase first outlet pipeline (110).

4. The low-temperature methanol washing carbon dioxide flash evaporation production system according to claim 3, characterized in that: The switching valve B (121) and the level regulating valve B (222) constitute a level-flow cascade control loop, which is used to control the level of the carbon dioxide flash tank (200) and the flow rate of the rich methanol returning to the hydrogen sulfide concentration tower (400).

5. The low-temperature methanol washing carbon dioxide flash evaporation production system according to claim 1, characterized in that: A methanol spraying pipeline (610) is installed on the thermal conversion gas pipeline (600).

6. The low-temperature methanol washing carbon dioxide flash evaporation production system according to claim 1, characterized in that: The operating pressure of the carbon dioxide flash evaporator (200) is controlled at 0.25~0.35MPa, and the operating temperature is controlled at -60~-40℃.

7. The low-temperature methanol washing carbon dioxide flash evaporation production system according to claim 6, characterized in that: The operating pressure of the carbon dioxide flash evaporator (200) is 0.31 MPa, and the operating temperature is -50℃.

8. The low-temperature methanol washing carbon dioxide flash evaporation production system according to claim 3, characterized in that: The switching valve A (111), regulating valve A (112), switching valve B (121), and level regulating valve B (222) form a parallel switchable dual-flow system. It is configured to close the switching valve B (121) and level regulating valve B (222) and open the switching valve A (111) and regulating valve A (112) within 3 seconds in case of a fault, so as to achieve seamless switching back to the original flow.

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