A methanol rectification heat coupling method and system using synthesis gas waste heat to directly gasify pre-column kettle liquid

Abstract

The application discloses a methanol rectification heat coupling method and system directly vaporizing pre-column kettle liquid by using synthesis gas waste heat, and belongs to the technical field of methanol rectification. The pre-column kettle liquid is taken as the only heat medium, the kettle liquid is led out, pressurized and then sent into a synthesis gas heat exchanger to directly exchange heat with synthesis gas from a methanol reactor; the kettle liquid after heat exchange is sent into a gas-liquid separation tank to be flash evaporated and separated, the gas phase obtained through separation is directly returned to a gas phase layer of the pre-column kettle as rectification rising steam, and the liquid phase obtained through separation is returned to a liquid phase area of the pre-column kettle to maintain the kettle liquid level; the kettle liquid forms a self-circulation heat supply loop between the synthesis gas heat exchanger and the pre-column. The application cancels an independent heat medium circulation system and a pre-column independent reboiler, realizes one-time heat exchange and direct utilization of synthesis gas waste heat, and has the advantages of low equipment investment, high heat efficiency, simple operation and remarkable energy-saving effect.

Description

Technical Field

[0001] This invention relates to the field of methanol distillation technology, specifically to a methanol distillation thermal coupling method and system that utilizes the waste heat of syngas to directly vaporize the pre-distillation bottom liquid. Background Technology

[0002] Methanol is an important basic chemical raw material and a clean energy carrier. The methanol production process typically includes two main stages: synthesis and distillation.

[0003] In the synthesis section, synthesis gas (mainly composed of CO, CO2, and H2) reacts with a copper-based catalyst at 200–300 °C and 5–10 MPaG to produce crude methanol. This reaction is strongly exothermic, with the outlet temperature of the reaction gas from the synthesis reactor reaching as high as 220–280 °C, containing a large amount of sensible heat. In traditional processes, this heat is removed after multiple stages of cooling, including a reaction gas preheater and a water cooler, resulting in significant energy waste.

[0004] In the distillation section, crude methanol is typically purified using distillation. The pre-distillation column (pre-column) is mainly used to remove light impurities such as dimethyl ether and methyl formate from crude methanol. The bottom operating temperature is typically 70–95 °C, requiring a continuous supply of heat. In traditional processes, the heat for the pre-column is provided by a separate reboiler, with the heat source generally being 0.3–0.6 MPaG steam or methanol vapor from the top of a coupled pressurized column.

[0005] This shows that in conventional methanol production plants, a large amount of high-temperature waste heat is wasted in the synthesis section, while the distillation section needs to consume external steam for heating, resulting in a serious energy imbalance.

[0006] To address the aforementioned energy imbalance problem, existing technologies have proposed solutions that utilize the waste heat of syngas to provide a heat source for distillation. For example, Chinese patent CN203007175U discloses a thermally integrated device for methanol synthesis and distillation. This device splits the syngas exiting the methanol synthesis tower into two streams: one stream exchanges heat with the incoming syngas, and the other exchanges heat with the pressurized tower bottom liquid heater. The two streams then merge and exchange heat with the reboiler of the methanol pre-distillation tower, providing heat to the reboiler. Finally, the reboiler is cooled by a water cooler. While this solution achieves some degree of syngas waste heat recovery, it still retains the pre-distillation tower reboiler, resulting in an indirect heat transfer link of "syngas → reboiler → tower bottom liquid." This leads to significant heat loss due to temperature differences, limited thermal efficiency, and high system complexity.

[0007] Furthermore, Chinese patent document CN121016230A discloses a methanol synthesis gas heat recovery and utilization system. This system uses an independent heat medium circulation system with saturated methanol or water as the intermediate heat medium. The heat from the synthesis gas is first transferred to the heat medium, and then from the heat medium to the pre-tower reboiler, thus transferring the waste heat from the synthesis gas to the pre-tower. However, this solution requires the addition of a separate heat medium tank, heat medium circulation pump, heat medium buffer tank, and replenishment equipment, resulting in high equipment investment, large footprint, significant secondary heat exchange losses, and complex operation.

[0008] Therefore, there is an urgent need to develop a method and system for thermally coupling the reaction heat of methanol synthesis with that of the distillation pre-tower, which is simpler in structure, more thermally efficient, and easier to operate, in order to solve the above-mentioned technical problems. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a methanol distillation thermal coupling method and system that utilizes the waste heat of syngas to directly vaporize the pre-distillate, thereby solving the technical problems of complex equipment, low thermal efficiency, and inconvenient operation in existing technologies.

[0010] The specific technical solution of this invention is as follows: In a first aspect, the present invention provides a methanol distillation thermal coupling method for directly vaporizing the pre-distillate liquid using syngas waste heat, comprising the following steps: S1. The bottom liquid of the pre-tower is drawn out as a heating medium, pressurized and sent to the syngas heat exchanger to exchange heat with the syngas generated by the methanol reactor. S2. The heat-exchanged bottom liquid is sent to a gas-liquid separator for flash separation. The separated gas phase is returned to the bottom gas phase layer of the pre-tower as rising steam for distillation. The separated liquid phase is returned to the bottom liquid phase zone of the pre-tower to maintain the bottom liquid level. The bottom liquid forms a self-circulating heat supply between the syngas heat exchanger and the pre-tower.

[0011] Furthermore, in step S1, the temperature of the liquid in the bottom of the column is 80~90 ℃ and the pressure after pressurization is 1.2~1.8 MPaG.

[0012] Furthermore, the temperature of the synthesis gas in step S1 is 110~130 ℃ and the pressure is 5~10 MPaG.

[0013] Furthermore, the vaporization rate of the bottom liquid in step S2 in the gas-liquid separator is 10%~30%.

[0014] Furthermore, all the heat in the pre-tower is provided by the syngas heat exchanger through the bottom liquid of the tower.

[0015] Secondly, the present invention provides a methanol distillation thermal coupling system that utilizes the waste heat of syngas to directly vaporize the pre-distillate, comprising: A methanol reactor is used to react reaction gases to produce crude methanol. The pre-column, whose inlet is connected to the liquid outlet of the methanol reactor, is used for distillation to remove light component impurities from the crude methanol; The pre-tower discharge pump has its inlet connected to the bottom liquid outlet of the pre-tower, and is used to pressurize and send out the bottom liquid; A syngas heat exchanger has its hot-side inlet connected to the syngas outlet of the methanol reactor, allowing syngas from the methanol reactor to pass through; its cold-side inlet is connected to the outlet of the pre-tower discharge pump, allowing the bottom liquid from the pre-tower to pass through; the syngas and the bottom liquid undergo direct heat exchange in the syngas heat exchanger. A gas-liquid separator, the inlet of which is connected to the cold side outlet of the syngas heat exchanger, is used to separate the heat-exchanged bottom liquid into a gas phase and a liquid phase; A gas phase return pipeline is connected at one end to the gas phase outlet of the gas-liquid separator and at the other end to the bottom gas phase layer of the pre-tower, for returning the gas phase as rising steam during distillation to the pre-tower to participate in distillation mass and heat transfer. A return pump, whose inlet is connected to the liquid phase outlet of the gas-liquid separator and whose outlet is connected to the bottom liquid phase zone of the pre-tower, is used to return the liquid phase to the pre-tower to maintain the bottom liquid level.

[0016] Furthermore, the methanol distillation thermal coupling system also includes a reaction gas preheater, the inlet of which is connected to the synthesis gas outlet of the methanol reactor, for preheating the reaction gas using the synthesis gas.

[0017] Furthermore, the methanol distillation thermal coupling system also includes a bypass pipeline and a control valve connected in parallel with the synthesis gas heat exchanger. The control valve controls the vaporization rate of the bottom liquid by adjusting the opening of the bypass pipeline.

[0018] Furthermore, the methanol distillation thermal coupling system also includes a syngas subsequent cooling system, which is connected to the hot side outlet of the syngas heat exchanger and is used to cool the syngas after heat exchange to the methanol separation temperature.

[0019] Furthermore, after the crude methanol enters the pre-column, it undergoes distillation under the action of the rising steam from the distillation process to separate and obtain the bottom liquid from which light components have been removed.

[0020] Beneficial effects This invention provides a thermally coupled method and system for methanol distillation that utilizes waste heat from syngas to directly vaporize the pre-distillate. Compared with existing technologies, it has the following significant advantages: (1) The equipment structure is greatly simplified, and the investment and maintenance costs are significantly reduced: This invention uses the pre-tower bottom liquid itself as the only heat medium, so that the bottom liquid forms a self-circulating heating loop between the synthesis gas heat exchanger and the pre-tower, completely eliminating the independent heat medium circulation system (including heat medium tank, heat medium circulation pump, heat medium buffer tank, liquid replenishment system, etc.) and the independent reboiler of the pre-tower that are required in the prior art. The number of equipment is reduced, the floor space is reduced, and the equipment investment and maintenance costs are significantly reduced.

[0021] (2) Significantly improved heat recovery efficiency: This invention utilizes the heat directly in a single heat exchange process from syngas to bottom liquid, eliminating the secondary heat exchange stage and the heat transfer temperature difference loss in each heat exchange as in the prior art. The gas phase generated after heat exchange is directly returned to the bottom gas phase layer of the pre-distillation column after flash separation, and directly participates in the mass and heat transfer of distillation in the column in the form of rising steam. The heat is effectively utilized in the form of latent heat, avoiding the heat loss of indirect heat transfer through the reboiler in the prior art, and the overall heat recovery efficiency is significantly improved.

[0022] (3) Simple operation and good operational stability: Since the heat medium is the liquid in the bottom of the pre-tower itself, its composition, temperature, and pressure are naturally consistent with the operating conditions of the pre-tower. There is no need to control the temperature, pressure, water quality, and liquid level of the independent heat medium loop. Operators only need to control the outlet pressure of the pre-tower discharge pump and the return flow of the return pump to maintain stable system operation. The operation is greatly simplified and the operational reliability is improved. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the methanol distillation thermal coupling system in Example 8, which utilizes the waste heat of syngas to directly vaporize the pre-tower bottom liquid.

[0024] Figure 2 This is a schematic diagram of the methanol distillation thermal coupling system in Example 9, which utilizes the waste heat of syngas to directly vaporize the pre-tower bottom liquid.

[0025] Figure label.

[0026] 1-Methanol reactor, 2-Reaction gas preheater, 3-Pre-tower discharge pump, 4-Synthesis gas heat exchanger, 5-Pre-tower, 6-Gas-liquid separator, 7-Gas phase return pipeline, 8-Return pump, 9-Synthesis gas subsequent cooling system, 10-Liquid phase return pipeline. Detailed Implementation

[0027] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter range described in the present invention. Reasonable variations derived therefrom are still within the protection scope of the present invention.

[0028] It should be noted that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0029] Unless otherwise defined, all terms, symbols, and other scientific terms used herein are intended to have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In some instances, terms having a conventional meaning are defined herein for clarification or ease of reference, and such definitions should not be construed as indicating a significant difference from conventional understanding in the art. The technical methods described or referenced herein are generally well understood by those skilled in the art and employed by conventional methods. Unless otherwise stated, the use of commercially available kits, reagents, and instruments shall be performed according to the manufacturer's instructions and parameters.

[0030] In a first aspect, the present invention provides a methanol distillation thermal coupling method for directly vaporizing the pre-distillate liquid using syngas waste heat, comprising the following steps: S1. The bottom liquid of the pre-tower is drawn out as a heating medium, pressurized and sent to the syngas heat exchanger to exchange heat with the syngas generated by the methanol reactor. S2. The heat-exchanged bottom liquid is sent to a gas-liquid separator for flash separation. The separated gas phase is returned to the bottom gas phase layer of the pre-tower as rising steam for distillation. The separated liquid phase is returned to the bottom liquid phase zone of the pre-tower to maintain the bottom liquid level. The bottom liquid forms a self-circulating heat supply between the syngas heat exchanger and the pre-tower.

[0031] The methanol distillation thermal coupling method provided by this invention, which utilizes the waste heat of syngas to directly vaporize the pre-distillation column bottom liquid, employs a core design of "using the pre-distillation column bottom liquid itself as the heat medium." This allows the bottom liquid to simultaneously serve as both a heat carrier and a distillation medium, thereby eliminating the need for an independent heat medium system and a separate reboiler for the pre-distillation column at the equipment level, thus simplifying the structure. Through the path design of "direct heat exchange" between the bottom liquid and syngas in the syngas heat exchanger, and the subsequent flash evaporation of the gas phase to "directly return to the pre-distillation column bottom gas phase layer," the secondary heat exchange of "syngas → heat medium → bottom liquid" in existing technologies is reduced to a single heat exchange of "syngas → bottom liquid." This eliminates heat transfer temperature difference losses in intermediate stages, and the rising steam directly participates in the distillation mass and heat transfer within the column, significantly improving heat utilization efficiency. Furthermore, since the heat medium is the bottom liquid itself, its composition, temperature, and pressure are naturally consistent with the pre-distillation operating conditions. Therefore, there is no need to additionally control the temperature, pressure, water quality, and liquid level of the heat medium; only the return flow rate of the bottom liquid needs to be controlled to maintain a stable liquid level, greatly simplifying the operation. The aforementioned technical features work together synergistically to achieve a simpler structure, higher thermal efficiency, and easier operation, demonstrating significant innovation.

[0032] Furthermore, in step S1, the temperature of the bottom liquid is 80~90 ℃, and the pressure after pressurization is 1.2~1.8 MPaG. The bottom liquid temperature of 80~90 ℃ matches the pre-column bottom operating temperature, ensuring that no additional heating or cooling is required when drawing out the bottom liquid; after pressurizing to 1.2~1.8 MPaG, the bubble point temperature of the bottom liquid increases, enabling it to form a reasonable heat transfer temperature difference of more than 10 ℃ with the syngas in the syngas heat exchanger, ensuring sufficient heat transfer driving force for the heat exchange process.

[0033] Furthermore, the temperature of the syngas in step S1 is 110~130 ℃, and the pressure is 5~10 MPaG. The syngas temperature of 110~130 ℃ and the bubble point temperature of the liquid in the bottom of the tower after pressurization form a reasonable heat transfer temperature difference, ensuring that the heat exchange process has sufficient heat transfer driving force; the syngas pressure of 5~10 MPaG is the typical operating pressure range of the methanol synthesis reactor. The syngas still maintains a relatively high pressure after the reaction gas preheater. This pressure is higher than the pressure on the liquid side of the tower bottom, which can ensure that a safe pressure difference is maintained between the tube side (high-pressure syngas side) and the shell side (low-pressure tower bottom liquid side) of the heat exchanger, ensuring the safe and reliable operation of the heat exchange process.

[0034] Furthermore, the vaporization rate of the bottom liquid in the gas-liquid separator in step S2 is 10% to 30%. Controlling the vaporization rate within the range of 10% to 30% ensures that the amount of gas phase returning to the bottom of the pre-tower is sufficient to provide the rising steam and heat required for distillation, and also ensures that there is still a sufficient flow of liquid phase at the bottom of the gas-liquid separator to return to the pre-tower to maintain the bottom liquid level, thus ensuring the stable operation of the pre-tower.

[0035] Furthermore, all the heat in the pre-tower is provided by the syngas heat exchanger through the bottom liquid. This design ensures that the pre-tower relies entirely on the waste heat of the syngas for heating under normal operating conditions, without consuming any external steam or other auxiliary heat sources. This maximizes the recovery and utilization of the sensible heat from the synthesis section, achieving deep thermal coupling between the synthesis and distillation sections.

[0036] Secondly, the present invention provides a methanol distillation thermal coupling system that utilizes the waste heat of syngas to directly vaporize the pre-distillate, comprising: Methanol reactor 1 is used to react the reaction gas to produce crude methanol; Pre-tower 5, whose inlet is connected to the liquid outlet of the methanol reactor 1, is used for distillation to remove light component impurities from the crude methanol; The pre-tower discharge pump 3 has its inlet connected to the bottom liquid outlet of the pre-tower 5, and is used to pressurize and send out the bottom liquid; Syngas heat exchanger 4 has its hot-side inlet connected to the syngas outlet of the methanol reactor 1, allowing syngas from the methanol reactor 1 to pass through; its cold-side inlet is connected to the outlet of the pre-tower discharge pump 3, allowing the bottom liquid from the pre-tower 5 to pass through; the syngas and the bottom liquid undergo direct heat exchange in the syngas heat exchanger 4. The gas-liquid separator 6 has its inlet connected to the cold side outlet of the syngas heat exchanger 4, and is used to separate the heat-exchanged bottom liquid into a gas phase and a liquid phase. The gas phase return pipeline 7 is connected at one end to the gas phase outlet of the gas-liquid separator and at the other end to the bottom gas phase layer of the pre-tower 5, for returning the gas phase as distillation rising vapor to the pre-tower 5 to participate in distillation mass and heat transfer. The return pump 8 has its inlet connected to the liquid phase outlet of the gas-liquid separator 6 and its outlet connected to the bottom liquid phase zone of the pre-tower 5, and is used to return the liquid phase to the pre-tower 5 to maintain the bottom liquid level.

[0037] The methanol distillation thermal coupling system provided by this invention utilizes the waste heat of syngas to directly vaporize the pre-distillation column bottom liquid. Through a syngas heat exchanger 4, the high-temperature syngas directly exchanges heat with the pre-distillation column bottom liquid. After heat exchange, the liquid undergoes flash evaporation in a gas-liquid separator. The gas phase returns directly to the pre-distillation column 5 as rising steam for distillation, while the liquid phase returns to the pre-distillation column 5 to maintain the liquid level. This forms a self-circulating heating loop with the column bottom liquid itself as the sole heat medium. This system eliminates the need for an independent heat medium system and a pre-distillation column reboiler, significantly simplifying the structure and reducing investment. It also eliminates secondary heat exchange losses, allowing the syngas waste heat to directly enter the pre-distillation column 5 for distillation through a single heat exchange, resulting in a significant improvement in thermal efficiency. Furthermore, since the heat medium is the column bottom liquid itself, there is no need for additional control of its temperature, pressure, and water quality, greatly simplifying the operation.

[0038] Furthermore, the methanol distillation thermal coupling system also includes a reaction gas preheater 2, whose inlet is connected to the syngas outlet of the methanol reactor 1, for preheating the reaction gas using the syngas. By adding a reaction gas preheater 1 upstream of the syngas heat exchanger 4, the high-temperature syngas from the methanol reactor 1 outlet is used to preheat the incoming reaction gas before entering the syngas heat exchanger 4, fully recovering the sensible heat of the high-temperature section of the syngas and further improving the energy utilization efficiency of the entire system.

[0039] Furthermore, the methanol distillation thermal coupling system also includes a bypass pipeline and control valve connected in parallel with the syngas heat exchanger 4. The control valve controls the vaporization rate of the bottom liquid by adjusting the opening of the bypass pipeline. By setting a bypass pipeline and control valve in parallel with the syngas heat exchanger 4, and adjusting the bypass opening using the control valve, the ratio of the bottom liquid flow rate entering the cold side of the syngas heat exchanger 4 to the direct bypass bottom liquid flow rate can be flexibly controlled, thereby adjusting the vaporization rate of the bottom liquid in the gas-liquid separator online.

[0040] Furthermore, the methanol distillation thermal coupling system also includes a syngas downstream cooling system 9, which is connected to the hot-side outlet of the syngas heat exchanger 4 and is used to cool the syngas after heat exchange to the methanol separation temperature. By setting the syngas downstream of the hot-side outlet of the syngas heat exchanger 4, the exothermic syngas is further cooled to the temperature required for methanol separation, ensuring that methanol in the syngas can be fully condensed, separated, and recovered, thereby improving the methanol product yield.

[0041] Furthermore, after the crude methanol enters the pre-tower 5, it undergoes distillation under the action of the rising steam from the distillation process, resulting in a bottom liquid with light components removed. The crude methanol completes distillation separation under the direct action of rising steam from the vapor return line 7. The rising steam passes upwards from the bottom of the tower through the trays or packing layer, engaging in gas-liquid contact and mass and heat transfer with the downward-flowing crude methanol liquid. While providing the heat required for distillation, it also promotes the transfer of light component impurities such as dimethyl ether and methyl formate from the liquid phase to the gas phase and their removal from the top of the tower by reducing the partial pressure of light components in the gas phase. The bottom of the tower yields crude methanol with light components removed. The gas phase returned by the vapor return line 7 can directly and effectively participate in the distillation process of the pre-tower 5, achieving integrated heating and distillation.

[0042] The technical solution of the present invention will be further described below with reference to specific embodiments and comparative examples. All reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing. The instruments used in the embodiments are also commercially available.

[0043] Example 1 This embodiment provides a methanol distillation thermal coupling method for directly vaporizing the pre-distillate liquid using syngas waste heat, including the following steps: S1. The bottom liquid of the pre-concentration tower is drawn from the liquid phase zone at a temperature of 83 °C and a pressure of 0.08 MPaG. After being pressurized to 1.2 MPaG, the bottom liquid is piped to the cold side of the syngas heat exchanger. Simultaneously, syngas from the methanol reactor outlet at a temperature of 230-240 °C and a pressure of 8.0 MPaG is preheated in the reaction gas preheater and then fed to the hot side of the syngas heat exchanger at a temperature of approximately 121 °C. The bottom liquid and syngas undergo countercurrent direct current heat exchange in the syngas heat exchanger. The bottom liquid absorbs the sensible heat of the syngas and is heated to above 85 °C, reaching above its bubble point at the operating pressure of the gas-liquid separator.

[0044] S2. The heat-exchanged bottom liquid is piped into a gas-liquid separator. Because the operating pressure in the separator is lower than the saturation pressure corresponding to the current temperature of the bottom liquid, flash vaporization occurs within the separator, with a vaporization rate of 20%, forming a gas-liquid two-phase mixture. The gas phase mainly consists of vaporized methanol, water, and light impurities. After the demister at the top of the separator removes entrained droplets, it returns to the bottom gas layer of the pre-separation column as rising vapor for distillation, passing upwards through the trays or packing to provide the necessary heat and rising gas velocity for the pre-separation distillation. The liquid phase at the bottom of the separator is the unvaporized bottom liquid. After pressurization, it returns to the bottom liquid zone of the pre-separation column to maintain a stable bottom liquid level. The syngas, after releasing heat in the syngas heat exchanger, cools to approximately 97°C and is further cooled to the temperature required for methanol separation, ready for use in subsequent methanol separation processes.

[0045] In this embodiment, the pre-tower does not require external steam consumption under normal operating conditions. Calculations show that, for a methanol plant with an annual production capacity of 700,000 tons, this process saves approximately 270,000 tons of steam annually compared to the traditional three-tower, two-effect distillation process, equivalent to approximately 30,000 tons of standard coal; and approximately 160,000 tons of steam annually compared to the multi-efficiency distillation four-tower, three-effect process, equivalent to approximately 20,000 tons of standard coal. Simultaneously, equipment investment is significantly reduced, operational procedures are greatly simplified, and the system operates stably and reliably.

[0046] Example 2 This embodiment provides a methanol distillation thermal coupling method that utilizes the waste heat of syngas to directly vaporize the pre-distillate, which differs from Embodiment 1 in that: In step S1, the temperature of the liquid in the bottom of the column is 80 ℃, and the pressure after pressurization is 1.8 MPag.

[0047] Except for the parameters mentioned above, the operation method of this embodiment is the same as that of Embodiment 1.

[0048] Example 3 This embodiment provides a methanol distillation thermal coupling method that utilizes the waste heat of syngas to directly vaporize the pre-distillate, which differs from Embodiment 1 in that: In step S1, the temperature of the liquid in the bottom of the column is 90 ℃, and the pressure after pressurization is 1.5 MPag; In step S2, the vaporization rate of the liquid in the bottom of the tower in the gas-liquid separator is approximately 25%.

[0049] Except for the parameters mentioned above, the operation method of this embodiment is the same as that of Embodiment 1.

[0050] Example 4 This embodiment provides a methanol distillation thermal coupling method that utilizes the waste heat of syngas to directly vaporize the pre-distillate, which differs from Embodiment 1 in that: In step S1, the synthesis gas from the methanol reactor outlet is sent to the hot side of the synthesis gas heat exchanger at a temperature of 110 °C after heat exchange in the reaction gas preheater. In step S2, the vaporization rate of the liquid in the bottom of the tower in the gas-liquid separator is 10-15%.

[0051] Except for the parameters mentioned above, the operation method of this embodiment is the same as that of Embodiment 1.

[0052] Example 5 This embodiment provides a methanol distillation thermal coupling method that utilizes the waste heat of syngas to directly vaporize the pre-distillate, which differs from Embodiment 1 in that: In step S1, the synthesis gas from the methanol reactor outlet is sent to the hot side of the synthesis gas heat exchanger at a temperature of 130 °C after heat exchange in the reaction gas preheater. In step S2, the vaporization rate of the liquid in the bottom of the tower in the gas-liquid separator is 30%.

[0053] Except for the parameters mentioned above, the operation method of this embodiment is the same as that of Embodiment 1.

[0054] Example 6 This embodiment provides a methanol distillation thermal coupling method that utilizes the waste heat of syngas to directly vaporize the pre-distillate, which differs from Embodiment 1 in that: In step S1, the syngas pressure at the methanol reactor outlet is 5 MPag, and after heat exchange in the reaction gas preheater, it is sent to the hot side of the syngas heat exchanger at about 120 °C. Except for the parameters mentioned above, the operation method of this embodiment is the same as that of Embodiment 1.

[0055] Example 7 This embodiment provides a methanol distillation thermal coupling method that utilizes the waste heat of syngas to directly vaporize the pre-distillate, which differs from Embodiment 1 in that: In step S1, the syngas pressure at the outlet of the methanol reactor is 10 MPag, and after heat exchange in the reaction gas preheater, it is sent into the syngas heat exchanger at about 120 °C. In step S2, the vaporization rate of the liquid in the bottom of the tower in the gas-liquid separator is 20%~30%.

[0056] Except for the parameters mentioned above, the operation method of this embodiment is the same as that of Embodiment 1.

[0057] Example 8 This embodiment provides a methanol distillation thermal coupling system that utilizes the waste heat of syngas to directly vaporize the pre-distillate, such as... Figure 1 As shown, it includes: Methanol reactor 1 is a fixed-bed shell-and-tube reactor with an operating temperature of 200-300 °C and an operating pressure of 8.0 MPa. It is used to react reactant gases with a copper-based catalyst to produce crude methanol. Methanol reactor 1 has a reactant gas inlet at the top, a crude methanol liquid outlet at the bottom, and a synthesis gas outlet at the top or side. The synthesis gas outlet of methanol reactor 1 is connected to the hot-side inlet of synthesis gas heat exchanger 4 via a pipeline.

[0058] Pre-tower 5, a plate or packed tower, operates at a temperature of 80-85 °C and a pressure of 0.08 MPa. It is used to remove dimethyl ether and methyl formate, light component impurities, from crude methanol. A crude methanol inlet is located in the upper middle part of pre-tower 5, which is connected to the crude methanol liquid outlet of methanol reactor 1 via a pipeline. The bottom of pre-tower 5 has a bottom liquid outlet and a bottom liquid phase zone; the space above the bottom liquid surface constitutes the bottom gas phase layer. A light component outlet is located at the top of pre-tower 5, and a crude methanol outlet (after light component removal) is located at the bottom.

[0059] Pre-tower discharge pump 3, with a flow rate of 400 m³ / s. 3 The pump has a flow rate of 1.2 MPa / h, a head of 50 m, and an outlet pressure of 1.2 MPa. Its inlet is connected to the bottom liquid outlet of the pre-tower 5 via a pipeline, and its outlet is connected to the cold side inlet of the synthesis gas heat exchanger 4 via a pipeline, which is used to pressurize the bottom liquid and send it out.

[0060] Syngas heat exchanger 4 is a shell-and-tube heat exchanger with a heat exchange area of ​​1000~1500 m². 2 The hot-side design pressure is 12 MPa, and the cold-side design pressure is 1.0 MPa. Its hot-side inlet is connected to the syngas outlet of methanol reactor 1 via a pipeline, allowing the high-temperature syngas from methanol reactor 1 to pass through. Its cold-side inlet is connected to the outlet of pre-tower discharge pump 3 via a pipeline, allowing the bottom liquid from pre-tower 5 to pass through. The syngas and bottom liquid undergo countercurrent direct heat exchange in syngas heat exchanger 4. The hot-side outlet of syngas heat exchanger 4 is connected to downstream equipment via a pipeline, and the cold-side outlet is connected to the inlet of gas-liquid separator 6 via a pipeline.

[0061] Gas-liquid separator 6, volume 80 m³ 3The design pressure is 1.0 MPag; its inlet is connected to the cold side outlet of the synthesis gas heat exchanger 4 via a pipeline, which is used to separate the heat-exchanged bottom liquid into gas and liquid phases. The gas-liquid separator 6 has a gas phase outlet at the top and a liquid phase outlet at the bottom, and a demister at the top to remove liquid droplets entrained in the gas phase.

[0062] The gas phase return line 7 is a temperature and pressure resistant line with a design temperature ≥150 ℃ and a design pressure ≥1.0 MPag. One end of it is connected to the gas phase outlet of the gas-liquid separator 6, and the other end is connected to the gas phase layer at the bottom of the pre-tower 5. It is used to return the gas phase as rising vapor in the distillation process to the pre-tower 5, and pass through the tray or packing layer from the bottom of the tower to participate in the distillation mass and heat transfer.

[0063] Return pump 8, flow rate 340 m³ / h 3 / h, head 50 m; its inlet is connected to the liquid phase outlet of the gas-liquid separator 6 through a pipeline, and its outlet is connected to the bottom liquid phase zone of the pre-tower 5 through the liquid phase return pipeline 10, which is used to return the liquid phase to the pre-tower 5 to maintain the bottom liquid level.

[0064] In this embodiment, during system operation, the crude methanol liquid produced by methanol reactor 1 is piped into pre-distillation column 5 for rectification. The pre-distillation column bottom liquid is pressurized by pre-distillation column discharge pump 3 and sent to the cold side of syngas heat exchanger 4, where it directly exchanges heat counter-currently with the high-temperature syngas from the outlet of methanol reactor 1. The bottom liquid absorbs the sensible heat of the syngas and is heated to above 85 °C, reaching above its bubble point at the operating pressure of gas-liquid separator 6.

[0065] After heat exchange, the bottom liquid enters the gas-liquid separator 6 for flash evaporation separation. Part of the bottom liquid vaporizes, forming a gas-liquid two-phase mixture. The gas phase mainly consists of vaporized methanol, water, and light component impurities. After the demister at the top of the gas-liquid separator 6 removes entrained droplets, it returns to the bottom gas layer of the pre-tower 5 through the gas phase return line 7, serving as rising vapor for distillation and providing the necessary heat and rising gas velocity for the distillation separation in the pre-tower 5. The liquid phase consists of the unvaporized bottom liquid, which is returned to the bottom liquid zone of the pre-tower 5 via the return pump 8 and the liquid phase return line 10 to maintain a stable bottom liquid level in the pre-tower.

[0066] In this embodiment, the system uses the pre-tower bottom liquid itself as the sole heat transfer medium. It does not include a separate heat transfer medium tank, heat transfer medium circulation pump, heat transfer medium buffer tank, or heat transfer medium replenishment system, nor does it include a separately installed pre-tower reboiler. All the heat of the pre-tower 5 is directly supplied by the syngas heat exchanger 4 through the bottom liquid, and the bottom liquid forms a self-circulating heating system between the syngas heat exchanger 4 and the pre-tower 5.

[0067] Example 9 This embodiment provides a methanol distillation thermal coupling system that utilizes the waste heat of syngas to directly vaporize the pre-distillate, such as... Figure 2As shown, the difference between this embodiment and Example 8 is that this embodiment also includes a syngas subsequent cooling system 9 and a reaction gas preheater 2.

[0068] The syngas post-cooling system 9, whose inlet is connected to the hot-side outlet of the syngas heat exchanger 4 via a pipeline, is used to further cool the syngas after heat exchange to the temperature required for methanol separation (typically around 40 °C). The syngas post-cooling system 9 can be a water cooler, an air cooler, or a combination of both. The syngas cooled by the syngas post-cooling system 9 is sent to the methanol separator for gas-liquid separation. The separated crude methanol is sent to the pre-distillation column 5 for rectification, and the gas is sent to the fuel gas system or for further processing.

[0069] The inlet (hot-side inlet) of the reaction gas preheater 2 is connected to the syngas outlet of the methanol reactor 1 via a pipeline, and its outlet (hot-side outlet) is connected to the hot-side inlet of the syngas heat exchanger 4 via a pipeline. The cold side of the reaction gas preheater 2 is supplied with reaction gas (cold reaction gas), which uses the sensible heat of the high-temperature syngas at the outlet of the methanol reactor 1 to preheat the reaction gas, thereby improving energy utilization efficiency.

[0070] In this embodiment, the high-temperature synthesis gas from the outlet of methanol reactor 1, with a temperature of 230~240 ℃, first enters the reaction gas preheater 2. After exchanging heat with the reaction gas, its temperature drops to about 121 ℃, and then it enters the hot side of the synthesis gas heat exchanger 4 to continue exchanging heat with the bottom liquid of the tower. The composition, connection relationship and operating principle of the remaining equipment are the same as in embodiment 8.

[0071] By adding a reaction gas preheater 2, the high-temperature sensible heat of the syngas was further recovered, improving the energy utilization efficiency of the entire system.

[0072] Example 10 This embodiment provides a methanol distillation thermal coupling system that utilizes the waste heat of syngas to directly vaporize the pre-distillate. The difference between this embodiment and Embodiment 8 is that this embodiment also includes a bypass pipeline and control valve connected in parallel with the syngas heat exchanger 4.

[0073] The bypass pipeline connects at both ends to the pipelines before the cold-side inlet and after the cold-side outlet of the syngas heat exchanger 4, forming a parallel connection with the cold side of the syngas heat exchanger 4. A control valve is installed on the bypass pipeline. By adjusting the opening of the control valve, the ratio of the flow rate of the bottom liquid entering the cold side of the syngas heat exchanger 4 to the flow rate of the bottom liquid directly bypassed through the bypass pipeline can be adjusted, thereby controlling the heating degree of the bottom liquid in the syngas heat exchanger 4, ultimately controlling the vaporization rate of the bottom liquid in the gas-liquid separator 6 within the range of 10% to 30%.

[0074] In this embodiment, when it is necessary to increase the gasification rate, the bypass control valve is closed to allow more bottom liquid to enter the synthesis gas heat exchanger 4 for sufficient heat exchange; when it is necessary to reduce the gasification rate, the bypass control valve is opened to allow some bottom liquid to bypass directly to the inlet of the gas-liquid separator 6 without heat exchange, mix with the high-temperature bottom liquid after heat exchange, and then enter the gas-liquid separator 6, thereby reducing the overall gasification rate.

[0075] Apart from the differences mentioned above, the remaining equipment composition, connection relationships, and operating principles are the same as in Example 8. This example, by setting up bypass pipelines and control valves, achieves flexible control of the gasification rate, enhancing the system's operational flexibility.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A methanol distillation thermal coupling method utilizing syngas waste heat to directly vaporize the pre-distillate, characterized in that, Includes the following steps: S1. The bottom liquid of the pre-tower is drawn out as a heating medium, pressurized and sent to the syngas heat exchanger to exchange heat with the syngas generated by the methanol reactor. S2. The heat-exchanged bottom liquid is sent to a gas-liquid separator for flash separation. The separated gas phase is returned to the bottom gas phase layer of the pre-tower as rising steam for distillation. The separated liquid phase is returned to the bottom liquid phase zone of the pre-tower to maintain the bottom liquid level. The bottom liquid of the tower forms a self-circulating heat supply between the syngas heat exchanger and the pre-tower.

2. The methanol distillation thermal coupling method for directly vaporizing the pre-distillate using syngas waste heat according to claim 1, characterized in that, The temperature of the liquid in the bottom of the column in step S1 is 80~90 ℃ and the pressure after pressurization is 1.2~1.8 MPaG.

3. The methanol distillation thermal coupling method for directly vaporizing the pre-distillate using syngas waste heat according to claim 1, characterized in that, The temperature of the synthesis gas in step S1 is 110~130 ℃ and the pressure is 5~10 MPaG.

4. The methanol distillation thermal coupling method for directly vaporizing the pre-distillate using syngas waste heat according to claim 1, characterized in that, The vaporization rate of the bottom liquid in step S2 in the gas-liquid separator is 10%~30%.

5. The methanol distillation thermal coupling method for directly vaporizing the pre-distillate using syngas waste heat according to claim 1, characterized in that, All the heat in the pre-tower is supplied by the syngas heat exchanger through the bottom liquid of the tower.

6. A methanol distillation thermal coupling system that utilizes waste heat from syngas to directly vaporize the pre-distillate, characterized in that, include: A methanol reactor (1) is used to react the reaction gas to produce crude methanol; The pre-tower (5) is connected to the liquid outlet of the methanol reactor (1) for distillation to remove light component impurities from the crude methanol. The pre-tower discharge pump (3) is connected to the bottom liquid outlet of the pre-tower (5) and is used to pressurize the bottom liquid and send it out. The syngas heat exchanger (4) has its hot side inlet connected to the syngas outlet of the methanol reactor (1) for the syngas from the methanol reactor (1) to pass through; its cold side inlet is connected to the outlet of the pre-tower discharge pump (3) for the bottom liquid from the pre-tower (5) to pass through; the syngas and the bottom liquid exchange heat directly in the syngas heat exchanger (4); A gas-liquid separator (6) has its inlet connected to the cold side outlet of the syngas heat exchanger (4) and is used to separate the heat-exchanged bottom liquid into a gas phase and a liquid phase. A gas phase return pipeline (7) is connected at one end to the gas phase outlet of the gas-liquid separator (6) and at the other end to the bottom gas phase layer of the pre-tower (5), for returning the gas phase as distillation rising vapor to the pre-tower (5) to participate in distillation mass and heat transfer. A return pump (8) has its inlet connected to the liquid phase outlet of the gas-liquid separator (6) and its outlet connected to the bottom liquid phase zone of the pre-tower (5) for returning the liquid phase to the pre-tower (5) to maintain the bottom liquid level.

7. The methanol distillation thermal coupling system for directly vaporizing the pre-distillation bottom liquid using syngas waste heat according to claim 6, characterized in that, The methanol distillation thermal coupling system also includes a reaction gas preheater (2), whose inlet is connected to the synthesis gas outlet of the methanol reactor (1) for preheating the reaction gas using the synthesis gas.

8. The methanol distillation thermal coupling system for directly vaporizing the pre-distillation bottom liquid using syngas waste heat according to claim 6, characterized in that, The methanol distillation thermal coupling system also includes a bypass pipeline and a control valve connected in parallel with the synthesis gas heat exchanger (4). The control valve controls the vaporization rate of the bottom liquid by adjusting the opening of the bypass pipeline.

9. The methanol distillation thermal coupling system for directly vaporizing the pre-distillation bottom liquid using syngas waste heat according to claim 6, characterized in that, The methanol distillation thermal coupling system also includes a syngas post-cooling system (9), which is connected to the hot side outlet of the syngas heat exchanger (4) and is used to cool the syngas after heat exchange to the methanol separation temperature.

10. The methanol distillation thermal coupling system for directly vaporizing the pre-distillate using syngas waste heat according to claim 6, characterized in that, After the crude methanol enters the pre-column (5), it is distilled under the action of the rising steam of the distillation to separate and obtain the bottom liquid of the column after removing light components.

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