Multi-utilization method of low-grade steam in rectification system

Abstract

The invention provides a multi-utilization method of low-grade steam in a rectification system. The method comprises the following steps: introducing high-temperature and high-pressure condensate water generated by a reboiler at the bottom of a rectifying tower into a flash tank, evaporating the condensate water through pressure reduction to generate low-grade steam, and applying the low-grade steam to low-pressure steam demand equipment in a rectifying system, such as rectifying tower feed preheating and tower top gas-phase material recycling equipment. Flash evaporation condensate is subjected to rectification tower feeding hot water preheating and alkali evaporation feeding preheating through a heat exchanger, then the condensate enters a cooling tower, and part of the condensate is fed into a waste heat boiler to generate regenerated steam. And the regenerated steam is used as supplementary steam of the system, so that the consumption of fresh steam is reduced. The steam utilization efficiency is effectively improved, energy is saved, and the production cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, and in particular to a method for multiple utilization of low-grade steam in a distillation system. Background Technology

[0002] In the production of unsymmetrical dimethylhydrazine (UDMH), the reboiler at the bottom of the distillation column uses high-pressure steam to heat the material, generating a large amount of condensate. This condensate still contains high temperatures and thermal energy, but it is usually not fully utilized, and direct discharge would result in energy waste. Furthermore, the recovery and reuse of low-grade steam is rarely addressed in traditional systems; therefore, how to efficiently utilize low-grade steam in distillation systems is a problem that urgently needs to be solved. Summary of the Invention

[0003] To overcome the above problems, this invention provides a method and system for the multi-stage utilization of low-grade steam in a distillation system. By introducing technologies such as flash evaporation, steam distribution, condensate recovery, and steam regeneration, it aims to achieve multi-stage utilization of low-grade steam, reduce the consumption of fresh steam, and optimize the energy efficiency of the distillation system. The technical solution adopted is as follows:

[0004] A method for multiple utilization of low-grade steam in a distillation system, comprising the following steps:

[0005] S1 introduces the high-temperature, high-pressure condensate generated by the reboiler at the bottom of the distillation column into the flash tank. The condensate is evaporated by depressurization, producing low-grade steam and flash condensate.

[0006] This low-pressure, low-grade steam can be used in low-pressure steam systems within distillation systems, such as for preheating feed to distillation columns.

[0007] S2, the low-grade steam is regulated and distributed to supply the low-pressure steam demand system in the distillation system after the low-grade steam distribution steam pressure is adjusted, and condensate is obtained. The low-pressure steam demand system includes a distillation column feed preheating heat exchanger and a distillation column top vapor phase material recovery device.

[0008] S3, the flash condensate is used for heat exchange and yields condensate.

[0009] S4 collects the condensate obtained from S2 and S3, sends it to the cooling tower, and after cooling, it is recycled back to the circulating water system to realize the recycling of water resources.

[0010] Furthermore, the temperature of the high-temperature and high-pressure condensate is 130°C, and the gauge pressure is 0.3 MPa.

[0011] Furthermore, the low-grade steam has a temperature of 128°C and a gauge pressure of 0.16 MPa.

[0012] Furthermore, in step S2, a steam distribution cylinder is used to regulate and distribute the steam pressure.

[0013] Furthermore, the temperature of both the flash condensate and the condensate is 90°C.

[0014] Furthermore, the above method also includes the following steps:

[0015] S5, the condensate from step S4 above is added to the waste heat boiler to regenerate steam. The regenerated steam can be used as supplementary steam for the system and directly enters the steam distribution cylinder to further supplement the system's steam demand and reduce the consumption of fresh steam.

[0016] On the other hand, the present invention provides a distillation system that employs the aforementioned method for multiple utilization of low-grade steam. The system includes a distillation column, a reboiler located at the bottom of the column for heating the bottom liquid to form a gaseous material, the reboiler connected via a pipe to a flash tank, the flash tank connected via a pipe to a gas distribution cylinder, and the steam outlet of the gas distribution cylinder connected to a distillation column feed preheater and a column top gaseous material recovery device, respectively. The flash condensate outlet of the flash tank is connected to a heat exchanger, which is also connected to the column top gaseous material recovery device.

[0017] The system also includes a cooling tower for collecting condensate from the distillation column feed preheater, the column top vapor recovery equipment, and the heat exchanger;

[0018] The system also includes a waste heat boiler for regenerating steam using a portion of the condensate, with the steam outlet of the waste heat boiler connected to a steam distribution cylinder.

[0019] Furthermore, the gaseous material recovery equipment at the top of the tower is an alkali-heated reaction vessel.

[0020] Furthermore, the heat exchanger is an alkali evaporation feed preheating heat exchanger.

[0021] The beneficial effects of the present invention include at least one of the following:

[0022] Beneficial effects

[0023] This invention generates low-grade steam by flash evaporation of high-temperature and high-pressure condensate, and then uses it in low-pressure steam demand systems, such as feed preheating of distillation columns and recovery of gaseous materials at the top of the column. This fully utilizes the low-grade steam in the system, reduces the consumption of fresh steam, and significantly improves energy efficiency.

[0024] This invention reduces the system's demand for external fresh steam by recovering flash condensate and using a low-pressure steam distribution system. The regenerated steam is used to supplement the system's steam demand, further reducing external steam consumption and lowering energy costs.

[0025] This invention achieves efficient recycling of water resources and reduces system water consumption by recycling the condensate after it passes through a cooling tower, with a portion of the condensate being used to replenish the waste heat boiler for regenerated steam. Attached Figure Description

[0026] Figure 1 The method steps provided by this invention are illustrated.

[0027] Figure 2 This is a process flow diagram in an embodiment of the present invention.

[0028] In the diagram: 1. First distillation column; 2. Second distillation column; 3. Third distillation column; 4. Reboiler; 5. Flash tank; 6. Distillation column feed preheating heat exchanger; 7. Alkali evaporation heating reactor; 8. Gas distribution cylinder; 9. Alkali evaporation feed preheating heat exchanger; 10. Cooling tower; 11. Waste heat boiler. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Reference Figure 1 This invention provides a method for the multiple utilization of low-grade steam in a distillation system, comprising the following steps:

[0031] S1 introduces the high-temperature, high-pressure condensate generated by the reboiler at the bottom of the distillation column into the flash tank. The condensate is evaporated by depressurization, producing low-grade steam and flash condensate.

[0032] This low-pressure, low-grade steam can be used in low-pressure steam demand systems in distillation systems, such as for preheating feed to distillation columns.

[0033] S2, the low-grade steam is regulated and distributed to supply the low-pressure steam demand system in the distillation system after the low-grade steam distribution steam pressure is adjusted, and condensate is obtained. The low-pressure steam demand system includes a distillation column feed preheating heat exchanger and a distillation column top vapor phase material recovery device.

[0034] S3, the flash condensate is used for heat exchange and yields condensate.

[0035] S4 collects the condensate obtained from S2 and S3, sends the condensate to the cooling tower, and after cooling, it is recycled back to the circulating water system to realize the recycling of water resources.

[0036] Specifically, the temperature of the high-temperature and high-pressure condensate is 130°C, and the gauge pressure is 0.3 MPa.

[0037] Specifically, the low-grade steam has a temperature of 128°C and a gauge pressure of 0.16 MPa.

[0038] Specifically, in step S2, a steam distribution cylinder is used to regulate and distribute the steam pressure.

[0039] Specifically, the temperature of the flash condensate is 90°C.

[0040] Specifically, the temperature of the condensate is 60°C.

[0041] Specifically, the above method also includes the following steps:

[0042] S5, the condensate from step S4 above is added to the waste heat boiler to regenerate steam. The regenerated steam can be used as supplementary steam for the system and directly enters the steam distribution cylinder to further supplement the system's steam demand and reduce the consumption of fresh steam.

[0043] Example 1:

[0044] Reference Figure 2 This embodiment describes a distillation system using the low-grade steam multiple utilization method of the present invention in a plant producing unsymmetrical dimethylhydrazine, to improve the energy efficiency and resource utilization of the distillation system. The distillation system includes a first distillation column 1, a second distillation column 2, and a third distillation column 3. The feedstock enters the column from the middle, and a reboiler 4 is located at the bottom. High-temperature, high-pressure steam is used for heating, evaporating the bottom liquid and forming a vapor phase that enters the column, promoting the separation process. The condensate produced by the reboiler 4 is connected to a flash tank via a pipeline.

[0045] The gaseous material at the top of the distillation column is condensed in a condenser, and the product enters the alkaline evaporation and heating reactor 7 for further processing to evaporate moisture. The non-volatile components at the bottom of the column exit in liquid form. The first and second distillation columns are heated by high-temperature and high-pressure steam to produce high-temperature and high-pressure condensate at a temperature of 130°C and a gauge pressure of 0.3 MPa.

[0046] Flash tank 5 generates low-grade steam and flash condensate by reducing pressure. Flash tank 5 is connected to a gas distribution cylinder through a pipeline. The steam outlet of the gas distribution cylinder is connected to the distillation column feed preheating heat exchanger 6 and the alkali evaporation heating reactor 7, respectively. Low-grade steam is distributed from the gas distribution cylinder 8 to the distillation column feed preheating heat exchanger 6 and the alkali evaporation heating reactor 7, and then forms secondary condensate. Flash tank 5 is connected to the alkali evaporation feed preheating heat exchanger 9 through a pipeline. The flash condensate enters the alkali evaporation feed preheating heat exchanger 9 and exchanges heat with the alkali evaporation feed, and then forms secondary condensate.

[0047] The system also includes a cooling tower 10. The condensate and secondary condensate are combined and enter the cooling tower for cooling. The cooled water enters the circulating water system, and a portion of the condensate enters the waste heat boiler 11.

[0048] The system also includes a waste heat boiler 11, which receives part of the condensate and generates supplementary steam through waste heat. The regenerated steam enters the gas distribution cylinder 8 through a pipeline as supplementary steam for the system, continuing to supply low-grade steam.

[0049] The method for multiple utilization of low-grade steam in this embodiment includes the following steps:

[0050] S1. Flash evaporation of high-temperature and high-pressure condensate

[0051] The high-temperature and high-pressure condensate from the first distillation column 1 and the second distillation column 2 is discharged from the reboiler 4 and enters the flash tank 5. Low-grade steam and flash condensate are generated by depressurization. The low-grade steam has a temperature of 128°C and a gauge pressure of 0.16 MPa, and the flash condensate has a temperature of 90°C.

[0052] The generated low-grade steam is mainly used in low-pressure steam demand systems, including the distillation column feed preheating heat exchanger 6 and the column top gas phase material recovery equipment, namely the alkali evaporation heating reactor 7, while the flash condensate is used for heat exchange.

[0053] S2. Regulation and distribution of low-pressure steam

[0054] Low-grade steam is fed into a distribution cylinder 8, where it is regulated and distributed to supply the low-pressure steam demand system. This system includes feed preheating heat exchangers 6 for the first distillation column 1, the second distillation column 2, and the third distillation column 3, as well as an alkali evaporation heating reactor 7, thus reducing the system's steam consumption. This low-pressure steam is primarily used for feed preheating of the distillation columns and for the recovery of vaporous materials from the top of the columns.

[0055] The low-pressure steam demand equipment produces condensate at a temperature of 90°C.

[0056] S3. Heat exchange and preheating of flash condensate

[0057] The flash condensate is used for heat exchange, primarily in the preheating heat exchanger for the feed hot water of the distillation column and the preheating heat exchanger for the alkali evaporation feed. Through this heat exchange process, the thermal energy of the flash condensate is fully utilized to raise the temperature of the feed material in the alkali evaporation heating reactor 7.

[0058] After heat exchange, the temperature of the flash condensate drops to 60°C, becoming secondary condensate.

[0059] S4. Collection and circulation of condensate

[0060] The condensate (90℃) and secondary condensate (60℃) enter the cooling tower 10 together. After being cooled, they are recycled back to the circulating water system as circulating water, ensuring the efficient recycling of water resources.

[0061] A portion of the condensate enters the waste heat boiler 11 for regenerating steam. The generated steam is used as supplementary steam for the system and directly enters the steam distribution cylinder 8, further reducing the consumption of fresh steam.

[0062] S5. Regenerated steam from waste heat boilers

[0063] The regenerated steam is then replenished to the system via the steam distribution cylinder 8 for use in equipment requiring low-pressure steam, further optimizing steam utilization efficiency.

[0064] Through this embodiment, low-grade steam in the system is recovered and utilized multiple times, effectively reducing the consumption of fresh steam, optimizing the system's energy efficiency, and significantly improving economic and environmental benefits. The steam consumption per ton of product in the plant's distillation system has been reduced from 72 tons / ton of product to 65 tons / ton of product, saving approximately 18,200 tons of fresh steam annually, or 2.08 tons of steam per hour, generating economic benefits of approximately 5.1 million yuan.

[0065] This invention, by making reasonable use of the thermal energy of low-grade steam and condensate, not only reduces system energy consumption but also significantly improves overall resource utilization efficiency, thus promoting energy conservation, consumption reduction, and environmental protection.

Claims

1. A method for multiple utilization of low-grade steam in a rectification system, characterized by, Including the following steps: S1, introduces the high-temperature and high-pressure condensate generated by the reboiler at the bottom of the distillation column into the flash tank, and flashes to obtain low-grade steam and flash condensate. S2, the low-grade steam is regulated and distributed to supply the low-pressure steam demand system in the distillation system after the low-grade steam distribution steam pressure is adjusted, and condensate is obtained. The low-pressure steam demand system includes a distillation column feed preheating heat exchanger and a distillation column top vapor phase material recovery device. S3, the flash condensate is used for heat exchange and yields condensate; S4 collects the condensate obtained from S2 and S3, sends it to the cooling tower, and after cooling, it is recycled back to the circulating water system to realize the recycling of water resources.

2. The method for multiple utilization of low-grade steam in a distillation system according to claim 1, characterized in that, The high-temperature and high-pressure condensate has a temperature of 130°C and a gauge pressure of 0.3 MPa.

3. The method for multiple utilization of low-grade steam in a distillation system according to claim 1, characterized in that, The low-grade steam has a temperature of 128°C and a gauge pressure of 0.16 MPa.

4. The method for multiple utilization of low-grade steam in a distillation system according to claim 1, characterized in that, The device used to regulate and distribute steam pressure in step S2 is a steam distribution cylinder.

5. The method for multiple utilization of low-grade steam in a distillation system according to claim 1, characterized in that, The temperature of both the flash condensate and the condensate is 90°C.

6. A method for multiple utilization of low-grade steam in a distillation system according to any one of claims 1 to 5, characterized in that, The above method also includes the following steps: S5, the condensate from step S4 above is added to the waste heat boiler to regenerate steam, and the regenerated steam can be used as supplementary steam for the system and directly enter the steam distribution cylinder.

7. A distillation system, characterized in that, The system employs a method for multiple utilization of low-grade steam in a distillation system as described in claim 6, comprising a distillation column, a reboiler located at the bottom of the distillation column for heating the liquid at the bottom of the distillation column to form a gaseous material, the reboiler being connected to a flash tank via a pipeline, the flash tank being connected to a gas distribution cylinder via a pipeline, the steam outlet of the gas distribution cylinder being connected to a distillation column feed preheater and a column top gaseous material recovery device respectively; the flash condensate outlet of the flash tank being connected to a heat exchanger, the heat exchanger being connected to the column top gaseous material recovery device; The system also includes a cooling tower for collecting condensate from the distillation column feed preheater, the column top vapor recovery equipment, and the heat exchanger; The system also includes a waste heat boiler for regenerating steam using a portion of the condensate, with the steam outlet of the waste heat boiler connected to a steam distribution cylinder.

8. A distillation system according to claim 7, characterized in that, The equipment for recovering gaseous materials at the top of the tower is an alkali-heated reaction vessel.

9. A distillation system according to claim 7, characterized in that, The heat exchanger is an alkali evaporation feed preheating heat exchanger.

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