A methylene chloride double-effect heat coupling rectification system

Abstract

The utility model discloses a dichloromethane double -effect heat coupling rectification system, including vacuum tower and the condenser and vacuum tower reflux tank of connecting on vacuum tower, and vacuum tower reflux tank is connected with the condenser through the pipeline, still including pressurized tower, the top of pressurized tower is connected with steam output pipeline, and the end of steam output pipeline is connected with vacuum tower reboiler, and the below of vacuum tower reboiler is connected with pressurized tower reflux tank, and the output of pressurized tower reflux tank is connected with pressurized tower reflux pipeline, and the pipe box of vacuum tower reboiler is connected with gas -liquid return pipeline and liquid phase pipeline, and gas -liquid return pipeline is linked with the lateral return mouth of the lower part of vacuum tower, and liquid phase pipeline is linked with the export of the bottom of vacuum tower, the design utilizes vacuum tower reboiler to become the condensation system of pressurized tower on one hand, and the other hand is as the heat source of vacuum tower and provides the source, with the mode of heat coupling, and the " waste heat " of pressurized tower becomes the " driving energy " of vacuum tower.

Description

Technical Field

[0001] This utility model relates to the field of chemical equipment technology, and in particular to a dichloromethane dual-effect thermal coupling distillation system. Background Technology

[0002] Dichloromethane is an important chemical raw material with broad application prospects. It is widely used in the chemical industry, including film production, pharmaceuticals, and cleaning agents, and is also extensively used as a refrigerant in industrial refrigeration systems.

[0003] Dichloromethane distillation is the process of purifying crude dichloromethane containing impurities (such as trichloromethane, other chlorides, and moisture) to obtain high-purity dichloromethane. Currently, most dichloromethane production processes use single-tower distillation. In traditional single-tower distillation, each distillation column requires an independent reboiler to provide heat. Separating dichloromethane requires changing it from a liquid to a gaseous state, a process that absorbs a large amount of latent heat of vaporization, resulting in very high steam consumption. Each column is heated with fresh steam, and there is no heat exchange between columns. The high-quality latent heat released when the steam at the top of one column condenses is not only not utilized but also needs to be removed with cooling water, further increasing the load and energy consumption of the cooling system. This leads to high production costs and significant energy waste in dichloromethane production. Utility Model Content

[0004] This invention addresses the technical problem of high steam consumption and significant energy waste during the distillation of dichloromethane by providing a dual-effect thermal coupling distillation system for dichloromethane. The system includes a vacuum distillation tower, a vacuum distillation tower condenser, and a vacuum distillation tower reflux tank connected to the vacuum distillation tower. The vacuum distillation tower reflux tank and the vacuum distillation tower condenser are connected by a pipeline to form an internal circulation.

[0005] It also includes a pressurization tower, the top of which is connected to a steam output pipe, the end of which is connected to a pressure reducing tower reboiler, the bottom of which is connected to a pressurization tower reflux tank, the output end of which is connected to a pressurization tower reflux pipe, and the pressurization tower reflux pipe is connected to the reflux inlet at the top of the pressurization tower.

[0006] The reboiler of the vacuum distillation tower is connected to a gas-liquid return pipe and a liquid phase pipe. The gas-liquid return pipe is connected to the side return port at the bottom of the vacuum distillation tower, and the liquid phase pipe is connected to the outlet at the bottom of the vacuum distillation tower.

[0007] Preferably, in the above technical solution, the middle section of the steam output pipeline is provided with a three-way connecting pipe and a main electric valve, and the main electric valve is located on the side close to the reboiler of the pressure reducing tower.

[0008] Preferably, in the above technical solution, the branch pipe of the three-way connecting pipe is connected to the standby condenser of the pressurized tower, and the output end of the standby condenser of the pressurized tower is connected to the top of the pressurized tower reflux tank.

[0009] Preferably, in the above technical solution, the branch pipe of the three-way connecting pipe is equipped with an auxiliary electric valve.

[0010] Preferably, in the above technical solution, a pressurizing reflux pump is provided on the pressurizing tower reflux pipeline, and a circulation pump is provided on the liquid phase pipeline.

[0011] Preferably, in the above technical solution, a pressure reducing tower reflux pipe is provided between the pressure reducing tower reflux tank and the pressure reducing tower, and a pressure reducing reflux pump is provided on the pressure reducing tower reflux pipe.

[0012] Preferably, in the above technical solution, the pressure reducing tower reboiler is a thermosiphon reboiler.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] This invention connects the steam output pipe at the top of the pressurization tower to the reboiler of the depressurization tower. The reboiler serves as both the condensation system for the pressurization tower and the heat source for the depressurization tower. Through thermal coupling, the "waste heat" of the pressurization tower is transformed into the "driving energy" for the depressurization tower, thus forming an energy closed loop.

[0015] This invention connects a branch of the steam output pipeline at the top of the pressurized tower to a standby condenser, and switches the operating states of the standby condenser and the reboiler of the pressure reducing tower via an electric valve. This achieves a flexible start-up procedure of "independent first, then coupled," avoiding drastic fluctuations during startup. The standby condenser isolates local faults, preventing a complete shutdown caused by a local fault and providing operators with time for maintenance. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of a dichloromethane dual-effect thermal coupling distillation system according to the present invention.

[0017] Explanation of key figure labels:

[0018] 1-Pressure reducing tower, 2-Pressure increasing tower, 3-Pressure reducing tower reflux tank, 4-Pressure reducing tower condenser, 5-Pressure reducing tower reboiler, 6-Pressure increasing tower standby condenser, 7-Pressure increasing tower reflux tank, 8-T-connecting pipe, 11-Circulation pump, 21-Steam output pipe, 31-Pressure reducing reflux pump, 32-Pressure reducing tower reflux pipe, 51-Gas-liquid return pipe, 52-Liquid phase pipe, 71-Pressure increasing reflux pump, 72-Finished product output pipe, 73-Exhaust pipe, 75-Pressure increasing tower reflux pipe, 81-Auxiliary electric valve, 82-Main electric valve. Detailed Implementation

[0019] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0020] like Figure 1As shown, this utility model discloses a dichloromethane double-effect thermally coupled distillation system, including a vacuum distillation tower 1, a vacuum distillation tower condenser 4, and a vacuum distillation tower reflux tank 3 connected to the vacuum distillation tower 1. The vacuum distillation tower reflux tank 3 is connected to the vacuum distillation tower condenser 4 through a pipeline to form an internal circulation. It also includes a pressurization tower 2, the top of which is connected to a steam output pipeline 21, the end of which is connected to a vacuum distillation tower reboiler 5. The bottom of the vacuum distillation tower reboiler 5 is connected to a pressurization tower reflux tank 7, the output end of which is connected to a pressurization tower reflux pipeline 75, which is connected to the reflux inlet at the top of the pressurization tower 2. The tube box of the vacuum distillation tower reboiler 5 is connected to a gas-liquid return pipeline 51 and a liquid phase pipeline 52. The gas-liquid return pipeline 51 is connected to the side return port at the bottom of the vacuum distillation tower 1, and the liquid phase pipeline 52 is connected to the outlet at the bottom of the vacuum distillation tower 1. A pressure reducing tower reflux pipe 32 is provided between the pressure reducing tower 1 and the pressure reducing tower reflux tank 3. A pressure reducing reflux pump 31 is installed on the pressure reducing tower reflux pipe 32. Normally, the high-temperature steam at the top of the pressure tower 2 is directly condensed by cooling water in the condenser, and its high-quality latent heat is completely transferred to the cooling water and eventually discharged into the atmosphere, resulting in huge energy waste. The pressure reducing tower reboiler 5 replaces the traditional condenser of the pressure tower 2. The steam at the top of the pressure tower 2 is no longer "annihilated" by cooling water, but enters the shell side of the reboiler of the pressure reducing tower 5 and is used as a "heat medium". The latent heat released when the steam is condensed is directly used to heat the pressure reducing tower. In this way, one unit of energy (the latent heat of the steam) is used twice, realizing the upgraded recovery of energy. The pressure reducing tower 1 no longer needs external steam heating, and this part of the steam consumption is directly reduced to zero. Since the steam at the top of the pressure tower no longer needs a separate condenser to condense with a large amount of cooling water, the cooling water load of the entire system is also reduced significantly, thereby achieving efficient thermal coupling. The pressure reducing tower reboiler 5 is a thermosiphon reboiler. The thermosiphon reboiler acts as a physical bridge connecting the pressurization tower and the depressurization tower. Through it, the condensation heat of the steam at the top of the pressurization tower is directly and efficiently transferred to the depressurization tower, replacing the need for external steam to provide heat. Due to the intense boiling process inside the tubes, the fluid velocity is high and the turbulence is strong, which greatly enhances heat transfer, allowing a large heat load to be transferred with a relatively small heat exchange area. Furthermore, the thermosiphon system possesses inherent stability. If the heating intensity increases (more steam comes from the pressurization tower), the vaporization rate increases, the density of the mixture inside the tubes becomes lower, the circulation driving force is stronger, the flow velocity increases, and excess heat is automatically carried away, preventing overheating of the equipment. In actual installation, the distance between depressurization tower 1 and pressurization tower 2 should be minimized as much as possible to avoid excessively long connecting pipes, which could lead to significant heat loss from the steam at the top of pressurization tower 2. If necessary, insulation measures can be implemented for all pipes requiring improved heat transfer.

[0021] It should be further explained that the middle section of the steam output pipe 21 is equipped with a three-way connecting pipe 8 and a main electric valve 82, which is located on the side near the reboiler 5 of the pressure reducing tower. A branch pipe of the three-way connecting pipe 8 is connected to the standby condenser 6 of the pressure boosting tower, and the output end of the standby condenser 6 is connected to the top of the reflux tank 7 of the pressure boosting tower. An auxiliary electric valve 81 is installed on the branch pipe of the three-way connecting pipe 8. The main electric valve 8 and the auxiliary electric valve 81 can be mechanically interlocked. During the start-up phase, the main electric valve 82 leading to the reboiler 5 of the pressure reducing tower is closed, and the standby condenser 6 of the pressure boosting tower is fully activated. At this time, the pressure boosting tower 2 operates as an independent distillation tower, and its top vapor is completely condensed by the standby condenser 6. The pressure boosting tower 2 can then smoothly establish normal temperature, pressure, and reflux without downstream interference, achieving a stable operating state. Once pressurization tower 2 is operating stably and depressurization tower 1 is ready, the heat load is slowly and controlledly switched from the standby condenser 6 to the depressurization tower reboiler 5, achieving seamless system switching. When the control system detects a fault in the thermal coupling loop (such as an abnormal increase in pressurization tower pressure or abnormal heat medium flow), it immediately activates interlock protection, automatically closing the main electric valve 8 and simultaneously fully opening the auxiliary electric valve 81. At this time, the steam at the top of the pressurization tower is instantly diverted to the standby condenser. The pressurization tower itself is almost unaware of downstream faults and can continue to operate stably as an independent unit. This achieves "fault isolation," controlling local faults (on the depressurization tower side) within a certain range and preventing them from evolving into a global paralysis (complete line shutdown). Operators thus gain valuable window time to calmly perform online maintenance on faulty equipment without stopping the entire production line. This greatly enhances the flexibility and anti-interference capability of production operations, enabling the complex coupling system to adapt to different production needs and cope with various operating condition fluctuations. While the backup condenser 6 increases initial investment, it breaks the inherent rigid connection of the thermally coupled system by providing a second path, injecting operational flexibility, safety redundancy, and operational agility, thereby ensuring that this advanced energy-saving technology can be safely and reliably implemented in continuous industrial production.

[0022] In actual operation, a liquid mixture containing dichloromethane (the main component) and impurities such as trichloromethane and other chlorides is fed into the vacuum distillation tower through the middle inlet. Due to the vacuum (low pressure) maintained inside the tower, the boiling point of the mixture decreases. Driven by the heat in the bottom of the tower, a large amount of the lighter components, such as dichloromethane, evaporates and rises, while the heavier components descend. Both the rising (gas phase) and descending (liquid phase) exist simultaneously within the tower. High-purity dichloromethane vapor rises to the top of the vacuum distillation tower and enters the condenser from the top vapor outlet. The vapor is condensed by cooling water, becoming a liquid phase. The condensate flows into the reflux tank, and a portion is pumped back to the top of the tower as reflux liquid via the reflux pump. The heavier liquid component, containing a small amount of dichloromethane, descends to the bottom of the vacuum distillation tower. Not all of the liquid from the bottom of the tower is retained as residue. A significant portion is pumped to the tube side of the reboiler by the bottom pump. Inside the reboiler, this portion of liquid is heated, becoming a gas-liquid mixture. Relying on density difference (thermosiphon effect), it naturally circulates back to the lower part of the vacuum distillation column, providing rising steam for the column. The heating source comes from the feed inlet in the middle of the pressurization column, where the crude feed undergoes distillation separation under the heating of steam outside the column bottom. The steam at the top of the pressurization column enters the shell side of the reboiler. Here, the high-temperature steam exchanges heat with the cold liquid from the vacuum distillation column in the tube side. The steam condenses and releases heat (transferring latent heat to the vacuum distillation column side), becoming liquid itself. The condensate then flows to the pressurization column reflux tank. A portion of it is returned to the top of the pressurization column as reflux, while the other portion is collected as high-purity dichloromethane from the finished product output pipe 72 and sent to the product tank area. An exhaust pipe 73 is also provided at the top of the pressurization column reflux tank, connecting to a non-condensable gas discharge pipe or a tail gas treatment system. During startup or operation fluctuations, trace amounts of non-condensable gases (such as air, nitrogen, or light components) may be present in the system. These gases will accumulate in the return tank and then be discharged from the exhaust pipe 73 to prevent the formation of an insulating layer, which would severely reduce heat transfer efficiency and cause abnormal fluctuations in system pressure.

[0023] This invention connects the steam output pipe at the top of the pressurization tower to the reboiler of the depressurization tower. The reboiler serves as both the condensation system for the pressurization tower and a heat source for it, thus thermally coupling the pressurization tower's waste heat into its driving energy, forming a closed-loop energy system. A branch of the steam output pipe at the top of the pressurization tower is connected to a backup condenser, and an electric valve switches the operating states of the backup condenser and the reboiler. This achieves a flexible start-up procedure of "independent operation first, then coupling," avoiding drastic fluctuations during startup. The backup condenser isolates local faults, preventing a complete shutdown caused by a local fault and providing operators with time for maintenance.

[0024] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A dichloromethane double-effect thermally coupled distillation system, characterized in that: It includes a pressure reducing tower (1) and a pressure reducing tower condenser (4) and a pressure reducing tower reflux tank (3) connected to the pressure reducing tower (1). The pressure reducing tower reflux tank (3) and the pressure reducing tower condenser (4) are connected by a pipeline to form an internal circulation. It also includes a pressurization tower (2), the top of which is connected to a steam output pipe (21), the end of which is connected to a pressure reducing tower reboiler (5), the bottom of which is connected to a pressurization tower reflux tank (7), the output end of which is connected to a pressurization tower reflux pipe (75), and the pressurization tower reflux pipe (75) is connected to the reflux inlet at the top of the pressurization tower (2); The reboiler (5) of the pressure reducing tower is connected to a gas-liquid return pipe (51) and a liquid phase pipe (52). The gas-liquid return pipe (51) is connected to the side return port at the bottom of the pressure reducing tower (1), and the liquid phase pipe (52) is connected to the outlet at the bottom of the pressure reducing tower (1).

2. The dichloromethane double-effect thermally coupled distillation system according to claim 1, characterized in that: The middle section of the steam output pipe (21) is provided with a three-way connecting pipe (8) and a main electric valve (82), and the main electric valve (82) is located on the side close to the reboiler (5) of the pressure reducing tower.

3. The dichloromethane double-effect thermally coupled distillation system according to claim 2, characterized in that: The branch pipe of the three-way connecting pipe (8) is connected to the standby condenser (6) of the pressurized tower, and the output end of the standby condenser (6) of the pressurized tower is connected to the top of the pressurized tower reflux tank (7).

4. The dichloromethane double-effect thermally coupled distillation system according to claim 3, characterized in that: An auxiliary electric valve (81) is provided on the branch pipe of the three-way connecting pipe (8).

5. The dichloromethane double-effect thermally coupled distillation system according to claim 1, characterized in that: The pressurization tower reflux pipeline (75) is equipped with a pressurization reflux pump (71), and the liquid phase pipeline (52) is equipped with a circulation pump (11).

6. The dichloromethane double-effect thermally coupled distillation system according to claim 1, characterized in that: A pressure reducing tower reflux pipe (32) is provided between the pressure reducing tower reflux tank (3) and the pressure reducing tower (1), and a pressure reducing reflux pump (31) is provided on the pressure reducing tower reflux pipe (32).

7. The dichloromethane double-effect thermally coupled distillation system according to claim 1, characterized in that: The pressure reducing tower reboiler (5) is a thermosiphon reboiler.

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