Cross-pipe falling-film multi-effect rectification system and process

Abstract

The present application belongs to the technical field of multi-effect rectification, and relates to a horizontal-tube falling-film multi-effect rectification system and process. The horizontal-tube falling-film multi-effect rectification system comprises, in sequence, a multi-effect evaporation chamber, a multi-effect rectification tower, a multi-effect circulating transfer pump, a multi-effect reflux tank, a multi-effect reflux pump and a one-effect condenser. The present application adopts a horizontal-tube falling-film evaporator in series connection, has a compact design, high equipment integration, small floor area and low occupied height, can be adjusted to two, three, four or five levels as needed, can be modularly combined and matched, and is flexible in assembly. The process of the present application has rectification function, can realize dehydration of waste solvent or recovery of solvent, has higher purity of recovered water or solvent, is low in energy consumption, high in separation efficiency, and solves the problems of large floor area, high occupied height and high production energy consumption of the existing vertical-tube falling-film rectification device.

Description

Technical Field

[0001] This invention belongs to the field of multi-effect distillation technology, and particularly relates to a horizontal tube falling film multi-effect distillation system and process. Background Technology

[0002] Multi-effect distillation has numerous applications in the chemical industry. Based on the principle that the boiling point of a liquid increases with pressure, when several distillation columns operate in parallel or series, the vapor from the top of the high-pressure column can be used as a heat source for the bottom of the low-pressure column through a vertical falling film evaporator due to the different operating pressures. Each column has a different energy level; the energy discharged from the higher-energy column is used in the lower-energy column, thus achieving energy savings. Except for the column with the lowest pressure, the latent heat of condensation of the vapor from the top of the other columns is recovered and utilized by the distillation system itself, thereby reducing the energy consumption of the distillation process.

[0003] Existing multi-effect distillation equipment typically includes a distillation column, a vertical falling film evaporator, and high-flow-rate and high-head pumps in each effect. The distillation column comprises a skirt, column body, and related internals, resulting in a relatively high overall height to ensure separation efficiency. During normal operation, the vertical falling film evaporator requires a pump to force circulation of the liquid to be evaporated; a high pump flow rate is needed to ensure uniform film distribution on the inner wall of the heat exchange tubes. Furthermore, a high pump head is required to ensure the liquid can flow from the tall vertical falling film evaporator, thus resulting in high pump power. Due to the low integration of existing equipment, the current multi-effect distillation process occupies a large overall area. Summary of the Invention

[0004] To address the shortcomings of the existing technology, this invention provides a horizontal tube falling film multi-effect distillation system and process, the specific technical solution of which is as follows:

[0005] The first objective of this invention is to provide a horizontal tube falling film multi-effect distillation system, wherein the multi-effect distillation system is a two-effect distillation system, comprising a first-effect evaporation chamber and a second-effect evaporation chamber arranged horizontally in sequence, and each of the first-effect evaporation chamber and the second-effect evaporation chamber is provided with a plurality of heat exchange tubes;

[0006] A first-effect evaporation chamber is connected to a first-effect distillation column above it, and a first-effect condenser is installed above the first-effect distillation column. The vapor outlet of the first-effect condenser is connected to a vacuum system. A first-effect circulating feed pump is connected to the bottom of the first-effect evaporation chamber. The first-effect evaporation chamber has a left-side chamber, which is connected to the vacuum system. A second-effect reflux tank is connected to the bottom of the left-side chamber, and the second-effect reflux tank is connected to a second-effect reflux pump. The first-effect evaporation chamber also has a right-side chamber, which is connected to the vapor outlet at the top of the second-effect distillation column.

[0007] The upper part of the double-effect evaporator is connected to a double-effect distillation column, and the lower part of the double-effect evaporator is connected to a double-effect circulating feed pump. The double-effect evaporator has a left tube side chamber 2, and the outlet of the left tube side chamber 2 is a steam condensate discharge outlet. The double-effect evaporator also has a right tube side chamber 2, which is connected to a heat source.

[0008] Furthermore, the multi-effect distillation system is a three-effect distillation system, including a first-effect evaporation chamber, a second-effect evaporation chamber, and a third-effect evaporation chamber arranged horizontally in sequence, and each of the first-effect evaporation chamber, the second-effect evaporation chamber, and the third-effect evaporation chamber is equipped with several heat exchange tubes;

[0009] A first-effect evaporation chamber is connected to a first-effect distillation column above it, and a first-effect condenser is installed above the first-effect distillation column. The vapor outlet of the first-effect condenser is connected to a vacuum system. A first-effect circulating feed pump is connected to the bottom of the first-effect evaporation chamber. The first-effect evaporation chamber has a left-side chamber, which is connected to the vacuum system. A second-effect reflux tank is connected to the bottom of the left-side chamber, and the second-effect reflux tank is connected to a second-effect reflux pump. The first-effect evaporation chamber also has a right-side chamber, which is connected to the vapor outlet at the top of the second-effect distillation column.

[0010] A second-effect distillation column is connected above the second-effect evaporation chamber, and a second-effect circulating feed pump is connected below the second-effect evaporation chamber. The second-effect evaporation chamber has a left-side chamber 2, which is connected to a third-effect reflux tank, and the third-effect reflux tank is connected to a third-effect reflux pump. The second-effect evaporation chamber also has a right-side chamber 2, which is connected to the vapor outlet at the top of the third-effect distillation column.

[0011] The triple-effect evaporator is connected to a triple-effect distillation column above and a triple-effect circulating feed pump below. The triple-effect evaporator has a left tube side chamber 3, the outlet of which is a steam condensate discharge outlet. The triple-effect evaporator also has a right tube side chamber 3, which is connected to a heat source.

[0012] Furthermore, the multi-effect distillation system is a four-effect distillation system or a five-effect distillation system.

[0013] Furthermore, a spray device is provided above the heat exchange tubes in the first-effect evaporation chamber and / or the second-effect evaporation chamber.

[0014] Furthermore, a spray device is provided above the heat exchange tubes in the first-effect evaporation chamber and / or the second-effect evaporation chamber and / or the third-effect evaporation chamber.

[0015] The second objective of this invention is to provide a horizontal tube falling film multi-effect distillation process, wherein the multi-effect distillation system is a two-effect distillation system, comprising the following steps:

[0016] The horizontal tube falling film multi-effect distillation system is evacuated using a vacuum system.

[0017] The raw material enters the shell side of the first-effect evaporator through a first-effect circulating transfer pump, where it undergoes forced circulation and falling film flow. Steam is generated on the outer wall of the heat exchange tubes in the first-effect evaporator. The generated steam enters the first-effect distillation column, where it is partially refluxed and collected after condensation in the first-effect condenser. The top product of the first-effect distillation column is collected at the top outlet. The heat source for the tube side of the first-effect evaporator comes from the top of the second-effect distillation column. The heat source enters the first-effect evaporator from the right tube side and exchanges heat in the heat exchange tubes. The left tube side of the first-effect evaporator is the condensed liquid phase, which enters the second-effect reflux tank. It is partially refluxed and collected by the second-effect reflux pump, and the second-effect reflux liquid is returned to the second-effect distillation column.

[0018] The concentrated liquid produced in the first-effect evaporator enters the shell side of the second-effect evaporator through the second-effect circulating transfer pump, where it undergoes forced circulation and falling film flow. Steam is generated on the outer wall of the heat exchange tubes in the second-effect evaporator. The generated steam passes through the second-effect distillation column and enters the right-side chamber 1 of the first-effect evaporator from the top of the column. A heat source is introduced into the right-side chamber 2 of the second-effect evaporator, while the left-side chamber 2 of the second-effect evaporator contains the condensate after steam heat exchange. Part of the concentrated liquid produced in the second-effect evaporator undergoes forced circulation and falling film flow through the second-effect circulating transfer pump, while the rest is collected.

[0019] Furthermore, the multi-effect distillation system is a triple-effect distillation system, and the triple-effect distillation process includes the following steps:

[0020] The horizontal tube falling film multi-effect distillation system is evacuated using a vacuum system.

[0021] The raw material enters the shell side of the first-effect evaporator through a first-effect circulating transfer pump, where it undergoes forced circulation and falling film flow. Steam is generated on the outer wall of the heat exchange tubes in the first-effect evaporator. The generated steam enters the first-effect distillation column, where it is partially refluxed and collected after condensation in the first-effect condenser. The top product of the first-effect distillation column is collected at the top outlet. The heat source for the tube side of the first-effect evaporator comes from the top of the second-effect distillation column. The heat source enters the first-effect evaporator from the right tube side and exchanges heat in the heat exchange tubes. The left tube side of the first-effect evaporator is the condensed liquid phase, which enters the second-effect reflux tank. It is partially refluxed and collected by the second-effect reflux pump, and the second-effect reflux liquid is returned to the second-effect distillation column.

[0022] The concentrated liquid produced in the first-effect evaporator enters the shell side of the second-effect evaporator through the second-effect circulating transfer pump, where it undergoes forced circulation and falling film flow. Steam is generated on the outer wall of the heat exchange tubes in the second-effect evaporator. The generated steam passes through the second-effect distillation column and enters the right-side tube side chamber 1 of the first-effect evaporator from the top of the second-effect distillation column. The heat source for the tube side of the second-effect evaporator comes from the top of the third-effect distillation column and enters the second-effect evaporator from the right-side tube side chamber 2. Heat exchange occurs in the heat exchange tubes of the second-effect evaporator. The condensed liquid phase in the left-side tube side chamber 2 of the second-effect evaporator enters the third-effect reflux tank, where it is partially refluxed and collected by the third-effect reflux pump. The reflux liquid is returned to the third-effect distillation column.

[0023] The concentrated liquid produced in the double-effect evaporator enters the shell side of the triple-effect evaporator through a triple-effect circulating transfer pump, where it undergoes forced circulation and falling film flow. Steam is generated on the outer wall of the heat exchange tubes in the triple-effect evaporator. The generated steam passes through the triple-effect distillation column and enters the right-side chamber 2 of the double-effect evaporator from the top of the column. A heat source is introduced into the right-side chamber 3 of the triple-effect evaporator, while the left-side chamber 3 contains the condensate after steam heat exchange. Part of the concentrated liquid produced in the triple-effect evaporator undergoes forced circulation and falling film flow through the triple-effect circulating transfer pump, while the rest is collected.

[0024] Furthermore, the raw material enters the shell side of the first-effect evaporation chamber through a first-effect circulating transfer pump, and is evenly sprayed onto the outer wall of the heat exchange tubes of the first-effect evaporation chamber through a spraying device.

[0025] Furthermore, the concentrated liquid produced in the first-effect evaporator enters the shell side of the second-effect evaporator through the second-effect circulating transfer pump, and is evenly sprayed onto the outer wall of the heat exchange tubes of the second-effect evaporator through a spraying device.

[0026] Furthermore, the concentrated liquid produced in the second-effect evaporator enters the shell side of the third-effect evaporator through the third-effect circulating transfer pump, and is evenly sprayed onto the outer wall of the heat exchange tubes of the third-effect evaporator through the spraying device.

[0027] The beneficial effects of this invention are as follows:

[0028] The horizontal tube falling film multi-effect distillation system of this invention features a horizontally arranged multi-effect evaporation chamber, employing horizontal tube falling film evaporators connected in series. This design is compact, highly integrated, occupies a small area, and has a low height requirement. It can be adjusted to two, three, four, or five stages as needed, and can be modularly combined for flexible assembly. The process of this invention possesses distillation capabilities, enabling the dehydration of waste solvents or solvent recovery. The recovered water or solvent has higher purity, lower energy consumption, and higher separation efficiency, solving the problems of large footprint, high height, and high energy consumption in existing vertical tube falling film distillation devices. Attached Figure Description

[0029] Figure 1 This is a flow chart of the horizontal tube falling film multi-effect distillation system according to an embodiment of the present invention;

[0030] Explanation of markings in the diagram:

[0031] V1, First-effect evaporator; V2, Second-effect evaporator; V3, Third-effect evaporator; V4, Second-effect reflux tank; V5, Third-effect reflux tank; V6, Left-side tube side chamber 1; V7, Right-side tube side chamber 1; V8, Left-side tube side chamber 2; V9, Right-side tube side chamber 2; V10, Left-side tube side chamber 3; V11, Right-side tube side chamber 3; P1, First-effect circulating feed pump; P2, Second-effect circulating feed pump; P3, Third-effect circulating feed pump; P4, Second-effect reflux pump; P5, Third-effect reflux pump; T1, First-effect distillation column; T2, Second-effect distillation column; T3, Third-effect distillation column; E1, First-effect condenser;

[0032] 1. Triple-effect reflux fluid; 2. Triple-effect produced fluid; 3. Second-effect reflux fluid; 4. Second-effect produced fluid; 5. First-effect top produced fluid; 6. Wastewater; 7. Raw materials; 8. First-effect concentrate; 9. Second-effect concentrate; 10. Triple-effect concentrate. Detailed Implementation

[0033] The principles and features of the present invention are described below with reference to examples. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0034] Example 1:

[0035] like Figure 1 As shown, a horizontal tube falling film triple-effect distillation system includes a first-effect evaporation chamber V1, a second-effect evaporation chamber V2, and a third-effect evaporation chamber V3 arranged horizontally in sequence. Each of the first-effect evaporation chamber V1, the second-effect evaporation chamber V2, and the third-effect evaporation chamber V3 is equipped with a plurality of heat exchange tubes. A spray device is provided above the heat exchange tubes in the first-effect evaporation chamber V1, the second-effect evaporation chamber V2, and the third-effect evaporation chamber V3.

[0036] A first-effect evaporation chamber V1 is connected above a first-effect distillation column T1, and a first-effect condenser E1 is installed above the first-effect distillation column T1. The vapor outlet of the first-effect condenser E1 is connected to a vacuum system. A first-effect circulating feed pump P1 is connected below the first-effect evaporation chamber V1. The first-effect evaporation chamber V1 has a left-side chamber V6, which is connected to a vacuum system. A second-effect reflux tank V4 is connected below the left-side chamber V6, and the second-effect reflux tank V4 is connected to a second-effect reflux pump P4. The first-effect evaporation chamber V1 also has a right-side chamber V7, which is connected to the vapor outlet at the top of the second-effect distillation column T2.

[0037] The second-effect evaporation chamber V2 is connected to a second-effect distillation column T2 above it, and a second-effect circulating feed pump P2 is connected to the bottom of the second-effect evaporation chamber V2. The second-effect evaporation chamber V2 has a left-side chamber V8, which is connected to a third-effect reflux tank V5, and the third-effect reflux tank V5 is connected to a third-effect reflux pump P5. The second-effect evaporation chamber V2 also has a right-side chamber V9, which is connected to the top vapor outlet of the third-effect distillation column T3.

[0038] The triple-effect evaporator V3 is connected to a triple-effect distillation column T3 above it, and a triple-effect circulating feed pump P3 is connected to the bottom of the triple-effect evaporator V3. The triple-effect evaporator V3 is equipped with a left tube side chamber V10, and the outlet of the left tube side chamber V10 is a steam condensate discharge outlet. The triple-effect evaporator V3 is equipped with a right tube side chamber V11, and the right tube side chamber V11 is connected to a heat source.

[0039] This embodiment describes a horizontal tube falling film multi-effect refining process, taking the treatment of raw material 7—methanol aqueous solution (methanol content 98wt%, water 2wt%)—as an example for illustration:

[0040] A methanol-water solution (98 wt% methanol, 2 wt% water) is continuously fed into the first-effect evaporation chamber V1 at a flow rate of 42.5 t / h via a circulating feed pump P1. The solution is evenly sprayed onto the outer wall of the heat exchange tubes in the first-effect evaporation chamber V1 through a spray device, and forced circulation and falling film flow are implemented. Steam is generated on the outer wall of the heat exchange tubes in the first-effect evaporation chamber V1. The generated steam enters the first-effect distillation column T1, and after condensation in the first-effect condenser E1, part of it is refluxed and collected. The first-effect condenser E1 uses ambient temperature water. As a cooling medium, the vapor phase in the tube side of the first-effect evaporator V1 comes from the top of the second-effect distillation column T2 and serves as the heat source for the first-effect evaporator V1. The operating pressure of the first-effect evaporator V1 is 50 kPaA, and the operating temperature is 49℃. The reflux ratio at the top of the first-effect distillation column T1 is controlled at R = 0.45, and the temperature at the top of the first-effect distillation column T1 is 47.6℃. The top product outlet of the first-effect distillation column T1 produces the top product liquid 5, which contains 99.85 wt% methanol and has a production rate of 14.4 tons / h.

[0041] The concentrated liquid 8 produced in the first-effect evaporator V1 enters the shell side of the second-effect evaporator V2 through the second-effect circulating transfer pump P2. It is then evenly sprayed onto the outer wall of the heat exchange tubes of the second-effect evaporator V2 via a spray device, and undergoes forced circulation and falling film flow. Steam is generated on the outer wall of the heat exchange tubes of the second-effect evaporator V2. This steam passes through the second-effect distillation column T2 and enters the right-side tube side chamber V7 of the first-effect evaporator V1 from the top of column T2. ​​The heat source for the tube side of the second-effect evaporator V2 is the top of the third-effect distillation column T3. The operating pressure of the second-effect evaporator V2 is atmospheric pressure. The operating temperature is 66.2℃, and the top temperature of the second-effect distillation column T2 is 64.5℃. The vapor phase at the top of the second-effect distillation column T2 enters the right tube side chamber - V7 and then enters the first-effect evaporation chamber V1 for heat exchange. The liquid phase in the left tube side chamber - V6 is condensed and enters the second-effect reflux tank V4. Through the second-effect reflux pump P4, part of it is used as second-effect reflux liquid 3 for reflux and part is collected as second-effect collected liquid 4. The reflux ratio is R = 0.65. The second-effect reflux liquid 3 is returned to the second-effect distillation column T2. ​​The second-effect collected liquid 4 has a methanol content of 99.85wt% and a collection rate of 14.2 tons / h.

[0042] The concentrated liquid 9 produced in the second-effect evaporator V2 enters the shell side of the third-effect evaporator V2 through the triple-effect circulating feed pump P3. It is then evenly sprayed onto the outer wall of the heat exchange tubes in the third-effect evaporator V3 via a spray device, resulting in forced circulation and falling film flow. Steam is generated on the outer wall of the heat exchange tubes in the third-effect evaporator V3. This steam passes through the triple-effect distillation column T3 and enters the right-side chamber 2 (V9) of the second-effect evaporator V2 from the top of T3. Low-pressure steam (0.6 MPaG) flows through the tube side of the third-effect evaporator V3, serving as the heat source. The left-side chamber 3 (V8) of the third-effect evaporator V3 contains condensate after steam heat exchange. The operating pressure of the third-effect evaporator V3 is 0.1 MPaG, and the operating temperature is 110.4℃. The top temperature of the triple-effect distillation column T3 is 82.9℃. The vapor phase from the top of the triple-effect distillation column T3 serves as the heat source for the second-effect evaporator V2, flowing from the right-side chamber 2 (V9). 9 enters the double-effect evaporator V2 for heat exchange. The condensed liquid phase in the left tube side of the double-effect evaporator V2, V8, enters the triple-effect reflux tank V5. Through the triple-effect reflux pump P5, part of it is returned as triple-effect reflux liquid 1 and part is collected as triple-effect collected liquid 2. The reflux ratio is controlled at R=1. Triple-effect reflux liquid 1 is returned to the triple-effect distillation column T3. The collected methanol content is 99.85wt%, and the collection rate is 13 tons / h.

[0043] Part of the triple-effect concentrate 10 produced in the triple-effect evaporator V3 is forced to circulate and fall film through the triple-effect circulating transfer pump P3, generating steam on the outer wall of the heat exchange tubes of the triple-effect evaporator V3. The other part is wastewater 6, with a collection rate of 0.9 t / h and a content of 10 wt% methanol and 90 wt% water.

[0044] The footprint of this embodiment can be reduced to 20m×6m, and the height of the steel structure can be reduced to 6m×3m.

[0045] If conventional triple-effect distillation process and equipment are used, i.e., the evaporation chamber is a vertical tube falling film evaporator, the equipment that meets the same processing capacity and product requirements as the example will occupy an area of ​​approximately 20m × 10m and the steel structure height will be 6m × 4m.

[0046] However, using triple-effect evaporation technology and equipment, it is impossible to extract a methanol aqueous solution with a purity higher than 99.8%.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. 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 cross-tube falling-film multi-effect rectification system, characterized by, The multi-effect distillation system includes a first-effect evaporation chamber and a second-effect evaporation chamber arranged horizontally in sequence, and each of the first-effect evaporation chamber and the second-effect evaporation chamber is equipped with several heat exchange tubes; A first-effect evaporation chamber is connected above a first-effect distillation column, and a first-effect condenser is installed above the first-effect distillation column; the vapor outlet of the first-effect condenser is connected to a vacuum system; a first-effect circulating feed pump is connected below the first-effect evaporation chamber; the first-effect evaporation chamber has a left-side chamber, which is connected to the vacuum system, and a second-effect reflux tank is connected below the left-side chamber, which is connected to a second-effect reflux pump; the first-effect evaporation chamber also has a right-side chamber, which is connected to the vapor outlet at the top of the second-effect distillation column. The upper part of the double-effect evaporation chamber is connected to a double-effect distillation column, and the lower part of the double-effect evaporation chamber is connected to a double-effect circulating feed pump. The first-effect circulating feed pump is connected to the second-effect circulating feed pump. The double-effect evaporation chamber is provided with a left tube side chamber 2, and the outlet of the left tube side chamber 2 is a steam condensate discharge outlet. The double-effect evaporation chamber is provided with a right tube side chamber 2, and the right tube side chamber 2 is connected to a heat source.

2. The cross-pipe falling-film multi-effect distillation system according to claim 1, characterized in that, The multi-effect distillation system also includes a triple-effect distillation column. The left tube side chamber 2 is connected to a triple-effect reflux tank, and the triple-effect reflux tank is connected to a triple-effect reflux pump; the right tube side chamber 2 is connected to the vapor outlet at the top of the triple-effect distillation column; A triple-effect distillation column is connected above the triple-effect evaporator, and a triple-effect circulating feed pump is connected below the triple-effect evaporator. The double-effect circulating feed pump is connected to the triple-effect circulating feed pump. The triple-effect evaporator has a left tube side chamber three, and the outlet of the left tube side chamber three is a steam condensate discharge outlet. The triple-effect evaporator also has a right tube side chamber three, which is connected to a heat source.

3. The cross-pipe falling-film multi-effect distillation system according to claim 1, characterized in that, The multi-effect distillation system is a two-effect distillation system, a four-effect distillation system, or a five-effect distillation system.

4. The cross-pipe falling-film multi-effect distillation system according to claim 1, wherein, A spray device is installed above the heat exchange tubes in the first-effect evaporation chamber and / or the second-effect evaporation chamber.

5. The cross-pipe falling-film multi-effect distillation system according to claim 2, wherein, A spray device is installed above the heat exchange tubes in the single-effect evaporation chamber and / or the double-effect evaporation chamber and / or the triple-effect evaporation chamber.

6. A cross tube falling film multi-effect rectification process, characterized in that, The system described in claim 1 includes the following steps: The horizontal tube falling film multi-effect distillation system is evacuated using a vacuum system. The raw material enters the shell side of the first-effect evaporator through a first-effect circulating transfer pump, where it undergoes forced circulation and falling film flow. Steam is generated on the outer wall of the heat exchange tubes in the first-effect evaporator. The generated steam enters the first-effect distillation column, where it is partially refluxed and collected after condensation in the first-effect condenser. The top product of the first-effect distillation column is collected at the top outlet. The heat source for the tube side of the first-effect evaporator comes from the top of the second-effect distillation column. The heat source enters the first-effect evaporator from the right tube side and exchanges heat in the heat exchange tubes. The left tube side of the first-effect evaporator is the condensed liquid phase, which enters the second-effect reflux tank. It is partially refluxed and collected by the second-effect reflux pump, and the second-effect reflux liquid is returned to the second-effect distillation column. The concentrated liquid produced in the first-effect evaporator enters the shell side of the second-effect evaporator through the second-effect circulating transfer pump, where it undergoes forced circulation and falling film flow. Steam is generated on the outer wall of the heat exchange tubes in the second-effect evaporator. The generated steam passes through the second-effect distillation column and enters the right-side chamber 1 of the first-effect evaporator from the top of the column. A heat source is introduced into the right-side chamber 2 of the second-effect evaporator, while the left-side chamber 2 of the second-effect evaporator contains the condensate after steam heat exchange. Part of the concentrated liquid produced in the second-effect evaporator undergoes forced circulation and falling film flow through the second-effect circulating transfer pump, while the rest is collected.

7. The horizontal-tube falling-film multi-effect rectification process according to claim 6, characterized in that The system described in claim 2 further includes the following steps: The heat source for the tube side of the second-effect evaporator comes from the top of the third-effect distillation column. It enters the second-effect evaporator from the right tube side and exchanges heat in the heat exchange tubes. The condensed liquid phase in the left tube side of the second-effect evaporator enters the third-effect reflux tank. It is partially refluxed and collected by the third-effect reflux pump. The reflux liquid is returned to the third-effect distillation column. The concentrated liquid produced in the double-effect evaporator enters the shell side of the triple-effect evaporator through a triple-effect circulating transfer pump, where it undergoes forced circulation and falling film flow. Steam is generated on the outer wall of the heat exchange tubes in the triple-effect evaporator. The generated steam passes through the triple-effect distillation column and enters the right-side chamber 2 of the double-effect evaporator from the top of the column. A heat source is introduced into the right-side chamber 3 of the triple-effect evaporator, while the left-side chamber 3 contains the condensate after steam heat exchange. Part of the concentrated liquid produced in the triple-effect evaporator undergoes forced circulation and falling film flow through the triple-effect circulating transfer pump, while the rest is collected.

8. The horizontal-tube falling-film multi-effect distillation process of claim 6, wherein, Using the system as described in claim 4 or 5, the raw material enters the shell side of the first-effect evaporation chamber through a first-effect circulating transfer pump, and is evenly sprayed onto the outer wall of the heat exchange tubes of the first-effect evaporation chamber by a spraying device.

9. The horizontal-tube falling-film multi-effect distillation process of claim 6, wherein, Using the system as described in claim 4 or 5, the concentrated liquid produced in the first-effect evaporation chamber enters the shell side of the second-effect evaporation chamber through the second-effect circulating transfer pump, and is evenly sprayed onto the outer wall of the heat exchange tubes of the second-effect evaporation chamber through a spraying device.

10. The horizontal-tube falling-film multi-effect distillation process of claim 7, wherein, Using the system as described in claim 5, the concentrated liquid produced in the second-effect evaporator enters the shell side of the third-effect evaporator through a third-effect circulating transfer pump, and is evenly sprayed onto the outer wall of the heat exchange tubes of the third-effect evaporator through a spraying device.

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