Multi-effect evaporator suitable for generating crystals and scales

Abstract

The multi-effect evaporator comprises a last-effect assembly, a first-effect assembly, a heating source and a stock solution source. The last-effect assembly comprises a last-effect evaporator, and a last-effect heat exchange pipe is arranged in an inner cavity of the last-effect evaporator. The first-effect assembly comprises a first-effect evaporator; a first-effect heat exchange pipe is arranged in an inner cavity of the first-effect evaporator, the inner cavity of the first-effect evaporator is directly or indirectly communicated with an inner cavity of the last-effect evaporator, and the inner cavity of the first-effect evaporator is directly or indirectly communicated with a pipe cavity of the last-effect heat exchange pipe; the heating source is communicated with a pipe cavity of the first-effect heat exchange pipe; and the stock solution source is communicated with the inner cavity of the last-effect evaporator or the inner cavity of the first-effect evaporator. On the basis of an existing evaporator integrating two heat exchange structures, an external heat exchanger of a low-concentration effect body is replaced by the built-in heat exchanger, and only heating media are introduced into the heat exchange tubes without feed liquid, so that calcium sulfate crystals are prevented from blocking inner holes of the heat exchange tubes of the external heat exchanger.

Description

Technical Field

[0001] The utility model relates to the technical field of evaporation crystallization equipment, in particular to a multiple-effect evaporator suitable for crystal scaling. Background Art

[0002] The utility model patent "Two-effect evaporator integrating two heat exchange structures" with authorization announcement number CN219517819U and the utility model patent "MVR evaporator integrating two heat exchange structures" with authorization announcement number CN219517818U both combine the advantages of the existing MVR evaporators with built-in heat exchange structure and external heat exchange structure, taking into account the easy cleaning of crystallization scaling and high heat exchange efficiency.

[0003] The reasons why the above two patents adopt built-in coil heat exchanger evaporation components (referred to as: built-in evaporation components) and external tube or plate heat exchanger evaporation components (referred to as: external evaporation components) are: 1. When using built-in evaporation components, multiple components need to be arranged to achieve the same heat exchange area as an external evaporation component, so the floor space is large. This is because the heat exchanger of the built-in evaporation component is built inside the evaporation container, and the internal space of the evaporation container is limited, resulting in a small heat exchange area. It is necessary to manufacture multiple sets to make up for the lack of heat exchange area, and thus the floor space is large. When using an evaporation device with an external heat exchanger, no matter how large the heat exchange area is required, only one set is manufactured to achieve the required heat exchange area, and thus the floor space is small. 2. In the prior art, it is generally believed that low-concentration sulfate will not produce scaling during evaporation and concentration, so an external evaporation component is set up to save space. In the prior art, it is generally believed that low-concentration sulfate solution will not scale on the heat exchange tube wall of the heat exchanger during the evaporation and concentration process after removing impurities, and will not affect the heat transfer of the heat exchanger or block the heat exchanger due to scaling.

[0004] The above two patents both place an external heat exchanger (tube heat exchanger or plate heat exchanger) in a relatively low-concentration effect in a multiple-effect evaporation system, and place an internal heat exchanger (coil heat exchanger) in a relatively high-concentration effect in a multiple-effect evaporation system. The main technical problem solved by these two patents is that the main product crystals are easily generated in the high-concentration effect, which makes the heat transfer wall of the heat exchanger easy to scale, while the heat transfer wall of the heat exchanger is not easy to scale because almost no crystals are generated in the low-concentration effect. Thus, the advantage of the internal heat exchanger that it is easy to clean the scale is effectively utilized, and the defect of the external heat exchanger that it is difficult to clean after the pipe is blocked by crystals is avoided.

[0005] However, the above two evaporators were found to have the following deficiencies in the actual production process: almost all divalent sulfates (for example: zinc sulfate, manganese sulfate, copper sulfate, ferrous sulfate and nickel sulfate, etc.) contain trace amounts of calcium (the production raw materials inevitably contain trace amounts of calcium, and trace amounts of calcium dissolved in the above sulfate solution are difficult to remove). When the above sulfate solution is evaporated and concentrated in a low-concentration effect body, before the main product reaches the precipitation concentration, calcium sulfate crystals will precipitate and condense in the solution, and the crystal nuclei of calcium sulfate will induce the precipitation of metal sulfate. These precipitated crystals adhere to the inner wall of the heat exchange tube of the external heat exchanger to form scale, which is difficult to clean (it is necessary to shut down the machine, dismantle the tube and then rinse with a high-pressure water gun), which seriously affects the heat exchange efficiency and production efficiency. This results in the above two patents still not avoiding the defect that the external heat exchanger is difficult to clean after being blocked by crystals. Summary of the invention

[0006] The purpose of the utility model is to overcome the shortcomings of the prior art and provide a multiple-effect evaporator suitable for the production of crystallization scaling, which solves the problem that calcium sulfate crystals precipitate and agglomerate during use of the existing evaporator integrating two heat exchange structures (especially the evaporator disclosed in CN219517819U and CN219517818U), which blocks the heat exchange tubes of the external heat exchanger of the low-concentration effect body and seriously affects the heat exchange efficiency and production efficiency.

[0007] The technical scheme of the utility model is: it is applicable to a multi-effect evaporator with crystal scaling, comprising a final effect component, a first effect component, a heating source and a raw liquid source;

[0008] The final effect component includes a final effect evaporator, and a built-in heat exchanger is arranged in the inner cavity of the final effect evaporator, and the built-in heat exchanger includes a final effect heat exchange tube;

[0009] The first-effect assembly includes a first-effect evaporator; a first-effect heat exchange tube is arranged in the inner cavity of the first-effect evaporator, the inner cavity of the first-effect evaporator is directly or indirectly connected with the inner cavity of the last-effect evaporator, and the inner cavity of the first-effect evaporator is directly or indirectly connected with the tube cavity of the last-effect heat exchange tube;

[0010] The heating source is communicated with the tube cavity of the first-effect heat exchange tube; the raw liquid source is communicated with the inner cavity of the last-effect evaporator or the inner cavity of the first-effect evaporator.

[0011] A further technical solution of the utility model is: it also includes an intermediate effect component; the intermediate effect component is installed between the first effect component and the last effect component; the number of the intermediate effect components is one group; the intermediate effect component includes an intermediate effect evaporator, an intermediate effect heat exchange tube is arranged in the inner cavity of the intermediate effect evaporator, the inner cavity of the intermediate effect evaporator is connected with the inner cavity of the first effect evaporator to realize the circulation of raw liquid, the inner cavity of the intermediate effect evaporator is connected with the tube cavity of the last effect heat exchange tube to realize the circulation of secondary steam, the inner cavity of the intermediate effect evaporator is connected with the inner cavity of the last effect evaporator to realize the circulation of raw liquid, and the tube cavity of the intermediate effect heat exchange tube is connected with the inner cavity of the first effect evaporator to realize the circulation of secondary steam.

[0012] A further technical solution of the utility model is: it also includes an intermediate effect component; a plurality of groups of intermediate effect components are sequentially connected from front to back and installed between the first effect component and the last effect component; the intermediate effect component includes an intermediate effect evaporator, and an intermediate effect heat exchange tube is arranged in the inner cavity of the intermediate effect evaporator;

[0013] The inner cavity of the front-end intermediate effect evaporator is connected with the inner cavity of the first-effect evaporator to realize the circulation of raw liquid, the inner cavity of the front-end intermediate effect evaporator is connected with the inner cavity of the next intermediate effect evaporator to realize the circulation of raw liquid, the lumen of the intermediate effect heat exchange tube of the front-end intermediate effect evaporator is connected with the inner cavity of the first-effect evaporator to realize the circulation of secondary steam, and the inner cavity of the front-end intermediate effect evaporator is connected with the lumen of the intermediate effect heat exchange tube of the next intermediate effect evaporator to realize the circulation of secondary steam;

[0014] The inner cavity of the last intermediate effect evaporator is connected with the inner cavity of the last effect evaporator to realize the circulation of the raw liquid, the inner cavity of the last intermediate effect evaporator is connected with the inner cavity of the previous intermediate effect evaporator to realize the circulation of the raw liquid, the inner cavity of the last intermediate effect evaporator is connected with the tube cavity of the last effect heat exchange tube of the last effect evaporator to realize the circulation of secondary steam, and the tube cavity of the intermediate effect heat exchange tube of the last intermediate effect evaporator is connected with the inner cavity of the previous intermediate effect evaporator to realize the circulation of secondary steam;

[0015] The connection of any intermediate effect evaporator located between the front end and the rear end is as follows: the inner cavity of the designated intermediate effect evaporator is connected with the inner cavity of the previous intermediate effect evaporator to realize the circulation of the original liquid, the inner cavity of the designated intermediate effect evaporator is connected with the inner cavity of the next intermediate effect evaporator to realize the circulation of the original liquid, the lumen of the intermediate effect heat exchange tube of the designated intermediate effect evaporator is connected with the inner cavity of the previous intermediate effect evaporator to realize the circulation of secondary steam, and the inner cavity of the designated intermediate effect evaporator is connected with the lumen of the intermediate effect heat exchange tube of the next intermediate effect evaporator to realize the circulation of secondary steam.

[0016] A further technical solution of the utility model is: it also includes a vacuum component; the vacuum component includes a condenser, a gas-liquid separator and a vacuum pump connected in sequence from front to back; the condenser is connected to the inner cavity of the last-effect evaporator.

[0017] A further technical solution of the utility model is that the last-effect heat exchange tube, the first-effect heat exchange tube and the intermediate-effect heat exchange tube are all spiral heat exchange coils, the two ends of the last-effect heat exchange tube are respectively extended outside the last-effect evaporator, the two ends of the first-effect heat exchange tube are respectively extended outside the first-effect evaporator, and the two ends of the intermediate-effect heat exchange tube are respectively extended outside the intermediate-effect evaporator.

[0018] A further technical solution of the utility model is that the heating source is saturated steam or heat transfer oil above 100°C.

[0019] A further technical solution of the utility model is that a stirrer is arranged in the inner cavity of the last effect evaporator, the first effect evaporator or the intermediate effect evaporator.

[0020] Compared with the prior art, the utility model has the following advantages:

[0021] Based on the existing evaporator integrating two heat exchange structures, the low-concentration external heat exchanger (tube heat exchanger or plate heat exchanger) is replaced with an internal heat exchanger (coil heat exchanger). The heat exchange tube does not pass the liquid but only the heating medium (saturated steam or heat transfer oil above 100°C), thereby preventing calcium sulfate and the main product sulfate mixed crystals from clogging the inner hole of the heat exchange tube of the external heat exchanger. During the evaporation process, if calcium sulfate and the main product sulfate mixed crystals are produced, they will adhere to the outer wall of the heat exchange tube. During the operation, due to the large temperature change of the heat exchange tube, the scale will be brittle and cracked under the action of thermal expansion and contraction, and then dissolved or fell off under the scouring and erosion of the liquid, realizing automatic descaling.

[0022] The utility model is further described below in conjunction with the figures and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of Example 1;

[0024] Figure 2 It is a structural schematic diagram of Example 2;

[0025] Figure 3 It is a structural schematic diagram of Example 3;

[0026] Figure 4 This is a schematic diagram of the structure of Example 4. DETAILED DESCRIPTION Example 1

[0027] like Figure 1 As shown, the multi-effect evaporator suitable for crystal scaling includes a last-effect component, a first-effect component, a heating source 4 and a raw liquid source 5.

[0028] The last-effect component includes a last-effect evaporator 1 (a group of last-effect components includes only one last-effect evaporator), and a built-in heat exchanger is arranged in the inner cavity of the last-effect evaporator 1. The built-in heat exchanger includes a last-effect heat exchange tube 11. The last-effect heat exchange tube 11 is a spiral heat exchange coil, and the front and rear ends of the last-effect heat exchange tube 11 both extend outside the last-effect evaporator 1.

[0029] The first-effect assembly includes a first-effect evaporator 3 (a group of first-effect assemblies includes only one first-effect evaporator), and a first-effect heat exchange tube 31 is arranged in the inner cavity of the first-effect evaporator 3. The first-effect heat exchange tube 31 is a spiral heat exchange coil, and the front and rear ends of the first-effect heat exchange tube 31 are extended outside the first-effect evaporator 3. The inner cavity of the first-effect evaporator 3 is connected with the inner cavity of the last-effect evaporator 1 through a pipeline with a delivery pump, so as to realize the delivery of feed liquid from the first-effect evaporator 3 to the last-effect evaporator 1. The inner cavity of the first-effect evaporator 3 is connected with the tube cavity (front end) of the last-effect heat exchange tube 11 through a pipeline, so as to realize the secondary steam generated by the first-effect evaporator 3 entering the last-effect heat exchange tube 11.

[0030] The heating source 4 is in communication with the tube cavity (front end) of the first-effect heat exchange tube 31 , and the heating source 4 is saturated steam. The raw liquid source 5 is in communication with the inner cavity of the first-effect evaporator 3 .

[0031] Preferably, it further comprises a vacuum assembly. The vacuum assembly comprises a condenser 61, a gas-liquid separator 62 and a vacuum pump 63 which are sequentially connected from front to back. The condenser 61 is communicated with the inner cavity of the last-effect evaporator 1.

[0032] Preferably, a stirrer is provided in the inner cavity of the last-effect evaporator 1 and the first-effect evaporator 3 .

[0033] Special note: Example 1 is a two-effect co-current, where two effects are two effect levels, and co-current means that the flow direction of the raw liquid is consistent with the flow direction of the steam (the flow directions of both are first-effect evaporator 3 → last-effect evaporator 1). Example 2

[0034] like Figure 2 As shown, the difference between this embodiment and embodiment 1 is that the raw liquid source 5 is connected to the inner cavity of the last effect evaporator 1 through a pipeline. The inner cavity of the first effect evaporator 3 is connected to the inner cavity of the last effect evaporator 1 through a pipeline with a delivery pump, so as to realize the delivery of the feed liquid from the last effect evaporator 1 to the first effect evaporator 3.

[0035] Special note: Example 1 is a two-effect countercurrent, where two effects are two effect stages, and countercurrent means that the flow direction of the raw liquid is opposite to the flow direction of the steam (the flow direction of the raw liquid is the last effect evaporator 1 → the first effect evaporator 3, and the flow direction of the steam is the first effect evaporator → the last effect evaporator). Example 3

[0036] like Figure 3As shown, the difference between this embodiment and embodiment 1 is that it is suitable for a multi-effect evaporator with crystal scaling, and also includes an intermediate effect component. The intermediate effect component is installed between the first effect component and the last effect component. The number of intermediate effect components is one group. The intermediate effect component includes an intermediate effect evaporator 2 (a group of intermediate effect components has only one intermediate effect evaporator), and an intermediate effect heat exchange tube 21 is provided in the inner cavity of the intermediate effect evaporator 2. The intermediate effect heat exchange tube 21 is a spiral heat exchange coil, and the front and rear ends of the intermediate effect heat exchange tube 21 both extend outside the intermediate effect evaporator 2. The inner cavity of the intermediate effect evaporator 2 is connected with the inner cavity of the first effect evaporator 3 through a pipeline with a delivery pump to realize the delivery of feed liquid from the first effect evaporator 3 to the intermediate effect evaporator 2, the inner cavity of the intermediate effect evaporator 2 is connected with the tube cavity (front end) of the final effect heat exchange tube 11 through a pipeline to realize the secondary steam generated by the intermediate effect evaporator 2 entering the final effect heat exchange tube 11, the inner cavity of the intermediate effect evaporator 2 is connected with the inner cavity of the final effect evaporator 1 through a pipeline with a delivery pump to realize the delivery of feed liquid from the intermediate effect evaporator 2 to the final effect evaporator 1, and the tube cavity (front end) of the intermediate effect heat exchange tube 21 is connected with the inner cavity of the first effect evaporator 3 through a pipeline to realize the secondary steam generated by the first effect evaporator 3 entering the intermediate effect heat exchange tube 21.

[0037] Preferably, a stirrer is provided in the inner cavity of the intermediate effect evaporator 3 .

[0038] Special note: Example 3 is a three-effect co-current, three-effect means three effect levels, and co-current means that the flow direction of the raw liquid is consistent with the flow direction of the steam (the flow directions of both are first-effect evaporator 3 → intermediate-effect evaporator 2 → final-effect evaporator 1). Example 4

[0039] like Figure 4 As shown, the difference between this embodiment and embodiment 3 is that the raw liquid source 5 is connected to the inner cavity of the last effect evaporator 1 through a pipeline. The inner cavity of the intermediate effect evaporator 2 is connected to the inner cavity of the first effect evaporator 3 through a pipeline with a delivery pump, so that the feed liquid is transported from the intermediate effect evaporator 2 to the first effect evaporator 3. The inner cavity of the intermediate effect evaporator 2 is connected to the inner cavity of the last effect evaporator 1 through a pipeline with a delivery pump, so that the feed liquid is transported from the last effect evaporator 1 to the intermediate effect evaporator 2.

[0040] Special note: Example 4 is a three-effect countercurrent, three effects means three effect levels, and countercurrent means that the flow direction of the raw liquid is opposite to the flow direction of the steam (the flow direction of the raw liquid is the last effect evaporator 1→intermediate effect evaporator 2→first effect evaporator 3, and the flow direction of the steam is the first effect evaporator 3→intermediate effect evaporator 2→last effect evaporator 1). Example 5

[0041] This embodiment is not shown in the figure. Compared with the embodiment 1, the only difference between this embodiment and the embodiment 1 is that it is suitable for a multi-effect evaporator with crystal scaling, and also includes an intermediate effect component. Multiple groups of intermediate effect components are connected in sequence from front to back and installed between the first effect component and the last effect component. The intermediate effect component includes an intermediate effect evaporator (a group of intermediate effect components has only one intermediate effect evaporator), and an intermediate effect heat exchange tube is provided in the inner cavity of the intermediate effect evaporator. The intermediate effect heat exchange tube is a spiral heat exchange coil, and the front and rear ends of the intermediate effect heat exchange tube both extend outside the intermediate effect evaporator.

[0042] The inner cavity of the front-end intermediate effect evaporator is connected to the inner cavity of the first-effect evaporator through a pipeline with a delivery pump to realize the delivery of feed liquid from the first-effect evaporator to the front-end intermediate effect evaporator. The inner cavity of the front-end intermediate effect evaporator is connected to the inner cavity of the intermediate effect evaporator of the next level through a pipeline with a delivery pump to realize the delivery of feed liquid from the front-end intermediate effect evaporator to the intermediate effect evaporator of the next level ("it" refers to the front-end intermediate effect evaporator). The tube cavity (front end) of the intermediate effect heat exchange tube of the front-end intermediate effect evaporator is connected to the inner cavity of the first-effect evaporator through a pipeline to realize the secondary steam generated by the first-effect evaporator entering the intermediate effect heat exchange tube of the front-end intermediate effect evaporator. The inner cavity of the front-end intermediate effect evaporator is connected to the tube cavity (front end) of the intermediate effect heat exchange tube of the next level intermediate effect evaporator through a pipeline to realize the secondary steam generated by the front-end intermediate effect evaporator entering the intermediate effect heat exchange tube of the next level intermediate effect evaporator.

[0043] The inner cavity of the last intermediate effect evaporator is connected with the inner cavity of the last effect evaporator through a pipeline with a delivery pump to realize the delivery of feed liquid from the last intermediate effect evaporator to the last effect evaporator. The inner cavity of the last intermediate effect evaporator is connected with the inner cavity of the previous intermediate effect evaporator through a pipeline with a delivery pump to realize the delivery of feed liquid from the previous intermediate effect evaporator ("it" refers to the last intermediate effect evaporator) to the last intermediate effect evaporator. The inner cavity of the last intermediate effect evaporator is connected with the tube cavity (front end) of the last effect heat exchange tube of the last effect evaporator through a pipeline to realize the secondary steam generated by the last intermediate effect evaporator entering the last effect evaporator. The tube cavity (front end) of the intermediate effect heat exchange tube of the last intermediate effect evaporator is connected with the inner cavity of the previous intermediate effect evaporator through a pipeline to realize the secondary steam of the previous intermediate effect evaporator ("it" refers to the last intermediate effect evaporator) entering the last intermediate effect evaporator.

[0044] The connection of any intermediate effect evaporator located between the front end and the rear end is as follows: the inner cavity of the designated intermediate effect evaporator is connected to the inner cavity of the intermediate effect evaporator of the previous stage through a pipeline with a delivery pump, so that the feed liquid is transported from the intermediate effect evaporator of the previous stage ("it" refers to the currently designated intermediate effect evaporator) to the currently designated intermediate effect evaporator. The inner cavity of the designated intermediate effect evaporator is connected to the inner cavity of the intermediate effect evaporator of the next stage through a pipeline with a delivery pump, so that the feed liquid is transported from the currently designated intermediate effect evaporator to the intermediate effect evaporator of the next stage ("it" refers to the currently designated intermediate effect evaporator). The tube cavity (front end) of the intermediate effect heat exchange tube of the designated intermediate effect evaporator is connected to the inner cavity of the intermediate effect evaporator of the previous stage through a pipeline, so that the secondary steam generated by the intermediate effect evaporator of the previous stage ("it" refers to the currently designated intermediate effect evaporator) enters the intermediate effect heat exchange tube of the currently designated intermediate effect evaporator. The inner cavity of the designated intermediate effect evaporator is connected to the tube cavity of the intermediate effect heat exchange tube of the subsequent intermediate effect evaporator through a pipeline, so that the secondary steam generated by the current designated intermediate effect evaporator can enter the subsequent intermediate effect evaporator ("its" refers to the current designated intermediate effect evaporator).

[0045] Special note: Example 5 is a four-effect or higher downstream flow, where four-effect or higher means the effect level is ≥4, and downstream means that the flow direction of the raw liquid is consistent with the flow direction of the steam (the flow directions of both are first-effect evaporator → intermediate-effect evaporators of various levels connected from front to back → last-effect evaporator). Example 6

[0046] This embodiment is not shown in the figure. Compared with embodiment 5, the only difference between this embodiment and embodiment 5 is that the raw liquid source is connected to the inner cavity of the last effect evaporator through a pipeline. The inner cavity of the front-end intermediate effect evaporator is connected to the inner cavity of the first effect evaporator through a pipeline with a delivery pump to realize the delivery of the feed liquid from the front-end intermediate effect evaporator to the first effect evaporator. The inner cavity of the front-end intermediate effect evaporator is connected to the inner cavity of the next intermediate effect evaporator through a pipeline with a delivery pump to realize the delivery of the feed liquid from the next intermediate effect evaporator ("it" refers to the front-end intermediate effect evaporator) to the front-end intermediate effect evaporator.

[0047] Briefly describe the working principle of the utility model: different concentrations of liquid flow between each stage of the effect body, each stage of the effect body adopts an evaporator structure of a built-in heat exchange coil that is easy to clean and scale, and scale will only occur on the outer wall of the heat exchange coil.

[0048] During the evaporation process, if calcium sulfate and main product sulfate mixed crystals are produced, they will adhere to the outer wall of the heat exchange tube. During operation, due to the large temperature changes in the heat exchange tube, the scale will become brittle due to thermal expansion and contraction, and then dissolve or fall off under the scouring and erosion of the feed liquid, achieving automatic scale removal.

Claims

1. Applicable to multiple-effect evaporators with crystal scaling, characterized by: It includes a final effect component, a first effect component, a heating source and a raw liquid source; The final effect component includes a final effect evaporator, and a built-in heat exchanger is arranged in the inner cavity of the final effect evaporator, and the built-in heat exchanger includes a final effect heat exchange tube; The first-effect assembly includes a first-effect evaporator; a first-effect heat exchange tube is arranged in the inner cavity of the first-effect evaporator, the inner cavity of the first-effect evaporator is directly or indirectly connected with the inner cavity of the last-effect evaporator, and the inner cavity of the first-effect evaporator is directly or indirectly connected with the tube cavity of the last-effect heat exchange tube; The heating source is communicated with the tube cavity of the first-effect heat exchange tube; the raw liquid source is communicated with the inner cavity of the last-effect evaporator or the inner cavity of the first-effect evaporator.

2. The multiple-effect evaporator suitable for crystal scaling as claimed in claim 1, characterized in that: It also includes intermediate effect components; The intermediate effect component is installed between the first effect component and the last effect component; The number of intermediate effect components is one group; the intermediate effect component includes an intermediate effect evaporator, and an intermediate effect heat exchange tube is arranged in the inner cavity of the intermediate effect evaporator; The inner cavity of the intermediate effect evaporator is connected with the inner cavity of the first effect evaporator to realize the flow of feed liquid, the inner cavity of the intermediate effect evaporator is connected with the tube cavity of the last effect heat exchange tube to realize the secondary steam flow, the inner cavity of the intermediate effect evaporator is connected with the inner cavity of the last effect evaporator to realize the flow of feed liquid, and the tube cavity of the intermediate effect heat exchange tube is connected with the inner cavity of the first effect evaporator to realize the secondary steam flow.

3. The multiple-effect evaporator suitable for crystal scaling as claimed in claim 1, characterized in that: It also includes an intermediate effect component; multiple groups of intermediate effect components are connected in sequence from front to back and installed between the first effect component and the last effect component; the intermediate effect component includes an intermediate effect evaporator, and an intermediate effect heat exchange tube is arranged in the inner cavity of the intermediate effect evaporator; The inner cavity of the front-end intermediate effect evaporator is connected with the inner cavity of the first-effect evaporator to realize the flow of feed and liquid, the inner cavity of the front-end intermediate effect evaporator is connected with the inner cavity of the next intermediate effect evaporator to realize the flow of feed and liquid, the lumen of the intermediate effect heat exchange tube of the front-end intermediate effect evaporator is connected with the inner cavity of the first-effect evaporator to realize the flow of secondary steam, and the inner cavity of the front-end intermediate effect evaporator is connected with the lumen of the intermediate effect heat exchange tube of the next intermediate effect evaporator to realize the flow of secondary steam; The inner cavity of the last intermediate effect evaporator is connected with the inner cavity of the last effect evaporator to realize the flow of feed liquid, the inner cavity of the last intermediate effect evaporator is connected with the inner cavity of the previous intermediate effect evaporator to realize the flow of feed liquid, the inner cavity of the last intermediate effect evaporator is connected with the tube cavity of the last effect heat exchange tube of the last effect evaporator to realize the secondary steam flow, and the tube cavity of the intermediate effect heat exchange tube of the last intermediate effect evaporator is connected with the inner cavity of the previous intermediate effect evaporator to realize the secondary steam flow; The connection of any intermediate effect evaporator located between the front end and the rear end is as follows: the inner cavity of the designated intermediate effect evaporator is connected with the inner cavity of the previous intermediate effect evaporator to realize the flow of feed and liquid, the inner cavity of the designated intermediate effect evaporator is connected with the inner cavity of the next intermediate effect evaporator to realize the flow of feed and liquid, the lumen of the intermediate effect heat exchange tube of the designated intermediate effect evaporator is connected with the inner cavity of the previous intermediate effect evaporator to realize the secondary steam flow, and the inner cavity of the designated intermediate effect evaporator is connected with the lumen of the intermediate effect heat exchange tube of the next intermediate effect evaporator to realize the secondary steam flow.

4. The multiple-effect evaporator suitable for crystal scaling as claimed in claim 2 or 3, characterized in that: It also includes a vacuum component; the vacuum component includes a condenser, a gas-liquid separator and a vacuum pump which are connected in sequence from front to back; the condenser is communicated with the inner cavity of the last-effect evaporator.

5. The multiple-effect evaporator suitable for crystal scaling as claimed in claim 4, characterized in that: The last-effect heat exchange tube, the first-effect heat exchange tube and the intermediate-effect heat exchange tube are all spiral heat exchange coils. The two ends of the last-effect heat exchange tube extend out of the last-effect evaporator, the two ends of the first-effect heat exchange tube extend out of the first-effect evaporator, and the two ends of the intermediate-effect heat exchange tube extend out of the intermediate-effect evaporator.

6. The multiple-effect evaporator suitable for crystal scaling as claimed in claim 5, characterized in that: The heating source is saturated steam.

7. The multiple-effect evaporator suitable for crystal scaling as claimed in claim 6, characterized in that: A stirrer is provided in the inner cavity of the last effect evaporator, the first effect evaporator or the intermediate effect evaporator.

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