A production process for scaling on the heating plate of a falling film evaporator

Abstract

The present invention belongs to the technical field of alkali recovery, and in particular, to a production process for scale formation on the heating plates of a falling film evaporator. In view of the problem that as the black liquor continues to evaporate in the II-effect falling film evaporator, inorganic salts in the black liquor will precipitate in the form of crystals, and a part of the inorganic salts will adsorb on the heating plate sheets to form scale. As time goes by, the scale gradually thickens, resulting in a gradual increase in the thermal resistance, thereby reducing the heat exchange efficiency, increasing the temperature difference of the evaporator, and ultimately destroying the stable operation of the entire evaporation system. The following solution is proposed. It includes a lifting and dissolving mechanism, which is arranged between the III-effect falling film evaporator and the II-effect falling film evaporator to send the black material to be fed into the III-effect falling film evaporator into the II-effect falling film evaporator; a reflux mechanism, which is arranged between the II-effect falling film evaporator and the III-effect falling film evaporator, and can effectively dissolve the dirt on the heating plates of the II-effect falling film evaporator.

Description

Technical Field

[0001] The present invention relates to the technical field of alkali recovery, and particularly to a production process for scale formation on the heating plates of a falling film evaporator. Background Art

[0002] The working principle of a falling film evaporator is to add a certain material at the top of the material chamber. After being distributed by the liquid distributor, it flows downward in a film shape. Heating can vaporize it, and the vaporized gas flows out through the heating tubes together with the liquid. By separating the liquid and the gas, concentrated liquid can be obtained. The working process of the falling film evaporator is particularly important. The residence time of the material in the evaporator is very short, but the heat transfer coefficient is relatively high. Therefore, most heat-sensitive materials are very suitable for the falling film evaporator.

[0003] In a VI-effect plate falling film evaporation system, the normal flow of black liquor is VI-effect → V-effect → IV-effect → III-effect falling film evaporator → II-effect falling film evaporator → I-effect falling film evaporator. As the number of effects progresses, the concentration of black liquor in the effect gradually increases. When the black liquor enters the II-effect falling film evaporator, its concentration has basically reached the crystallization points of Na2CO3, Na2SO4, and calcium inorganic substances. As the black liquor continues to evaporate in the II-effect falling film evaporator, the inorganic salts in the black liquor will precipitate in the form of crystals. Part of the inorganic salts will adsorb on the heating plate sheets to form scale. As time goes by, the scale gradually thickens, resulting in a gradual increase in the thermal resistance, thereby reducing the heat exchange efficiency, increasing the temperature difference of the evaporator, and ultimately destroying the stable operation of the entire evaporation system, and it is necessary to stop the machine to clean the dirt on the heating plates of the evaporator.

[0004] In view of the above problems, the present invention document proposes a production process for scale formation on the heating plates of a falling film evaporator. Summary of the Invention

[0005] The present invention provides a production process for scale formation on the heating plates of a falling film evaporator, which solves the drawbacks in the prior art that as the black liquor continues to evaporate in the II-effect falling film evaporator, the inorganic salts in the black liquor will precipitate in the form of crystals, part of the inorganic salts will adsorb on the heating plate sheets to form scale, as time goes by, the scale gradually thickens, resulting in a gradual increase in the thermal resistance, thereby reducing the heat exchange efficiency, increasing the temperature difference of the evaporator, and ultimately destroying the stable operation of the entire evaporation system.

[0006] The present invention provides the following technical solutions:

[0007] A production process for scale formation on the heating plate of a falling film evaporator, including a first-effect falling film evaporator, a second-effect falling film evaporator, a third-effect falling film evaporator, a fourth-effect falling film evaporator, a fifth-effect falling film evaporator, and a sixth-effect falling film evaporator; the first-effect falling film evaporator, the second-effect falling film evaporator, the third-effect falling film evaporator, the fourth-effect falling film evaporator, the fifth-effect falling film evaporator, and the sixth-effect falling film evaporator are respectively used for falling film evaporation in the first to sixth effects; multiple groups of connected feeding mechanisms, and multiple groups of connected feeding mechanisms are respectively arranged on the first-effect falling film evaporator, the second-effect falling film evaporator, the third-effect falling film evaporator, the fourth-effect falling film evaporator, the fifth-effect falling film evaporator, and the sixth-effect falling film evaporator to connect the first-effect falling film evaporator, the second-effect falling film evaporator, the third-effect falling film evaporator, the fourth-effect falling film evaporator, the fifth-effect falling film evaporator, and the sixth-effect falling film evaporator; a lifting and dissolving mechanism, which is arranged between the third-effect falling film evaporator and the second-effect falling film evaporator to send the black material to be fed into the third-effect falling film evaporator into the second-effect falling film evaporator; a reflux mechanism, which is arranged between the second-effect falling film evaporator and the third-effect falling film evaporator; an intermittent discharging mechanism, which is arranged between the first-effect falling film evaporator and the third-effect falling film evaporator.

[0008] In a possible design, two fixing rings are fixedly connected to the surfaces of the first-effect falling film evaporator, the second-effect falling film evaporator, the third-effect falling film evaporator, the fourth-effect falling film evaporator, the fifth-effect falling film evaporator, and the sixth-effect falling film evaporator. Two fixing frames are fixedly connected to the surfaces of multiple fixing rings. Both ends of the two fixing frames are fixedly connected with support frames, and the bottom ends of the two support frames are fixedly connected with fixing brackets.

[0009] In a possible design, an anti-slip pad is provided at the bottom end of the fixing bracket.

[0010] In a possible design, each group of the connected feeding mechanisms includes a first discharge pipe connected to the feed inlet of the first-effect falling film evaporator. The bottom end of the third-effect falling film evaporator is fixedly connected with a first feeding pipe connected to the discharge outlet of the third-effect falling film evaporator. A fixing plate is fixedly connected between the two support frames. A first water pump is fixedly connected to the upper side of the fixing plate. An inlet and an outlet are respectively arranged on both sides of the first water pump. The inlet is connected to the first feeding pipe, and the outlet is connected to the first discharge pipe.

[0011] In a possible design, a semi-concentrated black liquor storage tank is fixedly connected inside the fixing plate. The semi-concentrated black liquor storage tank is connected to the discharge outlet of the fourth-effect falling film evaporator. A second water pump is fixedly connected to the top end of the fixing plate. A second discharge pipe and a second feeding pipe are respectively fixedly connected to both sides of the second water pump. The second feeding pipe is connected to the semi-concentrated black liquor storage tank, and the second discharge pipe is connected to the feed inlet of the third-effect falling film evaporator.

[0012] In a possible design, the lifting and dissolving mechanism includes a first connecting pipeline. Two ends of the first connecting pipeline are respectively fixedly connected to the surfaces of a first discharge pipe and a second discharge pipe between a second-effect falling-film evaporator and a third-effect falling-film evaporator. The first connecting pipeline is respectively communicated with the first discharge pipe and the second discharge pipe between the second-effect falling-film evaporator and the third-effect falling-film evaporator. A first valve is arranged in the second discharge pipe, and the first valve is arranged after the second discharge pipe is communicated with the first connecting pipeline. A fourth valve is arranged in the first connecting pipeline, and a second valve is arranged in the first discharge pipe between the second-effect falling-film evaporator and the third-effect falling-film evaporator.

[0013] In a possible design, the reflux mechanism includes a third connecting pipeline. The third connecting pipeline is respectively fixedly connected to the circumferential surfaces of a first discharge pipe between a first-effect falling-film evaporator and a second-effect falling-film evaporator and the circumferential surface of a feed inlet of a third-effect falling-film evaporator. The third connecting pipeline is respectively communicated with the first discharge pipe between the first-effect falling-film evaporator and the second-effect falling-film evaporator and the feed inlet of the third-effect falling-film evaporator. A sixth valve is arranged in the third connecting pipeline, and a third valve is arranged in the first discharge pipe between the first-effect falling-film evaporator and the second-effect falling-film evaporator. The third valve is arranged after the first discharge pipe is communicated with the third connecting pipeline.

[0014] In a possible design, the interval discharging mechanism includes a second connecting pipeline. Two ends of the second connecting pipeline are respectively fixedly connected to the circumferential surfaces of two first discharge pipes on both sides of a second-effect falling-film evaporator. The second connecting pipeline is respectively communicated with the two first discharge pipes. A fifth valve is arranged in the second connecting pipeline.

[0015] It should be understood that the above general description and the following detailed description are only exemplary and do not limit the present invention.

[0016] In the present invention, by designing a spare pipeline and corresponding valves, during the switching process, the first valve and the second valve are closed and the fourth valve is opened, so that the black liquor originally entering the third-effect falling-film evaporator first enters the second-effect falling-film evaporator. Since the concentration of this part of the black liquor is lower than the crystallization points of Na2CO3, Na2SO4 and calcium inorganic substances, the dirt on the heating plate of the second-effect falling-film evaporator is gradually dissolved. The third valve is closed and the sixth valve is opened, so that the black liquor coming out of the second-effect falling-film evaporator enters the third-effect falling-film evaporator through the spare pipeline again. The fifth valve is opened to allow the black liquor of the third-effect falling-film evaporator to enter the first-effect falling-film evaporator along the spare pipeline, forming a process flow of the second-effect falling-film evaporator → the third-effect falling-film evaporator → the first-effect falling-film evaporator;

[0017] In the present invention, in the black liquor evaporation system, since the concentration of black liquor in the II-effect falling film evaporator has basically reached the crystallization points of Na2CO3, Na2SO4 and calcium inorganic substances, after normal operation for a period of time, due to the crystallization and precipitation of salts in the black liquor, scale forms on the heating plate surface of the II-effect falling film evaporator and gradually thickens, resulting in a decrease in heat exchange efficiency. It is observed that the temperature difference of the II-effect falling film evaporator reaches 8 - 9 °C, exceeding the normal range. At this time, through process switching, the process of "III-effect falling film evaporator → II-effect falling film evaporator → I-effect falling film evaporator" is switched to the process of "II-effect falling film evaporator → III-effect falling film evaporator → I-effect falling film evaporator". After operating in this mode for 2 days, the temperature difference of the II-effect falling film evaporator drops back to 4 - 5 °C. At this time, the process of the evaporation system is switched back to the normal process of "III-effect falling film evaporator → II-effect falling film evaporator → I-effect falling film evaporator" to continue production. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the front three-dimensional view of a production process for scale formation on the heating plate of a falling film evaporator provided by an embodiment of the present invention;

[0019] Figure 2 is the front view three-dimensional view of a production process for scale formation on the heating plate of a falling film evaporator provided by an embodiment of the present invention;

[0020] Figure 3 is the first partial three-dimensional view of a production process for scale formation on the heating plate of a falling film evaporator provided by an embodiment of the present invention;

[0021] Figure 4 is the second partial three-dimensional view of a production process for scale formation on the heating plate of a falling film evaporator provided by an embodiment of the present invention;

[0022] Figure 5 is the third partial three-dimensional view of a production process for scale formation on the heating plate of a falling film evaporator provided by an embodiment of the present invention;

[0023] Figure 6 is the process flow diagram of a production process for scale formation on the heating plate of a falling film evaporator provided by an embodiment of the present invention.

[0024] Reference Numerals:

[0025] 1. I-effect falling film evaporator; 11. II-effect falling film evaporator; 12. III-effect falling film evaporator; 13. IV-effect falling film evaporator; 14. V-effect falling film evaporator; 15. VI-effect falling film evaporator; 2. Support frame; 3. Fixed support; 4. Fixing frame; 5. Fixed ring; 6. Semi-concentrated black liquor storage tank; 7. First water pump; 71. First discharge pipe; 72. First feeding pipe; 8. No. 3 valve; 81. No. 2 valve; 82. No. 6 valve; 83. No. 1 valve; 84. No. 4 valve; 85. No. 5 valve; 9. First connecting pipeline; 91. Second connecting pipeline; 92. Third connecting pipeline; 10. Second water pump; 101. Second discharge pipe; 102. Second feeding pipe; 16. Fixed plate. Detailed implementation manners

[0026] The embodiments of the present invention will be described below with reference to the accompanying drawings in the embodiments of the present invention.

[0027] In the description of the embodiments of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "connection" and "installation" should be understood in a broad sense. For example, "connection" can be a detachable connection or a non-detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. In addition, "communication" can be a direct communication or an indirect communication through an intermediate medium. Among them, "fixing" means that they are connected to each other and the relative positional relationship after connection remains unchanged. The orientation terms mentioned in the embodiments of the present invention, such as "inside", "outside", "top", "bottom", etc., are only for reference to the direction of the accompanying drawings. Therefore, the orientation terms used are for better and clearer description and understanding of the embodiments of the present invention, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation to the embodiments of the present invention.

[0028] In the embodiments of the present invention, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features.

[0029] In the embodiments of the present invention, "and / or" is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after.

[0030] References to "one embodiment" or "some embodiments" or the like described in this specification mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in one or more embodiments of the present invention. Thus, the phrases "in one embodiment," "in some embodiments," "in other some embodiments," "in still other embodiments," etc., which appear in different places in this specification, are not necessarily all referring to the same embodiment, but mean "one or more but not all of the embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and their variants all mean "including but not limited to," unless otherwise specifically emphasized. Embodiment 1

[0031] Refer to Figures 1-6 , a production process for scale formation on the heating plate of a falling film evaporator, comprising a first-effect falling film evaporator 1, a second-effect falling film evaporator 11, a third-effect falling film evaporator 12, a fourth-effect falling film evaporator 13, a fifth-effect falling film evaporator 14, and a sixth-effect falling film evaporator 15; the first-effect falling film evaporator 1, the second-effect falling film evaporator 11, the third-effect falling film evaporator 12, the fourth-effect falling film evaporator 13, the fifth-effect falling film evaporator 14, and the sixth-effect falling film evaporator 15 are respectively used for performing falling film evaporation in the first to sixth effects; a plurality of groups of connected feeding mechanisms, and the plurality of groups of connected feeding mechanisms are respectively arranged on the first-effect falling film evaporator 1, the second-effect falling film evaporator 11, the third-effect falling film evaporator 12, the fourth-effect falling film evaporator 13, the fifth-effect falling film evaporator 14, and the sixth-effect falling film evaporator 15 to connect the first-effect falling film evaporator 1, the second-effect falling film evaporator 11, the third-effect falling film evaporator 12, the fourth-effect falling film evaporator 13, the fifth-effect falling film evaporator 14, and the sixth-effect falling film evaporator 15; a lifting and dissolving mechanism, which is arranged between the third-effect falling film evaporator 12 and the second-effect falling film evaporator 11 to send the black material to be fed into the third-effect falling film evaporator 12 into the second-effect falling film evaporator 11; a reflux mechanism, which is arranged between the second-effect falling film evaporator 11 and the third-effect falling film evaporator 12; and an intermittent discharging mechanism, which is arranged between the first-effect falling film evaporator 1 and the third-effect falling film evaporator 12.

[0032] In the black liquor evaporation system, since the concentration of black liquor in the second-effect falling film evaporator has basically reached the crystallization points of Na2CO3, Na2SO4, and calcium inorganic substances, after normal operation for a period of time, due to the crystallization and precipitation of salts in the black liquor, scale forms on the heating plate surface of the second-effect falling film evaporator and gradually thickens, resulting in a decrease in heat exchange efficiency. It is observed that the temperature difference of the second-effect falling film evaporator reaches 8 - 9 °C, exceeding the normal range. At this time, through process switching, the process of "III-effect falling film evaporator → II-effect falling film evaporator → I-effect falling film evaporator" is switched to the process of "II-effect falling film evaporator → III-effect falling film evaporator → I-effect falling film evaporator". After operating in this mode for 2 days, the temperature difference of the second-effect falling film evaporator drops back to 4 - 5 °C. At this time, the process of the evaporation system is switched back to the normal process of "III-effect falling film evaporator → II-effect falling film evaporator → I-effect falling film evaporator" to continue production.

[0033] Refer to Figure 1 and Figure 2 For each set of connected feeding mechanisms, each includes a first discharge pipe 71 connected to the feed inlet of the first-effect falling film evaporator 1. The bottom end of the third-effect falling film evaporator 12 is fixedly connected to a first feeding pipe 72 connected to the discharge outlet of the third-effect falling film evaporator 12. A fixed plate 16 is fixedly connected between two support frames 2. A first water pump 7 is fixedly connected to the upper side of the fixed plate 16. Both sides of the first water pump 7 are respectively provided with a water inlet and a water outlet. The water inlet is connected to the first feeding pipe 72, and the water outlet is connected to the first discharge pipe 71.

[0034] It facilitates the step-by-step circulation among the first-effect falling film evaporator 1, the second-effect falling film evaporator 11, the third-effect falling film evaporator 12, the fourth-effect falling film evaporator 13, the fifth-effect falling film evaporator 14, and the sixth-effect falling film evaporator 15.

[0035] Refer to Figures 1-6 For the lifting and dissolving mechanism, refer to Figures 1-6 . The lifting and dissolving mechanism includes a first connecting pipeline 9. The two ends of the first connecting pipeline 9 are respectively fixedly connected to the surfaces of the first discharge pipe 71 and the second discharge pipe 101 between the second-effect falling film evaporator 11 and the third-effect falling film evaporator 12. The first connecting pipeline 9 is respectively connected to the first discharge pipe 71 and the second discharge pipe 101 between the second-effect falling film evaporator 11 and the third-effect falling film evaporator 12. A first valve 83 is provided in the second discharge pipe 101, and the first valve 83 is arranged after the second discharge pipe 101 is connected to the first connecting pipeline 9. A fourth valve 84 is provided in the first connecting pipeline 9. A second valve 81 is provided in the first discharge pipe 71 between the second-effect falling film evaporator 11 and the third-effect falling film evaporator 12.

[0036] The above technical solution can achieve the following: By designing a spare pipeline and corresponding valves, when switching, close the first valve 83 and the second valve 81 and open the fourth valve 84, so that the black liquor originally entering the III-effect falling film evaporator first enters the II-effect falling film evaporator. Since the concentration of this part of the black liquor is lower than the crystallization points of Na2CO3, Na2SO4 and calcium inorganic substances, the dirt on the heating plate of the II-effect falling film evaporator is gradually dissolved.

[0037] Refer to Figures 1-6 , the reflux mechanism includes a third connecting pipeline 92. The third connecting pipeline 92 is fixedly connected to the circumferential surface of the first discharge pipe 71 between the I-effect falling film evaporator 1 and the II-effect falling film evaporator 11 and the circumferential surface of the feed inlet of the III-effect falling film evaporator 12 respectively. The third connecting pipeline 92 is respectively communicated with the first discharge pipe 71 between the I-effect falling film evaporator 1 and the II-effect falling film evaporator 11 and the feed inlet of the III-effect falling film evaporator 12. A sixth valve 82 is provided in the third connecting pipeline 92, and a third valve 8 is provided in the first discharge pipe 71 between the I-effect falling film evaporator 1 and the II-effect falling film evaporator 11. The third valve 8 is arranged after the first discharge pipe 71 and the third connecting pipeline 92 are communicated.

[0038] Close the third valve 8 and open the sixth valve 82, so that the black liquor coming out of the II-effect falling film evaporator enters the III-effect falling film evaporator through the spare pipeline again.

[0039] Refer to Figures 1-6 , the intermittent discharge mechanism includes a second connecting pipeline 91. The two ends of the second connecting pipeline 91 are fixedly connected to the circumferential surfaces of the two first discharge pipes 71 on both sides of the II-effect falling film evaporator 11 respectively. The second connecting pipeline 91 is respectively communicated with the two first discharge pipes 71, and a fifth valve 85 is provided in the second connecting pipeline 91.

[0040] Open the fifth valve 85 to allow the black liquor of the III-effect falling film evaporator to flow into the I-effect falling film evaporator along the spare pipeline, forming a process flow of II-effect falling film evaporator → III-effect falling film evaporator → I-effect falling film evaporator. Embodiment 2

[0041] Refer to Figures 1-6, A production process for scale formation on the heating plate of a falling film evaporator, including a first-effect falling film evaporator 1, a second-effect falling film evaporator 11, a third-effect falling film evaporator 12, a fourth-effect falling film evaporator 13, a fifth-effect falling film evaporator 14, and a sixth-effect falling film evaporator 15; the first-effect falling film evaporator 1, the second-effect falling film evaporator 11, the third-effect falling film evaporator 12, the fourth-effect falling film evaporator 13, the fifth-effect falling film evaporator 14, and the sixth-effect falling film evaporator 15 are respectively used for falling film evaporation in the first to sixth effects; multiple groups of connected feeding mechanisms are respectively arranged on the first-effect falling film evaporator 1, the second-effect falling film evaporator 11, the third-effect falling film evaporator 12, the fourth-effect falling film evaporator 13, the fifth-effect falling film evaporator 14, and the sixth-effect falling film evaporator 15 to connect the first-effect falling film evaporator 1, the second-effect falling film evaporator 11, the third-effect falling film evaporator 12, the fourth-effect falling film evaporator 13, the fifth-effect falling film evaporator 14, and the sixth-effect falling film evaporator 15; a lifting and dissolving mechanism is arranged between the third-effect falling film evaporator 12 and the second-effect falling film evaporator 11 to send the black material to be fed into the third-effect falling film evaporator 12 into the second-effect falling film evaporator 11; a reflux mechanism is arranged between the second-effect falling film evaporator 11 and the third-effect falling film evaporator 12; an intermittent discharging mechanism is arranged between the first-effect falling film evaporator 1 and the third-effect falling film evaporator 12.

[0042] In the black liquor evaporation system, since the concentration of black liquor in the second-effect falling film evaporator has basically reached the crystallization points of Na2CO3, Na2SO4, and calcium inorganic substances, after normal operation for a period of time, due to the crystallization and precipitation of salts in the black liquor, scale forms on the surface of the heating plate of the second-effect falling film evaporator and gradually thickens, resulting in a decrease in heat exchange efficiency. It is observed that the temperature difference of the second-effect falling film evaporator reaches 8 - 9 °C, exceeding the normal range. At this time, through process switching, the process of "third-effect falling film evaporator → second-effect falling film evaporator → first-effect falling film evaporator" is switched to the process of "second-effect falling film evaporator → third-effect falling film evaporator → first-effect falling film evaporator". After operating in this mode for 2 days, the temperature difference of the second-effect falling film evaporator drops back to 4 - 5 °C. At this time, the process of the evaporation system is switched back to the normal process of "third-effect falling film evaporator → second-effect falling film evaporator → first-effect falling film evaporator" to continue production.

[0043] Refer to Figure 1 , Two fixing rings 5 are fixedly connected to the surfaces of the first-effect falling film evaporator 1, the second-effect falling film evaporator 11, the third-effect falling film evaporator 12, the fourth-effect falling film evaporator 13, the fifth-effect falling film evaporator 14, and the sixth-effect falling film evaporator 15. Two fixing frames 4 are fixedly connected to the surfaces of multiple fixing rings 5. Both ends of the two fixing frames 4 are fixedly connected to support frames 2, and both bottoms of the two support frames 2 are fixedly connected to fixing brackets 3.

[0044] To fix the positions of the first-effect falling-film evaporator 1, the second-effect falling-film evaporator 11, the third-effect falling-film evaporator 12, the fourth-effect falling-film evaporator 13, the fifth-effect falling-film evaporator 14, and the sixth-effect falling-film evaporator 15.

[0045] The bottom end of the fixing bracket 3 is provided with an anti-slip pad, which is not shown in the figure.

[0046] Increase the overall stability of the device.

[0047] Refer to Figure 1 and Figure 2 Each set of connected feeding mechanisms includes a first discharge pipe 71 connected to the feed inlet of the first-effect falling-film evaporator 1. The bottom end of the third-effect falling-film evaporator 12 is fixedly connected to a first feeding pipe 72 connected to the discharge outlet of the third-effect falling-film evaporator 12. A fixing plate 16 is fixedly connected between the two support frames 2. The upper side of the fixing plate 16 is fixedly connected to a first water pump 7. The two sides of the first water pump 7 are respectively provided with a water inlet and a water outlet. The water inlet is connected to the first feeding pipe 72, and the water outlet is connected to the first discharge pipe 71.

[0048] Facilitate the step-by-step circulation between the first-effect falling-film evaporator 1, the second-effect falling-film evaporator 11, the third-effect falling-film evaporator 12, the fourth-effect falling-film evaporator 13, the fifth-effect falling-film evaporator 14, and the sixth-effect falling-film evaporator 15.

[0049] Refer to Figures 1-6 As shown in, a semi-concentrated black liquor storage tank 6 is fixedly connected inside the fixing plate 16. The semi-concentrated black liquor storage tank 6 is connected to the discharge outlet of the fourth-effect falling-film evaporator 13. The top end of the fixing plate 16 is fixedly connected to a second water pump 10. The two sides of the second water pump 10 are respectively fixedly connected to a second discharge pipe 101 and a second feeding pipe 102. The second feeding pipe 102 is connected to the semi-concentrated black liquor storage tank 6, and the second discharge pipe 101 is connected to the feed inlet of the third-effect falling-film evaporator 12.

[0050] After the fourth-effect evaporation, the semi-thick black liquor is stored in the semi-concentrated black liquor storage tank 6, which can ensure that the operation of the fourth-effect to the sixth-effect is not affected when switching the third-effect falling-film evaporator to the first-effect falling-film evaporator.

[0051] Refer to Figures 1-6, the lifting and dissolving mechanism includes a first connecting pipeline 9. The two ends of the first connecting pipeline 9 are respectively fixedly connected to the surfaces of the first discharge pipe 71 and the second discharge pipe 101 between the second-effect falling film evaporator 11 and the third-effect falling film evaporator 12. The first connecting pipeline 9 is respectively communicated with the first discharge pipe 71 and the second discharge pipe 101 between the second-effect falling film evaporator 11 and the third-effect falling film evaporator 12. A first valve 83 is provided in the second discharge pipe 101, and the first valve 83 is provided after the second discharge pipe 101 is communicated with the first connecting pipeline 9. A fourth valve 84 is provided in the first connecting pipeline 9, and a second valve 81 is provided in the first discharge pipe 71 between the second-effect falling film evaporator 11 and the third-effect falling film evaporator 12.

[0052] The above technical solution can achieve the technical effect that by designing a spare pipeline and corresponding valves, when switching, the first valve 83 and the second valve 81 are closed and the fourth valve 84 is opened, so that the black liquor originally entering the third-effect falling film evaporator first enters the second-effect falling film evaporator. Since the concentration of this part of the black liquor is lower than the crystallization points of Na2CO3, Na2SO4 and calcium inorganic substances, the dirt on the heating plate of the second-effect falling film evaporator is gradually dissolved.

[0053] Refer to Figures 1-6 , the reflux mechanism includes a third connecting pipeline 92. The third connecting pipeline 92 is respectively fixedly connected to the circumferential surfaces of the first discharge pipe 71 between the first-effect falling film evaporator 1 and the second-effect falling film evaporator 11 and the circumferential surface of the feed inlet of the third-effect falling film evaporator 12. The third connecting pipeline 92 is respectively communicated with the first discharge pipe 71 between the first-effect falling film evaporator 1 and the second-effect falling film evaporator 11 and the feed inlet of the third-effect falling film evaporator 12. A sixth valve 82 is provided in the third connecting pipeline 92, and a third valve 8 is provided in the first discharge pipe 71 between the first-effect falling film evaporator 1 and the second-effect falling film evaporator 11. The third valve 8 is provided after the first discharge pipe 71 is communicated with the third connecting pipeline 92.

[0054] Close the third valve 8 and open the sixth valve 82, so that the black liquor coming out of the second-effect falling film evaporator enters the third-effect falling film evaporator through the spare pipeline again.

[0055] Refer to Figures 1-6 , the intermittent discharging mechanism includes a second connecting pipeline 91. The two ends of the second connecting pipeline 91 are respectively fixedly connected to the circumferential surfaces of the two first discharge pipes 71 on both sides of the second-effect falling film evaporator 11. The second connecting pipeline 91 is respectively communicated with the two first discharge pipes 71. A fifth valve 85 is provided in the second connecting pipeline 91.

[0056] Open the fifth valve 85 to allow the black liquor of the third-effect falling film evaporator to flow into the first-effect falling film evaporator along the spare pipeline, forming a process flow of the second-effect falling film evaporator → the third-effect falling film evaporator → the first-effect falling film evaporator.

[0057] However, as is well known to those skilled in the art, the working principles and wiring methods of the first-effect falling-film evaporator 1, the second-effect falling-film evaporator 11, the third-effect falling-film evaporator 12, the fourth-effect falling-film evaporator 13, the fifth-effect falling-film evaporator 14, and the sixth-effect falling-film evaporator 15 are common knowledge. They all belong to conventional means or well-known common sense and will not be elaborated here. Those skilled in the art can make arbitrary selections according to their needs or convenience.

[0058] The working principle and usage process of this technical solution are as follows: By designing spare pipelines and corresponding valves, when switching, close the first valve 83 and open the fourth valve 84 while opening the second valve 81, so that the black liquor that originally entered the third-effect falling-film evaporator first enters the second-effect falling-film evaporator. Since the concentration of this part of the black liquor is lower than the crystallization points of Na2CO3, Na2SO4, and calcium inorganic substances, the dirt on the heating plate of the second-effect falling-film evaporator gradually dissolves. Close the third valve 8 and open the sixth valve 82, so that the black liquor coming out of the second-effect falling-film evaporator then enters the third-effect falling-film evaporator through the spare pipeline. Open the fifth valve 85 to let the black liquor in the third-effect falling-film evaporator flow along the spare pipeline into the first-effect falling-film evaporator, forming a process of the second-effect falling-film evaporator → the third-effect falling-film evaporator → the first-effect falling-film evaporator.

[0059] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, and all should be covered by the protection scope of the present invention; without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A production process for scale formation on the heating plate of a falling film evaporator, characterized in that, It includes the following steps: S1. By designing a standby pipeline and corresponding valves, when switching, close the first valve (83) and the second valve (81), open the fourth valve (84), and let the black liquor that originally entered the third-effect falling film evaporator (12) first enter the second-effect falling film evaporator (11). Since the concentration of this part of the black liquor is lower than the crystallization points of Na2CO3, Na2SO4, and calcium inorganic substances, the dirt on the heating plate of the second-effect falling film evaporator (11) gradually dissolves. S2. Close the third valve and open the sixth valve, let the black liquor coming out of the second-effect falling film evaporator (11) enter the third-effect falling film evaporator (12) through the standby pipeline again, and open the fifth valve to let the black liquor of the third-effect falling film evaporator (12) flow along the standby pipeline into the first-effect falling film evaporator (1), forming a process of the second-effect falling film evaporator (11) → the third-effect falling film evaporator (12) → the first-effect falling film evaporator (1). S3. In the black liquor evaporation system, after normal operation for a period of time, when it is observed that the temperature difference of the second-effect falling film evaporator reaches 8 - 9 °C, exceeding the normal range, at this time, through process switching, switch the process of "the third-effect falling film evaporator (12) → the second-effect falling film evaporator (11) → the first-effect falling film evaporator (1)" to the process of "the second-effect falling film evaporator → the third-effect falling film evaporator (12) → the first-effect falling film evaporator (1)". After operating in this mode for 2 days, the temperature difference of the second-effect falling film evaporator drops back to 4 - 5 °C. At this time, switch the process of the evaporation system back to the normal process of "the third-effect falling film evaporator (12) → the second-effect falling film evaporator (11) → the first-effect falling film evaporator (1)" to continue production. The first-effect falling film evaporator (1), the second-effect falling film evaporator (11), the third-effect falling film evaporator (12), the fourth-effect falling film evaporator (13), the fifth-effect falling film evaporator (14), and the sixth-effect falling film evaporator (15) are respectively used for falling film evaporation of the first to sixth effects. Multiple groups of connecting feeding mechanisms, and multiple groups of connecting feeding mechanisms are respectively used to connect the first to sixth-effect falling film evaporators. A lifting and dissolving mechanism, which is arranged between the third-effect falling film evaporator (12) and the second-effect falling film evaporator (11) and is used to send the black material to be fed into the third-effect falling film evaporator (12) into the second-effect falling film evaporator (11). A reflux mechanism, which is arranged between the second-effect falling film evaporator (11) and the third-effect falling film evaporator (12). An intermittent discharging mechanism, which is arranged between the first-effect falling film evaporator (1) and the third-effect falling film evaporator (12).

2. The production process for scale formation on the heating plate of a falling film evaporator according to claim 1, characterized in that, Two fixing rings (5) are fixedly connected to the surfaces of the first-effect falling film evaporator (1), the second-effect falling film evaporator (11), the third-effect falling film evaporator (12), the fourth-effect falling film evaporator (13), the fifth-effect falling film evaporator (14), and the sixth-effect falling film evaporator (15). Two fixing frames (4) are fixedly connected to the surfaces of multiple fixing rings (5). Both ends of the two fixing frames (4) are fixedly connected to support frames (2), and both bottoms of the two support frames (2) are fixedly connected to fixing brackets (3).

3. The production process for scale formation on the heating plate of a falling film evaporator according to claim 2, characterized in that, An anti-slip pad is provided at the bottom of the fixing bracket (3).

4. The production process for scaling on the heating plate of a falling film evaporator according to claim 3, characterized in that, Each of the said connected feeding mechanisms includes a first discharge pipe (71) connected to the feed inlet of the first-effect falling film evaporator (1). The bottom end of the third-effect falling film evaporator (12) is fixedly connected to a first feeding pipe (72) connected to the discharge outlet of the third-effect falling film evaporator (12). A fixed plate (16) is fixedly connected between the two support frames (2). Above the fixed plate (16), a first water pump (7) is fixedly connected. The two sides of the first water pump (7) are respectively provided with a water inlet and a water outlet. The water inlet is connected to the first feeding pipe (72), and the water outlet is connected to the first discharge pipe (71).

5. The production process for scale formation on the heating plate of a falling film evaporator according to claim 4, characterized in that, A semi-concentrated black liquor storage tank (6) is fixedly connected inside the fixed plate (16). The semi-concentrated black liquor storage tank (6) is connected to the discharge outlet of the fourth-effect falling film evaporator (13). At the top end of the fixed plate (16), a second water pump (10) is fixedly connected. The two sides of the second water pump (10) are respectively fixedly connected to a second discharge pipe (101) and a second feeding pipe (102). The second feeding pipe (102) is connected to the semi-concentrated black liquor storage tank (6), and the second discharge pipe (101) is connected to the feed inlet of the third-effect falling film evaporator (12).

6. The production process for scale formation on the heating plate of a falling film evaporator according to claim 5, characterized in that, The lifting and dissolving mechanism includes a first connecting pipeline (9). The two ends of the first connecting pipeline (9) are respectively fixedly connected to the surfaces of the first discharge pipe (71) and the second discharge pipe (101) between the second-effect falling film evaporator (11) and the third-effect falling film evaporator (12). The first connecting pipeline (9) is respectively connected to the first discharge pipe (71) and the second discharge pipe (101) between the second-effect falling film evaporator (11) and the third-effect falling film evaporator (12). A first valve (83) is provided in the second discharge pipe (101). The first valve (83) is provided after the second discharge pipe (101) is connected to the first connecting pipeline (9). A fourth valve (84) is provided in the first connecting pipeline (9). A second valve (81) is provided in the first discharge pipe (71) between the second-effect falling film evaporator (11) and the third-effect falling film evaporator (12).

7. A production process for scaling of the heating plate of a falling film evaporator according to claim 6, characterized in that, The reflux mechanism includes a third connecting pipeline (92). The third connecting pipeline (92) is respectively fixedly connected to the circumferential surface of the first discharge pipe (71) between the first-effect falling film evaporator (1) and the second-effect falling film evaporator (11) and the circumferential surface of the feed inlet of the third-effect falling film evaporator (12). The third connecting pipeline (92) is respectively connected to the first discharge pipe (71) between the first-effect falling film evaporator (1) and the second-effect falling film evaporator (11) and the feed inlet of the third-effect falling film evaporator (12). A sixth valve (82) is provided in the third connecting pipeline (92). A third valve (8) is provided in the first discharge pipe (71) between the first-effect falling film evaporator (1) and the second-effect falling film evaporator (11). The third valve (8) is provided after the first discharge pipe (71) is connected to the third connecting pipeline (92).

8. A production process for scale formation on the heating plate of a falling film evaporator according to claim 7, characterized in that, The intermittent discharging mechanism includes a second connecting pipeline (91), both ends of the second connecting pipeline (91) are fixedly connected to the circumferential surfaces of two first discharging pipes (71) on both sides of the II-effect falling film evaporator (11), the second connecting pipeline (91) is respectively communicated with the two first discharging pipes (71), and a fifth valve (85) is arranged in the second connecting pipeline (91).

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