A black liquor crystallization concentrator

Abstract

The present application provides a kind of black liquor seed crystal concentration evaporator, including outer flow pipe type falling film concentration evaporator unit, black liquor seed crystal mixing and steam separator.Outer flow pipe type falling film concentration evaporator unit includes medium-pressure steam inlet box, black liquor liquid inlet flow guide film forming box, black liquor outer flow falling film evaporation box and condensate and non-condensable gas discharge box.Outer flow pipe type falling film concentration evaporator unit is connected with black liquor seed crystal mixing and steam separator by concentration black liquor discharge pipe.Black liquor seed crystal mixing and steam separator.Due to the modular design of outer flow pipe type falling film concentration evaporator unit, different black liquor processing capacity can be connected with black liquor seed crystal mixing and steam separator by pipeline through multiple units to realize.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of evaporation and concentration of black liquor in the pulp and paper industry, and in particular to a black liquor seeding and concentration evaporator. BACKGROUND

[0002] In the pulp and paper industry, the evaporation and concentration of black liquor has always been the focus of research. The goal is to increase the concentration of the black liquor as much as possible, to improve the heat efficiency of the recovery boiler and the processing capacity of the black liquor, and to reduce the emissions of sulfur dioxide and total reduced sulfur (TRS) in the recovery boiler, thereby achieving good economic and environmental benefits.

[0003] In the 1980s, falling film evaporation and concentration technology was widely used to increase the concentration of black liquor. This technology mainly uses multi-effect evaporation and concentration with tubular or plate falling film evaporators to increase the concentration of the black liquor to more than 65% in the last effect evaporator, which allows the black liquor to be burned in the recovery boiler with low odor, reduces the emissions of SO2 and TRS in the flue gas, reduces the frequency of cleaning the recovery boiler, and improves the heat efficiency and utilization of the boiler. The higher the concentration of the black liquor, the more stable the operation of the recovery boiler, the less the ash accumulation, and the lower the emissions of SO2 and other pollutants in the flue gas. Therefore, super-concentration technology for black liquor was developed, which can increase the concentration of the black liquor to 78% to 84%. The ash accumulation in the recovery boiler, the frequency of cleaning, the emissions of SO2 and TRS, and other factors are greatly reduced, and the processing capacity of the recovery boiler, the gas production, and the utilization efficiency are greatly improved.

[0004] At present, the super-concentration technology of foreign black liquor all uses medium-pressure steam (120 kPa, 250℃) as heating medium, and heats the black liquor to 160-190℃, reduces the viscosity of the black liquor, and facilitates the transportation and storage of the black liquor; or uses black liquor falling film circulation evaporation technology and flash evaporation technology to reduce fouling as much as possible and facilitate cleaning; or uses heat treatment technology to degrade lignin macromolecules and hemicellulose macromolecules in the black liquor to reduce the viscosity of the black liquor; or uses black liquor alkali ash and inorganic salt crystallization control technology and online rotation washing technology to super-concentrate the black liquor while keeping the heating surface of the evaporator as clean as possible, and to wash or not to wash. The black liquor super-concentration technology can produce good economic and environmental benefits. However, the multi-effect falling film evaporator commonly used is an internal flow tube falling film evaporator or a plate falling film evaporator, which has the disadvantages of uneven distribution of liquid film, easy fouling and difficult cleaning on the inside of the tube or the plate. For example, the tube falling film evaporator devices disclosed in Chinese invention patents CN112316457A, CN103272394A and CN103285607A focus on the design and improvement of the liquid distribution device of the evaporated solution, and still use the process of external steam flow and internal solution flow. This internal flow tube falling film evaporator with black liquor flowing in the tube is more prone to fouling in the tube and difficult to clean as the black liquor is evaporated and concentrated; similarly, the plate falling film evaporator is also prone to fouling and difficult to clean as the concentration of the black liquor increases between the plates, which limits the flow of the black liquor and reduces the evaporation efficiency, and even requires frequent cleaning, affecting production. The present invention aims to address the current situation and provides a black liquor crystal seeding and concentration evaporator to promote the development of black liquor super-concentration technology in China. SUMMARY

[0005] In order to overcome the uneven distribution of liquid film, easy fouling and difficult cleaning of the existing tube or plate falling film evaporator in the black liquor concentration evaporation, the present invention provides a black liquor crystal seeding and concentration evaporator.

[0006] In order to achieve the purpose of the present invention, the present invention provides a black liquor crystal seeding and concentration evaporator, which comprises a black liquor crystal seeding and mixing and steam separator and at least one external flow tube falling film concentration evaporator unit connected with the black liquor crystal seeding and mixing and steam separator,

[0007] The outer flow pipe falling film concentration evaporator unit group comprises an evaporator shell, an upper head, a lower head, an upper cover plate, a liquid supporting plate, a lower cover plate and an outer flow falling film evaporating heat exchange pipe, the upper head and the lower head are arranged at two ends of the evaporator shell to close the evaporator shell, the upper cover plate and the liquid supporting plate are arranged in the evaporator shell in sequence from the upper head to the lower head, wherein the cavity between the upper head and the upper cover plate is a medium-pressure steam inlet chamber, the cavity between the upper cover plate and the liquid supporting plate is a black liquor liquid inlet flow guide film forming chamber, the cavity between the liquid supporting plate and the lower cover plate is a black liquor outer flow falling film evaporation chamber, the cavity between the lower cover plate and the lower head is a condensed water and non-condensable gas discharge chamber, and the outer flow falling film evaporating heat exchange pipe is fixed on the upper cover plate and the lower cover plate at two ends and communicates with the medium-pressure steam inlet chamber and the condensed water and non-condensable gas discharge chamber.

[0008] The black liquor seed crystal mixing and steam separator is provided with a concentrated black liquor inlet and a black liquor seed crystal mixture outlet, the concentrated black liquor inlet communicates with the concentrated black liquor outlet arranged in the outer flow pipe falling film concentration evaporator unit group, and the black liquor seed crystal mixture outlet communicates with the black liquor inlet arranged in the outer flow pipe falling film concentration evaporator unit group.

[0009] Further, the outer flow pipe falling film concentration evaporator unit group further comprises a buffer plate and a distance supporting screw, the buffer plate is located in the black liquor liquid inlet flow guide film forming chamber and is fixed on the liquid supporting plate through the distance supporting screw.

[0010] Further, the outer flow pipe falling film concentration evaporator unit group further comprises a flow guide cup, the flow guide cup is fixed in the processing hole of the liquid supporting plate through transition fit.

[0011] Further, a liquid level static pressure gauge is arranged on the evaporator shell and at a position corresponding to the black liquor liquid inlet flow guide film forming chamber. The liquid level static pressure gauge can be interlocked with the black liquor circulating pump to control the stability of the black liquor liquid level in the flow guide film forming chamber, and the stability of the static pressure ensures the uniformity of the falling film forming of the flow guide cup along the circumferential outer surface of the evaporating heat exchange pipe.

[0012] Further, the evaporator shell is further provided with a flushing pipe and a sight glass, the sight glass is used for monitoring the outer flow film evaporation state of the falling film evaporating pipe in the evaporator, and the flushing pipe is used for flushing the evaporating pipe.

[0013] Further, the evaporator shell is further provided with a cleaning manhole assembly.

[0014] Further, the evaporator shell is further provided with a support.

[0015] Further, the black liquor seed crystal mixing and vapor separator comprises a tank body, a black liquor seed crystal mixing area, a vapor-liquid separation area and a secondary vapor demisting area are arranged in the tank body, the black liquor seed crystal mixing area is used for mixing seed crystals and concentrated black liquor transported from the black liquor seed crystal mixing and vapor separator, the vapor-liquid separation area is used for vapor-liquid separation of secondary vapor generated by black liquor evaporation and concentration, and the secondary vapor demisting area is used for demisting of the secondary vapor after vapor-liquid separation.

[0016] Further, a concentrated black liquor inlet pipe is arranged on the tank body, and the concentrated black liquor inlet pipe is connected with the tank body in a tangential manner.

[0017] Further, a hemispherical mist baffle is arranged in the secondary vapor demisting area.

[0018] Further, the black liquor seed crystal mixing and vapor separator is designed to be externally provided with a heat preservation layer, and a conical tank body with the functions of the black liquor seed crystal mixing area, the black liquor vapor-liquid separation area and the secondary vapor demisting area.

[0019] The outflow pipe type falling film evaporation unit is designed to withstand a steam pressure of 1.5 MPa and a temperature of 250 degrees, and the medium-pressure steam flows in the pipe, and the black liquor falling film flows outside the pipe. The outflow pipe type falling film evaporation unit comprises a medium-pressure steam inlet box, a black liquor liquid inlet guide film forming box, a black liquor outflow falling film evaporation box, and a condensed water and non-condensed gas discharge box.

[0020] Compared with the prior art, the present application can at least achieve the following beneficial effects:

[0021] (1) The outflow falling film pipe type evaporation unit module of the black liquor seed crystal thickening evaporator adopted by the present application can be used in combination with a seed crystal mixing and separating device in multiple unit modules to adapt to different black liquor processing requirements.

[0022] (2) The outflow falling film pipe type evaporator adopted by the black liquor seed crystal thickening evaporator of the present application adopts a guide cup immersion type static pressure film distribution, and the black liquor liquid inlet pump and the liquid level meter are connected in a chain control manner to control the static pressure of the film distribution, so that the film distribution on the outer periphery of the heat exchange pipe can be ensured to be uniform and stable.

[0023] (3) The outflow falling film pipe type evaporator adopted by the black liquor seed crystal thickening evaporator of the present application has the medium-pressure steam flowing in the pipe and the seed crystal black liquor falling film flowing outside the pipe, which can reduce the scaling of the evaporator, and the evaporator is designed with a pressure water cleaning port and a sight glass, so that the scaling condition of the heating pipe of the evaporator can be observed, and the outer periphery of the heat exchange pipe can be cleaned in time to keep the heating surface clean. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a structural schematic diagram of a black liquor seed crystal thickening evaporator provided by an embodiment of the present application.

[0025] Figure 2It is an outer flow pipe type falling film concentration evaporator of a black liquor seed crystal concentration evaporator and a pressure water flushing pipe and sight glass amplification structure schematic diagram thereof provided by the embodiment of the present application.

[0026] Figure 3 It is an outer flow pipe type falling film concentration evaporator of a black liquor seed crystal concentration evaporator and a black liquor inlet flow guide film forming box amplification structure schematic diagram thereof provided by the embodiment of the present application.

[0027] Figure 4 It is a black liquor seed crystal mixing and steam separator structure schematic diagram of a black liquor seed crystal concentration evaporator provided by the embodiment of the present application. DETAILED DESCRIPTION

[0028] To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0029] Please refer to Figure 1 The present application provides a black liquor seed crystal concentration evaporator, which comprises a first outer flow pipe type falling film concentration evaporator unit group 100, a second outer flow pipe type falling film concentration evaporator unit group 200 and a black liquor seed crystal mixing and steam separator 300 coupled with the two. The concentrated black liquor evaporated by the first outer flow pipe type falling film concentration evaporator unit group 100 and the second outer flow pipe type falling film concentration evaporator unit group 200 flows into the black liquor seed crystal mixing and steam separator 300 through a pipeline 15, and is mixed with seed crystals (alkali ash or sodium sulfate / sodium carbonate) added from an e flange opening. The seed crystals are pumped into a1 and a2 flange openings by a circulating pump from a b3 flange opening, and then enter the first outer flow pipe type falling film concentration evaporator unit group 100 and the second outer flow pipe type falling film concentration evaporator unit group 200 through the a1 and a2 flange openings to realize black liquor seed crystal concentration evaporation and concentration. At the same time, due to the modular design of the outer flow pipe type falling film concentration evaporator unit, seed crystal concentration evaporation can be realized by multi-unit coupling combination according to different black liquor processing capacity.

[0030] Please refer to Figure 2 , Figure 3 The outer flow pipe type falling film concentration evaporator unit group provided by the present application can withstand a steam pressure of 1.5 Mpa and a temperature of 250 degrees. The medium-pressure steam flows in the pipeline, and the black liquor falling film flows in the pipeline.

[0031] The outer flow pipe type falling film concentration evaporator unit group comprises an evaporator shell 5, a first upper head 7 and a first lower head 1 are arranged at the upper and lower ends of the evaporator shell 5 respectively, the first upper head 7 is connected with the evaporator shell 5 through a flange, an upper cover plate 8, a buffer plate 9, a liquid receiving plate 10 and a lower cover plate 2 are sequentially arranged in the evaporator shell 5 from the first upper head 7 to the first lower head 1, and the upper cover plate 8 is welded in the interior of the evaporator shell 5; the cavity between the first upper head 7 and the upper cover plate 8 is a medium-pressure steam inlet chamber, and an inlet pipe c is welded on the top of the first upper head 7; the cavity between the upper cover plate 8 and the liquid receiving plate 10 is a black liquor liquid inlet flow guide film forming chamber, the liquid receiving plate 10 is welded in the interior of the evaporator shell 5, and the buffer plate 9 is fixed on the liquid receiving plate 10 through a distance supporting screw 6, a flow guide cup 11 is fixed in the processing hole of the liquid receiving plate 10 through transition fit, and the distance between the buffer plate and the liquid receiving plate is adjusted through the distance supporting screw 6, so that the height of the black liquor liquid level in the black liquor liquid inlet flow guide film forming chamber is adjusted; a black liquor liquid inlet pipe a is welded on the evaporator shell 5 and close to the lower side of the evaporator upper cover plate 8, and the buffer plate 9 can prevent the impact of inlet dynamic pressure on the flow guide film forming uniformity; the cavity between the liquid receiving plate 10 and the lower cover plate 2 is a black liquor outer flow falling film evaporation chamber, the outer flow falling film evaporation heat exchange pipe 3 is arranged in the black liquor outer flow falling film evaporation chamber, the lower end of the outer flow falling film evaporation heat exchange pipe 3 is welded in the hole of the lower cover plate 2, the upper end sequentially passes through the flow guide cup 11, the liquid receiving plate 10, the buffer plate 9 and the upper cover plate 8 and is welded in the hole of the upper cover plate 8, and the position of the evaporator shell 5 relative to the black liquor outer flow falling film evaporation chamber is welded with an expansion joint 4, a pressure water cleaning pipe K, a sight glass N, a black liquor discharge pipe and a flange b, wherein the expansion joint 4 is welded in the middle of the evaporator shell 5, the pressure water cleaning pipe K and the sight glass N are installed on the upper half of the evaporator shell 5 and are above the expansion joint 4, the lower cover plate 2 is welded on the bottom of the lower half of the evaporator shell 5, the black liquor discharge pipe and the flange b are welded on the upper side of the bottom lower cover plate 2 of the lower half of the evaporator shell 5 and are close to the lower cover plate 2, and the cavity between the lower cover plate 2 and the first lower head 1 is a condensate and non-condensable gas discharge chamber, the lower cover plate 2 is welded in the interior of the evaporator shell 5, a non-condensable gas discharge pipe h is welded on the bottom of the evaporator shell 5 and is close to the lower cover plate 2, and a condensate outlet pipe d is welded on the bottom of the first lower head 1. Thus, the four groups of functional areas of the medium-pressure steam inlet chamber, the black liquor liquid inlet flow guide film forming chamber, the black liquor outer flow falling film evaporation chamber and the condensate and non-condensable gas discharge chamber sequentially constitute the evaporator unit as a whole.

[0032] In some embodiments of the present application, a support 12 is welded on the upper half of the evaporator shell 5, which facilitates the installation and fixation of the outer flow pipe type falling film concentration evaporator unit group.

[0033] In some embodiments of the present application, a pressure gauge nozzle and flange g are installed on the first upper head 7 to monitor the pressure of the input steam in real time. A liquid level pressure gauge nozzle and flange f are arranged on the evaporator shell 5 at a position corresponding to the black liquor inlet flow film forming tank, and the liquid level pressure gauge nozzle and flange f are installed below the buffer plate 9 to monitor the liquid level and pressure of the input black liquor in the evaporator in real time. The stability of the black liquor film forming pressure and the uniformity of the film forming can be controlled by interlocking with the black liquor pump.

[0034] In some embodiments of the present application, the flushing pipe and flange K and the sight glass N are installed on the upper part of the black liquor outflow falling film evaporation tank expansion joint 4 on the evaporator shell 5, which can monitor the outflow film evaporation state of the falling film evaporation pipe in the evaporator, so as to flush the evaporation pipe in time to prevent scaling.

[0035] In some embodiments of the present application, a cleaning manhole assembly M is installed on the upper part of the lower cover plate 2 of the black liquor outflow falling film evaporation tank to facilitate regular maintenance.

[0036] Please refer to Figure 4 In some embodiments of the present application, the black liquor seed crystal mixing and steam separator C is a conical tank body 16 with a heat preservation layer. The tank body 16 is provided with a black liquor seed crystal mixing area, a vapor-liquid separation area, and a secondary steam demisting area. The conical tank body is designed with multiple concentrated black liquor inlet pipes, which can be connected with multiple outflow pipe type falling film concentration evaporator units according to the black liquor processing capacity. The tank body 16 is provided with a concentrated black liquor inlet pipe a, which is connected with the tank body 16 tangentially to ensure that the black liquor can enter the black liquor seed crystal mixing area of the seed crystal mixing and steam separator along the inner wall of the tank body 16.

[0037] Preferably, the black liquor crystal seed mixing and vapor separator 300 comprises a second upper head 13, a semi-spherical mist baffle 14, a mixing separator tank body 16, a second lower head 17, a base 18, a crystal seed e inlet pipe and flange installed on the second lower head 17 of the black liquor crystal seed mixing area of the tank body, a black liquor mixing liquid b outlet pipe and flange installed on the second lower head 17 of the black liquor crystal seed mixing area of the tank body and opposite to the crystal seed e inlet pipe, a secondary vapor c discharge pipe and flange installed on the top of the second upper head 13, a crystallized slag O discharge pipe and flange installed at the bottom of the lower head, a pressure gauge and flange g, a liquid level gauge and flange f installed on the tank body 16 at the corresponding functional detection positions respectively. The second upper head 13 and the second lower head 17 are respectively arranged at the openings on both sides of the tank body 16. The area in the tank body 16 and between the thickened black liquor inlet pipe and the second lower head 17 is the black liquor crystal seed mixing area. A thermometer and flange j, a crystal seed e inlet pipe, a black liquor mixing liquid b outlet pipe and flange, and a crystallized slag O discharge pipe and flange are arranged on the tank body 16 and at positions corresponding to the black liquor crystal seed mixing area. The area in the tank body 16 and between the thickened black liquor inlet pipe and below the semi-spherical mist baffle 14 is the black liquor vapor-liquid separation area. A pressure gauge and flange, a liquid level gauge and flange are arranged on the tank body 16 and at positions corresponding to the black liquor vapor-liquid separation area. The area in the tank body 16 and between the semi-spherical mist baffle 14 and the second upper head 13 is the secondary vapor mist removal area. The secondary vapor discharge pipe and flange are arranged at the top of the secondary vapor mist removal area.

[0038] The black liquor discharged from the bottom of the external flow pipe type falling film thickening evaporator unit group enters the black liquor crystal seed mixing and vapor separator through a pipe from the a inlet tangent of the black liquor crystal seed mixing and vapor separator Figure 4 The black liquor crystal seed mixing and vapor separator shown in the black liquor crystal seed mixing area mixes the black liquor with the crystal seed (alkali ash or sodium carbonate or sodium sulfide, the amount of crystal seed and the type of crystal seed added are determined by the composition of the specific concentrated black liquor) pumped from the e pipe mouth. After uniform mixing, the black liquor is pumped from the b pipe mouth at the bottom of the black liquor crystal seed mixing area by the black liquor circulating pump to the external flow pipe type falling film thickening evaporator unit group for seed thickening evaporation. The secondary vapor generated by the evaporation and concentration of the black liquor is subjected to vapor-liquid separation in the vapor-liquid separation area of the black liquor crystal seed mixing and vapor separator. After vapor-liquid separation, the secondary vapor is removed by the semi-spherical mist baffle 14 and then discharged from the secondary vapor outlet c for reuse.

[0039] The black liquor with solid content less than 60% pumped from the last effect of the multi-effect evaporation station is pumped into the inlet a1 of the outer falling film concentration evaporator (A) by the black liquor pump, enters the buffer plate 9 of the black liquor liquid inlet flow guide film forming box, flows into the black liquor liquid inlet flow guide film forming box along the edge of the buffer plate 9, and forms a film along the outer circle of the evaporator heating pipe 3 in the black liquor immersion flow guide cup 11. The medium-pressure steam is introduced into the medium-pressure steam inlet box by the medium-pressure steam inlet pipe c1, uniformly distributed into the heating pipe 3 of the evaporator in the medium-pressure steam inlet box, flows along the pipe to the condensate and non-condensable gas discharge box in the black liquor outer falling film evaporation box, and exchanges heat between the steam in the pipe and the film forming black liquor outside the pipe in the black liquor outer falling film evaporation box, so that the black liquor evaporates and concentrates. The concentrated black liquor is discharged from the bottom discharge port b1 of the black liquor outer falling film evaporation box and pumped into the black liquor seed crystal mixing area of the black liquor seed crystal mixing and steam separator through the pipeline 15, mixed with the seed crystal (alkali ash or sodium carbonate or sodium sulfide, the amount of the seed crystal and the type of the crystalline particles added are determined according to the composition of the concentrated black liquor), and then pumped into the outer falling film concentration evaporator from the bottom mixed black liquor discharge port b3 of the black liquor seed crystal mixing area by the black liquor circulating pump for seed crystal concentration evaporation, so that the solid content of the black liquor reaches the required range of 78% to 84% of the alkali furnace.

[0040] The above description of disclosed embodiments enables those skilled in the art to carry out or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A black liquor concentration evaporator with seeding, characterized in that, The black liquor seed crystal mixing and steam separator (300) and at least one outer flow pipe type falling film concentration evaporator unit group connected with the black liquor seed crystal mixing and steam separator (300) are included, The outer flow pipe type falling film concentration evaporator unit group comprises an evaporator shell (5), a first upper head (7), a first lower head (1), an upper cover plate (8), a liquid receiving plate (10), a lower cover plate (2) and an outer flow falling film evaporation heat exchange pipe (3), the first upper head (7) and the first lower head (1) are arranged at two ends of the evaporator shell (5) respectively to close the evaporator shell (5), the upper cover plate (8) and the liquid receiving plate (10) are arranged in the evaporator shell (5) in sequence from the first upper head (7) to the first lower head (1), wherein the cavity between the first upper head (7) and the upper cover plate (8) is a medium-pressure steam inlet box, the cavity between the upper cover plate (8) and the liquid receiving plate (10) is a black liquor liquid inlet flow guide film forming box, the cavity between the liquid receiving plate (10) and the lower cover plate (2) is a black liquor outer flow falling film evaporation box, and the cavity between the lower cover plate (2) and the first lower head (1) is a condensed water and non-condensable gas discharge box, and the two ends of the outer flow falling film evaporation heat exchange pipe (3) are fixed on the upper cover plate (8) and the lower cover plate (2) respectively and communicate with the medium-pressure steam inlet box and the condensed water and non-condensable gas discharge box; The outer flow pipe type falling film concentration evaporator unit group further comprises a flow guide cup (11), and the flow guide cup (11) is fixed in a processing hole of the liquid receiving plate (10) through transition fit; The black liquor seed crystal mixing and steam separator (300) is provided with a concentrated black liquor inlet and a black liquor seed crystal mixture outlet, the concentrated black liquor inlet communicates with a concentrated black liquor outlet arranged in the outer flow pipe type falling film concentration evaporator unit group, and the black liquor seed crystal mixture outlet communicates with a black liquor liquid inlet arranged in the outer flow pipe type falling film concentration evaporator unit group; The black liquor seed crystal mixing and steam separator (300) comprises a tank body (16), and the tank body (16) is provided with a black liquor seed crystal mixing area, a vapor-liquid separation area and a secondary steam demisting area, the black liquor seed crystal mixing area is used for mixing crystal seeds and concentrated black liquor transported from the black liquor seed crystal mixing and steam separator (300), the vapor-liquid separation area is used for vapor-liquid separation of secondary steam generated by black liquor evaporation concentration, and the secondary steam demisting area is used for demisting of the secondary steam after vapor-liquid separation.

2. A black liquor concentration evaporator according to claim 1, characterized in that The outer flow pipe type falling film concentration evaporator unit group further comprises a buffer plate (9) and a distance support screw (6), and the buffer plate (9) is located in the black liquor liquid inlet flow guide film forming box and is fixed on the liquid receiving plate (10) through the distance support screw (6).

3. A black liquor concentration evaporator according to claim 1, characterized in that A liquid level static pressure gauge is arranged on the evaporator shell (5) and at a position corresponding to the black liquor liquid inlet flow guide film forming box.

4. A black liquor concentration evaporator according to claim 1, characterized in that The evaporator shell (5) is further provided with a flushing pipe and a sight glass, the sight glass is used for monitoring the outer flow film evaporation state of the falling film evaporation pipe in the evaporator, and the flushing pipe is used for flushing the evaporation pipe.

5. A black liquor concentration evaporator according to claim 1, characterized in that The evaporator shell (5) is further provided with a cleaning manhole assembly.

6. A black liquor concentration evaporator according to claim 1, characterized in that The evaporator shell (5) is further provided with a support (12).

7. A black liquor concentration evaporator according to claim 1, characterized in that The tank body (16) is provided with a concentrated black liquor inlet pipe, and the concentrated black liquor inlet pipe is connected with the tank body (16) tangentially.

8. A black liquor concentration evaporator according to claim 1, characterized in that A semi-spherical mist baffle (14) is arranged in the secondary steam demisting zone.

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