A large-capacity thin-film evaporator for cellulose dissolution

Abstract

The present invention relates to a large-capacity thin-film evaporator for cellulose dissolution, comprising a chamber and a vertically arranged rotor rotatable in the chamber; the chamber is divided into a cloth-feeding area, a wiping film area and a discharging area arranged in sequence from top to bottom; the part of the rotor located in the wiping film area is cylindrical, and the peripheral surface thereof is provided with more than 40 rows of wiping film area scraping plates arranged along the axis direction of the rotor; the wiping film area scraping plates include vertical scraping plates and inclined scraping plates; the vertical scraping plates and the inclined scraping plates are distributed in different rows and are alternately arranged on the outer periphery of the rotor; the ends of each wiping film area scraping plate away from the outer periphery of the rotor form a comb-shaped structure through U-shaped openings arranged at intervals; the U-shaped openings on the wiping film area scraping plates in adjacent rows are staggeredly distributed. The structure of the thin-film evaporator of the present invention is simple, and can meet the production of Lyocell fibers under large capacity.

Description

Technical Field

[0001] The present invention belongs to the field of thin-film evaporators and relates to a high-capacity thin-film evaporator for cellulose dissolution. Background Art

[0002] The method of using an NMMO aqueous solution as a solvent to dissolve cellulose for producing Lyocell fibers has received increasing attention. Lyocell fibers are made from natural renewable plant fibers and have inherent resource advantages. Their chemical structure is basically the same as that of viscose fibers. In addition to having the properties of natural fibers such as hygroscopicity, air permeability, comfort, and degradability, they also have the advantage of high strength of synthetic fibers. At the same time, compared with other solution-spun cellulose fibers, it has the advantages of a short production process, a pure physical preparation process, low energy consumption, little environmental pollution, and recyclable raw materials, showing obvious resource and environmental protection advantages. It is known as the green fiber with the greatest development potential in the 21st century and is expected to replace traditional viscose fibers, fundamentally solving the environmental problems brought about by fiber production. The research and development of a thin-film evaporator for producing high-quality and high-capacity spinning solutions is expected to change the current situation that most of the spinning raw materials for domestic Lyocell fibers are imported from abroad, meet the requirements of high solubility of spinning pulp and high quality of spinning solutions, and break through the bottleneck restricting the development of the domestic Lyocell fiber industry.

[0003] The thin-film evaporator can be used to complete the continuous and uniform dissolution and output of the mixed materials of cellulose, NMMO, and water in the industrialization of Lyocell fibers. This equipment and its key components are disclosed in patent numbers such as CN104826349, CN217661550U, CN217794557, CN217246796, CN216755416, etc., and improvements and optimizations have been made to the distributor, scraper structure, material extrusion device, equipment form, function, etc. of the equipment. The dehydration efficiency and dissolution capacity per unit area of the thin-film evaporator determine the production capacity of the production line, and the heating temperature conditions and residence time of the materials determine the safety of the production line. These two points depend on the design, arrangement method, vacuum system, and dissolution process of the scraper; the distributor has functions of introducing materials, initial cloth feeding, conveying materials, and steam dissipation. The quality of the initial liquid film formed by the distributor cloth feeding and the smoothness of steam dissipation also affect the dehydration efficiency and dissolution capacity of the materials in the film scraping area; the material extrusion device at the bottom of the thin-film evaporator includes a conical section and a screw. The sufficient mixing of the materials before discharge and the continuous and uniform extrusion of the materials to overcome the negative pressure inside the evaporator and the viscosity of the materials depend on the structural design of the extrusion device.

[0004] CN104826349A discloses a thin-film evaporator for cellulose dissolution, which optimizes the scraper structure of the thin-film evaporator. The vertically arranged scraper and the inclined scrapers at positive and negative angles to the vertical direction provide an anti-mixing effect during the material dissolution process, improving the dissolution capacity and dissolution uniformity of the evaporator. However, there are also problems such as low frequency of film surface renewal, low heat transfer efficiency, and weak mass exchange ability between material agglomerates and liquid films, which may not be able to meet the film formation under large production capacity, thus affecting continuous production.

[0005] CN216755416 provides a feed distribution device and a thin-film evaporator. The device includes a body and a sealing ring. The sealing ring is arranged on the outer wall of the body. Strengthening rib plates are dispersedly arranged along the circumferential direction inside the body, and cutting blades are dispersedly arranged along the circumferential direction outside the body. This design makes the material distribution more uniform in the circumferential direction, reduces the accumulation of materials during feeding, can avoid the loss of materials, and reduces material waste. However, there are still potential problems such as material overflow and low steam dissipation ability in the feeding area for this distributor.

[0006] CN217661550U designs a discharge structure for a thin-film evaporator. The discharge structure includes a hollow screw sleeve and a discharge screw arranged inside the screw sleeve. The discharge screw includes a screw rotor and at least two spiral bands. The screw rotor is coaxially arranged with the screw sleeve. Each spiral band surrounds the screw rotor at intervals and is fixedly connected to the screw rotor. The discharge structure of this thin-film evaporator can overcome the negative pressure inside the evaporator and the viscosity of the material after optimization, and continuously and evenly extrude the material. However, there are still defects such as uneven dispersion and mixing of materials and relatively high equipment working power in the improved discharge structure provided by this patent.

[0007] The above patents have improved the distributor, the scraper structure in the film scraping area, and the extrusion device of the thin-film evaporator, increasing the production capacity. However, there are also potential problems such as slow renewal of the liquid film surface in the film scraping area, weak mass exchange ability between material agglomerates and liquid films, low heat transfer efficiency; low steam dissipation ability in the feeding area, uneven initial liquid film, material overflow; insufficient mixing of materials in the extrusion device at the bottom of the evaporator, relatively high equipment working power, and fouling on the heating surface. The existing potential problems weaken the production capacity of the thin-film evaporator and fail to meet the production of Lyocell fibers under large production capacity. Summary of the Invention

[0008] The purpose of the present invention is to solve the problems existing in the prior art and provide a large-production-capacity thin-film evaporator for cellulose dissolution with an annual output of 40,000 - 80,000 tons of Lyocell fibers.

[0009] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0010] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0011] A large-capacity thin-film evaporator for cellulose dissolution, comprising a chamber and a vertical rotor rotatably disposed within the chamber; the chamber is divided into a cloth zone, a wiping film zone, and a discharging zone arranged in sequence from top to bottom;

[0012] The part of the rotor located in the wiping film zone is cylindrical, and the circumferential surface thereof is provided with more than 40 columns of wiping film zone scrapers arranged along the axis direction of the rotor;

[0013] The wiping film zone scrapers include vertical scrapers and inclined scrapers;

[0014] The total number of columns of the wiping film zone scrapers is e columns, and the diameter of the part of the rotor (2) located in the wiping film zone is f mm. The value range of e / f is 4 / 171 to 7 / 171 (that is, assuming the diameter of the part of the rotor located in the wiping film zone is 171 mm, the total number of columns of the wiping film zone scrapers is 4 to 7 columns); the vertical scrapers and the inclined scrapers are distributed in different columns and are alternately arranged on the outer circumference of the rotor (that is, one column of vertical scrapers and one column of inclined scrapers are alternately arranged). Since the rotation direction of the vertical scrapers is perpendicular to the overall downward flow direction of the material, the rotation resistance is relatively large, and a larger torque is required compared to the inclined scrapers. Generally, the number of columns of the vertical scrapers accounts for 1 / 2 or less of the total number of columns of the evaporator. In the present invention, the number of columns of the inclined scrapers is the same as that of the vertical scrapers;

[0015] The ends of each wiping film zone scraper away from the outer circumference of the rotor form a comb structure through U-shaped openings arranged at intervals, and the part between adjacent two U-shaped openings is a comb tooth; the U-shaped openings on the wiping film zone scrapers in adjacent columns are staggeredly distributed;

[0016] The root of the vertical scraper is vertically arranged and connected to the rotor. The end face of the comb tooth away from the outer circumference of the rotor forms an angle of 0° with the vertical direction, that is, the vertical scraper includes opposite ends, one of which is connected to the rotor, and this end is the root, and the angles of both ends with the vertical direction are 0°; the root of the inclined scraper is vertically arranged and connected to the rotor. The end face of the comb tooth away from the outer circumference of the rotor forms a positive angle α with the vertical direction, and α is 10° to 45°, that is, the inclined scraper includes opposite ends, one of which is connected to the rotor, and this end is the root, and the angle of this end with the vertical direction is 0°, and the angle of the other end with the vertical direction is α;

[0017] In addition to the functions of wiping the film and renewing the liquid film, the inclined scraper has a downward thrust on the material after rotation, enhancing the axial transmission of the material, reducing the residence time of the material inside the evaporator, and reducing the risk of decomposition of heat-sensitive materials. Compared with the inclined scraper, the vertical scraper has a larger film wiping area and can quickly renew the liquid film to promote cellulose dissolution;

[0018] The gap between the end of the squeegee in each film scraping area, which is far from the outer periphery of the rotor, and the chamber is 3.5 - 4.5 mm (preferably 3.5 - 4.5 mm); the reason why the present invention sets the gap range to 3.5 - 4.5 mm is as follows: there is a certain mass transfer between the liquid mass and the liquid film, enabling the material to continuously spread into a film on the wall surface and be updated. The mass transfer rate can be understood as a quantitative index for the renewal of the liquid film. The change in the gap has a minimal impact on the centrifugal force, and the change in the gap mainly affects the shear strain rate. The gaps of 3.5 mm and 4.5 mm are relatively small, and the shear strain rate is relatively large. Moreover, when the gap decreases, the flow velocity of the fluid scraped into the gap will increase under the same conditions. Therefore, the liquid film thickness and volume ratio of the 3.5 mm gap are higher than those of the 4.5 mm gap; in addition, the present invention defines the mass transfer situation of the material flowing through a specific cylindrical surface per unit time as the mass transfer rate and has statistically analyzed the mass transfer situation between the liquid mass and the liquid film; when the gap is 3.5 and 4.5 mm, the mass transfer rate between the liquid mass and the liquid film is relatively high; when the gap continues to increase, the mass transfer rate decreases and there is no obvious change with the change of the gap. This is because when the gap is too large, the shear strain rate decreases, and at the same time, the material mass further accumulates, and the axial transport ability becomes poor, and the mass transfer ability naturally also becomes poor; in summary, the gap between the squeegee in the film scraping area and the wall surface is preferably 3.5 - 4.5 mm, and the power is the lowest at 4.5 mm, which is more in line with the engineering requirements and economic benefits.

[0019] The present invention effectively solves the problems of low renewal frequency of the thin film surface, low heat transfer efficiency, and weak mass transfer ability between the material mass and the liquid film existing in CN104826349A. The mechanism is as follows:

[0020] The present invention sets that "the ratio of the total number of rows of the squeegee in the film scraping area to the diameter of the part of the rotor located in the film scraping area is 4 / 171 - 7 / 171 (rows / mm)" and "the squeegee in the film scraping area includes a vertical squeegee and an inclined squeegee. The root of the vertical squeegee is vertically arranged and connected to the rotor, the angle between the end face of the comb teeth far from the outer periphery of the rotor and the vertical direction is 0°, the root of the inclined squeegee is vertically arranged and connected to the rotor, and the angle between the end face of the comb teeth far from the outer periphery of the rotor and the vertical direction is a positive angle α, and α is 10° - 45°", which further improves the renewal frequency of the thin film surface compared with CN104826349A. The reasons are as follows: ① The dense arrangement of the squeegee in the film scraping area can improve the mass transfer ability between the liquid mass and the liquid film in the evaporator and promote the renewal of the internal material; ② The angle between the vertical squeegee and the vertical direction is 0°, and its film scraping area is larger than that of the inclined squeegee, which can quickly renew the liquid film and promote the dissolution of cellulose.

[0021] The present invention sets that "the ratio of the total number of columns of the scraping plates in the scraping film area to the diameter of the part of the rotor located in the scraping film area is 4 / 171 - 7 / 171 (columns / mm)", "the vertical scraping plates and the inclined scraping plates are distributed on different columns and are alternately arranged on the outer periphery of the rotor", "the ends of the scraping plates in each scraping film area away from the outer periphery of the rotor form a comb-shaped structure by arranging U-shaped openings with a spacing", "the U-shaped openings on the adjacent scraping plates in the scraping film area are staggeredly distributed", and "the gap between the ends of the scraping plates in each scraping film area away from the outer periphery of the rotor and the chamber is 3.5 - 4.5 mm", which effectively improves the heat transfer efficiency of the thin-film evaporator. The reasons are as follows: ① The scraping plate structure and arrangement in the scraping film area adopted by the present invention enable the formation of liquid film fluctuations on the wall surface during the rotation of the device (i.e., the liquid film presents an obvious wavy structure). The wavy liquid film enhances the turbulent kinetic energy of the material inside the thin-film evaporator, increases the gas-liquid interface area on the liquid film surface, reduces the liquid film thermal resistance at the same time, enhances the convective heat transfer on the liquid film surface, the heat transfer efficiency is strengthened, and at the same time, due to the increased heat transfer area, liquid film thinning and convective effects caused by the fluctuations, the heat transfer rate is strengthened; ② The dense arrangement of the scraping plates in the scraping film area can improve the mass transfer ability between the agglomerates and the film in the evaporator, promote the renewal of the internal material, and improve the heat transfer efficiency; ③ In the present invention, the vertical scraping plates and the inclined scraping plates are distributed on different columns and are alternately arranged on the outer periphery of the rotor. At the same time, the U-shaped openings on the adjacent scraping plates in the scraping film area are staggeredly distributed, so that the material flows out from the U-shaped opening and reaches the top of the comb teeth of the adjacent scraping plate in the rear scraping film area. This setting method enhances the axial transport of the material, breaks the agglomeration of the material, forms a high-frequency shear thinning effect, avoids the rapid recovery of the viscosity of shear thinning type materials, and improves the heat transfer efficiency; ④ In the present invention, the gap between the ends of the scraping plates in each scraping film area away from the outer periphery of the rotor and the chamber is reasonably set, which avoids the appearance of bubbles on the wall surface due to too large a gap and reduces the heat transfer performance;

[0022] The present invention sets that "the gap between the ends of the scraping plates in each scraping film area away from the outer periphery of the rotor and the chamber is 3.5 - 4.5 mm", which improves the mass transfer ability between the material agglomerates and the liquid film. Compared with CN104826349A, it more deeply and reasonably explains the beneficial effects brought by this technical feature. The reason is that the gap design of the present invention is reasonable. Under this gap range, the mass transfer rate between the liquid agglomerates and the liquid film is relatively high. When the gap continues to increase, the mass transfer rate decreases and there is no obvious change with the change of the gap. This is because when the gap is too large, the shear strain rate decreases, and at the same time, the material agglomerates further accumulate, and the axial transport ability becomes poor, and the mass transfer ability naturally becomes poor; Figure 15 The curve graph showing the change of the average radial velocity with the gap between the ends of the scraping plates in each scraping film area away from the outer periphery of the rotor and the chamber is shown. In the figure, the positive velocity refers to the transmission from the liquid agglomerate to the liquid film direction, and the negative velocity refers to the transmission from the liquid film to the liquid agglomerate direction. The greater the average velocity, the higher the mass transfer rate. It can be seen from this figure that the present invention improves the mass transfer ability between the material agglomerates and the liquid film.

[0023] In addition, the present invention sets that "the gap between the end of the scraper in each wiping film area away from the outer periphery of the rotor and the chamber is 3.5 - 4.5 mm", which can also ensure the evaporation efficiency, effectively limit the torque, and reduce the power. The reason is that within the range of 3.5 - 4.5 mm gap, the power of the wiping film device first decreases and then increases with the increase of the gap. The increase in power is due to the enlargement of the material mass, which increases the contact area with the scraper in the wiping film area, resulting in a significant rise in power. At the same time, the power required by the device is the lowest at a 4.5 mm gap, which is more in line with engineering requirements and economic benefits. As the gap increases, the residence time also increases because the further formation of large material masses due to the increased gap leads to a decrease in the axial transport capacity of the material, resulting in a continuous increase in the residence time with the increase of the gap, thereby increasing the risk of material decomposition. An overly small gap will cause a large amount of material to exist in the form of liquid masses, reducing the evaporation efficiency and increasing the torque.

[0024] In addition, the present invention sets that "the ratio of the total number of rows of the scrapers in the wiping film area to the diameter of the part of the rotor located in the wiping film area is 4 / 171 - 7 / 171 (rows / mm)", "the ends of the scrapers in each wiping film area away from the outer periphery of the rotor form a comb-shaped structure by arranging U-shaped openings at intervals", and "the U-shaped openings on the scrapers in adjacent wiping film areas are staggered", which can also ensure that the evaporator can handle non-Newtonian fluid materials with a viscosity of up to 10,000 Pa·s. The pseudoplastic characteristics of non-Newtonian fluid materials require shear thinning for good film formation. The scrapers in the wiping film area of the present invention are densely arranged, and the U-shaped openings on the scrapers in adjacent wiping film areas are staggered, mainly playing the role of timely thinning of non-Newtonian high-viscosity materials. During the rotation of the scrapers in the wiping film area, the material accumulated at the leading edge of the comb teeth will form a film on the cylinder wall under the action of shear thinning, and at the same time, part of the material will leak out from the U-shaped openings to form liquid strands at the trailing edge of the comb teeth, and its viscosity begins to recover after losing the shear action. Therefore, through the staggered U-shaped openings, the liquid strands can be received by the comb teeth of the following wiping film area scrapers when they encounter them, realizing continuous thinning. Combined with the dense arrangement of the scrapers in the wiping film area, the material can be continuously transported in a stepped manner in the evaporator and continuously thinned in the entire circumference, and then form a good film.

[0025] As a preferred technical solution:

[0026] For a large-capacity thin-film evaporator for cellulose dissolution as described above, the angles between the end faces of the comb teeth of all inclined scrapers away from the outer periphery of the rotor and the vertical direction are the same.

[0027] For a large-capacity thin-film evaporator for cellulose dissolution as described above, the ratio of the opening depth S of the U-shaped opening to the gap L between adjacent comb teeth is less than 1.7 (preferably less than 1.4), S is less than 80 mm (preferably S is 40 - 70 mm); the ratio of the gap K between adjacent U-shaped openings to the gap L between adjacent comb teeth is less than 2.2 (preferably less than 2), and K is less than 120 mm (preferably 90 - 110 mm).

[0028] In the present invention, the distribution of U-shaped openings and the distribution of comb teeth on the scraper in the film scraping area need to be in a certain proportion, and neither of them can be excessive or insufficient. This is determined by the film-forming mechanism of shear thinning. The rotation of the scraper in the film scraping area causes the material to accumulate on the scraper in the film scraping area. Part of the material flows out from the U-shaped openings on the scraper in the film scraping area and is received by the subsequent scraper in the film scraping area, realizing the periodic shear thinning of high-viscosity materials, preventing them from staying at the leading edge of a single scraper in the film scraping area for a long time, which is not conducive to circumferential film formation, and enhancing the axial transport capacity of the material. The material tends to achieve spatial transport through the U-shaped openings, completing wall film formation and mass exchange. When the material passes through the U-shaped openings, part of the material will adhere to the structural tip part of the U-shaped openings. These adhered materials form a ribbon-like liquid film on the cylinder wall with the rotation of the scraper in the film scraping area. The initial ribbon-like film is narrow and thin. After multiple film scrapings, the ribbon-like film gradually becomes wider and thicker. When the thickness of the liquid film is greater than or equal to the gap height, it can be further scraped and extended into a film by the comb teeth part on the scraper in the film scraping area. With the accumulation of time, a uniform liquid film distribution can be gradually formed on the wall surface. This way of forming a film by drawing requires the combined action of the U-shaped openings and the comb teeth on the scraper in the film scraping area. The scraper structure in the film scraping area of the present invention can quickly form a uniform and continuous liquid film on the cylinder wall.

[0029] In a large-capacity thin-film evaporator for cellulose dissolution as described above, the U-shaped openings in each scraper in the film scraping area are arranged at equal intervals.

[0030] In a large-capacity thin-film evaporator for cellulose dissolution as described above, each vertical scraper is formed by bending a rectangular vertical plate I in the clockwise direction, with a bending angle Φ of 1° to 40°, and the fold line is a vertical line; each inclined scraper is formed by bending a rectangular vertical plate II in the clockwise direction, with a bending angle Φ of 1° to 40°, and the fold line is an oblique line, and the bending area is a trapezoid with a narrower upper part and a wider lower part.

[0031] The present invention designs the scraper in the film scraping area as a bent plate, which has the following benefits: reasonable bending of the scraper in the film scraping area will increase the probability of the material contacting the wall surface and thinning into a film, forming a liquid film with better uniformity. The uniformity of the liquid film affects the thermal resistance of the liquid film to a certain extent, and thus affects heat transfer. The wedge-shaped structure formed by the bent plate and the inner wall of the evaporator provides a pressure for the annular wave fluid in addition to the centrifugal force, increasing the fluid pressure inside the annular wave, making the fluid more easily squeezed into the gap between the scrapers in the film scraping area to achieve film scraping, enhancing the radial mixing effect between the liquid film and the material mass, and making the renewal amplitude of the liquid film larger. The wedge-shaped structure formed by the bent plate and the inner wall of the evaporator enables the material between the bent plate and the inner wall to be used as a lubricant to form wedge-shaped lubrication. This structure is beneficial to the stable operation of the evaporator, reducing vibration and noise. There is an optimal bending angle for the scraper in the film scraping area. If the bending angle is too large, the rotor torque will further increase, resulting in an increase in power consumption. At the same time, the retention amount of the liquid inside the evaporator and the proportion of the annular wave fluid continue to increase, which is not conducive to the processing of the material in the thin-film evaporator with scrapers in the film scraping area.

[0032] A large-capacity thin-film evaporator for cellulose dissolution as described above, the part of the rotor located in the feeding area is cylindrical, and there are more than 20 rows of feeding area scrapers arranged along the axis direction of the rotor on its circumferential surface;

[0033] Each feeding area scraper is composed of 1 vertical plate and multiple inclined plates arranged at intervals from top to bottom. The number of inclined plates is m pieces, and the length of the feeding area scraper is n mm. The value range of m / n is 2 / 540 - 5 / 540 (that is, assuming the length of the feeding area scraper is 540 mm, then the number of inclined plates is 2 - 5 pieces); the vertical plate is arranged vertically, the inner surface of the vertical plate faces the rotor, and the outer surface of the vertical plate faces away from the rotor; the inclined plates are arranged obliquely and form a negative angle θ with the vertical direction, θ is 10° - 70°, and the inclined plates are fixed on the outer surface of the vertical plate; the inner surface of the vertical plate is connected to the outer circumference of the rotor through a vertically arranged support steel plate, and a connecting groove is provided on the support steel plate.

[0034] The functions played by the feeding area of the present invention are: ① introducing materials; ② spreading and scraping the film; ③ conveying materials; ④ providing a better escape channel for steam; ⑤ air extraction; as the included angle between the inclined plate and the vertical direction increases, the residence time of the material decreases, which can effectively inhibit the overflow of the material, but will make the liquid film distribution uneven and is not conducive to the formation of the initial liquid film; as the number of inclined plates increases, the liquid film thickness has a tendency to decrease and the uniformity is better, the fluid mixing is more intense, and the mixing effect of promoting the liquid film flow can be effectively achieved; compared with the feeder in CN216755416, the present invention effectively improves the situations of material overflow and low steam escape ability in the feeding area, and the mechanism is as follows:

[0035] The end of the feeding area scraper adopts multiple inclined plates, which plays a role in hindering the climbing rod effect based on viscous materials, inhibits the overflow of materials, and is conducive to the formation of a uniform initial liquid film at the same time;

[0036] The feeding area scraper is connected to the outer circumference of the rotor through a steel plate, so that there is an annular steam escape channel between the scraper and the rotor, the space is larger, the steam is easier to be discharged, and the disturbance of the air flow near the pipe wall is reduced;

[0037] The structure formed by the connection of the steel plate and the rotor (similar to an axial flow fan) concentrates the air flow in the area near the wall of the rotor, the axial gas transmission is smoother, the steam discharge will not affect the flow of the material, inhibits the overflow of the material, and also plays a role in air extraction ( Figure 14 shows the simulation diagram of the steam trace line in the feeding area. It can be seen from this that during the operation of the feeder, it significantly drives the upward discharge of steam, and the air flow is mainly concentrated in the area near the wall of the rotor), which can help the steam in the film scraping area to be discharged more effectively under the condition of constant vacuum degree, improve the dissolution efficiency of the film scraping area, reduce the working load of the vacuum pump, and reduce the energy consumption; Figure 16The curve graph showing the variation of the material overflow coefficient with θ is presented. Structure II is the distributor structure of the present invention, and Structure I is similar to the distributor structure in the patent CN216755416. The larger the material overflow coefficient, the more serious the material overflow. By comparison, it can be seen that Structure II can effectively inhibit the overflow phenomenon compared to Structure I.

[0038] As described above, for a large-capacity thin-film evaporator for cellulose dissolution, the angles between all the inclined plates and the vertical direction are the same.

[0039] As described above, for a large-capacity thin-film evaporator for cellulose dissolution, the total number of columns of the scraping plates in the feeding area is p columns, and the diameter of the part of the rotor located in the feeding area is q mm. The value range of p / q is 2 / 171 to 4 / 171 (that is, assuming the diameter of the part of the rotor located in the feeding area is 171 mm, then the total number of columns of the scraping plates in the feeding area is 2 to 4 columns); the number of scraping plates in the same column in the feeding area is 1.

[0040] As described above, for a large-capacity thin-film evaporator for cellulose dissolution, the chamber and the rotor are coaxial; the discharge area includes a conical section located above and a straight section located below. The part of the rotor located in the conical section is in the shape of an inverted frustum, and blades are distributed on its circumferential surface. The part of the rotor located in the straight section is cylindrical, and spiral bands are distributed on its circumferential surface. The part of the rotor located in the straight section and the spiral bands together form a screw; the clearance D between the screw and the wall surface is 0.5 to 2 mm, preferably 1.2 to 1.8 mm; the lead H of the screw is 150 to 200 mm, preferably 160 to 190 mm.

[0041] Compared with the discharge structure provided by the patent CN217661550U, the present invention adds a conical section above the screw, which can effectively solve the problem of uneven dispersion and mixing of materials before the evaporator discharges materials; and the discharge structure of the device of the present invention is integrally connected with the rotor of the film scraping section, and no additional motor is required to assist in discharging materials;

[0042] Inside the conical section of the chamber, the blades distributed on the surface of the conical column can continuously stir the materials that have just been dissolved, making them fully dispersed and mixed. At the same time, material exchange between the liquid mass at the end of the blade and the liquid film on the wall surface is realized. After the materials are fully stirred and mixed, the materials enter the straight section of the chamber downward. A screw is provided in the straight section, and the materials accumulate here continuously, finally forming a certain liquid level height, forming a fixed balance with the outlet pressure. Finally, under the continuous rotation of the screw, a thrust is provided for the solution flowing into the spiral part, enabling the dissolved materials to be discharged from the thin-film evaporator in a timely and rapid manner, and transporting a continuous stream of materials to the next stage;

[0043] The clearance D between the screw and the wall surface is 0.5 - 2 mm, preferably 1.2 - 1.8 mm. Under this clearance, the leakage flow rate of the material is low, the residence time is short, the material dispersion and mixing ability is strong, and the material transportation is smoother; if the clearance between the screw ribs is too small, it will not only cause violent fluctuations in the flow rate at the outlet, generate a large amount of viscous heat, easily cause material decomposition, and the friction between the screw and the barrel will increase, making mechanical damage more likely to occur, but also greatly increase the working power of the extrusion equipment; when the clearance is too large, the shear rate drops rapidly, its shear thinning ability for the material becomes weak, which is not conducive to the dispersion and mixing of the material;

[0044] The lead H of the screw is 150 - 200 mm, preferably 160 - 190 mm. There are differences in the material rates among different regions inside the screw. The area where the material speed in the extrusion equipment is less than one percent of its maximum speed is called the dead zone, and the proportion of the dead zone is defined as the percentage of the dead zone material volume in the total volume of the reactor material; in the dead zone area, there is basically no energy exchange between materials, their momentum is almost zero, and it is easy to form small clusters and accumulate on the reactor wall, which will lead to a significant reduction or even blockage of the effective reaction area of the material in the extrusion equipment, thus affecting problems such as material transportation; the proportion of the dead zone in the selected lead range of the present invention is relatively low, the risk of material coking is reduced, the residence time of the material is shortened, and the conveying ability of the screw is strong; as the lead increases, the residence time of the material becomes shorter, the cavity space inside the screw increases, the spiral surface is relatively flat, and the conveying efficiency is high. Continuing to increase the lead has little effect on reducing the proportion of the dead zone, but will reduce the mixing effect of the material; under this structure, the transportation of the extrusion equipment is relatively stable, the energy consumption is low, the product quality is good, and the extrusion effect is excellent.

[0045] As described above, a large-capacity thin-film evaporator for cellulose dissolution, both the film scraping area and the cloth feeding area are cylindrical, with a diameter of 2 - 2.4 m.

[0046] As described above, a large-capacity thin-film evaporator for cellulose dissolution, the evaporation area of the large-capacity thin-film evaporator for cellulose dissolution is 49 - 96 m 2 。

[0047] Beneficial effects:

[0048] (1) The thin-film evaporator of the present invention has a large production capacity, and it is a large-capacity thin-film evaporator for an annual output of 40,000 - 80,000 tons of Lyocell fiber for cellulose dissolution;

[0049] (2) The thin-film evaporator of the present invention can enhance the renewal frequency of the liquid film and the exchange ability between the material mass and the liquid film, improve the heat transfer efficiency of the device, and effectively improve the dissolution ability and dissolution uniformity of the thin-film evaporator;

[0050] (3) The thin-film evaporator of the present invention can enhance the steam dissipation ability of the cloth feeding area and inhibit the overflow of the material;

[0051] (4) The thin-film evaporator of the present invention can fully mix the materials and discharge the high-quality spinning solution in a timely and stable manner; reduce vibrations during the operation of the device;

[0052] (5) In the thin-film evaporator of the present invention, the scraper structure and arrangement are reasonably designed, enabling good spatial transmission and circumferential distribution of the highly viscous materials inside the evaporator;

[0053] (6) In the thin-film evaporator of the present invention, the gap between the end of each scraper film area away from the outer periphery of the rotor and the chamber is reasonably set. The thin-film evaporator can achieve a relatively good ratio of agglomerates to films and an ideal liquid film state, that is, ensuring the evaporation efficiency while effectively limiting the torque and reducing the power; meeting the engineering requirements and ensuring economic benefits;

[0054] (7) For macromolecular substances such as cellulose, there are non-uniformities in aspects such as molecular weight and molecular structure, which in turn cause non-uniformity in the cellulose solution formed during the dissolution process; the present invention can further reduce the size of the material agglomerates, promote the radial mixing of the material agglomerates and the liquid film, avoid the influence of the unupdated liquid material inside the large-size material agglomerates on the product quality, and improve the surface renewal speed of the liquid film and the mass transfer ability between the material agglomerates and the liquid film; this effect can avoid cellulose dissolution non-uniformity to a certain extent, is beneficial to forming high-quality spinning dope and reducing the phenomenon of filter screen blockage in the solution filtration process, and reducing material waste caused during the process of replacing the filter screen;

[0055] (8) In the thin-film evaporator of the present invention, after the cellulose material enters, continuous processes of feeding, film scraping, evaporation, dissolution, and discharging are realized. The formed cellulose solution is uniform, thorough, and has excellent performance, and large-capacity production is achieved; moreover, in addition to being used in the production of cellulose fibers, this thin-film evaporator is also suitable for the cellulose dissolution process in the production of various products such as non-woven fabrics, sponges, and cellulose films. Description of the Drawings

[0056] Figure 1 is the overall structural schematic diagram of the thin-film evaporator of the present invention;

[0057] Figure 2 is the structural schematic diagram of the vertical scraper in the thin-film evaporator of the present invention;

[0058] Figure 3 is the front view of the inclined scraper in the thin-film evaporator of the present invention;

[0059] Figure 4 is the schematic diagram of the projection of the comb tooth end faces of the inclined and vertical scrapers onto the rotating shaft. Among them, the inclination angle α is: the angle between the projection of the comb tooth end face onto the rotating shaft and the vertical direction;

[0060] Figure 5Left view of the inclined scraper in the thin-film evaporator of the present invention;

[0061] Figure 6 Top view of the inclined scraper in the thin-film evaporator of the present invention;

[0062] Figure 7 Three-dimensional view of the inclined scraper in the thin-film evaporator of the present invention;

[0063] Figure 8 Schematic diagram of the discharging structure of the thin-film evaporator of the present invention;

[0064] Figure 9 Schematic diagram of the film scraping principle of the film scraping area scraper in the thin-film evaporator of the present invention;

[0065] Figure 10 Front view of the cloth feeding area scraper in the thin-film evaporator of the present invention;

[0066] Figure 11 Left view of the cloth feeding area scraper in the thin-film evaporator of the present invention;

[0067] Figure 12 Top view of the cloth feeding area scraper in the thin-film evaporator of the present invention;

[0068] Figure 13 Three-dimensional view of the cloth feeding area scraper in the thin-film evaporator of the present invention;

[0069] Figure 14 Simulation diagram of the steam trace in the cloth feeding area of the thin-film evaporator of the present invention;

[0070] Figure 15 Variation curve graph of the average radial velocity of the thin-film evaporator of the present invention with the gap between the end of each film scraping area scraper far from the outer periphery of the rotor and the chamber;

[0071] Figure 16 Variation curve graph of the material overflow coefficient with θ;

[0072] Figure 17 Comparison of the heat transfer coefficient between the inner wall surface of the thin-film evaporator of the present invention and the material and the thin-film evaporator of CN104826349A;

[0073] Among them, 1 is the motor, 2 is the rotor, 3 is the inclined plate, 4 is the support steel plate, 5 is the feed inlet, 6 is the heating medium inlet, 7 is the chamber, 8 is the vertical scraper, 9 is the blade, 10 is the screw, 11 is the steam outlet, 12 is the inclined scraper, 13 is the heating medium outlet, 14 is the vertical plate, 15 is the U-shaped opening, 16 is the liquid film, 17 is the material mass. Specific embodiments

[0074] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

[0075] A large-capacity thin-film evaporator for cellulose dissolution, as Figure 1 shown, includes a chamber 7 and a vertically rotatable rotor 2 (driven by a motor 1) disposed within the chamber 7, and the chamber 7 and the rotor 2 are coaxial; the chamber 7 is divided into a cloth-feeding area, a film-scraping area, and a discharging area arranged in sequence from top to bottom; wherein, both the film-scraping area and the cloth-feeding area are cylindrical, with a diameter of 2 - 2.4 m;

[0076] The part of the rotor 2 located in the cloth-feeding area is cylindrical, and its circumferential surface is provided with more than 40 columns of cloth-feeding area scrapers arranged along the axis direction of the rotor 2;

[0077] The total number of columns of the cloth-feeding area scrapers is p columns, the diameter of the part of the rotor 2 located in the cloth-feeding area is q mm, and the value range of p / q is 2 / 171 - 4 / 171; the number of cloth-feeding area scrapers in the same column is 1;

[0078] As Figures 10 - 13 shown,

[0079] Each cloth-feeding area scraper is composed of a vertical plate 14 and multiple inclined plates 3 arranged at intervals from top to bottom. The number of inclined plates 3 is m pieces, and the length of the cloth-feeding area scraper is n mm. The value range of m / n is 2 / 540 - 5 / 540; the vertical plate 14 is vertically arranged, the inner surface of the vertical plate 14 faces the rotor 2, and the outer surface of the vertical plate 14 faces away from the rotor 2; the inclined plates 3 are inclined and form a negative angle θ with the vertical direction, θ is 10° - 70°, and the angles of all the inclined plates 3 with the vertical direction are the same. The inclined plates 3 are fixed on the outer surface of the vertical plate 14; the inner surface of the vertical plate 14 is connected to the outer circumference of the rotor 2 through a vertically arranged support steel plate 4, and the support steel plate 4 is provided with a connecting groove;

[0080] The part of the rotor 2 located in the film-scraping area is cylindrical, and its circumferential surface is provided with more than 20 columns of film-scraping area scrapers arranged along the axis direction of the rotor 2; the film-scraping area scrapers are composed of vertical scrapers 8 and inclined scrapers 12, and the vertical scrapers 8 and the inclined scrapers 12 are provided with mounting holes;

[0081] The total number of columns of the film-scraping area scrapers is e columns, the diameter of the part of the rotor 2 located in the film-scraping area is f mm, and the value range of e / f is 4 / 171 - 7 / 171; the vertical scrapers 8 and the inclined scrapers 12 are distributed in different columns and are alternately arranged on the outer circumference of the rotor 2;

[0082] The end of each scraping film area scraper away from the outer periphery of the rotor 2 forms a comb-shaped structure by setting U-shaped openings 15 arranged at equal intervals, and the part between two adjacent U-shaped openings is a comb tooth; as Figure 2 shown, the ratio of the opening depth S of the U-shaped opening 15 to the gap L between adjacent comb teeth is less than 1.7, and S is less than 80 mm; the ratio of the gap K between adjacent U-shaped openings 15 to the gap L between adjacent comb teeth is less than 2.2, and K is less than 120 mm; the U-shaped openings 15 on the scraping film area scrapers in adjacent columns are staggered;

[0083] The root of the vertical scraper 8 is vertically arranged and connected to the rotor 2, and the end face of the comb tooth away from the outer periphery of the rotor 2 forms an angle of 0° with the vertical direction; as Figures 3 - 7 shown, the root of the inclined scraper 12 is vertically arranged and connected to the rotor 2, and the end face of the comb tooth away from the outer periphery of the rotor 2 forms a positive angle α with the vertical direction, and α is 10° - 45°; the end faces of the comb teeth of all the inclined scrapers 12 away from the outer periphery of the rotor 2 form the same angle with the vertical direction;

[0084] As Figure 9 shown, each vertical scraper is formed by bending a rectangular vertical plate I in the clockwise direction, the bending angle Φ is 1° - 40°, and the crease is a vertical line; each inclined scraper is formed by bending a rectangular vertical plate II in the clockwise direction, the bending angle Φ is 1° - 40°, and the crease is an oblique line, and the bending area is a trapezoid with a narrow upper part and a wide lower part;

[0085] The gap between the end of each scraping film area scraper away from the outer periphery of the rotor 2 and the chamber 7 is 3.5 - 4.5 mm;

[0086] As Figure 1 and Figure 8 shown, the discharge area includes a conical section at the upper part and a straight section at the lower part. The part of the rotor 2 located in the conical section is in the shape of an inverted frustum of a cone, and blades 9 are distributed on its circumferential surface. The part of the rotor 2 located in the straight section is cylindrical, and a spiral ribbon is distributed on its circumferential surface. The part of the rotor 2 located in the straight section and the spiral ribbon together form a screw 10; the gap D between the screw 10 and the wall surface is 0.5 - 2 mm; the lead H of the screw 10 is 150 - 200 mm;

[0087] The evaporation area of the large-capacity thin-film evaporator for cellulose dissolution is 49 - 96 m 2 .

[0088] Now, the working principle of the thin-film evaporator of the present invention will be described:

[0089] The overall process of liquid film formation in the thin-film evaporator shows a pattern of first forming filaments and then a film. Under the action of the scraper in the wiping film area, the material is first scraped into a ribbon-shaped film. The initial ribbon-shaped film is narrow and thin. After repeated scraping, the ribbon-shaped film gradually becomes wider and thicker. When the liquid film thickness is greater than or equal to the gap height, it can be further scraped and extended into a film by the scraper in the wiping film area. With the accumulation of time, a uniform liquid film distribution can be gradually formed on the wall surface. As Figure 9 shown, there are mainly three flow states of the material in the wiping film device, namely liquid strands, liquid film 16, and material clusters 17. In the U-shaped opening of the scraper in the wiping film area and the gap between the scrapers in the wiping film area, a strand-like liquid distribution can be seen. The present invention refers to this as liquid strands, which are mainly responsible for the axial transport of the material. At the leading edge of the scraper in the wiping film area, the material further accumulates into clusters. The fluid in the material cluster 17 shows a "vortex" velocity distribution. The streamlines in the material cluster 17 near the thin film are in the same direction as the streamlines of the thin film fluid. The material cluster 17 will be carried into the thin film fluid for mixing to achieve mass transfer. The mass transfer mainly occurs between the periphery of the material cluster 17 and the liquid film 16 because the liquid material at the periphery of the material cluster 17 has a lower viscosity and better fluidity, making it easier to carry out mass transfer with the liquid film 16. The liquid film 16 itself has no material transport function. The actual material transport is carried out by the liquid strand fluid. The liquid strand is transported through the U-shaped opening 15 of the scraper in the wiping film area and the gap between the scrapers in the wiping film area. When it is transported to the leading edge of the scraper in the wiping film area, a part of it will form the material cluster 17, which is then scraped and spread into a thin film by the scraper in the wiping film area to achieve circumferential distribution and mass transfer; the other part continues to be transported downward to achieve the axial transport of the material.

[0090] Similar to the prior art, the outer side of the thin-film evaporator of the present invention is a heating jacket. Saturated steam is introduced into the heating jacket through the heating medium inlet 6 and discharged from the heating medium outlet 13 to form a heating cycle. The steam condenses at a certain temperature and releases latent heat. After the steam condenses, a liquid film is formed, and the heat reaches the inner wall surface of the thin-film evaporator through a steady-state heat conduction of the liquid film, thereby realizing heat transfer and evaporation of the liquid film formed on the inner wall surface, and enabling the moisture in the material to evaporate rapidly. In the thin-film evaporator, after the fluid near the wall surface of the scraper in the scraping film area is shear-thinned, its fluidity increases and it is easy to spread into a film. The heat exchange between the fluid and the wall surface is mainly single-phase convective heat transfer. As the distance from the scraper in the scraping film area increases, the viscosity recovers, bubbles begin to form on the heating wall surface, and gradually develop into an air ring along the fluid flow direction, and the heat transfer mode gradually turns to two-phase boiling heat transfer. The overflow of the bubbles also causes the rupture of the local liquid film. Under the action of the scraper in the scraping film area, the liquid film forms a ring-shaped distribution on the wall surface. At the same time, the growth and rupture process of the bubbles will promote the fluid flow and improve the convective heat transfer effect in the fluid. The high-viscosity material inside the thin-film evaporator of the present invention is mainly two-phase boiling heat transfer and has a relatively high heat transfer coefficient. A relatively high vacuum degree is formed inside the thin-film evaporator through a vacuum pump, which is conducive to the smooth extraction of water vapor in the thin-film evaporator from the steam outlet 11 and reduces the saturation temperature of the material, thereby increasing the temperature difference with the heating wall surface. The material enters the inside of the thin-film evaporator from the feed port 5. After being distributed by the distributor, the scraper in the scraping film area spreads the material into a liquid film with a smaller thickness on the heating wall surface, reducing the thermal resistance and enhancing the heat transfer efficiency. This enables the moisture in the cellulose pulp to boil and evaporate rapidly and be removed quickly, the moisture content of the NMMO solution continuously decreases, and the cellulose is rapidly dissolved to form a spinning solution.

[0091] Example 1

[0092] A cellulose dissolution method using the above-mentioned thin-film evaporator, wherein:

[0093] The evaporation area is 69 m 2 ;

[0094] The inner cylinder diameters of both the scraping film area and the distribution area are 2.2 m;

[0095] The total number of rows of the scrapers in the distribution area is 26 rows, and the diameter of the part of the rotor located in the distribution area is 1710 mm;

[0096] The number of inclined plates in each scraper in the distribution area is 6 pieces, and the length of the scraper in the distribution area is 1080 mm;

[0097] θ is 52.22°;

[0098] The total number of rows of the scrapers in the scraping film area is 52 rows, and the diameter of the part of the rotor located in the scraping film area is 1710 mm;

[0099] S is 62.75 mm, K is 100 mm, and L is 50 mm;

[0100] Φ is 30°; α is 25°;

[0101] The gap between the end of each scraping film area scraper away from the outer periphery of the rotor and the chamber is 4.5 mm;

[0102] D is 1.5 mm; H is 171 mm;

[0103] The rotational speed of the thin-film evaporator is 80 rpm, and the feed temperature is 80 °C.

[0104] The ternary ratio of the inlet material is cellulose / NMMO / water (10.8% / 68.7% / 20.5%). Based on this ternary ratio, in the Lyocell production line with NMMO and water as solvents, the production capacity of Lyocell fiber is 50,000 tons per year. At this production capacity, the residence time of the material in the thin-film evaporator is 56 seconds, and the dissolution temperature is lower than 120 °C.

[0105] When using the thin-film evaporator of this embodiment for cellulose dissolution, the material absorbs the heat at the wall surface through convective heat transfer under the scraping and stirring action of the rotating scraper. Compared with another thin-film evaporator, the present invention has beneficial effects such as an obvious air extraction effect of the distributor and stronger liquid film fluctuations due to the dense and staggered arrangement of the scrapers. Under such circumstances, the heat transfer coefficient of the inner wall surface of the thin-film evaporator is increased by about 30%, thereby effectively improving the heat transfer efficiency between the inner wall surface and the material, as specifically shown in Figure 17 as follows.

Claims

1. A large-capacity thin-film evaporator for cellulose dissolution, characterized in that, it includes a chamber (7) and a vertically rotatable rotor (2) disposed within the chamber (7); the chamber (7) is divided into a cloth-feeding area, a film-scraping area, and a discharging area arranged in sequence from top to bottom; The part of the rotor (2) located in the film-scraping area is cylindrical, and the circumferential surface thereof is provided with more than 40 columns of film-scraping area scrapers arranged along the axis direction of the rotor (2); The film-scraping area scrapers include vertical scrapers (8) and inclined scrapers (12); The total number of columns of the film-scraping area scrapers is e columns, and the diameter of the part of the rotor (2) located in the film-scraping area is f mm. The value range of e / f is 4 / 171 to 7 / 171; the vertical scrapers (8) and the inclined scrapers (12) are distributed in different columns and are alternately arranged on the outer circumference of the rotor (2); The ends of each film-scraping area scraper away from the outer circumference of the rotor (2) form a comb-shaped structure by arranging U-shaped openings at intervals, and the part between adjacent two U-shaped openings is a comb tooth; the U-shaped openings on the film-scraping area scrapers in adjacent columns are staggered; The root of the vertical scraper (8) is vertically arranged and connected to the rotor (2), and the end surface of the comb tooth away from the outer circumference of the rotor (2) forms an angle of 0° with the vertical direction; the root of the inclined scraper (12) is vertically arranged and connected to the rotor (2), and the end surface of the comb tooth away from the outer circumference of the rotor (2) forms a positive angle α with the vertical direction, and α is 10° to 45°; The gap between the end of each film-scraping area scraper away from the outer circumference of the rotor (2) and the chamber (7) is 3.5 to 4.5 mm.

2. The large-capacity thin-film evaporator for cellulose dissolution according to claim 1, characterized in that, the end surfaces of the comb teeth of all the inclined scrapers (12) away from the outer circumference of the rotor (2) form the same angle with the vertical direction.

3. The large-capacity thin-film evaporator for cellulose dissolution according to claim 1, characterized in that, the ratio of the opening depth S of the U-shaped opening to the gap L between adjacent comb teeth is less than 1.7, and S is less than 80 mm; the ratio of the gap K between adjacent U-shaped openings to the gap L between adjacent comb teeth is less than 2.2, and K is less than 120 mm.

4. The large-capacity thin-film evaporator for cellulose dissolution according to claim 3, characterized in that, the U-shaped openings in each film-scraping area scraper are arranged at equal intervals.

5. The large-capacity thin-film evaporator for cellulose dissolution according to claim 1, characterized in that, each vertical scraper is formed by bending a rectangular vertical plate I in the clockwise direction, and the bending angle Φ is 1° to 40°, and the fold line is a vertical line; each inclined scraper is formed by bending a rectangular vertical plate II in the clockwise direction, and the bending angle Φ is 1° to 40°, and the fold line is an oblique line, and the bending area is a trapezoid with a narrow upper part and a wide lower part.

6. The large-capacity thin-film evaporator for cellulose dissolution according to claim 1, characterized in that, the part of the rotor (2) located in the cloth-feeding area is cylindrical, and the circumferential surface thereof is provided with more than 20 columns of cloth-feeding area scrapers arranged along the axis direction of the rotor (2); Each scraper in the cloth area is composed of a vertical plate (14) and multiple inclined plates (3) arranged at intervals from top to bottom. The number of inclined plates (3) is m, and the length of the scraper in the cloth area is n mm. The value range of m / n is 2 / 540 - 5 / 540; the vertical plate (14) is vertically arranged, the inner surface of the vertical plate (14) faces the rotor (2), and the outer surface of the vertical plate (14) faces away from the rotor (2); the inclined plates (3) are inclined and form a negative angle θ with the vertical direction, θ is 10° - 70°, and the inclined plates (3) are fixed on the outer surface of the vertical plate (14); the inner surface of the vertical plate (14) is connected to the outer circumference of the rotor (2) through a vertically arranged support steel plate (4).

7. A large-capacity thin-film evaporator for cellulose dissolution according to claim 6, characterized in that, all the inclined plates (3) have the same angle with the vertical direction.

8. A large-capacity thin-film evaporator for cellulose dissolution according to claim 6, characterized in that, the total number of columns of the scrapers in the cloth area is p columns, the diameter of the part of the rotor (2) located in the cloth area is q mm, and the value range of p / q is 2 / 171 - 4 / 171; the number of scrapers in the cloth area in the same column is 1.

9. A large-capacity thin-film evaporator for cellulose dissolution according to claim 1, characterized in that, the chamber (7) and the rotor (2) are coaxial; the discharge area includes a conical section at the upper part and a straight section at the lower part. The part of the rotor (2) located in the conical section is in the shape of an inverted frustum of a cone, and blades are distributed on its circumferential surface. The part of the rotor (2) located in the straight section is cylindrical, and spiral bands are distributed on its circumferential surface. The part of the rotor (2) located in the straight section and the spiral bands together form a screw (10); the clearance D between the screw (10) and the wall surface is 0.5 - 2 mm; the lead H of the screw (10) is 150 - 200 mm.

10. A large-capacity thin-film evaporator for cellulose dissolution according to claim 1, characterized in that, The evaporation area of the large-capacity thin-film evaporator for cellulose dissolution is 49 to 96 m 2 .

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