Evaporation process for reducing NMMO solvent discoloration through one-time material passing

Abstract

The invention relates to the technical field of evaporation processes, and particularly discloses an evaporation process for reducing NMMO solvent discoloration through one-time material passing, which comprises multiple-effect heaters and a separator, the multiple-effect heaters and the separator form an evaporation circulation system, the multiple-effect heaters are connected in series, and the separator is connected with the evaporation circulation system. The multi-effect heater is composed of a distribution device, a heater shell, a heat exchange pipe, a pipe plate, a guide cylinder and a discharging bin, a feeding pipe is installed at the top of the distribution device, materials enter the heater from the feeding pipe, the heat exchange pipe is fixedly installed in the heater, the materials enter the bottom discharging bin after heat exchange at the heat exchange pipe, and part of material liquid forms steam; by arranging the evaporation circulation system, only a small amount of live steam is needed, the use amount of the live steam is greatly reduced, the system operation cost is reduced, the investment and operation cost of a boiler are reduced, environmental pollution is reduced, and compared with a traditional evaporator, the temperature difference is small, mild evaporation is achieved, the product quality is improved, and scaling of a heat exchange pipe is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of evaporation processes, and more particularly to an evaporation process for reducing the discoloration of NMMO solvent by single-pass feeding. Background Art

[0002] The production of chemical fibers by the solvent method is a production process method for new fibers. The solvent used is an aqueous solution of N-methylmorpholine-N-oxide (NMMO). The concentration of this solution after dissolving and separating the fibers is 15-20%, and the required concentration for reuse after concentration is 85% or 65%.

[0003] When using a multi-effect evaporation process for NMMO solvent concentration, there are certain limitations. From the principle of multi-effect evaporation, the more effects, the more energy-saving. While ensuring a reasonable temperature difference between each effect will limit the number of effect bodies; too small a temperature difference will not only increase equipment investment but also not achieve obvious energy-saving effects. Therefore, when the temperature of the last effect is determined, the number of effects depends on the temperature of the primary steam. The higher the temperature of the primary steam, the more effects can be set for the device.

[0004] Experiments have proved that the NMMO solvent begins to show signs of accelerated decomposition at ≥110°C. As the temperature continues to rise, the solvent decomposition reaction intensifies; this easy decomposition characteristic of the NMMO solvent limits the maximum temperature of the primary steam. At the same time, during the concentration process, as the concentration of the NMMO solvent increases, the boiling point of the solution will correspondingly increase. In summary, the evaporation concentration system of the NMMO solvent is generally selected as 6-effect, and it is difficult to have major improvements and optimizations.

[0005] It can be seen that the current evaporator cannot accurately control the heating temperature, the temperature difference is large, and the evaporation process is relatively intense, resulting in a large color change of the produced product when the temperature difference is large, leading to low production quality of the product and high energy consumption. In addition, the direct discharge separator used in the current evaporation makes it impossible to increase the retention time of the steam, resulting in a large water content in the steam and ineffective compression and utilization for secondary precise temperature increase. Summary of the Invention

[0006] In order to overcome the above-mentioned defects of the prior art, the present invention provides an evaporation process for reducing the discoloration of NMMO solvent by single-pass feeding to solve the problems existing in the above background art.

[0007] The present invention provides the following technical solution: An evaporation process for reducing the discoloration of NMMO solvent by one-time feeding, which includes a multi-effect heater and a separator. The multi-effect heater and the separator form an evaporation circulation system. The multi-effect heaters are connected in series. The multi-effect heater is composed of a distribution device, a heater shell, a draft tube and a blanking bin. A feed pipe is installed at the top of the distribution device. The material enters the interior of the heater from the feed pipe. Heat exchange tubes are fixedly installed inside the heater. After heat exchange at the heat exchange tubes, the material enters the bottom blanking bin. Part of the liquid forms steam. The liquid accumulates at the blanking bin, and the liquid is discharged from the bottom discharge port. The heated steam enters the separator through the tangential pipe, and after rotation, it is compressed and heated again by the compression component and then enters the heater;

[0008] Further, a rotary collection device is provided at the top of the separator. The rotary collection device includes a secondary gas pipe and a collection cover. The secondary gas pipe extends a certain distance inside the upper head. Air holes are provided on the outer side of the end of the secondary gas pipe extending inward. The bottom of the extended end is fixedly connected with the collection cover.

[0009] Further, the tangential pipe is installed at the tangent position of the circular cylinder wall. The secondary gas entraining the material enters the separator through the tangential pipe. Since the tangential pipe and the separator are at an oblique cut angle, the secondary gas forms a swirling airflow after entering the separator.

[0010] Further, the multi-effect heater includes a first-effect heater, a second-effect heater, a third-effect heater, a fourth-effect heater, a fifth-effect heater and a sixth-effect heater. The heat exchange gas used in the first-effect heater is live steam and compressed secondary steam, and the steam used in the remaining heaters is secondary steam.

[0011] Further, the distribution device is composed of an upper receiving plate, a lower cloth plate, a disk body, an anti-impact baffle, a disk opening and a support. A plurality of distribution holes are evenly distributed on the receiving plate and the cloth plate according to equilateral triangles. The positions of the small holes on the receiving plate are staggered with the positions of the small holes on the cloth plate and correspond to the small holes on the tube plate. Correspondingly, the positions of the small holes on the cloth plate are staggered with the positions of the tube plate holes.

[0012] Further, a feed pump and a raw material tank are placed on the side of the heater, and a compression component is placed on the other side. Both ends of the compression component are communicated with the steam outlet of the heater and the steam outlet of the separator through pipelines respectively.

[0013] Further, the compression component is a blower or a compressor. The blower is installed in a single or two-series connection mode.

[0014] Further, a discharge port is provided at the bottom of the separator. The discharge port is communicated with the bottom discharge port of the heater, and the other end is jointly connected with the feed port of the next-stage heater.

[0015] The technical effects and advantages of the present invention:

[0016] 1. The present invention is provided with an evaporation circulation system, which is beneficial for only requiring a small amount of live steam, greatly reducing the consumption of live steam, lowering the system operation cost, reducing the investment and operation expenses of the boiler, reducing environmental pollution, having a smaller temperature difference compared with traditional evaporators, gentle evaporation, improving product quality, and reducing the scaling of heat exchange tubes.

[0017] 2. The present invention is provided with a compression component, which is beneficial for controlling the process temperature below 90°C. Through the temperature control during the concentration process, the antioxidant performance of the NMMO solvent is enhanced, thereby improving the solvent recovery rate and effectively solving the problem of solvent color change.

[0018] 3. The present invention is provided with a rotary complementation device, which is beneficial for using the gas to turn back downward and discharging from the bottom air holes, increasing the residence time, fully separating the materials entrained in the secondary steam, and thus making the secondary steam relatively clean and reusable. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the evaporation process for the color change of the NMMO solvent of the present invention.

[0020] Figure 2 It is a schematic diagram of single - fan compressed steam of the present invention.

[0021] Figure 3 It is a schematic diagram of multi - fan compressed steam of the present invention.

[0022] Figure 4 It is a schematic diagram of the inlet and outlet of materials and steam of the present invention.

[0023] Figure 5 It is a schematic diagram of the overall structure of the present invention.

[0024] Figure 6 It is a schematic diagram of the steam flow direction inside the separator structure of the present invention.

[0025] Figure 7 It is a top view of the separator structure of the present invention.

[0026] Figure 8 It is a schematic diagram of the distribution device structure of the present invention.

[0027] Figure 9 It is a top view of the distribution device structure of the present invention.

[0028] Figure 10 It is an assembly schematic diagram of the distribution device structure of the present invention.

[0029] The reference numerals are: 1, raw material tank; 2, feed pump; 3, feed pipe; 4, distribution device; 5, material receiving plate; 6, cloth distributing plate; 7, disc body; 8, disc opening; 9, tube sheet; 10, distribution holes; 11, heat exchange tubes; 12, heating steam; 13, heater housing; 14, impact baffle; 15, draft tube; 16, baffle plate; 17, blanking bin; 18, tangential tube; 19, circular cylinder wall; 20, upper head; 21, rotary collection device; 22, secondary gas pipe; 23, collection cover; 24, compression assembly; 25, rotary air flow. Detailed implementation manners

[0030] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the accompanying drawings in the present invention. In addition, the forms of each structure described in the following implementation manners are only examples. An evaporation process for reducing the discoloration of NMMO solvent by one-time feeding does not limit to the structures described in the following implementation manners. All other implementation manners obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0031] Referring to Figure 1 and Figure 5 , the present invention provides an evaporation process for reducing the discoloration of NMMO solvent by one-time feeding, including a multi-effect heater and a separator. The multi-effect heater and the separator form an evaporation circulation system. The multi-effect heaters are connected in series. The multi-effect heater is composed of a distribution device 4, a heater housing 13, a draft tube 15 and a blanking bin 17. The top of the distribution device 4 is provided with a feed pipe 3. The material enters the interior of the heater from the feed pipe 3. The heat exchange tubes 11 are fixedly installed inside the heater. The material forms heating steam 12 at the heat exchange tubes 11 and enters the bottom blanking bin 17 through the baffle plate 16. The liquid material accumulates at the blanking bin 17, and the liquid is discharged from the bottom discharge port. The heated steam enters the separator from the tangential tube 18 and is compressed again by the compression assembly 24 after rotation. The feed pump 2 and the raw material tank 1 are placed on the side of the heater, and the compression assembly 24 is placed on the other side. Both ends of the compression assembly are communicated with the steam outlet of the heater and the steam outlet of the separator through pipelines respectively;

[0032] In this embodiment, it should be specifically noted that: the multi-effect heater includes a first-effect heater, a second-effect heater, a third-effect heater, a fourth-effect heater, a fifth-effect heater and a sixth-effect heater. The heat exchange gas used in the first-effect heater is live steam and compressed secondary steam, and the steam used in the remaining heaters is secondary steam to reuse the steam and reduce energy consumption.

[0033] The main difference between this embodiment and the prior art is that in this embodiment, when starting up with a small amount of live steam, supplementary steam heating is required, which greatly reduces the consumption of live steam, lowers the system operation cost, avoids the long-term circulation of the liquid material in the equipment, and reduces the heating time of the liquid material. Specifically, it lies in the evaporation circulation system and the compression component 24;

[0034] The above structure is the main structure of this embodiment, which solves the problem of high energy consumption caused by the direct discharge of high-temperature steam in the evaporation process of NMMO solvent at present, and reduces the Maillard reaction of the liquid material.

[0035] Refer to Figures 2-4 , for the compression component 24, a blower or a compressor is used. In a mechanical vapor recompression (MVR) evaporator: the secondary steam generated after the gas-liquid separation in the separator is compressed by the compressor blower, and its pressure and temperature increase, and the enthalpy increases. Then it is transported to the heater as the heat source of the heating steam 12, so that the secondary steam that was originally to be discarded and cooled is fully utilized, the latent heat is recovered, and the thermal efficiency is improved; the demand for external heating and cooling resources is reduced, the energy consumption is lowered, and the pollution is reduced.

[0036] In this embodiment, it should be specifically noted that: for a once-through MVR evaporator, attention should be paid to the selection of the temperature rise of the NMMO solvent under different concentration conditions. After the concentration of the NMMO solvent reaches 78%, the boiling point elevation value ≥ 30°C. Therefore, live steam is used as the heat source, and the concentration of the liquid material is increased from the concentration after two-stage blower concentration to 78% through a single-effect evaporator to complete the third concentration, meeting the discharge concentration requirement of the finished product and entering the next process.

[0037] Refer to Figures 6-7 , a rotary collection device 21 is provided at the top of the separator. The rotary collection device 21 includes a secondary gas pipe 22 and a collection cover 23. The secondary gas pipe 22 extends a certain distance inside the upper head 20. An air hole is opened on the outer side of the end of the secondary gas pipe 22 extending inward. The bottom of the extended end is fixedly connected with the collection cover 23, so that the gas directly upward cannot directly discharge from the secondary gas pipe 22 from bottom to top under the action of the collection cover 23, but is blocked by the collection cover 23 and bypasses the collection cover 23 to discharge upward from the air hole. The gas rotating upward along the cylinder wall also cannot directly discharge from the secondary gas pipe 22. Under the influence of the extended part, the gas turns back downward and discharges from the bottom air hole, increasing the residence time, enabling the materials entrained in the secondary vapor to be fully separated, and thus making the secondary steam relatively clean and reusable.

[0038] In this embodiment, it should be specifically noted that: a discharge port is opened at the bottom of the separator. The discharge port is communicated with the bottom discharge port of the heater, and the other end is jointly connected to the feed port of the next-stage heater.

[0039] Refer to Figure 7, the tangential pipe 18 is installed at the tangent position of the circular cylinder wall 19, and the secondary gas entraining materials enters the separator through the tangential pipe 18. Since the tangential pipe 18 and the separator are at an oblique cutting angle.

[0040] In this embodiment, it should be specifically noted that: the material mixed with the secondary steam falls into the heater feed bin 17 for primary separation. The concentrated liquid converges in the heater feed bin 17. The secondary steam entraining materials enters the separator through the tangential pipe 18. The tangential pipe 18 and the separator are at an oblique cutting angle to separate the materials entrained by the secondary steam through tangential feeding. The pressure pushes the gas to rush quickly towards the circular cylinder wall 19 to form a rotating air flow 25. The air flow forms a rotating air flow when it encounters the circular cylinder wall 19 and moves upward along the container wall in a rotating manner.

[0041] Refer to Figures 8-10 , the distribution device 4 is composed of an upper material receiving plate 5, a lower material distributing plate 6, a disc body 7, a disc opening 8 and a support. A plurality of small holes are evenly distributed on the material receiving plate 5 and the material distributing plate 6 in an equilateral triangle pattern. The positions of the small holes on the material receiving plate 5 are staggered with those on the material distributing plate 6 and correspond to the small holes on the tube sheet 9. Correspondingly, the positions of the small holes on the material distributing plate 6 are staggered with those of the holes on the tube sheet 9.

[0042] In this embodiment, it should be specifically noted that: after the liquid enters the distribution device 4, the liquid falls onto the material receiving plate 5. The material receiving plate 5 distributes the liquid to the material distributing plate 6 through the distribution holes 10. The material distributing plate 6 then continues to evenly distribute it onto the surface between the tubes of the tube sheet 9 through the distribution holes 10. The liquid on the surface of the tube sheet 9 is evenly distributed onto the inner surface of each heat exchange tube 11 to form a uniformly downward flowing thin liquid film on the inner wall of the tube bank and realize heat exchange with the heating medium outside the tube.

[0043] The working principle of the present invention:

[0044] The main problems solved by this embodiment are: when starting up with a small amount of live steam, steam heating needs to be supplemented, which greatly reduces the consumption of live steam, reduces the system operation cost, avoids the long-term circulation of the liquid in the equipment, reduces the heating time of the liquid, solves the problem of high energy consumption caused by the direct discharge of high-temperature steam in the evaporation process of the current NMMO solvent, and reduces the Maillard reaction of the liquid.

[0045] The specific steps are as follows:

[0046] The material is pumped out from the raw material tank 1 by the feed pump 2, enters the upper head 20 of the heater, and exits the feed pipe 3 for feeding, and enters the distribution device 4 for distribution. After the liquid material enters the distribution device 4, the liquid material falls to the receiving plate 5, and the receiving plate 5 distributes the liquid material to the distribution plate 6 through the distribution holes 10. The distribution plate 6 continues to distribute the liquid material to the surface of the tubes of the tube sheet 9 through the distribution holes 10. The liquid material on the surface of the tube sheet 9 is evenly distributed to the inner surface of each heat exchange tube 11, forming a uniform thin liquid film flowing downward on the inner wall of the tube array, and realizing heat exchange with the heating medium outside the tube;

[0047] At this time, the heating steam 12 enters from the heater shell 13, passes through the anti-collision baffle 14, the guide tube 15, the baffle 16, and spreads all over the heater shell 13;

[0048] The heating steam 12 flows outside the heat exchange tube 11, and the heat is transferred to the liquid film through the wall surface, causing it to heat up rapidly and partially evaporate;

[0049] The material mixed with the secondary steam falls into the lower hopper 17 of the heater for a separation. The concentrated liquid material gathers in the lower hopper 17 of the heater. The secondary steam carries the material into the separator through the tangential pipe 18. The tangential pipe 18 is at an oblique angle to the separator to carry out tangential feeding and separation of the material carried by the secondary steam. The pressure pushes the gas to rush quickly toward the circular cylinder wall 19. The airflow encounters the circular cylinder wall 19 to form a rotating airflow, which rotates and moves upward along the container wall. Most of the material in the secondary steam condenses into concentrated liquid during the rising process and separates from the gas and gathers at the bottom of the separator. When it reaches the upper head 20 of the separator, only a small part of the material is carried by water vapor. Since the secondary gas pipe 22 extends a distance inside the upper head 20 and a supplementary cover 23 is provided at the end, the secondary steam cannot directly go up from the bottom or rotate out directly from the head, which increases the residence time and obstruction, allowing the material carried by the secondary steam to be fully separated, so that the secondary steam is relatively clean and can be reused.

[0050] The relatively clean secondary steam is sucked in and compressed by the compression assembly 24. After compression, the temperature and pressure of the secondary steam are significantly increased, and it becomes high-temperature and high-pressure steam. The generated steam is sent back to the heater housing 13 and used as a heat source to heat the liquid again, so that only a small amount of raw steam is needed for the entire evaporation process, which greatly reduces the use of raw steam and reduces the system operation cost.

[0051] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A one-time material transfer and NMMO solvent discoloration evaporation process, comprising a multi-effect heater and a separator, characterized in that: The multi-effect heater and the separator form an evaporation circulation system. The multi-effect heater is connected in series. The multi-effect heater is composed of a distribution device (4), a heater shell (13), a heat exchange tube (11), a tube sheet (9), a guide tube (15) and a lower bin (17). A feed pipe (3) is installed on the top of the distribution device (4). The material enters the interior of the heater from the feed pipe (3). A heat exchange tube (11) is fixedly installed inside the heater. The material forms heating steam (12) through heat exchange at the heat exchange tube (11). The heating steam passes through a baffle (16) and enters the lower bin (17) at the bottom. The material liquid accumulates at the lower bin (17). The liquid is discharged from the bottom discharge port. The heated steam enters the separator from the tangential tube (18). After rotation, the steam is compressed and heated again through a compression assembly (24) and enters the heater. A rotary collecting device (21) is arranged at the top of the separator, and the rotary collecting device (21) comprises a secondary air pipe (22) and a collecting cover (23). The secondary air pipe (22) extends a certain distance inside the upper cover (20), and an air hole is provided on the outer side of the end of the secondary air pipe (22) extending inwardly, and the bottom of the extending end is fixedly connected to the collecting cover (23).

2. The evaporation process of reducing NMMO solvent discoloration by one-time feeding according to claim 1, characterized in that: The tangential pipe (18) is installed at a tangent position of the circular cylinder wall (19). The secondary gas carries the material through the tangential pipe (18) and enters the separator. Since the tangential pipe (18) and the separator are at an oblique angle, the secondary gas forms a rotating airflow (25) after entering the separator.

3. The evaporation process of reducing NMMO solvent discoloration by one-time feeding according to claim 1, characterized in that: The multi-effect heater includes a single-effect heater, a double-effect heater, a triple-effect heater, a quadruple-effect heater, a five-effect heater and a six-effect heater, wherein the heat exchange gas used by the single-effect heater is raw steam and compressed secondary steam, and the steam used by the other heaters is secondary steam.

4. The evaporation process of reducing NMMO solvent discoloration by one-time feeding according to claim 1, characterized in that: The distribution device (4) is composed of an upper material receiving plate (5), a lower material distributing plate (6), a disk body (7), an impact baffle (14), a disk mouth (8) and a support. The material receiving plate (5) and the material distributing plate (6) are provided with a plurality of distribution holes (10) evenly distributed in the form of an equilateral triangle. The positions of the small holes on the material receiving plate (5) are staggered with the positions of the small holes on the material distributing plate (6) and correspond to the small holes on the tube plate (9). Accordingly, the positions of the small holes on the material distributing plate (6) and the holes on the tube plate (9) are staggered.

5. The evaporation process of reducing NMMO solvent discoloration by one-time feeding according to claim 1, characterized in that: A feed pump (2) and a raw material tank (1) are placed on one side of the heater, and a compression assembly (24) is placed on the other side. Both ends of the compression assembly (24) are connected to the steam outlet of the heater and the steam outlet of the separator through pipelines.

6. The evaporation process of reducing NMMO solvent discoloration by one-time feeding according to claim 5, characterized in that: The compression assembly (24) is a compressor used by a fan, and the fan is installed in a single or two series manner.

7. The evaporation process of claim 1 for reducing discoloration of NMMO solvent by one-time feeding, characterized in that: A discharge port is provided at the bottom of the separator, the discharge port is communicated with the discharge port at the bottom of the heater, and the other end is connected with the feed port of the next-stage heater.

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