A production device for efficient solvent recovery in the slurry-based CMC production process

Abstract

This utility model relates to a production device for efficient solvent recovery in the slurry-based CMC production process, belonging to the field of chemical solvent recovery and environmental protection and energy-saving technology. It includes a stripper, a scrubbing absorption tower, a vacuum pump, a condenser, and a water absorption tower. The exhaust gas from the stripper, containing CMC dust, solvent, and water vapor, is directly fed into the scrubbing absorption tower. Fresh filtrate from the filter is used as the scrubbing liquid to efficiently wash and recover the dust in the exhaust gas, while the gaseous solvent and water vapor are condensed and absorbed. The scrubbing liquid is circulated under controlled temperature by a cooler, and a portion of the enriched liquid is returned to the filtration system to achieve solid-liquid separation and resource reuse. The purified exhaust gas sequentially passes through the pre- and post-vacuum pump condensers and the water absorption tower to complete multi-stage solvent recovery. This device avoids the clogging problem caused by dust adhesion in traditional dust removal equipment, significantly improves the solvent recovery rate and system operational stability, achieves full recovery of CMC dust and solvent, and reduces resource waste and environmental pollution.

Description

Technical Field

[0001] This application relates to the fields of chemical solvent recovery and environmental protection and energy conservation technology, and in particular to a production device for efficient solvent recovery in the slurry-based CMC production process. Background Technology

[0002] Sodium carboxymethyl cellulose (CMC), an important water-soluble cellulose ether, is widely used in food, pharmaceuticals, daily chemicals, and oil drilling. In the slurry production process, isopropanol, ethanol, or methanol are typically used as solvents in the reaction and washing processes. These solvents do not participate in the chemical reaction but are present throughout the entire production process; therefore, efficient recycling is essential to achieve reuse, reduce production costs, and minimize environmental pollution.

[0003] In existing technologies, residual solvent in CMC filter cake is mainly recovered by evaporation under vacuum and heating conditions using a jacketed twin-shaft horizontal stripper. The exhaust gas generated during the stripping process contains solvent vapor, water vapor, and fine CMC dust. Traditional processes use cyclone dust collectors or bag filters to remove dust first, then condense and recover the solvent using two-stage condensers before and after the vacuum pump, and finally send the solvent to a water absorption tower for further absorption of residual solvent. Although this process can achieve basic recovery, it has revealed many problems in actual operation.

[0004] Regarding the aforementioned technologies, the coexistence of dust and water vapor in the exhaust gas easily leads to condensation under temperature gradient changes, which combines with CMC dust to form a viscous substance. This causes severe clogging of the inner walls of cyclone dust collectors, filter bags in baghouse dust collectors, and discharge valves, requiring frequent shutdowns for cleaning. More seriously, dust that is not effectively removed enters the subsequent condenser with the exhaust gas, causing scaling and blockage of the heat exchange tube bundles, reducing condensation efficiency. Some fibrous dust even enters the water absorption tower, adhering to the surface of the packing material, disrupting mass transfer and reducing absorption capacity. Therefore, effectively solving the system blockage problem caused by the synergistic effect of dust and moisture in the exhaust gas has become a key technical challenge for improving solvent recovery efficiency and ensuring continuous and stable operation of the equipment. Utility Model Content

[0005] To solve the above-mentioned technical problems, this utility model provides a production device for efficient solvent recovery in the slurry-based CMC production process.

[0006] This utility model provides a production device for efficient solvent recovery in the slurry-based CMC production process, which adopts the following technical solution:

[0007] A production apparatus for efficient solvent recovery in the slurry-based CMC production process includes a stripper, a washing absorption tower, a circulating pump, a washing liquid cooler, a vacuum pump, a pre-vacuum pump condenser, a post-vacuum pump condenser, and a water absorption tower. The tail gas outlet of the stripper is directly connected to the tail gas inlet of the washing absorption tower via a pipeline. The washing liquid outlet of the washing absorption tower is connected to a spray device at its top via the circulating pump. The washing liquid cooler is located on the pipeline between the circulating pump and the spray device. The bottom of the washing absorption tower has a solid-containing washing liquid discharge outlet for discharging a portion of the circulating washing liquid to a filter for solid-liquid separation. The top clean gas outlet of the washing absorption tower is sequentially connected to the vacuum pump, the pre-vacuum pump condenser, and the post-vacuum pump condenser. The tail gas outlet of the post-vacuum pump condenser is connected to the bottom air inlet of the water absorption tower. The water absorption tower has a three-layer countercurrent absorption structure, including a top clean water spray section, a middle cooling absorption section, and a bottom low-temperature absorption section.

[0008] Optionally, the washing liquid cooler is a shell-and-tube heat exchanger, and the cooling medium is circulating water or chilled water, used to control the temperature of the circulating washing liquid within the range of 30 to 60°C, so as to improve the condensation and absorption efficiency of the gaseous solvent.

[0009] Optionally, the stripper is a twin-shaft horizontal stripper with an outer jacket, the outer jacket is heated by steam at 130-190°C, the internal operating pressure is -0.70 to -0.98 kPa(G), and the material temperature is maintained at 65-140°C.

[0010] Optionally, the vacuum pump is a water ring vacuum pump, wherein the water ring liquid is an isopropanol aqueous solution, an ethanol aqueous solution, or a methanol aqueous solution that is matched with the recovered solvent, and the water ring liquid is cooled by chilled water through an external cooler to improve vacuum stability.

[0011] Optionally, both the pre-vacuum pump condenser and the post-vacuum pump condenser are shell-and-tube multi-pass condensers, with 32°C circulating water and -15°C chilled water as the cooling media, respectively. The exhaust gas outlet temperature of the pre-vacuum pump condenser is controlled between 20°C and 35°C, and the exhaust gas outlet temperature of the post-vacuum pump condenser is controlled between 10°C and 30°C.

[0012] Optionally, the water absorption tower adopts a structured packing or random packing, and the tower is divided into three absorption zones from top to bottom: the top is a cold water spray zone at 10-20℃, the middle section absorbent is cooled to 20-35℃ by chilled water, the bottom air inlet temperature is 10-30℃, and the absorbent temperature is controlled at 15-30℃.

[0013] Optionally, the operating liquid-to-gas ratio of the washing absorption tower is 0.015 to 0.030 (volume ratio), and the operating pressure is consistent with that of the stripper, which is -0.70 to -0.98 kPa (G).

[0014] Optionally, the stripper exhaust pipe is equipped with a heat insulation layer throughout to prevent moisture in the gas phase from condensing prematurely and causing dust to stick to the wall.

[0015] Optionally, a removable filter screen is provided on the pipeline at the outlet of the washing liquid of the washing absorption tower.

[0016] In summary, this utility model has at least one of the following beneficial technical effects:

[0017] 1. By using a scrubbing absorption tower instead of a traditional cyclone or bag filter, and by using fresh filtrate to directly scrub the stripping exhaust gas, the simultaneous recovery of CMC dust and solvent is achieved, avoiding dust clogging problems and significantly improving the system's continuous operation capability.

[0018] 2. By adopting a multi-stage condensation and three-layer water absorption tower structure, a higher solvent recovery rate is achieved due to the optimization of temperature gradient and absorption path, while reducing exhaust gas emissions and achieving a dual improvement in environmental protection and economic benefits. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of a production device for efficient solvent recovery in the slurry-based CMC production process.

[0020] Figure 2 This is a cross-sectional schematic diagram of a production device for efficient solvent recovery in the slurry-based CMC production process.

[0021] Figure 3 yes Figure 2 Enlarged view of section A.

[0022] Explanation of reference numerals in the attached drawings: 1. Stripper; 2. Washing absorption tower; 21. Circulating pump; 22. Washing liquid cooler; 23. Filter screen; 231. Connecting plate; 232. Connecting rod; 233. Clamping block; 234. Handle; 24. Condenser before vacuum pump; 25. Condenser after vacuum pump; 26. Water absorption tower; 27. Spraying device. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to all the accompanying drawings.

[0024] Example 1

[0025] Reference Figure 1 , Figure 2 and Figure 3This embodiment discloses a production apparatus for efficient solvent recovery in the slurry-based CMC production process, including a stripper, a washing absorption tower, a circulating pump, a washing liquid cooler, a vacuum pump, a pre-vacuum pump condenser, a post-vacuum pump condenser, and a water absorption tower. The stripper is a twin-shaft horizontal stripper with an external jacket. Its tail gas outlet is directly connected to the tail gas inlet at the lower side of the washing absorption tower via a pipe with an insulation layer, and the top of the stripper is connected to the vacuum pump. A spray device is installed at the top of the washing absorption tower. The washing liquid outlet at the bottom of the washing absorption tower is connected to the inlet of the spray device via the circulating pump. The washing liquid cooler is a shell-and-tube heat exchanger installed on the outlet pipe of the circulating pump, using -15℃ chilled water as the cooling medium to control the temperature of the circulating washing liquid at approximately 45℃. A solids-containing washing liquid discharge outlet is also provided at the bottom of the washing absorption tower.

[0026] Reference Figure 1 , Figure 2 and Figure 3 The clean gas outlet at the top of the scrubbing absorption tower is sequentially connected to a water ring vacuum pump, a pre-vacuum pump condenser, and a post-vacuum pump condenser. The latter two are both multi-pass tubular structures, cooled by 32℃ circulating water and -15℃ chilled water, respectively, with tail gas outlet temperatures controlled at 30℃ and 20℃. The tail gas from the post-vacuum pump condenser enters the bottom of the water absorption tower, which is filled with structured packing material in three layers: the top layer is a 15℃ cold water spray section; the middle layer's absorbent liquid is cooled to 25℃ by chilled water; and the bottom layer has an inlet gas temperature of 20℃ and an absorbent liquid temperature controlled at 20℃. When the bottom absorbent liquid concentration reaches 5%, it is returned to the production system for reuse.

[0027] Reference Figure 1 , Figure 2 and Figure 3 The washing liquid outlet of the washing absorption tower is equipped with a detachable filter screen. A semi-circular connecting plate is connected to the filter screen, and the connecting plate has several connecting slots. Several connecting rods are fixedly connected to the filter screen, with each connecting rod corresponding to a connecting slot. A locking block is hinged to the end of each connecting rod away from the filter screen. When the filter screen is stable, the connecting rod is located at the connecting slot, and the locking block is locked onto the side of the filter screen away from the connecting rod. The connecting plate has a handle for removing the connecting plate and bolts for connecting the pipeline to the connecting plate. When the connecting plate needs to be installed, the operator installs the filter screen on the connecting plate, then inserts it into the opening of the pipeline, and then secures it with bolts, which improves work efficiency.

[0028] The implementation principle of Example 1 is as follows: The wet CMC filter cake from the reaction system enters the stripper. Under jacketed steam heating (160°C) and vacuum (-0.90 kPa(G)), the solvent and water rapidly vaporize, carrying fine CMC dust to form "stripping tail gas." This tail gas enters the scrubbing absorption tower directly through an insulated pipe, where it comes into countercurrent contact with the filtrate from the circulating pump. The scrubbing liquid washes the dust into the liquid phase, while the gaseous solvent and water vapor are condensed and absorbed, and the heat is removed by the scrubbing liquid cooler. The enriched solid-containing scrubbing liquid is partially discharged, the filter cake is recovered, and the diluted filtrate is returned to the system. The purified tail gas is compressed by a vacuum pump and the solvent is further recovered in a two-stage condenser. Finally, the residual gas undergoes three-stage countercurrent absorption in a water absorption tower to meet emission standards. The entire system avoids dust clogging and achieves efficient recovery of solvent and product.

[0029] Example 2

[0030] The difference in this embodiment is that the spray device in Embodiment 1 is replaced with a ceramic umbrella-shaped nozzle array, which has a wide flow channel design and also has anti-clogging capabilities. Simultaneously, the washing liquid cooler is replaced from a shell-and-tube type to a plate heat exchanger, resulting in higher heat exchange efficiency and a smaller footprint. The remaining structure and connections remain unchanged. After the replacement, the spray is more uniform, and the cooling response is faster, making it particularly suitable for high-solids-content circulating liquid conditions, further improving washing efficiency and system stability.

[0031] Example 3

[0032] The difference in this embodiment is that the top clear water spraying section of the water absorption tower in Embodiment 1 is omitted, and only the intermediate cooling absorption section and the bottom low-temperature absorption section are retained. By increasing the spray density of the intermediate section and reducing the temperature of the bottom absorbent liquid to 18°C, the residual solvent concentration in the exhaust gas can still meet the emission standards. This reduction simplifies the structure, lowers operating energy consumption, and is suitable for production scenarios with slightly lower solvent recovery requirements.

[0033] Example 4

[0034] This embodiment discloses a high-efficiency ethanol solvent recovery device using a slurry method. It includes the same main structure as in Embodiment 1, but to address the characteristics of ethanol solvent, the water ring liquid in the water ring vacuum pump is replaced with a 10% ethanol aqueous solution, and the temperature of the chilled water in the vacuum pump cooler is adjusted to -10°C to accommodate the volatility and solubility characteristics of ethanol. Simultaneously, the concentration of the absorbent at the bottom of the water absorption tower is controlled at 4% before being returned to the system to prevent excessive dilution of the ethanol. This solution achieves optimized adaptation to different solvents while maintaining a general structure.

[0035] The above are all preferred embodiments of this utility model, and are not intended to limit the scope of protection of this utility model. Therefore, all equivalent changes made to the structure, shape and principle of this utility model should be covered within the scope of protection of this utility model.

Claims

1. A production apparatus for efficient solvent recovery in the slurry-based CMC production process, characterized in that: The system includes a stripper, a washing absorption tower, a circulating pump, a washing liquid cooler, a vacuum pump, a pre-vacuum pump condenser, a post-vacuum pump condenser, and a water absorption tower. The tail gas outlet of the stripper is directly connected to the tail gas inlet of the washing absorption tower via a pipeline. The washing liquid outlet of the washing absorption tower is connected to a spray device at its top via a circulating pump. The washing liquid cooler is located on the pipeline between the circulating pump and the spray device. The bottom of the washing absorption tower has a solid-containing washing liquid outlet for discharging part of the circulating washing liquid to a filter for solid-liquid separation. The top clean gas outlet of the washing absorption tower is sequentially connected to the vacuum pump, the pre-vacuum pump condenser, and the post-vacuum pump condenser. The tail gas outlet of the post-vacuum pump condenser is connected to the bottom air inlet of the water absorption tower. The water absorption tower has a three-layer counter-current absorption structure, including a top clean water spray section, a middle cooling absorption section, and a bottom low-temperature absorption section.

2. The production apparatus for efficient solvent recovery in the slurry-based CMC production process according to claim 1, characterized in that, The washing liquid cooler is a shell-and-tube heat exchanger, and the cooling medium is circulating water or chilled water. It is used to control the temperature of the circulating washing liquid within the range of 30 to 60°C to improve the condensation and absorption efficiency of the gaseous solvent.

3. The production apparatus for efficient solvent recovery in the slurry-based CMC production process according to claim 1, characterized in that, The stripper is a twin-shaft horizontal stripper with an outer jacket. The outer jacket is heated by steam at 130-190°C. The internal operating pressure is -0.70 to -0.98 kPaG, and the material temperature is maintained at 65-140°C.

4. The production apparatus for efficient solvent recovery in the slurry-based CMC production process according to claim 1, characterized in that: The vacuum pump is a water ring vacuum pump, and its water ring liquid is an isopropanol aqueous solution, ethanol aqueous solution or methanol aqueous solution that is matched with the recovered solvent. The water ring liquid is cooled by chilled water through an external cooler to improve vacuum stability.

5. The production apparatus for efficient solvent recovery in the slurry-based CMC production process according to claim 1, characterized in that: Both the pre-vacuum pump condenser and the post-vacuum pump condenser are shell-and-tube multi-pass condensers, with 32°C circulating water and -15°C chilled water as the cooling media, respectively. The exhaust gas outlet temperature of the pre-vacuum pump condenser is controlled between 20°C and 35°C, and the exhaust gas outlet temperature of the post-vacuum pump condenser is controlled between 10°C and 30°C.

6. The production apparatus for efficient solvent recovery in the slurry-based CMC production process according to claim 1, characterized in that: The water absorption tower adopts a structured packing or random packing. The tower is divided into three absorption zones from top to bottom: the top is a cold water spray zone at 10-20°C, the middle section absorbent is cooled to 20-35°C by chilled water, the bottom air inlet temperature is 10-30°C, and the absorbent temperature is controlled at 15-30°C.

7. The production apparatus for efficient solvent recovery in the slurry-based CMC production process according to claim 1, characterized in that: The operating liquid-to-gas ratio of the washing absorption tower is 0.015 to 0.030 by volume, and the operating pressure is consistent with that of the stripper, which is -0.70 to -0.98 kPaG.

8. The production apparatus for efficient solvent recovery in the slurry-based CMC production process according to claim 1, characterized in that: The stripper exhaust pipe is equipped with a heat insulation layer throughout to prevent moisture in the gas phase from condensing prematurely and causing dust to stick to the wall.

9. A production apparatus for efficient solvent recovery in the slurry-based CMC production process according to claim 1, characterized in that: The washing liquid outlet of the washing absorption tower is equipped with a removable filter screen.

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