Paraformaldehyde production system and process

Abstract

The invention relates to the technical field of paraformaldehyde production, in particular to a paraformaldehyde production system and a paraformaldehyde production process. The paraformaldehyde production system comprises a first-effect rising film generator and a rake dryer which are communicated in sequence; the first-effect rising film generator is communicated with a first-effect concentrated aldehyde tank and a first-effect concentrated aldehyde pump; a second-effect scraper evaporator is arranged between the first-effect rising film generator and the rake dryer in a communicating manner, and a second-effect concentrated aldehyde pump and a concentrated aldehyde flowmeter are communicated with the second-effect scraper evaporator; the alcohol-aldehyde separator is used for carrying out gas-phase alcohol-aldehyde separation on the first-effect exhaust gas and the second-effect exhaust gas; the diluted alcohol absorption tower is used for absorbing gas-phase diluted alcohol; the dilute aldehyde absorption tower is used for absorbing gas-phase dilute aldehyde; and the liquid-phase dilute alcohol and the liquid-phase dilute aldehyde are recycled. According to the paraformaldehyde production system and the paraformaldehyde production process, alcohol and aldehyde in the process are recycled respectively, quantitatively mixed with raw materials and concentrated aldehyde liquid respectively and stored respectively; therefore, the content of methanol in the solution is increased, and formaldehyde is prevented from self-polymerization in the storage process.

Description

Technical Field

[0001] The present invention relates to the technical field of paraformaldehyde production, and specifically to a paraformaldehyde production system and process. Background Art

[0002] Paraformaldehyde is a linear polymer of formaldehyde, usually in the form of white powder or granules as the final product, and is widely used in resin synthesis, disinfection, and the agricultural field.

[0003] The main process steps of paraformaldehyde production are as follows: a 37%-55% formaldehyde solution containing a small amount of methanol is subjected to vacuum distillation or evaporation to remove part of the water, and the formaldehyde concentration is increased to 60%-80%; stirring reaction is carried out at 50-80°C to cause formaldehyde to condense and form a linear polymer, and during this period, the degree of polymerization is adjusted by controlling the reaction time and temperature; the paraformaldehyde solid particles are separated from the mother liquor by centrifugation or filtration, and the residual unreacted formaldehyde is removed by washing with pure water or an organic solvent, and clean and dry granular paraformaldehyde is obtained through a fluidized bed drying device or a vacuum drying device; the granular paraformaldehyde is crushed / packaged as needed for transportation and storage.

[0004] Currently, during the paraformaldehyde production process, the main by-products are mother liquor, waste gas, and waste water, among which: the mother liquor contains unreacted formaldehyde, so the mother liquor is recycled to the original process for recycling; formaldehyde and methanol tail gas are absorbed by an absorption tower; the waste water is subjected to medium and post biochemical treatment until it meets the environmental protection discharge standards.

[0005] In addition to formaldehyde, the raw material solution also contains methanol. Low content of methanol will promote the self-polymerization of formaldehyde, while high content of methanol will inhibit the self-polymerization of formaldehyde; formaldehyde and methanol in the tail gas are simultaneously subjected to absorption treatment to obtain a dilute solution, which is then concentrated and used as a raw material. However, in conventional paraformaldehyde production, the following technical problems still exist:

[0006] When the formaldehyde solution is stored in the tank area, low content of methanol will cause the self-polymerization of formaldehyde. The most direct manifestation is the generation of white suspended matter or solid precipitate in the formaldehyde solution, and the increase in the solution viscosity. During the self-polymerization, slight heat release occurs. The direct impact on the production process is: blocking pipelines and conveying equipment, resulting in a decrease in flow rate, and frequent shutdowns for cleaning are required; continuous polymerization during storage leads to fluctuations in the concentration of the stored formaldehyde solution, a decrease in the effective formaldehyde content, and an increase in the heat energy consumption during the polymerization process; after the activity of formaldehyde decreases, the molecular weight distribution of the self-polymerization is uneven, affecting the performance of downstream products. Summary of the Invention

[0007] To solve the technical problems existing in the background art, the present invention provides a paraformaldehyde production system and process, which respectively recover alcohols and aldehydes in the process, and quantitatively mix and store them with raw materials and concentrated aldehyde solution respectively; thereby increasing the methanol content in the solution and preventing the self-polymerization of formaldehyde during storage.

[0008] The technical solution adopted by the present invention to solve the problems is as follows:

[0009] A paraformaldehyde production system includes:

[0010] A first-effect rising film generator and a rake dryer connected in sequence;

[0011] A material port, a circulation port, and a first-effect exhaust port are connected to the above-mentioned first-effect rising film generator. The above-mentioned material port is connected to the raw materials, and the above-mentioned circulation port and the material port are connected to each other and are sequentially connected with a first-effect concentrated aldehyde tank and a first-effect concentrated aldehyde pump;

[0012] The outlet of the above-mentioned first-effect concentrated aldehyde pump is connected to a first-effect concentrated aldehyde storage tank and a rake dryer. A finished product particle port and a drying exhaust port are connected to the rake dryer;

[0013] An alcohol-aldehyde separator is connected to the above-mentioned first-effect exhaust port. The discharge ports of the alcohol-aldehyde separator are a gas-phase dilute alcohol port, a liquid-phase dilute alcohol port, a gas-phase dilute aldehyde port, and a liquid-phase dilute aldehyde port;

[0014] A dilute aldehyde absorption tower is connected to the above-mentioned gas-phase dilute aldehyde port, liquid-phase dilute aldehyde port, and drying exhaust port. The discharge end of the dilute aldehyde absorption tower is connected to a first-effect concentrated aldehyde-mixed alcohol device. The first-effect concentrated aldehyde-mixed alcohol device is connected in a cycle with a first-effect concentrated aldehyde flow meter, a first-effect concentrated aldehyde mixing tank, and a first-effect concentrated aldehyde mixing and conveying pump;

[0015] A dilute alcohol absorption tower is connected to the above-mentioned gas-phase dilute alcohol port and liquid-phase dilute alcohol port. The discharge end of the dilute alcohol absorption tower is connected to a second-effect concentrated aldehyde-mixed alcohol device. The second-effect concentrated aldehyde-mixed alcohol device is connected in a cycle with a second-effect concentrated aldehyde flow meter, a second-effect concentrated aldehyde mixing tank, and a second-effect concentrated aldehyde mixing and conveying pump.

[0016] Further, the above-mentioned first-effect rising film generator includes a separation tower and a heating tower connected up and down;

[0017] The above-mentioned material port is connected to the bottom of the heating tower and is connected to the formaldehyde storage tank in the raw material area. The shell side of the heating tower is connected to a steam pipeline and a condensate pipeline for heating the material in the tube side of the heating tower;

[0018] The above-mentioned first-effect exhaust port is connected to the top of the separation tower and is connected to the intake end of the alcohol-aldehyde separator;

[0019] The above-mentioned circulation port is connected to the side wall below the liquid level in the separation tower.

[0020] Further, a deflector plate is provided above the liquid level in the separation tower;

[0021] A circulation connecting pipe is connected between the side wall of the separation tower and the bottom of the heating tower.

[0022] Further, the above-mentioned rake dryer is arranged in a horizontal structure. One side of the upper end of the rake dryer is connected to the outlet of the second-effect concentrated aldehyde pump through a concentrated aldehyde flowmeter; the drying exhaust port is connected to the other side of the upper end of the rake dryer and is connected to the inlet end of the dilute aldehyde absorption tower; the finished product particle port is connected below the drying exhaust port of the rake dryer and is connected to the crushing / packaging process;

[0023] A jacket group connected to the steam pipe and the condensate pipe is arranged on the outer wall of the rake dryer, and the jacket group is used to heat the materials in the rake dryer.

[0024] Further, a second-effect scraper evaporator is connected between the first-effect climbing film evaporator and the rake dryer;

[0025] A scraper is rotatably arranged in the second-effect scraper evaporator. The upper end of the scraper rotating shaft is coaxially rotatably provided with a gas-liquid separation partition plate and a distributor. A second-effect exhaust port is arranged on the side wall of the second-effect scraper evaporator on one side of the gas-liquid separation partition plate, and the connection port with the first-effect concentrated aldehyde pump is arranged on the side wall of the second-effect scraper evaporator on one side of the distributor;

[0026] A jacket connected to the steam pipe and the condensate pipe is arranged outside the second-effect scraper evaporator, and the jacket is used to heat the materials on the inner wall of the second-effect scraper evaporator.

[0027] Further, the above-mentioned alcohol-aldehyde separator includes:

[0028] Multiple groups of adsorption and desorption towers arranged in parallel. A packing layer is arranged in the adsorption and desorption towers. The upper and lower ends of the multiple groups of adsorption and desorption towers are respectively connected with a desorption discharge port and an adsorption discharge port;

[0029] The desorption discharge port is connected to the first-effect exhaust port and the second-effect exhaust port. A dilute aldehyde cooler is also connected to the desorption discharge port. The outlet of the dilute aldehyde cooler is connected to a cold dilute aldehyde tank. The liquid-phase dilute aldehyde port is connected to the lower end of the cold dilute aldehyde tank. The exhaust port at the upper end of the cold dilute aldehyde tank is connected to a dilute aldehyde vacuum pump. The outlet of the dilute aldehyde vacuum pump is connected to a dilute aldehyde steam-water separator. The lower drain port of the dilute aldehyde steam-water separator is connected to the lower end of the cold dilute aldehyde tank. The gas-phase dilute aldehyde port is connected to the exhaust port of the dilute aldehyde steam-water separator;

[0030] The above-mentioned adsorption discharge port is connected with a dilute alcohol cooler, the outlet of the above-mentioned dilute alcohol cooler is connected with a cold dilute alcohol tank, the above-mentioned liquid-phase dilute alcohol port is connected with the lower end of the cold dilute alcohol tank, the exhaust port at the upper end of the cold dilute alcohol tank is connected with a dilute alcohol vacuum pump, the outlet of the above-mentioned dilute alcohol vacuum pump is connected with a dilute alcohol steam separator, the lower liquid discharge port of the above-mentioned dilute alcohol steam separator is connected with the lower end of the cold dilute alcohol tank, and the above-mentioned gas-phase dilute alcohol port is connected with the exhaust port of the dilute alcohol steam separator;

[0031] Steam pipes are connected to the adsorption discharge ports at the lower ends of multiple adsorption and desorption towers for heating the packing during the desorption process.

[0032] Furthermore, a supplementary dilute aldehyde cooler is connected between the supplementary liquid inlet of the above-mentioned dilute aldehyde vacuum pump and the lower end of the cold dilute aldehyde tank;

[0033] A supplementary dilute alcohol cooler is connected between the supplementary liquid inlet of the above-mentioned dilute alcohol vacuum pump and the lower end of the cold dilute alcohol tank.

[0034] Furthermore, the above-mentioned dilute alcohol absorption tower includes:

[0035] A dilute alcohol spray tower and a dilute alcohol storage tower that are connected vertically;

[0036] The side wall above the liquid level in the above-mentioned dilute alcohol storage tower is connected with the gas-phase dilute alcohol port, the bottom of the dilute alcohol storage tower is connected with the liquid-phase dilute alcohol port, a dilute alcohol circulation pump is also connected to the bottom of the dilute alcohol storage tower, the outlet of the above-mentioned dilute alcohol circulation pump is connected with a dilute alcohol tank, and a dilute alcohol flowmeter is connected to the lower end of the above-mentioned dilute alcohol tank; in the above-mentioned dilute alcohol spray tower, a demisting layer, a spray pipe, and a packing layer are arranged in sequence from top to bottom, the spray pipe extends outside the dilute alcohol spray tower and is connected with the outlet of the dilute alcohol circulation pump;

[0037] The above-mentioned dilute alcohol flowmeter is connected with a two-effect concentrated aldehyde and mixed alcohol mixer, the main liquid inlet of the two-effect concentrated aldehyde and mixed alcohol mixer is connected with a two-effect concentrated aldehyde flowmeter, the secondary liquid inlet of the two-effect concentrated aldehyde and mixed alcohol mixer is connected with the dilute alcohol tank through the dilute alcohol flowmeter, the discharge port of the two-effect concentrated aldehyde and mixed alcohol mixer is connected with a two-effect concentrated aldehyde mixing tank, the lower end of the above-mentioned two-effect concentrated aldehyde mixing tank is connected with a two-effect concentrated aldehyde mixing and conveying pump, the outlet of the above-mentioned two-effect concentrated aldehyde mixing and conveying pump is connected with a first-effect concentrated aldehyde storage tank and is connected with the main liquid inlet of the two-effect concentrated aldehyde and mixed alcohol mixer through a two-effect concentrated aldehyde flowmeter; the inlet of the two-effect concentrated aldehyde mixing and conveying pump is connected with a two-effect concentrated aldehyde storage tank.

[0038] Furthermore, the above-mentioned dilute aldehyde absorption tower includes:

[0039] A dilute aldehyde spray tower and a dilute aldehyde storage tower that are connected vertically;

[0040] The side wall above the liquid level in the dilute aldehyde storage tower is connected to the drying exhaust port and the gas-phase dilute aldehyde port. The bottom of the dilute aldehyde storage tower is connected to the liquid-phase dilute aldehyde port. A dilute aldehyde circulation pump is also connected to the bottom of the dilute aldehyde storage tower. The outlet of the dilute aldehyde circulation pump is connected to a dilute aldehyde tank. A dilute aldehyde flowmeter is connected to the lower end of the dilute aldehyde tank. The dilute aldehyde spray tower is sequentially provided with a demisting layer, a spray pipe, and a packing layer from top to bottom. The spray pipe extends outside the dilute aldehyde spray tower and is connected to the outlet of the dilute aldehyde circulation pump.

[0041] The dilute aldehyde flowmeter is connected to a first-effect concentrated aldehyde mixer. The main inlet of the first-effect concentrated aldehyde mixer is connected to a first-effect concentrated aldehyde flowmeter. The secondary inlet of the first-effect concentrated aldehyde mixer is connected to the dilute aldehyde tank through the dilute aldehyde flowmeter. The discharge port of the first-effect concentrated aldehyde mixer is connected to a first-effect concentrated aldehyde mixing tank. A first-effect concentrated aldehyde mixing and conveying pump is connected to the lower end of the first-effect concentrated aldehyde mixing tank. The outlet of the first-effect concentrated aldehyde mixing and conveying pump is connected to the storage tank in the raw material area and is also connected to the main inlet of the first-effect concentrated aldehyde mixer through the first-effect concentrated aldehyde flowmeter. The inlet of the first-effect concentrated aldehyde mixing and conveying pump is connected to the first-effect concentrated aldehyde storage tank.

[0042] A process for producing paraformaldehyde includes:

[0043] A. First-effect evaporation:

[0044] The raw material formaldehyde is subjected to first-effect evaporation through a first-effect rising film generator to remove water and methanol in the raw material formaldehyde to obtain first-effect concentrated aldehyde.

[0045] B. Second-effect evaporation:

[0046] The first-effect concentrated aldehyde is subjected to second-effect evaporation through a second-effect scraper evaporator to remove water and methanol in the first-effect concentrated aldehyde to obtain second-effect concentrated aldehyde.

[0047] C. Drying:

[0048] The first-effect concentrated aldehyde or the second-effect concentrated aldehyde is dried through a rake dryer to remove water and methanol in the concentrated aldehyde to obtain paraformaldehyde finished particles.

[0049] D. Separation of first-effect exhaust gas and second-effect exhaust gas:

[0050] The first-effect exhaust gas and the second-effect exhaust gas are subjected to alcohol and aldehyde separation through an alcohol-aldehyde separator to obtain gas-phase dilute alcohol, liquid-phase dilute alcohol, gas-phase dilute aldehyde, and liquid-phase dilute aldehyde.

[0051] E. Recovery of dilute alcohol:

[0052] The gas-phase dilute alcohol is adsorbed through a dilute alcohol absorption tower to obtain liquid-phase dilute alcohol, which is mixed with the second-effect concentrated aldehyde and sent to the first-effect concentrated aldehyde storage tank.

[0053] F. Recovery of dilute aldehyde:

[0054] The dilute aldehyde in the gas phase is adsorbed by the dilute aldehyde absorption tower to obtain liquid-phase dilute aldehyde, which is mixed with the concentrated aldehyde in the first effect and sent to the formaldehyde storage tank in the raw material area.

[0055] The beneficial effects of a paraformaldehyde production system and process of the present invention:

[0056] For the exhaust gas from the first-effect evaporation process and the second-effect evaporation process, alcohol and aldehyde are separated to produce dilute alcohol and dilute aldehyde;

[0057] The dilute alcohol is recovered by the dilute alcohol absorption tower and quantitatively and fully mixed with the product liquid of the second-effect evaporation process, and stored in the concentrated aldehyde storage tank in the first effect to prevent the formaldehyde solution in the concentrated aldehyde storage tank in the first effect from self-polymerizing;

[0058] The exhaust gas from the dilute aldehyde and drying process is recovered by the dilute aldehyde absorption tower, quantitatively and fully mixed with the product liquid of the first-effect evaporation process, and stored in the storage tank in the raw material area to prevent the formaldehyde solution in the storage tank in the raw material area from self-polymerizing. Description of the Drawings

[0059] Figure 1 It is a schematic process flow diagram of the paraformaldehyde production system in the example of the present invention;

[0060] Figure 2 It is a schematic process flow diagram of the recovery process for the exhaust gas from the first effect and the second effect in the example of the present invention;

[0061] Figure 3 It is a schematic process flow diagram of the dilute alcohol recovery process in the example of the present invention;

[0062] Figure 4 It is a schematic process flow diagram of the dilute aldehyde recovery process in the example of the present invention.

[0063] In the figure:

[0064] 10. First-effect rising film generator, 11. Heating tower, 12. Separation tower, 13. First-effect concentrated aldehyde tank, 14. First-effect concentrated aldehyde pump,

[0065] 20. Second-effect scraper evaporator, 21. Second-effect concentrated aldehyde tank, 22. Second-effect concentrated aldehyde pump,

[0066] 40. Rake dryer, 41. Concentrated aldehyde flowmeter,

[0067] 50. Alcohol-aldehyde separator, 51. Adsorption and desorption tower,

[0068] 521. Dilute aldehyde cooler, 531. Cold dilute aldehyde tank, 541. Dilute aldehyde vacuum pump, 551. Dilute aldehyde steam-water separator,

[0069] 561. Supplementary dilute aldehyde cooler,

[0070] 522. Dilute alcohol cooler, 532. Cold dilute alcohol tank, 542. Dilute alcohol vacuum pump, 552. Dilute alcohol steam-water separator,

[0071] 562. Supplementary dilute alcohol cooler,

[0072] 60. Dilute alcohol absorption tower, 61. Dilute alcohol liquid storage tower, 62. Dilute alcohol spray tower, 63. Dilute alcohol circulation pump, 64. Dilute alcohol tank,

[0073] 65. Dilute alcohol flowmeter,

[0074] 70. Dilute aldehyde absorption tower, 71. Dilute aldehyde liquid storage tower, 72. Dilute aldehyde spray tower, 73. Dilute aldehyde circulation pump, 74. Dilute aldehyde tank,

[0075] 75. Dilute aldehyde flowmeter,

[0076] 801. Second-effect concentrated aldehyde and alcohol mixer, 802. Second-effect concentrated aldehyde flowmeter, 803. Second-effect concentrated aldehyde mixing tank,

[0077] 804. Second-effect concentrated aldehyde mixing and conveying pump,

[0078] 901. First-effect concentrated aldehyde and alcohol mixer, 902. First-effect concentrated aldehyde flowmeter, 903. First-effect concentrated aldehyde mixing tank,

[0079] 904. First-effect concentrated aldehyde mixing and conveying pump. Detailed implementation mode

[0080] In order to more clearly and explicitly illustrate the specific implementation purpose and implementation mode of the present invention, the technical solution of the present invention will be completely described below. The described embodiments are part of the embodiments of the present invention, rather than all embodiments. All other embodiments based on the embodiments described in the present invention without creative efforts belong to the protection scope of the present invention.

[0081] A paraformaldehyde production system of the present invention, as Figure 1 shown, includes:

[0082] Includes: A first-effect rising film generator 10 and a rake dryer 40 connected in sequence through a material pipeline.

[0083] The above-mentioned first-effect climbing film generator 10 includes a separation tower 12 and a heating tower 11 which are connected up and down. A material port communicating with the formaldehyde storage tank in the raw material area is arranged at the bottom of the heating tower 11. A steam pipeline and a condensate pipeline communicating with the shell side of the heating tower 11 are respectively arranged at the upper and lower ends of the side wall of the heating tower 11 for heating the material in the tube side of the heating tower 11. An exhaust port of the first effect is connected to the top of the separation tower 12. A deflector is arranged above the liquid level in the separation tower 12. A circulation port is connected to the side wall below the liquid level in the separation tower 12. The circulation port and the material port are interconnected and connected to a first-effect concentrated aldehyde tank 13. A first-effect concentrated aldehyde pump 14 is connected to the bottom of the first-effect concentrated aldehyde tank 13. The first-effect concentrated aldehyde pump 14 is connected to a first-effect concentrated aldehyde storage tank. A circulation connecting pipe is connected between the side wall of the separation tower 12 and the bottom of the heating tower 11.

[0084] The above-mentioned rake dryer 40 is set as a horizontal structure. A material inlet is arranged on one side of the upper end of the rake dryer 40. A concentrated aldehyde flowmeter 41 is connected to the material inlet. A jacket group is arranged on the outer wall of the rake dryer 40. A steam pipeline and a condensate pipeline are respectively connected to the upper and lower ends of the jacket group for heating the material in the rake dryer 40. A drying exhaust port is connected to the other side of the upper end of the rake dryer 40. A finished product granule port is connected to the lower end of the rake dryer 40 below the drying exhaust port and is connected to the crushing / packaging process.

[0085] In order to increase the concentration of the first-effect concentrated aldehyde and improve the output efficiency of the rake dryer 40, a second-effect scraper evaporator 20 is connected between the first-effect climbing film generator 10 and the rake dryer 40. A scraper is rotatably arranged in the second-effect scraper evaporator 20. A gas-liquid separation partition plate and a distributor are coaxially rotatably arranged at the upper end of the rotating shaft of the scraper. A second-effect exhaust port is connected to the side wall of the second-effect scraper evaporator 20 on one side of the gas-liquid separation partition plate. The side wall of the second-effect scraper evaporator 20 on one side of the distributor is connected to the outlet of the first-effect concentrated aldehyde pump 14. A jacket is arranged outside the second-effect scraper evaporator 20. A steam pipeline and a condensate pipeline are respectively connected to the upper and lower ends of the jacket for heating the material on the inner wall of the second-effect scraper evaporator 20. A second-effect concentrated aldehyde tank 21 is connected to the bottom of the second-effect scraper evaporator 20. A second-effect concentrated aldehyde pump 22 is connected to the bottom of the second-effect concentrated aldehyde tank 21. The second-effect concentrated aldehyde pump 22 is connected to a second-effect concentrated aldehyde storage tank.

[0086] The material inlet of the rake dryer 40 is connected to the outlets of the first-effect concentrated aldehyde pump 14 and the second-effect concentrated aldehyde pump 22 through the concentrated aldehyde flowmeter 41, and whether the second-effect scraper evaporator 20 is incorporated into the system is adjusted according to the content of formaldehyde in the storage tanks in the raw material area and the first-effect concentrated aldehyde storage tank.

[0087] The exhaust port of the first effect and the exhaust port of the second effect are connected to an alcohol-aldehyde separator 50, including:

[0088] Multiple sets of adsorption and desorption towers 51 arranged in parallel, with a packing layer provided inside the adsorption and desorption towers 51;

[0089] The upper ends of multiple sets of adsorption and desorption towers 51 are connected and provided with a desorption discharge port, and the desorption discharge port is connected to the first-effect exhaust port and the second-effect exhaust port. The desorption discharge port is also connected and provided with a dilute aldehyde cooler 521. The outlet of the dilute aldehyde cooler 521 is connected and provided with a cold dilute aldehyde tank 531. The lower end of the cold dilute aldehyde tank 531 is connected and provided with a liquid-phase dilute aldehyde port. The exhaust port at the upper end of the cold dilute aldehyde tank 531 is connected and provided with a dilute aldehyde vacuum pump 541. The outlet of the dilute aldehyde vacuum pump 541 is connected and provided with a dilute aldehyde steam separator 551. The lower drain port of the dilute aldehyde steam separator 551 is connected to the lower end of the cold dilute aldehyde tank 531. The exhaust port of the dilute aldehyde steam separator 551 is connected and provided with a gas-phase dilute aldehyde port. The liquid replenishment port of the dilute aldehyde vacuum pump 541 is connected and provided with a supplementary dilute aldehyde cooler 561. The outlet of the supplementary dilute aldehyde cooler 561 is connected to the lower end of the cold dilute aldehyde tank 531;

[0090] The lower ends of multiple sets of adsorption and desorption towers 51 are connected and provided with an adsorption discharge port, and the adsorption discharge port is connected and provided with a dilute alcohol cooler 522. The outlet of the dilute alcohol cooler 522 is connected and provided with a cold dilute alcohol tank 532. The lower end of the cold dilute alcohol tank 532 is connected and provided with a liquid-phase dilute alcohol port. The exhaust port at the upper end of the cold dilute alcohol tank 532 is connected and provided with a dilute alcohol vacuum pump 542. The outlet of the dilute alcohol vacuum pump 542 is connected and provided with a dilute alcohol steam separator 552. The lower drain port of the dilute alcohol steam separator 552 is connected to the lower end of the cold dilute alcohol tank 532. The exhaust port of the dilute alcohol steam separator 552 is connected and provided with a gas-phase dilute alcohol port. The liquid replenishment port of the dilute alcohol vacuum pump 542 is connected and provided with a supplementary dilute alcohol cooler 562. The outlet of the supplementary dilute alcohol cooler 562 is connected to the lower end of the cold dilute alcohol tank 532;

[0091] The adsorption discharge port at the lower end of multiple sets of adsorption and desorption towers 51 is connected and provided with a steam pipeline for heating the packing during the desorption process.

[0092] The gas-phase dilute alcohol port and the liquid-phase dilute alcohol port are connected and provided with a dilute alcohol absorption tower 60, including:

[0093] A dilute alcohol spray tower 62 and a dilute alcohol storage tower 61 connected up and down;

[0094] The side wall above the liquid level inside the dilute alcohol storage tower 61 is connected to the gas-phase dilute alcohol port. The bottom of the dilute alcohol storage tower 61 is connected to the liquid-phase dilute alcohol port. The bottom of the dilute alcohol storage tower 61 is also connected and provided with a dilute alcohol circulation pump 63. The outlet of the dilute alcohol circulation pump 63 is connected and provided with a dilute alcohol tank 64. The lower end of the dilute alcohol tank 64 is connected and provided with a dilute alcohol flow meter 65; Inside the dilute alcohol spray tower 62, a demisting layer, a spray pipe, and a packing layer are sequentially arranged from top to bottom. The spray pipe extends outside the dilute alcohol spray tower 62 and is connected to the outlet of the dilute alcohol circulation pump 63.

[0095] The above-mentioned dilute alcohol flowmeter 65 is connected to a second-effect concentrated aldehyde and alcohol mixer 801. The main inlet of the second-effect concentrated aldehyde and alcohol mixer 801 is connected to a second-effect concentrated aldehyde flowmeter 802. The secondary inlet of the second-effect concentrated aldehyde and alcohol mixer 801 is connected to the dilute alcohol tank 64 through the dilute alcohol flowmeter 65. The discharge port of the second-effect concentrated aldehyde and alcohol mixer 801 is connected to a second-effect concentrated aldehyde mixing tank 803. The lower end of the second-effect concentrated aldehyde mixing tank 803 is connected to a second-effect concentrated aldehyde mixing transfer pump 804. The outlet of the second-effect concentrated aldehyde mixing transfer pump 804 is connected to the first-effect concentrated aldehyde storage tank and is also connected to the main inlet of the second-effect concentrated aldehyde and alcohol mixer 801 through the second-effect concentrated aldehyde flowmeter 802; the inlet of the second-effect concentrated aldehyde mixing transfer pump 804 is connected to the second-effect concentrated aldehyde storage tank.

[0096] The above-mentioned dry exhaust port, gas-phase dilute aldehyde port, and liquid-phase dilute aldehyde port are connected to a dilute aldehyde absorption tower 70, including:

[0097] A dilute aldehyde spray tower 72 and a dilute aldehyde liquid storage tower 71 that are connected up and down;

[0098] The side wall above the liquid level in the above-mentioned dilute aldehyde liquid storage tower 71 is connected to the dry exhaust port and the gas-phase dilute aldehyde port. The bottom of the dilute aldehyde liquid storage tower 71 is connected to the liquid-phase dilute aldehyde port. The bottom of the dilute aldehyde liquid storage tower 71 is also connected to a dilute aldehyde circulation pump 73. The outlet of the dilute aldehyde circulation pump 73 is connected to a dilute alcohol tank 74. The lower end of the dilute alcohol tank 74 is connected to a dilute alcohol flowmeter 75; the above-mentioned dilute aldehyde spray tower 72 is sequentially provided with a demisting layer, spray pipes, and a packing layer from top to bottom. The spray pipes extend outside the dilute aldehyde spray tower 72 and are connected to the outlet of the dilute aldehyde circulation pump 73.

[0099] The above-mentioned dilute alcohol flowmeter 75 is connected to a first-effect concentrated aldehyde and alcohol mixer 901. The main inlet of the first-effect concentrated aldehyde and alcohol mixer 901 is connected to a first-effect concentrated aldehyde flowmeter 902. The secondary inlet of the first-effect concentrated aldehyde and alcohol mixer 901 is connected to the dilute alcohol tank 74 through the dilute alcohol flowmeter 75. The discharge port of the first-effect concentrated aldehyde and alcohol mixer 901 is connected to a first-effect concentrated aldehyde mixing tank 903. The lower end of the first-effect concentrated aldehyde mixing tank 903 is connected to a first-effect concentrated aldehyde mixing transfer pump 904. The outlet of the first-effect concentrated aldehyde mixing transfer pump 904 is connected to the raw material area storage tank and is also connected to the main inlet of the first-effect concentrated aldehyde and alcohol mixer 901 through the first-effect concentrated aldehyde flowmeter 902; the inlet of the first-effect concentrated aldehyde mixing transfer pump 904 is connected to the first-effect concentrated aldehyde storage tank.

[0100] According to a paraformaldehyde production system in the above-mentioned embodiment, a paraformaldehyde production process is further described below:

[0101] A. First-effect evaporation:

[0102] The raw material formaldehyde is supplied from the formaldehyde storage tank in the raw material area to the heating tower 11, and is transported upward through the tube side of the heating tower 11 into the separation tower 12. Since the raw material formaldehyde in the tube side of the heating tower 11 is heated and vaporized, and is circulated and heated through the circulation connecting pipe in the tube side of the heating tower 11, the water and methanol in the raw material formaldehyde are vaporized;

[0103] The generated first-effect exhaust gas is discharged from the top of the separation tower 12, and the generated liquid-phase first-effect concentrated aldehyde is discharged from the bottom of the heating tower 11 into the first-effect concentrated aldehyde tank 13, and then is transported to the first-effect concentrated aldehyde storage tank by the first-effect concentrated aldehyde pump 14.

[0104] B. Second-effect evaporation:

[0105] The first-effect concentrated aldehyde is transported to the second-effect scraper evaporator 20 by the first-effect concentrated aldehyde pump 14 or the tank area feeding pump, and is distributed by the distributor to the inner wall of the second-effect scraper evaporator 20 heated by the jacket, so that the water and methanol in the first-effect concentrated aldehyde are vaporized;

[0106] The generated second-effect exhaust gas is discharged from the side wall of the second-effect scraper evaporator 20 on one side of the gas-liquid separation partition plate, and the generated second-effect concentrated aldehyde is scraped by the scraper to the second-effect concentrated aldehyde tank 21 at the bottom of the second-effect scraper evaporator 20, and then is transported to the second-effect concentrated aldehyde storage tank by the second-effect concentrated aldehyde pump 22.

[0107] C. Drying:

[0108] The first-effect concentrated aldehyde or the second-effect concentrated aldehyde is metered by the concentrated aldehyde flowmeter 41, and is respectively transported to the rake dryer 40 heated by the jacket group by the first-effect concentrated aldehyde pump 14, the second-effect concentrated aldehyde pump 22 or the tank area feeding pump, so that the water and methanol in the concentrated aldehyde are vaporized;

[0109] The generated drying exhaust gas is discharged from the upper end of the rake dryer 40, and the generated paraformaldehyde finished product particles are discharged from the lower end of the rake dryer 40 and transported to the crushing / packaging process.

[0110] D. Separation of the first-effect exhaust gas and the second-effect exhaust gas:

[0111] The first-effect exhaust gas and the second-effect exhaust gas are subjected to aldehyde adsorption through the adsorption and desorption tower 51;

[0112] The gas after aldehyde adsorption is cooled by the dilute alcohol cooler 522, and the condensed liquid-phase dilute alcohol is sent to the cold dilute alcohol tank 532. The gas-phase dilute alcohol in the cold dilute alcohol tank 532 is discharged successively through the dilute alcohol vacuum pump 542 and the dilute alcohol steam separator 552. The liquid-phase dilute alcohol in the cold dilute alcohol tank 532 is replenished to the dilute alcohol vacuum pump 542 through the supplementary dilute alcohol cooler 562 to ensure the vacuum degree of the dilute alcohol vacuum pump 542;

[0113] After the aldehyde adsorption is completed, steam is reversely introduced into the adsorption and desorption tower 51 for aldehyde desorption;

[0114] The gas after aldehyde desorption is cooled by the dilute aldehyde cooler 521, and the condensed liquid-phase dilute aldehyde is sent into the cold dilute aldehyde tank 531. The gaseous-phase dilute aldehyde in the cold dilute aldehyde tank 531 is discharged successively through the dilute aldehyde vacuum pump 541 and the dilute aldehyde steam-water separator 551. The liquid-phase dilute aldehyde in the cold dilute aldehyde tank 531 is fed to the dilute aldehyde vacuum pump 541 through the supplementary dilute aldehyde cooler 561 to ensure the vacuum degree of the dilute aldehyde vacuum pump 541.

[0115] E. Dilute alcohol recovery:

[0116] The gaseous-phase dilute alcohol and the liquid-phase dilute alcohol are sent into the dilute alcohol storage tower 61 through a fan and a pump respectively;

[0117] The liquid-phase dilute alcohol in the dilute alcohol storage tower 61 is sprayed out through the spray pipe in the dilute alcohol spray tower 62 by the dilute alcohol circulation pump 63 to adsorb the gaseous-phase dilute alcohol sent into the dilute alcohol storage tower 61;

[0118] The generated water vapor is discharged from the top of the dilute alcohol spray tower 62 through the demisting layer; the liquid-phase dilute alcohol that has absorbed the gaseous-phase dilute alcohol is sent to the dilute alcohol tank 64 by the dilute alcohol circulation pump 63. The liquid-phase dilute alcohol in the dilute alcohol tank 64 is metered by the dilute alcohol flowmeter 65 and then sent into the second-effect concentrated aldehyde and mixed alcohol mixer 801. The second-effect concentrated aldehyde is metered by the second-effect concentrated aldehyde flowmeter 802 and then sent into the second-effect concentrated aldehyde and mixed alcohol mixer 801 through the second-effect concentrated aldehyde mixing and conveying pump 804. The second-effect concentrated aldehyde and the liquid-phase dilute alcohol are mixed in the second-effect concentrated aldehyde and mixed alcohol mixer 801 and then sent to the second-effect concentrated aldehyde mixing tank 803. The mixed liquid of the second-effect concentrated aldehyde and the liquid-phase dilute alcohol in the second-effect concentrated aldehyde mixing tank 803 is sent into the first-effect concentrated aldehyde storage tank through the second-effect concentrated aldehyde mixing and conveying pump 804.

[0119] F. Dilute aldehyde recovery:

[0120] The gaseous-phase dilute aldehyde and the dry exhaust gas are sent into the dilute aldehyde storage tower 71 through a fan, and the liquid-phase dilute aldehyde is sent into the dilute aldehyde storage tower 71 through a pump respectively;

[0121] The liquid-phase dilute aldehyde in the dilute aldehyde storage tower 71 is sprayed out through the spray pipe in the dilute aldehyde spray tower 72 by the dilute aldehyde circulation pump 73 to adsorb the gaseous-phase dilute aldehyde and the dry exhaust gas sent into the dilute aldehyde storage tower 71;

[0122] The generated water vapor is discharged from the top of the dilute aldehyde spray tower 72 through the demisting layer; the liquid-phase dilute aldehyde that has absorbed the gaseous-phase dilute aldehyde is sent to the dilute aldehyde tank 74 by the dilute aldehyde circulation pump 73. The liquid-phase dilute aldehyde in the dilute aldehyde tank 74 is metered by the dilute aldehyde flowmeter 75 and then sent into the first-effect concentrated aldehyde and mixed alcohol mixer 901. The first-effect concentrated aldehyde is metered by the first-effect concentrated aldehyde flowmeter 902 and then sent into the first-effect concentrated aldehyde and mixed alcohol mixer 901 through the first-effect concentrated aldehyde mixing and conveying pump 904. The first-effect concentrated aldehyde and the liquid-phase dilute aldehyde are mixed in the first-effect concentrated aldehyde and mixed alcohol mixer 901 and then sent to the second-effect concentrated aldehyde mixing tank 903. The mixed liquid of the first-effect concentrated aldehyde and the liquid-phase dilute aldehyde in the second-effect concentrated aldehyde mixing tank 903 is sent into the formaldehyde storage tank in the raw material area through the first-effect concentrated aldehyde mixing and conveying pump 904.

[0123] In summary, the above are only the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Through the above description, relevant staff can make various changes and modifications without departing from the technical idea of the present invention. The technical scope of the present invention is not limited to the content in the specification. All equivalent changes and modifications to the above-mentioned shape, structure, features and spirit according to the scope of the claims of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A paraformaldehyde production system, characterized in that: Including: An evaporator (10) and a rake dryer (40) are connected in sequence; The evaporator (10) is connected with a material port, a circulation port and a first-effect exhaust port. The material port is connected with the raw material, and the circulation port and the material port are connected to each other and are connected in sequence with a first-effect concentrated aldehyde tank (13) and a first-effect concentrated aldehyde pump (14); The outlet of the first-effect concentrated aldehyde pump (14) is connected with a first-effect concentrated aldehyde storage tank and the rake dryer (40). The rake dryer (40) is connected with a finished product granule port and a drying exhaust port; The first-effect exhaust port is connected with an alcohol-aldehyde separator (50). The discharge ports of the alcohol-aldehyde separator (50) are a gas-phase dilute alcohol port, a liquid-phase dilute alcohol port, a gas-phase dilute aldehyde port and a liquid-phase dilute aldehyde port; The gas-phase dilute aldehyde port, the liquid-phase dilute aldehyde port and the drying exhaust port are connected with a dilute aldehyde absorption tower (70). The discharge end of the dilute aldehyde absorption tower (70) is connected with a first-effect concentrated aldehyde mixer (901). The first-effect concentrated aldehyde mixer (901) is connected in a cycle with a first-effect concentrated aldehyde flowmeter (902), a first-effect concentrated aldehyde mixing tank (903) and a first-effect concentrated aldehyde mixing and conveying pump (904); The gas-phase dilute alcohol port and the liquid-phase dilute alcohol port are connected with a dilute alcohol absorption tower (60). The discharge end of the dilute alcohol absorption tower (60) is connected with a second-effect concentrated aldehyde mixer (801). The second-effect concentrated aldehyde mixer (801) is connected in a cycle with a second-effect concentrated aldehyde flowmeter (802), a second-effect concentrated aldehyde mixing tank (803) and a second-effect concentrated aldehyde mixing and conveying pump (804).

2. The paraformaldehyde production system according to claim 1, characterized in that: The evaporator (10) includes a separation tower (12) and a heating tower (11) connected up and down; The material port is connected to the bottom of the heating tower (11) and is connected with the formaldehyde storage tank in the raw material area. The shell side of the heating tower (11) is connected with a steam pipeline and a condensate pipeline to heat the material in the tube side of the heating tower (11); The first-effect exhaust port is connected to the top of the separation tower (12) and is connected with the intake end of the alcohol-aldehyde separator (50); The circulation port is connected to the side wall below the liquid level in the separation tower (12).

3. The paraformaldehyde production system according to claim 2, characterized in that: A baffle is arranged above the liquid level in the separation tower (12); A circulation connecting pipe is connected between the side wall of the separation tower (12) and the bottom of the heating tower (11).

4. The paraformaldehyde production system according to claim 2, characterized in that: The rake dryer (40) is arranged in a horizontal structure. One side of the upper end of the rake dryer (40) is connected with the outlet of the second-effect concentrated aldehyde pump (22) through a concentrated aldehyde flowmeter (41); the drying exhaust port is connected to the other side of the upper end of the rake dryer (40) and is connected with the intake end of the dilute aldehyde absorption tower (70); the finished product granule port is connected below the drying exhaust port of the rake dryer (40) and is connected with the crushing / packaging process; A jacket group is provided on the outer wall of the rake dryer (40) and is respectively communicated with a steam pipe and a condensate pipe. The jacket group is used to heat the materials in the rake dryer (40).

5. The polyoxymethylene production system according to claim 4, characterized in that: A second-effect scraper evaporator (20) is communicatively arranged between the first-effect rising-film generator (10) and the rake dryer (40); A scraper is rotatably arranged in the second-effect scraper evaporator (20). A gas-liquid separation partition plate and a distributor are coaxially and rotatably arranged at the upper end of the scraper rotating shaft. A second-effect exhaust port is arranged on the side wall of the second-effect scraper evaporator (20) on one side of the gas-liquid separation partition plate, and the connection port with the first-effect concentrated aldehyde pump (14) is arranged on the side wall of the second-effect scraper evaporator (20) on one side of the distributor; A jacket communicated with a steam pipe and a condensate pipe is arranged outside the second-effect scraper evaporator (20). The jacket is used to heat the materials on the inner wall of the second-effect scraper evaporator (20).

6. The polyoxymethylene production system according to claim 5, characterized in that: The alcohol-aldehyde separator (50) includes: Multiple groups of adsorption and desorption towers (51) arranged in parallel. A packing layer is arranged in the adsorption and desorption tower (51). Desorption discharge ports and adsorption discharge ports are respectively communicatively arranged at the upper and lower ends of the multiple groups of adsorption and desorption towers (51); The desorption discharge port is communicated with the first-effect exhaust port and the second-effect exhaust port. A dilute aldehyde cooler (521) is also communicatively arranged at the desorption discharge port. The outlet of the dilute aldehyde cooler (521) is communicatively arranged with a cold dilute aldehyde tank (531). The liquid-phase dilute aldehyde port is communicated with the lower end of the cold dilute aldehyde tank (531). The exhaust port at the upper end of the cold dilute aldehyde tank (531) is communicatively arranged with a dilute aldehyde vacuum pump (541). The outlet of the dilute aldehyde vacuum pump (541) is communicatively arranged with a dilute aldehyde steam-water separator (551). The lower liquid discharge port of the dilute aldehyde steam-water separator (551) is communicated with the lower end of the cold dilute aldehyde tank (531). The gas-phase dilute aldehyde port is communicated with the exhaust port of the dilute aldehyde steam-water separator (551); The adsorption discharge port is communicatively arranged with a dilute alcohol cooler (522). The outlet of the dilute alcohol cooler (522) is communicatively arranged with a cold dilute alcohol tank (532). The liquid-phase dilute alcohol port is communicated with the lower end of the cold dilute alcohol tank (532). The exhaust port at the upper end of the cold dilute alcohol tank (532) is communicatively arranged with a dilute alcohol vacuum pump (542). The outlet of the dilute alcohol vacuum pump (542) is communicatively arranged with a dilute alcohol steam-water separator (552). The lower liquid discharge port of the dilute alcohol steam-water separator (552) is communicated with the lower end of the cold dilute alcohol tank (532). The gas-phase dilute alcohol port is communicated with the exhaust port of the dilute alcohol steam-water separator (552); Steam pipes are communicatively arranged at the adsorption discharge ports at the lower ends of the multiple groups of adsorption and desorption towers (51) for heating the packing in the desorption process.

7. The polyoxymethylene production system according to claim 6, characterized in that: A supplementary dilute aldehyde cooler (561) is communicatively arranged between the liquid supplement port of the dilute aldehyde vacuum pump (541) and the lower end of the cold dilute aldehyde tank (531); A dilute alcohol cooler (562) is connected in communication between the liquid replenishing port of the dilute alcohol vacuum pump (542) and the lower end of the cold dilute alcohol tank (532).

8. A paraformaldehyde production system according to claim 6, wherein: The dilute alcohol absorption tower (60) includes: A dilute alcohol spray tower (62) and a dilute alcohol storage tower (61) which are connected in communication up and down; The side wall above the liquid level in the dilute alcohol storage tower (61) is connected in communication with the gas-phase dilute alcohol port, the bottom of the dilute alcohol storage tower (61) is connected in communication with the liquid-phase dilute alcohol port, and a dilute alcohol circulation pump (63) is further connected in communication at the bottom of the dilute alcohol storage tower (61). The outlet of the dilute alcohol circulation pump (63) is connected in communication with a dilute alcohol tank (64), and a dilute alcohol flowmeter (65) is connected in communication at the lower end of the dilute alcohol tank (64); in the dilute alcohol spray tower (62), a demisting layer, a spray pipe, and a packing layer are sequentially arranged from top to bottom. The spray pipe extends outside the dilute alcohol spray tower (62) and is connected in communication with the outlet of the dilute alcohol circulation pump (63); The dilute alcohol flowmeter (65) is connected in communication with a second-effect concentrated aldehyde and alcohol mixer (801). The main liquid inlet of the second-effect concentrated aldehyde and alcohol mixer (801) is connected in communication with a second-effect concentrated aldehyde flowmeter (802). The secondary liquid inlet of the second-effect concentrated aldehyde and alcohol mixer (801) is connected to the dilute alcohol tank (64) through the dilute alcohol flowmeter (65). The discharge port of the second-effect concentrated aldehyde and alcohol mixer (801) is connected in communication with a second-effect concentrated aldehyde mixing tank (803). The lower end of the second-effect concentrated aldehyde mixing tank (803) is connected in communication with a second-effect concentrated aldehyde mixing and conveying pump (804). The outlet of the second-effect concentrated aldehyde mixing and conveying pump (804) is connected to the first-effect concentrated aldehyde storage tank and is also connected to the main liquid inlet of the second-effect concentrated aldehyde and alcohol mixer (801) through the second-effect concentrated aldehyde flowmeter (802); the inlet of the second-effect concentrated aldehyde mixing and conveying pump (804) is connected to the second-effect concentrated aldehyde storage tank.

9. A paraformaldehyde production system according to claim 8, wherein: The dilute aldehyde absorption tower (70) includes: A dilute aldehyde spray tower (72) and a dilute aldehyde storage tower (71) which are connected in communication up and down; The side wall above the liquid level in the dilute aldehyde storage tower (71) is connected in communication with the dry exhaust port and the gas-phase dilute aldehyde port, the bottom of the dilute aldehyde storage tower (71) is connected in communication with the liquid-phase dilute aldehyde port, and a dilute aldehyde circulation pump (73) is further connected in communication at the bottom of the dilute aldehyde storage tower (71). The outlet of the dilute aldehyde circulation pump (73) is connected in communication with a dilute aldehyde tank (74), and a dilute aldehyde flowmeter (75) is connected in communication at the lower end of the dilute aldehyde tank (74); in the dilute aldehyde spray tower (72), a demisting layer, a spray pipe, and a packing layer are sequentially arranged from top to bottom. The spray pipe extends outside the dilute aldehyde spray tower (72) and is connected in communication with the outlet of the dilute aldehyde circulation pump (73); The dilute aldehyde flowmeter (75) is connected to a primary-effect concentrated aldehyde and alcohol mixer (901). The main liquid inlet of the primary-effect concentrated aldehyde and alcohol mixer (901) is connected to a primary-effect concentrated aldehyde flowmeter (902). The secondary liquid inlet of the primary-effect concentrated aldehyde and alcohol mixer (901) is connected to a dilute aldehyde tank (74) through the dilute aldehyde flowmeter (75). The discharge port of the primary-effect concentrated aldehyde and alcohol mixer (901) is connected to a primary-effect concentrated aldehyde mixing tank (903). The lower end of the primary-effect concentrated aldehyde mixing tank (903) is connected to a primary-effect concentrated aldehyde mixing and conveying pump (904). The outlet of the primary-effect concentrated aldehyde mixing and conveying pump (904) is connected to a storage tank in the raw material area and is also connected to the main liquid inlet of the primary-effect concentrated aldehyde and alcohol mixer (901) through the primary-effect concentrated aldehyde flowmeter (902). The inlet of the primary-effect concentrated aldehyde mixing and conveying pump (904) is connected to a primary-effect concentrated aldehyde storage tank.

10. A paraformaldehyde production process, according to the paraformaldehyde production system described in claim 9, characterized in that: A. Primary-effect evaporation: The raw material formaldehyde is subjected to primary-effect evaporation through a primary-effect rising-film generator (10) to remove water and methanol in the raw material formaldehyde, obtaining primary-effect concentrated aldehyde. B. Secondary-effect evaporation: The primary-effect concentrated aldehyde is subjected to secondary-effect evaporation through a secondary-effect scraper evaporator (20) to remove water and methanol in the primary-effect concentrated aldehyde, obtaining secondary-effect concentrated aldehyde. C. Drying: The primary-effect concentrated aldehyde or secondary-effect concentrated aldehyde is dried through a rake dryer (40) to remove water and methanol in the concentrated aldehyde, obtaining paraformaldehyde finished product particles. D. Separation of primary-effect exhaust gas and secondary-effect exhaust gas: The primary-effect exhaust gas and secondary-effect exhaust gas are subjected to alcohol and aldehyde separation through an alcohol-aldehyde separator (50) to obtain gaseous dilute alcohol, liquid dilute alcohol, gaseous dilute aldehyde, and liquid dilute aldehyde. E. Recovery of dilute alcohol: The gaseous dilute alcohol is adsorbed through a dilute alcohol absorption tower (60) to obtain liquid dilute alcohol, which is mixed with the secondary-effect concentrated aldehyde and sent to the primary-effect concentrated aldehyde storage tank. F. Recovery of dilute aldehyde: The gaseous dilute aldehyde is adsorbed through a dilute aldehyde absorption tower (70) to obtain liquid dilute aldehyde, which is mixed with the primary-effect concentrated aldehyde and sent to the formaldehyde storage tank in the raw material area.

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