A paraformaldehyde production system and process

Abstract

The present invention relates to the technical field of paraformaldehyde production, specifically a paraformaldehyde production system and process, comprising: a first-effect rising film generator and a rake dryer connected in sequence; a first-effect concentrated aldehyde tank and a first-effect concentrated aldehyde pump connected to the first-effect rising film generator; a second-effect scraper evaporator is connected between the first-effect rising film generator and the rake dryer, and a second-effect concentrated aldehyde pump and a concentrated aldehyde flowmeter are connected to the second-effect scraper evaporator; the second-effect scraper evaporator also comprises: an alcohol-aldehyde separator for separating gaseous alcohol and aldehyde from the first-effect exhaust and the second-effect exhaust; a dilute alcohol absorption tower for absorbing gaseous dilute alcohol; a dilute aldehyde absorption tower for absorbing gaseous dilute aldehyde; and recycling liquid dilute alcohol and liquid dilute aldehyde. A paraformaldehyde production system and process of the present invention recycles alcohol and aldehyde in the process respectively, and quantitatively mixes and stores them with raw materials and concentrated aldehyde solution respectively; thereby increasing the methanol content in the solution and preventing formaldehyde from self-polymerizing during storage.

Description

Technical Field

[0001] The present invention relates to the technical field of paraformaldehyde production, in particular 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 agriculture.

[0003] The main process steps for producing paraformaldehyde are: removing part of the water from a 37%-55% formaldehyde solution containing a small amount of methanol by reduced pressure distillation or evaporation to increase the formaldehyde concentration to 60%-80%; stirring the reaction at 50-80°C to condense the formaldehyde and form a linear polymer, during which the degree of polymerization is adjusted by controlling the reaction time and temperature; separating the paraformaldehyde solid particles from the mother liquor by centrifugation or filtration, removing residual unreacted formaldehyde by washing with pure water or an organic solvent, and obtaining clean and dry granular paraformaldehyde through fluidized bed drying equipment or vacuum drying equipment; and crushing / packaging the granular paraformaldehyde as needed for transportation and storage.

[0004] At present, the main by-products in the production process of polyformaldehyde are mother liquor, waste gas and wastewater. Among them: the mother liquor contains unreacted formaldehyde, so the mother liquor is recycled into the original process; the formaldehyde and methanol tail gas is absorbed by the absorption tower; the wastewater undergoes post-biochemical treatment until it meets the environmental emission standards.

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

[0006] When formaldehyde solution is stored in tanks, low levels of methanol can cause it to self-polymerize. This is most directly manifested by the formation of white suspended matter or solid precipitation, an increase in solution viscosity, and a slight exotherm during the polymerization process. This direct impact on the production process includes: blockage of pipelines and conveying equipment, reduced flow rates, and the need for frequent downtime and cleaning. Continued polymerization during storage causes fluctuations in the concentration of the stored formaldehyde solution, reducing the effective formaldehyde content and increasing heat consumption during the polymerization process. Reduced formaldehyde activity leads to uneven molecular weight distribution in the self-polymerized formaldehyde, impacting the performance of downstream products. Summary of the Invention

[0007] In order to solve the technical problems existing in the background technology, the present invention provides a paraformaldehyde production system and process, which recovers the alcohol and aldehyde in the process respectively, and quantitatively mixes them with the raw materials and concentrated aldehyde solution and stores them separately; thereby increasing the methanol content in the solution and preventing formaldehyde from self-polymerization during storage.

[0008] The technical solution adopted by the present invention is:

[0009] A paraformaldehyde production system, comprising:

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

[0011] The first-effect rising film generator is connected with a material port, a circulation port, and a first-effect exhaust port. The material port is connected with the raw material. The circulation port and the material port are connected with each other and are connected in sequence with a first-effect concentrated aldehyde tank and a first-effect concentrated aldehyde pump.

[0012] The outlet of the first-effect concentrated aldehyde pump is connected to the first-effect concentrated aldehyde storage tank and the rake dryer, and the rake dryer is connected to the finished product particle outlet and the drying exhaust outlet;

[0013] The first-effect exhaust port is connected to an alcohol-aldehyde separator, and the exhaust ports of the alcohol-aldehyde separator are a gas phase diluted alcohol port, a liquid phase diluted alcohol port, a gas phase diluted aldehyde port, and a liquid phase diluted aldehyde port;

[0014] The gas phase diluted aldehyde port, the liquid phase diluted aldehyde port, and the drying exhaust port are connected to a diluted aldehyde absorption tower, the discharge end of the diluted aldehyde absorption tower is connected to a first-effect concentrated aldehyde mixing device, and the first-effect concentrated aldehyde mixing device is circulated and connected to a first-effect concentrated aldehyde flowmeter, a first-effect concentrated aldehyde mixing tank, and a first-effect concentrated aldehyde mixing delivery pump;

[0015] The gas phase diluted alcohol inlet and the liquid phase diluted alcohol inlet are connected to a diluted alcohol absorption tower, the discharge end of the diluted alcohol absorption tower is connected to a second-effect concentrated aldehyde mixing device, and the second-effect concentrated aldehyde mixing device is circulated and connected with a second-effect concentrated aldehyde flowmeter, a second-effect concentrated aldehyde mixing tank, and a second-effect concentrated aldehyde mixing delivery pump.

[0016] Furthermore, the above-mentioned single-effect rising film generator includes: a separation tower and a heating tower connected to each other in the upper and lower parts;

[0017] The 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 the steam pipe and the condensate pipe to heat the material in the heating tower tube side.

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

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

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

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

[0022] Furthermore, the rake dryer is configured as a horizontal structure, and one side of the upper end of the rake dryer is connected to the outlet of the second-effect concentrated aldehyde pump via 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 air inlet of the dilute aldehyde absorption tower; the finished particle port is connected to the lower side of the drying exhaust port of the rake dryer and is connected to the crushing / packaging process;

[0023] The outer wall of the rake dryer is provided with a spacer group which is connected with the steam pipe and the condensate pipe respectively. The spacer group is used to heat the material in the rake dryer.

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

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

[0026] A spacer sleeve connected to the steam pipe and the condensate pipe is provided outside the second-effect scraper evaporator. The spacer sleeve is used to heat the material on the inner wall of the second-effect scraper evaporator.

[0027] Furthermore, the above-mentioned alcohol-aldehyde separator comprises:

[0028] Multiple groups of adsorption and desorption towers are arranged in parallel, each of which is provided with a packing layer, and the upper and lower ends of the multiple groups of adsorption and desorption towers are connected to each other and are provided with a desorption outlet and an adsorption outlet respectively;

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

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

[0031] The adsorption outlets at the lower ends of the multiple groups of adsorption and desorption towers are connected with steam pipes for heating the fillers during the desorption process.

[0032] Furthermore, a dilute aldehyde replenishment cooler is provided between the dilute aldehyde vacuum pump replenishment port and the lower end of the cold dilute aldehyde tank;

[0033] A dilute alcohol replenishment cooler is provided between the dilute alcohol vacuum pump replenishment port and the lower end of the cold dilute alcohol tank.

[0034] Furthermore, the above-mentioned diluted alcohol absorption tower comprises:

[0035] A dilute alcohol spray tower and a dilute alcohol storage tower are connected in upper and lower directions;

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

[0037] The above-mentioned diluted alcohol flowmeter is connected to a second-effect concentrated aldehyde alcohol mixer, the main liquid inlet of the above-mentioned second-effect concentrated aldehyde alcohol mixer is connected to a second-effect concentrated aldehyde flowmeter, the secondary liquid inlet of the second-effect concentrated aldehyde alcohol mixer is connected to the diluted alcohol tank through the diluted alcohol flowmeter, the discharge outlet of the second-effect concentrated aldehyde alcohol mixer is connected to a second-effect concentrated aldehyde mixing tank, the lower end of the above-mentioned second-effect concentrated aldehyde mixing tank is connected to a second-effect concentrated aldehyde mixing delivery pump, the outlet of the above-mentioned second-effect concentrated aldehyde mixing delivery pump is connected to the first-effect concentrated aldehyde storage tank, and is connected to the main liquid inlet of the second-effect concentrated aldehyde alcohol mixer through the second-effect concentrated aldehyde flowmeter; the inlet of the second-effect concentrated aldehyde mixing delivery pump is connected to the second-effect concentrated aldehyde storage tank.

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

[0039] A dilute aldehyde spray tower and a dilute aldehyde liquid storage tower are connected in upper and lower directions;

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

[0041] The above-mentioned dilute aldehyde flowmeter is connected to a first-effect concentrated aldehyde mixing device, the main liquid inlet of the above-mentioned first-effect concentrated aldehyde mixing device is connected to a first-effect concentrated aldehyde flowmeter, the auxiliary liquid inlet of the first-effect concentrated aldehyde mixing device is connected to the dilute aldehyde tank through the dilute aldehyde flowmeter, the discharge outlet of the first-effect concentrated aldehyde mixing device is connected to a first-effect concentrated aldehyde mixing tank, the lower end of the above-mentioned first-effect concentrated aldehyde mixing tank is connected to a first-effect concentrated aldehyde mixing delivery pump, the outlet of the above-mentioned first-effect concentrated aldehyde mixing delivery pump is connected to the raw material area storage tank, and is connected to the main liquid inlet of the first-effect concentrated aldehyde mixing device through the first-effect concentrated aldehyde flowmeter; the inlet of the first-effect concentrated aldehyde mixing delivery pump is connected to the first-effect concentrated aldehyde storage tank.

[0042] A paraformaldehyde production process, comprising:

[0043] A. Single-effect evaporation:

[0044] The raw formaldehyde is evaporated in one effect by a single-effect rising film generator to remove water and methanol in the raw formaldehyde to obtain a single-effect concentrated formaldehyde;

[0045] B. Second-effect evaporation:

[0046] The concentrated aldehyde in the first effect is evaporated in the second effect by a second-effect scraper evaporator to remove water and methanol in the concentrated aldehyde in the first effect to obtain the concentrated aldehyde in the second effect;

[0047] C. Drying:

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

[0049] D. Separation of primary and secondary exhaust:

[0050] The alcohol and aldehyde are separated from the exhaust gas of the first effect and the exhaust gas of the second effect by an alcohol-aldehyde separator to obtain gaseous dilute alcohol, liquid dilute alcohol, gaseous dilute aldehyde and liquid dilute aldehyde;

[0051] E. Recovery of dilute alcohol:

[0052] The gaseous dilute alcohol is adsorbed by the dilute alcohol absorption tower to obtain liquid 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 gaseous dilute aldehyde is adsorbed by the dilute aldehyde absorption tower to obtain liquid dilute aldehyde, which is mixed with the first-effect concentrated aldehyde and sent to the formaldehyde storage tank in the raw material area.

[0055] Beneficial effects of the paraformaldehyde production system and process of the present invention:

[0056] The exhaust gas from the first-effect evaporation process and the second-effect evaporation process is separated into alcohol and aldehyde to produce dilute alcohol and dilute aldehyde;

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

[0058] The exhaust gas from the dilute formaldehyde and drying process is recovered through the dilute formaldehyde absorption tower, and is quantitatively and fully mixed with the output liquid of the single-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-polymerization. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 It is a schematic diagram of a process flow chart of a paraformaldehyde production system according to an embodiment of the present invention;

[0060] Figure 2 This is a schematic diagram of a single-effect exhaust and double-effect exhaust recovery process flow chart of an embodiment of the present invention;

[0061] Figure 3 Schematic diagram of the dilute alcohol recovery process flow chart of an example of the present invention;

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

[0063] In the picture:

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

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

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

[0069] 561, dilute aldehyde cooler,

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

[0071] 562, dilute alcohol cooler,

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

[0073] 65. Dilute alcohol flow meter,

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

[0075] 75. Dilute aldehyde flow meter,

[0076] 801, Second-effect concentrated aldehyde mixing device, 802, Second-effect concentrated aldehyde flow meter, 803, Second-effect concentrated aldehyde mixing tank,

[0077] 804, two-effect concentrated aldehyde mixing delivery pump,

[0078] 901, first-effect concentrated aldehyde mixing device, 902, first-effect concentrated aldehyde flow meter, 903, first-effect concentrated aldehyde mixing tank,

[0079] 904. Single-effect concentrated aldehyde mixing and delivery pump. DETAILED DESCRIPTION

[0080] In order to more clearly and specifically illustrate the specific implementation objectives and implementation methods of the present invention, the following is a complete description of the technical solution of the present invention. The described embodiments are only part of the embodiments of the present invention, not all of them. Without creative work, all other embodiments based on the described embodiments of the present invention fall within the scope of protection of the present invention.

[0081] The present invention provides a paraformaldehyde production system, such as Figure 1 As shown, including:

[0082] The invention comprises: a single-effect rising film generator 10 and a rake dryer 40 which are connected to each other via a material pipeline.

[0083] The above-mentioned single-effect rising film generator 10 includes: a separation tower 12 and a heating tower 11 which are connected in an upper and lower manner; a material port connected to the formaldehyde storage tank in the raw material area is provided at the bottom of the above-mentioned heating tower 11, and a steam pipe and a condensate pipe connected to the shell side of the heating tower 11 are respectively provided at the upper and lower ends of the side wall of the heating tower 11, so as to heat the material in the pipe side of the heating tower 11; a single-effect exhaust port is provided at the top of the above-mentioned separation tower 12, a guide plate is provided above the liquid level in the separation tower 12, and a circulation port is provided on the side wall below the liquid level in the separation tower 12, the circulation port and the material port are connected to each other and are connected to a single-effect concentrated aldehyde tank 13, the bottom of the above-mentioned single-effect concentrated aldehyde tank 13 is connected to a single-effect concentrated aldehyde pump 14, and the above-mentioned single-effect concentrated aldehyde pump 14 is connected to the single-effect concentrated aldehyde storage tank; a circulation 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 arranged in a horizontal structure, and one side of the upper end of the rake dryer 40 is arranged as a material inlet, and the above-mentioned material inlet is connected to a concentrated aldehyde flowmeter 41; a spacer group is provided on the outer wall of the rake dryer 40, and the upper and lower ends of the above-mentioned spacer group are respectively connected to a steam pipe and a condensate pipe for heating the material in the rake dryer 40; the other side of the upper end of the rake dryer 40 is connected to a drying exhaust port, and the lower end of the rake dryer 40 below the above-mentioned drying exhaust port is connected to a finished product particle port, and is connected to the crushing / packaging process.

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

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

[0087] The first-effect exhaust port and the second-effect exhaust port are connected to an alcohol-formaldehyde separator 50, which includes:

[0088] Multiple groups of adsorption and desorption towers 51 are arranged in parallel, and a packing layer is provided in the adsorption and desorption towers 51;

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

[0090] The lower ends of the multiple groups of adsorption and desorption towers 51 are connected with adsorption outlets, which are connected with a dilute alcohol cooler 522. The outlet of the dilute alcohol cooler 522 is connected with a cold dilute alcohol tank 532. The lower end of the cold dilute alcohol tank 532 is connected with a liquid-phase dilute alcohol port. The exhaust port at the upper end of the cold dilute alcohol tank 532 is connected with a dilute alcohol vacuum pump 542. The outlet of the dilute alcohol vacuum pump 542 is connected with a dilute alcohol steam-water separator 552. The liquid discharge port at the lower end of the dilute alcohol steam-water separator 552 is connected with the lower end of the cold dilute alcohol tank 532. The exhaust port of the dilute alcohol steam-water separator 552 is connected with a gaseous dilute alcohol port. The liquid replenishment port of the dilute alcohol vacuum pump 542 is connected with a supplementary dilute alcohol cooler 562. The outlet of the supplementary dilute alcohol cooler 562 is connected with the lower end of the cold dilute alcohol tank 532.

[0091] The adsorption outlets at the lower ends of the multiple groups of adsorption and desorption towers 51 are connected to steam pipes for heating the fillers during the desorption process.

[0092] The gas phase diluted alcohol inlet and the liquid phase diluted alcohol inlet are connected to a diluted alcohol absorption tower 60, which includes:

[0093] A dilute alcohol spray tower 62 and a dilute alcohol storage tower 61 are connected to each other.

[0094] The side wall above the liquid level in the above-mentioned diluted alcohol storage tower 61 is connected to the gas phase diluted alcohol inlet, and the bottom of the diluted alcohol storage tower 61 is connected to the liquid phase diluted alcohol inlet. The bottom of the diluted alcohol storage tower 61 is also connected to a diluted alcohol circulation pump 63, and the outlet of the above-mentioned diluted alcohol circulation pump 63 is connected to a diluted alcohol tank 64, and the lower end of the above-mentioned diluted alcohol tank 64 is connected to a diluted alcohol flowmeter 65; the above-mentioned diluted alcohol spray tower 62 is sequentially provided with a demisting layer, a spray pipe, and a packing layer from top to bottom, and the above-mentioned spray pipe extends to the outside of the diluted alcohol spray tower 62 and is connected to the outlet of the diluted alcohol circulation pump 63.

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

[0096] The drying exhaust port, the gas phase diluted aldehyde port, and the liquid phase diluted aldehyde port are connected to a diluted aldehyde absorption tower 70, which includes:

[0097] A dilute aldehyde spray tower 72 and a dilute aldehyde liquid storage tower 71 are connected to each other.

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

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

[0100] Based on the paraformaldehyde production system in the above embodiment, a paraformaldehyde production process is further described below:

[0101] A. Single-effect evaporation:

[0102] The raw formaldehyde is supplied from the formaldehyde storage tank in the raw material area to the heating tower 11 and transported upward to the separation tower 12 through the pipe side of the heating tower 11. As the raw formaldehyde is heated and vaporized in the pipe side of the heating tower 11, it is circulated through the circulating pipe in the pipe side of the heating tower 11 to be heated, so that the water and methanol in the raw formaldehyde are vaporized.

[0103] The generated first-effect exhaust gas is discharged from the top of the separation tower 12, and the generated liquid first-effect concentrated aldehyde is discharged from the bottom of the heating tower 11 to the first-effect concentrated aldehyde tank 13, and then 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 delivered to the second-effect scraper evaporator 20 by the first-effect concentrated aldehyde pump 14 or the tank area feed pump, and is distributed to the inner wall of the second-effect scraper evaporator 20 heated by the spacer through the distributor, 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, and the generated second-effect concentrated aldehyde is scraped down by the scraper to the second-effect concentrated aldehyde tank 21 at the bottom of the second-effect scraper evaporator 20, and then 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 measured by the concentrated aldehyde flowmeter 41 and respectively delivered to the rake dryer 40 heated by the spacer group through the first-effect concentrated aldehyde pump 14, the second-effect concentrated aldehyde pump 22 or the tank area feed pump to vaporize the water and methanol in the concentrated aldehyde;

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

[0110] D. Separation of primary and secondary exhaust:

[0111] The exhaust gas of the first effect and the exhaust gas of the second effect pass through the adsorption and desorption tower 51 to adsorb aldehyde;

[0112] The gas after aldehyde adsorption is cooled by the dilute alcohol cooler 522, and the condensed liquid dilute alcohol is sent to the cold dilute alcohol tank 532. The gaseous dilute alcohol in the cold dilute alcohol tank 532 is discharged in sequence through the dilute alcohol vacuum pump 542 and the dilute alcohol steam-water separator 552. The liquid 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, so as to ensure the vacuum degree of the dilute alcohol vacuum pump 542.

[0113] After the aldehyde adsorption is completed, steam is introduced into the adsorption-desorption tower 51 in the reverse direction to desorb the aldehyde;

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

[0115] E. Recovery of dilute alcohol:

[0116] The gaseous phase diluted alcohol and the liquid phase diluted alcohol are respectively delivered to the diluted alcohol storage tower 61 by a fan and a pump;

[0117] The liquid phase diluted alcohol in the diluted alcohol storage tower 61 is sprayed out from the spray pipe in the diluted alcohol spray tower 62 through the diluted alcohol circulation pump 63, and adsorbs the gas phase diluted alcohol sent to the diluted 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 dilute alcohol that has absorbed the gaseous dilute alcohol is sent to the dilute alcohol tank 64 by the dilute alcohol circulation pump 63, the liquid dilute alcohol in the dilute alcohol tank 64 is measured by the dilute alcohol flowmeter 65, and then sent to the second-effect concentrated aldehyde mixing device 801, the second-effect concentrated aldehyde is measured by the second-effect concentrated aldehyde flowmeter 802, and then sent to the second-effect concentrated aldehyde mixing device 801 through the second-effect concentrated aldehyde mixing pump 804, the second-effect concentrated aldehyde and liquid dilute alcohol are mixed in the second-effect concentrated aldehyde mixing device 801 and then sent to the second-effect concentrated aldehyde mixing tank 803, the second-effect concentrated aldehyde and liquid dilute alcohol mixture in the second-effect concentrated aldehyde mixing tank 803 is sent to the first-effect concentrated aldehyde storage tank through the second-effect concentrated aldehyde mixing pump 804.

[0119] F. Recovery of dilute aldehyde:

[0120] The gaseous dilute aldehyde and dry exhaust gas are sent to the dilute aldehyde liquid storage tower 71 by a fan, and the liquid dilute aldehyde is sent to the dilute aldehyde liquid storage tower 71 by a pump;

[0121] The liquid phase diluted aldehyde in the diluted aldehyde liquid storage tower 71 is sprayed out from the spray pipe in the diluted aldehyde spray tower 72 through the diluted aldehyde circulation pump 73, and adsorbs the gas phase diluted aldehyde and dry exhaust gas sent to the diluted aldehyde liquid 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 dilute aldehyde that has absorbed the gaseous dilute aldehyde is sent to the dilute aldehyde tank 74 by the dilute aldehyde circulation pump 73, the liquid dilute aldehyde in the dilute aldehyde tank 74 is measured by the dilute aldehyde flowmeter 75, and then sent to the first-effect concentrated aldehyde mixing device 901, the first-effect concentrated aldehyde is measured by the first-effect concentrated aldehyde flowmeter 902, and then sent to the first-effect concentrated aldehyde mixing device 901 through the first-effect concentrated aldehyde mixing pump 904, the first-effect concentrated aldehyde and liquid dilute aldehyde are mixed in the first-effect concentrated aldehyde mixing device 901 and sent to the second-effect concentrated aldehyde mixing tank 903, the first-effect concentrated aldehyde and liquid dilute aldehyde mixture in the second-effect concentrated aldehyde mixing tank 903 is sent to the formaldehyde storage tank in the raw material area through the first-effect concentrated aldehyde mixing pump 904.

[0123] In summary, the above description is only a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. Based on the above description, relevant personnel can make various changes and modifications without departing from the technical concept of this invention. The technical scope of the present invention is not limited to the contents of the specification. All equivalent changes and modifications of the above-mentioned shapes, structures, features and spirits according to the scope of the claims of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A paraformaldehyde production system, characterized in that: include: A single-effect rising film generator (10) and a rake dryer (40) are sequentially connected; The first-effect rising film generator (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, the circulation port and the material port are connected with 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 to the first-effect concentrated aldehyde storage tank and the rake dryer (40), and the rake dryer (40) is connected to the finished product particle port and the drying exhaust port; The first-effect exhaust port is connected to an alcohol-aldehyde separator (50), and the exhaust ports of the alcohol-aldehyde separator (50) are a gas-phase diluted alcohol port, a liquid-phase diluted alcohol port, a gas-phase diluted aldehyde port, and a liquid-phase diluted aldehyde port; The gas phase diluted aldehyde port, the liquid phase diluted aldehyde port, and the dry exhaust port are connected to a diluted aldehyde absorption tower (70); the discharge end of the diluted aldehyde absorption tower (70) is connected to a first-effect concentrated aldehyde mixing device (901); the first-effect concentrated aldehyde mixing device (901) is circulated and connected to a first-effect concentrated aldehyde flowmeter (902), a first-effect concentrated aldehyde mixing tank (903), and a first-effect concentrated aldehyde mixing delivery pump (904); the first-effect concentrated aldehyde and liquid phase diluted aldehyde mixture in the first-effect concentrated aldehyde mixing tank (903) is delivered to a formaldehyde storage tank in the raw material area through the first-effect concentrated aldehyde mixing delivery pump (904); and the inlet of the first-effect concentrated aldehyde mixing delivery pump (904) is connected to the first-effect concentrated aldehyde storage tank; The gas phase diluted alcohol inlet and the liquid phase diluted alcohol inlet are connected to a diluted alcohol absorption tower (60), the discharge end of the diluted alcohol absorption tower (60) is connected to a second-effect concentrated aldehyde mixing device (801), the second-effect concentrated aldehyde mixing device (801) is circulated and connected to a second-effect concentrated aldehyde flowmeter (802), a second-effect concentrated aldehyde mixing tank (803), and a second-effect concentrated aldehyde mixing delivery pump (804), the second-effect concentrated aldehyde and liquid phase diluted alcohol mixture in the second-effect concentrated aldehyde mixing tank (803) is delivered to a first-effect concentrated aldehyde storage tank through the second-effect concentrated aldehyde mixing delivery pump (804), and the inlet of the second-effect concentrated aldehyde mixing delivery pump (804) is connected to the second-effect concentrated aldehyde storage tank.

2. A paraformaldehyde production system according to claim 1, characterized in that: The single-effect rising film generator (10) comprises: a separation tower (12) and a heating tower (11) which are connected to each other from top to bottom; The material port is connected to the bottom of the heating tower (11) and is connected to the formaldehyde storage tank in the raw material area. The shell side of the heating tower (11) is connected to the steam pipe and the condensate pipe to heat the material in the pipe side of the heating tower (11); The first-effect exhaust port is connected to the top of the separation tower (12) and is connected to the air inlet end of the alcohol-aldehyde separator (50); The circulation port is connected to and arranged on the side wall below the liquid level in the separation tower (12).

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

4. A paraformaldehyde production system according to claim 2, characterized in that: The rake dryer (40) is configured as a horizontal structure, and one side of the upper end of the rake dryer (40) is connected to the outlet of the second-effect concentrated aldehyde pump (22) via a concentrated aldehyde flowmeter (41); the drying exhaust port is connected and arranged on the other side of the upper end of the rake dryer (40), and is connected to the air inlet of the dilute aldehyde absorption tower (70); the finished particle port is connected and arranged below the drying exhaust port of the rake dryer (40), and is connected to the crushing / packaging process; A spacer group connected to the steam pipe and the condensate pipe is provided on the outer wall of the rake dryer (40), and the spacer group is used to heat the material in the rake dryer (40).

5. A paraformaldehyde production system according to claim 4, characterized in that: A second-effect scraper evaporator (20) is provided in communication between the first-effect rising film generator (10) and the rake dryer (40); A scraper is rotatably provided in the second-effect scraper evaporator (20), a gas-liquid separation partition and a distributor are coaxially provided on the upper end of the scraper rotation shaft, a second-effect exhaust port is provided on the side wall of the second-effect scraper evaporator (20) on the side of the gas-liquid separation partition, and a connection port with the first-effect concentrated aldehyde pump (14) is provided on the side wall of the second-effect scraper evaporator (20) on the side of the distributor; A spacer sleeve connected to a steam pipe and a condensate pipe is provided outside the second-effect scraper evaporator (20), and the spacer sleeve is used to heat the material on the inner wall of the second-effect scraper evaporator (20).

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

7. A paraformaldehyde production system according to claim 6, characterized in that: A dilute aldehyde replenishment cooler (561) is provided between the dilute aldehyde vacuum pump (541) and the lower end of the cold dilute aldehyde tank (531); A dilute alcohol replenishment cooler (562) is provided between 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, characterized in that: The dilute alcohol absorption tower (60) comprises: A dilute alcohol spray tower (62) and a dilute alcohol storage tower (61) are connected to each other in the upper and lower parts; The side wall above the liquid level in the diluted alcohol storage tower (61) is connected to the gas phase diluted alcohol port, the bottom of the diluted alcohol storage tower (61) is connected to the liquid phase diluted alcohol port, the bottom of the diluted alcohol storage tower (61) is also connected to a diluted alcohol circulation pump (63), the outlet of the diluted alcohol circulation pump (63) is connected to a diluted alcohol tank (64), and the lower end of the diluted alcohol tank (64) is connected to a diluted alcohol flowmeter (65); the diluted alcohol spray tower (62) is provided with a demisting layer, a spray pipe, and a packing layer from top to bottom, the spray pipe extends to the outside of the diluted alcohol spray tower (62) and is connected to the outlet of the diluted alcohol circulation pump (63); The dilute alcohol flowmeter (65) is connected to a second-effect concentrated aldehyde mixing alcohol device (801), a main liquid inlet of the second-effect concentrated aldehyde mixing alcohol device (801) is connected to a second-effect concentrated aldehyde flowmeter (802), a secondary liquid inlet of the second-effect concentrated aldehyde mixing alcohol device (801) is connected to the dilute alcohol tank (64) via the dilute alcohol flowmeter (65), a discharge outlet of the second-effect concentrated aldehyde mixing alcohol device (801) is connected to a second-effect concentrated aldehyde mixing tank (803), a lower end of the second-effect concentrated aldehyde mixing tank (803) is connected to a second-effect concentrated aldehyde mixing delivery pump (804), an outlet of the second-effect concentrated aldehyde mixing delivery pump (804) is connected to a first-effect concentrated aldehyde storage tank, and is connected to the main liquid inlet of the second-effect concentrated aldehyde mixing alcohol device (801) via the second-effect concentrated aldehyde flowmeter (802); and an inlet of the second-effect concentrated aldehyde mixing delivery pump (804) is connected to the second-effect concentrated aldehyde storage tank.

9. A paraformaldehyde production system according to claim 8, characterized in that: The dilute aldehyde absorption tower (70) comprises: A dilute aldehyde spray tower (72) and a dilute aldehyde liquid storage tower (71) are connected to each other in the upper and lower parts; The side wall above the liquid level in the diluted aldehyde liquid storage tower (71) is connected to the drying exhaust port and the gas phase diluted aldehyde port, the bottom of the diluted aldehyde liquid storage tower (71) is connected to the liquid phase diluted aldehyde port, and the bottom of the diluted aldehyde liquid storage tower (71) is also connected to a diluted aldehyde circulation pump (73), the outlet of the diluted aldehyde circulation pump (73) is connected to a diluted aldehyde tank (74), and the lower end of the diluted aldehyde tank (74) is connected to a diluted aldehyde flowmeter (75); the diluted aldehyde spray tower (72) is sequentially provided with a demisting layer, a spray pipe, and a packing layer from top to bottom, and the spray pipe extends to the outside of the diluted aldehyde spray tower (72) and is connected to the outlet of the diluted aldehyde circulation pump (73); The diluted aldehyde flowmeter (75) is connected to a first-effect concentrated aldehyde mixing alcohol device (901), the main liquid inlet of the first-effect concentrated aldehyde mixing alcohol device (901) is connected to a first-effect concentrated aldehyde flowmeter (902), the secondary liquid inlet of the first-effect concentrated aldehyde mixing alcohol device (901) is connected to the diluted aldehyde tank (74) via the diluted aldehyde flowmeter (75), the discharge outlet of the first-effect concentrated aldehyde mixing alcohol device (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 delivery pump (904), the outlet of the first-effect concentrated aldehyde mixing delivery pump (904) is connected to the formaldehyde storage tank in the raw material area, and is connected to the main liquid inlet of the first-effect concentrated aldehyde mixing alcohol device (901) via the first-effect concentrated aldehyde flowmeter (902); the inlet of the first-effect concentrated aldehyde mixing delivery pump (904) is connected to the first-effect concentrated aldehyde storage tank.

10. A paraformaldehyde production process, comprising the paraformaldehyde production system according to claim 9, characterized in that: A. Single-effect evaporation: The raw formaldehyde is evaporated in one effect by a single-effect rising film generator (10) to remove water and methanol in the raw formaldehyde to obtain a single-effect concentrated formaldehyde; B. Second-effect evaporation: Performing a second-effect evaporation on the first-effect concentrated aldehyde by a second-effect scraper evaporator (20) to remove water and methanol in the first-effect concentrated aldehyde to obtain the second-effect concentrated aldehyde; C. Drying: Drying the first-effect concentrated aldehyde or the second-effect concentrated aldehyde by a rake dryer (40) to remove water and methanol in the concentrated aldehyde to obtain finished paraformaldehyde particles; D. Separation of primary and secondary exhaust: The alcohol-aldehyde separator (50) is used to separate the alcohol and aldehyde from the exhaust gas of the first effect and the exhaust gas of the second effect 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 by the dilute alcohol absorption tower (60) to obtain the liquid dilute alcohol, which is mixed with the second-effect concentrated aldehyde and sent to the first-effect concentrated aldehyde storage tank; F. Recovery of dilute aldehyde: The gaseous dilute aldehyde is adsorbed by the dilute aldehyde absorption tower (70) to obtain liquid dilute aldehyde, which is mixed with the concentrated aldehyde and sent to the formaldehyde storage tank in the raw material area.

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