Preparation system and process for producing formaldehyde by replacing refined methanol with crude methanol

Abstract

The invention belongs to the technical field of formaldehyde preparation, and particularly relates to a preparation system and process for producing formaldehyde by replacing refined methanol with crude methanol. In order to solve the technical problems of high energy consumption and high cost in formaldehyde production, the invention provides the technical scheme that a crude methanol filter is used for receiving crude methanol and preliminarily filtering mechanical impurities in the crude methanol; the activated carbon filter or the granular carbon filter is used for purifying the crude methanol from which the mechanical impurities are removed; the methanol precision filter is used for finely filtering the purified crude methanol and filtering mechanical impurities again; the crude methanol preheater is used for preheating the crude methanol of which the mechanical impurities are filtered again; the methanol combined evaporator is used for evaporating, vaporizing, overheating and adjusting the preheated crude methanol to obtain ternary mixed gas; the ternary mixed gas subjected to proportion adjustment enters the oxidation furnace, oxidation and dehydrogenation reactions are carried out, and formaldehyde is generated; and the formaldehyde generated by the reaction enters an absorption tower and is absorbed by water to generate 37% formaldehyde.

Description

Technical Field

[0001] This invention belongs to the field of formaldehyde preparation technology, specifically relating to a preparation system and process for producing formaldehyde by replacing refined methanol with crude methanol. Background Technology

[0002] The traditional raw material for industrial formaldehyde production is refined methanol. The main cost of refining crude methanol into refined methanol is the energy consumption in the distillation process, which accounts for more than 10% of the cost of refined methanol. Therefore, directly using crude methanol to produce formaldehyde has a significant energy-saving effect.

[0003] The original method for synthesizing crude methanol used a Zn-Cr catalyst, resulting in crude methanol containing 3%-4% organic impurities such as dimethyl ether, higher alcohols, and ketones. Since 1985, a copper-based catalyst has been used for crude methanol synthesis, reducing the amount of organic impurities in the crude methanol to only 0.3%-0.5%, and increasing the methanol content from 86%-88% to 92%-94%. This has made it possible to directly produce formaldehyde from crude methanol. The process used domestically involves purifying crude methanol by adding alkali and filtering with H2O2. However, due to insufficient purification, impurities gradually increase within the methanol evaporator, necessitating the continuous discharge of residual liquid from the evaporator into a methanol pre-distillation tower for further treatment.

[0004] Another process involves mixing pre-distilled methanol (60%) and crude methanol (40%) as raw materials for formaldehyde production.

[0005] In the traditional production method, crude methanol is first distilled to obtain refined methanol, which then enters the formaldehyde production system to be oxidized and dehydrogenated to produce formaldehyde. The process is cumbersome, and the purification of crude methanol into refined methanol through the distillation system requires a large amount of energy such as steam and electricity, resulting in high energy consumption.

[0006] In view of the shortcomings of crude methanol to formaldehyde production processes at home and abroad, this invention provides a preparation process for formaldehyde production using crude methanol instead of refined methanol. Summary of the Invention

[0007] To address the technical problem of "high energy consumption and high cost in formaldehyde production," this invention provides the following technical solution: Firstly, This invention provides a system for producing formaldehyde using crude methanol instead of refined methanol, comprising: A coarse methanol filter is used to receive crude methanol and perform coarse filtration to initially remove mechanical impurities; the outlet of the coarse methanol filter is connected to the inlet of an activated carbon filter. Activated carbon filters or granular carbon filters are used to purify crude methanol after removing mechanical impurities and to adsorb impurities harmful to the catalyst added to the oxidation furnace; the outlet of the activated carbon filter or granular carbon filter is connected to the inlet of the methanol precision filter. A methanol precision filter is used to further filter the purified crude methanol, further filtering out mechanical impurities; the outlet of the methanol precision filter is connected to the inlet of the crude methanol preheater. A crude methanol preheater is used to preheat crude methanol that has been filtered again for mechanical impurities; the outlet of the crude methanol preheater is connected to a methanol combined evaporator. The methanol combined evaporator is used to evaporate, vaporize, superheat, and adjust the preheated crude methanol to obtain a three-way mixture of methanol, air, and steam in a certain ratio; the outlet of the methanol combined evaporator is connected to the inlet of the oxidation furnace. The oxidizing furnace receives a ternary gas mixture after adjusting its proportions. At a certain temperature, the mixture undergoes oxidation and dehydrogenation reactions to produce formaldehyde. The outlet of the oxidizing furnace is connected to the inlet of a multi-stage absorption tower. The multi-stage absorption tower is used to absorb the formaldehyde generated in the reaction. The formaldehyde is absorbed by water to form 37% formaldehyde, which is then cooled and extracted as a product.

[0008] Furthermore, the coarse methanol filter uses a glass fiber filter.

[0009] Furthermore, the methanol precision filter uses high-precision filter paper with a filtration accuracy of 5 microns.

[0010] Furthermore, the multi-stage absorption tower includes absorption tower #1 and absorption tower #2 connected in series.

[0011] Furthermore, the crude methanol preheater is located between the oxidation furnace and the No. 1 absorption tower.

[0012] Furthermore, the crude methanol preheater preheats the crude methanol to 80℃-85℃.

[0013] Furthermore, after the crude methanol enters the methanol combined evaporator, the equilibrium concentration of the methanol combined evaporator is reduced to 45%-70%.

[0014] Furthermore, the oxygen-to-methanol ratio is controlled at 0.42-0.65; the molar fraction of water in the ternary gas mixture is maintained at ≥30%, corresponding to an upper limit for methanol explosion with an oxygen-to-methanol ratio ≤0.77.

[0015] Furthermore, the ternary gas mixture enters the oxidation furnace, where oxidation and dehydrogenation reactions occur at a temperature of 620℃-660℃.

[0016] Secondly, This invention provides a process for producing formaldehyde using crude methanol instead of refined methanol, comprising: S1. Crude methanol with a concentration of 70%-85%, a temperature of 5℃-45℃, and a pressure of 0.1MPa-0.3MPa enters the crude methanol filter for coarse filtration to initially filter out mechanical impurities; S2. The crude methanol, which has been initially filtered to remove mechanical impurities, is then purified by an activated carbon filter or a granular carbon filter to adsorb impurities that are harmful to the catalyst added to the oxidation furnace. S3. After being purified by an activated carbon filter or a granular carbon filter, crude methanol enters a precision methanol filter for fine filtration. S4. After filtering out mechanical impurities again, the crude methanol enters the crude methanol preheater to preheat the crude methanol temperature to 80℃-85℃. S5. After coarse filtration, activated carbon adsorption, and fine filtration, the crude methanol enters the methanol combined evaporator for evaporation, vaporization, and superheating. Adjust the ratio of the ternary mixture of methanol, air, and steam introduced into the methanol combined evaporator; connect the outlet of the methanol combined evaporator to the inlet of the oxidation furnace; S6. The ternary mixed gas, after being proportioned and adjusted, enters the oxidation furnace and undergoes oxidation and dehydrogenation reactions at 620℃-660℃ to generate formaldehyde; S7. The formaldehyde generated in the reaction enters the No. 1 and No. 2 absorption towers and is absorbed by water to generate 37% formaldehyde, which is then cooled and extracted as a product.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The preparation system of this invention uses external circulating activated carbon to purify crude methanol in a methanol evaporator to produce formaldehyde. Compared with the production of refined methanol, crude methanol is used instead of refined methanol. Crude methanol is directly fed into the system, skipping the crude methanol distillation step, which saves a lot of energy such as steam and electricity. The energy savings reduce the cost of materials, equipment maintenance, and personnel management. It also avoids the wastewater generated by crude methanol distillation being sent out, thus reducing the cost of formaldehyde production.

[0018] This invention installs a crude methanol preheater between the oxidation furnace and the absorption tower. The filtered crude methanol is preheated in the crude methanol preheater by making full use of the reaction heat of the oxidation furnace, thus recovering the reaction heat and raising the temperature of the crude methanol by 60°C-70°C before it enters the evaporator. This compensates for the heat required by the methanol combined evaporator due to the reduction in methanol concentration, further saving energy consumption.

[0019] The present invention utilizes a methanol combined evaporator to evaporate moisture from crude methanol with a concentration of 70%-85%, a temperature of 5℃-45℃, and a pressure of 0.1MPa-0.3MPa. This evaporates the moisture, partially replacing the feed steam and increasing the amount of external steam supplied. Furthermore, the moisture in the crude methanol reduces the methanol concentration (equilibrium concentration) in the methanol combined evaporator, thereby increasing the oxygen-to-methanol ratio (the molar ratio of oxygen to methanol) and reducing the methanol consumption per ton of formaldehyde. Compared to the traditional method of increasing the feed steam to improve the oxygen-to-methanol ratio, this invention saves steam consumption. Crude methanol with a concentration of 70%-85%, a temperature of 5℃-45℃, and a pressure of 0.1MPa-0.3MPa enters the methanol combined evaporator. After entering the evaporator, the equilibrium concentration of the evaporator is reduced to 45%-70%, and the oxygen-methanol ratio is controlled at 0.42-0.65. This achieves formaldehyde production with a low equilibrium concentration in the evaporator and a high oxygen-methanol ratio in the oxidizer. The high oxygen-methanol ratio enhances the oxidation reaction and reduces methanol consumption. The methanol consumption per ton of formaldehyde (37%) produced is reduced from 445kg / t-450kg / t to 425kg / t-440kg / t.

[0020] In this invention, the moisture in crude methanol with a concentration of 70%-85% is evaporated by a methanol combined evaporator, and the crude methanol carries in 15%-30% moisture. This 15%-30% moisture can partially replace the feed steam, increasing the amount of external steam supplied. Some moisture is generated from the methanol combined evaporator. To maintain moisture balance, the feed steam supply is reduced from 4.2t / h to 2t / h, while increasing the external steam supply by 2t-3t at 0.45MPa(A). This achieves formaldehyde production with low feed steam, while increasing the external steam supply by 2t-3t / h at 0.45MPa(A), thus reducing production costs.

[0021] The moisture content of the crude methanol in this invention increases the molar fraction of water vapor in the ternary gas mixture, thereby expanding the upper limit of methanol explosion corresponding to an oxygen-methanol ratio from 0.6 to 0.77, and increasing the upper limit of safe operation of the oxygen-methanol ratio. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the system and method of the present invention.

[0023] Figure label: 1 is a crude methanol filter; 2 is an activated carbon filter; 3 is a methanol precision filter; 4 is a methanol combined evaporator; 5 is a flame arrester; 6 is an oxidizer; 61 is an oxidizer quench section; 62 is a hot water circulation section; 7 is a crude methanol preheater; 8 is an absorption tower #1; 9 is an absorption tower #2; 10 is a tail gas furnace; 11 is an oxygen furnace steam drum; 12 is a tail gas furnace steam drum; 13 is an evaporative cooler for absorption tower #1; 14 is a hot water circulation tank; 15 is an evaporative cooler for absorption tower #2; 16 is a water seal tank; 17 is an air Roots blower. Detailed Implementation

[0024] The technical solution of the present invention will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are not all embodiments of the present invention. All other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0025] Example 1 like Figure 1As shown, the present invention provides a preparation system for producing formaldehyde by replacing refined methanol with crude methanol. The preparation system includes: a crude methanol filter 1, an activated carbon filter 2 or a granular carbon filter, a methanol precision filter 3, a crude methanol preheater 7, a methanol combined evaporator 4, an oxidation furnace 6, an absorption tower 1 # 8 and an absorption tower 2 # 9.

[0026] The crude methanol filter 1 is a glass fiber filter; it is used to receive crude methanol with a concentration of 70%-85%, a temperature of 5℃-45℃, and a pressure of 0.1MPa-0.3MPa, and to perform coarse filtration on it to initially filter out mechanical impurities; the outlet of the crude methanol filter 1 is connected to the inlet of the activated carbon filter 2 or the granular carbon filter.

[0027] Activated carbon filter 2 or granular carbon filter is used to purify crude methanol after removing mechanical impurities. Activated carbon or granular carbon adsorbs trace amounts of iron, nickel, and sulfur, as well as other impurities that are harmful to the catalyst added to oxidation furnace 6. The outlet of activated carbon filter 2 or granular carbon filter is connected to the inlet of methanol precision filter 3.

[0028] The methanol precision filter 3 uses high-precision filter paper with a filtration accuracy of 5 microns; it is used to finely filter the coarse methanol purified by the activated carbon filter 2 or granular carbon filter, and to filter mechanical impurities again; the outlet of the methanol precision filter 3 is connected to the coarse methanol inlet of the coarse methanol preheater 7.

[0029] The crude methanol preheater 7 is used to preheat the crude methanol, which has been filtered again for mechanical impurities, to a temperature of 80℃-85℃. The crude methanol preheater 7 is located between the oxidizer 6 and the No. 1 absorption tower 8. The crude methanol preheater 7 has a reaction gas inlet and a reaction gas outlet. The reaction gas inlet of the crude methanol preheater 7 is connected to the oxidizer 6, and the reaction gas outlet of the crude methanol preheater 7 is connected to the No. 1 absorption tower 8. The crude methanol preheater 7 also has a crude methanol inlet and a crude methanol outlet. The crude methanol inlet of the crude methanol preheater 7 is connected to the methanol precision filter 3, and the crude methanol outlet of the crude methanol preheater 7 is connected to the methanol combined evaporator 4.

[0030] After the reaction in oxidizer 6, the reaction gas enters the No. 1 absorption tower 8 via the crude methanol preheater 7. The crude methanol preheater 7 recovers the heat of reaction from the reaction gas, which exchanges heat with the crude methanol entering the preheater 7 (indirect heat exchange, the reaction gas and crude methanol do not come into contact), preheating the crude methanol to 80℃-85℃. The preheated crude methanol is then sent to the methanol combined evaporator 4. The lower part of oxidizer 6 has a hot water circulation section 62, which generates hot water.

[0031] Methanol combined evaporator 4 is used to evaporate, vaporize, and superheat preheated crude methanol.

[0032] A flame arrester 5 is installed between the top of the methanol combined evaporator 4 and the top of the oxidation furnace 6.

[0033] A hot water circulation tank 14 is installed between the bottom of the methanol combined evaporator 4 and the hot water circulation section 62 of the oxidizer 6. The hot water circulation tank 14 recovers the hot water generated in the oxidizer 6 and is pumped to the methanol combined evaporator 4 to evaporate the crude methanol. The hot water can circulate between the methanol combined evaporator 4 and the oxidizer 6. The hot water in the hot water circulation section 62 circulates between the hot water circulation tank 14, the methanol combined evaporator 4, and the hot water circulation section 62, with heat exchange between the indirect walls. The hot water does not come into contact with the high-temperature gas in the oxidizer 6 and the methanol combined evaporator 4.

[0034] An air Roots blower 17 is connected to one side of the bottom of the methanol combined evaporator 4, and the air Roots blower 17 is used to supply air to the methanol combined evaporator 4.

[0035] The top of the methanol combined evaporator 4 is connected to an oxygen furnace steam drum 11, which sends the steam after process water separation into the methanol combined evaporator 4 as feed steam. By adjusting the temperature of the methanol combined evaporator 4, the ratio of methanol, air, and steam introduced into the methanol combined evaporator 4 is adjusted to obtain a ternary mixture of methanol, air, and steam with a certain ratio.

[0036] After crude methanol enters methanol combined evaporator 4, the equilibrium concentration of methanol combined evaporator 4 is reduced to 45%-70%. After the equilibrium concentration stabilizes, the temperature of methanol combined evaporator 4 is adjusted to 50℃-62℃ to control the oxygen-methanol ratio in the three-way mixture at 0.42-0.65. Reduce the amount of feed steam added to methanol combined evaporator 4 to 2000kg / h-3000kg / h to maintain the molar fraction of water in the ternary gas mixture ≥30%, corresponding to an upper limit of methanol explosion oxygen-to-methanol ratio ≤0.77.

[0037] Oxidation furnace 6: The ternary mixed gas, after being proportioned and adjusted, enters the oxidation furnace through flame arrester 5. At 620℃-660℃, under the catalysis of an electrolytic silver catalyst, oxidation and dehydrogenation reactions occur, producing formaldehyde, water, and hydrogen, and releasing heat of reaction; wherein: Oxidation reaction: CH3OH + 1 / 2O2 → CH2O + H2O; Dehydrogenation reaction: CH3OH→CH2O+H2.

[0038] An oxidizer quench section 61 is installed above the hot water circulation section 62 of the oxidizer 6. The oxidizer quench section 61 is connected to the oxygen furnace steam drum 11, which receives process water. The bottom of the oxygen furnace steam drum 11 is connected to the oxidizer quench section 61. The reaction gases from the oxidation and dehydrogenation reactions in the oxidizer 6 descend in the oxidizer 6. First, the heat is sent to the oxygen furnace steam drum 11, where it is absorbed by the process water and generates low-pressure steam at 0.45 MPa. Part of this low-pressure steam is used as feed steam for the ternary gas mixture, and part is sent out.

[0039] Water separated from the oxygen furnace steam drum 11 enters the quench section 61 of the oxidizer, where it exchanges heat with the reaction gas that moves down into the quench section 61 through the partition wall, thus cooling the reaction gas.

[0040] The outlet of oxidizer 6 is connected to the inlet of absorber 8 via crude methanol preheater 7. The reaction gas in oxidizer 6 moves down to hot water circulation section 62 through the oxidizer quench section 61 and exchanges heat through the partition wall. The reaction gas continues to cool down. After being cooled down again by crude methanol preheater 7, the reaction gas enters absorber 8. Crude methanol preheater 7 recovers the reaction heat of the reaction gas and preheats the crude methanol.

[0041] The hot water circulation section 62, the hot water circulation tank 14 and the methanol combined evaporator 4 are replenished with water only once. After replenishment, the closed-loop heat exchange occurs between the hot water circulation section 62 and the methanol combined evaporator 4.

[0042] The reacting gases (including formaldehyde and hydrogen) sequentially enter absorption tower 8 (1#) and absorption tower 9 (2#). Absorption tower 8 (1#) is equipped with an evaporator cooler (13), and absorption tower 9 (2#) is equipped with an evaporator cooler (15). Formaldehyde sequentially passes through absorption tower 8 (1#) and absorption tower 9 (2#), comes into countercurrent contact with water, and is absorbed, forming a 37% formaldehyde product at the bottom of absorption tower 8 (1#). After cooling, it is collected as the product.

[0043] A preparation system for producing formaldehyde by replacing refined methanol with crude methanol further includes: a tail gas incinerator 10, a tail gas drum 12, and a water seal tank 16. The outlet of the No. 2 absorption tower 9 is connected to the water seal tank 16, and the outlet of the water seal tank 16 is connected to the inlet of the tail gas incinerator 10. The tail gas incinerator 10 is connected to the tail gas drum 12.

[0044] The hydrogen produced by the dehydrogenation reaction, after passing through the No. 1 receiving tower 8 and the No. 2 absorption tower 9, is not absorbed. It is released from static electricity by passing through the water seal tank 16 with the tail gas and then enters the tail gas incinerator 10 for combustion, releasing a large amount of heat. This heat enters the tail gas drum 12 and is absorbed by the process water added to the tail gas drum 12, generating low-pressure steam of 0.45 MPa which is then sent out. The water in the tail gas drum 12 enters the tail gas incinerator 10 for heating.

[0045] Example 2 A process for producing formaldehyde using crude methanol instead of refined methanol includes: S1. Crude methanol with a concentration of 70%-85%, a temperature of 5℃-45℃, and a pressure of 0.1MPa-0.3MPa enters the crude methanol filter 1 for coarse filtration, initially filtering out mechanical impurities; S2. The crude methanol, which has been initially filtered to remove mechanical impurities, is then purified by an activated carbon filter 2 or a granular carbon filter to adsorb trace amounts of iron, nickel, sulfur, and other impurities that are harmful to the catalyst. S3. After being purified by an activated carbon filter or granular carbon filter, crude methanol enters a methanol precision filter for further filtration to remove mechanical impurities. S4. After filtering out mechanical impurities again, the crude methanol enters the crude methanol preheater 7 to preheat the crude methanol temperature to 80℃-85℃. S5. After coarse filtration, activated carbon or granular carbon adsorption, and fine filtration, the crude methanol enters the methanol combined evaporator for evaporation, vaporization, and superheating. Adjust the ratio of methanol, air, and steam in the three-way mixture introduced into the methanol combined evaporator: after crude methanol enters the methanol combined evaporator, the equilibrium concentration of methanol in the combined evaporator is reduced to 45%-70%, and the oxygen-to-methanol ratio is controlled at 0.42-0.65; reduce the amount of feed steam added to maintain the molar fraction of water in the three-way mixture at ≥30%, corresponding to an oxygen-to-methanol ratio ≤0.77, which is the upper limit of methanol explosion. The outlet of the methanol combined evaporator 4 is connected to the inlet of the oxidation furnace 6; S6. The ternary mixed gas, after being proportioned and adjusted, enters the oxidation furnace and undergoes oxidation and dehydrogenation reactions at 620℃-660℃ to generate formaldehyde; Oxidation reaction: CH3OH + 1 / 2O2 → CH2O + H2O Dehydrogenation reaction: CH3OH → CH2O + H2; S7. The formaldehyde generated in the reaction enters the No. 1 and No. 2 absorption towers, where it is absorbed by water to generate 37% formaldehyde, which is then cooled and extracted as a product.

[0046] The above technical features constitute the preferred embodiment of the present invention, which has strong adaptability and optimal implementation effect. Non-essential technical features can be added or removed according to actual needs to meet the needs of different situations.

[0047] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A production system for producing formaldehyde from crude methanol instead of refined methanol, characterized by, The method comprises the following steps: A crude methanol filter is used to receive crude methanol and coarsely filter the crude methanol to preliminarily filter mechanical impurities; the outlet of the crude methanol filter is connected to the inlet of an activated carbon filter; The activated carbon filter or granular carbon filter is used to purify the crude methanol from which the mechanical impurities are removed and to adsorb harmful impurities to the catalyst added into the oxidation furnace; the outlet of the activated carbon filter or granular carbon filter is connected to the inlet of a methanol precision filter; The methanol precision filter is used to precisely filter the purified crude methanol and to filter the mechanical impurities again; the outlet of the methanol precision filter is connected to the inlet of a crude methanol preheater; The crude methanol preheater is used to preheat the crude methanol from which the mechanical impurities are filtered again; the outlet of the crude methanol preheater is connected to a methanol combined evaporator; The methanol combined evaporator is used to evaporate, vaporize and superheat the preheated crude methanol and to adjust the ratio of the obtained methanol, air and steam ternary mixture; the outlet of the methanol combined evaporator is connected to the inlet of an oxidation furnace; The oxidation furnace is used for the ternary mixture with the adjusted ratio to enter the oxidation furnace to generate formaldehyde through oxidation and dehydrogenation reaction at a certain temperature; the outlet of the oxidation furnace is connected to the inlet of a multi-stage absorption tower; The multi-stage absorption tower is used for the generated formaldehyde to enter the multi-stage absorption tower to be absorbed by water to generate 37% formaldehyde which is taken out as a product after being cooled.

2. A system for producing formaldehyde from crude methanol instead of refined methanol according to claim 1, characterized in that, The crude methanol filter adopts a glass fiber filter.

3. A system for producing formaldehyde from crude methanol instead of refined methanol according to claim 1, characterized in that, The methanol precision filter adopts a high-precision filter paper with a filtering precision of 5 microns.

4. The system for producing formaldehyde according to claim 1, wherein the system for producing formaldehyde is a system for producing formaldehyde from crude methanol instead of refined methanol. The multi-stage absorption tower comprises a 1# absorption tower and a 2# absorption tower connected in series.

5. A system for producing formaldehyde from crude methanol instead of refined methanol according to claim 4, characterized in that, The crude methanol preheater is arranged between the oxidation furnace and the 1# absorption tower.

6. A system for producing formaldehyde from crude methanol instead of refined methanol according to claim 5, characterized in that, The crude methanol preheater preheats the crude methanol to 80-85°C.

7. A system for producing formaldehyde from crude methanol instead of refined methanol according to claim 6, characterized in that, After the crude methanol enters the methanol combined evaporator, the equilibrium concentration of the methanol combined evaporator is reduced to 45-70% and the oxygen-methanol ratio is controlled to be 0.42-0.

65.

8. The system for producing formaldehyde according to claim 7, wherein the system for producing formaldehyde is a system for producing formaldehyde by using crude methanol instead of refined methanol. The molar fraction of water in the ternary mixture is kept to be greater than or equal to 30% and the upper limit of the oxygen-methanol ratio corresponding to the methanol explosion is less than or equal to 0.

77.

9. The system for producing formaldehyde according to claim 8, wherein the system for producing formaldehyde is a system for producing formaldehyde by using crude methanol instead of refined methanol. The ternary mixture enters the oxidation furnace to generate formaldehyde through oxidation and dehydrogenation reaction under the temperature condition of 620-660°C.

10. A process for the production of formaldehyde from crude methanol instead of refined methanol, characterized in that, The method comprises the following steps: S1. crude methanol with a concentration of 70-85%, a temperature of 5-45°C and a pressure of 0.1-0.3 MPa enters a crude methanol filter to be coarsely filtered to preliminarily filter mechanical impurities; S2. the crude methanol from which the mechanical impurities are preliminarily filtered is purified through an activated carbon filter or a granular carbon filter to adsorb harmful impurities to the catalyst added into the oxidation furnace; S3. the crude methanol purified through the activated carbon filter or the granular carbon filter enters a methanol precision filter to be precisely filtered; S4. the crude methanol from which the mechanical impurities are filtered again enters a crude methanol preheater to be preheated to 80-85°C; S5. the crude methanol filtered coarsely, adsorbed by activated carbon and precisely filtered enters a methanol combined evaporator to be evaporated, vaporized and superheated; The ratio of the methanol, air and steam ternary mixture entering the methanol combined evaporator is adjusted; S6. the ternary mixture with the adjusted ratio enters an oxidation furnace to generate formaldehyde through oxidation and dehydrogenation reaction under the temperature condition of 620-660°C. S7. The formaldehyde generated in the reaction is absorbed by water in the 1# absorption tower and the 2# absorption tower to generate 37% formaldehyde, which is taken out as a product after cooling.

Images