A method for producing high-concentration formaldehyde, along with steam and nitrogen, using the iron-molybdenum process.

Abstract

This invention belongs to the field of formaldehyde production and preparation processes, specifically a method for producing high-concentration formaldehyde and co-producing steam and nitrogen using the iron-molybdenum process. The method includes the following steps: (1) process gas preparation and preheating; (2) methanol vaporization; (3) methanol oxidation reaction; (4) formaldehyde absorption to prepare high-concentration formaldehyde; (5) tail gas catalytic combustion; and (6) pressure swing adsorption to produce nitrogen. This method recovers heat from the tail gas through efficient heat exchange to preheat the raw material gas and produce by-product steam. It achieves self-circulating operation of the heat transfer oil system without external work through the thermosiphon principle of heat transfer oil. It fully utilizes thermodynamic and kinetic principles to achieve low-energy operation of the iron-molybdenum formaldehyde reaction. Simultaneously, the tail gas is used to produce nitrogen through pressure swing adsorption, achieving low-energy nitrogen production. The circulating gas uses higher-purity nitrogen mixed with fresh air, which is more friendly to catalysts and equipment compared to the circulating gas in traditional processes. This invention's production method has low energy consumption, a compact layout, small footprint, and produces by-product steam and nitrogen.

Description

Technical Field

[0001] This invention belongs to the field of formaldehyde production and preparation technology, specifically a method for producing high-concentration formaldehyde and co-producing steam and nitrogen using the iron-molybdenum method. Background Technology

[0002] Formaldehyde is an important organic synthetic chemical raw material, mainly used in 1-4 butanediol, paraformaldehyde, urea-formaldehyde resin, phenolic resin, melamine-formaldehyde resin, hexamethylenetetramine products and polyols and other chemical products. According to statistics, in 2021, my country's formaldehyde production capacity reached 34.49 million tons and output reached 8.69 million tons, making my country the world's largest producer and consumer of formaldehyde.

[0003] Currently, over 90% of formaldehyde is produced through methanol oxidation, which primarily utilizes two processes: the "silver method" and the "iron-molybdenum method." Compared to the "iron-molybdenum method," the "silver method" suffers from higher reaction temperatures, higher methanol consumption, shorter catalyst lifespan, higher methanol content in the product (making further production of high-concentration formaldehyde impossible), lower byproduct steam pressure, higher reactor equipment requirements and shorter service life, and lower formaldehyde yield. Newly developed "iron-molybdenum method" processes are mainly used to support the production of high-concentration formaldehyde from upstream sources such as BDO and thermosetting resins. Current "iron-molybdenum method" technologies are primarily based on foreign technologies from Johnson Matthey (UK), D.B. Wester (USA), and Clariant (Switzerland). Domestically, mature technology for this process has not yet been developed, necessitating substantial investment in licensing foreign patents.

[0004] Patent CN216125190U discloses an apparatus for producing formaldehyde using the iron-molybdenum process. This apparatus mainly includes an evaporator, reactor, cooler, absorption tower, tail gas treatment unit, and steam generator. Its advantage lies in the efficient utilization of the heat source through formaldehyde steam heat exchange, tail gas heat exchange to generate steam, and steam supply to the trimethylolpropane production unit. Patent CN206051890U discloses an iron-molybdenum process formaldehyde production apparatus. This apparatus, through process improvement, achieves the substitution of imported catalysts with domestically produced ones, reducing catalyst usage costs and supply cycles.

[0005] Because the "iron-molybdenum process" operates within the explosive limits of air, the volume concentrations of methanol and oxygen in the feed gas must be strictly controlled to prevent deflagration that could harm production equipment and personnel. Appropriate oxygen and methanol concentrations also extend catalyst lifespan, reduce catalyst replacement frequency, minimize downtime, and increase formaldehyde production. During the reaction, exothermic gases must be removed promptly to prevent heat buildup, bed overheating, and catalyst deactivation. Furthermore, the system's exothermic gases should be maximized through heat exchange and byproduct steam generation to reduce the unit production cost of formaldehyde.

[0006] Currently, domestic patents still need further improvement in areas such as safety and environmental monitoring, heat recovery and control, and monitoring of the operating status of the iron-molybdenum catalyst in the entire reaction device. If CO in the circulating tail gas is not completely removed and is directly returned to the device, it will accelerate the reduction of the oxidized catalyst and cause deactivation. If CO2 in the circulating tail gas is not removed and is directly returned to the device, it will react with methanol to produce dimethyl ether. At the same time, CO2 will also cause serious corrosion to pipelines and equipment. If high-nitrogen tail gas resources are not utilized and are directly emitted, it will result in resource waste. Therefore, it is imperative to develop a highly efficient, energy-saving and safe "iron-molybdenum process" production method. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a method for producing high-concentration formaldehyde and co-producing steam and nitrogen using the iron-molybdenum process, thereby solving problems such as low heat utilization efficiency, rapid catalyst deactivation, and low formaldehyde yield in actual production.

[0008] The above-mentioned objective of this invention is achieved through the following technical solution:

[0009] A method for producing high-concentration formaldehyde and co-producing steam and nitrogen using the iron-molybdenum process includes the following steps:

[0010] (1) Process gas preparation and preheating: Fresh air is mixed with circulating air in proportion after impurity removal and then enters the gas mixer to become process gas. The process gas is then preheated and enters the methanol vaporization furnace tube layer.

[0011] More specifically, the process involves fresh air entering the gas mechanical cleaner via a fresh air frequency converter and booster fan, then mixing it with circulating air via a circulating air frequency converter and booster fan in a certain proportion before entering the gas mixer. The gas then enters the gas preheating furnace tube layer for preheating to 120-160°C before entering the methanol vaporization furnace tube layer. The process gas needs to meet the requirement that the oxygen concentration is between 10% and 12%.

[0012] (2) Methanol vaporization: Methanol is fed into the tube layer of the methanol vaporization furnace through a metering pump and mixed with the process gas. Then, after heat exchange with the product gas, the raw material gas is obtained.

[0013] As a preferred method, heat is exchanged to 180-210℃ to obtain the raw material gas.

[0014] (3) Methanol oxidation reaction: The raw gas from the methanol gasifier tube layer enters the methanol oxidation reactor tube layer and undergoes an incomplete oxidation reaction to generate formaldehyde under the action of the catalyst. The formaldehyde product gas enters the methanol gasifier shell layer and the gas preheating furnace shell layer through the outlet for heat exchange. The heat transfer oil removes the heat released by the reaction through vaporization in the methanol oxidation reactor shell layer. The methanol volume concentration at the inlet of the methanol oxidation reactor is 8-10%, and the oxygen volume concentration at the inlet of the methanol oxidation reactor is 9-11%.

[0015] More preferably, the temperature after heat exchange is 150-160℃. The heat transfer oil removes the heat released by the reaction through vaporization in the shell of the methanol oxidation reactor. At the end of the methanol oxidation reaction, due to the loss of catalyst activity, the vaporization temperature can be increased by increasing the pressure of the heat transfer oil system, thereby increasing the bed wall temperature and achieving complete conversion of methanol at the end.

[0016] (4) Formaldehyde absorption to prepare high-concentration formaldehyde: The formaldehyde product gas from the preheated furnace shell is introduced into the formaldehyde primary spray absorption tower through the bottom inlet of the primary absorption tower for two-stage spray absorption. It is discharged from the top gas outlet of the primary absorption tower to the bottom of the secondary absorption tower and then into the secondary multi-stage spray absorption tower. It is discharged from the top of the secondary absorption tower. When the formaldehyde concentration in the absorption tower reaches the required value, the product is discharged from the formaldehyde outlet after heat exchange through the plate heat exchanger.

[0017] (5) Catalytic combustion of tail gas: The tail gas from the secondary spray absorption tower enters the tube layer of the catalyst combustion reactor and reacts with the catalyst. The gas after combustion enters the tube layer of the tail gas steam generator and exchanges heat with the process water to produce steam. Then it enters the shell layer of the catalyst combustion reactor. The steam generated after heat exchange is supplied to the outside. The tail gas after cooling is used as a raw material for nitrogen production and enters the pressure swing adsorption nitrogen production step.

[0018] (6) Pressure swing adsorption nitrogen production: The tail gas from the tail gas catalytic combustion step enters temperature swing adsorption dehydration tower 1 and temperature swing adsorption dehydration tower 2 through the gas regulating valve. After dehydration, it enters pressure swing adsorption nitrogen production tower 1 and pressure swing adsorption nitrogen production tower 2 through the gas regulating valve and gas compressor, respectively. The adsorption and desorption pressure is adjusted by the gas back pressure valve. Then, part of it enters the nitrogen system through the gas regulating valve, and the other part is mixed with fresh gas through the gas regulating valve and returned to the oxidation reaction unit.

[0019] The temperature swing adsorption dehydration tower and the pressure swing adsorption nitrogen generator in this unit both adopt a one-on-one standby mode.

[0020] Preferably, the composition of the exhaust gas from the catalytic combustion of exhaust gas in step (6) is: 1~4% CO2, total organic matter less than 10ppm, CO content less than 0.1%, and the remainder is nitrogen.

[0021] A system for producing high-concentration formaldehyde, along with steam and nitrogen, using the iron-molybdenum process described above. The system includes a methanol oxidation reaction unit, a formaldehyde absorption unit, a heat transfer oil unit, a steam production unit, a tail gas treatment unit, and a pressure swing adsorption (PSA) nitrogen generation unit. The steam production unit is connected to the heat transfer oil unit; the heat transfer oil unit is connected to the methanol oxidation reaction unit; the methanol oxidation reaction unit is connected to the formaldehyde absorption unit; the formaldehyde absorption unit is connected to the tail gas treatment unit, but a steam production unit is added between the formaldehyde absorption unit and the tail gas treatment unit; the tail gas treatment unit is connected to the PSA nitrogen generation unit; and the PSA nitrogen generation unit is connected to the methanol oxidation reaction unit.

[0022] As a preferred embodiment of this application, the methanol oxidation reaction unit mainly includes a shell-and-tube methanol oxidation reactor, a methanol gasification furnace, a methanol one-way check valve, a methanol liquid feed shut-off valve, a methanol feed electronic metering pump, an explosion-proof oxidation variable frequency booster fan, a gas preheating furnace, a gas regulating valve eight, a gas regulating valve nine, a circulating nitrogen variable frequency booster fan, a circulating gas one-way valve one, a circulating gas one-way valve two, a nitrogen solenoid valve, a nitrogen regulating valve, a circulating nitrogen mass flow meter, a gas mixer, a fresh air gas mass flow meter, a fresh air variable frequency booster fan, a gas one-way valve, and a gas mechanical impurity remover two; wherein, methanol in the methanol conveying device sequentially enters the tube layer of the methanol gasification furnace through the methanol feed electronic metering pump, the methanol liquid feed shut-off valve, and the methanol one-way check valve; the methanol oxidation reactor and the methanol gasification furnace are connected; the top of the methanol gasification furnace is connected to the explosion-proof oxidation variable frequency booster fan through a pipeline; the gas preheating furnace is connected to the upper part of the methanol gasification furnace through a pipeline, and the gas... The preheating furnace is connected to the gas mixer; nitrogen from the plant system enters the circulating nitrogen variable frequency booster fan through gas regulating valve 8 and gas regulating valve 9. The nitrogen from the circulating nitrogen variable frequency booster fan is split into two: one path is connected to the gas mixer through circulating gas check valve 2 and circulating nitrogen mass flow meter; the other path is connected to the gas mixer through circulating gas check valve 1 and nitrogen regulating valve; some nitrogen from the system is connected to the pipeline between circulating gas check valve 1 and nitrogen regulating valve through nitrogen solenoid valve; fresh air is connected to the gas mixer through pipelines sequentially through gas mechanical impurity remover 2, gas check valve, fresh air variable frequency booster fan and fresh air gas mass flow meter; reaction overpressure interlock alarm system and reaction overtemperature interlock alarm system are installed at the inlet, outlet and inside the reactor tube layer of the methanol oxidation reactor; oxygen concentration monitoring safety interlock alarm system and methanol concentration monitoring safety interlock alarm system are installed on the pipeline connecting the methanol oxidation reactor and methanol gasification furnace.

[0023] In a preferred embodiment of this application, the formaldehyde absorption unit mainly includes a primary spray absorption tower, a liquid circulation pump 1, a plate heat exchanger 1, a liquid circulation pump 2, a plate heat exchanger 2, a formaldehyde level regulating valve 1, a secondary spray absorption tower, a liquid circulation pump 3, a plate heat exchanger 3, a plate heat exchanger 4, a liquid circulation pump 4, a regulating valve, a formaldehyde level regulating valve 2, a liquid circulation pump 5, a water-cooled plate heat exchanger, and a formaldehyde product outlet. Formaldehyde product gas from the gas preheating furnace shell enters the primary spray absorption tower through the inlet at the bottom of the primary spray absorption tower; after exiting through the gas outlet at the top of the primary spray absorption tower, it enters the secondary spray absorption tower from the bottom. At the top of the primary spray absorption tower, circulating water enters the primary spray absorption tower through the plate heat exchanger 2, and the primary spray absorption tower then... The second circulating pump is connected to the second plate heat exchanger. At the bottom of the first-stage spray absorption tower, circulating water enters the first-stage spray absorption tower through the first plate heat exchanger, which is then connected to the first plate heat exchanger through the first liquid circulating pump. At the top of the second-stage spray absorption tower, circulating water is connected to the second-stage spray absorption tower through the third liquid circulating pump and the third plate heat exchanger. At the bottom of the second-stage spray absorption tower, circulating water is connected to the fourth liquid circulating pump, the regulating valve, and the fourth plate heat exchanger. A formaldehyde level regulating valve is installed on the pipe between the fourth liquid circulating pump and the regulating valve. A formaldehyde level regulating valve is installed at the bottom of the first-stage spray absorption tower. A liquid circulating pump is installed on the pipe between the first and second formaldehyde level regulating valves, and is connected to the water-cooled plate heat exchanger. The water-cooled plate heat exchanger is connected to the formaldehyde product outlet.

[0024] The second steam production unit mainly includes a steam generator, a second steam regulating valve, a second steam compression pump, a second steam pressure storage tank, and a second steam back pressure valve. The water-cooled plate heat exchanger of the formaldehyde absorption unit is connected to the steam generator. The steam generator is connected to the second steam pressure storage tank via the second steam regulating valve and the second steam compression pump. The second steam pressure storage tank outputs steam through the steam back pressure valve, and the generated steam pressure is 2-2.4 MPa.

[0025] In a preferred embodiment of this application, the heat transfer oil unit mainly includes a cooling-state heat transfer oil storage tank, a high-temperature explosion-proof heat transfer oil pump, a first automatic heat transfer oil regulating valve, a second automatic heat transfer oil regulating valve, a third automatic heat transfer oil regulating valve, an oil-water heat exchanger, a heat transfer oil electric heater, a gas-liquid separator, and a pressure safety regulating valve; wherein, process water enters the gas-liquid separator through a delivery pipeline and the oil-water heat exchanger; the oil-water heat exchanger is connected to the bottom of the gas-liquid separator through the third automatic heat transfer oil regulating valve; The oil-water heat exchanger is connected to the cold-state heat transfer oil storage tank; the bottom of the cold-state heat transfer oil storage tank is connected to the gas-liquid separator via a high-temperature explosion-proof heat transfer oil pump, a second automatic heat transfer oil regulating valve, and a heat transfer oil electric heater; a pressure safety regulating valve is installed at the top of the gas-liquid separator; the top of the cold-state heat transfer oil storage tank is connected to the high-temperature explosion-proof heat transfer oil pump and the second automatic heat transfer oil regulating valve via a pipeline; the gas-liquid separator is connected to the shell of the methanol oxidation reactor in the methanol oxidation reaction unit; the steam production unit mainly includes a steam regulating valve, a steam compression pump, a steam pressure storage tank, and a steam back pressure valve; the gas-liquid separator of the heat transfer oil unit is connected to the steam pressure storage tank via the steam regulating valve and the steam compression pump, and the steam generated by the heat exchange of the gas-liquid separator is stored in the steam pressure storage tank; the steam pressure storage tank delivers steam to the outside via the steam back pressure valve, and the steam pressure obtained is 2.0-2.4 MPa.

[0026] In a preferred embodiment of this application, the exhaust gas treatment unit mainly includes a catalytic combustion reactor, a three-way automatic switching valve, and an aerial flare tower; wherein, the steam generator of the steam production unit is connected to the middle shell of the catalytic combustion reactor; the catalytic combustion reactor is connected to the aerial flare tower through the three-way automatic switching valve.

[0027] In a preferred embodiment of this application, the pressure swing adsorption (PSA) nitrogen generation unit mainly includes a circulating gas frequency converter booster fan, gas regulating valve one, gas regulating valve two, temperature swing adsorption dehydration tower No. 1, gas regulating valve three, gas regulating valve four, temperature swing adsorption dehydration tower No. 2, gas regulating valve five, gas compressor one, gas regulating valve six, PSA nitrogen generation tower No. 1, gas back pressure valve one, gas regulating valve seven, gas compressor two, PSA nitrogen generation tower No. 2, gas back pressure valve two, and gas mechanical separator one; wherein, the catalytic combustion reactor of the tail gas treatment unit is connected to the tail gas frequency converter booster fan through a three-way automatic switching valve; the outlet pipe of the tail gas frequency converter booster fan is divided into two parts, one part is connected to the temperature swing adsorption dehydration tower No. 1 through gas regulating valve two, and the other part is connected to the temperature swing adsorption dehydration tower No. 1 through gas regulating valve one. The bottom of water tower No. 2 is connected; a gas regulating valve four is installed between the top of temperature swing adsorption dehydration tower No. 1 and temperature swing adsorption dehydration tower No. 2; the outlet pipe of temperature swing adsorption dehydration tower No. 2 is split into two parts, one part is connected to pressure swing adsorption nitrogen generation tower No. 1 through gas regulating valve five and gas compressor one, and pressure swing adsorption nitrogen generation tower No. 1 is connected to gas compressor two through gas regulating valve seven, and the other part is connected to pressure swing adsorption nitrogen generation tower No. 2 through gas regulating valve six and gas compressor two; pressure swing adsorption nitrogen generation tower No. 1 and pressure swing adsorption nitrogen generation tower No. 2 are connected to gas mechanical impurity remover one through gas back pressure valve one and gas back pressure valve two respectively, and the outlet pipe of gas mechanical impurity remover one is split into two parts, which are connected to the methanol oxidation reaction unit and the plant system nitrogen device respectively; the nitrogen produced by the pressure swing adsorption nitrogen generation unit has a purity >99.9%.

[0028] In a preferred embodiment of this application, the methanol oxidation reactor includes a reactor inlet, an inlet temperature interlock monitoring point, an inlet pressure interlock monitoring point, a heat transfer oil outlet, a heat transfer oil inlet, an outlet temperature interlock monitoring point, an outlet pressure interlock monitoring point, and a reactor outlet; wherein, the reactor inlet, the inlet temperature interlock monitoring point, and the inlet pressure interlock monitoring point are located at the top of the methanol oxidation reactor; the outlet temperature interlock monitoring point, the outlet pressure interlock monitoring point, and the reactor outlet are located at the bottom of the methanol oxidation reactor; and the heat transfer oil outlet and the heat transfer oil inlet are respectively located at the upper and lower parts of the side of the methanol oxidation reactor.

[0029] As a preferred embodiment of this application, a steam pressure interlock alarm system and a steam temperature interlock alarm system are installed at one inlet of the steam pressure storage tank to perform real-time online interlock monitoring and alarm of steam pressure and temperature.

[0030] As a preferred embodiment of this application, a steam pressure interlock alarm system and a steam temperature interlock alarm system are installed at the second inlet of the steam pressure storage tank to perform real-time online interlock monitoring and alarm of steam pressure and temperature.

[0031] Furthermore, in this application, the methanol oxidation reactor adopts a shell-and-tube structure, with the tube layers filled with domestically produced iron-molybdenum catalyst and high-efficiency thermally conductive ceramic rings; the shell layer is an oil layer, primarily using the temperature of the heat transfer oil itself to heat the system and the heat transfer through vaporization of the heat transfer oil to achieve stable operation of the methanol oxidation reactor; the tube layers of the methanol oxidation reactor are connected to the tube layers of the methanol gasification furnace; a single methanol oxidation reactor contains 10,000-30,000 reaction tubes, and the total number of reaction tubes in the methanol oxidation reactor is selected to be 0.05- based on the number of reaction tubes in the shell-and-tube configuration. The 0.1% reaction tube serves as a temperature monitoring tube for the reaction hotspot. It is equipped with a 6-10 thermocouple with a diameter of 3mm running through the reactor. The catalyst performance and replacement time are determined based on the change in the hotspot location. The dimensions of the reaction tube are (18-28)mm inner diameter × (22-32)mm outer diameter × (1400-2000)mm length. The catalyst loading height is 1000~1400mm (of which the dilution layer loading height is 400~800mm and the pure phase layer loading height is 400~1000mm). There are remote temperature and pressure monitoring points at both the inlet and outlet of the oxidation reactor. The main pipeline of the reactor is connected to the nitrogen system. When the temperature and pressure exceed the upper and lower limits, an interlocking alarm is triggered, which shuts off the methanol feed and opens the nitrogen regulating valve and nitrogen solenoid valve. The top of the methanol oxidation reactor tube layer is connected to the bottom of the methanol gasification furnace tube layer, the bottom of the methanol oxidation reactor tube layer is connected to the methanol gasification furnace shell layer, and the methanol oxidation reactor shell layer is connected to the upper tube layer of the gas-liquid separator.

[0032] Furthermore, in this application, the gas preheating furnace is mainly used for preheating process gas. The preheating furnace mainly exchanges heat with product gas from the methanol vaporization furnace through tubes, and the heat exchange tubes are equipped with high-temperature resistant thermally conductive ceramic rings.

[0033] Furthermore, in this application, the methanol gasification furnace is preferably a tube-and-tube heat exchanger, which exchanges heat between the inlet raw material gas and the outlet product gas. The heat exchange tubes are filled with high-temperature resistant and thermally conductive ceramic rings, thereby achieving efficient utilization of heat and thorough mixing of materials.

[0034] Furthermore, in this application, the methanol (liquid) feed shut-off valve is mainly used to shut off the methanol feed in case of abnormal conditions in the oxidation reactor.

[0035] Furthermore, in this application, the gas preheater is mainly used for heat exchange between the inlet process gas and the outlet raw material gas, reducing the outlet gas temperature to 150~160℃ to prevent the absorption tower from entering at too high an outlet temperature and reducing the absorption efficiency.

[0036] Furthermore, in this application, the oxygen concentration monitoring safety interlock alarm system mainly ensures that the volume concentration of the feed oxygen is maintained between 9% and 11%. If it is higher than the upper limit or lower than the lower limit, an interlock will be triggered to prevent the reaction system from entering the explosion limit.

[0037] Furthermore, in this application, the methanol concentration monitoring safety concentration interlocking alarm system mainly ensures that the methanol volume concentration in the raw gas is maintained between 8% and 10%. If it is higher than the upper limit or lower than the lower limit, an interlocking mechanism will be triggered to prevent the reaction system from entering the explosion limit.

[0038] Furthermore, in this application, the inlet feed gas temperature of the methanol oxidation reactor is limited to 180-210°C, the pressure is limited to 40-200 kPa, the catalyst bed hot spot temperature is 300-480°C, and the gas hourly space velocity is 6000-12000 h⁻¹. -1 The liquid hourly space velocity (LHSV) of methanol is 1-1.5 h⁻¹. -1 .

[0039] Furthermore, in the formaldehyde absorption unit of this application, the primary and secondary spray absorption towers mainly absorb formaldehyde through formaldehyde solution spraying and rinsing. During the absorption process, alkaline solution can be added to prevent formaldehyde polymerization and blockage of the tower body and pipelines. The primary spray absorption tower is internally filled with two sections of Raschig annular granular ceramic ring packing to increase the gas-liquid contact surface, while the secondary spray absorption tower is internally filled with integral honeycomb ceramic ring packing.

[0040] Furthermore, in the heat transfer oil unit described in this application, the cold heat transfer oil storage tank is used for storing cold heat transfer oil. A pressure relief safety valve is installed on the top, and the level gauge on the side provides feedback on the amount of heat transfer oil in the storage tank. The heat transfer oil used is a biphenyl-diether mixture. In the initial stage of the reaction, the heat transfer oil is transported to the reactor by a high-temperature explosion-proof hot oil pump to provide heat for the oxidation reaction. As the reaction proceeds, the heat transfer oil vaporizes and transfers heat. Then, it is condensed into steam through a gas-liquid separator. The heat transfer oil pump and regulating valve are then turned off to realize the thermosiphon self-circulation of the heat transfer oil during the reaction process.

[0041] Furthermore, in the heat transfer oil unit described in this application, the gas-liquid separator mainly condenses the gaseous heat transfer oil coming out of the methanol oxidation reactor, and then returns it to the heat transfer oil storage tank by its own gravity or establishes a siphon level, thereby maintaining the operation of the system's heat transfer oil by establishing a certain liquid level.

[0042] Furthermore, in the heat transfer oil unit described in this application, the heat transfer oil level interlocking alarm system mainly determines the upper and lower limits of the liquid level through a remote level gauge. If the liquid level is higher than the upper limit or lower than the lower limit, an interlocking alarm is triggered.

[0043] Furthermore, in the heat transfer oil unit described in this application, the heat transfer oil level regulation system mainly determines the liquid level by the liquid level of the heat transfer oil storage tank and the gas-liquid separator, and then automatically adjusts the amount of oil in the reflux storage tank and the reactor by the reflux electric regulating valve.

[0044] Furthermore, in the heat transfer oil unit described in this application, the heat transfer oil pressure interlock alarm system mainly uses a pressure sensor to set upper and lower pressure limits. When the pressure of the heat transfer oil system exceeds the upper and lower limits, an interlock will be triggered. The pressure is regulated by a pressure safety valve, and the boiling point of the heat transfer oil is controlled by controlling the pressure of the heat transfer oil.

[0045] Furthermore, in the heat transfer oil unit described in this application, the heat transfer oil temperature interlock alarm system mainly triggers an interlock alarm when the upper and lower limits of the heat transfer oil are set by the temperature sensor, and adjusts the temperature by adjusting the return pump and the amount of condensate return water.

[0046] Furthermore, in the steam production unit described in this application, the steam generator is mainly used for heat exchange between exhaust gas and circulating water to generate steam. The steam pressure interlock alarm system is mainly used for monitoring the upper and lower limits of steam pressure, triggering an interlock alarm when the temperature or pressure exceeds the upper or lower limit. The pressure of the by-product steam can reach 2.4 MPa.

[0047] In a preferred embodiment of this application, the upper part of the catalytic combustion reactor is a tubular heat exchanger, and the lower part is an adiabatic electrically heated fixed-bed reactor. The upper tubular section is filled with a spherical molecular sieve-supported Pt-Pd dual noble metal catalyst, and the lower section is filled with an integral honeycomb-coated cordierite-supported Pt-Pd dual noble metal catalyst. The inlet exhaust gas temperature of the catalytic combustion reactor is 90-120℃, the reaction pressure is 20-200 kPa, the bed hot spot temperature is 500-600℃, and the gas hourly space velocity is 30000-60000 h⁻¹. -1 .

[0048] In a preferred embodiment of this application, the bottom layer of the methanol reactor tube is a pure phase ceramic ring layer (preferably 50-200 mm), a pure phase catalyst layer (preferably 500-600 mm) is laid above the pure phase ceramic ring layer, and then a dilution layer (preferably composed of 40% inert ceramic rings and 60% catalyst, with a laying height of 400-600 mm), an inert ceramic ring layer (preferably 200-300 mm), and an empty layer (preferably 240 mm) are successively filled on top.

[0049] In a preferred embodiment of this application, the temperature swing adsorption dehydration tower in the pressure swing adsorption nitrogen generation unit adopts a fixed-bed adsorption-desorption mode with two towers, one in operation and one on standby. The dehydration tower is filled with a high-efficiency adsorption-desorption molecular sieve dehydrating agent. The pressure swing adsorption nitrogen generation tower also adopts a fixed-bed adsorption-desorption mode with two towers, one in operation and one on standby. The adsorption tower is filled with a molecular sieve material that is highly efficient at adsorbing acidic gases such as CO2. The nitrogen gas produced can reach a pressure of over 2 MPa, and the CO2 concentration and CO concentration in the nitrogen gas are both below 0.01%.

[0050] Compared with the prior art, the present invention has the following advantages:

[0051] (i) Based on the existing production process, an automatic adjustment alarm for important parameters such as temperature and pressure has been added, interlocked with the methanol shut-off valve and nitrogen safety valve, ensuring the safe operation of the system. Furthermore, by controlling the optimal reaction temperature, reaction pressure, methanol and oxygen concentrations, the service life of the catalyst can be extended, reducing the frequency of catalyst replacement and operating costs for the company.

[0052] (ii) A multi-thermocouple is installed in the oxidation reaction tube to monitor the hot spots of the catalyst. The activity of the catalyst is judged based on the changes in the position of the hot spots, so as to adjust the pressure of the heat transfer oil to increase the wall temperature of the reaction tube and improve the methanol conversion rate and formaldehyde yield.

[0053] (iii) This invention maximizes the efficient utilization of the heat source through a multi-stage high-efficiency packed heat exchanger.

[0054] (iv) The absorption device was changed to use multi-layer packing for absorption, which improved the absorption efficiency and reduced the formaldehyde escape rate without increasing the resistance.

[0055] (V) The nitrogen content in the tail gas of the device of this invention is as high as 95% or more, with the remainder mainly being CO2. The energy consumption for nitrogen production is much lower than that for air separation nitrogen production, thus saving nitrogen energy consumption in the plant area. At the same time, the high-purity nitrogen can be mixed with air to prepare the process feed gas for methanol oxidation reaction. The removal of CO in the tail gas by the catalytic combustion device reduces the reducing effect of CO on the catalyst. Compared with the circulating gas of the traditional process, the circulating gas of this invention is more catalyst-friendly, and the catalyst has a longer service life. The removal of CO2 reduces the formation of dimethyl ether. At the same time, CO2 also causes serious corrosion to pipelines and equipment. The removal of CO2 reduces the corrosion of pipelines and equipment by the circulating gas, extending their service life. Attached Figure Description

[0056] Figure 1 This is a flowchart of the method for producing high-concentration formaldehyde and co-producing steam and nitrogen using the iron-molybdenum process described in this invention.

[0057] Among them, 1-cold thermal oil storage tank, 2-high temperature explosion-proof thermal oil pump, 3-thermal oil automatic regulating valve one, 4-thermal oil automatic regulating valve two, 5-thermal oil automatic regulating valve three, 6-oil-water heat exchanger, 7-thermal oil heater, 8-gas-liquid separator, 9-steam regulating valve one, 10-steam compression pump one, 11-steam pressure storage tank one, 12-steam back pressure valve one, 13-pressure regulating safety valve, 14-methanol oxidation reactor, 15-methanol gasification furnace, 16-methanol one-way check valve, 17-methanol liquid feed shut-off valve, 18-methanol feed electronic metering pump, 19-explosion-proof oxygen... 20-Variable frequency booster fan, 21-Gas preheating furnace, 22-First-stage spray absorption tower, 23-Liquid circulation pump one, 24-Plate heat exchanger one, 25-Plate heat exchanger two, 26-Formaldehyde level regulating valve one, 27-Second-stage spray absorption tower, 28-Liquid circulation pump three, 29-Plate heat exchanger three, 30-Plate heat exchanger four, 31-Liquid circulation pump four, 32-Regulating valve, 33-Formaldehyde level regulating valve two, 34-Liquid circulation pump five, 35-Plate heat exchanger five, 36-Formaldehyde product outlet, 37-Steam generator, 38-Steam regulating valve two 39-Steam compression pump II, 40-Steam pressure storage tank II, 41-Steam back pressure valve II, 42-Catalyst combustion reactor, 43-Three-way switching valve, 44-High-altitude flare tower, 45-Circulating gas variable frequency booster fan, 46-Gas regulating valve I, 47-Gas regulating valve II, 48-Temperature swing adsorption dehydration tower No. 1, 49-Gas regulating valve III, 50-Gas regulating valve IV, 51-Temperature swing adsorption dehydration tower No. 2, 52-Gas regulating valve V, 53-Gas compressor I, 54-Gas regulating valve VI, 55-Pressure swing adsorption nitrogen production tower No. 1, 56-Gas back pressure valve I, 57-Gas Regulating valve 7, 58-Gas compressor 2, 59-Pressure swing adsorption nitrogen generator tower 1, 60-Gas back pressure valve 2, 61-Gas mechanical impurity remover 1, 62-Gas regulating valve 8, 63-Gas regulating valve 9, 64-Circulating nitrogen variable frequency booster fan, 65-Circulating gas check valve 1, 66-Circulating gas check valve 2, 67-Nitrogen solenoid valve, 68-Nitrogen regulating valve, 69-Circulating nitrogen mass flow meter, 70-Gas mixer, 71-Fresh air gas mass flow meter, 72-Fresh air variable frequency booster fan, 73-Fresh air gas check valve, 74-Gas mechanical impurity remover 2.

[0058] Pipeline color coding: 1. Red indicates formaldehyde-containing gas and liquid phases. 2. Brown indicates heat transfer oil lines. 3. Blue indicates steam, process water, and circulating water lines. 4. Green indicates methanol lines. 5. Cyan indicates gas lines.

[0059] Figure 2 This is a schematic diagram of the methanol oxidation reactor described in Example 1;

[0060] Figure 3This is a schematic diagram of the methanol oxidation reactor described in Example 4;

[0061] Figure 2 and Figure 3 In the diagram, 1: reactor inlet, 2: inlet temperature interlock monitoring point, 3: inlet pressure interlock monitoring point, 4: heat transfer oil outlet, 5: heat transfer oil inlet, 6: outlet temperature interlock monitoring point, 7: outlet pressure interlock monitoring point, 8: reactor outlet.

[0062] Figure 4 This is a schematic diagram of the methanol tube distribution and filling in Example 2;

[0063] Figure 5 This is a schematic diagram of the methanol tube distribution and filling in Example 3;

[0064] Figure 6 This is a schematic diagram of the methanol tube distribution and filling in Example 4;

[0065] Figure 7 This is a schematic diagram of the methanol tube distribution and filling in Example 5;

[0066] Figure 8 This is a schematic diagram of the methanol tube distribution and filling in Example 6;

[0067] Figure 9 This is a schematic diagram of the methanol tube distribution and filling in Comparative Example 1;

[0068] Figure 10 This is a schematic diagram of the methanol tube distribution and filling in Comparative Example 2.

[0069] Figures 4-10 In the diagram, 1 represents the diameter and center-to-center distance of the reaction tube, 2 represents the single-tube loading diagram, and 3 represents the distribution of multiple thermocouple temperature measurement points (7-10 hot spot temperature monitoring points).

[0070] Figure 11 A flowchart of the existing iron-molybdenum process for producing high-concentration formaldehyde and co-generating steam.

[0071] The components are as follows: 1-Heat transfer oil storage tank; 2-High temperature explosion-proof heat transfer oil pump; 3-Heat transfer oil automatic regulating valve one; 4-Heat transfer oil automatic regulating valve two; 5-Heat transfer oil automatic regulating valve three; 6-Oil-water heat exchanger; 7-Heat transfer oil heater; 8-Gas-liquid separator; 9-Steam regulating valve one; 10-Steam compression pump one; 11-Steam pressure storage tank one; 12-Steam back pressure valve one; 13-Pressure regulating safety valve; 14-Methanol oxidation reactor; 15-Methanol gasification furnace; 16-Methanol one-way check valve; 17-Methanol liquid feed shut-off valve; 18-Methanol feed electronic metering pump; 19-Explosion-proof oxidation variable frequency booster fan; 20-Gas preheating furnace; 21-Gas mechanical impurity remover; 22-Fresh air one-way valve; 23-Fresh air variable frequency booster fan; 24-Fresh air mass flow meter; 25-Gas mixer; 26-Nitrogen mass flow meter; 27-Gas regulating valve. 28 - Circulating gas check valve 1; 29 - Circulating gas check valve 2; 30 - Nitrogen solenoid valve; 31 - Plate heat exchanger 1; 32 - Liquid circulating pump 1; 33 - Plate heat exchanger 2; 34 - Liquid circulating pump 2; 35 - Primary spray absorption tower; 36 - Formaldehyde level regulating valve 1; 37 - Liquid circulating pump 3; 38 - Formaldehyde level regulating valve 2; 39 - Plate heat exchanger 3; 40 - Liquid circulating pump 3; 41 - Plate heat exchanger IV. 42-Liquid Circulation Pump IV. 43-Secondary Spray Absorption Tower. 44-Liquid Circulation Pump V. 45-Plate Heat Exchanger V. 46-Formaldehyde Product Inlet / Outlet. 47-Steam Generator. 48-Steam Regulating Valve II. 49-Steam Compression Pump II. 50-Steam Pressure Storage Tank II. 51-Steam Back Pressure Valve II. 52-Catalyst Combustion Reactor. 53-Three-Way Switching Valve. 54-High-Altitude Flare Tower. 55-Circulating Gas Variable Frequency Booster Fan. Detailed Implementation

[0072] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0073] Example 1

[0074] This example is a 175,000-ton / year formaldehyde production unit (based on 37% wt formaldehyde) upstream of a BDO plant. The designed inlet process gas flow rate of this unit is 56,000 Nm³. 3 The methanol oxidation reactor has an inlet methanol concentration of 10% and an inlet oxygen concentration of 10%, and is loaded with CNFM-01 and CNFM-02 catalysts (CNFM-01 and CNFM-02 catalysts are existing technologies and commercially available products). The designed gas hourly space velocity is 8000 h⁻¹. -1 The inlet exhaust gas temperature of the catalytic combustion reactor is 120℃, the reaction pressure is 50 kPa, the bed hot spot temperature is 550℃, and the gas hourly space velocity is 30,000 h⁻¹.-1 .

[0075] like Figure 1 As shown, a system for producing high-concentration formaldehyde, along with steam and nitrogen, using the iron-molybdenum process described above includes a methanol oxidation reaction unit, a formaldehyde absorption unit, a heat transfer oil unit, a steam production unit, a tail gas treatment unit, and a pressure swing adsorption (PSA) nitrogen generation unit. The steam production unit is connected to the heat transfer oil unit; the heat transfer oil unit is connected to the methanol oxidation reaction unit; the methanol oxidation reaction unit is connected to the formaldehyde absorption unit; the formaldehyde absorption unit is connected to the tail gas treatment unit, but a steam production unit is added between the formaldehyde absorption unit and the tail gas treatment unit; the tail gas treatment unit is connected to the PSA nitrogen generation unit; and the PSA nitrogen generation unit is connected to the methanol oxidation reaction unit.

[0076] The methanol oxidation reaction unit mainly includes a shell-and-tube methanol oxidation reactor, a methanol gasification furnace, a methanol one-way check valve, a methanol liquid feed shut-off valve, a methanol feed electronic metering pump, an explosion-proof oxidation variable frequency booster fan, a gas preheating furnace, gas regulating valve eight, gas regulating valve nine, a circulating nitrogen variable frequency booster fan, a circulating gas one-way valve one, a circulating gas one-way valve two, a nitrogen solenoid valve, a nitrogen regulating valve, a circulating nitrogen mass flow meter, a gas mixer, a fresh air gas mass flow meter, a fresh air variable frequency booster fan, a gas one-way valve, and a gas mechanical impurity remover two. Methanol from the methanol conveying device sequentially enters the tube layer of the methanol gasification furnace through the methanol feed electronic metering pump, the methanol liquid feed shut-off valve, and the methanol one-way check valve. The methanol oxidation reactor and the methanol gasification furnace are connected. The top of the methanol gasification furnace is connected to the explosion-proof oxidation variable frequency booster fan via a pipeline. The gas preheating furnace is connected to the upper part of the methanol gasification furnace via a pipeline. The mixer is connected as follows: Nitrogen gas from the plant system enters the circulating nitrogen variable frequency booster fan through gas regulating valve 8 and gas regulating valve 9. The gas from the circulating nitrogen variable frequency booster fan is split into two: one path connects to the gas mixer through circulating gas check valve 2 and circulating nitrogen mass flow meter; the other path connects to the gas mixer through circulating gas check valve 1 and nitrogen regulating valve. Part of the system nitrogen gas is connected to the pipeline between circulating gas check valve 1 and nitrogen regulating valve through a nitrogen solenoid valve. Fresh air is connected to the gas mixer through pipelines sequentially through gas mechanical impurity remover 2, gas check valve, fresh air variable frequency booster fan, and fresh air gas mass flow meter. An overpressure interlock alarm system and an overtemperature interlock alarm system are installed at the inlet, outlet, and inside the reactor tube layer of the methanol oxidation reactor. An oxygen concentration monitoring safety interlock alarm system and a methanol concentration monitoring safety interlock alarm system are installed on the pipeline connecting the methanol oxidation reactor and the methanol gasification furnace.

[0077] The formaldehyde absorption unit mainly includes a primary spray absorption tower, a liquid circulation pump 1, a plate heat exchanger 1, a liquid circulation pump 2, a plate heat exchanger 3, a formaldehyde level regulating valve 1, a secondary spray absorption tower, a liquid circulation pump 3, a plate heat exchanger 4, a liquid circulation pump 5, a regulating valve, a formaldehyde level regulating valve 2, a liquid circulation pump 5, a water-cooled plate heat exchanger, and a formaldehyde product outlet. Formaldehyde product gas from the gas preheating furnace shell enters the primary spray absorption tower through the inlet at the bottom; after exiting from the gas outlet at the top of the primary spray absorption tower, it enters the secondary spray absorption tower from the bottom. At the top of the primary spray absorption tower, circulating water enters the primary spray absorption tower through plate heat exchanger 2. The primary spray absorption tower is then connected to the plate heat exchanger by liquid circulation pump 2. Heat exchanger 2 is connected; at the bottom of the primary spray absorption tower, circulating water enters the primary spray absorption tower through plate heat exchanger 1, and the primary spray absorption tower is connected to plate heat exchanger 1 through liquid circulation pump 1; at the top of the secondary spray absorption tower, circulating water is connected to the secondary spray absorption tower through liquid circulation pump 3 and plate heat exchanger 3; at the bottom of the secondary spray absorption tower, circulating water is connected to plate heat exchanger 4 through liquid circulation pump 4, regulating valve, and plate heat exchanger 4; formaldehyde level regulating valve 2 is installed on the pipeline between liquid circulation pump 4 and regulating valve; formaldehyde level regulating valve 1 is installed at the bottom of the primary spray absorption tower; liquid circulation pump 5 is installed on the pipeline between formaldehyde level regulating valve 1 and formaldehyde level regulating valve 2, and liquid circulation pump 5 is connected to water-cooled plate heat exchanger; water-cooled plate heat exchanger is connected to formaldehyde product outlet.

[0078] The second steam production unit mainly includes a steam generator, a second steam regulating valve, a second steam compression pump, a second steam pressure storage tank, and a second steam back pressure valve. The water-cooled plate heat exchanger of the formaldehyde absorption unit is connected to the steam generator. The steam generator is connected to the second steam pressure storage tank via the second steam regulating valve and the second steam compression pump. The second steam pressure storage tank outputs steam through the steam back pressure valve, and the generated steam pressure is 2-2.4 MPa.

[0079] The heat transfer oil unit mainly includes a cooling-state heat transfer oil storage tank, a high-temperature explosion-proof heat transfer oil pump, heat transfer oil automatic regulating valve one, heat transfer oil automatic regulating valve two, heat transfer oil automatic regulating valve three, an oil-water heat exchanger, a heat transfer oil electric heater, a gas-liquid separator, and a pressure safety regulating valve; wherein, process water enters the gas-liquid separator through a delivery pipeline and the oil-water heat exchanger; the oil-water heat exchanger is connected to the bottom of the gas-liquid separator through the heat transfer oil automatic regulating valve three; The oil-water heat exchanger is connected to the cold-state heat transfer oil storage tank; the bottom of the cold-state heat transfer oil storage tank is connected to the gas-liquid separator via a high-temperature explosion-proof heat transfer oil pump, a second automatic heat transfer oil regulating valve, and a heat transfer oil electric heater; a pressure safety regulating valve is installed at the top of the gas-liquid separator; the top of the cold-state heat transfer oil storage tank is connected to the high-temperature explosion-proof heat transfer oil pump and the second automatic heat transfer oil regulating valve via a pipeline; the gas-liquid separator is connected to the shell of the methanol oxidation reactor in the methanol oxidation reaction unit; the steam production unit mainly includes a steam regulating valve, a steam compression pump, a steam pressure storage tank, and a steam back pressure valve; the gas-liquid separator of the heat transfer oil unit is connected to the steam pressure storage tank via the steam regulating valve and the steam compression pump, and the steam generated by the heat exchange of the gas-liquid separator is stored in the steam pressure storage tank; the steam pressure storage tank delivers steam to the outside via the steam back pressure valve, and the steam pressure obtained is 2.0-2.4 MPa.

[0080] The exhaust gas treatment unit mainly includes a catalytic combustion reactor, a three-way automatic switching valve, and an aerial flare tower; wherein, the steam generator of the steam production unit is connected to the middle shell of the catalytic combustion reactor; the catalytic combustion reactor is connected to the aerial flare tower through the three-way automatic switching valve.

[0081] The pressure swing adsorption (PSA) nitrogen generation unit mainly includes a circulating gas frequency converter blower, gas regulating valve 1, gas regulating valve 2, temperature swing adsorption dehydration tower 1, gas regulating valve 3, gas regulating valve 4, temperature swing adsorption dehydration tower 2, gas regulating valve 5, gas compressor 1, gas regulating valve 6, PSA nitrogen generation tower 1, gas back pressure valve 1, gas regulating valve 7, gas compressor 2, PSA nitrogen generation tower 2, gas back pressure valve 2, and gas mechanical separator 1. The catalytic combustion reactor of the exhaust gas treatment unit is connected to the exhaust gas frequency converter blower via a three-way automatic switching valve. The outlet pipe of the exhaust gas frequency converter blower is divided into two parts: one part is connected to the temperature swing adsorption dehydration tower 1 via gas regulating valve 2, and the other part is connected to the bottom of the temperature swing adsorption dehydration tower 2 via gas regulating valve 1. A gas regulating valve four is installed between the tops of temperature swing adsorption dehydration tower 1 and temperature swing adsorption dehydration tower 2. The outlet pipe of temperature swing adsorption dehydration tower 2 is split into two parts. One part is connected to pressure swing adsorption nitrogen generation tower 1 through gas regulating valve five and gas compressor one. Pressure swing adsorption nitrogen generation tower 1 is connected to gas compressor two through gas regulating valve seven. The other part is connected to pressure swing adsorption nitrogen generation tower 2 through gas regulating valve six and gas compressor two. Pressure swing adsorption nitrogen generation tower 1 and pressure swing adsorption nitrogen generation tower 2 are connected to gas mechanical impurity remover one through gas back pressure valve one and gas back pressure valve two, respectively. The outlet pipe of gas mechanical impurity remover one is split into two parts, which are connected to the methanol oxidation reaction unit and the nitrogen device of the plant system, respectively. The nitrogen produced by the pressure swing adsorption nitrogen generation unit has a purity > 99.9%.

[0082] The methanol oxidation reactor includes a reactor inlet, an inlet temperature interlock monitoring point, an inlet pressure interlock monitoring point, a heat transfer oil outlet, a heat transfer oil inlet, an outlet temperature interlock monitoring point, an outlet pressure interlock monitoring point, and a reactor outlet. The reactor inlet, inlet temperature interlock monitoring point, and inlet pressure interlock monitoring point are located at the top of the methanol oxidation reactor; the outlet temperature interlock monitoring point, outlet pressure interlock monitoring point, and reactor outlet are located at the bottom of the methanol oxidation reactor; the heat transfer oil outlet and heat transfer oil inlet are located at the upper and lower parts of the sides of the methanol oxidation reactor, respectively.

[0083] A steam pressure interlock alarm system and a steam temperature interlock alarm system are installed at the inlet of the steam pressure storage tank to monitor and alarm the steam pressure and temperature in real time.

[0084] A steam pressure interlock alarm system and a steam temperature interlock alarm system are installed at the second inlet of the steam pressure storage tank to monitor and alarm the steam pressure and temperature in real time.

[0085] The method for producing high-concentration formaldehyde, along with steam and nitrogen, using the above system and apparatus via the iron-molybdenum process includes the following steps:

[0086] (1) Process gas preparation and preheating: Fresh air enters the gas mechanical cleaner through the fresh air frequency converter blower to remove impurities. After removal, it is mixed with nitrogen through the circulating air from the circulating nitrogen frequency converter blower in proportion and then enters the gas mixer to become process gas. Then the process gas is preheated and enters the methanol vaporization furnace tube layer.

[0087] More specifically, this step involves: fresh air entering the gas mechanical impurity remover via a fresh air frequency converter blower, then mixing with recirculated air via a recirculated air frequency converter blower at a certain ratio before entering the gas mixer. The mixture then enters the gas preheating furnace tube layer for preheating to 150-160℃ before entering the methanol vaporization furnace tube layer. The process gas needs to maintain an oxygen concentration between 10% and 12%. The gas pressure is maintained at 80-90 kPa in the initial stage of the reaction and at 180-200 kPa in the final stage.

[0088] (2) Methanol vaporization: Methanol is fed into the methanol vaporization furnace tube layer through a metering pump and mixed with the process gas. Then it is heated with the product gas to 180-210℃ to obtain the raw material gas; the volume concentration of methanol in the raw material gas is kept at 8-9%.

[0089] (3) Methanol oxidation reaction: The feed gas (preheated to 180~210℃) from the methanol gasifier tube bed enters the methanol oxidation reactor tube bed, where it undergoes an incomplete oxidation reaction under the action of the catalyst to produce formaldehyde. The formaldehyde product gas enters the methanol gasifier shell bed and the gas preheating furnace shell bed through the outlet for heat exchange to 150-160℃. The heat transfer oil removes the heat released by the reaction through vaporization in the methanol oxidation reactor shell bed. At the end of the methanol oxidation reaction, due to the loss of catalyst activity, it is necessary to increase the vaporization temperature of the heat transfer oil system by increasing the pressure, thereby increasing the bed wall temperature and achieving complete conversion of methanol at the end. The initial pressure of the heat transfer oil is atmospheric pressure, and the final pressure is 200Kpa. The initial heat transfer temperature is 260℃, and the final heat transfer oil temperature is 310-315℃.

[0090] (4) Formaldehyde absorption to prepare high-concentration formaldehyde: The formaldehyde product gas from the preheated furnace shell enters the formaldehyde primary spray absorption tower through the bottom inlet of the primary absorption tower for two-stage spray absorption. It is discharged from the top gas outlet of the primary absorption tower to the bottom of the secondary absorption tower and enters the secondary multi-stage spray absorption tower. It is discharged from the top of the secondary absorption tower. When the formaldehyde concentration in the absorption tower reaches the required value, the product is discharged from the formaldehyde outlet after heat exchange in the plate heat exchanger. The average concentration of the obtained formaldehyde product is 54.8%.

[0091] (5) Catalytic combustion of tail gas: The tail gas from the secondary spray absorption tower enters the tube layer of the catalyst combustion reactor and reacts with the catalyst. The gas after combustion enters the tube layer of the tail gas steam generator and exchanges heat with the process water to produce steam. Then it enters the shell layer of the catalyst combustion reactor. The steam generated after heat exchange is supplied to the outside. The tail gas after cooling is used as a raw material for nitrogen production and enters the pressure swing adsorption nitrogen production step. If the reaction system, pressure swing adsorption system or absorption system fails, it is discharged through combustion in the high-altitude flare tower.

[0092] (6) Pressure swing adsorption nitrogen production: The tail gas from the tail gas catalytic combustion step enters temperature swing adsorption dehydration tower 1 and temperature swing adsorption dehydration tower 2 through the gas regulating valve. After dehydration, it enters pressure swing adsorption nitrogen production tower 1 and pressure swing adsorption nitrogen production tower 2 through the gas regulating valve and gas compressor, respectively. The adsorption and desorption pressure is adjusted by the gas back pressure valve. Then, part of it enters the nitrogen system through the gas regulating valve, and the other part is mixed with fresh gas through the gas regulating valve and returned to the oxidation reaction unit.

[0093] Methanol oxidation reactor, such as Figure 2 As shown, the methanol oxidation reactor adopts a shell-and-tube structure containing 20,000 fixed-bed reaction tubes. The reactor inlet is equipped with an inlet temperature interlock monitoring point and an inlet pressure interlock monitoring point. The side wall of the reactor has a heat transfer oil outlet and a heat transfer oil inlet, and the bottom is the reactor outlet, which is equipped with an outlet temperature interlock monitoring point and an outlet pressure interlock monitoring point.

[0094] like Figure 4 The reactor shown has a core-to-core spacing of 36 mm, an inner diameter of 22 mm, an outer diameter of 26 mm, and a total tube length of 1640 mm. The iron-molybdenum catalyst is packed in a single tube configuration. Figure 4 The reactor is filled with tubes of size 3. Ten thermocouples are installed to monitor hot spot temperatures in 0.07% of the total number of reaction tubes in the methanol oxidation reactor. Seven thermocouples have seven hot spot temperature monitoring points (A, B, and C). When more than 70% of the seven thermocouple hot spot temperatures are below point B, the iron-molybdenum-formaldehyde catalyst needs to be replaced, thus achieving online synchronous monitoring of the reactor.

[0095] Example 2

[0096] This example is a 170,000-ton / year formaldehyde production unit (based on 37% wt formaldehyde) upstream of a BDO plant. The design inlet process gas flow rate of this unit is 70,000 Nm³. 3 The methanol inlet concentration is 8%, the oxygen concentration is 11%, and the catalysts are CNFM-01 and CNFM-02, with a designed gas hourly space velocity of 12000 h⁻¹. -1 The inlet exhaust gas temperature of the catalytic combustion reactor is 120℃, the reaction pressure is 50 kPa, the bed hot spot temperature is 550℃, and the gas hourly space velocity is 30,000 h⁻¹. -1 The process is as follows: Figure 1 As shown, the specific structure and connection relationship are the same as in Example 1.

[0097] Methanol oxidation reactor, such as Figure 2 As shown, the methanol oxidation reactor adopts a shell-and-tube structure containing 10,000 fixed-bed reaction tubes. The reactor inlet is equipped with an inlet temperature interlock monitoring point and an inlet pressure interlock monitoring point. The side wall of the reactor has a heat transfer oil outlet and a heat transfer oil inlet, and the bottom is the reactor outlet, which is equipped with an outlet temperature interlock monitoring point and an outlet pressure interlock monitoring point.

[0098] like Figure 5 The reactor shown has a core-to-core spacing of 45 mm, an inner diameter of 30 mm, an outer diameter of 34 mm, and a total tube length of 1750 mm. The iron-molybdenum catalyst is packed in a single tube configuration. Figure 5 For the size treatment in section 3, the methanol oxidation reactor uses nine thermocouples to monitor hot spot temperatures, representing 0.1% of the total number of reaction tubes. Each thermocouple has nine hot spot temperature monitoring points (AI). When more than 50% of the nine thermocouple hot spot temperatures are below point B, the iron-molybdenum-formaldehyde catalyst needs to be replaced.

[0099] The inlet exhaust gas temperature of the catalytic combustion reactor is 120℃, the reaction pressure is 50 kPa, the bed hot spot temperature is 500℃, and the gas hourly space velocity is 50,000 h⁻¹. -1 .

[0100] Example 3:

[0101] This example is a 190,000-ton / year formaldehyde production unit (based on 37% wt formaldehyde) upstream of a BDO plant. The designed inlet process gas flow rate of this unit is 62,000 Nm³. 3 The methanol inlet concentration is 10%, the oxygen concentration is 11%, and the catalysts are CNFM-01 and CNFM-02, with a designed gas hourly space velocity of 6000 h⁻¹. -1 The inlet exhaust gas temperature of the catalytic combustion reactor is 120℃, the reaction pressure is 50 kPa, the bed hot spot temperature is 550℃, and the gas hourly space velocity is 30,000 h⁻¹. -1 The process is as follows: Figure 1 As shown, the specific structure and connection relationship are the same as in Example 1.

[0102] Methanol oxidation reactor, such as Figure 2 As shown, the methanol oxidation reactor adopts a shell-and-tube structure containing 20,000 fixed-bed reaction tubes. The reactor inlet is equipped with an inlet temperature interlock monitoring point and an inlet pressure interlock monitoring point. The side wall of the reactor has a heat transfer oil outlet and a heat transfer oil inlet, and the bottom is the reactor outlet, which is equipped with an outlet temperature interlock monitoring point and an outlet pressure interlock monitoring point.

[0103] like Figure 5The reactor shown has a core-to-core spacing of 42 mm, an inner diameter of 25 mm, an outer diameter of 29 mm, and a total tube length of 1990 mm. The iron-molybdenum catalyst is packed in a single tube configuration. Figure 5 For the size treatment in section 3, the methanol oxidation reactor uses nine thermocouples to monitor hot spot temperatures, representing 0.07% of the total number of reaction tubes. Ten thermocouples have nine hot spot temperature monitoring points (AI). When more than 50% of the ten thermocouple hot spot temperatures are below point B, the iron-molybdenum-formaldehyde catalyst needs to be replaced.

[0104] Example 4

[0105] This example is a formaldehyde production unit with a capacity of 410,000 tons / year (based on 37% wt formaldehyde) in a certain factory. The designed inlet process gas flow rate of this unit is 150,000 Nm³. 3 The methanol inlet concentration is 9%, the oxygen concentration is 11%, and the catalysts are CNFM-01 and CNFM-02, with a designed gas hourly space velocity of 10000 h⁻¹. -1 The inlet exhaust gas temperature of the catalytic combustion reactor is 120℃, the reaction pressure is 50 kPa, the bed hot spot temperature is 550℃, and the gas hourly space velocity is 30,000 h⁻¹. -1 The process is as follows: Figure 1 As shown, the specific structure and connection relationship are the same as in Example 1.

[0106] Methanol oxidation reactor, such as Figure 3 As shown, the methanol oxidation reactor adopts a shell-and-tube structure containing 30,000 fixed-bed reaction tubes. The reactor inlet is equipped with an inlet temperature interlock monitoring point and an inlet pressure interlock monitoring point. The side wall of the reactor has a heat transfer oil outlet and a heat transfer oil inlet, and the bottom is the reactor outlet, which is equipped with an outlet temperature interlock monitoring point and an outlet pressure interlock monitoring point.

[0107] like Figure 6 The reactor shown has a core-to-core spacing of 42 mm, an inner diameter of 25 mm, an outer diameter of 29 mm, and a total tube length of 1990 mm. The iron-molybdenum catalyst is packed in a single tube configuration. Figure 5 For the size treatment in section 3, the methanol oxidation reactor uses nine thermocouples to monitor hot spot temperatures, representing 0.05% of the total number of reaction tubes. Ten thermocouples have nine hot spot temperature monitoring points (AI). When more than 50% of the ten thermocouple hot spot temperatures are below point B, the iron-molybdenum-formaldehyde catalyst needs to be replaced.

[0108] Example 5:

[0109] This example is a 300,000-ton / year formaldehyde production unit (based on 37% wt formaldehyde) upstream of a BDO plant. The designed inlet process gas flow rate of this unit is 108,000 Nm³. 3 / h, methanol inlet concentration of 9%, oxygen concentration of 11%, CNFM-01 and CNFM-02 catalysts, design space velocity of 12000h -1 The inlet exhaust gas temperature of the catalytic combustion reactor is 120℃, the reaction pressure is 30 kPa, the bed hot spot temperature is 490℃, and the gas hourly space velocity is 30,000 h⁻¹. -1 The process is as follows: Figure 1 As shown, the specific structure and connection relationship are the same as in Example 1.

[0110] Methanol oxidation reactor, such as Figure 2 As shown, the methanol oxidation reactor adopts a shell-and-tube structure containing 20,000 fixed-bed reaction tubes. The reactor inlet is equipped with an inlet temperature interlock monitoring point and an inlet pressure interlock monitoring point. The side wall of the reactor has a heat transfer oil outlet and a heat transfer oil inlet, and the bottom is the reactor outlet, which is equipped with an outlet temperature interlock monitoring point and an outlet pressure interlock monitoring point.

[0111] like Figure 7 The reactor shown has a core-to-core spacing of 42 mm, an inner diameter of 25 mm, an outer diameter of 29 mm, and a total tube length of 1640 mm. The iron-molybdenum catalyst is packed in a single tube configuration. Figure 3 For the methanol oxidation reactor, 0.05% of the total number of reaction tubes are equipped with nine thermocouples to monitor hot spot temperatures. Ten thermocouples have seven hot spot temperature monitoring points (A, G). When more than 50% of the ten thermocouple hot spot temperatures are below point B, the iron-molybdenum-formaldehyde catalyst needs to be replaced.

[0112] Example 6:

[0113] This example is a 240,000-ton / year formaldehyde production unit (based on 37% wt formaldehyde) in a factory. The designed inlet process gas flow rate of this unit is 80,000 Nm³. 3 The methanol inlet concentration is 10%, the oxygen concentration is 12%, and the catalysts are CNFM-01 and CNFM-02, with a designed gas hourly space velocity of 7500 h⁻¹. -1 The inlet exhaust gas temperature of the catalytic combustion reactor is 120℃, the reaction pressure is 20 kPa, the bed hot spot temperature is 530℃, and the gas hourly space velocity is 60,000 h⁻¹. -1 The process is as follows: Figure 1 As shown, the specific structure and connection relationship are the same as in Example 1.

[0114] Methanol oxidation reactor, such as Figure 2As shown, the methanol oxidation reactor adopts a shell-and-tube structure containing 24,000 fixed-bed reaction tubes. The reactor inlet is equipped with an inlet temperature interlock monitoring point and an inlet pressure interlock monitoring point. The side wall of the reactor has a heat transfer oil outlet and a heat transfer oil inlet, and the bottom is the reactor outlet, which is equipped with an outlet temperature interlock monitoring point and an outlet pressure interlock monitoring point.

[0115] like Figure 8 The reactor shown has a core-to-core spacing of 42 mm, an inner diameter of 25 mm, an outer diameter of 29 mm, and a total tube length of 1990 mm. The iron-molybdenum catalyst is packed in a single tube configuration. Figure 8 For the methanol oxidation reactor, 0.05% of the total number of reaction tubes are equipped with nine thermocouples to monitor hot spot temperatures. Ten thermocouples have seven hot spot temperature monitoring points (A, B, and C). When more than 50% of the ten thermocouple hot spot temperatures are below point B, the iron-molybdenum-formaldehyde catalyst needs to be replaced.

[0116] Comparative Example 1

[0117] This example is a 160,000-ton / year formaldehyde production unit (based on 37% wt formaldehyde) upstream of a BDO plant. The design inlet process gas flow rate of this unit is 80,000 Nm³. 3 The methanol inlet concentration is 7%, the oxygen concentration is 10%, and the catalysts are CNFM-01 and CNFM-02, with a design gas hourly space velocity of 5900 h⁻¹. -1 The inlet exhaust gas temperature of the catalytic combustion reactor is 140℃, the reaction pressure is 40 kPa, the bed hot spot temperature is 470℃, and the gas hourly space velocity is 61,000 h⁻¹. -1 The process is as follows: Figure 1 As shown, the specific structure and connection relationship are the same as in Example 1.

[0118] Methanol oxidation reactor, such as Figure 2 As shown, the methanol oxidation reactor adopts a shell-and-tube structure containing 20,000 fixed-bed reaction tubes. The reactor inlet is equipped with an inlet temperature interlock monitoring point and an inlet pressure interlock monitoring point. The side wall of the reactor has a heat transfer oil outlet and a heat transfer oil inlet, and the bottom is the reactor outlet, which is equipped with an outlet temperature interlock monitoring point and an outlet pressure interlock monitoring point.

[0119] like Figure 9 The reactor shown has a core-to-core spacing of 33 mm, an inner diameter of 20 mm, an outer diameter of 24 mm, and a total tube length of 1640 mm. The iron-molybdenum catalyst is packed in a single tube configuration. Figure 9For the methanol oxidation reactor, 0.05% of the total number of reaction tubes are equipped with nine thermocouples to monitor hot spot temperatures. Ten thermocouples have seven hot spot temperature monitoring points (A, B, and C). When more than 50% of the ten thermocouple hot spot temperatures are below point B, the iron-molybdenum-formaldehyde catalyst needs to be replaced.

[0120] Comparative Example 2

[0121] This example is a 200,000-ton / year formaldehyde production unit (based on 37% wt formaldehyde) in a factory. The designed inlet process gas flow rate of this unit is 75,000 Nm³. 3 The methanol inlet concentration is 9%, the oxygen concentration is 11%, and the catalysts are CNFM-01 and CNFM-02, with a designed gas hourly space velocity of 12500 h⁻¹. -1 The inlet exhaust gas temperature of the catalytic combustion reactor is 80℃, the reaction pressure is 30 kPa, the bed hot spot temperature is 610℃, and the gas hourly space velocity is 27,000 h⁻¹. -1 The process is as follows: Figure 1 As shown, the specific structure and connection relationship are the same as in Example 1.

[0122] Methanol oxidation reactor, such as Figure 2 As shown, the methanol oxidation reactor adopts a shell-and-tube structure containing 20,000 fixed-bed reaction tubes. The reactor inlet is equipped with an inlet temperature interlock monitoring point and an inlet pressure interlock monitoring point. The side wall of the reactor has a heat transfer oil outlet and a heat transfer oil inlet, and the bottom is the reactor outlet, which is equipped with an outlet temperature interlock monitoring point and an outlet pressure interlock monitoring point.

[0123] like Figure 10 The reactor shown has a core-to-core spacing of 42 mm, an inner diameter of 25 mm, an outer diameter of 29 mm, and a total tube length of 1890 mm. The iron-molybdenum catalyst is packed in a single tube configuration. Figure 3 For the methanol oxidation reactor, 0.05% of the total number of reaction tubes are equipped with nine thermocouples to monitor hot spot temperatures. Ten thermocouples have seven hot spot temperature monitoring points (A, B, and C). When more than 50% of the ten thermocouple hot spot temperatures are below point B, the iron-molybdenum-formaldehyde catalyst needs to be replaced.

[0124] Comparative Example 3

[0125] This example is a 180,000-ton / year formaldehyde production unit (based on 37% wt formaldehyde) upstream of a BDO plant. The design inlet process gas flow rate of this unit is 60,000 Nm³. 3 The methanol inlet concentration is 9%, the oxygen concentration is 11%, and the catalysts are CNFM-01 and CNFM-02, with a design gas hourly space velocity of 8600 h⁻¹. -1The inlet exhaust gas temperature of the catalytic combustion reactor is 80℃, the reaction pressure is 30 kPa, the bed hot spot temperature is 520℃, and the gas hourly space velocity is 30,000 h⁻¹. -1 The process is as follows: Figure 11 As shown.

[0126] Methanol oxidation reactor, such as Figure 2 As shown, the methanol oxidation reactor adopts a shell-and-tube structure containing 20,000 fixed-bed reaction tubes. The reactor inlet is equipped with an inlet temperature interlock monitoring point and an inlet pressure interlock monitoring point. The side wall of the reactor has a heat transfer oil outlet and a heat transfer oil inlet, and the bottom is the reactor outlet, which is equipped with an outlet temperature interlock monitoring point and an outlet pressure interlock monitoring point.

[0127] like Figure 2 The reactor shown has a core-to-core spacing of 36 mm, an inner diameter of 22 mm, an outer diameter of 26 mm, and a total tube length of 1640 mm. The iron-molybdenum catalyst is packed in a single tube configuration. Figure 3 For the methanol oxidation reactor, 0.05% of the total number of reaction tubes are equipped with nine thermocouples to monitor hot spot temperatures. Ten thermocouples have seven hot spot temperature monitoring points (A, B, and C). When more than 50% of the ten thermocouple hot spot temperatures are below point B, the iron-molybdenum-formaldehyde catalyst needs to be replaced.

[0128] The flow chart of the iron-molybdenum process for producing high-concentration formaldehyde and co-producing steam (existing technology) is as follows: Figure 11 As shown, the main processes include the following:

[0129] (1) Process gas preparation and preheating: Fresh air enters the gas mechanical cleaner through the fresh air frequency converter blower and then mixes with nitrogen through the circulating gas frequency converter blower in a certain proportion. It then enters the gas mixer and then enters the gas preheating furnace tube layer for preheating. It is preheated to 120~150℃ and enters the methanol vaporization furnace tube layer. The process gas needs to meet the requirement that the oxygen concentration is between 10% and 12%. In the initial stage of the reaction, the gas pressure is maintained at 70~90 kPa and in the final stage of the reaction, the gas pressure is maintained at 150~200 kPa.

[0130] (2) Methanol vaporization: Methanol is fed into the methanol vaporization furnace tube layer in a certain amount through a methanol feed electronic metering pump and mixed with the process gas. Then it is heated with the product gas to 180~210℃ to obtain the raw material gas, ensuring that the methanol volume concentration in the raw material gas is maintained at 8~10%.

[0131] (3) Methanol oxidation reaction: The raw gas from the methanol gasification furnace is preheated to 180~210℃ in the tube layer and then enters the methanol oxidation reactor (14). The tube layer undergoes an incomplete oxidation reaction under the action of the catalyst to generate formaldehyde. The formaldehyde product gas enters the shell layer of the methanol gasification furnace and the shell layer of the gas preheating furnace through the outlet, and the heat exchange is brought to 150-160℃. The heat transfer oil removes the heat released by the reaction through vaporization in the shell layer of the methanol oxidation reactor. At the end of the methanol oxidation reaction, due to the loss of catalyst activity, it is necessary to increase the vaporization temperature of the heat transfer oil system by increasing the pressure, thereby increasing the bed wall temperature and achieving complete conversion of methanol at the end. The initial pressure of the heat transfer oil is atmospheric pressure, and the final pressure is 200Kpa. The initial heat transfer temperature is 257-265℃, and the final heat transfer oil temperature is 295-302℃.

[0132] (4) Formaldehyde absorption to prepare high-concentration formaldehyde: The product gas from the preheated furnace shell enters the primary formaldehyde spray absorption tower through the bottom absorption tower inlet for spray absorption. The gas is discharged from the top outlet to the secondary multi-stage spray absorption tower. When the formaldehyde concentration in the absorption tower reaches the required value, the product is discharged from the formaldehyde outlet after heat exchange through a plate heat exchanger.

[0133] Exhaust gas catalytic combustion: Exhaust gas from the secondary spray absorption tower enters the catalytic combustion reactor tube layer to react with the catalyst. The combusted gas then enters the exhaust gas steam generator tube layer to exchange heat with process water to produce steam, which then enters the catalytic combustion reactor shell layer. The steam generated after heat exchange is supplied externally. A portion of the purified exhaust gas is mixed with fresh air and returned to the oxidation reaction unit via a circulating nitrogen variable frequency booster fan. The remaining completely purified exhaust gas is directly discharged through an elevated flare tower.

[0134] The methods in Examples 1-6 and Comparative Examples 1-3 were processed according to the following operating process parameters. The specific conditions and results are shown in the table below:

[0135] Table 1-1 Comparison of Actual Operating Process Parameters

[0136]

[0137] Summarize:

[0138] This production method utilizes efficient heat exchange to recover heat from the exhaust gas, preheating the raw material gas and producing by-product steam. It achieves self-circulating operation of the heat transfer oil system without external processing through the thermosiphon principle, fully leveraging thermodynamic and kinetic principles to achieve low-energy operation of the iron-molybdenum-formaldehyde reaction. Simultaneously, the exhaust gas is used for nitrogen production through pressure swing adsorption, achieving low-energy nitrogen generation. The circulating gas uses higher-purity nitrogen mixed with fresh air, which is more beneficial to the catalyst and equipment compared to the circulating gas in traditional processes. During the reaction, controlling key parameters such as optimal reaction temperature, reaction pressure, methanol, and oxygen concentrations ensures safe system operation, extends catalyst lifespan, and reduces catalyst replacement frequency and operating costs. The two-stage absorption system produces high-concentration formaldehyde products with a concentration of 50-55%, achieving one-step production of high-concentration formaldehyde with thorough absorption, and the total organic matter concentration in the outlet exhaust gas is less than 10 ppm. The production method of this invention features low energy consumption, compact layout, small footprint, and byproducts of steam and nitrogen. It is suitable for the oxidation of methanol to formaldehyde using the iron-molybdenum process. When used with a domestically produced iron-molybdenum formaldehyde catalyst, this invention can produce formaldehyde independently or be used as an upstream formaldehyde raw material production unit for BDO, polyoxymethylene, and thermosetting resin processes, depending on the requirements. It has flexible and varied applications, low energy consumption, and no pollution, making it an environmentally friendly green production method.

[0139] The above description is merely a preferred embodiment of the invention and does not constitute any limitation on the invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments based on the technical essence of the invention and within the spirit and principles of the invention shall still fall within the protection scope of the invention's technical solution.

Claims

1. A process for the production of high concentration formaldehyde co-producing steam and nitrogen by the iron-molybdenum method, characterized by It comprises the following steps: (1) Process gas preparation and preheating: After the impurities are removed, the fresh air is mixed with the circulating air in proportion to enter the gas mixer to become the process gas, then the process gas is preheated, and after preheating, it enters the methanol vaporization furnace pipe layer; the preheating temperature is 120-160 DEG C; the process gas needs to meet the oxygen concentration between 10%-12%; (2) Methanol vaporization: methanol is input into the methanol vaporization furnace pipe layer by the metering pump and mixed with the process gas, then after heat exchange with the product gas, the raw material gas is obtained; (3) Methanol oxidation reaction: the raw material gas from the methanol gasification furnace pipe layer enters the methanol oxidation reactor pipe layer, and under the action of the catalyst, the incomplete oxidation reaction occurs to generate formaldehyde, and the formaldehyde product gas is sequentially introduced into the methanol gasification furnace shell layer and the gas preheating furnace shell layer for heat exchange through the outlet; the heat transfer oil in the methanol oxidation reactor shell layer is vaporized to remove the reaction heat release heat to vaporize the heat transfer oil; (4) Preparation of high-concentration formaldehyde by methanol absorption: the formaldehyde product gas from the gas preheating furnace shell layer enters the first-stage absorption tower from the bottom inlet, and is sprayed and absorbed in the first-stage spray and spray absorption tower, and is discharged from the top gas outlet of the first-stage absorption tower to the second-stage absorption tower, and enters the second-stage multi-stage spray absorption tower from the bottom, and is discharged from the top of the second-stage absorption tower; when the formaldehyde concentration of the absorption tower reaches the required value, the product is heat exchanged by the plate heat exchanger and discharged from the formaldehyde outlet; (5) Tail gas catalytic combustion: the tail gas from the second-stage spray absorption tower enters the catalyst combustion reactor pipe layer and reacts with the catalyst, and the combusted gas enters the tail gas steam generator pipe layer and exchanges heat with the process water to produce steam, and then enters the catalyst combustion reactor shell layer, and the steam produced after heat exchange is used externally; the cooled tail gas enters the variable pressure adsorption nitrogen production step through the tail gas variable frequency booster fan to be used as the raw material for nitrogen production; The upper part of the catalytic combustion reactor is a tube heat exchanger, and the lower part is an adiabatic electric heating fixed bed reactor. The upper part of the tube is filled with a spherical molecular sieve loaded with a Pt-Pd double noble metal catalyst, and the lower part is a monolithic honeycomb coated with a Pt-Pd double noble metal catalyst on cordierite. The inlet tail gas temperature of the catalytic combustion reactor is 90-120℃, the reaction pressure is 20-200KPa, the bed hot spot temperature is less than 600℃, and the gas volume space velocity is 30000-60000h -1 ; (6) Pressure swing adsorption nitrogen production: the tail gas from the tail gas catalytic combustion enters the temperature swing adsorption dehydration No. 1 tower and the temperature swing adsorption dehydration No. 2 tower through the gas regulating valve respectively, is dehydrated, and then enters the pressure swing adsorption nitrogen production No. 1 tower and the pressure swing adsorption nitrogen production No. 2 tower through the gas regulating valve and the gas compressor respectively, the adsorption and desorption pressure is adjusted through the gas back pressure valve, then part of it enters the nitrogen system through the gas regulating valve, and the other part returns to the oxidation reaction unit by mixing with fresh air; the composition of the tail gas from the tail gas catalytic combustion is: 1-4% CO2, total organic matter less than 10 ppm, CO content less than 0.1%, and the rest is nitrogen.

2. The method of claim 1, wherein A system for producing high-concentration formaldehyde, steam and nitrogen by iron-molybdenum method is adopted, which comprises a methanol oxidation reaction unit, a formaldehyde absorption unit, a heat transfer oil unit, a steam production unit one and a steam production unit two, a tail gas treatment unit and a pressure swing adsorption nitrogen production unit; wherein, the steam production unit one is connected with the heat transfer oil unit; the heat transfer oil unit is connected with the methanol oxidation reaction unit; the methanol oxidation reaction unit is connected with the formaldehyde absorption unit; the formaldehyde absorption unit is connected with the tail gas treatment unit, but the steam production unit two is additionally arranged between the formaldehyde absorption unit and the tail gas treatment unit; the tail gas treatment unit is connected with the pressure swing adsorption nitrogen production unit; the pressure swing adsorption nitrogen production unit is connected with the methanol oxidation reaction unit.

3. The method of claim 2, wherein: The methanol oxidation reaction unit mainly includes a shell-and-tube methanol oxidation reactor (14), a methanol gasification furnace (15), a methanol one-way check valve (16), a methanol liquid feed cut-off valve (17), a methanol feed electronic metering pump (18), an explosion-proof oxidation variable frequency booster fan (19), a gas preheating furnace (20), a gas regulating valve eight (62), a gas regulating valve nine (63), a circulating nitrogen variable frequency booster fan (64), a circulating gas one-way valve one (65), a circulating gas one-way valve two (66), a nitrogen electromagnetic valve (67), a nitrogen regulating valve (68), a circulating nitrogen mass flow meter (69), a gas mixer (70), a fresh air gas mass flow meter (71), a fresh air variable frequency booster fan (72), a gas one-way valve (73), and a gas mechanical impurity remover two (74); wherein the methanol in the methanol delivery device sequentially passes through the methanol feed electronic metering pump (18), the methanol liquid feed cut-off valve (17), and the methanol one-way check valve (16) to enter the tube layer of the methanol gasification furnace (15); the methanol oxidation reactor (14) is connected with the methanol gasification furnace (15); the top of the methanol gasification furnace (15) is connected with the explosion-proof oxidation variable frequency booster fan (19) through a pipeline; the gas preheating furnace (20) is communicated with the upper part of the methanol gasification furnace (15) through a pipeline, and the gas preheating furnace (20) is connected with the gas mixer (70); the plant system nitrogen enters the circulating nitrogen variable frequency booster fan (64) through the gas regulating valve eight (62) and the gas regulating valve nine (63), and is divided into two parts after coming out of the circulating nitrogen variable frequency booster fan (64), one part is connected with the gas mixer (70) through the circulating gas one-way valve two (66) and the circulating nitrogen mass flow meter (69); the other part is connected with the gas mixer (70) through the circulating gas one-way valve one (65) and the nitrogen regulating valve (68); part of the system nitrogen is communicated with the pipeline between the circulating gas one-way valve one (65) and the nitrogen regulating valve (68) through the nitrogen electromagnetic valve (67); the fresh air is connected with the gas mixer (70) through a pipeline in sequence through the gas mechanical impurity remover two (74), the gas one-way valve (73), the fresh air variable frequency booster fan (72), and the fresh air gas mass flow meter (71); a reaction overpressure interlocking alarm system and a reaction overtemperature interlocking alarm system are arranged at the inlet and outlet of the methanol oxidation reactor (14) and inside the reactor tube layer, an oxygen concentration monitoring safety interlocking alarm system and a methanol concentration monitoring safety concentration interlocking alarm system are arranged on the pipeline connecting the methanol oxidation reactor (14) and the methanol gasification furnace (15).

4. The method of claim 3, wherein: The formaldehyde absorption unit mainly comprises a first-stage spray spray absorption tower (21), a liquid circulating pump one (22), a plate heat exchanger one (23), a liquid circulating pump two (24), a plate heat exchanger two (25), a formaldehyde liquid level regulating valve one (26), a second-stage spray absorption tower (27), a liquid circulating pump three (28), a plate heat exchanger three (29), a plate heat exchanger four (30), a liquid circulating pump four (31), a regulating valve (32), a formaldehyde liquid level regulating valve two (33), a liquid circulating pump five (34), a water-cooled plate heat exchanger (35) and a formaldehyde product outlet (36); wherein the formaldehyde product gas from the shell layer of the gas preheating furnace (20) enters the first-stage spray spray absorption tower (21) through the inlet at the bottom of the first-stage spray spray absorption tower (21); after being discharged from the gas outlet at the top of the first-stage spray spray absorption tower (21), the formaldehyde product gas enters the second-stage spray absorption tower (27) from the bottom of the second-stage spray absorption tower (27); at the upper part of the first-stage spray spray absorption tower (21), the circulating water enters the first-stage spray spray absorption tower (21) through the plate heat exchanger two (25), and the first-stage spray spray absorption tower (21) is connected with the plate heat exchanger two (25) through the liquid circulating pump two (24); at the lower part of the first-stage spray spray absorption tower (21), the circulating water enters the first-stage spray spray absorption tower (21) through the plate heat exchanger one (23), and the first-stage spray spray absorption tower (21) is communicated with the plate heat exchanger one (23) through the liquid circulating pump one (22); at the upper part of the second-stage spray absorption tower (27), the circulating water is connected with the second-stage spray absorption tower (27) in circulation through the liquid circulating pump three (28) and the plate heat exchanger three (29); at the lower part of the second-stage spray absorption tower (27), the circulating water is connected in circulation through the liquid circulating pump four (31), the regulating valve (32) and the plate heat exchanger four (30); the formaldehyde liquid level regulating valve two (33) is arranged on the pipeline between the liquid circulating pump four (31) and the regulating valve (32); the formaldehyde liquid level regulating valve one (26) is arranged at the bottom of the first-stage spray spray absorption tower (21); the liquid circulating pump five (34) is arranged on the pipeline between the formaldehyde liquid level regulating valve one (26) and the formaldehyde liquid level regulating valve two (33), and the liquid circulating pump five (34) is connected with the water-cooled plate heat exchanger (35); the water-cooled plate heat exchanger (35) is connected with the formaldehyde product outlet (36). The steam production unit two mainly comprises a steam generator (37), a steam regulating valve two (38), a steam compression pump two (39), a steam pressure storage tank two (40) and a steam back pressure valve two (41); wherein the water-cooled plate heat exchanger (35) of the formaldehyde absorption unit is connected with the steam generator (37); the steam generator (37) is connected with the steam pressure storage tank two (40) through the steam regulating valve two (38) and the steam compression pump two (39); the steam pressure storage tank two (40) outputs steam through the steam back pressure valve two (41), and the prepared steam pressure is 2-2.4 MPa.

5. The method of claim 2 or 3, wherein: The heat conducting oil unit mainly comprises a cold-state heat conducting oil storage tank (1), a high-temperature explosion-proof heat conducting oil pump (2), a heat conducting oil automatic regulating valve one (3), a heat conducting oil automatic regulating valve two (4), a heat conducting oil automatic regulating valve three (5), an oil-water heat exchanger (6), a heat conducting oil electric heater (7), a gas-liquid separator (8) and a pressure safety regulating valve (13); wherein the process water enters the gas-liquid separator (8) through a conveying pipeline and the oil-water heat exchanger (6); the oil-water heat exchanger (6) is connected with the bottom of the gas-liquid separator (8) through the heat conducting oil automatic regulating valve three (5); the oil-water heat exchanger (6) is connected with the cold-state heat conducting oil storage tank (1); the bottom of the cold-state heat conducting oil storage tank (1) is communicated with the gas-liquid separator (8) through the high-temperature explosion-proof heat conducting oil pump (2), the heat conducting oil automatic regulating valve two (4) and the heat conducting oil electric heater (7); the pressure safety regulating valve (13) is arranged at the upper portion of the gas-liquid separator (8); the top of the cold-state heat conducting oil storage tank (1) is communicated with the pipeline between the high-temperature explosion-proof heat conducting oil pump (2) and the heat conducting oil automatic regulating valve two (4) through the heat conducting oil automatic regulating valve one (3); the gas-liquid separator (8) is connected with the shell of a methanol oxidation reactor (10) of a methanol oxidation reaction unit; the steam production unit one mainly comprises a steam regulating valve one (9), a steam compression pump one (10), a steam pressure storage tank one (11) and a steam back pressure valve one (12); wherein the gas-liquid separator (8) of the heat conducting oil unit is connected with the steam pressure storage tank one (11) through the steam regulating valve one (9) and the steam compression pump one (10); the steam pressure storage tank one (11) delivers steam outward through the steam back pressure valve one (12), and the prepared steam pressure is 2.0-2.4 MPa.

6. The method of claim 4, wherein: The tail gas treatment unit mainly comprises a catalytic combustion reactor (42), a three-way automatic switching valve (43) and a high-altitude flare tower (44); wherein the steam generator (37) of the steam production unit two is connected with the middle shell layer of the catalytic combustion reactor (42); the catalytic combustion reactor (42) is connected with the high-altitude flare tower (44) through the three-way automatic switching valve (43); the upper part of the catalytic combustion reactor (42) is a tube-type heat exchanger, and the lower part is an adiabatic electric heating fixed bed reactor; the upper part of the tube is filled with a spherical molecular sieve loaded with a Pt-Pd double noble metal catalyst, and the lower part is a whole honeycomb coated cordierite loaded with a Pt-Pd double noble metal catalyst; the tail gas temperature at the inlet of the catalytic combustion reactor (42) is 90-120 DEG C, the reaction pressure is 20-200 KPa, the bed layer hot spot temperature is less than 600 DEG C, the gas volume space velocity is 30000-60000 h -1 .

7. The method of claim 6, wherein: The pressure swing adsorption nitrogen production unit mainly comprises a circulating gas variable frequency booster fan (45), a gas regulating valve I (46), a gas regulating valve II (47), a temperature swing adsorption dehydration No. 1 tower (48), a gas regulating valve III (49), a gas regulating valve IV (50), a temperature swing adsorption dehydration No. 2 tower (51), a gas regulating valve V (52), a gas compressor I (53), a gas regulating valve VI (54), a pressure swing adsorption nitrogen production No. 1 tower (55), a gas back pressure valve I (56), a gas regulating valve VII (57), a gas compressor II (58), a pressure swing adsorption nitrogen production No. 2 tower (59), a gas back pressure valve II (60) and a gas mechanical impurity remover I (61); wherein the catalytic combustion reactor (42) of the tail gas treatment unit is connected with the circulating gas variable frequency booster fan (45) through a three-way automatic switching valve (43); the outlet pipeline I of the circulating gas variable frequency booster fan (45) is divided into two parts, one part is connected with the temperature swing adsorption dehydration No. 1 tower (48) through the gas regulating valve II (47), and the other part is connected with the bottom of the temperature swing adsorption dehydration No. 2 tower (51) through the gas regulating valve I (46); the gas regulating valve IV (50) is arranged between the top of the temperature swing adsorption dehydration No. 1 tower (48) and the top of the temperature swing adsorption dehydration No. 2 tower (51); the outlet pipeline I of the temperature swing adsorption dehydration No. 2 tower (51) is divided into two parts, one part is connected with the pressure swing adsorption nitrogen production No. 1 tower (55) through the gas regulating valve V (52) and the gas compressor I (53), the pressure swing adsorption nitrogen production No. 1 tower (55) is communicated with the gas compressor II (58) through the gas regulating valve VII (57), and the other part is connected with the pressure swing adsorption nitrogen production No. 2 tower (59) through the gas regulating valve VI (54) and the gas compressor II (58); the pressure swing adsorption nitrogen production No. 1 tower (55) and the pressure swing adsorption nitrogen production No. 2 tower (59) are connected with the gas mechanical impurity remover I (61) through the gas back pressure valve I (56) and the gas back pressure valve II (60) respectively, the outlet pipeline I of the gas mechanical impurity remover I (61) is divided into two parts and connected with the methanol oxidation reaction unit and the plant system nitrogen device respectively; the nitrogen gas prepared by the pressure swing adsorption nitrogen production unit has a purity of >99.9%.

8. The method of claim 3, wherein: The methanol oxidation reactor (14) comprises a reactor inlet, an inlet temperature interlocking monitoring point, an inlet pressure interlocking monitoring point, a heat conducting oil outlet, a heat conducting oil inlet, an outlet temperature interlocking monitoring point, an outlet pressure interlocking monitoring point and a reactor outlet; wherein the reactor inlet, the inlet temperature interlocking monitoring point and the inlet pressure interlocking monitoring point are arranged at the top of the methanol oxidation reactor (14); the outlet temperature interlocking monitoring point, the outlet pressure interlocking monitoring point and the reactor outlet are arranged at the bottom of the methanol oxidation reactor (14); the heat conducting oil outlet and the heat conducting oil inlet are arranged at the upper part and the lower part of the side of the methanol oxidation reactor (14) respectively.

9. The method of claim 3 or 8, wherein: The methanol oxidation reactor (14) adopts a shell-and-tube structure, an upper part is provided with a gas distributor to make the gas distribution more uniform, a tube layer is filled with iron-molybdenum catalyst and high-efficiency heat-conducting porcelain rings; an oil layer is arranged in a shell layer, mainly through the temperature of the heat-conducting oil itself to provide heat for the system, and the vaporization of the heat-conducting oil to remove heat to realize the stable operation of the methanol oxidation reactor, the tube layer of the methanol oxidation reactor (14) is connected with the tube layer of the methanol gasification furnace (15); a single methanol oxidation reactor contains 10,000-30,000 reaction tubes, the total number of reaction tubes is selected as 0.05-0.1% of the total number of reaction tubes according to the number of reaction tubes in the methanol oxidation reactor, 6-10 joint thermocouples with a diameter of 3mm are arranged in the reaction tubes as reaction hot spot temperature monitoring tubes, the performance of the catalyst and the time for replacing the catalyst are determined according to the change of the hot spot position, the size of the reaction tube is 21-30mm in inner diameter x 25-34mm in outer diameter x 1400-2000mm in length, the center distance between the tubes is 34-45mm, the filling height of the catalyst is 1000-1400mm, the filling height of the dilution layer is 400-800mm, and the filling height of the pure phase layer is 400-1000mm; the inlet and outlet of the oxidation reactor are provided with remote temperature and pressure monitoring points, and the main pipeline of the reactor is connected with a nitrogen system. The upper and lower limits of the temperature of the raw material gas at the inlet of the methanol oxidation reactor are 180-210℃, the upper and lower limits of the pressure are 40-200KPa, the hot spot temperature of the catalyst bed is 300-480℃; the volume space velocity of the reaction gas is 6000-12000h -1 , and the liquid volume space velocity of the methanol is 1-1.5h -1 .

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