CN1032813C - Prepn. of formaldehyde with low energy consumption - Google Patents

Abstract

The present invention relates to a production method for producing low-energy-consumption formaldehyde of formaldehyde by an oxidation dehydrogenation reaction of methanol and air under the action of a silver catalyst, which mainly comprises the steps that a soft water preheating section for preheating soft water by utilizing high-temperature gas reaction products is additionally arranged behind a quenching waste heat boiler; the product gas from the soft water preheating section is introduced into a shell side of a superheater; the product gas from the shell side of the superheater is introduced into a tube side of a methanol evaporator; the gas product of formaldehyde from the tube side of the methanol evaporator enters a condensing absorption tower for three-section countercurrent absorption. A gas distributor which is composed of sieve plates is arranged on the upper part of a catalyst layer of a reactor used in the process of production.

Description

Prepn. of formaldehyde with low energy consumption

The present invention relates to methyl alcohol and air the equipment that less energy-consumption Formaldehyde Production method and this method that oxidative dehydrogenation generates formaldehyde are adopted takes place under the silver catalyst effect.

Under the silver catalyst effect, the process that methyl alcohol and air reaction generate formaldehyde comprises based on the thermo-negative reaction of methanol dehydrogenation with based on the thermopositive reaction of the hydrogen of dehydrogenation reaction gained and the oxygen water generation reaction in the feeding air.General reaction is thermopositive reaction, and temperature of reaction is higher.How to be power savings that the formaldehyde industry is being inquired into always rationally with utilizing these reaction heat fully.

The technical process that methyl alcohol and air reaction generate formaldehyde is normally: methanol gas, air and batching steam are with predetermined mixed; This gas mixture is sent into reactor; Under the silver catalyst effect, gas mixture reacts, and generates formaldehyde gas product temperature up to 550～700 ℃, because the formaldehyde in the gaseous product at high temperature easily decomposes, side reaction takes place, reduce yield, therefore gaseous product must be quenched to below 230 ℃ as early as possible, sends to condensation then and absorbs.

For the heat that utilizes the formaldehyde gas product to have, the clear 48-20527 of clear 34-6718 of Japanese patent laid-open publication gazette and Japanese patent laid-open publication gazette proposes to reclaim the method for this hotwork for concentrating formaldehyde or removing a kind of thermal source of unreacted methanol from gaseous product.Yet these methods are all satisfactory not to the utmost aspect the heat that effectively utilizes gaseous product to have.The clear 55-11653 of clear 55-30783 of Japanese patent laid-open publication gazette and Japanese patent laid-open publication gazette proposes to reclaim the method that this hotwork is a kind of thermal source of formaldehyde evaporation.

The 26th page of Figure 14 of " national formaldehyde census of manufacturing report " (national formaldehyde trades council (1990.6), national formaldehyde industry collaboration group, Xinan Chemical Research Inst., Ministry of Chemical Industry compile) is the advanced at present Formaldehyde Production energy-saving technique flow process of China, as shown in Figure 1.Methyl alcohol becomes gas with air at methanol evaporator 1 internal heating, mixes according to a certain percentage with batching steam, and gas mixture enters preheater 2 heating, enters reactor 3 then oxidative dehydrogenation takes place.The reaction product temperature is up to 650 ℃, then at waste heat boiler 4 internal cooling to 200 ℃, gaseous reaction product enters interchanger 5, further be cooled to about 80 ℃, enter absorption tower 7 at last, the measure that this flow process is taked aspect UTILIZATION OF VESIDUAL HEAT IN mainly contains: 1, utilize reaction product high temperature sensible heat chilling, the vapor recovery utilization takes place in waste heat boiler; 2, utilize reaction product sensible heat or part latent heat to circulate as the methanol evaporator thermal source by a kind of heating agent (hot water etc.); 3, a small amount of water vapor condensation of bottom, absorption tower and formaldehyde solution heat are recycled.Accompanying drawing 2 is hot and cold stream match map of this technical process.The potential temperature T of expression reaction product heat release or heat absorption and corresponding thermal load Q.Figure upper right quarter broken line AB and BC represent that reaction product gas is to leave beds in the reactor 3 to the exotherm that enters before the tail gas boiler 6.To be reaction product begin to be transformed into the transformation temperature of liquid by gas to the B point, also claims dew point, is approximately 80 ℃.The lower left is each hot trap be heated potential temperature and thermal load curve among the figure.9 is water vapor evaporation at constant temperature line in the waste heat boiler 4; A last curve of 10 is a soft water intensification line in the interchanger 5, and next bar curve is the methyl alcohol evaporation line; 11 is the pre-hot lines of absorption tower 7 bottom methyl alcohol; A last curve of 12 is the warm modified line that circulating absorption solution heats up in tower and lowers the temperature in water cooler 8, and next bar curve is a water coolant intensification line in the water cooler 8.From Fig. 2 as seen, about 1/3 reaction heat does not obtain utilizing, and the potential temperature that steam takes place is also lower, thereby (available energy) rate of recovery is less relatively.The weak point of this flow process is: 1, flow process adopts secondary heat transfer evaporation methyl alcohol, and not only because of needs two cover heat transfer equipments investments are big, and damage is big; 2, the absorption tower adopts secondary to conduct heat, and conducts heat and decreases greatly, and the heat-obtaining potential temperature is low, and the latent heat of most of reaction product can't utilize, and every grade of driving force of heat transfer is all less, and recirculated cooling water and circulating absorption solution temperature rise are little, and flow is big, the power consumption height, process cost is big, and the facility investment expense is also high; 3, temperature is lower soft water directly feeds waste heat boiler, lacks the soft water preheating section, has reduced the output of steam, and the efficient of reaction product sensible heat utilization is lower; 4, impurity such as water, heavy constituent and metal or nonmetallic ion make vaporization temperature raise in the base of evaporator enrichment, cause more impurity to bring reaction bed into, by product are increased, catalyst deactivation, the lost of life.

The objective of the invention is to overcome above-mentioned weak point of the prior art, design by economic optimization, a kind of energy that makes full use of in the formaldehyde production is provided, the generation steam self-support is had a surplus and the low temperature thermal output is arranged, simultaneously, reduce the equipment that less energy-consumption Formaldehyde Production method and this method of formaldehyde unit consumption and process cost are adopted.

Characteristics of the present invention are: 1, set up the soft water preheating section that utilizes high-temperature gas reaction product soft water preheating behind the quenching waste heat boiler, make reaction product continue the cooling heat release, soft water is preheated to and 183 ℃ of the corresponding temperature of saturation of vapor pressure; 2, soft water preheating section outlet product gas is introduced the superheater shell side with its sensible heat heating methanol air Mixture; 3, the product gas of superheater shell side outlet is introduced the methanol evaporator tube side, and with its condensation latent heat and part formaldehyde solution heat, hydration heat is a thermal source evaporation methyl alcohol; 4, the formaldehyde gas product of methanol evaporator tube side outlet enters the condensation absorption tower of three sections pure counter-current absorption, the heat of condensation of being emitted and absorb heat by with the heat exchange of circulation soft water after recycle; 5, the methyl alcohol of drawing 15-25% from the methanol evaporator bottom is to the methanol rectifying tower of setting up, and this methanol rectifying tower can be industrial general rectifying tower, and cat head is only established partial condenser, makes part methanol steam condensing reflux, and product is drawn with gas phase.The high purity methanol that the methanol rectification column overhead is come out mixes with the methanol evaporator exit gas and introduces superheater; 6, set up a steam ejector between superheater and the reactor, make its supercharging with batching steam ejection methyl alcohol air Mixture.This steam ejector is industrial general injector; 7, oxidation reactor catalyst layer top is equipped with gas distribution grid.This grid distributor is industrial sieve plate commonly used, and the aperture is less than 10 millimeters.Its function also can make the rapid vaporization of the fine droplet that may carry in the gas and not cause catalyzer to produce inactivating effect except making gas along beds is evenly distributed; 8, all interchanger can use industrial general interchanger among the present invention, and especially shell and tube enhanced heat exchange device can improve heat transfer coefficient greatly, reduce pressure drop, save heat transfer area and investment.

Technical process of the present invention as shown in Figure 3.Methanol feedstock enters vaporizer 16 shell sides, utilizes the product gas condensation latent heat evaporation methyl alcohol of introducing vaporizer 16 tube sides from superheater 17 shell sides.Gaseous product sprayed an amount of product formaldehyde solution before entering vaporizer 16, the evaporation of part formaldehyde solution, make the gaseous product humidifying cooling reach 80 ℃ of dew-point temperatures, improve heat transfer coefficient by condensation heat transfer, avoid inefficient pure gas---gas transmission of heat by convection, methyl alcohol was depressed in low the branch in vaporizer 16 shell sides, 40～50 ℃ of evaporations down, take out 15～25% methyl alcohol from base of evaporator and enter methanol rectifying tower 14, the methyl alcohol air Mixture that high purity methanol that comes out from rectifying tower top and evaporator outlet come out is converged, and introduce superheater 17 tube sides simultaneously, superheater 17 is a thermal source with the sensible heat of reaction product, air methanol mixed gas is heated to 120 ℃, injector 18 makes the methyl alcohol air Mixture of coming out from superheater 17 even with the batching vapor mixing, obtains methyl alcohol, air, mixture of steam enters reactor 19, carries out the methanol oxidation dehydrogenation reaction and generates formaldehyde.The reaction product temperature is up to 640～660 ℃, the high-temperature gas reaction product is cooled to be approximately 240 ℃ rapidly in waste heat boiler 20, liberated heat is used to make the soft water evaporation to produce about 0.1MPa steam, gaseous product enters soft water preheating section 21 then, continue the cooling heat release, soft water is preheated to 183 ℃ of the corresponding temperature of saturation of vapor pressure.Then, gaseous product enters the shell side of superheater 17, enter methanol evaporator 16 tube sides again, direct thermal source as the methyl alcohol evaporation, 72 ℃ of gaseous products that come out from methanol evaporator 16 enter condensation absorption tower 22 from the tower bottom, soft water heat exchange in elder generation and the hypomere comb 28, again with stage casing coiled pipe 26 in the soft water heat exchange, soft water heat exchange in last and the epimere coiled pipe 25, temperature reduction, the continuous condensation of water vapor wherein, formaldehyde constantly dissolves in water, absorb the water counter current contact after double overflow valve tray column section 24 is filled with cold-patch, formaldehyde is fully absorbed after, insoluble gas drains into tail gas boiler combustion generation steam from cat head.A small amount of formalin that condensation is got off at the bottom of the tower uses pump 30 after 29 coolings of a water cooler, drench down from the sparger on coiled pipe top, stage casing, the solution that flows down with epimere, further absorb the formaldehyde in the rising gas phase, enrichment reaches product index 37% gradually, be collected in the liquid-collecting box 31 that riser 27 outer walls and inner wall of tower surround, draw since then and be 37% (weight) formalin product.The non-condensable gases that contains a large amount of H2 and CO enters burning in the tail gas boiler 23, produces a certain amount of water vapor.Hot and cold stream match map of the present invention as shown in Figure 4.Scheming top-right two sections broken lines is reaction product exotherms, and meaning and accompanying drawing 2 are similar.The figure lower left is each hot trap be heated potential temperature and thermal load curve.32 is the soft water evaporation line of waste heat boiler 20, and 33 is the soft water intensification line in the soft water preheating section 21, and 34 is the intensification line of methyl alcohol air Mixture in superheater 17, and 35 is the methyl alcohol evaporation line in the vaporizer 16, and 36 are circulation soft water intensification line in the condensation absorption tower 20.As seen from the figure, almost 100% reaction heat has obtained utilization, and heat-obtaining potential temperature and the rate of recovery are all higher.

The present invention compared with prior art has following advantage: the sensible heat that 1, utilizes reaction product can reduce 30～100 kilograms/ton (product) batching steam directly as the superheater thermal source; 2, utilize the methyl alcohol of gaseous reaction product condensation latent heat direct evaporation about 80%, the heat transfer area of saving the heat exchange of heating agent secondary is over half; 3, set up methanol rectifying tower, solve base of evaporator water and impurity enriched problem, it can remove the impurity that makes poisoning of catalyst, thereby prolongation life of catalyst, before also having reduced methyl alcohol unit consumption, 4, soft water and entering waste heat boiler, be preheated to 183 ℃ of the corresponding temperature of saturation of vapor pressure through preheating section, reduced damage like this, improved steam production; 5, after gas distributor is installed on reactor catalyst bed top, improve the distribution of reactant flow on the one hand at beds, on the other hand with the further preheated feed air of the reaction bed radiant heat that it was absorbed, and make under superheater temperature reduction situation, the droplets of feed that may bring into is vaporized on sparger, it is excessive to prevent to occur the material concentration part in the reaction bed effectively, has also kept activity of such catalysts, has prolonged the life-span; 6, batching steam is placed on after the superheater by the position, and adopted induction apparatus, can make methyl alcohol, air, batching vapor mixing even, and make the supercharging of batching steam ejection methyl alcohol air Mixture, remain basically stable through the pressure drop that equipment, pipeline increased with reaction product in the overall procedure; 7, condensation absorption tower change two-stage heat and mass and heat transfer are split up into the one-level heat and mass and the associating of conducting heat, and can make full use of the latent heat of most of reaction product, save a large amount of recirculated cooling waters and absorption liquid recycle pump power consumption; 8, as seen comparison diagram 2, Fig. 4 have only 9,10,11,12 3 parts to obtain recycling among Fig. 2, and 10,12 two sections to be two sections heat transfer temperature differences very little, need heat transfer area and investment very big.And 32,33,34,35,36 5 parts all are recovered utilization among Fig. 4, and promptly reaction heat almost 100% obtains recycling.

Embodiment

According to technical process of the present invention, to produce the formalin product of 50 tons speed production 37% (weight) every day.

Methyl alcohol with 197.2 kilograms/time flow velocity enter methanol rectifying tower 14, with 985.8 kilograms/time flow velocity enter methanol evaporator 16, blast air, mix with the high purity methanol that methanol rectifying tower ejects from the methyl alcohol air Mixture that methanol evaporator goes out, in superheater 17, be heated to 120 ℃, in injector 18,, form mol ratio and be 1: 1.96: 1.38 methyl alcohol, air, mixture of steam with 725 kilograms/time batching vapor mixing.This gas mixture enters the beds of reactor 19,657 ℃ of reactions down.Product gas is quenched to 236 ℃ earlier in waste heat boiler 20, take place 1130 kilograms of 0.1MPa steam/time defeated outward, in soft water preheating section 21, be cooled to 153 ℃ then, product gas enters superheater 17 heating methanol air Mixture subsequently, enter methanol evaporator 16 evaporation methyl alcohol again, product gas is cooled to 72 ℃, and final product gas enters condensation absorption tower 22, obtain 207 kilograms/time 37% (weight) formalin product.Contain a large amount of H ₂With the non-condensable gases of CO from cat head cause the tail gas boiler combustion produce 1000 kilograms of 0.4MPa steam/time (personal 960 kilograms/time, defeated 40 kilograms outward/time).Water vapor condensation and formaldehyde absorb and gas cooling heat release 660kw altogether in the absorption tower, and wherein 600kw is absorbed by two sections coiled pipes and one section comb heat exchange in the tower by 35～55 ℃ soft water, and output is supplied with other device and used.

Like this, the formaldehyde that every production is 1 ton 37% can outwards export 1170 kilograms of steam and 600kw is low warm, the cooling load and the low amounts of power that only consume 40kw.

Claims (3)

1, a kind of under the silver catalyst effect methyl alcohol and air generation oxidative dehydrogenation generate the less energy-consumption Formaldehyde Production method of formaldehyde, production process comprises: methyl alcohol evaporation, the preheating of methyl alcohol air Mixture, gas mixture react in reactor, the reaction product chilling, absorb formaldehyde, it is characterized in that:

1) gaseous product directly enters the soft water preheating section behind the waste heat boiler chilling, utilizes high-temperature gas product soft water preheating;

2) soft water preheating section outlet product gas is introduced the superheater shell side, with its sensible heat heating methanol air Mixture;

3) product gas of superheater shell side outlet is introduced the methanol evaporator tube side, is thermal source evaporation methyl alcohol with its condensation latent heat and part formaldehyde solution heat, hydration heat;

4) the formaldehyde gas product of methanol evaporator tube side outlet enters the condensation absorption tower of three sections pure counter-current absorption from the tower bottom, recycles after the heat of condensation of being emitted and absorption heat and the soft water heat exchange;

5) draw 15-25% methyl alcohol to methanol rectifying tower from methanol evaporator bottom, the high purity methanol that cat head comes out mixes with the methanol evaporator exit gas and introduces superheater;

6) the methyl alcohol air Mixture that exports by steam ejector and superheater of batching steam is mixed and is made its supercharging, enters reactor then.

2, a kind of reactor that is used for claim 1 method is characterized in that reactor catalyst layer top installs the gas distribution grid that is made of less than 10 millimeters sieve plate the aperture.

3, a kind of condensation absorption tower that is used for claim 1 method is characterized in that this tower epimere is made of double overflow valve tray column and coiled pipe, and the stage casing is made of coiled pipe and riser, and hypomere is made of comb.

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