CN109232217B - Method and device for producing formaldehyde by smoke circulation - Google Patents
Method and device for producing formaldehyde by smoke circulation Download PDFInfo
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- CN109232217B CN109232217B CN201811324867.7A CN201811324867A CN109232217B CN 109232217 B CN109232217 B CN 109232217B CN 201811324867 A CN201811324867 A CN 201811324867A CN 109232217 B CN109232217 B CN 109232217B
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- WSFSSNUMVMOOMR-UHFFFAOYSA-N Formaldehyde Chemical compound O=C WSFSSNUMVMOOMR-UHFFFAOYSA-N 0.000 title claims abstract description 387
- 238000000034 method Methods 0.000 title claims abstract description 46
- 239000000779 smoke Substances 0.000 title claims description 16
- 238000010521 absorption reaction Methods 0.000 claims abstract description 190
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims abstract description 186
- 239000007789 gas Substances 0.000 claims abstract description 145
- 239000007788 liquid Substances 0.000 claims abstract description 69
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims abstract description 35
- 239000003546 flue gas Substances 0.000 claims abstract description 32
- 239000008098 formaldehyde solution Substances 0.000 claims abstract description 24
- 239000007800 oxidant agent Substances 0.000 claims abstract description 12
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 32
- 238000001816 cooling Methods 0.000 claims description 27
- 238000004519 manufacturing process Methods 0.000 claims description 20
- 125000002485 formyl group Chemical class [H]C(*)=O 0.000 claims description 19
- 239000000047 product Substances 0.000 claims description 17
- 238000006356 dehydrogenation reaction Methods 0.000 claims description 10
- 238000000926 separation method Methods 0.000 claims description 10
- 238000005406 washing Methods 0.000 claims description 10
- 239000006227 byproduct Substances 0.000 claims description 9
- 238000007254 oxidation reaction Methods 0.000 claims description 9
- 238000004064 recycling Methods 0.000 claims description 8
- 230000003647 oxidation Effects 0.000 claims description 7
- 238000000605 extraction Methods 0.000 claims description 6
- 238000011084 recovery Methods 0.000 claims description 6
- 238000005507 spraying Methods 0.000 claims description 6
- 238000012856 packing Methods 0.000 claims description 3
- 239000001257 hydrogen Substances 0.000 abstract description 7
- 229910052739 hydrogen Inorganic materials 0.000 abstract description 7
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 abstract description 3
- WSFSSNUMVMOOMR-NJFSPNSNSA-N methanone Chemical compound O=[14CH2] WSFSSNUMVMOOMR-NJFSPNSNSA-N 0.000 abstract description 3
- 238000006243 chemical reaction Methods 0.000 description 16
- 239000003570 air Substances 0.000 description 11
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 10
- 238000006116 polymerization reaction Methods 0.000 description 7
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 6
- 239000003054 catalyst Substances 0.000 description 6
- 239000001301 oxygen Substances 0.000 description 6
- 229910052760 oxygen Inorganic materials 0.000 description 6
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 5
- 229910002092 carbon dioxide Inorganic materials 0.000 description 5
- 239000002994 raw material Substances 0.000 description 5
- 229910052709 silver Inorganic materials 0.000 description 5
- 239000004332 silver Substances 0.000 description 5
- 229910002091 carbon monoxide Inorganic materials 0.000 description 4
- 238000002485 combustion reaction Methods 0.000 description 4
- 150000002431 hydrogen Chemical class 0.000 description 4
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 4
- 238000003860 storage Methods 0.000 description 4
- 230000009286 beneficial effect Effects 0.000 description 3
- 238000004880 explosion Methods 0.000 description 3
- 239000000945 filler Substances 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- 239000011261 inert gas Substances 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 239000006096 absorbing agent Substances 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 239000001569 carbon dioxide Substances 0.000 description 2
- 238000007599 discharging Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000001914 filtration Methods 0.000 description 2
- 238000004321 preservation Methods 0.000 description 2
- 230000002035 prolonged effect Effects 0.000 description 2
- 238000002407 reforming Methods 0.000 description 2
- 239000002918 waste heat Substances 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 1
- BDAGIHXWWSANSR-UHFFFAOYSA-N Formic acid Chemical compound OC=O BDAGIHXWWSANSR-UHFFFAOYSA-N 0.000 description 1
- 230000002745 absorbent Effects 0.000 description 1
- 239000002250 absorbent Substances 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 238000006555 catalytic reaction Methods 0.000 description 1
- 238000012824 chemical production Methods 0.000 description 1
- 238000004939 coking Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 238000011049 filling Methods 0.000 description 1
- OIUSLRACRMDIAV-UHFFFAOYSA-N formaldehyde;silver Chemical compound [Ag].O=C OIUSLRACRMDIAV-UHFFFAOYSA-N 0.000 description 1
- 235000019253 formic acid Nutrition 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- DSMZRNNAYQIMOM-UHFFFAOYSA-N iron molybdenum Chemical compound [Fe].[Fe].[Mo] DSMZRNNAYQIMOM-UHFFFAOYSA-N 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000013021 overheating Methods 0.000 description 1
- 231100000572 poisoning Toxicity 0.000 description 1
- 230000000607 poisoning effect Effects 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 229920006324 polyoxymethylene Polymers 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 238000007086 side reaction Methods 0.000 description 1
- 239000008234 soft water Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- -1 steam delivery Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
- C07C45/27—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation
- C07C45/32—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen
- C07C45/37—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen of >C—O—functional groups to >C=O groups
- C07C45/38—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen of >C—O—functional groups to >C=O groups being a primary hydroxyl group
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
- B01D53/1406—Multiple stage absorption
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
- B01D53/1487—Removing organic compounds
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
- B01D53/18—Absorbing units; Liquid distributors therefor
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2257/00—Components to be removed
- B01D2257/70—Organic compounds not provided for in groups B01D2257/00 - B01D2257/602
- B01D2257/704—Solvents not covered by groups B01D2257/702 - B01D2257/7027
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Analytical Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Treating Waste Gases (AREA)
- Gas Separation By Absorption (AREA)
Abstract
The invention discloses a method and a device for producing formaldehyde by flue gas circulation, wherein the method comprises the steps of reacting in an oxidizer to generate formaldehyde, and then entering a formaldehyde absorption system; the lower circulation cavity of the first absorption tower fully absorbs the gas and liquid in a countercurrent way at a higher temperature to generate a high-concentration formaldehyde solution, and part of the formaldehyde solution is extracted as a formaldehyde finished product; the other part of the liquid is returned to the tower for circulation after the temperature of the liquid is reduced by a methanol evaporator; the formaldehyde gas which is incompletely absorbed in the lower circulation cavity enters the upper circulation cavity and is in countercurrent contact with formaldehyde in the upper circulation cavity, and after the formaldehyde which is discharged out of the lower circulation cavity is cooled by the plate cooler, part of the formaldehyde gas circulates in the tower, and the other part of formaldehyde gas overflows into the lower circulation cavity; the formaldehyde tail gas at the top of the first absorption tower enters a second absorption tower for further absorption; tail gas generated in the absorption process is treated by a tail gas treatment system. Compared with the prior art, the invention reduces the hydrogen content in the flue gas, improves the system safety, improves the formaldehyde productivity and saves the operation cost.
Description
Technical Field
The invention relates to the technical field of chemical production equipment, in particular to a method and a device for producing formaldehyde by recycling flue gas.
Background
At present, methanol is used as a raw material in the industrial formaldehyde production at home and abroad, and the production process comprises an air excess method, wherein the methanol is completely oxidized, and the method is also called an iron-molybdenum method and a methanol excess method; methanol is partially oxidatively dehydrogenated, also known as the silver process. The tail gas circulation process for silver formaldehyde production adopts tail gas led out from the formaldehyde absorption tower, and the tail gas is pressurized and heated to reenter the system for use, and the direct steam is substituted to take away the reaction heat of the oxidation reaction part, so that the consumption of the steam is reduced, and the formaldehyde concentration in the absorption liquid is improved. There are two types of silver methods: partial conversion of methanol (conversion of 78% -87% of methanol, low oxygen-alcohol ratio), heating unconverted methanol to control reaction temperature, and distilling unconverted methanol to remove formaldehyde; the other methanol is almost completely converted (the conversion rate of the methanol is 97% -98%, the ratio of high oxygen to alcohol) and gases which do not participate in the reaction, such as steam and formaldehyde tail gas, are added to control the reaction temperature, so that the formaldehyde method which almost has no methanol or a small amount of methanol is obtained, and the added steam is condensed into a product, so that only about 37% formaldehyde aqueous solution can be obtained; if the tail gas is replaced by all water vapor, the side reaction for generating carbon dioxide is increased, a small amount of water vapor is also needed, and the concentration of formaldehyde can reach more than 44 percent. In addition, the main components of formaldehyde tail gas are as follows: 18-20% of hydrogen, 0.5% of carbon monoxide, 3.5% of carbon dioxide and 0.2% of oxygen; the rest of the gas is nitrogen and a little amount of combustible gas such as methane, methanol, formaldehyde and the like, and the gas has strong pungent smell due to the existence of a little formaldehyde gas, directly discharges the gas to pollute the environment, contains a great amount of hydrogen and has great explosion hazard.
For example, a conventional formaldehyde production system (application number: 201510808769.0) including a methanol feed tank, a methanol intermediate tank, a methanol filtration tank, a methanol reboiler, a methanol evaporator, a quaternary mixer, a methanol evaporator, an air heater, a steam filter, a tail gas heater, a filter, an oxidizer, a first absorption tower, a second absorption tower, a tail gas processor, a tail gas heater, a formaldehyde intermediate tank; the system completes the following procedures of evaporation and gas production to prepare quaternary mixed gas meeting the technological requirements of the procedures; oxidation procedure: under the action of an electrolytic silver catalyst, carrying out oxidation and dehydrogenation reactions of methanol, converting the methanol into formaldehyde and generating a small amount of byproducts; absorption process: in the filler absorption tower, water and formaldehyde solution are used as absorbent, and industrial formaldehyde solution is prepared through continuous countercurrent absorption. The method can fully utilize tail gas to circularly prepare formaldehyde, and has the advantages of high raw material utilization rate and less waste.
However, the disadvantages are as follows:
1. When the temperature control of the absorption tower is low, structured packing in the tower is easy to polymerize, so that the product turns yellow, the iron content is high, the production is seriously stopped, and the packing is replaced; 2. when the temperature control of the absorption tower is high, the absorption is incomplete, so that a large amount of formaldehyde gas escapes, and the material consumption is high; 3. the hydrogen, carbon monoxide and the like in the formaldehyde tail gas can influence the conversion of the methanol, and the conversion rate of the methanol is reduced.
Disclosure of Invention
The technical task of the invention is to provide a method and a device for producing formaldehyde by recycling flue gas aiming at the defects.
The technical scheme adopted for solving the technical problems is as follows: a smoke circulating formaldehyde production device comprises a formaldehyde generation system, a formaldehyde absorption system and a tail gas treatment system; the formaldehyde absorption system comprises a first absorption tower and a second absorption tower, wherein the first absorption tower is divided into a lower circulation cavity and an upper circulation cavity; the upper and lower circulating cavities are respectively provided with efficient filler and a spraying device, and are respectively provided with an upper and a lower circulating pumps; the lower circulation cavity is positioned at the lower part of the first absorption tower; the upper circulating cavity is positioned at the middle upper part of the first absorption tower; the lower circulation cavity is connected with the product extraction outlet and the formaldehyde inlet, and the upper circulation cavity is provided with an absorption liquid inlet from the second absorption tower; the lower circulation cavity is connected with the methanol evaporator through a pipeline, and formaldehyde liquid at the outlet of the upper circulation cavity is connected with the plate cooler through a pipeline.
Further, the preferred structure is that the top of the first absorption tower is provided with a tail gas outlet, and the first absorption tower is connected with the second absorption tower through the tail gas outlet.
Further, it is preferable that the structure is,
The tail gas treatment system comprises a water seal tank, a tail gas processor, a tail gas cooling tower, a water washing circulating pump, a tail gas separator and a Roots blower; the water seal tank tail gas processor, the tail gas cooling tower, the water washing circulating pump, the tail gas separator and the Roots blower are connected in sequence;
The tail gas passage comprises that the tail gas passes through a water seal groove, enters a tail gas treatment device for combustion, and part of the combusted flue gas is exhausted after heat recovery by-product steam, and the other part of the combusted flue gas enters a tail gas cooling tower for washing and cooling, enters a tail gas separator, and the flue gas after water-gas separation is sent into a mixer by a Roots blower; and discharging condensate water obtained after the separation of the tail gas separator into a tail gas cooling tower, and recovering formaldehyde liquid in the tail gas cooling tower to a third absorption tower.
Further, it is preferable that the structure is,
The formaldehyde absorption system also comprises a third absorption tower and a bubble cap tower, wherein the third absorption tower is positioned at the upper part of the second absorption tower, and the bubble cap tower, the third absorption tower, the second absorption tower and the first absorption tower are connected in sequence; the third absorption tower and the second absorption tower are respectively provided with a circulating pump and a circulating cooler, namely a plate cooler;
Wherein the circulating path of the formaldehyde absorbing liquid is as follows: the absorption process water enters from the bubble cap tower and overflows to the bottom of the third absorption tower, the dilute aldehyde liquid generated by the third absorption tower is partially circulated in the third absorption tower by a circulating pump of the third absorption tower, and the dilute aldehyde liquid partially enters into the second absorption tower; the dilute aldehyde liquid generated by the second absorption tower is partially self-circulated in the second absorption tower by a circulating pump of the second absorption tower, and partially enters the first absorption tower; and part of formaldehyde liquid generated by the first absorption tower is taken as a finished product, and the part of formaldehyde liquid enters a methanol evaporator to heat methanol for circulation.
Further, a preferable structure is that a mutual backup pump is arranged between the upper circulating pump and the lower circulating pump; the spraying device comprises a liquid distributor and a gas-liquid distributor; the pipeline of the product extraction outlet is provided with a formaldehyde filter.
A method for producing formaldehyde by recycling flue gas includes that formaldehyde is generated in an oxidizer through oxidation and dehydrogenation of methanol, and then enters a formaldehyde absorption system;
The formaldehyde solution enters from the lower circulation cavity of the first absorption tower, the lower circulation cavity of the first absorption tower is fully circulated at a higher temperature (gas-liquid countercurrent absorption) to generate a high-concentration formaldehyde solution, and part of the formaldehyde solution is extracted as a formaldehyde finished product; the other part of the liquid is returned to the tower for circulation after the temperature of the liquid is reduced by a methanol evaporator; the formaldehyde gas which is incompletely absorbed in the lower circulation cavity enters the upper circulation cavity and is in countercurrent contact (further absorption) with formaldehyde in the upper circulation cavity, and after the formaldehyde discharged from the lower circulation cavity is cooled by the plate heat exchanger, part of the formaldehyde circulates in the tower, and the other part of the formaldehyde overflows into the lower circulation cavity; then formaldehyde tail gas at the top of the first absorption tower enters the second absorption tower for further absorption;
tail gas generated in the absorption process is treated by a tail gas treatment system.
Further, it is preferable that the method is,
The method further comprises the steps that the absorption process water enters from the bubble cap tower and overflows to the bottom of the third absorption tower, part of dilute aldehyde liquid generated by the third absorption tower is subjected to internal self-circulation through a third absorption tower circulating pump, the part of dilute aldehyde liquid enters the second absorption tower and is further subjected to internal self-circulation as absorption liquid of the second absorption tower, the part of dilute aldehyde liquid generated by the second absorption tower enters the first absorption tower and is further subjected to formaldehyde absorption as absorption liquid of the first absorption tower, the part of formaldehyde liquid generated by the first absorption tower is extracted as a finished product, and the part of formaldehyde liquid enters the methanol evaporator to heat methanol for circulation.
Further, it is preferable that the method is,
The tail gas treatment method of the tail gas treatment system comprises the steps that the tail gas which is not absorbed at the top of a bubble cap passes through a water seal groove, enters a tail gas treatment device for combustion, part of the combusted smoke is exhausted after heat recovery by-product steam, and the other part of the combusted smoke enters a tail gas cooling tower for washing and cooling, enters a tail gas separator, and the smoke after water-gas separation is sent into a mixer by a Roots blower, so that quaternary mixed gas is formed in the mixer and enters an oxidizer; and the condensed water obtained after the separation of the tail gas separator is periodically discharged into a tail gas cooling tower, and the formaldehyde concentration in the tail gas cooling tower reaches a certain concentration and is pumped into a third absorption tower.
Further, it is preferable that the method is,
The temperature in the lower circulation cavity is 65-80 ℃; the temperature in the upper circulation cavity is 30-40 ℃.
Further, it is preferable that the method is,
After the concentration of formaldehyde liquid in the tail gas cooling tower is more than 1%, recycling the formaldehyde liquid to a third absorption tower; the concentration of formaldehyde solution in the lower circulation cavity in the first absorption tower is 50% -55%; the concentration of formaldehyde solution in the circulating cavity on the first absorption tower is 30% -37%.
Compared with the prior art, the method and the device for producing the formaldehyde by using the smoke circulation have the following beneficial effects:
(1) The safety is high; the flue gas recycling method adopts the burned flue gas, the main components of the flue gas are inert gases such as nitrogen, carbon monoxide and the like, the flue gas is put into the system, and the safety is better than that of the tail gas containing about 20% of hydrogen entering the reaction system, and the flue gas does not corrode system equipment.
(2) The yield is high; in actual production, the tail gas processor (tail gas incinerator) is provided with a low-pressure head large-air-volume fan, so that the flue gas contains 5-10% of excessive oxygen. The oxygen content is increased, and the yield can be improved by 10 to 20 percent.
(3) The byproduct steam is high; the formaldehyde tail gas of the flue gas circulation process is completely combusted to generate more steam than the tail gas of the tail method, and the flue gas circulation method adopts the combusted inert gas, so that the flue gas input system does not inhibit dehydrogenation reaction because of no hydrogen, and the by-product steam is much higher than the tail method.
(4) The unit consumption is low; the tail gas contains 18-20% of H2, when the tail gas is recycled to prepare the concentrated aldehyde, the dehydrogenation reaction can be inhibited, and the burnt flue gas contains no hydrogen, so that the dehydrogenation reaction can not be influenced when the concentrated aldehyde is recycled. The main components of the flue gas are inert gases such as N2, CO2 and the like, so that the flue gas does not participate in the reaction during the conversion of methanol, and the generation of CO2, CO, CH4, HCOOH and the like can be inhibited; therefore, after the flue gas is changed, CO2 can be reduced to 2.2-2.8%, CO is reduced to 0.1-0.1%, CH4 is reduced to 0.1-0.2%, and the total amount of methanol can be saved by 8-10 kg/t. Calculated by a formaldehyde production line of 6 ten thousand tons/year: 600 tons of methanol can be saved each year, and 180 ten thousand yuan of operation cost can be saved each year according to 3100 yuan per ton of formaldehyde.
(5) The No. 1 absorption tower is reformed into independent circulation from top to bottom, the temperature of the lower part is high, the concentration of formaldehyde in the absorption tower is high, and the polymerization phenomenon of high-concentration formaldehyde in the absorption tower is avoided; the upper temperature is low, the formaldehyde concentration in the tower is low, the polymerization phenomenon in the plate cooler can be reduced, and the absorption efficiency is improved as a whole;
(6) The load of the second absorption tower is effectively lightened, and the concentration of formaldehyde liquid in the second absorption tower is effectively reduced, so that the aldehyde content in tail gas is reduced, the operation period of the device is prolonged, and the productivity is improved.
Drawings
The invention is further described below with reference to the accompanying drawings.
FIG. 1 is a flow chart of a portion of the recycle tail gas;
FIG. 2 is a flow diagram of a reforming section of an absorber;
FIG. 3 is a flow chart of a method for producing formaldehyde by recycling flue gas.
Wherein, A101 is an absorption tower I; a102, a second absorption tower; a103, a third absorption tower; b101 is a circulating pump of the first absorption tower; b102, a circulating pump of the second absorption tower; b103 is a circulating pump of a third absorption tower; e101, an absorption tower plate cooler (plate cooler); e102, a plate cooler of a second absorption tower; e103, a third absorption tower plate type cooler; c101, an evaporator; d101: a bubble column; v101: a water seal groove; v102: a tail gas separator; v103: a formaldehyde separator; v108: a cold soft water elevated tank; f101: a tail gas treatment device; t101: a tail gas cooling tower; p101: a water washing circulation pump; B101I is an upper circulating pump; b101 II is a lower circulating pump; b101 III, mutual backup pump.
Detailed Description
The invention will be further described with reference to the drawings and the specific examples.
The invention is a method for producing formaldehyde by smoke gas circulation and its apparatus, methanol is pressurized from methanol metering tank through methanol pump, after the flow is controlled by regulating valve, it enters the bottom of methanol evaporator, methanol in the methanol evaporator and air sent by Roots blower are mixed into binary mixed gas in mixer, then a certain quantity of saturated steam and tail gas are added to prepare quaternary mixed gas with a certain concentration ratio, the quaternary mixed gas is sent into superheater, heated to 110 deg.C indirectly by steam, and passed through fire-retarding device, and then sent into four-element gas filter, and then sent into oxidizer with catalyst (silver catalysis), and passed through catalyst layer from top to bottom, oxidation and dehydrogenation reactions of methanol are simultaneously carried out at 630 deg.C, the produced gas is quickly quenched (to 150 deg.C) by quenching section (waste heat recovery) of oxidizer, then sent into absorber for absorption operation.
The formaldehyde solution enters from the lower circulation cavity of the first absorption tower, the lower circulation cavity of the first absorption tower is fully circulated at a higher temperature to generate a high-concentration formaldehyde solution, and part of the formaldehyde solution is extracted as a formaldehyde finished product; the other part of the liquid is returned to the tower for circulation after the temperature of the liquid is reduced by a methanol evaporator; the formaldehyde gas which is incompletely absorbed in the lower circulation cavity enters the upper circulation cavity and is in countercurrent contact with formaldehyde in the upper circulation cavity, and after the formaldehyde which is discharged out of the lower circulation cavity is cooled by the plate cooler, part of the formaldehyde gas circulates in the tower, and the other part of formaldehyde gas overflows into the lower circulation cavity; the formaldehyde tail gas at the top of the first absorption tower enters a second absorption tower for further absorption; and (5) carrying out smoke circulation treatment on tail gas generated in the absorption process.
Example 1:
a smoke circulating formaldehyde production device comprises a formaldehyde generation system, a formaldehyde absorption system and a tail gas treatment system; the formaldehyde generating system has mature technology, and comprises the operation processes of methanol, air, tail gas, steam delivery, gas mixture preparation, gas overheating, filtration, fire resistance and the like. Delivery of methanol: the purpose of the methanol delivery is to continuously and stably supply methanol to the methanol evaporator; the methanol is delivered by a centrifugal pump. Delivery of air: the purpose of air delivery is to continuously and stably provide the needed oxygen for the methanol oxidation reaction, and simultaneously remove redundant reaction heat by utilizing components such as nitrogen in the air; air is taken from the atmosphere by a blower. Flue gas transportation: the purpose of flue gas transportation is three. First, instead of steam, it acts as a heat carrier; secondly, the addition of part of flue gas reduces the explosion range of methanol in the air, which is beneficial to safe production; thirdly, because the components of the flue gas are unique, the concentrated formaldehyde can be produced, the dehydrogenation reaction is inhibited, the oxygen temperature is reduced, and the negative reaction is reduced, so that the unit consumption is reduced. Delivery of water vapor: the purpose of the steam transmission is three, namely, the steam transmission plays a role of a heat carrier, reduces the explosion range of methanol in the mixed gas, is beneficial to safe production, can prevent the occurrence of a coking reaction, cleans a silver catalytic bed, and prolongs the service life of a catalyst; the batching vapor is supplied by the byproduct vapor of the system waste heat.
Preparing a raw material mixed gas: the purpose of preparing raw material gas with a certain proportion by methanol-air-water vapor according to the technological requirement is to ensure the composition ratio of methanol, air and water vapor so as to meet the requirements of the reaction process and the safe production. And (3) superheating operation: the task of the superheating operation is to control the temperature of the quaternary mixture before it enters the oxidizer, preventing the creation of droplets, in order to preserve the activity of the catalyst. The control of the superheat temperature is achieved by indirectly heating the quaternary gas with steam. In order to remove harmful substances in raw materials and prevent catalyst poisoning from losing activity, the quaternary mixed gas is purified by passing quaternary gas through a filter to remove solid impurities entrained in the gas. Specific processes for the oxidation and dehydrogenation of formaldehyde from the oxidizer are described in reference to the process formaldehyde production system (application number: 201510808769.0).
The formaldehyde absorption system comprises a first absorption tower, a second absorption tower, a third absorption tower and a bubble cap tower, wherein the third absorption tower is positioned at the upper part of the second absorption tower, and the bubble cap tower, the third absorption tower, the second absorption tower and the first absorption tower are connected in sequence; the third absorption tower and the second absorption tower are respectively provided with a circulating pump and a plate cooler; the first absorption tower is divided into a lower circulation cavity and an upper circulation cavity; the upper and lower circulating cavities are respectively provided with efficient filling and spraying devices, and the spraying devices comprise liquid distributors and gas-liquid distributors; the upper and lower circulating cavities are respectively provided with an upper and lower circulating pump; a mutual backup pump is arranged between the upper circulating pump and the lower circulating pump; the lower circulation cavity is positioned at the lower part of the first absorption tower; the upper circulating cavity is positioned at the middle upper part of the first absorption tower; the lower circulation cavity is connected with a product extraction outlet and a formaldehyde inlet, and a formaldehyde filter is arranged on a pipeline of the product extraction outlet. The upper circulation cavity is provided with an absorption liquid inlet from the second absorption tower; the lower circulation cavity is connected with the methanol evaporator through a pipeline, and the upper circulation cavity is connected with the plate cooler through a pipeline. The top of the first absorption tower is provided with a tail gas outlet, and the first absorption tower is connected with the second absorption tower through the tail gas outlet.
The bubble cap tower is a plate tower with bubble caps as gas-liquid contact elements on the tray, and the tray mainly comprises a tray plate with a plurality of bubble caps and air risers, an overflow weir, a liquid receiving tray and a downcomer. Liquid passes from the upper tray through the downcomer, across the tray via the bubble cap, and into the downcomer via the weir. Steam enters the riser of the bubble cap from bottom to top, is dispersed into the liquid layer between the bubble caps through the tooth gaps of the bubble caps, and is fully contacted with the liquid.
The tail gas treatment system comprises a water seal tank, a tail gas processor, a tail gas cooling tower, a water washing circulating pump, a tail gas separator and a Roots blower; the water seal tank tail gas processor, the tail gas cooling tower, the water washing circulating pump, the tail gas separator and the Roots blower are connected in sequence;
The tail gas passage comprises that the tail gas passes through a water seal groove, enters a tail gas treatment device for combustion, and part of the combusted flue gas is exhausted after heat recovery by-product steam, and the other part of the combusted flue gas enters a tail gas cooling tower for washing and cooling, enters a tail gas separator, and the flue gas after water-gas separation is sent into a mixer by a Roots blower; and discharging condensate water obtained after the separation of the tail gas separator into a tail gas cooling tower, and recovering formaldehyde liquid in the tail gas cooling tower to a third absorption tower.
Wherein the circulating path of the formaldehyde absorbing liquid is as follows: the absorption process water enters from the bubble cap tower and overflows to the bottom of the third absorption tower, the dilute aldehyde liquid generated by the third absorption tower is partially circulated in the third absorption tower by a circulating pump of the third absorption tower, and the dilute aldehyde liquid partially enters into the second absorption tower; the dilute aldehyde liquid generated by the second absorption tower is partially self-circulated in the second absorption tower by a circulating pump of the second absorption tower, and partially enters the first absorption tower; and part of formaldehyde liquid generated by the first absorption tower is taken as a finished product, and the part of formaldehyde liquid enters a methanol evaporator to heat methanol for circulation.
A method for producing formaldehyde by recycling flue gas includes that formaldehyde is generated in an oxidizer through oxidation and dehydrogenation of methanol, and then enters a formaldehyde absorption system; the method further comprises the steps that the absorption process water enters from the bubble cap tower and overflows to the bottom of the third absorption tower, part of dilute aldehyde liquid generated by the third absorption tower is subjected to internal self-circulation through a third absorption tower circulating pump, the part of dilute aldehyde liquid enters the second absorption tower and is further subjected to internal self-circulation as absorption liquid of the second absorption tower, the part of dilute aldehyde liquid generated by the second absorption tower enters the first absorption tower and is further subjected to formaldehyde absorption as absorption liquid of the first absorption tower, the part of formaldehyde liquid generated by the first absorption tower is extracted as a finished product, and the part of formaldehyde liquid enters the methanol evaporator to heat methanol for circulation.
Because the preservation temperature of the formaldehyde solution is 5-8 ℃ higher than the concentration percentage value of the formaldehyde solution, and the formaldehyde solution with the concentration percentage value of 55% is preserved at the temperature of more than 60 ℃, the precipitation of formaldehyde solution polymers can be slowed down, so that the structure of a first absorption tower is improved, the whole of the first absorption tower is lifted, a section of tower body (filled with efficient filler, a liquid distributor and a gas-liquid distributor) is added at the lower section of the tower in a dividing way, and the lower circulation of the absorption tower is increased; the No. 1 absorption tower is changed into two-section circulation, the lower circulation is only used for heating a methanol evaporator and extracting products, about 50% of high-concentration formaldehyde does not pass through a plate cooler, the high-concentration formaldehyde in the tower bottom is continuously pumped and circulated by a No. 1 absorption tower bottom pump, the high-concentration formaldehyde is extracted to a finished product tank when the liquid level is high, the formaldehyde polymerization phenomenon in the No. 1 absorption tower is stopped by reforming because the temperature of the No. 1 absorption tower bottom is about 75 ℃ and is higher than the critical polymerization temperature of formaldehyde, the incomplete formaldehyde gas absorbed by the tower bottom enters the middle part and the upper part of the No. 1 absorption tower to be further absorbed, the formaldehyde content of the upper part of the No. 1 absorption tower is about 30%, the polymerization phenomenon can not occur as long as the formaldehyde polymerization temperature is higher than the formaldehyde polymerization temperature in the plate cooler, the temperature of the tower top of the No. 1 absorption tower can be reduced to be lower as possible, the absorption efficiency is increased, the load of the No. 2 absorption tower is lightened, the running period of the device is prolonged, and the productivity is improved.
Wherein the temperature in the lower circulation cavity is 65-80 ℃, and the temperature is optimally 75 ℃ when the lower circulation cavity is used as about 50% formaldehyde solution; the temperature in the upper circulation cavity is 30-40 ℃; the concentration of formaldehyde solution in the upper circulation cavity is about 30%, and the optimal temperature is 35 ℃; after the high-concentration formaldehyde solution is usually extracted, a storage tank for storing the high-concentration formaldehyde solution is used for integral heat preservation and heat tracing at the bottom. Hot water with the temperature of more than 70 ℃ is usually used as a heat source, so that the temperature in a storage tank can be kept at about 60 ℃, a stirring device is required to be arranged on the storage tank, the formaldehyde solution in the storage tank is ensured to be in a flowing state, and local cold spots are avoided to generate polyformaldehyde.
The tail gas treatment method of the tail gas treatment system comprises the steps that the tail gas which is not absorbed at the top of a bubble cap passes through a water seal groove, enters a tail gas treatment device for combustion, part of the combusted smoke is exhausted after heat recovery by-product steam, and the other part of the combusted smoke enters a tail gas cooling tower for washing and cooling, enters a tail gas separator, and the smoke after water-gas separation is sent into a mixer by a Roots blower, so that quaternary mixed gas is formed in the mixer and enters an oxidizer; and the condensate water obtained after the separation of the tail gas separator is periodically discharged into a tail gas cooling tower, and the condensate water is recycled to the third absorption tower after the concentration of formaldehyde liquid in the tail gas cooling tower is more than 1%.
The present invention can be easily implemented by those skilled in the art through the above specific embodiments. It should be understood that the invention is not limited to the particular embodiments described above. Based on the disclosed embodiments, a person skilled in the art may combine different technical features at will, so as to implement different technical solutions.
Claims (2)
1. A method for producing formaldehyde by flue gas circulation is characterized in that formaldehyde is generated in an oxidizer through oxidation and dehydrogenation of methanol and then enters a formaldehyde absorption system;
Entering from the lower circulation cavity of the first absorption tower, fully circulating at 65-80 ℃ in the lower circulation cavity of the first absorption tower to generate high-concentration formaldehyde solution, and extracting a part of formaldehyde as a formaldehyde finished product; the other part of the liquid is returned to the tower for circulation after the temperature of the liquid is reduced by a methanol evaporator; the formaldehyde gas which is incompletely absorbed in the lower circulation cavity enters the upper circulation cavity, the upper circulation cavity further absorbs the formaldehyde gas at the temperature of 30-40 ℃, and then the formaldehyde tail gas at the top of the first absorption tower enters the second absorption tower for further absorption; tail gas generated in the absorption process is treated by a tail gas treatment system,
The upper and lower circulating cavities of the first absorption tower are respectively provided with efficient packing and a spraying device, and the upper and lower circulating cavities are respectively provided with an upper and lower circulating pump; the lower circulation cavity is positioned at the lower part of the first absorption tower; the upper circulating cavity is positioned at the middle upper part of the first absorption tower; the lower circulation cavity is connected with the product extraction outlet and the formaldehyde inlet, and the upper circulation cavity is provided with an absorption liquid inlet from the second absorption tower; the lower circulation cavity is connected with the methanol evaporator through a pipeline, and the upper circulation cavity is connected with the plate cooler;
the absorption process water enters from the bubble cap tower and overflows to the bottom of the third absorption tower, part of dilute aldehyde liquid generated by the third absorption tower is subjected to internal self-circulation through a third absorption tower circulating pump, part of dilute aldehyde liquid enters into the second absorption tower to be further subjected to formaldehyde absorption as absorption liquid of the second absorption tower, part of dilute aldehyde liquid generated by the second absorption tower is subjected to internal self-circulation through a second absorption tower circulating pump, part of dilute aldehyde liquid enters into the first absorption tower to be further subjected to formaldehyde absorption as absorption liquid of the first absorption tower,
The third absorption tower is positioned at the upper part of the second absorption tower, and the third absorption tower and the second absorption tower are respectively provided with a circulating pump and a circulating cooler;
The tail gas treatment method of the tail gas treatment system comprises the following steps: the tail gas which is not absorbed at the top of the bubble cap is combusted by a water seal groove and enters a tail gas treatment device, a part of combusted smoke is exhausted after heat recovery by-product steam, a part of combusted smoke enters a tail gas cooling tower, after washing and cooling, the combusted smoke enters a tail gas separator, the gas is sent into a mixer by a Roots blower after water-gas separation, and quaternary mixed gas is formed in the mixer and enters an oxidizer; condensed water obtained after the separation of the tail gas separator is periodically discharged into a tail gas cooling tower, and the formaldehyde concentration in the tail gas cooling tower reaches a certain concentration and then is pumped into a third absorption tower;
After the concentration of formaldehyde liquid in the tail gas cooling tower is more than 1%, recycling the formaldehyde liquid to a third absorption tower; the concentration of formaldehyde solution in the lower circulation cavity in the first absorption tower is 50% -55%; the concentration of formaldehyde solution in the circulating cavity on the first absorption tower is 30% -37%.
2. The method for producing formaldehyde by flue gas circulation according to claim 1, wherein a mutual backup pump is arranged between the upper circulation pump and the lower circulation pump; the spraying device comprises a liquid distributor and a gas-liquid distributor; the pipeline of the product extraction outlet is provided with a formaldehyde filter.
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