CN116496225A - Melamine production method and equipment - Google Patents
Melamine production method and equipment Download PDFInfo
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- CN116496225A CN116496225A CN202210072095.2A CN202210072095A CN116496225A CN 116496225 A CN116496225 A CN 116496225A CN 202210072095 A CN202210072095 A CN 202210072095A CN 116496225 A CN116496225 A CN 116496225A
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- gas
- melamine
- reactor
- fluidized bed
- bed
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- 229920000877 Melamine resin Polymers 0.000 title claims abstract description 125
- JDSHMPZPIAZGSV-UHFFFAOYSA-N melamine Chemical compound NC1=NC(N)=NC(N)=N1 JDSHMPZPIAZGSV-UHFFFAOYSA-N 0.000 title claims abstract description 125
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 28
- 238000000034 method Methods 0.000 claims abstract description 33
- 239000003054 catalyst Substances 0.000 claims abstract description 28
- 238000002425 crystallisation Methods 0.000 claims abstract description 28
- 230000008025 crystallization Effects 0.000 claims abstract description 28
- 238000006555 catalytic reaction Methods 0.000 claims abstract description 22
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 claims abstract description 21
- 239000004202 carbamide Substances 0.000 claims abstract description 21
- 239000000463 material Substances 0.000 claims abstract description 18
- 238000006243 chemical reaction Methods 0.000 claims abstract description 9
- 230000003197 catalytic effect Effects 0.000 claims abstract description 7
- 239000000843 powder Substances 0.000 claims abstract description 4
- 239000007789 gas Substances 0.000 claims description 162
- 239000007787 solid Substances 0.000 claims description 38
- 239000002245 particle Substances 0.000 claims description 31
- 238000000926 separation method Methods 0.000 claims description 25
- 239000007788 liquid Substances 0.000 claims description 23
- 238000004062 sedimentation Methods 0.000 claims description 19
- 210000002700 urine Anatomy 0.000 claims description 19
- 238000001816 cooling Methods 0.000 claims description 17
- 239000012159 carrier gas Substances 0.000 claims description 16
- 238000005406 washing Methods 0.000 claims description 14
- 239000000047 product Substances 0.000 claims description 11
- 230000000630 rising effect Effects 0.000 claims description 10
- 238000005243 fluidization Methods 0.000 claims description 9
- 238000009826 distribution Methods 0.000 claims description 8
- 238000005192 partition Methods 0.000 claims description 8
- 238000009833 condensation Methods 0.000 claims description 7
- 230000005494 condensation Effects 0.000 claims description 7
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 6
- 238000004321 preservation Methods 0.000 claims description 6
- 150000003839 salts Chemical class 0.000 claims description 6
- 238000001704 evaporation Methods 0.000 claims description 4
- ZFSLODLOARCGLH-UHFFFAOYSA-N isocyanuric acid Chemical compound OC1=NC(O)=NC(O)=N1 ZFSLODLOARCGLH-UHFFFAOYSA-N 0.000 claims description 4
- 239000000126 substance Substances 0.000 claims description 4
- 150000001408 amides Chemical class 0.000 claims description 3
- 150000001412 amines Chemical class 0.000 claims description 3
- 229910021529 ammonia Inorganic materials 0.000 claims description 3
- 239000013067 intermediate product Substances 0.000 claims description 3
- 239000008247 solid mixture Substances 0.000 claims description 3
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims description 2
- 239000013078 crystal Substances 0.000 claims description 2
- 239000003546 flue gas Substances 0.000 claims description 2
- 238000010438 heat treatment Methods 0.000 claims description 2
- 239000012948 isocyanate Substances 0.000 claims description 2
- 150000002513 isocyanates Chemical class 0.000 claims description 2
- 230000000149 penetrating effect Effects 0.000 claims description 2
- 239000000203 mixture Substances 0.000 claims 1
- 238000005265 energy consumption Methods 0.000 abstract description 5
- 239000006227 byproduct Substances 0.000 description 11
- 238000010791 quenching Methods 0.000 description 7
- 230000000171 quenching effect Effects 0.000 description 7
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 4
- 238000010586 diagram Methods 0.000 description 4
- 239000000741 silica gel Substances 0.000 description 4
- 229910002027 silica gel Inorganic materials 0.000 description 4
- 230000005611 electricity Effects 0.000 description 3
- OWIKHYCFFJSOEH-UHFFFAOYSA-N Isocyanic acid Chemical compound N=C=O OWIKHYCFFJSOEH-UHFFFAOYSA-N 0.000 description 2
- XLJMAIOERFSOGZ-UHFFFAOYSA-N anhydrous cyanic acid Natural products OC#N XLJMAIOERFSOGZ-UHFFFAOYSA-N 0.000 description 2
- 238000004140 cleaning Methods 0.000 description 2
- 238000007599 discharging Methods 0.000 description 2
- 239000010419 fine particle Substances 0.000 description 2
- 229910001220 stainless steel Inorganic materials 0.000 description 2
- 238000000859 sublimation Methods 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 229910000831 Steel Inorganic materials 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000003889 chemical engineering Methods 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 238000002309 gasification Methods 0.000 description 1
- 239000000499 gel Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000002808 molecular sieve Substances 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 230000008022 sublimation Effects 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07D—HETEROCYCLIC COMPOUNDS
- C07D251/00—Heterocyclic compounds containing 1,3,5-triazine rings
- C07D251/02—Heterocyclic compounds containing 1,3,5-triazine rings not condensed with other rings
- C07D251/12—Heterocyclic compounds containing 1,3,5-triazine rings not condensed with other rings having three double bonds between ring members or between ring members and non-ring members
- C07D251/26—Heterocyclic compounds containing 1,3,5-triazine rings not condensed with other rings having three double bonds between ring members or between ring members and non-ring members with only hetero atoms directly attached to ring carbon atoms
- C07D251/40—Nitrogen atoms
- C07D251/54—Three nitrogen atoms
- C07D251/56—Preparation of melamine
- C07D251/60—Preparation of melamine from urea or from carbon dioxide and ammonia
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
- B01J8/02—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with stationary particles, e.g. in fixed beds
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
- B01J8/18—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles
- B01J8/24—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles according to "fluidised-bed" technique
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07D—HETEROCYCLIC COMPOUNDS
- C07D251/00—Heterocyclic compounds containing 1,3,5-triazine rings
- C07D251/02—Heterocyclic compounds containing 1,3,5-triazine rings not condensed with other rings
- C07D251/12—Heterocyclic compounds containing 1,3,5-triazine rings not condensed with other rings having three double bonds between ring members or between ring members and non-ring members
- C07D251/26—Heterocyclic compounds containing 1,3,5-triazine rings not condensed with other rings having three double bonds between ring members or between ring members and non-ring members with only hetero atoms directly attached to ring carbon atoms
- C07D251/40—Nitrogen atoms
- C07D251/54—Three nitrogen atoms
- C07D251/62—Purification of melamine
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Engineering & Computer Science (AREA)
- Combustion & Propulsion (AREA)
- Phenolic Resins Or Amino Resins (AREA)
Abstract
A process for the production of melamine comprising the steps of: the urea reacts in a fluidized bed reactor, wherein the reaction temperature is about 390 ℃ and the pressure is 0.25-2.2 MPa; the melamine material gas at about 390 ℃ which comes out of the reactor directly enters a hot gas filter to remove catalyst fine powder; clean gas from the hot gas filter is subjected to fixed bed catalytic reaction; and (3) carrying out circulating fluidized bed melamine crystallization on the gas at the temperature of about 390 ℃ obtained through the fixed bed catalytic reaction. Also comprises a catalytic reactor of equipment for producing melamine and a circulating fluidized bed melamine crystallizer. Compared with the prior art, the optimized circulating fluidized bed crystallizer avoids the cyclone separator wall in the accompanying bed, can run for a long period, solves the problems of high gas circulation amount, high energy consumption and further large-scale restriction of the existing device, provides high-pressure tail gas, and ensures that the tail gas co-production urea has low energy consumption, simple flow and low equipment investment.
Description
Technical Field
The invention relates to the field of chemical engineering, in particular to a production process and equipment of melamine.
Background
Melamine production is an important process in the chemical industry. The current production process with less investment and lower energy consumption is a low-pressure gas-phase quenching method as shown in figure 1. The melamine material gas from the fluidized bed reactor 1 enters a gas-phase quenching crystallizer 4 after passing through a hot gas cooler 2 and a hot gas filter 3, meets circulating cold gas, is quenched and separated out in a crystallization state, and passes through a finished cyclone 5 to obtain a final product. The process gas after separating out melamine is boosted by a cold air blower 6 and enters a liquid urine washing tower 7, the melamine which is not crystallized and separated and the unreacted isocyanic acid are washed and recovered, and the isocyanic acid is cooled and reacts with ammonia in the process gas to generate urea. The process gas from the liquid urine washing tower 7 passes through the gas-liquid separator 8, and the discharged gas is divided into three paths: one path of the gas-phase-removing quenching crystallizer 4 is used as circulating cold air, the other path of the gas-phase-removing quenching crystallizer is compressed by a carrier gas compressor 11 to be used as circulating carrier gas of the fluidized bed reactor 1, and the other path of the gas-phase-removing quenching crystallizer is used as tail gas-removing treatment device.
Fig. 2 is a schematic view of the melamine production process of patent CN95104455.9, which, although reducing the gas circulation and reducing the energy consumption, does not solve the problem of fouling of the hot gas cooler 2.
Disclosure of Invention
The invention aims to solve the technical problems that:
1. the gas circulation quantity is large, and the electricity consumption is high; the crystallizer can not produce byproduct steam, and low-grade steam with the byproduct of about 120 ℃ in the urine washing tower is not utilized, so that heat is wasted; the hot gas cooler 2 has the advantages of wall formation, short operation period, one on-one standby, large manual cleaning workload for periodic switching, cleaning in a thermal state, shell side temperature of over 300 ℃ and serious safety accidents caused by excessive generation, and the hot gas cooler 2 has the function of cooling and crystallizing and separating unreacted and completely high-sublimation point products in melamine material gas.
2. The melamine production process of the patent CN95104455.9 also has the defect that cyclone separators in a circulating fluidized bed crystallizer concomitant bed (cooling bed) can be blocked and cannot run for a long period; the main process gas of the main bed (crystallization bed) has large resistance, the solid circulation amount is limited, the temperature of byproduct steam is low, and the utilization of the steam is limited; the patent currently has no problems with industrial equipment.
In order to solve the problems, a method and equipment for producing melamine are provided.
The object of the invention is achieved in the following way:
a process for the production of melamine comprising the steps of:
(1) The urea reacts in a fluidized bed reactor, wherein the reaction temperature is about 390 ℃ and the pressure is 0.25-2.2 MPa;
(2) The melamine material gas at about 390 ℃ which comes out of the reactor directly enters a hot gas filter to remove catalyst fine powder;
(3) The clean gas from the hot gas filter is subjected to fixed bed catalytic reaction, so that intermediate products of isocyanate and melamine which are not completely reacted, namely cyanuric acid, miller amine and amide substances are further reacted to generate melamine;
(4) The method for crystallizing the melamine in the circulating fluidized bed by using the gas at the temperature of about 390 ℃ obtained by the fixed bed catalytic reaction comprises the following steps: in the columnar space, the middle part of the cross section of the columnar space is provided with rising fluidizing gas, the rising fluidizing gas is firstly mixed with gas at about 390 ℃ obtained by catalytic reaction of a fixed bed through cooling to crystallize and separate melamine, the crystallized melamine is mixed with the rising fluidizing gas and cooled after sinking along the periphery of the columnar space, then mixed with gas at about 390 ℃ obtained by catalytic reaction of the fixed bed to crystallize melamine, the crystallized melamine is mixed with the rising fluidizing gas and cooled after sinking along the periphery of the columnar space, meanwhile, part of the melamine after crystallization continuously rises and settles along with air flow in a heat-preserving state, the settled melamine crystals are mixed with the rising fluidizing gas and cooled after sinking along the periphery of the columnar space, and the settled process gas is discharged from the top of the columnar space and melamine products are discharged from the periphery of the lower part of a melamine crystallization area according to circulation;
(5) The process gas discharged from the top of the columnar space in the step (4) is divided into two paths: one path of compressed gas is compressed by a carrier gas compressor, one path of compressed gas is used as the fluidizing gas of the fluidized bed reactor, the second path of compressed gas is used as the atomizing gas of the liquid urine feeding nozzle of the reactor, and the other path of compressed gas enters a liquid urine washing tower for washing and cooling; gas from the liquid urine washing tower is separated into two paths after gas-liquid separation: one way is boosted by a cold air fan to be used as fluidizing gas of a circulating fluidized bed melamine crystallizer, and the other way is used as tail gas of melamine reaction to be discharged into a tail gas utilization device, and especially when the system pressure is about 1.8MPa, the tail gas can be directly sent into a medium-pressure condenser of a urea device to be condensed, and the condensation heat is used for evaporating urea solution.
The melamine in the step (4) is crystallized and separated out, and enters into circulating melamine solid particles, the upward flowing gas-solid mixture passes through a gas-solid sedimentation separation section at the upper part, most of the solid particles are separated from gas, and the separated solid particles flow downwards along the inner wall of the cylinder body to the outer side of a lower guide cylinder, enter into the lower part of a heat exchanger, and flow upwards together with the fluidized gas at the bottom to form the circulation of the solid particles; the gas from the upper separation section enters a two-stage cyclone separator connected in series in a jacket to further separate melamine solid particles, the separated solid particles return to the barrel of the sedimentation separation section, flow downwards into the outer side of a lower guide barrel along the inner wall of the barrel, enter the lower part of a heat exchanger, discharge melamine products through a discharge port on the side surface of the lower barrel of the crystallizer and maintain the stability of the material level, and the outlet temperature of process gas can be controlled by adjusting the pressure of byproduct steam of the circulating fluidized bed crystallizer or adjusting the quantity of bottom fluidization gas.
In the step (4), a fluidizing gas distributor is arranged at the bottom of the circulating fluidized bed melamine crystallizer, the entering fluidizing gas enables melamine solid particles in the bed to be in a fluidized state, a heat exchange tube bundle is arranged above the distributor to form a cooling bed, a plurality of material gas inlet tubes are arranged above the heat exchange tube bundle to form a crystallization bed, concentric guide cylinders are arranged on the cooling bed and the crystallization bed section to form a solid particle circulation loop, a discharge port is arranged on an outer cylinder of the crystallization section, and a gas-solid sedimentation separation section and a cyclone separator are arranged on the upper part of the outer cylinder of the crystallization section.
The fixed bed catalytic reaction device is a fixed bed catalytic reactor, the fixed bed catalytic reactor comprises a columnar tank body, the columnar tank body is divided into three parts by two layers of partition boards, the upper part is a mixed gas cabin before catalysis, the lower part is a mixed gas cabin after catalysis, the middle part is a catalyst cabin, an upper partition board is provided with an air inlet screen pipe downwards to extend into the catalyst cabin, a lower partition board is provided with an air outlet screen pipe to extend into the catalyst cabin, the mixed gas cabin before catalysis is provided with a mixed gas inlet, the mixed gas cabin after catalysis is provided with a mixed gas outlet, the upper partition board is provided with a catalyst feeding pipe, and the catalyst cabin is provided with a catalyst discharging pipe.
The circulating fluidized bed melamine crystallization equipment comprises a columnar tank body, wherein a fluidization airflow nozzle is arranged in the middle of the cross section of the bottom of the columnar tank body, a concentric guide cylinder is arranged at the periphery of the fluidization airflow nozzle, a cooling heat exchanger is arranged at the lower part in the guide cylinder, a melamine hot gas inlet pipe penetrating through an inner cylinder and an outer cylinder is arranged on the side wall of the upper tank body of the cooling heat exchanger, gas at about 390 ℃ from a fixed bed catalytic reactor enters the guide cylinder from the hot gas inlet pipe, a crystallization separation area of melamine mixed gas is arranged at the upper part of the hot gas inlet pipe, a sedimentation area is arranged at the upper part of the crystallization separation area, the sedimentation area is positioned above the guide cylinder, a hot air jacket heat preservation layer is arranged outside the tank of the sedimentation area, and an inlet and an outlet of a heat preservation medium are arranged on the jacket heat preservation layer; the bottom of the tank body and the fluidization gas nozzle are arranged, the diameter of the tank body is reduced, and the side wall of the tank body forms a diversion surface.
The circulating fluidized bed melamine crystallization equipment is characterized in that a cyclone separator is arranged in the jacket heat-insulating layer, an inlet of the cyclone separator is communicated with an outlet at the top of the tank body, an air outlet of the cyclone separator is connected with an outlet main pipe, a lower material leg of the cyclone separator is positioned in the jacket heat-insulating layer, the lower material leg is communicated with the tank body through a wing valve, and a melamine product outlet is arranged on the side surface of a lower barrel of the tank body; the cyclone separators arranged in the jacket heat-insulating layer are connected in series to form a group, and a plurality of groups of cyclone separators are connected in parallel according to the size of the device.
The method can also be used for other process devices for producing melamine by reacting urea in a gas fluidized bed reactor (such as a fluidized bed with pure ammonia as circulating carrier gas).
The gas entering the carrier gas compressor is directly from the outlet of the circulating fluidized bed melamine crystallizer.
The gas from the carrier gas compressor can be preheated by molten salt, flue gas of a molten salt furnace or other heating modes and then enters the reactor.
Compared with the prior art, the invention provides a melamine production method and equipment, which have the advantages of small gas circulation amount, low pressure, energy consumption saving, catalyst removal firstly, and then continuous reaction of byproducts to generate melamine, so that the phenomenon that the product with complete unreacted high sublimation point in melamine material gas is cooled and crystallized to separate out is avoided.
Drawings
FIG. 1 is a schematic diagram of a prior art melamine production process.
Fig. 2 is a schematic diagram of the melamine production process of patent CN 95104455.9.
Fig. 3 is a schematic view of the melamine production process according to the invention.
Fig. 4 is a schematic diagram of a fixed bed reactor required for the melamine production process of the present invention.
Fig. 5 is a schematic view of a circulating fluidized bed melamine crystallizer required for the inventive melamine production process.
Wherein, 1, a fluidized bed reactor; 2. a hot gas cooler; 3. a hot gas filter; 4. a gas-phase quenching crystallizer; 5. a finished cyclone separator; 6. a cold air blower; 7. a liquid urine washing tower; 8. a gas-liquid separator; 9. a liquid urine storage tank; 10. a liquid urine circulation pump; 11. a carrier gas compressor; 111. a carrier gas compressor from the gas-liquid separator to the melamine solids recycle crystallizer; 112. a carrier gas compressor from the melamine solids recycle crystallizer to the fluidized bed reactor; 12. a melamine solid circulation crystallizer; 13. a condenser; 14. a fixed bed reactor; 141. a reactor housing; 142. an upper tube sheet; 143. an air inlet distribution pipe; 144. an air outlet collecting pipe; 145. a attrition resistant, fine particle catalyst having a particle size of 20 to 200 μm; 146. a lower tube sheet; 147. a catalyst discharge port; 148. an outlet of the reactor; 149. a catalyst inlet; 1410. a reactor gas inlet; 15. a circulating fluidized bed melamine crystallizer; 151. a gas distributor; 152. a heat exchange tube bundle; 153. a guide cylinder; 154. a gas-solid sedimentation separation cylinder; 155. a cyclone separator; 156. and a heat-insulating jacket of the sedimentation separation cylinder.
A. Fused salt; b, fused salt; C. steam; D. water; E. a melamine product; F. melamine tail gas; G. liquid urine; H. insulating gas of the jacket; I. melamine feed gas; J. and (3) fluidizing gas.
Detailed Description
The method comprises the steps that urea reacts in a fluidized bed reactor 1, the reaction temperature is about 390 ℃, the pressure is 0.25 MPa (absolute pressure), or the pressure is 2.2MPa (absolute pressure), or any pressure value between 0.25 and 2.2MPa (absolute pressure), melamine material gas at the temperature of about 390 ℃ which is discharged from the fluidized bed reactor 1 directly enters a hot gas filter 3 to remove catalyst fine powder, clean gas which is discharged from the hot gas filter 3 enters a fixed bed reactor 14, and intermediate products of cyanuric acid and melamine which are not completely reacted, such as cyanuric acid, miller amine and amide substances, are further reacted to generate melamine, so that the conversion rate of urea is improved, the purity of melamine products in subsequent working sections is ensured, and the problem that the hot gas cooler 2 is easy to crystallize and block in the original process is solved; the gas with the temperature of 390 ℃ which comes out of the fixed bed reactor 14 enters the upper part of the heat exchange section of the circulating fluidized bed melamine crystallizer 15, is mixed with the upward flowing cold melamine particles, the melamine is crystallized and separated out, and enters the circulating melamine solid particles, the upward flowing gas-solid mixture passes through the gas-solid sedimentation separation section at the upper part, most of the solid particles are separated from the gas, and the separated solid particles flow downwards along the inner wall of the cylinder to the outer side of the lower guide cylinder 153, enter the lower part of the heat exchanger 152, and are mixed with the bottom fluidizing gas to flow upwards to form the circulation of the solid particles; the gas from the upper separation section enters a two-stage cyclone separator 155 connected in series in a heat-insulating jacket 156 of the settling separation section to further separate melamine solid particles, the separated solid particles return to the barrel of the settling separation section, flow downwards along the inner wall of the barrel to the outer side of a lower guide barrel 153, enter the lower part of a heat exchanger 152, discharge melamine products through a discharge port on the side surface of the lower barrel of the circulating fluidized bed melamine crystallizer 15 and maintain the stability of the material level, and the outlet temperature of the process gas can be controlled by adjusting the steam pressure or the bottom fluidization air quantity. The gas coming out of the circulating fluidized bed melamine crystallizer 15 is split into two paths: one path of compressed gas is compressed from the melamine solid circulation crystallizer 15 to the carrier gas compressor 112 of the fluidized bed reactor 1, the compressed gas is divided into two branches, one branch is used as the fluidizing gas (carrier gas) of the fluidized bed reactor 1, the second branch is used as the atomizing gas of the liquid urine feeding nozzle of the fluidized bed reactor 1, and the other path of the atomized gas enters the liquid urine washing tower 7 for washing and cooling; the gas from the liquid urine washing tower 7 is separated into two paths: one way is boosted by a cold air fan 111 to serve as fluidizing gas (carrier gas) of the circulating fluidized bed melamine crystallizer 15, and the other way is discharged as tail gas of the melamine reaction to enter a tail gas utilization device, and particularly when the system pressure is about 1.8MPa (absolute pressure), the tail gas can be directly sent to a medium-pressure section of the urea device for condensation, and the condensation heat is used for evaporation of urea solution.
FIG. 4 is a schematic view of a fixed bed reactor 14 according to the present invention, wherein 141 is the reactor shell, 142 is the upper tube sheet, 143 is the inlet distribution tube, 144 is the outlet collection tube, 143 and 144 are the sieve tubes, and the sieve tube is: the tube body is provided with a through hole, the screen tube is formed by wrapping more than two layers of stainless steel wire meshes with about 120 meshes outside a perforated steel tube, or a plurality of layers of stainless steel sintered wire mesh plates with the aperture not smaller than 20 mu m are rolled and welded into a round tube, a 145 wear-resistant fine particle catalyst with any numerical value with the particle size of 20-500 mu m is filled between the distribution tubes, the air inlet distribution tubes and the air outlet collecting tubes are arranged in a regular triangular square grid, a 146 is a lower tube plate, a 147 is a catalyst discharging outlet, a 148 is a reactor outlet, a 149 is a catalyst adding inlet, a 1410 is a reactor gas inlet, and the number and the tube diameter are determined by a process professional according to the permission of the device production capacity and the resistance.
The particularly preferred fixed bed reactor 14 selected in the process of the invention has the advantages of small gas resistance, uniform gas distribution and high catalyst utilization rate, and the catalyst can be the same as or different from the catalyst used in the melamine fluidized bed reactor 1, and can be silica gel, silica gel and alumina gel or composite silica gel and silica gel added with molecular sieve.
Fig. 5 is a schematic diagram of a circulating fluidized bed melamine crystallizer according to the present invention, in which 151 is a gas distributor, 152 is a heat exchanger, 153 is a guide cylinder, 154 is a gas-solid settling separation cylinder, 155 is a cyclone, and 156 is a settling separation cylinder heat-preserving jacket.
The particularly preferred circulating fluidized bed melamine crystallizer 15 selected in the process is provided with a gas distributor 151 at the bottom, a heat exchanger 152 is arranged above the gas distributor 151, a heat exchange tube bundle is arranged in the heat exchanger 152, saturated steam with the temperature of about 220 ℃ can be generated by adding water and gasification in the heat exchange tube bundle, a plurality of inlet tubes of material gas are arranged above the heat exchange tube bundle, the inlet tubes pass through a guide cylinder 153, hot material gas is mixed with cold solid particles flowing upwards, the gas is cooled, melamine is crystallized and separated out, the crystallization process occurs among particles flowing upwards at the upper part of the heat exchanger 152 because the heat exchange tube bundle is distributed below the material gas inlet, so that the wall of the heat exchange tube bundle is not influenced by heat transfer and the operation period, the guide cylinder 153 is arranged at the periphery of the heat exchanger 152, so that the solid particles form a circulation loop inside and outside the guide cylinder 153, the solid particle flow between the heat exchange tube bundles is effectively increased, and the temperature difference of the heat exchange tube bundle is increased, thereby achieving the purposes of improving the temperature of byproduct steam or reducing the heat transfer area; the upper part of the heat exchange tube bundle is a sedimentation separation section, a sedimentation separation cylinder heat-preserving jacket 156 is arranged outside the sedimentation separation section, and the gas after sedimentation separation enters a cyclone separator 155 again, so that the cyclone separator 155 is arranged in the sedimentation separation cylinder heat-preserving jacket 156 for preventing crystallization of the inner wall of the cyclone separator 155, and the temperature outside the cyclone separator 155 and the material leg is higher than the temperature inside the wall so as not to cause crystallization blockage. The pressure of the circulating fluidized bed melamine crystallizer 15 is determined according to the pressure of a melamine production device, the pressure of the circulating fluidized bed melamine crystallizer 15 is 0.2MPa (absolute pressure), or is 2.0MPa (absolute pressure), or can be any pressure value between 0.2 and 2.0MPa (absolute pressure), the crystallization point of the melamine is also increased along with the increase of the pressure, the solid particle temperature of the circulating fluidized bed is correspondingly increased, the circulating particle temperature of the circulating fluidized bed melamine crystallizer 15 is determined according to the by-product steam temperature requirement and the crystallization completeness requirement of the melamine, and the temperature is 200 ℃ or 240 ℃, or can be any temperature between 200 and 240 ℃.
The invention is characterized in that:
1. the fixed bed reactor 14 replaces the original shell-and-tube hot gas cooler 2 to remove byproducts, and thoroughly solves the bottleneck problems of long-period operation and large-scale operation of the hot gas cooling unit.
2. The circulating fluidized bed melamine crystallizer 15 is used for replacing the original gas-phase quenching crystallizer 4, and due to the optimized structural design, high-grade medium-pressure steam can be produced as a byproduct, so that the byproduct steam can meet various urea process requirements, and about 1.65t medium-pressure steam of a t-triamine byproduct is used for a urea device, thereby reducing the steam consumption of co-production of urea by melamine tail gas; the cold air quantity required by the crystallizer is reduced by 80%, the loads of the liquid urine washing tower 7, the gas-liquid separator 8 and the liquid urine circulating pump 10 are greatly reduced, the electricity consumption is reduced, and when the pressure of the system reactor reaches 2.2MPa, the electricity consumption of ton melamine is reduced from the existing 600-700 KW.h to 200-220 KW.h; and the wall of the heat exchange tube bundle and other parts is not formed, so that the problems of long-period operation and large scale of the melamine device are thoroughly solved.
3. The pressure of the whole triamine device is increased, so that the triamine tail gas can directly enter a middle pressure section of the urea device for condensation, the treatment links such as compression or low-pressure absorption and middle pressure analysis are not needed, and NH of the tail gas is not needed 3 And CO 2 The molar ratio is 2.3, or 2.6, or any value between 2.3 and 2.6, the high condensation temperature and high condensation heat can be used for evaporating urine, and the method is equivalent to that the ton of triamine provides 980kg of low-pressure steam for a urea co-production device, or 1356kg of low-pressure steam, or any quality of low-pressure steam between 980 and 1356kg according to different urea processes; the tail gas amount is small, the tail gas amount of melamine is lower than 2.3t, and the investment of tail gas treatment equipment is small.
The foregoing is merely a preferred embodiment of the present invention, and it should be noted that it will be apparent to those skilled in the art that several changes and modifications can be made without departing from the general inventive concept, and these should also be regarded as the scope of the invention.
Claims (10)
1. A process for the production of melamine comprising the steps of:
(1) The urea reacts in a fluidized bed reactor, wherein the reaction temperature is about 390 ℃ and the pressure is 0.25-2.2 MPa;
(2) The melamine material gas at about 390 ℃ which comes out of the reactor directly enters a hot gas filter to remove catalyst fine powder;
(3) The clean gas from the hot gas filter is subjected to fixed bed catalytic reaction, so that intermediate products of the isocyanate and the melamine which are not completely reacted, namely cyanuric acid, miller amine and amide substances are further reacted to generate melamine;
(4) The method for crystallizing the melamine in the circulating fluidized bed by using the gas at the temperature of about 390 ℃ obtained by the fixed bed catalytic reaction comprises the following steps: in the columnar space, the middle part of the cross section of the columnar space is provided with rising fluidizing gas, the rising fluidizing gas is firstly mixed with gas at about 390 ℃ obtained by catalytic reaction of a fixed bed through cooling to crystallize and separate melamine, the crystallized melamine is mixed with the rising fluidizing gas and cooled after sinking along the periphery of the columnar space, then mixed with gas at about 390 ℃ obtained by catalytic reaction of the fixed bed to crystallize melamine, the crystallized melamine is mixed with the rising fluidizing gas and cooled after sinking along the periphery of the columnar space, meanwhile, part of the melamine after crystallization continuously rises and settles along with air flow in a heat-preserving state, the settled melamine crystals are mixed with the rising fluidizing gas and cooled after sinking along the periphery of the columnar space, and the settled process gas is discharged from the top of the columnar space and melamine products are discharged from the periphery of the lower part of a melamine crystallization area according to circulation;
the process gas discharged from the top of the columnar space in the step (4) is divided into two paths: one path of compressed gas is compressed by a carrier gas compressor, one path of compressed gas is used as the fluidizing gas of the fluidized bed reactor, the second path of compressed gas is used as the atomizing gas of the liquid urine feeding nozzle of the reactor, and the other path of compressed gas enters a liquid urine washing tower for washing and cooling; gas from the liquid urine washing tower is separated into two paths after gas-liquid separation: one way is boosted by a cold air fan to be used as fluidizing gas of a circulating fluidized bed melamine crystallizer, and the other way is used as tail gas of melamine reaction to be discharged into a tail gas utilization device, and especially when the system pressure is about 1.8MPa, the tail gas can be directly sent into a medium-pressure condenser of a urea device to be condensed, and the condensation heat is used for evaporating urea solution.
2. The method for producing melamine according to claim 1, wherein melamine in the step (4) is crystallized and separated, and enters into circulating melamine solid particles, the upward flowing gas-solid mixture passes through the upper gas-solid sedimentation separation section, most of the solid particles are separated from gas, and the separated solid particles flow downwards along the inner wall of the cylinder to the outer side of the lower guide cylinder, enter into the lower part of the heat exchanger, and flow upwards together with the mixture of the fluidizing gas at the bottom to form the circulation of the solid particles; the gas from the upper separation section enters a two-stage cyclone separator connected in series in a jacket to further separate melamine solid particles, the separated solid particles return to the barrel of the sedimentation separation section, flow downwards into the outer side of a lower guide barrel along the inner wall of the barrel, enter the lower part of a heat exchanger, discharge melamine products through a discharge port on the side surface of the lower barrel of the crystallizer and maintain the stability of the material level, and the outlet temperature of process gas can be controlled by adjusting the steam pressure of the catalytic reaction of a fixed bed or adjusting the bottom fluidization gas quantity.
3. The method for producing melamine according to claim 2, wherein in the step (4), a fluidizing gas distributor is arranged at the bottom of the circulating fluidized bed melamine crystallizer, the entering fluidizing gas enables melamine solid particles in the bed to be in a fluidized state, a heat exchange tube bundle is arranged above the distributor to form a cooling bed, a plurality of material gas inlet tubes are arranged above the heat exchange tube bundle to form a crystallization bed, the cooling bed and the crystallization bed section are provided with concentric guide cylinders to form a solid particle circulation loop, a discharge port is arranged on an outer cylinder of the crystallization section, and a gas-solid sedimentation separation section and a cyclone separator are arranged at the upper part of the cooling bed and the crystallization bed section.
4. The fixed bed catalytic reaction device according to claim 1, wherein the fixed bed catalytic reaction device is a fixed bed catalytic reactor, the fixed bed catalytic reactor comprises a columnar tank body, the columnar tank body is divided into three parts by two layers of partition boards, the upper part is a mixed gas cabin before catalysis, the lower part is a mixed gas cabin after catalysis, the middle part is a catalyst cabin, the upper partition board is downwards provided with an air inlet screen pipe which extends into the catalyst cabin, (the screen pipe is closed at one end and is provided with through holes on the pipe body), the lower partition board is inwards provided with an air outlet screen pipe which extends into the catalyst cabin, the mixed gas cabin before catalysis is provided with a mixed gas inlet, the mixed gas cabin after catalysis is provided with a mixed gas outlet, the upper partition board is provided with a catalyst feed pipe, and the catalyst cabin is provided with a catalyst discharge pipe.
5. The circulating fluidized bed melamine crystallization equipment according to claim 1, wherein the circulating fluidized bed melamine crystallizer comprises a columnar tank body, a fluidization airflow nozzle is arranged in the middle of the cross section of the bottom of the columnar tank body, a concentric guide cylinder is arranged at the periphery of the fluidization airflow nozzle, a cooling heat exchanger is arranged at the lower part in the guide cylinder, a melamine hot gas inlet pipe penetrating through the inner cylinder and the outer cylinder is arranged on the side wall of the upper tank body of the cooling heat exchanger, gas at the temperature of about 390 ℃ from the fixed bed catalytic reactor enters the guide cylinder from the hot gas inlet pipe, a crystallization area of melamine mixed gas is arranged at the upper part of the hot gas inlet pipe, a sedimentation area is arranged at the upper part of the crystallization area and is positioned above the guide cylinder, a hot air jacket heat preservation layer is arranged outside the tank of the sedimentation area, and an inlet and an outlet of heat preservation medium are arranged on the jacket heat preservation layer; the bottom of the tank body and the fluidization gas nozzle are arranged, the diameter of the tank body is reduced, and the side wall of the tank body forms a diversion surface.
6. The circulating fluidized bed melamine crystallization equipment according to claim 5, wherein a cyclone separator is arranged in the jacket heat-insulating layer, an inlet of the cyclone separator is communicated with an outlet at the top of the tank body, an air outlet of the cyclone separator is connected with an outlet main pipe, a blanking leg of the cyclone separator is positioned in the jacket heat-insulating layer, the blanking leg is communicated with the tank body through a wing valve, and a melamine product outlet is arranged on the side surface of a lower cylinder of the tank body; the cyclone separators arranged in the jacket heat-insulating layer are connected in series to form a group, and a plurality of groups of cyclone separators are connected in parallel according to the size of the device.
7. A process for the production of melamine according to steps (3) and (4) of claim 1, characterized in that it can also be used in a process plant for the production of melamine by reacting other urea in a gas fluidized bed reactor, such as a fluidized bed with pure ammonia as a circulating carrier gas.
8. A process for the production of melamine according to claim 1, characterized in that the gas entering the carrier gas compressor is directly coming from the outlet of the circulating fluidized bed melamine crystallizer.
9. The method for producing melamine according to claim 9, wherein the gas from the carrier gas compressor can be preheated by molten salt, flue gas of a molten salt furnace or other heating means and then fed into the reactor.
10. The fixed bed reactor of the melamine production method step (3) according to claim 1, which is characterized by comprising a reactor shell (141), wherein an upper tube plate (142) is arranged in the reactor shell (141), an air inlet distribution tube (143) is fixed on the upper tube plate (142), a lower tube plate (146) is arranged in the reactor shell (141), an air outlet collection tube (144) is fixed on the lower tube plate (146), the air inlet distribution tube (143) and the air outlet collection tube (144) are sieve tubes, the air inlet distribution tube and the air outlet collection tube are arranged in a regular triangle or square grid, staggered arrangement is realized, a catalyst discharge outlet (147) is fixed on the lower tube plate (146) and extends downwards out of the reactor shell (141), a catalyst addition inlet (149) is fixed on the upper tube plate (142) and extends upwards out of the reactor shell (141), a reactor gas inlet (1410) is arranged at the top of the reactor shell (141), and a reactor outlet (148) is arranged at the bottom of the reactor shell (141).
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| Application Number | Priority Date | Filing Date | Title |
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| CN202210072095.2A CN116496225A (en) | 2022-01-21 | 2022-01-21 | Melamine production method and equipment |
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| Application Number | Priority Date | Filing Date | Title |
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| CN202210072095.2A CN116496225A (en) | 2022-01-21 | 2022-01-21 | Melamine production method and equipment |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117928298A (en) * | 2024-03-21 | 2024-04-26 | 阳煤丰喜肥业(集团)有限责任公司平陆分公司 | Novel hot gas cooling system of melamine |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117928298A (en) * | 2024-03-21 | 2024-04-26 | 阳煤丰喜肥业(集团)有限责任公司平陆分公司 | Novel hot gas cooling system of melamine |
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