CN213708198U - Melamine production system for high-pressure synthesis low-pressure gas-phase quenching method - Google Patents
Melamine production system for high-pressure synthesis low-pressure gas-phase quenching method Download PDFInfo
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- CN213708198U CN213708198U CN202021538827.5U CN202021538827U CN213708198U CN 213708198 U CN213708198 U CN 213708198U CN 202021538827 U CN202021538827 U CN 202021538827U CN 213708198 U CN213708198 U CN 213708198U
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Abstract
The utility model relates to a melamine production system of high-pressure synthesis low pressure gaseous phase quenching method, including urea scrubbing tower, the reactor of being connected with urea scrubbing tower, hot gas filter, the crystallizer of being connected with hot gas filter and the triamine trap of being connected with the crystallizer, the triamine trap is connected with urea scrubbing tower, its characterized in that, urea scrubbing tower passes through high-pressure urea pump and is connected with the reactor, the reactor is first high-pressure reactor; the reactor is connected with a flash evaporator, and the flash evaporator is connected with a hot gas filter; the urea washing tower is sequentially connected with a cold air demister and a cold air blower, and the cold air blower is connected with the crystallizer; the first high-pressure reactor is connected with an ammonia gas supply assembly. The system adopts the components such as the high-pressure reactor, the flash evaporator, the crystallizer, the cold air blower and the like to realize gas-phase quenching, and the production process of the high-pressure reactor does not need to carry out gas-phase catalytic reaction through a catalyst, so that the resource consumption of the system is reduced and the system is more environment-friendly.
Description
Technical Field
The utility model relates to a melamine production technical field, more specifically relates to melamine production system of high pressure synthesis low pressure gaseous phase quenching method.
Background
Melamine (C)3N6H6) Melamine is a kind of product with wide applicationOrganic chemical raw materials. The melamine formaldehyde resin is mainly used for synthesizing melamine formaldehyde resin, manufacturing adhesives, decorative veneers, daily utensils, textile finishing agents and the like, and can also be used as an environment-friendly high-performance coating cross-linking agent, a flame retardant material and the like.
At present, melamine is usually produced by using urea as a raw material, namely, the raw material urea is subjected to the following reaction under certain temperature and certain pressure or under the action of a catalyst:
6CO(NH2)2(urea ═ C3N6H6(Melamine) +6NH3+3CO2
The above synthesis process can be generally classified into a high-pressure liquid-phase quenching method and a low-pressure gas-phase quenching method according to the difference of reaction conditions.
The production process of melamine by a high-pressure liquid-phase quenching method belongs to liquid-phase reaction, and has no catalyst, the reaction pressure is generally 7-10 MPa, and the reaction temperature is 360-420 ℃. The production process of melamine by high-pressure liquid-phase quenching method generally adopts liquid ammonia, ammonia water or mother liquor as liquid-phase quenching agent to carry out quenching, and the melamine product can be obtained only after refining. The high-pressure liquid-phase quenching method has the advantages that the pressure of tail gas (ammonia and carbon dioxide) is high, the tail gas can directly return to a urea device, and the loss of raw materials can be effectively reduced; the method has the disadvantages that liquid-phase quenching medium needs to be introduced for quenching and refining, the process flow is long, the steam consumption is high (6-10 tons of steam are consumed for each ton of products), the production equipment conforming to liquid quenching is expensive, and meanwhile, waste water is generated in the production process, so that certain pollution is caused to the environment.
The production process of melamine by low pressure gas phase quenching method belongs to gas phase catalytic reaction, generally takes alumina, silica-alumina gel or silica gel as catalyst, the reaction pressure is generally 0.1-1.0 MPa, and the reaction temperature is 350-450 ℃. The production process of melamine by low-pressure gas-phase quenching method generally adopts gas-phase quenching process to carry out post-treatment on reaction products, i.e. the crystallization and purification of the products are completed by using the mixed gas of ammonia and carbon dioxide as quenching medium. The low-pressure gas-phase quenching method has the advantages of shorter process flow, less equipment investment and no waste water generation; the disadvantages are as follows: firstly, because a large amount of carrier gas and cold air are needed for circulation, the power consumption is high; secondly, because a large amount of solid waste residues such as catalyst powder and the like are generated, the method is not beneficial to environmental protection. For example, chinese patent document publication No. CN102219754A, published as 2011, 10, and 19, discloses an energy-saving and cost-saving system and process for producing melamine by gas-phase quenching method, wherein the reactor in the process is a fluidized bed reactor, and a large amount of fluidized carrier gas and a large amount of cold gas are needed for crystallization, so that the power consumption of a carrier gas compressor and a cold gas blower is very high; meanwhile, a large amount of fluidizing carrier gas is supplied to the fluidized bed reactor, and in order to maintain the reaction temperature of the fluidized bed reactor, a large amount of heat needs to be supplied into the reactor, the heat consumption of the molten salt furnace is high, and the system and the production process need to perform catalytic reaction through a catalyst, and the catalyst in the fluidized bed reactor is continuously abraded, formed into powder and carried out during the production operation process. Because a large amount of solid waste residues such as catalyst powder and the like are generated, the environment is polluted.
SUMMERY OF THE UTILITY MODEL
The utility model discloses an overcome among the above-mentioned prior art three get cyanamide production system production resource consumption big and not environmental protection problem, provide the melamine production system of high pressure synthesis low pressure gaseous phase quenching method, reduce the production of the resource energy consumption in the production process and reduction production pollutant.
In order to solve the technical problem, the utility model discloses a technical scheme is: the melamine production system comprises a urea washing tower, a reactor connected with the urea washing tower, a hot gas filter, a crystallizer connected with the hot gas filter and a triamine catcher connected with the crystallizer, wherein the triamine catcher is connected with the urea washing tower; the urea washing tower is connected with the reactor through a high-pressure urea pump, and the reactor is a first high-pressure reactor; the reactor is connected with a flash evaporator, and the flash evaporator is connected with the hot gas filter; the urea washing tower is sequentially connected with a cold air demister and a cold air blower, and the cold air blower is connected with the crystallizer;
the first high-pressure reactor is connected with an ammonia gas supply assembly, and comprises an ammonia gas preheater, a liquid ammonia evaporator and a high-pressure liquid ammonia pump which are sequentially connected; the ammonia gas preheater is connected with the first high-pressure reactor.
In the above technical solution, the specific generation process flow of the system is as follows: the method comprises the following steps: boosting and preheating liquid ammonia; pressurizing liquid ammonia to 5.0-10.0 MPa by a high-pressure liquid ammonia pump, heating to 100-150 ℃ by a liquid ammonia evaporator, evaporating to obtain gas ammonia, heating by using molten salt in an ammonia preheater, heating the gas ammonia to 360-420 ℃, and then feeding the gas ammonia into a first high-pressure reactor;
step two: synthesizing melamine; pressurizing molten urea at the temperature of 135-155 ℃ from a urea washing tower to 5.0-10.0 MPa by a high-pressure urea pump, and then feeding the urea into a first high-pressure reactor; under the conditions that the reaction pressure is 5.0-10.0 MPa and the temperature is 360-420 ℃, urea reacts to generate a reaction product containing melamine, ammonia and carbon dioxide; in the reaction, the chemical reaction speed is greatly increased due to the increase of the partial pressure of reactants, and more than 95 percent (wt) of urea generates the chemical reaction of generating melamine in the high-pressure reactor; meanwhile, because the high-pressure reactor adds ammonia through the ammonia preheater, the partial pressure of the ammonia is improved, the melamine deamination reaction is inhibited, and the content of melamine deamination products (high-boiling-point byproducts) is greatly reduced.
Step three: flashing reaction products; the reaction product is discharged from the first high-pressure reactor and enters a flash evaporator; controlling the pressure of the flash evaporator to be 0.1-2.5 MPa, and controlling the temperature to be 330-360 ℃ by adopting a high-temperature heat carrier, so that a reaction product is changed into a gas phase, and meanwhile, a high-boiling-point byproduct in the reaction product is fully crystallized and separated out; the high-temperature heat carrier can be molten salt or heat conducting oil.
Step four: filtering a reaction product; filtering the reaction product from the flash evaporator in a hot gas filter to intercept the high boiling point by-products, wherein the temperature in the hot gas filter is higher than or equal to that of the reaction product from the flash evaporator, but the temperature difference is not more than 3 ℃; the outlet temperature of the hot gas filter is required to be consistent with or slightly higher than the inlet temperature so as to prevent melamine from crystallizing and separating out in the filtering process; the gas enters the filter under the action of pressure difference, the high-boiling point by-products are intercepted by the filter medium, and the reaction products are purified. The filter cake attached to the outside of the filter medium is stripped by the back blowing gas and falls to the bottom of the filter, and is discharged out periodically.
Step five: gas-phase quenching crystallization; and (3) enabling a reaction product from the hot gas filter to enter a crystallizer, mixing the reaction product with cold crystallized air from the cold air blower, controlling the final temperature of the mixed gas to be 180-240 ℃, quenching the hot gas by the cold air, and sublimating gaseous melamine into melamine crystals to crystallize and separate out from the reaction product.
Step six: collecting melamine; the reaction product with the melamine crystals enters a triamine catcher to complete gas-solid separation; the temperature in the triamine catcher is higher than or equal to the temperature of the gas-solid mixture from the crystallizer, but the temperature difference is not more than 3 ℃.
Step seven: cooling and purifying the process gas; and the gas from which the melamine crystals are separated comes out of the triamine catcher and then enters the urea washing tower, the gas is mixed with the molten urea at the temperature of 135-155 ℃ and flows downwards, the gas is washed and cooled by the urea, melamine particles and unreacted substances in the process gas enter the molten urea, and the temperature of the gas is reduced to 140-150 ℃ from 180-240 ℃. The heat released by cooling the process gas is taken away by an evaporative heat exchanger in the urea washing tower, saturated water circulates in the heat exchanger pipe, and the saturated water is evaporated to generate low-pressure steam. In order to prevent the urea from forming crystal scale on the heat exchange tube, the preferred saturated water evaporation temperature is 125-150 ℃.
Step eight: and (5) gas-liquid separation. The gas from the lower part of the urea washing tower enters the cold air demister, and is separated by the cold air demister to obtain urea and process gas; urea returns to the bottom of the urea washing tower, one part of the urea at the bottom of the urea washing tower is used for gas washing circulation again, and the other part of the urea is pressurized by a high-pressure urea pump and then is sent to the first high-pressure reactor to synthesize melamine;
step nine: distributing process gas; the pressure of the process gas separated by the cold gas demister is 0.1-2.4 Mpa, one part of the process gas is pressurized by a cold gas blower and then is circulated back to the crystallizer from the lower part of the crystallizer to be used as crystallization cold gas, and the other part of the process gas is discharged as tail gas.
The system adopts the high-pressure reactor for reaction, simultaneously realizes gas-phase quenching through the components such as the flash evaporator, the crystallizer, the cold air blower and the like, and does not need to carry out gas-phase catalytic reaction through a catalyst in the production process of the high-pressure reactor, so that a large amount of fluidization carrier gas and cold air crystallization are not needed, and the cold air amount required by subsequent gas-phase quenching is greatly reduced. Meanwhile, the system carries out gas-phase quenching through a gas flash evaporator and a crystallizer after the high-pressure reactor, thereby avoiding the defect that in the production process of melamine by the high-pressure liquid-phase quenching method, a large amount of steam is consumed because reaction products are quenched and refined by adopting liquid-phase quenching medium; meanwhile, the defect that a gas phase quenching system needs to consume a large amount of heat preservation steam in the existing low-pressure gas phase quenching method melamine production process is avoided, and the steam consumption is greatly reduced. The system of the utility model is produced by a catalyst-free high-pressure reaction back gas-phase quenching mode, and has no waste water discharge and no waste slag discharge, thereby being more environment-friendly.
Preferably, a second high-pressure reactor is arranged between the first high-pressure reactor and the flash evaporator, the second high-pressure reactor is connected with the ammonia preheater, namely the two high-pressure reactors are connected in series, and after the first high-pressure reactor finishes the chemical reaction, the generated chemical product enters the second high-pressure reactor to continue the reaction, so that the conversion rate of the urea into the melamine is improved.
Preferably, the first high pressure reactor and the second high pressure reactor are both natural convection circulation reactors. Compared with the fluidized bed reactor in the prior art, the natural convection circulation reactor does not need a large amount of fluidization carrier gas when high-pressure reaction is carried out.
Preferably, an in-pipe evaporative heat exchanger is arranged in the urea washing tower and is connected with the liquid ammonia evaporator. In the liquid ammonia evaporator, 0.1-0.5 MPa low-pressure steam generated by an evaporative heat exchanger in a urea washing tower is used for heating, liquid ammonia is heated to 100-150 ℃ and evaporated into gas ammonia, system heat energy is fully utilized, and the defect that the heat energy consumption of a molten salt furnace is high due to the fact that an ammonia preheater directly adopts molten salt for heating in the existing high-pressure liquid-phase quenching method melamine production process is overcome.
Preferably, the hot gas filter and the flash evaporator are provided with two sets, the hot gas filter is connected with the flash evaporator, and the flash evaporator is connected with the reactor. The outlet temperature of the hot gas filter is required to be kept consistent with or slightly higher than the inlet temperature so as to prevent melamine from crystallizing and separating out in the filtering process; the gas enters the filter under the action of pressure difference, the high-boiling point by-products are intercepted by the filter medium, and the reaction products are purified. The filter cake attached to the outside of the filter medium is stripped by the back blowing gas and falls to the bottom of the filter, and is discharged out periodically. In order to facilitate the high-efficient online cleaning regeneration, the utility model discloses preferred the hot gas filter is bag filter. In addition, as a preferable arrangement mode, two sets of flash evaporators and filters can be arranged, and when one set is in operation, the other set is in on-line regeneration cleaning and standby.
Preferably, a regenerator is connected to the hot gas filter.
Preferably, a tube type heat exchanger is arranged in the flash evaporator; the hot air filter is a bag filter, and the cold air demister is a cyclone demister. In order to clean the crystal scale of the high-boiling point by-product, the heat exchange device in the flash evaporator is preferably in the form of a tubular heat exchanger. In order to facilitate the high-efficient online cleaning regeneration, the utility model discloses preferred the hot gas filter is bag filter.
Compared with the prior art, the beneficial effects of the utility model are that: 1. the power consumption is low; the system adopts the high-pressure reactor for reaction, simultaneously realizes gas-phase quenching through the components such as the flash evaporator, the crystallizer, the cold air blower and the like, and does not need to carry out gas-phase catalytic reaction through a catalyst in the production process of the high-pressure reactor, so that a large amount of fluidization carrier gas and cold air crystallization are not needed, the cold air quantity required by subsequent gas-phase quenching is greatly reduced, the power consumption of the cold air blower is greatly reduced, and the power consumption of the production system is reduced;
2. the steam consumption is low; the system carries out gas-phase quenching through the gas flash evaporator and the crystallizer after the high-pressure reactor, avoids the defect that a large amount of steam is consumed in the high-pressure liquid-phase quenching melamine production process because reaction products are quenched and refined by adopting liquid-phase quenching medium, and simultaneously avoids the defect that a large amount of heat-preserving steam is consumed in a gas-phase quenching system in the existing low-pressure gas-phase quenching melamine production process, and the steam consumption required by the system production is greatly reduced compared with the two methods;
3. the environmental protection effect is good; the system is produced in a gas-phase quenching mode after catalyst-free high-pressure reaction, and is not only free of waste water discharge but also free of waste slag discharge, so that the system is more environment-friendly.
Drawings
FIG. 1 is a schematic diagram of a melamine production system of the high pressure synthesis low pressure gas phase quench process of the present invention;
FIG. 2 is a schematic view of another embodiment of the melamine production system of the high-pressure synthesis low-pressure gas-phase quenching process of the present invention;
figure 3 is a schematic diagram of another embodiment of the melamine production system of the high pressure synthesis low pressure gas phase quench process of the present invention.
Detailed Description
The drawings are for illustrative purposes only and are not to be construed as limiting the patent; for the purpose of better illustrating the embodiments, certain features of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted. The positional relationships depicted in the drawings are for illustrative purposes only and are not to be construed as limiting the present patent.
The technical solution of the present invention is further described in detail by the following specific embodiments in combination with the accompanying drawings:
example 1
Fig. 1 shows an embodiment of a melamine production system for high-pressure synthesis and low-pressure gas-phase quenching, which comprises a urea washing tower 1, a reactor connected with the urea washing tower 1, a hot gas filter 2, a crystallizer 3 connected with the hot gas filter 2, and a triamine catcher 4 connected with the crystallizer 3, wherein the triamine catcher 4 is connected with the urea washing tower 1; the urea washing tower 1 is connected with a reactor through a high-pressure urea pump 5, and the reactor is a first high-pressure reactor 6; the reactor is connected with a flash evaporator 7, and the flash evaporator 7 is connected with a hot gas filter 2; the urea washing tower 1 is sequentially connected with a cold air demister 8 and a cold air blower 9, and the cold air blower 9 is connected with the crystallizer 3;
the first high-pressure reactor 6 is connected with an ammonia gas preheater 10, a liquid ammonia evaporator 11 and a high-pressure liquid ammonia pump 12 in sequence.
The working principle or working process of the embodiment is as follows:
the system specifically comprises the following steps:
the method comprises the following steps: boosting and preheating liquid ammonia; liquid ammonia is pressurized to 8.5MPa by a high-pressure liquid ammonia pump 12, heated to 120 ℃ by a liquid ammonia evaporator 11 and evaporated into gaseous ammonia, and then heated by molten salt in an ammonia preheater 10, and the gaseous ammonia is heated to 400 ℃ and enters a first high-pressure reactor 6;
step two: synthesizing melamine; the molten urea with the temperature of 140 ℃ is pressurized to 8.5MPa by a high-pressure urea pump 5 from a urea washing tower 1 and then enters a first high-pressure reactor 6; under the conditions that the reaction pressure is 8MPa and the temperature is 380 ℃, urea reacts to generate reaction products comprising melamine, ammonia and carbon dioxide; in the reaction, the chemical reaction speed is greatly increased due to the increase of the partial pressure of reactants, and more than 95 percent (wt) of urea generates the chemical reaction of generating melamine in the high-pressure reactor; meanwhile, because the high-pressure reactor is added with ammonia through the ammonia preheater 10, the partial pressure of the ammonia is improved, the melamine deamination reaction is inhibited, and the content of melamine deamination products (high-boiling point byproducts) is greatly reduced.
Step three: flashing reaction products; the reaction product is discharged from the first high-pressure reactor 6 and enters a flash evaporator 7; controlling the pressure of the flash evaporator 7 to be 0.5MPa, and controlling the temperature to be 340 ℃ by adopting a high-temperature heat carrier, so that a reaction product is changed into a gas phase, and meanwhile, a high-boiling-point byproduct in the reaction product is fully crystallized and separated out; the high-temperature heat carrier can be molten salt or heat conducting oil.
Step four: filtering a reaction product; the reaction product from the flash evaporator 7 enters the hot gas filter 2 for filtering, and high boiling point byproducts are intercepted, the temperature in the hot gas filter 2 is higher than or equal to the temperature of the reaction product from the flash evaporator 7, but the temperature difference does not exceed 3 ℃, in the embodiment, the temperature of the hot gas filter 2 is 340 ℃, because the temperature of the reaction product is slightly reduced in the process from the flash evaporator 7 to the hot gas filter 2, the temperature of the hot gas filter 2 is consistent with the temperature of the flash evaporator 7, and the temperature difference can meet the requirement; here the outlet temperature of the hot gas filter 2 must be kept the same as or slightly higher than the inlet temperature to prevent melamine from crystallizing out during the filtration process; the gas enters the filter under the action of pressure difference, the high-boiling point by-products are intercepted by the filter medium, and the reaction products are purified. The filter cake attached to the outside of the filter medium is stripped by the back blowing gas and falls to the bottom of the filter, and is discharged out periodically.
Step five: gas-phase quenching crystallization; and the reaction product from the hot gas filter 2 enters the crystallizer 3 to be mixed with the cold crystallized gas from the cold gas blower 9, the final temperature of the mixed gas is controlled to be 200-220 ℃, the hot gas is quenched by the cold gas, and the gaseous melamine is desublimated and changed into melamine crystals to be crystallized and separated from the reaction product.
Step six: collecting melamine; the reaction product with the melamine crystals enters a triamine catcher 4 to complete gas-solid separation; the temperature in the triamine trap 4 was kept constant at 220 ℃.
Step seven: cooling and purifying the process gas; the gas from which the melamine crystals are separated comes out of the triamine catcher 4 and enters the urea washing tower 1, the gas is mixed with the molten urea at the temperature of 140 ℃ and flows downwards, the gas is washed and cooled by the urea, and the melamine particles and unreacted substances in the process gas enter the molten urea.
Step eight: and (5) gas-liquid separation. The gas from the lower part of the urea washing tower 1 enters a cold gas demister 8, and is separated by the cold gas demister 8 to obtain urea and process gas; wherein urea returns to the bottom of the urea washing tower 1, one part of the urea at the bottom of the urea washing tower 1 is used for gas washing circulation again, and the other part of the urea is pressurized by a high-pressure urea pump 5 and then is sent to a first high-pressure reactor 6 to synthesize melamine;
step nine: distributing process gas; the pressure of the process gas separated by the cold air demister 8 is 0.4Mpa, after a part of the process gas is pressurized to 0.45Mpa by the cold air blower 9, the process gas is circulated from the lower part of the crystallizer 3 to be used as cold crystallization air, and the other part of the process gas is discharged as tail gas.
In the technical scheme, the system adopts the high-pressure reactor for reaction, meanwhile, the components such as the flash evaporator 7, the crystallizer 3, the cold air blower 9 and the like are used for realizing gas-phase quenching, and a catalyst is not needed for gas-phase catalytic reaction in the production process of the high-pressure reactor, so that a large amount of fluidization carrier gas and cold air crystallization are not needed, and the cold air amount needed by subsequent gas-phase quenching is greatly reduced. Meanwhile, the system carries out gas-phase quenching through the gas flash evaporator 7 and the crystallizer 3 after the high-pressure reactor, thereby avoiding the defect that in the high-pressure liquid-phase quenching method melamine production process, a large amount of steam is consumed because reaction products are quenched and refined by adopting liquid-phase quenching medium; meanwhile, the defect that a gas phase quenching system needs to consume a large amount of heat preservation steam in the existing low-pressure gas phase quenching method melamine production process is avoided, and the steam consumption is greatly reduced. The system of the utility model is produced by a catalyst-free high-pressure reaction back gas-phase quenching mode, and has no waste water discharge and no waste slag discharge, thereby being more environment-friendly.
The beneficial effects of this embodiment: 1. the power consumption is low; the system adopts the high-pressure reactor for reaction, and simultaneously realizes gas-phase quenching through the components such as the flash evaporator 7, the crystallizer 3, the cold air blower 9 and the like, and a catalyst is not needed to perform gas-phase catalytic reaction in the production process of the high-pressure reactor, so that a large amount of fluidization carrier gas and cold air crystallization are not needed, the cold air quantity required by subsequent gas-phase quenching is greatly reduced, the power consumption of the cold air blower 9 is greatly reduced, and the power consumption of the production system is reduced;
2. the steam consumption is low; the system carries out gas-phase quenching through the gas flash evaporator 7 and the crystallizer 3 after the high-pressure reactor, avoids the defect that a large amount of steam is consumed in the high-pressure liquid-phase quenching method melamine production process because reaction products are quenched and refined by adopting liquid-phase quenching medium, and simultaneously avoids the defect that a large amount of heat-preservation steam is consumed in a gas-phase quenching system in the existing low-pressure gas-phase quenching method melamine production process, and the steam consumption required by the system production is greatly reduced compared with the two methods;
3. the environmental protection effect is good; the system is produced in a gas-phase quenching mode after catalyst-free high-pressure reaction, and is not only free of waste water discharge but also free of waste slag discharge, so that the system is more environment-friendly.
Example 2
Fig. 2 shows another embodiment of the melamine production system for the high-pressure synthesis low-pressure gas-phase quenching process, which is further defined on the basis of example 1.
Specifically, preferably, a second high-pressure reactor 13 is arranged between the first high-pressure reactor 6 and the flash evaporator 7, the second high-pressure reactor 13 is connected with the ammonia preheater 10, that is, the two high-pressure reactors are connected in series, and after the first high-pressure reactor 6 completes the chemical reaction, the generated chemical product enters the second high-pressure reactor 13 to continue the reaction, so that the conversion rate of the urea into the melamine is improved.
Preferably, the first high pressure reactor 6 and the second high pressure reactor 13 are both natural convection circulation reactors. Compared with the fluidized bed reactor in the prior art, the natural convection circulation reactor does not need a large amount of fluidization carrier gas when high-pressure reaction is carried out.
Preferably, an in-pipe evaporative heat exchanger is arranged in the urea washing tower 1, and the in-pipe evaporative heat exchanger is connected with the liquid ammonia evaporator 11. In the liquid ammonia evaporator 11, 0.1-0.5 MPa low-pressure steam generated by an evaporative heat exchanger in the urea washing tower 1 is used for heating, liquid ammonia is heated to 100-150 ℃ and is evaporated into gas ammonia, system heat energy is fully utilized, and the defect that the heat energy consumption of a molten salt furnace is high due to the fact that an ammonia preheater directly adopts molten salt for heating in the existing high-pressure liquid-phase quenching melamine production process is overcome.
Preferably, two sets of the hot gas filter 2 and the flash evaporator 7 are arranged, the hot gas filter 2 is connected with the flash evaporator 7, and the flash evaporator 7 is connected with the reactor. The outlet temperature of the hot gas filter 2 must be kept consistent with or slightly higher than the inlet temperature to prevent the melamine from crystallizing and separating out in the filtering process; the gas enters the filter under the action of pressure difference, the high-boiling point by-products are intercepted by the filter medium, and the reaction products are purified. The filter cake attached to the outside of the filter medium is stripped by the back blowing gas and falls to the bottom of the filter, and is discharged out periodically. In order to facilitate efficient on-line cleaning and regeneration, the hot gas filter 2 is preferably a bag filter. In addition, as a preferable arrangement mode, two sets of flash evaporators 7 and filters can be arranged, and when one set is in operation, the other set is in on-line regeneration cleaning and standby.
Preferably, a regenerator 14 is connected to the hot gas filter 2.
Preferably, a tube type heat exchanger is arranged in the flash evaporator 7; the hot gas filter 2 is a bag filter, and the cold gas demister 8 is a cyclone demister. In order to clean the crystal scale of the high-boiling point by-product, the heat exchange device in the flash evaporator 7 is preferably in the form of a tubular heat exchanger. In order to facilitate efficient on-line cleaning and regeneration, the hot gas filter 2 is preferably a bag filter.
The remaining operation principle and effects of this embodiment are the same as those of embodiment 1.
Example 3
As shown in fig. 3, the melamine production system by the high-pressure synthesis low-pressure gas-phase quenching method comprises a urea washing tower 1, a first high-pressure reactor 6 connected with the urea washing tower 1, a second high-pressure reactor 13 connected with the first high-pressure reactor 6, a crystallizer 3 connected with the second high-pressure reactor 13, and a triamine catcher 4 connected with the crystallizer 3, wherein the triamine catcher 4 is connected with the urea washing tower 1; the urea washing tower 1 is connected with the reactor through a high-pressure urea pump 5; the urea washing tower 1 is sequentially connected with a cold air demister 8 and a cold air blower 9, and the cold air blower 9 is connected with the crystallizer 3;
the first high-pressure reactor 6 is connected with an ammonia gas preheater 10, a liquid ammonia evaporator 11 and a high-pressure liquid ammonia pump 12 in sequence.
The production process corresponding to the production system of the embodiment is as follows:
the method comprises the following steps: and boosting pressure and preheating liquid ammonia. Liquid ammonia is pressurized to 8.5MPa by a high-pressure liquid ammonia pump 12, heated to 120 ℃ by a liquid ammonia evaporator 11 and evaporated into gas ammonia, then heated to 400 ℃ by a gas ammonia preheater, and enters a high-pressure reactor and a post-reactor respectively in two paths.
Step two: and (3) synthesizing melamine. Pressurizing molten urea with the temperature of 150 ℃ from a urea washing tower 1 to 8.5MPa by a high-pressure urea pump 5, feeding the urea into a high-pressure reactor, and reacting the urea to generate a reaction product comprising melamine, ammonia and carbon dioxide under the conditions that the reaction pressure is 8.0MPa and the temperature is 380 ℃; a small amount of unconverted urea and reaction products enter the post-reactor together, and under the conditions that the reaction pressure is 8.0MPa and the temperature is 380 ℃, the urea is further and completely converted into the reaction products comprising melamine, ammonia and carbon dioxide.
Because the high-pressure reactor and the post-reactor both adopt high-efficiency reactor internals, more than 98 percent (wt) of urea in the high-pressure reactor generates chemical reaction for generating melamine; in the post-reactor, more than 99.9% (wt) of the urea undergoes a chemical reaction to form melamine; meanwhile, because ammonia is added into the high-pressure reactor and the post reactor respectively, the partial pressure of the ammonia is improved, the melamine deamination reaction is inhibited, and the content of melamine deamination products (high-boiling point byproducts) in reaction products discharged from the post reactor is reduced by more than 95 percent.
By the process technology of connecting the high-efficiency high-pressure reactor in series and the high-efficiency post-reactor, the contents of low-boiling point by-products (OAT) and high-boiling point by-products (deamination products) in the melamine in the reaction product are reduced to below 10 ppm.
Step three: and (5) carrying out gas-phase quenching crystallization. And reducing the pressure of a reaction product discharged from the post reactor to 2.1MPa, then feeding the reaction product into a crystallizer 3, mixing the reaction product with cold crystallized air discharged from a cold air blower 9, controlling the final temperature of the mixed gas to be 230-240 ℃, quenching hot gas by the cold air, and sublimating most gaseous melamine into melamine crystals to crystallize and separate out from the reaction product.
Step four: and (4) collecting melamine. The reaction product with the melamine crystals enters the triamine catcher 4 to complete the gas-solid separation, and the constant temperature in the triamine catcher 4 is kept at 240 ℃.
Step five: the process gas is cooled and cleaned. The process gas after the melamine crystals are separated is discharged from the triamine catcher 4, enters the urea washing tower 1, is mixed with the molten urea at the temperature of 150 ℃ and flows downwards, the gas is washed and cooled by the urea, and the melamine particles and unreacted substances in the process gas enter the molten urea.
Step six: and (5) gas-liquid separation. The process gas from the lower part of the urea washing tower 1 enters a cold air demister 8, the process gas is separated by the cold air demister 8 to obtain urea and the process gas, and the urea returns to the bottom of the urea washing tower 1; and one part of the urea at the bottom of the urea washing tower 1 is used for washing the process gas for circulation again, and the other part of the urea is pressurized by a high-pressure urea pump 5 and then is sent to a high-pressure reactor for synthesizing the melamine.
Step seven: and (4) distributing the process gas. The pressure of the process gas separated by the cold gas demister 8 is 2.0Mpa, one part of the process gas is used as the cold crystallization gas, the other part of the process gas is discharged as the tail gas, wherein the cold crystallization gas is pressurized to 2.05MPa by the cold gas blower 9 and then is circulated back to the crystallizer 3 from the lower part of the crystallizer 3.
The heat released by the process gas cooling in the step five is taken away by the evaporative heat exchanger in the urea washing tower 1, saturated water circulates in the heat exchanger, the saturated water is evaporated to generate low-pressure steam, and the evaporation temperature of the saturated water is 145 ℃.
In the above embodiment, the first high-pressure reactor 6 and the second high-pressure reactor 13 are both natural convection circulation reactors.
Comparative example
In order to prove the utility model discloses in the high pressure synthesis low pressure gaseous phase quenching method melamine production system compare and have obvious technological effect in prior art, it is right to combine the actual production effect of embodiment and comparative example below the utility model discloses a technological effect carries out further explanation. The comparative example 1 adopts a high-pressure liquid-phase quenching melamine production system in the prior art; comparative example 2 a melamine production process according to the prior art using a low-pressure gas-phase quenching process, in particular the solution described in the patent document with publication number "CN 102219754A".
The process parameters and technical effects in the above examples and comparative examples are shown in table 1.
It can be seen from table 1 that the utility model discloses in production system compare in high pressure liquid phase quenching method melamine production system or low pressure gas phase quenching method melamine production system among the prior art have the power consumption low, steam consumption low, heat energy consumption low, the investment is little, environmental protection advantage such as effectual, consequently, the technical scheme of the utility model compare and have substantive technological effect in prior art.
It is obvious that the above embodiments of the present invention are only examples for clearly illustrating the present invention, and are not limitations to the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.
Claims (10)
1. The melamine production system of the high-pressure synthesis low-pressure gas-phase quenching method comprises a urea washing tower (1), a reactor connected with the urea washing tower (1), a hot gas filter (2), a crystallizer (3) connected with the hot gas filter (2) and a triamine trap (4) connected with the crystallizer (3), wherein the triamine trap (4) is connected with the urea washing tower (1), and is characterized in that the urea washing tower (1) is connected with the reactor through a high-pressure urea pump (5), and the reactor is a first high-pressure reactor (6); the reactor is connected with a flash evaporator (7), and the flash evaporator (7) is connected with the hot gas filter (2); the urea washing tower (1) is sequentially connected with a cold air demister (8) and a cold air blower (9), and the cold air blower (9) is connected with the crystallizer (3); the first high-pressure reactor (6) is connected with an ammonia gas supply assembly.
2. Melamine production system for high-pressure synthesis low-pressure gas-phase quenching process according to claim 1, characterized in that said ammonia gas supply assembly comprises, connected in sequence, an ammonia gas preheater (10), a liquid ammonia evaporator (11) and a high-pressure liquid ammonia pump (12); the ammonia gas preheater (10) is connected with the first high-pressure reactor (6).
3. Melamine production system for a high-pressure synthesis low-pressure gas-phase quench process according to claim 2, characterised in that a second high-pressure reactor (13) is arranged between the first high-pressure reactor (6) and the flash vessel (7), the second high-pressure reactor (13) being connected to the ammonia preheater (10).
4. Melamine production system for a high-pressure synthesis low-pressure gas-phase quenching process according to claim 3, characterized in that the first high-pressure reactor (6) and the second high-pressure reactor (13) are both natural convection circulation reactors.
5. Melamine production system for high-pressure synthesis low-pressure gas-phase quenching process according to claim 2, characterized in that an internal pipe evaporation type heat exchanger is arranged in the urea scrubber (1), and the internal pipe evaporation type heat exchanger is connected with the liquid ammonia evaporator (11).
6. Melamine production system according to claim 1, characterised in that two sets of hot gas filters (2) and flash evaporators (7) are provided, the hot gas filters (2) being connected to the flash evaporators (7) and the flash evaporators (7) being connected to the reactor.
7. Melamine production system according to claim 1, characterised in that a regenerator (14) is connected to the hot gas filter (2).
8. Melamine production system for a high-pressure synthesis low-pressure gas-phase quenching process according to claim 1, characterized in that a shell and tube heat exchanger is arranged in the flash evaporator (7).
9. Melamine production system of a high-pressure synthesis low-pressure gas-phase quenching process according to claim 1, characterized in that the cold gas demister (8) is a cyclone demister.
10. Melamine production system for a high-pressure synthesis low-pressure gas-phase quenching process according to claim 1, characterized in that the hot gas filter (2) is a bag filter.
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| CN115944942A (en) * | 2022-12-06 | 2023-04-11 | 四川金象赛瑞化工股份有限公司 | Preparation method of cyanamide substance |
| CN115944942B (en) * | 2022-12-06 | 2024-04-12 | 四川金象赛瑞化工股份有限公司 | Preparation method of cyanamide substance |
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