JPS58501374A - Urea manufacturing method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Urea manufacturing method The net heat generated by the urea synthesis reaction can be used more efficiently and more effectively. Regarding a method for producing urea from ammonia and carbon dioxide at high temperature and high pressure that can be used .

One of the methods for producing urea that is actually widely used is the European Che mical News Urea Supplement, January 1, 1969 7 days % on pages 17-20. In the method disclosed therein, high temperature After forming the urea synthesis solution in a reaction zone maintained at high pressure, this solution is heated and Stripped at synthetic pressure by countercurrent contact with carbon stripping gas. , decomposes most of the ammonium carbamate contained in the solution. Stoli A product containing ammonia and carbon dioxide along with gas and a small amount of water vapor The resulting gas mixture is separated from the residual urea production stream and introduced into a condensation zone where it is Condensation forms an aqueous ammonium carbamate solution. This ammonium cal Bamate aqueous solution and residual uncondensed gas are recycled to the reaction zone and converted to urea. Ru. When this gas mixture is returned to the reaction zone and condenses, it forms ammonium carbamate water. There is no need to supply heat externally to the reaction zone as the heat required for conversion to solution is available. do not have.

The heat required for the stripping process is carried out in the vertical tubular heat exchanger where the stripping takes place. Obtained by high-pressure steam that condenses outside. According to the above literature, 1 ton of urea Approximately 1,000 kg of steam is required at a pressure of approximately 25 bar.

In practice, the consumption of high pressure steam (25 bar) is approximately 850 kli per ton of urea. is suppressed. Additionally, the heat used in the stripping process is A portion can be recovered by condensation of the gas mixture. However, this condensation occurs at relatively low pressure. At this power level, only about 3 to 5 bar of steam can be obtained, and the In contrast, this steam can hardly be used either inside or outside the system. It is. For this reason, and especially considering the ever-increasing cost of energy, For example, it is highly desirable to suppress the consumption of high-pressure steam as much as possible, and Depending on the conditions and needs, the generation of excess low pressure steam can be avoided or significantly reduced. Both are equally desirable.

Released during the formation of ammonium carbamate from ammonia and carbon dioxide meet at least a portion of the heat required for the stripping process. Various proposals have already been made for this purpose. However, for various reasons, neither proposal Realistic and lick. For example, British Patent No. 1.147.754 states that A method is described for the synthesis of monium carbamate and urea in two consecutive reaction zones. It is. Newly supplied ammonia and newly supplied carbon dioxide At least a portion of the ammonium carbamate is sent to the first reaction zone, and the ammonium carbame The heat released by the formation of the the urea synthesis solution formed in the second reaction zone at a pressure equal to or less than the pressure in the second reaction zone; transmitted to. As a result, unreacted ammonium carbamate is decomposed. obtained The decomposition products are recovered from the residual urea solution by stripping with inert gas. do.

When carrying out this known method, ammonium carbamate is added in the stripping zone. In order to obtain enough heat to decompose the The carbon oxide must be heated beforehand to a high temperature, e.g. the synthesis temperature maintained in the first reactor. Must be. This preheating of the reactants consumes a significant amount of high pressure steam. and However, only a small portion of the surplus heat obtained during urea synthesis is used in the second reaction. Only about 5 bar of steam can be recovered via the cooling system in the reaction area. child Most of the excess heat is absorbed by the absorption column operated at the pressure in the second reaction zone - in this column Ammonia and carbon dioxide are separated from an inert stripping gas - in It is recovered at relatively low temperatures. The pressure of the steam obtained is low, about 2 bar. Therefore, it can hardly be used within the system.

Another method described in U.S. Pat. No. 952,868 involves a urea synthesis reaction. In this case, the upper part of the tube opens into the space on the tube body side of the heat exchanger. Perform on the torso side. The urea synthesis solution generated in the reaction zone on the tube body side flows down inside the tube and reaches the The ammonium carbamate decomposes due to the heat of reaction transferred through the tube wall, and The ammonia and carbon dioxide released from the solution are It will be collected.

The highest possible temperature is required for maximum decomposition of ammonium carbamate. When using the heat of reaction at the level, ensure heat transfer to the solution to be injected. Indeed, optimization is necessary. To achieve this, the above specification proposes The method involves urea synthesis and S) Perform IJ pinning and compare the NHJCOt molar ratio in the liquid phase in the reaction zone. the gaseous ammonium carbamate fed to the reaction zone ammonium carbamate. By condensing only part of the carbon dioxide and carbon dioxide, the gas can be used for recirculation. With the surplus of the gas mixture, a portion of the gas mixture recovered from the stripping zone is It consists of recycling to the bottom of the reaction zone. Therefore, the amount of urea obtained is in the reaction zone. The amount will be small compared to the amount of ammonia and carbon dioxide supplied.

Due to the high temperatures applied in this method, the materials of construction used must meet high standards of corrosion resistance. Must be satisfied. In addition, one reactor/strip while applying high pressure. Since the combination of uppers has a special design, the capital investment is relatively high. this If the factors are integrated, if this method is actually applied, it will be The European Chemical New+s Urea S UPLEMENT K is not considered to be more economical than the method described. stomach.

The purpose of the present invention is to realize the amount of high-pressure steam necessary for decomposing unconverted ammonium carbamate. We propose a method for producing urea which can be reduced qualitatively and which overcomes the drawbacks of the known methods mentioned above. It is about providing.

These objectives were achieved by a high temperature and high pressure aeration from carbon dioxide and excess ammonia in the reaction zone. forming a solution containing ammonium carbamate and unconverted ammonia; Part of the ammonium carbamate is converted to urea, and the resulting ammonium carbamate is The urea synthesis solution containing carbonate is stripped in the stripping zone to ammonium carbamate is formed in the stripping zone by heat exchange with the reaction zone. While obtaining the necessary heat, process the IJ tubed urea synthesis solution. This can be accomplished according to the present invention to form the product urea either in solution or as a solid. Main departure According to Akira, the pressure of the stripping zone is the same as that of the reaction zone that exchanges heat with the stripping zone. Power - maintained at a pressure of 125-250 bar - maintained at a lower pressure.

Condensation of ammonia and carbon dioxide in the reaction zone results in the presence of relatively large amounts of urea and water. It is preferred to carry out the reaction in a controlled manner, as this increases the average temperature of the reaction zone considerably. reaction The heat of reaction from the reaction zone is exchanged in the stripping zone at a pressure lower than that of the reaction zone. The ammonium carnomate in the urea product stream is utilized to break down this When carried out in this manner, the heat of reaction from the reaction zone is available at high temperature levels and therefore the urea During the decomposition and stripping of ammonium carnogmate from the product stream. can be used more efficiently and effectively than known methods.

As the pressure in the reaction zone increases, the ammonium of carbon dioxide and ammonia Condensation to carbamates occurs at higher temperatures and therefore more heat is transferred to the strip. Can be used to decompose carbamates in the ping region. Preferably a heat exchange reaction zone ) The temperature difference between parts of the IJ tubbing area must be at least about 20 bar. No. As a result, the average temperature difference and driving force between both zones can be increased, and heat exchange is improved. Be effective. Theoretically, a temperature difference of 120 bar or more can be applied, but the The structure of the stripper device becomes complicated. More preferably, the reaction zone is stripped The pressure should be maintained at 40-60 bar above the range. In this way, suitable heat exchange Replacement drive power can be obtained without the use of more complex devices. Furthermore, large Gas mixture released in a low pressure stripping zone rather than applying a pressure differential There is no need to compress the gas to a pressure high enough to recycle it into one reaction zone, so It is advantageous for If the pressure difference is in the range of approx. 40-60 bar, cooling in the middle The gas mixture can be compressed without Heat can be used.

The amount of heat transferred from the reaction zone to the stripping zone is It can be made larger by converting the mate to total urea and water. Thus ammonia and diacid The carbonized carbon is absorbed and the formed ammonium carbamate is dissolved in urea and Due to the presence of water, the temperature of the reaction zone increases by the fraction to which they are added. anti Depending on the pressure maintained in the reaction zone, the temperature increases by about 10-20°C.

To further increase and make maximum use of the heat released in the reaction zone, Stir the contents vigorously to raise the temperature level and It is desirable to increase the heat transfer efficiency of the area. For this purpose, in the pipes of a vertical heat exchanger Stripping is carried out according to a known method, and the tube body side of the heat exchanger is used as a reaction zone. The contents of the reaction zone should be thoroughly mixed to minimize the temperature difference between the top and bottom of the reaction zone. Limit temperature to at least 5℃. To maximize heat transfer, this temperature difference should be kept at a maximum of approximately 2°C. It is preferable to maintain the

The invention will now be described with reference to FIGS. 1-4 of the drawings.

Figure 1 shows urea produced in two steps at the same pressure, and A practice of the invention in which a portion of the gas mixture is fed to a reaction zone that exchanges heat with a stripping zone. The embodiment will be explained.

Figure 2 shows a two-step urea production process in which the second reaction step is carried out at a lower pressure than the first reaction step. A similar implementation of the law.

FIG. 6 shows one embodiment of the invention in which stripping is performed in two consecutive steps. Explain.

Figure 4 shows the present invention which performs stripping by arranging two stripping areas in parallel. An embodiment of this will be described.

In each figure, the device indicated by A has the reaction zone located on the tube body side, and The reactor/steam is illustrated as a vertical shell-and-tube heat exchanger with the beating zone located within the tubes. It's a tripper. In each figure, Bt-j carbamate condenser, C is post-reactor , D is the heater/decomposer, E is the flapper, and F, G, H and K are respectively Carbon dioxide compressor, ammonia heater, ejector and ammonia pump shows. L is the carbamate pump, M is the gas compressor, and N is something else. Showing the ejector.

In the embodiment of the invention illustrated in FIG. 1, urea, water, uncondensed carbamate and free All lines 51 of the urea synthesis solution containing ammonia are connected to the reactor/stripper A. is introduced into the stripping zone, heated and directed against the gaseous stream of carbon dioxide. Flow with the flow. diacid compressed by compressor F to a pressure of e.g. 140 bar carbon is fed through line 1 and into the stripping area through line 2. Introduce. Adding air containing an inert gas mixture or oxygen to the carbon dioxide to maintain the substances in contact with the ammonium carbamate-containing solution in a passive state and at high temperature. Ru. The stripping zone absorbs the heat needed to decompose the ammonium carbamate. Ammonia and carbon dioxide gases supplied and formed by heat exchange from the reaction zone The mixture is forced out of the urea synthesis solution along with the newly introduced carbon dioxide and added to the line. 4 from the stripping zone of reactor/stripper A. line 5 recover the stripped urea product stream from the stripping area through the Small amounts of ammonium carbamate still present after treatment using known methods Remove the solution and process to form concentrated urea solution or solid urea.

The gas mixture removed from the stripping zone through line 4 is transferred to compressor M K, for example to a high pressure of 190 bar, and then divided into two parts. on the other hand part of the reactor through line 10) The bottom of the reaction zone on the tube body side of IJ tube A and the remainder to carbamate condenser B maintained at the same pressure as the reaction zone. through line 12. Mainly, the ammonia required for the synthesis reaction is from line 3, port 1 ammonia is fed directly to the reaction zone through heater G and line 11. death However, a portion of the required ammonia is also sent via line 39 to carbamate condenser B. send to In the carbamate condenser B, the air is supplied from the flapper E through line 16. ammonium carbamate solution supplied and freshly supplied through line 59. Gas supplied from the stripping area through line 12 in the presence of ammonia The gas mixture is partially condensed and this heat of condensation is used to generate steam at e.g. 3-6 bar. create.

The level difference between the Suffler E and carbamate condensate 3 is too small, and the Suffler – There is sufficient hydrostatic pressure to transport the carbamate solution from carbamate condenser B to E. When not, the ejector is powered by ammonia supplied through line 39. N is used to assist this conveyance.

The ammonium carbamate solution formed in carbamate condenser B is passed through line 17. to the bottom of the reaction zone of reactor/stripper A. In this reaction zone, the line Most of the ammonia and carbon dioxide supplied through 10 and 11 are ammonia Converted to umcarbamate. Contained in carbamate solution through line 17 This ammonium carbamate is partially converted along with ammonium carbamate. It becomes urea and water. To ammonium carbamate of ammonia and carbon dioxide The conversion of carbamate to urea and water is an exothermic reaction that releases heat. oxidation is an endothermic reaction that consumes heat. However, as a result of the true reaction, excess heat is generated. , this heat is removed from the reaction zone by heat exchange in the reactor/stripper A. transmitted to the region. According to the present invention, the heat maintained in the IJ tube region is higher than Ammonium carbamate and urea are formed in the reaction zone under pressure, so Excess heat is available at lower temperature levels. Therefore, through line 31 the stripper Significant amounts of ammonium carbamate present in the urea product stream fed to the Parts can be decomposed without the need for additional heat from an external heat source.

Furthermore, the reaction area is The reaction is carried out by continuing the conversion of ammonium carbamate to urea and water at The temperature in the zone can be further increased, thus reducing the excess transferred to the stripping zone. The amount of excess heat increases. This effect occurs as the reactivity in the synthesis zone shifts to an equilibrium state. It will further increase. For example, in the exemplary embodiment illustrated in FIG. pressure in bar, ammonia dicarbon dioxide molar ratio of 340:1, and (146: When an equilibrium amount of urea of approximately 50% is produced at a water:carbon dioxide molar ratio of 1, the reaction zone is leveled. The average temperature will be approximately 195°C. The amount of urea produced is 60%, 70%, 80% (4 and 90%, the temperatures are approximately 196.199, 201 and 206, respectively. It becomes ℃.

The temperature increase resulting from higher conversion of ammonium carbamate to urea and water The rise is important for the temperature difference between the two ends of the heat exchange surface of the reactor/stritz/:-A. . in general.

Make sure that the amount of urea produced is at least 70% more than the amount of urea produced in equilibrium. Select conditions. However, as the production of urea shifts to equilibrium, the reaction rate decreases. Since the amount of urea decreases extremely, it is necessary to produce urea in an amount exceeding the equilibrium amount of 90 requires longer contact times and therefore increases the reaction zone volume to the point that there is no benefit to it. Must.

If the pressure in the reaction zone is given, the amount of excess ammonia, the molar ratio of H, O/COt and contact time are determined. In this case, the gas mixture supplied through line 10 The amount is also determined in the same way. This is because the amount of this gas mixture determines the contact time. It is from. Therefore, increasing the amount of gas mixture introduced will not increase the amount of heat transfer. do not have. Unutilized heat is discharged from the stripping zone of reactor/stripper A. A portion of the discharged gas mixture is condensed in carbamate condenser B and scrubber E. to produce steam, or the heat released by this condensation can be used to The gas stream is heated and recovered from the process.

Equalize the temperature distribution as much as possible and minimize heat transfer to the stripping zone. Vigorous agitation within the reaction zone is highly desirable to achieve this. A certain level of The mixing is done by flowing the gas mixture and ammonium carno(mate solution) from bottom to top in the reaction zone. You can achieve it if you do. However, this mixing requires the use of baffles, guide plates, and other members in the reaction zone. If it is, it can be made even stronger, and as a result, the heat transfer efficiency will also be improved.

Together with a predetermined amount of a gas mixture powered from ammonia, carbon dioxide, water and an inert gas , reactor/s) Urea, water, and ammonia discharged from the reaction zone of IJ horn <-A The solution of a and unconverted carbamate is passed through line 19 to one reactor/stripper. After being maintained at the same pressure as the reaction zone of A, it is introduced into reactor C. Reaction conditions in the post-reactor until at least 90% of the equilibrium amount of urea obtainable under conditions has been produced. Continue the conversion of monium carbamate to urea. The heat required for this conversion is line 1 The uncondensed part of the gas mixture fed to the Carno (mate condenser B) is 40 to a post-reactor where the portion is condensed to release the heat of condensation and the ammonium It is obtained by releasing both the heat obtained by the formation of carbamates. or Separately, together with the carbamate solution formed in the carbamate condensation zone B, The uncondensed gas mixture from the condensation zone B is sent to the reaction zone of the reactor/IJ tube A. can be done. However, in the latter case, the heat required in post-reactor C is For example, most of the gas mixture from the reaction zone of the reactor/Stritz/C-A is post-reacted. It needs to be sent to a vessel and condensed there.

The urea synthesis solution formed in the post-reactor C is passed through an expansion valve (pressure reducing valve) 41 to a stripping area. The pressure of 0 to a gas-liquid separator SK where ammonia, A gas mixture consisting of carbon dioxide and water vapor is separated. Reactor/Stritz<- line 42 to the gas mixture withdrawn from the stripping zone of A through line 4; Add this gas mixture via. The remaining urea product stream from the gas-liquid separator S is In 31 to the stripping zone of reactor/stripper A.

A gas mixture consisting of inert gas, carbon dioxide and water vapor is removed from post-reactor C. Then, the reaction zone of reactor/stritz-A, carbamate condenser B and post-reaction It is supplied through line 21 to Scratchno Z-E, which is maintained at the same pressure as vessel C. school At the rubber E, water or dilute Carnomeme, supplied through line 25, Recover ammonia and carbon dioxide by scrubbing with a solution At the same time, the absorbed heat is extracted. The resulting ammonium carbamate solution is passed through line 16. Then, if necessary, it is sent to carbamate condenser B via ejector N, while the remaining The exhaust gas mixture leaves Skratno<-E via line 24. This invention In embodiments, high pressure steam is used to decompose unconverted ammonium carbamate. Not applicable.

In the embodiment shown in FIG. 2, only the reaction zone of reactor/stripper A, e.g. Except for maintaining a high pressure of 0 bar, B, post-reactor C and scrubber E are all at the same low pressure, e.g. 140 bar. maintain. In this case, the gas sent from the stripping zone to the reaction zone through line 10 is Only a portion of the gas mixture needs to be compressed to high reaction zone pressure. Therefore, in Figure 1 A smaller compressor can be used than in the embodiment. Urine generated in the reaction zone Reduce the pressure of the raw product solution to the stripper, carbamate condenser, post-reactor, and scrubber. Lower the pressure to the low-pressure part of the system consisting of the tube, and use pump L to remove the carburetor. The carbamate solution formed in the mate condenser is pressurized to the reaction zone pressure, and this into the reaction zone. In this embodiment of the invention, the unconverted Decomposes ammonium carbamate.

In the embodiment of the invention shown in FIG. The mate-containing urea synthesis solution is sent through line 43f to the heater/decomposer, where it is Decomposes a portion of the ammonium carbamate and recovers it from the remaining urea product solution do. The pressure in the heater/decomposer is maintained at approximately the same pressure as in the reaction zone and post-reactor C. is preferred, but this pressure may be lower than the reactor pressure. This heater/decomposer may be a countercurrent or cocurrent type heater, in other words, the liquid flow and the free gas flow Any heater that allows co-current or counter-current flow may be used. The heater/decomposer is connected through line 44. ammonium carboxylate at high temperature by supplying a small amount of air or other oxygen-containing gas mixture to Passivates equipment that comes into contact with the mate solution and increases its corrosion resistance.

In the heater/decomposer, urea synthesis is carried out at a temperature of, for example, 180-220°C using steam. The solution is heated to decompose some of the ammonium carbamate present and Generates a gas mixture consisting of ammonia, carbon dioxide, water vapor and an inert gas . This gas mixture is passed through line 10 to the ejector H to the reactor/stripper. A is introduced into the reaction zone. Renewed by pump K through heater G and line 11 This ejector is driven by ammonia supplied to the ejector.

Made from urea from heaters/decomposers that still contain ammonium albamate. The product stream is depressurized by expansion valve 41 and the resulting gas-liquid mixture is separated by line 20. into separator S, where the gas mixture generated by the expansion is separated from the urea product stream. and sent to carbamate condenser B via lines 42 and 12. Next, the urea The stream is sent from separator S to the reaction zone of reactor/stripper A for further ammonia Decomposes nium carbamate. Some of the ammonium carbamates are already heated The decomposition in this stripping area is more This can be achieved with a small heat transfer area and therefore a small amount of carbon dioxide stripping gas. . In this way, all the carbon dioxide is passed through the stripping zone into line 2 and into the system. Alternatively, a portion of the total amount of carbon dioxide required by the system may be added to the reaction zone. can be supplied directly via line 45.

The gas mixture leaving post-reactor C is sent via expansion valve 22 to scrubber E to Collect ammonia and carbon dioxide. In this embodiment, skratno (-E is an anti- Same pressure maintained in reactor/stripper A reaction zone and carbamate condenser B operated by.

In the embodiment according to the present invention shown in FIG. 4, the reactor/s) IJ collar A stripping In the processing area, only a part of the urea synthesis solution produced in the post-reactor C is treated, and the remaining It is also possible to treat the second part with a heater/decomposer. Preferably a heater /The pressure maintained in the decomposer is the same as that in the stripping zone. but, It is also possible to apply lower pressures in the heater/decomposer, in which case an ejector that can be driven by a portion of the freshly supplied ammonia, e.g. The released gas mixture can be sent to the Carno (mate condenser B).

In this embodiment, similar to the embodiment of FIG. Stripping reactor/stripper A by decomposing only a portion of the carbamate Therefore, a smaller heat transfer area is sufficient, and the storage A lower amount of carbon dioxide stripping gas can be applied in the ripping zone. Ru.

The embodiment of the invention shown in FIGS. 1 and 2 will be explained in more detail by the following examples. explain.

Example■ Urea was produced according to the embodiment shown in FIG. per ton of urea production Ammonia pump K supplies 400 kg of ammonia, and heater G supplies 11 kg of ammonia. heated to a temperature of 0°C and reactor/stripper A through line 11. be introduced into the area. On the other hand, the reactor/stripping via compressor F and line 2 763 units of carbon dioxide and 29 kg of inert gas ( Mainly air). Reaction zone and stripping zone of reactor/stripper A pressures are maintained at 186 bar and 137 bar, respectively.

The reaction zone of the reactor/store IJ tube A is supplied with a line 10 having a temperature of 227°C. Ammonia 513 kg, carbon dioxide 721 k17, water 43 yu and inert gas 21 A gas mixture consisting of 624 kg of carbon dioxide, 540 kg of carbon dioxide, and 173 kg of water are supplied.

Reactor/S) The volume of the reaction zone of IJ tube A, and therefore the contact time therein, is: At that pressure and a corresponding temperature of about 193°C, 1084 kg of ammonia, Contains 674 yu of carbon dioxide, aookg of urea, 456 yu of water, 9 yu of inert gas, and 21 yu of inert gas. so that a gas-liquid mixture is formed. Carbamate condensation through line 40 Along with the gas mixture withdrawn from vessel B, it is withdrawn from the synthesis zone through a 19 ft line. The gas-liquid mixture taken is then maintained at the same pressure as the reaction zone (186 bar) in reactor C. During the reaction, at a temperature of 196°C, 842 kg of ammonia and 456 kg of carbon dioxide were produced. 1,000 kg of urea, and 510 yu of water to form a urea synthesis solution. reaction The amount of urea produced in the This is approximately 76% of the amount that would be obtained if

After expanding this urea synthesis solution to 137 bar with an expansion valve 41, ammonia 44 kg, 21 kg of carbon dioxide and 9' kg of water vapor. It is separated in a liquid separator S, and from this separator at a temperature of 188°C, 798 ml of ammonia, A urea product solution consisting of 415 kg of carbon dioxide, 1000 yu of urea and 501 kg of water. Take out the liquid. This urea product stream is then transferred to the stripping pin in reactor/stripper A. stripping area, where it is brought into countercurrent contact with freshly supplied carbon dioxide and stripped. 1000 kg of urea, 450 kg of water, 124 U of ammonia and carbon dioxide. A urea product containing 161 kg of urea remains. Gases released during the stripping process 674 kg of ammonia, diacid, along with carbon dioxide stripping gas used Gas containing 987 kg of carbonized carbon, 51 kg of water vapor, and 9I in inert gas 29 Form a mixture. This gas mixture is combined with the gas mixture separated by the gas-liquid separator S. compressed to a pressure of 186 bar. The gas mixture compressed together in this way is partially was supplied to the reaction zone of IJ tube A, and ammonia 205 was added to 9 , a residual portion consisting of 287 units of carbon dioxide, 17 units of water vapor and 8 kg of inert gas. Ammonia 227 generated in the newly supplied ammonia and the flapper E ammonium carbamate solution consisting of 271 units of carbon dioxide and 157 units of water A part of it is condensed together with carbamate condenser B. The heat released by this condensation is recycled and used to produce 355 kg of saturated steam at 55 bar. This invention According to an embodiment of the invention, high pressure steam (20-30 bar) for the decomposition of unconverted carbamates ) consumption is zero.

Example■ Urea is produced according to the embodiment illustrated in FIG.

For each ton of urea produced, 1 ampere is added to the pump in the reaction zone of reactor/stripper A. 400 kg of ammonia is heated at 110°C by the monia heater G and line 11. 569 kg of ammonia, 781' kg of carbon dioxide, a gas mixture consisting of 45 kg of water and 22 kg of inert gas and into line 17. Therefore, at 165°C, 611 kg of ammonia, 516 kg of carbon dioxide, and 172 kg of water A carbamate solution consisting of g. In the reaction zone, ammonia was heated at a temperature of 193°C. Near 1127kl11. 710 kg of carbon dioxide, 800 yu of urea, 457 yu of water, and A gas-liquid mixture is formed consisting of 22 kg of inert gas. The amount of urea generated in the reaction zone is Possible urea when the conversion of ammonium carbamate to urea reaches equilibrium The amount is approximately 67-. This gas-liquid mixture is expanded to a pressure of about 167 bar, and Contains 18 kg of ammonia, 15 kg of carbon dioxide, 1 part of water and 7 kg of inert gas. reacted in post-reactor C together with the gas mixture fed through line 40 with and produce an additional 200 kg of urea. As a result, 9 out of 1000 urea 9 is obtained in the urea synthesis solution 2862 containing. Temperature and pressure are each 18 At 2°C and 175 bar, in addition to 9 in 1000 urea, 883 kg of ammonia A. React this urea synthesis solution containing 469 units of carbon dioxide and 510 units of water. Gaseous carbon dioxide 75 Stripping is performed using 5 kg at a pressure of 137 par. As a result, 100 0 kg of urea, 450 kl? of water, 124 kg of ammonia and 161 U. A urea product stream containing carbon oxide remains.

Of the gas mixture withdrawn from the stripping zone of reactor/stripper A, 1417 kliJ is compressed by compressor M at a pressure of 186 bar, Continue pumping into the reaction zone. On the other hand, ammonia 190 kII, carbon dioxide 260 The remaining gas mixture, consisting of 15 parts water and 7 kli of inert gas, is ammonia. 167 kg of ammonia, 272 kg of ammonia, 271 kg of carbon dioxide, and 157 kg of water Carbamate condenser using carbamate solution from flapper E consisting of g. Partly condense in B. The resulting ammonium carbamate solution was prepared as described above. Pump L and line 17 feed the reaction zone of reactor/stripper A; The remaining uncondensed gas mixture is supplied to the post-reactor via line 40 as previously described. supply.

The heat released in carbamate condenser B is recovered to produce 527 bar of saturated steam. Used to break down kg.

This embodiment of the invention also provides high decomposition of unconverted ammonium carbamate. Pressure steam (20-30 bar) is necessary.

FIG.1 FIG.4 1) Anzu Kuni beef Continuation of page 1 ○Inventor - y' Kogel Mario Fustaf Rozier Tailly Netherlands 6191

Claims (1)

[Claims] (1) Reaction zone and step) Ammonia and diacid at high temperature and high pressure using IJ wrapping zone. When producing urea from carbon dioxide, carbon dioxide and the ammonia are produced in the reaction zone. The ammonium carbamate is converted into ammonium carbamate. The product urea, unconverted ammonium carbamate and excess atom are converted to urea. forming a reaction zone effluent containing ammonia; these conversions generate net heat; and In the stripping zone, a urea product stream containing unconverted ammonium carbamate is is heated to remove a small amount of the ammonium carbamate by heat exchange with the reaction zone. The gaseous ammonia and gaseous ammonia produced from the urea product stream are In the method for recovering carbon dioxide, the reaction zone that exchanges heat with the reaction zone is The stripping zone is maintained at a pressure of between ~250 bar and the reaction The above method is characterized in that the pressure is maintained at a pressure lower than the pressure in the region. (2) Bringing the strain to a pressure approximately 20 to 120 bar lower than the pressure maintained in the reaction zone. 2. A method according to claim 1, characterized in that the ripping zone is maintained. (3) the strip is placed at a pressure approximately 40 to 60 bar lower than the pressure maintained in the reaction zone; 3. A method according to claim 2, characterized in that a ping area is maintained. (4) In the reaction zone, the amount of urea produced is obtained in equilibrium under the reaction conditions of the reaction zone. Ammonium carbamate urine until at least 50% of the amount of urea that should be removed The method according to any one of claims 1 to 5 that continues the conversion to Law. (5) In the reaction zone, the amount of urea formed is obtained in equilibrium under the reaction conditions of the reaction zone. Ammonium carbamate urine until the amount of urea that should be removed is at least 70%. 2. The method according to claim 1, characterized in that the conversion to elementary particles continues. (6) Claim No. 1 characterized in that the contents of the reaction zone are vigorously stirred. The method according to any one of items 1 to 5. (7) The reaction zone and the step) The IJping zone is provided in a vertical shell-and-tube heat exchanger, The stripping zone is provided in the tube of the heat exchanger, and the reaction zone is provided in the tube of the heat exchanger. It was installed in the tube body of the exchanger, and the temperature difference between the upper and lower parts of the reaction zone was limited to a maximum of 5°C. A method according to claim 6, characterized in that: (8) A patent application characterized in that the temperature difference between the upper and lower portions of the reaction zone is limited to a maximum of 2°C. The method described in item 7 of the scope of the request. (9) The reaction zone outflow zone is introduced into the post-reaction zone, where the ammonium carbamate further converted to urea, unconverted ammonium carbamate, and the reaction zone. urea in an amount that is at least 9° of the amount of urea that would be produced in equilibrium under conditions of and stripping this hindlimb urea product stream. According to any one of claims 1 to 8, the invention is characterized in that the invention is introduced into a region the method of. αQ Heating the urea product stream from the post-reaction zone before introducing it into the stripping zone ammonium carbamate, where at least a portion of the ammonium carbamate is added. Decomposes thermally to produce a gas mixture containing ammonia and carbon dioxide and carbames. forming a urea product stream with a reduced urea content and directing the gas mixture to the reaction zone. and introducing the urea product stream into the IJ wrapping area. A method according to any one of claims 1 to 9. α Co.) Direct the urea product flow from the IJ stripping zone to the second stripping zone. where the ammonium carbamate is further decomposed and converted into urea According to any one of claims 1 to 9, which is characterized in that the product flow is recovered. Method described. (2) Only a portion of the urea product stream from the post-reaction zone is introduced into the stripping zone. and the remaining portion of the urea product stream from one post-reaction zone to a second stripping zone. The ammonium carbamate is decomposed into ammonia and carbon dioxide. forming a gas mixture containing urea and passing this gas mixture into the remaining urea product stream. 10. The method according to claim 9, characterized in that the method is separated from the above. (To) A patent application for maintaining the second stripping area at the same pressure as the stripping area. The method according to claim 11 or 12.