JP4627959B2 - Urea synthesis method - Google Patents

Description

【００５１】
【表２】

【００５２】
【表３】

【００５３】
【発明の効果】
本発明によれば、合成圧力下では、混合ガスの凝縮の温度が高いことを利用し、従来技術では低圧蒸気の発生にのみ用いられた凝縮熱を、ストリッパーからの尿素液（好ましくは減圧後）と凝縮液とを直接に、間接熱交換させ、中圧分解のための熱量を効率的に回収できるようになった。
【００５４】
尿素合成圧力下での混合ガスの凝縮熱を中圧分解の熱回収へ利用することは、従来技術でも行われていたが、機器数が多くなり、混合ガスを分配する必要があるなど系が複雑になっていた。本発明では、縦型凝縮反応器が、Ｕ型冷却チューブの縦型熱交換器であることを利用し、機器数を増加することなく、またはガスの分配をすることなく、チューブシートに仕切りを入れることにより、低圧蒸気の発生と尿素合成液の加熱の両方を同時に行うことが可能となった。この構造により、チューブシートを仕切ることで他の冷媒、例えば、液安、回収液等を導入することがその熱交換器の構造から容易に行い得る。
【図面の簡単な説明】
【図１】本発明の一実施態様を示すプロセスフロー図である。
【図２】本発明の他の実施態様を示すプロセスフロー図である。
【図３】従来技術を示すプロセスフロー図である。
【図４】他の従来技術を示すプロセスフロー図である。
【符号の説明】
１ 尿素合成塔
２ ストリッパー
３ 中圧分離器
４ 縦型凝縮反応器
５ 充填部
６ 中圧分解塔
７ 熱交換器
８ 減圧バルブ
９ａ 縦型凝縮器
９ｂ 縦型凝縮器
１０ エジェクター
１９、２３ 冷却チューブ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in a urea synthesis method, and more particularly to a heat recovery method in a urea synthesis step.
[0002]
[Prior art]
The present applicant has already proposed a heat recovery method in the urea synthesis step, for example, in Japanese Examined Patent Publication No. 62-15070, Japanese Unexamined Patent Publication No. 61-109760, Japanese Unexamined Patent Publication No. 10-182587, and the like.
[0003]
The method disclosed in Japanese Patent Publication No. 62-15070 or Japanese Patent Application Laid-Open No. 61-109760 is as shown in FIG. 3, and urea synthesis is performed via line 11, heat exchangers (ammonia preheaters) 7 and 12. The raw material ammonia supplied to the column 1 is reacted with a condensate (described later) supplied from the line 30 at urea synthesis pressure and temperature. The obtained urea synthesis liquid consisting of urea, unreacted ammonia and carbon dioxide and water is sent to the stripper 2 via a line 16 where it is brought into contact with the raw material carbon dioxide supplied from the line 14 and unreacted from the urea synthesis liquid. The reaction ammonia and carbon dioxide are separated as a mixed gas of ammonia, carbon dioxide and water. This mixed gas is extracted from the line 18, distributed and supplied to the tube side of the two multi-tube vertical condensers 9 a and 9 b arranged in parallel via the lines 32 and 33, and condensed. In the vertical condenser 9a, the condensation heat generated at that time is recovered by supplying water from the line 36 to the shell side and generating low-pressure steam from the line 37, while in the vertical condenser 9b, The urea solution containing unreacted unreacted ammonia and unreacted carbon dioxide, which is supplied to the shell side via the line 19 and is extracted from the stripper 2 via the line 17 and decompressed by the pressure reducing valve 8, is obtained by indirect heat exchange. By heating, it is used as a heating source for decomposition of unreacted ammonia and carbon dioxide remaining in the urea synthesis solution. The urea synthesis liquid heated in the vertical condenser 9b and sent to the intermediate pressure decomposition tower 6 via the line 35 is a urea liquid almost free of unreacted ammonia and carbon dioxide extracted from the line 25, and the line. 26 is separated into a mixed gas composed of ammonia, carbon dioxide, and water. The mixed gas composed of ammonia, carbon dioxide and water discharged from the top of the urea synthesis tower through the line 29 is absorbed by the absorption medium supplied from the line 20 in the filling section 5 of the washing tower, The obtained absorption liquid is sent from the line 31 to the vertical condenser 9 a and absorbs the mixed gas from the line 32. Unabsorbed ammonia and carbon dioxide are sent via line 24 to the recovery process (not shown) along with the gas mixture from line 26. The condensate from the vertical condenser 9b is introduced into the urea synthesis tower 1 via the line 22 together with the condensate extracted from the vertical condenser 9a via the line 34.
[0004]
According to this method, the condensation temperature of the mixed gas composed of ammonia, carbon dioxide and water from the stripper 2 is 170 to 180 ° C., and the temperature level is higher than the temperature 150 to 155 ° C. of the low pressure steam. The temperature can be increased and heat can be recovered efficiently. Further, instead of the vertical condenser 9b, an intermediate pressure decomposition tower, a reboiler or a falling film heater can be installed (not shown) to similarly recover heat.
[0005]
However, in the case of the above heat recovery, the urea synthesis system becomes complicated due to the increase in the number of urea production apparatuses and the need to distribute the mixed gas to the two vertical condensers. Further, the condensation of the mixed gas is performed on the tube side of the vertical condenser, but because of the thin film condensation on the tube surface, it is compared with the bubble column type vertical condensation reactor described in JP-A-10-182587. However, the heat transfer performance is poor and the heat transfer area is increased. For this reason, the vertical condenser is increased in size, resulting in an increase in equipment manufacturing cost and, consequently, construction cost. Further, since the mixed gas is supplied to the tubes of the vertical condensers 9a and 9b and the cooling medium is supplied to the shell side, a plurality of cooling mediums can be supplied by partitioning the shell side to exchange heat with each other. It is not suitable for construction.
[0006]
As shown in FIG. 4, the heat recovery of the above-mentioned JP-A-10-182587 is performed by supplying the mixed gas extracted from the stripper 2 to the line 18 to the vertical condensation reactor 4 having the cooling pipe 23 therein and condensing it. The condensation heat generated at this time is generated by generating low-pressure steam in the cooling pipe 23, and the generated low-pressure steam is a (low) pressure decomposition and separation step of unreacted ammonia and carbon dioxide in the urea synthesis step ( Alternatively, it is used in a urea aqueous solution concentration step). The method of FIG. 4 will be further explained. The raw material ammonia is supplied to the ejector 10 via the line 11, the heat exchanger (ammonia preheater) 7 and the line 12, the condensate from the line 22 is sucked and urea is passed via the line 13 It is introduced into the synthesis tower 1. Part of the raw carbon dioxide from the line 14 is supplied to the urea synthesis tower 1 via the line 15, the rest is supplied to the stripper 2, and the urea synthesis liquid supplied to the stripper 2 from the urea synthesis tower 1 via the line 16 Contact is made alternatingly to separate unreacted ammonia and carbon dioxide in the urea synthesis solution as a mixed gas of ammonia, carbon dioxide and water. The mixed gas is supplied to the vertical condensation reactor 4 via a line 18, while the urea synthesis liquid 17 containing unseparated unreacted ammonia and carbon dioxide is depressurized through a pressure reducing valve 8 and passed through a line 19. It is supplied to the pressure decomposition tower 6. This mixed gas is introduced from the line 20 and is condensed in contact with the absorbing medium flowing down through the filling section 5. The condensation heat generated at this time is removed by the generation of steam as described above. The condensate obtained in the vertical condensation reactor 4 is supplied to the suction side of the ejector 10 via a line 22. The mixed gas that has not been absorbed in the vertical condensation reactor 4 comes into contact with the absorbing medium in the filling section 5 and is then sent to a recovery process (not shown) via the line 24. The urea synthesis solution supplied to the intermediate pressure decomposition tower 6 is heated by steam (steam collected by the cooling pipe 23) and high-pressure steam condensate supplied to the heaters 38 and 39, respectively, and is not discharged from the line 25. The reaction liquid is separated into a urea solution containing almost no ammonia and carbon dioxide, and a mixed gas of ammonia, carbon dioxide and water discharged via the line 26. The mixed gas from the line 26 is sent to the recovery step and recovered together with the mixed gas from the line 24 as described above.
[0007]
However, the use of low-pressure recovered steam with a low temperature level in this method makes it difficult to secure a temperature difference for heating in the separation process of unreacted ammonia and carbon dioxide, which requires a high temperature level. This increases the heat transfer area of the heater of the apparatus.
[0008]
As described above, the related art relating to the heat recovery method in the urea synthesis process has various problems to be solved.
[0009]
[Problems to be solved by the invention]
The present invention seeks to provide a method of performing effective heat recovery in the urea synthesis process and greatly reducing the heat transfer area required in the entire urea production process.
[0010]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems of the prior art, the present inventors have reduced the temperature level to 150 to 155 ° C., which is the temperature of the low-pressure steam, without generating low-pressure steam. In addition, if the heat of condensation of the mixed gas at a high temperature level, that is, a high temperature level of 170 to 180 ° C., is directly used as a heat source for the separation process of unreacted ammonia and carbon dioxide, the heat transfer efficiency is greatly improved. Thus, the present inventors have found that the heat transfer area required for the entire urea synthesis process is greatly reduced, and the present invention has been completed.
[0011]
The present invention provides the following urea synthesis method.
(1) In the urea synthesis column, the raw material ammonia and carbon dioxide are reacted under a urea synthesis temperature and urea synthesis pressure, the resulting urea, unreacted ammonia, a urea synthesis solution comprising unreacted carbon dioxide and water, string Tsu in Pa over, into contact under heating with at least a portion of the raw material carbon dioxide at approximately equal pressure urea synthesis pressure, urea synthesis whereby unreacted ammonia and unreacted carbon dioxide, ammonia, a mixed gas of carbon dioxide and water Separated from the liquid, this mixed gas is supplied to the barrel side of a single vertical condensation reactor having a cooling tube inside and brought into contact with the absorption medium under cooling to condense the mixed gas, and the resulting condensation The liquid is circulated to the urea synthesis tower, while the unreacted ammonia is further removed from the urea synthesis liquid containing unreacted unreacted ammonia and carbon dioxide. A urea synthesis method for separating urea and carbon dioxide to obtain urea,
The urea synthesis liquid from which the mixed gas has been separated in the stripper is supplied to the cooling tube of the vertical condensation reactor, while the mixed gas separated in the stripper is supplied to the barrel side of the vertical condensation reactor. Condensing by indirect heat exchange with the urea synthesis liquid in the cooling tube, heating the urea synthesis liquid in the cooling tube by the condensation heat generated at that time,
Using vertical condensation reactor of the one group, the other heating the supplied urea synthesis solution in the cooling tube, the generation of steam, and / or cooling other than urea synthesis solution supplied to the cooling tube A urea synthesis method, wherein the medium is heated simultaneously .
[0012]
(2) the string Tsu from Pa over, unseparated unreacted ammonia and unreacted urea synthesis solution containing carbon dioxide and reduced to a pressure lower than the urea synthesis pressure of the vertical condensation reactor cooling Ju - The urea synthesis method according to (1) above, wherein the urea synthesis method is supplied to the tank.
[0013]
(3) from the string Tsu Pa over, non-supplied to the unseparated a urea synthesis solution containing unreacted ammonia and unreacted carbon dioxide decompressed intermediate pressure separator is contained in the urea synthesis solution The urea synthesis method according to (1), wherein a part of the reaction ammonia and unreacted carbon dioxide is separated and then supplied to the cooling tube of the vertical condensation reactor.
[0014]
(4) The urea synthesis liquid supplied to the cooling tube side of the vertical condensation reactor is heated to a temperature of 150 to 170 ° C. by the condensation heat of the mixed gas supplied to the vertical condensation reactor. The urea synthesis method according to any one of (1) to (3).
[0015]
(5) The heat recovery method in urea synthesis according to any one of (1) to (4), wherein the cooling tube of the vertical condensation reactor is a U-shaped tube having multiple channels.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the urea synthesis liquid containing unreacted ammonia and the remaining unreacted carbon dioxide discharged from the bottom of the stripper (hereinafter simply referred to as urea liquid) is decompressed by a pressure reducing valve and then the vertical condenser. It is preferably supplied to the cooling tube. This is because the temperature of the urea solution is reduced by reducing the pressure, so that the temperature difference from the condensate on the cylinder side can be increased by being supplied to the cooling tube of the vertical condenser. At this time, the pressure is preferably reduced to an intermediate pressure of 0.01 to 3.0 MPa, more preferably 1.0 to 2.5 MPa, and particularly preferably about 1.5 to 2.0 MPa. It is preferable to separate the mixed gas composed of ammonia, carbon dioxide and water separated from the urea solution by the reduced pressure in the intermediate pressure separator before the urea solution reduced to the intermediate pressure enters the cooling tube. By removing the mixed gas separated before supplying to the cooling tube and supplying only the urea solution to the cooling tube, the urea solution is evenly distributed to each tube, improving the efficiency of heat exchange. is there.
[0017]
The vertical condensation reactor is a vertical heat exchanger having a multi-channel U-shaped cooling tube. By using this vertical condensation reactor, in addition to heating the urea solution from the stripper, the generation of low-pressure steam and other cooling without increasing the number of equipment and / or without distributing gas Heating a medium, for example, raw material liquid ammonia, can be easily performed at the same time.
[0018]
The present invention will now be described in detail with reference to FIGS.
[0019]
FIG. 1 is a process flow diagram illustrating one embodiment of the present invention. The raw material ammonia is pressurized to about 25 MPa from the line 11 and then supplied to the heat exchanger 7, heated to about 175 ° C. with the recovered low-pressure steam and steam condensed water, and supplied to the ejector 10 from the line 12, and the urea synthesis pressure The condensed liquid supplied from the down pipe 22 is sucked and supplied from the line 13 to the urea synthesis tower 1. Raw material carbon dioxide and anticorrosive air are supplied from the line 14 to the bottom of the stripper 2, but a part is supplied to the urea synthesis tower 1 via the line 15.
[0020]
In the urea synthesis tower 1, the urea synthesis reaction proceeds while ammonia, carbon dioxide and anticorrosive air rises in the urea synthesis tower 1 operated at a pressure of 13 to 25 MPa and a temperature of 180 to 200 ° C. After completion of the reaction, the urea synthesis solution is extracted from the upper part of the urea synthesis tower 1 to the line 16 and supplied to the upper part of the stripper 2.
[0021]
The stripper 2 is operated at a pressure of 13 to 25 MPa and a temperature of 160 to 200 ° C., and unreacted ammonium carbamate (unreacted ammonia and unreacted carbon dioxide) contained in the urea synthesis solution is thermally decomposed to ammonia, carbon dioxide, It is separated as a mixed gas consisting of water and inert gas.
[0022]
The separated mixed gas is supplied from the upper part of the stripper 2 via the line 18 to the shell side (body side) of the vertical condensation reactor 4, while urea synthesis containing unreacted unreacted ammonia and unreacted carbon dioxide. The liquid is extracted from the bottom of the stripper 2 to the line 17 and supplied to the cooling tube side of the vertical condensation reactor 4.
[0023]
In the vertical condensation reactor 4, the recovered liquid as an absorption medium supplied from the line 20 (the unreacted ammonium carbamate contained in the urea synthesis liquid from the stripper 2 is mixed with ammonia, carbon dioxide and water at medium pressure and / or low pressure. The solution was separated as a mixed gas and absorbed in water, dilute aqueous ammonia, etc.) at a temperature of about 110 ° C., and the pressure was increased to about 13.5 to 25.5 MPa, and was installed at the top of the vertical condensation reactor 4. It is supplied to the filling unit 5. The filling unit 5 is operated at a pressure of 13 to 25 MPa and a temperature of 160 to 190 ° C., and the absorption liquid from the bottom of the filling unit 5 flows down from the down pipe 21 to the bottom of the vertical condensation reactor 4, Contact with the mixed gas under cooling to absorb and condense it. The shell side of the vertical condensation reactor 4 is filled with the absorption liquid and the condensate from the filling section 5 (both are referred to as condensate together), and the condensation heat (absorption heat) is supplied to the cooling tube 19 and, if desired, Heat is removed by the cooling medium supplied to the cooling tube 23.
[0024]
The vertical condensation reactor 4 is a vertical heat exchanger having a multi-channel U-shaped cooling tube as described above, and preferably supplies water to other channels as the urea solution is heated from the stripper 2. To generate low-pressure steam. In addition, other cooling media such as raw material liquid ammonia can be easily heated.
[0025]
The temperature on the shell side of the vertical condensation reactor 4 is adjusted to 170 to 190 ° C., but the adjustment is preferably performed by adjusting the heat of condensation of the mixed gas by heating two cooling media, for example, heating the urea synthesis liquid and generating steam. Can be done by removing.
[0026]
The condensate on the shell side of the vertical condensation reactor 4 is supplied to the suction side of the ejector 10 through a down pipe 22 having an opening in the upper part on the shell side.
[0027]
The urea synthesis solution supplied from the line 19 to the cooling tube side of the vertical condensation reactor 4 is heated to a temperature of 150 to 170 ° C., which is desirable for decomposing unreacted ammonium carbamate at medium pressure. Since the amount of heat necessary for the medium pressure decomposition is covered by the heat of condensation in the vertical condensation reactor 4, heating of the medium pressure decomposition tower 6 becomes unnecessary.
[0028]
The heated urea synthesis solution is supplied to the intermediate pressure decomposition tower 6 operated at a pressure of 1.5 to 2.5 MPa and a temperature of 150 to 170 ° C., and the urea solution containing almost no unreacted ammonium carbamate is supplied from the line 25. It is supplied to a low-pressure decomposition tower (not shown) in the next step. On the other hand, the mixed gas separated from the urea synthesis solution is supplied from the line 26 to the recovery process.
[0029]
The condensate produced by absorbing the mixed gas from the line 18 flows down through the down pipe 22 by gravity, and after being pressurized by the ejector 10, is supplied to the urea synthesis tower 1. Is supplied to the next process.
[0030]
FIG. 2 is a process flow diagram showing another embodiment of the present invention, in which the urea liquid separated from the mixed gas by the stripper 2 is supplied to the intermediate pressure separator 3, and the mixed gas in the urea liquid is further separated. Then, it is supplied to the cooling tube of the vertical condensation reactor 4.
[0031]
The stripper 2 is operated at a pressure of 13 to 25 MPa and a temperature of 160 to 200 ° C. In the urea synthesis solution, unreacted ammonium carbamate is decomposed into a mixed gas of ammonia and carbon dioxide by stripping with raw material carbon dioxide. It is separated as a mixed gas composed of ammonia, carbon dioxide, water and inert gas. This mixed gas is supplied from the upper part of the stripper 2 to the shell side of the vertical condensation reactor 4 through the line 18, the urea liquid containing unreacted unreacted ammonia and unreacted carbon dioxide is decompressed, and the bottom of the stripper 2 To the line 17 and supplied to the intermediate pressure separator 3.
[0032]
The intermediate pressure separation column 3 is operated at a pressure of 1.5 to 2.5 MPa and a temperature of 120 to 150 ° C. For this reason, the urea synthesis liquid is lowered from the operating pressure and temperature of the stripper 2 to the operating pressure and temperature of the intermediate pressure separator 3 due to adiabatic change to be in a gas-liquid two-phase state, and the gas in the urea liquid is separated. . The urea solution from which the gas in the urea synthesis solution has been separated is supplied from the bottom of the vertical condensation reactor 4 to the cooling tube side via the line 19, while the mixed gas separated from the urea solution is fed from the line 27. Supplied to the recovery process.
[0033]
In the vertical condensation reactor 4, the recovered liquid as an absorption medium supplied from the line 20 is pressurized to about 13.5 to 25.5 MPa at a temperature of about 110 ° C., and is installed on the upper side of the vertical condensation reactor 4. Is supplied to the filled portion 5. The filling unit 5 is operated at a pressure of 13 to 25 MPa and a temperature of 160 to 190 ° C., and the bottom liquid of the filling unit 5 is supplied from the down pipe 21 to the bottom of the vertical condensation reactor 4.
[0034]
The shell side of the vertical condensation reactor 4 is filled with the absorption liquid and the condensate from the filling unit 5, the mixed gas is absorbed and condensed, and the condensation heat is removed by the cooling tubes 19 and 23.
[0035]
In the intermediate pressure separator, the pressure of the urea solution drops from the pressure of the synthesis tower to the pressure of the intermediate pressure separator and becomes a gas-liquid two-layer, so if it is supplied to the cooling tube as it is, the distribution of the urea solution to each tube is uneven. However, if the urea liquid after the mixed gas in the urea liquid is separated by the intermediate pressure separator 3 is supplied to the vertical condensation reactor 4, the distribution to the cooling tubes is performed uniformly, and the heat is Exchange efficiency is improved.
[0036]
The urea synthesis liquid supplied to the tube side is separated from the gas in the urea synthesis liquid by the intermediate pressure separator 3 considering the improvement of heat transfer performance by even distribution to the tube, and only the liquid phase is cooled by the tube. It is preferable to supply to the side.
[0037]
The use of the embodiment of FIG. 1 and the embodiment of FIG. 2 of the present invention depends on the cost of the equipment of the cooling tube and the intermediate pressure separator 3, but when a large vertical condensation reactor 4 is used. If the intermediate pressure separation tower 3 is installed, the cost of the equipment can be reduced somewhat.
[0038]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
[0039]
Example 1
According to the process flow shown in FIG. 1, 1,725 tons / day of urea synthesis was performed. As a result, the heat transfer area required for heating the urea solution from the stripper to 155 ° C. was 285 m 2. This was reduced to about 2/10 to 3/10 of the heat transfer area required in the prior art. The material balance is shown in Table 1. The vertical column represents the number of each line shown in FIG. 1, and the horizontal line represents the pressure, temperature, flow rate and composition of the substance flowing through each line. Table 3 shows the shell side temperature, tube side temperature, overall heat transfer coefficient, and required heat transfer area of the vertical condensation reactor.
[0040]
As shown in Table 3, the temperature difference between the shell side temperature and the tube side outlet temperature of the vertical condensation reactor can be greatly increased, and the overall heat transfer coefficient has been greatly improved. The heat transfer area has been greatly reduced.
[0041]
Example 2
According to the process flow shown in FIG. 2, 1,725 tons / day of urea synthesis was performed. As a result, the heat transfer area required for heating the urea solution from the stripper to 155 ° C. after depressurization was 252 m 2. The heat transfer area required in the prior art was reduced to about 2/10 to 3/10.
[0042]
The material balance is shown in Table 1. The vertical column represents the number of each line shown in FIG. 2, and the horizontal line represents the pressure, temperature, flow rate and composition of the substance flowing through each line. Table 3 shows the shell side temperature, tube side temperature, overall heat transfer coefficient, and required heat transfer area of the vertical condensation reactor.
[0043]
As shown in Table 3, since the mixed gas and the urea liquid were separated from each other and only the urea synthesis liquid was supplied to the tube side as compared with Example 1, it was not necessary to raise the temperature of the mixed gas, and the urea synthesis liquid The uniform heat distribution further improves the overall heat transfer coefficient and further reduces the heat transfer area.
[0044]
Comparative Example 1
According to the process flow shown in FIG. 3, 1,725 tons / day of urea synthesis was performed.
[0045]
The material balance is shown in Table 2. The vertical column represents the number of each line shown in FIG. 3, and the horizontal run represents the pressure, temperature, flow rate and composition of the substance flowing through each line. Table 3 shows the shell side temperature, tube side temperature, overall heat transfer coefficient, and required heat transfer area of the vertical condensation reactor.
[0046]
As shown in Table 3, the temperature difference between the tube side temperature and the shell side outlet temperature of the vertical condensation reactor can be taken, but since the overall heat transfer coefficient is poor due to the thin film flow-down condensation, urea from the stripper The heat transfer area required for heating the liquid to 155 ° C. after decompression was 1,028 m 2.
[0047]
Comparative Example 2
According to the process flow shown in FIG. 4, 1,725 tons / day of urea synthesis was performed.
[0048]
The material balance is shown in Table 2. The vertical column represents the number of each line shown in FIG. 4, and the horizontal line represents the pressure, temperature, flow rate and composition of the substance flowing through each line. Table 3 shows the shell side temperature, tube side temperature, overall heat transfer coefficient, and required heat transfer area of the vertical condensation reactor.
[0049]
As shown in Table 3, the overall heat transfer coefficient can be larger than that of Comparative Example 1, but the recovered low pressure steam cannot sufficiently obtain the temperature difference between the tube side temperature and the shell side outlet temperature of the vertical condensation reactor. The heat transfer area required for heating the urea solution from the stripper to 155 ° C. after depressurization was 842 m 2.
[0050]
[Table 1]

[0051]
[Table 2]

[0052]
[Table 3]

[0053]
【The invention's effect】
According to the present invention, under the synthesis pressure, the condensation temperature of the mixed gas is utilized, and in the prior art, the condensation heat used only for the generation of low-pressure steam is converted into urea liquid (preferably after decompression). ) And the condensate can be directly and indirectly heat exchanged to efficiently recover the amount of heat for medium pressure decomposition.
[0054]
Utilizing the heat of condensation of mixed gas under the pressure of urea synthesis for heat recovery in medium pressure decomposition was also performed in the prior art, but the number of devices is increased, and it is necessary to distribute the mixed gas. It was complicated. In the present invention, the vertical condensation reactor is a vertical heat exchanger of a U-shaped cooling tube, and the tube sheet is partitioned without increasing the number of devices or distributing gas. It was possible to perform both the generation of low-pressure steam and the heating of the urea synthesis solution at the same time. With this structure, it is possible to easily introduce other refrigerants such as liquid ammonium, recovered liquid, and the like from the heat exchanger structure by partitioning the tube sheet.
[Brief description of the drawings]
FIG. 1 is a process flow diagram illustrating one embodiment of the present invention.
FIG. 2 is a process flow diagram illustrating another embodiment of the present invention.
FIG. 3 is a process flow diagram showing the prior art.
FIG. 4 is a process flow diagram showing another conventional technique.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Urea synthesis tower 2 Stripper 3 Medium pressure separator 4 Vertical condensation reactor 5 Packing part 6 Medium pressure decomposition tower 7 Heat exchanger 8 Pressure reducing valve 9a Vertical condenser 9b Vertical condenser 10 Ejectors 19, 23 Cooling tube

Claims (5)

In urea synthesis column, the raw material ammonia and carbon dioxide are reacted under a urea synthesis temperature and urea synthesis pressure, the resulting urea, unreacted ammonia, a urea synthesis solution comprising unreacted carbon dioxide and water, in the string Tsu path over Contacting at least part of the raw material carbon dioxide under heating at a pressure substantially equal to the urea synthesis pressure, thereby separating unreacted ammonia and unreacted carbon dioxide as a mixed gas of ammonia, carbon dioxide and water from the urea synthesis solution Then, this mixed gas is supplied to the barrel side of one vertical condensation reactor having a cooling tube inside, and brought into contact with the absorption medium under cooling to condense the mixed gas, and the resulting condensate is On the other hand, the unreacted ammonia is further circulated from the urea synthesis solution containing unreacted unreacted ammonia and unreacted carbon dioxide. And carbon dioxide was separated by a urea synthesis method for obtaining urea,
The urea synthesis liquid from which the mixed gas has been separated in the stripper is supplied to the cooling tube of the vertical condensation reactor, while the mixed gas separated in the stripper is supplied to the barrel side of the vertical condensation reactor. Condensing by indirect heat exchange with the urea synthesis liquid in the cooling tube, heating the urea synthesis liquid in the cooling tube by the condensation heat generated at that time,
Using vertical condensation reactor of the one group, the other heating the supplied urea synthesis solution in the cooling tube, the generation of steam, and / or cooling other than urea synthesis solution supplied to the cooling tube A method for synthesizing urea, wherein the medium is heated at the same time . Supplied to Bed - said from string Tsu Pa over, non-separation of unreacted ammonia and unreacted carbon dioxide containing urea synthesis solution under reduced pressure to a pressure lower than the urea synthesis pressure the vertical condensation reactor cooling Ju The urea synthesis method according to claim 1. From the string Tsu Pa over, and supplies to the unseparated unreacted ammonia and medium urea synthesis solution containing unreacted carbon dioxide and vacuum pressure separator, unreacted ammonia and contained in the urea synthesis solution The urea synthesis method according to claim 1, wherein a part of unreacted carbon dioxide is separated and then supplied to a cooling tube of the vertical condensation reactor.   The urea synthesis liquid supplied to the cooling tube side of the vertical condensation reactor is heated to a temperature of 150 to 170 ° C by the condensation heat of the mixed gas supplied to the vertical condensation reactor. 4. The urea synthesis method according to any one of items 3 to 3.   The urea synthesis method according to any one of claims 1 to 4, wherein the cooling tube of the vertical condensation reactor is a U-shaped tube having multiple channels.

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