前苏联专利SU1731045A3 None

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专利摘要:
In a process for the production of urea from ammonia and CO2, the carbamate decomposers and/or condensers are equipped with tubes internally lined with zirconium.
公开号:SU1731045A3
申请号:SU853885101
申请日:1985-04-19
公开日:1992-04-30
发明作者:Меникатти Серджо；Миола Чезаре；Гранелли Франко
申请人:Снампрогетти С.П.А. (Фирма)；
IPC主号:

专利说明:

The invention relates to a process for the preparation of urea used as fertilizer in agriculture.
A method of producing urea by chemical interaction of ammonia and carbon dioxide in one or several reactors with the formation of a complex aqueous solution containing urea, ammonium carbamate and excess ammonia used for the synthesis of urea, decomposition of ammonium carbamate in the respective apparatus with the possibility of distillation of decomposition, condensation apparatuses - condensers of the products of decomposition of the carbamate together with a stripping agent of distillation, which may be present in the products of decomposition, which decomposition apparatuses and capacitors are protected from corrosion by using special steels.
The disadvantage of this method is a significant corrosion of the apparatus.
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The purpose of the invention is the elimination of equipment corrosion.
The goal is to achieve a consistent method of urea production by chemical interaction of ammonia and carbon dioxide in a single reactor with the formation of an aqueous solution containing urea, ammonium carbamate and excess ammonia used for the synthesis of urea, decomposition of ammonium carbamate in the corresponding apparatus with the distillation of decomposition, condensation The condensers of the carbamate decomposition products together with the desorption distillation agents that are present in the decomposition products j. moreover, decomposition apparatuses are used, which are protected functional elements of equipment and equipped with pipes in the contact zone with reagents, a distinctive feature of which is the use of pipes, the outer part of which is made of conventional urea-resistant steel and the inner working part -
stainless steel, clad from the inside with a layer of 0.3–0.8 mm zirconium foil not welded to the outer tube sections, and the gap between the outer part and the zirconium foil is 0.2-0.5 mm
It is desirable to conduct the process using cladged process tubes9 obtained by sealing pipe sections made of zirconium inside stainless steel pipe, the external stainless steel pipes being crimped and tightly connected to the zirconia pipes or vice versa, expanding the internal zirconium pipe to obtain the required tight and tight connection to the external pipe section "stainless steel9" from which the inner clad working section is made, is used also to manufacture the outer pipe sections bolochek with
Fig. 1 shows an equipment diagram; , carrying out the proposed method for and 3 - two versions of the welded fastening in the mounting plate of the outer pipe section of stainless steel.
The apparatus f (Fig. 01) for the decomposition and stripping of the carbamate comprises an upper mounting plate 2 and a lower plate 3S through which the working tubes pass
shown pipe 4) stainless steel clad inside zirconia.
In the embodiment shown in FIG. 2, the outer tube section is welded to the mounting plate without removing a part of the inner tube section (from zirconium), which also participates in the welded joint.
In the embodiment shown in FIG. 3, the welding between the outer pipe section and the mounting plate is carried out after the removal of a part of the inner (zirconium) pipe
External pipe sections are recommended to be made of stainless steels or equivalent carbamide resistant alloyed steels, for example, 25 Cr, 22 Nis 2 Mo, or austenitic and / or two-phase austeite-ferritic steels.

Tests carried out on industrial plant strippers with zirconium clad pipes showed that such pipes did not show any visible damage and signs of corrosion after 7000 hours of development in media containing urea and carbamate. Example Carbon dioxide (9167 kg / h) and air (61 kg / h) as inert carrier are fed to the synthesis reactor through a pipeline at 155 bar. Recycled ammonia and ammonium carbamate are also fed to the reactor at 155 bar and 135 ° C through the pipeline and this stream includes 14711 kg / h of ammonia, 8750 kg / h, ammonium carbamate and 3462 kg / h of water. From the reactor (residence time 45 min ) at 150 bar and 190 ° C, water
thief containing, kg / h; ammonia 7628, ammonium carbamate 8750, urea 12500, water 7212 and non-condensable products. The resulting solution is fed through a pipeline to a steamer operating essentially at the same pressure5 as the reactor.
The steamer is a heat exchanger with a falling film of urea-resistant nerve.
pressing steel with the ratio Cr: Ni:: Mo 25: 22/2, in which a water solution flows through the inner part of the tubes in the form of a film, the cap of the exchanger is heated
the wire (5875 kg / h) saturated steam under a pressure of 22 bar to decompose the ammonium carbamate coming from the reactor. Condensates are discharged through the pipeline.
At the bottom of the steamer, a solution (205 ° C) is obtained consisting of ammonia 5593, ammonium carbamate 3777, urea 12500 and water 6198, which are fed by pipeline to the ammonium carbamate residue recovery section.
In the upper part of the stripper, a gaseous mixture is obtained, heated to 190 ° C, including, kg / h: ammonia 4203, carbon dioxide 2805, water 1014, and non-condensable products, which are mixed in a mixer with the ammonium carbamate recirculated solution obtained in the extraction sections downstream from the steamers.
Such a solution of ammonium carbamate, coming through pipeline 10, consists, kg / h: ammonia 2580, ammonium carbamate 3777 and water 2448 (105 ° C and 150 bar),
The resulting mixture of liquid with steam (180 ° C) is fed through a pipeline to a carbamate cooler, in which the vapors fully condense, and heat, condensation is used to create low pressure steam, intended for use in the carbamate recovery sections in the downstream direction,
The output solution from the cooler, riri 155 ° C, is fed through a pipeline to a carbamate separator, in which non-condensable products are separated and sent to the separation section in a downward direction from the steamer via a pipeline
Heated to 155 ° C. The liquid phase consists of 4615 kg / h of ammonia, 8750 kg / h of ammonium carbamate and 3462 kg / h of water and is recycled to the reactor through a pipeline and through a liquid - liquid ejector, in which ammonia is used as a carrier liquid.
As a result, 10096 kg / h of ammonia (95 ° C, 220 bar), obtained by mixing 7083 kg / h of fresh ammonia and 3013 kg / h of recycled ammonia, are fed through the ejector through the pipeline.
Corrosion testing. Tubes are removed from the stripper and replaced with urea-resistant stainless steel tubes with a Cr: N1: Mo ratio of 25: 22: 2, covered from the inside with a layer of various material of different thickness.
Tests. Installing 20 tubes of urea-resistant stainless steel, coated on the inside with a 2 mm thick zirconium layer, after operation for 2000 hours, the corrosion is 3 mm / year.
Testing Install urea-resistant stainless steel tubes coated inside with a layer of 0.3 mm zirconium, of which: 5 tubes have a gap (the difference is
0 between the outer diameter of the outer tube and the inner diameter of the inner tube of stainless steel) 0.2 mm; 10 tubes with an interval of 0.5 mm; 5 tubes with a gap in
5 0.8 mm.
In addition, 20 tubes of urea-resistant stainless steel, coated with a layer of zirconium with a thickness of 0.5 mm, are installed, of which:
0 5 tubes with an interval of 0.2 mm; 10 tubes with an interval of 0.5 mm; 5 tubes with a gap of 0.8 mm.
Finally, 20 stainless steel urea resistant tubes have been installed.
5 stainless steel coated with a layer of zirconium with a thickness of 0.8 mm, of which: 5 tubes with a gap of 0.2 mm; 10 tubes with an interval of 0.5 mm; 5 tubes with a spacing of 0.8 mm.
0 After working for 7000 4
signs of corrosion in the tubes with a gap of 0.2 and 0.5 mm were not detected, while in tubes installed with a gap of 0.8 mm, corrosion was noticeable.
Tests Install 20 urea-resistant silver-coated stainless steel tubes and 20 tantalum-coated stainless steel tubes. After working for 2500 hours, the corrosion for silver-coated tubes is 3.2 mm / year, and for tantalum-coated pipes - 3.5 mm / year.
In tests A and C, corrosion occurs due to leakage of corrosive fluid between the coating tube and the stainless steel tube. In the test, corrosion is due to the fact that silver and tantalum are so soft that they break down under the load they are subjected to when applied as a coating on stainless steel tubes, and their elastic response is inadequate to the operating temperatures at which separation of the coating from the wall of stainless steel tubes.
0
In test A, the zirconium layer of thickness 2 does not have sufficient elasticity to ensure a satisfactory fit to the tube wall.
And in the test, Zirconia coatings of 0.3, 0.5 and 0.8 mm thick, as shown, have sufficient elasticity to fit perfectly to the tube wall with the exception of penetration of corrosive fluid, and in the case of a gap of 0.8 mm such leakage going on.
As a result of the tests, it was established that the coating should be from zirconium with a thickness of 0.3–0.8 mm, and the gap should be 0.2–0.5 mm.
Zirconium coatings less than 0.3 mm thick would be acceptable, but such coatings have difficulty due to mechanical weakness.
Thus, the proposed method allows, in comparison with the known method, to exclude corrosion of the equipment used.

权利要求:
Claims (2)
[1]
Invention Formula
1 about The method of urea production by chemical interaction of ammonia and carbon dioxide in one reactor with the formation of an aqueous solution containing urea, ammonium carbamate and excess ammonia used for the synthesis of urea, decomposition of ammonium carbamate in the corresponding apparatus with the distillation of decomposition products, condensation in the condensers of products
carbamate decomposition together with desorption distillation agents that are present in the decomposition products, decomposition apparatus being used which are protected functional elements of the equipment and equipped with pipes in the contact zone with reagents so as to prevent corrosion equipment, use pipes, the outer part of which is made of ordinary urea-resistant steel, and the inner working part is made of stainless steel, clad from the inside with a layer of 0.3–0.8 mm zirconium foil, rennoy to the outer tube section m, and the gap between the outer and Tew zirconium foil is
0 0.2 - 0.5 mm.
[2]
2. Method pop. 1, characterized in that they use the above-mentioned composite cladded process tubes obtained by sealing the tubular sections of zirconium into stainless steel pipes, the external stainless steel pipes being crimped and tightly connected to the zirconium pipes or vice versa expansion of the inner zirconium tube to obtain the necessary tight and tight connection with the outer tube section.
The method according to claim 1, wherein stainless steel, from which the inner clad working section is made, is also used to make the outer pipe sections of the shells.
0
Fig. /
FIG. 2

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引用文献:

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US4210600A|1976-10-28|1980-07-01|Snamprogetti, S.P.A.|Method for the preparation of urea with a high-yield reactor|

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法律状态:

优先权:

申请号 | 申请日 | 专利标题

IT8420635A|IT1209532B|1984-04-20|1984-04-20|PROCESS FOR THE SYNTHESIS OF UREA AND MATERIAL USED IN ITSELF.|

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