CS219889B2 - Method of combined production of ammonium and urea - Google Patents

Abstract

In a process of the so-called integrated type for the production of ammonia and urea, the absorption of CO2 from the crude gases passing to the ammonia synthesis reactor is effected by means of an absorption apparatus which is divided into two sections, one of which is of the type with adiabatic plates (6) and the other is of the type with a thin-film tube bundle (9). Most of the CO2 is removed in the thin-film absorber, and the remainder in the adiabatic plate absorber. <IMAGE>

Description

(54) A method for the combined production of ammonia and urea ⁱⁿ yn ^and falsehood relates komibinovaneho urea production process and ammonia, in particular, ^p and ^k combined · urea production process and ammonia is improved in the absorption of carbon dioxide · the zone in which the formed ammonium carbamate .

From Italian patent no. 907469 it is known that the absorption of carbon dioxide contained in the raw gas for ammonia synthesis is carried out using an ammoniacal aqueous ^eh a solution in fhmoivém exchanger, the aqueous ammoniacal _ solution was fed to both · bottom, and ^{the time} t in the top and ^{it to} him b ^s · ^t mangers heat ftlmověto ypu.

Unfortunately ^, about 20% of the ammonia evaporates during the absorption step. This ammonia must be partially condensed and reintroduced into the carbon dioxide absorption device. Zb ^y tek ammonia which is still present in the pl ^{y H} NEC leaving the zone ^Y 'absorption kyshčmku carbons ^itéh O ·, which is zón'a in ^the mechanics with a TVOne karbamman am · ^Onny, UV ^Adi after the above-mentioned ^s · partial condensation in the absorber amornaku ^wh e this ammonia together with ammonia coming from the device with • ^y ntézu ammonias absorbate ev ^{e j} water.

The inventive method eliminates the complication of the production ^{of YKL} c ua considerable costs Ojen ^{p s p} s · Rovai tions · ^d and ^b sor ^p tion of carbon dioxide as described above · · · according to the prior art.

The present invention is a process for combined production of ammonia and urea, in which ^even if amoQ synthesized. this ammonia is absorbed in water and the resulting concentrated ammonia solution. The carbon dioxide from the raw ammonia synthesis gas is absorbed, and then the resulting solution of ammonium carbaminate in the concentrated ammonia solution is treated to urea. The process according to the invention is characterized. in that the raw gas for ammonia synthesis is de-carbonated by a two-stage absorption in an α-absorber consisting of two independent sections, the lower section of which is a film absorber and the upper section is a plate absorber, the absorption solution in bottom · section using ammoniacal ammonium carbonate solution, odpadajícího · distillation of urea solution as an absorbent solution in the upper section using concentrated aqueous · ammonia solution, whereby the raw gas for ammonia synthesis contain carbon-carbon ^chit characterized initially judicious · ^ ^d of the bottom section · bottom section. after · passing through the bottom section of the ^h orn ^s CASTTM of ^d weighing ^says to S-stimulus No. ^& STI Torn section and after passage through the upper section of · the upper part removed, whereby the above-mentioned absorption solution into individual sections result in counter current to the raw gas stream for ammonia synthesis.

Known measures of the combined process of the present invention include the production of ammonia in an ammonia synthesis plant by absorbing ammonia leaving the synthesis reactor in water to form a concentrated ammonia solution, which is then used to absorb the carbon dioxide contained in the raw gases for ammonia synthesis. Following the carbon dioxide absorption of the present invention to form ammonium carbaminate, the ammonium carbaminate is partially converted to urea in the urea synthesis reactor, the unconverted carbaminate is thermally decomposed to urea, and the decomposition products are stripped off with a gas selected from ammonia, carbon dioxide and inert gases, ammonia being preferred; the urea solution still containing carbamate is discharged from the stripping zone, the carbamate decomposition products are recycled to the urea synthesis reactor, the urea solution is recycled. subjected to distillation at a pressure of 0.29 to 2.9 MPa in one or more stages to obtain liquid ammonia and one or more ammonium ammonium carbonate solutions, on the one hand, and a final aqueous ammonium carbaminate-free urea solution, on the other hand.

The carbon dioxide is then absorbed in two separate sections of the same apparatus.

The main part of the carbon dioxide is absorbed in the tube section. The absorbent solution is an ammoniacal ammonium carbonate solution obtained by distillation of the urea solution under reduced pressure after the bulk of the ammonium carbaminate has been removed at a pressure substantially equal to the pressure during synthesis. This absorbent solution flows smoothly over the walls of the tubes in the form of a thin film and the heat of absorption is removed by the action of a cooling liquid which flows around the outer wall of the tubes. The remainder of the carbon dioxide is removed in a plate section that is substantially adiabatic. The absorption liquid in this section is a concentrated solution of ammonia in water.

The pressure at which the urea solution is distilled to obtain an ammoniacal ammonium carbonate solution is from 0.29 to 2.9 MPa.

Liquid ammonia is preferably used in competition with the concentrated aqueous ammonia solution. The preferred weight ratio of liquid ammonia to concentrated aqueous ammonia solution is from 1 to 5.

The absorbent liquid is introduced into the film-type absorption section through a distributor device located in the intermediate zone between the two absorption sections.

Similarly, the absorbent liquid (concentrated aqueous ammonia additive, optionally supplemented with liquid ammonia) is introduced into the plate-absorbent section at a point in or near the top of the plate-absorbent section. The solution leaving the plate section is fed directly into the urea synthesis reactor. Alternatively, it may be passed through a suitable distributor to a film absorption section where it flows in the form of a film along the surface of the tubes together with an ammoniacal ammonium carbonate solution which is directly fed to the film absorption section.

In the film absorption zone, the carbon dioxide is absorbed to such an extent that its residual gas content is 2 to 3% by volume.

During this step, some ammonia evaporation occurs so that the carbon dioxide-free gas has an ammonia content of 10-12% by volume. This gas then enters the top of the plate absorption section, where it completely removes both carbon dioxide and ammonia by washing.

In the process according to the invention, it is not only possible to reduce the required exchange surface, but can also operate under conditions of high safety due to the considerable excess of ammonia and its relative heat capacity.

According to the invention, the carbon dioxide is thus absorbed in two serially arranged absorption sections. In the first section, the absorption takes place in a film-like manner, while in the second section the remaining carbon dioxide which has not been absorbed in the film section is absorbed in the plate section of the apparatus.

The carbon dioxide-containing raw ammonia synthesis gas is introduced into the bottom or near the bottom of the film absorption section and the absorption liquid (ammoniacal ammonium carbonate solution) is introduced into or near the top of the absorption section. The gas discharged from the top of the film-absorbent section is fed to the bottom or to a location near the bottom of the plate-absorbent section. The absorbent liquid in the second section, consisting of a concentrated solution of ammonia in water, optionally supplemented with liquid ammonia, is fed in countercurrent to the top of the plate section. The carbon dioxide-free gas is discharged from the top of the plate-absorbing section, while the solution obtained at the bottom of the plate-absorbing section may optionally be utilized as an additional absorbent liquid in the film-absorbing section.

One possible embodiment of the method according to the invention is shown in the attached drawing:

Raw ammonia synthesis gas is passed through line 2 to the bottom of absorber 1. Ammonia solution is fed into line 3 through absorber 1. The recycled carbonate is passed through line 4 to the film section of absorber 1. The concentrated carbamate solution is discharged from the bottom of the absorber 1 via line 5 to a urea synthesis reactor. From the film section, the gas partial removal of carbon dioxide discharged d> o · plate section 6. In the bottom plate section 6 via line 8 discharged solution, which is further processed in the reactor with ^the n zu ^y n ^y. Pl ^y n ^P ro · synthesis of ammonia stripped ^to ysličníku dioxide is withdrawn from the upper portion labbor, bé'ru conduit 9th

Následujírn ^p of manufacture ^to ice lepmmu serve ^to illustrate the invention. The example is merely ilustra6 tive charalkter and range in ^y n and ^l in Cutting ^None way limited.

Example

In order to obtain 100,000 t / h of urea, a raw gas having the following composition is introduced into the lower part of the absorber 1 shown in the accompanying drawing, which operates at a pressure of 19.1 MPa, via line 2:

Component Amount (nm ^{3 /} h) Lynn ^P content in the mixture (% ° bj). Ar 215 0.24 H2 55 425 61.52 N2 18 161 19.99 CH4 251 0.28 WHAT 390 0.43 CO2 15 804 17.54

The working temperature is ¹⁷⁵ ° C.

Line 3 refers to a 50 ° C ammonia solution having the following composition:

NH3 HaO total

370 kg / h

6343 to ^g / h 31713 kg / h ⁸ 0 wt.

²⁰ %. ^h mot.

The recycled carbonate is introduced into the film section of absorber 1 via line 4 at a temperature of 103 ° C.

NHs 5,558 kg / h 2, ^6, 75 wt. CO2 7076 kg / hr ^34.24 % wt. H2O 8,059 to ^g / h 3 ^9.0 1 wt. total 20,663 k ^g / h

The concentrated carbamate solution exits the bottom of absorber 1 and is fed to the urea reactor via line 5 at 140 ° C.

NH3 24,834 to ^g / h ^35.43 % wt. CO2 31,343 kg / h ^{44 7} 1%. H2O 13,920 to ^g / h ^19, 86 wt. total 70,097 kg / h ¹⁰⁰ 00% 'by weight.

From the film section, the partially de-carbonated gas is passed at 125 ° C to the plate section 6. j

Ar - 215 non-normal m ^{3 /} h 0.25% ^j ob. H2 ^55,425 normal m ³ / h ^63,44 % vol N2 ^18,161 normal m ³ / h 20/78% ^j ob. CH4 251 normal m ^{3 /} h ^0, 29% sheet. WHAT ³⁹⁰ normal m ^{3 /} h ^0,45 % vol. CO2 ³⁴⁵¹ normal m ³ / h ^3, 95% ^j ob. NH3 9 ⁴ 67 normal m ³ / h 10 ^{, 8} 4% db ^j . total 87 ³ 60 normal m ^{3 /} h 100.00% ^j ob.

Aibfeorpčrá heat for weighing ^{said to d} of the absorber in a casing .for low pressure ^{P y} ares. The upper part of the plate section 6 reads:

Ammonia solution (temperature 50 ° C), from line 3

NHj. ^{12 684} kg ^{/ h 80} wt.

^{% H} 2 ^O 3-172 to ^{g /} h ²⁰ wt.

No'žstv Recy ^{M s h} o ^{to b} trolled EFTA ^dé him ammonia te ^p ture of 38 ° C ^cr rt ^ru 7 is running: 35,874 to ^g / h.

A solution having the following composition is removed from the bottom of the plate section via line 8 at a temperature of 117 ° C:

а

NH3 45,939 kg / h 82.20% wt. CO2 6,778 kg / h 12.13 wt. H2O 3172 kg / hr. 5.67 wt. total 55,889 kg / h 100.00 wt.

This solution is fed to a urea synthesis reactor.

From the top of the plate section β, at a temperature of 43 ° C, through a line 9 of carbon dioxide with the following composition:

removes de-gased

Ar 215 normal m ³ / h 0,25% vol. H2 55,425 normal m ³ / h 63.44% Order no. On 18,161 normal m ³ / h 20,79% vol. CH4 251 normal m ³ / h 0,29% vol. WHAT 390 normal m ³ / h 0,45% vol. NH3 12,918 normal · m3 / h 14,78% vol. total 87 360 normal im3 / h 100,00% vol.

This gas is fed to the mechanization.

Claims (1)

OBJECT OF THE INVENTION A process for the combined production of ammonia and urea in which ammonia is synthesized, the ¹ ammonia is absorbed in water and carbon dioxide from the raw ammonia synthesis gas is absorbed in the concentrated ammonia solution, and the resulting ammonium carbaminate solution in concentrated ammonia solution is urea, characterized in that the raw ammonia synthesis gas is freed of carbon dioxide by a two-stage absorption in an absorber consisting of two independent sections, the lower section of which is a film absorber and the upper section is a plate absorber, Ammoniacal ammonium carbonate solution resulting from the distillation of the urea solution is used in the section and concentrated aqueous ammonia solution is used as the absorption solution in the upper section, the raw ammonia synthesis gas containing carbon dioxide being first mentioned. into the lower part of the lower section, after passing through the lower section, it is discharged from its upper part to the lower part of the upper section and after. The above-mentioned absorption solutions are led into the individual sections in countercurrent with the raw gas stream for ammonia synthesis.