DE2143583B2 - Process for the production of urea - Google Patents

Description

Gases for the production of carbamate are used at lower pressures than in the case of urea synthesis Case is carried out using aqueous solutions that contain the decomposition products of the carbamate, which is not in Urea has been transferred, and optionally contain added ammonia, can be used.

The carbamate decomposition products are then partially washed out in the column into which the synthesis gases are _{introduced to absorb CO 8} , and partially in a second column into which dilute ammonia solution is introduced as an absorber. The solution emerging from this second column is introduced into the aforementioned first column as an absorbent.

The crude synthesis gases are after the separation of COj and the subsequent known treatments introduced into the ammonia synthesis stage.

A process for the production of urea has now been found which has the advantages indicated above made possible in a completely new way in addition to other advantages.

The invention therefore relates to a method for producing urea by converting the exhaust gases the synthesis of ammonia with carbon dioxide and decomposition of the unconverted ammonium carbamate with the help of ammonia as a scraper, which is characterized in that one of the urea synthesis device In addition to the decomposition products of the carbamate that are not converted into urea, a concentrated ammonium carbamate solution which is supplied by absorption of the carbon dioxide contained in the raw gases for the ammonia synthesis with the concentrated ammonia solution obtained by absorption of the ammonia synthesis device leaving gases with water or a dilute aqueous ammonia solution is obtained, both the absorption of ammonia and carbon dioxide in a film heat exchanger each known design takes place according to the countercurrent principle.

The method according to the invention enables

the separation of the ammonia from the effluents of the ammonia synthesis device by water absorption and the direct use of the in this way .; obtained ammonia solution for separating carbon dioxide from the converted gas which forms the carbamate;
the direct introduction of this solution, which contains all of the supplied CO ₂ , into the urea synthesis device and

a new isobaric cycle for converting the carfaamate into urea, which also has the Comprises the step of decomposing the unreacted carbamate into urea, the decomposition step is known in part from the Italian Patert writings 684 929 and 812 030.

The advantages that result from the particular solutions used in the method according to the invention in addition to other properties, can be clearly seen from the following.

Thus, the method according to the invention enables a considerable reduction in investment costs, since, if other conditions remain the same, there will be fewer and fewer devices Operating costs needed and the consumption of mechanical energy and thermal energy per Ton of urea produced significantly reduced.

In the method of manufacture according to the invention of urea are the raw gases of ammonia synthesis, which are produced by a steam cleaning stage originate or are formed in any other usual way and in which the carbon monoxide has been almost completely converted, compressed to a pressure that is slightly higher than that required for urea synthesis.

After compression, there is a difscr gas stream, which still contains all the carbon dioxide required for production of urea is required, fed into the lower part of a vertical tube exchanger, wherein inside the tubes in countercurrent to an ammonia solution flowing down in the form of a film meets and forms carbamate, the heat of reaction by a coolant, e.g. B. Water that is used to feed the boiler and the Shell side of the film exchanger flows, is discharged. The selection of a device of this type is intended ao not a limitation as any other film exchanger can also be used.

The carbamate formed comes out of the lower part of the exchanger in the form of a very concentrated solution, which is used to convert it to urea, in which the temperature is kept between 100 and 250 ° C and the pressure between 100 and 250 kg / cm ² , the end. Such a conversion is described below. The absorption solution can also be introduced into the lower part of the exchanger. The gas stream freed from carbon dioxide and saturated with ammonia is passed from the upper part of the exchanger and fed into a cooler, in which part of the saturated ammonia is condensed and reintroduced into the exchanger, preferably into the lower part of the exchanger.

The cooled gas is methanized after it has been preheated in exchangers. At the end of the methanation stage, after the heat obtained from cooling has been recovered, the gas is fed into a further vertical tube exchanger . ^ühTt> J ⁿ the gas in counterflow with a water film a diluted ammonia solution contacts that the ή ™™ contained in the gases ^{0 "11} * ^ ⁰ * ¹ ^. This ^" exchanger ebenfa Is is cooled by a coolant, that flows along the jacket in such a way that a temperature of 10 to 60 ° C. and a pressure of ¹⁰⁰ J - ¹⁸ 250 kg / cm "results in the exchanger, also in this case

I ^st not the selection of the apparatus used beschrankend since each film heat exchanger can be used accordingly. The gases resulting from the synthesis of Ammomak enter this exchanger and meet water in countercurrent

"° ^{which a} dilute ammonia solution which practically ^{absorbs the} 2" anite ammonia ^{contained in the gases.}

A very concentrated ammonia solution (e.g. 75 to 85 percent by weight) emerges from the lower part of this second exchanger and is introduced into the first layer exchanger as an absorbent, in which it absorbs _{CO 2 with the formation of carbamate.}

In the top of the second exchanger is a gas outlet for part of the gas flow from the Ammonia synthesis originates, arranged to avoid an accumulation of the inert gases.

The gas-bearing which is saturated with water in this way

The mixture is then "quenched" and expands and becomes just like the drained

dehydrated with ammonia, as in the DT-OS inert gases taken from the device and further-

2,055,977. subjected to common treatments.

The oasis are in particular drained. It should be noted, however, that the inventive

that one liquid ammonia, which works well with the 5 process, the possibility of ammonia synthesis

like oases mixed and partially evaporated, to be carried out at higher pressures, does not exclude

introduces a device that has a large exchange- although the specified pressure range is preferred.

Surface between the gas and the ammonia It should also be said that - if necessary - between

enables. see the aforementioned two film exchangers

Both the condensation, which interposed a fractional distillation as a consequence of the io-cooling by the adiabatic evaporation of one of the can, such that the in the first of the two Part of the ammonia is produced, as well as the concentrated ammonia solution formed by the exchanger, Solution of the ammonia itself, which is passed through a large before being used as an absorption solution in the exchanger, Exchange surface between the gas and the ammo in which the carbamate is formed is guided, niac is made easy, cause a separation »5 a fractional distillation according to the usual method last traces of water from the gases, which the is subjected to liquid ammonia and Separation already to a large extent in a water or a very dilute ammonia solution Heat exchanger takes place in which part of the cooling is obtained. The liquid ammonia then becomes preferred units the dehydrated gas is recovered in the lower part of the second layer and in which the gas is led in countercurrent to the to ao exchanger, while the water or the treatment Gas is led. thin ammonia solution on the top of the exchanger

A short distance downstream of the ammonia is introduced and in the form of a layer or a

point of contact, the z. B. through a Venturi tube film in countercurrent to that of carbon dioxide

Can be formed, a gas-liquid separator is liberating gas flows.

arranged from which the cooled gases in the above- »5 It is also evident that it is possible

mentioned heat exchanger are performed and then only a part of the method according to the invention

very concentrated ammonia solution escapes, which should be used if instead of the ammonia solution

is preferably added to the urea solution, the niaksynthesis resulting gases a CO ₂ -rich gas

- as it will be described in the following - is available. In fact, it's next to that

downstream of the urea reactor from the carb-ammonia synthesis and that for the above synthesis

Substance decomposition device leaks. used gas treatments by use

To such a separated solution any ammonia solution becomes possible, if urea

preferably also the weak ammonia solution is to be produced, the carb according to the invention

added, the amate formation stage formed in the heat exchanger, the stage of the invention

is, in which the cooling units of the dehydrated 35 carbamate dehydration, when urea is formed

Gas can be recovered. is, and the inventive step in which not

The gases treated in this way will pass through until dehydrated carbamate is decomposed,

to the ammonia synthesis pressure, which is between 100 and Es in the process according to the invention

250 kg / cm ² lies, compressed and then in the Ent- possible, at much lower pressures than them

speaking device introduced. 40 are required for ammonia synthesis to work

The gases emanating from the above device are th. In most cases, ammonia occurs when it is released cooled and then in an ammonia synthesis the separation of the ammonia from the absorption device and devices for wide-synthesis effluent at low pressure through cones Treatment introduced. condense ammonia in heat exchangers that

The fresh carbamate solution will be cooled together with 45 by evaporation of ammonia, the circulated carbamate and the ammo , separation of the ammonia from the synthesis effluent resulting from the carbamate decomposition, gasified in a cheaper and more efficient way by conducting, whereby the vapors condense and in this way use a device which can establish the thermal equilibrium that can At the same time, the amount of heat required over a single surface of the reaction device results in a very good exchange of heat and material. The temperature made possible by the amount of. This allows, among other things, to use the water introduced into the vapors circuit introduced into the reaction device twice, to be regulated, from 150 to 250 ⁰ C 55 first for the absorption of ammonia and then and the pressure of 100 to 250 atmospheres. to form the concentrated carbamate solution that stretch. The urea, the carbamate and the urea are then used to convert to urea. Substance solution that emerge from the upper part of the reaction precursors. Another very important feature of the process according to the invention is that it is possible in an advantageous manner or by means of a suitable device in the carbamate-like manner Main devices introduced decomposition device, which is heated by the steam condensing of the process, such as the Ammomaksynthesvorrichtung. It is also device to use the absorber for the ammonia, which is possible from this, evaporated NH ₃ , which emerges in the device, the CO ₂ absorber, in which the countercurrent flows and serves as a stripping agent, with carbamate being formed device for Umwandunter these conditions somewhat carbamate and 6 ₅ development of carbamate into urea and the decomposition most of the dissolved ammonia stripped device for carbamate, which returned not in urea and in the reaction apparatus advertising has been transferred, the same at substantially the the. The urea solution obtained in this way has a pressure of between 100 and 150 atmospheres,

7 8

to operate. However, it is not excluded, in order to appropriately increase the excess ammonia at different stages at different pressures without increasing the pressure of the system,
work. In such a case, the pressure ranges between 30 and 300 atmospheres, preferably in an isobaric cycle method. it is the case with the method according to the invention, Furthermore, the operating pressure - what the 5 makes it possible to have large ammonia circulations in Han; -toff section of the method concerns - in which a closed circuit between the Zerer invention method and the introduction of the settlement device and the synthesis device with a small amount of heat to be supplied formed in the carbamate decomposition device directly into the lower part of the urea synthesis works, whereby the conditions of the ammonia device In addition to solving thermal problems io solution are very close to the critical conditions, such a device the relevant con Such conditions allow to eliminate in the synthesis sensor, which is always a critical point device high NH ₃ / COj ratios, which in the in the urea plant because of the range of 2: 1 to 12: 1 (preferably 4: 1 to 8: 1) considerable corrosion problems that are to develop in one of these, whereby very high yield-like device occurs. As already obtained and the supply of large amounts of heat has been carried out, the absorption of the NH ₃ from can be avoided. From the above, the ammonia synthesis gases and the separation of the ammonia synthesis gases can be seen that the inventive integrated Ammo-CO ₂ from the crude ammonia synthesis gases under the nia / urea process practically allows all the formation of the carbamate to be carried out in any device that benefits the integration of the two processes , although it is preferred that ao can result, with further advantages arising from the difficult carbamate formation in a bed by a substantial reduction in urea exchangers (film exchangers), ie in one device, production costs.

the effective heat and material exchange on the basis of those shown in the drawing before allows a single surface, the continuous embodiment, the invention is carried out below is, this also explained in more detail for the ammonia as the example. This concerns the absorption applies. more general case where the gases treated, the

The heat of carbamate formation will mainly be raw gases from an ammonia synthesis.

du.oh preheating of z. B. Recovered water, stir.

that is introduced into the boilers and the extra- The raw synthesis gas, all of which for the urine the tubes in the flow with the liquid film 30 contains the necessary carbon dioxide to form flows to it at a temperature which is higher than at a pressure which is slightly higher than it is for the temperature of the carbamate crystallization. urea synthesis is required, compressed

The drying of the moist synthesis gases takes place, and then via line 1 in the lower part of the

by inserting part of the exchanger 2 in the urea section. This device is in

ammonia to be returned is used, which essentially creates a film exchanger in which the

the energy required for ammonia separation is converted into gas that flows inside the tubes

energy is saved and a corresponding injection of a layer of an ammonia solution in contact

pump is not required. comes, whereby the carbamate is formed. the

The urea cycle was designed so that post-reaction heat is z. B. by circulating

parts, such as the absence of the heat of formation 4 ° boiler process water outside the pipes.

of the carbamate in the device and the introduction. The water used for this is via the

a large amount of water is eliminated in the cycle, line 32 is introduced and exits line 33.

will. A very concentrated carbamate solution is produced

In fact, because of the lack of the carbamate that forms via line 23 in the urea syn-

heat of formation the synthesis device is passed through a thesis device.

external heat source in thermal equilibrium The gas freed from carbon dioxide, the spurer

being held. The more convenient way that contains the required of CO ₂ and is saturated with ammonia

Adding heat consists in using the (by coming into contact with ammonia,

Heat content of the vapors coming from the carbamate - the gas tends to be saturated with ammonia),

Exit decomposition device by placing this 5c via line 3 into cooling device A.

Introduces gases directly into the synthesizer. On performed in which part of the ammonia condenses

In this way, both the reactants and, via line 27, are returned to exchanger 2.

Preheating stage as well as the carbamate condensate is performed. The cooled gas is then methane

sationsstufe eliminated, whereby the urea syntese- siert to the CO and the CO ₂ contained in it

process is considerably simplified by being single and poisons for the ammonia synthesis catalyst

borrowed the synthesizer and the carbamate represent to eliminate. Through the line 5 wire

Decomposition device are required. The ther- this gas passed into the preheater 6, in which it mii

mix equilibrium of the reacted urea is heated to the methanated gas. It will be dam

can, if desired, by changing the in after further preheating in the heat

Synthesis device returned amount of carb exchanger 7 and then into the device 8, in which you

at decomposition vapors can be varied. Methanation continues to take place. The methani

affect the introduction of the ammosed gas is formed after the heat recovery ii

niaklösung necessary process water and at the preheater 6 (the one for which the device J

then the fresh carbamate _{solution (the NH 3} / CO ₈ - leaving stream represents a precooler) into the

Ratio and result at the same temperature a 65 cooler 9 further cooled and together with the

Decrease in yield. However, this does not occur in the exiting synthesis device 20

a, if according to the invention the larger gas cooled in the synthesis cooler 22 in the film absorber ΐ,

device available amount of water is used, in which the ammonia contained in the gas]

9 10

by a layer introduced via line 28, evaporated ammonia as a stripping agent into the

Water or a dilute ammonia solution to introduce the decomposition device is line 39

flows downwards inside the tubes, is absorbed. superfluous.

The heat of reaction is generated by cooling water which The following example is intended to make the present invention

enters via the line 30 and from the line 31 5 further explain with reference to the drawing.

escapes and flows through the lines. . .

The gas freed from ammonia is on the Lei example

device 13 in the cooling recovery device 14 over - It was an operating facility with a day

leads in which the condensation uses a dilute capacity of 10001, with 9901 Ammo

Ammonia solution is carried out, which is converted into ammonium carbamate via the ι ο nia per day

Lines 49 and SO are led into line 47, which processed to 17001 urea per day

and that was additionally in the venturi tube 15 with the help of, and with 10 tons of ammonia per day for others

of imported liquid ammonia were used on the purpose.

Line 24 is cooled and dried. All of the following have been introduced into exchanger 2:

existing water is separated by ammonia 15 Via line 1 raw synthesis gas under the following

and in the form of a concentrated ammonia solution, the following conditions:

drained from the separator 16 via the line 25. Throughput 151 900 Nm '/ hour

This concentrated ammonia solution is over the pressure 200 ke / cm ³ abs

Line 50 inserted into line 47. The getrock temperature 125 ⁰ C

nete gas is after the cooling recovery in the pre ao composition · '

direction 14 via line 17 to the circulatory system _H * _{'61 22 percent by volume}

pressors 18 and from there via line 19 into the qq q ₃ g volume percent

Synthesis device IiO out. The exhaust gases are ^ q YJ 1 \ percent by volume

via line 29 from the layer absorber 12 ^ V. '.'. '.'. '.'. '.'. '.'. '. l & S percent by volume

ff · 2 "u L- ♦» ι- α λ * ^{5 CH} 4 0.50 percent by volume

The carbamate _{concentrate solution from the A} 0.24 volume percent

Exchanger 2 is supplied with a via line 48 Carbonate solution mixed and via the line 26 an ammonia solution with folung 34 introduced into the lower part of the device 35. properties:

The line 43 is also used from other 30 throughput 78 350 kg / hour

Stages recycled ammonia in the lower part of the composition · '

Synthesis device introduced. This ammonia _NH " _{? Gg percent by weight}

stream is divided into two streams, one stream _{H 0 21 2} percent by weight

Via the line 24 into the Venturi tube 15 to the Ent- temperature 45 ⁰ C

watering is introduced by quenching, while 35

the other stream in the exchanger 41, in which it via the line 27 liquid ammonia under the following

is introduced via line 42, is evaporated lowing conditions:

and then partially through the line 39 in the throughput 8 500 kg / btd

Carbamate decomposition device 38 is carried out in temperature 40 ° C

the NH _{3 is used} as a stripping agent and the 40th

partly via line 40 into the lower part of the From exchanger 2, the following was withdrawn: Reaction device 35 is introduced. A carbamate and ammonia from the top of the synthesizer solution with the following properties via line 23: discharged via the line 36, the inert gas, while the temperature of the line 37, a solution of urea, water 45 _Pieter ^P _hsatz 150 ° C, \ \\\\\ '\ m ₀ 50 kg / hour and carbamate with a large excess of Am- composition

moniak escapes and into the decomposition device _{38 NH 2 COONH 4} .. 80.00 percent by weight

is introduced, in which it is converted in countercurrent to _NH <■ _Qn / -. ".; t, _t _ _ _t

steamed ammonia flows via line 39 “* 3? _Λ ? ™ S Ε «™ ί

λ ". . , '_ ". , ". . j ^D. Xl ₂ VJ 14.10 percent by weight

is introduced into the decomposition device 38. In 50 ' ^r

the jacket of the decomposition device 38 is a via line 3 a freed from carbon dioxide

Heating means introduced, which enters via line 45, gas having the following properties:

and exits via line 46. In this way throughput 154QnnNm3 / <? M

rinds both due to the wiping effect of the temperature 75 ° ^

vaporized ammonia as well as due to the pressure of 199 9 ke / cm ² abs

Solution introduced from the synthesizer Composition: "'

^ out heat decomposition of the bulk of _H * "JSS volume percent

of the carbamate present and its curvature p _{O n} , "vniimnrm r> t

in the form of a gas phase as NH ₃ and CO ₂ together {£; |; 11 ;;;;;;;; ^ g ν ^ οϊηί

with large amounts of ammonia vapor. Over the 60 _{CH 49 percent by volume}

Line 44 will be defined by the Ammoniakstroft ^ ^ £ _{Vohun rcent}

Carbamate decomposition products carried in the un- _{NH 19 3Q volume percent}

Upper part of the Synthesevornchtung 35 introduced. The ^v

aqueous urea solution, which in equilibrium The heat of reaction of 14,500,000 kcal / hour. would( The ammonia present dissolves and practically carbamate 65 by preheating the boiler feed water

is free, is removed via line 47 and recovered to 140 ⁰ C.

further treatments supplied. In the case where as In the exchanger 12, the following materials were used

has already been mentioned above, it is not necessary to introduce:

11 12

Via the line 11 gases from the Syrithesevorrich- throughput 521,000 Nm ³ / hour.

tion under the following conditions: pressure 195 kg / cm ² abs.

Throughput 466 (XX) Nm ³ / h Temperature -17 ⁰ C

Pressure 198 kg / cm * abs. Composition:

Temperature 40 ° C ⁵ g * ^ 6.00 percent by weight

Composition: JJ · ²² > ™ weight percent

H ₂ 56.12 percent by volume; H ₄ 7.85 percent by weight

N ₂ 18.71 percent by volume argon 2.15 percent by weight

CH ₄ S, 77 volume percent ^ H ₃ 2.00 weight percent

Argon 2.40 percent by volume ^{10 H} «° ^ ³ PP ^m

NH ₃ 14.00 volume percent

Via line 10 methanated gas with fol- This gas is after the recovery of the cooling

properties: units in the device 14 with the help of the com-

15 pressors 18 to a pressure of 207 kg / cm ^a abs.

Throughput 141 060 Nm ³ / hour compressed and the synthesis unit 20 introduced.

Pressure '^ _o ^at the carbamate dehydrator 35, which at

Temperature 40 ⁰ C a pressure of 195 kg / cm ^{2 is} operated and a

Composition: 70% conversion (conversion) is made possible

H ₂ 64.26 percent by volume _{ao m} j _t charged with the following:

N ₂ 21.37 percent by volume U _or the line 23 the above-mentioned carbamates 0.94 percent by _{volume unc} j ammonia solution, via the line 48 the carbon

Argon 0.25 percent by volume natural circulation solution with the following properties:

NH ₃ 13.18 volume percent

_n . ,. _T. " _O ,,,. ,, "* ⁵ throughput 39 950 kg / hour.

Via line 28. Water under the following loading Temoeratur 100 ⁰ C.

^din 8 ^un g ^s: Composition "

Throughput 16 290 kg / h CO ₂ 30.9 percent by weight

Temperature 4O ⁰ C NH ₃ 39.0 weight percent

. . . ,. ". . . , _Ot .. ³⁰ H ₂ O 30.1 percent by weight

The following streams were generated from exchanger 12

discharged:

Via line 13 synthesis gas with the following ammonia via line 40 with the following properties: conditions:

Throughput 513 600 Nm ³ / hour ³⁵

Pressure 197.8 at throughput 34 780 kg / h

Temperature 45 ° C Temperature 140 ⁰ C

Composition:

H ₂ 67.01 percent by volume ... .... .. ", .. .... -7

N 22.34 percent by volume * ° ^{over the} . ^Le > ^tun S * J ^Dam P ^fe · ^d ' ^e . ^{from the} _c ^Zer -

qIi _{7 97} volume percent settlement device 38 emerge and the following properties

_{7 97} percent by volume

Argon ....... Υ ... 2 ^! , 18 percent by ^volume:

NH ₃ 0.50 percent by volume

Water 200 kg / hour Throughput 117 370 kg / h

..,. _T. "" _Λ1 . ,,. ⁴⁵ temperature 190 ⁰ C

Via line 29 exhaust gas with the following inherent composition:

^properties: CO ₂ 7.9 percent by weight

Throughput 13100 Nm ³ / hour NH ₃ 85.3 percent by weight

Composition: H ₂ O 6.8 percent by weight

H ₂ 64.93 volume percent ⁵ °

CH _{10 '15} percent by volume ^{From this Vorricntun} S ^{occurs via the} line 3Ί

Argon '.'. '.'. '.'. '.'. '.'. '. 2.7% by volume of ^a urea solution with the following properties

NH ₃ 0.50 percent by volume ^from:

Via line 26, an ammonia solution with a throughput of 309,545 kg / hour.

the characteristics given above: temperature 180 ⁰ C.

The moist synthesis gas is in 14 to -8 ⁰ C. Composition: '

cools (via line 49 325 kg / h. of a _{c0 7 2} percent by weight

Ammonia solution discharged, the 40 percent by weight 60 ^ - ^ _{51 3} percent by weight

Contains ammonia) and further ^{cooled to -17 0} C, _HQ ³ '.'. '.'. '/'''''] ^ 5 percent by weight

by introducing 6145 kg / hour. liquid ammonia, urea 23.0 percent by weight

that almost completely evaporates (the last traces of water

are via line 25 in the form of 68 kg / hour.

an ammonia solution discharged, the 87 Ccwichts- 65 from the decomposition device 38 passes over di

percent ammonia). At the outlet of the discharge line 47, the urea solution, which is in the EndbehaTid

Scheider 16 you get a gas with the following treatment stage is transferred and the following property

Properties: has properties from:

13 14

Throughput 192 175 kg / h The one required in the decomposition device 38

Temperature 220 ° C heat is achieved by adding 55 000 kg

Composition: steam per hour at a pressure of 40 kg / cm ^a

CO, 6.8 percent by weight fed via line 45.

NHj 30.5 percent by weight 5 In the present example, no

H ₁ O 25.7 percent by weight of vaporized NH _{3 is introduced} into the decomposition urea 37.0 percent by weight device 38 via line 39.

For this purpose 2 sheets of drawings

Claims (2)

Energy used in the separation of the ammonia Claims: to be used from the unconverted gases; Saving of operating costs by eliminating 1, process for the production of urea generation of the ammonia separation stage; by converting the exhaust gases of ammonia 5 saving of mechanical energy for synthesis with carbon dioxide and decomposition of the priming of CO ₂ and unconverted ammonium carbamate with savings in operating costs for the CO _s -Comp- With the help of ammonia as a stripping agent, priming. characterized by that one of the Urea Synthesis Apparatus in addition to the Unintegrated Urea-converted decomposition products are well known. For example, a concentrated ammonium patent 3,303,215 known method from the USA.-des carbamate feeds the crude carbamate solution, which is compressed by absorption gases for the ammonia synthesis and introduced into one of the column in the crude gases for the ammonia synthesis, the upper part of which for the CO ₂ -Abenthaltte carbon dioxide with the concentrated 15 sorption with the help of ammonia solutions and an ammonia solution, which is used by absorption of the subsequent carbamate formation, leave the ammonia synthesis device while the lower part of this column to convert gases with water or a dilute aqueous treatment of the carbamate formed in the urea is used. Ammonia solution is obtained, whereby both the strong heat development in the carbamate Absorption of the ammonia as well as the formation of coal and the presence of inert gases (H ₂ + N ₂ ), dioxides in each case in a film heat exchanger, which reduce the partial pressure of the NH ₃ and the CO ₂ , make this known design according to the countercurrent principle Operation at high pressures (approximately follows. 250 kg / cm ² ) is required to keep the reactants 2. The method according to claim 1, thereby keeping GE in the liquid phase. B ^ i one such indicates that the decomposition products are 35 process management is not a facility for Abfühdes not converted into urea, indicated with ammorisation of the developing heat, and The introduction of ammonium carbamate in gaseous form makes the equilibrium colder leads into the Ha nstoffsynthese device and absorbent solutions maintained. The recondensed. Conversion of the carbamate to urea is carried out in the 30 same device, namely in the lower part of this Device carried out. As stated above the difficult heat dissipation and the presence of inert gases (H ₂ + N ₂ ) make it necessary to have a sufficiently high carbon dioxide partial Usually the production of urea is achieved in 35 pressure, at relatively high pressures too Industrial scale with the help of two factory jobs. facilities that are independent of each other, the absorbent solution is made by anhydrous carried out. For this purpose, an operating facility for ammonia is set up, to which an aqueous solution that produces liquid ammonia, which gives rise to carbon dioxide as decomposition products of the unconverted carb byproduct, is used and added 40 amats. Such a decomposition is carried out in another facility for the production of urine at low pressure.
Itoff on the synthesis of these two mentioned pro * - The raw gases for the ammonia synthesis are products used. In any case, in which the end after the absorption of the CO ₁ and after further Beprodukt is mainly urea, ammonia can act for the ammonia synthesis, which at high is referred to as an intermediate product, whereby 45 pressure, especially at a pressure between 400 die Possibility of integrating the two operating and 500 kg / cm ² is used,
facilities results. From the fact that the ammonia produced, An ideal integration scheme is a scheme in which for the production of the aqueous ALsorptionsdem the possibility of direct reaction between solution is used, is anhydrous at the beginning and Ammonia and carbon dioxide with the formation of 50 because of the high synthesis pressure can be closed Carbamates, which are then converted into urea, that the ammonia separation from the Can be used to handle two expensive down-streams in a suitable manner, in particular Separation phases necessary for the production of ammonia by freezing out water and by evaporation are typical to avoid, namely the carbon dioxide from ammonia, takes place. In another, from the United States patent specification, solvents and the further compression of the 3,349,126 known, integrated process, not all of the raw synthesis gases formed by the regeneration of the solvent are formed for the absorption of the carbon dioxide on the urea synthesis pressure and CO ₂ contained therein, but partly in the phase of the separation of ammonia by the usual way for the production of pure CO ₂ liquid from the unconverted gases, which are set from 60. This is done because the carb from the synthesizer leak. amate formation and its conversion to urea in The obtained according to such a scheme are carried out before two separate devices, parts are the following: on what - about the temperature of that zone in which urea forms to an acceptable level Saving of thermal energy, which keep at 65 - ammonia and carbon dioxide are added a customary carbon dioxide separation process, which is produced by the reaction to form the carbamate ren must be expended; develop required heat. Saving of thermal or mechanical The absorption of CO ₂ from the raw synthesis