SE409203B - INTEGRATED URBAN PROCEDURE - Google Patents

Description

7'1'1i'1 146-.2 2 carbon dioxide formed by regeneration of the solvent up to the urea synthesis pressure, and the separation step by condensation of the ammonia from the unreacted gases leaving the synthesis reactor.

The advantages obtained by such a reaction scheme are as follows: on the saving of heat energy required by the conventional decarbonisation plant;, on the other hand - saving of heat or mechanical energy in connection with the separation of the ammonia from the unreacted gases; - saving construction costs for the elimination of the ammonia separation step; - saving of the mechanical energy required for the compression of carbon dioxide; - saving on construction costs for carbon dioxide compression: including ammonia production in the urea synthesis process can seemingly be considered a negative aspect of the integrated process.

It has been said "apparently", because the integrated scheme can in fact only be accepted in cases where the whole quantity or at least a large part of what is produced is converted into urea.

In these types of plants, ammonia must then be considered as an intermediate product.

The integrated processes for urea production are well known.

According to one of these, the crude gases for the ammonia synthesis are compressed and transported to a column, the upper part of which is used for the absorption of CO2 by carbamate, while the lower part is used for the formation of the carbamate by means of ammonia solutions and subsequent conversion to urea.

The large amount of heat generated during the formation of the carbamate, and the presence of inert gases (H2 + NZ), which 'reduce' the partial pressure of NH3 and CO2, make it necessary to work at high pressures (about 250-kP / cd 'to reactant In the scheme of such a process, no measures have been taken to dissipate such heat as it is formed, and the balance is obtained by introducing cold, absorbent solutions. The conversion of the urea to urea is effected in the same apparatus, and more specifically in its lower part.As mentioned above, the difficult removal of heat and the presence of the inert gases H2 + NZ make it necessary to operate at relatively high pressures in order to maintain the carbon dioxide at sufficient partial pressure.

The absorbent solution is formed from anhydrous ammonia, to which is added aqueous solution of the decomposed Ü: products of the unconverted carbamate. Such decomposition is carried out at low pressure. ßf-. After absorption of the carbon dioxide and other treatments, the crude ammonia synthesis gases are fed to the ammonia synthesis under high pressure, namely between 400 and 500 cp / cm 2. Since the ammonia produced to obtain the aqueous absorption solution is initially anhydrous, it must, also due to its high synthetic pressure, be separated from the exhaust gases by cooling with water and with evaporation. ammonia. In another integrated process, not all of the synthesis crude gases are led to the absorption of the carbon dioxide present therein, but some of these * lf are treated in a known manner to obtain pure CO2. This has been done _? because the production and conversion of the urea to urea is carried out in two different devices and the required temperature in the urea formation zone for this feed is supplied with ammonia and carbon dioxide, which when converted to urea supply the heat necessary for this. The absorption of CO 2 from the crude synthesis gases for the production of the urea is carried out at a lower pressure than that used in the urea synthesis. Aqueous solutions containing carbamate decomposition. products, are not converted to urea, and temporary additives of ammonia are used. Then the decomposition products of the carbamate are washed, partly in the column to which the crude synthesis gases for absorption of CO 2 are directed, and partly to a second column, to which a dilute ammonia solution leads as absorbent. The solution leaving the second column is passed as absorbent to the first column. After the removal of the carbon dioxide and the subsequent known treatments, the crude synthesis gases are fed to the ammonia synthesis. According to the invention there is now provided an integrated process for the production of urea which makes it possible to obtain in a completely new way the above-mentioned advantages and other, special advantages for the new process. The method according to the invention, which has obtained the features stated in claim 1, has the following main properties: the use of special types of apparatus in cases where, in addition to a material exchange, it is also very important to achieve a heat exchange, of course without precluding the use by any apparatus suitable for this purpose; » K _ _ _ - a special method for dehydration of the gases to be led to the ammonia synthesis, which, on the other hand, is already known from the 1AL1E patent 891998, in fi Filed on 15 November 1969, and its appendix, patent 953035, filed on 2 ? August V 1970 by the same applicant; 4 '- ammoniaase separation from the exhaust gases from the ammonia synthesis reactor by water absorption and the direct use of the ammonia solution thus obtained for decarbonating the converted gas to form carbamate; - _V - direct feeding of the solution, which contains all the carbon dioxide supplied, to the urea reactor; y - a new isobaric cycle for the conversion of the urea to urea, which cycle also comprises the decomposition of the unconverted urea to urea, which decomposition step is partly known from Italian patents 694,929 and 812,030 by the same applicant.

The advantages obtained by the use of the special solutions in the process according to the invention will be explained in more detail in the following. The following description shows that the process according to the invention enables a significant reduction in investment costs, since under otherwise equal conditions it requires a smaller number of devices and lower operating costs, since the consumption of mechanical. energy and heat energy per tonne of urea produced will be significantly less. In the integrated process for the production of urea proposed according to the invention, it is effected that the crude gases from the ammonia synthesis, which come from a steam reforming or from products in another customary manner, and in which the carbon monoxide has been almost completely converted, are compressed to a pressure which is slightly higher than the pressure used in the urea synthesis; and leaving compression of the gas stream, which still contains all the carbon dioxide necessary for urea production, feeds the gas stream to the bottom of a vertical tube heat exchanger, where it meets a film of ammonia solution inside the tubes in countercurrent to form carbamate. The reaction-V heat is removed. cooling of the pipes by means of a coolant, e.g. the feed water for the steam boilers. The choice of this type of apparatus is of course not limiting, but any other type of suitable apparatus can be used for the purpose. The urea is drained from the bottom of the heat exchanger at a temperature varying between 100 and 250 ° C and a pressure of between 10 and 250 kp / cm 2 in the form of a highly concentrated solution, which is then fed to the urea synthesis reactor. Such a conversion of the urea to urea will be described in the following. In addition to being fed to the top of the heat exchanger, the absorbent solution can also be fed to its bottom. The carbon dioxide-emitted gas stream, which is saturated with ammonia each is ammonia, is discharged from the top of the heat exchanger and fed into a cooler where part of the ammonia is condensed and fed back to the heat exchanger, preferably until bottom. The cooled gas is led to the methanation after being suitably heated in suitable heat exchangers. At the outlet of the methanation step, the gas is transported, after the recovery of the heat obtained by cooling, to another vertical tube heat exchanger, where it countercurrently meets a film of dilute ammonia solution, which absorbs the ammonia present inside the gases. This film heat exchanger is also cooled by a coolant, which is caused to flow along the side of the jacket in such a way that the temperature in the heat exchanger is kept in the range 10 - ÖOOC and the pressure in the range 100 «250 kp / omg. In this case, too, the choice of this type of device is not limiting, since any other suitable device can be used for the purpose. The gases emanating from the ammonia synthesis are fed to this heat exchanger and also meet in countercurrent water or a dilute ammonia solution, which absorbs practically all the ammonia present in the gases. From the bottom of this second heat exchanger a highly concentrated ammonia solution is drained {e.g. 75l ~ 85%), which as an absorbent is passed to the first heat exchanger, where it absorbs the 'CO2-producing carbamate. From the top of the second heat exchanger a part of the gas stream is diverted from the ammonia synthesis in order to avoid accumulation of the inert gases. The gas mixture thus obtained, saturated with water, is then passed to the dehydration step, which is carried out by cooling. with ammonia in the manner described in. the 'ïtaLiEnSka pate-I fi íetrr- 891098, which was submitted on 15 November 196-9; and its' cíLsL- Patent Patent 953035, filed on 27 August1'_1_97Q_ by the applicant. The gases are then dehydrated by feeding liquid ammonia, which is thoroughly mixed with them and partially evaporated, into an apparatus which is suitable for producing a large exchange area between gas and ammonia. Both the condensation due to the cooling caused by the adiabatic evaporation of a part of the ammonia and the dissolution of the ammonia itself, which is facilitated by the large exchange area between the gas and the ammonia, fi i.e. as a result of the last traces of the water being removed from the gases , which removal is already largely achieved in a heat exchanger, where a part of the cooling units from the dehydrated gas is recovered and the gas is forced to flow in countercurrent to the gas to be treated. Immediately downstream of the above-mentioned ammonia-gas exchange, which can be carried out, for example, in a Venturi tube, there is a gas-liquid-separator.- / s% ¿/ ;; oN “Ã, ee 'QEAUT 11111ne-2 D .ssg¿6l from which the cooled gases are passed to the above-mentioned heat exchanger and a highly concentrated ammonia solution, which is preferably added to the urea solution leaving the urea decomposer downstream of the urea reactor, as will be explained in more detail below. U I I i.

To such a separated solution is preferably also added the weak ammonia solution formed in the heat exchanger in which the cooling units of the dehydrated gas are recovered.

The gases thus treated are compressed into ammonia; the synthesis pressure which is in the range 100 - 250 kp / cm 2, and is then fed to the corresponding reactor. After cooling the gases emanating from the above-mentioned reactor, these are led to the ammonia absorption and to the subsequent treatments in the manner previously described. The new carbamate solution is led together with the recycled carhamate and ammonia to the bottom of the urea reactor in the same zone where the steam emanating from the carbamate decomposer is injected, these vapors are condensed and supply the necessary heat for the reactor's heat balance. The vapors fed into the reactor can vary from 150 to 250 ° C and the pressure from 100 to 250 kp / cm 2. The solution of ammonia, urea and urea emanating from the top of the reactor is guided by the action of gravity or by other suitable means. the karhamate decomposer, in which it is heated by means of the condensing steam. to use the vaporized ammonia flowing in countercurrent and in. plays the role of stripping agent, with some of the carhamate and most of the dissolved ammonia being evaporated under these conditions and returned to the reactor. The urea solution thus obtained expands and is led, like the inlet gases discharged from the reactor, to further per se known treatments. It should be emphasized, however, that the process according to the invention does not exclude the possibility of carrying out the ammonia synthesis at higher pressures. the pressure range is preferred; It should further be noted that, if appropriate, a fractional distillate tip may be introduced between the above two film heat exchangers, in that the concentrated ammonia solution formed in the first heat exchanger, before being absorbed solution is passed to the heat exchanger where the carbamate is formed, can be subjected to fractional distillation in a manner known per se to obtain liquid ammonia and water or a very dilute ammonia solution. The liquid ammonia is then preferably passed to the bottom of the second film heat exchanger, and the water or dilute ammonia solution is led to its top to flow countercurrently inside the tubes as a film to meet the gas from which carbon dioxide is to be removed.

It is obviously also possible to use only a part of the process according to the invention, when a CO 2 -rich gas is available instead of the gases emanating from the ammonia synthesis. Apart from the ammonia synthesis and the gas treatments used for the above-mentioned synthesis, according to the invention it is in fact possible to use the urea formation step, the step in which the urea is dehydrated to urea, and the step in which the undehydrated urea is decomposed, in the case of the production of urea.

In the process according to the invention it is possible to work at substantially lower pressures in the ammonia synthesis. In the case of ammonia synthesis at low pressure, the ammonia itself has in most cases been separated from the leaving reaction gases by condensing the ammonia in the heat exchangers cooled by evaporating ammonia. The efficient dehydration system using the recycle gas according to the invention enables the removal of ammonia from the effluent reaction gases in a much cheaper and more efficient manner, in that in this way an apparatus can be used which at the same time provides a very good heat over a single surface. and material exchange. This enables, among other things, the use of double the amount of water introduced into the cycle, firstly to absorb ammonia and then to form the concentrated urea solution which is then to be converted to urea. Another very important aspect of the invention is that the ammonia synthesis reactor can function as the main apparatus of the process, while the other apparatuses included in the system, namely the absorption apparatus for the ammonia leaving the ammonia synthesis reactor, the CO 2 absorption apparatus in which the carbamate is formed, the conversion reactor , in which the urea is converted to urea, and the decomposition apparatus is passed the urea unconverted to urea, can operate at substantially the same pressure of 100 - 150 atm with all the advantages thereof. However, it is not excluded that one can work at different pressures in the different steps. In such a case the pressure range can be determined between 30 and 300 atm: Furthermore, the working procedure, with regard to the urea section in the process according to the invention and then the injection of the vapors produced in the urea decomposer directly into the bottom of the urea synthesis reactor, makes it possible not only to solve thermal problems. 11111ß6-2 'H but in such a reactor, but also to eliminate the ammonia condenser, which is always a critical point in urea plants, also with regard to the corrosion problems prevailing in such an apparatus. As already mentioned, the absorption of ammonia from the ammonia synthesis gases and the removal of the carbon dioxide from the crude ammonia synthesis gases to form carbamate can be carried out in any suitable type of apparatus. However, it is preferred that the difficult operation in carbamate production is carried out in a film heat exchanger, ie an apparatus which makes it possible to achieve an efficient heat and material exchange on a single surface. This also applies to the ammonia absorption.

The heat of formation of carbamate can for the most part be recovered, e.g. by preheating steam boiler feed water, which is allowed to flow over the outside of the heat exchanger tubes in co-current relative to the liquid film to maintain it at a higher temperature than the temperature at which the carbamate is caused to crystallize.

The drying of the wet synthesis gases is carried out by using a part of the ammonia intended for return to the urea section, thereby saving the energy required for the ammonia separation, and thus eliminating the injection pump. It is desirable to design the urea cycle in such a way that negative factors are eliminated, such as the lack of carbamate formation heat in the reactor and the injection of a larger amount of water into the cycle "Due to the lack of carbamate heat of formation in the reactor, its thermal This method of maintaining such heat is to utilize the heat content of the vapors leaving the carbamate decomposer by injecting them directly into the reactor, thus eliminating both the preheating step of the reagents and the condensates of the reagents. the urea, by substantially simplifying the urea synthesis process, which is limited only to the reactor and the carbamate decomposer.The thermal level of the reacted urea can, if desired, be varied by varying the amount of the vapor from the decomposition of the urea which is returned to the reactor itself. of the ammonia solution, and for In addition, the new carbamate solution, the required process water in the urea cycle also means a reduction in the reaction yield, provided that the NH 3 / CO 2 ratio and the temperature are constant. However, such a reduction in the reaction yield does not occur when, according to the new process, the larger amount of water in the reactor is used to appropriately increase the excess ammonia without significantly increasing the system. In a cycle, preferably isobaric, similar to that of "ß 7111146- According to the present process, it is in fact possible to achieve large ammonia circulations in a closed circuit between decomposer and reactor, with a small amount of heat that needs to be supplied, the conditions of the ammonia solution being very close to the critical conditions.

Such conditions make it possible to maintain in the reactor high NH 3 / CO 2 ratios in the range 2: 1 to 12: 1 (preferably 4: 1 to 8: 1), and consequently very high yields, and to reduce the supply of high-quality heat. It can be seen from the foregoing that the integrated ammonia-urea process according to the invention makes it possible to achieve all the advantages that the integration of two processes can provide, which advantages entail a significant reduction in the production costs of the urea. The following is an example of a possible embodiment of the process according to the invention with reference to the more general case where the untreated gases are the raw gas coming from the ammonia synthesis. Referring to the accompanying drawing, the crude synthesis gas, which still contains all the carbon dioxide required for the V urea production, is compressed to a pressure slightly higher than the pressure used in the urea synthesis, and then injected through a line 1 to the bottom. of an exchanger 2. This apparatus is essentially a film exchanger, in which the transformed gas flowing on the inside of the tubes comes into contact with a film of an ammonia solution and thereby forms carbamate. The heat of reaction is removed, for example, by causing steam boiler feed water to flow on the outside of the pipes. This water is fed through an inlet 32 and discharged through an outlet 33. A highly concentrated urea solution is prepared, which is fed through a line 23 into the urea reactor.

The carbon dioxide-free gas, which contains traces of CO 2 COh which has become saturated with ammonia through the contact with the ammonia solution, is fed through a line 3 to a cooler 4, in which part of the ammonia is condensed, which is led back to the exchanger via a line 27 2.

The cooled gas is then passed to a methanation step so that the CO and CO 2 gases present, which are poisons for the catalyst used in the ammonia synthesis, are converted into methane in a known manner. The gas is then fed through a line 5 to a preheater 6. , in which it is heated with the methanized gas, and after a further preheating in a heat exchanger 7, the gas is fed into a reactor 8, where the methanation reaction is carried out. After heat recovery in the heat exchanger 6, the methanized gas is cooled in a cooler 9 and, together with the gas discharged from the synthesis reactor 20 and cooled in a cooler 22, is passed into a film absorption apparatus in which the ammonia present in the gas is absorbed in a film of water or a dilute ammonia solution which flows down the inside of the tubes and is fed into the absorber 12 through a line 28. The heat of reaction is removed with cooling water which is fed into the tubes through an inlet 30 and leaves them through an outlet 31. The ammonia-free the gas is sent through a line 13 to the cold recovery apparatus 14, where the condensation of a dilute ammonia solution takes place, which ammonia solution through lines 49 and 50 is fed into a line 47 and further cooled and dried in a Venturi tube 15 by injecting liquid ammonia through an inlet 24.

The present water is removed from the ammonia and discharged in the form of a concentrated ammonia solution through an outlet 25 from the separator 16. Such a concentrated ammonia solution is fed into the line 47 through a line 50; From the cold recovery apparatus 14 the dried gas is fed through a line 17 to compressors 18 and from these through a line 19 to the synthesis reactor 20. From its top 12 the exhaust gases are removed through a line 29.

The concentrated carbamate solution leaving the film exchanger 2 is mixed with a carbonate solution recycled through lines 48 and 34, after which the mixture is fed to the bottom of the reactor 35.

Ammonia, which is recycled from other parts of the plant through a line 43, is also fed to the bottom of the reactor. The ammonia stream is divided into two substreams, one of which is fed into the Venturi tube 15 through the inlet 24 'and subjected to the dehydrating cooling. the other, while the other is led through a line 42 to a heat exchanger 41 and evaporated therein, and from there partly fed through a line 39 to the carbamate decomposer 38, in which NH 3 is used as stripping agent, and partly through a line 40 to the reactor 35 bottom.

From the top of the reactor the inert gases are discharged through an outlet 36, and through an outlet 37 an aqueous solution of urea and urea with a large excess of ammonia is drained, which aqueous solution is led to the carbamate decomposer 38 and flows down the pipes and meets vaporized ammonia. which is fed into the bottom of the reactor 38 through the inlet 39. From the jacket side a suitable heating agent is fed through an inlet 45 and discharged through an outlet 46. In this case most of the carbamate present decomposes both due to the evaporation action of the evaporated ammonia and due to the heat given off to the solution coming from the reactor, and the gas mixture of NH 3 and CO 2 formed during the decomposition of the carbamate, together with large amounts of ammonia vapor, the line 44 is fed into the bottom of the reactor 35. The aqueous urea solution, which contains ammonia in equilibrium concentration and is practically carbamate-free, is drained through a line F 47 and led to further treatments. In the case mentioned, when it is not necessary to feed evaporated ammonia as a propellant to the disintegrator 38, the line 39 shall be omitted.

To illustrate the advantages of the present invention, a numerical example will be given in the following with reference to the accompanying drawing, without the invention being considered to be limited thereto for that reason.

Example This example provides operating data for a plant with a capacity corresponding to 1000 t / d ammonia, of which 990 t / d is converted to ammonium urea, which in turn is to be converted to 1700 t / d urea, while an amount of 10 t / d d becomes available for other uses.

In the exchanger 2 is fed: through the inlet 1 crude synthesis gas with the following data: volume-tender 151 .9oo Nm3 / h 'pressure _ 200 kp / emz abs. temperature 125 ° C Composition: H2 61.22 volume percent co o .38 H CO2 17.71 H 2 19.95 "CH4 g _ 0.50" Å _ 0.24 "through the inlet 26 ammonia solution with the following data: mass flow 78350 kg / h Composition: In NH3 78.8% by weight H2O 21.2 N temperature 0 45 ° C through line 27 liquid ammonia with the following data: mass flow 8500 kg / h * temperature 40 OC From the same exchanger 2 is discharged: through line 27 an ammonia-containing carbamate solution with the following data: temperature 150 ° C mass flow - 117050 kg / h Composition: NH 2 COONH 4 80.00% by weight NH 3 5.90 "H 0 14.10 H 2 11101106-2 e 12 through line 3 a gas released from CO 2 is discharged with the following datazy 154,900 -Nm3 / h volume flow temperature 75 ° C pressure ~ I 199.9 kp / cmz abs.

Composition: H2 60.02% by volume co H _ 0 0.38 H _Nz 0 '19.58 H ° “4. 0.49 'H g A 0.23 _ H NH3 19.30 H The reaction heat, 14,500,000 kcal / h, was recovered by preheating steam boiler feed water to 140 ° C.

'In the film absorber 12 were fed: through the line 11 gases from the synthesis reactor with the following data: 466,000 nmf / h volume flow pressure - 198 kg / cm 2 abs temperature 40 ° C' Compositions H2 56.12 volumorocenthg N2 18.71 H CH4 8.77 " 'A. * 2.40 H N33'. 14, oo 'H through line 10 methanized gas with the following data: 0 141.960 Nm3 / h' volume flow pressure 198 ata temperature I 040 ° C Composition: H2 N "II. 64.26 volume percent NZ ¿21.37 H CH4 - _ 0.94 H Å, § ° Ä? 5 "N33 '' -H 1 & É8 H through the inlet 28 water with the following data: mass flow 16290 kg / h temperature 40 OC š. 0711111622 13 _ 'v From the same exchanger 12 is discharged: I through line 13 synthesis gas with the following data: volume flow 513600 Nm3 / h pressure 197.8 ata temperature 45 ° C Composition: _ H2 67.01 volume percent NZ 22.34 “CH4 7, 97 "A 2.18 fl N53 o, so H water ~ zoo kg / h through line 29 waste gas with the following data: volume flow 13100 Nm3 / h Composition: H2 6H, 93 volume percent M2. 21.61 + H cnu 10.15 "A 2.78 n NH 3 0.50" The moist synthesis gas is cooled in 1% to -8 ° C (through # 9 325 kg / h ammoniacal solution containing # 0% by weight ammonia is removed) and is further cooled to -1700 by injecting 61.5 kg / h of liquid ammonia, which evaporates almost completely in the gas mass (the last traces of water are removed via 25 in the form of 68 kg / h of ammoniacal solution containing 87% by weight of ammonia. the following properties leave the separator 16: volume flow 521000 Nma / h pressure 195 kg / emz. H 0 3 PPm É 71111lr6-2 114- After cold recovery in the apparatus 14, this gas is compressed to 207 kp / cm 2 abs. By means of the compressor 18 and fed to the synthesis reactor 20. To the carbamate dehydration driven at a pressure of 195 kp / cm 2 abs. the ring reactor 35, capable of giving 70% conversion, is fed: through line 23 the above-mentioned ammonia-containing carbamate solution; through line 48 the recycled carbonate solution with the following data: 'in mass flow 39950 kg / h temperature 100 ° C Composition:. f CO 30 30.9% by weight NH 3 39.0 "H 2 O 30.1" through the inlet 40 ammonia with the following data: mass flow 34780 kg / h temperature 140 ° C through the inlet 44 the steam mixture leaving the decomposer 38 with the following data: mass-am _. 117370 _ ka / h temperature 190 OC Composition: CO 7 7.9% by weight NH 85.3 "3 H 2 O 6, 8" From the same reactor a urea solution is drained through line 37 with the following data: .- mass flow k 309545 kg / h temperature '180 OC Composition: C02 7.2% by weight NH3 - - 51.3 "H2O" 18, 5 "urea '23.0 ¿" From the decomposer 38 a urea solution is drained through the line 47, which must be sent to the final treatment, and which has the following data : _111114s-2 15 mass sore 192 175 - kg / h temperature 220 ° C l Composition: CO 2 6.8% by weight NH3 30.5 "H2O 25.7 _" urea 37.0 '"The heat requirements of the decomposer 38 are covered by 55000 kg / h steam of 40 kp / cm2 is fed through line 95. -3 In this example, vaporized NH3 was not led to the decomposer 38 through line 39.

Claims (10)

111146'2 16 Patent claims An integrated process for the production of carhamide, wherein NH is synthesized in an NH-synthesis step and reacted with the carbon dioxide in a crude gas mixture obtained by steam reforming of hydrocarbons or by another known method, and thereby decarbonized to the substantially hydrogen and nitrogen-containing starting mixture to said NH3 synthesis step, characterized in that the following steps are included: 'a) the exhaust gases from the NH3 synthesis are treated by absorption with water or dilute NH3 solution in a film contacting apparatus, whereby a concentrated NH3 solution is obtained; b) said raw gas mixture is absorbed with the concentrated NH3 solution from step a) in a film contacting apparatus, whereby carbon dioxide is removed from the raw gas and a concentrated ammonium carbamate solution is obtained; In c) the urea solution from b) is treated in a urea formation cycle, whereby an urea solution is obtained and still undissolved carbamate is decomposed. Integrated method according to claim 1, characterized in that the film contact apparatus in step a) and / or step b) is a vertical tube heat exchanger, where a film of absorbent solution flows down along the insides of the tubes in countercurrent contact with the upwardly flowing gases, while a coolant is caused to flow over the outside of the heat exchanger tubes to remove the heat of reaction. An integrated process according to claim 1 or 2, characterized in that the NH content of the decarbonized crude gases, which after step b) are saturated with NH3, is removed by absorption treatment of said gases after being treated in a methanation step. together with the exhaust gases from the NH3 synthesis in the film contactor used in step-a). Ä.. In an integrated process {according to any one of claims 1 - 3, characterized in that the ammonia synthesis, step a), step b) and step c) is carried out at the same or substantially the same, in the range 100 - 250 kp / cm 2 horizontal, pressure. An integrated process according to any one of claims 1 - H, characterized in that the urea formation cycle c) consists of two separate steps, in a first step the urea is mainly dehydrated to urea, preferably in the presence of NH 3 -7 71111lr 6-'2 17. excess, in a reactor, where the desired reaction temperature is maintained by using the sensitive and latent heat of the decomposition products in the solution leaving the reactor, which heat is recovered by recirculating to the reactor the decomposition products from a second stage, in which it from the first stage the decomposed carbamate is decomposed by heat supply and any feed of vaporized ammonia in countercurrent to the solution, the decomposition products in the gas phase are recycled to said reactor to maintain there, as mentioned, the dehydration temperature, and the resulting resulting treatments. An integrated process according to claim 5, characterized in that the temperature of the reactor used for the dehydration of the urea into urea is adjusted by controlling the amount of the vapors from the decomposition of the urea which have not been converted to urea fed into the reactor, said temperature being maintained at range 15o-25o ° »c. An integrated process according to any one of claims 1 to 6, characterized in that the exhaust gases from step a), which consist essentially of unreacted gases from the NH3 synthesis and of the decarbonized raw gases, are compressed and dried before being recycled to the NH3 the synthesis, the drying being effected by injecting the gases together with liquid NH 3 into a liquid-gas contact chamber and wherein said liquid NH 3 forms part of the ammonia recycled to the urea synthesis reactor obtained from the urea solution leaving the urea decomposer. An integrated process according to any one of claims 2 to 7, characterized in that the removal of the heat of reaction from the tube heat exchanger in step b), where the carbamate is formed, is controlled by keeping the temperature of the liquid film formed by the carbamate solution at levels, rising from the top downwards in such a way that the temperature of the liquid film is always higher than the crystallization temperature of the ammonium carbamate, the coolant, which preferably consists of steam boiler feed water, being caused to flow outside the heat exchanger tubes in co-current relative to the liquid film. An integrated process according to any one of the preceding claims, characterized in that the gas stream freed of carbon dioxide, 'l1_11146-2 -. Which leaves the top of the film contactor in step b) and is saturated with NH, is fed into a cooler, in which a portion of NH is condensed and returned to the film contactor, preferably to its bottom. 10. An integrated process according to any one of the preceding claims, characterized in that the ammonia solution produced in step a) before it is fed as absorbent to step b), where the carbamate is formed, is subjected to fractionation in a manner known per se. to obtain liquid ammonia and water or a dilute aqueous solution of ammonia, and then to the top of the film contactor, preferably always as an absorbent; feeds the water or the dilute aqueous solution of ammonia, while the ammonia is fed to the bottom of the film contactor. PROMISED PUBLICATIONS: Sweden patent application 4,640/70, 220,099 (12 0: 17/03), 402 280 (CO7C 126/02) France 1,356,508 ~ United Kingdom 1,185,944 Other publications on the Encyclopedia of chemical technology. Oath. by Kirk 8 D F Othmer. Vol. 1. New York 1947, pp. 789-803.