Abstract: A method for the modernization of a plant for urea production of the type comprising a reactor (2) for urea synthesis, a stripping unit (3) with carbon dioxide and at least one vertical condensation unit (4) of the film type, foresees the provision of means (36) for feeding a major portion of a flow comprising ammonia and carbon dioxide in vapor phase leaving the stripping unit (3) to the condensation unit (4) and the provision in said condensation unit (4) of means (37) for subjecting to substantially total condensation such major portion of the flow comprising ammonia and carbon dioxide in vapor phase, obtaining a flow comprising urea and carbamate in aqueous solution, then fed to the reactor (2) for urea synthesis. Thanks to the present method of modernization, the efficiency of the condensation unit (4) is remarkably improved, thus permitting an increase of its capacity.

Abstract: Process for the revamping of urea production plants for the synthesis of ammonia (NH3) and carbon dioxide, with a stripping section with NH3, in which the process carries out with differentiated yields, a majority reaction a) between highly pure reagents and a reaction b) between less pure substantially recycled reagents, according to European Patent No. 91116297.2/0479103. According the invention, the urea solution is now fed upstream the stripping section and a reactor with heat removal is utilized. Advantageous, the production capacity of the existing reactor is reduced, with respect to the projected one, in a quantity of 35% to 5%, preferably from 20% to 10%, in favor of the capacity of the “once-through” reactor.

Abstract: A reactor for two-phase reaction, in particular for urea synthesis at high pressure and temperature of the type wherein a co-current flow of a gaseous phase and a liquid phase takes place, comprises a substantially cylindrical vertical external shell (2) in which is supported a plurality of superimposed horizontal perforated plates (6a-6e) in mutually spaced relationship and at least one opening (12a-12e) for liquid flow being defined in correspondence of each of the perforated plates. Advantageously the openings (12a-12e) for liquid flow are mutually offset so as to obtain a substantially zigzag preferential flow path for the liquid phase in the reactor.

Abstract: A reactor for the synthesis of urea from ammonia and carbon dioxide at elevated temperature and pressure is provided with perforated reactor trays in which at least a pair of spaced part perforated reactor trays each have at least one opening at least a distance closer towards the periphery than the center, such as on or near the edge of a perforated reactor tray, and each of such pair perforated reactor trays is provided with a tube with a height of 50-500 mm located on and depending from an underside, e.g. bottom side in a column reactor, of each of such pair perforated reactor tray. The tubes extend to no more than 1/3 of the distance between two adjacent reactor trays.

Abstract: An improved process for urea production as well as a method of retrofitting a pre-existing urea plant based on the Stamicarbon process are disclosed. According to the invention, a high yield reaction space fed by highly pure reagents (NH3 and CO2) and a separating section of the solution leaving the high yield reaction space are added to the pre-existing urea plant, means being provided for recirculating ammonia and carbammate solutions obtained in the separating section to the added high yield reaction space and to the pre-existing reactor respectively.

Abstract: A process is disclosed for preparing N,N'-disubstituted urea by reacting an amine and CO/O.sub.2 mixture gas in the presence of a catalyst system comprising at least one selenium compound selected from SeO.sub.2, (CH.sub.3 O)Se(O)(OH) and (CH.sub.3 CH.sub.2 O)Se(O)(OH), and M.sub.2 CO.sub.3 (M=alkali metal) as a co-catalyst. The process enables less active aromatic amine with a low reactivity as well as an aliphatic amine to be easily transformed into disubstituted urea avoiding the use of expensive precious metal catalysts.

Abstract: A reactor for two-phase reaction, in particular for urea synthesis at high pressure and temperature of the type wherein a co-current flow of a gaseous phase and a liquid phase takes place, comprises a substantially cylindrical vertical external shell (2) in which is supported a plurality of superimposed horizontal perforated plates (6a-6e) in mutually spaced relationship and at least one opening (12a-12e) for liquid flow being defined in correspondence of each of the perforated plates. Advantageously the openings (12a-12e) for liquid flow are mutually offset so as to obtain a substantially zigzag preferential flow path for the liquid phase in the reactor.

Abstract: Method for increasing the capacity of an existing urea process, the existing urea process comprising a reactor (R), a pressure-reduction section (SC) and a urea-recovery section (U), characterized in that(i) a stripping column (S) is added, in which ammonium carbamate from the reaction mixture is stripped with carbon dioxide or is thermally stripped at almost the same elevated pressure, resulting in a gaseous mixture (G1) and a liquid mixture (M4), which liquid mixture (M4) is fed to the pressure-reduction section (SC),(ii) a condenser (C) is added, which is fed with the gaseous mixture (G1), ammonia and optionally carbon dioxide, in which the gaseous mixture (G1) is condensed at almost the same elevated reactor pressure (P) and at least 30% of the equilibrium amount of urea obtainable under the condensation conditions is furthermore formed, in which a liquid mixture containing urea, water and ammonium carbamate (MS) is formed, which mixture is fed to the bottom of the existing reactor (R), and a gaseous mixt

Abstract: In the present process for the preparation of urea, an off-gas stream released during the synthesis of melamine in a high-pressure melamine process which consists predominantly of ammonia and carbon dioxide, is introduced into at least one high-pressure section of a urea stripping plant and is used in the synthesis of urea. The off-gas stream can be used directly without any further treatment.

Abstract: The present invention provides an improved process for synthesizing urea from ammonia and carbon dioxide while preventing corrosion of sites, that are to be in contact with a condensate, of the joints of a tube plate and cooling tubes in a condenser installed vertically or horizontally. According to this process, the sites, that are to be in contact with the condensate, of the joints of the tube plate and the cooling tubes in the condenser are prevented from corrosion by enveloping the sites with liquid ammonia or a solution rich in ammonia in the synthesis of urea comprising separating unreacted ammonia and carbon dioxide as a gaseous mixture thereof from a urea synthesis solution at a pressure substantially equal to the urea synthesis pressure, bringing the gaseous mixture into contact with an absorption medium in the condenser to form a condensate, and recirculating the condensate to the synthesis column.

Abstract: A process for reducing the residual free ammonia emissions from an urea production plant comprises the step of feeding a gas flow comprising carbon dioxide (8) to a melt urea flow (3) coming from the concentration section (13) of the plant.

Abstract: A vertical condenser is installed on or above a urea synthesis column to condense the mixed gas from the stripper by bringing it into contact with an absorption medium under cooling. A first down pipe for making the top part of the condenser communicate with the bottom part of the synthesis column is provided to allow the resultant condensate to flow down to the bottom part of the synthesis column by gravity. The condensate is subjected to urea synthesis together with feed ammonia or a part of feed carbon dioxide supplied thereto. The urea synthesis solution thus formed is introduced into the stripper by gravity through a second down pipe having an opening in the top part of the synthesis column. Unreacted ammonia and carbon dioxide are separated as the aforesaid mixed gas by the rest of the feed carbon dioxide and introduced into the bottom part of the aforesaid condenser so as to be condensed.

Abstract: An in-situ modernization method is provided for a reactor of the type having a plurality of spaced apart perforated plates disposed within a hollow cylindrical vessel wherein the plates are perforated and spaced from the vessel wall to define an annular gap between the periphery of each plate and the vessel wall. The method includes the steps of providing a substantially annular baffle to substantially close the gap while leaving an opening with the openings of adjacent plates being diametrically opposed to each other. Alternatively, the annular gap may be substantially closed by an annular baffle and an enlarged opening is provided in each plate with the openings of adjacent plates being diametrically opposed to each other.

Abstract: Improved yield process for urea synthesis by starting from ammonia and carbon dioxide, comprising a reaction zone under high pressure and temperature conditions, a section wherein a portion of unreacted ammonia and carbon dioxide are stripped and recycled to the reactor, which section operates under substantially the same reactor pressure, and a subsequent section, operating under medium and/or low pressure conditions, for urea purification and simultaneous recovery of residual carbon dioxide and a portion of residual ammonia contained in the effluent stream from the stripping section, as an aqueous solution of ammonium carbamate, in which said aqueous ammonium carbamate solution is either totally or partially fed to said stripping section. Said process makes it possible a conversion of carbon dioxide into urea to be obtained in the reactor which is higher than 70%.

Abstract: A urea production process with high energy efficiency, in which the urea solution obtained from the synthesis stage is subjected to a first stage of high pressure thermal decomposition of the ammonium carbamate which has not undergone conversion to urea together with simultaneous self-stripping by excess ammonia, the gaseous products from said decomposition being condensed in two stages at different temperatures, in the first of which the heat is directly transferred to a second ammonium carbamate decomposition stage which is divided into two parts, namely a first thermal decomposition part and a second part consisting of adiabatic stripping with part of the carbon dioxide feed to the process.

Abstract: Urea is formed by the synthesis of ammonia with carbon dioxide at high pressure and temperature in an internal space of reactors through which flow a liquid phase cocurrently with a gas phase. The reactors are divided into compartments to avoid excessive mixing of the entire liquid phase and to allow the intermittent redistribution of the gas in bubbles of a suitable size for increasing the transfer of heat and mass between the two phases. At each passage from one compartment to the next, the liquid phase and the gas phase are made to flow on separate routes and are distributed in each compartment with a continuous, permanent, and even flow.

Abstract: An improved process for urea production as well as a method of retrofitting a pre-existing urea plant based on the Stamicarbon process are disclosed. According to the invention, a high-yield reactor with partial removal of the reaction heat and a urea recovery section of the solution leaving the high-yield reactor, are added to the pre-existing urea plant, means being provided for recycling unreacted ammonia and carbon dioxide vapors as well as a carbamate solution obtained in the urea recovery section to the pre-existing reactor.

Abstract: The present invention relates to a process and apparatus for the preparation of urea, and in particular for urea obtained from ammonium carbamate formulated from carbon dioxide and ammonia at a pressure of about 125 bar to about 350 bar in a urea synthesis solution in a urea reactor. The reactor defines a horizontally arranged condensation zone and contains a heat exchanger. According to this process, NH.sub.3 and CO.sub.2 are supplied to the reactor and are largely absorbed into the urea synthesis solution. A substantial portion of the heat formed in the condensation is discharged by means of the heat exchanger. The residence time of the urea synthesis solution in the reactor preferably is selected so that at least about 85% of the theoretically obtainable amount of urea is prepared. Thereafter, the urea synthesis solution can be processed into a urea solution or solid urea.

Abstract: Improved yield process for urea synthesis by starting from ammonia and carbon dioxide, comprising a reaction zone under high pressure and temperature conditions, a section wherein a portion of unreacted ammonia and carbon dioxide are stripped and recycled to the reactor, which section operates under substantially the same reactor pressure, and a subsequent section, operating under medium and/or low pressure conditions, for urea purification and simultaneous recovery of residual carbon dioxide and a portion of residual ammonia contained in the effluent stream from the stripping section, as an aqueous solution of ammonium carbamate, in which said aqueous ammonium carbamate solution is either totally or partially fed to said stripping section. Said process makes it possible a conversion of carbon dioxide into urea to be obtained in the reactor which is higher than 70%.

Abstract: A process for the synthesis of urea starting from ammonia and carbon dioxide, comprising a reaction step carried out in at least two distinct operating zones basically at the same pressure, but having a different operating temperature, the difference being preferably between 5.degree. and 60.degree. C., and subsequent separation steps of the non-converted reagents, wherein a gaseous stream is transferred from the first zone, at a higher temperature, to the second zone, at a lower temperature, and a liquid stream, containing urea and/or ammonium carbamate, is transferred from the second zone to the first, so that said gaseous stream is preferably at least 5% by weight with respect to the stream effluent from the first zone to the subsequent separation steps. This process allows a ratio urea/(urea+carbamate), in the stream leaving said reaction step, of more than 70%, to be obtained.

Abstract: Process for the preparation of urea, wherein in a first step ammonia and carbon dioxide react in suitable conditions so as to form a first mixture containing a quantity of urea, wherein in one or more subsequent steps ammonia and carbon dioxide are removed from the first mixture and the obtained urea is concentrated until a urea concentration has been reached suitable to be granulated in a gas stream, whereby apart from urea granules a second mixture containing air, gaseous ammonia and urea dust is formed which subsequently is washed, and wherein before or during the washing an amount of formaldehyde is added to the second mixture of air, ammonia and urea under circumstances wherein the ammonia can react with the formaldehyde in order to form hexamethylenetetramine (HMTA) whereupon the so formed HMTA is separated from the gas stream and is returned into the process before the granulation step.

Abstract: An improved process for urea production as well as a method of retrofitting a pre-existing urea plant based on the Stamicarbon process are disclosed. According to the invention, a high-yield reactor with partial removal of the reaction heat and a urea recovery section of the solution leaving the high-yield reactor, are added to the pre-existing urea plant, means being provided for recycling unreacted ammonia and carbon dioxide vapors as well as a carbamate solution obtained in the urea recovery section to the pre-existing reactor.

Abstract: An improved process for urea production as well as a method of retrofitting a pre-existing urea plant based on the Stamicarbon process are disclosed. According to the invention, a high-yield reactor with partial removal of the reaction heat and a urea recovery section of the solution leaving the high-yield reactor, are added to the pre-existing urea plant unreacted ammonia and carbon dioxide vapors as well as a carbamate solution obtained in the urea recovery section are recycled to the pre-existing reactor.

Abstract: Process and apparatus for the revamping of urea production plants for the synthesis of ammonia (NH3) and carbon dioxide, with a stripping section with NH3, in which the process carries out with differentiated yields, a majority reaction a) between highly pure reagents and a reaction b) between less pure substantially recycled reagents. According to the invention, the urea solution is now fed upstream the stripping section and a reactor with heat removal is utilized. Advantageously, the production capacity of the existing reactor is reduced, with respect to the projected one, in a quantity of 35% to 5%, preferably from 20% to 10%, in favor of the capacity of the "once-through" reactor.

Abstract: A process is described for the industrial synthesis of urea, making the ammonia (NH3) and the carbon dioxide (CO2) react, in at least one reaction space, at high pressures and temperatures and recycling at least in part the unreacted products obtained in a recycle section, characterized by: a) a synthesis reaction between reactants of high purity; and b) a synthesis reaction between less pure reactants, substantially recycled by the so-called recycle section.The corresponding new plant includes a reactor (R1) of high yield "once through"), a reactor (R2) of lower yield and a section of recovery and recycle.The application of the process to preexisting plants requires the simple addition of a reactor of high yield and of pumping devices.

Abstract: A process is described for the industrial synthesis of urea, making the ammonia (NH3) and the carbon dioxide (CO2) react, in at least on reaction space, at high pressures and temperatures and recycling at least in part the unreacted products obtained in a recycle section, characterized by: a) a synthesis reaction between reactants of high purity; and b) a synthesis reaction between less pure reactants, substantially recycled by the so-called recycle section. The corresponding new plant includes a rector (R1) of high yield ("once through"), a reactor (R2) of lower yield and a section of recovery and recycle. The application of the process to preexisting plants requires the simple addition of a reactor of high yield and of pumping device.

Abstract: A process for neutralizing the ammonia present in the molten urea originating from the concentration section of a plant for its production, comprising adding to the molten urea a small quantity of an acid.

Abstract: In a process of producing urea in which ammonia and carbon dioxide are reacted in a first reaction space (E-1, R-1) the unreacted carbamate present in the reaction mixture is subjected to a thermal decomposition treatment, so as to obtain ammonia and carbon dioxide which are sent to a second reaction space (R-2) in which they react with a solution of recycled carbamate coming from an urea recovery section (3). Advantageously, the regulation of the temperature and of the ammonia/carbon dioxide molar ratio in the second reaction space (R-2) is carried out by respectively regulating the temperature of the recycled carbamate solution and the temperature of the thermal decomposition treatment of the residual carbamate leaving the first reaction space (E-1, R-1).

Abstract: A process is described for the industrial synthesis of urea, making the ammonia (NH3) and the carbon dioxide (CO2) react, in at least one reaction space, at high pressures and temperatures and recycling at least in part the unreacted products obtained in a recycle section, characterized by: a) a synthesis reaction between reactants of high purity; and b) a synthesis reaction between less pure reactants, substantially recycled by the so-called recycle section.The corresponding new plant includes a reactor (R1) of high yield ("once through"), a reactor (R2) of lower yield and a section of recovery and recycle.The application of the process to preexisting plants requires the simple addition of a reactor of high yield and of pumping devices.

Abstract: Process for the industrial synthesis of urea, by reacting ammonia (NH.sub.3) and carbon dioxide (CO.sub.2) in at least one reaction space, at high pressures and temperatures and by recirculating at least part of the non-reacted products obtained in a recovery section, characterized by the fact that the following takes place : a synthesis reaction A) between highly pure reagents, and a synthesis reaction B) between less pure reagents, substantially recycled from the said recovery section, the reaction A) being either of adiabatic type A1) or with partial reaction heat removal A2).

Abstract: A urea production process in which the urea solution produced in the reaction zone is treated in sequence with a first thermal decomposer at the same pressure as the reaction, to decompose part of the residual ammonium carbamate into its components, then with an adiabatic stripper in which the free ammonia is stripped with CO.sub.2 operating at a pressure which is 1-7 MPa less than the synthesis pressure, then with two further carbamate thermal decomposition stages at decreasing pressures. The gaseous products obtained from those stages at pressures less than the synthesis pressure are mixed with the recycle solutions from the downstream stages, condensed by heat transfer against said downstream stages, and then recycled to the reaction as liquid.

Abstract: Urea is formed by the synthesis of ammonia with carbon dioxide at high pressure and temperature in an internal space of reactors through which flow a liquid phase cocurrently with a gas phase. The reactors are divided into compartments to avoid excessive mixing of the entire liquid phase and to allow the intermittent redistribution of the gas in bubbles of a suitable size for increasing the exchange of heat and matter between the two phases. At each passage from one compartment to the next, the liquid phase and the gas phase are made to flow on separate routes and are distributed in each compartment with a continuous, permanent, and even flow.

Abstract: Process for the industrial synthesis of urea, in which ammonia (NH3) and carbon dioxide (CO2) are reacted in at least one reaction space SR at high temperature and pressure and the unreacted materials are treated in a recovery section, said synthesis comprising: a) a reaction between highly pure reagents; and b) a reaction between less pure reagents substantially recycled from said recovery section, characterized by the fact that reaction stage A for high Yield majority synthesis (HEPC), between very pure reagents, operating at a higher pressure (Pmax) for example above 300 kg/cm2 abs and preferably at about 400 kg/cm2 abs, is followed by a flash stage F1 operating at pressures lower by at least 40% than said pressure (Pmax) preferably lower than 200 kg/cm2 abs, the gas effluent GF1 from the above-mentioned flash stage F1 being fed to reaction stage B for minority synthesis of less pure reagents operating at a pressure below 200 kg/cm2 abs, while the liquid effluent EL1 from the abovementioned flash stage, to

Abstract: A process for the production of urea comprising the steps of reacting carbon dioxide and ammonia to form ammonium carbamate and subsequent decomposition of ammonium carbamate to form a reaction mixture comprising urea and water, wherein the reaction mixture is contacted with one side of a semi-permeable membrane, and a drying fluid capable of removing water and possibly other reaction products(s) from the reaction mixture is contacted with the other side of the semi-permeable membrane.

Abstract: The process of the present invention which produces the flexible integration for the production of ammonia and urea uses adiabatic reforming of the carbonaceous feedstock such as natural gas. With adiabatic reforming of natural gas, a surplus of carbon dioxide is produced. With adiabatic reforming, substantially pure oxygen and nitrogen may be used which does not involve inert gases such as argon in the system. More importantly, adibatic reforming allows operation at much higher pressure than standard primary reforming, namely, between 700 and 3000 psig. When these pressures are used, the process includes a recycle of the methane and hydrogen from the ammonia synthesis loop to the adiabatic reformer.The process of the present invention uniquely removes the carbon dioxide which is produced by the reforming of the carbonaceous feedstock and treatment by the watergas shift reaction in two independent stages.

Abstract: An integrated ammonia urea process where the reaction of carbon dioxide and ammonia is in a urea reactor having a condensing section, a reaction section having more than one stage and a stripping section. The raw ammonia synthesis gas containing carbon dioxide is introduced into the stripping section of the urea reactor at a pressure selected within the range of 2000 and 3500 psig. The stripping effluent removed from the stripping section comprises the raw ammonia synthesis gas, carbon dioxide and ammonia which is introduced into a state of the reaction section.

Abstract: Process for the preparation of urea in whicha urea synthesis solution containing carbamate and free ammonia is formed in a high-pressure part in a synthesis zone at an NH.sub.3 /CO.sub.2 molar ratio of up to 4:1, a temperature of at least 175.degree. C.

Abstract: Process for the preparation of urea in whicha urea synthesis solution containing carbamate and free ammonia is formed in a high-pressure part in a synthesis zone at an NH.sub.3 /CO.sub.2 molar ratio of up to 4:1, a temperature of at least 175.degree. C.

Abstract: An improved process for recovering usable components from waste streams containing urea, including a dilute aqueous urea solution, which result from the preparation of particulate urea products. The dilute aqueous urea solution is used to wash a urea containing waste gas stream whereby urea contained in the gas stream is dissolved in the aqueous urea solution. The aqueous urea solution thus obtained is then subjected to a hydrolysis treatment whereby the urea contained therein is hydrolyzed, and the ammonia and carbon dioxide thus formed are separated from the residual liquid stream.

Abstract: A process for isolating liquid urea and its thermal decomposition products from the off-gas of melamine synthesis, which gas has been freed from melamine by fractional condensation and then been washed with molten urea, wherein the off-gas, containing 2-10 kg of melt per kg of pure gas, is passed at 8-30 m/sec tangentially into the upper part of an axially symmetrical separation zone. As a result of the rotation imparted to the gas/liquid mixture, the two phases are separated from one another, and both pass downward through the separation zone. The gas and liquid are separately taken off at the bottom end of the separation zone. The residence time of the gas mixture in the separation zone is not less than 0.5 second.

Abstract: A process for the production of urea from ammonia and carbon dioxide via synthesis where the urea formation takes place in a synthesis zone (or zones) in which an excess of free ammonia is kept to favor high conversions, said synthesis zone (or zones) being followed by an ammonia separation and direct recycle to the reaction step, where the urea solution from said reaction zone (or zones) is intimately contacted for a short duration time with a minor portion of the fresh CO.sub.2. The separation step is followed by a CO.sub.2 stripping step where the residual carbamate is removed using a countercurrent fresh CO.sub.2 stream.

Abstract: A process for the displacement to the gaseous phase, at 80-250 Kg/cm.sup.2, of the excess NH.sub.3 contained in an aqueous urea solution, coming, at 150.degree.-230.degree. C., from a former stripping, isobaric with the urea synthesis, and containing also CO.sub.2 as ammonium carbamate. The CO.sub.2 is, at most, 25% b.w. of the urea, and the displacement is performed by means of a CO.sub.2 stripping within a falling-film exchanger, hereinafter called the CO.sub.2 stripper, isobaric too with said synthesis. The amount of carbamate leaving the bottom of said CO.sub.2 stripper is substantially equal to the amount of carbamate entering the same stripper. The global NH.sub.3 :CO.sub.2 ratio, in the solution entering the CO.sub.2 stripper, is from 2 to 8 b.w. and heat is supplied only to the uppermost portion of the pipes of the CO.sub.

Abstract: Disclosed herein is a process of synthesizing urea including reacting ammonia and carbon dioxide at a urea synthesis pressure and temperature in a urea synthesis zone, separating excess ammonia and unreacted ammonium carbamate from the thus-obtained urea synthesis melt as a gaseous mixture containing ammonia and carbon dioxide, recirculating the gaseous mixture to the urea synthesis zone, and, on the other hand, obtaining urea from an aqueous urea solution which has been obtained by separating the excess ammonia and unreacted ammonium carbamate. The above process features ingeniously combined conditions of various process steps. It produces urea using less high-pressure steam and recovers less low-pressure steam. A stripping operation making use of carbon dioxide can be effectively incorporated in the above process. The above process permits to cut the construction cost of a urea synthesis plant.

Abstract: The specification describes a process for synthesizing urea. The process comprises reacting ammonia and carbon dioxide in a molar ratio of 3:1-5:1 and at a pressure of 150-250 Kg/cm.sup.2 G, subjecting the resultant reaction mixture to a stripping step using gaseous carbon dioxide at a pressure substantially equal to the urea synthesis pressure and a temperature of 195.degree.-210.degree. C. to remove unreacted ammonia and unreacted carbon dioxide contained in the reaction mixture so that the content of unreacted ammonia is lowered to 10-15% by weight. This invention ensures a high conversion ratio from carbon dioxide to urea, considerably little formation of biuret during the stripping step, and reduced consumption of high pressure steam.

Abstract: In a synthesis of urea using ammonia in a highly excessive molar ratio, unreacted materials are decomposed and separated by subjecting the urea synthesis effluent to a stripping step using carbon dioxide at a pressure equal to the urea synthesis pressure. The thus-separated gaseous mixture of ammonia and carbon dioxide is condensed through an indirect heat exchange with an effluent stream discharged from the stripping step and lowered to a predetermined pressure level. Resulting condensation heat is used for the decomposition and separation of unreacted materials still remaining in said effluent stream. By choosing suitable operation conditions for each step of the present invention, it is possible to reduce the amount of high pressure steam to be required and to minimize the amount of low pressure steam to be recovered.

Abstract: In a process in which a urea synthesis effluent obtained by reacting ammonia with carbon dioxide is subjected to a stripping step of bringing the urea synthesis effluent into countercurrent contact with carbon dioxide under heating to obtain an aqueous urea solution containing a small amount of ammonia and ammonium carbamate, the improvement comprises first bringing the urea synthesis effluent is into contact with a separated gas evolved in the stripping step under adiabatic conditions or with a little cooling. The use of the above process enables a reduction in size of the stripper and a recovery of the high pressure steam without keeping the ammonia to carbon dioxide molar ratio lower than that of the conventional method.

Abstract: An inert gas containing carbon dioxide and ammonia and separated from a urea synthesis effluent under urea synthesis pressures is brought into contact with an absorbent along with unreacted carbon dioxide and ammonia separated in high pressure distillation at a pressure of from 10 to 25 kg/cm.sup.2 G to absorb substantially all of the carbon dioxide and the major portion of the ammonia, and is cooled to be separated from the resulting liquid ammonia and then is discharged. The inert gas can be treated with little or no danger of explosion by the above method.

Abstract: A process for synthesizing urea in which a urea synthesis effluent obtained by reacting carbon dioxide and ammonia at urea synthesis pressures and temperatures is subjected to stripping treatment with carbon dioxide under pressures substantially equal to urea synthesis pressures to separate the unreacted carbon dioxide and ammonia contained in the urea synthesis effluent as a gaseous mixture, and a sufficient amount of said gaseous mixture to maintain the urea synthesis temperatures at a predetermined level is recycled to the urea synthesis in the gaseous state, the balance being subjected to condensation to be recycled in the liquid state to the urea synthesis.

Abstract: In an integrated or combined process for the production of ammonia and urea, the improvement consisting in that the absorption of CO.sub.2 from the raw gas going to the synthesis reactor for ammonia is carried out with an absorption apparatus which is divided into two sections, one being of the plate type and the other of the thin film type. The predominant fraction of CO.sub.2 is stripped in the thin-film section, the remainder in the adiabatic plate section.

Abstract: A process and a device for treating urea solutions coming from synthesis reactors and containing in addition to the formed urea also free ammonia, water and unreacted ammonium carbammate having two steps wherein in the first step, a substantial amount of ammonia is distilled while ammonium carbammate is only partially decomposed, and in the second step, the bulk of carbammate is decomposed and the residual ammonia is distilled.