Abstract: In a process for the production of urea, substantially pure ammonia and carbon dioxide are reacted in a reaction space (1) from which comes out a reaction mixture subjected to stripping (2) to obtain a partially purified mixture sent to a urea recovery section (3, 4, 7, 8). From the recovery section (3, 4, 7, 8) it is obtained a dilute carbamate solution, which is subjected to stripping (9) with recycling of vapors to the reaction space (1) after condensation (6). This process achieves high conversion yield with reduced energy consumption and low implementation costs.

Abstract: The invention relates to a process for the preparation of urea from ammonia and carbon dioxide, the preparation being effected in whole or in part in a vertical combi-reactor. The gas stream leaving the stripper is fed to the condenser section of a vertical combi-reactor in which this gas stream is wholly or partially condensed in the carbamate stream which is transferred from the scrubber section to the condenser section via a downcomer. Ammonia and carbon dioxide are partially converted into urea in this condenser section of the combi-reactor. The urea conversion is completed in the reaction section of the combi-reactor.

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: In a process for the production of urea, substantially pure ammonia and carbon dioxide are reacted in a reaction space (1) from which comes out a reaction mixture subjected to stripping (2) to obtain a partially purified mixture sent to a urea recovery section (3, 4, 7, 8). From the recovery section (3, 4, 7, 8) it is obtained a dilute carbamate solution, which is subjected to stripping (9) with recycling of vapors to the reaction space (1) after condensation (6). This process achieves high conversion yield with reduced energy consumption and low implementation costs.

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: 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: 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 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: 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: 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: A urea production process combining lower pressure urea concentration and carbamate recovery steps into a single non-vacuum operation. Following high pressure stripping wherein a bulk of unreacted carbamate is recovered from the reaction effluent, remaining carbamate is stripped by heated air at atmospheric pressure wherein urea is concurrently concentrated without the use of vacuum evaporators. Weak carbamate solution subsequently formed is stripped of water (and residual urea is hydrolyzed) using air and steam at a medium pressure single tower hydrolyzer/stripper to obtain a concentrated carbamate stream suitable for recycle to the reactor. The process employs heat integration for enhanced energy efficiency and produces a good quality aqueous condensate suitable for direct use as boiler feed water. Thus the aqueous condensate produced requires no additional cooling and ammonia treatment. The process employs simplified and reduced process unit operation to eliminate equipment for cost reduction.

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: 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: A process to modernize existing urea plants which use a stripping with carbon dioxide, and to increase urea yields and flexibility under overload conditions while at the same time reducing energy consumption, corrosion phenomena and possible risks of explosive mixtures. The plant includes: a passivation stage with the introduction of an oxidizing agent and reduction of the air fed to the system; a medium pressure distillation stage of the products leaving the stripping section, and a condensation of the products of the distillation, effected in a pre-evaporation phase to concentrate at low pressure the urea solution.The modernized plant, includes at the start at least a reactor, a scrubber, a condenser, a stripper and the evaporators, includes also a passivation section, a medium pressure distillation section, and a distillation section with double-effect technique.

Abstract: A process for purifying the effluent originating from urea production plants, consisting of three successive treatment stages, namely stripping of the volatile components, thermal hydrolyis of the urea and biuret in a plurality of zones traversed with piston flow, and final stripping of the volatile components produced by the hydrolysis.

Abstract: Disclosed herein is a method of utilizing inert gases, which are introduced as impurities in the feed raw materials for the synthesis of urea and also as an anti-corrosion agent into a urea process, as a stripping agent of unreacted materials in one or more of the below-mentioned separation steps, in a urea process in which: urea is synthesized from ammonia and carbon dioxide in the presence of an excess ammonia; unreacted materials including the excess ammonia are separated from the resulting urea synthesis solution as gaseous mixtures of ammonia and carbon dioxide successively at a plurality of pressure levels; the gaseous mixtures thus-separated are absorbed in solvents or condensed at the corresponding pressure levels; and the solutions or condensates thus-formed are circulated to the urea synthesis step.

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 the preparation of urea from carbon dioxide and excess ammonia at an elevated temperature and pressure to form a urea synthesis solution containing uncoverted ammonium carbamate and free ammonia. A portion of the ammonium carbamate contained in the urea synthesis solution is decomposed in a first decomposition zone by the supply of heat, and the first gas mixture thus obtained is separated and at least partially condensed in a first condensation zone. The residual area solution is heated in a second decomposition zone maintained at a pressure of between about 4 and 40 bar thereby decomposing a further portion of ammonium carbamate and the second gas mixture thus obtained is separated from the second residual urea containing stream. This second residual area stream is introduced into a further decomposition zone wherein remaining ammonium carbamate is substantially removed, and a third gas mixture thereby formed is processed to form a dilute aqueous ammonium carbamate solution.

Abstract: A process for the synthesis of urea from ammonia and carbon dioxide in which high yield reaction and optimal reactor heat balance control are achieved at the same time by using two reaction zones, where two different NH.sub.3 /CO.sub.2 molar ratios are maintained, and by treating the effluent from the second reaction zone in a separation treatment in two steps in series; the reactant gas stream discharged from the second treatment step is recycled, after partial condensation, to the first reaction zone, while at least part of the gas stream discharged from the first treatment step is recycled directly to the second reaction zone, the gas stream from both the first and second treatment step being so controlled as to obtain optimal NH.sub.3 /CO.sub.2 ratios and optimal reaction temperatures in the two reaction zones.

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: 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: A process for the production of urea starting from ammonia and carbon dioxide in a NH.sub.3 /CO.sub.2 molar ratio of from 5/1 to 8/1, comprising the synthesis and decomposition of the ammonium carbamate contained in the solution of urea, in two steps; the first of these provides for ammonia as the stripping agent and the second for carbon dioxide as the stripping agent.In the process of the invention the synthesis and the decomposition in the first decomposition step are carried out at an equal or substantially equal pressure comprised between 180 and 250 atm., while the decomposition in the second step is carried out at a pressure of from 30 to 50 atm. lower than the pressure in the first step.

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 the process for urea synthesis, an effluent from a reactor 2 containing urea, ammonium carbamate, excess ammonia and water is introduced in a first heater 3 to separate excess ammonia and to decompose ammonium carbamate, thereby separating them from the liquid phase; then the liquid effluent from the first heater 3 is introduced in a second heater 6 to separate the remaining excess ammonia and to decompose ammonium carbamate in the presence of starting carbon dioxide used as stripping gas, thereby separating them from the liquid phase; the liquid effluent from the second heater 6 is introduced into a urea solution purification step in which pressure is lower than in the above step; and the separated gaseous effluents from the first and the second heaters are returned into the reactor.

Abstract: In a urea producing method by synthesis, the improvement which consists in feeding liquid ammonia in excess to the reactor so that a urea solution which contains ammonium carbamate is produced, the carbamate is decomposed in a high-pressure decomposer and the stripping agent is an inert, oxygen-containing gaseous stream, the carbamate decomposition products are sent to a high pressure condenser and ammonium carbamate is formed, whereafter the carbamate is separated from the inerts and the solution of urea coming from the high-pressure decomposer is fed to a medium-pressure decomposer which is fed through its bottom with inerts. The heat for operating the medium-pressure decomposer is a hot condensate from the high-pressure-decomposer-heating steam, and the products of decomposition of the carbamate coming from the medium-pressure decomposer are sent to a medium-pressure condenser together with a solution of ammonium carbonate coming from the low-pressure sections of the installation.

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: An improvement in the cyclic process for producing urea wherein CO.sub.2 and NH.sub.3 are reacted in the presence of an aqueous ammoniacal solution in a urea synthesis reactor at an elevated temperature and at an elevated pressure in excess of 1800 PSIG to form a urea synthesis reactor effluent fluid at high pressure. The said effluent fluid is split into a minor stream and a major stream. The major stream is let down in pressure and then passed into a gas liquid separator wherein the gas stream rises through a packed midsection into the upper portion of the separator and is then taken off.

Abstract: An integrated ammonia-urea process is disclosed which uses as the starting gas mixture a stream coming, for example, from steam reforming of hydrocarbons, carbon dioxide being stripped from the stream by the action of a very concentrated ammonia solution (above 70% by wt) first and the the action of an ammoniated solution of ammonium carbonate secondly, a solution of ammonium carbamate being obtained together with a gas stream composed of nitrogen and hydrogen; sending the carbamate solution to the urea reactor, discharging from the urea reactor the urea solution containing unconverted carbamate and excess ammonia, decomposing said carbamate and sending evolved ammonia to the urea reactor again along with carbon dioxide, discharging the urea solution having now 50% of the original carbamate to an adiabatic stripper in which the stripping gas is essentially composed of hydrogen and nitrogen, removing ammonia and carbon dioxide with water from the adiabatic stripper and condensing ammonia and carbon dioxide by