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 method for "in-situ" modernization of a reactor for effecting heterogeneous exothermic synthesis reactions, especially of the so-called Kellogg type, including the preliminary step of providing at least three radial or axial-radial catalyst beds (11, 12, 13), includes the steps of providing a first gas/gas heat exchanger (18) between the first (11) and second (12) catalyst beds and a second gas-gas heat exchanger (29) in the third catalyst bed (13). Thanks to the provision of two exchangers (18, 29) for cooling of the gases flowing between the catalyst beds by means of indirect heat exchange, the present modernization method allows to achieve a reactor with a high conversion yield.

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: 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: 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: 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: Improved process to convert in situ conventional reactors with four catalytic beds with axial flow and with intermediate quenching (Kellogg reactor), Third and fourth original beds are combined thus obtaining a reactor with three beds through which the synthesis gas now flows with a substantially radial flow.

Abstract: Reactors for the catalytic conversion of carbon monoxide into carbon dioxide are advantageously modified in situ from axial flow reactors into substantially radial flow reactors, and more particularly into axial-radial flow reactors. To this end at least an external cylindrical wall perforated for its whole length and an internal wall preferably perforated for most of its length are inserted inside the conventional reactor shell and cartridge.

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: Synthesis gas is reacted in several catalytic beds having axial-radial or radial flow. Reacted gas is collected at an outlet of a final catalytic bed and is transferred to a reaction heat recovery system situated at a top of a reactor. The reactor includes three catalytic beds, two or more beds having inverted, curved bottoms. A first quenching system is located in the reactor and includes a distributor situated inside a first, upper bed at a location immediately under an unperforated portion of an internal wall of that bed. A gas/gas heat exchanger is located centrally within one or more of two upper beds located within the reactor. A water pre-heater or boiler is located inside an upper bottleneck portion of a shell of the reactor and is fed with reacted gas collected from a lowermost catalytic bed.

Abstract: In a process for exothermic and heterogeneous synthesis, for example of ammonia, in which the synthesis gas is reacted in several catalytic beds with axial-radial or only radial flow, the reaction gas is collected at the outlet from the last catalytic bed but one and is transferred to a system for heat recovery external to the reactor, and is re-introduced into the last catalytic bed.

Abstract: A converter for heterogeneous catalytic synthesis under pressure, consisting of an external shell in a single piece and inside this of at least a cartridge containing a catalyst arranged in one or more beds contained in catalyst-carrying baskets. An external wall of these baskets is provided with means that protrude from the closed bottom and are coupled, in order to be supported, with means protruding from the internal continuous face which extends substantially along the entire axial height of the converter and is the nearest to the internal wall of the baskets. An unflanged labyrinth seal is located between two centrally located heat exchangers contained within the converter.For reactions at high pressures, the wall holding the protruding support rings at the bottom of the baskets is a cartridge wall in a single piece that extends substantially along the whole shell and forms with this an airspace.

Abstract: A system for modernizing exothermic heterogeneous reactors used in the synthesis of ammonia, methanol and the like, which include a pressure shell, a wall for forming an airspace, a wall or cartridge for containing a catalyst bed, and catalyst-containing basket. An airspace-forming wall is formed of a single piece substantially the whole axial length of the reactor. A bed forming wall is distinct from, and unconnected to, the airspace forming wall, and it constitutes independent modules, each module containing at least one catalyst bed and each module resting either on an underlying module or on an extension of an inside gas distribution collector. The bed forming walls contain the catalyst and distribute gas therethrough. A portion of the catalyst contacts the airspace-forming wall.

Abstract: In reactors for heterogeneous synthesis, comprising a boiler and a heat exchanger inserted at least partially into the end catalytic beds, and at least an intermediate catalytic bed, two airspaces are now provided in each catalytic bed by introducing couples of annular walls, one of said airspaces being produced between the cartridge's internal wall and the perforated wall inserted close to it.

Abstract: Improved process for heterogeneous synthesis and related reactors according to which the synthesis catalyst is distributed in three catalytic beds either axial-radial or radial, control of the temperature between beds being effected by means of fresh quench gas between the first and the second bed and by means of indirect cooling with an exchanger between the second and the third bed of the gas leaving the second bed, using fresh gas which is heated inside the tubes of said exchanger.

Abstract: A reactor for heterogeneous synthesis with reduced energy consumption. The reactor includes two cylindrical walls that are at least partly perforated and which annularly deliminate the catalytic beds. An outer wall (Fe) has height (Hi) and a diameter (Di) that is slightly smaller than diameter (Dc) of cartridge (C). An internal, cylindrical wall (Fi) has a height (H'i) and a diameter (D'i) much smaller than diameter (Di). The diameter (D'i) is about equal to diameter (Dt) of a central tube (T) which is an outlet for reacted gas (RG). The top of the cylindrical wall (Fi) is closed by a cover (CO) and is located at a distance (D) from the upper edge of the external wall of the basket (Fe). The basket is closed at its bottom by a tapered wall (PR).

Abstract: A method for passivating the surface of the strippers of the urea plants, where the temperatures are very high, where the pressures range from 120 to 240 Kg/cm.sup.2 and where the effluent process flow from the synthesis reactor undergoes one or more falling-film evaporations, preferably in countercurrent with a driving gas consisting of NH.sub.3 or CO.sub.2, characterized by the fact that the passivation is carried out by means of a sinergistic combination of oxygen, preferably injected into the bottom of at least one stripper, and of a second passivating agent, preferably injected into the process flow entering the head of at least one stripper, wherein said second passivating agent is injected in the liquid state or as a liquid solution, before or contemporaneously to the start of the evaporation.