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: The energy consumption of conventional reactors for heterogeneous synthesis, e.g., ammonia synthesis and methanol synthesis, wherein the synthesis gas flows substantially axially through catalyst beds, is substantially reduced by inserting in at least one catalyst bed: two concentric cylindrical substantially perforated walls to laterally delimit the bed; a bottom closure between these walls; and optionally a diaphragm on top of the bed. Optionally also, a catalyst granulometry gradient may be employed in the upper part of the bed. An upper minor portion of at least one of the cylindrical walls may be unperforated. The synthesis gas now traverses the bed substantially radially.

Abstract: The system to reduce the energy consumption of heterogeneous synthesis reactors, particularly of ammonia reactors, f.i. the "Chemico"-type reactor, foresees the insertion of two cylindrical walls at least partially perforated in order to annularly delimit the catalytic beds; the first outer wall (Fe) having a diameter (Di) slightly smaller than diameter (Dc) of the cartridge (C), has a height (Hi) higher than (H'i) of the internal cylindrical wall (Fi) which has a diameter inferior to the above mentioned (Di), but superior to the external diameter (Dt) of the central feed pipe (T) of the quench gas (QG). The top (SO) of the internal cylindrical wall (Fi) is closed by a cover (CO) that has a distance from the bottom (FO) of the basket equal to the mentioned height (H'i) of the internal cylindrical wall. The catalytic bed is therefore annular in diameter (Di-D'i) on all of the said height (H'i), but is substantially cylindrical (of diameter Di) on the height (Hi-H'i).

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: The energy consumption of conventional reactors for heterogeneous synthesis, e.g., ammonia synthesis and methanol synthesis, wherein the synthesis gas flows substantially axially through catalyst beds, is substantially reduced by inserting in at least one catalyst bed: two concentric cylindrical substantially perforated walls to laterally delimit the bed; a bottom closure between these walls; and optionally a diaphragm on top of the bed. Optionally also, a catalyst granulometry gradient may be employed in the upper part of the bed. An upper minor portion of at least one of the cylindrical walls may be unperforated. The synthesis gas now traverses the bed substantially radially.

Abstract: A system to make walls for catalyst baskets for heterogeneous synthesis reactors, particularly the distribution walls which are inserted in axial reactors in order to modify them into substantially radial (or axial-radial) reactors with low energy consumptions. The distribution walls are divided into n sections. By attaching each section end to a device consisting of two flange elements, the radially longer one protruding over the distribution wall, the invention achieves truing and stiffening of the entire device. The other end extends slightly into the inside of the catalyst bed. Between the internal walls of the basket and the perforated distribution sheet, an airspace is formed by using separating rods or, in their absence, using a perforated bridge plate as the distribution wall.

Abstract: The general conditions of the thermal exchange are improved by ameliorating the mixing of reacted gases together with quench gases, in order to increase in the yields and to reduce the energy consumption in reactors used for heterogeneous synthesis (ammonia, methanol, etc.), consisting of an external shell, of an internal cartridge with catalytic baskets lying one above the other, at least one of such baskets being traversed axially by the reaction gas, and of means to feed the quench gas between the bottom of one basket and the top of the following basket, said gas mixing being carried out in a peripheral zone near the internal cartridge wall.

Abstract: Process for obtaining an optimal synthesis gas distribution in catalytic beds for heterogeneous reactions in reactors comprising a cylindrical pressure vessel with an internal cartridge containing a catalyst.

Abstract: A converter for heterogeneous synthesis. The converter contains a variable number of internal cartridges, each having a non-perforated external wall which forms an interspace with a internal shell wall. The converter also has a corresponding variable number of catalytic beds, each having granular catalyst. The catalyst beds are contained in a vessel having a closed bottom, an open top, and two cylindrical concentric perforated walls. The perforated walls allow for adduction and extraction of reaction gases which flow axially and radially through the catalyst beds. Heat exchangers are orientated on the same axis with the annular catalyst beds and consist of tube-bundles within a shell. Reaction gas feed tubes extend through some of the heat exchanger tube bundles.

Abstract: The energy consumption of conventional reactors for heterogeneous synthesis, e.g., ammonia synthesis and methanol synthesis, wherein the synthesis gas flows substantially axially through catalyst beds, is substantially reduced by inserting in at least one catalyst bed: two concentric cylindrical substantially perforated walls to laterally delimit the bed; a bottom closure between these walls; and optionally a diaphragm on top of the bed. Optionally also, a catalyst granulometry gradient may be employed in the upper part of the bed. An upper minor portion of at least one of the cylindrical walls may be unperforated. The synthesis gas now traverses the bed substantially radially.

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: In a reactor comprising an outer shell and an internal cartridge preferably obtained by assembling a number of stackable modular cartridges, each comprising from the outside to the inside at least one solid wall forming an air space with the shell inside wall, a continuous bottom to the solid wall, a first wall perforated for the whole of its length, a second internal wall only partially perforated, and a catalytic bed inserted between the said bottom and said walls totally respectively partially perforated, at least one heat exchanger is arranged centrally and axially in a catalytic bed; the feed gas which has cooled the external wall of the shell collects in a duct in the middle of the exchanger along which it runs in one way (for example, from top to bottom) running successively along the exchanger in the other way inside the exchanger tubes emerging preheated in the free zone over the top layer of the catalytic bed where it is mixed with fresh gas fed directly from the outside of said zone.

Abstract: Disclosed is a reactor for heterogeneous catalytic reactions of gaseous reactants under pressure, comprising: a container having an inlet for introduction of gaseous reactants and an outlet for the efflux of products of the reactions; a cartridge having a cylindrically shaped wall placed within the container and communicating with the inlet and the outlet; at least two stationary-bed, catalyst-containing baskets supported within the cartridge, each of the baskets including an imperforate bottom section, a cylindrical outer perforated wall, a cylindrical inner concentric perforated wall and an annular opening defined by the inner and outer perforated walls in the upper end of each stationary-bed, catalyst-containing basket, the opening formed in a plane approximately perpendicular to the longitudinal axis of the inner and outer perforated walls, the bottom section and the inner and outer perforated walls cooperating with the cylindrically shaped cartridge wall to form a partially restrictive axial flow means,