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: 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: 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: 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: 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 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: Compounds of the formula (I): ##STR1## wherein: X=O, S, or NOH;R.sup.1 is H or CH.sub.3 ;n=1, 2, or 3;R.sup.2, R.sup.3, and R.sup.4 are as defined in one of the following paragraphs(a) R.sup.2 and R.sup.3 are independently Cl or Br, and R.sup.4 is H;(b) R.sup.2, R.sup.3 and R.sup.4 are independently Cl or Br;(c) R.sup.2 is F, R.sup.3 is Cl, and R.sup.4 is H; or(d) R.sup.2 and R.sup.3 are CH.sub.3 or C.sub.2 H.sub.5, and R.sup.4 is H;R.sup.5, R.sup.6 and R.sup.7 are as defined in one of the following paragraphs(a) one of R.sup.6 and R.sup.7 is CF.sub.3, R.sup.5 and the other of R.sup.6 and R.sup.7 is H;(b) R.sup.5 and R.sup.6 are H; and R.sup.7 is F, Cl, or Br;(c) R.sup.5 and R.sup.7 are independently F, Cl or Br and R.sup.6 is H;(d) R.sup.5 and R.sup.6 are independently F, Cl, or Br, and R.sup.7 is H;(e) R.sup.6 and R.sup.7 are independently F, Cl, or Br, and R.sup.5 is H; or(f) R.sup.6 is phenoxy and R.sup.5 and R.sup.7 are Hare plant fungicides.

Abstract: An improved process and apparatus for the concentration of an aqueous urea solution by evaporation of water in a single pass shell and tube heat exchanger having a substantially vertical tube bundle within the shell. The aqueous urea solution is introduced into the top of the vertical tube bundle and caused to fall as a film down the inside of said tubes whereby it is heated and water evaporated therefrom to form a concentrated urea solution. The heat for this evaporation is provided by condensing at least a part of a gas mixture containing NH.sub.3, CO.sub.2 and H.sub.2 O in the shell side of the heat exchanger. This gas mixture is introduced into a lower portion of the shell wherein it is caused to flow upwardly in shell in contact with said tube bundle, counter-current to the flow of the aqueous urea solution within the tubes whereby heat from said condensation is transferred to said aqueous urea solution flowing down the inside of the tubes.

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 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: A process for the preparation of urea from ammonia and carbon dioxide at an elevated temperature and pressure having a reaction zone and a stripping zone. In the reaction zone, carbon dioxide and a portion of the ammonia are converted to ammonium carbamate, and a portion of the ammonium carbamate is converted to urea, the combined conversions resulting in a net formation of heat. In the stripping zone, a urea product stream containing unconverted ammonium carbamate is heated by heat exchange with the reaction zone to decompose a portion of the ammonium carbamate. In the reaction zone, the conversion of ammonium carbamate into urea is continued until the quantity of urea formed is at least 50 percent of that quantity of urea that would be obtained at equilibrium under the reaction conditions present in the reaction zone.

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: 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: 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.