Ammonia, CO.sub.2 and ammonium carbamate are reacted in a reactor at elevated temperature and pressure to form urea. From 10 to 100 percent of the CO.sub.2 fresh reactor feed stream, which is substantially equivalent to the stoichiometric net amount of urea formed in the reactor, is reacted with NH.sub.3 at 10 - 670 psia to form an aqueous ammonium carbamate solution, and this solution is charged to the reactor to form urea.
Urea process in which part of the fresh CO.sub.2 reactor feed is reacted to carbamate with ammonia gas contained in decomposer off-gas, in presence of urea and water. Exothermic heat of reaction thereof is internally recovered in indirect heat exchange with the reactor effluent let down in pressure for carbamate decomposition and excess ammonia evaporation, and producing said off-gas in the carbamate decomposer. Part of the total heat required in the carbamate decomposer for complete carbamate decomposition is supplied by reacting fresh CO.sub.2 feed with the off-gas from the carbamate decomposer in a first decomposing zone. The remaining part of the heat of decomposition can be supplied by indirect steam heating in a second decomposing zone directly following the first such zone. After substantial completion of the reaction of the fresh CO.sub.2 feed with the ammonia from the decomposer off-gas to form carbamate, the resulting solution is further cooled in a separate cooler and fresh ammonia feed is supplied to the cooler and dissolved in the carbamate solution for the purpose of increasing the molar ratio of HN.sub.3 to CO.sub.2 in the carbamate solution above about 3.8 to one. The final aqueous ammoniacal solution of ammonium carbamate containing urea thus obtained, is introduced into the urea reactor with the remaining part of the fresh CO.sub.2 and NH.sub.3 feeds to form urea.
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. The minor stream is cooled and then let down in pressure and passed into the upper portion of the gas liquid separator to produce a gas phase which is taken off from the upper portion and a liquid phase which passes down through the packed midsection and contacts the upwardly rising gas phase from the major stream wherein the downwardly passing liquid phase absorbs carbon dioxide and water vapor from said upwardly passing gaseous phase. The said liquid phase enriched in carbon dioxide and water vapor is then taken off from the lower section of the separator and withdrawn together with the liquid phase portion of the major stream. This liquid product is passed to a carbamate decomposer. The gaseous product taken from the upper section of the separator is, after further processing, at least in part recycled to the urea synthesis reactor.
Urea synthesis process with liquid carbamate recycle, in which the reactor effluent is divided into major and minor streams. The major stream is reduced in pressure and subjected to heating and substantial carbamate decomposition to ammonia and carbon dioxide decomposer off gas, either directly or after preliminary ammonia separation. The minor stream is reduced in pressure and is contacted with decomposer off gas and fresh make up carbon dioxide, either directly or after preliminary ammonia separation, and in indirect heat exchange with a relatively colder fluid, whereupon ammonium carbamate is formed from the mixture of the minor stream, fresh make up CO.sub.2 and decomposer off gas in an aqueous solution of urea and the resulting solution is recycled to the urea synthesis reactor.
A process is described for the preparation of urea at a high temperature and pressure whereby the quantity of water recycled to the urea-synthesis reactor along with the recycle ammonium carbamate may be reduced. The high pressure aqueous urea solution from the reactor is expanded into two or more ammonium carbamate decomposition stages operating at successively lower pressures. In at least one of the ammonium carbamate decomposition stages the expanded aqueous urea solution is heated in a controlled manner and a first off-gas is separated. The residual aqueous urea solution is again heated and a second off-gas is removed, which off-gas is combined with the first off-gas, condensed and recycled to the urea-synthesis reactor.
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.
