IPC분류정보
국가/구분 |
United States(US) Patent
등록
|
국제특허분류(IPC7판) |
|
출원번호 |
US-0810271
(1997-03-03)
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우선권정보 |
JP-0032308 (1992-02-19) |
발명자
/ 주소 |
- Carloni Giuseppe,ITX
- Granelli Franco,ITX
|
출원인 / 주소 |
|
대리인 / 주소 |
|
인용정보 |
피인용 횟수 :
5 인용 특허 :
5 |
초록
▼
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 e
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.
대표청구항
▼
[ We claim:] [1.] In a process for producing urea from ammonia and carbon dioxide having a synthetic step yielding a gaseous phase consisting of urea, carbamate ammonia, and water, wherein the process has a high pressure decomposition stage yielding an aqueous urea solution having carbamate containe
[ We claim:] [1.] In a process for producing urea from ammonia and carbon dioxide having a synthetic step yielding a gaseous phase consisting of urea, carbamate ammonia, and water, wherein the process has a high pressure decomposition stage yielding an aqueous urea solution having carbamate contained therein, and a medium pressure decomposition stage operating at 10-30 bars, wherein the urea solution is fed from the high pressure decomposition stage to the medium pressure decomposition stage after flash vapor is separated therefrom, wherein the carbamate is thermally decomposed by direct transfer of heat released by the condensation of the vapor, wherein the process also has an adiabatic stripping stage for receiving the urea solution from the medium pressure decomposition stage, wherein the adiabatic stripping stage is substantially at the same pressure as the medium pressure decomposition stage, wherein after separating gas produced by the decomposition of the carbamate, the urea solution, residual carbamate, and free ammonia, the urea solution is brought into counter-current contact with a fraction of the carbon dioxide, wherein the fraction is about 3% to about 20%, wherein the process also has a vacuum preconcentration stage for recovering the heat of condensation from gaseous streams and a first transferring stage for transferring gas from the medium pressure decomposition stage and the adiabatic stripping stage to the vacuum preconcentration stage, wherein the process further has a second transferring stage for transferring the urea solution to the vacuum preconcentration stage, wherein the vacuum preconcentration stage has a heat exchanger operating at a pressure of about 0.3 bars to about 0.95 bars, and wherein the urea solution is preconcentrated to about 80% to about 95% by weight by direct transfer of the heat released by the partial condensation of the vapor, and wherein the process still further has a condensation stage and a low pressure decomposition stage each operating at substantially the same pressure for low pressure condensation of the vapor stream, and wherein the heat of condensation is for preheating the ammonia, the process comprising:(a) reacting in a synthesis reactor the ammonia and the carbon dioxide containing inerts and passivating air (hereinafter known collectively as noncondensables), and unconverted recycled ammonium carbamate at a temperature of 175.degree. C.-195.degree. C., and a corresponding pressure of 130-220 bars, while maintaining in the synthesis reactor a molar NH.sub.3 /CO.sub.2 ratio of between 3.0 and 5.0;(b) transferring the product from step (a), essentially consisting of an aqueous solution of urea, carbamate and free ammonia, to the high pressure decomposition stage essentially consisting of a falling film heat exchanger and operating substantially at the same pressure as in step (a), to produce a gaseous phase and an aqueous urea solution;(c) transferring the gaseous phase obtained from step (b), essentially consisting of ammonia, carbon dioxide, and water to condensation in the medium pressure decomposition stage;(d) transferring the aqueous urea solution from step (b) to the medium pressure decomposition stage;(e) transferring the ammonium carbamate solution and uncondensed vapor resulting from step (d) to a further high pressure condensation stage in which recovery of the heat available in the high pressure vapor is completed, wherein in this stage heat is recovered to produce low pressure steam, noncondensables are separated, and ammonium carbamate solution is recycled to step (a) by a liquid-liquid ejector using the feed ammonia as drive fluid;(f) feeding the urea solution leaving the medium pressure decomposition stage to the adiabatic stripping stage resulting in an aqueous urea solution containing a small quantity of free ammonia, and wherein the molar NH.sub.3 /CO.sub.2 ratio is 2.2-4.0;(g) transferring the gaseous phase obtained from the medium pressure decomposition stage and the gaseous phase obtained from the medium pressure adiabatic stripping to a urea solution vacuum preconcentration stage to recover the heat of condensation of said gaseous streams;(h) transferring the urea and ammonium carbamate solution from step (f) to the low pressure decomposition stage which operates at a pressure of about 4 bars, and which essentially consists of a falling film heat exchanger in which the ammonium carbamate still present in the solution is further decomposed to obtain as a bottom product a urea solution containing residual quantities of ammonia and carbon dioxide;(i) transferring the urea solution obtained in step (h) to the vacuum preconcentration stage wherein a vapor stream is produced;(j) feeding the preconcentrated urea solution from step (i) to a final concentration stage and solidifying the urea therein either by prilling it in a tower to produce prilled urea or granulating it to produce granulated urea, thereby also producing a vapor stream;(k) condensing the vapor streams produced in the concentration steps (i) and (j), treating the resulting condensate to obtain a practically pure effluent, and recycling the ammonia and carbon dioxide to a low pressure condensation stage;(l) condensing, at low pressure, the vapor streams obtained from steps (h) and (k) in a condensation stage operating substantially at the same pressure as the low pressure decomposition stage of step (h), the heat of condensation being used to preheat the ammonia feed in step (a) and the condensate obtained being recycled to step (i) on the condensing vapor side;(m) transferring the ammonium carbamate solution and the vapor resulting from the partial condensation on the shell side of the film heat exchanger of step (i) to a condensation/separation stage wherein a first liquid phase containing ammonium carbamate and a second liquid phase containing substantially pure ammonia are produced;(n) recycling the first liquid phase containing ammonium carbamate as per steps (d) and (e); and(o) mixing the second liquid phase essentially consisting of substantially pure ammonia with the feed ammonia of step (a), preheating the total ammonia in the preceding low pressure condensation step (1) and feeding the resulting preheated ammonia to the synthesis reactor of step (a) through a liquid/liquid ejector for recycling the ammonium carbamate, in which the liquid ammonia acts as the drive fluid.
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