CA1110659A - Integrated ammonia-urea process - Google Patents
Integrated ammonia-urea processInfo
- Publication number
- CA1110659A CA1110659A CA323,007A CA323007A CA1110659A CA 1110659 A CA1110659 A CA 1110659A CA 323007 A CA323007 A CA 323007A CA 1110659 A CA1110659 A CA 1110659A
- Authority
- CA
- Canada
- Prior art keywords
- urea
- carbamate
- ammonia
- solution
- stream
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C273/00—Preparation of urea or its derivatives, i.e. compounds containing any of the groups, the nitrogen atoms not being part of nitro or nitroso groups
- C07C273/02—Preparation of urea or its derivatives, i.e. compounds containing any of the groups, the nitrogen atoms not being part of nitro or nitroso groups of urea, its salts, complexes or addition compounds
- C07C273/04—Preparation of urea or its derivatives, i.e. compounds containing any of the groups, the nitrogen atoms not being part of nitro or nitroso groups of urea, its salts, complexes or addition compounds from carbon dioxide and ammonia
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE .
An integrated ammonia-urea process is disclosed which uses as the starting gas mixture a stream coming, for example, from steam reforming of hydrocarbons, carbon dioxide being stripped from said stream by the action of a very concentrated ammonia solution (above 70% by wt) first and of an ammoniated solution of ammo-nium carbonate secondly, a solution of ammonium carbamate being obtained together with a gas stream composed by nitrogen and hydrogen, sending the carbamate solution to the urea reactor, discharging from the urea reactor the urea solution containing unconverted carbamate and excess ammonia, decomposing said carbamate and sending evolved ammonia to the urea reactor again along with carbon dioxide, discharging the urea solution having now 50% of the original carbamate to an adiabatic stripper in which the stripping gas is essentially composed by hydrogen and nitrogen, removing ammonia and carbon dioxide with water from the adiabatic stripper and condensing am-monia and carbon dioxide by heat exchange, sending the stream of hydrogen and nitrogen to methanization and ammo-nia synthesis and concentrating the urea solution direct-ly until obtaining a urea melt.
An integrated ammonia-urea process is disclosed which uses as the starting gas mixture a stream coming, for example, from steam reforming of hydrocarbons, carbon dioxide being stripped from said stream by the action of a very concentrated ammonia solution (above 70% by wt) first and of an ammoniated solution of ammo-nium carbonate secondly, a solution of ammonium carbamate being obtained together with a gas stream composed by nitrogen and hydrogen, sending the carbamate solution to the urea reactor, discharging from the urea reactor the urea solution containing unconverted carbamate and excess ammonia, decomposing said carbamate and sending evolved ammonia to the urea reactor again along with carbon dioxide, discharging the urea solution having now 50% of the original carbamate to an adiabatic stripper in which the stripping gas is essentially composed by hydrogen and nitrogen, removing ammonia and carbon dioxide with water from the adiabatic stripper and condensing am-monia and carbon dioxide by heat exchange, sending the stream of hydrogen and nitrogen to methanization and ammo-nia synthesis and concentrating the urea solution direct-ly until obtaining a urea melt.
Description
6~i9 INTEGRATED AMMONIA-UREA PROCESS
This invention relates to an integrated ammonia-urea process.
A number of integrated processes are known for the synthesis of urea in combination with the synthesis of ammonia.
, One of these is, more particularly, the one dis-closed in the Canadian Patent application N 292.378 filed on December 5, 1977.
10 - The method described in the patent application aforementioned comprises the steps of feeding to a urea-- synthesis reactor a stream of anhydrous ammonia and/or aquéous solution of ammonia and a stream contalning ammonium carbamate, reaction carbon dioxide with the ammonia in said urea-syn-thesis reactor, discharging from the urea-synthesis reactor . . .
a solution of urea which contains unconverted ammonium carbamate, thermally decomposing about the 50% of the carbamate contaîned in the urea solution and separating the decompositlon products, recycling the decomposition products ~- 20 to the urea-synthesis reactor, adiabatically decomposing, ~, . . .
i.e. without admlnistering heat from an external source, the ammonium carbamate still contained in the urea solution in an adiabatic stripper in which there is introduced, as the ~ stripping agent, the gas stream obtained by steam-: ' ;l .
~' ' "''.' ;, :
.
.. ~ . .
~' ',.
~106~9 reforming or partial oxidation of liquid or gaseous hydrocarbons~ essentially composed by C02, N2 and H2 to be used generally for the synthesis of ammonia, remov-ing from the adiabatic stripper both C02 and the NH3 deriving from the decomposition of the residual ammo-nium carbamate and the stripping agent, feeding the gas mixture aforesaid to a C02-absorber in which said C02 is absorbed by an ammoniacal solution thus obtaining a stream containing ammonium carbamate to be fed to the urea-synthesis reactor~ discharging from the adiabatic stripper the solution of urea substantially devoid of carbamate, which is sent to the subsequent treatments of low-pressure decomposition and concentration under vacuum.
A shortcoming of the method outlined above is that the contents of C02 of the solution going from the bottom of the adiabatic stripper to the low-pressure decomposition stage, is rather high (10% to 15% by wt.) the result being an oversizing of the decomposition stage and an increase of the consumptions in the same ..~
apparatus.
On the other hand~ the run of the adiabatic str~P-per according to the patent application aforementioned was bound to the use of C02 among the stripping agents~
inasmuch as said C02 permitted~ by its partial reaction with the ammonia contained in the urea solution~ to supply at least partially the heat which was required -; for the decomposition of the ammonium carbamate as contained in the urea solution. Regrettably~ as out-lined above~ the C02 contents remains high so that the low-pressure decomposition stage must be significantly oversized.
'.'.
' " .
. ~
., .
,, .
"` 1~1(~659 3.
It has been surprisingly found that it is possible to dispense with C02 as the stripping agent~ and con-sequently to have-an end product substantially depri-ved of C02 without thereby giving up the adiabatic stripping.
~his achievement has been made possible by select-ing appropriate ratios between H20 and C02 and between NH3 and C02 in the urea synthesis reactor.
An object of the present inven~ion is to provide an integrated ammonia-urea process comprising the follow-ing stages :
a) to send the gaseous stream as obtained from steam-reforming or partial oxidation of liquid or gaseous hydrocarbons which make up the raw gas stream for the synthesis of ammonia and which essentially comprise H2, N2 and C02~ to a C02-absorption system using a concentrated aqueous solution of ammonia ; and which is more particularly composed by two : serially arranged discrete absorption stages, in the first of which the absorbing liquor is a con-centrated aqueous solution of ammonia (concentra-~ tion above 70% by wt of ammonia~ 80% being pre-.; ferred), whereas in the second stage the absorpt-`~ ion liquor is an aqueous ammoniated solution of ammonium carbonate as obtained from the low-pres-sure decomposition stage~ or, in the case in which the latter is not provided~ from the stage of de-composition under vacuum of the urea solution;
`: b) to discharge from the C02-absorption section a ~: 30 gas stream which is essentially composed by N2 and H2 (with possible traces of NH3 and C02) together . . .,: .
. , .
~ .
.,. . . ~ ~
. . .
.` . ' , ' ''., ' .' . . . ~ :
4.
with a liquid stream which essentially comprises an aqueous solution of ammonium carbamate;
c) to feed with the aqueous solution of ammonium carbamate a urea-synthesis reactor wherein the S ammonium carbamate is partially converted into urea;
d) to discharge from the urea-synthesis reactor an aqueous solution of urea which contains the un-converted ammonium carbamate and the excess of ammonia over the stoichiometric amount and possibly a gaseous stream from the reactor top, said stream essentially comprising inerts with a certain 3 2;
e) to feed the aqueous solution of urea from stage d) ~ 15 hereinabove to a decomposer in which the ammonium ; carbamate is decomposed into ammonia and carbon : dioxide~ the latter being both drawn from said decomposer together with the water which evaporated :~ off~ to be recycled in the vapor phase to the urea-synthesis reactor;
. .
f~ to discharge from the decomposer an aqueous solution ~ of urea which contains about the 50% of the carba-,-~ mate originally contained in the urea solution exit-ing the synthesis reactor and to feed said aqueous solution to an adiabatic stripper wherein it is . . .
`~ exploited as a stripping agent the gaseous stream of b) above;
;~ g) to discharge through the bottom of the adiabatic stripper the solution of urea substantially devoid of ammonium carbamate, and to discharge from the . ~ top of the stripper the stripping agent (N2+H2) ~ ~ .
., ~
,.. .
~' ', ' ' ' . , ' ~'r :.;: ; ' , '.
, :
'.. : . .
with the products of decomposition of the carba-mate (NH3+C02) and the evaporated water;
h) to introduce the gaseous mixture drawn from the top of the adiabatic stripper to a condenser wherein the ammonia and the carbon dioxide are condensed by cooling as a result of an indirect heat exchange with a cold fluid in the presence of an ammoniated solution of ammonium carbonate : coming from the low-pressure decomposition stage whereas the stream with H2 and N2 is discharged at the top and fed, upon methanization, to the ammonia synthesis together with the inert gases N2 and H2 exiting the C0~-absorption system;
i) to send the condensate from h) to the C02-absorber;
15 1) to send the urea solution of stage g) to the stage of concentration under vacuum~ either directly or through a previous low-pressure decomposition stage (4 to 5 atmospheres), there being obtained both . from the head of the low-pressure decomposition stage and from that of the concentration a gas mix-ture composed bv ammonia, C02 and water~ which,when condensed~ is the ammoniated solution of ammonium : carbonate to be used for the steps a) and h), .: melted urea being obtained through the bottom of the concentration stage under vacuum.
: The method according to the present ~nvention will now be illustrated in a preferred embodiment with the aid ~ of the accompanying drawing.
; The raw gas which essentially comprises C02, N2 ~ 30 and H2~ is sent~ after having been compressed~ via the :. piping 1~ to the C02-absorber 17~ wherein the absorbing :''' : . : . ., :.:
.`: , '.. . - ' ' ': ' ' . :
. , : . . , . - .
, ' . '. ,~ , ' ~ -. ,' ' : . ' - ;:
;. : ' ' ., ' ' ' '' . -, : ' ' .
:1111~659 liquid is mainly composed by an aqueous solution of am-monia which comes via the piping 6 from the ammonia synthesis reactor: the ammonium carbamate coming from the absorber 17 is sent via the piping 7 to the urea-.
synthesis reactor 18.
The decarbonated gas exits the absorber 17 and, via the piping 2, goes to the NH3-stripping condenser 19~ in which NH3 is absorbed by an aqueous solution of ammonium carbonate coming, through the pipe 16, from the low-pressure liquor-recovering section by the agency of the pump 20.
The ammoniated solution formed at 19 is sent via the piping 13 to the absorber 17.
. The purified gas is sent via the piping 3 to the adiabatic stripping column 21 ~rhich is fed via the piping 10, with the urea ~olution coming from the car-bamate decomposer 22. The gas stream exits the column 21 and~ via the piping 4~ is fed to the carbamate con-denser 23 where it is combined with an aqueous solu-tion of ammonium carbonate 14, as fed via the pump 20 and the piping 15 from the low-pressure liquor-recovery . section. The carbamate produced at 23 is sent via the piping 12 and the pump 24 to the C02-absorber 17.
The purified gases exiting the condenser 23 are . 25 sent via the piping 5 to methanization and, therefrom~
to the ammonia synthesis in which an ammoniated solu-: tion is produced to be sent to the absorber 17 via the piping 6 as outlined above.
J .
. The carbamate solution~ via the piping 7~ is sent .~ 30 to the urea reactor 18 in which the reaction of dehy-. dration of the carbamate into urea takes place. The `,i~;
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~l~a6~s thusly obtained solution of urea reaches, via the pipe 8~ the carbamate decomposer 22 wherein said carbamate is decomposed into C02 and NH3 and these latter are recycled via the piping 9 to the reactor 18.
The urea solution, along with the carbamate which has not been decomposed~ is sent via the piping 10 to the adiabatic stripping column 21 which has been de-scribed above.
The solution of urea exiting the bottom of the column 21 is sent via to the section of evaporation under vacuum (not shown)~ wherein it is treated in the conventional manner.
It is quite surprising that, when operating with the process according to the present invention, it becomes possible to obtain at the exit of the adiaba-tic stripper a solutlon of urea which is so highly ~ concentrated as to be sent directly to the final treat-;~ ment u~der vacuum. By so doing~ the considerable ad-vantage is achieved that the expensive operations of ~; 20 decomposition of the undecomposed carbamate under me-`~ dium (18 atm) and low (4.5 atm) pressure are dispensed with and so is the recondensation of the produced vapors.
.:
This is the contrary of the teachings of the prior ` ~ art, according to which the solution to be sent to the ,~ 25 evaporation under vacuum is obtained at the expense of `` a considerable power useup.
~ All that which has been described above requires `~ in the urea reactor a selection of the ratio of H20 to C2 within the range from 0.9 and 1.3~ the preferred ; 3 value being 1.1, and of the ratios of NH3 to C02 com l prised between 4.5 and 6.5~ the preferred value being :'" 5.5-~ ~ .
~;:
,~" ' ' ; :~
, ~ . . ... . . . .
,. .. - .-, . , : ~ , ., . . . . -, . . ~ - . . - .
~11~9 8.
A modification which has not been shown in the drawings consists in using, instead of the pump 24 for recycling the carbonate towards the absorber 17, an ejector, the working fluid for which is the 80% ammo-niated solution coming from the ammonia synthesis react-or via the piping 6.
As regards the pressures, the method according to the present invention works under a pressure comprised between 100 kg/cm2 and 300 kg/cm , a pressure which is virtually equal to that at which the ammonia synthesis reactor operates, and in such a case a pump may be re-quired for sending the ammoniated solution from the am-monia synthesis reactor to the cycle described above~ or under a pressure which is from 10 kg/cm to 100 kg/cm below the pressure at which the ammonia synthesis reactor works~ and in this case the pump can be dispensed with.
A practical example will now be given in order that the invention may be better illustrated but without li~iting it in any way.
EXAMPLE
:~ Reference will be had to the single FIGURE of ` the drawing.
TABLES 1 and 2 report the working conditions, the concentrations and the rates of flow.
: ~ TABLE
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This invention relates to an integrated ammonia-urea process.
A number of integrated processes are known for the synthesis of urea in combination with the synthesis of ammonia.
, One of these is, more particularly, the one dis-closed in the Canadian Patent application N 292.378 filed on December 5, 1977.
10 - The method described in the patent application aforementioned comprises the steps of feeding to a urea-- synthesis reactor a stream of anhydrous ammonia and/or aquéous solution of ammonia and a stream contalning ammonium carbamate, reaction carbon dioxide with the ammonia in said urea-syn-thesis reactor, discharging from the urea-synthesis reactor . . .
a solution of urea which contains unconverted ammonium carbamate, thermally decomposing about the 50% of the carbamate contaîned in the urea solution and separating the decompositlon products, recycling the decomposition products ~- 20 to the urea-synthesis reactor, adiabatically decomposing, ~, . . .
i.e. without admlnistering heat from an external source, the ammonium carbamate still contained in the urea solution in an adiabatic stripper in which there is introduced, as the ~ stripping agent, the gas stream obtained by steam-: ' ;l .
~' ' "''.' ;, :
.
.. ~ . .
~' ',.
~106~9 reforming or partial oxidation of liquid or gaseous hydrocarbons~ essentially composed by C02, N2 and H2 to be used generally for the synthesis of ammonia, remov-ing from the adiabatic stripper both C02 and the NH3 deriving from the decomposition of the residual ammo-nium carbamate and the stripping agent, feeding the gas mixture aforesaid to a C02-absorber in which said C02 is absorbed by an ammoniacal solution thus obtaining a stream containing ammonium carbamate to be fed to the urea-synthesis reactor~ discharging from the adiabatic stripper the solution of urea substantially devoid of carbamate, which is sent to the subsequent treatments of low-pressure decomposition and concentration under vacuum.
A shortcoming of the method outlined above is that the contents of C02 of the solution going from the bottom of the adiabatic stripper to the low-pressure decomposition stage, is rather high (10% to 15% by wt.) the result being an oversizing of the decomposition stage and an increase of the consumptions in the same ..~
apparatus.
On the other hand~ the run of the adiabatic str~P-per according to the patent application aforementioned was bound to the use of C02 among the stripping agents~
inasmuch as said C02 permitted~ by its partial reaction with the ammonia contained in the urea solution~ to supply at least partially the heat which was required -; for the decomposition of the ammonium carbamate as contained in the urea solution. Regrettably~ as out-lined above~ the C02 contents remains high so that the low-pressure decomposition stage must be significantly oversized.
'.'.
' " .
. ~
., .
,, .
"` 1~1(~659 3.
It has been surprisingly found that it is possible to dispense with C02 as the stripping agent~ and con-sequently to have-an end product substantially depri-ved of C02 without thereby giving up the adiabatic stripping.
~his achievement has been made possible by select-ing appropriate ratios between H20 and C02 and between NH3 and C02 in the urea synthesis reactor.
An object of the present inven~ion is to provide an integrated ammonia-urea process comprising the follow-ing stages :
a) to send the gaseous stream as obtained from steam-reforming or partial oxidation of liquid or gaseous hydrocarbons which make up the raw gas stream for the synthesis of ammonia and which essentially comprise H2, N2 and C02~ to a C02-absorption system using a concentrated aqueous solution of ammonia ; and which is more particularly composed by two : serially arranged discrete absorption stages, in the first of which the absorbing liquor is a con-centrated aqueous solution of ammonia (concentra-~ tion above 70% by wt of ammonia~ 80% being pre-.; ferred), whereas in the second stage the absorpt-`~ ion liquor is an aqueous ammoniated solution of ammonium carbonate as obtained from the low-pres-sure decomposition stage~ or, in the case in which the latter is not provided~ from the stage of de-composition under vacuum of the urea solution;
`: b) to discharge from the C02-absorption section a ~: 30 gas stream which is essentially composed by N2 and H2 (with possible traces of NH3 and C02) together . . .,: .
. , .
~ .
.,. . . ~ ~
. . .
.` . ' , ' ''., ' .' . . . ~ :
4.
with a liquid stream which essentially comprises an aqueous solution of ammonium carbamate;
c) to feed with the aqueous solution of ammonium carbamate a urea-synthesis reactor wherein the S ammonium carbamate is partially converted into urea;
d) to discharge from the urea-synthesis reactor an aqueous solution of urea which contains the un-converted ammonium carbamate and the excess of ammonia over the stoichiometric amount and possibly a gaseous stream from the reactor top, said stream essentially comprising inerts with a certain 3 2;
e) to feed the aqueous solution of urea from stage d) ~ 15 hereinabove to a decomposer in which the ammonium ; carbamate is decomposed into ammonia and carbon : dioxide~ the latter being both drawn from said decomposer together with the water which evaporated :~ off~ to be recycled in the vapor phase to the urea-synthesis reactor;
. .
f~ to discharge from the decomposer an aqueous solution ~ of urea which contains about the 50% of the carba-,-~ mate originally contained in the urea solution exit-ing the synthesis reactor and to feed said aqueous solution to an adiabatic stripper wherein it is . . .
`~ exploited as a stripping agent the gaseous stream of b) above;
;~ g) to discharge through the bottom of the adiabatic stripper the solution of urea substantially devoid of ammonium carbamate, and to discharge from the . ~ top of the stripper the stripping agent (N2+H2) ~ ~ .
., ~
,.. .
~' ', ' ' ' . , ' ~'r :.;: ; ' , '.
, :
'.. : . .
with the products of decomposition of the carba-mate (NH3+C02) and the evaporated water;
h) to introduce the gaseous mixture drawn from the top of the adiabatic stripper to a condenser wherein the ammonia and the carbon dioxide are condensed by cooling as a result of an indirect heat exchange with a cold fluid in the presence of an ammoniated solution of ammonium carbonate : coming from the low-pressure decomposition stage whereas the stream with H2 and N2 is discharged at the top and fed, upon methanization, to the ammonia synthesis together with the inert gases N2 and H2 exiting the C0~-absorption system;
i) to send the condensate from h) to the C02-absorber;
15 1) to send the urea solution of stage g) to the stage of concentration under vacuum~ either directly or through a previous low-pressure decomposition stage (4 to 5 atmospheres), there being obtained both . from the head of the low-pressure decomposition stage and from that of the concentration a gas mix-ture composed bv ammonia, C02 and water~ which,when condensed~ is the ammoniated solution of ammonium : carbonate to be used for the steps a) and h), .: melted urea being obtained through the bottom of the concentration stage under vacuum.
: The method according to the present ~nvention will now be illustrated in a preferred embodiment with the aid ~ of the accompanying drawing.
; The raw gas which essentially comprises C02, N2 ~ 30 and H2~ is sent~ after having been compressed~ via the :. piping 1~ to the C02-absorber 17~ wherein the absorbing :''' : . : . ., :.:
.`: , '.. . - ' ' ': ' ' . :
. , : . . , . - .
, ' . '. ,~ , ' ~ -. ,' ' : . ' - ;:
;. : ' ' ., ' ' ' '' . -, : ' ' .
:1111~659 liquid is mainly composed by an aqueous solution of am-monia which comes via the piping 6 from the ammonia synthesis reactor: the ammonium carbamate coming from the absorber 17 is sent via the piping 7 to the urea-.
synthesis reactor 18.
The decarbonated gas exits the absorber 17 and, via the piping 2, goes to the NH3-stripping condenser 19~ in which NH3 is absorbed by an aqueous solution of ammonium carbonate coming, through the pipe 16, from the low-pressure liquor-recovering section by the agency of the pump 20.
The ammoniated solution formed at 19 is sent via the piping 13 to the absorber 17.
. The purified gas is sent via the piping 3 to the adiabatic stripping column 21 ~rhich is fed via the piping 10, with the urea ~olution coming from the car-bamate decomposer 22. The gas stream exits the column 21 and~ via the piping 4~ is fed to the carbamate con-denser 23 where it is combined with an aqueous solu-tion of ammonium carbonate 14, as fed via the pump 20 and the piping 15 from the low-pressure liquor-recovery . section. The carbamate produced at 23 is sent via the piping 12 and the pump 24 to the C02-absorber 17.
The purified gases exiting the condenser 23 are . 25 sent via the piping 5 to methanization and, therefrom~
to the ammonia synthesis in which an ammoniated solu-: tion is produced to be sent to the absorber 17 via the piping 6 as outlined above.
J .
. The carbamate solution~ via the piping 7~ is sent .~ 30 to the urea reactor 18 in which the reaction of dehy-. dration of the carbamate into urea takes place. The `,i~;
-, "
, ~ ~
~' ,.~ .. . .
.. ", ...... . .
.. ~ ' ~ . .
~,: . . .
, . . ,. .. .. . ,;, : . ~ -: ,' .
: ' ' - ~ ' '' : . '', : .
~l~a6~s thusly obtained solution of urea reaches, via the pipe 8~ the carbamate decomposer 22 wherein said carbamate is decomposed into C02 and NH3 and these latter are recycled via the piping 9 to the reactor 18.
The urea solution, along with the carbamate which has not been decomposed~ is sent via the piping 10 to the adiabatic stripping column 21 which has been de-scribed above.
The solution of urea exiting the bottom of the column 21 is sent via to the section of evaporation under vacuum (not shown)~ wherein it is treated in the conventional manner.
It is quite surprising that, when operating with the process according to the present invention, it becomes possible to obtain at the exit of the adiaba-tic stripper a solutlon of urea which is so highly ~ concentrated as to be sent directly to the final treat-;~ ment u~der vacuum. By so doing~ the considerable ad-vantage is achieved that the expensive operations of ~; 20 decomposition of the undecomposed carbamate under me-`~ dium (18 atm) and low (4.5 atm) pressure are dispensed with and so is the recondensation of the produced vapors.
.:
This is the contrary of the teachings of the prior ` ~ art, according to which the solution to be sent to the ,~ 25 evaporation under vacuum is obtained at the expense of `` a considerable power useup.
~ All that which has been described above requires `~ in the urea reactor a selection of the ratio of H20 to C2 within the range from 0.9 and 1.3~ the preferred ; 3 value being 1.1, and of the ratios of NH3 to C02 com l prised between 4.5 and 6.5~ the preferred value being :'" 5.5-~ ~ .
~;:
,~" ' ' ; :~
, ~ . . ... . . . .
,. .. - .-, . , : ~ , ., . . . . -, . . ~ - . . - .
~11~9 8.
A modification which has not been shown in the drawings consists in using, instead of the pump 24 for recycling the carbonate towards the absorber 17, an ejector, the working fluid for which is the 80% ammo-niated solution coming from the ammonia synthesis react-or via the piping 6.
As regards the pressures, the method according to the present invention works under a pressure comprised between 100 kg/cm2 and 300 kg/cm , a pressure which is virtually equal to that at which the ammonia synthesis reactor operates, and in such a case a pump may be re-quired for sending the ammoniated solution from the am-monia synthesis reactor to the cycle described above~ or under a pressure which is from 10 kg/cm to 100 kg/cm below the pressure at which the ammonia synthesis reactor works~ and in this case the pump can be dispensed with.
A practical example will now be given in order that the invention may be better illustrated but without li~iting it in any way.
EXAMPLE
:~ Reference will be had to the single FIGURE of ` the drawing.
TABLES 1 and 2 report the working conditions, the concentrations and the rates of flow.
: ~ TABLE
.
` ! ' ~ , .~ , .
~' ,~' .
~ .
,'. ' ' .,, . . . ,. ', ~ .
. ' . . ' ' . ' ' , ' , ' . . ' ' , ' ' ' ' ' ' ' ' ' ' ., ' ' .. ' . , "'' . ' .
, ' ~ ' .' '".' . . ' ' ' ' ' ' '' ' . ' ' '''' ' . , ' ~' ' .' , ' ~ ' ' ~- ff .~ ` ~ i i f 'f r la _ ~ y O O, O
_ ~ H Z ¦__ 3 c~ oo j ~') ~ ~) ~ d O
U-~ ~ ~ O ~ ~ O~ ~
~ ~ ~ $ ~ _ ~
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a . ~ ~ ~ ~ ~
,; a~ ~ ¢ ~ ~ t~ e~
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cq ~Z ~ 3 ~ ~ . <~
'~ _ ~ . ........... . _ . 8 ~'' o ~ oo o ~ ~ ~0O~ ~P ~ ~ a .. . ~ O,~ ~ ~ ~ ~ ~
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Claims (3)
1. An integrated ammonia-urea process comprising the steps of :
a) Sending the gaseous stream obtained from steam reforming or partial oxidation of liquid or gaseous hydrocarbons, containing H2, N2 and CO2, to a CO2-ab-sorption system in which CO2 is absorbed by a concen-trated aqueous solution of ammonia, b) discharging from the CO2-absorption system a ga-seous stream composed essentially by H2 and N2 and a liquid stream essentially composed by an aqueous solution of ammonium carbamate, c) feeding with the aqueous solution of ammonium carbamate a urea synthesis reactor wherein the carbamate is partially converted into urea, d) discharging from the urea synthesis reactor an aqueous solution of urea containing the unconverted ammo-nium carbamate and the excess of ammonia relative to the stoichiometric amount, e) feeding the aqueous solution of urea which con-tains the uncoverted carbamate to a decomposer and ther-mally decomposing therein about the 50% of said carbamate, discharging a solution of urea containing carbamate and the decomposition products, the latter being recycled in the vapor phase to the urea synthesis reactor, f) decomposing the carbamate contained in the solu-tion of urea exiting the decomposer of the carbamate of stage e) in an adiabatic stripper in which the ga-seous stream of stage b) is used as the stripping agent, a urea solution substantially devoid of carbamate being obtained at the bottom, whereas the decomposition products, the stripping agent and the evaporated water are obtained at the stripper head, g) condensing the decomposition products and the evaporated water in the presence of an ammoniated solution of ammonium carbonate by indirect heat exchange with a cold fluid, the inert gases (H2+N2) to be used for the ammonia synthesis upon methani-zation being discharged through the condenser head, h) sending the condensate as produced in stage g) to the CO2-absorption stage, i) sending the solution of urea exiting the bottom of the adiabatic stripper, to a concentration stage and discharging melted urea from the latter, wherein, in the urea reactor the ratio H2O to CO2 is comprised between 0.9 and 1.3, and the ratio of NH3 to CO2 is comprised between 4.5 and 6.5.
a) Sending the gaseous stream obtained from steam reforming or partial oxidation of liquid or gaseous hydrocarbons, containing H2, N2 and CO2, to a CO2-ab-sorption system in which CO2 is absorbed by a concen-trated aqueous solution of ammonia, b) discharging from the CO2-absorption system a ga-seous stream composed essentially by H2 and N2 and a liquid stream essentially composed by an aqueous solution of ammonium carbamate, c) feeding with the aqueous solution of ammonium carbamate a urea synthesis reactor wherein the carbamate is partially converted into urea, d) discharging from the urea synthesis reactor an aqueous solution of urea containing the unconverted ammo-nium carbamate and the excess of ammonia relative to the stoichiometric amount, e) feeding the aqueous solution of urea which con-tains the uncoverted carbamate to a decomposer and ther-mally decomposing therein about the 50% of said carbamate, discharging a solution of urea containing carbamate and the decomposition products, the latter being recycled in the vapor phase to the urea synthesis reactor, f) decomposing the carbamate contained in the solu-tion of urea exiting the decomposer of the carbamate of stage e) in an adiabatic stripper in which the ga-seous stream of stage b) is used as the stripping agent, a urea solution substantially devoid of carbamate being obtained at the bottom, whereas the decomposition products, the stripping agent and the evaporated water are obtained at the stripper head, g) condensing the decomposition products and the evaporated water in the presence of an ammoniated solution of ammonium carbonate by indirect heat exchange with a cold fluid, the inert gases (H2+N2) to be used for the ammonia synthesis upon methani-zation being discharged through the condenser head, h) sending the condensate as produced in stage g) to the CO2-absorption stage, i) sending the solution of urea exiting the bottom of the adiabatic stripper, to a concentration stage and discharging melted urea from the latter, wherein, in the urea reactor the ratio H2O to CO2 is comprised between 0.9 and 1.3, and the ratio of NH3 to CO2 is comprised between 4.5 and 6.5.
2. A process according to claim 1, characterized in that the CO2-absorption system is composed by two serially arranged absorption stages, in the first of which the absorp-tion liquor is a concentrated aqueous solution of ammonia containing more than 70% by wt of ammonia, and in the second of which the absorption liquor is an ammoniated aqueous solution of ammonium carbonate.
3. A process according to claim 1, wherein the ratio of H2O to CO2 is 1.1, whereas the ratio of NH3 to CO2 is 5.5.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IT21993A/78 | 1978-04-05 | ||
| IT21993/78A IT1094295B (en) | 1978-04-05 | 1978-04-05 | INTEGRATED AMMONIA-UREA PROCEDURE |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1110659A true CA1110659A (en) | 1981-10-13 |
Family
ID=11189914
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA323,007A Expired CA1110659A (en) | 1978-04-05 | 1979-03-08 | Integrated ammonia-urea process |
Country Status (23)
| Country | Link |
|---|---|
| JP (1) | JPS54132525A (en) |
| AU (1) | AU519817B2 (en) |
| BE (1) | BE875346A (en) |
| BR (1) | BR7902122A (en) |
| CA (1) | CA1110659A (en) |
| CH (1) | CH637633A5 (en) |
| CS (1) | CS230563B2 (en) |
| DD (1) | DD142709A5 (en) |
| DE (1) | DE2913793C3 (en) |
| DK (1) | DK139179A (en) |
| EG (1) | EG13847A (en) |
| ES (1) | ES479940A1 (en) |
| FR (1) | FR2421847A1 (en) |
| GB (1) | GB2018249B (en) |
| IE (1) | IE48099B1 (en) |
| IN (1) | IN150631B (en) |
| IT (1) | IT1094295B (en) |
| LU (1) | LU81113A1 (en) |
| MX (1) | MX151216A (en) |
| NL (1) | NL7902566A (en) |
| PL (1) | PL116665B1 (en) |
| SE (1) | SE432591B (en) |
| SU (1) | SU1225485A3 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS61109760A (en) * | 1984-11-02 | 1986-05-28 | Toyo Eng Corp | Production of urea |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS4832091B1 (en) * | 1968-02-12 | 1973-10-04 | ||
| IT1014987B (en) * | 1974-06-12 | 1977-04-30 | Snam Progetti | INTEGRATED PROCEDURE UREA AM MONIACA |
| IT1034674B (en) * | 1975-03-28 | 1979-10-10 | Snam Progetti | FLEXIBLE INTERGRATED PROCESS FOR THE PRODUCTION OF EDUREA AMMONIA |
| IT1065422B (en) * | 1976-12-23 | 1985-02-25 | Snam Progetti | INTEGRATED AMMONIA-UREA PROCESS FOR UREA PRODUCTION |
-
1978
- 1978-04-05 IT IT21993/78A patent/IT1094295B/en active
-
1979
- 1979-03-07 AU AU44876/79A patent/AU519817B2/en not_active Ceased
- 1979-03-08 CA CA323,007A patent/CA1110659A/en not_active Expired
- 1979-03-15 GB GB7909086A patent/GB2018249B/en not_active Expired
- 1979-03-24 IN IN289/CAL/79A patent/IN150631B/en unknown
- 1979-03-28 FR FR7907848A patent/FR2421847A1/en active Granted
- 1979-03-28 EG EG195/79A patent/EG13847A/en active
- 1979-03-29 JP JP3633279A patent/JPS54132525A/en active Pending
- 1979-03-30 ES ES479940A patent/ES479940A1/en not_active Expired
- 1979-04-02 NL NL7902566A patent/NL7902566A/en not_active Application Discontinuation
- 1979-04-03 DD DD79211973A patent/DD142709A5/en unknown
- 1979-04-03 PL PL1979214649A patent/PL116665B1/en unknown
- 1979-04-03 LU LU81113A patent/LU81113A1/en unknown
- 1979-04-04 DK DK139179A patent/DK139179A/en not_active IP Right Cessation
- 1979-04-04 SE SE7903018A patent/SE432591B/en not_active IP Right Cessation
- 1979-04-04 CS CS792292A patent/CS230563B2/en unknown
- 1979-04-04 CH CH313979A patent/CH637633A5/en not_active IP Right Cessation
- 1979-04-04 SU SU792749003A patent/SU1225485A3/en active
- 1979-04-04 MX MX177195A patent/MX151216A/en unknown
- 1979-04-05 BE BE0/194424A patent/BE875346A/en not_active IP Right Cessation
- 1979-04-05 BR BR7902122A patent/BR7902122A/en unknown
- 1979-04-05 DE DE2913793A patent/DE2913793C3/en not_active Expired
- 1979-08-08 IE IE706/79A patent/IE48099B1/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| IT1094295B (en) | 1985-07-26 |
| IE790706L (en) | 1979-10-05 |
| SU1225485A3 (en) | 1986-04-15 |
| CS230563B2 (en) | 1984-08-13 |
| AU4487679A (en) | 1979-10-18 |
| SE7903018L (en) | 1979-10-06 |
| NL7902566A (en) | 1979-10-09 |
| DD142709A5 (en) | 1980-07-09 |
| IE48099B1 (en) | 1984-09-19 |
| PL214649A1 (en) | 1979-12-17 |
| DE2913793B2 (en) | 1980-06-04 |
| PL116665B1 (en) | 1981-06-30 |
| AU519817B2 (en) | 1981-12-24 |
| BE875346A (en) | 1979-10-05 |
| FR2421847B1 (en) | 1982-10-22 |
| EG13847A (en) | 1982-12-31 |
| BR7902122A (en) | 1979-12-04 |
| SE432591B (en) | 1984-04-09 |
| IT7821993A0 (en) | 1978-04-05 |
| GB2018249A (en) | 1979-10-17 |
| FR2421847A1 (en) | 1979-11-02 |
| DK139179A (en) | 1979-10-06 |
| GB2018249B (en) | 1982-09-02 |
| IN150631B (en) | 1982-11-20 |
| DE2913793A1 (en) | 1979-10-11 |
| MX151216A (en) | 1984-10-11 |
| CH637633A5 (en) | 1983-08-15 |
| ES479940A1 (en) | 1979-12-01 |
| JPS54132525A (en) | 1979-10-15 |
| LU81113A1 (en) | 1979-06-19 |
| DE2913793C3 (en) | 1981-05-27 |
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