U.S. patent application number 09/984486 was filed with the patent office on 2002-06-27 for process for the synthesis of urea.
This patent application is currently assigned to Toyo Engineering Corporation. Invention is credited to Kojima, Yasuhiko, Yoshida, Kinichi, Yoshimoto, Kenji.
Application Number | 20020082451 09/984486 |
Document ID | / |
Family ID | 18810318 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020082451 |
Kind Code |
A1 |
Yoshida, Kinichi ; et
al. |
June 27, 2002 |
Process for the synthesis of urea
Abstract
A urea synthesis process with improved heat economy, wherein a
urea synthesis solution obtained by removing most of the unreacted
ammonium carbamate by stripping with carbon dioxide at a pressure
approximately equal to a urea synthesis pressure is subjected to a
high and low pressure decomposition. The gas mixture obtained from
the high-pressure decomposition is condensed in at least two steps.
Gases obtained from the stripping of the urea synthesis solution,
after an initial condensation may be alternatively routed into the
high-pressure decomposition column thus facilitating the
decomposition of unreacted ammonium carbamate; may be mixed with
off-gases from the high-pressure decomposition column and routed to
an indirect heat-exchanger for concentrating the aqueous urea
solution and facilitating the condensation of the off-gases from
the high pressure decomposition column; or may be routed to a
condenser for the gas mixture obtained from the high-pressure
decomposition after it has underwent indirect heat-exchange with
the aqueous urea solution, thus facilitate the further condensation
of these gases.
Inventors: |
Yoshida, Kinichi;
(Chiba-shi, JP) ; Yoshimoto, Kenji; (Chiba-shi,
JP) ; Kojima, Yasuhiko; (Sakura-shi, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
Toyo Engineering
Corporation
2-5, Kasumigaseki 3-chome
Chiyoda-ku
JP
|
Family ID: |
18810318 |
Appl. No.: |
09/984486 |
Filed: |
October 30, 2001 |
Current U.S.
Class: |
564/70 |
Current CPC
Class: |
C07C 273/04
20130101 |
Class at
Publication: |
564/70 |
International
Class: |
C07C 273/04 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 1, 2000 |
JP |
2000-334395 |
Claims
1. A process for synthesizing urea comprising: (a) reacting carbon
dioxide with ammonia at temperature and pressure suitable for
synthesis of urea in a urea synthesis zone to form a urea synthesis
solution; (b) stripping said urea synthesis solution with carbon
dioxide at a pressure substantially equal to the urea synthesis
pressure to decompose unreacted ammonium carbamate contained in the
urea synthesis solution as a gas mixture of ammonia, carbon dioxide
and water; (c) condensing the gas mixture obtained from (b) and
recycling the condensate into the urea synthesis zone; (d)
decomposing at high pressure the unreacted ammonium carbamate in
the urea synthesis solution obtained from stripping the urea
synthesis solution, thereby decomposing unreacted ammonium
carbamate remaining in the stripped urea synthesis solution into a
gas mixture of ammonia, carbon dioxide and water; (e) decomposing
at low pressure unreacted ammonium carbamate in the urea synthesis
solution obtained from the high pressure decomposition, thereby
obtaining a low pressure gas mixture of ammonia, carbon dioxide and
water, and obtaining an aqueous urea solution substantially free of
unreacted ammonium carbamate; (f) condensing the low pressure gas
mixture obtained from the low pressure decomposition to obtain a
condensate of the low pressure gas mixture; (g) condensing the high
pressure gas mixture obtained from the high pressure decomposition
of the urea synthesis solution by: (i) contacting it with a
condensate of gases obtained from the high and low pressure
decomposition of the urea synthesis solution, (ii) indirectly
contacting the mixture of (i) with aqueous urea solution under
conditions suitable for indirect heat exchange, thus heating the
aqueous urea solution and obtaining a partially condensed mixture
of gases, (iii) introducing the partially condensed mixture of
gases (ii) into a first cooling and condensation zone under
conditions suitable for further condensation of said mixture of
gases, and recycling the resulting condensate to (c) to facilitate
cooling and condensation of the gases obtained from (b), (iv)
introducing the remaining uncondensed mixture of gases (iii) into a
second cooling and condensation zone under conditions suitable for
further condensation of said mixture of gases, and mixing the
resulting condensate with the off-gases from high-pressure
decomposition (d), (v) washing the remaining uncondensed gases from
(iv) with a washing solution comprising the pressurized condensate
of gases from low pressure decomposition (f), introducing said
washing solution to the second cooling zone (iv), and optionally
discharging inert gas.
2. The process of claim 1, wherein the carbon dioxide contains a
slight amount of oxygen for corrosion protection.
3. The process of claim 1, wherein the high pressure decomposition
is performed at a pressure ranging from 1 to 4 Mpa.
4. The process of claim 1, wherein the low pressure decomposition
is performed at a pressure ranging from 0.1 to 0.5 Mpa.
5. The process of claim 1, wherein the aqueous urea solution in (g)
is further heated by steam.
6. The process of claim 1, wherein the uncondensed gas mixture
obtained from condensing the gases obtained by stripping (b) the
urea synthesis solution is introduced into the high pressure
decomposition (d) of ammonium carbamate.
7. The process of claim 1, wherein the uncondensed gas mixture
obtained from condensing the gases obtained by stripping (b) the
urea synthesis solution is mixed with the gas mixture from the
high-pressure decomposition (d) and the mixture is used to
indirectly heat the aqueous urea solution.
8. The process of claim 1, wherein the uncondensed gas mixture
obtained from condensing the gases obtained by stripping (b) the
urea synthesis solution is introduced into a condenser for
condensing uncondensed gases obtained from the high-pressure
decomposition after the gas mixture from the high-pressure
decomposition is partially condensed by indirect heat exchange with
the aqueous urea solution.
9. A process for synthesizing urea substantially as shown in FIG.
1.
10. A process for synthesizing urea substantially as shown in FIG.
2.
11. A process for synthesizing urea substantially as shown in FIG.
3.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention is directed to an improved, more
efficient and economical process for the synthesis of urea from
carbon dioxide and ammonia: 1
[0003] This process involves reacting ammonia and carbon dioxide to
form urea, followed by separation of unreacted ammonia and carbon
dioxide by stripping with carbon dioxide at a pressure
approximately equal to the urea synthesis pressure and by high and
low pressure decomposition of residual ammonium carbamate. The
process of the present invention efficiently uses off-gases from
the high and low pressure decomposition and condensates of these
gases and provides a more economical processes for synthesizing
urea. For instance, improved conservation and recovery of heat
provided by the present invention reduces process costs and
improves the overall efficiency and economy of urea synthesis.
[0004] 2. Description of the Related Art
[0005] Urea is synthesized by reacting carbon dioxide and ammonia
at a high temperature and pressure. Conventionally, this reaction
is performed inside of a urea synthesis zone or reactor at a
suitable pressure and temperature for synthesis of urea and
involves the formation and subsequent dehydration of ammonium
carbamate to form urea: 2
[0006] As shown above, the formation of ammonium carbamate and its
subsequent dehydration into urea essentially occur simultaneously
yielding urea. However, purity and yield of urea in the resulting
reaction mixture (urea synthesis solution) can be improved by
stripping using carbon dioxide and by high-pressure decomposition
of ammonium carbonate.
[0007] Processes for obtaining urea from carbon dioxide and ammonia
are known, see Japanese Patent Laid-Open No. 10-182587. Urea may be
synthesized by the following process steps:
[0008] reacting ammonia and carbon dioxide at a urea synthesis
pressure and a urea synthesis temperature to form a urea synthesis
solution,
[0009] separating the unreacted ammonium carbamate from the urea
synthesis solution as a gas mixture of ammonia, carbon dioxide and
water by bringing the solution into contact with carbon dioxide at
a pressure substantially equal to the urea synthesis pressure,
[0010] condensing the resulting gas mixture and recycling the
condensate to the urea synthesis zone,
[0011] further treating the urea synthesis solution from which the
unreacted ammonium carbamate is separated to obtain an aqueous urea
solution, and
[0012] concentrating the aqueous urea solution.
[0013] In the above-described method, after stripping and
condensation of the off-gases from the stripper, an uncondensed gas
mixture containing inert gas, ammonia, carbon dioxide and water
remains. This uncondensed gas mixture is washed in a scrubber using
an absorption medium to absorb ammonia and carbon dioxide in the
uncondensed gas mixture. After scrubbing substantially only the
inert gas is discharged from the scrubber to the outside of the
system.
[0014] Japanese Patent Laid-Open No. 61-109760, discloses that such
an inert gas may be introduced into the high pressure decomposition
step of the unreacted ammonium carbamate remaining in the urea
synthesis solution after carbon dioxide stripping.
[0015] Other urea synthesis methods attempt to concentrate the
aqueous urea solution formed by the above reactions using the
condensation heat generated from condensation of the off-gases from
the high pressure decomposition step, see e.g. Japanese Patent
Publication No. 62-15070, Japanese Patent Laid-Open No. 63-112552,
Japanese Patent Laid-Open No. 62-39559, Japanese Patent Laid-Open
No. 60-166656, Japanese Patent Laid-Open No. 62-39560, Japanese
Patent Laid-Open No. 63-126857, and EP A1 0329214).
[0016] However, the above-described methods do not describe the
improved heat recovery, efficiencies and economies provided by the
present invention, in which the off-gases from the high pressure
decomposition of the unreacted ammonium carbamate in the urea
synthesis solution are condensed in at least two steps, the
condensate is recycled to the scrubber, and the uncondensed gases
from the scrubber are routed as shown in FIGS. 1, 2 and 3.
SUMMARY OF THE INVENTION
[0017] One object of the present invention is to provide a process
with improved heat economy for synthesizing urea that comprises
stripping unreacted ammonium carbamate using carbon dioxide (e.g.
raw material carbon dioxide) under a pressure equal to the urea
synthesis pressure. In the present invention, the phrases,
"condense a gas mixture" or "condensing a gas mixture", may
optionally encompass condensing and washing a gas mixture,
condensing and absorbing a gas mixture, or both.
[0018] The above-described object of the present invention may be
achieved by the following urea synthesis process:
[0019] (1) Reacting carbon dioxide, which may contain a slight
amount of oxygen for corrosion prevention, with ammonia at pressure
and temperature suitable for the synthesis of urea in a urea
synthesis zone or reactor, thus forming a urea synthesis
solution;
[0020] bringing the urea synthesis solution into contact with
carbon dioxide at a pressure substantially equal to the urea
synthesis pressure to separate a major or substantial part of the
unreacted ammonium carbamate contained in the urea synthesis
solution as a gas mixture of ammonia, carbon dioxide and water;
[0021] condensing the resulting gas mixture and recycling the
condensate into the urea synthesis zone or reactor;
[0022] subjecting the urea synthesis solution having a major or
substantial part of the unreacted ammonium carbamate removed to a
high pressure decomposition, preferably at about 1 to 4 Mpa,
thereby separating unreacted ammonium carbamate remaining in the
urea synthesis solution as a gas mixture of ammonia, carbon dioxide
and water;
[0023] subjecting the resulting urea synthesis solution containing
the remaining unreacted ammonium carbamate to low pressure
decomposition, preferably at about 1 to 0.5 MPa, in at least one
stage, thereby separating the substantially all of the remaining
unreacted ammonium carbamate as a gas mixture of ammonia, carbon
dioxide and water to obtain an aqueous urea solution;
[0024] cooling and condensing the low pressure gas mixture
separated in the low pressure decomposition to obtain a low
pressure condensate;
[0025] condensing the off-gases from the high-pressure
decomposition of ammonium carbamate by:
[0026] contacting them with a condensate of the off-gases from the
high and low pressure decompositions of ammonium carbamate, and
[0027] by indirectly exchanging heat with the aqueous urea solution
to condense the high pressure gas mixture to obtain condensate of
the gases from the high-pressure decomposition;
[0028] utilizing the condensation heat generated at that time for
at least a part of the heat source for concentrating the aqueous
urea solution; and
[0029] introducing the high pressure condensate (see e.g. line 6 in
FIGS. 1, 2 and 3) into the condensation step for the gas mixture
obtained from stripping the urea synthesis solution with carbon
dioxide at a pressure substantially equal to the urea synthesis
pressure (see e.g. element "B" in FIGS. 1, 2, and 3);
[0030] wherein the high pressure gas mixture resulting from the
high pressure decomposition of unreacted ammonium carbamate is
condensed by indirect heat exchange with the aqueous urea solution
(e.g. condensing element K in FIGS. 1, 2 and 3), followed by at
least two condensations and a washing (e.g. as respectively shown
in P, Q and R in FIGS. 1, 2 and 3).
[0031] The condensation of the high-pressure gas mixture or
off-gases resulting from the high-pressure decomposition may be
carried out by:
[0032] condensing the high-pressure gas mixture from the
high-pressure decomposition step (e.g. line 20 in FIGS. 1, 2 and
3)by mixture with condensates of gases obtained from the high and
low pressure decomposition of ammonium carbamate and by indirect
heat-exchange with aqueous urea solution (see e.g. "K" in FIGS. 1,
2 and 3);
[0033] condensing remaining high-pressure gas mixture in a first
condensation zone or first condenser (e.g. "P" in FIGS. 1, 2 and
3)and recycling the liquid condensate to a scrubber (e.g. scrubber
"F" in FIGS. 1, 2 and 3).
[0034] condensing remaining high-pressure gas mixture from the
prior condensation step in a second condensation zone or second
condenser (e.g. "Q" in FIGS. 1, 2 and 3),
[0035] bringing any remaining uncondensed ammonia and carbon
dioxide into contact with the pressurized, low-pressure condensate
from low-pressure decomposition of unreacted ammonium carbamate
(e.g. from col. H in FIGS. 1, 2 and 3)in the step of washing (e.g.
"R" in FIGS. 1, 2 and 3)and optionally discharging inert gas from
the washing step.
[0036] Other objects of the present invention include:
[0037] (2) The process as described above in section (1), wherein
the uncondensed gas mixture containing inert gas, ammonia, carbon
oxide, and water obtained from stripping the urea synthesis
solution (e.g. from stripper "B" in FIGS. 1, 2 and 3) and from the
scrubber (e.g. scrubber "B" in FIGS. 1, 2 and 3) is introduced into
the high pressure decomposition (e.g. "G" in FIG. 1) to decompose
the unreacted ammonium carbamate.
[0038] (3) The process as described in above in section (1),
wherein the uncondensed gas mixture containing inert gas, ammonia,
carbon oxide, and water obtained from stripping the urea synthesis
solution (e.g. from stripper "B" in FIGS. 1, 2 and 3) and from the
scrubber (e.g. scrubber "B" in FIGS. 1, 2 and 3) is introduced into
the step of condensing by indirect heat exchange (e.g. "L" in FIG.
2) to condense at least a part of ammonia, carbon dioxide and water
in the gas mixture. (
[0039] 4) The process as described in above in section (1), wherein
the uncondensed gas mixture containing inert gas, ammonia, carbon
oxide, and water obtained from stripping the urea synthesis
solution (e.g. from stripper "B" in FIGS. 1, 2 and 3) and from the
scrubber (e.g. scrubber "B" in FIGS. 1, 2 and 3) is introduced into
the step of first cooling and condensing (e.g. "P" in FIG. 3) to
condense at least a part of ammonia, carbon dioxide and water in
the gas mixture.
[0040] In the present invention, gas from a high pressure
decomposition column is condensed in at least two steps (or in
three steps including the condensation occurring in the aqueous
urea solution heating apparatus). Moreover, gas from a scrubber may
also be condensed together with the gas from the high-pressure
decomposition. Thus, the temperature in the condensing part of the
aqueous urea solution heating apparatus can be increased and heat
recovery can efficiently be carried out. Owing to the presence of
oxygen from the scrubber, apparatus corrosion can also be
avoided.
[0041] Further, the present invention allows the use of condensates
having a pressure equal to the pressure of the high pressure
decomposition column as an absorption medium for gases from the
high pressure decomposition column without requiring a further
increase of pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] In the accompanying drawings:
[0043] FIG. 1 is a flow sheet showing an embodiment of the present
invention where an uncondensed gas mixture from the stripper and
scrubber is introduced into the high-pressure decomposition;
[0044] FIG. 2 is a flow sheet showing an embodiment of the present
invention where an uncondensed gas mixture from the stripper and
scrubber is introduced into the condensation by indirect
heat-exchange; and
[0045] FIG. 3 is a flow sheet showing an embodiment of the present
invention where an uncondensed gas mixture from the stripper and
scrubber is introduced into the condensing of the high-pressure gas
mixture from the high-pressure decomposition step.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] In the present invention, the urea synthesis conditions are
preferably as follows:
[0047] a pressure ranging from about 13 to 25 MPaG,
[0048] a temperature ranging from about 180 to 200.degree. C.,
[0049] the mole ratio (N/C) of ammonia to carbon dioxide ranging
from about 3.0 to 4.0, and
[0050] the mole ratio (H/C) of water to carbon dioxide of
approximately 1 or lower.
[0051] The conditions for stripping the urea synthesis solution
from the urea synthesis with raw material carbon dioxide are
preferably as follows: the pressure is approximately equal to the
urea synthesis pressure and the temperature ranges from about 160
to 200.degree. C.
[0052] The gas mixture of ammonia, carbon dioxide and water
separated by stripping the urea synthesis solution is introduced
into the bottom part of a condensation zone (condenser). The
condensation conditions are preferably about 160 to 180.degree. C.
for the temperature, about 3.0 to 4.5 for N/C and approximately 1
or lower for H/C. The gas mixture is condensed by contacting it
with an aqueous ammonium carbamate solution residing in a condenser
and at that time, whereby condensation heat is generated. The
condensation heat is recovered by generation of low pressure
steam.
[0053] The gas mixture of an inert gas, ammonia, carbon dioxide and
water which is not condensed in the condensation zone is introduced
into a scrubber installed in the top part of the condensation zone
and washed with the condensate of a gas mixture from high pressure
decomposition, which will be described later. The resulting washing
solution is introduced into the bottom of the condensation zone
through a down pipe installed in the condensation zone. Most of
ammonia and carbon dioxide in the above-described gas mixture are
absorbed and together with remaining ammonia and carbon dioxide to
discharge the inert gas from the scrubber. The discharged inert gas
is utilized for stripping, as it will be described later,
preferably in the high pressure decomposition.
[0054] In the condensation step, the condensate flows down through
the down pipe laid in the condensation zone and having an opening
in the upper part, enter an ejector derived by raw material ammonia
having a pressure of about 15 to 30 MPa and a temperature of about
100 to 200.degree. C., whereby the pressure of the condensate is
increased by about 0.2 to 1 Mpa. The condensate is then introduced
into the urea synthesis zone (e.g. element "A" in FIGS. 1, 2 and
3).
[0055] The pressure of the urea synthesis solution from the
stripping step is reduced to about 1 to 4 MPaG, preferably 1.5 to
2.5 MPaG, and introduced into the high pressure decomposition step
to decompose the unreacted ammonium carbamate remaining in the
synthesis solution to a gas mixture of ammonia, carbon dioxide and
water at the temperature of 120 to 170.degree. C. At that time, the
inert gas from the above-described scrubber may be introduced into
the high pressure decomposition to be used as a stripping agent. In
such a manner, the unreacted ammonium carbamate remaining in the
aqueous urea solution can be decreased.
[0056] The aqueous urea solution from the high pressure
decomposition still contains a small amount of the unreacted
ammonium carbamate. The aqueous urea solution is further decreased
in pressure to about 0.1 to 0.5 MPaG and the unreacted ammonium
carbamate is decomposed at about 100 to 130.degree. C. At that
time, some of raw material carbon dioxide may be used as a
stripping agent. In such a manner, ammonia in the aqueous urea
solution can be substantially removed.
[0057] The aqueous urea solution containing substantially no
ammonia from the low pressure decomposition (e.g. element "H" in
FIGS. 1, 2 and 3) is introduced into a concentration (evaporation)
apparatus through a pipe side of an indirect heat exchanger. On the
other hand, the gas mixture from the high pressure decomposition is
introduced into the trunk part of the indirect heat exchanger to be
heat-exchanged with the aqueous urea solution. The aqueous urea
solution is heated by condensation heat generated at that time. In
such a manner, the condensation heat of the high pressure gas
mixture is utilized for concentrating the aqueous urea solution.
Incidentally, the aqueous urea solution heated by the condensation
heat may further be heated by low pressure steam. The concentration
is preferably carried out at about 100 to 130.degree. C. On the
other hand, the condensation of the high pressure gas mixture is
preferably carried-out at about 100 to 120.degree. C. The
condensation may be carried out under a normal or reduced
pressure.
[0058] The condensate and the uncondensed gas mixture from the
indirect heat exchanger are introduced into a first zone of high
pressure condensation where the uncondensed gas mixture is
partially condensed under cooling. The remaining uncondensed gas
mixture is further introduced into a second zone of the high
pressure condensation while the resulting condensate is fed to a
scrubber to be used for absorbing the ammonia and carbon dioxide in
the uncondensed gas mixture. In the second step of the high
pressure condensation, the gas mixture is further condensed under
cooling and the condensate is introduced into the trunk part of the
indirect heat exchanger (e.g. element "K" in FIGS. 1, 2 and 3) to
be used for the condensation of the high pressure gas obtained from
the high pressure decomposition step (e.g. element "G" in FIGS. 1,
2 and 3).
[0059] The uncondensed gas still remaining in the second step of
the high pressure condensation mainly contains inert gas, but is
further washed with an absorption medium in a washing column (e.g.
element R in FIGS. 1, 2 and 3) to remove residual ammonia and
carbon dioxide from the inert gas. The remaining inert gas is
discharged out of the top of the washing column. The washing
solution from the bottom part of the washing column is fed to the
second step of the high pressure condensation (e.g. element "Q" in
FIGS. 1, 2 and 3).
[0060] The gas mixture containing the inert gas from the scrubber
(e.g. scrubber "F" in FIGS. 1, 2 and 3) may be used as a stripping
agent in the high pressure decomposition (see e.g. FIG. 1, element
"G"); alternatively it may be mixed together with the gas mixture
from the high pressure decomposition and introduced into the trunk
part of the indirect heat exchanger for heating the aqueous urea
solution (see e.g. FIG. 2, element "K"); alternatively, it may also
be directly introduced to a first step of high pressure
condensation of the gas mixture from the high pressure
decomposition to be condensed (see e.g. FIG. 3, element "P").
[0061] Hereinafter, the present invention is concretely described
with the reference to the attached drawings.
[0062] With the reference to FIG. 1 which is a flow sheet showing
an embodiment of the present invention, a part of liquid ammonia
with the pressure of about 15 to 30 MPaG from the line 1 is
preheated to about 100 to 200.degree. C. with high or low pressure
steam in a preheater D and then fed to the driving side of an
ejector E to increase the pressure of a condensate aspirated
through a down pipe 3 of a condenser C. by 0.2 to 1 Mpa. The
ammonia from the ejector E is introduced into the bottom part of a
urea synthesis column A together with carbon dioxide containing
about 0.2 to 5% by volume of air as oxygen.
[0063] The urea synthesis column A is operated at a pressure
ranging from about 13 to 25 MPaG, a temperature ranging from about
180 to 200.degree. C., an N/C ratio of about 3.5 to 5.0, and an H/C
ratio of about 1.0 or less. The introduced ammonia, carbon dioxide,
and the condensate are converted to urea while rising in the
synthesis column and the produced urea synthesis solution is
introduced into the top part of a stripper B at a pressure
substantially equal to the urea synthesis pressure through the line
4.
[0064] While flowing down in the stripper B, the urea synthesis
solution is brought into contact with carbon dioxide fed in counter
flow through a line 2B at 160 to 200.degree. C. to separate the
unreacted ammonium carbamate contained in the urea synthesis
solution as a gas mixture of ammonia, carbon dioxide, an inert gas
and water.
[0065] The separated gas mixture is introduced into the bottom part
of the condenser C through the line 5. The gas mixture is brought
into contact with a washing liquid flowing down from a scrubber F
installed in the top part through a washing liquid receiver 7 and a
down pipe 8 to the bottom part of the condenser to be condensed at
170 to 190.degree. C. The condensation heat generated at that time
is eliminated by generating steam from water introduced from a line
9 and discharged through a line 10. The resulting condensate flows
down in the down pipe 3 having the opening in the upper part of the
condenser and is introduced, as described above, into the synthesis
column A through the ejector E. The remaining of the liquid ammonia
from the line 1 is supplied to the condenser C. through a line 1A
to maintain the N/C ratio at 3.0 to 4.5 and the H/C ratio at 1 or
less in the condensate in the condenser C.
[0066] A high pressure absorption solution, which will be described
later, is introduced into the scrubber F to wash the uncondensed
gas mixture of the inert gas, ammonia, and carbon dioxide, thereby
absorbing a part of ammonia and carbon dioxide in the gas mixture.
A gas mixture of mainly an inert gas is discharged from the top
part of the scrubber.
[0067] The pressure of the urea synthesis solution from which the
major part of the unreacted ammonium carbamate is separated in the
stripper B is reduced to a preferable pressure of from 1.2 to 2.5
MPaG and the solution is then introduced through a line 12 into a
high pressure decomposition column G and heated to 120 to
160.degree. C. to decompose most of the unreacted ammonium
carbamate. At that time, the inert gas from the line 11 is
introduced into the bottom part of the high pressure decomposition
column G as a stripping agent to make separation of the unreacted
ammonium carbamate easy. A gas mixture of ammonia, carbon dioxide,
the inert gas and water is discharged through a line 20 from the
top of the column.
[0068] The resulting urea synthesis solution from which most of the
unreacted ammonium carbamate is separated in the high pressure
decomposition column G flows through the line 13 and after the
pressure of the solution is reduced to 0.1 to 0.5 MPaG, the
solution is introduced into the top of a low pressure decomposition
tower H and heated to 110 to 140.degree. C. to separate the
substantially all of the remaining unreacted ammonium carbamate as
a gas mixture of ammonia, carbon dioxide and water. At that time,
any of the raw material carbon dioxide may be introduced as a
stripping agent from a line 2C. into the bottom part of the low
pressure decomposition column. The separated gas mixture is
discharged through a line 26. An aqueous urea solution discharged
from the bottom part of the low pressure decomposition column H
through a line 14 is introduced through the line 15 into a
gas-liquid separator I after the pressure is decreased to a normal
pressure, and the gas mixture of ammonia, carbon dioxide and water
in a slight amount is separated and discharged through a line 17.
The resulting aqueous urea solution is introduced into an aqueous
urea solution storage tank J through a line 16.
[0069] The aqueous urea solution from the aqueous urea solution
storage tank J flows through a line 19 and is fed to a condensing
part K and then a heating part L of an aqueous urea solution
heating apparatus by means of a pump 18 to be heated. The urea
solution is then introduced into a concentration apparatus M
through a line 23 to be concentrated, and the concentrated urea
solution is taken out through a line 24. At the time of
concentration, the evaporated steam accompanied with slight amounts
of ammonia and carbon dioxide is discharged through a line 25. The
gas mixture from the line 20 and a condensate from a line 21, which
will be described later, are introduced into the trunk side of the
condensing part K of the aqueous urea solution heating apparatus to
be condensed by indirect heat exchange with the aqueous urea
solution flowing in the pipe side. The aqueous urea solution is
heated with the condensation heat of the gas mixture generated at
that time. The temperature of the trunk part of the condensing part
K is kept at 100 to 120.degree. C. Steam is introduced into the
trunk part of the heating part L of the aqueous urea solution
heating apparatus to heat the aqueous urea solution flowing in the
pipe side to about 110 to 138.degree. C. The condensed liquid and
the uncondensed gas mixture obtained in the condensation part of
the aqueous urea solution heating apparatus are introduced into the
trunk part of a first condenser P through a line 22 and are cooled
by water flowing in the pipe side to be condensed. The temperature
of the trunk side of the first condenser P is kept at about 90 to
120.degree. C. The produced condensate is sent to the scrubber F
through a line 6.
[0070] In the first condenser P, the uncondensed gas mixture is
introduced into the trunk part of a second condenser Q through a
line 29 and condensed under cooling by being brought into contact
with a high pressure washing solution, which will be described
later, introduced through the line 31. The obtained condensate is
sent to the condensing part K of the aqueous urea solution heating
apparatus as described above through the line 21. The temperature
of the trunk side of the second condenser Q is kept at about 40 to
70.degree. C. The gas mixture which is not condensed in the trunk
side of the second condenser Q is introduced through a line 30 into
a washing column and brought into contact with the low pressure
condensate introduced from the top part through a line 28 and
pressurized at a pressure of about 1.2 to 2.5 MPaG to absorb
substantially all of the remaining ammonia and carbon dioxide. The
inert gas that is not absorbed is discharged out through the line
32.
[0071] The gas mixture separated in a lower pressure decomposition
column H is sent to a low pressure condenser N, and brought into
contact under cooling with an aqueous diluted ammonium carbonate
solution (which may contain a slight amount of urea) introduced
through the line 27, which solution has absorbed slight amounts of
ammonia and carbon dioxide from lines 17, 25 (and a gas mixture
separated in a condenser if there is the condenser after the low
pressure decomposition column H) to be condensed to be a low
pressure condensate which is then introduced from the line 28 into
the washing column R after the pressure is increased.
[0072] Another embodiment will be described with the reference to
FIG. 2. In this embodiment, the different point from the embodiment
described along with FIG. 1 is only that the gas mixture of an
inert gas, ammonia, carbon dioxide and water from the scrubber F is
directly fed to the condensing part K through a line 11.
[0073] Further, another embodiment will be described with the
reference to FIG. 3. In this embodiment, the different point from
the embodiment described along with FIG. 1 is only that the gas
mixture of an inert gas, ammonia, carbon dioxide and water from the
scrubber F is directly fed to the second condenser through a line
11.
[0074] Exemplary embodiments of the present invention are now
described with reference to FIGS. 1, 2 and 3 which respectively
describe the embodiments of Examples 1, 2 and 3. Table 1, which
appears after Example 3 below, provides a side-by-side
stoichiometric comparison of the processes of Examples 1, 2 and 3.
The processes of the present invention may be described by
particular discrete steps described in a particular order, however,
it is understood that these processes involve the interaction of
multiple components and interrelation of different steps.
Therefore, while the various process steps are interrelated as
described, the invention may be alternatively described by
different orderings of steps which describe the same overall
process. While these particular embodiments exemplify aspects of
the present invention, it is understood that the present invention
is not restricted only to these embodiments.
EXAMPLE 1
[0075] The process shown in FIG. 1 was carried out as follows. The
urea synthesis reaction was conducted at the temperature of
182.degree. C. and the pressure of 15.2 MPaG in an urea synthesis
column by introducing 39,588.75 kg/hr of liquid ammonia heated to
140.degree. C. by a preheater D through line 1, 7,140.00 kg/hr of
raw material carbon dioxide through line 2A which was supplied in
52,639.17 kg/hr together with 1,205 kg/hr of air and an inert gas
through line 2, and a condensate containing 50,604.46 kg/hr of
urea, 57,049.10 kg/hr of ammonia, 45,132.18 kg/hr of carbon
dioxide, 36,655.50 kg/hr of water, and 154.59 kg/hr of biuret
through down pipe 3.
[0076] The resulting urea synthesis solution containing:
[0077] 77,240.55 kg/hr of urea,
[0078] 81,517.63 kg/hr of ammonia,
[0079] 32,729.53 kg/hr of carbon dioxide,
[0080] 44,657.29 kg/hr of water, and
[0081] 179.58 kg/hr of biuret
[0082] was introduced into a stripper B through a line 4 and
brought into contact with 43,342.92 kg/hr of the raw material
carbon dioxide introduced from the bottom part through a line 2B
and the major part of unreacted ammonium carbamate was separated as
a gas mixture containing:
[0083] 66,607.50 kg/hr of ammonia,
[0084] 61,227.50 kg/hr of carbon dioxide, and
[0085] 6,442.92 kg/hr of water.
[0086] The separated gas mixture was introduced into the bottom
part of condenser C. and while rising through condenser C., was
brought into contact with a high pressure condensate
containing:
[0087] 249.17 kg/hr of urea,
[0088] 19,154.99 kg/hr of ammonia,
[0089] 22,909.59 kg/hr of carbon dioxide, and
[0090] 15,205.00 kg/hr of water and
[0091] introduced through a line 6 to the top part of a scrubber F
disposed at the top of the condenser C.
[0092] From the top of a scrubber F, a gas mixture containing:
[0093] 1,137.92 kg/hr of ammonia,
[0094] 1,969.17 kg/hr of carbon dioxide,
[0095] 1,205.00 kg/hr of an inert gas, and
[0096] 155.42 kg/hr of water
[0097] was discharged out through a line 11.
[0098] The urea synthesis solution discharged from the bottom of
the stripper B containing:
[0099] 73,500.87 kg/hr of urea,
[0100] 16,970.74 kg/hr of ammonia,
[0101] 17,481.46 kg/hr of carbon dioxide,
[0102] 37,134.84 kg/hr of water, and
[0103] 301.67 kg/hr of biuret
[0104] was sent through line 12 and decreased in the pressure to 1.
72 MPaG, and then introduced into the top of a high pressure
decomposition column G, and brought into contact with the gas
mixture introduced into the bottom part of the column G through
line 11 in a counter-flow at 155.degree. C. and most of the
unreacted ammonium carbamate was separated as a gas mixture
containing:
[0105] 10,497.36 kg/hr of ammonia,
[0106] 16,841.16 kg/hr of carbon dioxide,
[0107] 1,205.00 kg/hr of an inert gas, and
[0108] 3,516.68 kg/hr of water through line 20.
[0109] The urea synthesis solution containing:
[0110] 72,747.30 kg/hr of urea,
[0111] 8,010.27 kg/hr of ammonia,
[0112] 3,112.75 kg/hr of carbon dioxide,
[0113] 33,567.62 kg/hr of water, and
[0114] 358.95 kg/hr of biuret
[0115] was discharged from the bottom part of the column G through
line 13, decreased in the pressure to 0.25 NPaG, introduced into
the top part of a low pressure decomposition column H, and heated
to 123.degree. C.
[0116] A gas mixture containing:
[0117] 7,644.32 kg/hr of ammonia,
[0118] 5,148.89 kg/hr of carbon dioxide, and
[0119] 3,198.30 kg/hr of water
[0120] was discharged from the top part of column H.
[0121] On the other hand, from the bottom part of the column of
column H, an aqueous urea solution containing:
[0122] 72,230.09 kg/hr of urea,
[0123] 663.15 kg/hr of ammonia,
[0124] 492.02 kg/hr of carbon dioxide,
[0125] 30,217.42 kg/hr of water, and
[0126] 367.25 kg/hr of biuret
[0127] was taken out through line 14. After the pressure was
decreased, the aqueous urea solution was sent through line 15 to a
gas-liquid separator I where residual ammonia and carbon dioxide
were removed. The resulting aqueous urea solution and was sent to
storage tank J through line 16. From this storage tank the aqueous
urea solution is available for concentration and further processing
in elements K, L and M shown in FIG. 1.
[0128] The gas mixture obtained from low pressure decomposition
column H was introduced into a low pressure condenser N through
line 26 and brought into contact under cooling with an aqueous
diluted ammonium carbonate solution containing a slight amount of
urea (from line 27) and was condensed. This condensate of gases
from the low pressure decomposition contained:
[0129] 249.17 kg/hr of urea,
[0130] 8,664.30 kg/hr of ammonia,
[0131] 6,075.10 kg/hr of carbon dioxide, and
[0132] 11,169.99 kg/hr of water.
[0133] This condensate was introduced into the top part of washing
column R through line 28 and brought into contact with a gas rising
from the bottom part of column R to absorb ammonia and carbon
dioxide from the rising gas thereby obtaining a washing solution
containing:
[0134] 249.17 kg/hr of urea,
[0135] 9,052.21 kg/hr of ammonia,
[0136] 6,078.85 kg/hr of carbon dioxide, and
[0137] 11,184.15 kg/hr of water.
[0138] The washing solution was introduced into a second condenser
Q through line 31. The inert gas that was not absorbed was
discharged out through a line 32. The washing solution was brought
into contact at 51.degree. C. with a gas mixture containing:
[0139] 5,990.82 kg/hr of ammonia,
[0140] 1,684.14 kg/hr of carbon dioxide,
[0141] 1,023.48 kg/hr of water, and
[0142] 1,205.00 of an inert gas
[0143] from line 29 to obtain a condensate containing:
[0144] 249.17 kg/hr of urea,
[0145] 14,648.45 kg/hr of ammonia,
[0146] 7,752.55 kg/hr of carbon dioxide, and
[0147] 12,171.80 kg/hr of water.
[0148] The gas mixture (394.58 kg/hr of ammonia, 10.42 kg/hr of
carbon dioxide, 35.83 kg/hr of water, and 1,205.00 kg/hr of the
inert gas) that was not condensed was introduced into the bottom
part of the washing column R through a line 30 and was washed.
[0149] The condensate was introduced into the trunk side of the
condensing part K of the aqueous urea solution heating apparatus
through line 21 and condensed at a temperature of 110.degree. C.
together with the gas mixture from the high pressure decomposition
column G introduced through line 20 while being indirectly
heat-exchanged with the aqueous urea solution sent through line 19
from the aqueous urea solution storage tank J. Line 22 exits the
indirect heat-exchanger and contained an uncondensed gas mixture
of:
[0150] 10,507.73 kg/hr of ammonia,
[0151] 7,408.84 kg/hr of carbon dioxide,
[0152] 1,544.14 kg/hr of water, and
[0153] 1,205.00 kg/hr of the inert gas,
[0154] and a condensate of:
[0155] 249.17 kg/hr of urea,
[0156] 14,638.08 kg/hr of ammonia,
[0157] 17,184.87 kg/hr of carbon dioxide, and
[0158] 14,144.35 kg/hr of water
[0159] the contents of line 22 were introduced into a first
condenser P and condensed under cooling at 100.degree. C. to obtain
a condensate containing:
[0160] 249.17 kg/hr of urea,
[0161] 19,154.99 kg/hr of ammonia,
[0162] 22,909.59 kg/hr of carbon dioxide, and
[0163] 14,665.00 kg/hr of water.
[0164] The resulting condensate from condenser P was mixed with 540
kg/hr of water added from line 33 for sealing a pump, and this
mixture was introduced into the top part of the scrubber F through
line 6. The uncondensed gas mixture (a gas mixture containing
5,990.82 kg/hr of ammonia, 1,684.14 kg/hr of carbon dioxide,
1,023.48 kg/hr of water, and 1,205.00 kg/hr of the inert gas) in
the first condenser P was sent to a second condenser Q through line
29 and condensed to obtain the condensate mentioned above that is
introduced into line 21.
[0165] The aqueous urea solution stored in tank J as described
above, was introduced into condensing part K of the aqueous urea
solution heating apparatus, then into heating part L of the aqueous
urea solution heating apparatus and then further heated by steam
and introduced into a concentration apparatus M through a line 23
to obtain urea solution containing approximately 95% urea by
weight.
EXAMPLE 2
[0166] This example was carried out along the process shown in FIG.
2. In the process, since the gas mixture from a line 11 was to be
introduced directly to the condensing part K of the aqueous urea
solution heating apparatus, the liquids and the gas compositions
after the high pressure decomposition were as follows.
Incidentally, the operation conditions were controlled to be
substantially the same as those used in Example 1. The reaction
contents at various points in the process shown in FIG. 2 are
described below:
[0167] At the High pressure decomposition column G:
1 gas composition in line 20: ammonia 8,623.33 kg/hr carbon dioxide
13,611.25 kg/hr water 3,510.00 kg/hr urea synthesis solution
composition in line 13: urea 72,747.30 kg/hr ammonia 8,746.37 kg/hr
carbon dioxide 4,373.49 kg/hr water 33,418.89 kg/hr biuret 358.95
kg/hr
[0168] At the Low pressure decomposition column H:
2 gas composition in line 26: ammonia 8,380.43 kg/hr carbon dioxide
6,409.63 kg/hr water 3,049.56 kg/hr aqueous urea solution in line
14: urea 72,230.09 kg/hr ammonia 655.14 kg/hr carbon dioxide 492.02
kg/hr water 30,217.13 kg/hr biuret 367.25 kg/hr
[0169] At the washing column R:
3 liquid composition in line 28: urea 249.17 kg/hr ammonia 9,400.41
kg/hr carbon dioxide 7,335.84 kg/hr water 11,021.25 kg/hr liquid
composition in line 31: urea 249.17 kg/hr ammonia 9,788.32 kg/hr
carbon dioxide 7,339.59 kg/hr water 11,035.41 kg/hr gas composition
in line 30: ammonia 394.58 kg/hr carbon dioxide 10.42 kg/hr water
35.83 kg/hr the inert gas 1,205.00 kg/hr gas composition in line
32: ammonia 6.67 kg/hr carbon dioxide 6.67 kg/hr water 21.67 kg/hr
inert gas 1,205.00 kg/hr
[0170] At the second condenser Q:
4 liquid composition in line 21: urea 249.17 kg/hr ammonia
14,964.47 kg/hr carbon dioxide 8,887.21 kg/hr water 12,066.34
kg/hr
[0171] At condensation part K of the aqueous urea solution heating
apparatus:
5 gas composition in the line 11: ammonia 1,137.92 kg/hr carbon
dioxide 1,969.17 kg/hr water 155.42 kg/hr the inert gas 1,205.00
kg/hr liquid composition in line 22: urea 249.17 kg/hr ammonia
14,954.82 kg/hr carbon dioxide 17,613.42 kg/hr water 14,122.33
kg/hr gas composition in line 22: ammonia 9,770.89 kg/hr carbon
dioxide 6,854.21 kg/hr water 1,609.43 kg/hr the inert gas 1,205.00
kg/hr
[0172] At the first condenser P:
6 liquid composition in line 6: urea 249.17 kg/hr ammonia 19,154.99
kg/hr carbon dioxide 22,909.59 kg/hr water 14,665.00 kg/hr gas
composition in line 29: ammonia 5,570.73 kg/hr carbon dioxide
1,558.04 kg/hr water 1,066.76 kg/hr the inert gas 1,205.00
kg/hr
[0173] At the concentration apparatus M:
7 aqueous urea solution in line 19: urea 72,230.09 kg/hr ammonia
467.34 kg/hr carbon dioxide 342.72 kg/hr water 27,111.52 kg/hr
biuret 367.52 kg/hr aqueous urea solution in line 24: urea
71,922.45 kg/hr ammonia 0 kg/hr carbon dioxide 0 kg/hr water
3810.89 kg/hr biuret 484.48 kg/hr
EXAMPLE3
[0174] This example was carried out as shown in FIG. 3, but the
operation conditions were controlled to be substantially the same
as those used in Example 1. In this embodiment, the gas mixture
from line 11 was introduced directly to the trunk part of the first
condenser P. The liquid and the gas compositions after the high
pressure decomposition were as follows.
[0175] At the high pressure decomposition column G:
8 gas composition in line 20: ammonia 8,623.33 kg/hr carbon dioxide
13,611.25 kg/hr water 3,510.00 kg/hr urea synthesis solution
composition in line 13: urea 72,747.30 kg/hr ammonia 8,746.37 kg/hr
carbon dioxide 4,373.49 kg/hr water 33,418.89 kg/hr biuret 358.95
kg/hr
[0176] At the low pressure decomposition column H:
9 gas composition in line 26: ammonia 8,380.43 kg/hr carbon dioxide
6,409.63 kg/hr water 3,049.56 kg/hr aqueous urea solution in line
14: urea 72,230.09 kg/hr ammonia 655.14 kg/hr carbon dioxide 492.02
kg/hr water 30,217.13 kg/hr biuret 367.25 kg/hr
[0177] At the washing colulmn R:
10 liquid composition in the line 28: urea 249.17 kg/hr ammonia
9,400.41 kg/hr carbon dioxide 7,335.84 kg/hr water 11,021.25 kg/hr
liquid composition in line 31: urea 249.17 kg/hr ammonia 9,788.32
kg/hr carbon dioxide 7,339.59 kg/hr water 11,035.41 kg/hr gas
composition in line 30: ammonia 394.58 kg/hr carbon dioxide 10.42
kg/hr water 35.83 kg/hr the inert gas 1,205.00 kg/hr gas
composition in line 32: ammonia 6.67 kg/hr carbon dioxide 6.67
kg/hr water 21.67 kg/hr the inert gas 1,205.00 kg/hr
[0178] At the second condenser Q:
11 In line 21: urea 249.17 kg/hr ammonia 14,963.83 kg/hr carbon
dioxide 9,137.91 kg/hr water 12,124.13 kg/hr
[0179] At condensation part K of the aqueous urea solution heating
apparatus:
12 liquid composition in line 22: urea 249.17 kg/hr ammonia
14,955.31 kg/hr carbon dioxide 16,761.24 kg/hr water 14,092.94
kg/hr gas composition in line 22: ammonia 8,631.85 kg/hr carbon
dioxide 5,987.92 kg/hr water 1,541.19 kg/hr
[0180] At the first condenser P:
13 liquid composition in line 6: urea 249.17 kg/hr ammonia
19,154.99 kg/hr carbon dioxide 22,909.59 kg/hr water 14,665.00
kg/hr gas composition in line 11: ammonia 1,137.92 kg/hr carbon
dioxide 1,969.17 kg/hr water 155.42 kg/hr the inert gas 1,205.00
kg/hr gas composition in line 29: ammonia 5,570.09 kg/hr carbon
dioxide 1,808.74 kg/hr water 1,124.55 kg/hr the inert gas 1,205.00
kg/hr
[0181] At the concentration apparatus M:
[0182] aqueous urea solution in line 19:
14 urea 72,230.09 kg/hr ammonia 467.34 kg/hr carbon dioxide 342.72
kg/hr water 27,111.52 kg/hr biuret 367.52 kg/hr
[0183] aqueous urea solution in line 24:
15 urea 71,922.45 kg/hr ammonia 0 kg/hr carbon dioxide 0 kg/hr
water 3810.89 kg/hr biuret 484.48 kg/hr
[0184] Table I which follows, compares the embodiments of Examples
1, 2 and 3.
16 Ex. 1 Ex. 2 Ex. 3 Column G-high pressure decomposition line 20
(gas) ammonia 10,497.36 8,623.33 8,623.33 carbon dioxide 16,841.16
13,611.25 13,611.25 water 3,516.68 3,510.00 3,510.00 inert gas
1,205.00 0 0 line 13 (urea synthesis solution) urea 72,747.30
72,747.30 72,747.30 ammonia 8,010.27 8,746.37 8,746.37 carbon
dioxide 3,112.75 4,373.49 4,373.49 water 33,567.62 33,418.89
33,418.89 biuret 358.95 358.95 358.95 line 11 (gas) ammonia
1,137.92 N/A N/A carbon dioxide 1,969.17 N/A N/A water 155.42 N/A
N/A inert gas 1,205.00 N/A N/A Column H-low pressure decomposition
line 26 (gas) ammonia 7,644.32 8,380.43 8,380.43 carbon dioxide
5,148.89 6,409.63 6,409.63 water 3,198.30 3,049.56 3,049.56 line 14
(aqueous solution) urea 72,230.09 72,230.09 72,230.09 ammonia
663.15 655.14 655.14 carbon dioxide 492.02 492.02 492.02 water
30,217.42 30,217.13 30,217.13 biuret 367.25 367.25 367.25 Column
R-washing line 28 (liquid) urea 249.17 249.17 249.17 ammonia
8,664.30 9,400.41 9,400.41 carbon dioxide 6,075.10 7,335.84
7,335.84 water 11,169.99 11,021.25 11,021.25 line 31 (liquid) urea
249.17 249.17 249.17 ammonia 9,052.21 9,788.32 9,788.32 carbon
dioxide 6,078.85 7,339.59 7,339.59 water 11,184.15 11,035.41
11,035.41 line 30 (gas) ammonia 394.58 394.58 394.58 carbon dioxide
10.42 10.42 10.42 water 35.83 35.83 35.83 inert gas 1,205.00
1,205.00 1,205.00 line 32 (gas) ammonia 6.67 6.67 6.67 carbon
dioxide 6.67 6.67 6.67 water 21.57 21.67 21.67 inert gas 1,205.00
1,205.00 1,205.00 Condenser Q (second condenser) line 21 (liquid)
urea 249.17 249.17 249.17 ammonia 14,648.45 14,964.47 14963.83
carbon dioxide 7,752.55 8,887.21 9137.91 water 12,171.80 12,066.34
12124.13 Condensation part K line 11 (gas) ammonia N/A 1,137.92 N/A
carbon dioxide N/A 1,969.17 N/A water N/A 155.42 N/A inert gas N/A
1,025.00 N/A line 22 (liquid) urea 249.17 249.17 249.17 ammonia
14,638.08 14,954.82 14,955.31 carbon dioxide 17,184.87 17,613.42
16,761.24 water 14,144.35 14,122.33 14,092.94 line 22 (gas) ammonia
10,507.73 9,770.89 8,631.85 carbon dioxide 7,408.84 6,854.21
5,987.92 water 1,544.14 1,609.43 1,541.19 inert gas 1,205.00
1,205.00 0 Condenser P (first condenser) line 6 (liquid) urea
249.17 249.17 249.17 ammonia 19,154.99 19,154.99 19,154.99 carbon
dixoide 22,909.59 22,909.59 22,909.59 water 14,665.00 14,665.00
14,665.00 line 11 (gas) ammonia N/A N/A 1,137.92 carbon dioxide N/A
N/A 1,969.17 water N/A N/A 155.42 inert gas N/A N/A 1,205.00 line
29 (gas) ammonia 5,990.82 5,570.73 5,570.09 carbon dioxide 1,684.14
1,558.04 1,808.74 water 1,023.48 1,066.76 1,124.55 inert gas
1,205.00 1,205.00 1,205.00 Concentration Apparatus M line
19-aqueous urea solution urea 72,230.09 72,230.09 72,230.09 ammonia
467.34 467.34 467.34 carbon dioxide 342.72 342.72 342.72 water
27,111.52 27,111.52 27,111.52 biuret 367.52 367.52 367.52 line
24-aqueous solution urea 71,922.45 71,922.45 71,922.45 ammonia --
-- -- carbon dioxide -- -- -- water 3,810.89 3,810.89 3,810.89
biuret 484.48 484.48 484.48
[0185] Modifications and Other Embodiments
[0186] Various modifications and variations of the described
processes for synthesizing urea as well as the concept of the
invention will be apparent to those skilled in the art without
departing from the scope and spirit of the invention. Although the
invention has been described in connection with specific preferred
embodiments, it should be understood that the invention as claimed
is not intended to be limited to such specific embodiments. Various
modifications of the described modes for carrying out the invention
which are obvious to those skilled in the chemical, chemical
engineering arts or related fields are intended to be within the
scope of the following claims.
[0187] Incorporation by Reference
[0188] Each document, patent application or patent publication
cited by or referred to in this disclosure is incorporated by
reference in its entirety. The priority document of the present
application, Japanese Patent Application 2000-334395, filed Nov. 1,
2000, is herein incorporated by reference.
* * * * *