FIELD
The present invention relates to an operation method of
a urea production plant including multiple systems.
5 BACKGROUND
To produce urea, in general, ammonia (NH3) obtained by
using natural gas and the like as a raw material by an
ammonia synthesis facility and carbon dioxide (Con) separated
at the time of ammonia synthesis are used to synthesize urea
10 (CH4N20) by a urea synthesis unit (Patent Literature 1).
CITATION LIST
P a t e n t L i t e r a t u r e
Patent Literature 1: Japanese Patent Application Laid-
15 open No. 2000-159519
SUMMARY
Technical Problem
Meanwhile, in a urea production plant that synthesizes
20 ammonia and urea from natural gas and the like, if an
ammonia synthesis facility is shut down, one week or more is
normally necessary to resume operations of the facility.
As a result, if it happens, the urea production amount
of the facility in the year decreases. If shutdown of the
25 ammonia synthesis facility occurs many times throughout the
year, a considerable decrease in the urea production amount
occurs throughout the year. Therefore, there has been
desired a method of increasing the urea production amgunt.
The present invention has been achieved to solve the
30 above problem, and an object of the present invention is to
provide an operation method of a urea production plant
including multiple systems that can prevent a considerable
decrease in urea production even when a ammonia synthesis
facility is shut down.
Solution to Problem
According to an aspect of the present invention, an
operation method of a urea production plant including
5 multiple systems, at a time of producing urea by using a
urea synthesis plant that includes: an ammonia synthesis
facility including a reforming device having a reforming
furnace that reforms natural gas to hydrogen (Hz) and carbon
monoxide (CO) by using water vapor, a CO-shift converter
10 that converts carbon monoxide (CO) in reformed gas to carbon
dioxide, a carbon-dioxide removal device that removes
obtained carbon dioxide (C02) in the reformed gas, a
synthesis gas compressor that compresses synthesis material
gas containing hydrogen and nitrogen, from which carbon
15 dioxide has been removed by the carbon-dioxide removal
device, and an ammonia synthesis reactor that synthesizes
ammonia from compressed synthesis material gas; a liquefied
ammonia storage facility that branches ammonia obtained by
the ammonia synthesis reactor from an ammonia supply line
20 for supplying ammonia to a urea synthesis unit and stores a
part of synthesized ammonia in a liquefied state; a carbondioxide
recovery facility that recovers carbon dioxide in
fuel flue gas from the reforming furnace; and a carbondioxide
supply line for supplying the removed carbon dioxide
25 (removed CO2) and the recovered carbon dioxide (recovered
C02) to a urea synthesis unit, comprising: providing at least
two systems of the urea synthesis plants; storing a
predetermined amount of obtained ammonia in a liquefied
state in the liquefied ammonia storage facility; when a
30 trouble occurs in the ammonia synthesis facility of one of
the systems and production of ammonia is stopped,
temporarily supplying carbon dioxide (recovered COz)
recovered by the other system to a C02 supply line of the
shut down system via an emergency C02 supply line in order to
supply the temporarily suppiied C02 to the urea synthesis
unit; supplying a predetermined amount of liquefied ammonium
stored in the shut down system from an ammonia supply line
to the urea synthesis unit; producing urea by using the
5 temporarily supplied C02 and stored liquefied ammonia even in
the shut down system, thereby enabling to perform a
continuous operation when the ammonia synthesis facility is
shut down. Advantageously, in the operation method of a
urea production plant including multiple systems, the carbon
10 dioxide recovery facility recovers recovered COz to a maximum
extent.
Advantageous Effects of Invention
According to the present invention, at the time of
15 producing urea from C02 and ammonia, in a case where urea
production plants including at least two systems are
arranged in parallel, when an ammonia production facility of
one of the systems is shut down, liquefied ammonia stored in
the shut down system is used, and a C02 recovery amount in a
20 C02 recovery facility in the ammonia synthesis facility of
the other system is increased. Synthesis of urea can be
continued even in the shut down system by using the
increased recovered C02 and the liquefied ammonia.
As a result, operations of the remaining one of the two
25 systems are normally performed to synthesize urea, and urea
synthesis can be continued until restart even in the urea
production plant of the one system, which has been
conventionally shut down, thereby enabling to avoid a
considerable decrease in a production amount throughout the
' 30 year.
Brief Description of Drawings
FIG. 1 is a schematic diagram of a urea production
plant including multiple systems according to a first
embodiment (in a normal operation state).
F I G . 2 is a schematic diagram of the urea production
plant including multiple systems according tu the first
embodiment (in a state where one system is shut down).
5 F I G . 3 is a schematic diagram of another urea
production plant including multiple systems according to the
first embodiment (in a state where one system is shut down).
F I G . 4 is a schematic diagram of the urea production
plant including multiple systems according to the first
10 embodiment with a production amount added thereto (in a
normal operation state).
FIG. 5 is a schematic diagram of the urea production
plant including multiple systems according to the first
embodiment with a production amount added thereto (in d sLdLe
15 where one system is shut down).
FIG. 6 is a schematic diagram of a urea production
plant including multiple systems according to a second
embodiment (in a normal operation state).
F I G . 7 is a schematic diagram of the urea production
20 plant including multiple systems according to the second
embodiment (in a state where one system is shut down).
F I G . 8 is a schematic diagram of a urea production
plant including multiple systems according to a third
embodiment (in a normal operation state).
2 5 FIG. 9 is a schematic diagram of the ured production
plant including multiple systems according to the third
embodiment (in a state where one system is shut down).
F I G . 10 is a schematic diagram of a urea production
plant including multiple systems according to a fourth
30 embodiment (in a normal operation state).
F I G . 11 is a schematic diagram of the urea production
plant including multiple systems according to the fourth
embodiment (in a shut down state) .
FIG. 12 is a schematic diagram of an ammonia synthesis
facility according to the first embodiment.
Description of Embodiments
The present invention will be explained below in detail
5 with reference to the accompanying drawings. The present
invention is not limited the following embodiments, and
configurations achieved by combininq these embodiments are
also included in the present invention. In addition,
constituent elements in the following embodiments include
10 those that can be easily anticipated by persons skilled in
the art or that are substantially equivalent.
First Embodiment
An operation method of a urea production plant
15 including multiple systems according to an embodiment of the
present invention is explained with reference to the
drawings. FIG. 1 is a schematic diagram of a urea
production plant including multiple systems according to a
first embodiment (in a normal operation state). FIG. 2 is a
20 schematic diagram of the urea production plant including
multiple systems according to the first embodiment (in a
state where one system is shut down). FIG. 3 is a schematic
diagram of another urea production plant including multiple
systems according to the first embodiment (in a state where
25 one system is shut down). FIG. 12 is a schematic d i d y ~ d l n of
an ammonia synthesis facility according to the first
embodiment. In the present embodiment, as shown in FIG. 1,
a parallel-type urea production plant is provided in which
urea is produced, respectively, by two systems of an ammonia
30 synthesis facility 10A and an ammonia synthesis facility 10B.
An example of the ammonia synthesis facility that
produces a raw material for urea production is explained
first with reference to FIG. 12.
As shown in FIG. 12, an ammonia synthesis facility 10
includes a reforming device 1 4 having a reforming furnace 13
that reforms natural gas 11 to hydrogen (H2) and carbon
monoxide (CO) by using water vapor 12, a CO-shift converter
16 that converts carbon monoxide (CO) in reformed gas 15 to
5 carbon dioxide, a carbon-dioxide removal device 17 that
removes obtained carbon dioxide ( C o p ) in the reformed gas 15,
a synthesis gas compressor 19 that compresses synthesis
material gas 18 containing hydrogen and nitrogen, in which
carbon dioxide has been removed by the carbon-dioxide
10 removal device 17, and an ammonia synthesis reactor 20 that
synthesizes ammonia from the compressed synthesis material
gas.
The reforming device 14 produces hydrogen by reforming
the natural gas 11, and includes a primary reformer 14A and
15 a secondary reformer 14B. In primary reforming, the water
vapor 12 is added t o t h e n a t u r a l gas 11, t o reform t h e most
part of methane. Air is added thereto by an amount of
nitrogen corresponding to the generated hydrogen amount to
perform secondary reforming.
2 0 The CO-shift converter 16 first converts CO to C02 in
order to remove carbon, thereby obtaining the reformed gas
15.
The carbon-dioxide removal device 17 removes carbon
dioxide ( C O z ) , which is then regenerated as C02 having a high
25 purity fur d rclw material of urea.
In the synthesis material gas 18 in which COz has been
removed, a hydrogen to nitrogen ratio is 3:1, and the
pressure of the synthesis material gas 18 is raised to a
high pressure required for synthesis by the synthesis gas
30 compressor 19.
The ammonia synthesis reactor 20 synthesizes ammonia
(NH3) from hydrogen and nitrogen.
[0014] Fuel F is supplied to the reforming furnace 13 in
the primary reformer 14A of the reforming device 14, so that
combustion flue gas 2 2 generated thereby is discharged to
outside. COz contained in the combustion flue gas 22 is
recovered by a Con recovery facility 23 as described below.
The urea production plant of one system (an A system)
5 in FIG. 1 supplies ammonia obtained by the ammonia synthesis
reactor 2 0 in the ammonia synthesis facility 10A and CO2
removed by the C02 removal device 17 (removed COz) to a urea
synthesis unit 3 0 (urea synthesis units 30A1 and 30A2), where
urea is synthesized by the urea synthesis units 30A1 and 30Az
1 0 (normal synthesis).
A urea production plant of the other system (a B
system) in FIG. 1 supplies ammonia obtained by the ammonia
synthesis reactor 2 0 in the ammonia synthesis facility 10B
and C02 removed by the C02 r e r n o v a l device 1 7 (removed C02) to
15 the urea synthesis unit 3 0 (urea synthesis units 30B1 and
30B2), where urea is synthesized by the urea synthesis units
30B1 and 30B2 (normal synthesis) .
A C02 recovery facility 23 that recovers CO2 in the
combustion flue gas 22 discharged from the primary reformer
2 0 14A in the ammonia synthesis facility 10B is installed in
the urea production plant of the B system (a lower stage).
In FIG. 1, reference sign L1 denotes an ammonia supply
line, L2 denotes an ammonia storage line, L3 denotes a
removed CO2 supply line, L4 denotes a recovered C02 supply
25 line, Lb denotes an emergency COZ supply line, L6 denotes an
ammonia supply line, V1 denotes a recovered COz supply valve,
V ~ Aan d V ~ Bde note a removed C02 slipply valve, and V3A and V3B
denote an ammonia supply valve.
Further, liquefied NH3 storage facilities 21A and 21B
3 0 that can store a predetermined amount of ammonia obtained
from the respective systems (the A system and the B system)
in a liquefied state are installed.
In such facilities, at the time of a normal operation,
ammonia is synthesized by the ammonia synthesis facilities
10A and 10B of the A system and the B system, and urea is
synthesized from ammonia and C02, respectively, by the urea
synthesis unlts 30A1, 30A2, 30B1, and 30B2, by using removed
C02 removed from the ammonia synthesis facilities 10A and 10B.
5 In thc B system, because recovered C02 recovered by the
C02 recovery facility 23 can be supplied for urea synthesis,
a total amount of urea synthesis in the urea synthesis unit
of the B system can be increased than that of the urea
synthesis unit of the A system.
10 In the urea production facility, such a plurality of
systems are operated in parallel, so that urea is produced
continuously throughout the year to ensure a predetermined
annual production amount.
Meanwhile, in the ammonia synthesis facility, when a
15 failure (such as trip of ancillary facilities) occurs in the
facility or power supply is stopped, one week or more is
normally necessary to resume operations. This is because
the ammonia synthesis facility is formed by a combination of
devices in a plurality of processes and the reforming
20 furnace 13 is operated in a high temperature condition,
therefore, if the ammonia synthesis facility is shut down
once, a certain period of time (at least one week) is
required for raising the temperature and pressure and for
stabilization.
2 5 Therefore, in the present invention, even in the period
until restart (at least one week), urea can be produced
stably.
As shown in FIG. 2, when ammonia synthesis in the A
system is stopped, carbon dioxide (recovered C02) recovered
30 by the other system (for example, the B system) is
temporarily supplied to the removed C02 supply line L3 of the
shut down system (the A system) via the emergency C02 supply
line Lg (the thick line in FIG. 2). The temporarily supplied
recovered C02 is supplied by switching the removed C02 supply
valve VZA to the urea synthesis unit 30A1 side.
Liquefied ammonium stored in the liquefied NH3 storage
facility 21A in the ammonia synthesis facility 10A of the
shut down system (the A system) is supplied from the ammonia
5 supply line L1 by switching the NH3 supply valve V ~ Ato the
urea synthesis unit 30A1 side.
As a result, even in the shut down system (the A
system), urea can be produced in the urea synthesis unit 30A1
by using the temporarily supplied C02 and the stored
10 liquefied ammonia.
Accordingly, in the ammonia synthesis facility 10A of
the A system, even if supply of removed C02 is stopped due to
shutdown of the ammonia synthesis facility, recovered CO2 is
supplied from the B system via the emergency C02 supply line
15 (the thick line in FIG. 2) L5, thereby enabling to perform
ammonia synthesis continuously.
As an amount to be stored in the liquefied NH3 storage
facility 21A, an amount for at least one week, which is
required for resuming operations in the shut down ammonia
20 synthesis facility 10A, needs only to be stored in a
liquefied state.
Further, it is desired that the C02 recovery facility 23
in the B system has a size more sufficient than a C02
recovery amount of a general COP recovery facility (four to
25 five times the size of a general size).
Furthermore, the recovered C02 can be supplied to the A
system side by recovering C02 to a maximum extent (recovery
efficiency: 90%) at the time of shutdown of one plant.
As a result, a decrease in the urea production amount
30 throughout the year can be prevented, and a problem of
considerable decrease in the urea production amount
occurring throughout the year can be resolved, thereby
enabling to stabilize urea production.
This is advantageous because urea is an important
material as a fertilizer; stable production thereof
throughout the year is desired.
Furthermore, as shown in FIG. 3, when the operation of
the ammonia synthesis facility 10A of the A system is not
5 resumed even if all of the liquefied ammonium stored in the
liquefied NH3 storage facility 21A of the A system has been
consumed, liquefied ammonium in the liquefied NH3 storage
facility 21B of the B system can be supplied to the ammonia
supply line L1 on the A system side via the ammonia supply
10 line SO that a continuous operation of urea synthesis for
one more week can be performed.
In FIG. 4, which corresponds to FIG. 1, examples of an
ammonia production amount, a removed C02 amount, a recovered
C02 amount, a liquefied NH3 amount, and a urea production
15 amount in the normal operation are shown.
As shown in FIG. 4, production of 1,765 T/D i s
performed respectively in the urea synthesis units 30A1 and
30A2, and the urea synthesis units 30B1 and 30B2. The urea
amount of 220 T/D in brackets in the B system is a
20 production amount at the time of using recovered C02.
Consequently, in this plant, urea production of up to
7,500 T/D is possible.
A continuous urea production amount when the ammonia
synthesis facility of the A system is shut down is shown in
25 FIG. 5.
Even if the A system is shut down, the B system can
continue normal production, thereby enabling to produce urea
in an amount of 3,970 T/D.
Further, recovered CO2 is supplied to the A system along
30 with the supply of liquefied ammonium, thereby enabling to
produce urea in an amount of 1,114 T/D.
As a result, conventionally, when the A system is shut
down, the urea production amount is only 3,970 T/D by the B
system. However, because urea in an amount of 1,114 T/D can
be produced continuously in the A system, a total amount of
production becomes 5,084 T/D, and thus a considerable
lncrease in the production amount can be achieved with
respect to a case where the A system is shut down (3,970
5 T/D).
In this manner, according to the present embodiment,
when urea is produced from CO2 and ammonia, in a case where
at least two systems of the urea production plants are
arranged in parallel, when the ammonia synthesis facility
10 10A of one of the systems is shut down, liquefied ammonia
stored in the shut down system is used, the C02 recovery
amount in the C02 recovery facility 23 in the ammonia
synthesis facility 10B of the other system is increased, and
the increased recovered COz and the liquefied ammonia can be
15 used to continue urea synthesis in the urea synthesis unit
30A1 cvcn in thc shut down system.
As a result, the remaining one of the two systems is
normally operated to perform urea synthesis, and urea
synthesis can be also continued until restart even in the
20 urea production plant of the one system, which has been
conventionally shut down, thereby enabling to avoid a
considerable decrease in the production amount throughout
the year.
At the time of resuming operations of one of the
25 systems after being shut down, because the primary reformer
14A in the ammonia synthesis facility of the A system first
starts to operate, even if a device on a downstream side
thereof has not yet been operated, C02 can be recovered from
the combustion flue gas 22 of the reforming device 14.
30 Second embodiment
An operation method of a urea production plant
including multiple systems according to a second embodiment
of the present invention is explained with reference to the
drawings. FIG. 6 is a schematic diagram of the urea
production plant including multiple systems according to the
second embodiment (in a normal operation state). FIG. 7 is
a schematic diagram of the urea production plant including
multiple systems according to the second embodiment (in a
5 state where one system is shut down). Constituent elements
in the second embodiment that are identical to those in the
first embodiment are denoted by like reference signs and
explanations thereof will be omitted.
In the first embodiment, the C02 recovery facility 23 is
10 provided only in the B system; however, in the present
embodiment, a C02 recovery facility 23A is provided in the A
system, and a CO;! recovery facility 23B is provided in the B
system.
According to the present embodiment, in both the A
15 system and the B system, when the ammonia synthesis facility
10A or 10B is shut down, the both systems can complement
each other.
In FIG. 7, recovered C02 is temporarily supplied to the
removed C02 supply line L3 of the A system from the B system
20 via the emergency C02 supply line L5 for supplying recovered
C02 (the thick line L5 in FIG. 7) .
On the other hand, in an opposite case where the B
system is shut down, recovered C02 can be temporarily
supplied to the removed COz supply line L3 of the B system
25 Lrom the A system via the emergency Con supply line L5 for
supplying recovered Con (the dotted line L5 in FIG. 7).
As a result, the both systems can complement each other.
Third Embodiment
3 0 An operation method of a urea production plant
including multiple systems according to a third embodiment
of the present invention is explained with reference to the
drawings. FIG. 8 is a schematic diagram of the urea
production plant including multiple systems according to the
third embodiment (in a normal operation state). FIG. 9 is a
schematic diagram of the urea production plant including
multiple systems dccor diriy Lu the third embodiment (in a
state where one system is shut down) . Constituent elements
5 in the third embodiment that are identical to those in the
first embodiment are denoted by like reference signs and
explanations thereof will be omitted.
In the first embodiment, the COz recovery facility 23 is
provided only in the B system; however, in the present
10 embodiment, three systems (A to C systems) are arranged, and
a C02 recovery facility 23 that recovers C02 in the
combustion flue gas 22 from the B system and the C system is
provided.
In the present embodiment, because recovered C02
15 recovered by the C02 recovery facility 23 is supplied to each
of the urea synthesis units 30A1, 30A2, 30B1, 30B2, 30C1, and
30C2, even if any of the ammonia synthesis facilities 10A to
10C is shut down in the A to C systems, these systems can
complement each other.
2 0
Fourth Embodiment
An operation method of a urea production plant
including multiple systems according to a fourth embodiment
of the present invention is explained with reference to the
25 drawings. FIG. 10 is a schematic diagram uf the urea
production plant including multiple systems according to the
fourth embodiment (in a normal operation state). FIG. 11 is
a schematic diagram of the urea production plant including
multiple systems according to the fourth embodiment (in a
30 shut down state). Constituent elements in the fourth
embodiment that are identical' to those in the first
embodiment are denoted by like reference signs and
explanations thereof will be omitted.
In the first embodiment, a case where the ammonia
synthesis facility is shut down in multiple systems has been
explained. However, in the present embodiment, even when
the ammonia synthesis facility in one system is shut down,
urea production can be performed.
5 As shown in FIG. 30, a liquefied C02 storage facility 31
is provided on a downstream side of the C02 recovery facility
23, so that recovered Con recovered by the C02 recovery
facility 23 is liquefied and stored.
As a result, even when the ammonia synthesis facility
10 10 is shut down, the stored COz from the liquefied C02
storage facility 31 can be used to continue urea production
in the urea synthesis units 301 and 302.
Furthermore, in the present embodiment, the recovered
C02 liquefied and stored is used. However, C02 in con&ustion
15 flue gas discharged from an external plant other than the
ammonia production facility can be recovered separately by a
CO2 recovery device, and the recovered C02 can be supplied
from outside to the urea synthesis unit.

WE CLAIM:
1. An operation method of a urea production plant including
multiple systems, at a time of producing urea by using a
urea synthesis plant that includes: an ammonia synthesis
facility including a reforming device having a reforming
furnace that reforms natural gas to hydrogen (Hz) and
carbon monoxide (CO) by using water vapor, a CO-shift
converter that converts carbon monoxide (CO) in reformed
gas to carbon dioxide, a carbon-dioxide removal device
that removes obtained carbon dioxide (Con) in the
reformed gas, a synthesis gas compressor that compresses
synthesis material gas containing hydrogen and nitrogen,
from which carbon dioxide has been removed by the
carbon-dioxide removal device, and an ammonia synthesis
reactor that synthesizes ammonia from compressed
synthesis material gas; a liquefied ammonia storage
facility that branches ammonia obtained by the ammonia
synthesis reactor from an ammonia supply line for
supplying ammonia to a urea synthesis unit and stores a
part of synthesized ammonia in a liquefied state; a
carbon-dioxide recovery facility that recovers carbon
dioxide in fuel flue gas from the reforming furnace; and
a carbon-dioxide supply line for supplying the removed
carbon dioxide (removed COL) and the recovered carbon
dioxide (recovered COz) to a urea synthesis unit,
comprising :
providing at least two systems of the urea
synthesis plants;
storing a predetermined amount of obtained ammonia
in a liquefied state in the liquefied ammonia storage
facility;
when a trouble occurs in the ammonia synthesis
facility of one of the systems and production of ammonia
is stopped,
temporarily supplying carbon dioxide (recovered
C02) recovered by the other system to a CO2 supply line
of the shut down system via an emergency CO2 supply line
in order to supply the temporarily supplied CO:! to the
urea synthesis unit;
supplying a predetermined amount of liquefied
ammonium stored in the shut down system from an ammonia
supply line to the urea synthesis unit;
producing urea by using the temporarily supplied
C02 and stored liquefied ammonia even in the shut down
system, thereby enabling to perform a continuous
operation when the ammonia synthesis facility is shut
down.
15
2. The operation method of a urea production plant
including multiple systems according to claim 1, wherein
the carbon dioxide recovery facility recovers
recovered C02 to a maximum extent.