AMMONIA SYNTHESIS PROCESS

METHODE DE SYNTHESE DE L'AMMONIAC

English Abstract

A B S T R A C T O F T H E D I S C L O S U R E

A catalytic gas synthesis process is described which utilizes four
fixed radial flow beds of gas synthesis catalyst in two reactor vessels.
The process is particularly suited to ammonia synthesis, and has the
advantages of attaining lower equilibrium temperatures than processes using
conventional technology, and of producing high pressure steam by utilizing
the heat of the exothermic catalytic reaction. A novel radial-flow gas
synthesis reactor is also disclosed.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a process for the production of ammonia which comprises a series of
process steps including producing a synthesis gas containing a mixture of
hydrogen and nitrogen, the improvement which comprises:
reacting said hydrogen and nitrogen in an ammonia synthesis converter
to produce an ammonia product wherein said converter comprises a primary
reaction vessel having at least two radial flow catalytic reactor beds with
interbed heat exchange means; a secondary reaction vessel having at least
one radial flow catalytic reactor bed; and separate high temperature level
heat recovery means positioned between said primary and secondary reaction
vessels; or
said converter comprises a primary reaction vessel having a single
radial flow catalytic reactor bed; a secondary reaction vessel having at
least two radial flow catalytic reactor beds with interbed heat exchange
means; and separate high temperature level heat recovery means positioned
between said primary and secondary reaction vessels.

2. The process according to claim 1 wherein said primary reaction vessel
comprises three radial flow catalytic reactor beds and which further
comprises a first heat exchange means between the first catalytic reaction
bed and the second catalytic reaction bed and a second heat exchange means
between the second catalytic reaction bed and the third catalytic reaction
bed; and wherein said secondary reaction vessel comprises one radial flow
catalytic reactor bed.



17


3. In a process for the production of ammonia which comprises a series of
process steps including producing a synthesis gas containing a mixture of
hydrogen and nitrogen and reacting the synthesis gas so produced in an
ammonia synthesis converter vessel having at least two catalytic reaction
beds, the improvement which comprises:
dividing said synthesis gas into three separate feedstreams;
directing one feedstream to an indirect heat exchanger located between
the first and second of said catalytic reaction beds;
directing a second feedstream to an indirect heat exchanger located
downstream from the second of said catalytic reaction beds;
directing the remaining feedstream to an annular indirect heat
exchanger channel about the interior of said converter;
combining said one feedstream, said second feedstream, and said
remaining feedstream into a single feedstream;
passing said single feedstream radially through one of said catalytic
reaction beds;
passing the effluent of said bed through an indirect heat exchanger
and radially through another of said catalytic reaction beds;
passing the effluent from the second catalytic reaction bed through an
indirect heat exchanger located downstream from the second of said
catalytic reaction beds; and
removing the resulting stream from said converter vessel and passing
said stream through a separate high temperature level heat recovery means
located downstream of said converter vessel.

4. The process according to claim 3 wherein said ammonia synthesis
converter comprises two reaction vessels the first of which contains in



18

downstream order a first catalytic reaction bed, a first indirect heat
exchanger, a second catalytic reaction bed, a second indirect heat
exchanger, and a third catalytic reaction bed, and the second vessel
contains a fourth catalytic reaction bed, all of said catalytic beds being
designed as radial flow beds so that the gas passing through the beds
travels from the exterior to the interior of each reaction bed.

5. A high pressure reactor for carrying out catalytic gas synthesis
comprising a pressure shell, an outer, tubular chamber disposed within said
pressure shell and defining an outer annular cooling channel between said
outer tubular chamber and said pressure shell; an inner tubular chamber
disposed within said outer tubular chamber and defining an inner annular
gas channel between said inner tubular chamber and said outer tubular
chamber; first and second heat exchangers adapted for indirect heat
exchange of gas streams and being disposed separately and vertically within
said inner tubular chamber; first, second and third annular-shaped catalyst
beds disposed separately and vertically within said inner tubular chamber,
each said catalyst bed being adapted for housing solid catalyst particles
and for radial flow of gas therethrough, inwardly from the outer annular
surface of said catalyst bed; first tube means for passing a first reactant
gas stream from one end of said inner tubular chamber to said first heat
exchanger, said first exchanger being positioned at the opposite end of
said inner tubular chamber; second tube means for passing a second reactant
gas stream to said first catalyst bed; first catalyst bed effluent means
for directing effluent gas from said first catalyst bed to said first heat
exchanger for indirect heat exchange with said first reactant gas stream
and thence as feed to the outer surfaces of said second annular catalyst


19

bed; second catalyst bed effluent means for directing effluent gas
withdrawn from said second catalyst bed to said second heat exchanger for
indirect heat exchange with said second reactant gas stream and thence as
feed to the outer annular surfaces of said third catalyst bed; second
exchanger effluent means for passing said second reactant gas stream from
said second heat exchanger as additional feed to said first catalyst bed
along the outer annular surfaces thereof; third tube means for supplying a
third reactant gas stream to said annular cooling channel for cooling of
said outer tubular chamber and thence into said inner annular gas channel
for passage to said first catalyst bed as additional feed thereto along the
outer annular surfaces thereof; and third catalyst bed effluent means for
recovering effluent gas from said third catalyst bed and for withdrawal of
said recovered effluent gas from said reactor as a gaseous product stream;
said second catalyst bed, said second heat exchanger and said third
catalyst bed being positioned in that order from said first catalyst bed
toward said one end of said inner tubular chamber.

6. The apparatus according to claim 5 wherein said first heat exchanger
is positioned within said first catalyst bed.

Description

~000~3


1 This invention relates to process and apparatus useful in catalytic
2 gas synthesis reactions, and more specifically to process and apparatus3 useful in the synthesis of ammonia.
4 Generally, the manufacture of ammonia consists of preparing an ammonia
synthesis gas from a nitrogen source, usually air, snd from a hydrogen
6 source, which is conventionally either coal, petroleum fractions, or
7 natural gases. In the preparation of ammonia synthesis gas from natural8 gases, for example, a raw (that is, hydrogen-rich) synthesis gas is formed
9 by first removing gaseous contaminants such as sulfur from the natural gas
by hydrogenation and adsorption, and then by reEorming the contaminant-free
11 gas. The carbon monoxide in the raw qynthesis gas is converted to carbon
12 dioxide and additional hydrogen in a shift conversion vessel, and the
13 carbon dioxide is removed by scrubbing. Further treatment of the raw
14 synthesis gas by methanation may be used to remove additional carbon
dioxide and carbon monoxide from the hydrogen rich gas, resulting
16 subsequèntly in an ammonia synthesis gas containing approximately three17 parts oÇ hydrogen and one part of nitrogen, that is, that 3:1
18 stoichiometric ratio of hydrogen to nitrogen in ammonia. The ammonia
19 synthesis gas is then converted to ammonia by passing the ammonia synthesis
gas over a catalytic surface based on metallic iron (conventionally
21 magnetite) which has been promoted with other metallic oxides, and allowing
22 the ammonia to be synthesi~ed according to the following exothermic
23 reaction:
24 N2 + 3H2 - -) 2NH3
There are a number of exampleg of ammonia synthesis reactors in the
26 literature. Generally, they can be divided into one of three groups
27 according to the direction in which gases are allowed to pass through the
.,,

1~000~3

1 respective catalyst beds: transversely, axially or radially. Dealing
2 first with the transverse reactors, V.S. Patent 3,440,021 discloses the use
3 of a single horizontal catalyst vessel wherein the fresh synthesis gas~4 feedstream is pflssed through the catalyst layers in the transverse
direction relative to the length of the reactor, that is, through each
6 catalyst layer downwardly from above and serially through each following
7 interposed heat exchanger upwardly from below. Annular cooling gas is
8 passed serially through each of the main heat exchangers before ultimately
9 passing into a first catalyst bed.
U.S. Patent 3,472,631 discloses another transverse reactor in which
11 the reactant gases pas~ transversely through each catalyst bed. Again,12 annular cooling gase~ are passed first into the heat exchanger within the
13 reactor before entering any of the catalyst beds.
14 Axial flow reactors are illustrated in numerous publications. Forexample, H.~. Graeve, in '~igh Pressure Steam Equipment for a Low Energy
16 Ammonia Plant", Chemical Engineer ng Progress, pages 54-58 (October 1981)
17 discloses ta~ Figure 2) a typical axial flow reactor. Other axial flow18 reactors are disclosed in U.S. Patent 3,492,099, which employs a plurality
19 of axial-flow catalyst beds and which provides annular cooling gas which is
first passed to an interstage heat exchanger before ultimately being passed
21 into contact with the catalyst.
22 U.S. Patent 3"'21,532 for an ammonia synthesis system, discloses the
23 use of dual converter vessels, each containing a single catalyst bed,
24 through which a synthesis gas (or partially synthesized gas) stream flows
axially. Following passage through the second converter vessel, the
26 effluent ammonia gas stream is passed through a steam generator wherein the



~t
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~20(~0~3


1 effluent is cooled by generating steam for use in ~he reforming of the
2 feedstock materials.
3 U.S. Patent 4Jl809543 discloses means for achieving low pressure drop
4 in an ammonia synthesis reactor operating at a pre~sure of 100-500 atm.abs. by utilizing parallel axial synthesis gas flow catalyst beds: four
6 beds in a primary vessel containing a single heat exchanger, ancl two beds
7 in a secondary vessel with a steam generator positioned between the two reactor vessels.
9 U.S. Patent 3,663,179 employs an axial flow reactor with a single
catalyst bed.
11 Radial flow reactors are themselves divided into two groups. The
12 first group of radial flow reactors directs the reactant gases outwardly
13 from the center of the reactor through the catalyst beds and then withdraws
14 the effluent ga~es from each catalyst bed for further trestment along the
outer surfaces of each bed. In the second group of radial reactors J ~he
16 reactant gases sre passed to each bèd along the outer surfaces and are
17 passed inwardly through the catalyst bed, being ultimately withdrawn from
18 the inner surfaces for further treatment.
19 U.S. Patent 4~181~701J for an apparatus and process for the synthesis
of ammoniaJ discloses the use of an ammonia converter wherein the synthesis
21 gas process stream passes in succession radially inwardly through a first
22 catalyst bedJ a central heat exchangerJ and radiallyJ inwardly through a23 second cAtalyst bed. Annular cooling gas is first pss~ed to the main heat
24 exchanger and then to the first catalyst bed as a portion of the feed
the~eto.
26 A radial ammonia converter system i~ descr;bed in U.S. Patent
27 ~ 4,230,669 which utilizes three radial flow catalyst beds in either two or


~ 3 ~

~0~0~3

1 three converter vessels. Catalyst bed inlet temperature control to the
2 second and third beds is accomplished by partial by-passing of the first3 and second catalyst bed effluents around the heat exchanger integrated with
4 each bed, with the feed gas flowing in series through these interchangers.
S Fresh annular cooling gases are not employed. U.S. Patent 4,230,680 is
6 directed to a method of heat control and is related to U.S. Patent
7 4,230,669 discussed above.
8 U.S. Patent 4,101,281 discloses a radial flow reactor with two
9 catalyst beds and a tube bundle heat exchanger for concurrent generation of
steam within the reactor vessel.
11 British Patent 1,118,750 relates to a reactor housing,a radial flow
12 reactor and a heat exchanger. Annular cooling gases are passed to the heat
13 exchanger before entering the catalyst bed. British Patents 1,204,634 and
14 1,387,044 employ a reactor shell containing three catalyst beds and at
least one heat exchanger. In the British Patent 1,204,634, two of the
16 three catalyst beds are axial flow beds, with a third bed being radial
17 flow. British Patent 1,387,044 passes annular cooling gases to a main heat
18 exchanger and thence serially passes these gases through additional
19 exchangers before entering one of three radial flow catalyst beds. The
present invention is generally directed to an improved process and
21 apparatus for the production of gaseous products such as ammonia by
22 catalyticj exothermic gaseous reactions and is specifically directed to an
23 improved process which utilizes a gas-phase catalytic reaction of nitrogen
24 and hydrogen for the synthesis of ammonia. This improved process for the
production of a~monia utilizes an ammonia converter apparatus designed to
26 comprise four radial flow beds of catalyst in two reactor vessels.



~ 4 -
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1 The ammonia synthesis process of the present invention, which utilize3
2 four fixed radial flow beds of ammonia synthe~is catalyst in two ammonia3 converter ve3sels, overcomes many of the faults of the ammonia synthesis4 processes that utilize either axial flow or fewer catalyst beds. The
radial flow cataly~t bed design utilized in the present process provides a
6 reaction kinetics advantage over an axial flow catalyst bed design. Due to
7 the smaller pressure drop which occurs in a radial designed bed, the more
8 preferred smaller particles of catalyst may be used, whereas they would
9 cause excessive pre~sure drop in an axial flow bed. Also, the radial bed's
inflow nature maximizes gas velocity near the bed outlets, minimizing the
11 potential for undesirable backmixing in regions where the gas is close to
12 equilibrium.
13 The ammonia synthesis process of the present invention, which utilizes
14 four fixed radial flow beds of ammonia synthesis catalyst in two ammonia
converter vessels, also allows the converter to follow the ideal kinetic
16 temperature proEile much more closely than is possible with fewer catalyst
17 beds, as for example with the two catalyst beds in series as described in
18 U.S. Patent 3,721,532. The closer the converter approache~ the optimum
19 kinetic temperature profile, the less catalyst is required to achieve the
same conversion levels, or alternatively, substantially higher conversion
21 levels can be reached over comparable amounts of catalyst. Furthermore,22 while the operatin~ pressure range for axial catalyst beds is high in the
23 process disclosed in the process of U.S. Patent 3,i21,532 (about 88 to 307
24 atmospheres), and in the process disclosed in U.S. Patent 4,180,543
~ (100-500 atmospheres), the ammonia synthesis process of the present
26 invention is capable of operation at much lower operation pressures as
27 outlined in the Table below.


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~00073


1 FIG. 1 is a schematic fLowsheet of an ammonia synthesis process
2 utilizing the ammoni~ reactor of the present invention;
3 FIG. 2 i9 a ~ectional elevation flow diagram of the first a~monia
4 reactor vessel showing details of the catalyst beds and heat exchangers; and
6 FIG. 3 is a sectional elevation flow diagram of the second ammonia
7 reactor vessel showing details of the catalyst bed.
8 The apparatus of this invention will be described below particularly
9 in relation to its use in the synthesis of ammonia. However, it will be
understood that the apparatus is useful in any catalytic, exothermic gas
11 synthesis reaction.
12 Referring to the drawings, and specifically to FIG. 1, the ammonia13 converter of the present invention comprises two ammonia synthesis reactor
14 vessels, a primary reactor vessel generally indicated by the numeral 10,
and a ~econdary reactor vessel generally indicated by the numeral 20.
16 Located between the primary snd sec~ndary reactor vessels is a third unit,
17 generally described as an indirect steam generator 30, for high temperature
18 level heat recovery.
19 An ammonia synthesis converter feedstream 1, comprising hydrogen and
nitrogen, illustrated by assuming the ammonia stoichiometric ratio of 3:1,
21 having approximately 6 mole percent (argon plu9 methane) inerts and being
22 at approximately a, 600 psia average converter pressure, enters the
23 converter feed/effluent heat exchanger, generally indicated by the numeral
24 60, where the ammonia synthesis converter feedstream is indirectly heated
~ by cooling converter effluent 53. The now heated feedstream is divided
26 into three separate streams. Stream 2 is directed into the heat exchanger
27 12 located between the first catalytic reactor bed 11 and the second


~ 6 -



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:120~0';'3


1 catalytic reactor bed 13; and stream 3 is directed into the heat exchanger
2 14 located between the second catalytic reactor bed 13 and the third
3 catalytic reactor bed 15. As will be di~cussed later, streams 2 and 3 are
4 used a~ cooling fluids in indirect heat exchangers 12 and 1~, respectively.
The tbird stream, stream 4, is used for annular cooling of the primary
6 reactor vessel 10. The actual design of the individual internal components
7 of the primary reactor vessel 10 will become more apparent by referring to
8 FIG. 2.
9 After passing through indirect heat exchangers 12 and 14, and the
lQ annular cooling channel 113, (as shown in FIG. 2) streams 2, 3 and 4,
11 respectively, are combined and the combined straam 5 is directed into the
12 first catalytic reactor bed 11. The temperature of the reacted gas stream
13 6 leaving bed 11 is increased as a result of the exothermic ammonia
14 synthesis reaction in the first catalytic reactor bed. The reacted gas
stream 6 next passes through indirect heat exchanger 12 and is cooled by
16 indirect heat exchange with stream 2 to the required optimum feed
17 temperature of the second catalytic reactor bed 13. Similarly, the
18 temperature of the reacted gas stream 7 leaving bed 13 is increased as a
19 result of the exothermic ammonia synthesis reaction taking place in bed 13
and is cooled by indirect heat exchange with stream 3 to the required
21 optimum feed temperature of the third catalytic reactor bed 15. The cooled
22 gas stream 7a is withdrawn from exchanger 14 for feed to bed 15.
23 The effluent from bed 15, which now comprises approximately 7-10 mole
24 percent ammonia, 60-66 mole percent hydrogen, and 20-22 mole percent
nitrogen, is removed fsom primary vessel 10 as stream 8 and is cooled to
26 the feed temperature of the fourth catalytic bed 21 by steam production in
27 indirec~ ~team generator 30 which comprises a boiler feed water inlet 31


-- 7 --



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1200~73


1 and a steam outlet 32. Although described a~ an indirect steam generator,
2 the numeral 30 could also indicate other means of high temperature level3 heat recovery such as a steam superheater or high pressure boiler feedwater
4 heater. Steam generation, e3pecially at a high pressure level, is a
particularly advantageous mode of interbed cooling because it permits
6 recovery of waste heat at an energy efficient high temperature level, which
7 becomes increasingly difficult to do using the final reactor effluent
8 (stream 9) as higher overall conversion levels, and correspondingly
9 relatively low outlet temperatures, are achieved. Furthermore, by
physically separating indirect steam generator 30 from the
ll catalyst-containing vessels, maintenance of the generator is simplified,
12 and safety factors are improved by minimizing the risk of boiler water
13 leakage into the reduced synthesis catalyst.
14 Stream 8a i3 withdrawn from indirect steam generator 30 and is next
passed through a water knock-out drum 40 which is provided to ensure that
16 no liquid water (as would occur in the case of a tube rupture in generator
17 30) is able to enter the catalyst bed 21 in the secondary reactor vessel
18 20. If a tube rupture does occur, the liquid water carried in line 8a
19 would be removed from the system along line 41 to a blowdown drum or other
conventional system tbat could safely handle any inadvertent 1O88 of
21 synthesis gas.
22 After passing through the knock-out drum 40, stream 8a, which ha~ been
23 cooled by steam generator 30 to the optimum reaction feed temperature,
24 enters the fourth catalytic reactor bed 21 contained in the secondary
reactor vessel 20. This secondary reaction vessel may be conveniently
26 designed as a hot walled inflow radial reactor, that is a vessel as shown
27 in FIG. 3, and having a cylindrical pressure resist~nt vessel ~hell 300

-- 8 --

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1200073

1 having a centrally located outlet aperature 305 at the outlet end, having a
2 full bore closure member 301 with a centrally located inlet aperature 3023 for introducing the gaseous feedstream into the reactor vessel at the inlet
4 end of the vessel. The interior chamber of shell 300 contains a
cylindrically shaped catalyst cartridge 303 arranged coaxially within the
6 chamber. The catalyst cartridge is designed to have a gas permeable outer7 cylindrical wall 304, a gas permeable inner cylindrical surface 307 defined
8 by a bore 306 extending through, and along the axis of the catalyst
9 cartridge 303 and having a gas impermeable seal 308 at one end thereof
(preferably at the upper end as shown).
11 In manufacture, the catalyst cartridge 303 is sized to be less in
12 diameter than the interior diameter of the vessel shell 300, and to be of a
13 height less than the interior depth of the vessel shell 300. The open end14 of bore 306 is manufactured to allow alignment of the open end with the
outlet aperature 305. The uppermost (inlet) circular surface 309, and the
16 lowermost (outlet) circular surface 310 are gas impermeable.
17 When placed within the vessel shell 300, the catalyst cartridge 303
18 will be aligned coaxially with the outlet bore 305. Because the diameter
19 of catalyst cartridge 303 is less than the interior diameter of the vessel
shell 300, an annular channel 311 will exist between the gas permeable
21 circumferential surface wall 304 of the cartridge and the interior wall of
22 the shell. Also, because the height of the cartridge 303 i9 less than the23 interior depth of the vessel shell 300, a header space 312 will be formed24 between the inlet circular surface 309 of the cartridge 303, and the
interior facing surface of bore closure member 301.
26 The size of the annular channel 311 and header space 312 is not
27 critical to this invention.


s _ g _



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lZ000~3

1 The gas stream exiting the knock-out drum 40 enters the secondary
2 reactor vessel 20 through inlet port 302. Once in header space 312, the3 gas flows radially outward and downward through the annular channel 311.
4 The gas will then flow radially inward through the gas permeable
circumferential walls 304 of the catalyst cartridge 303, through catalyst
6 bed 21, into the internal cartridge bore 306, and exit the secondary vessel
7 20 through outlet port 305 as stream 9.
8 After passing through the secondary vessel 20, the gas stream 9, which
9 has been elevated in temperature because of the exothermic reaction
occurring in catalytic bed 21, is cooled by generating steam in indirect
11 steam generator 50, which comprises a boiler feed water inlet 51 and a
12 steam output 52. After passing through indirect steam generator 50, the13 now cooled gas stream 53 is cycled through heat exchanger 60, where further
14 heat i3 released to the incoming synthesis converter feedstream 1. After
passing through heat exchanger 60, the effluent stream 61 enters a cooling
16 and ammonia separation system, which may be of any type such as the
17 conventional systems of compression refrigeration, absorption
18 refrigeration, or water absorption~
19 One embodiment o the primary reactor vessel 10 of the present
invention is ~hown in FIG. 2. It comprises a cylindrical pressure
21 resistant vessel shell 100 having a full bore closure member 101 with a22 centrally located aperature 102 at its uppermost end by which stream 4
23 ~ enters the primary reactor vessel (aperature 102, although shown in FIG. 2
24 as described, may al~o be located eccentrically in member 101, or in shell
100 80 as to terminate into header space 119). The lowermost end of shell




26: 100 also has a centrally located aperature 103 through which passes a
27 coaxial gas tubing assembly 104... This assembly compri~es an outer tube 105

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-- ~2~ 3

1 for product gas stream 8 to exit the vessel, an inner tube 106 for gas
2 stream 2 to enter vessel 10, and an intermediate tube 107 for gas stream 3
3 to enter vessel 10.
4 Within shell 100, interior baffle cartridge 114 is spaced from the
inner-facing surface of closure member 101 to form a top header space 119
6 between the uppermost end 115 of cartridge 114 and the inner-facing surface
7 of closure member 101, and also coaxially spaced from the inner-facing
8 walls of shell 100 defining an annular gas channel 113. The lowermost end
9 of cartridge 114 has an opening 116 of sufficient diameter to allow for
psssage of coaxial gas tubing assembly 104, and gaseous material in channel
11 113 to enter the interior of cartridge 114.
12 The interior of cartridga 114 is comprised of inner baffle housing
13 114a defining upper header space 112 and a lower header 6pace 120, inner
14 baffle housing 114a being also positioned along the longitudinal axis of
cartridge 114. ~ith inner baffle housing 114a four individual annualar
16 units are positioned in stacked arrangement. These units, beginning at the
17 lowermost end of housing 114a, are the third catalytic reactor bed 15,
18 indirect heat exchanger 14, second catalytic reactor bed 13, and a fourth
19 unit comprising an annular first catalytic reactor bed 11 and an indirect
heat exchanger 12 located within bed 11 along its core axis. An additional
21 annular channel 118 is located immediately adjacent to, and is defined by,
22 exterior walls o~ :inner housing 114a and the interior walls of baffle
23 cartridge 114. Thiis channel 118 extends from lower header space 120 to
24 upper header space 112.
Each indirect heat exchanger (12 and 14) as illustrated is of the type
26 known as tube-in-shell wherein tubes 111 carrying the cooler fluid to the
27: ~ exchanger are positioned vertically through the exchanger shell, and



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horizontally positioned baffles 108 in the exchanger shell are used to
2 direc~ the fluid to be cooled around and abou~ the tubes 111 within the
3 shell. The actual design of the type of heat exchanger, however, is a
4 matter of sound engineering practice and other types may obviously be
employed depending upon the various parameters of the systems design.
6 Each catalytic reactor bed has an external cylindrical gas permeable
7 outer wall 109 and an in~ernal cylindrical gas permeable inner wall 110
8 which allows for radial flow of reactant gases from the exterior to the
9 interior of each catalytic reactor bed. Each catalytic bed is also 90
constructed to have an exterior single closed end annular channel (121 of
ll bed 15; 131 of bed 13; and 141 of bed 11) defined by the inner walls of
12 baffle housing 114a and the respective gas permeable wall 110 to direct the
13 flow of gas radially into the catalytic reactor bed. Each catalytic bed is
14 al9o 90 constructed to have an interior single closed end annular channel
(123 of bed lS; 133 of bed 13; and 143 of bed 11) having a channel opening
16 (124 of bed 15; 134 of bed 13; and 144 of bed 11) extending about the
17 circumference of each bed to direct the flow of gas out of the catalytic
18 bed.
19 Inner baffle housing 114a is provided with opening 142 therein
adjacent to the lower portion of annular catalyst bed 11 about the outer
21 circumference thereof to permit gas stream 5 to pass into annular channel
22 141 from inner chamnel 118. Inner baffle housing 114a is also provided23 with opening 150 adjacent to the lower portion of second catalyst bed 113
24 and the upper portion of second heat exchanger 14, said opening 150
extending about the circumference of said catalyst bed 13 and heat
26 exchanger 14 90 as to permit heated fluid to be withdrawn from the tube
27 side of exchanger 14 upwardly înto and through inner gas channel 118.


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~20~73

1 In the process, according to the present invention, the cold inlet ga~
2 stream 4 enters the primary reactor vessel 10, is diverted as indicated by
3 the diagram arrows radially outward in top header apace 119 to annular4 channel 113, and flows downward in this channel to effect annular cooling
of the reactor vessel. From the lowermost end of channel 113, the gas
6 stream 4 enters lower header space 120 and then passes upwardly through7 inner channel 118, past the third catalytic reactor bed 15 and indirect
8 heat exchanger 14. Stream 3 enters the primary reactor vessel 10 through
9 intermediate tube 107 and flows upward past the inner circumferential
interior of the third catalytic reactor bed 15, and through tubes 111 of
11 indirect heat exchanger 14. After passing through indirect heat exchanger
12 14, where stream 3 cools the effluent from the second catalytic reactor bed
13 13, stream 3 is mixed with stream 4 and continues to flow upwardly in
14 channel 118 past the second catalytic reactor bed 13. Stream 2 enters the
primary reactor vessel 10 through inner tube 106 and flow3 upwardly past
16 the third catalytic reactor bed 15, indirect heat exchanger 14, catalytic
17 reactor bed 13, and at the uppermost end of inner tube 106, through tubes
18 111 of indirect heat exchanger 12, where stream 2 cools the effluent from
19 the first catalytic reactor bed 11. After passing through indirect heatexchanger 12, stream 2 enters upper header space 112 where it is diverted
21 radially outward to annular gas channel 118, and flows downwardly in the
22 channel:118 to opening 142 where stream 2 is mixed with the combined
23 streams 3 and 4, thereby forming feedstream 5 which thereafter passes as a
24 ~ single stream tkrough the primary reaction vessel.
~ Tkis combined feedstream 5 enters opening 142 of bed 11 and flows into
26 exterior closed end annular channel 141 from where the stream flows
27 inwardly through wall 109, radially through bed 11, through wall 110, into


13 -

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lZ000~3


1 channel 143, and out of the bed unit through opening 144. This bed 11
2 effluent, because of the exothermic reaction taking place in bed 11, is now
3 heated to about 910F, a temperature higher than the optimum feed
4 temperature of bed 13. The bed 11 effluent is therefore caused to follow a
tortuous route through heat exchanger 12 by placement of baffle.~ 108 in
6 order to cool the bed 11 effluent (and conversely heat stream 2) to the7 optimum bed 13 feed temperature. After passing through this heat
8 exchanger, the stream is diverted outwardly through opening 132 to channel
9 131 of bed 13 from which the gas stream flows radially inwardly through bed
13 and exit into channel 133. This bed 13 effluent, becau~e of the
11 exothermic reaction taking place in the bed, is now heated to about
12 825F, a tempersture higher than ~he optimum feed temperature of bed 15.
13 The bed 13 effluent exiting through opening 134 is therefore caused to pass
14 through heat exchànger 14 where it i9 cooled by feedstream 3 to a
temperature of about 715 F. The stream exiting heat exchanger 14 passes
16 through annular opening 122 into channel 121 and from this channel
17 radially, inwardly through bed 15 and thence into channel 123 from where it
18 exits primsry vessel 10 as ammonia product stream 8 via tube 105.




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~L200073


1 The following table shows the temperatures, pressures, and ammonia
2 mole percents for a typical am~onia process carried out in accordance with
3 the process of the present invention. The numbers in parenthesis indicate
4 stream location in FIG. 1.
TABLE




7 Pressure
8 NH3(~) Temp.(F) (Psia)
10Cold Converter
11Feed* (1~ 0.10 103 618
12
13Coolant for first
14heat exchange (2) 0.10 549 615
16Coolant for second
17heat exchange (3) 0.10 549 615
18
19Annular cooling (4)
20 gas 0.10 549 615
21
22First bed gas
23feed (5) 0.10 774 612
24
25Fir~t bed effluent (6) 4.45 911 609
26
27Second bed gas feed (6) 4.45 767 605
28
29Second bed effluent (7) 6.74 824 602
31Third bed gas feed (7) 6.74 747 598
32
33Third bed effluent ~8) 8.33 786 59
34
35Fourth bed gas feed (8) 8.33 716 591
36
37Fourth bed effluellt (9) 9.57 746 588
38
39 * The cold converter feed composition used in the example discussed in
this application is 70.43 mole percent hydrogen; 23.48 mole percent

41 ~nitrogen; 1.37 mole percent argon; 4.62 mole percent methane; and 0.10
42 ~ mole percent ammonia.

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1 While the foregoing description has illustrated the lJse of an ammonia
2 Yynthesis feedstream 1 assuming a 3:1 H2:N2 ammonia stoichiometric
3 ratio, 6-percent inerts and 600 psia average converter pressure, it will be
4 readily under~tood that the process is operative with any conventional
ammonia synthesis gas feed and ammonia reaction conditions. Thus, the
6 feedstream 1 can contain up to 20-percent inerts (argon plus me~:hane) and
7 can be characterized by a H2:N2 raeio of from about 2.5:1 to 3.5:1, at
8 an average converter pres~ure of from 30 to 200 atm. The precise
9 temperatures and pressures selected for use will, of course, vary depending
on the feed composition, the degree of conversion desired, the amount and
11 type of catalyst selected and other factors; can fall outside the
12 aforementioned ranges; and can be readily determined by one having ordinary
13 skill in the art.
14 From the foregoing description, one skilled in the art can easily
aocertain the essential characteristics of this invention and without
16 departing from the spirit and scope thereof can make various changes and/or
17 modifications to the invention for adapting it to various usages and
18 conditions. Accordingly, such changes and modifications are properly
19 inte~nded to be within the full range of equivalents of the following
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