Note: Descriptions are shown in the official language in which they were submitted.
31B8~
Background of the Invention
.
1. Field of the Invention
This invention relates to ammonia converters and
is a divisional of Canadian application Serial No. 326,409,
filed April 26, 1979. Specifically, the ammonia converters
of this invention are the radial design where the ammonia
synthesis gas flows radially through the catalyst beds.
Further, the design is full flow~ meaning all the synthesis
gas feed passes through the first catalyst bed, all the
effluent from the first catalyst bed passes through the
second catalyst bed and all the effluent from the second
catalyst bed passes through the third catalyst bed~
2. Prior Art
U.S~ Patent 3,372,988 assigned to Haldor Topsoe
discloses an apparatus for ammonia gas synthesis which
includes a plurality of annular-shaped, vertically-spaced
catalyst beds through which the synthesis gas feed is passed
at least in part in a radially outward direction; temperature
control of the synthesis gas or catalyst effluent is con
trolled by the addition of quench gas. The same or an
apparatus similar to that of U.5. Patent 3~372,988 is dis~
closed in the November 1974 issue of Petroleum International,
Volume 14, in an article entitled ~Radial Converter Shows
Big Benefits for Ammonia". A modified version o~ this
~onverter, which is known as the "Topsoe" converter in the
industry~ is generally described in the May/June 1976 issue
of Nitrogen, in an article entitled "Modified Topsoe Converter
Increases Yieldsl'~ As understood, the modified Topsoe
con~erter utilizes alternating radial flow through each of
separate, annular-shaped catalytie beds. An intermediate
heat exchanger is utilized in this modified Topsoe converter
--1--
0 3l~3~
to heat a secondary quench gas for controlling the temperature
of the sy~lthesis ~as feed.
The book "~mmonia Part III", edited by A. V. Slack
and G. Russell James, published by Marcel Decker, Inc.,
1977, also illustrates Topsoe converters on pages 346-347
The Topsoe converter shown on page 346 utilizes radially
outward flow; and, the Topsoe converter shown on page 347
utilizes radially outward flow in a first bed and radially
inward flow in a second bed. A radial flow ammonia converter
designed by Chemoprojekt is illustrated on page 355 of
"Ammonia Part III". In the Chemoprojekt unit, a first heat
exchanger is positioned radially below an annular-shaped
catalyst bed and a second heat exchanger is located at th~
top of the catalyst bed, which also receives guench gas
flow. The Braun adiabatic synthesis converter illustrated
on page 365 of the same book utilizes downflow through the
catalyst bed. ~he OSW ammonia converter illustrated on page
315 utllizes interbed heat transfer with axial flow through
annular-shaped catalyst beds.
U.S. Patent 3,918,918 discloses a catalytic
reactor for processes such as ammonia synthesis which
includes a two-stage, single catalyst bed and heat exchanger
positioned within 2 single vessel. In the catalytic reactor
of U.S. Patent 3,918,918, the synthesis gas feed i5 paS5ed
through a heat exchanger and then mixed with a second feed
line priox to successively passing radially outwardly
through first and second stages of the catalytic bed. T~e
ccmbined feed gas stream is passed through the tube side of
the initial heat exchanger fox heating the entering feed gas
prior to passing to the second st~ge catalytic bed~
U.S. Patent 3,754,07~ discloses a vessel containing an
annular catalyst bed utilizing gradation of the surface oE
the catalyst bed exposed to flow for a more uni~orm dis-
tribution of gas through the bed.
U.S. Patent 3,567,404 illustrates a reactor vessel
which includes a heat exchanger and a series of catalytic
reaction beds having entrance areas disposed parallel to
the longitudinal axis of the outer and inner vessel shells
for the purpose of providing reactant gas flow through
consecutive catalyst beds in a direction perpendicular
to the longitudinal axis of the vessel. U.S. Patents
3,784,361; 3~964,169; 3,475,136; and, 3,031,274 illustrate
ammonia synthesis converters or vessels which utilize
catalyst zones providing for axial gas flow therethrough.
The utilization of annular-shaped catalyst beds for
ammonla synthesis is thus known in the art. See, in
addition, U.S. Patents 3,998,932 and 3,941,869 which
disclose catalytic processes for the synthesis of ammonia
utilizing annular-shaped catalyst beds. U.S Patents
3,944,394; 3,844,936; and, 2,27g,153 disclose the use
of annular-shaped catalyst beds in other fields.
Summary of the_Inventio_
The present invention relates to an ammonia converter,
comprising: a vessel which includes a bottom head, a main
shell and a top head; an internal annular catalyst bed
mounted in said vessel and spaced from sa;d main shell to
form an annular space between said catalyst bed and said
shell from the top to the bottom of said bed; gas transfer
means which include inlet means entering the bottom of said
vessel~ a vertical pipe section along the axis of said
--3--
3 3.3~
vessel and ~paced from said annular catalyst bed and means
for directing gas to said annular space between said
catalyst bed and said shell, and outlet means concentric
with said inlet means for removing the effluent from said
catalyst bed from said vessel.
An embodiment of the ammonia converter system of this
invention includes first, second and third annular-shaped
ammonia synthesis catalyst beds utilized in combination
with first and second heat exchange means, interchangers,
for cooling at least a portion of the effluent of the
second and first catalyst beds, respectively. Synthesis
gas flows radially inwardly through the first catalyst bed
~ to produce a first catalyst bed effluent. A first effluent
transfer means is provided for transferring the first
catalyst bed effluent to the second catalyst bed and
includes a heat exchange means or interchanger for cooling
at least a portion of the first catalyst bed effluent
prior to introduction of the effluent into the second
catalyst bed. ~ second effluent transfer means is
; 20 provided for directing the second catalyst bed effluent
to the third catalyst bed. The second effluent transfer
means includes a first heat exchange means or interchanger
which is positiioned adjacent to the second catalyst bed
for cooling at least a portion of the second catalyst bed
effluent prior to introducton of the effluent into the
third catalyst bed~ Each of the first and second effluent
transfer means may further include flow control means for
bypassing a portion of the first and second catalyst bed
effluent past the first and second heat exchange means
or interchangers in order to control the temperature of
effluent enterin~ the second and third catalyst beds.
--4--
.
~L~3:~85~
Brief Description of the Drawings
; Fig. 1 is a process schematic for the synthesis of -~
ammonia wherein the present invention of a radial ammonia
converter system may be utilized;
Figs. 2A and 2B are upper and lower sectional views
of a first ammonia converter vessel illustrating a first
;~ embodiment of an ammonia converter system of this
invention;
Fig. 3 is a sectional view of a vessel utilized in
conjunction with the vessel in Figs. 2A and 2B or the
vessels in Figs. 6 and 7 to provide an ammonia converter
system of this invention;
-4a-
!
.
Fig. 4 is a sectional view of the support assembly for
the second interchanger and first catalyst bed of the
ammonia converter vessel of Figs. ~A and 2B;
Fig. 5 is a sectional view taken al.ong lines A-A of
Fig. 4 which includes the details of the flow control
means for the first catalyst bed effluent in -the ammonia
converter vessel of Figs. 2A and 2B;
Fig. 6 (on a sheet with F.ig. 3) is a sectional view
of a first vessel illustrating a second embodiment of an
ammonia converter system of this invention; and
: Fig. 7 is a sectional view of the second vessel of
the second embodiment of an ammonia converter system, the
vessels of Fig. 6 and 7 being used in conjunction with the
vessel of Fig. 3.
Fig. 1 is a flow diagram of a process that may be
utilized in the radial converter systems 100 and 200 of
this invention for producing ammonia from a synthesis gas
feed. Preparation of the synthesis gas feed, which is a
gas mixture of hydrogen and nitrogen, may be carried out
in a variety of known ways. Natural gas or naphtha may
be steam reformed to produce the hydrogen and nitrogen
mixture; also, the synthesis feed gas can be produced by
partial oxidation
. .
~3~
of fuel oils or coal or by simply mixing hydrogen and
nitrogen from separate sources. In any event, the synthesis
mixture is a mixture consisting essentially of hydrogen and
nitrogen in approximately a 3 to 1 ratio. ~or best results,
these two gases would be the only gases present, although in
most commercial operations, small amounts of other gases are
present.
Utilizing the process, the synthesis of ammonia is
carried out in three catalyst beds wherein the exothermic
ammonia synthesis reaction occurs to produce effluent con-
taining ammonia. The process is designed so that the tempera-
ture conditions of synthesis gas and catalyst effluent may
be optimized under changing conditions within the catalyst -~
beds or interchangers. Such temperature control is attained,
without resorting to the use of quench gas, by cooling a
portion of the effluent from each catalyst bed and mixing
the cooled portion with the remainder of the effluent prior
to entry into the next catalyst bed.
In the schematic of Fig. 1, a first heat exchanger
stage 10 may be a heat exchanger adapted to eceive on the
tube side synthesis feed gas from incoming line 11. The
exchanger 10 is used to partially raise the synthesis feed
gas to a first reaction temperature as the synthesis feed
gas flows into line 12. The synthesis gas from feed line 12
passes through line 13 and then the tube side of a fixst
process heat exchang~r or interchanger 14. The heated
synthesis gas is heated ~uxther in another heat exchanger or
interchanger 15 and exits through line 16. A bypass line 17
connects line 12 to heat exchange exit line 16 and includes
a control valve 18 for controlling the volumetric amount of
--6--
~ ~.3~8~
gas flow which bypasses the heat exchangers ~4 and 15.
Temperature monitoring instrumentation 19 (e.g. a thermo-
couple) is mounted in exit line 16 and is operably connected
~o the control valve 18 mounted in line 17 in order to
control the volume of feed gas which proceeds directly from
line 12 to line 16. Thus, the synthesis feed gas is raised
to a fixst reaction temperature.
The heated synthesis gas is d:Lrected from line 16
into the ammonia converter(s) 20. The ammonla converter(s)
20 is schematically shown (the number of vessels may be one
or two or even three) but will include three catalyst beds:
first catalyst bed 21; second catalyst bed 22 arld third
catalyst bed 23. Each catalyst b~d is annular such that the
synthesis gas passes radially therethroughO Each catalyst
bed is separate ~rom the other as illustrated schematically
at 20a and 20b. The types of catalyst utilized in catalyst
beds 21, 22, and 23 may be the iron and promoted iron cata-
lyst which are well-known in the art. The small sized
catalyst (1.5-6mm) is preferred.
The synthesis gas which has been heated to a first
reaction temperature of between 315 and 400C enters the
first catalyst bed 21 through line 16 and passes radially
through satalyst bed 21. ~s the synthesis gas passes
through the catalyst bed 21 J an exothermic reaction occurs
to pr~duce an effluent containing 4 to 8~ ammonia depending
on the specific plant designO The first effluent passes
outwardly through first catalyst bed exit line 24. The
first catalyst bed exi~ line 24 may be connected to the
shell side of the heat exchanger 15. A portion of the first
effluent is cooled in heat exchanger 15 and passes outwardly
through exit line 25. The cooled irst effluent is passed
by line 25 to ~he second catalyst bed 22.
A bypass line 26 having bypass valve 27 mounted
therein is attached to the first catalyst bed exit line 24
and to the heat exchanger exit line 25. Temperature con-
trolling instrument~tion 28 is mounted in the heat exchanger
exit line 25 downstream of line 26 and is operably connected
to the valve 27 in bypass line 26 to control the direct
transfer o first effluent from first catalyst bed exit line
24 to the heat exchanger exit line 25, thus allowing some
effluent to bypass the heat exchanger 15 as is necessary to
control the temperature of the effluent entering the second
catalyst bed 22 so that the effluent enters the second cata-
lyst bed 22 at a second reaction temperature which is at-
tained a~ a result of the mixing of the portion of the first
catalyst bed effluent cooled in heat exchanger 15 and the
remainder which bypasses the heat exchanger through line 26.
If at any time the condition of the catalyst in bed 22 re-
~uires that the second reaction temperature be higher, less
of the effluent portion is passed through the heat exchanger
15 and more of the effluent gas flows through the bypass
line 26 directly to line 25 thereby raising the second
reaction temperature.
~he first effluent which is maintained a~ a
second reaction temperature of between 315 and 400C enters
the second catalyst bed 22 through line 25 and is passed
radially therethrough. The hydrogen and nitrogen in the
ef~luent is exothermically reacted in the presence of the
catalyst therein to produce a second effluent which contains
between 6 and 10% ammonia, or an increase of 2 to 6% over
-8
3~
the amount of ammonia in the first effluent. This second
effluent exits the second catalyst bed through exit line 29.
The exit line 29 may be connected to the shell side of heat
exchanger 14 which has an exit line 30 connected to the
inlet of the third catalyst bed 23.
A portion of the second effluent is cooled in heat
exchanger 14 and exits the heat exchan~er by line 30.
bypass line 31 having bypass valve 32 mounted therein ex-
tends between the second catalyst bed exit line 29 and the
heat exchanger exit line 30 providing or the direct trans-
fer of effluent frsm the second catalyst bed 22 to line 30,
wherein a mixing of the bypassed effluent ~nd the cooled
effluent portion occurs to control the temperatuxe of the
second effluent entering the ~hird catalyst bed ~3O Suitar
ble temperature control instrumentation 33 is mounted in
line 30 in operative connection with the valve 3Z for con
trolling the amount of effluent flowing through bypass line
31.
The second effluent, after mixing in line 30 of
the part which has been cooled in the heat exchanger 14 and
the remainder which is passed directly to third catalyst bed
entry line 30 through bypass line 31, is at a thlxd reaction
temperature of between 315 and 400C. The second effluent
i5 then passed radially through the third catalyst bed 23 to
produce a third effluent which contains ~etween 8 and 14%
ammonia or a still further increase sf ammonia over the
amount in the second effluent. This third effluent exits
outwardly through ~he third catalyst bed exit line 34. The
third effluent contains ~mmonia gas generated r~m each of
the three catalytic reactions. This final effluent may then
_9_
be processed in a known manner for the recovery of the syn-
thesized ammonia. ~rior to the removal of the ammonia from
the effluent, the effluent from the third catalyst bed may
be passed through line 34 to the shell side of a heat ex-
changer 35 and then lnto line 36 which connects the shell
side of the heat exchanger 10. The heat exchanger 35 may be
connected on the tube side to various plant fluid lines 37
in order to heat other fluids such as boiler feed water as
is necessary or desirable. A bypass line 38 is connected
between lines 34 and 36 and includes control valve 39 for
bypassing the heat exchanger 35 either partially or com-
pletely. The ammonia-containing effluent in line 36 is then
passed through shell side of the heat exchanger lO and into
line 40 for direction to the subsequent recovery operations
known in the art.
Therefore, the temperature of the synthesis gas
and effluents is controlled in a closed loop system without
the use of synthesis gas feed as quench gas. In the process
described, the synthesis gas may be passed through the tube
side of heat exchangers 14 and 15; however, the heat ex-
changers 14 and 15 may utilize fluids other than the syn-
thesis gas such as plant water to cool the first and second
catalyst bed effluent. The process has specific application
to a low pressure, low energy process. The pressure used in
the process is within a pressure range of 20 to 95 atmospheresO
The synthesis pressure may range between 30 and 85 atmospheres
and may specifically be about 35 atmospheres. The utiliza
tion of a lower pressure process provides a savings in
energy due to a reduction in the capacity of compressors and
other equipment needed to maintain the synthesis gas in
the higher pressure range aboYe lO0 atmospheres.
~10--
- Referring to Figs. 2A, 2B, 3, 4 and ~, a first
embodlment 100 of a r~dial ammonia converter system of this
invention is illustrated. The radial ammonia converter
system 100 may be used to practice the process of ammonia
synthesis which has just been describ~d. The system 100
includes the vessel V-l illustrated in Figs. 2A and 2B (with
certain structural details being shown in Figs. ~ and 5) and
the vessel V-2 illustrated in Fig. 3.
Referring to Figs. 2A and 2B, the vessel V-l is
supported upon a cylindrical support assembly 101 which is
mounted on the foundation 102. The vessel V-l includes a
bottom hemispherical head 103a, a main cylindrical shell
103b and a top hemispherical head 103c. The heads 103a and
103c may be welded to the main shell 103b. Vessel V~l inlet
means 104, the synthesis gas feed inlet to the system, is a
generally L-shaped pipe section lQ5 which is mounted in
opening 103d of the vessel bottom head 103a. The pipe
; section 105 corresponds to the process flow inlet line 13 of
Fig. 1~ Vessel outlet means 106 may be a pipe section that
is positioned in opening 103e of the vessel bottom head 103a
and extends through the wall of vessel support 101 for
connection to inlet means 107 of vessel V-2 of Fig. 3. The
outlet means 106 corresponds to process flowline 30 of Fig.
1. :
~Ihe main vessel shell 103b includes openings 108
which are blind-flanged to provide access to the vessel V~
interior. The vessel shell 103b includes thermowell housings
109, 110, 111 and 112 for positioning thermocouples at
necessary locations within the vessel to record the tempera-
tures at various positions in the vessel V-l. The top
~11--
~3~8~
hemispherical head 103c has mounted ther~with thermowell
housings 113, 114 and 115.
The main vessel shell 103b and hemispherical heads
103a and 103c may be manufactured out of any suitable
material capable of withstanding the high temperatures
and/or corrosive atmospheres of catalytic reactions. If
necessary, the vessel sections 103a-c can be insulated on
the outside.
The vessel V-l has mounted therein a first heat
exchange means or interchanger 116, a second heat exchange
means or interchanger 117, first catalyst bed 118 and second
catalyst bed 119 which cooperate with a third catalyst bed
120 in vessel V-2 of Fig. 3 to form the radial am~onia
converter system 100.
A synthesis gas transfer means generally designated
) as 121 is provided for directing the ammonia synthesis gas
feed into vessel V-l and through the tube side of inter-
changer 116 and interchanger 117 for heating the gas prior
to its passing through first catalyst bed 1180 The~syn-
- 20 thesis gas transfer means 121 includes inlet pipe section
105 tFig. 2B) and the i~ternal portion of a conical support
122 on which interchanger 116 is positioned in vessel V-l,
; and which prevents comingling of shell and tube side gas
streams.
The interchanger 116 includes a tube bundle 123 which
terminates in a lower tube sheet 123a and an upper tube sheet
123b. The tube sheets 123a and 123b support the tube bundle
123 in a vertical position when vessel V-l is in its operating
position. The lower tube sheet 123a is attached directly to
the top rim of the conical support 122. A dome-shaped outlet
-12-
f 125. The upper end of conduit 125 (FigD 2A3 is attached to
a dome-shaped inlet 126 vf interchanger 117. The inter~
changer 117 is positioned on an interna:l, annular support
assembly generally designated as 127, which assembly is
illustrated further in ~igures 4 and 5.
The interchanger 117 includes a tube bundle 128
which terminates in a lower tube sheet :128a and an upper
tube sheet 128b. The lower tube sheet :128a is attached to
the dome-shaped inlet 126. The upper header 128b seats on
an upper support ledge 129 which is positioned internally of
cylindrical ~all 130 o~ support assembly 127. The area
above interchanger 117 within the cylindrical wall 130 is
referred to as chamber C-l. The area above the support
assembly 127 and the vessel top head 103c forms chamber C-2
in which the s'ynthesis gas feed reverses its upwardly axial
flow to a downward flow for radially inward flow through
first catalyst bed 118.
The synthesis gas transfer means 121 further in-
cludes the tube side of tube bundle 123, the outlet head
123c, expansion joint 124, the transfer conduit 125, the dome
inlet 126, the tube side of tube bundle 128 and chamber C-l
and chamber C-2 as formed by the support assembly 127 and
the shell 103b and top head 103c of vessel V-l. The syn-
thesis gas feed is thus introduced into vessel V-l and heated
while passing through the tubes of interchanger 116~ trans-
ferred through txansfer conduit 125, and heated still fur-
ther while passing thrcugh the tubes of interchanger 117 to
a first reaction temperature for synthesis of the hydrogen
and nitrogen to ammonia in the first catalyst bed 118.
The annular support as~embly 127 (the details of
which are shown in Figures 4 and 5) includes a first annular
-.~3-
~l3~8~
f base plate 131 which is supported on a plurality of gussets
132 attached to the i.nterior wall of the vessel shell 103b~
The gussets terminate in inwardly facing plates 13~a which
~uide and support the lower portion of :interchanger 117.
The base plate 131 has a central opening 131a and cylindri-
cal support wall 133 surrounds the open:ing 131a and extends
upwardly to the upper support ledge 1290 The cylindrical
wall 130 which extends from the uppermost portion of the
support assembly 127 extends downwardly and spaced from wall
133 approxLmately to the level of an upper annular base
plate 134. ~ cylindrical wall 135 extends between base
plate 131 and upper base plate 134 forming an annular plenum
136. Extending from the upper base plate 134 are an outer
cylindrical catalyst retainer wall 137 and an inner cylin-
drical catalyst retainer wall 138. The retainer walls 137
and 138 are permeable walls having a plurality of openings
such as a cylindrical plate having hundreds of openings to
aid in the distribution and radial flow and which may have a
screen (shown in Figs. 2A, 2B, 4 and 5) on the inner side to
maintain the ammonia synthesis catalyst between retainer
walls 137 and 138 to form the first catalyst bed 118. A top
annular plate or cover means 139 extends from outer catalyst
retainer wall 137 to within chamber C-l. A permeable plate
139a may cover chamber C-l.
The synthesis gas feed after passing through the
synthesis gas transfer means 121 is distributed in the
annular space S-l between vessel wall 103b and outer catalyst
retainer wall 137. The gas feed then passes radially through
catalyst bed 118 wherein an exothermic reaction occurs and a
first catalyst bed effluent containing ammonia flows out of
the catalyst bed 118 into a first catalyst bed effluent
transfer means generally designated 140. The transfer means
~14-
~.3~l8~3~
140 includes annular spaces S-2, S-3 and S~4. Annular space
S-2 is ~etween inner catalyst retainer wall 138 and wall
130. The flow of ~he first catalyst bed effluent is down- -
wardly until it reaches the annular space S-3 between
cylindrical wall 135 and support wall 133 where most o the
effluent flows upwardly in annular space S-4 between wall :
130 and support wall 133. At the top of support wall 133
are a plurality of openings 141 through which the first
: catalyst bed effluent passes for contact with the shell Siae :
of tube bundle 128. The effluent passes downwarclly in a
serpentine manner caused by a plurality of alternately
donut-shaped baffles 142 and disc~shaped baffles 143 as the
effluent is cooled and passes outwardly between base plate
131 and lower header 128a into a chamber C-3.
The first catalyst bed effluent transfer means 140 -~ :
further includes a first flow control means generally desig-
nated as 144 (Fig~ 2A and 5). The flow control means 144
includes an opening 145 in wall 135 wherein a portion of the
first catalyst bed effluent passes into a distribution
chamber enclosure 146 positioned in annular plenum 136.
Distribution chamber enclosure 146 is formed by base plate
131, wall 135 and vessel shell wall 103b, enclosure side
walls 146a and 146b and enclosure top wall 146c~ The enclosure
top wall 146c has an opening 146d with a valve or by-pass
control means 147 mounted therein. The valve or by-pass
control means 147 may be a damper valve or any other valve
that allows a variable flow of gas through opening 146d and
can be either automatically or manually operated. The valve
or by-pass control means 147 is set initially to allow the
design portion of the first catalyst bed effluent to by pass
--15--
the contact with the tube bundle 123. The effluent (eOg~
20~ or less~ passes thro~gh opening 145 into distribution
chamber enclosure 146 and through valve 147 into the plenum
136. A plurality of holes 131b are in base plate 131 whereby
I the effluent flows out of plenum 136 into chamber C-3 to
admix with that portion of the effluent which is cooled as
it passes in contact with the tube bundle 128. The first
catalyst bed transfer means 140 also includes temperature
control means. The temperature of the first catalyst ~ed
effluent after being mixed is measured by a thermocouple in
:~ thermocouple well 110 whereas the temperature of the efflu-
ent after leaving the catalyst bed 118 is measured by a
thermocouple in thermocouple well 111. The thermocouples
may be connected to a panel (not shown) for visual observa-
tion and manual adjustment of the valve 147 or automatically
adjusted for controlling the temperature of the first cata-
lyst bed effluent entering the second catalyst ~ed 119 by
- adjusting the amount of by-pass.
Referring to Figs. 2A and 2B, the second or lower
annular-shaped catalyst bed 119 is positioned below chamber
C-3 and is concentric with transfer conduit 125. The cata-
lyst bed 119 is formed by an annular bottom support or base
plate 148 and outer cylindrical retainer wall 149 and inner
cylindrical retainer wall 150~ The retainer walls 149 and
150, xespectively, are permeable walls constructed similarly ,~
as catalyst retainer walls 137 and 138 of catalyst bed 118,
and are mounted on base plate 148 and extend upwardly there-
from to fon~ an annular space therebetween for containing
: the ammonia synthesis catalyst similarly as first catalyst
bed 118. The base plate 148 of catalyst bed 119 is supported
-16-
-
3~
on a pluralicy of inwardly extending gussets 15~ attached 'o
the inside of main vessel shell 103b. Each of the gussets
151 terminate in an inwardly facing plate portion 151a which
serve as a support and guide to the transfer conduit 1~5.
~n annular top plate 152 is attached to both the cylindrical
walls 149 and 150 and extends radially inwardly to attach ko
a slip joint guide member 153. The slip joint member 153 is :
circular and is mounted about the transfer conduit 125 so as
to provide a seal to gas flow. The slip joint member 153
provides slight relative movement between the transfer
conduit 125 and the top plate 152 upon expansion.
The first catalyst bed effluent after passing :
through the first catalyst bed effluent transfer means 14Q,
with the cooled portion and non-cooled portion being remixed
in chamber C-3, is distributed and flows into the annular
space S-5 formed between outer cylindrical retainer wall 149
and the inside surface of vessel shell 103b. The effluent
then passes radially through second catalyst bed 119 wherein
an exothel~ic reaction occurs and a second catalyst bed
effluent flows out of the catalyst bed 119 into a second
catalyst bed effluent transfer means generally designated
154. The transfer means 154 includes annular space S-6
which is between inner catalyst retainer wall 150 and the
transfer conduit 125. The flow of the second catalyst bed
effluent is downward in space S-6 until it reaches chamber
C-4 which is the annular space surrounding the upper portion
of interchanger 116. A horizontally oriented circular plate
or barrier 155 extends from the vessel shell wall 103~ across
the tube bundle 123. The barrier 155 is positionecl approximately
midway of the tube bundle 123 and includes a plurality of
:
-17-
~3~89
~` :
openings for the tubes however it provides a barrier to
prevent vertical flow on the shell side of tube btlndle 123
between the portion above and ~he portion below the barrier
155 except through an opening 155a. The opening 155a is
positioned in the center of the barrier 155 so that effluent
flow on the upper portion of tube bundle 123 is radially in~
ward above the barrier 155 and radially outward below the
barrier 155. The effluent flows out~ard through a cylindri-
cal wall 156 having a plurality of openin~s 157 ~o a:Llow the
cooled second catalyst bed effluent to pass into chamber C-
5.
The second catalyst bed effluent transfer means
154 further includes a flow control means 158. The flow
control means l58 includes a by-pass flange assembly 159
mounted on barrier 155. The flange assembly 159 has an
opening 159a which extends between chamber C-4 and ch~mber
C-5, and mounted within the opening 159a is a by-pass valve
160. The by-pass valve 160 may be a damper valve or other
suitable type valve which is adjustable to allow a portion
~e.g. less than 20~) of the second catalyst bed effluent to
flow rom chamber C-4 to chamber C 5 without contacting the
tube bundle 123. The effluent which by-passes the tube
bundle 123 is admixed with the effluent cooled by contacting
tube bundle 123 in chamber C-5 and the admixed and cooled
second catalyst bed effluent exits the vessel V-l by line
106. The second catalyst bed effluent txansfer means 154
also includes temperature control means. The temperature of
the second catalyst bed effluent prior to entering the third
catalyst bed 120 is measured and the temperature of the
~0 effluent leaving the second catalyst bed 11~ is measured by
-18~
~ "~
~L~3~
~ ' .
a thermocouple in thermocouple well 109. Valve 160 is
adjusted either manually or automatically to control the
amount of second catalyst bed effluent for by-pass to
control the temperature of the second catalyst bed e~1uent
entering the third catalyst bed 120.
The effluent from the second catalyst bed 119
flows outwardly of vessel outlet 106 and through suitable
piping (not shown) into inlet 107 of vessel V-2 (Fig. 3)
of the first embodiment 100. The vessel V-2, which is
illustrated in Fig. 3, is a generally cylindrical vessel
including upper head 170a, main shell 170b and lcwer head
170c supported on a base 1710 The vessel inlet 107 includes
an ~-shaped pipe section 107a and a vertical pipe section
107b~ Effluent entering the vessel inlet 107 flows through
~-shaped pipe section 107a and then upwardly through section
107b and outwardly into chamber C-6 at the top of the vessel
V-2. A third catalyst bed generally designated as 120 is
mounted on the lower head 170c of vessel V-2. The third,
annular-shaped catalyst bed 120 is formed by outer ~ylindrical
retainer wall 172 which is spaced from the main shell 170b and
inner cylindrical retainer wall 173 for housing catalyst.
Both catalyst retainer walls 172 and 173 are permeable walls,
similarly as catalyst retainer walls 137 and 138 described
previously.
The second catalyst bed effluent which has entered
vessel V-2 through vessel inlet 107 and the chamber C-6
flows downwardly into annular space S-7 formed between the
interior of main shell portion 170b and the outer cylindri-
cal retainer wall 172. The effluent then flows radially
inwardly through the catalyst ~ed 120 into annular area S-8
-19~
8~
~, '
formed between the inlet section 107b and the inner cylindrical
retainer wall 173~ The hydrogen and nitrogen in the ef1uent
is catalytically reacted in order to form additional ammonia
fQr the third time, and the third catalyst bed effluent
flows downwardly through the annular space S-8 and outwardly
through outlet ~onduit 174. The third catalyst bed effluent
flowing outwardly through conduit 174 flows to known ammonia
recovery equipment or, as an alternative, may flow through a
plant heat exchanger 35 and through a preheater 10 as described
with xespect to Fig. 1.
The actual size of each catalyst bed and each
interchanger is determined by the volume of ~atalyst and the
gas flow xates needed to meet process requirements for
ammonia synthesis. The size of the catalyst and the thickness
of the beds are also determined by such process requirements
including flow and pressure drop parametexs determined by
overall process requirements~ Each catalyst bed 118, 119
and 120 has a catalyst removal or dropout section 175, 176
and 177, respectively. Thus, in each vessel there is an
access opening above each catalyst bed for loading from the
top of the bed.
Referring now to Figs. 6, 7, and 3 another emodi-
ment 200 of this invention is illustrated. The ammonia
converter system of second embodiment 200 includes a first
heat exchanger or interchanger 201 and second catal~st bed
202 in vessel V-3 of Fig. 6, a second heat exchanger or
interchanger 203 and second catalyst bed 204 in vessel Y-4
of Fig. 7 and a third catalyst ~ed in vessel ~-2 of Fig. 3,
referred to as catalyst bed 205 for the purpose of this
system~ The emboaiment 200 is also designed to prac~tice the
ammonia process of Fig. 1.
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~L~3~ 3~3
The ~essel V-3 of Fig. 6 includes a cylindrical
vessel 206 m~unted on a cylindrical vessel support 206a.
The ~essel 206 includes an upper head 206b, main cylindrical
vessel shell 206c and bottom head 2a6d. The ammon:ia synthesis
gas is introduced by synthesis gas transfer means 207 into
the system 200 through the tube side of lnte.rchanger 201 of
vessel V-3 and then through the tube side of interchanger
203 of vessel V-4 for heating the gas prior to its passing
through the first catalyst bed 204. The synthesis gas
transfer means 207 includes a bottom vessel inlet 208 in
vessel V-3. The feed gas inlet 208 opens into an internal
conical support chamber 209, which supports a first inter-
changer 201. The interchanger 201 includes a tube bundle
210 which terminates in a lower tube sheet header 210a and
an tube sheet header 210b. The tube sheets 210a and 210b
support the tube bundle 210 in a vertical position when
vessel V-3 is in its operating position. The lower tube sheet
210a is attached directly to the top rim of the conical
support 209. An elliptically outlet head 210c is mounted
over the upper tube sheet 210b.
.~ The outlet head 210c is connected through an
expansion joint 211 to the lower end of a transfer conduit
212. The upper end of condult 212 terminates in a flange
213 outside the vessel V-3 for connecting suitable piping
; lnot shown) between vessel Y-3 and flange 214 of vessel V-4.
The synthesis gas transfer means 207 thus includes bottom
- vessel inlet 208 in vessel V-3, the conical support chamber
209, the tube side of tube bundle 210, the outlet head 210c,
expansion joint 211, transfer conduit 212 and the piping
(not shown) between flange 213 of vessel V-3 and flange 214
of vessel V-4.
b; 8~
Referring to Fig. 7, the vessel V-4 includes a
cylindrical vessel 215 which is supported on a cylindrical
support structure 216. ~he vessel 215 includes an upper
vessel head 215a, a main cylindr.ical shell 215b and a bottom
head 215c. q'he upper vessel head 215a i:ncludes a feed gas
inlet 217 which includes flange 2].4 and opens int~ a conical
tube-side inlet structure 218 for second interchanger 203
which is positioned vertically within thle vessel 215.
Second interchanger 203 includes a tube bundle 219, with an
upper tube sheet 219a connected to inlet structure 218 and a
lower tube sheet 219b. The lower tube sheet 219b of the
second interchanger 203 terminates at its bottom end in a
dcme-shaped outlet 219c and expansion joint 220, all of
which is connected to a bottom semi elliptical shaped internal
head 221 supported on a plurality of radially extending
support gussets 222.
The gas transfer means 207 further includes feed
gas inlet 217 of vessel V-4, conical inlet structure 218,
the tube side of tube bundle 219, the d~me-shaped outlet
219c, expansion joint ~20 and chamber C-7, the area below
the expansion joint 220 formed by the bottom head 215c
of vessel V-4 and botto~n internal head 221. The synthesis
gas is thus introduced into the bottom of vessel V-3 and
heated while passing upwardly axially through the tubes of
- interchanger 201 and then transferred through transfer
conduit 212 to the piping connecting vessel V-3 and ~essel
V-4~ The synthesis gas is then passed downwardly in vessel
V-4 and heated while passing through the tubes of inter-
changer 203 to a first reaction temperature for partial
synthesls of the hydrogen and nitrogen to ammonia in the
first catalyst bed 204.
22
~L~3~
An annular-shaped ~irst catalyst bed ~04 is
supported within ~he ~-4 vessel 215 on bottom internal
head 221 and is positioned concentrically a~out the second
interchanger 203. The catalyst bed 204 is formed by outer
cylindrical catalyst retainer wall 223 and an i.nner cylind
rical catalyst retainer wall 224. Catalyst retainer walls
223 and 224 are permeable walls, similarly as catalyst re-
tainer walls 137 and 138 described previously, above, and
are mounted on bottom internal head 221 which is supported
by gussets 222. A top annular plate or cover Tneans 225
covers the catalyst bed 204 extending from the main shell
215b. An annular plenum means 226, positioned between the
catalyst bed 204 and interchanger 203, which includes a rim
227 mounted to the upper tube sheet 219a to form an annular
plenum radially inwardly from catalyst bed 204 for flow
upwardly or downwardly in the plenum.
The synthesis gas feed after passing into the
- system 200 through the synthesis gas transfer means 207 is
diverted in chamber C-7 oE vessel V-4 ~Fig. 7) to the outer
annular space S-9 between main shell 215b and outer catalyst
retainer wall 223. The gas then passes radially through
catalyst bed 204 wherein an exothermic reaction occurs and a
first catalyst bed effluent containing ammonia flows out of
catalyst bed 204 into a first catalyst bed effluent transfer
means generally designated 228. The transfer means 228
includes annular space S-10 between the inner catalyst
xetainer wall 224 and the plenum means 226. ~he flow in the
plenum or space S-10 for the major portion of the effluent
is downward until it reaches the lower part of tube bundle
219 where ~he effluent flows upwardly in contact with the
she~l side of tube bundle 219. Donut baffles 279 and disk
~23-
~3~
baffles 230 aid the radial flow inwardly and outwardly as
the first catalyst bed effluent flows upwardly in a serpen-
tine manner until the effluent reaches outlet 231.
The first catalyst bed effluent transfer means 228
further includes a first ~low control means generally desig-
nated as 232. The flow control means 232 includes a by pass
line 233 attached to an upper head 234 which is mounted on
cover means 225 and sealingly engages conical inlet structure
218, wherein a small portion (e.g. 20~ or less~ of the first
catalyst bed effluent passes upwardly in plenum or space
S-10 and then out of vessel V-4 through by-pass line 233 and
by-pass valve 235. The first catalyst bed effluent passing
through the by-pass line 233 is combined with the effluent
which has been cooled and passes out through outlet 231.
The transfer means 228 may also include temperature control
means (not shown) similarly as was described in regard to
embodiment 100.
Referring to Fig. 6, the vessel V-3 has an annular-
shaped second catalyst bed 2G2 supported in the upper portion.
The catalyst bed 202 is ormed by outer cylindrical retainer
wall 235 and an inner cylindrical retainer wall 236 which
extend upwardly from annular base plate 237. Catalyst re
tainer walls 235 and 236 are permeable wallsl similarly as
catalyst retainer walls 137 and 138 escribed previously.
Base plate 237 and the catalyst bed 202 are supported in
vessel V-3 on a plurality of gussets 238 which extend inward-
ly from vessel shell 206c. An annular upper plate 239
; closes the top of catalyst bed 202 and forms a gas seal
~9 around transfer conduit 212.
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~3~8~
The first catalyst bed effluent after passing
through first catalyst bed transfer means 228 enters vessel
V-3 through inlet 240 into chamber C-8. Chamber C-8 is
formed between the vessel head 206b and the upper plate 239
which diverts the ~ffluent into the annul~r space S lO
between the vessel shell 206c and the outer cylindrical
retainer wall 235. The first catalyst bed effluent is then
passed radially through second catalyst bed 202 wherein the
hydrcgen and nitrogen in the effluent react in an exothermic
reaction to form additional ammonia. The second catalyst
bed effluent flows out of catalyst bed 202 into a second
catalyst bed effluent transfer means generally designated
241. The transfer means 241 includes annular space S-ll
which is between inner cylindrical retainer wall 236 and the
transfer conduit 212. The effluent flows downward in space
S-ll to chamber C-9 which is below the catalyst bed ~02. A
barrier 242 extends in~ardly fr~m ~essel shell 206c to an
opening 243 midway between the upper and lower tube sheets of _.:
tube bundle 210. The barrier 242 prevents vertical flow on
the shell side of tube bundle 210 between the portion above
and the portion below the barrier 242 except through the
opening 243. The second catalyst bed effluent thus flows
radially inward above the barrier 242 and radially outward
below the barrier 242 into a chamber C-lO, the area formed
between the vessel bottom head 206d and interchanger 201 and
its support 209.
The second catalyst bed effluent transfer means
241 further includes a flow control means 244. The flow
control means 244 is a by-pass pipe mounted in barrier 242
having a valve ~45 thereinO The by-pass valve 245 may
be a damper valve or other suitable type which is adjustable
to allow a portion (e~g. less than 20%) of the ~econd cata-
-25~
~l3~
lyst bed effluent to flow from chamber C-9 to chamber C-lO
without contacting tube bundle 2]0. The effluent which
bvpasses the tube bundle 210 thr~ugh contxol means 244 is
admixed in ch~mber C-lO with the effluent cooled by contacting
the tube bundle 210. The admixed and rooled secon~ catalyst
bed effluent exits vessel V~3 by line 246 at a temperature
desired for the second catalyst bed efEluent to enter the
third catalyst bed 205 in vessel V-2, illustrated in Fig. 3~
The description of vessel V-2 need not be repeated
since it is the same in the system 200 embodiment as de
scribed in the system lO0 embodiment. Each catalyst bed
202, 204 and 205 in this embodlment has a catalyst dropout
section 247, 248 and 177, respectively. Furthermore, each
vessel has an access opening 249 in vessel V-3, 250 in
vessel V-4 and 251 in Vessel V-3) above the catalyst ~ed
- for loading the bed with catalyst.
The foregoing disclosure and description of the
; invention are illustrative and explanatory thereof, and
various changes in the size, shape and materials as well as
in the details of the illustrated construction may be made
without departing from the spirit of the invention.
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