CA1285899C - Integrated process and apparatus for the primary and secondary catalyticsteam reforming of hydrocarbons - Google Patents

Abstract

INTEGRATED PROCESS AND APPARATUS FOR
THE PRIMARY AND SECONDARY CATALYTIC STEAM
REFORMING OF HYDROCARBONS
Abstract of the Disclosure Integrated primary-secondary reforming operations are carried out with the partly reformed product effluent from the reformer tubes of the primary reforming zone passing to a catalyst-free reaction space at the feed end of a catalyst bed in the secondary reforming zone. The exothermic heat of reaction generated in said reaction space supplies the necessary heat for the endothermic reforming reaction that occurs in the catalyst bed of the secondary reforming zone, and the still hot secondary product effluent leaving the secondary reforming zone is passed in the shell side of the primary reformer zone to supply the endothermic heat of reaction required in said primary reforming zone. Essentially autothermal operating conditions are thereby achieved so as to essentially eliminate the necessity for employing an external fuel-fired primary reformer and/or for consuming a portion of the hydrocarbon feed material for fuel purposes.

Description

~Z85f~3~3 t - INTEGRATED PROCESS AND APPARATUS FOR
TH~ PRIM~RY AND SECONDARY CATALYlIC STEAM
REFORMING OF HYDROCARBONS
Back~round of the Invention Field of the Invention The invention relates to the stea~
reforming of fluid hydrocarbons. More particularly, it relates to an improved process and apparatus fo~
reducing the fuel consumption of such ~team reforming operations.
Descri~tion of the Prior ~rt In the primary stesm re~orming of fluid hydrocarbons, such as'natural gas, the feed material and ~team are passed through catalyst-containing vertically hanging reformer tubes maintained at an elevated temperature by radiant heat transfer and~or by contact with combustion gases in the furnace portion of the tubular reactor. The hot reformer tube effluent may be passed to a waste heat recoYery ~one for the generation of steam that can be used in the steam reforming operations. Conventional primary 6team reforming operations are commonly carried out at temperatures of from about 750C to about 850C or above, with a mole ratio of ~team to hydrocarbon feed of about 2/1 - 4~1.
The primary steam reforming reaction is a highly endothermic reaction, and the large amounts of required heat are typically provided by combusting external fuel at close to atmospheric pressures in the reforming furnace. The walls of the reformer tubes must necessarily be capable of D 14,002 '. - , . .
- . ' ''' . ''' , . :

, - - - -- , :, ~ . . .
, ~
- - ": ., - -~ ' ~'. `- -~z~s~

-- 2 ~

withstanding extreme operating conditions, ~uch as 6kin temperatu~e6 on the order of 750-880C and pre~ure differences of about 15-~0 bar Consequently, the reformer tube6 are generally made of high alloy, expensive mate~ials having a limited operating life under such extreme condition6. The reaction temperature6 exi~ting inside the reformer tube6 are generally lower than about 8~0C 60 tha~
the effluent gas rscovered from the primary reformer typically ~ontains 2-6~ methane.
In further accordance with conventional practice, the effluent from primary reforming is sometimes passed to a secondary reforming zone in which unconverted methane present in the re~ormed gas mixture is catalytically reacted with air, oxygen or other suitable oxygen-con~aining gas. The secondary reforming reaction of methane and oxygen i6 an exothermic combustion reaction in which the temperature rise~ generally to above 950C, with no external heat being supplied a~ in primary reforming. The wall6 of the secondary refor~ing reactor can thus be protected by refractories and kept at much lower temperatures, e.g. 300C, than is the case with the primary reformer tube6. In6tead of such reactor tubes, ~ single, large diameter secondary reforming reactor can be employed using le6s costly materials than must be employed in the primary reformer. Becau6e of the very high reaction temperature employed, ~ery little unconverted methane remain6 in the effluent gas removed from ~he secondary reformer reactor.

~-14,002 . ~ . - . . . , . :
- . - - - : ,.. . . .. . -~;28~9~3 Large quantities of hydrogen, or of an ammonia syngas mixture o~ hydrogen and nitrogen, are produced either ~y such steam reforming operations or by partial oxidation reactions. Partial S oxidation, like secondary reforming, i8 an exothermicD autothermal, internal combustion process. While secondary reforming i5 also a catalytic process, however, the variou~ known partial oxidation processes employ non-cataly~ic reactions, and thus operate at higher reaction temperatures on the order of about 1300C. The significant advantages obtainable by the use of secondary reforming, or by the use of par~ial oxidation processing, are off-set to some extent by the need to compress the oxygen-containing gas to the desired reaction pressure or higher. Another disadvantage of secondary reforming and of partial oxidation processing is that part of the feed gas is combusted to carbon dioxide and water instead of to desired product. As a result, more natural gas or othec feed gas is required to produce a given amount of hydrogen or synthesis ga~, although the autothermic proces6es do not reguire any fuel. By contrast, the fuel consumption rate for primary refor~ing is typically between 30~ and 50% of the feed cate.
Those skilled in the art will appreciate that it is not practical to employ secondary ceforming proc~sses alone, apart from an initial primary reforming of the feed gas. In practical commercial operations, therefore, primary reforming alone or partial oxidation with oxygen are the most D-14,002 . - . . - . - - . ~ - , . -. .
.

~85~3~9 frequently employed proce~ses for the production of pure hydrogen product. When it i8 desired to produce an ammonia syngas mixture of hydrogen and nitrogen, on the other hand, a combination of S primary reforming followed by 6econdary reforming, with air rather than oxygen, i8 most commonly employed. While such a combination of primary and secondary reforming is partly autothermic, in ~hat no external fuel ~equire~ent exists for the secondary reormer, it nevertheles~ has the disadvantage& of requiring the use of a relatively large primary reformer and of having relatively low thermal efficiency. Such disadvantages have been recognized in the art and efforts have been made to improve the overall process by the recovery of heat in order to reduce the size of the external fuel-fired primary reformer furnace. In the Quartulli et al patent, U.S. 3,264,066, the problems peculiar to primary-secondary reforming operations for the production of ammonia 6ynthesis gas were addressed, including the requirements for large ~ized equipmen~ and for the use of large amounts of steam and fuel under desirable operating conditions. Quartulli et al disclose the u~e of a heat exchanger between the primary and secondary reformers for indirect heat exchànge of the primary and secondary reformer effluents. The temperature of the primary reformer effluent, which is the ~eed to the secondary reformer, is thereby raised, while the temperature of the effluent from the secondary ; reformer is decreased. In the Craw~ord et al patent, U.S. 4,079,017, another approach is D-14,002 .
.

9~3 sugge6ted wherein parallel ~team ceformers are used for the primary reforming of a hydrocarbon feed.
One portion of the feed is heated by mean6 of radiant heat, i.e. by use of a steam reforming furnace, while another portion is heated by indire~t heat exchange with the effluent from the ~econdary reforming operation, i.e. in an exchanger-reactor unit. While the approach of both of the6e patents is to recover heat for utilization in the reforming reactions, thus reducing the size of the external fuel-fired primary reformee, either all of the feed, a~ in U.S. 3,264,066, or at least a major portion thereof, as ;n U~S. 4,079,017, passes through such a primary reformer. Both patent6 also have the disadvantage of the typical apparatus problems that are commonly encountered due to the difficult mechanical de~ign problem6 as60ciated with conventional-type heat exchangers operated at the relatively high temperatures involved in the reformin~ application.
Another approach to improving steam reforming operations by reduction of fuel consumption is disclo6ed in the Fuderer patent, U.S.
4,337,170. Thi~ patent teaches the reforming of 20-30~ of a feed stream in a primary reformer-exchanger unit in which the hot product effluent from conventional reforming, together with the hot product effluent from the reformer-exchanger itself, 6upplies the heat foc said reformec-exchanger unit. The conventional reforminq compri6e6 either conventional pcimary reforming alone, or such primary reforming coupled with a D-14,002 .

. -.: ; . : :: , .:

: -, : . -. . . .

~ s~

secondary reforming ope~ation. In the latter case, the hot effluent from the secondary reforme~ pa86e8 to the reformer-exchanger. By contrast with the approach of Crawford et al wherein the product effluent of each of the parallel primary stea~
reformers i6 necessarily pagsed to a secondary refo~mer with the product effluent therefro~ being used to supply the heat required for the primary refoeming of a portion of th2 feed stream, the Fuderer approach does not require the use of a - secondary reformer. While the processing flexibility afforded thereby is desirable, the portion of the feed stream that passes directly to -~ the reformer is not subjected to secondary reforming lS in any event, even when a econdary reformer is used to treat the effluent from a conventional primary reforme~. As a refiult, the residual met~ane concentration of the mixed product effluent i8 much higher than that of a product stream from secondary 20 reforming. This loss of unconverted methane is not desirable even though the use of a reformer-exchanger as disclosed by Fuderer enables a ~ignificant eeduction in fuel con~umption to be achieved together with other operating advantagefi.
25 As with the techniques of Quartulli et al and Crawford et al, it also will be seen that Fuderer requires that an external fuel-fired primacy reformer furnace be employed, although the fuel requirements ~hereof are reduced.
Despite such efforts to improve fiteam refo~ming operations, it will be appreciated that there remains a desire in the art to achieve lower D-14,002 . - . . , . . - . . :, . ..
~ . . . .
-. - ' ~ . ' ' , ' ' - .
. . . .. , . . ~ .
.. . . . .

-~team and fuel requirements and higher thermal efficiencie~ in such operations. In addition, improved mechanical designs are al60 desired to reduce the size of the overall reforming systems employed and to achieve other useful purposes. such as a reduction for the thermal stresse6 to which the primary reformer tubes are sub3ected. It is al~o desired ~o carry out ~team reforming operations a~
higher pressures, as in the range o~ 20-100 Bar.
Such desired improvements also relate to the integration of primary and secondary reforming operations. so as to obtain the benefits of secondary reforming while achieving a more efficien~
overall reforming operation than has heretofore been possible in the art.
It is an object of the invention, therefore, to provide an improved process and apparatus for the reforming of hydrocarbons.
It is another object of the inven~ion to provide a process and apparatus for minimizing the fuel reguicements of reforming operations.
It is another object of the invention to provide a process and apparatus for the integrated primary and secondary reforming of hydrocarbon6.
It is another object of the invention to provide a reforming process having low stea~
requirements and enhanced thermal s~iciency.
It is a further object of the invention to proYide a primary and secondary reforming apparatus of compact design and of reduced thermal stre6s of the primary reformer ~ubes.

D-14,00z .

- . .
, , - ,- . . , : , .

.
.. . .

S~9 It i8 a further object of the invention to provide a process and appala~us for carrying out ~team cefocming operations at higher pressures, as in the range of about 20-100 ~ar.
With these and other objec~s in mind, t~a invention is hereinafter described in detail, the novel featuces theceo~ being particularly pointed out in the appended claims.

SummarY of the Invention The invention results in an integrated primary and secondary reforming proce~s and apparatus utilized in a manner providing for the fully autothecmal conver~ion of hydrocarbons and steam ~o hydrogen and carbon oxides. The need fo~
an external ~uel-fired primary reformer is thereby avoided. The partly reformed effluent from the pcimary reformer zone of the apparatus passes, in a suitable conduit, through the catalyst bed to the 2Q space at the feed end of the secondary refo~mer zone for which preheated oxygen-containing ga~ is being introduced. The hot secondary ceformec effluent does not leave the apparatus, but passes on the shell side of the primary reformer zone, thereby applying the heat required for the endothermic primary ceforming reaction that occurs within the catalyst-containing reactor tube~ of said primary cefocmer zone.

Brief DescriPtion of the Drawinqs The invention ls hereinafter described with cefe~ence to the accompanying drawing illustcating ,~ :

; D-14,002 ' ::, . . ~ , . , -.
-~B~

the apparatus and the proces6 flow employed in the practice of the invention.
Detailed DescriDtion of the Invention The object of the invention are accomplished by integrating primary and ~econdary reformers into a totally autothermal unit that has no essential need for the direct fired primary refo~mer of conventional primary reforming techniques. The steam requirement~ for the practice of the invention are very low, and the reforming opera~ions carried out thereby are characterized by exceptionally high thermal efficiencies.
The catalytic conversion of hydrocarbons by reaction with steam at elevated temperature is, of course, well known in the art. A fluid hydrocarbon~
such as natural gas, is converted to a hot reformed gas mixture containing principally hydrogen and carbon monoxide in this process according to reaction (l) as follows:
(l) C~4 + H20 ~ C0 1 3H2 that i8 generally known as pri~ary reforming and i8 widely used in the production of 6ynthesis gas or pure hydrogen. This endothermic reaction i6 carried out in the practice of the invention, as in conventional practice, by passing a ga~eous mixture of fluid hydrocarbon and steam through an externally heated reaction tube or group of tubes packed with a suitable catalyst compo~ition, such as solid catalyst granules deposited on an inert carrier material. Whereas the neces ary heat is com~only 6upplied in conventional primary re~orming by burning a fluid hydsocarbon fuel, such a~ a side D-14,002 , .

-. . : . .
. . , , -. ~ . , . - : .' : ' ~ . . . .
. . ~- ~ .. , - ~

3S~39~

-- 10 -- , stream from the fluid hydrocarbon feed stream, with air on the 6hell ~ide of the primary reformer, the invention utilized the heat content of the 6econdary reformer effluent for this purpo6e as is herein disclosed and claimed.
The hot reformer tube effluent of the - p~imary reforming operation is passed, as it often is in conventional practice, to a secondary reformer. Unlike ~uch practice in which the - 10 secondary reformer is commonly a separate processing unit, the secondary reformer of the invention comprise6 a separate processing zone contained within an integrated primary and secondary reforming ' apparatus. In the practice o~ the invention and in conventional practice, the 6econdary reforming operation is carried out to react unconverted methane present in the primary re~ormer effluent with air or other oxygen-containing ~as. As the preheated gases reach the reaction space at the feed end of the secondary reforming catalyst bed in the practice of the invention, the following reaction6, with methane as the hydrogen feed gas, are found to occur in this initial portion of the seconda~y reforming zone:

(2) CH4 , 202 ~ Co2 ~ 2H20, (3) 2CH4 + 2 ~ 4H2 + 2C0, and Reactions t2), (3) and (4) are exothermic reaction~ that tend to occur quite rapidly in ~aid reaction space. As the resulting gas mixture passes through the catalyst bed of the secondary reformer zone, the remaining methane is converted by reaction D-14,002 .

- - ~ - . , .

,: -. : : . ~ ., -' , ' ' ' , ' .

~.2&?~

with steam in accordance with reaction (l) above 80 that ~ery little methane remains in the product ya~
of the process. The strongly endothermic reaction ( 1) i6 a relatiYely 810w reaction that occurs throughout the pas6age of the gases through the catalyst bed of the secondary reforming zone, the~eby cooling the gases from the high temperatures reached upon reactions (2), (3) and (4) occurring at the space at the feed end of said catalyst bed. In the practice of the invention, the proportions of - oxygen and of the fluid hydrocarbons feed passed to the integrated primary-secondary reformer are such that the reactions alone are carried out in a manner essentially, or even completely, au~othermal in nature, i.e. with essantially no fuel requirement and with an external fuel-fired primary steam reformer essentially eliminated as a necessary feature of the overall reforming operation. ~s is hereinafter discussed, an important feature of the invention i6 the flexibility of being a~le to bypass a po~tion of the hydrocarbon feed stream directly to the hot, catalyst-free reaction space at the feed end of the secondary reforming catalyst bed, as illustrated in the drawing.
With reference to the drawing, a fluid hydrocarbon feed gas stream in line l, together with steam from line 2, enters the bottom of the integrated primary and secondary steam reformer.
designated overall by the numeral 3, for passage upward thro~-gh the catalyst-filled primary reactor tubes 4 of primary reforming zone 5. Upon discharges from such tubes, the partly reformed D-14,002 - . - , -- .
. - .. . , :- .

.- - ' . ' - . ' "~ ' ' ' ', . . ' , - . . ~. ., ~ '' - . .

~85899 primary reformer ef1uent passes to the secondary reforming zone 6 through conduit 7. As shown in the drawing, conduit 7 extends through secondary reforming catalyst bed 3 to a reaction space 9 in the upper portion of 6aid secondary reforming zone 6 at the feed end of said catalyst bed 8. Preheated air or other oxygen-containing gas is passed to the reaction space 9 through line 10, as i~ a portion of the hydrocarbon feed and steam through bypass line - 10 11. As the bypass o~ a portion of the-hydrocarbon feed to secondary reforming zone 6 is an optimal feature of the invention, line 11 is shown with control valve 13. Similarly, steam line 2 contains control valve 14 and bypass line 15, with control valve 16. for control of the steam/hydrocarbon feed ration in the portion of the feed pa~sed to primary reforming zone 5 or bypassed directly to secondary refQrming zone 6. As is also illustrated in the drawing, it is within the scope of the in~ention, if so desired in particular processing opelations, to pa6s the portion of the steam/hydrocarbon feed mixture that bypass,es primary reforming zone 5 of integrated primary and secondary reformer 3 to ~ .
conventional primary reformer unit 17 by passage through diversion line 12 containing this unit, and discharge therefrom in line 18 to bypass 11, with control valve 19 being employed in line 11 for this purpose. As will be appreciated from the discus~ion above, howeveL, the inclusion of such a conventional primary reformel unit 17 in the overall operation of i~tegrated primary and secondary reformer 3 is not an essential requirement of the invention.
. ~ .
.

D-14,002 . - ~- . .- ~ . .

~2~

- 1~

In reaction space 9, the preheated oxygen-containing ga6 wi}l react with hydrocarbons or methane or hydrogen from the by-passed hydrocarbon feed and/or present in the primary reformer effluent so that reactions (2), ~3) and (4) occur therein, with the resulting reaction mixture pas6ing downward through secondary reforming catalyst bed ~ 6hown as being supported by a bed 20 of ball-shaped alumina particles.
~ 10 The reaction ~ixture temperature rises - rapidly in reaction space 9 due to the exothermic reactions that takes place therein, but are cooled as a re6ult of the 610wer endothermic reaction of methane conver6ion with steam that occurs upon pas6age of the reaction mixture through secondary re~orming cataly~t bed 8 to the discharge end thereof. The effluent ga6 from secondary ceforming zone 6, which is at a lower ele~ated temperature than the gas in the reaction space, does not leave the apparatus of the invention at this point. but passes directly to the shell ~ide of primary reforming zone 5. It i~ further cooled a~, it passes from the discharge end to the feed end thereof countercurrently to the passage of the steam~hydrocarbon feed mixture being passed through the catalysC-filled reactor tubes 4 therein.
Appropriate baf1es, 6uch as those indica~ed by the numeral 21, can be employed to direct the flow of the secondary reforming effluent gas across said reactor tubes on its passage from the discharge e~d to the feed end of primary reforming zone 4 prior to ' ` D-14,002 ,,-- . , .
- . . .
- ' - - ' '. . ~ , '' ; ' : ' ' - , , , ~

exit from integrated reformer 3 at the bottom through line 22 near the bottom feed inlet thereto.
It will be apprecîated from the drawing that all of the hotter part6 of the apparatufi of the invention can be made perfectly concentric, resulting in excellent gas flow distribution and the minimizing of thermal stresse6. The apparatu~ can - be constructed with no longitudinal parts having different temperature being rigidly connected to each other.
Consequen~ly, they ~an freely expand when heated and contract when cooled, thereby also minimizing thermal stresses. Pressure differen~ials between the shell and the tube sides of the primary reforming zone exist only as a consequence of the pressure drops of the flowing gas streams. Thus, the pressure difference between the shell and the tube side is typically only 3-4 Ba~ at the cold feed end of primary reforming zone 5, while the tube tempera~ures are on the order of 440C. At the upper, discharge end of primary reforming zone S, on the other hand, the pressure differential is only about 1 Bar, while the local wall ~emperature is around 800C. In a conventional primary reformer unit, by contrast, the pressure differential is typically about 30 Bar at a wall temperature of about 800C. Since the reformer tubes have to withstand only fimall pressure differences, the total operating pressure can be raised to 100 Bars or even higher.
Integrated primary and secondary reformer 3 preferably co~prises an internally insulated ; D-14,002 , .

. ~., .- - ~ -. - -: - . - , . . . , . -8'3~3 cylindrical metal ves&el. For thi6 purpose, the inner wall on the shell side of primary reforming - zone 5, as well as the inner wall of secondary - reformi~g zone 6, can be lined with MgO or other convenient refractoey material so as to protect the outer shell of the reformer and to effectively : utilize the available heat of the processing gas ~treams. It is also wi~hin the scope of the invention to employ a double shell construction, together with means for passing steam or a small portion of the hydrocarbon feed gas. or boiler feed water or other coolant through the annular fipace between the inner and outer hells, desirably at the reactor operating pressure, thereby cooling the inner wall supporting the refractory material. By the use of such construction, neither the inner ~essel, nor the outer shell of the reformer reach a `~ high temperature, and both shell6 can be made of less costly alloys. The outer shell will typically be insulated 60 that heat losses Prom the reformer are negligible in customary practice.
The drawing illustrates ehe use of vertically oriented reformer tubes although i~ will be appreciated that horizontally oriented tubes can also be employed in the practice of the invention.
The use of vertical, hanging tubes is particularly desirable in the reformer of the invention as the hot effluent from the hanging reformer tubes, following steam reforming during the preferable upward passage of the steam~hydrocarbon mixture in the hanging tubes, can conveniently be passed through one or more suitable conduits placed inside D-14,00Z
.
.: . . .
, , ~ .. .
.- : . . . ; ~;

S~9'3 ~he ~econdary reforming catalyst bed for discharge in the reaction ~pace located near the feed end of the catalys~ bed. As is the embodiment of the drawing, the primary reforme! effluent can conveniently be passed upward in said conduit mean~
through the ~econdary ceforming cataly~t bed, preferably concentrically, to the ceaction space above said bed. As disclosed above, the preheated oxygen-containing ga6 and any bypass port;on of the steam/hydrocaebon feed mixture are likewise passed to this reaction space that forms a part of the secondary reformer prior to passage of the reaction mixture through the catalyst bed in the opposite direction, e,g. downward in the illustrated embodiment. As the pres~ure inside and autside the hanging tubes i8 essentially the same, tube rupture is avoided without the necessity for incurring undue C08tS in this regard. In the illustrated embodiment, integrated primaly and secondary reformer 3 is shown with an outer shell 23 and an inner shell 24, defining an annular space 25 therebetween, throush which boiler faed water or other coolant may be added through line 26 con~aining valve 27 therein. If desired, a portion of the hydrocarbon feed gas can be passed through line 28 containing valve 29 for passage to said annulae space 25.
~s also shown in the drawing, refractory material 30 is 6upported on the inside wall of inner shell 24. In a convenient embodiment, an enlarged portion 31 of refractory is provided to extend inward at the juncture between the lower primary D-14,002 '. . . - . , ,. . ~ ', - ~ .

reforming %one S and the upper secondary reforming zone 6, with said enlarged portion of refractory 31 being used, together with heat resistant material, such as alumina bars or a bad of balls Zo, to support catalyst bed 8 of said secondary re~orming zone 6.
In the practice of the integrated primary and secondary processes of the invention, the fluid hydrocalbon desulphuried feed gas and ~team mixture is introduced to the tube side of the ~rimary reforming zone at a temperature of generally from about 200C to about 500C. The conditions in the primary reforming zone serve to promote con~ersion of the fluid hydrocarbon feed stream to hydrogen and carbon monoxide. The feed gas-steam mixture in the reformer tubes is thus gradually heated by the countercurrent passage of secondary reformer effluent product gas on the shell side of said primary reforming zone. At the hot discharge end of said primary reforming zone, tha temperature of the primary ceformer effluent is from about 650C to about 900C. The gas stream, partly reduced in - ac~ordance with reaction (1) above, is passed through one or more conduits that pass through ~he catalyst bed of the secondary reforming zone for discharge into the reaction space at the feed end of the secondary catalyst bed. Air andtor oxygen or another oxygen-containing gas is preheated and passed to ~aid reaction space generally at about ~00C to 600C.
The temperature in the reaction space at the feed end of the ~econdary reforming cataly~t bed D-14,002 .~ , ............................. . .
' .: ' , . -tends to rise rapidly as a result of exothermic reactions (2), 13~ and (4) that occur therein, e.g.
above about 930C in typical operation~. As the gases p~oceed from said reaction space and pas~
through the catalyst bed portion of the secondary reforming zone downwardly in the embodiment illustrated in the drawing, however, the ga~ stream is cooled due to the endothermic reaction (1) - wherein cemaininq methane i~ converted with steam to form additional amounts of hydrogen and C0. At the discharge end of the catalyst bed, therefore, the gas temperature is typically in the range of ~ro~
about 900C to abou~ 1100C. As indicated above and shown in the drawing, the ~econdary reformer effluent remains within the integrated primary and ~econdary reformer, passing to the shell ~ide of the primary reforming zone where it is ~ooled by supplying heat for the endothermic reaction (1) occurring in said zone.
The ratio of steam to hydrocarbon feed will vary, as i~ known in the art, depending upon the overall conditions employed in the reforming zones.
The amount of steam employed is influenced by the general requirement of avoiding carbon deposition on the catalyst and by the acceptable amount of methane remaining in the effluent gas under the reforming conditions employed. on this basis, the mole ratio of steam to hydrocarbon feed in the conventional primary reformer units is preferably from a~out 2/1 to about 4/1. Steam/hydrocarbon ratios in this range are also commonly employed in the primary reforming section of the apparatus of the :;
D-14,00Z ~;

. . .

~S8~9 invention. As indicated above, however, it i~
posxible to bypas6 a portion of the feed gas directly to the hot catalyst-~ree reaction space at the feed end of the cataly6t bed of the secondary reforming zone, i.e. the reaction space above said bed in the illustrated embodiment. This embodim~nt enables a very substantial improvement in the steam/hydrocarbon feed g~as ratio to be achieved, greatly enforcing the overall performance of the invention. Thus, the steam to hydrocarbon ~eed ratio in the bypassed gas can be much lower than in the mixture fed to the primary reforming ~one, because the bypassed gas is mixed with ~ufficient oxygen and steam so that no coke or carbon formation occurs on the catalyst in said 6econdary reforming zone at the higher temperatures therein. As a result, steam/hydrocarbon mole ratios in the ranqe of from about 0.4 to about 1.4 can often be employed in the bypassed portion of the feed 6tream. As a ~ubstantial portion of the overall feed can be bypassed to the secondary reforming zone in the practice of the invention, exceptionally low overall steam/hydrocarbon feed ratios can be achieved, as between about 1.6 and 2.2 in preferred embodiments of the invention.
It has been determined that, as indicated above, a substantial portion of the overall feed to the integrated primary and secondary reformer of the system can be bypassed to the secondary reforming zone thereof. Thus, from about 50 to about BO mole % of the total hydrocarbon feed gas ~tream can advantageously be bypassed to said secondary D-14,002 ' ;' ' - - ', ' - . . .
, - - . . .
-.

~5~399, reforming zone in preferred embodiments, with from about 20% to about 50 mole % passing to the primary reforming space in such embodiments. Those skilled in the art will appreciate that amounts falling outside this range may also be employed within the scope of the invention with the total amount of hydrocarbon feed and oxygen-containing gas added to - the system being such that essentially all of the heat required for operation of the primary reforming 20ne is supplied by the heat content of the secondary reformer effluent in an essentially autothermal primary and secondary reforming operation. Apart from the lower overall steam/hydrocarbon feed ratio achievable in the practice of the invention by the use of the feed bypass feature, it ~hould ~lso be noted that the lesser hydrocarbon feed to the primary reformer zone as a result of said bypass results in a lower pressure drop, or in a higher shell height to diameter ratio than pertains where no bypass is included in the process. It ~hould also be noted that when feed bypass is practicad, the catalyst-free reaction space in the secondary reforming ~one functions really as a partial oxidation zone with relatively low oxygen requirements in terms of ~he overall refining operation. In this regard, the oxygen-containing gas will be understood to pre-mix with the by-pas~ed hydrocarbon feed upon passage from their re~pec~ive ~upply lines into said reaction space, with a relatively high oxygen/feed ratio exi~ting at this point. After complete combu~tion under ~uch D-14,002 ,. . . .......................... - .

- ~ . . . . - ,, . ~: . :

~s~

conditions, a reaction temperature of about 1300C
or above would be reached as in a partial oxidation reactor. Before the combustion is fully completed and such high temperature is reached, however, the product effluent from the primary refoeming zone passes through the secondary reforming catalyst bed, as through conduit 7 of the drawing, and i8 dis~harged into the reaction space to mix with the mixture of oxygen, bypassed feed and the reaction produ~ts ~hereof. As a result, the temperature in the reaction space may rise rapidly to about 1100C
or some such temperature less than the 1300C level that would pertain in a partial oxidation application. As the reaction gas mixture then proceeds to pass through the secondary reforming catalyst bed, the gas mixture i~ further cooled by - the heat requirements of the endothermi~ methane conversion reaction occurring therein, as indicated above, so that the product effluent existing from the secondary reforming zone will have a temperature typically on the order of between about 900C and 1000C, although temperatures outside this range may also pertain and be useful for supplying essentially all of the heat required in the primary refocming zone.
The invention i6 hereinafter further described with reference to a particular illustcative embodiment carried out in the integrated double shell apparatus shown in the drawing. A desulphurised natural gas feed ~tream, comprising essentially 1,450 kgmolfh methane, i~ the total feed gas flow to the apparatus. The steam D-14,002 .: -- . . .

... .- , . .
; ~ - ',, . : . ~ -3'3 plus water flowra~e to the apparatus is 2,770 kgmol/h. A total of 700 kgmol/h~of said methane i6 passed to the primary reforming zone of said appaLatu6, while an additional 700 kgmol/h of methane are bypassed to the catalyst-free reaction ~pace at the feed end of the catalyst bed in said secondary refocming zone. In addition, 50 kgmol/h of methane are passed through the annular sp3ce between the inner and outer ~hells of ~aid integrated apparatus as coolant fluid.- Included in the total amount of steam and water added to the apparatus are 2,070 kgmol/h of steam that are passed to the primary reforming zone, and 640 kgmol/h of s~eam that are bypassed to ~aid reaction space in the secondary reforming zone. A total of 60 kgmol/h of water is passed through said annular space as coolant fluid. Thus, the overall mole ratio of steam to hydrocarbon feed is 2,770~1,450 or 1.91, for this embodiment of the invention. Rich air is used as the oxygen-containing gas for secondary reforming, with 700 + 1273 kgmol/h of oxygen nitrogen being used for this purpo~e.
The methane feed gas, steam, boiler feed wa~er and rich air were all employed at a pressure of 50 Bar, and the primary reforming effluent, secondary reforming effluent, and product effluent from the integrated apparatus are at pressures of 46, 45.5 and 45.0, respectively. The methane feed gas and rich air are both preheated to 400C, while the steam is employed at 300C, with the primary reforming effluent, secondary reforming effluent and product effluent from the apparatus being at D-14,002 . . .

-.
. ' ': . ~ -. '- . : .
.. ~ . . .
~ ' " .' -' '...... . . .

temperatures of 750, 990 and 550C, respect~vely.
The primary reforming zone comprises 375 tube6, each housing a length of 6.3m and an inside diameter o~
56mm. The heat exchanger area of the primary reforming zone is 415m , with ~he average temperature difference being 200C between the inside and the outside of the tubes. The total heat tran~ferred i~ 130 G Joule/h (36.3MW). Under such general conditions, the outlet gas obtained in the primary and secondary reforming zones, measured in kgmolth, is as set forth in the Table belo~
TABLE
-Primary Reforming Secondary Reforminq Effluent _ Effluent _ Hydrogen 1,148 3,187 Carbon dioxide 200 434 Carbon monoxide 116 950 Methane 434 66 Nitrogen ~-- 1,271 Steam 1,554 Total3,452 8,251 The pressure drop on the tube-side is 2 Bar, while the ~hell-side p~essure drop is 0.5 ~ar.
The overall dimen~ions of the integrated primary and ~econdary reforming apparatu~ are l~m in length, 3.3m outside diameter and 12~m3 volume. It i~ :
estimated that, in a conventional ammonia plant producing the same syngas as in the example above, the external fuel-fired primary reformer of conventional reforming operations has abou~ a 30 ~ times larger volume than that of said integrated : reformer apparatus.

D-14,002 .

. , ~ . ,. . -.. , .: .. . ., ' . : :

: . : ~ , - , ~ . - . :

., The fluid hydrocarbon feed of the fnvention will be understood to include Yarious normally gaseou~ hydrocarbon~ othe~ than natural ga6 or methane. such a6 propane and butane, as well as prevaporized normally liquid hydroc~rbon6, 6uch as hexane or petroleum refining low-boiling fraction6 3uch as naphtha. It will be unders~ood by those skilled in the ar~ that the invention can be practiced for the refining of hydrocarbons as part of overall proce~6ing techniques for a variety of industrial applications, i.e. as in the production of hydrogen, methanol, ammonia or of (oxo)syngas.
When ammonia syngas production i~ desired, the use of air or oxygen enriched air a~ the oxygen-containing ga~ is generally prefecred whereas, for example, in the production of hydrogen rather than of a hydrogen-nitrogen mixture, the use of oxygen is more generally preferred for use in the secondary reforming zone of the integrated refoemer.
The catalyst employed in the practice of the invention can be any one or more ~uitable reforming catalysts employed in conventional reforminq operations. The metal~ of ~roup VIII of the Periodic System having an atomic number not greater than 28 and/or oxides thereof and metals of the lefthand elements of Group V~ and/or oxides thereof are known reforming catalysts. Specific examples of reforming catalysts that can be used are ~ nickel, nickel oxide, cobalt oxide, chromia and - 30 molybdenum oxide. The catalyst can be employed with promoters and can al~o have been subject to vaeious 6pecial treatments known in the art for enhancing :`
D-14,002 .

. ., .
,. - :
: . ~ , . - . ~ :

8S~39~3 it8 properties. Promoted nickel oxiae catalysts are generally preferred, and the primary reformer tubes are packed with solid catalyst granules, u~ually comprising such nickel or other catalytic agent deposited on a suitable inert carrier material. The secondacy reforming zone commonly contains a bed of such catalyst material in addition to the catalyst-f~ee reaction space at the feed end thereof as discussed above.
It will be appreciated that the steam reforming operations, including those of the present invention, are commonly carried out at ~uperatmospheric pressure. The specific operating pressure employed is influenced by the pressure requirements of the subsequent processing operations in which the reformed gas mixture, comprising C0 and hydrogen, or hydrogen itself is to be employed.
Although any superatmospheric pressure can be used in practicing the invQntion, pressures of from about 20 to 60 Bar (about 300 to about 870 p~ia) are commonly employed, although pressures lower than 20 Bar, and up tO as high as lO0 Bar ~1450 psia) or more can be maintained in particular embodiments of the invention.
The present invention will be appreciated as enabling essentially autothermal reforming operations to be carried out in primary and secondary reforming zones of the integrated reformer unit not requiring the use of an èxternal fuel-fired primary reformer as a necessary part of said uni~.
Thusc the hydrocarbon feed to the reformer, with all of said ~eed passing to the primary reforming zone D-14,002 ' . ` . ~: , - , ~ :
, ' : - , .. :- ~ . .

- 26 _ thereo~ or with a portion, preferably about 50~80~
thereof bypassed to the secondary reforming zone, is employed in conjunction with the introduction of BUff icient oxygen to the reformer 60 that essentially all of the heat required or carrying out the endothermic primary steam ceforming reaction in the primary reforming zone is supplied by the hot effluent gas exiting from the secondary reforming zone prior to discharge of ~aid effluent gas fro~
the reformer unit for subsequent cooling and purification by conventional means to provide a final prQduct that is either methanol syngas, hydrogen or hydrogen-nitrogen mixtures a~ in the production of ammonia synqas.
Those skilled in the art will appre~iate that the precise amount of oxygen o~
oxygen-containing gas and the amount of hydrocarbon feed passed to the integrated reformer of the invention will depend upon the particular conditions applicable to any given reforming operation, including the nature of the h~drocarbon feed, the particular catalyst employed~ the steam/hydrocarbon ratio employed in the primary reforming zone and in the bypassed steam~hydrocarbon mixture passed to the secondary reforming zone so as to produce sufficient heat so that, despite the endothermic reaction that occur6 in the catalyst bed of the secondary reforming zone, the product e~fluent thereof has ~ufficient heat to ~upply the requirements of the primary reforming zone prior to exit with very little, i.e. typically less than 1 mole ~, residual hydrocarbon remaining in the product effluent as D-14,002 .. . .. . - -' ' , ' - : :

- - . , . ., - . . .

..

~2~5899 compared to that present in the effluent from the primary reforming zone. In this regard, it ~hould be noted that the product effluent from the primary reforming zone of the invention will commonly have an unconverted meehane content of fLom about 2-3S up ~o about 20 mole ~ on a dry basi~ as compared with the typical 2-6% residual methane conten~ of the product effluent from conventional fuel-fired primary reforming operations. Such variation in the amount of unconverted methane passed to the secondary reforming zone will be understood to affect the heat requirements of the primary re~ormin~ zone and the ovecall oxygen eequirements for a given amount of hydrocarbon feed ~or the overall purpo~es of the invention. As was indicated above, it i8 within the scope of the invention to employ an optional fuel-fired conventional primary reformer for treatment of bypassed feed. In embodiments in which this optional feature is employed, it will be understood that the steamJhydrocarbon feed ratio and the amount of oxygen supplied to the integrated primary-secondary reformer unit will vary from the operable conditions that pertain where no such optional primary reformer on bypassed feed i~ actually employed. Those skilled in the art will aepreciate that various other ~odifications and variations can be employed in the details of the process and apparatu~ herein described without depaeting from the scope of the invention as set forth in the appended claims.
Because of its capability of achieving essentially autothermal operation, with the need for ., D-14,002 - ' :, ' ~ : ' .' ~ ., . - ' ' ' - . : . ... .

,.. ; - : ' :: -S~

a fuel-fired primary reformer being essentially eliminated, the invention provides a highly de~irable and significant advance in the field of reforming of natural gas and other fluid S hydrocarbons. Because of its potential for appreciable saving~ in operating investment costs, the invention is of genuine practical commercial interest, particularly in light of the substantial savings obtainable as a result of the ability to substantially eliminate the fuel consumption aspect of carrying out hydrocarbon reforming operations.
The technical and economic advantages of the invention thereby appreciably enhance the -desirability by carrying out hydrocarbon reforming operations for practical commercial application~.

D-14,002 : .- . . . - . :~
~ - - , , , - .
.:

.. . .
' ' : ' . , ~- : -

Claims (36)

1. An integrated, essentially autothermal, catalytic process for the primary and secondary reforming of fluid hydrocarbons comprising:
(a) catalytically reacting a fluid hydrocarbon feed stream with steam in catalyst-containing reformer tubes positioned within the primary reforming zone of an integrated primary-secondary reformer, said primary reforming zone being maintained at an elevated temperature by the passage of hot product effluent from the secondary reforming zone of said reformer on the shell side of said primary reforming zone;
(b) passing the partly reformed product effluent from said primary reforming zone to the catalyst-free reaction space at the feed end of the catalyst bed in the secondary reforming zone;
(c) introducing an oxygen-containing gas to said catalyst-free reaction space in the secondary reforming zone of said integrated reformer, exothermic reaction of said oxygen with unconverted fluid hydrogen feed and hydrogen causing the temperature of the reaction mixture in said reaction space to rise;
(d) passing the reaction mixture from said reaction space to the secondary reforming catalyst bed, unconverted hydrocarbon feed present in said reaction mixture reacting with steam in an endothermic reaction during the passage of the reaction mixture through said catalyst bed so as to reduce the temperature of the reaction mixture from the temperature reached in said catalyst-free reaction space to a lower-elevated temperature;
(e) introducing the secondary reforming product effluent gas passing from the discharge end of the secondary reforming catalyst bed to the shell side of the primary reforming zone to supply heat to maintain said elevated temperature for the endothermic steam reforming reaction taking place within the catalyst-filled reactor tubes of said primary reforming zone; and (f) discharging cooled effluent from the shell side of said primary reforming zone as the product effluent of said integrated primary-secondary reformer, whereby the desired overall primary and secondary reforming of the fluid hydrocarbon feed is accomplished with essentially all of the heat required in the primary reforming zone being supplied by the product effluent of the secondary reforming zone so that the need for an external fuel-fired primary reformer and/or for the burning of a portion of the hydrocarbon feed for fuel purposes is essentially eliminated.

2. The process of Claim 1 in which the mole ratio of steam to hydrocarbon feed in the primary reforming zone is from about 2/1 to about 4/1, the temperature of the partly reformed product effluent from the primary reforming zone being from about 650°C to about 900°C.

3. The process of Claim 2 in which the oxygen-containing gas is preheated to from about 200°C to about 600°C prior to being into said catalyst-free reaction space of said secondary reforming zone, the exothermic reaction of oxygen with hydrocarbon feed causing the temperature in the reaction space to rise above about930°C.

4. The process of Claim 3 in which the temperature of the secondary reforming product effluent passing to the shell side of the primary reforming zone is from about 900°C to about 1,000°C.

5. The process of Claim 1 in which said hydrocarbon feed comprises methane.

6. The process of Claim 5 in which the partly reformed product effluent of the primary reforming zone has an unconverted methane content of from about 3 t about 20 vol. % on a dry basis.

7. The process of Claim 5 in which the oxygen-containing gas comprises air.

8. The process of Claim 1 and including bypassing a portion of the hydrocarbon feed and steam to the secondary reforming zone of the integrated primary-secondary reformer.

9. The process of Claim 8 in which said hydrocarbon feed and steam bypassed to the secondary reforming zone passes to the catalyst-free reaction space at the feed end of the catalyst bed in said zone.

10. The process of Claim 9 in which said bypass stream has a mole ratio of steam to hydrocarbon feed of from about 0.4/1 to about 1.4/1.

11. The process of Claim 10 in which said steam/hydrocarbon feed ratio is from about 0.5/1 to about 1/1.

12. The process of Claim 10 in which about 50% to about 80% by volume of the hydrocarbon feed to the integrated reactor is bypassed to the secondary reforming zone therein.

13. The process of Claim 2 in which the product effluent from said primary reforming zone is at a temperature of from about 700°C to about 800°C.

14. The process of Claim 9 in which said integrated reformer comprises a durable shell unit and including passing a coolant fluid through the annular space between the inner and outer shells.

15. The process of Claim 14 in which said coolant is employed at essentially the reaction pressure within the integrated reactor.

16. The process of Claim 15 in which said coolant comprises hydrocarbon feed gas.

17. The process of Claim 1 in which said hydrocarbon feed comprises propane or butane.

18. The process of Claim 1 in which said hydrocarbon feed comprises light naphtha.

19. The process of Claim 1 and including bypassing a portion of the hydrocarbon feed and steam to an external, fuel-fired primary reforming unit, the product effluent from said external reformer being passed to the catalyst-free reaction space at the feed end of the catalyst bed in the secondary reforming zone of said integrated reactor.

20. The process of Claim 19 in which from about 50% to about 80% by volume of the hydrocarbon feed to the integrated reformer by bypassed to said external fuel feed primary reforming unit.

21. The process of Claim 1 in which said partly reformed product effluent passes from a lower primary reforming zone upwardly in conduit means extending through the catalyst bed of the secondary reforming zone to said catalyst zone to said catalyst-free reaction space positioned in the secondary reforming zone above said catalyst bed.

22. An apparatus for the essentially autothermal, integrated primary and secondary reforming of hydrocarbons comprising:
(a) a primary reforming zone having catalyst-containing reformer tubes positioned therein;
(b) by means for introducing a fluid hydrocarbon feed stream and steam to said reformer tubes in said primary reforming zone;
(c) a secondary reforming zone containing a secondary reforming catalyst bed and a catalyst-free reaction space at the feed end of said catalyst bed;
(d) conduit means for passing partly reformed product effluent from the primary reforming zone to said catalyst-free reaction space in the secondary reforming zone;
(e) means for introducing secondary product effluent gas removed from the discharge end of the catalyst bed in said reforming zone to the shell side of the primary reforming zone; and (f) discharge means for removing secondary product effluent from the shell side of the primary reforming zone after passage therethrough.

23. The apparatus of Claim 22 and including means for preheating the hydrocarbon feed and the oxygen-containing gas being introduced to said integrated primary-secondary reformer.

24. The apparatus of Claim 22 in which said secondary reforming zone is positioned above the primary reforming zone.

25. The apparatus of Claim 24 in which said primary reforming zone contains vertical reformer tubes, the hydrocarbon feed/steam reaction mixture to said zone being introduced to the lower end of said tubes at a bottommost inlet portion thereof, the partly reformed product effluent leaving the reformer tubes at the upper end thereof.

26. The apparatus of Claim 25 in which said catalyst-free reaction space at the feed end of the catalyst bed is positioned above said catalyst bed.

27. The apparatus of Claim 26 in which said conduit means for passing partly reformed effluent to the catalyst-free reaction space on the secondary reforming zone passes upward through said catalyst bed in said secondary reforming zone.

28. The apparatus of Claim 27 in which said conduit means is positioned concentrically on said secondary reforming zone.

29. The apparatus of Claim 27 in which said means for introducing an oxygen-containing gas to said catalyst-free reaction space is adapted to introduce said gas to the upper portion of said reaction space.

30. The apparatus of Claim 22 and including means for bypassing a portion of said hydrocarbon feed and steam being passed to said integrated reformer to said secondary reforming zone.

31. The apparatus of Claim 30 in which said means for bypassing hydrocarbon feed and steam to said secondary reforming zone are adapted to deliver said hydrocarbon feed and steam to said catalyst-free reaction space in said secondary reforming zone.

32. The apparatus of Claim 31 in which said means for bypassing hydrocarbon feed and steam are adapted to introduce said reactants to the upper portion of said catalyst-free reaction space.

33. The apparatus of Claim 22 and including an external fuel-fired primary reformer unit and means for bypassing a portion of said hydrocarbon feed and steam to said primary reformer unit, together with means for passing the product effluent from said unit to said secondary reforming space.

34. The apparatus of Claim 33 in which said means for passing product effluent from said primary reformer unit to the catalyst-free reaction space in said secondary reforming zone passes through said secondary reforming catalyst bed.

35. The apparatus of Claim 27 in which said primary-secondary reformer has an outer shell which refractory material supported thereon.

36. The apparatus of Claim 35 in which said outer shell comprises a double shell and including means for passing a coolant fluid through the annular space between the inner and outer shells.