CA1209511A - Catalytic reforming process - Google Patents
Catalytic reforming processInfo
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- CA1209511A CA1209511A CA000435587A CA435587A CA1209511A CA 1209511 A CA1209511 A CA 1209511A CA 000435587 A CA000435587 A CA 000435587A CA 435587 A CA435587 A CA 435587A CA 1209511 A CA1209511 A CA 1209511A
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- reformate
- heat exchange
- hydrogen
- indirect heat
- column
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Abstract
"CATALYTIC REFORMING PROCESS"
ABSTRACT
A catalytic reforming process is disclosed in which sub-stantially all of the heat requirements of the product stabilizer column are supplied by multiple indirect heat exchange.
ABSTRACT
A catalytic reforming process is disclosed in which sub-stantially all of the heat requirements of the product stabilizer column are supplied by multiple indirect heat exchange.
Description
S~
"CATALYTIC REFORMING PROCESS"
SPECI FI CATION
_ The art of ca~alytic reforming is well known in the petro-leum refining industry and does not require detailed description herein. In brief~ catalytic reforming a~t is largely concerned with the treatment of hydrocarbonaceous feedstocks to improve their anti-knock characteristics. Generally the hydrocarbonaceous feedstockcomprises a petroleum gasoline fraction. Such a gasoline fraction may be a ~ull boiling range fraction having an initial boiling point of from 50-110F (10-38C) and an end boiling poin~ of from 325-425F (163-218C~.
More frequentlyl the gasoline fraction will have an initial boiling point of from 150-250F (66-121C) and an end boiling point of from 350-425F
(177-218C), this higher boiling fraction being commonly referred to as naphtha.
The reforming process is particularly applicable to the treatment of those straight-run gasolines comprising relatively large concentra-tions of naphthenic and substantially straight chain paraffinic hy-drocarbons which are subject to aromatization through dehydrogena-tion and/or cyclization reactions. Various other concomitant reac-tions also occur, such as isomerization and hydrogen transfer, which are beneficial in upgrading the anti-knock properties of the selec-ted gasoline fraction.
As will be hereinaf~er described in greater detail, in the typical catalytic reforming operation, feedstock, preferably a petro-leum gasoline fraction, is first admixed with hydrogen. The feed-stock and hydrogen mixture is thereafter heated to reaction tempera-ture and then contacted with reforming catalyst. The reaction efflu-ent is then separated to provide a vapor phase comprising hydrogen ~ZI~
at least a portion of which is recycled for admixture with the feed-stock and to provide a liquid phase which comprises a hydrocarbon reformate of improved anti-knock characteristics with volatile Cl to C4 components dissolved therein. The liquid phase is then stabil-ized to remove the volatile Cl to C4 components by fractionation, typically in a debutan;z;ng fract;onation column.
As noted above various reactions take place during cataly-tic reforming. These reactions include dehydrogenation, cyclization, hydrocracking and isomerization. The net result is that catalytic reform;ng ;s h;ghly endothermic. It ;s therefore common practice to effect catalytic reforming in more than one catalyst bed ~o allow reheat;ng of the reactants in order to assure that they remain at react;on temperature. Thus the reaction effluent from a preceding catalyst bed may be reheated to react;on temperature before passage to a subsequent catalys~ bed.
The highly endothermic nature of catalyt;c reforming neces-s;tates great quantities of heat. Typ;cally heat for catalytic re-forming is provided by a f;red heater. The hydrocarbon and hydrogen mixture is passed through the radiant heating section of the fired heater where i~ is heated to react;on temperature. S;nce only a por-tion of the total heat liberated in the fired heater is actually absorbed by the hydrocarbon and hydrogen mixture, large quantities of fuel must be combusted in the fired heaters to assure sufficient heat for catalytic reforming.
In order to conserve fuel and reduce the fired heater duty, it has become common practice to recover heat by preheating the feed-stock and hydrogen mixture through indirect heat exchange with the reforming react;on e~fluent. Thus the feedstock and hydrogen mixture ~Z~P~S~L
is first subjected to indirect heat exchange with the reforming reac-tion effluent and the preheated mixture is ~hen passed to the fired heater where it is further heated to reaction temperature. Such a preheating step is disclosed in U.S. Patent 4,110,197 and results in fuel savings because of the decrease in fired heater duty.
As no~ed previously, it is also com~on practice ~o subject unstabilized hydrocarbon reformate to a fractionat;on step ~ollowing the separation thereof from the hydrogen-containing vapor phase.
Typically the fractionation step is effected to remove hydrogen and Cl to C4 hydrocarbons from the unstabilized reformate. Such a frac-tionation step requires heat input into the fractionation column.
Commonly, a source of such heat is a fired heater in which reformate, withdrawn from the column bottom, is heated to a desired temperature and reintroduced into the column. As with the fired heater used to heat the catalytîc reforming reactants, the stabilizer column fired heater consumes significant amounts of fuel with only a percentage of the total heat liberated being absorbed by the reformate from the column bottomY It wnuld, therefore, be ad~antageous to eliminate the stabilizer column fired heater.
As noted previously, only a percentage of the heat libera-ted in the reforming reactants fired heater is absorbed by the hydro-carbon and hydrogen mixture in the radiant heating section of the heater. The balance of the heat liberated by combust;on leaves the radiant section of the heater via high temperature combustion gases.
Such hot combustion gases could serve as a source of heat for the stabilizer column by indirect heat exchange with reformate from the reboiler. However, traditional unit operations require that a small fired heater be employed for p~rposes of eontrolling the heat input ~lZ~531 ~
to the column thereby negating part of the advantages to be derived from elimination of the stabilizer column fired heater.
It has now been determined that it is possible to achieve significant fuel savings by utilizing the reforming reactants fired heater as a source of heat for the reformate stabilizer column with-out having to utilize a second fired heater for control. It is therefore possible to utilize the catalytic reactants fired heater as a source of heat for reformate stabilization and fully realize the advantages to be derived by eliminating the stabilizer column fired heater. Instead of utilizing a small fired heater to control heat input into the column, it has been determined that the reform-ing reaction effluent can serve as a substitute heat source for pur-poses of controlling heat input into the stabilizer column. The re-forming reaction effluent is subjected to indirect heat exchange with reformate from the bottom of the stabilizer column prior to heat exchanging the reaction effluent with the feedstock and hydro-gen mixture. The heated reformate is then returned to the column.
Use of the reforming reaction zone effluent as a stabilizer column heat inpu~ control source will increase the duty of the reforming reactants fired heater, there being less heat available in the reac-tion effluent for preheating the feedstock and hydrogen mixture.
Notwithstanding the increased reforming reactants fired heater duty, there is still an overall fuel savings compared to the traditional practice of utilizing a separate stabilizer column fired heater with-out benefit of the reforming reactants fired heater as a heat source for the stabilizer column.
5~L~
Accordingly it is an object of this invention to achieve a significant reduction in the fuel consumption of a catalytic reform-ing process by providing essentially all of the heat requirements for the reformate stabili7er column by indirect heat exchange. More specifically, it is an object of this invention to provide essential-ly all of said heat requirements from indirect heat exchange with the refor.mate reaction effluent and from the reformate reactants fired heater.
In one of its broad aspects, the present invention embod-ies a process for catalytic reforming which comprises the steps of:
(a) heating a mixture of a hydrocarbonaceous feedstock and hydrogen in a radiant heating sectiun of a fired heater and thereafter con-tacting the heated mixture with a reform;ng catalyst at reforming conditions to produce a reaction effluent; (b) subjecting at least lS a portion of the reaction effluent to a first indirect heat exchange with a portion of a hereinafter spec;fied hydrocarbon reformate; (c) subjecting at least a portion of the reaction effluent to a second indirect heat exchange with said mixture of hydrocarbonaceous feed-stock and hydrogen prior to the heating thereof in the fired heater;
(d) separating the reaction effluent into a hydrogen-rich vapor phase and a substantially liquid hydrocarbon phase and recycling at least a portion of said hydrogen-rich vapor phase for admixture with said hydrocarbonaceous feedstock, (e) introducing said liquid phase into a stabilizer column, said column being maintain~d at fractiona-tion conditions sufficient to provide an overhead fraction compris-ing hydrocarbons normally gaseous at standard temperature and pres-sure, and a bottom fraction comprising a hydrocarbon reformate; (f) recovering and reheating a first predetermined amount of the hydro-~2~5~
carbon reformate by indirect heat exchange with hot combustion gases in a convection heating section of ~he fired heater of step (a) and returning the reheated refonmate to the stabilizer column to supply a fixed quantity of hea~ to the column reboiler; ~9) recovering a second portion of the hydrocarbon reformate and subjec~ing i~ to in-direct h~at exchange with the reaction effluent as set for~h in step (b) and returning the seco~d por~ion to the stabilizer column to pro-vide the balance of the reboiler hea~ requirement of the column; and, (h) recovering a third por~ion of the hydrocarbon reformate as prod-uct.
In one preferred embodiment of this invention, said fixed quantity of heat supplied by the first predetermined amount of hydro-carbon reformate is from 50 to 80% of the reboiler heat requirement of the stabilizer column.
In another preferred embodiment of this ;nvention, the quan-tity of said portion of reaction effluent which is subjeoted to the first indirect heat exchange with the hydrocarbon reformate is deter-mined in response to a predetermined stabilizer column reboiler tem-perature.
Other objects and e~bod~ments will become apparent in the following more de~ailed specificat~on.
The catalytic reforming of petroleum gasoline fr~ctions is a Yapor phase operation and is generally effected at conversion oonditions which include catalyst bed temperatures in the range of from a~out $00 to abo~t 1050F (260 to about ~66C~, and preferab1y ~rom about 600 to about 1000F
(316 to about 538C). O~her reforming conditions include a pressure of from about 5~ to about 1000 psig (345 to about 6900 kPa gauge), preferably from about 75 to about 350 psig ~520 ~o about 240~ kPa gauge), and a liquid hourly space Yelocity (defined as liquid Yolume of fresh ~2Q~5~L~
charge per volume of catalyst per hour) of from about 0.2 to about 10 hr.l The reforming reaction is carried out generally in the presence of sufficient hydrogen to provide a hydrogen/hydrocarbon mole ratio of from about 0.5:1.0 to about 10.0:1Ø
S The catalytic reforming reaction is carried out at the aforementioned reforming condit;ons in a reaction one comprising either a fixed or a moving catalyst bed. Usually, the reaction zone will comprise a plurality of catalyst beds, commonly referred to as stages, and the catalyst beds may be stacked and enclosed w;thin a single reactor or the catalyst bed may be enclosed in a separate re-actor in a side-by-side reactor arrangement. The reaction zones will generally comprise two to four catalyst beds in either the stacked or side-by-side configuration. In any case, as noted previously the endothermic nature of catalytic reform;ng requires the heating of both fresh charge stock and catalyst bed effluents before the intro-duction thereof to subsequent catalyst beds. The amount of catalyst used in each of the catalyst beds may be varied to compensate for the endothermic natur,e of the reforming reaction. For example, three catalyst beds are used to illustrate one preferred embodiment of this invention w;th about 12 vol.% being employed in the first bed and about 44 vol.% in each of the succeeding beds. Generally, the first bed will conta;n from about 10 to about 30 Vol.%9 the sec-ond from about 25 to about 45 vol.%, and the third from about 40 to about 60 vol.~. With respect to a four-catalyst bed syste~, suit-able catalyst loadings would be from about 5 to about 15 vol.% in the first bed, from about 15 to about 25 vol.% in the second, from about 25 to about 35 vol.% in the third, and from about 35 to about 50 vol.% in the fourth. Unequal catalyst distribution, ;ncreasing 5 iL~
in the serial direction of reactant stream flow9 facilitates and en-hances the distribution of the reactions as well as ~he overall heat of reaction.
Reforming catalytic composites known and described in the S art are intended for use ~n the process encompassed by the present invention. As noted previously. catalytic reforming reactions are multifarious and include dehydrogena~ion of naphthenes ~o aromatics, the d~hydrocyclization of paraffins to aroma~ics, the hydrocracki ng of long-chain paraffins into lower boiling normally liquid material and, to a certain ex~ent, the iso~erization of paraffins. These re-actions are generally effected through utilization of catalysts com-prising one or more Group VIII noble metals (e.g. platinum, osmium, iridium, rhodium, ruthenium, palladium) combined with a halogen (e.g. chlorine and/or fluorine) and a porous carrier material such as alumina. Recent investigations have indicated ~hat additional advantageous results are attainable and enjoyed through the cojoint use of a catalytic modifier; these are generally selected from the group of iron, cobalt, copper, nickel, gallium, zinc5 germanium, tin, cadmium, rhenium, bismuth, vanadium, alkali and alkaline-earth metals, and mixtures thereof.
As noted earlier, the reforming operation further includes the separation of the hydrogen-rich vapor phase from the reaction effluent recovered from the reaction zone, at least a portion of which is recycled to the reaction zone. This separat;on is usually effected at substantially th~ same pressure as employed in the reac-tion zone, allowing for pressure drop 1n ~he system, and at a temperature in the ra~ge of about 60 to about 120F ~16C to about 49C) to yield a va~or phase c~mprising relatively pure hydrogen. The principally liquid .. , ; ~D
S~Ll hydrocar~on phase is further trea~ed in a product stabilizer column for the recovery cf the reformed product which is commonly referred to as reformate.
The reformate product stabilizer is operated at conditions selec~ed to separate a nonmally gaseous hydrocarbon fraction general-ly comprising C~~ hydrocarbons or, if desired, C5- hydrocarbons, and usually some residual hydrogen. Operating condit;ons ~ypically in-clude a pressure of from about 10~ to about 30~ psig (6gO to about 2100 kPa gauge), ~he pressure generally bein~ less than that at which the hydrogen-rich vapor phase is separated from reac~ion effluent tn avoid the necessity of pumping the liquid hydrocarbon phase into the stabilizer column.
Other operating conditions within the column include a botto~s tem-perature of from about 400 to about 500F (200 to about 260~C), and a top temperature of from about 110 to about 200F (43 to about 93C). In the past a major portion of the heat requirement of the stabilizer column was generally provided by a separate fired heater. However, in con~rast to past practice, the present invention utilizes the reforming reactants fired heater as a source of heat for the stabilizer column without use of a separate fired heater.
Fired heaters which may be employed in the present inven-tion are those commonly used in the petroleum and chemical industries.
They may be gas or oil fired. Fired heaters of the box or rectangu-lar form may be used as well as the center-wall updraft type. Such heaters incorporate a radiant heat section comprising one or more banks of tubes, carrying the process fluid, along the different wall surfaces positioned in a manner to receive radiant heat from the burners. In the center-wall configuration, the radiant heat section comprises a row of burners which fire against each side of a longitu-dinal center partitioning wall and the resulting radiant heat is sup-plied to the process fluid tubes positioned along each sidewall. As an alternative to the traditional tube banks, it is also possible to employ inverted U-tube sections such as those disclosed in U.S.
Patent 3,566,845. A preferred process fluid tube configuration and heater design is set forth in U.S. Patent 3,572,296 which discloses a low pressure drop heater particularly well suited for application in catalytic reforming operations.
Regardless of the configuration of the radiant heating sec-tion, not all the heat liberated by the firing of the fuel is absorbed by the process fluid in the radiant heating section. Rather, a sub-stantial amount of heat leaves the radiant heating section with the combustion gases. It has become the practice to recover this heat from the hot combustion gases in the fired heater convection heating section. As with the radiant heat sections~ convection heat sections may have various configurations. They may be designed to allow uni-form flow of combustion gases through the convection heating section.
Alternatively nonuniform flow of combustion gases may be employed by varying the symmetry of the combustion gas flow path. Irrespective of its exact configuration, the convection section is arranqed to allow the hot combustion gases to contact process fluid tubes~ there-by effectin~ convective heat transfer between the gases and the tubes.
Of course the foregoing discussion on fired heaters is in-tended as a general explanatiQn and is not meant to be an undue limi-tation on the scDpe of the present invention.
ILLUSTRATIVE EMBODIMENT
Further description of the process of this invention is presented with reference to the attached schematic drawing. The dra~ing and accompanying description represent a preferred illustra-tive embodiment of the invention. The data in the description are based on detailed calculations made for the purpose of design. The following illustrative embodiment is not intended as an undue limita-tion on ~he generally brGad sc~pe of the invention as set out in the appended claims. Miscellaneous hardware, such as certain pumps, com-pressors, heat exchangers, valves, instrumentation and controls have been omitted or reduced in number as not essential to a clear under-standing of the process, the utilization of such hardware being well within the purview of one skilled in the art.
Referring then to the drawing, a petroleum-deri~ed naphtha fraction is charged to the process at a rate of about 529.8 moles per hour for a liquid hourly space velocity of about 3 hr.l by way of line 1. It is then admixed with about 3336.2 moles per hour of a hydrogen-rich gaseous stream, originating as hereinafter described, comprisin~ about 71 mol.% hydrogen introduced from line 2 for a hy-drogen to hydrocarbon ratio of about 4.5. The fresh feed is contin-ued through heat exchanger 3 in line 1 wherein it is preheated to about 879F (470C) by indirect heat exchange with an effluent stream in line 13 recovered from reactor 11. The preheated reaction mixture -is continued through line 1 to a gas-fired heater 4 and passed through a charge heating coil la in the radiant heating section thereof to provide a temperature of about 990F (530C) at the inlet to the catalyst bed of reactor 5. Reactor 5 is the first of three reactors comprising the catalytic reforming reaction zone, each of said reac-tors being maintained at reforming conditions including a temperature of about 990F (530C) and a pressure of about 325 psig (2240 kPa gauge). Said reform-_ 1 1 _ ~2~$5~
ing conditions further incl`ude the utilization of a platinum-contain-ing catalyst. The heated reaction mixture is transferred from said heater 4 to the initial reactor 5 via line 5.
Since the catalytic reforming reaction is endothermic in nature, the effluent stream from reactor 5 is directed through line 7 to another heating coil 7a in the radiant heating section of the fired heater 4 wherein said effluent stream is reheated to prov;de a temperature of about 990F (530DC) at the inlet to the catalyst bed of re-actor 9. The reheated reactor 5 effluent stream is withdrawn from the heater 4 and introduced into the second reactor 9 by way of line 8.
The effluent from reactor 9 is recovered through line 10 and passed to still another heating coil lOa in the radiant heat;ng section of ~he fired heater 4 to be reheated before introduction in-to the last reactor 11 of the series of reactors which comprise the catalytic reaction zone, the reheated effluent bein~ withdrawn from said heater and introduced into sa;d reactor 11 by way of line 12.
The effluent stream from the last reactor 11 is withdrawn through line 13 at a temperature of about 970F (520~C) and at a rate of about 4540.5 moles per hour. Approximately 183.7 moles per hour of the last men-tioned effluent stream is diverted from line 13 into line 14, and this diverted stream is passed through heat exchanger 15 associa-ted with stabilizer column 16. The diverted effluent stream is utilized in said exchanger 15 to effect indirect heat exchange with a portion of the reformate product recovered from thç-stabili-zer column 16 and recycled thereto by way of line 24. The amount of reactor 11 effluent that is diverted to exchanger 15 i5 controlled by control valve 26 in a manner hereinafter related. From the ex-~LZ~3 5~L~L
changer 15, the diverted effluent stream continues through line 14 to be recombined with the ma;n portion of the reactor 11 effluent stream frGn line 13~ this main portion, about 4356.8 moles per hour, having been routed through heat exchanger 3 to preheat the fresh S feed passing through line 1 as heretofore mentioned. The recombined reactor 11 efFluent stream is passed through cooler 17 contained in line 14 and deposited into a separator 18 at a t~mperature of about 100F (38~C). The separator 18 is maintained at conditions to sepa-rate a hydrogen-rich gaseous phase and a substantially liquid hydro-carbon phase, said conditions including a temperature of about 100F. (38C) and a pressure of about 305 psig (152 kPa gauge~. The hydrogen-rich gaseous phase, comprising about 71 mol.% hydrogen, is recovered through an overhead line 19 with one portion, about 3336.2 moles per hour, being diver-ted through line 2 and admixed wit~ the aforementioned naphtha frac-tion charged to the process through line 1. The balance of the gase-ous phase from the separator 18 is discharged from the process through line 19 at a rate of abou' 583 moles per hour.
The substantially liquid hydrocarbon phase is withdrawn from the separator 18 by way of line 20 and introduced into the sta-bilizer column 16 which is maintained at conditions of temperature and pressure to separate an overhead fraction comprising normally gaseous hydrocarbons, i.e. C4- hydrocarbons. ~his overhead fraction is withdrawn from the stabilizer column through line 21 at a rate approximating 122 moles per hour. The reformate product is withdrawn as a bottoms fraction from the stabilizer column 16 via line 22 at a rate of about 13~2.3 moles per hour at a temperature of about 459F. (237C).
Approximately 820.8 moles per hour of the reformate product stream is diverted into line 23 with a predetermined amount, about 75%, of 5~
said stream being passed through line 23 and processed through heating coil 23a in the convection heating section of the fired heat-er 4 in indirect heat exchange with the hot combustion gases passing therethrough. In this case9 the predetermined amount is selected to provide about 75% of the reboiler heat requirement of the s~abilizer column. The predetermined amount may be controlled by any convention-al means such as a pump or flow controller. The reformate prsduc~
stream, after heating in the convection heating section, is returned to the stabilizer column via lines 25and 24 at a temperature of about 503F. (262C).
About 25% of the reformate product stream diverted into line 23 is recycled to the stabilizer column 16 via line 24 and through exchanger 15. In heat exchanger 15, the thus-recycled stream is heated to about 503F (262C) to provide the balance of the reboiler heat 15~ requirements of the stabilizer column, about 25% in this case. The recycle stream is heated in exchanger 1~ by indirect heat exchange with reactor 11 effluent passing through line 14. As previously men-tioned, the flow oF a rcactor 11 effluent diverted to exchanger 15 is controlled by control valve 26. Control valve 26 operates, through appropriate instrumentation, in response to the reboiler tem-perature of the stabilizer column. A predetermined reboiler tempera-ture is selected to provide the desired overhead and bottoms product quality. A predetermined amount of the reboiler heat requirement to be obtained from the fired heater convection heating section is deter-mined. Control valve 26 in turn operates to divert from line 13 suffi-cient quantities of reactor 11 effluent to exchanger 15 to provide the re-mainder of the heat necessary to obtain the predetermined stabilizer reboiler temperature. Control valve 26 fur~her operates to maintain " ~L~Q~.S~L~L
the predetermined reboiler temperature by varying the flow of reac-tor 11 effluent to exchanger 15 as necessary.
A comparison of the fired heater fuel consumption of the invention as described in the i~1ustrative embodiment set out above with that of one prior art re~orming process clearly exemplifies the ad-vantages to be achieved by use of the lnvention. For purposes of the comparison such aprior art reforming process, having two separate fired heaters and a charge rate equal to that of the illustrative embodiment, would have a reforming reactants fired heater duty of about 23.7 x 106 BTU/hr (25.0 x lo6 kJ/hr) and a stabilizer reboiler fired heater duty of about 5.8 x lo6 BUT/hr (6.1 x 106 kJ/hr). An all radiant reforming reactants fired heater, not employing a convection heating section~ typically has a heater efficiency of about 54% based on the lower heating value of the fuel. Accordingly, the reforming reactants fired heater would necessarily need to fire about 43.9 x 10~ BTU/hr (46~3 x lo6 kJ/hr) to achieve a heater duty of 23.7 x 106 BTU/hr (25.0 x lo6 kJ/hr). A stabilizer reboiler fired heater would typically have a heater efficiency of about 84.5 % based on a 100F (38C) approach temperature with the heater flue gas and the lower heating value of the fuel. This would necessitate that about 6.8 x 106 BTU/hr (7.2 x lo6 kJ/hr) of fuel be fired to achieve the s~ab~lizer reboiler fired heater duty. The overall prior art process then would require 43.9 x 106 BTU/hr + 6.8 x 106 BTU/hr or 50.7 x 106 BTU/hr (46.3 x lo6 kJ/hr 7.2 x 106 kJ/hr or 53.5 x lo6 kJ/hr) of fuel fired which results in an overall fuel efficiency of:
23.7 x 106 BTU/hr + 5.8 x 106 BTU/hr 50.7 x lOb BT~/hr -- - or 58.1%
(25 0 x 106 kJ/hr + 6 1 x 106 kJ/hr ( 53.5 x lo6 kJ/hr In con~rast a catalytic reforming process in accordance with the illustrative embodiment of the invention has a reforming reactants fired heater duty of about 25.0 x 106 ~U/hr (26.4 x 106kJ/h* It should ~LZQ$5~L~
be noted that this heater duty is larger than the corresponding heat-er duty of ~he prior art. This results from ~he fact ~hat, in accord-ance with the invention, a portion of the reactor ll effluent heat is utilized to reboil the stabilizer and consequently is not avail-able to preheat the fresh feed. In ~he prior art process9 all of the reactor effluent is available for preheat of the reactor feed and therefore the feed enters the reforming reactants fired heater at a higher inlet temperature, reducing the fired heater duty. Since the 25 x 106 BTU/hr (26 x 106 kJ/hr) heater duty in the fired heater of the illustra-tive embodiment is essentially pioked up in ~he radiant heating sec-tion, the heater efficiency would be about 54% as before. Thus the amount Qf fuel fired to achieve the heater duty is 46.2 x lO& BTU/hr.~48.7 ~ 106kJ/hr). In addition, about 75% of the sta~ilizer reboiler duty or about 4.3 x 106 ~U/hr ~4.~ x 106 kJ/hr) is picked up in the convection heating section of the fired heater. However, this heat comes from the hot combustion gases rather than by firing additional fuel. Therefore, the inven-tion results in an oYerall fuel efficiency of:
25.0 x 106 BTU/____~4.3 x 106_BTU/hr. or about 63.2%
46.2 x lO ~TU/hr.
(26.4 x 106 kJ/hr + 4.~ x 106 kJ/hr) ( 48.7 x 106 kJ/hr) It is important to note that the invention results in in-creased efficiency even though the reforming reactan~s fired heater has a greater duty thar the corresponding hea~er in the prior art process. This is because reactor ll effluen~ is utilized to provide part of the heat requirenlents fQr the stabi1izer and is not avail able to preheat the feed mixture. Accordingly, the reforming reac-tants fired heater duty is increased to compensa~e for the lower level of feed preheat. For this reason, it would not be readily apparent that utilizing the reactor effluent and convection heating -~6-5~
section to reboil the stabilizer would lead to an increase in fuel efficiency. Especially since heater duty is in effect being shifted from the higher efficiency prior art stabili~er reboiler fired heater to the less efficient radiant heating section sf the reforming reac-tants ~ired heater in the invention, it would not be expected that shifting heater duty from a more efficient heater to a less efficient hea~er would lead to the overall increase in fuel efficiency achieved by the invention.
Of course it is apparent to those of ordinary skill in the art that various reactor effluent heat exchange flow patterns may be utilized in the invent;on although not with equal results. In the embodiment depicted in the drawing, the portion of the reaction ef-fluent which is subjected to the first indirect heat exchange with the reformate is a different portion than the portion of the reac-tion effluent which is subjected to the second indirect heat exchange wikh the mixture of hydrocarbonaceous feedstock and hydrogen. Alter-natively the reactor effluent heat exchange flow pattern may be ar-ranged so that the portion of the reaction effluent which is subjec-ted to the second indirect heat exchange with the hydrocarbonaceous feedstock and hydrogen includes at least part of the portion of the reaction effluent previously subiected to the first indirect heat exchange with the reformate.
"CATALYTIC REFORMING PROCESS"
SPECI FI CATION
_ The art of ca~alytic reforming is well known in the petro-leum refining industry and does not require detailed description herein. In brief~ catalytic reforming a~t is largely concerned with the treatment of hydrocarbonaceous feedstocks to improve their anti-knock characteristics. Generally the hydrocarbonaceous feedstockcomprises a petroleum gasoline fraction. Such a gasoline fraction may be a ~ull boiling range fraction having an initial boiling point of from 50-110F (10-38C) and an end boiling poin~ of from 325-425F (163-218C~.
More frequentlyl the gasoline fraction will have an initial boiling point of from 150-250F (66-121C) and an end boiling point of from 350-425F
(177-218C), this higher boiling fraction being commonly referred to as naphtha.
The reforming process is particularly applicable to the treatment of those straight-run gasolines comprising relatively large concentra-tions of naphthenic and substantially straight chain paraffinic hy-drocarbons which are subject to aromatization through dehydrogena-tion and/or cyclization reactions. Various other concomitant reac-tions also occur, such as isomerization and hydrogen transfer, which are beneficial in upgrading the anti-knock properties of the selec-ted gasoline fraction.
As will be hereinaf~er described in greater detail, in the typical catalytic reforming operation, feedstock, preferably a petro-leum gasoline fraction, is first admixed with hydrogen. The feed-stock and hydrogen mixture is thereafter heated to reaction tempera-ture and then contacted with reforming catalyst. The reaction efflu-ent is then separated to provide a vapor phase comprising hydrogen ~ZI~
at least a portion of which is recycled for admixture with the feed-stock and to provide a liquid phase which comprises a hydrocarbon reformate of improved anti-knock characteristics with volatile Cl to C4 components dissolved therein. The liquid phase is then stabil-ized to remove the volatile Cl to C4 components by fractionation, typically in a debutan;z;ng fract;onation column.
As noted above various reactions take place during cataly-tic reforming. These reactions include dehydrogenation, cyclization, hydrocracking and isomerization. The net result is that catalytic reform;ng ;s h;ghly endothermic. It ;s therefore common practice to effect catalytic reforming in more than one catalyst bed ~o allow reheat;ng of the reactants in order to assure that they remain at react;on temperature. Thus the reaction effluent from a preceding catalyst bed may be reheated to react;on temperature before passage to a subsequent catalys~ bed.
The highly endothermic nature of catalyt;c reforming neces-s;tates great quantities of heat. Typ;cally heat for catalytic re-forming is provided by a f;red heater. The hydrocarbon and hydrogen mixture is passed through the radiant heating section of the fired heater where i~ is heated to react;on temperature. S;nce only a por-tion of the total heat liberated in the fired heater is actually absorbed by the hydrocarbon and hydrogen mixture, large quantities of fuel must be combusted in the fired heaters to assure sufficient heat for catalytic reforming.
In order to conserve fuel and reduce the fired heater duty, it has become common practice to recover heat by preheating the feed-stock and hydrogen mixture through indirect heat exchange with the reforming react;on e~fluent. Thus the feedstock and hydrogen mixture ~Z~P~S~L
is first subjected to indirect heat exchange with the reforming reac-tion effluent and the preheated mixture is ~hen passed to the fired heater where it is further heated to reaction temperature. Such a preheating step is disclosed in U.S. Patent 4,110,197 and results in fuel savings because of the decrease in fired heater duty.
As no~ed previously, it is also com~on practice ~o subject unstabilized hydrocarbon reformate to a fractionat;on step ~ollowing the separation thereof from the hydrogen-containing vapor phase.
Typically the fractionation step is effected to remove hydrogen and Cl to C4 hydrocarbons from the unstabilized reformate. Such a frac-tionation step requires heat input into the fractionation column.
Commonly, a source of such heat is a fired heater in which reformate, withdrawn from the column bottom, is heated to a desired temperature and reintroduced into the column. As with the fired heater used to heat the catalytîc reforming reactants, the stabilizer column fired heater consumes significant amounts of fuel with only a percentage of the total heat liberated being absorbed by the reformate from the column bottomY It wnuld, therefore, be ad~antageous to eliminate the stabilizer column fired heater.
As noted previously, only a percentage of the heat libera-ted in the reforming reactants fired heater is absorbed by the hydro-carbon and hydrogen mixture in the radiant heating section of the heater. The balance of the heat liberated by combust;on leaves the radiant section of the heater via high temperature combustion gases.
Such hot combustion gases could serve as a source of heat for the stabilizer column by indirect heat exchange with reformate from the reboiler. However, traditional unit operations require that a small fired heater be employed for p~rposes of eontrolling the heat input ~lZ~531 ~
to the column thereby negating part of the advantages to be derived from elimination of the stabilizer column fired heater.
It has now been determined that it is possible to achieve significant fuel savings by utilizing the reforming reactants fired heater as a source of heat for the reformate stabilizer column with-out having to utilize a second fired heater for control. It is therefore possible to utilize the catalytic reactants fired heater as a source of heat for reformate stabilization and fully realize the advantages to be derived by eliminating the stabilizer column fired heater. Instead of utilizing a small fired heater to control heat input into the column, it has been determined that the reform-ing reaction effluent can serve as a substitute heat source for pur-poses of controlling heat input into the stabilizer column. The re-forming reaction effluent is subjected to indirect heat exchange with reformate from the bottom of the stabilizer column prior to heat exchanging the reaction effluent with the feedstock and hydro-gen mixture. The heated reformate is then returned to the column.
Use of the reforming reaction zone effluent as a stabilizer column heat inpu~ control source will increase the duty of the reforming reactants fired heater, there being less heat available in the reac-tion effluent for preheating the feedstock and hydrogen mixture.
Notwithstanding the increased reforming reactants fired heater duty, there is still an overall fuel savings compared to the traditional practice of utilizing a separate stabilizer column fired heater with-out benefit of the reforming reactants fired heater as a heat source for the stabilizer column.
5~L~
Accordingly it is an object of this invention to achieve a significant reduction in the fuel consumption of a catalytic reform-ing process by providing essentially all of the heat requirements for the reformate stabili7er column by indirect heat exchange. More specifically, it is an object of this invention to provide essential-ly all of said heat requirements from indirect heat exchange with the refor.mate reaction effluent and from the reformate reactants fired heater.
In one of its broad aspects, the present invention embod-ies a process for catalytic reforming which comprises the steps of:
(a) heating a mixture of a hydrocarbonaceous feedstock and hydrogen in a radiant heating sectiun of a fired heater and thereafter con-tacting the heated mixture with a reform;ng catalyst at reforming conditions to produce a reaction effluent; (b) subjecting at least lS a portion of the reaction effluent to a first indirect heat exchange with a portion of a hereinafter spec;fied hydrocarbon reformate; (c) subjecting at least a portion of the reaction effluent to a second indirect heat exchange with said mixture of hydrocarbonaceous feed-stock and hydrogen prior to the heating thereof in the fired heater;
(d) separating the reaction effluent into a hydrogen-rich vapor phase and a substantially liquid hydrocarbon phase and recycling at least a portion of said hydrogen-rich vapor phase for admixture with said hydrocarbonaceous feedstock, (e) introducing said liquid phase into a stabilizer column, said column being maintain~d at fractiona-tion conditions sufficient to provide an overhead fraction compris-ing hydrocarbons normally gaseous at standard temperature and pres-sure, and a bottom fraction comprising a hydrocarbon reformate; (f) recovering and reheating a first predetermined amount of the hydro-~2~5~
carbon reformate by indirect heat exchange with hot combustion gases in a convection heating section of ~he fired heater of step (a) and returning the reheated refonmate to the stabilizer column to supply a fixed quantity of hea~ to the column reboiler; ~9) recovering a second portion of the hydrocarbon reformate and subjec~ing i~ to in-direct h~at exchange with the reaction effluent as set for~h in step (b) and returning the seco~d por~ion to the stabilizer column to pro-vide the balance of the reboiler hea~ requirement of the column; and, (h) recovering a third por~ion of the hydrocarbon reformate as prod-uct.
In one preferred embodiment of this invention, said fixed quantity of heat supplied by the first predetermined amount of hydro-carbon reformate is from 50 to 80% of the reboiler heat requirement of the stabilizer column.
In another preferred embodiment of this ;nvention, the quan-tity of said portion of reaction effluent which is subjeoted to the first indirect heat exchange with the hydrocarbon reformate is deter-mined in response to a predetermined stabilizer column reboiler tem-perature.
Other objects and e~bod~ments will become apparent in the following more de~ailed specificat~on.
The catalytic reforming of petroleum gasoline fr~ctions is a Yapor phase operation and is generally effected at conversion oonditions which include catalyst bed temperatures in the range of from a~out $00 to abo~t 1050F (260 to about ~66C~, and preferab1y ~rom about 600 to about 1000F
(316 to about 538C). O~her reforming conditions include a pressure of from about 5~ to about 1000 psig (345 to about 6900 kPa gauge), preferably from about 75 to about 350 psig ~520 ~o about 240~ kPa gauge), and a liquid hourly space Yelocity (defined as liquid Yolume of fresh ~2Q~5~L~
charge per volume of catalyst per hour) of from about 0.2 to about 10 hr.l The reforming reaction is carried out generally in the presence of sufficient hydrogen to provide a hydrogen/hydrocarbon mole ratio of from about 0.5:1.0 to about 10.0:1Ø
S The catalytic reforming reaction is carried out at the aforementioned reforming condit;ons in a reaction one comprising either a fixed or a moving catalyst bed. Usually, the reaction zone will comprise a plurality of catalyst beds, commonly referred to as stages, and the catalyst beds may be stacked and enclosed w;thin a single reactor or the catalyst bed may be enclosed in a separate re-actor in a side-by-side reactor arrangement. The reaction zones will generally comprise two to four catalyst beds in either the stacked or side-by-side configuration. In any case, as noted previously the endothermic nature of catalytic reform;ng requires the heating of both fresh charge stock and catalyst bed effluents before the intro-duction thereof to subsequent catalyst beds. The amount of catalyst used in each of the catalyst beds may be varied to compensate for the endothermic natur,e of the reforming reaction. For example, three catalyst beds are used to illustrate one preferred embodiment of this invention w;th about 12 vol.% being employed in the first bed and about 44 vol.% in each of the succeeding beds. Generally, the first bed will conta;n from about 10 to about 30 Vol.%9 the sec-ond from about 25 to about 45 vol.%, and the third from about 40 to about 60 vol.~. With respect to a four-catalyst bed syste~, suit-able catalyst loadings would be from about 5 to about 15 vol.% in the first bed, from about 15 to about 25 vol.% in the second, from about 25 to about 35 vol.% in the third, and from about 35 to about 50 vol.% in the fourth. Unequal catalyst distribution, ;ncreasing 5 iL~
in the serial direction of reactant stream flow9 facilitates and en-hances the distribution of the reactions as well as ~he overall heat of reaction.
Reforming catalytic composites known and described in the S art are intended for use ~n the process encompassed by the present invention. As noted previously. catalytic reforming reactions are multifarious and include dehydrogena~ion of naphthenes ~o aromatics, the d~hydrocyclization of paraffins to aroma~ics, the hydrocracki ng of long-chain paraffins into lower boiling normally liquid material and, to a certain ex~ent, the iso~erization of paraffins. These re-actions are generally effected through utilization of catalysts com-prising one or more Group VIII noble metals (e.g. platinum, osmium, iridium, rhodium, ruthenium, palladium) combined with a halogen (e.g. chlorine and/or fluorine) and a porous carrier material such as alumina. Recent investigations have indicated ~hat additional advantageous results are attainable and enjoyed through the cojoint use of a catalytic modifier; these are generally selected from the group of iron, cobalt, copper, nickel, gallium, zinc5 germanium, tin, cadmium, rhenium, bismuth, vanadium, alkali and alkaline-earth metals, and mixtures thereof.
As noted earlier, the reforming operation further includes the separation of the hydrogen-rich vapor phase from the reaction effluent recovered from the reaction zone, at least a portion of which is recycled to the reaction zone. This separat;on is usually effected at substantially th~ same pressure as employed in the reac-tion zone, allowing for pressure drop 1n ~he system, and at a temperature in the ra~ge of about 60 to about 120F ~16C to about 49C) to yield a va~or phase c~mprising relatively pure hydrogen. The principally liquid .. , ; ~D
S~Ll hydrocar~on phase is further trea~ed in a product stabilizer column for the recovery cf the reformed product which is commonly referred to as reformate.
The reformate product stabilizer is operated at conditions selec~ed to separate a nonmally gaseous hydrocarbon fraction general-ly comprising C~~ hydrocarbons or, if desired, C5- hydrocarbons, and usually some residual hydrogen. Operating condit;ons ~ypically in-clude a pressure of from about 10~ to about 30~ psig (6gO to about 2100 kPa gauge), ~he pressure generally bein~ less than that at which the hydrogen-rich vapor phase is separated from reac~ion effluent tn avoid the necessity of pumping the liquid hydrocarbon phase into the stabilizer column.
Other operating conditions within the column include a botto~s tem-perature of from about 400 to about 500F (200 to about 260~C), and a top temperature of from about 110 to about 200F (43 to about 93C). In the past a major portion of the heat requirement of the stabilizer column was generally provided by a separate fired heater. However, in con~rast to past practice, the present invention utilizes the reforming reactants fired heater as a source of heat for the stabilizer column without use of a separate fired heater.
Fired heaters which may be employed in the present inven-tion are those commonly used in the petroleum and chemical industries.
They may be gas or oil fired. Fired heaters of the box or rectangu-lar form may be used as well as the center-wall updraft type. Such heaters incorporate a radiant heat section comprising one or more banks of tubes, carrying the process fluid, along the different wall surfaces positioned in a manner to receive radiant heat from the burners. In the center-wall configuration, the radiant heat section comprises a row of burners which fire against each side of a longitu-dinal center partitioning wall and the resulting radiant heat is sup-plied to the process fluid tubes positioned along each sidewall. As an alternative to the traditional tube banks, it is also possible to employ inverted U-tube sections such as those disclosed in U.S.
Patent 3,566,845. A preferred process fluid tube configuration and heater design is set forth in U.S. Patent 3,572,296 which discloses a low pressure drop heater particularly well suited for application in catalytic reforming operations.
Regardless of the configuration of the radiant heating sec-tion, not all the heat liberated by the firing of the fuel is absorbed by the process fluid in the radiant heating section. Rather, a sub-stantial amount of heat leaves the radiant heating section with the combustion gases. It has become the practice to recover this heat from the hot combustion gases in the fired heater convection heating section. As with the radiant heat sections~ convection heat sections may have various configurations. They may be designed to allow uni-form flow of combustion gases through the convection heating section.
Alternatively nonuniform flow of combustion gases may be employed by varying the symmetry of the combustion gas flow path. Irrespective of its exact configuration, the convection section is arranqed to allow the hot combustion gases to contact process fluid tubes~ there-by effectin~ convective heat transfer between the gases and the tubes.
Of course the foregoing discussion on fired heaters is in-tended as a general explanatiQn and is not meant to be an undue limi-tation on the scDpe of the present invention.
ILLUSTRATIVE EMBODIMENT
Further description of the process of this invention is presented with reference to the attached schematic drawing. The dra~ing and accompanying description represent a preferred illustra-tive embodiment of the invention. The data in the description are based on detailed calculations made for the purpose of design. The following illustrative embodiment is not intended as an undue limita-tion on ~he generally brGad sc~pe of the invention as set out in the appended claims. Miscellaneous hardware, such as certain pumps, com-pressors, heat exchangers, valves, instrumentation and controls have been omitted or reduced in number as not essential to a clear under-standing of the process, the utilization of such hardware being well within the purview of one skilled in the art.
Referring then to the drawing, a petroleum-deri~ed naphtha fraction is charged to the process at a rate of about 529.8 moles per hour for a liquid hourly space velocity of about 3 hr.l by way of line 1. It is then admixed with about 3336.2 moles per hour of a hydrogen-rich gaseous stream, originating as hereinafter described, comprisin~ about 71 mol.% hydrogen introduced from line 2 for a hy-drogen to hydrocarbon ratio of about 4.5. The fresh feed is contin-ued through heat exchanger 3 in line 1 wherein it is preheated to about 879F (470C) by indirect heat exchange with an effluent stream in line 13 recovered from reactor 11. The preheated reaction mixture -is continued through line 1 to a gas-fired heater 4 and passed through a charge heating coil la in the radiant heating section thereof to provide a temperature of about 990F (530C) at the inlet to the catalyst bed of reactor 5. Reactor 5 is the first of three reactors comprising the catalytic reforming reaction zone, each of said reac-tors being maintained at reforming conditions including a temperature of about 990F (530C) and a pressure of about 325 psig (2240 kPa gauge). Said reform-_ 1 1 _ ~2~$5~
ing conditions further incl`ude the utilization of a platinum-contain-ing catalyst. The heated reaction mixture is transferred from said heater 4 to the initial reactor 5 via line 5.
Since the catalytic reforming reaction is endothermic in nature, the effluent stream from reactor 5 is directed through line 7 to another heating coil 7a in the radiant heating section of the fired heater 4 wherein said effluent stream is reheated to prov;de a temperature of about 990F (530DC) at the inlet to the catalyst bed of re-actor 9. The reheated reactor 5 effluent stream is withdrawn from the heater 4 and introduced into the second reactor 9 by way of line 8.
The effluent from reactor 9 is recovered through line 10 and passed to still another heating coil lOa in the radiant heat;ng section of ~he fired heater 4 to be reheated before introduction in-to the last reactor 11 of the series of reactors which comprise the catalytic reaction zone, the reheated effluent bein~ withdrawn from said heater and introduced into sa;d reactor 11 by way of line 12.
The effluent stream from the last reactor 11 is withdrawn through line 13 at a temperature of about 970F (520~C) and at a rate of about 4540.5 moles per hour. Approximately 183.7 moles per hour of the last men-tioned effluent stream is diverted from line 13 into line 14, and this diverted stream is passed through heat exchanger 15 associa-ted with stabilizer column 16. The diverted effluent stream is utilized in said exchanger 15 to effect indirect heat exchange with a portion of the reformate product recovered from thç-stabili-zer column 16 and recycled thereto by way of line 24. The amount of reactor 11 effluent that is diverted to exchanger 15 i5 controlled by control valve 26 in a manner hereinafter related. From the ex-~LZ~3 5~L~L
changer 15, the diverted effluent stream continues through line 14 to be recombined with the ma;n portion of the reactor 11 effluent stream frGn line 13~ this main portion, about 4356.8 moles per hour, having been routed through heat exchanger 3 to preheat the fresh S feed passing through line 1 as heretofore mentioned. The recombined reactor 11 efFluent stream is passed through cooler 17 contained in line 14 and deposited into a separator 18 at a t~mperature of about 100F (38~C). The separator 18 is maintained at conditions to sepa-rate a hydrogen-rich gaseous phase and a substantially liquid hydro-carbon phase, said conditions including a temperature of about 100F. (38C) and a pressure of about 305 psig (152 kPa gauge~. The hydrogen-rich gaseous phase, comprising about 71 mol.% hydrogen, is recovered through an overhead line 19 with one portion, about 3336.2 moles per hour, being diver-ted through line 2 and admixed wit~ the aforementioned naphtha frac-tion charged to the process through line 1. The balance of the gase-ous phase from the separator 18 is discharged from the process through line 19 at a rate of abou' 583 moles per hour.
The substantially liquid hydrocarbon phase is withdrawn from the separator 18 by way of line 20 and introduced into the sta-bilizer column 16 which is maintained at conditions of temperature and pressure to separate an overhead fraction comprising normally gaseous hydrocarbons, i.e. C4- hydrocarbons. ~his overhead fraction is withdrawn from the stabilizer column through line 21 at a rate approximating 122 moles per hour. The reformate product is withdrawn as a bottoms fraction from the stabilizer column 16 via line 22 at a rate of about 13~2.3 moles per hour at a temperature of about 459F. (237C).
Approximately 820.8 moles per hour of the reformate product stream is diverted into line 23 with a predetermined amount, about 75%, of 5~
said stream being passed through line 23 and processed through heating coil 23a in the convection heating section of the fired heat-er 4 in indirect heat exchange with the hot combustion gases passing therethrough. In this case9 the predetermined amount is selected to provide about 75% of the reboiler heat requirement of the s~abilizer column. The predetermined amount may be controlled by any convention-al means such as a pump or flow controller. The reformate prsduc~
stream, after heating in the convection heating section, is returned to the stabilizer column via lines 25and 24 at a temperature of about 503F. (262C).
About 25% of the reformate product stream diverted into line 23 is recycled to the stabilizer column 16 via line 24 and through exchanger 15. In heat exchanger 15, the thus-recycled stream is heated to about 503F (262C) to provide the balance of the reboiler heat 15~ requirements of the stabilizer column, about 25% in this case. The recycle stream is heated in exchanger 1~ by indirect heat exchange with reactor 11 effluent passing through line 14. As previously men-tioned, the flow oF a rcactor 11 effluent diverted to exchanger 15 is controlled by control valve 26. Control valve 26 operates, through appropriate instrumentation, in response to the reboiler tem-perature of the stabilizer column. A predetermined reboiler tempera-ture is selected to provide the desired overhead and bottoms product quality. A predetermined amount of the reboiler heat requirement to be obtained from the fired heater convection heating section is deter-mined. Control valve 26 in turn operates to divert from line 13 suffi-cient quantities of reactor 11 effluent to exchanger 15 to provide the re-mainder of the heat necessary to obtain the predetermined stabilizer reboiler temperature. Control valve 26 fur~her operates to maintain " ~L~Q~.S~L~L
the predetermined reboiler temperature by varying the flow of reac-tor 11 effluent to exchanger 15 as necessary.
A comparison of the fired heater fuel consumption of the invention as described in the i~1ustrative embodiment set out above with that of one prior art re~orming process clearly exemplifies the ad-vantages to be achieved by use of the lnvention. For purposes of the comparison such aprior art reforming process, having two separate fired heaters and a charge rate equal to that of the illustrative embodiment, would have a reforming reactants fired heater duty of about 23.7 x 106 BTU/hr (25.0 x lo6 kJ/hr) and a stabilizer reboiler fired heater duty of about 5.8 x lo6 BUT/hr (6.1 x 106 kJ/hr). An all radiant reforming reactants fired heater, not employing a convection heating section~ typically has a heater efficiency of about 54% based on the lower heating value of the fuel. Accordingly, the reforming reactants fired heater would necessarily need to fire about 43.9 x 10~ BTU/hr (46~3 x lo6 kJ/hr) to achieve a heater duty of 23.7 x 106 BTU/hr (25.0 x lo6 kJ/hr). A stabilizer reboiler fired heater would typically have a heater efficiency of about 84.5 % based on a 100F (38C) approach temperature with the heater flue gas and the lower heating value of the fuel. This would necessitate that about 6.8 x 106 BTU/hr (7.2 x lo6 kJ/hr) of fuel be fired to achieve the s~ab~lizer reboiler fired heater duty. The overall prior art process then would require 43.9 x 106 BTU/hr + 6.8 x 106 BTU/hr or 50.7 x 106 BTU/hr (46.3 x lo6 kJ/hr 7.2 x 106 kJ/hr or 53.5 x lo6 kJ/hr) of fuel fired which results in an overall fuel efficiency of:
23.7 x 106 BTU/hr + 5.8 x 106 BTU/hr 50.7 x lOb BT~/hr -- - or 58.1%
(25 0 x 106 kJ/hr + 6 1 x 106 kJ/hr ( 53.5 x lo6 kJ/hr In con~rast a catalytic reforming process in accordance with the illustrative embodiment of the invention has a reforming reactants fired heater duty of about 25.0 x 106 ~U/hr (26.4 x 106kJ/h* It should ~LZQ$5~L~
be noted that this heater duty is larger than the corresponding heat-er duty of ~he prior art. This results from ~he fact ~hat, in accord-ance with the invention, a portion of the reactor ll effluent heat is utilized to reboil the stabilizer and consequently is not avail-able to preheat the fresh feed. In ~he prior art process9 all of the reactor effluent is available for preheat of the reactor feed and therefore the feed enters the reforming reactants fired heater at a higher inlet temperature, reducing the fired heater duty. Since the 25 x 106 BTU/hr (26 x 106 kJ/hr) heater duty in the fired heater of the illustra-tive embodiment is essentially pioked up in ~he radiant heating sec-tion, the heater efficiency would be about 54% as before. Thus the amount Qf fuel fired to achieve the heater duty is 46.2 x lO& BTU/hr.~48.7 ~ 106kJ/hr). In addition, about 75% of the sta~ilizer reboiler duty or about 4.3 x 106 ~U/hr ~4.~ x 106 kJ/hr) is picked up in the convection heating section of the fired heater. However, this heat comes from the hot combustion gases rather than by firing additional fuel. Therefore, the inven-tion results in an oYerall fuel efficiency of:
25.0 x 106 BTU/____~4.3 x 106_BTU/hr. or about 63.2%
46.2 x lO ~TU/hr.
(26.4 x 106 kJ/hr + 4.~ x 106 kJ/hr) ( 48.7 x 106 kJ/hr) It is important to note that the invention results in in-creased efficiency even though the reforming reactan~s fired heater has a greater duty thar the corresponding hea~er in the prior art process. This is because reactor ll effluen~ is utilized to provide part of the heat requirenlents fQr the stabi1izer and is not avail able to preheat the feed mixture. Accordingly, the reforming reac-tants fired heater duty is increased to compensa~e for the lower level of feed preheat. For this reason, it would not be readily apparent that utilizing the reactor effluent and convection heating -~6-5~
section to reboil the stabilizer would lead to an increase in fuel efficiency. Especially since heater duty is in effect being shifted from the higher efficiency prior art stabili~er reboiler fired heater to the less efficient radiant heating section sf the reforming reac-tants ~ired heater in the invention, it would not be expected that shifting heater duty from a more efficient heater to a less efficient hea~er would lead to the overall increase in fuel efficiency achieved by the invention.
Of course it is apparent to those of ordinary skill in the art that various reactor effluent heat exchange flow patterns may be utilized in the invent;on although not with equal results. In the embodiment depicted in the drawing, the portion of the reaction ef-fluent which is subjected to the first indirect heat exchange with the reformate is a different portion than the portion of the reac-tion effluent which is subjected to the second indirect heat exchange wikh the mixture of hydrocarbonaceous feedstock and hydrogen. Alter-natively the reactor effluent heat exchange flow pattern may be ar-ranged so that the portion of the reaction effluent which is subjec-ted to the second indirect heat exchange with the hydrocarbonaceous feedstock and hydrogen includes at least part of the portion of the reaction effluent previously subiected to the first indirect heat exchange with the reformate.
Claims (5)
1. A catalytic reforming process comprising the steps of:
(a) heating a mixture of a hydrocarbonaceous feedstock and hydrogen in a radiant heating section of a fired heater and there-after contacting the heated mixture with a reforming catalyst at re-forming conditions to produce a reaction effluent;
(b) subjecting at least a portion of the reaction effluent to a first indirect heat exchange with a portion of a hereinafter specified hydrocarbon reformate;
(c) subjecting at least a portion of the reaction effluent to a second indirect heat exchange with said mixture of hydrocarbona-ceous feedstock and hydrogen prior to the heating thereof in the fired heater;
(d) separating the reaction effluent into a hydrogen-rich vapor phase and a substantially liquid hydrocarbon phase and recycl-ing at least a portion of said hydrogen-rich vapor phase for admix-ture with said hydrocarbonaceous feedstock;
(e) introducing said liquid phase into a stabilizer column, said column being maintained at fractionation conditions sufficient to provide an overhead fraction comprising hydrocarbons normally gaseous at standard temperature and pressure, and a bottom fraction comprising a hydrocarbon reformate;
(f) recovering and reheating a first predetermined amount of the hydrocarbon reformate by indirect heat exchange with hot com-bustion gases in a convection heating section of the fired heater of step (a) and returning the reheated reformate to the stabilizer col-umn to supply a fixed quantity of heat to the column reboiler;
(g) recovering a second portion of the hydrocarbon refor-mate and subjecting it to indirect heat exchange with the reaction effluent as set forth in step (b) and returning the second portion to the stabilizer column to provide the balance of the reboiler heat requirement of the column; and, (h) recovering a third portion of the hydrocarbon reformate as product.
(a) heating a mixture of a hydrocarbonaceous feedstock and hydrogen in a radiant heating section of a fired heater and there-after contacting the heated mixture with a reforming catalyst at re-forming conditions to produce a reaction effluent;
(b) subjecting at least a portion of the reaction effluent to a first indirect heat exchange with a portion of a hereinafter specified hydrocarbon reformate;
(c) subjecting at least a portion of the reaction effluent to a second indirect heat exchange with said mixture of hydrocarbona-ceous feedstock and hydrogen prior to the heating thereof in the fired heater;
(d) separating the reaction effluent into a hydrogen-rich vapor phase and a substantially liquid hydrocarbon phase and recycl-ing at least a portion of said hydrogen-rich vapor phase for admix-ture with said hydrocarbonaceous feedstock;
(e) introducing said liquid phase into a stabilizer column, said column being maintained at fractionation conditions sufficient to provide an overhead fraction comprising hydrocarbons normally gaseous at standard temperature and pressure, and a bottom fraction comprising a hydrocarbon reformate;
(f) recovering and reheating a first predetermined amount of the hydrocarbon reformate by indirect heat exchange with hot com-bustion gases in a convection heating section of the fired heater of step (a) and returning the reheated reformate to the stabilizer col-umn to supply a fixed quantity of heat to the column reboiler;
(g) recovering a second portion of the hydrocarbon refor-mate and subjecting it to indirect heat exchange with the reaction effluent as set forth in step (b) and returning the second portion to the stabilizer column to provide the balance of the reboiler heat requirement of the column; and, (h) recovering a third portion of the hydrocarbon reformate as product.
2. The process of Claim 1 further characterized in that said fixed quantity of heat supplied by the first predetermined amount of hydrocarbon reformate is from 50 to 80% of the reboiler heat requirement of the stabilizer column.
3. The process of Claim 1 or 2 wherein the quantity of said portion of reaction effluent which is subjected to the first indirect heat exchange with the hydrocarbon reformate is determined in response to a predetermined stabilizer column reboiler temperature.
4. The process of Claim 1 wherein the portion of the reac-tion effluent which is subjected to the first indirect heat exchange with the reformate is a different portion than the portion of the reaction effluent which is subjected to the second indirect heat ex-change with the mixture of hydrocarbonaceous feedstock and hydrogen.
5. The process of Claim 1 wherein the portion of the reac-tion effluent which is subjected to the second indirect heat exchange with the hydrocarbonaceous feedstock and hydrogen includes at least part of the portion of the reaction effluent previously subjected to the first indirect heat exchange with the reformate.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000435587A CA1209511A (en) | 1983-08-29 | 1983-08-29 | Catalytic reforming process |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000435587A CA1209511A (en) | 1983-08-29 | 1983-08-29 | Catalytic reforming process |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1209511A true CA1209511A (en) | 1986-08-12 |
Family
ID=4125968
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000435587A Expired CA1209511A (en) | 1983-08-29 | 1983-08-29 | Catalytic reforming process |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1209511A (en) |
-
1983
- 1983-08-29 CA CA000435587A patent/CA1209511A/en not_active Expired
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