Title of Invention

"PROCESS FOR HEATING A STREAM FOR A HYDROCARBON CONVERSION PROCESS"

Abstract

One exemplary embodiment of the present invention can be a hydrocarbon conversion process. The process may include passing a hydrocarbon stream through at least one heater (300) including at least one burner (308), a radiant section (310), and a convection section (318). Generally, the stream passes through the radiant section (310) and then through the convection section (318) before exiting the heater. Desirably, the hydrocarbon stream includes, in percent or parts by weight based on the total weight of hydrocarbons in the stream: C4 or less: less than 0.5%; sulfur or sulfur containing compounds: less than 1 ppm; and nitrogen or nitrogen containing compounds: less than 1 ppm. Preferably, the sulfur or sulfur containing compounds and the nitrogen or nitrogen containing compounds are measured as, respectively, elemental sulfur or nitrogen.

Full Text

FIELD OF THE INVENTION [0001] The field of this invention is heating a stream entering a reaction zone BACKGROUND OF THE INVENTION [0002} Hydrocarbon conversion processes often employ multiple reaction zones through which hydrocarbons pass in t series flow Each reaction zone in the series often has a unique set of design requirements A minimum design requirement of each reaction zone m the series is the hydraulic capacity to pass the desired throughput of hydrocarbons that pass through the series An additional design requirement of each reaction zone is sufficient heating to perform a specified degree of hydrocarbon conversion [0003] One well-known hydrocarbon conversion process can be catalytic reforming Generally, catalytic reforming is a well-established hydrocarbon conversion process employed in the petroleum refining industry for improving the octane quality of hydrocarbon feedstocks, the primary product of reforming being a motor gasoline blending component or a source of aromabcs for petrochemicals Reforming may be defined as the total effect produced by dehydrogenation of cyclohexanes and dehydroisomenzation of alkylcyclopentanes to yield aromatics, dehydrogenation of paraffins to yield olefins, dehydrocyclization of paraffins and olefins to yield aromatics, lsomenzation of n-paraffins, lsomenzation of alkylcycloparaffins to yield cyclohexanes, lsomenzation of substituted aromatics, and hydrocracking of paraffins A reforming feedstock can be a hydrocracker, straight run, FCC, or coker naphtha, and can contain many other components such as a condensate or a thermal cracked naphtha Typically, such a hydrocarbon feedstock contains high levels of impurities unsuited for a conversion product, such as reformate These impurities can include sulfur and nitrogen, and such a feed can have levels of sulfur ranging from 10 - 17,500 wt -ppm and nitrogen ranging from 0 2 - 450 wt -ppm [0004] Heaters or furnaces are often used in hydrocarbon conversion processes, such as reforming, to heat the process fluid before it is reacted Generally fired heaters or furnaces include an all radiant fired heating zone to heat the fluid with a convection section being used for another service, such as producing steam Other fired heaters can have an initial convection section followed in a series by a radiant section Having the convection section first allows for the process fluid to recover more heat from the flue gas because, generally, the convection section is at a lower temperature as compared to the radiant section of the heater Additionally, both of these heater designs are applicable to charge heaters and interheaters Each section includes tubes to contain the process fluid flowing through the heater [0005] However, these conventional designs suffer disadvantages Sometimes a conversion unit is limited by the heater if increasing the firing of the heater raises the temperature of the radiant and/or convection tubes to their maximum tube wall limit If the throughput of a heater is limited by a maximum tube wall temperature, then the production rate of the entire conversion unit can be constrained [0006] Moreover, generally there are three problems associated with operating a heater at or near the maximum temperature of the tube walls First, high tube wall temperatures increase the tendency of flue gas to oxidize on the sides of the tubes, leading to the formation of scale that decreases the radiant efficiency of the heater Second, high tube wall temperatures, particularly with respect to the first two reactors in a conversion process such as reforming, can cause cracking of the feed reducing yield Third, an additional complication is that reforming heaters are also susceptible to having metal-catalyzed coking in the fired heater tubes at higher temperatures Metal catalyzed coking can cause the shutdown of reforming units for maintenance work to remove the coke deposits in the reactors resulting from the onset of metal catalyzed coke formation in the fired heater tubes As a result, lower tube wall temperatures are very desirable [0007] There are several solutions to coking problems associated with high tube wall temperatures, but each has its drawbacks a) sulfur can be injected that inhibits coke formation, but this solution generally decreases reformer yields and may be unnecessary for some feeds that do not tend to coke, b) the radiant tubes can be replaced with tubes of different alloys that can raise the maximum allowable heater tube wall temperature, but these alloys tend to be more expensive, c) the heater can be enlarged with more tubes and/or burners to increase surface area, but enlarging a heater is usually expensive, and d) a heater can be added to the senes of heaters to provide some of the required duty, so the size of the existing heater can be decreased However, adding a heater is also usually expensive [0008] Additionally, sometimes conversion units are refurbished during shutdowns to increase the capacity of the units High fired heater tube wall temperatures can limit the potential feed rate increase or reformate octane increase for conversion units, such as reforming units Such tube wall temperature limitations can result in the installation of large expensive fired heater cells Such fired heater cells can be 20% to 25% of the estimated cost of a conversion unit, such as a reforming unit [0009] Therefore, there is a desire to increase the feed through a conversion unit and not exceed the maximum tube wall temperature without incurring at least some of the disadvantages discussed above INFORMATION DISCLOSURE [0010] U S Pat No 4,986,222 (Pickell) discloses a bottom fired fixed vertical heater including radiant and convection coils that heats a hydrocarbon feedstock, preferably naphtha, before the feedstock is desulfunzed in a desulfunzing unit and then to a reforming unit The convection coils communicate with the radiant coils to receive, convey and pass the hydrocarbon feedstock from the radiant coils to the desulfunzing unit [00U] US Pat No 5,879,537 (Peters) discloses a multistage catalytic hydrocarbon conversion system where hydrocarbons flow senally through at least two reaction zones [0012] US Pat No 6,106,696 (Fecteau et al) discloses a reforming process that employs at least two moving bed reaction zones {0013] U S Pat Nos 4,986,222, 5,879,537, and 6,106,696 are hereby incorporated by reference in their entirety BRIEF SUMMARY OF THE INVENTION [0014] One exemplary embodiment of the present invention can be a hydrocarbon conversion process The process may include passing a hydrocarbon stream through at least one heater including at least one burner, a radiant section, and a convection section Generally, the stream passes through the radiant section and then through the convection section before exiting the heater Desirably, the hydrocarbon stream includes, in percent or parts by weight based on the total weight of hydrocarbons in the stream C4 or less less than 0 5%, sulfur or sulfur containing compounds less than 1 ppm, and nitrogen or nitrogen containing compounds less than 1 ppm Preferably, the sulfur or sulfur containing compounds and the nitrogen or nitrogen containing compounds are measured as, respectively, elemental sulfur or nitrogen [0015] Another exemplary reforming process can include operating a reforming unit and passing a stream including hydrocarbons through the radiant section, next through the convection section, and then to an inlet of the reaction zone Generally, the reforming unit includes at least one heater including at least one burner, a radiant section, and a convection section, and a reforming reactor including a reaction zone [0016] An exemplary refinery or petrochemical production facility can include a reforming unit, which in turn may include a heater including a burner, a radiant section, and a convection section, and a reforming reactor The radiant section can include a first tube having an inlet and an outlet for receiving a hydrocarbon stream entering the heater, and a convection section can include a second tube having an inlet and an outlet for receiving the hydrocarbon stream exiting the first tube of the radiant section The reforming reactor can have a reaction zone, which can receive the hydrocarbon stream from the outlet of the second tube [0017] In another exemplary embodiment, a hydrocarbon process may include passing a stream at a feed rate to at least one heater having at least one burner, a radiant section, and a convection section The stream may include hydrocarbons and a concentration of sulfur less than 1 wt-ppm based on the weight of hydrocarbons in the stream, and the radiant section of the heater can operate at a maximum tube wall temperature An enhancement to such an embodiment can include increasing the feed rate and decreasing the tube wall temperature by passing the stream through the radiant section and then through the convection section before exiting at least one heater [0018] The present invention can, with respect to conversion units such as reforming units, allow the economic design or expansion of an existing reforming unit by adding a convection section process coil after the radiant coil in one or more fired heater cells In an existing heater unit, such a modification may be done with minimal changes to the existing heater components, thereby reducing both the capital costs of equipment and shutdown time Thus, the present invention can be particularly well-suited for revamping an existing heater suffering from maximum tube wall temperature limitations, which is generally below 640' C (1,184° F), preferably no more than 635° C (1,175° F ) The lower resultant fired heater tube wall teraperature(s) may also reduce the potential for metal catalyzed coking in the fired heater tubes, which can increase the reliability of the subsequent reactor zones and avoid some of the disadvantages associated with other coking solutions as discussed above BRIEF DESCRIPTION OF THE DRAWING [0019] FIG 1 is a schematic depiction of an exemplary refinery that can include a desulfurization unit and a reforming unit of the present invention [0020] FIG 2 is a schematic depiction of at least a portion of an exemplary reforming unit of the present invention [0021] FIG 3 is a schematic dual cross-sectional view of an exemplary heater with a common convection section and a plurality of radiant sections of the present invention DEFINITIONS [0022] As used herein, the term "hydrocarbon stream" can be a stream including various hydrocarbon molecules, such as straight-chain, branched, or cyclic alkanes, alkenes, alkadienes, and alkynes, and optionally other substances, such as gases, e g, hydrogen, or impurities, such as heavy metals The hydrocarbon stream may be subject to reactions, e g, reforming reactions, but still may be referred to as a hydrocarbon stream, as long as at least some hydrocarbons are present in the stream after the reaction Thus, the hydrocarbon stream may include streams that are subjected to, e g , a hydrocarbon stream effluent, or not subjected to, e g , a naphtha feed, one or more reactions As used herein, a hydrocarbon stream can also include a raw hydrocarbon feedstock, a hydrocarbon feedstock, a feed, a feed stream, a combined feed stream or an effluent Moreover, the hydrocarbon molecules may be abbreviated C1, C2, C3 C„ where "n" represents the number of carbon atoms in the hydrocarbon molecule [0023] As used herein, the term "radiant section" generally refers to a section of a heater receiving 35 - 65% for substantially fouled tubes or 45 - 65% for relatively clean tubes of the heat, primarily by radiant and convective heat transfer, released by, e g, the fuel gas burned by the heater [0024] As used herein, the term "convection section" generally refers to a section of a heater receiving 10 - 45% of the heat, primarily by convective and radiant heat transfer by, e g, the flue gas, released by the fuel gas bumed by the heater Typically, 7-15% of the heat is lost through the stack, so usually no more than 93% of the heat released by the fuel is utilized in the radiant and convection sections [002S] As used herein, the term "heater" can include a furnace, a charge heater, or an interheater A heater can include at least one burner and can include at least one radiant section, at least one convection section, or a combination of at least one radiant section and at least one convection section DETAILED DESCRIPTION OF THE INVENTION [0026] Generally, a catalytic conversion of a hydrocarbon-containing reactant stream in a reaction system has at least two reaction zones where the reactant stream flows serially through the reaction zones Reaction systems having multiple zones generally take one of two forms a side-by-side form or a stacked form In the side-by-side form, multiple and separate reaction vessels, each that can include a reaction zone, may be placed along side each other In the stacked form, one common reaction vessel can contain multiple and separate reaction zones that may be placed on top of each other In both reaction systems, there can be intermediate heating or cooling between the reaction zones, depending on whether the reactions can be endothermic or exothermic [0027] Although the reaction zones can include any number of arrangements for hydrocarbon flow such as downflow, upflow, and crossflow, the most common reaction zone to which this invention is applied may be radial flow A radial flow reaction zone generally includes cylindrical sections having varying nominal cross-sectional areas, vertically and coaxially disposed to form the reaction zone Briefly, a radial flow reaction zone typically includes a cylindrical reaction vessel containing a cylindrical outer catalyst retaining screen and a cylindrical inner catalyst retaining screen that are both coaxially-disposed within the reaction vessel The inner screen may have a nominal, internal cross-sectional area that is less than that of the outer screen, which can have a nominal, internal cross-sectional area that is less than that of the reaction vessel Generally, the reactant stream is introduced into the annular space between the inside wall of the reaction vessel and the outside surface of the outer screen The reactant stream can pass through the outer screen, flow radially through the annular space between the outer screen and the inner screen, and pass through the inner screen The stream that may be collected within the cyhndncal space inside the inner screen can be withdrawn from the reaction vessel Although the reaction vessel, the outer screen, and the inner screen may he cyhndncal, they may also take any suitable shape, such as triangular, square, oblong, or diamond, depending on many design, fabncation, and technical considerations As an example, generally it is common for the outer screen to not be a continuous cyhndncal screen but to instead be an arrangement of separate, elliptical, tubular screens called scallops that may be arrayed around the circumference of the inside wall of the reaction vessel The inner screen is commonly a perforated center pipe that may be covered around its outer circumference with a screen {0028] Preferably, the catalytic conversion processes include catalyst that can include particles that are movable through the reaction zones The catalyst particles may be movable through the reaction zone by any number of motive devices, including conveyors or transport fluid, but most commonly the catalyst particles are movable through the reaction zone by gravity Typically, in a radial flow reaction zone, the catalyst particles can fill the annular space between the inner and outer screens, which may be called the catalyst bed Catalyst particles can be withdrawn from a bottom portion of a reaction zone, and catalyst particles may be introduced into a top portion of the reaction zone The catalyst particles withdrawn from the final reaction zone can subsequently be recovered from the process, regenerated in a regeneration zone of the process, or transferred to another reaction zone Likewise, the catalyst particles added to a reaction zone can be catalyst that is being newly added to the process, catalyst that has been regenerated in a regeneration zone within the process, or catalyst that is transferred from another reaction zone [0029] Illustrative reaction vessels that have stacked reaction zones are disclosed in U S Pat Nos 3,706,536 (Greenwood et al) and 5,130,106 (Koves et al), the teachings of which are incorporated herein by reference in their entirety Generally, the transfer of the gravity-flowing catalyst particles from one reaction zone to another, the mtroduction of fresh catalyst particles, and the withdrawal of spent catalyst particles are effected through catalyst transfer conduits [O030] The feedstocks converted by these processes can include various fractions from a range of crude oils One exemplary feedstock converted by these processes generally includes a stream, which may be a naphtha, including, in percent or parts by weight based on the total weight of hydrocarbons in the stream as disclosed in Table I Table 1 (Table Removed) [0031] The sulfur or sulfur containing compounds and the nitrogen or nitrogen containing compounds are measured as, respectively, elemental sulfur or nitrogen The amounts of sulfur and nitrogen can be measured by, respectively, standard test methods D-4045-04 and D-4629-02 available from ASTM International, 100 Barr Harbor Drive, P O Box C700, West Conshohocken, Pennsylvania, USA [0032] Processes having multiple reaction zones may include a wide vanety of hydrocarbon conversion processes such as reforming, hydrogenation, hydrotreating, dehydrogenation, isomerization, dehydroisomenzation, dehydrocyclization, cracking, and hydrocracking processes Catalytic reforming also often utilizes multiple reaction zones, and will be referenced hereinafter in the embodiments depicted in the drawings Further information on reforming processes may be found in, for example, U S Pat Nos 4,119 526 (Peters et al), 4,409,095 (Peters), and 4,440,626 (Winter et al) [0033] Usually, in catalytic reforming, a feedstock is admixed with a recycle stream comprising hydrogen to form what is commonly referred to as a combined feed stream, and the combined feed stream is contacted with a catalyst in a reaction zone The usual feedstock for catalytic reforming is a petroleum fraction known as naphtha and having an initial boiling point of 82° C (180° F ), and an end boiling point of 203° C (400° F ) The catalytic reforming process is particularly applicable to the treatment of straight run naphthas comprised of relatively large concentrations of naphtheme and substantially straight chain paraffinic hydrocarbons, which are subject to aromatization through dehydrogenation and/or cycltcization reactions The preferred charge stocks are naphthas consisting principally of naphthenes and paraffins that can boil within the gasoline range, although, in many cases, aromatics also can be present This preferred class includes straight-run gasolmes, natural gasolines, synthetic gasolines, and the like As an alternative embodiment, it is frequently advantageous to charge thermally or catalytically cracked gasolines or partially reformed naphthas Mixtures of straight-run and cracked gasoline-range naphthas can also be used to advantage The gasoline-range naphtha charge stock may be a full-boiling gasoline having an initial boiling point of 40 - 82° C (104-180° F ) and an end boiling point within the range of 160 - 220° C (320 - 428° F), or may be a selected fraction thereof which generally can be a higher-boiling fraction commonly referred to as a heavy naphtha, for example, a naphtha boiling in the range of 100 - 200° C (212 - 392° F) In some cases, it is also advantageous to charge pure hydrocarbons or mixtures of hydrocarbons that have been recovered from extraction units, for example, raffinates from aromatics extraction or straight-chain paraffins, which are to be converted to aromatics In some other cases, the feedstock may also contain light hydrocarbons that have 1 - 5 carbon atoms, but since these light hydrocarbons cannot be readily reformed into aromatic hydrocarbons, these light hydrocarbons entering with the feedstock are generally minimized (0034] An exemplary flow through the train of heating and reaction zones is a 4-reaction zone catalytic reforming process, having first, second, third and fourth reaction zones, which can be described as follows [0035] A naphtha-contaimng feedstock can admix with a hydrogen-containing recycle gas to form a combined feed stream, which may pass through a combined feed heat exchanger In the combined feed heat exchanger, the combined feed can be heated by exchanging heat with the effluent of the fourth reaction zone However, the heating of the combined feed stream that occurs in the combined feed heat exchanger is generally insufficient to heat the combined feed stream to the desired inlet temperature of the first reaction zone [0036] Generally, hydrogen is supphed to provide an amount of I - 20 moles of hydrogen per mole of hydrocarbon feedstock entering the reaction zones Hydrogen is preferably supplied to provide an amount of less than 3 5 moles of hydrogen per mole of hydrocarbon feedstock entenng the reaction zones If hydrogen is supphed, it may be supplied upstream of the combined feed exchanger, downstream of the combined feed exchanger, or both upstream and downstream of the combined feed exchanger Alternatively, no hydrogen may be supplied before entering the reforming zones with the hydrocarbon feedstock Even if hydrogen is not provided with the hydrocarbon feedstock to the first reaction zone, the naphthene reforming reactions that occur within the first reaction zone can yield hydrogen as a by-product This by-product, or m-situ-produced, hydrogen leaves the first reaction zone in an admixture with the first reaction zone effluent and then can become available as hydrogen to the second reaction zone and other downstream reaction zones This in situ hydrogen in the first reaction zone effluent usually amounts to 0 5 - 2 moles of hydrogen per mole of hydrocarbon feedstock [0037J Usually, the combined feed stream, or the hydrocarbon feedstock if no hydrogen is provided with the hydrocarbon feedstock, enters a heat exchanger at a temperature of generally 38 - 177' C (100 - 350' F), and more usually 93 - 121° C (200 - 250° F) Because hydrogen is usually provided with the hydrocarbon feedstock, this heat exchanger may be referred to herein as the combined feed heat exchanger, even if no hydrogen is supplied with the hydrocarbon feedstock Generally, the combined feed heat exchanger heats the combined feed stream by transferring heat from the effluent stream of me last reforming reaction zone to the combined feed stream Preferably, the combined feed heat exchanger is an indirect, rather than a direct, heat exchanger, in order to prevent valuable reformate product in the last reaction zone's effluent from intermixing with the combined feed, and thereby being recycled to the reaction zones, where the reformate quality could be degraded [0038] Although the flow pattern of the combined feed stream and the last reaction zone effluent stream within the combined feed heat exchanger could be completely cocurrent, reversed, mixed, or cross flow, the flow pattern is preferably countercurrent By a countercurrent flow pattern, it is meant that the combined feed stream, while at its coldest temperature, contacts one end (i e, the cold end) of the heat exchange surface of the combined feed heat exchanger while the last reaction zone effluent stream contacts the cold end of the heat exchange surface at its coldest temperature as well Thus, the last reaction zone effluent stream, while at its coldest temperature within the heat exchanger, exchanges heat with the combined feed stream that is also at its coldest temperature within the heat exchanger At another end (i e, the hot end) of the combined feed heat exchanger surface, the last reaction zone effluent stream and the combined feed stream, both at their hottest temperatures within the heat exchanger, contact the hot end of the heat exchange surface and thereby exchange heat Between the cold and hot ends of the heat exchange surface, the last reaction zone effluent stream and the combined feed stream flow in generally opposite directions, so that, in general, at any point along the heat transfer surface, the hotter the temperature of the last reaction zone effluent stream, the hotter is the temperature of the combined feed stream with which the last reaction zone effluent stream exchanges heat For further information on flow patterns in heat exchangers, see, for example, pages 10-24 to 10-31 of Perry's Chemical Engineers' Handbook, Sixth Edition, edited by Robert H Perry et al, published by McGraw-Hill Book Company in New York, in 1984, and the references cited therein [0039] Generally, the combined feed heat exchanger operates with a hot end approach that is generally less than 56° C (100° F), and preferably less than 33° C (60° F), and more preferably less than 28° C (50° F) As used herein, the term "hot end approach" is defined as follows based on a heat exchanger that exchanges heat between a hotter last reaction zone effluent stream and a colder combined feed stream, where TI is the inlet temperature of the last reaction zone effluent stream, T2 is the outlet temperature of the last reaction zone effluent stream, tl is the inlet temperature of the combined feed stream, and t2 is the outlet temperature of the combined feed stream Then, as used herein, for a countercurrent heat exchanger, the "hot end approach" is defined as the difference between Tl and t2 In general, the smaller the hot end approach, the greater is the degree to which the heat in the last reactor zone's effluent is exchanged to the combined feed stream [0040] Although shell-and-tube type heat exchangers may be used, another possibility is a plate type heat exchanger Plate type exchangers are well known and commercially available in several different and distinct forms, such as spiral, plate and frame, brazed-plate fin, and plate fin-and-tube types Plate type exchangers are described generally on pages 11-21 to 11-23 in Perry's Chemical Engineers' Handbook, Sixth Edition, edited by R H Perry et al, and published by McGraw Hill Book Company, in New York, in 1984 [0041] In one embodiment, the combined feed stream can leave the combined feed heat exchanger at a temperature of 399 - 516° C (750 - 960° F) [0042] Consequently, after exitmg the combined feed heat exchanger and prior to entenng the first reactor, the combined feed stream often requires additional heating This additional heating can occur in a heater, which is commonly referred to as a charge heater, which can heat the combined feed stream to the desired inlet temperature of the first reaction zone Such a heater can be a gas-fired, an oil-fired, or a mixed gas-and-oil-fired heater, of a land that is well known to persons of ordinary skill in the art of reforming The heater may heat the first reaction zone effluent stream by radiant and/or convective heat transfer Commercial fired heaters for reforming processes typically have individual radiant heat transfer sections for individual heaters, and a common convective heat transfer section that is heated by the flue gases from the radiant sections [0043] Desirably, the stream first enters the radiant section of the heater The stream can enter and exit the top or lower portion of the radiant section through U-shaped or inverted U-shaped tubes, or enter the top portion where the temperature is lowest in the radiant section and exit at the bottom where the temperature is hottest in the radiant section, or conversely, enter at the bottom and exit at the top Preferably, the stream enters and exits the top portion of the radiant section for this and any subsequent heaters [0044] Afterwards, the combined feed stream can enter the convection section of that same heater The stream can enter and exit the top or lower portion of the convection section, or enter the top portion where the temperature is lowest in the convection section and exit at the bottom where the temperature is hottest in the convection section through U-shaped tubes that are usually orientated sideways, or conversely, enter at the bottom and exit at the top Preferably, the stream enters the top portion and exits the bottom portion of the convection section for this and any subsequent heaters It should be understood that one or more heaters described herein (e g, a charge or an interheater) can have the stream enter the radiant section then the convection section, may have the stream enter the convection section and then the radiant section, or may have the stream enter only the radiant or convection section, depending, e g, on the maximum tube wall temperature limitations [0045] Commercial fired heaters for reforming processes typically have individual radiant heat transfer sections for individual heaters and a common convective heat transfer section that may be heated by the flue gases from the radiant sections The temperature of the combined feed stream leaving the charge heater, which may also be the inlet temperature of the first reaction zone, is generally 482 - 560* C (900 - 1,040" F), preferably 493 - 549' C (920-1,020" F) [0044] Once the combined feed stream passes to the first reaction zone, the combined feed stream may undergo conversion reactions In a common form, the reforming process can employ the catalyst particles in several reaction zones interconnected in a series flow arrangement There may be any number of reaction zones, but usually the number of reaction zones is 3,4 or 5 Because reforming reactions occur generally at an elevated temperature and are generally endothermic, each reaction zone usually has associated with it one or more heating zones, which heat the reactants to the desired reaction temperature [0047] This invention can be particularly applicable in a reforming reaction system having at least two catalytic reaction zones where at least a portion of the reactant stream and at least a portion of the catalyst particles flow serially through the reaction zones These reforming reaction systems can be a side-by-side form or a stacked form, as discussed above [0048] Generally, the reforming reactions are normally effected in the presence of catalyst particles comprised of one or more Group VIII (IUPAC 8-10) noble metals (e g, platinum, iridium, rhodium, and palladium) and a halogen combined with a porous earner, such as a refractory inorganic oxide U S Pat No 2,479,110 (Haensel), for example, teaches an alumina-platinum-halogen reforming catalyst Although the catalyst may contain 0 05 - 2 0 wt-% of Group VIII metal, a less expensive catalyst, such as a catalyst containing 0 05 - 0 5 wt-% of Group VIII metal may be used The preferred noble metal is platinum In addition, the catalyst may contain indium and/or a lanthanide series metal such as cerium The catalyst particles may also contain 0 05 - 0 5 wt-% of one or more Group IVA (TUPAC 14) metals (e g tin, germanium, and lead), such as described in U S Pat No 4,929,333 (Moser et al), U S Pat No 5,128,300 (Chao et al), and the references cited therein Generally, the halogen is normally chlorine and the alumina is commonly the earner Preferred alumina matenals axe gamma, eta, and theta alumina, with gamma and eta alumina generally being most preferred One property related to the performance of the catalyst is the surface area of the carrier Preferably, the earrier has a surface area of 100-500 m2/g The activity of catalysts having a surface area of less than 130 m2/g tend to be more detrimentally affected by catalyst coke than catalysts having a higher surface area Generally, the particles are usually spheroidal and have a diameter of 1 6 to 3 1 mm (1/16th - 1/8th inch), although they may be as large as 6 35 mm (1/4th inch) or as small as I 06 mm (1/24th inch) In a particular reforming reaction zone, however, it is desirable to use catalyst particles which fall in a relatively narrow size range A preferred catalyst particle diameter is 1 6 mm (1/16th inch) [0049] A reforming process can employ a fixed catalyst bed, or a moving bed reaction vessel and a moving bed regeneration vessel In the latter, generally regenerated catalyst particles are fed to the reaction vessel, which typically includes several reaction zones, and the particles flow through the reaction vessel by gravity Catalyst may be withdrawn from the bottom of the reaction vessel and transported to the regeneration vessel In the regeneration vessel, a multi-step regeneration process is typically used to regenerate the catalyst to restore its Ml ability to promote reforming reactions US PatNos 3,652,231 (Greenwood etal), 3,647,680 (Greenwood et al) and 3,692,496 (Greenwood et al) desenbe catalyst regeneration vessels that are suitable for use in a reforming process Catalyst can flow by gravity through the various regeneration steps and then be withdrawn from the regeneration vessel and transported to the reaction vessel Generally, arrangements are provided for adding fresh catalyst as make-up to and for withdrawing spent catalyst from the process Movement of catalyst through the reaction and regeneration vessels is often referred to as continuous though, in practice, it is semicontinuous By semicontinuous movement it is meant as the repeated transfer of relatively small amounts of catalyst at closely spaced points in time For example, one batch every twenty mmutes may be withdrawn from the bottom of the reaction vessel and withdrawal may take five minutes, that is, catalyst can flow for five mmutes If the catalyst inventory in a vessel is relatively large in companson with this batch size, the catalyst bed in the vessel may be considered to be continuously moving A moving bed system can have the advantage of maintaining production while the catalyst is removed or replaced [0050] Typically, the rate of catalyst movement through the catalyst beds may range from as little as 45 5 kg (100 pounds) per hour to 2,722 kg (6,000 pounds) per hour, or more [0051] The reaction zones of the present invention can be operated at reforming conditions, which include a range of pressures generally from atmospheric pressure of 0 -6,895 kPa(g) (0 psi(g) - 1,000 psi(g)), with particularly good results obtained at the relatively low pressure range of 276 - 1,379 kPa(g) (40 - 200 psi(g)) The overall liquid hourly space velocity (LHSV) based on the total catalyst volume in all of the reaction zones is generally 0 1-10 hr-1, preferably 1 - 5 hr1, and more preferably 1 5 - 2 0 hr-1 [0052] As mentioned previously, generally naphthene reforming reactions that are endothermic occur in the first reaction zone, and thus the outlet temperature of the first reaction zone can be less than the inlet temperature of the first reaction zone and is generally 316 - 454° C (600 - 850° F) The first reaction zone may contain generally 5% - 50%, and more usually 10% - 30%, of the total catalyst volume in all of the reaction zones Consequently, the liquid hourly space velocity (LHSV) in the first reaction zone, based on the catalyst volume in the first reaction zone, can be generally 0 2 - 200 hr-1, preferably 2-100 hr-1, and more preferably 5-20 hr-1 Generally, the catalyst particles are withdrawn from the first reaction zone and passed to the second reaction zone, such particles generally have a coke content of less than 2 wt-% based on the weight of catalyst [0053] Because of the endothermic reforming reactions that occur in the first reaction zone, generally the temperature of the effluent of the first reaction zone falls not only to less than the temperature of the combined feed to the first reaction zone, but also to less than the desired inlet temperature of the second reaction zone Therefore, the effluent of the first reaction zone can pass through another heater, which is commonly referred to as the first interheater, and which can heat the first reaction zone effluent to the desired inlet temperature of the second reaction zone [0054] Generally, a heater is referred to as an interheater when it is located between two reaction zones, such as the first and second reaction zones The first reaction zone effluent stream leaves the interheater at a temperature of generally 482 - 560° C (900 -1,040° F) Accounting for heat losses, the interheater outlet temperature is generally not more than 5° C (10° F ), and preferably not more than 1° C (2° F ), more than the inlet temperature of the second reaction zone Accordingly, the inlet temperature of the second reaction zone is generally 482 - 560° C (900 -1,040° F ), preferably 493 - 549° C (920 -1,020° F ) The inlet temperature of the second reaction zone is usually at least 33° C (60° F) greater than the inlet temperature of the first reaction zone, and may be at least 56° C (100° F ) or even at least 83° C (150° F) higher than the first reaction zone inlet temperature [0055] On exiting the first mterheater, generally the first reaction zone effluent enters the second reaction zone As in the first reaction zone, the endothermic reactions can cause another decline in temperature across the second reaction zone Generally, however, the temperature decline across the second reaction zone is less than the temperature decline across the first reaction zone, because the reactions that occur in the second reaction zone are generally less endothermic than the reactions that occur in the first reaction zone Despite the somewhat lower temperature decline across the second reaction zone, the effluent of the second reaction zone is nevertheless still at a temperature that is less than the desired inlet temperature of the third reaction zone [0056] The second reaction zone generally includes 10% - 60%, and more usually 15% -40%, of the total catalyst volume in all of the reaction zones Consequently, the liquid hourly space velocity (LHSV) in the second reaction zone, based on the catalyst volume in the second reaction zone, is generally 0 13 - 134 hr"1, preferably 1 3 - 67 hr"1, and more preferably3 3-l34hr-1, [0057] The second reaction zone effluent can pass a second mterheater (the first mterheater being the previously described mterheater between the first and the second reaction zones), and after heating, can pass to a third reaction zone However, one or more additional heaters and/or reactors after the second reaction zone can be omitted, that is, the second reaction zone may be the last reaction zone in the tram The third reaction zone contains generally 25% - 75%, and more usually 30% - 50%, of the total catalyst volume in all of the reaction zones Likewise, the third reaction zone effluent can pass to a thud mterheater and from there to a fourth reaction zone The fourth reaction zone contains generally 30% - 80%, and more usually 40% - 50%, of the total catalyst volume in all of the reaction zones The inlet temperatures of the third, fourth, and subsequent reaction zones are generally 482 - 560° C (900 - 1,040° F), preferably 493 - 549° C (920 -1,020° F) [0058] Because the reforming reactions that occur in the second and subsequent (i e, third and fourth) reaction zones are generally less endothermic than those that occur in the first reaction zone, the temperature drop that occurs in the later reaction zones is generally less than that that occurs in the first reaction zone Thus, the outlet temperature of the last reaction zone may be 11° C (20° F ) or less below the inlet temperature of the last reaction zone, and indeed may conceivably be higher than the inlet temperature of the last reaction zone [0059] The desired refonnate octane of the C5 + fraction of the reformate is generally 85 - 107 clear research octane number (C5 + RONC), and preferably 98 - 102 C5 + RONC (0060) Moreover, any inlet temperature profiles can be utilized with the above-descnbed reaction zones The mlet temperature profiles can be flat or skewed, such as ascending, descending, hill-shaped, or valley-shaped Desirably, the mlet temperature profile of the reaction zones is flat [0061] The last reaction zone effluent stream can be cooled in the combined feed heat exchanger by transferring heat to the combined feed stream After leaving the combined feed heat exchanger, the cooled last reactor effluent passes to a product recovery section Suitable product recovery sections are known to persons of ordinary skill in the art of reforming Exemplary product recovery facilities generally include gas-liquid separators for separating hydrogen and C1 - C3 hydrocarbon gases from the last reaction zone effluent stream, and fractionation columns for separating at least a portion of the C4 - C5 light hydrocarbons from the remainder of the refonnate In addition, the refonnate may be separated by distillation into a light reformate fraction and a heavy reformate fraction [0062] During the course of a reforming reaction with a moving catalyst bed, catalyst particles become deactivated as a result of mechanisms such as the deposition of coke on the particles, that is, after a penod of tune in use, the ability of catalyst particles to promote reforming reactions decreases to the point that the catalyst is no longer useful The catalyst can be reconditioned, or regenerated, before it is reused in a reforming process (0063] The drawings illustrate an embodiment of the present invention as applied to a catalytic reforming process The drawings are presented solely for purposes of illustration and are not intended to limit the scope of the invention as set forth in the claims The drawings show only the equipment and lines necessary for an understanding of the invention and do not show equipment such as pumps, compressors, heat exchangers, and valves which are not necessary for an understanding of the invention and which are well known to persons of ordinary skill in the art of hydrocarbon processing DETAILED DESCRIPTION OF THE DRAWINGS [0064] Referring to FIG 1, a refinery 100 is schematically depicted The refinery 100 can include a desulfunzation unit 150 and a reforming unit 200 The desulfunzation unit 150 may include an inlet 154, an outlet 158, and a desulfunzation reactor 180 [0065] The reforming unit 200 can include a heat exchanger 204, a reforming reactor 210 having an inlet 212, an outlet 214, and a plurality of reaction zones 216, a separator 290, and at least one heater or furnace 300 Generally, the heat exchanger 204 heats the feed to the plurality of reaction zones 216 receiving an effluent 286 from a reaction zone Generally, the plurality of reaction zones 216 includes a first reaction or a reaction zone 230 having an inlet 232 and an outlet 234, a second reaction zone 240 having an inlet 242 and an outlet 244, and a third reaction zone 250 having an inlet 252 and an outlet 254, and a fourth reaction zone 260 having an inlet 262 and an outlet 264 The first reaction zone inlet 232 can also be the inlet 212 of the reforming reactor 210 Similarly, the fourth reaction zone outlet 264 can also be the outlet 214 of the reforming reactor 210 The at least one heater 300, such as a plurality of heaters 302, can include a first or charge heater 306, and a plurality of interheaters 328 The plurality of interheaters 328 can include a first interheater 330, a second mterheater 350, and a third mterheater 370 The charge heater 306 can include at least one burner, preferably a plurality of burners, 308, a radiant section 310, and a convection section or a separate convection section 318, the first interheater 330 can include at least one burner, preferably a plurality of burners, 332, a radiant section 334, and a convection section 342, the second interheater 350 can include at least one burner, preferably a plurality of burners, 352, a radiant section 354, and a convection section 362, and the third mterheater 370 can include at least one burner, preferably a plurality of burners, 372, a radiant section 374, and a convection section 382 [0066] Each radiant section 310, 334,354 and 374 generally includes, respectively, at least one radiant tube 312, 336, 356 and 376, and each convection section 318,342,362 and 382 generally includes, respectively, at least one convection tube 320, 344, 364 and 384 Each radiant tube 312, 336, 356, and 376 can include, respectively, an inlet 314 and an oudet 316, an inlet 338 and an outlet 340, an inlet 358 and an outlet 360, and an inlet 378 and an outlet 380 Each convection tube 320, 344, 364, and 384 can include, respectively, an inlet 322 and an outlet 324, an inlet 346 and an outlet 348, an inlet 366 and an outlet 368, and an inlet 386 and an outlet 388 Moreover, although only one tube is discussed for each section 310, 318,334,342,354,362,374 and 382 and the plurality of burners 308,332,352, and 372 for each respective heater 306, 330, 350, and 370 in the reforming unit 200, it should be understood that generally each section can include an inlet manifold, a senes of parallel tubes, and an outlet manifold and each heater can include several burners [0067] Moreover, in this exemplary embodiment, the reforming reactor 210 can be a moving bed reactor, where fresh or regenerated catalyst particles can be introduced through a line 220 via an inlet nozzle 222 and spent catalyst can exit via an outlet nozzle 224 via a line 226 [0068] During processing, a raw hydrocarbon feed 140 enters the desulfunzation unit 150 via an inlet 154 Generally, the raw hydrocarbon feed 140 is preferably naphtha optionally containing hydrogen that has not yet been desulfunzed The raw hydrocarbon feed 140 usually has high levels of impunties, such as sulfur and nitrogen, as discussed above The raw hydrocarbon feed 140 may enter the desulfunzation reactor 180 to remove sulfur and/or nitrogen containing compounds, as well as other possible contaminants Desirably, the amounts of sulfur and nitrogen are reduced to the levels as disclosed above \n Table I (0069] Afterwards, a stream, a hydrocarbon stream, or a desulfunzed hydrocarbon stream 270 may exit the desulfunzation unit 150 and enter the reforming unit 200 Initially, the stream 270 may receive a recycled hydrogen gas stream 292 from the separator 290 Next, the stream 270 can enter the heat exchanger 204 to be heated by an effluent 286 That being done, generally the stream 270 enters the radiant section 310 via the inlet 314 to be heated in the at least one tube 312 by the plurality of burners 308 of the charge heater 306, and then can enter the convection section 318 via the inlet 322 to be heated in the at least one tube 320 by the flue gases At this point, the stream 270 is sufficiently heated to be a feed 272 to the first reaction zone 230 The feed 272 may enter the first reaction zone 230 via the inlet 232 and exit via the outlet 234 An effluent 274 from the first reaction zone 230 can enter the radiant section 334 via the inlet 338 to be heated by the plurality of burners 332 of the first interheater 330, and then enter the convection section 342 to be heated by the flue gases Afterwards, the stream 270 can be a feed 276 to the second reaction zone 240 The feed 276 may enter the second reaction zone 240 via the inlet 242 and exit via the outlet 244 [0070] Subsequently, the stream 270 can be an effluent 278 from the second reaction zone 240 and enter via the inlet 358 of the radiant section 354 to be heated in the at least one tube 356 by the plurality of burners 352 of the second interheater 350 After exiting the radiant section 354 via the outlet 360, the stream 270 may enter the convection section 362 via the inlet 366 to he heated in the at least one tube 364 by the flue gases before entering the third reaction zone 250 via the inlet 252 as a feed 280 to the third reaction zone 250 Afterwards, the stream 270 can exit via the outlet 254 as the effluent 282 from the third reaction zone 250 that may enter the radiant section 374 of the third interheater 370 via the inlet 378 to be heated in the at least one tube 376 by the plurality of burners 372 That being done, the stream 270 can enter the convection section 382 via the inlet 386 to be heated by flue gases Next, the stream 270 can enter via the inlet 262 as a feed 284 of the fourth reaction zone 260 After undergoing additional conversion, the stream 270 can exit as an effluent 286 of the fourth reaction zone 260 via the outlet 264 That being done, the effluent 286 can pass through the exchanger 204 to heat the stream 270, as discussed above [0071] Afterwards, the effluent 286 can enter the separator 290, where the recycled hydrogen gas stream can exit at the top of the separator 290 and a reformate stream 294 can exit at the bottom [0072] Although in this exemplary embodiment the stream 270 flows through the radiant section and then through the convection section in all of the heaters 306, 330,350, and 370, it should be understood that one, two or three heaters in the senes can have this flow sequence, and the remaining heaters can have a different arrangement, such as an opposite sequence, i e, the stream 270 can flow through the convection section then the radiant section, or the stream 270 can flow only through a radiant section and not a convection section, or vice-versa [0073] In another exemplary embodiment as depicted in FIG 2, at least a portion of a reforming unit 400 may include at least one heater or furnace 410 and at least one reforming reactor 440 including a reaction zone 450 Although only one furnace 410 and one reforming reactor 440 are depicted, it should be understood that the reforming unit 400 may include other furnaces or reforming reactors, such as side-by-side reforming reactors As depicted, a stream 270 may enter the furnace 410 to be heated in a radiant section 412 having an upper portion 416 and a lower portion 418 by at least one burner, preferably a plurality of burners, 414 before entenng a convection section 420 Generally, the stream 270, discussed above, enters and exits from the upper portion 416 of the radiant section 412 before entering the convection section 420 Desirably, the stream 270 enters a cooler, upper portion 422 of the convection section 420 and exits a hotter, lower portion 424 Afterwards, the stream 270 can enter the reforming reactor 440 [0074] Although the embodiments discussed above can be designed for a new reforming unit, it should be understood that die disclosed features can implemented during the revamp of an existing heater to overcome, for example, limitations imposed by maximum tube wall temperatures The maximum tube wall temperature for a heater can depend upon, for example, the composition or alloy of the tube Generally, it is desired for the maximum tube wall temperature not to exceed 640' C (1,184° F) For revamping such a heater in the reforming unit, it is estimated, although not wanting to be bound, that the unit could have an increased feed rate of 10% - 30%, possibly 20% [0075] Although the embodiments descnbed above depict heaters with their own convection section, it should be understood that the reforming units descnbed above may include one or more heaters or furnaces that have a plurality of radiant sections sharing a common convection section Particularly, refernng to FIG 3, a heater 500 can include a common convection section 502 and a plurality of radiant sections 516, such as a first radiant or charge section 520, a second radiant or first interheater section 540, and a third radiant or second interheater section 550 The flue gas nsing from the radiant sections 520, 540 and 550 can enter the convection section 502 and exit a stack 560 The common convection section 502 generally includes several convection tubes 506 in a parallel configuration 508 Each tube 506 having an inlet 510 and an outlet 512 can be somewhat U-shaped and orientated on its side, where several tubes 506 can be stacked front-to-back in rows In this exemplary embodiment, the common convection section 502 can be divided into portions or rows 514 One or more convection tubes 506 can conespond to the first radiant section 520, namely the stream 270 can flow from the radiant section 520 to the row or portion 514 in the common convection section 502 Although convection tubes 506 can be onentated sideways it should be understood that other onentations are possible, such as onentating the U-shaped tubes flat and stacking several tubes 506 vertically in rows [0076] Although only indicated in the first radiant section 520 generally each radiant section 520, 540 and 550 can include several radiant tubes 524 in a parallel configuration 526, desirably each radiant tube 522 having an inlet 528 and an outlet 530 may be somewhat U-shaped and orientated upwardly, and several such tubes 522 can be stacked front-to-back The radiant sections 520, 540, and 550 can be separated by firewalls 572 and 574 and include, respectively, a plurality of burners 532,542, and 552 Utilizing the heater 500, a hydrocarbon stream can enter, e g, the first radiant section 520, then at least a portion of a convection section 502 before entering, e g, a reforming reaction zone 230, as depicted in FIG 1 [0077] Without further elaboration, it is believed that one skilled in fee art can, using the preceding description, utilize the present invention to its fullest extent The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever ILLUSTRATIVE EMBODIMENTS [0078] The following examples are intended to further illustrate the subject process These illustrations of embodiments of the invention are not meant to limit the claims of this invention to the particular details of these examples These examples are based on engineering calculations and actual operating expenence with similar processes [0079] In these prophetic examples, different options for fired heater designs are analyzed for revamping a reforming unit A first set of Example 1 discusses a revamp of one heater and a second set of Examples 2-5 discusses the revamp of another heater For each set, unless otherwise indicated, the heater duties are for 4-reactor/4-heater processes, which are moving bed processes with continuous regeneration that within each set reform the same feedstock composition at the same feed rate and the LHSV, hydrogen to hydrocarbon molar ratio, reactor pressure, catalyst, C5+RONC, catalyst distribution, and catalyst circulation rate each are the same within each set EXAMPLES Example 1 [0080] The existing first interheater (second heater in a series of heaters) of the reforming unit has a maximum tube wall temperature limitation that prevents an increase in feed rate In this example, it is desirable that the tube wall temperature be below 635" C (1,175° F) Before revamping, the first interheater includes a process coil in the convection section followed, in the direction of flow of the first reaction zone effluent, by a process coil in the radiant section An analysis of this fired heater cell shows that the calculated maximum tube wall temperature is 639° C (1,183° F ) By reversing the order of the convection section and radiant sections, l e placing the radiant section first followed by the convection section, the maximum tube wall temperature drops to 606° C (1,123 ° F) Additionally, it can then be determined that the charge heater (the first heater in the senes) has a maximum tube wall temperature of 638° C (1,181 ° F ) for the revamp, and could also be modified by adding a process convection section coil in series and after with the existing radiant section This new convection section coil is placed above the first interheater coil The resultant charge heater maximum tube wall temperature drops from 638° C (1,181° F) to 619° C (1,147° F) Examples 2-5 [0081] In this set, an existing heater is analyzed for revamping to meet increased duty requirements The heater has five radiant cells sharing a common convection section The common convection section has four rows of tubes, namely rows 1 and 2 in the lower portion of the convection section and rows 3 and 4 in the upper portion of the convection section These radiant cells are a first charge cell (Cell A), a second charge cell (Cell Al), and three interheater cells (Cell B, Cell C and Cell D with Cell D being initially shutdown) These cells are used to heat the feed to respective reforming reaction zones Moreover, in these examples it is generally desirable that the maximum tube wall temperature be below 640° C (1,184° F) Example 2 [0082] Initially, it is proposed to add a new radiant section as the first interheater (No 1 IH), as disclosed in the following Table 2 Table 2 (Table Removed) [0083] It is generally more economical to use an existing interheater rather than construct a new one due to a longer turnaround time and a larger capital expense However, even using a new radiant cell for the first interheater can result in the radiant section of Cells Al, B, and C exceeding the maximum tube wall temperature of 640° C (1,184° F) Emphasis added in the above and later tables Example 3 [0084] In this example, the existing heater is modified in an attempt to meet the increased duty requirements As discussed above, modifying an existing heater is generally more economical than mstallmg new radiant cells In this example, Cell A is the radiant section of a charge heater, Cell A1 is the radiant section of the first interheater, Cells C and D are the radiant sections of a second interheater, and Cell B is the radiant section of the third interheater Rows 3 and 4 and rows 1 and 2 of the convection section provide preheating to, respectively, Cell A and Cell A1 Cells B-D have no convective preheating The existing heater coils are utilized The results are depicted below in Table 3 Table 3 (Table Removed) [0085] The existing heater suffers several deficiencies, namely, the desired duty requirements could elevate maximum tube wall temperatures for Cells A, B, C and D to above 640° C (1,184° F), even with convection coil preheating the charge and first interheater radiant coils Thus, the existing pass number, coil inside diameter (ID) and available radiant surface area are unacceptable for revamping to meet the desired duty requirements, even if the existing coils have good process hydraulics Example 4 [0086] In this example, the original coils of Cells A, Al and B are changed to schedule 40 pipe, average wall Moreover, the flow is split proportionally through Cells C and D of the second mtcrheater The results are depicted below in Table 4 Table 4 (Table Removed) [0087] The average radiant flux values in Cell A approach the maximum revamp limit of 38,000 kcal/m2*h (14,012 BTU/sq ft 2*hr) and in Cell Al exceed the allowable flux limit, which is the first or No 1 mtcrheater radiant section The maximum tube wall temperature limit 640° C (1,184° F) is exceeded in cells Al, C, and D No additional passes can be added to the radiant coils Generally, although smaller ID coils have lower film temperatures and a resulting lower tube wall temperature, the smaller ID coils have less surface area per linear foot and less radiant surface area. Usually, larger ID coils have higher film temperatures and higher maximum tube wall temperatures Achieving a balance between maximum radiant surface area and maximum tube wall temperature is typically desired In this example, proportioning the flow in Cells C and D does not prevent exceeding the maximum tube wall temperature, while Cell B with a new, smaller coil inside diameter does not exceed the maximum tube wall temperature Example 5 [0088] In this example, the flow through rows 3 and 4 and rows 1 and 2 is reversed with respect to, respectively, Cells A and Al In other words, the hydrocarbon flow first flows through Cells A and Al before entering, respectively, rows 3 and 4 and rows I and 2 In addition, Cell D is recoiled to be a mirror image of Cell C and the flow through Cells C and D is put in senes The results are depicted below in Table 5 Table 5 (Table Removed) [0089] Reversing the flow patterns between the radiant and convection sections result in the radiant sections of the charge heater and first interheater (Cells A and Al) not exceeding the maximum tube wall temperature, despite that additional surface area is required to lower the maximum average radiant flux in the first interheater radiant section (Cell Al) Also, section b of the second interheater (Cell D) exceeds the maximum tube wall temperature, so the senes flow through parts a and b of the second interheater (Cells C and D) does not appear to remedy the maximum tube wall temperature limitation for this heater ]0090] To remedy these shortcomings, other modifications can be made As an example, the process duty load of a heater can be increased, the convection surface area in the reforming process service can be increased, and service may be added to the charge heater In addition, smaller diameter coils can replace existing coils and the flow may be split to pass through two or more cells in a parallel configuration Another modification can be adding coil surface area to at least one cell [0091] As depicted above, reversing the flow so that hydrocarbons pass first through the radiant section before entering the convection section can aid in the reduction of tube wall temperature to avoid maximum temperature limit constraints [0092] In the foregoing, all temperatures are set forth uncorrected in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated [0093] The entire disclosures of all applications, patents and publications cited herein are hereby incorporated by reference [0094] From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this mvention and, without departing from the spirit and scope thereof, can make various changes and modifications of the mvention to adapt it to various usages and conditions We Claims 1. A hydrocarbon conversion process, comprising: a) passing a hydrocarbon stream comprising, in percent or parts by weight based on the total weight of hydrocarbons in the stream: C4 or less: less than 0.5%, sulfur or sulfur containing compounds: less than 1 ppm, and nitrogen or nitrogen containing compounds: less than 1 ppm, wherein the sulfur or sulfur containing compounds and the nitrogen or nitrogen containing compounds are measured as, respectively, elemental sulfur or nitrogen; through at least one heater comprising at least one burner, a radiant section, and a convection section wherein the stream passes through the radiant section and then through the convection section before exiting the heater. 2. The hydrocarbon conversion process according to claim 1, further comprising passing the stream through a plurality of reaction zones; wherein the at least one heater comprises a charge heater comprising a plurality of burners, a radiant section, and a convection section wherein the stream passes through the radiant section and then through the convection section before exiting the heater to enter a first reaction zone. 3. The hydrocarbon conversion process according to claim 2, wherein the at least one heater further comprises a plurality of interheaters, wherein each interheater comprises at least one burner and a radiant section, and forms a common convection section with at least one other interheater and further comprising passing an effluent from a first reaction zone to a first interheater wherein the effluent from the first reaction zone passes through the radiant section and then through the convection section before exiting the first interheater to enter a second reaction zone. 4. The hydrocarbon conversion process according to claim 1, further comprising passing the stream through a plurality of reaction zones; wherein the at least one heater comprises a plurality of interheaters, wherein each interheater comprises at least one burner, a radiant section, and a convection section or forms a common convection section with at least one other heater and further comprising passing an effluent from a first reaction zone to a first interheater wherein the effluent from the first reaction zone passes through the radiant section and then through the convection section before exiting the first interheater to enter a second reaction zone. 5. The hydrocarbon conversion process according to claim 1 wherein the hydrocarbon conversion process is a reforming process, the process further comprising operating a reforming unit comprising the at least one heater and a reforming reactor comprising a reaction zone; and passing the stream comprising hydrocarbons, after exiting the heater, to an inlet of the reaction zone. 6. The hydrocarbon conversion process according to claim 5, wherein operating the reforming unit, further comprises operating a plurality of heaters, wherein each heater comprises at least one burner, a radiant section, and at least a portion of a convection section; and wherein the reforming reactor comprises a first, a second, a third, and a fourth reaction zone. 7. The hydrocarbon conversion process according to claim 6, wherein operating the plurality of heaters, comprising operating a charge heater before the first reaction zone and an interheater before each of the second, third and fourth reaction zones. 8. The hydrocarbon conversion process according to claim 7, wherein passing the stream comprises at least one of: passing a feed through a radiant section and next through a convection section of the charge heater to the first reaction zone; passing an effluent from the first reaction zone through a radiant section and next through a convection section of a first interheater to the second reaction zone; passing an effluent from the second reaction zone through a radiant section and next through a convection section of a second interheater to the third reaction zone; and passing an effluent from the third reaction zone through a radiant section and next through a convection section of a third interheater to the fourth reaction zone. 9. A facility consisting of at least one of a refinery and a petrochemical production facility, comprising: a) a reforming unit comprising: i) a heater comprising a burner, a radiant section comprising a first tube having an inlet and an outlet for receiving a hydrocarbon stream entering the heater, and a convection section comprising a second tube having an inlet and an outlet for receiving the hydrocarbon stream exiting the first tube of the radiant section; and ii) a reforming reactor comprising a reaction zone wherein the reaction zone receives the hydrocarbon stream from the outlet of the second tube. 10. The facility according to claim 9, further comprising: a desulfurization unit comprising a desulfurization reactor; wherein an outlet of the desulfurization unit provides a desulfurized hydrocarbon stream to the reforming unit. 11. A hydrocarbon conversion process, substantially as hereinbefore described with reference to the foregoing description, examples and accompanying drawings.

Documents:

2198-delnp-2009-abstract.pdf

2198-delnp-2009-Claims-(26-09-2013).pdf

2198-delnp-2009-claims.pdf

2198-delnp-2009-Correspondence Others-(20-09-2013).pdf

2198-delnp-2009-Correspondence Others-(26-09-2013).pdf

2198-delnp-2009-correspondence-others.pdf

2198-delnp-2009-description (complete).pdf

2198-delnp-2009-drawings.pdf

2198-delnp-2009-form-1.pdf

2198-delnp-2009-form-2.pdf

2198-delnp-2009-form-26.pdf

2198-delnp-2009-Form-3-(20-09-2013).pdf

2198-delnp-2009-form-3.pdf

2198-delnp-2009-form-5.pdf

2198-delnp-2009-GPA-(26-09-2013).pdf

2198-delnp-2009-pct-304.pdf

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