MXPA00003152A - Flameless combustor process heater - Google Patents

Abstract

A process heater is provided utilizing flameless combustion, the process heater having:an oxidation reaction chamber (8), the oxidation reaction chamber (4) having an inlet for oxidant, an outlet for combustion products (15), and a flow path between the inlet and the outlet;a fuel conduit (5) capable of transporting a fuel mixture to a plurality of fuel nozzles (6) within the oxidation reaction chamber (4), each nozzle providing communication from within the fuel conduit to the oxidation chamber, with each nozzle along the flowpath between the inlet and the outlet;a preheater (7) in communication with the oxidation chamber inlet, the preheater capable of increasing the temperature of the oxidant to a temperature resulting in the combined oxidant and fuel from the fuel nozzle closest to the oxidation chamber inlet being greater than the autoignition temperature of the combined oxidant and fuel from the fuel nozzle closest to the oxidation chamber inlet;and a process chamber in a heat exchange relationship to the oxidationreaction chamber wherein the heat transferred from the oxidation section does not cause the temperature of the mixture within the oxidation reaction chamber in the vicinity of each fuel nozzle to decrease below the autoignition temperature of the combined mixture in the oxidation chamber in the vicinity of that fuel nozzle.

Description

FLAME-FREE COMBUSTION PROCESS HEATER Field of Invention The invention relates to a process heater for high temperature reactions with improved control of heat transfer.

Background of the Invention High temperature reactions, typically endothermic, such as reforming methane vapor to form hydrogen from steam and hydrocarbons, and pyrolysis of hydrocarbons to produce olefins are typically carried out in boiler tubes with radiant heat transfer in flames Direct to the outer surface of the tubes, and the flow reagents inside the tubes. Direct flame heat is often beneficial due to the high temperature level of heat required, high heat flow required, and relatively low capital cost of the boiler. However, it is difficult to maintain a uniform heat transfer in the boiler to fire. For the Ref: 33147 Therefore, these boiler tubes must operate at an average wall temperature of the tube which is a little below the maximum allowable tube wall temperature due to variations in tube wall temperatures. These variations are composed of difficulties in the measurement of these temperatures. Maximum controlled temperatures are important since coke can generally develop faster on the side of the tube as higher temperature zones. Thick coke imparts increased resistance to heat transfer, and causes the hottest zone to heat up. This effects a rapid growth and can result in a failure in the tube if it is not detected and a corrective action is taken. The corrective action is typically to reduce the fire of one of the burners that are next to the area with the highest temperature. The reduction of fire then decreases the heat transfer around the zone with higher temperature, and generally reduces the performance of the heater.

The lengths of the tubes in the boilers are also generally limited due to the physical constants. In some methane vapor reforming boilers, multiple levels of burners are provided in order to distribute the radiant heat more constantly to the tubes, but even with the multiple levels of burners, the vertical distance over which the burners are provided is limited, due to the difficulty of providing a distribution of fuel and air with varying amounts of airflow in the boiler. In this way, when a long flow path is desired within the boiler, multiple passes with a plurality of bends are generally provided within the combustion chamber. These elbows are common points of problems due to uneven flow and temperatures, and allow erosion along the inner radii.

The combustion of fuels to provide heat inherently generates nitrogen oxides ("NOx") as a result of the exposure of nitrogen, oxygen and free radicals at elevated temperatures. In certain areas, NOx emission is limited, and expensive measurements such as fuel flow treatments such as Selective NOx Catalytic Reduction systems are occasionally required. Burner systems are available to reduce N0X generation by controlling combustion temperatures, but combustion temperatures are hardly controlled, and yet under ideal conditions, a significant amount of N0X is generated.

Another problem with fire process heaters is typically the limited efficiency of the radiant section of the heater. Particularly if a preheating of the combustion air is not provided, a considerable amount of the combusted fuel is used to heat the combustion air for the flame temperatures.While a preheating of the combustion air is provided, the preheating of the combustion air typically does not reach the temperature of the combustion air to approach the flame temperatures, so the efficiencies of the radiant section can be considerably improved with a more effective preheating of the combustion air, and a preheating of the fuel typically is not practice since significant preheating can result in fuel coke formation.

Many methods have been suggested for coping with direct flame from reaction boilers. Additives to feed the pyrolysis boilers have been proposed, including U.S. Patent Nos. 5,567,305, and 5,330,970. These components are said to reduce and defer the principle of coke formation, but they do not eliminate the formation of coke.

Coatings and pretreatments with ceramic to boiler tubes have also been suggested as being effective in reducing coking in, for example, U.S. Patent Nos. 5,600,051, 5,463,159, and 5,424,095. But even with these raw material treatments, these are only marginally effective.

Indirect heating and electric heating have also been suggested, for example, in US Patent Nos. 5,559.51.0, 5,554,347, 5,536,488, 5,321,191, and 5,306,481 as methods that provide more constant heat flux in such a reaction. These methods avoid the disadvantages of fire boilers, but incur additional capital and / or operation costs when compared to fire boiler heaters.

Generally, the yields of such reactions as hydrocarbon reformers to produce hydrogen and carbon oxides, production of olefin by hydrocarbon pyrolysis, and styrene production are improved with increasing temperatures, this is therefore generally desirable to operate at such increased temperatures. These temperatures are generally limited by metallurgical limitations of materials that are economical and consistent for heat transfer from the tubes.

U.S. Patent No. 4,104,018 discloses a combustion chamber for heating a liquid fluid, such as for use in water heaters, wherein a fuel mixture passes through small diameter tubes in which free flames can not form and occurs a low combustion temperature with a low emission of nitrogen oxide.

In addition, oxidation without flame as a heat source in accordance with the preamble of claims 1 and 8 is known from U.S. Patent No. 5,255,742. The well-known flameless heater is thus used to inject heat into an underground formation to coat the oil thereof.

It will be understood that it is desired to provide a heater process for use in an endothermic chemical process in which the metallurgical constraints may be closer together and the chemical reaction process is optimized while maintaining a uniform heat transfer. It will be additionally desirable to provide such a heater which may not require excessive capital or operation costs, and which operate at a higher thermal efficiency. It will also be desirable to provide a process heater wherein NOx generation is reduced as much as possible. It will also be desirable to provide a process heater wherein the heat can be provided to the processes in a controllable manner. The objects of the present invention therefore include performing these results, and other objects that are apparent from the examination of the following description of the invention.

Brief Description of the Invention These and other objects are made by the process heater according to claim 1 and the heating method according to claim 8.

The combustion distributor process heater of the present invention can be used to provide a controllable heat flow in a process chamber, from a heat source having a uniform temperature, and very low NOx creation. Uniform temperatures can be used to increase average temperatures without exceeding maximum temperatures, or to reduce the cost of materials.

Brief Description of the Drawings.

Figure 1 shows a partial section of a heater of the present invention.

Figures 2 through 9 are schematic views of alternative heaters of the present invention.

Detailed description of the invention.

The process heater of the present invention eliminates the combustion chamber of a conventional process heater and provides a uniform heat flow at a controlled temperature level. The combustion chamber is replaced by, for example, concentric tubes that can be spiral, or straight. The fuel and the oxidant are mixed in stages and at a temperature that results in the oxidation of the fuel without producing a flame, thus eliminating the flame as a radiant source of high heat, and replacing the flame with a vapor flow of high temperature fuel. In an endothermic process, this can result in higher temperatures within the metallurgical constants, thus resulting in many processes in improved, selective and / or yielding conversions and reducing by-product production. The elimination of irregular temperatures also reduces the risk of tube failures due to areas with higher local heating. The radial efficiency of flameless combustion in accordance with the present invention may also be greater, resulting in low energy consumption.

The flameless combustion in accordance with the present invention also avoids the high temperature levels within the flames, and the free radicals that occur within the flame. This results in a substantially reduced formation of NOx compounds. The N0X levels of the present invention are less than about one hundred of the levels of conventional fire heaters, and about ten of the levels executed with heaters that use mesh flame stabilizers.

In some endothermic processes, the multiple stages of the heaters are necessary in order to reheat the reagents to complete the reaction at a desired level. The present invention can be applied in such processes to continuously add heat to the reaction, resulting in a simple reaction step, and whose stage is in a controlled temperature profile. This advantage can be used to significantly reduce the residence time requirements, lower the drop pressure through the system, and / or reduce the temperatures as much as possible.

The heaters of the present invention which utilize flameless combustion of fuel gas at temperature levels from about 900 ° C to about 1100 ° C can be manufactured from high temperature alloys such as, for example, WASPALLOY, INCONEL 601, INCONEL 617 , ONCOLOY 800HT, HASTELLOY 235, UNIMET 500 and INCOLOY DS (WASPALLOY, INCONEL, INCOLOY, HASTELLOY, UNIMET and INCOLOY DS are registered trademarks). High temperature ceramic materials can be used and preferred. Less expensive metals can be used in the outer conduits if the internal refractor is used to limit the temperature at which such external conductors are exposed. Ceramic materials with acceptable strength at temperatures of 900 ° C to around 1400 ° C are generally ceramics containing aluminum oxide. Other ceramics that may be useful include chromium oxide, zirconium oxide, and magnesium oxide based on ceramics. The National Refractories and Minerals, Inc., of Livermore, California, A.P. Green Industries, Inc., of Mexico, Missouri, and Alcoa, of Alcoa Center, Penn., Provide such materials.

Generally, flameless combustion is done by preheating the combustion air and fuel gas above the temperature at which when the two vapors are combined, the temperature of the mixture exceeds the auto-ignition temperature of the mixture, but at a temperature less than that which may result in oxidation during mixing being limited by the mixing ratio. In addition, the design of the fuel nozzles and the oxidation chamber is such that the fuel and air velocities are sufficiently large to eliminate the blowing of any stabilized flame. Re-circulation or low velocity regions are provided where a flame can be attached to the fuel nozzle. The preheating of the currents at a temperature between about 850 ° C and about 1400 ° C and then mixing the combustible gas in the combustion air in relatively small increments, can result in a flameless combustion. The increments in which the combustion gas mixes with the fuel gas stream results in a temperature increase of about 20 ° C to 100 ° C in the flue gas stream due to fuel combustion.

In many cases, it is preferable to increase the fuel mixture as heat by stirring the process stream to realize a relatively uniform temperature profile, but this is not a necessary part of the present invention. For example, it may be desired to have an increased or reduced temperature profile. The advantage of the present invention is that the temperature profile, or heat flow, can be controlled as desired. In exothermic processes, the present invention can be used to provide a temperature profile that increases more rapidly than the adiabatic profile.

Through the present invention it is said that it is most useful when maintaining a constant temperature profile in an endothermic reaction, without it being necessary for a reaction to occur. For example, heat can be used to create a phase change such as vaporized water to high steam, or glass processing. The process chamber may contain a process current vapor phase, a liquid phase stream, and / or a solid phase stream.

With reference to Figure 1, a heater of the present invention is shown in a partial sectional view. An oxidation reaction chamber 1 having an inlet 2 and an outlet 3 is shown. Between the inlet and the outlet, a flow path 4 in a heat exchange relationship with a process chamber 8 is provided. Fuel 5 provides a conduit for transporting the fuel to the nozzles 6 scattered along the flow path 4. The nozzles are spread so that the fuel is added to the oxidation reaction chamber in a ratio that results in the flow of the fuel. Fuel through each nozzle without resulting in a flame as the fuel blends with the oxidation stream flowing through the flow path of the oxidation chamber. The fuel, instead of being burned with a luminous flame, reacts with the oxidant in a relatively uniform manner totally to the volume of the oxidation chamber. Four placements of the fuel nozzles are shown, but any number of fuel nozzles can be provided, depending on the heat flow required in the process chamber. The volume of the oxidation chamber between the placement of the nozzles is preferably sufficient so that the residence time of the mixture is sufficient for a significant portion of the fuel to flow through the placement of the oxidized nozzles before it is added. more fuel.

A process chamber 8 is in the ratio of the heat exchange to the oxidation reaction chamber 1. The process stream enters the inlet 11 and exits at the outlet 12. The quench heat exchanger 10 is shown to cool the process stream leaving the process chamber. The current can be hot, so the shut-off heat exchanger enters to turn off the input 14 and exits through the turned-off output 13. The current that can be heated by the shut-off heat exchanger can be, for example, a current of process input, a heater water feed stream that is heated and / or vaporized. In some processes, such as pyrolysis of hydrocarbons to produce olefins, rapid quenching is desirable to reduce reactions to by-products.

A coke inhibitor can be added to the fuel through an inhibitor injection system shown as injection line 9. The inhibitor injection line can include a control valve and a control system for an inhibitor-to-fuel ratio .

The fuel conduits contain a plurality of nozzles 6 (four locations shown) along the length of the oxidation chamber. The nozzles provide communication between the fuel conduit and the oxidation reaction chamber. A plurality of nozzles is provided for a distribution of heat released within the oxidation reaction chamber. The nozzles are of a size to perform a distribution at a desired temperature within the process chamber. A purely constant temperature profile within the process chamber is generally desired since this may result in lower maximum temperatures for a given heat flow. Since the construction materials of the devices dictate the maximum temperatures, constant temperature profiles can increase the possible heat ratio by the same building materials. The number of nozzles is limited only by the size of the nozzles that can be used. If more nozzles are used, they should be of a smaller size. Smaller nozzles can plug in more easily than large nozzles. The number of nozzles is a relation between the uniformity of the temperature profile and the possibility of plugging.

The process chamber and the oxidation chamber are shown to be in a concurrent flow, but may be in a counting current flow, or a combination of the two, with for example, the oxidation chamber being in a U-tube configuration Such a configuration may be desirable for the purposes of managing differential thermal expansion of the conduits.

A catalyst can be provided in the process chamber, depending on the particular process.

A preheater 7 is shown to heat the oxidant stream to a temperature at which the oxidant stream mixtures with the fuel from the first nozzle placement can be hot enough to result in oxidation without flame. The preheater can be, for example, a burner where the fuel is mixed with some of the oxidant and the burner to raise the temperature of the oxidant, or the oxidant can be preheated by heat exchange with either or both of the effluent process chamber or the effluent oxidation reaction chamber. A combination of heat exchange and then a burner can be used.

Alternatively, the oxidant may be in one stage in the fuel provided by the nozzles in an oxidant conduit instead of the fuel conduit, and force the oxidant in a fuel rich stream at a temperature above the resulting mixtures.

Referring now to Figure 2, a cross section of an alternative embodiment is shown. In this embodiment, the process chamber 8 is in tubes that are packaged together in an insulated case 104. The insulated case need not be a pressure vessel, but it reduces the heat loss of the tubes containing the reaction chambers. . The fuel lines 5 are inside the oxidation reaction chamber 1, with the nozzles 6 providing communication between the two chambers.

Referring now to Figure 3, another alternative mode is shown. In this embodiment, the process chamber 8 is in the tubes that are packaged together in an insulated case 401. The insulated case also defines the combustion chamber. The fuel conduits 5 are inside the insulated sheath between the tubes defining the process chambers. The tubes define the process chambers and the fuel lines are shown to be relatively tightly packed, but can be spaced as necessary to provide a relationship between the pressure drop and the size of the shell required. This can alternatively approximate the appearance of a shell and the heat exchange tube with diverters to space the tubes, and to the flow channel of the combustion gases by returning them and placing them through the tubes that define the process chambers.

The oxidation chamber can also be provided with an oxidation catalyst. The oxidation catalyst may be provided in a support such as aluminum oxide, or covered in the walls of the tubes. The oxidation catalyst can be useful to expand the effective range of temperatures at which oxidation without flame can operate with stability. The oxidation catalyst may also be useful for igniting the pre-oxidation chamber phase by reaching a temperature at which the uncatalyzed oxidation reaction may proceed. Alternatively, the catalyst may be effective to reduce the volume regulated in the oxidation chamber.

Preheating hydrocarbon fuels to obtain flameless combustion can result in significant carbon generation within the fuel conduit unless a carbon-forming suppressant is included in the fuel stream. The carbon-forming suppressant can be carbon dioxide, steam, hydrogen or mixtures thereof. Carbon dioxide and steam are preferred due to the generally higher cost of hydrogen.

Carbon is formed from methane at elevated temperatures in accordance with the following reaction: CH < C + 2H_ (1) This reaction is a reversible reaction, and the functions of hydrogen as a suppressor of carbon formation by the reverse reaction.

Carbon dioxide suppresses carbon formation by the following reaction: co2 + c 2CO (2) Steam suppresses carbon formation by the following reactions: H20 + C? CO + H_ (3) 2H20 + C? CO, + 2H_ (4) Carbon dioxide and carbon monoxide are left in equilibrium at elevated temperatures in accordance with the gas exchange reaction: CO + H20? C02 + H_ (5) When the fuel is essentially methane, a molar ratio of 1: 1 vapor to methane may be sufficient to suppress carbon formation at temperatures around 1370 ° C. The molar ratios of steam to methane are preferably in the range of about 1: 1 to about 2: 1 when the steam is used as a suppressor of carbon formation. The molar ratio of carbon dioxide to methanol is preferably within the range of about 1: 1 to about 3: 1 when carbon dioxide is used as the suppressor of carbon formation. The fuel preferably consists essentially of methane because the methane is more thermally stable than other light hydrocarbons. The suppressor is additionally beneficial since it has lower combustion ranges and reduces temperature peaks.

The need for a suppressor of carbon formation can be eliminated if the fuel is not significantly preheated before addition to the oxidant stream, if the residence time of any preheated fuel is short enough.

The cold ignition of the heater of the present invention can use combustion with a flame. The initial ignition can be done by injecting pyrophoric material, an electric igniter, a spark plug lighter, or temporarily inserting a lighter. The heater is preferably conducted rapidly to a temperature at which flameless combustion is sustained to minimize the period of time in which a flame exists. The heating ratio of the heater can typically be limited by the thermal gradients that the heater can tolerate.

Flameless combustion generally occurs when a reaction between an oxidizing stream and a fuel is not limited by a mixture and the mixing stream is at a temperature higher than the auto-ignition temperature of the mixing stream. This is done by allowing high temperatures at the mixing point and mixing relatively small increments of fuel in the oxidant. The existence of flame is evidenced by an illuminated interface between the unburned fuel and the combustion products. To prevent the creation of a flame, the fuel and the oxidant are preferably heated to a temperature between about 815 ° C and about 1370 ° C before mixing. The fuel is preferably mixed with the oxidant stream in relatively small increments to allow more rapid mixing. For example, enough fuel may be added in an increment to allow combustion to raise the temperature of the current by about 20 ° C to about 100 ° C.

~ The process in which the heater of the present invention may be useful includes, but is not limited to: methane vapor reformers, olefin production, styrene production, ammonia production, cyclohexane production, catalytic reforming of hydrocarbons, and manufacture of allyl or vinyl chloride, production of glass or ceramics, calcination, reboiling of liquids in distillation, re-boiling or temperature profile control in reactive distillation.

Referring now to Figure 4, the process chamber is within the combustion chamber ducts defining the combustion chamber 1, and the ducts defining the combustion chamber 6 are within a larger duct, the fuel flow within the larger duct and outside the ducts defining the oxidation chamber. The fuel nozzles 6 are located in the ducts separating the fuel from the oxidation chambers, with the fuel flow through the nozzles in the oxidation nozzles. The advantage of this configuration is that only one large conduit is required for fuel flow.

Referring now to Figure 5, an alternative placement is shown wherein, instead of concentric tubes, the fuel conduit 5 and the conduit defining the process chamber 8 are located within a conduit defining an oxidation chamber 1. This configuration conveniently provides a large cross-sectional area for the flow of combustion gases. This is desirable to reduce compression costs for the combustion gases, and also lowers the cost of the tubes having the larger diameter tube also containing the lowest pressure.

Referring now to Figure 6, an alternative similar to that shown in Figure 5 is shown, the difference being that the fuel conduit is shown outside the conduit defining the combustion chamber 1. The nozzles 6 are tubular connections between the fuel conduit 5 and the tube defining the combustion chamber 1. The advantage of this arrangement is that the temperature of the fuel can be more easily limited, and the need for a coke inhibitor additive is eliminated.

Referring now to Figure 7, a placement similar to that of Figure 5 is shown with the further description that the flow of the combustion chamber is split, with the inlet to the oxidation chamber 2 being close to the center of the length of the oxidation chamber 8. The flow of the split entry in a flow goes in each direction. This split oxidation chamber allows a large process flow path through the distance of the flow path of the combustion chamber, and reduces the flow in the oxidation chamber by half. In this way, the pressure drop is reduced by a factor of about eight by similar dimensions for the combustion flow path. This can be beneficial since the importance of the compression costs in the exmómicos of the process. This alternative may be desirable to have a relatively large straight flow path for the processes. As another alternative, the fuel conduit may be outside the oxidation chamber as in Figure 6. i Referring now to Figure 8, another alternative with a split flow of the oxidant stream is shown. This alternative has the oxidant in an inner tube, and the inlet divided into a "T" in the flow coming out in each direction.

Referring now to Figure 9, an embodiment of the present invention utilizing an oxidation chamber having a rectangular cross section is shown. Process cameras are pipes in a box. The rectangular oxidation chamber may suitably be made large enough to contain a significant number of process chamber tubes 8. The process chamber tubes may be all parallel flow tubes, series flow, or combinations of parallels and series. A layer of the process chamber tubes is shown, however multiple layers can be provided.

When the flow is at least partially in series, this may be desirable to have the inputs and outputs at the same end and thereby reduce the problems caused by the thermal expansion of the tubes.

Another configuration of heat exchangers, such as corrugated tray heat exchangers such as those described in US Patent No. 4,029,146, incorporated herein by reference, may also be used. With corrugated tray heat exchangers, either a fuel conduit can be inserted into the oxidation flow space for proper fuel distribution, or a third flow-stream placement can be proportional to the nozzles between the spaces for flow of fuel and for the oxidant flow.

The oxidation chambers can be vertical, horizontal or inclined, and are preferably vertical when the process chamber contains a fixed bed catalyst.

The process heater of the present invention can be used in the production of styrene in the dehydrogenation of ethyl benzene to vinyl benzene (styrene) on a catalyst such as an iron-potassium oxide-promoting oxide catalyst. This dehydrogenation can be performed, for example, between 550 ° C and 680 ° C, at pressures that range from four to 20 kPa (3 psia) to 140 kPa (20 psia). The steam is added to the ethylbenzene feed to reduce the partial pressure of the hydrocarbons (thereby improving the equilibrium ratios of the products), to act as a heat introducer to reduce the temperature reduction due to the endothermic reaction, and to reduce the formation of coke by a gas water reaction. Most catalysts require steam for molar hydrocarbon ratios of around seven to ten. The space velocity of each liquid hour based on the liquid fed is generally between about 0.4 to 0.5 hour-1. Lower pressures are desirable due to catalyst performance and stability, but high pressures reduce the compression cost of the product (including capital cost of compression equipment). This is an endothermic reaction and it is desirable to perform the reaction closely isothermally. With increased temperatures, undesirable byproducts (including coke) are produced at increased ratios, and at reduced temperatures, yields are reduced. In this way, it is desirable to operate the dehydrogenation process at closely isothermal conditions. The benefits that can be realized by providing a more uniform temperature include the reduction of the use of steam, operation to larger placements through it, increase in the yield and selectivity, reduction in the elaboration of coke, and / or increase in the operating pressure. . The application of the present invention for the dehydrogenation of ethylbenzene for styrene can be either as a heater or as a heater before heating, however the preferred embodiment is to use the present invention as a heater with a dehydrogenation catalyst in at least a portion of the process chamber that is heated by combustion without flame.

As a steam reforming boiler, the present invention uses a catalyst process chamber to convert a hydrocarbon and steam into hydrogen, carbon monoxide and carbon dioxide. This is a highly endothermic reaction with high temperatures favoring the balance of hydrogen and carbon monoxide for hydrocarbon feeds. Methane is the preferred feed for the production of hydrogen by steam reforming, but other hydrocarbons than methane can be used. The higher the molecular weight, the greater the tendency to form coke. In this way, when using the feed such as naphthas, a higher steam to carbon ratio is generally needed. The molar ratios of steam to carbon are generally between about three and five, the space rates are generally very high, in the order of 5000 to 8000 hour-1, the temperatures are generally between about 800 and 870 ° C, and the pressures are typically between about 2 and 2.5 MPa (300 to 350 psig). High temperatures favor the equilibrium of hydrogen over methane, and this is typical for the output of the hydrogen purity heater to be at least one hydrogen purity that can be equilibrated at a temperature within 25 ° F (3.89 ° F). C) of the temperature of the heater outlet. The catalyst is a nickel-based catalyst, and may contain potassium to inhibit coke formation.

The production of hydrogen by steam reforming can also be processed by a secondary reformer to produce, for example, methanol or ammonia.

The use of the present invention in steam reforming can result in higher average temperatures for a maximum reaction chamber temperature determined due to the uniform heat distribution resulting from the combustion distribution. In this way, either the vapor ratios can be reduced, or the conversion can be increased for similar tube wall temperatures.

When the present invention is used in a heater for thermal breakage of hydrocarbons for olefin products, the reaction temperatures in the range of 775 to 950 ° C and residence times of 0.1 to 0.8 seconds can be used. The reaction temperatures are very dependent on the hydrocarbon fed in particular, and the residence time. Light feeds, such as ethane, can be processed at higher temperatures and higher conversions. Heavy feeds, such as gas oils, require lower temperatures because of their tendency to increase the formation of coke and other undesirable by-products. Residence times of around 0.1 to 0.15 seconds are preferred. The vapor dilution is added to the hydrocarbon fed to the heater to inhibit the deposit of coke, and to reduce the partial pressure of the hydrocarbons. The effluent from the heater is preferably quenched rapidly because the selectivity of the olefin is reduced by side reactions. The shutdown after the reaction chamber can be either by direct contact with, for example, a gas oil stream, or indirectly by heat exchange. Indirect shutdown is preferred because the energy can be recovered to a more useful level.

The present invention can be used in, for example, a distillation column reheater, or a vacuum flash distillation heater. These applications frequently involve heating hydrocarbons to temperatures that are limited by the tendency of the hydrocarbons to form coke, and the present invention results in a more uniform heat transfer to the hydrocarbon stream, and thus minimizes the temperatures of the hydrocarbons inside the heaters. In addition, advantages such as the reduction of N0x generation are also realized.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (12)

Claims

1. A process heater characterized comprising: an oxidation reaction chamber, the oxidation reaction chamber having an inlet for the oxidant, an outlet for the combustion products, a flow path between the inlet and the outlet; a fuel conduit capable of transporting a fuel mixture to a plurality of fuel nozzles within the oxidation reaction chamber, each nozzle providing communication between the fuel conduit to the oxidation chamber, with each nozzle along the flow path between the entrance and the exit; a preheater in communication with the inlet of the oxidation chamber, the preheater capable of increasing the temperature of the oxidant to a temperature resulting in the combination of oxidant and fuel from the fuel nozzle near the scamara oxidation inlet being greater than the temperature of auto-ignition of the combination of oxidant and fuel from the fuel nozzle near the inlet of the oxidation chamber, where the heat transfer of the oxidation section does not cause the temperature __e the mixture inside the chamber of - Oxidation reaction in the vicinity of each fuel nozzle to reduce the auto-ignition temperature of the combined mixture in the oxidation chamber in the vicinity of the fuel nozzle, characterized in that the heater further comprises an endothermic reaction process chamber in the heat exchange ratio to the oxidation reaction chamber.

2. The confounding process heater with claim 1, characterized in that it further comprises a coke inhibitor injection system, the coke inhibitor system in communication with the fuel supply conduit wherein a quantity of coke inhibitor supplied can be effective to inhibit the formation of coke in the fuel conduit at operating temperatures.

3. The process heater according to claim 1, characterized in that the fuel conduit is a substantially centered tubular conduit located within the oxidation reaction chamber.

4. The process heater according to claim 3, characterized in that the oxidation reaction chamber is essentially centered located within the process chamber.

5. The process heater according to claim 1, characterized in that the process chamber is a pyrolysis reaction chamber for the production of olefins.

6. The process heater according to claim 1, characterized in that the process chamber is a methane vapor reforming reaction chamber.

7. The process heater in accordance with the rei indication 1, characterized in that the process heater is a dehydrogenation heater of ethylbenzene.

8. A method for providing heat to a process by means of an oxidation reaction chamber, the oxidation reaction chamber having an inlet for oxidant, an outlet for combustion products, and a flow path between inlet and outlet, The method includes the steps of: provide a fuel; adding a coke inhibitor component to the fuel in an amount effective to inhibit coke formation at heater operating temperatures; transporting a fuel mixture to a plurality of fuel nozzles within the oxidation reaction chamber, with each nozzle along the flow path between inlet and outlet; Preheat the oxidant to a temperature resulting in the combination of oxidant and fuel from the fuel nozzle near the inlet of the oxidation chamber siena or greater than the auto-ignition temperature of the oxidant and fuel combination from 1 .. nozzle of fuel near the entrance of the oxidation chamber, characterized in that the method further comprises the transfer of heat-from the oxidation reaction chamber to an endothermic reaction process chamber in a heat exchange ratio for the reaction chamber. of oxidation wherein the heat transfer of the oxidation section does not cause the temperature of the mixture within the oxidation reaction chamber in the vicinity of each fuel nozzle to reduce the auto-ignition temperature of the combined mixture in the oxidation chamber in the vicinity of the fuel nozzle.

9. The method of. according to claim 8, characterized in that the process is a process of reforming methane vapor.

10. The method according to claim 8, characterized by the process is a pyrolysis reaction for the production of olefins.

11. The method according to claim 8, characterized in that the process is a process of dehydrogenation of ethylbenzene.

12. The method according to claim 8, characterized in that the coke inhibitor component is selected from the group consisting of carbon dioxide and steam.