HYBRID ELECTRIC AND FIRED HEATER FOR OLEFIN PRODUCTION

Abstract

A process including preheating a hydrocarbon feed, feeding the preheated hydrocarbon stream to a second preheat zone for cracking, and feeding the cracking feed stream to one or more coils in a radiant section to recover a cracked hydrocarbon product. The process includes injecting excess air and cooling the cracked hydrocarbon product in a transfer line exchanger. The system includes a pyrolysis heater, a first and second preheat zone of the convection heating zone, and one or more coils in the radiant heating zone. The system includes one or more inlets for injecting an amount of excess air, one or more electrical heating elements in the radiant heating zone, and a feedline for directing the cracked hydrocarbon product to a transfer line exchanger.

Claims

1. A pyrolysis process using a hybrid heater for converting a hydrocarbon mixture to produce olefins, the process comprising: preheating a hydrocarbon feed in a first preheat zone of a convection section, recovering a preheated hydrocarbon stream; feeding the preheated hydrocarbon stream to a second preheat zone of the convection section to further heat the preheated hydrocarbon stream, recovering a cracking feed stream; cracking hydrocarbons in the cracking feed stream in one or more coils in a radiant section comprising one or more fuel fired burners and one or more electrical heating elements, recovering a cracked hydrocarbon product; injecting an amount of excess air in the convection section or the radiant section; and cooling the cracked hydrocarbon product in a transfer line exchanger, recovering a cooled hydrocarbon product stream, wherein the amount of excess air injected is in a range from about 10 mol % to 300 mol % excess air relative to a quantity of air required to combust fuel provided to the one or more fuel fired burners.

2. The process of claim 1, further comprising: mixing a dilution steam stream with the preheated hydrocarbon stream, producing a mixed hydrocarbon-steam stream; and feeding the mixed hydrocarbon-steam stream to the second preheat zone of the convection section and recovering the cracking feed stream.

3. The process of claim 1, further comprising heating a combustion gas from the radiant section using one or more electrical heating elements in the convection section.

4. The process of claim 1, further comprising: feeding a preheated air stream to the radiant section using one or more radiant section air inlet nozzles.

5. The process of claim 1, further comprising: feeding a preheated air stream to the convection section using one or more convection section air inlet nozzles.

6. The process of claim 1, further comprising preheating a second air stream in one or more air preheaters, electric heaters, or hot oil recirculation systems and feeding the second preheated air stream to the one or more fuel fired burners, preheating a burner fuel in one or more fuel preheaters, electric heaters, or hot oil recirculation systems, producing a preheated burner fuel, and feeding the preheated burner fuel to the one or more fuel fired burners, or both.

7. The process of claim 1, further comprising feeding the cooled hydrocarbon product stream to a downstream recovery process.

8. The process of claim 1, wherein at least a portion of the excess air is generated by a forced draft fan.

9. The process of claim 1, wherein at least a portion of the excess air is preheated by an air preheater.

10. The process of claim 1, wherein the convection section further comprises a plurality of electrical heating elements installed in one or more regions of the convection section.

11. The process of claim 1, wherein the convection section further comprises a plurality of heat exchangers providing heat through a fluid flowing to low temperature regions of the convection section.

12. The process of claim 1, wherein the amount of excess air injected is in a range from about 50 mol % to 300 mol % excess air.

13. The process of claim 1, wherein the injecting an amount of excess air comprises feeding excess air to an air inlet disposed proximate the one or more fuel fired burners.

14. The process of claim 1, wherein the injecting an amount of excess air comprises feeding excess air to the one or more fuel fired burners.

15. The process of claim 1, wherein the injecting an amount of excess air comprises feeding excess air to an air inlet in the convection section.

16. The process of claim 1, wherein the injecting an amount of excess air comprises feeding excess air to an air inlet disposed proximate the one or more electric heaters in the radiant section.

17. A pyrolysis system using a hybrid heater for converting a hydrocarbon mixture to produce olefins, the system comprising: a pyrolysis heater comprising a convection heating zone and a radiant heating zone; a first preheat zone of the convection heating zone configured for preheating a hydrocarbon feed and recovering a preheated hydrocarbon stream; a second preheat zone of the convection heating zone configured for vaporizing a portion of the preheated hydrocarbon stream and recovering a cracking feed stream; one or more coils in the radiant heating zone configured for cracking hydrocarbons in the cracking feed stream and recovering a cracked hydrocarbon product; one or more inlets for injecting an amount of excess air in the convection heating zone or the radiant heating zone; one or more electrical heating elements in the radiant heating zone configured for providing additional heat duty for cracking hydrocarbons; and a feed line for directing the cracked hydrocarbon product to a transfer line exchanger for cooling cracked hydrocarbon product and recovering a cooled hydrocarbon product stream.

18. The system of claim 17, further comprising a dilution steam stream inlet configured for providing a dilution steam stream to the preheated hydrocarbon stream between the first preheat zone and the second preheat zone.

19. The system of claim 17, further comprising one or more electrical heating elements in the convection heating zone for heating a combustion gas from the radiant heating zone.

20. The system of claim 17, further comprising: one or more radiant heating zone air inlet nozzles for feeding an air stream to the radiant heating zone.

21. The system of claim 17, further comprising: one or more convection heating zone air inlet nozzles for feeding an air stream to the convection heating zone.

22. The system of claim 20, further comprising a radiant heating zone air preheater configured to preheat an air stream fed to the radiant heating zone.

23. The system of 17, further comprising a convection zone air preheater configured to preheat an air stream fed to the convection heating zone.

24. The system of claim 17, wherein the one or more inlets for injecting is disposed proximate one or more fuel fired burners.

25. The system of claim 17, wherein the one or more inlets for injecting is disposed proximate the one or more electric heaters in the radiant section.

26. The system of claim 17, further comprising a product outlet for recovering the cooled hydrocarbon product stream and feeding the cooled hydrocarbon product stream to a downstream recovery process.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0009] FIG. 1 illustrates a simplified process flow diagram of systems and processes according to one or more embodiments disclosed herein.

[0010] FIG. 2 illustrates a simplified process flow diagram of systems and processes according to one or more embodiments disclosed herein.

DETAILED DESCRIPTION

[0011] Embodiments disclosed herein relate generally to a pyrolysis process using a hybrid heater for converting hydrocarbon mixtures, such as whole crudes or other hydrocarbon mixtures, to produce olefins, such as ethylene.

[0012] Hydrocarbon mixtures useful in embodiments disclosed herein may include various hydrocarbon mixtures having a boiling point range, where the end boiling point of the mixture may be greater than 450 C. or greater than 500 C., such as greater than 525 C., 550 C., or 575 C. The amount of high boiling hydrocarbons, such as hydrocarbons boiling over 550 C., may be as little as 0.1 wt %, 1 wt % or 2 wt %, but can be as high as 10 wt %, 25 wt %, 50 wt % or greater. Processes disclosed herein can be applied to crudes, condensates and hydrocarbon mixtures with a wide boiling curve and end points higher than 500 C. Such hydrocarbon mixtures may include whole crudes, virgin crudes, hydroprocessed crudes, gas oils, vacuum gas oils, heating oils, jet fuels, diesels, kerosenes, gasolines, synthetic naphthas, raffinate reformates, Fischer-Tropsch liquids, Fischer-Tropsch gases, natural gasolines, distillates, virgin naphthas, natural gas condensates, atmospheric pipestill bottoms, vacuum pipestill streams including bottoms, wide boiling range naphtha to gas oil condensates, heavy non-virgin hydrocarbon streams from refineries, vacuum gas oils, heavy gas oils, atmospheric residuum, hydrocracker wax, and Fischer-Tropsch wax, among others. In some embodiments, the hydrocarbon mixture may include hydrocarbons boiling from the naphtha range or lighter to the vacuum gas oil range or heavier. If desired, these feeds may be pre-processed to remove a portion of the sulfur, nitrogen, metals, and Conradson Carbon upstream of processes disclosed herein. Lighter hydrocarbon feeds, such as ethane, propane, butanes, etc., and mixtures of multiple of these various lighter hydrocarbons may also be used as feedstocks to cracking furnaces herein.

[0013] The thermal cracking reaction proceeds via a free radical mechanism. Hence, high ethylene yield can be achieved when hydrocarbons are cracked at high temperatures in the presence of a diluent including but not limited to diluent steam. Lighter feeds, like butanes and pentanes, require a high reactor temperature to obtain high olefin yields. Heavy feeds, like gas oil and vacuum gas oil (VGO), require lower temperatures. Crude contains a distribution of compounds from butanes to VGO and residue (material having a normal boiling point over 520 C., for example).

[0014] Many countries are requiring a reduction in CO2 emissions. When fossil fuels are burnt to supply energy, CO2 production is often high. Embodiments disclosed herein aim to reduce the fuel consumption for the same process duty by efficiently designing the heaters. In conventional processes, excess enthalpy in the flue gas is used to generate and superheat high pressure steam. It may be possible to reduce the steam production and utilize the heat energy available in the fuel only for process duty. In doing so, the heater may reduce, or eliminate, CO2 production and H2 import.

[0015] Current heater designs are based on producing and superheating high pressure steam to form super high pressure steam (SHP) to meet the olefin plant energy requirements to drive turbines. This results in firing more fuel in the cracking heater. Embodiments disclosed herein aim to reduce the fuel consumption by redesigning the heater to be more fuel efficient to produce less steam. This reduces CO2 emissions in the heater, which is a major source of CO2 emissions in the ethylene plant. In some embodiments, ethane cracking also produces a significant amount of hydrogen, but the amount is not sufficient to meet the firing demand. To obtain zero CO2 emission, additional H2 has to be imported. Accordingly, embodiments disclosed are related to a heater design that requires zero H2 import and still produces zero, or low, CO2 emission.

[0016] To reduce the CO2 emission in the heaters, one method proposed in the prior art is to use air preheat or to preheat the fuel. When air preheat is used with traditional heater design, super high pressure (SHP) steam production is high and hence the reduction in fuel consumption is small. Alternate heater designs are proposed to quench the hot effluents using an exchanger heating the process fluid first and then the residual energy to generate SHP steam.

[0017] In one or more embodiments, the air, the burner fuel, or both the air and burner fuel may be preheated before being fed to the fuel fired burners. For example, the combustion air may be preheated using an air preheater, an electric heater, or a hot oil recirculation system. The air preheater may be an integrated part of the convection section or a separate heat exchange unit, such as an electric heater. An electric heater may allow higher temperatures to be obtained compared to a conventional air preheater. In an electric heater, the air may be preheated up to 500 C. In some embodiments, a hot oil recirculation system uses hot oil in a recirculation loop to heat the air. Such systems would heat the air used for combustion in the burners. In one or more embodiments, the air may be pre-heated in the convection section before being additionally preheated in an external heater prior to being fed to one or more burners. Similarly, for example, the burner fuel may be preheated before using a fuel preheater, an electric heater, or a hot oil recirculation system. The fuel preheater may be an integrated part of the convection section or a separate heat exchange unit, such as an electric heater. In some embodiments, a hot oil recirculation system uses hot oil in a recirculation loop to heat the fuel. Such systems would heat the fuel used for combustion in the burners. In one or more embodiments, the fuel may be pre-heated in the convection section before being additionally preheated in an external heater prior to being fed to one or more burners.

[0018] Embodiments disclosed herein use the convection section of a pyrolysis reactor (or a heater) to preheat and separate the feed hydrocarbon mixture into various fractions. Steam may be injected at appropriate locations to increase the vaporization of the hydrocarbon mixture and to control the heating and degree of separations. The vaporization of the hydrocarbons occurs at relatively low temperatures and/or adiabatically, so that coking in the convection section will be suppressed.

[0019] For mixed feeds, such as crude or other hydrocarbon mixtures having high boiling temperature components, the convection section may thus be used to heat the entire hydrocarbon mixture, forming a vapor-liquid mixture. The vaporous hydrocarbons will then be separated from the liquid hydrocarbons, and only the vapors separated will be fed to radiant coils in one or more radiant sections of a single heater. For lighter mixtures or single component feeds, such as ethane feeds, a separation of unevaporated hydrocarbons may be unnecessary. The radiant coil geometry can be any type. An optimum residence radiant coil may be chosen to maximize the olefins and the run length, for the feed hydrocarbon vapor mixture and reaction severity desired.

[0020] Multiple heating steps may be used to heat the hydrocarbons and diluent steam to the desired temperature. This will permit cracking optimally, such that the throughput, steam to oil ratios, heater inlet and outlet temperatures and other variables may be controlled at a desirable level to achieve the desired reaction results, such as to a desired product profile while limiting coking in the radiant coils and associated downstream equipment.

[0021] The process of cracking hydrocarbons in a pyrolysis reactor may be divided into three parts, namely a convection section, a radiant section, and a quench section, such as in a transfer line exchanger (TLE). In the convection section, the feed is preheated, partially vaporized, and mixed with diluent steam. In the radiant section, the feed is cracked (where the main cracking reaction takes place). In the TLE, the reacting fluid is quickly quenched to stop the reaction and control the product mixture. Instead of indirect quenching via heat exchange, direct quenching with oil is also acceptable.

[0022] Embodiments herein efficiently utilize the convection section to enhance the cracking process. Heating may be performed in a convection section of a single pyrolysis reactor in some embodiments. In other embodiments, separate heaters may be used for the respective fractions. In some embodiments, the hydrocarbon feed enters the top row of the convection bank and is preheated with hot flue gas generated in the radiant section of the heater, at the operating pressure to medium temperatures without adding any superheated steam to heat the hydrocarbon feed in the convection section. The outlet temperatures may be in the range from 150 C. to 400 C., depending upon the hydrocarbon feed and throughput. At these conditions, 5% to 70% (volume) of a crude may be vaporized. For example, the outlet temperature of this first heating step may be such that naphtha (having a normal boiling point of up to about 200 C.) is vaporized. Other cut (end) points may also be used, such as 350 C. (gas oil), among others. Because the hydrocarbon mixture is preheated with hot flue gas generated in the radiant section of the heater, limited temperature variations and flexibility in the outlet temperature can be expected.

[0023] Following cracking in the radiant coils, one or more transfer line exchangers (TLE) may be used to cool the products very quickly and generate steam. One or more coils may be combined and connected to one or more TLE(s). The TLE(s) can be double pipe or multiple shell and tube exchanger(s). Embodiments disclosed herein are directed toward TLEs that reduce SHP steam production, and thus reduce CO2 generation, H2 import requirements, and need for supplemental heating.

[0024] In one or more embodiments, maximum fuel energy may be transferred to heating the reaction mixture and to initiate the reaction. Olefin selectivity may be high only when the effluent mixture is quickly quenched after the reaction. One way to quickly quench the reaction, stopping the production of olefins, is to directly quench the effluent with cold fluid. Water, oil, or steam can be used as the cold fluid. Since coil outlet pressure is low, low-pressure steam or medium pressure steam can also be used. When indirect quench is used, a small TLE may be used, and a minimum amount of steam may be needed. In such embodiments, the temperature may be reduced sufficiently so that reaction rate is reduced quickly, and, at the same time, the effluent mixture is still hot enough to pre-heat the reaction mixture using one or more downstream exchangers. As the TLE may be small, SHP steam production may be low. Since SHP steam production is reduced, the convection section may be modified to be flexible for different feeds and operating modes. The same convection section may also work during decoke and high steam conditions.

[0025] Referring now to FIG. 1, a simplified process diagram of the above embodiments is illustrated. A fired tubular furnace 100 is used for cracking hydrocarbons in a hydrocarbon feed stream 10 to ethylene and other olefinic compounds. The fired tubular furnace 100 has a convection section 110 and a radiant section 120. The furnace contains one or more process tubes (radiant coils) 122 through which a portion of the hydrocarbons fed through hydrocarbon feed line 10 are cracked to produce product gases upon the application of heat. Radiant and convective heat is supplied by combustion of a heating medium introduced to the radiant section 120 of the furnace through a plurality of burner nozzles 124, such as hearth burners, floor burners, or wall burners, and exiting through an exhaust at the top of the furnace. Additional heating is also supplied by one or more electrical heating elements 200 located in the convection section 110, the radiant section 120, or both.

[0026] The one or more electrical heating elements 200 can supply electrical heating by radiative, convective, conductive, or any combination. Air preheat and fuel preheat is also used to reduce electrical load to the radiant section electrical heating elements. The one or more heating elements 200 are placed in the reactor walls where wall burners are typically located. In some embodiments, the one or more heating elements 200 may cover the entire furnace wall. Additional electrical heating elements 200 (covered with metal or non-metal sheaths) are placed in convection section 110 proximate the bottom of convection section 110. The electrical heating elements 200 placed in convection section 110 heat the flue gas during times when the operating temperature is low. The electrical heating elements 200 in convection section 110 can be of different type from those used in the radiant section 120 due to the relatively low temperatures in convection section 110.

[0027] In addition to electrical heating elements 200, preheated hot air or cold air can be injected as excess air at suitable locations in the radiant or convection section. The excess air added to the system may be in excess of that typically fed to burners to ensure complete combustion. Rather, excess air provided in embodiments herein is provided to generate an exhaust gas that may be used with a typical convective heating section to provide feed preheat, steam generation, and superheating, etc. The excess air, in entirety or a portion of it, may be preheated by an external air preheater. The excess air may be generated by a forced draft fan. When excess air is injected in the radiant section, the air will spread across the box and elements heating the air and cooling the elements thereby prolonging the life of the elements. This excess air with external preheating (not illustrated) will be required only when the fuel fired duty is very low and the amount of flue gas is too low to supply enough heat duty in the convection section, which may occur when using the electrical heating elements in the radiant section. In a traditional process, the flue gas produced from the burners assists in heating the convection section. Without the burners or with less burners, due to the use of the electrical heating elements in the radiant section, the flue gas volume is decreased. To ensure the convection section performance is maintained, excess air is added. Excess air may be in the range of 10 mol % to 300 mol % relative to a quantity of air required to combust fuel provided to the one or more fuel fired burners, based on the requirements of the convection section. In some embodiments, excess air may be in the range of 50 mol % to 200 mol %. In various embodiments, excess air may be in a range from a lower limit of 10, 20, 30, 40, 50, 75, 100, 125, 150, 175, or 200 mol % to an upper limit of 100, 125, 150, 175, 200, 225, 250, 275, 300, 325, or 350 mol %, where any lower limit may be combined with any mathematically compatible upper limit. Excess air may be added to one or more fuel fired burners through air inlets proximate to the fuel fired burners. In other embodiments, excess air may be added through air inlets proximate to one or more electric heaters in the radiant section. As used herein, proximate refers to the excess air inlet(s) being located on a floor or a wall of the furnace such that the injected excess air interacts with the associated heat source (burner or electric heating element) to heat the excess air to a temperature sufficient to provide the required heat in the convective heating section of the furnace. In some embodiments, the excess air may be preheated by an air preheater using either electrical heating or heat exchange with hot fluids. Electrical heating may be radiative, convective, conductive, or any combination of these methods. An additional strategy to maintain the performance of the convection section may be to use low temperature electrical heating elements installed in or providing heat to low temperature regions of the convection section. In some embodiments, the low temperature electrical heating elements may be installed within the convection section. In other embodiments, the low temperature electrical heating elements may be configured as a heat exchanger with a fluid entering into the convection section. These heating elements may be covered with metallic or non-metallic sheaths. In some embodiments, the heating elements may be equipped with cooling air to prolong the life of the heating elements.

[0028] Returning to FIG. 1, downstream of the radiant section 120 is a transfer line exchanger (TLE) 130. In convection section 110, hydrocarbon stream 10 is preheated in a first preheat zone and superheated in a second preheat zone before entering the radiant section 120. In radiant section 120, cracking reactions proceed to produce desired products. Fuel consumption is completely dictated by the radiant section 120 by burner nozzles 124 on the bottom end of radiant section 120, the one or more electrical heating elements 200, or both. The hydrocarbon stream 10 is mixed with a dilution steam 16 between the first preheat zone and the second preheat zone and heated in the convection section 110 as a mixed hydrocarbon-steam stream. After passing through the convection section 110 for the second time, the heated mixed hydrocarbon-steam stream 18, i.e. the cracking feed stream, is then fed to the radiant section 120 for cracking to produce olefins such as ethylene. The cracked product exiting the radiant section is then fed to a TLE 130 for rapid quenching.

[0029] The radiant section 120 fuel consumption may be reduced if the reaction duty is minimized to convert only the feed to products. This may be accomplished by feeding the feedstock at high inlet temperature. After the feedstock is fed to the radiant section 120 at high inlet temperature, to preserve the olefins, the reaction mixture may be quenched quickly. Direct quenching may be performed by mixing the effluent with a fluid such as water, steam or oil. Alternatively, indirect quenching can be used. With indirect quenching, high pressure steam is generated. The reaction mixture will enter the tube side (or shell side) of a TLE 130. The other side of the TLE 130 will generate (superheat) steam 22 through a boiler feed water steam generating system 160. Since generating steam has a very high heat transfer coefficient, the mixture may be quenched quickly in a short distance in the TLE 130. Typically, the radiant coil outlet temperature will be 750 to 950 C. depending upon the feed and coil design. The product mixture is cooled to 300 to 450 C. at start of run and may reach 500 to 650 C. at the end of run due to coke deposition on the TLE. Most cracking reactions stop around 650 C. and hence the TLE 130 is designed to achieve high start-of run outlet temperatures (600 C.). This will produce only a small quantity of SHP steam. As a result, the convection section 110 need not superheat a large quantity of SHP steam and thereby saves energy in the superheating of the steam. By only generating a small amount of SHP steam, the energy in the steam make is shifted to process fluid for improved cracking performance. This may reduce the heating duty significantly, and consequently the required fuel consumption and CO2 production are reduced. Since all SHP steam generated in the TLE is superheated to a required temperature, there is no need for a separate steam superheater. SHP steam for use in driving steam turbines has to be superheated to some degree to prevent damaging the blades. By keeping the convection section 110 integral, all of the steam produced may be used in the recovery section by minimizing the electrical load for driving the compressors.

[0030] Alternatively (not shown here) the effluents can be cooled by generating low pressure steam, medium pressure steam, or high-pressure steam after the TLE, and a resulting hot stream is exchanged with preheat air.

[0031] Referring now to FIG. 2, an embodiment with hot air being fed to the radiant section, the convection section, or both, is illustrated. As with FIG. 1, one or more electrical heating elements 200 may be used to reduce the amount of fuel used by the burner nozzles 124.

[0032] One or more hot air inlets 210 may be located in the radiant section 120 and one or more hot air inlets 220 may be located in the convection section 110. For existing heaters, the inlet temperature of the flue gas entering the convection section (known as bridge wall temperature) and the flow rate of the flue gas have to be similar to those of 100% fuel fired heater designs. Air temperature and electrical duty in the one or more heating elements can be adjusted to achieve these operating conditions. Once comparable flue gas values are attained, the convection section performance is similar to that of a conventional fired heater.

[0033] In such embodiments, the amount of hydrogen produced in the plant through cracking may be used in the burners in the radiant section. However, the hydrogen may not be recovered as hydrogen product for H2 fuel. More than 90% of the hydrogen produced after satisfying the amount for acetylene and MAPD hydrogenation can be recovered as product. Only this amount of hydrogen is available as fuel for combustion in the cracking heaters. Based on available hydrogen after satisfying the hydrogenation requirements, only the excess hydrogen is fired as fuel inside the heater. Radiant efficiency may be increased by using the pre-heated air and one or more electrical heating elements, as necessary. All energy available for feed heating and pre-heating the air is limited by the energy available in the flue gas. Therefore, the maximum amount of energy is available to process fluids (ethane and dilution steam (DS)) only when the minimum amount of SHP is superheated, thus producing a minimum amount of SHP.

[0034] Hydrocarbon leaks from the coils, including holes, coil rupture, welding failure, or other causes, during usage of fuel fired burners do not present safety hazards as the leaked hydrocarbons will simply burn. Also, when there is a power failure, there is still fuel fired duty available. Supplement fuel like natural gas can be added to the fuel if additional hydrogen is not available and the operation of the heater can be maintained without electricity. Otherwise, the coil will cool and the plant has to be shut down or back up electricity must be imported. In any case, the floor burners are capable of providing 100% fuel fired heating as long as adequate fuel pressure is available. With 100% electrical heating, a continuous purge stream must be supplied (N2, air, or steam) to vent any potential hydrocarbon leak. When carbon containing fuels are used, some CO2 will be produced. When only 100% H2 is used as fuel, the heater produces zero CO2.

TABLE-US-00001 TABLE 1 Case 1 2 3 Feed rate, % of Base 100 100 100 TXO, F. Base Base Base Coil Outlet Temp, F. 1535 1535 1535 Radiant duty, MMBTU/h 129.1 129.1 129.1 Bridge wall Temp., F. Base Base + 44 Base + 44 Fuel liberation, % of base 100 50.8 50.8 Total Heat In, MMBTU/h 289.8 281.7 281.7 H2 content of Fuel, v % 82.43 100 100 Excess air, % 10 140 140 Fuel Fired, lb/h as % of base 100 31.7 31.7 Temp. of Air, F. 95 95 1100 Air flowrate, % 100 102.2 102.2 Flue gas flowrate, % 100 100 100 Stack Temp., F. 254 248 248 SHP steam, % 100 97.1 97.1 External APH duty, MMBTU/h 0 0 64.2 Radiant Electrical duty, MW 32.4 17.1 Elec. Flux, KW/m.sup.2 87.8 46.3

[0035] Table 1 shows calculations of existing fuel fired heaters (base, case 1), electrical heating elements (case 2), and electrical heating elements with preheated air inlets (case 3).

[0036] In case 1, the conventional fuel fired heater with 100% floor firing produces 167KTA of ethylene per heater with ethane feed. Base Plant is the 100% fuel fired ethane cracker. Plant material balance shows 82.4 vol % H2 in the fuel. Generally, ethane plants have high H2 in the fuel and a small addition of green H2 or electrical heating will produce zero CO2 emission. Though only primary TLE is shown, for gas cracking, primary TLE and a secondary TLE are used.

[0037] In case 2, electrical heating supplements fuel fired heating. This is a retrofitted case of case 1. All fuel is fired in the hearth burners and only sidewalls contain electric elements. To obtain the same flue gas flow rate, excess air must be increased to 140% using a forced draft fan. No other electrical heating (other than used in a radiant box) or hot air is used.

[0038] In case 3, electrical heating supplements fuel fired heating and preheated air is fed to the radiant and convection sections. Instead of using a radiant box to preheat the air, a more efficient external air preheater is used. Though the total duty remains the same, external preheating is less expensive, and the life of the electrical heating element is longer. Air preheaters are commercially available for temperatures as high as 1300 F. By reducing the electrical duty supplied in the radiant cell, radiant electric duty is significantly reduced. In addition, many more low-cost metallic elements can be used at these conditions.

[0039] Some heated air can be added in the convection section in addition to electrical heating in the convection section. This will reduce the heat flux required for metallic elements in the radiant section and will use the low cost and low temperature elements in the convection section.

[0040] In these embodiments, the same amount of SHP steam with required outlet temperature for turbines is produced. Instead of using electricity to generate steam and then using the steam to drive the turbines in the recovery section, the heated air can be more efficiently used to provide direct heat.

[0041] Unless defined otherwise, all technical and scientific terms used have the same meaning as commonly understood by one of ordinary skill in the art to which these systems, apparatuses, methods, processes and compositions belong.

[0042] The singular forms a, an, and the include plural referents, unless the context clearly dictates otherwise.

[0043] As used here and in the appended claims, the words comprise, has, and include and all grammatical variations thereof are each intended to have an open, non-limiting meaning that does not exclude additional elements or steps.

[0044] Optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0045] When the word approximately or about are used, this term may mean that there can be a variance in value of up to +10%, of up to 5%, of up to 2%, of up to 1%, of up to 0.5%, of up to 0.1%, or up to 0.01%.

[0046] Ranges may be expressed as from about one particular value to about another particular value, inclusive. When such a range is expressed, it is to be understood that another embodiment is from the one particular value to the other particular value, along with all particular values and combinations thereof within the range.

[0047] While the disclosure includes a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the present disclosure. Accordingly, the scope should be limited only by the attached claims.