System and method for heating a stream of hydrocarbons, with a reduced carbon footprint and improved operation

Abstract

The invention relates to a system (100) and a method for heating a stream of hydrocarbons, comprising a combustion furnace (10) and at least one electrical heating device (40) mounted downstream and / or upstream of the combustion furnace. The heating system comprises a management system (50) configured to: - control the at least one electrical heating device (40) and the combustion furnace (10), in order to heat the stream of hydrocarbons exiting the heating system to a target temperature; and - control the at least one electrical heating device (40) so as to maintain a temperature difference of the stream of hydrocarbons between the inlet and the outlet of the combustion furnace at less than or equal to a threshold value.

Description

system and method for heating a hydrocarbon stream with a reduced carbon footprint and improved operation Technical field of the invention

[0001] The present invention relates to a system and method for heating a hydrocarbon stream with a reduced carbon footprint and improved performance, particularly for use in a refinery unit. The heating method and system according to the invention are particularly suitable for heating a hydrocarbon stream prior to its processing. Technological background

[0002] In the refining sector, hydrocarbon streams are generally heated using combustion furnaces. However, such furnaces generate significant CO2 and nitrogen oxide emissions that must be reduced from an environmental perspective.

[0003] Before entering a combustion furnace, the hydrocarbon stream is generally preheated by one or more heat exchangers that preheat the stream by recovering heat from hot streams within the unit. This preheating process is therefore dependent on the temperature and flow rate of the hot streams used and does not allow for precise and constant control of the temperature at the combustion furnace inlet.

[0004] However, a change in the heating system can have impacts on heating efficiency, coke formation, heated fluid pressure, and the downstream refining process.

[0005] Furthermore, these ovens are subject to coking which disrupts their operation.

[0006] There is therefore a need to reduce coke formation and to reduce the carbon footprint of existing heating systems without disrupting the operation of downstream processes.

[0007] To this end, the invention proposes a system for heating a hydrocarbon stream comprising: - a combustion furnace including an inlet and an outlet for the hydrocarbon stream, - a supply line for the hydrocarbon stream to be heated connected to the inlet of the combustion furnace, - a hydrocarbon stream charging pump mounted on the supply line;- a heated hydrocarbon flow discharge line connected to the combustion furnace outlet, - at least one electric heating device mounted on the supply line downstream of the charging pump, and / or mounted on the combustion furnace discharge line, - a management system configured to: - control at least one electric heating device and the combustion furnace to heat the hydrocarbon flow exiting the heating system to a target temperature and, - control at least one electric heating device in such a way as to maintain a temperature difference of the hydrocarbon flow between the inlet and outlet of the combustion furnace less than or equal to a threshold value.

[0008] Implementing an electric heating device mounted upstream and / or downstream of a combustion furnace, based on a temperature difference inside the combustion furnace, reduces coke formation inside the combustion furnace and / or in the electric heating device, and improves the overall efficiency of the heating system.

[0009] The use of at least one electric heating device helps to homogenize the heat flow and thus prevent the formation of hot spots that could cause coking. The temperature of a hydrocarbon stream exiting an electric heating system is also stable and consistent over time.

[0010] In general, using at least one electric heating device upstream or downstream of the combustion furnace reduces the heat the furnace needs to generate to reach the target temperature. This, in turn, reduces fuel consumption and CO2 emissions, and also limits coking within the combustion furnace. This allows for an increase in the heating system's operating time between decoking operations. This increase in operating time can reach 400% compared to a heating system without an electric heating device.

[0011] Furthermore, when at least one electric heating device is installed upstream of the combustion furnace, the hydrocarbon inlet flow, particularly into a combustion zone, maintains a homogeneous and stable temperature over time. This improves burner settings (especially the airflow required for combustion within the combustion furnace), thereby enhancing energy efficiency, limiting the formation of hot spots within the combustion furnace, and consequently reducing the risk of coking.

[0012] When at least one electric heater is installed downstream of the combustion furnace, the heat required from the combustion furnace to reach the target temperature is reduced. By heating less in the combustion furnace, the risk of coking within it is reduced. The remaining heating is provided by the electric heater, which delivers much more even heat, thus limiting the risk of coking due to the formation of hot spots in the electric heater.

[0013] The at least one electric heating device used in the present invention is not intended to replace the heat exchanger(s) normally used to preheat the feed into the combustion furnace. Thus, the heating system according to the invention may further include one or more heat exchangers mounted in series and / or parallel on the combustion furnace feed line, upstream of the electric heating device, these heat exchangers transferring heat from hot fluids to the hydrocarbon stream.

[0014] An electric heating device positioned upstream of the combustion furnace has the advantage of being easier to integrate and less bulky than an electric heating device positioned downstream of the combustion furnace, in particular because the volumetric flow rate to be treated at the outlet of the combustion furnace is generally greater than at the inlet of the combustion furnace.

[0015] An electric heating device positioned downstream of the combustion furnace offers the advantage of greater coking reduction compared to an electric heating device positioned upstream. A heating system according to the invention, with the heating device positioned downstream, is thus particularly well-suited for heating hydrocarbon streams from vacuum distillation or visbreaking units in a refinery. A heating system according to the invention, with the heating device positioned upstream, can be used to heat hydrocarbon streams from other units in a refinery.

[0016] In one embodiment, the heating system according to the invention may include only at least one electric heating device mounted upstream of the combustion furnace.

[0017] In another embodiment, the heating system according to the invention may comprise only at least one electric heating device mounted downstream of the combustion furnace.

[0018] In one embodiment, the heating system according to the invention may include at least one electric heating device mounted upstream of the combustion furnace and at least one electric heating device mounted downstream of the combustion furnace.

[0019] Regardless of the embodiment, at least one electric heating device may be chosen from an electric oven and an electric heat exchanger.

[0020] Regardless of the embodiment, at least one electric heating device may be chosen from a Joule effect (i.e. resistive), induction, radiant, microwave, plasma, shock wave heating system, or a combination of these heating methods.

[0021] The aforementioned threshold value can be determined beforehand from tests and / or modeling.

[0022] Advantageously, the threshold value can be from 20 to 120 °C, preferably from 40 to 120 °C.

[0023] Advantageously, the combustion furnace can include a convection zone and a radiation zone equipped with burners. This radiation zone is typically positioned below the convection zone. Thus, the convection zone is permeated by the combustion fumes from the hot heat produced by the burners. The radiation zone is subjected to the radiation from the flames produced by the burners.

[0024] Often, the hydrocarbon stream enters the combustion furnace at its convection zone and then enters the furnace's radiation zone before exiting. Alternatively, the hydrocarbon stream could enter directly into the furnace's radiation zone. Advantageously, the convection zone, through which the fumes exiting the radiation zone pass, may include at least one heat transfer zone to preheat the hydrocarbon stream before it enters the radiation zone, where the hydrocarbon stream is further heated, for example, at least partially vaporized. In addition, the convection zone may include at least one steam generation and / or superheating system. Typically, the hydrocarbon stream circulates through at least one tube bundle within the combustion furnace.

[0025] Advantageously, in one embodiment, the heating system according to the invention may include at least one electric heating device mounted upstream of the combustion furnace, namely mounted on the feed line downstream of the charge pump. Preferably, the combustion furnace comprises a convection zone and a radiation zone equipped with burners as previously described. The hydrocarbon flow then enters the combustion furnace at a convection zone, then enters a radiation zone of the combustion furnace before exiting the combustion furnace. The examples in this application show that this configuration reduces coking in the radiation zone.

[0026] In this embodiment, the heating system according to the invention may further include at least one electric heating device mounted downstream of the combustion furnace, namely mounted on the combustion furnace's exhaust pipe. This further reduces coking.

[0027] Advantageously, in another embodiment, the heating system according to the invention may include at least one electric heating device mounted downstream of the combustion furnace, namely mounted on the combustion furnace's exhaust pipe. The examples in this application show that this configuration limits coking in the electric heating device and allows for a further reduction in coking. Preferably, the combustion furnace comprises a convection zone and a radiation zone equipped with burners as previously described. The hydrocarbon flow then enters the combustion furnace at a convection zone, then enters a radiation zone of the combustion furnace, before exiting the combustion furnace.

[0028] In this embodiment, the heating system according to the invention may further include at least one electric heating device mounted upstream of the combustion furnace, namely mounted on the feed line downstream of the charge pump. This further reduces coking.

[0029] The invention also relates to a method of heating a hydrocarbon stream implemented in a heating system according to the invention, in which: - the hydrocarbon stream is introduced into the combustion furnace and at least one electric heating device by means of the charging pump, - the combustion furnace is operated, - at least one electric heating device and the combustion furnace are controlled to heat the hydrocarbon stream exiting the heating system to a target temperature, - and at least one electric heating device is controlled so as to maintain a temperature difference of the hydrocarbon stream between the inlet and outlet of the combustion furnace less than or equal to a threshold value.

[0030] The threshold value can be as previously defined.

[0031] When the heating system according to the invention includes at least one electric heating device mounted upstream of the combustion furnace, namely mounted on the supply line downstream of the charging pump, the hydrocarbon flow is then introduced into at least one electric heating device and then into the combustion furnace using the charging pump, or into at least one electric heating device and then into the convection zone of the combustion furnace when the latter includes a convection zone and a radiation zone equipped with burners as previously described.

[0032] When the heating system according to the invention includes at least one electric heating device mounted downstream of the combustion furnace, namely mounted on the combustion furnace exhaust pipe, the hydrocarbon flow is then introduced into the combustion furnace by means of the charging pump, and then into at least one electric heating device, or into the convection zone of the combustion furnace by means of the charging pump when the combustion furnace includes a convection zone and a radiation zone equipped with burners as previously described, and then into at least one electric heating device. Definitions

[0033] For the purposes of this description, the following definitions are given:

[0034] The terms "including" and "comprises" as used herein are synonymous with "including", "includes" or "contains", "containing", and are inclusive or boundless and do not exclude additional features, elements or unspecified method steps.

[0035] The specification of a numeric domain without decimals includes all whole numbers and, where appropriate, fractions of them (for example, 1 to 5 may include 1, 2, 3, 4 and 5 when reference is made to a number of elements, and may also include 1.5, 2, 2.75 and 3.80, when reference is made to, for example, a measure.).

[0036] The specification of a decimal also includes the decimal itself (for example, "from 1.0 to 5.0" includes both 1.0 and 5.0). Any range of numeric values ​​stated here also includes any subrange of numeric values ​​mentioned above.

[0037] The expressions % by weight and % by mass have an equivalent meaning and refer to the proportion of the mass of a product relative to 100g of a composition comprising it.

[0038] The term "hydrocarbon" refers to alkanes (saturated hydrocarbons), cycloalkanes, aromatics and unsaturated hydrocarbons.

[0039] The terms "alkane" or "alkanes" used here describe branched or unbranched acyclic hydrocarbons having the general formula C n H 2n+2 , and therefore composed entirely of hydrogen atoms and saturated carbon atoms; see, for example, IUPAC. Compendium of Chemical Terminology, 2nd edition (1997). The term "alkanes" thus refers to unbranched alkanes ("normal paraffins" or "n-paraffins" or "n-alkanes" or "paraffins") and branched alkanes ("iso-paraffins" or "iso-alkanes"), but excludes naphthenes (cycloalkanes). They are sometimes designated by the symbol "HC-".

[0040] The terms "olefin" or "alkene" used here refer to an unsaturated hydrocarbon compound containing at least one carbon-carbon double bond. They are sometimes designated by the symbol "HC=".

[0041] The particular characteristics, structures, properties, embodiments of the invention can be freely combined into one or more embodiments not specifically described here, as may be apparent to specialists in the processing of plastic liquefaction oils implementing their general knowledge. Detailed description of the invention Description of the figures

[0042] The invention is now described with reference to the accompanying, non-limiting drawings, in which:

[0043] The diagram schematically represents a heating system for a hydrocarbon flow according to an embodiment of the invention.

[0044] The diagram schematically represents a hydrocarbon flow heating system according to another embodiment of the invention.

[0045] This is a graph representing the evolution of the temperature of the hydrocarbon flow in example 1 as a function of the length of the tube inside which the hydrocarbon flow circulates in the combustion furnace.

[0046] This is a graph representing the evolution of the average heat flux of example 1 as a function of the length of the tube inside which the hydrocarbon flow circulates in the combustion furnace.

[0047] laest a graph representing the evolution of the external skin temperature and the film temperature of example 1 as a function of the length of the tube inside which the hydrocarbon flow circulates in the combustion furnace.

[0048] laest a graph representing the evolution of the relative coking rate of example 1 as a function of the length of the tube inside which the hydrocarbon flow circulates in the combustion furnace.

[0049] This is a graph representing the evolution of the temperature of the hydrocarbon flow in example 2 as a function of the length of the tube inside which the hydrocarbon flow circulates in the combustion furnace.

[0050] This is a graph representing the evolution of the average heat flux of example 2 as a function of the length of the tube inside which the hydrocarbon flow circulates in the combustion furnace.

[0051] laest a graph representing the evolution of the external skin temperature and the film temperature of example 2 as a function of the length of the tube inside which the hydrocarbon flow circulates in the combustion furnace.

[0052] laest a graph representing the evolution of the relative coking rate of example 2 as a function of the length of the tube inside which the hydrocarbon flow circulates in the combustion furnace.

[0053] Lare represents a heating system 100 of a hydrocarbon stream comprising: - a combustion furnace 10 comprising an inlet 12 and an outlet 14 for the hydrocarbon stream, - a supply line 20 for the hydrocarbon stream to be heated connected to the inlet 12 of the combustion furnace, - a charging pump 22 for the hydrocarbon stream mounted on the supply line 20, - an outlet line 30 for the heated hydrocarbon stream connected to the outlet 14 of the combustion furnace, - at least one electric heating device 40, here only one, mounted on the supply line 20 of the combustion furnace downstream of the charging pump 22, - a management system 50 for the combustion furnace and the at least one electric heating device 40.

[0054] According to the invention, the management system 50 is configured, in particular programmed, to:

[0055] to control the electric heating device(s) 40 and the combustion furnace 10 to heat the hydrocarbon flow exiting the heating system 100 to a target temperature, and

[0056] order at least one electric heating device40 mounted on the supply line so as to maintain a temperature difference of the hydrocarbon flow between the inlet and outlet of the combustion furnace less than or equal to a threshold value.

[0057] For this purpose, the management system 50 can control the power supply to the electric heating device as well as the combustion of the combustion furnace, for example by controlling the fuel and oxidizer supply to a combustion system 16 of the furnace. This combustion system 16 typically comprises a plurality of burners.

[0058] The management system 50 can also be configured, in particular programmed, to control the charging pump 22 allowing the hydrocarbon flow to be introduced inside at least one heating device.

[0059] The management system used in the present invention typically comprises one or more processors, for example a microprocessor, a microcontroller, or the like. It can be configured (in particular programmed) to control the heating device(s) used in the present invention, as well as the combustion furnace, and optionally the regulating pump. It can thus be connected to the components of this / these device(s), to the power supply of the electric heating device, and optionally to one or more valve(s), pump(s), and / or other element used for fluid circulation, particularly for supplying fuel and / or oxidizer to the combustion furnace.

[0060] The management system50 can also receive various pieces of information from one or more appropriately arranged sensors relating to:

[0061] - to the power supply (electrical and / or thermal) of the electric heating device(s) and / or the combustion furnace (quantity of current received and consumed, temperature and / or flow rate of fluids whose temperature is controlled),

[0062] - to the quantity of electrical and / or thermal energy received / produced by the electric heating device(s) and / or the combustion furnace (quantity of current, flow rate and / or temperature of fluids, flow rate of fuel feeding the combustion furnace),

[0063] - at the temperature of the hydrocarbon flow entering / exiting the electric heating device(s) and / or the combustion furnace,

[0064] - to the pressure of the hydrocarbon flow entering / exiting the electric heating device(s) and / or the combustion furnace,

[0065] - to the flow rate of hydrocarbons entering / exiting the electric heating device(s) and / or the combustion furnace.

[0066] The management system typically includes output or input / output interfaces. These may be wireless communication interfaces (Bluetooth, Wi-Fi, or other) or connectors (network port, USB port, serial port, FireWire® port, SCSI port, or other). These input and / or output interfaces can provide communication, optionally bidirectional, between the management system and the electric heating device(s) and the combustion furnace.

[0067] The management system may also include storage means such as random access memory (RAM), electrically erasable programmable read-only memory (EEPROM), flash memory, external memory, or other storage devices. These storage means can, among other things, store received data, measured values, calculated values, and one or more computer programs.

[0068] The threshold value can advantageously be determined by tests and / or simulations. In particular, it can be determined based on the operating parameters of the combustion furnace, and especially the target temperature of the hydrocarbon flow exiting the combustion furnace.

[0069] In particular, this threshold value is typically determined to limit coking in the combustion furnace. It can be from 20 to 120 °C, preferably from 40 to 120 °C.

[0070] Regardless of the embodiment, it will be possible to determine a threshold value such that a relative coking rate, as defined by equation 3 of the model used in the examples, is reduced by 5 to 75%, preferably by 10 to 75%, compared to a case where the electric heating device(s) is / are not working.

[0071] In this embodiment, the electric heating device 40 can advantageously be an electric heat exchanger or similar device, as shown. In the embodiment shown, this electric heating device thus comprises an inlet 42 and an outlet 44 for the hydrocarbon flow. The heat it produces can be obtained by Joule heating (i.e., resistive heating), induction, radiation, microwaves, plasma, shock waves, or a combination of these methods of electric heating.

[0072] In this embodiment, when the combustion furnace 10 is operating, the hydrocarbon stream to be heated is introduced into the electric heating device 40 by means of the charging pump 22. Then, in the combustion furnace, for example, at a convection zone thereof, again by means of the charging pump, the electric heating device 40 and the combustion furnace 10 are controlled to heat the hydrocarbon stream exiting the heating system 100 to the desired target temperature. The electric heating device 40 is also controlled to maintain a temperature difference of the hydrocarbon stream between the inlet 12 and the outlet 14 of the combustion furnace that is less than or equal to the threshold value. This makes it possible to both reduce the coking of the combustion furnace and reduce the carbon footprint of the heating system according to the invention.

[0073] In the particular embodiment shown in the figure, the installation 100 also includes one or more optional heat exchangers 24 for preheating the charge using a hot fluid from the refinery, located between the charge pump 22 and the electric heating device 40.

[0074] Figure 100 represents a hydrocarbon flow heating system which differs from that described in reference to lacquer by the position of the electric heating device 40 which is here arranged on the exhaust pipe 14 of the combustion furnace 10. The target temperature to which the hydrocarbon flow must be heated is therefore reached here at the outlet 44 of the electric heating device, the hydrocarbon flow entering the electric heating device through an inlet 42 connected to the exhaust pipe 14 of the combustion furnace 10.

[0075] In this embodiment, the management system50 is configured, in particular programmed, in the same way as described with reference to the embodiment of the.

[0076] In this embodiment, the electric heating device 40 may advantageously be an electric oven or similar. The heat it produces may be obtained by Joule effect (i.e., resistive), by induction, by radiation, by microwaves, by plasma, by shock waves, or by a combination of these methods of electric heating.

[0077] In this embodiment, when the combustion furnace 10 is operating, the hydrocarbon stream to be heated is introduced by means of the feed pump 22 into the combustion furnace 10, for example, at a convection zone thereof, and then into the electric heating device 40. The electric heating device 40 and the combustion furnace 10 are controlled to heat the hydrocarbon stream exiting the heating system 100 to the desired target temperature. The electric heating device 40 is also controlled to maintain a temperature difference of the hydrocarbon stream between the inlet 12 and the outlet 14 of the combustion furnace that is less than or equal to the threshold value. This makes it possible to both reduce the coking of the combustion furnace and reduce the carbon footprint of the heating system according to the invention.

[0078] In order to further limit coking in the combustion furnace, the management system can advantageously be configured to control at least one downstream electric heating device so that the pressure loss through it(s) is less than a target value which can be determined by tests and / or simulations.

[0079] In the embodiments described with reference to Figures 1 and 2, only one electric heating device 40 is provided. However, the invention is not limited to a particular number of electric heating devices, and the heating system 100 according to the invention may comprise two or more electric heating devices 40 mounted in series and / or in parallel on the supply line 20 of the combustion furnace, downstream of the charging pump 22, or on the discharge line 30 of the combustion furnace. Furthermore, in each embodiment, one or more electric heat exchangers, one or more electric furnaces, or combinations thereof may be used interchangeably. Moreover, the embodiments of Figures 1 and 2 may be combined.

[0080] Regardless of the embodiment, the combustion furnace 10 typically comprises a lower radiant section 10a and an upper convection section 10b. The heat from the radiant section 10a is supplied by the combustion of a fuel (generally combustible gas, such as methane or H2) in the presence of an oxidizer (air, etc.) in a combustion system 16 comprising at least one burner. The combustion furnace 10 thus comprises one or more fuel supply lines (not shown in the figures) and one or more oxidizer supply lines (not shown) to one or more burners. Combustion takes place in one or more burners located in the base, the ceiling, and / or the side walls of the lower part of the furnace enclosure 10.

[0081] The hydrocarbon stream, and possibly water, is injected into at least one heat exchange tube bundle (not shown) located in the convection zone 10b. The hydrocarbon stream is then distributed inside one or more tubular reactors 18 located in the radiation zone 10a. By means of the burners in the radiation zone, the tubular reactors are further heated to reach the target temperature or a temperature lower than the target temperature at the outlet of the combustion furnace in the embodiment of the.

[0082] The thermal energy required to heat the hydrocarbon stream is thus provided by the combustion of combustible gas with an oxidizer (air, etc.) in the combustion system.16 Approximately 40 to 50% of the heat of combustion is absorbed in the radiant zone of the furnace10a, the remainder passing to the convection zone10b where the majority of the sensible heat from the combustion gases is exchanged to preheat the hydrocarbon stream and / or water and / or steam in a heat transfer zone, for example via at least one heat exchanger (not shown). In some furnaces, the hydrocarbon stream may be heated only in the radiant zone10a.

[0083] The target temperature of the hydrocarbon stream exiting the combustion furnace or electric heating device, depending on the embodiment, varies according to its subsequent use. This target temperature is most often constant. For example, this target temperature can be from 300 to 550 °C for furnaces in naphtha distillation, hydrotreating, and reforming units.

[0084] The present invention makes it possible, in particular, to reduce the coking rate regardless of the target temperature. The invention thus allows for delaying coking and increasing the operating time of the combustion furnace between two maintenance shutdowns for decoking. Examples

[0085] The implementation methods of this description will be better understood by reference to the various non-limiting examples presented below.

[0086] Example 1: Electric heating device located upstream of a combustion furnace

[0087] A system comprising a combustion furnace and an external electric heating device located upstream of the furnace was studied.

[0088] The combustion furnace includes a convection zone in which the hydrocarbon charge is preheated and which also serves to generate steam, and a radiation zone in which the hydrocarbon charge is heated and partially vaporized.

[0089] In this study, the combustion furnace is a two-cell cabin furnace (two-cell radiant section) and has the following characteristics:

[0090] Radiation zone:

[0091] Dimensions of a cell: L = 23.50 m; W = 3.98 m H = 8.48 m.

[0092] Charge vaporization: - 4 tube passes per cell, - 12 roof tubes per cell, external diameter: 5.563 inches, length: 26.03 m - 40 wall tubes per cell, external diameter: 5.563 inches, length: 26.03 m - 4 wall tubes per cell, external diameter: 8.625 inches, length: 26.03 m, - 4 wall tubes per cell, external diameter: 10.75 inches, length: 26.03 m.

[0093] Convection zone:

[0094] Dimensions: Length: 23.50 m; Width: 1.84 m; Height: 4.12 m.

[0095] Preheating of the charge: - 8 tube passages, - 56 horizontal tubes with an external diameter of 5.563 inches, length: 23.50 m.

[0096] Low pressure steam superheating: - 4 tube passages, - 8 horizontal tubes with an external diameter of 4.5 inches, length: 23.50 m.

[0097] High pressure steam superheating: - downward flow: 8 tube passages, 16 horizontal bare tubes with an external diameter of 4.5 inches, length: 23.50 m, - upward flow: 8 tube passages, 16 horizontal studded tubes with an external diameter of 4.5 inches, length: 23.50 m (stud height: 1 inch, stud diameter: 0.5 inches – 16 studs per ring, 0.57 rings per centimeter, material: CS i.e. silicon carbide).

[0098] High pressure steam generation: - 4 tube passages, - 16 horizontal bare tubes with an external diameter of 4.5 inches, length: 23.50 m, - 32 horizontal studded tubes with an external diameter of 4.5 inches, length: 23.50 m (stud height: 1 inch, stud diameter: 0.5 inches - 16 studs per ring, 0.57 rings per centimeter, material: CS i.e. silicon carbide).

[0099] The material of the combustion furnace tube is a steel containing 9% by mass of Cr and 1.0% by mass of Mo.

[0100] A model was created using the FRNC5 model (version 9.6.0) assuming a constant radiation temperature (i.e., homogeneous combustion, homogeneous heat flux, no flame impact), and a reference temperature of 825 °F. The charge is considered to be free of impurities (such as caustic soda).

[0101] The above model uses a relative coking rate defined as being equal to a base value multiplied by a temperature adjustment term defined by the following equation 1:

[0102] (Equation 1)

[0103] Where: - Ea is the activation energy (BTU / lb-mole), - R is a gas constant, 1.987 Btu / Lb-mole-°R, - Tf is the average temperature of the film at the surface of the process tube (°R), - Tb is a reference temperature (°R).

[0104] The base value used for the relative coking ratio is expressed by equation 2:

[0105] (Equation 2)

[0106] where C1 is a constant and Cf a characterization factor (defect value: 2), µ is the viscosity of the hydrocarbon charge (Pa.s), ρ its density, ν its velocity (m3 / h).

[0107] The Ea value used is 40 Kca / g-mole (72000 Btu / lb-mole), and the reference temperature Tb is 825 °F (1285 °R).

[0108] The model determines a relative coking rate between the different tubes of the combustion furnace and uses equation 3 to estimate a normalized coking rate (relative to 825 °F).

[0109] (Equation 3)

[0110] Where: - Rc is the relative coking rate, - C2, C3 are constants, - the other terms are as previously defined.

[0111] Table 1 summarizes the different cases studied to obtain a temperature of approximately 400 °C at the outlet of the combustion furnace.

[0112] In the baseline scenario, the electric heating device does not function. For tests 1 to 3, the electric heating device provides 10, 20, and 40% of the thermal energy required to heat the hydrocarbon stream to the target temperature of 399 °C, respectively.

[0113] Unit Base Case Test 1 Test 2 Test 3 Electrical Energy % 0 10 20 40 Combustion Furnace Energy % 10 0 90 80 60 Pressure Loss in Combustion Furnace kPa 436.8 44 41.4 44 5.8 45 5.2 Combustion Furnace Outlet Temperature °C 399.0 399.0 399.0 399.0 Fraction of Load Vaporized at Combustion Furnace Outlet % by Mass 414 141 41 Power Absorbed by Load in Electric Heating Device (1) (a) MW 0.00 4.4 0 8.8 0 17.5 9 Power Absorbed by Load in Combustion Furnace (2) (b) MW 43.9 8 39.4 4 35.0 7 26.3 1 Total Thermal Power Delivered by Combustion Furnace (c)MW63,8256,5049,6836,48 Combustion furnace efficiency%7878,7079,3080,50 Combustion furnace efficiency + electric heating device (3)%7880,8482,4186,84

[0114] (1) Assumed efficiency of the electric heating device: 100% (power absorbed = power input)

[0115] (2) includes preheating the load and generating steam

[0116] (3) Total power absorbed in the process / (load of the combustion furnace + load of the electrical system) = (a+b) / (a+c).

[0117] Table 1 also highlights the improved efficiency of the heating system according to the invention.

[0118] La represents the temperature variation of the hydrocarbon flow (temperature at the center of the flow) as it progresses through the combustion furnace, from the convection zone (tube length from 0 to approximately 160 m) to the radiation zone (from approximately 160 to 550 m). The boundary between the two zones is symbolized by the vertical line. In the basic case, without preheating by the electric heating device, the temperature at the inlet of the combustion furnace is approximately 292 °C. When the electric heating device takes over 10, 20, and 40% of the heating of the charge, respectively, the temperature at the inlet of the combustion furnace is approximately 310, 320, and 350 °C, respectively.

[0119] Lamontre that the average heat released inside the combustion furnace decreases when the electric heating device is operating due to the reduction in heat to be supplied by the combustion furnace to heat the hydrocarbon stream to the same target temperature, here 399 °C at the outlet of the combustion furnace.

[0120] Lamontre describes the evolution of the temperature at the outer surface of the tubes and the film temperature, defined as the temperature of the fluid in contact with the inner surface of the tubes. In the coldest tubes (in the convection zone), when the electric heating device takes over 10 to 40% of the heating, the film temperature increases. This effect is reversed in the last tubes of the combustion furnace's radiation zone, where a decreasing film temperature can be observed.

[0121] Lamet highlights that the average coking rate increases in the coldest part of the radiation zone when the electric heating device takes on 10 to 40% of the heating. This appears to be primarily due to the film temperature. In the warmer part of the radiation zone, a positive impact is observed as the electric heating device takes on more heating, which seems to be due to a reduction in the film temperature (considering that a temperature above 400 °C causes coking).

[0122] The variations in average coking rates for the different parts of the radiation zone are summarized in Table 2.

[0123] Cold section (a) Variation in the coking rate of the cold section Hot section (b) Variation in the coking rate of the hot section Baseline case 1.25 6.39 10% 1.39 +12% 5.62 -12% 20% 1.56 +25% 4.96 -22% 40% 1.99 +60% 4.0 -39%

[0124] Cold section (a): from tube No. 1 in the radiation zone to tube No. 11 (where the film temperature is 408 °C)

[0125] Hot section (b): from tube No. 12 of the radiation zone to tube No. 15.

[0126] The results in Table 2 show that the coking rate increases in the cold section while it decreases in the hot section. However, since the risk of coking is greatest in the hot section, reducing the coking rate there is more beneficial than increasing it in the cold section.

[0127] Positioning the electric heating device upstream increases the operating time of the combustion furnace between two stops for decoking by 2 to 7%.

[0128] Example 2: Electric heating device located downstream of a combustion furnace

[0129] The combustion furnace is the same as the one in example 1.

[0130] In this example, the vaporization of the charge also occurs downstream of the combustion furnace, namely in the electric heating device. The latter thus acts as an electric furnace.

[0131] In this example, various tests were carried out considering that we are at the hydraulic limit of the combustion furnace (limit established when heating is done solely with the combustion furnace).

[0132] Table 3 summarizes the different cases studied to obtain a temperature of approximately 400 °C at the outlet of the electric heating device.

[0133] In the baseline scenario, the electric heating device does not function. For tests 1 and 2, the electric heating device provides 20% and 40% respectively of the thermal energy required to heat the hydrocarbon stream to the target temperature of 400 °C.

[0134] Unit Base Case Test 1 Test 2 Electrical Energy % 0 20 40 Combustion Furnace Energy % 10 0 80 60 Power absorbed by the load in the combustion furnace MW 43.98 35.07 26.30 Power absorbed by the load in the electric heating device (1) (a) MW 0.00 8.76 917.54 Total power absorbed by the load in the combustion furnace + electric heating device MW 43.98 43.84 43.84 Total power absorbed in the combustion furnace + electric heating device (2) (b) MW 49.77 39.09 28.83 Total thermal power supplied by the combustion furnace (c) MW 63.81 48.99 35.38 Combustion furnace efficiency % 78 78.90 81.50 Combustion furnace efficiency + electric heating device (3)%82.8787.63

[0135] (1) Assumed efficiency of the electric oven: 100% (power absorbed = power input)

[0136] (2) includes preheating the load and generating steam

[0137] (3) Total power absorbed in the process / (load of the combustion furnace + load of the electrical system) = (a+b) / (a+c).

[0138] Tables 4 and 5 show the pressure drop in the combustion furnace and the electric heating device in the different cases tested, for various pressure drops in the electric heating device. As the pressure drop inside the electric furnace increases, the vaporized fraction in the combustion furnace decreases, resulting in a decrease in velocity and an increase in residence time in the combustion furnace. Thus, at an equivalent temperature, the coking rate will increase in the combustion furnace if the pressure drop increases in the electric furnace. Furthermore, it is observed that in tests 1 and 2, the hydraulic limit of the circuit is reached before this increase in coking occurs. The hydraulic limit (denoted as Limite Hydr.) is related to the characteristics of the charging pump (flow rate and pressure).

[0139] Unit Base Case Test 1 Electrical Energy % 0 20 Total Process Energy % 10 0 80 Pressure Loss in Combustion Furnace kPa 436.8 326.5 285.2 268.7 Combustion Furnace Outlet Temperature °C 399.0 392.0 392.0 393.0 Quantity of Steam at Combustion Furnace Outlet wt 0.4 10.1 20.0 90.08 Pressure Loss in Electric Heating Device Bar 0.0 1.1 1.72 Overall Pressure Loss of Furnace + Electric Heating Device kPa 436.8 436.5 455.2 468.7 Hydration Limit Augm. Coking (*) (*) Increase in coking compared to the base case

[0140] Unit Base Case Test 2 Electrical Energy %0 40 Total Process Energy %10 0 60 Pressure Loss in Combustion Furnace kPa 436.8 286.1 211.1 149.2 95.8 Combustion Furnace Outlet Temperature °C 399.0 370.0 370.0 371.0 372.0 Quantity of Steam at Combustion Furnace Outlet wt 0.4 10.0 70.0 40.0 30.02 Pressure Loss in Electric Heating Device Bar 0.0 1.5 358 Overall Pressure Loss of Furnace + Electric Heating Device kPa 436.8 436.1 511.1 16 49.2 895.8 Hydration Limit Augm. Coking (*) (*) Increase in coking compared to the base case

[0141] La represents the temperature variation of the hydrocarbon flow (temperature at the center of the flow) as it progresses through the combustion furnace, from the convection zone (tube length from 0 to approximately 160 m) to the radiation zone (from approximately 160 to 550 m). The boundary between the two zones is symbolized by the vertical line. In the baseline scenario, without activation of the downstream electric heating device, the temperature at the combustion furnace inlet is approximately 295 °C. When the electric heating device takes over 20% and 40% of the load heating, respectively, the temperature at the combustion furnace outlet is approximately 390 and 370 °C, respectively.

[0142] Lamontre that the average heat flux released inside the combustion furnace decreases when the electric heating device is operating due to the reduction in heat to be supplied by the combustion furnace to heat the hydrocarbon flow to the same target temperature, here 400 °C at the outlet of the electric heating device.

[0143] Lamontre shows the evolution of the external tube temperature (outer skin – dashed lines in the figure) and the film temperature (solid lines in the figure) when the electric heating device takes on 20% and 40% of the heating load, respectively, and for different pressure losses across the electric heating device. In both the colder tubes (in the convection zone) and the hotter tubes (radiation zone), when the electric heating device takes on 20% to 40% of the heating, the film temperature decreases, thus reducing coking.

[0144] Lamet highlights a positive impact of the increasing use of electric heating devices for film heating, which appears to be due to a reduction in film temperature (considering that temperatures above 400°C cause coking). A reduction in the relative coking rate of approximately 6 to 70% can be achieved.

[0145] Positioning the electric heating device downstream increases the operating time of the combustion furnace between two stops for decoking by 20 to 410%.

Claims

A hydrocarbon flow heating system (100) comprising: - a combustion furnace (10) including an inlet (12) and an outlet (14) for the hydrocarbon flow, the combustion furnace including a convection zone and a radiation zone equipped with burners and in which the hydrocarbon flow enters the combustion furnace at the level of the convection zone of the latter and then enters the radiation zone of the furnace before exiting the combustion furnace, - a supply line (20) for the hydrocarbon flow to be heated connected to the inlet of the combustion furnace, - a charging pump (22) for the hydrocarbon flow mounted on the supply line (20), - a discharge line (30) for the heated hydrocarbon flow connected to the outlet of the combustion furnace, - at least one electric heating device (40) mounted on the supply line downstream of the charging pump (22).- a management system (50) configured to: - control at least one electric heating device (40) and the combustion furnace (10) to heat the hydrocarbon flow exiting the heating system to a target temperature, and - control at least one electric heating device (40) so as to maintain a temperature difference of the hydrocarbon flow between the inlet and outlet of the combustion furnace less than or equal to a threshold value. Heating system (100) according to claim 1, characterized in that it further comprises at least one electric heating device mounted on the exhaust pipe of the combustion furnace. A hydrocarbon stream heating system (100) comprising: - a combustion furnace (10) including an inlet (12) and an outlet (14) for the hydrocarbon stream, - a supply line (20) for the hydrocarbon stream to be heated connected to the inlet of the combustion furnace, - a charging pump (22) for the hydrocarbon stream mounted on the supply line (20), - a discharge line (30) for the heated hydrocarbon stream connected to the outlet of the combustion furnace, - at least one electric heating device (40) mounted on the discharge line of the combustion furnace, - a control system (50) configured to: - control the at least one electric heating device (40) and the combustion furnace (10) to heat the hydrocarbon stream exiting the heating system to a target temperature, and- to control at least one electric heating device (40) so as to maintain a temperature difference of the hydrocarbon flow between the inlet and outlet of the combustion furnace less than or equal to a threshold value. Heating system (100) according to claim 3, characterized in that it further comprises at least one electric heating device mounted on the supply line downstream of the charging pump (22). Heating system according to any one of the preceding claims, characterized in that at least one electric heating device is selected from an electric furnace and an electric heat exchanger. Heating system (100) according to any one of the preceding claims, characterized in that at least one electric heating device is selected from a Joule effect, induction, radiative, microwave, plasma, shock wave heating system, or a combination of these heating methods. Heating system (100) according to any one of the preceding claims, characterized in that the threshold value is from 20 to 120 °C, preferably from 40 to 120 °C. A method for heating a hydrocarbon stream implemented in a heating system (100) according to claim 1 or 2, or according to any one of claims 5 to 7 when they depend on claim 1 or 2, wherein: - the hydrocarbon stream is introduced into at least one electric heating device and then into the convection zone of the combustion furnace by means of the charge pump (22), - the combustion furnace (10) is operated, - at least one electric heating device (40) and the combustion furnace (10) are controlled to heat the hydrocarbon stream exiting the heating system to a target temperature, - and at least one electric heating device is controlled so as to maintain a temperature difference of the hydrocarbon stream between the inlet and outlet of the combustion furnace less than or equal to a threshold value. A method for heating a hydrocarbon stream implemented in a heating system (100) according to claim 3 or 4 or according to any one of claims 5 to 7 when they depend on claim 3 or 4, in which: - the hydrocarbon stream is introduced into the combustion furnace (10) by means of the charging pump (22), then into at least one electric heating device, - the combustion furnace (10) is operated, - at least one electric heating device (40) and the combustion furnace (10) are controlled to heat the hydrocarbon stream exiting the heating system to a target temperature, - and at least one electric heating device is controlled so as to maintain a temperature difference of the hydrocarbon stream between the inlet and outlet of the combustion furnace less than or equal to a threshold value. Heating method according to claim 8 or 9, characterized in that the threshold value is from 20 to 120 °C, preferably from 40 to 120 °C.

Images