Electric furnace for cracking hydrocarbon feedstocks with heat recovery.

Abstract

An electrocracker system for converting a hydrocarbon feedstock to cracked gas includes a mixing device for mixing the hydrocarbon feedstock with slightly superheated steam and / or saturated steam. The system includes a steam drum, an electric furnace, a primary transfer line exchanger (PTLE), a secondary transfer line exchanger (STLE), and a tertiary transfer line exchanger (TTLE). The electric furnace includes a feed inlet for the hydrocarbon feedstock-saturated steam mixture and an outlet for the cracked gas. The steam drum includes a saturated steam outlet connected to the mixing device, and a water outlet and a steam inlet both connected to the STLE. The PTLE is configured to preheat the hydrocarbon feedstock-saturated steam mixture before it enters the electric furnace and to cool the cracked gas provided by the electric furnace. The STLE is configured to generate steam and to cool the cracked gas provided by the PTLE.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims priority to and the benefit of U.S. patent application Ser. No. 17 / 727,700, filed April 22, 2022, the contents of which are incorporated herein by reference in their entirety.

[0002] The present disclosure relates to an electrocracker system for converting a hydrocarbon feedstock into cracked gases and a process for cracking a hydrocarbon feedstock using the system. More particularly, the present disclosure relates to a process for producing ethylene and propylene from a hydrocarbon feedstock. [Background technology]

[0003] In a conventional ethylene plant with a fired cracker, sufficient high pressure (HP) steam is produced to power the machinery and also to generate dilution steam to suppress the hydrocarbon partial pressures, improving product selectivity and reducing coke formation in the cracking reactor.

[0004] In the high temperature section of the plant, dilution steam is conventionally generated from medium pressure (MP) steam, which is generated from HP steam after generating electricity via one or more steam turbines. Furthermore, if a primary fractionator known for cracking liquid feedstock is available, heat recovery of the furnace effluent (cracked products) in the pump-around circuit of the primary fractionator, the quench oil circuit of the primary fractionator, helps to generate dilution steam and allows more MP steam to be reduced to a lower pressure level for maximum power production. At the same time, excess heat from the effluent can be recovered in a quench tower and transferred to low temperature users via the pump-around loop. This low level heat is used, for example, to preheat the furnace feedstock. Vaporization of further feedstock is usually performed by flue gas in the convection section of the conventional cracking furnace.

[0005] More specifically, a conventional gas cracking furnace includes the following features: - Radiant section, where the radiant coil is in the fire chamber (at least one radiant coil) and the chemical reaction occurs in the radiant coil. Combustion occurs in the fire chamber with fuel to the burner to provide the heat required for the pyrolysis reaction. - The convection section is used to preheat the feed, dilution steam, and the mixture of feed and dilution steam, generate high pressure steam, and preheat the boiler feed water. In some cases, it can also be used to preheat the combustion air as an air preheater (also called "APH") for fossil fuel combustion in the burners. The purpose of the convection section is to recover the available hot flue gas heat from the combustion of fuel and air in the firebox. - Flue gas contains mainly N2, O2, H2O, CO2, argon, traces of NOx / CO, and certain substances (PM2.5, PM5, and PM10). Several ethylene producers have announced targets to reduce CO2 emissions by 25% in 2030 and reach net-zero CO2 emissions by 2050. In some cases, DeNOx units (otherwise called SCR) are installed in the convection section to further reduce NOx generated from combustion to meet on-site emission requirements. A transfer line exchanger (TLE) is located at the outlet of the radiant coil via a transfer line to cool the cracked gas from the outlet of the radiant coil to a desired temperature before it leaves the cracking furnace. The transfer line exchanger can be one or more exchangers. - Saturated high pressure steam is generated in the TLE by quenching the cracked gases through risers and downcomers between the TLE and the steam drum. The saturated high pressure steam is further heated in the high pressure steam superheater coils (HPSSH-1 and HPSSH-2) in the convection section to generate superheated high pressure steam, which is then discharged from the cracking furnace. -Dilution steam to the furnace is supplied from the rest of the plant by a dilution steam generator drum. Saturated dilution steam is generated by medium pressure steam as a vaporizer, separated in the dilution steam generator drum, and then slightly superheated by MP steam before proceeding to the furnace, or by injecting hot steam before entering the furnace. In addition, the quench water stripper condensate is preheated with MP steam before proceeding to the dilution steam generator drum. The dilution steam is mixed with the preheated dry feed from the upper bank of the convection section. The mixed feed is further preheated in the lower bank of the convection section to the radiant coil inlet temperature required for cracking in order to reduce the coking rate and increase the olefin yields in the furnace discharge, such as ethylene and propylene yields.

[0006] The prior art has been deemed satisfactory for their intended purposes. However, there continues to be a need for improved electrolysis furnace systems and methods. The present disclosure provides a solution to this need. Summary of the Invention

[0007] An embodiment of the present disclosure aims to improve heat recovery and simplify the cracking of hydrocarbon feedstock. An embodiment of the present disclosure includes an electrocracker system for converting a hydrocarbon feedstock into cracked gas, the electrocracker system including at least a mixing device for mixing the hydrocarbon feedstock with slightly superheated or saturated steam, a steam drum, an electric furnace, a primary transfer line exchanger (PTLE), a secondary transfer line exchanger (STLE), and a tertiary transfer line exchanger (TTLE). The electric furnace includes a feed inlet for the hydrocarbon feedstock-slightly superheated steam mixture or saturated steam mixture and an outlet for the cracked gas. The steam drum includes a saturated steam outlet connected to the mixing device for mixing the hydrocarbon feedstock with the saturated steam, and a water outlet and a steam inlet both connected to the secondary transfer line exchanger STLE. The primary transfer line exchanger (PTLE) is configured to preheat the hydrocarbon feedstock-saturated steam mixture before entering the electric furnace and to cool the cracked gas provided by the electric furnace. The secondary transfer line exchanger (STLE) is configured to generate steam and to cool the cracked gas provided by the primary transfer line exchanger (PTLE). The tertiary transfer line exchanger (TTLE) is configured to preheat the hydrocarbon feedstock prior to mixing with the saturated steam and to cool the cracked gas provided by the secondary transfer line exchanger (STLE). The electrocracker system can include a cracked gas compressor accompanied by an electric turbine. The secondary transfer line exchanger (STLE) is configured to generate steam and ... secondary transfer line exchanger (STLE). 2 g. The electrolysis furnace system may include a heat exchanger upstream of the mixing device for preheating the saturated steam provided by the steam drum. The electrolysis furnace system may include a second mixing device upstream of the mixing device for mixing the saturated steam provided by the steam drum with the preheated steam. The electrolysis furnace system may include N electric furnaces, N to 10N primary transfer line exchangers PTLE, N to 2N secondary transfer line exchangers STLE, N to 2N tertiary transfer line exchangers TTLE, N≧2, and N or less than N steam drums, N≧2.

[0008] According to another aspect, a process for cracking a hydrocarbon feedstock in an electrocracker system can include preheating the hydrocarbon feedstock in a tertiary transfer line exchanger (TTLE). The process includes mixing the preheated hydrocarbon feedstock with at least one of saturated steam or slightly superheated steam to generate at least one of a hydrocarbon feedstock-saturated steam mixture or a hydrocarbon feedstock-slightly superheated steam mixture. The process includes preheating at least one of the hydrocarbon feedstock-saturated steam mixture or the hydrocarbon feedstock-slightly superheated steam mixture in a primary transfer line exchanger (PTLE). The process includes cracking the preheated hydrocarbon feedstock-saturated steam mixture or the hydrocarbon feedstock-slightly superheated steam mixture in an electric furnace to generate cracked gas. The process includes providing a first cooling of the cracked gas in the primary transfer line exchanger (PTLE). The process includes providing a second cooling of the cracked gas exiting the primary transfer line exchanger (PTLE) in a secondary transfer line exchanger (STLE). The process includes generating steam in the secondary transfer line exchanger (STLE). The process includes providing a third cooling of the cracked gas exiting the secondary transfer line exchanger (STLE) in a tertiary transfer line exchanger (TTLE).

[0009] The hydrocarbon feedstock may be a dry gas. The process may include generating saturated steam or slightly superheated steam in a steam drum. The steam generated in the secondary transfer line exchanger (STLE) may be generated from water from the steam drum. The steam generated in the secondary transfer line exchanger (STLE) may be sent to the steam drum. Preheating at least one of the hydrocarbon feedstock-saturated steam mixture or the hydrocarbon feedstock-slightly superheated steam mixture may include preheating at a temperature between 180° C. and 300° C. Preheating at least one of the hydrocarbon feedstock-saturated steam mixture or the hydrocarbon feedstock-slightly superheated steam mixture may include preheating at a temperature between 200° C. and 260° C. The steam generated in the secondary transfer line exchanger (STLE) may include a steam drum having a steam density of 4 kg / cm. 2 ~15kg / cm 2 g pressure, or 6 kg / cm 2 g~8kg / cm 2 The pressure is g.

[0010] Cooling the cracked gas in the primary transfer line exchanger (PTLE) may include cooling the cracked gas at a temperature between 750° C. and 900° C., or between 820° C. and 875° C. Cooling the cracked gas in the secondary transfer line exchanger (STLE) may include cooling the cracked gas at a temperature between 375° C. and 600° C., or between 420° C. and 520° C. These and other features of the disclosed systems and methods will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments read in conjunction with the drawings. [Brief description of the drawings]

[0011] Preferred embodiments of the present disclosure are described in detail herein below with reference to specific figures so that those skilled in the art to which the present disclosure pertains will readily understand how to make and use the devices and methods of the present disclosure without undue experimentation. [Figure 1]FIG. 1 is a schematic diagram of an embodiment of an electric furnace system constructed in accordance with the present disclosure showing one primary transfer line exchanger, one secondary transfer line exchanger, and one tertiary transfer line exchanger. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Reference is now made to the drawings, where like reference numbers identify like structural features or aspects of the present disclosure. For purposes of explanation and illustration, and without limitation, a schematic diagram of an exemplary embodiment of an electrolysis furnace system according to the present disclosure is shown in FIG. 1 and is generally designated by the reference numeral 100. Other embodiments of electrolysis furnace systems according to the present disclosure, or aspects thereof, are described below. The systems and methods described herein can be used to improve heat recovery and simplify the cracking of hydrocarbon feedstocks. Embodiments of the present disclosure are directed to improving heat recovery and simplifying the cracking of hydrocarbon feedstocks.

[0013] An embodiment of the present disclosure provides an electrocracker system for converting a hydrocarbon feedstock 1 into a cracked gas 4, comprising at least: a mixing device 9 for mixing the hydrocarbon feedstock 1 with slightly superheated or saturated steam 2; - Steam drum 5; - 3 electric furnaces, - a Primary Transfer Line Exchanger (PTLE); - a secondary transfer line exchanger (STLE); - Tertiary Transport Exchange (TTLE); In this case, The electric furnace 3 is provided with a feed inlet for the hydrocarbon feedstock-slightly superheated or saturated steam mixture 10 and an outlet for the cracked gas 4; The steam drum 5 comprises a saturated steam outlet connected to a mixing device 9 for mixing the hydrocarbon feedstock with saturated steam, and a water 6 outlet and a steam 7 inlet both connected to a secondary transfer line exchanger STLE; A primary transfer line exchanger (PTLE) configured to preheat the hydrocarbon feedstock-saturated steam mixture before it enters the electric furnace 3 and to cool the cracked gas 4 provided by the electric furnace 3; The secondary transfer line exchanger (STLE) is configured to generate steam 7 and to cool the cracked gas 4 provided by the primary transfer line exchanger (PTLE); The tertiary transfer line exchanger (TTLE) is configured to preheat the hydrocarbon feedstock 1 before mixing with the saturated steam 2 and to cool the cracked gas 4 provided by the secondary transfer line exchanger (STLE).

[0014] 1 illustrates an electric furnace system 100 according to one embodiment of the present disclosure. The electric furnace system 100 includes one primary transfer line exchanger, one secondary transfer line exchanger, and one tertiary transfer line exchanger.

[0015] The steam drum 5 includes a blowdown outlet 11 .

[0016] According to an embodiment of the present disclosure, superheated steam is steam having a temperature higher than that of saturated steam, and preferably the difference between the temperature of saturated steam and the temperature of superheated steam is less than 10°C.

[0017] According to an embodiment of the present disclosure, the "electric furnace" is an electrically powered pyrolysis reactor.

[0018] A variety of suitable devices can be used as the mixing device 9. According to embodiments of the present disclosure, the mixing device 9 can be a gas mixer with a mechanical mixing valve, a gas mixer with an electrical mixing valve, a gas mixer with an air flow controller, a gas mixer with a flow controller (e.g., a mass flow controller), and the like.

[0019] The transfer line exchanger (TLE) is a heat exchanger arranged to cool or quench the cracked gas. According to the embodiments of the present disclosure, the furnace efficiency can be significantly improved by using the waste heat of the cracked gas in the transfer line exchanger to heat the feed in the transfer line exchanger instead of heating the feed in the convection section as is done in the prior art systems. The furnace efficiency is the ratio between the heat absorbed by at least one radiant coil to convert the hydrocarbon feed to cracked gas by pyrolysis, an endothermic reaction, and the heat released by the combustion process in the combustion zone, based on the lower heating value of 25°C or 15.6°C.

[0020] The optimum inlet temperature of the feedstock to the radiant section is determined by the thermal stability of the feedstock, as known to those skilled in the art. Ideally, the feedstock enters the radiant section at a temperature slightly lower than the temperature at which the thermal cracking reaction starts. If the feedstock inlet temperature is too low, additional heat is required to heat the feedstock in the radiant section, increasing the heat that needs to be supplied to the radiant section and the corresponding power consumption. If the feedstock inlet temperature is too high, thermal cracking may already start in the transfer line exchangers or pipes, which is undesirable because the reaction is accompanied by the formation of coke that cannot be easily removed.

[0021] The secondary transfer line exchanger (STLE) is disposed in series after the primary transfer line exchanger (PTLE) to further cool the cracked gas from the electric furnace. The primary transfer line exchanger (PTLE) is configured to heat the feedstock before it enters the electric furnace, while the secondary transfer line exchanger is configured to partially vaporize the boiler water by quenching the cracked gas. The system may include one or more secondary heat exchangers. The system includes a steam drum connected to the secondary transfer line exchanger (STLE). The boiler water flows from the steam drum of the cracking furnace system to the secondary transfer line exchanger. After the steam and water mixture is partially vaporized inside one of the secondary transfer line exchangers (STLE), it may be pumped back to the steam drum, where the steam may be separated from the remaining liquid water.

[0022] The electrolysis furnace system may advantageously comprise several primary transfer line exchangers (PTLEs).

[0023] Depending on the embodiment, electrolysis furnace systems according to embodiments of the invention can include one or more of the following features: The electrolysis furnace system comprises at least a compressor 17 for the cracked gases 4 accompanied by an electric turbine. Preferably, the compressor comprises several stages, advantageously between 1 and 5 stages. -Secondary transfer line exchanger (STLE) is 4~15kg / cm 2 It is configured to generate steam 7 at a pressure of 100 g. Upstream of the mixing device 9 for mixing the hydrocarbon feedstock with saturated or slightly superheated steam, the electrolysis furnace system comprises a heat exchanger 12 for preheating the saturated steam provided by the steam drum, or a second mixing device for mixing the saturated steam provided by the steam drum with the preheated steam 8.

[0024] The electrolysis furnace system comprises N electric furnaces 3, N-10N primary transfer line exchangers PTLE, N-2N secondary transfer line exchangers STLE, N-2N tertiary transfer line exchangers TTLE, N>2, and N or less than N steam drums 5, N>2. In other words, the electrolysis furnace system also comprises only one steam drum with multiple risers (minimum one) and downcomers (minimum one) for one or more electric furnaces. Another object of an embodiment of the present disclosure is a process for cracking a hydrocarbon feedstock in an electrolysis furnace system as defined in the present disclosure, comprising: a) preheating a hydrocarbon feedstock 1 in a tertiary transfer line exchanger (TTLE); b) a step 9 of mixing the preheated hydrocarbon feedstock 1 with saturated or slightly superheated steam 2; c) preheating the hydrocarbon feedstock-saturated steam mixture or slightly superheated steam mixture 10 provided in step a) in a primary transfer line exchanger (PTLE); d) decomposing the mixture preheated in step b) in an electric furnace 3 to produce decomposition gas 4; e) a first cooling step of cooling the cracked gas 4 in a primary transfer line exchanger (PTLE); f) a second cooling step in which the cracked gas 4 leaving the primary transfer line exchanger (PTLE) is cooled in a secondary transfer line exchanger (STLE); g) generating steam 7 in a secondary transfer line exchanger (STLE); h) a third cooling step in which the cracked gas 4 leaving the secondary transfer line exchanger (STLE) is cooled in a tertiary transfer line exchanger (TTLE); It is a process that includes:

[0025] Depending on the embodiment, the process for cracking a hydrocarbon feedstock according to the present disclosure can include one or more of the following features: The hydrocarbon feedstock 1 is a dry gas. Preferably, the hydrocarbon feedstock 1 comprises 50% to 100% by volume of ethane and 50% to 0% by volume of propane, more preferably 80% to 100% by volume of ethane and 20% to 0% by volume of propane. The process for cracking a hydrocarbon feedstock comprises a step of generating saturated or slightly superheated steam 2 in a steam drum 5 . - The steam 7 produced in step g) is generated from water 6 coming from a steam drum 5. - The steam 7 produced in step g) is passed into the steam drum 5. - In step c) the hydrocarbon feedstock-saturated steam mixture or slightly superheated steam mixture 10 is preheated to a temperature between 180°C and 300°C, preferably between 200°C and 260°C. In step g), the steam 7 generated has a flow rate of 4 kg / cm 2 ~15kg / cm 2 g, preferably 6 kg / cm 2 g~8kg / cm 2 The pressure is g. - In step e) the cracked gas 4 is cooled to a temperature between 750°C and 900°C, preferably to a temperature between 820°C and 875°C. In step f), the cracked gases (4) are cooled to a temperature between 375°C and 600°C, preferably to a temperature between 420°C and 520°C. - The steam 7 produced in step g) is generated from water 6 coming from a steam drum 5. - The steam 7 produced in step g) is passed into the steam drum 5.

[0026] The electric furnace has no convection section, no flue gas generation, and therefore no emissions such as NOx / CO / PM and CO2, compared to conventional cracking furnaces where fossil fuel / air is supplied for combustion by burners. Instead, the electric furnace supplies heat to the cracking radiant section by electrical resistance heating. Heat input can be controlled by power generation along the radiant coil. Unlike conventional furnace designs, a transfer line exchanger (TLE) is used to generate high pressure steam (HP). In the embodiments of the present disclosure, none of the transfer line exchangers are used to generate high pressure steam. Instead, one of the transfer line exchangers is used to generate dilution steam by quenching the cracked gas effluent. This is the role of the second transfer line exchanger (STLE). The other two transfer line exchangers are used to: 1. Preheat the dry feed by quenching the cracked gas effluent. This is the role of the tertiary line exchanger (TTLE). 2. Further preheat the mixed feed (mixture of dilution steam and dry feed) by quenching the cracked gas effluent before proceeding to the radiant coil inlet for cracking. This is the role of the Primary Transfer Line Exchanger (PTLE). This process according to an embodiment of the present disclosure is applied to gas feed crackers, primarily ethane, ethane / propane mixtures, and propane gas crackers.

[0027] It is well known that since the primary reaction towards olefins is favored at lower hydrocarbon partial pressures, it is necessary to mix dilution steam with the feed in the convection section of the cracking furnace to reduce the coking rate in the radiant coils and increase the olefin yield. The total TLE load of the gas cracking furnace is higher than the load required to preheat the dry hydrocarbon (HC) feed and the mixed feed (HC+DS). To achieve efficient TLE heat recovery, it is important to recover the extra heat from the TLE in the electric furnace design. The use of a transfer line exchanger (TLE) as a boiler from the furnace to generate dilution steam in the dilution steam generation drum by quenching the cracked gas effluent is a new idea.

[0028] Furthermore, if a dilution steam generating drum is connected to a TLE to generate dilution steam, such application can be done in one drum by connecting its TLE through risers and downcomers from each electric furnace, or can be shared by multiple electric furnaces by connecting to various TLEs (dilution steam-effluent exchangers) through multiple risers and downcomers to increase cost-effectiveness. The downcomer is the connecting piping from the steam drum to the TLE, and the fluid in the downcomer is in saturated liquid phase (saturated water) to provide liquid head (driving force for natural circulation). And the riser is the connecting piping from the TLE back to the steam drum to form a closed loop of the steam / TLE system, and the fluid in the riser is two-phase flow (water / steam) after heat exchange in the TLE to generate steam. To form natural circulation between the steam drum and the TLE, the liquid head in the downcomer needs to overcome the pressure drop of the entire system (TLE and piping pressure loss).

[0029] For example, for a conventional ethane, ethane / propane mixture, or propane cracking furnace, two types of TLEs are typically used. Primary and / or secondary TLEs are used to generate saturated high pressure steam, which can then be passed to the steam turbine of the cracked gas compressor to generate electricity for compression in the convection section. Tertiary TLEs are used to preheat the boiler feed water before it goes to the convection section to further preheat it before it goes to the high pressure steam drum to provide heat for steam generation. The conventional concept is to generate dilution steam by heat exchange with medium pressure steam (MP) in multiple exchangers using a common dilution steam generator drum from the rest of the plant, and then slightly superheat the MP steam (e.g., at 15° F. (8° C.)) before it goes to the furnace. In addition, MP steam is often used to preheat the quench water stripper condensate before it goes to the dilution steam generator drum to provide available heat for the dilution steam generator drum.

[0030] However, in the case of an electric furnace, there is no convection section and the saturated high pressure steam cannot proceed to the convection section due to superheating. There is no utilization of the saturated high pressure steam. When the tertiary TLE is applied, the preheated BFW (BFW = boiler feed water) from the tertiary TLE also cannot proceed to the convection section. Therefore, it is essential to minimize or have no HP steam generation from the cracking furnace since there is no accommodation for the HP steam. All three main cracking gas cooling compressors, ethylene cooling compressor, and propylene cooling compressor can be made with electric turbines rather than steam turbines. These are the typical three main compressors in an ethylene plant (i.e., cracking gas cooling compressor, ethylene cooling compressor, and propylene cooling compressor).

[0031] If the heat to the radiant coils is supplied by electricity rather than fossil fuels, there should be little or no steam generated from the furnace. Normally in a conventional furnace, HP steam is generated from the cracking furnace, but if the cracking furnace is electric, there is no HP steam generated from the TLE, and therefore the cracked gas compressor usually needs to be electrically driven rather than steam turbine driven (unless there is steam from another source other than the ethylene cracking furnace). The other two compressors (ethylene and / or propylene cooling compressors) can also be electrically driven if there is no or not enough steam available generated in the plant. If HP or MP steam generation is used instead of DS steam generation in the secondary TLE (S-TLE) to achieve the required heat recovery, the saturated steam must be superheated to be useful, thus requiring an additional steam superheater. In addition, if HP steam is used to generate lower steam levels, a new steam turbine may be required. If zero emissions are required, the steam superheater must have an electric heater or be fired with 100% H2 to minimize CO2 emissions in the furnace stack. In addition, a dilution steam generation system from the rest of the plant is still required, which makes the electric furnace and its steam supply system expensive. In any case, dilution steam is still always required for cracking to reduce the coking rate and increase the olefin yields, such as ethylene and propylene yields.

[0032] Thus, the solution of the disclosed embodiments allows optimal heat recovery of the TLE in electric furnace applications while maintaining the overall heat recovery at the same TLE as a conventional cracking furnace in order to avoid overloading the downstream quench tower system.

[0033] By applying S-TLE to generate dilution steam, the cracked gas outlet temperature after the tertiary TLE can be made the same as the tertiary TLE outlet temperature from a conventional cracking furnace design (e.g., about 149-177°C for ethane cracking). Thus, the overall required heat recovery is achieved in the TLE, which reduces the load on the downstream quench tower, and therefore less cooling quench water circulation flow is required.

[0034] For gas cracking electric furnaces (ethane, ethane / propane mixtures, propane), the dry feed can be heated in a tertiary TLE, the mixed feed can be further heated in the primary TLE by quenching the hot cracked gas, and dilution steam can be generated by a secondary TLE along with a dilution steam generator drum, also by quenching the hot cracked gas. The saturated dilution steam from the dilution steam generator drum can be slightly superheated (e.g., 15°F (8.3°C)) using a small MP steam exchanger or small electric heaters, or by injecting some available steam for superheating before proceeding to the furnace.

[0035] The advantages of the present invention are summarized below. i. Fully utilize the total available heat load from the Transfer Line Exchangers (TLEs) to achieve optimal heat recovery for the EAF design and generate dilution steam by one of the TLEs (usually the secondary TLE, this TLE is called "Dilution Steam-Effluent Exchanger") along with the dilution steam generating drum to feed back directly to the furnace as a self-contained closed loop system for the EAF design. ii.This application can be extended to multiple furnace applications with one common dilution steam generating drum.Multiple TLEs can be connected to this drum via multiple risers / downcomers to generate dilution steam for feedback to multiple furnaces, further reducing the overall equipment count if needed. iii.By applying this innovation, high pressure or medium to high pressure steam generation is not required since high pressure or medium to high pressure steam is not useful for EAF applications either. It is essential in EAF design to minimize or eliminate HP steam generation from the TLE of the furnace. iv. The furnace can efficiently generate dilution steam by itself, so there is no need for a traditional dilution steam generation system from the rest of the plant (or called the recovery section of an ethylene plant). The inventors use the available load from the dilution steam-effluent exchanger to generate dilution steam, thus saving energy to generate dilution steam using MP steam in multiple dilution steam generators. Therefore, these multiple dilution steam generators are not needed. There is also a significant savings in MP steam consumption. v. The working pressure of dilution steam is generally 85 to 115 psig (6 to 8 kg / cm 2 g), which is much lower than the HP steam pressure (e.g., nominal 1500 psig system (steam pressure can range from 400 psig to 2000 psig)), this provides excellent heat transfer for cooling the cracked gas for this TLE design. In addition, it has good cost benefits due to the much lower design pressure and smaller heat exchanger. Furthermore, the height of the dilution steam generator drum is lower due to the lower operating pressure, which saves piping for riser and downcomer and also saves structural steel material compared to the conventional high pressure steam system TLE.

Claims

1. 1. An electrolysis furnace system for converting a hydrocarbon feedstock into a cracked gas, comprising at least: a mixing device for mixing the hydrocarbon feedstock with slightly superheated or saturated steam; Steam drum, An electric furnace, a primary transfer line exchanger (PTLE); a secondary transfer line exchanger (STLE); a tertiary transfer line exchanger (TTLE); Equipped with the electric furnace includes a feed inlet for a hydrocarbon feedstock-saturated steam mixture and an outlet for cracked gas; the steam drum including a saturated steam outlet connected to the mixing device, and a water outlet and a steam inlet both connected to the secondary transfer line exchanger (STLE); the primary transfer line exchanger (PTLE) is configured to preheat the hydrocarbon feedstock-saturated steam mixture prior to entering the electric furnace and to cool the cracked gas provided by the electric furnace; the secondary transfer line exchanger (STLE) configured to generate steam and to cool the cracked gas provided by the primary transfer line (PTLE); The tertiary transfer line exchanger (TTLE) is configured to preheat the hydrocarbon feedstock prior to mixing with saturated steam and to cool the cracked gas provided by the secondary transfer line exchanger (STLE). Electrolysis furnace system.

2. 2. The electrolysis furnace system of claim 1, comprising at least a compressor of the cracked gas accompanied by an electric turbine.

3. The secondary transfer line exchanger (STLE) has a flow capacity of 4 to 15 kg / cm ２ 10. The electrolysis furnace system of claim 1 configured to generate steam at a pressure of 100 g.

4. 2. The electrolysis furnace system of claim 1, further comprising a heat exchanger upstream of the mixing device for preheating the saturated steam provided by the steam drum.

5. 2. The electrolysis furnace system of claim 1, further comprising a second mixing device upstream of the mixing device for mixing the saturated steam provided by the steam drum with preheated steam.

6. 2. The electrolysis furnace system of claim 1, comprising: N electric furnaces; N to 10N primary transfer line exchangers PTLE; N to 2N secondary transfer line exchangers STLE; N to 2N tertiary transfer line exchangers TTLE, N>2; and N or less than N steam drums, N>2.

7. 1. A method for cracking a hydrocarbon feedstock in an electrocracker system, comprising: a) preheating a hydrocarbon feedstock in a tertiary transfer line exchanger (TTLE); b) mixing the preheated hydrocarbon feedstock with at least one of saturated steam or slightly superheated steam to generate at least one of a hydrocarbon feedstock-saturated steam mixture or a hydrocarbon feedstock-slightly superheated steam mixture; c) preheating at least one of the hydrocarbon feedstock-saturated steam mixture or the hydrocarbon feedstock-slightly superheated steam mixture in a primary transfer line exchanger (PTLE); d) cracking the preheated hydrocarbon feedstock-saturated steam mixture or the hydrocarbon feedstock-slightly superheated steam mixture in the electric furnace to produce cracked gas; e) providing a first cooling of the cracked gas in the primary transfer line exchanger (PTLE); f) providing a second cooling of the cracked gas exiting the primary transfer line exchanger (PTLE) in a secondary transfer line exchanger (STLE); g) producing steam in said secondary transfer line exchanger (STLE); h) providing a third cooling of the cracked gas exiting the secondary transfer line exchanger (STLE) in the tertiary transfer line exchanger (TTLE); The method includes:

8. 8. The method for cracking a hydrocarbon feedstock according to claim 7, wherein the hydrocarbon feedstock is a dry gas.

9. 8. The method for cracking a hydrocarbon feedstock according to claim 7, further comprising producing saturated or slightly superheated steam in a steam drum.

10. 8. The method for cracking a hydrocarbon feedstock according to claim 7, wherein the steam produced in the secondary transfer line exchanger (STLE) is generated from water coming from a steam drum.

11. 8. The method for cracking a hydrocarbon feedstock according to claim 7, wherein the steam produced in the secondary transfer line exchanger (STLE) is sent into a steam drum.

12. 8. The method for cracking a hydrocarbon feedstock according to claim 7, wherein preheating at least one of the hydrocarbon feedstock-saturated steam mixture or the hydrocarbon feedstock-slightly superheated steam mixture comprises preheating at a temperature between 180° C. and 300° C.

13. 8. The method for cracking a hydrocarbon feedstock according to claim 7, wherein preheating at least one of the hydrocarbon feedstock-saturated steam mixture or the hydrocarbon feedstock-slightly superheated steam mixture comprises preheating at a temperature between 200° C. and 260° C.

14. The steam generated in the secondary transfer line exchanger (STLE) has a flow rate of 4 kg / cm ２ ~15kg / cm ２ 8. The method of claim 7, wherein the pressure is 100 g.

15. The steam generated in the secondary transfer line exchanger (STLE) has a flow rate of 6 kg / cm ２ g ~ 8 kg / cm ２ 8. The method of claim 7, wherein the pressure is 100 g.

16. 8. The method of claim 7, wherein cooling the cracked gas in the primary transfer line exchanger (PTLE) comprises cooling the cracked gas at a temperature between 750°C and 900°C.

17. 8. The method of claim 7, wherein cooling the cracked gas in the primary transfer line exchanger (PTLE) comprises cooling the cracked gas at a temperature between 820°C and 875°C.

18. 8. The method of claim 7, wherein cooling the cracked gas in the secondary transfer line exchanger (STLE) comprises cooling the cracked gas at a temperature between 375°C and 600°C.

19. 8. The method of claim 7, wherein cooling the cracked gas in the secondary transfer line exchanger (STLE) comprises cooling the cracked gas at a temperature between 420°C and 520°C.

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