Ethylene plant with electrically powered pyrolysis reactor and feed-effluent heat exchanger

Abstract

The present disclosure relates to an ethylene plant comprising an electrically powered pyrolysis reactor and a process for producing a pyrolysis reactor effluent using the ethylene plant. The pyrolysis reactor comprises a feed inlet for a hydrocarbon feedstock-diluent mixture and an outlet for a pyrolysis reactor effluent comprising ethylene. The plant further comprises a heat exchanger (90) configured to transfer heat from the pyrolysis reactor effluent to a feed for the pyrolysis reactor. The heat exchanger (90) comprises a feed inlet and a feed outlet upstream of the pyrolysis reactor and further comprises a pyrolysis reactor effluent inlet and a pyrolysis reactor effluent outlet. A feed passage exists between the feed outlet of the heat exchanger and the feed inlet of the pyrolysis reactor, and a further feed passage exists between the reactor effluent outlet of the pyrolysis reactor and the cracked gas inlet of the heat exchanger.

Description

[Technical Field]

[0001] The present invention relates to an ethylene plant comprising an electrically powered pyrolysis reactor. The present invention further relates to a process for producing ethylene from a hydrocarbon feed using an ethylene plant according to the invention. [Background technology]

[0002] In conventional ethylene plants with fired cracking furnaces, sufficient high pressure (HP) steam is produced to generate power to drive machinery and also to generate dilution steam to suppress hydrocarbon partial pressures, improve product selectivity, and maintain coke formation in the bays within the cracking reactor.

[0003] In the high-temperature section of the plant, dilution steam is traditionally 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 from the furnace effluent (cracked products) in the primary fractionator's pump-around circuit, the quench oil circuit, can aid in the generation of dilution steam, allowing 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 can be used, for example, to preheat the furnace feedstock. Further feedstock vaporization is typically achieved by flue gas in the convection section of the conventional cracking furnace.

[0004] FIG. 1 shows an example of a scheme for (the high-temperature section of) a conventional combustion ethylene plant for gaseous hydrocarbon feedstocks. Fresh gaseous feedstock 1, such as ethane, propane, or a mixture thereof, is first preheated in preheater 30 with a low-temperature heat source, such as quench water, external to cracking furnace 1000 to heat it from ambient conditions to a temperature of approximately 50°C suitable for entering cracking furnace 1000. Further preheating of the feedstock is achieved by hydrocarbon feed preheater 31 using flue gas in the convection section of the furnace. To suppress the hydrocarbon partial pressure in the thermal cracking reactor, which is beneficial for product yield and suppression of coke formation, mildly superheated dilution steam 24 is added. When mixed, the feedstock and dilution steam are preheated to above the water dew point, which is approximately 120-130°C. Further superheating of the steam-diluted hydrocarbon feedstock 3 is achieved in a feed superheater in the convection section of furnace 33 using flue gas. Once properly superheated, the steam-diluted feedstock enters the pyrolysis reactor 34 at approximately 650°C to 730°C. This reactor is traditionally heated by burning fuel gas in a firebox. The reactor operates at relatively low pressures and high temperatures, which are favorable for olefin yield. Typical operating conditions at the reactor outlet are 800°C to 870°C and a pressure of 1.6 to 2.2 bara, resulting in products such as ethylene, propylene, butadiene, benzene, toluene, and xylenes. Typical by-products are hydrogen, methane, gasoline, and fuel oil. A portion of the products, such as ethane and propane, are recycled to the reactor. The reactor effluent 4 contains all of these products and by-products. This reactor effluent 4 is cooled to approximately 160°C to 220°C in the cracking furnace section 1000. Heat from the effluent above 350°C is conventionally recovered using a first transfer line exchanger 35 by generating saturated high pressure steam at about 100-125 bar. Lower level heat can be recovered in a second transfer line exchanger 36 to preheat boiler feedwater or superheat steam diluted feedstock.

[0005] From the furnace section, the effluent 4 is sent to the high-temperature separation section of the plant, consisting primarily of a water quench tower 60, a sour water stripper 70, and a dilution steam drum 80. In the water quench tower 60, the effluent 4 is further cooled to near ambient conditions. Cooling is achieved using a pump-around circuit, which collects accumulated water bottoms product, known as quench water 14, and injects it at various levels within the quench tower 60. The quench water circuit typically has two stages: a quench water bottoms cooling circuit 64 serves the quench water tower bottoms section 61, and a quench water tops cooling circuit 66 serves the quench water tower tops section 62. The overhead product, the cooled vapor phase of the reactor effluent, called cracked gas 9, is sent downstream to the cracked gas compression section for further separation in a low-temperature separation unit. The quench water bottoms circuit cooler 65 is typically a process user to recover as much quench water load as possible. Such a user could be, for example, the feed preheater 30. Excess heat must be removed by air or cooling water. A quench water overhead circuit cooler 67 typically uses cooling water to remove excess heat. Cooled injection water from the pumparound circuit is used in a quench tower to remove heat from the cracked gas by direct heat exchange within the appropriate tower. The main function of this tower, apart from cooling the cracked gas, is the condensation and recovery of dilution steam. The condensed dilution steam, along with a small stream of heavy pyrolysis gasoline product 8, are the net products from the bottom of the tower. These are usually separated from each other using a gasoline / water separator 63. Sometimes, this separator also collects quench water 14 for the quench water circuit. This condensed dilution steam, called sour water 20, contains sour gas, which is stripped by strip steam 21 in a sour water stripper 70. These sour gases 22 are returned to the quench water tower 60. The stripped water, called process water 23, is suitable for dilution steam generation. This occurs at a higher pressure of approximately 6-7 bar so that it can be pumped back to the cracking furnace. Dilution steam generation is achieved using medium-pressure steam as a heat source. Process water is collected in dilution steam drum 80, and via a thermosiphon circuit, dilution steam 24 is generated from the condensed medium-pressure steam in dilution steam generator 81.Superheat in the medium pressure steam is used to gently superheat the dilution steam in dilution steam superheater 83 to a temperature of 180°C to 210°C before returning it to cracking furnace 1000 for diluting the hydrocarbon feedstock 1. Blowdown 26 from and dilution steam system arrangement 25 to dilution steam drum 80 prevents the buildup of fouling contaminants in the dilution steam generation circuit.

[0006] The integrated power generation scheme of a conventional ethylene plant is shown in Figure 2. MP steam required for dilution steam generation is generated from boiler feedwater in a high-pressure steam system. The boiler feedwater is made from demineralized water 101 in a deaerator 120 and steam-stripped with stripping steam 102 to remove CO2 and oxygen via a deaerator vent 103. The generated boiler feedwater 104 is preheated by either cracked gas or flue gas, or both, in a boiler feedwater preheater 121 in a cracking furnace 1000 and collected in a high-pressure steam drum 122. A steam drum connected by natural circulation to a thermosiphon-type heat exchanger called transfer line exchanger 35 recovers heat from the reactor effluent 4 to generate saturated high-pressure steam 105, which is superheated by flue gas in the convection section of the furnace 1000 using a high-pressure steam superheater 123. The superheated high-pressure steam is used to generate power to drive the main machinery in the separation section of the ethylene plant, such as the cracked gas compressor and refrigeration compressors in the cracked gas compressor region and cryogenic separation section (not shown for clarity) of the plant, respectively. To this end, the superheated high-pressure steam 107 is reduced from high pressure to intermediate pressure using a back-pressure steam turbine to generate power 124 and from intermediate pressure to vacuum using a condensing turbine to generate power 125. While most of the steam 110 is condensed in a surface condenser 126 of the condensing turbine 125 to maximize power output, some steam 108 is only reduced to the intermediate-pressure level. This intermediate-pressure steam 108 is used for dilution steam generation and accounts for a significant portion of the total high-pressure steam flow 107 made available. The intermediate-pressure steam 108 is desuperheated in a dilution steam superheater 83 to superheat the dilution steam and condensed in a dilution steam generator 81 to generate dilution steam 24. The produced intermediate pressure condensate 109 as well as vacuum condensate 111 are combined and the combined condensate 112 is returned to the deaerator for recycling as boiler feedwater. A small blowdown 106 from the high pressure steam drum prevents the buildup of fouling contaminants in the high pressure steam circuit.

[0007] The high-temperature section of a plant flow scheme for a process utilizing a liquid hydrocarbon feedstock is shown in Figure 3. In a typical liquid feedstock furnace, fresh liquid feedstock 2 is first preheated in preheater 30 using a low-temperature heat source, such as quench water external to the ethylene plant 1000, to heat it from ambient conditions to a temperature of approximately 50°C suitable for entering the cracking furnace 1000. Further preheating and partial vaporization of the feedstock is achieved by flue gas in the convection section of the furnace, by hydrocarbon feedstock preheater 31, and by hydrocarbon feedstock vaporizer 32, respectively. To suppress the hydrocarbon partial pressure in the pyrolysis reactor (which is beneficial for product yield and suppression of coke formation), dilution steam 24 coming from the high-temperature separation section is further superheated using flue gas in the convection section. This is done in dilution steam superheater 84 to ensure complete vaporization of the partially vaporized feedstock once mixed. To vaporize the feedstock, the dilution steam is heated until the mixture reaches a temperature well above the water dew point, which is approximately 130-140°C. Further superheating of the steam-diluted hydrocarbon feedstock 3 is achieved in a feedstock superheater in the furnace convection section 33 using flue gas. Once properly superheated, the steam-diluted feedstock enters the pyrolysis reactor at approximately 600°C to 640°C. This reactor is traditionally heated by burning fuel gas in a firebox. The reactor operates at relatively low pressures and high temperatures, which are favorable for olefin yield. Typical operating conditions at the reactor outlet are 800°C to 870°C and pressures of 1.6 to 2.2 bara, yielding products such as ethylene, propylene, butadiene, benzene, toluene, and xylenes. Typical by-products are hydrogen, methane, gasoline, and fuel oil. A portion of the products, such as ethane and propane, is recycled to the reactor. The reactor effluent contains all of these products and by-products.

[0008] This reactor effluent 4 is cooled to approximately 350°C in the cracking furnace section 1000. Heat from the effluent above 350°C is conventionally recovered using a first transfer line exchanger 35 by generating saturated high-pressure steam at approximately 100-125 bar. Lower levels of heat, between 350°C and 160°C, cannot be recovered using indirect heat exchange due to the fouling nature of the effluent, but are recovered at the so-called quench oil fitting 37 using quench oil injection 27 and intermediate oil injection 28, if an intermediate oil loop is available. From the furnace section, the effluent 4 is sent to the high-temperature separation section of the plant, consisting primarily of a primary fractionator 50, a water quench tower 60, a sour water stripper 70, and a dilution steam drum 80.

[0009] In the primary fractionator 50, the effluent is further cooled to approximately 100°C, maintaining the temperature above the water dew point to ensure that water does not condense in this column. The effluent is then cooled using the quench oil and intermediate oil pumparounds and gasoline reflux, respectively. The quench oil cooling circuit 54 originates from the heavy fuel oil product 6 collected at the bottom of the column. This quench oil 10 is cooled by the quench oil circuit cooler 55. A portion of it is sent to the quench oil fitting 27, and the remainder is reinjected into the column below the intermediate oil total draw-off tray. The quench oil circuit cooler 55 is typically used to generate dilution steam in the dilution steam generator 82. If the bottom temperature of the primary fractionator is not sufficient to generate dilution steam, low-pressure steam can be generated instead. The quench oil cooling circuit 54 recovers all heat from the effluent, typically above 170°C to -180°C if the intermediate oil cooling circuit 56 is present, and recovers heat from the effluent up to 125°C to 130°C if not. The quench oil cooling circuit serves the primary fractionator wash section 51, which is the bottom section of the column.

[0010] The intermediate oil cooling circuit 56 is optional and is intended to provide a relatively clean / non-fouling intermediate cooling circuit that recovers lower levels of heat from the effluent than the quench oil circuit 54, typically 125°C to 130°C. The intermediate oil 11 is collected on a draw-off tray at the bottom of the primary fractionator intermediate oil section 52, located above the wash section 51 in the column. The intermediate oil reflux 12 is sent to the quench oil wash section 51 at the bottom of the column so that the quench oil load can be shifted to the intermediate oil loop. Additionally, the intermediate oil stream 28 is sent to the quench oil fitting 37. The remainder is cooled by the intermediate oil circuit cooler 57 and returned to the column below the light fuel oil draw point. The intermediate oil cooling circuit 56 serves the primary fractionator intermediate oil section 52.

[0011] The gasoline reflux 13 coming from the gasoline / water separator 63 is treated for heat recovery at the top of the column, primary fractionator gasoline reflux section 53, and the recovered load is shifted to the quench water circuit.

[0012] Suitable internals are installed within the column to efficiently transfer heat from the effluent to the injected quench oil, middle oil, and gasoline reflux. In addition to cooling the effluent, the light and heavy oil fractions are condensed in the primary fractionator. Heavy fuel oil 6 is collected at the bottom 51, and light fuel oil 7 is collected on a light oil draw-off tray at the bottom of reflux section 53. These can be stripped to recover the lighter quench oil fractions for flash point control of the total fuel oil product 5 and / or viscosity control of the quench oil circuit.

[0013] In the water quench tower 60, the effluent 4 is further cooled to near ambient conditions. The overhead product, the cooled vapor phase of the reactor effluent, called cracked gas 9, is sent to downstream units for further separation. Cooling is achieved using a pump-around circuit that collects the accumulated water bottoms product, known as quench water 14, and injects it at various levels within the quench tower 60. The quench water circuit typically has two stages: a quench water bottoms cooling circuit 64 serves the quench water tower bottom section 61, and a quench water top cooling circuit 66 serves the quench water tower top section 62. The quench water bottoms circuit cooler 65 is typically a process user to recover as much quench water load as possible. Such users are, for example, the feed preheater 30 and / or the propylene splitter reboiler (not shown). Excess heat must be removed by air or cooling water cooling. The quench water top circuit cooler 67 typically uses cooling water to remove excess heat. The cooled injection water from the pump-around circuit is used in the quench tower to remove heat from the cracked gas by direct heat exchange within the appropriate tower. The primary function of this tower, apart from cooling the cracked gas, is the condensation and recovery of dilution steam. The condensed dilution steam, along with a small amount of heavy pyrolysis gasoline product 8, is the net product from the bottom of the tower. These are typically separated from each other using a gasoline / water separator 63. Sometimes, this separator also collects quench water for the quench water circuit. This condensed dilution steam, called sour water 20, contains sour gas, which is stripped by stripping steam 21 in the sour water stripper 70. These sour gases 22 are returned to the quench tower 60. The stripped water, called process water 23, is suitable for dilution steam generation. This occurs at a higher pressure of approximately 6-7 bar so that it can be returned to the cracking furnace. Dilution steam generation is achieved using medium-pressure steam. The process water is collected in dilution steam drum 80 and via a thermosiphon circuit, dilution steam 24 is generated from condensing medium pressure steam in dilution steam generator 81 and from the quench oil cooling circuit using dilution steam generator 82.Superheat in the intermediate pressure steam is used to gently superheat the dilution steam in dilution steam superheater 83 to a temperature of 180°C to 210°C before returning it to cracking furnace 1000 for dilution of the hydrocarbon feedstock 2. Blowdown 26 from and configuration 25 to dilution steam drum 80 prevents the buildup of fouling contaminants in the dilution steam generation circuit. The MP steam required for dilution steam generation is generated in the high pressure steam system from boiler feedwater in the same manner as the conventional gaseous ethylene plant flow scheme shown in Figure 2 and described above.

[0014] In view of the need to reduce greenhouse gas emissions, such as carbon dioxide and methane emissions, there is considerable interest in improving ethylene plants and the processes for operating ethylene plants that allow for a reduction in energy requirements, or at least a reduction in the fossil fuel requirements for generating the heat necessary to operate the plants.

[0015] A possible approach would be to replace fossil fuels with hydrogen, which could be produced by electrolysis. The required electricity could be generated using renewable energy sources or in power plants where carbon dioxide is effectively captured to prevent its release into the air.

[0016] The inventors have found that it is also interesting to directly use electricity to provide part of the sensible heat (heat for raising the temperature of the hydrocarbon-vapor mixture) and reaction heat for the cracking reaction. However, when applying an electrically powered pyrolysis reactor, there is no flue gas as a high-temperature utility, so preheating and vaporization of the liquid feedstock cannot be performed using conventional methods. In the absence of MP steam, dilution steam cannot be generated using conventional methods.

[0017] The concept of using an electrically heated thermal cracking reactor to produce olefins from hydrocarbons is known in the art. EP 3249028 A1 relates to a method for producing olefins by steam cracking, in which multiple cracking tubes are used. At least one of the cracking tubes is heated by fuel combustion (i.e., a combustion cracking tube), and at least one other cracking tube is electrically heated. The reactor effluent (cracked product) is rapidly cooled (quenched) to avoid undesirable side reactions. Further downstream processing, such as fractionation of the cracked product, is described. Little information is disclosed about preheating the feedstock and generating dilution steam. Since this process requires fuel combustion, hot flue gases are available for heating. Direct supply of steam to the cracking tubes is described, as is generating steam inside the cracking tubes.

[0018] EP 3730592 (A1) relates to an olefin synthesis plant with a thermal cracking section, which includes one or more of the following: a feed pretreatment section, one or more thermal cracking reactors for cracking hydrocarbons in the presence of a diluent, a primary fractionation and compression section, and / or a product separation section, wherein a greater proportion of the energy and / or net energy required by the plant in that section is provided by a non-carbon-based energy source compared to conventional plants. EP 3730592 (A1) generally proposes various options for using electricity to heat the feed and generate dilution steam upon use. For example, the plant may be configured for a steam cracking process, e.g., where some or all of the cracking reactors are electrically heated and heat is generated electrically for the evaporation of recycled water to create diluent steam. Furthermore, the feed to the cracking reactor can be electrically preheated. Heating can be achieved using much of the heat recovered from cooling the hot product gas, or indirect heating can be achieved using a heat transfer agent (e.g., Dowtherm or steam). While several written examples are provided for specific embodiments, diagrams showing the relative positions of units and steam between units are lacking, e.g., to clarify how heat recovery of process streams occurs. The examples rely on generating dilution steam directly from the effluent. This design appears to be limited to processing ethane feedstocks due to the lower fouling characteristics of the effluent compared to processes run on heavier feedstocks.

[0019] It is an object of the present invention to provide a new ethylene plant including an electro-thermal pyrolysis reactor, each a new process for producing ethylene by steam cracking, that is robust in feedstock tolerance while being effective in reducing carbon dioxide emissions without the need to use combustion of a fuel (such as methane or hydrogen) to provide a portion of the heating of the hydrocarbon feed to the electro-thermal pyrolysis reactor. In particular, it is an object of the present invention to integrate the electro-thermal pyrolysis reactor into the ethylene plant in a manner that is achieved without utilizing high-pressure steam as a source for dilution steam and without utilizing high-pressure steam as a heating medium for the hydrocarbon feed.

[0020] It has been discovered that it is possible to efficiently integrate an electric pyrolysis unit with a feed-effluent heat exchanger to recover sufficient heat from the pyrolysis reactor effluent (cracked product). Specifically, this is achieved by using a downstream high-temperature separation section of the plant to superheat the feed (hydrocarbon feedstock dilution vapor mixture) for the pyrolysis reactor so that excess power is minimized. Excess power is understood as the power required for the electric pyrolysis reactor in addition to the power required to preheat, vaporize, and optionally superheat the feedstock, and to generate dilution vapor or humidify the feedstock. The additional power required to drive machinery in the back end of the plant, such as the cracked gas compressor and refrigeration compressor, can be handled as taught in EP 3748138 A1. Summary of the Invention

[0021] Thus, the present invention relates to an ethylene plant comprising an electrically powered pyrolysis reactor, the electrically powered pyrolysis reactor comprising a feed inlet for a hydrocarbon feedstock-diluent mixture and an outlet for a pyrolysis reactor effluent comprising ethylene, the ethylene plant further comprising a heat exchanger configured to transfer heat from the pyrolysis reactor effluent to a feed for the pyrolysis reactor, the heat exchanger comprising a feed inlet and a feed outlet upstream of the pyrolysis reactor, and a pyrolysis reactor effluent inlet and a pyrolysis reactor effluent outlet. In a preferred embodiment, a feed passage exists between the feed outlet of the heat exchanger and the feed inlet of the pyrolysis reactor, and a further feed passage exists between the reactor effluent outlet of the pyrolysis reactor and a cracked gas inlet of the heat exchanger. In this way, the generation of high-pressure steam due to heat transfer from the reactor effluent can be minimized or even eliminated, and the plant can be operated without generating high-pressure steam from heat transferred from the reactor effluent.

[0022] Advantageously, the temperature of the pyrolysis reactor effluent exiting the heat exchanger can be well below the range for ultra-high pressure steam generation, typically well below 500°C, preferably below 450°C.

[0023] In another or further preferred embodiment, as described in more detail below, heat may be used to preheat the feed prior to the heat exchanger using heat from a downstream processing unit where the reactor effluent is further cooled.

[0024] The present invention further relates to a process for producing a pyrolysis reactor effluent comprising ethylene from a hydrocarbon feed using an ethylene plant according to the present invention, comprising: feeding a hydrocarbon feed-steam mixture to an electro-thermal pyrolysis reactor, cracking the hydrocarbon feed in the presence of steam in the electro-thermal pyrolysis reactor of the ethylene plant to produce a pyrolysis reactor effluent comprising ethylene, feeding the pyrolysis reactor effluent to a heat exchanger configured to transfer heat from the pyrolysis reactor effluent to the hydrocarbon feed-steam mixture prior to cracking of the hydrocarbon feed, and transferring heat from the pyrolysis reactor effluent to the hydrocarbon feed-steam mixture in the heat exchanger, thereby cooling the pyrolysis reactor effluent to a temperature at the heat exchanger pyrolysis reactor effluent outlet, preferably below 500°C, more preferably below 450°C, for example in the range of 300°C to 450°C, even more preferably in the range of 325°C to 425°C. [Brief explanation of the drawings]

[0025] These and other features, aspects, and advantages of the devices, systems, and methods of the present disclosure will become better understood from the following description, appended claims, and accompanying drawings. [Figure 1] An example of a scheme for (the high temperature part of) a conventional combustion ethylene plant for gaseous hydrocarbon feedstock is shown. [Figure 2] 1 shows an integrated power generation scheme of a conventional ethylene plant. [Figure 3] 1 shows a schematic representation of the high temperature section of an ethylene plant according to the invention; [Figure 4] 1 illustrates a schematic representation of an embodiment of an electrically powered pyrolysis reactor in combination with a feed-effluent heat exchanger. [Figure 5] 1 shows a schematic representation of an ethylene plant / process according to the present invention. [Figure 6] 1 shows a schematic representation of an ethylene plant / process according to the present invention. [Figure 7] 1 shows a schematic representation of an ethylene plant / process according to the present invention. [Figure 8]1 shows a schematic representation of an ethylene plant / process according to the present invention. [Figure 9] 1 shows a schematic representation of an embodiment of a heat bump in an ethylene plant / process according to the present invention. [Figure 10] 1 shows a schematic representation of an ethylene plant / process according to the present invention. [Figure 11] 1 shows a schematic representation of an ethylene plant / process according to the present invention. [Figure 12] 1 shows a schematic representation of a cooling embodiment for an ethylene plant / process according to the present invention. [Figure 13] 1 shows a schematic representation of a cooling embodiment for an ethylene plant / process according to the present invention. [Figure 14] 1 shows dew point as a function of absolute operating pressure in an exemplary saturator of an ethylene plant / process according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention provides several alternative solutions, particularly for operating ethylene plants lacking a high-pressure steam generation system and a furnace where flue gas is formed. Thus, the plant or process according to the present invention is particularly suitable for operation during periods when neither preheating and vaporization of the feedstock by heating with flue gas nor superheating of dilution steam is available. This is achieved, particularly by utilizing other heat integration means within the ethylene plant. This can limit the need for extra power in addition to the power used for the pyrolysis reaction. For example, in at least some embodiments, the plant can operate during normal (steady-state) operation without using power to generate dilution steam, without electrical preheating of the feedstock, etc. This allows power use to remain relatively limited without compromising greenhouse gas emissions. This is particularly advantageous when it is desirable to rely on renewable power resources, the supply of which can be highly variable, for example, depending on weather conditions.

[0027] Those skilled in the art can use this disclosure, in combination with common general knowledge and, optionally, one or more of the references cited herein, to design and operate suitable operating units for an ethylene plant. In addition to the operational units, passages, etc. described herein, a plant according to the present invention may include one or more additional units. Such units may be based on units generally known in the art or described in the references cited herein for such purposes. For the sake of brevity, such units, which may be conventional, will not be discussed in detail. In particular, upstream of the feedstock supplies 1 and 2, one or more units may be present to pretreat the feedstock, e.g., one or more units configured to remove impurities. In particular, downstream of the high-temperature section (downstream of line 9 in the diagram), one or more units may be present to purify the cracked product gas or to recover useful products therefrom, e.g., hydrogen or methane therefrom.

[0028] In accordance with the present invention, the electrically powered pyrolysis reactor 91 is combined with a feed-effluent heat exchanger 90 configured to transfer heat from the pyrolysis reactor effluent 4 to the pyrolysis reactor feed 3, i.e., a mixture of hydrocarbon feedstock and diluent (typically diluent steam), before the feed enters the pyrolysis reactor. This is shown schematically in Figure 4.

[0029] Such heat exchangers are generally known in the art. They can have, for example, a shell-and-tube design. Typically, feed-effluent heat exchangers are operated in a counterflow configuration. Therefore, there is usually a temperature crossover, i.e., the outlet temperature of the cold side exceeds the outlet temperature of the hot side. In principle, crossflow is also possible. The feed-effluent exchanger typically has a passage for the reactor effluent (cracked products) and a separate passage for the feed (hydrocarbon-vapor mixture). Both passages are separated by a heat-conducting partition arranged to transfer heat from one passage to the other. Thus, waste heat from the reactor effluent is used directly to heat the feed, and thereby, none of the reactor effluent load is used for high-pressure steam generation. Therefore, the ethylene plant of the present invention is typically configured to operate without a high-pressure steam generator. The feed-effluent heat exchanger 90 is also distinguished from a quench device, e.g., a quench water tower, in which the reactor effluent is typically brought into direct contact with a quench medium, e.g., quench water. A quench unit configured to further cool the reactor effluent (cracked products) is advantageously provided downstream of the feed-effluent exchanger 90, as will be discussed in more detail below.

[0030] The present invention allows for the cracking of gaseous feedstocks, liquid feedstocks, and mixtures thereof without requiring the combustion of hydrocarbon fuels to generate sensible heat or heat of reaction for the pyrolysis reaction, allows for essentially complete avoidance of direct CO2 emissions (essentially no CO2 is produced in the plant), and is ready for the introduction of renewable power sources. CO2 emissions can be kept to a minimum if the generation of dilution steam and superheating of gaseous feedstocks and / or preheating and evaporation of liquid feedstocks are performed with minimal additional power requirements. This is to facilitate the ethylene industry's net-zero emissions goal in the most efficient manner possible.

[0031] An electric pyrolysis apparatus for producing olefins in an ethylene plant can be based on a known electrically heated pyrolysis reactor. For example, the pyrolysis reactor can be a directly heated reactor, in which the reactor walls (such as the walls of the cracking coil) are heated by resistance heating using electrical conductors. For example, WO 2015 / 197181 (A1) describes an apparatus and method for heating a fluid in a pipeline (see cracking reactor tube) in the context of steam reforming. This principle can be used in the pyrolysis reactor of the present invention. It should be noted that in the cracking of the present invention, the space in which the pyrolysis takes place generally does not contain catalytic material. Furthermore, the operating pressure at which the pyrolysis takes place is significantly lower than the 10-50 bar present in the reforming tube. The cracking coils are indirectly heated by electrical heating of the housing in which the cracking coils (typically multiple cracking coils) reside. Furthermore, rotodynamic devices (RDRs) are particularly well suited to providing sensible and reactive loads for pyrolysis reactions by increasing kinetic energy through static and dynamic rotors, thus transferring the power of a mechanical driver to transfer the load to the reactive mixture (see, for example, U.S. Patent Application Publication No. 2021 / 0171836 A1). Known suppliers of RDRs are Coolbrook (Helsinki, Finland) and Geleen, the Netherlands.

[0032] Yet another example of a suitable pyrolysis reactor is based on U.S. Pat. No. 7,288,690 (B2) (see especially claims 8-13). Instead of a feed-effluent exchanger, a co-generator waste heat boiler is used to preheat the diluted feedstock, and the electricity generated in an alternator is used to power the pyrolysis reactor. Suitable heating methods include direct resistance heating, also known as Joule heating, induction heating, and ultrasound.

[0033] The electricity required for the ethylene plant according to the invention can be taken from a power system that is part of the plant, or the ethylene plant can have a power connection to a power system external to the plant. At least a substantial portion of the power, preferably essentially all of the power, is received from renewable sources. This is to minimize CO2 emissions. Thus, the power connection between the energy-consuming parts of the ethylene section, in particular the pyrolysis reactor (91), and the power system can be a connection to the ethylene plant's internal power grid to supply at least a portion of the required power, or it can be a connection to an external (remote) power plant connected to the same power grid as the ethylene plant according to the invention.

[0034] Power systems that provide electricity from renewable sources typically include one or more power systems selected from the group consisting of wind systems, solar energy systems, hydroelectric systems, geothermal energy systems, and osmotic power systems (also known as blue energy). Alternatively, or in addition, one or more systems configured to generate electricity from biomass and / or one or more systems configured to generate electricity from bio-renewable fuels, such as bioethanol or biodiesel, may be used.

[0035] Although the use of renewable energy is preferred, in principle, the electricity, or a portion thereof, can be recovered from a different source. Such plants still benefit from improved heat integration. For example, the reactor effluent of a steam cracking furnace typically contains some methane and some hydrogen. These can be recovered from the reactor effluent as a methane-rich stream and a hydrogen-rich stream. Either or both of these can be used to generate electricity in a manner known per se. For hydrogen, this does not result in increased CO2 emissions. If methane is combusted with the formation of CO2, it can be captured to prevent its release into the environment. However, in an advantageous embodiment, the methane, hydrogen, or both can be used for higher-value purposes, for example, as a feedstock for another chemical process.

[0036] In the process according to the invention, the weight-to-weight ratio of diluent gas (vapor) to hydrocarbon feedstock (also called dilution steam (weight) ratio) can be selected within wide limits. Typically, this ratio is selected within the range of about 0.25 to about 1.0, preferably within the range of about 0.35 to 0.9, more preferably within the range of about 0.4 to 0.8, depending on the feedstock.

[0037] For example, for gaseous feedstocks, the dilution steam ratio is generally relatively low, typically between 0.3 and 0.4. For lighter liquid feedstocks such as naphtha, higher ratios may be preferred, typically in the range of 0.4 to 0.6. Heavier feedstocks, such as gas oil, are typically operated at higher dilution steam ratios of 0.6 to 1.0. Higher dilution steam ratios are generally possible but economically unattractive. Lower values ​​are less preferred because they can cause yield loss and fouling. The mixture of hydrocarbon feedstock and dilution steam 3 is generally fed to the feed-effluent heat exchanger 90 at a temperature above the water dew point. Quantitatively, the temperature of the mixture of hydrocarbon feedstock and diluent at the inlet of the feed-effluent heat exchanger 90 is generally in the range of 80°C to 230°C, preferably 120°C to 180°C, depending on the feedstock. For example, if the mixture is a steam-diluted gaseous feed coming from a humidifier, the temperature preferably ranges from 80°C to 150°C, more preferably from 90°C to 130°C. If a compressor is applied in addition to the humidifier to compress the steam-diluted gaseous feed to furnace inlet pressure, the operating temperature can generally be increased by 60°C to 120°C, depending on the polytropic efficiency and discharge pressure of the compressor. For steam-diluted liquid feed, the temperature preferably ranges from 120°C to 200°C, more preferably from 130°C to 180°C. Providing a diluted feed inlet at a temperature within a specific range, as opposed to superheating the feed to a higher temperature before entering the feed-effluent exchanger, advantageously reduces power requirements.

[0038] In the heat exchanger, the mixture of hydrocarbon feedstock and diluent is heated by heat from the pyrolysis reactor effluent to a temperature at the inlet of the pyrolysis reactor (91) generally in the range of 550°C to 750°C, preferably in the range of 570°C to 730°C, depending on the feedstock. For example, if the mixture is a steam-diluted gaseous feedstock such as ethane or propane, the coil inlet temperature is preferably in the range of 630°C to 750°C, more preferably in the range of 650°C to 730°C. Liquid feedstocks preferably have coil inlet temperatures in the range of 550°C to 670°C, more preferably in the range of 570°C to 650°C. For ethane, it has been found that preheating to 730°C is possible without fouling the upstream convection section.

[0039] The hydrocarbon feedstock-vapor mixture does not need to be heated to temperatures where pyrolysis can occur. A portion of the sensible heat is typically supplied to the mixture using electrical power within the pyrolysis reactor, which also provides the heat of reaction. In the feed-effluent heat exchanger 90, the mixture is superheated. By maintaining a relatively low temperature of the feed mixture at the inlet to the heat exchanger, most of the excess heat in the reactor effluent can be recovered, thereby reducing the electrical power required to further heat the feed inside the pyrolysis reactor.

[0040] The temperature of the reactor effluent (cracked product) at the cracked product inlet of the heat exchanger 90 depends on the residence time inside the reactor. For RDR, this is relatively low, resulting in a relatively high coil outlet temperature compared to conventional radiant coils. The feedstock also plays an important role. Gaseous feedstocks have lower conversion rates than liquid feedstocks, such as naphtha, and are cracked at relatively low coil outlet temperatures. The effluent temperature at the inlet of the heat exchanger 90 can range from 770°C to 900°C. The reactor effluent (cracked product) at the cracked product outlet of the heat exchanger 90 generally has a temperature at least 125°C, preferably 150°C to 250°C, higher than the feed-side outlet temperature of the feed-effluent exchanger. The reactor effluent (cracked product) at the cracked product outlet of the heat exchanger 90 generally has a temperature at least 150°C, preferably 175°C to 275°C, higher than the temperature of the diluted feed at the feed inlet of the feed-effluent exchanger. Typically, the reactor effluent temperature at the cracked product outlet of heat exchanger 90 is below 500° C., preferably in the range of 300° C. to 450° C., and more preferably in the range of 325° C. to 425° C. If a compressor is applied in addition to the humidifier to compress the steam-diluted gaseous feedstock to furnace inlet pressure, this operating temperature can be increased by typically 40 to 100° C., depending on the compressor's polytropic efficiency and discharge pressure.

[0041] An ethylene plant according to the present invention typically further comprises a cooling section configured to further cool the cracked product after it exits the feed-effluent heat exchanger 90. The cooling section may also be referred to as the high-temperature section of the plant. Generally, the ethylene plant according to the present invention is advantageously operated without a high-pressure steam generator. Thus, in the cooling section, the pyrolysis reactor effluent is further cooled to near ambient conditions (outdoor temperature) without substantial high-pressure steam generation. Suitable devices for cooling the pyrolysis reactor effluent are known in the art and may be selected from, among others, water quenchers, oil quenchers, and air coolers. Preferably, the plant comprises at least one device selected from the group consisting of a water quencher and an oil quencher. As discussed below, such devices are not only effective for cooling. They may also be used in product purification or fractionation, which may also be based on principles known in the art. Furthermore, the inventors have recognized that streams used in the water quench, oil quench, or both may be used, inter alia, to provide dilution steam to address the lack of high-pressure steam generation. According to the present invention, instead of utilizing dilution steam as a (hot) stream mixed with the hydrocarbon feed, a humidifier (this term is used interchangeably herein with the term saturator) can be used to humidify, and in particular saturate, the feed with water (liquid) during normal operation. Water from the water quench can be used as a water source for humidifying the feed. Such a method is particularly advantageous for humidifying at least substantially gaseous feeds. When a humidifier is used, dilution steam is generally not required during normal operation, but can be useful for start-up, decarbonization, hot standby, and backup operation. Therefore, in plants / processes that include / use a humidifier to humidify the feed, a dilution steam generator is typically provided. This can have a relatively small capacity compared to plants in which dilution steam is used during normal operation. In particular, a dilution steam drum 80 with an electric boiler 85 can be provided to provide dilution steam 24 (see, for example, FIG. 6 ). This is discussed further below.

[0042] Figure 5 shows a schematic of a plant / process according to the present invention, illustrating how a water quench can be used to cool the cracked products to near ambient conditions. Additionally, it illustrates how sour water (condensed dilution steam containing acid gases and recovered during cooling and scrubbing of the cracked products in the water quench) can be treated and used to provide a diluent without the need for high pressure steam.

[0043] From the furnace section 1001, the pyrolysis reactor effluent (cracked product) 4, cooled in the feed-effluent heat exchanger 90, is sent to the high temperature separation section of the plant, which includes a water quench tower 60, a sour water stripper 70, and a humidifier (saturator) 150.

[0044] In the water quench tower 60, the effluent 4 is further cooled to near ambient conditions. This is typically done using a pump-around circuit, which collects the accumulated water bottoms product, so-called quench water 14, and injects it at various levels within the quench tower 60. The quench water circuit typically has two stages: a quench water bottoms cooling circuit 64 serves the quench water tower bottom section 61, and a quench water tops cooling circuit 66 serves the quench water tower top section 62. The quench water bottoms circuit cooler 65 is typically a process user to recover as much of the quench water load as possible.

[0045] The plant can operate without a feed preheater configured to preheat the hydrocarbon feedstock before combining it with the diluent (water / steam). The quench water load is used to heat the saturator water circuit 151, which preheats and saturates the feedstock with water. Excess heat in the quench water circuit is typically removed by air or cooling water. A quench water overhead circuit cooler 67 typically uses cooling water to remove excess heat. Cooled injection water from the pumparound circuit is typically used in a quench water tower to remove heat from the pyrolysis reactor effluent (cracked product) by direct heat exchange within a suitable tower. The main function of this tower, apart from cooling the cracked product, is the condensation and recovery of dilution vapor. The condensed dilution vapor is the net product from the bottom of the tower, in addition to the gasoline product stream (which is generally small compared to the condensed dilution vapor stream for gaseous feedstocks). These are typically separated from each other using a gasoline / water separator 63. This separator may also be used to collect quench water 14 for the quench water circuit. This condensed dilution steam, called sour water 20, contains dissolved sour gases, which are typically stripped by strip steam 21 in the sour water stripper 70. These sour gases 22 are returned to the quench water tower 60. The stripped water, called process water 23, is suitable for humidifying (saturating) the feedstock. This occurs at a pressure higher than that in the water quench tower and sour water stripper, typically about 2 to about 8 bar, and more typically about 4 to about 6 bar, to supply it to the furnace section 1001 without the need for a compressor. Humidifying (saturating) the feedstock is accomplished in the saturator water heating circuit 151 using the quench water as the heating medium. Process water is collected at the bottom of the saturator 150 and returned to the top of the saturator via the saturator water heating circuit 151. The water is heated using the saturator water circuit heater on the quench water 152. Fresh hydrocarbon feedstock 1 enters the bottom of the saturator and, using suitable internals, typically random packing, is saturated with hot saturator water flowing down the column. By controlling the saturator water inlet temperature, the level of humidification can be controlled to achieve the correct steam dilution level for the pyrolysis reactor.The steam-diluted hydrocarbon feedstock is returned to the cracking furnace 1001 and directly to the feed-effluent exchanger 90. The blowdown 26 from the saturator 150 and the configuration 25 to the saturator prevent the accumulation of fouling contaminants in the saturator water heating circuit. The quench water temperature level is limited to about 80°C, so the hot saturator water inlet temperature is limited. The level of humidification depends on the hot saturator temperature and the partial pressure the feedstock can generate in the column. The lower the boiling point of the feedstock, the easier it is to achieve high humidification. Therefore, the principles illustrated in Figure 5 are particularly useful for at least substantially gaseous feedstocks for this embodiment, preferably feedstocks consisting of at least substantially ethane, propane, or a mixture of ethane and propane. Figure 14 shows the absolute operating pressure (kg / cm) in an exemplary saturator. 2 Dew point (°C, vertical axis) as a function of temperature (°C, horizontal axis) is shown at a dilution steam (weight) ratio of 0.35. The rectangular box (gray) indicates the desired operating window of the system. Thus, a cooling water temperature of 80°C is too low to be used in combination with a feedstock at ambient temperature to reach a dilution steam ratio of 0.35. Therefore, at least without further measures, the scheme of FIG. 5 has its limitations in terms of applicable pressure and dilution steam ratio (weight ratio of dilution steam to hydrocarbon feedstock). Possible measures include further heating the quench water, the feedstock, or both, before entering the saturator; using a relatively low diluent-to-feedstock ratio; and feeding the feedstock-diluent mixture to the pyrolysis reactor at a relatively low pressure.

[0046] The inventors have discovered several methods that are particularly suited to addressing the limitations discussed in the discussion of FIG. 5, as will now be discussed.

[0047] In a preferred embodiment, the ethylene plant according to the present invention is configured to further cool the pyrolysis reactor effluent (cracked product) and includes a quench oil cooling system 51 located downstream of the feed-effluent heat exchanger 90. When present, it is typically used in combination with a quench water cooling system 60 (or alternatively, an air cooler), with the quench oil cooling system located upstream. By utilizing a quench oil cooling system with a quench oil cooling circuit, heat recovery levels can be increased to substantially higher levels. This allows all dilution steam to be generated in the saturator using waste heat from the effluent, even at relatively high steam dilution ratios, defined as dilution steam to hydrocarbon weight ratios, for example, steam dilution ratios of about 0.35 or greater. This also reduces low-temperature utility requirements, such as the demand for air cooling, water cooling water, or both. According to the present invention, the quench oil cooling system is advantageous for gaseous feedstocks (especially in combination with the saturator / humidifier described above and shown in FIG. 5), liquid feedstocks, and combinations thereof. The quench oil cooling system 51 may be or be part of a primary fractionator system, which systems are known in the art, especially in plants that utilize liquid feedstocks.

[0048] A particularly suitable ethylene plant and process of the present invention that overcomes the shortcomings of the scheme shown in Figure 5 is shown in Figure 6. This plant / process is particularly preferred for at least substantially gaseous feedstocks. In use, the feed-effluent exchanger 90 and pyrolysis reactor 91 may be used as described above.

[0049] From the furnace section 1001, the cooled effluent 4 is sent to the high temperature separation section of the plant, which includes a quench oil unit 50 (typically including a primary fractionator 51 and a quench oil cooling circuit 55), a water quench cooling system 60 (typically a water quench tower), a sour water stripper 70, and a humidifier (saturator) 150.

[0050] After leaving the feed-effluent heat exchanger 90, the cracked product 4 (thermal cracking reactor effluent) enters the high-temperature separation section of the plant. Before entering the primary fractionator 50, quench oil is usually mixed with the cracked product. Typically, quench oil is injected into a so-called quench oil fitting before entering the primary fractionator. Injecting quench oil upstream of the furnace can be advantageously used to control the bottom temperature of the primary fractionator (column). In the primary fractionator 50, the thermal cracking reactor effluent is further cooled, for example to about 110°C to 125°C. The temperature is advantageously lowered to a value closer to the dew point of water (typically about 75°C to 80°C), for example, to a temperature 10 to about 50°C above the dew point, preferably within 20 to about 45°C above the dew point, more particularly, to a temperature 30 to about 40°C above the dew point, but generally to a higher value, to ensure that water does not condense in this unit. A primary fractionator for cracking cracked products obtained from an essentially gaseous feedstock can be relatively simple compared to a primary fractionator used for cracking liquid feedstocks. Generally, a quench oil wash section 51 (plus a quench oil cooling circuit) is sufficient to crack cracked products obtained from an essentially gaseous feedstock. In known olefin production plants, the primary fractionator typically further comprises at least a gasoline reflux section 53 and, optionally, an intermediate oil section 52 (not shown in FIG. 6). These are not required when using the primary fractionator for processing cracked products obtained from at least an essentially gaseous feedstock according to the present invention. The present invention (as shown in FIGS. 5 and 6) allows for the dilution of a (gaseous) feedstock without generating a separate dilution steam stream combined with the feedstock. Instead, by utilizing a saturator / humidifier in which water (i.e., in liquid form) contacts the feedstock to humidify it, the temperature level of the injected water at the top inlet of the saturator / humidifier is so low that the operating temperature at the bottom of the primary fractionator can be reduced below that of the dilution steam temperature level. The primary fractionator can be operated at 150°C so that the saturator circulating water can be heated to 140°C. This is significantly lower than the operating temperature of the dilution steam drum, which is about 165°C, allowing for steam dilution ratios in excess of 0.35.It should be noted that having a primary fractionator for a gaseous feed ethylene plant is not a conventional feature, and in particular, to the best of the inventors' knowledge, the use of a primary fractionator for a gaseous feed ethylene plant in combination with a humidifier / saturator, which is required purely to reduce supplied energy needs, is not previously known in the art.

[0051] The pyrolysis reactor effluent (cracked product) is cooled by quench oil. Advantageously, the quench oil load can be recovered from the pyrolysis reactor effluent. The quench oil cooling circuit 54 is derived from the heavy fuel oil product 6 collected as a liquid product at the bottom of the primary fractionator. This quench oil 10 is cooled by the quench oil circuit cooler 55. This liquid product is typically cooled to about 80°C. It is also cooled together with the quench oil by the quench oil circuit cooler 55, and can then be further cooled by other available cooling media. If the flash point is too high for storage, a steam stripper can be added to the light component flash. Details are not shown. When in use, a portion is typically sent to the quench oil fitting 27, and the remainder is typically reinjected into the top of the tower along with a small amount of gasoline reflux 13. This flow rate is relatively small compared to the reflux in conventional liquid crackers. In this case, the cooling is primarily provided by the quench oil, not the reflux. A small amount of reflux can be used to return fuel components thereto. In known olefin production plants, it is common to use a quench oil circuit cooler 55 to generate at least a portion of the dilution steam. However, advantageously, in accordance with the present invention, the quench oil circuit is instead used (or configured to be used) to heat the saturator water circuit 151, if present. The quench oil cooling circuit can serve the complete primary fractionator 50 in accordance with the present invention. In addition to cooling the pyrolysis reactor effluent, a heavy oil fraction is condensed in the primary fractionator. This heavy fuel oil 6 is the bottom product of the primary fractionator.

[0052] As described above (see particularly the description of FIG. 5 ), in the water quench tower 60, the cracked product 4 is further cooled to near ambient conditions. Saturation of the feedstock is achieved in the saturator water heating circuit 151 using quench water as the heating medium, for example, as described above. Process water is collected at the bottom of the saturator 150 and returned to the top of the saturator via the saturator water heating circuit 151. The water is heated using a saturator water circuit heater on the quench water 152. In addition to plants / processes that include / use a saturator / humidifier without a quench oil cooling system, a quench oil cooling system allows for a further heating step: heating of the quench oil. When a plant is configured for both water quenching and oil quenching, the quench water cooling circuit and the quench oil cooling circuit are typically arranged as follows: in use, the process water supplied to the saturator is heated using the saturator water circuit heater on the quench water 152, followed by heating using the saturator water circuit heater on the quench oil 153. An inlet for fresh (gaseous) feedstock 1 is provided within the saturator (typically at or near the bottom of the saturator tower). The saturator has internals that improve contact between the feedstock (typically moving upward) and saturator water, which typically has a higher temperature than the feedstock and typically moves downward through the saturator. By controlling the saturator water inlet temperature, the level of humidification can be controlled to achieve the correct steam dilution level for the thermal cracking reactor. The steam-diluted hydrocarbon feedstock is returned to the cracking furnace 1001 and directly back to the feed-effluent exchanger 90.

[0053] In principle, this scheme can provide most of the load for achieving the required level of feedstock preheating and steam dilution during normal operation (e.g., steady-state operation). Sufficient waste heat is available in the effluent to saturate nearly the required amount of feedstock, and the quench oil is hot enough to provide the required temperature level. However, some operations require dilution steam. These include start-up situations, decarbonization operations, and hot standby operations. In these cases, the feedstock is not sent to a separate furnace, such as the furnace in the decarbonization operation. For this reason, a dilution steam drum 80 with an electric boiler 85 is preferably provided in the flow scheme to provide dilution steam 24. Furthermore, the dilution steam can be used to provide the required amount of sour water stripping steam and equipment purge steam. The capacity of this system may be limited compared to known plants where dilution steam is required during normal operation. In addition, stripping steam can be used to provide the required amount of sour water stripper. During normal operation, a certain amount of dilution steam can be mixed with the steam-diluted feedstock coming from the saturator to provide a small amount of superheat as needed. Advantageously, the contribution of the dilution steam drum 80 with the electric boiler 85 to the total dilution steam demand is preferably less than 40%, more preferably less than 30%, and even more preferably less than 20%. Dilution steam can be sent separately to the furnace for start-up, decarbonization, hot standby and back-up operation.

[0054] The blowdown 26 from the dilution steam drum 80 and the associated arrangement 25 to the saturator water heating circuit prevents the buildup of fouling contaminants in the saturator water and dilution steam generation circuits, and therefore their presence is preferred.

[0055] As an alternative to, or in combination with, the use of heat from a quench oil cooler (as shown by the embodiment of Figure 6), limitations on the use of a saturator as discussed in the description regarding Figure 5, particularly with respect to the maximum achievable dilution steam-to-feed ratio, the inventors have recognized that it is possible to reach higher saturations of the (essentially gaseous) feed with water (steam) when humidifying the feed in saturator 150 at relatively low pressures near or above atmospheric pressure, i.e., pressures below the pressure at which the thermal cracking reactor is configured to operate, and then compressing the humidified feed (i.e., feed-diluent mixture) before feeding it to the cracking section. An ethylene plant / process in accordance with the present invention, comprising / including the use of a compressor to compress the humidified feed, is shown schematically in Figure 7.

[0056] The scheme may be essentially the same as that of FIG. 5. However, the plant further includes a compressor 154 downstream of the saturator / humidifier 150, which is typically configured to operate at approximately atmospheric pressure. During use, the feedstock is humidified, specifically essentially saturated, at a pressure below the pressure at which the electric cracking furnace 1001 is configured to operate. Conventional radiant coil pyrolysis reactors typically operate at pressures ranging from 1.5 to 4.0 bar, specifically 1.7 to 3.0 bar. Other designs, such as the Coolbrook rotodynamic device, may require lower pressures, potentially as low as about 2 bar, typically about 4 bar. The humidified gas is compressed to a precise pressure, typically ranging from 2.0 to 6 bar, specifically 2.5 to 4 bar, using the saturated gas feedstock compressor 154 to supply the humidified feedstock 3 to the furnace section 1001. In contrast to the scheme of FIG. 6, this typically allows operation without the need for any additional (electrical) power to provide the required level of feedstock preheating and steam dilution. While this option requires power to drive the compressor, compared to using an electric boiler to generate dilution steam, this option still requires 40-50% less power, depending on the feed pressure applied to the furnace. Furthermore, the combination of a relatively low-pressure humidifier and a compressor for compressing the hydrocarbon feed-diluent mixture allows the hydrocarbon feed-diluent mixture to have a desirably high dilution steam ratio, e.g., a ratio of about 0.35. As with the scheme of FIG. 6, a dilution steam drum 80 with an electric boiler 85 is advantageously present to provide dilution steam 24.

[0057] In a further embodiment, particularly suitable for cracking essentially gaseous feedstocks by steam cracking, as well as for cracking liquid feedstocks or mixtures of gaseous and liquid feedstocks, the ethylene plant includes a dilution steam generator and a heat pump configured to generate the dilution steam. Figure 8 shows a schematic diagram of an advantageous plant / process according to the present invention that employs a heat pump and a refrigerant. The refrigerant typically has a normal boiling point in the range of 0°C to 80°C. This range is preferred for practical reasons, but it will be understood that refrigerants with other boiling points may be used. The flow scheme of Figure 8 may be similar to that of Figure 5, except for the presence of a dilution steam generator configured to utilize condensed refrigerant 86 and a dilution steam superheater 87 that uses refrigerant instead of a saturator / humidifier. The refrigerant load for generating the dilution steam during use is made available by using a heat pump to increase the quench water load to a higher level. Details of a particularly suitable heat pump are shown in Figure 9. Subcooled medium-pressure refrigerant liquid 190 from the medium-pressure refrigerant drum 173 is reduced in pressure to low pressure 181 by the liquid refrigerant pressure reducing valve, producing flashing low-pressure refrigerant 191. This refrigerant is separated in the low-pressure refrigerant drum 170. The liquid fraction is recycled by natural circulation over the thermosiphon-type reboiler and low-pressure refrigerant vaporizer 171 and evaporated using a low-level quench water load from the quench water circuit. Alternatively, the low-pressure refrigerant drum 170 and low-pressure refrigerant vaporizer 171 can be combined in a kettle-type reboiler since the refrigerant is a clean fluid. The low-pressure saturated refrigerant vapor 192 is compressed to medium-pressure slightly superheated refrigerant vapor 195a in the low-pressure-to-intermediate-pressure refrigerant compressor 172.

[0058] The subcooled high-pressure refrigerant liquid 193 from the refrigerant economizer 175 is reduced in pressure to intermediate pressure 180 by the liquid refrigerant pressure reducing valve, producing flashing medium-pressure refrigerant 194. This refrigerant is separated in the medium-pressure refrigerant drum 173. The liquid fraction is recycled by natural circulation over a thermosiphon-type reboiler, medium-pressure refrigerant vaporizer 174, for evaporation using the higher level quench water load from the quench water circuit. Alternatively, the medium-pressure refrigerant drum 173 and medium-pressure refrigerant vaporizer 174 can be combined in a kettle-type reboiler since the refrigerant is clean / fluid. The medium-pressure saturated refrigerant vapor 195b is combined with the medium-pressure slightly superheated refrigerant vapor 195a and superheated in the refrigerant economizer 175 to produce medium-pressure superheated refrigerant vapor 196. After being compressed in the medium to high pressure refrigerant compressor 176 to a temperature level above that for dilution vapor generation, the refrigerant is desuperheated by saturated dilution vapor in the high pressure refrigerant attemperator 177. The high pressure attemperated refrigerant vapor 198 is condensed by process water from the dilution vapor drum in the high pressure refrigerant condenser 178. The condensed high pressure refrigerant liquid 199 is subcooled in the refrigerant economizer 175. The subcooled high pressure refrigerant liquid 193 is recycled.

[0059] In this system, excess heat available in the quench water circuit can be upgraded to a temperature level high enough to produce dilution steam. Low-pressure refrigerant provides the quench water at a lower temperature level, while medium-pressure refrigerant provides the quench water at a higher temperature level. A third pressure level can be introduced to recover the quench water load at three levels instead of two. The refrigerant pressure and the refrigerant itself are selected so that the quench water load can be recovered by evaporating liquid refrigerant at various temperature levels compatible with the quench water circuit cooler and condensing the refrigerant vapor at a temperature level suitable for dilution steam production.

[0060] The use of a heat pump system for dilution steam generation in an ethylene plant requires power in addition to the power required for the pyrolysis reactor. However, the power requirements are typically up to about 50-70% less, depending on the feed pressure used for the furnace, compared to using an electric boiler to generate dilution steam. This is similar to that of plants utilizing a humidifier and compressor for humidified feedstock (see, e.g., FIG. 7). An advantage of using a heat pump, such as that shown in FIG. 8, over a saturator, such as that shown in FIG. 6 or FIG. 7, is that the heat pump system can also take over the role of the electric boiler outside of normal operation (e.g., during start-up). Furthermore, it is contemplated that embodiments utilizing a heat pump are particularly advantageous for high steam-to-hydrocarbon feed ratios, e.g., ratios greater than 0.35, compared to plants / processes utilizing a saturator.

[0061] For cracking at least substantially liquid feedstocks or mixtures of liquid and gaseous feedstocks, it is particularly preferred to utilize a system configured to heat the feedstock and vaporize it using heat recovered from quench water and quench oil, respectively. It is also preferred to utilize heat recovered from intermediate oil. Dilution steam is advantageously generated from a heat-pumped quench water load, as described above, preferably using a refrigerant scheme such as that described in the discussion of FIG. 9. The advantage of an ethylene plant or process of the present invention including these measures is that the feedstock can be vaporized without the aid of flue gases, and the dilution steam can be vaporized without the use of MP steam. By using a heat pump to generate MP steam, power can be reduced by more than 50% compared to using an electric MP boiler for this service, thereby significantly reducing additional power requirements. Such an advantageous process is further illustrated in FIG. 10. Generally, as shown in Figure 10, in use, Feed 2, preferably a liquid feed such as liquefied butane, pentane, or naphtha, or a mixture thereof, is first preheated in preheater 30 with a low temperature heat source, such as quench water, external to furnace 1001, to a temperature from ambient conditions to a temperature close to the maximum temperature of the low temperature heat source, such as the maximum temperature in the quench water circuit, typically within 5-10°C of the maximum temperature. For a maximum quench water temperature of about 75-80°C, preheating to 70-75°C is possible.

[0062] Further preheating and partial vaporization of the feedstock is achieved by intermediate oil in the hydrocarbon feedstock preheater with intermediate oil 43 and in the hydrocarbon partial feedstock vaporizer with intermediate oil 44 outside the furnace. The partially vaporized feedstock is separated in the hydrocarbon feedstock drum 45. The liquid fraction is recycled by natural circulation over the thermosiphon-type reboiler, the hydrocarbon feedstock vaporizer, by quench oil vaporizer 46 for vaporization using quench oil load from the natural circulation circuit. The fully vaporized feedstock is sent to the feed-effluent exchanger 90 of the electric cracking furnace 1001. If quench oil load is available and the temperature level is high enough, the feedstock can be slightly superheated by quench oil and in the hydrocarbon feedstock superheater by quench oil 47.

[0063] To suppress the hydrocarbon partial pressure in the pyrolysis reactor (which is beneficial for product yield and suppression of coke formation), the superheated dilution vapor 24 coming from the high temperature separation section (typically superheated by 30-50°C depending on the refrigerant compressor efficiency) is also sent to the feed-effluent exchanger 90 before being fed to the electrically powered pyrolysis reactor 91 in the cracking furnace section 1001.

[0064] The mixture of hydrocarbon feedstock and dilution steam 3 enters feed-effluent exchanger 90 above the water dew point and is heated by feed-effluent exchanger 90 with waste heat from the effluent to a suitable inlet temperature for electrically powered pyrolysis reactor 91, which provides sensible heat and heat of reaction to the steam-diluted hydrocarbon feedstock 3 for conversion of the feedstock to products. Waste heat from the reactor effluent 4 is recovered by feed-effluent exchanger 90.

[0065] The effluent is then cooled at quench oil fitting 37 using quench oil injection 27 and intermediate oil injection 28, if an intermediate oil loop is available. From the furnace section, effluent 4 is sent to the high temperature separation section of the plant, which consists primarily of primary fractionator 50, water quench tower 60, sour water stripper 70, and dilution steam drum 80.

[0066] In the primary fractionator 50, the pyrolysis reactor effluent (cracked product) is further cooled. To ensure that water does not condense in this column, the temperature is maintained above the dew point of water, preferably 5°C above the dew point, and more preferably 5°C to 40°C above the dew point. For example, for a dew point of approximately 90°C, the operating temperature can be controlled within a range of 95 to 110°C, e.g., up to approximately 100°C, by controlling the reflux injection. The effluent is then cooled using quench oil and intermediate oil pump-arounds and gasoline reflux, respectively. The quench oil cooling circuit 54 originates from the heavy fuel oil product 6 collected at the bottom of the column. This quench oil 10 is cooled by the quench oil circuit cooler 55. A portion of it is sent to the quench oil fitting 27, and the remainder is reinjected into the column below the intermediate oil total draw-off tray. The quench oil circuit cooler 55 is used to vaporize the feedstock in the hydrocarbon feed vaporizer, in this case via the quench oil vaporizer 46. The temperature at the bottom of the primary fractionator can be adjusted to a temperature level that allows this. A person skilled in the art would be able to do this based on common general knowledge and the contents of this disclosure, for example, by controlling the amount of quench oil injected into the quench oil fitting. The quench oil cooling circuit serves the primary fractionator wash section 51, which is the bottom section of the column.

[0067] The intermediate oil cooling circuit 56 is preferred. It provides a relatively clean / non-fouling intermediate cooling circuit that recovers a lower level of heat from the effluent than the quench oil circuit 54. The intermediate oil 11 is collected on a draw-off tray at the bottom of the primary fractionator intermediate oil section 52, located above the wash section 51 in the column. The intermediate oil reflux 12 is sent to the quench oil wash section 51 at the bottom of the column so that the quench oil load can be shifted to the intermediate oil loop. Further intermediate oil is sent to the quench oil fitting 28. The remainder is cooled by the intermediate oil circuit cooler 57 and returned to the column below the light fuel oil draw point. The intermediate oil cooling circuit 56 serves the primary fractionator intermediate oil section 52. In this case, the intermediate oil can be used to preheat and partially vaporize the hydrocarbon feedstock in the hydrocarbon feedstock preheater with intermediate oil 43 and the hydrocarbon partial feedstock vaporizer with intermediate oil 44. Optionally, quench oil can be used for this purpose.

[0068] The gasoline reflux 13 coming from the gasoline / water separator 63 is processed for heat recovery at the top of the tower, in the primary fractionator gasoline reflux section 53, and the recovered load is shifted to the quench water circuit. Suitable internals are installed in the tower to efficiently transfer heat from the effluent to the injected quench oil, middle oil, and gasoline reflux. In addition to cooling the effluent, the light and heavy oil fractions are condensed in the primary fractionator. Heavy fuel oil 6 is collected at the bottom 51, and light fuel oil 7 is collected on a light oil fraction draw-off tray at the bottom of the reflux section 53. These products can be stripped to control the flash point of the total fuel oil product 5 and / or lighter quench oil fractions can be recovered for viscosity control in the quench oil circuit. They can also be cooled. These details are not shown here, as they are not relevant to the present application.

[0069] In the water quench tower 60, the effluent 4 is further cooled to near ambient conditions. This is done using a pump-around circuit, which collects the accumulated water bottoms product, so-called quench water 14, and injects it at various levels within the quench tower 60. The quench water circuit typically has two stages: a quench water bottoms cooling circuit 64 serves the quench water tower bottom section 61, and a quench water tops cooling circuit 66 serves the quench water tower top section 62. The quench water bottoms circuit cooler 65 is typically a process user to recover as much quench water load as possible. Such users are, for example, the feed preheater 30 and / or a propylene splitter reboiler (not shown). In this case, the load is used for feed preheating using the feed preheater 30 and for refrigerant evaporation using the medium-pressure refrigerant vaporizer 174 and / or the low-pressure refrigerant vaporizer 171 in the refrigerant circuit of FIG. 9. Excess heat must typically be removed by air or cooling water cooling. The refrigerant loop reduces these low-temperature utilities and transfers the quench water load to a level suitable for dilution steam production. The cooled injection water from the pumparound circuit is used in the quench tower to remove heat from the cracked gas by direct heat exchange within the appropriate tower. The primary function of this tower, apart from cooling the cracked gas, is to condense and recover the dilution steam. The condensed dilution steam, along with a small stream of gasoline product, is the net product from the bottom of the tower. These are typically separated from each other using a gasoline / water separator 63. Sometimes, this separator also collects quench water for the quench water circuit. This condensed dilution steam, called sour water 20, contains sour gas, which is stripped by strip steam 21 in the sour water stripper 70. These sour gases 22 are returned to the quench tower 60. The stripped water, called process water 23, is suitable for dilution steam production. This occurs at a higher pressure than in the quench tower and sour water stripper, typically about 2 to about 7 bar, and more particularly about 4 to about 6 bar, to feed the furnace section 1001. The generation of dilution steam is accomplished using a refrigerant. Process water is collected in dilution steam drum 80, and via a thermosiphon circuit, dilution steam 24 is generated from the condensed refrigerant in dilution steam generator 86 using condensed refrigerant.Superheat in the refrigerant is used to gently superheat the dilution steam in the dilution steam superheater 87 to a temperature of 180°C to 210°C before it is returned to the electric cracking furnace 1001 to dilute the hydrocarbon feedstock 1. The blowdown 26 from the dilution steam drum 80 and the dilution steam system arrangement 25 to that drum prevent the buildup of fouling contaminants in the dilution steam generation circuit.

[0070] An alternative plant / process according to the invention is based on the heat integration scheme shown in Figure 11. This scheme is similar to the scheme of Figure 10, except for the heat integration. It is also particularly useful for cracking liquid feedstocks and mixtures of liquid and gaseous feedstocks.

[0071] In a process or plant according to the invention based on the scheme of Figure 11, the quench oil load is not used (but is configured to be used) for feed evaporation, but is used for dilution steam generation by a dilution steam generator using quench oil 82. In use, evaporation of the feed is in this case performed by a refrigerant in the hydrocarbon feed evaporator by condensing refrigerant 48, which is superheated by the hydrocarbon feed superheater by refrigerant 49.

[0072] The performance of a process or plant based on Figure 10 or Figure 11 is very similar for these two schemes. In the scheme of Figure 11, the refrigeration circuit needs to be adjusted to also supply heat to the feed evaporator 49. Depending on the feed, this can be at a temperature level higher or lower than that of the dilution steam generation. A separate compressor can be installed to fulfill this role, or two compressors can be placed in series.

[0073] Figures 12 and 13 show refrigeration compressor systems that can be used in a process or plant according to the invention. These refrigeration compressors can be mounted on a single shaft and, if desired, can be mounted in a single casing. Refrigeration compressor systems can be used to further reduce power requirements.

[0074] FIG. 12 shows two separate parallel high-pressure loops: a high-pressure refrigeration circuit branch 1010 and a high-pressure-to-high-pressure refrigeration circuit branch 1011. Each of these two branches is operated at a different pressure and corresponding operating temperature to best match the temperature levels of dilution vapor generation and feedstock evaporation. This minimizes power requirements. One branch handles feedstock evaporation via the hydrocarbon feedstock evaporator by condensing refrigerant 48, while the other branch handles dilution vapor generation via the dilution vapor generator using condensed refrigerant 86. When the operating temperature of the hydrocarbon feedstock evaporator is higher than that of the dilution vapor generator, the hydrocarbon feedstock evaporator is operated by the high-pressure-to-high-pressure branch 1011, and the dilution vapor generator is operated by the high-pressure branch 1010. When the operating temperature of the hydrocarbon feedstock evaporator is lower than that of the dilution vapor generator, the hydrocarbon feedstock evaporator is operated by the high-pressure branch 1010, and the dilution vapor generator is operated by the high-pressure branch 1011.

[0075] Subcooled medium-pressure refrigerant liquid 190 from the medium-pressure refrigerant drum 174 is reduced in pressure to low pressure 181 by the liquid refrigerant pressure reducing valve, producing flashing low-pressure refrigerant 191. This refrigerant is separated in the low-pressure refrigerant drum 170. The liquid fraction is recycled by natural circulation over the thermosiphon-type reboiler, low-pressure refrigerant vaporizer 171, and can be evaporated using a low-level quench water load from the quench water circuit. Alternatively, the low-pressure refrigerant drum 170 and low-pressure refrigerant vaporizer 171 can be combined in a kettle-type reboiler since the refrigerant is clean / fluid. The low-pressure saturated refrigerant vapor 192 is compressed to medium-pressure slightly superheated refrigerant vapor 195a in the low-pressure to medium-pressure refrigerant compressor 172.

[0076] Subcooled high-pressure refrigerant liquid 206 from high-pressure-high-pressure refrigerant economizer 182 and subcooled high-pressure refrigerant liquid 193 from high-pressure refrigerant economizer 175 are reduced in pressure to intermediate pressure 180 by a liquid refrigerant pressure reduction valve to produce flashing medium-pressure refrigerant 194. This refrigerant is separated in intermediate-pressure refrigerant drum 173. The liquid fraction can be recycled by natural circulation over a thermosiphon-type reboiler, intermediate-pressure refrigerant vaporizer 174, for evaporation using a higher level of quench water load from the quench water circuit. Alternatively, the intermediate-pressure refrigerant drum 173 and intermediate-pressure refrigerant vaporizer 174 can be combined in a kettle-type reboiler since the refrigerant is a clean fluid. Medium-pressure saturated refrigerant vapor 195b is mixed with medium-pressure slightly superheated refrigerant vapor 195a.

[0077] At this point, the combined streams 195a and 195b are sent to two parallel refrigeration circuit branches 1010 and 1011.

[0078] The portion sent to the high-pressure branch 1010 is superheated in the high-pressure refrigerant economizer 175 to produce intermediate-pressure superheated refrigerant vapor 196. After being compressed in the low-to-intermediate-to-high-pressure refrigerant compressor 176 to a temperature level above that of dilution steam generation or hydrocarbon feed evaporation, whichever is lower, the refrigerant is desuperheated in the high-pressure refrigerant attemperator 177 with saturated dilution steam or hydrocarbon feed using a dilution steam superheater with refrigerant 87 or a hydrocarbon feed superheater with refrigerant 49. The high-pressure desuperheated refrigerant vapor 198 is condensed with process water from the dilution steam drum or hydrocarbon feed in the high-pressure refrigerant condenser 178 using a dilution steam generator with condensing refrigerant 86 or a hydrocarbon feed evaporator with condensing refrigerant 48, respectively. The condensed high-pressure refrigerant liquid 199 is subcooled in the high-pressure refrigerant economizer 175. The subcooled high-pressure refrigerant liquid 193 is recycled.

[0079] The portion sent to the high-pressure-high-pressure branch 1011 is superheated in the high-pressure-high-pressure refrigerant economizer 182 to become intermediate-pressure superheated refrigerant vapor 196. After being compressed in the intermediate-pressure to high-pressure-high-pressure refrigerant compressor 183 to a temperature level above that of dilution steam generation or hydrocarbon feed evaporation, either of the two is at a higher temperature level. The refrigerant is desuperheated with saturated dilution steam or hydrocarbon feed in the high-pressure-high-pressure refrigerant attemperator 185 using a dilution steam superheater with refrigerant 87 or a hydrocarbon feed superheater with refrigerant 49, respectively. The high-pressure-high-pressure desuperheated refrigerant vapor 186 is condensed with process water from the dilution steam drum or hydrocarbon feed in the high-pressure-high-pressure refrigerant condenser 187 using a dilution steam generator with condensing refrigerant 86 or a hydrocarbon feed evaporator with condensing refrigerant 48, respectively. The condensed high-pressure-high-pressure refrigerant liquid 205 is subcooled in the high-pressure-high-pressure refrigerant economizer 182. The subcooled high-pressure-high-pressure refrigerant liquid 206 is recycled.

[0080] This scheme makes it possible to upgrade the excess heat available in the quench water circuit to a temperature level high enough to generate dilution steam in two separate branches of the refrigeration system and vaporize the hydrocarbon feedstock.

[0081] The scheme of Figure 13 is similar to the scheme of Figure 12 except that the split between the two branches is downstream of the medium to high pressure compressor 176 and the medium to high pressure compressor 183 has been replaced by a high to high pressure compressor 183 so that the compressors in branches 1010 and 1011 are in series rather than parallel.

[0082] As used herein, the singular forms "a," "an," and "the" are intended to include the plural; for example, "a cracking furnace" includes "cracking furnaces." "A burner" includes "a plurality of burners," etc., unless the context requires otherwise. The term "or" includes any and all combinations of one or more of the associated listed items unless the context clearly indicates otherwise (e.g., when an "either...or" configuration is used). It will be understood that the terms "comprises" and "comprising" specify the presence of stated features but do not exclude the presence or addition of one or more other features. When a particular step of a method is referred to following another step, it will be further understood that it may follow directly from the other step, or that one or more intermediate steps may be performed prior to performing the particular step, unless otherwise specified. Similarly, when a connection between structures or components is described, it will be understood that this connection may be established directly or through intermediate structures or components, unless otherwise specified.

[0083] In the context of the present application, the term "about" particularly includes deviations of up to 10%, more particularly 5%, more particularly 3% from a given value.

[0084] The terms "(at least) substantial" or "(at least) essential" are generally used herein to indicate having the general characteristic or function of something specified. When referring to a quantifiable characteristic, the term is particularly used to indicate at least 75%, more specifically 90% or more, and even more specifically 95% or more of the maximum value of that characteristic. The term "essentially free" is generally used herein to indicate that a substance is either absent (below the limit of detection achievable with analytical techniques available at the effective filing date) or present in such small amounts that it does not significantly affect the properties of a product essentially free of that substance.

[0085] The term "high pressure steam" (HP steam) is well known in the art. As a rule of thumb, the pressure of HP steam is typically at least about 40 bar, such as 80 bar or more, for example, from about 100 bar to about 130 bar, for example, from 100 to 125 bar.

[0086] The term "medium pressure steam" (MP steam) refers to steam with an upper pressure limit of 40 bar. As used herein, the term MP typically refers to a range of about 6 to about 20 bar, more specifically a range of 7 to 13 bar.

[0087] The term "low pressure steam" relates to steam having a pressure lower than the MP steam pressure.

[0088] The present invention is described more fully herein with reference to the accompanying drawings, in which embodiments of the invention are shown. In the drawings, absolute and relative sizes of systems, components, layers, and regions may be exaggerated for clarity. Embodiments may be described with reference to schematic and / or cross-sectional illustrations of possible idealized embodiments and intermediate structures of the invention. In the description and drawings, like numbers refer to like elements throughout. Relative terms and their derivatives should be construed to refer to orientations as then described or as shown in the drawings under discussion. These relative terms are for convenience of description and do not require that the system be constructed or operated in a particular orientation, unless specifically specified.

[0089] Although, for purposes of clarity and conciseness of description, features may be described herein as part of the same or separate embodiments, it will be understood that the scope of the present invention may include embodiments having all or any combination of the described features. [Example]

[0090] The invention will now be illustrated by the following non-limiting examples.

[0091] To demonstrate how the present invention can be applied, several examples were prepared for a gas feed cracker: Comparative Example 1 with a conventional flow scheme according to FIG. 1 which serves as a base case for comparison; Example 2 with a flowsheet including a primary fractionator and humidifier / saturator according to FIG. 6; Example 3 with a flowsheet including a low-pressure humidifier / saturator and diluted feed compressor according to FIG. 7; and Example 4 with a flowsheet according to FIG. 8 including a heat pump according to FIG. 9.

[0092] A 1500 kilotons per year (kta) ethane cracker was selected as the base case. Unconverted ethane and propane are recycled back to the furnace section as recycle gas and mixed with fresh gaseous feed. This combined feed is handled in the cracking furnace for all examples.

[0093] Example 1, the comparative base case, has 359.8 t / h of gaseous feedstock, 233.5 t / h of fresh ethane feedstock, and 126.3 t / h of recycle gas, primarily recycle ethane. It is fed at 20°C and heated to 55°C in hydrocarbon feedstock preheater 30. In the convection section of the furnace, the feedstock is further heated to 225°C in hydrocarbon feedstock preheater 31. Dilution steam at 180°C is added to dilute the feedstock. The diluted feedstock is heated to 703°C in steam-diluted hydrocarbon feedstock superheater 33. At 4 bar, the dilution gas is fed via a critical flow venturi to multiple parallel radiant coils in the cracking furnace and to a pyrolysis reactor in the fuel-fired furnace firebox 34, where it is heated to 855°C. The pressure at the reactor outlet is 1.8 bar. During this process, the feedstock is converted to products. Conversion does not stop at the reactor outlet, but continues in the passage to transfer line exchanger 35 and in the transfer line exchanger itself. In the passage from the coil to the transfer line exchanger, the temperature drops to 840°C due to endothermic reactions. In the transfer line exchanger, the pyrolysis reactor effluent 4 (also called the cracked product) is cooled to 350°C, producing high-pressure steam. The effluent is then further cooled to 180°C in a second transfer line exchanger 36, heating the boiler feedwater.

[0094] The effluent is further cooled to 30°C in the quench tower 60 to produce cracked gas product 9. During this process, the dilution steam is condensed along with a small amount of gasoline 8. The gasoline / sour water mixture is separated in the gasoline-water separator at 80°C. The sour water 20 is pumped to the sour water stripper 70, where it is stripped to remove dissolved sour gas 22 at 1.7 bar. The purified process water 23 is pumped to the dilution steam drum 80, where dilution steam 24 is produced from the condensed MP steam at 6 bar and 160°C. The dilution steam is superheated to 180°C in the superheater 83 by the superheated MP steam. The superheated dilution steam is sent to the furnace to dilute the gaseous feedstock 1. The amount of dilution steam produced is 125.9 t / h. This means that the steam dilution ratio is 0.35 (125.9 t / h / 359.8 t / h feedstock). Furthermore, 12.5 t / h of sour water strip steam 21 is generated for stripping sour water.

[0095] Example 2 uses 359.8 t / h of the same gas feedstock, which is fed at 20°C at the bottom of the saturator 150 operating at 6 bar. Within the saturator, the gas comes into contact with circulating saturator water at 140°C, which enters at the top of the saturator. This is a practically achievable temperature with 150°C quench oil and 77°C quench water heating the saturator circulating water 151.

[0096] A portion of the process water (103 t / h) is mixed with the circulating saturator water to replace the amount of water evaporated in the saturator. The remainder of the process water is sent to a dilution steam drum 80 with an electric boiler 80 to produce 22.8 t / h of dilution steam, generated at 6 bar and 160°C, raising the total steam dilution to 125.9 t / h, with a corresponding steam dilution ratio of 0.35 (125.9 t / h / 359.8 t / h feed). In addition, 12.5 t / h of sour water strip steam 21 is generated to strip the sour water.

[0097] The saturated steam-diluted ethane 3 is sent to the feed-effluent exchanger 90 in the electro-cracking furnace section 1001 at a temperature of 123°C and heated to 703°C before entering the electro-thermal cracking reactor 91. In the thermal cracking reactor, the diluted feedstock is heated to 855°C. The pressure at the reactor outlet is 1.8 bar. In the passage from the reactor to the feed-effluent exchanger, the temperature drops to 840°C due to endothermic reactions. In the feed-effluent exchanger, the thermal cracking reactor effluent 4 (also called the cracked product) is cooled to 330°C relative to the diluted hydrocarbon feedstock 3.

[0098] The effluent is further cooled to 170°C in the quench oil fitting 37 and to 120°C in the primary fractionator 50 using circulating quench oil 54. A small amount of liquid heavy fuel oil 6 is condensed in the primary fractionator. The bottom of the primary fractionator can be operated at 150°C to produce a 150°C quench oil stream. This quench oil is cooled to 110°C to control the primary fractionator overhead temperature at 120°C. This quench oil is entirely used to heat the saturator circulating water 151 to 140°C (via the saturator water circuit heater on the quench oil load 153) using the quench oil circuit cooler 55, as already mentioned above.

[0099] Finally, the effluent is cooled to 30°C in quench water tower 60 using circulating quench water 64 and 66 to produce cracked gas product 9. The tower operates at just below the dew point at 77°C. A quench water bottoms circuit cooler 65 (via a saturator water circuit heater on quench water 152) is used to heat the saturator circulating water 151 to 72°C before it enters the saturator water circuit heater on quench oil load 153.

[0100] In the quench tower, the dilution steam is condensed along with a small amount of gasoline 8. The gasoline / sour water mixture is separated in a gasoline water separator at 80° C. The sour water 20 is pumped to a sour water stripper 70 where it is stripped to remove dissolved sour gas 22 at 1.7 bar. The purified process water is pumped to a saturator 150 and a dilution steam drum 80.

[0101] Example 3 has the same gas feed of 359.8 t / h. This is fed at 20°C at the bottom of the saturator 150. In contrast to the previous example, this column is operated at 1.1 bar instead of 6 bar. Within the saturator, the gas comes into contact with circulating saturator water at 75°C, which enters at the top of the saturator. This is a practical temperature with the 80°C quench water heating the saturator circulating water 151.

[0102] A portion of the process water (125.9 t / h) is mixed with the circulating saturator water to replace the amount of water evaporated in the saturator. This corresponds to a steam dilution ratio of 0.35 (125.9 t / h / 359.8 t / h feed). The remaining process water is sent to a dilution steam drum 80 with an electric boiler 80 to produce 12.5 t / h of sour water strip steam.

[0103] The steam-diluted ethane 3 is compressed to 6 bar in the saturated gas feed compressor 154, raising the temperature from 74°C to 214°C. The compressed gas is sent to the feed-effluent exchanger 90 in the electro-cracking furnace section 1001, where it is heated to 703°C before entering the electro-thermal cracking reactor 91. In the thermal cracking reactor, the diluted feed is heated to 855°C. The pressure at the reactor outlet is 1.8 bar. In the passage from the reactor to the feed-effluent exchanger, the temperature drops to 840°C due to endothermic reactions. In the feed-effluent exchanger, the thermal cracking reactor effluent 4 (also called the cracked product) is cooled to 400°C relative to the diluted hydrocarbon feed 3.

[0104] The effluent is further cooled to 30°C in quench water tower 60 using circulating quench water 64 and 66 to produce cracked gas product 9. The tower is operated at 80°C. A quench water bottom circuit cooler 65 (via a saturator water circuit heater on quench water 152) is used to heat saturator circulating water 151 to 75°C.

[0105] In the quench tower, the dilution steam is condensed along with a small amount of gasoline 8. The gasoline / sour water mixture is separated in a gasoline water separator at 80° C. The sour water 20 is pumped to a sour water stripper 70 where it is stripped to remove dissolved sour gas 22 at 1.7 bar. The purified process water is pumped to a saturator 150 and a dilution steam drum 80.

[0106] Example 4 has the same gaseous feedstock as the other cases, 359.8 t / h. It is fed at 20°C and heated to 75°C in the hydrocarbon feedstock preheater 30. Dilution steam at 200°C is added to dilute the feedstock. The diluted feedstock is sent to the feed-effluent exchanger 90 in the electro-cracking furnace section 1001 and heated to 703°C before entering the electro-thermal pyrolysis reactor 91. In the pyrolysis reactor, the diluted feedstock is heated to 855°C. The pressure at the reactor outlet is 1.8 bar. In the passage from the reactor to the feed-effluent exchanger, the temperature drops to 840°C due to endothermic reactions. In the feed-effluent exchanger, the pyrolysis reactor effluent 4 (also called the cracked product) is cooled to 316°C relative to the diluted hydrocarbon feedstock 3.

[0107] The effluent is further cooled to 30°C in quench water tower 60 using circulating quench water 64 and 66 to produce cracked gas product 9. The tower is operated at 80°C. A quench water bottom circuit cooler 65 (via a saturator water circuit heater on quench water 152) is used to heat saturator circulating water 151 to 75°C.

[0108] In the quench tower, the dilution steam is condensed along with a small amount of gasoline 8. The gasoline / sour water mixture is separated in a gasoline-water separator at 80°C. The sour water 20 is pumped to a sour water stripper 70 where it is stripped to remove dissolved sour gas 22 at 1.7 bar. The purified process water is pumped to a dilution steam drum 80 using a dilution steam generator using a condensing refrigerant 86 to produce 125.9 t / h dilution steam, generated at 6 bar and 160°C, required to have a dilution steam ratio corresponding to 0.35 (125.9 t / h / 359.8 t / h feed). In addition, 12.5 t / h of sour water strip steam 21 is produced to strip the sour water. The dilution steam is superheated in a dilution steam superheater 87 using a superheated refrigerant.

[0109] Using the low-pressure refrigerant evaporator 171 and the intermediate-pressure refrigerant condenser 174, refrigerant vapor is produced by the two quench water bottom circuit coolers 65 at 62.5°C and 70°C, respectively. The quench water is cooled once from 80°C to 75°C and once more to 67°C. Using the low-pressure to intermediate-pressure and intermediate-pressure to high-pressure compressors 172, 176, respectively, high-pressure superheated refrigerant vapor is produced at 216°C. This is used to superheat the dilution vapor in the dilution vapor superheater 87 (via the high-pressure refrigerant attemperator 177) and to produce the dilution vapor itself in the dilution vapor generator using the condensed refrigerant 86 (via the high-pressure refrigerant condenser 178).

[0110] Table 1 summarizes the loads for various implementations along with the associated compressor outputs.

[0111] [Table 1]

[0112] Table 2 shows the potential reduction in power demand and excess power, as defined above, for various examples when comparing the power demand for diluting the feedstock with the power demand required for dilution steam generation in a conventional process calculated for Example 1, i.e., 90.3 MW in the absence of MP steam. It shows that the flowsheet of Figure 6 (Example 2) has the highest reduction potential, 73%. The flowsheet of Figure 7 (Example 3) has a reduction value of 45%. The flowsheets of Figures 8 and 9 (Example 4) have an intermediate level at 60%.

[0113] [Table 2] * Heat provided by fuel combustion

[0114] Legend for the figure 1. Hydrocarbon feedstock (gas) 2. Hydrocarbon feedstock (liquid) 3. Steam diluted hydrocarbon feedstock 4. Pyrolysis reactor effluent (also called cracked products) 5. Total fuel oil products 6. Heavy fuel oil products 7.Light fuel oil products 8. Heavy pyrolysis gasoline 9. Cracked gas products (exit the high temperature section and are cooled / cleaned) 10. Quenching oil 11. Intermediate oil 12. Intermediate oil reflux 13. Gasoline reflux 14.Quick cooling water 20. Sour Water 21. Stripping steam 22. Sour Gas 23. Process water 24. Diluted steam 25. Configuration of dilution steam system 26. Blowdown 27. Quenching oil for quenching fittings 28. Intermediate oil-quench fitting 30. Furnace external hydrocarbon feed preheater 31. Hydrocarbon feed preheater in the furnace convection section 32. Hydrocarbon feed vaporizer in the furnace convection section 33. Steam diluted hydrocarbon feed superheater in furnace convection section 34. Pyrolysis reactor in the firebox of a fuel-fired furnace 35. Transfer line exchanger for generating high-pressure steam 36. Second Transfer Line Exchanger 37. Quenching oil fitting 43. Hydrocarbon feedstock preheater with intermediate oil 44. Hydrocarbon partial feedstock evaporator with intermediate oil 45. Hydrocarbon feed drum 46. ​​Hydrocarbon feedstock vaporizer with quenching oil 47. Hydrocarbon feed superheater with quench oil 48. Hydrocarbon feed evaporator by condensing refrigerant 49. Hydrocarbon Feed Superheater with Refrigerant 50.Primary fractionator 51. Primary fractionator cleaning section 52. Primary fractionator intermediate oil section 53. Primary fractionator gasoline reflux section 54.Quenching oil cooling circuit 55.Quenching oil circuit cooler 56.Intermediate oil cooling circuit 57. Intermediate oil circuit cooler 60. Quenching Water Tower 61. Quench Tower Bottom Section 62. Quench Tower Top Section 63. Gasoline / water separator 64. Quenching water bottom cooling circuit 65. Quench water bottom circuit cooler 66.Quenching water top cooling circuit 67.Quench water top circuit cooler 70. Sour Water Stripper 80. Dilution steam drum 81. Dilution steam generator using MP steam 82. Dilution steam generator using quenching oil 83. Dilution steam superheater outside the furnace 84. Dilution steam superheater in furnace convection section 85. Electric boiler 86. Dilution vapor generator using condensed refrigerant 87. Diluted steam superheater using refrigerant 90.Feed-Effluent Exchanger 91. Electric pyrolysis reactor 101.Demin water refill 102. Strip Steam 103. Deaerator Vent 104. Boiler feedwater 105. Saturated High-Pressure Steam 106. Steam drum blowdown 107. Superheated high-pressure steam 108. Medium-pressure steam 109. Medium Pressure Condensate 110. How to condense steam in a vacuum 111. Vacuum condensate 112. Combined Condensate 120. Deaerator 121. Boiler feedwater preheater 122. High-pressure steam drum 123. High-pressure steam superheater 124. High-pressure to intermediate-pressure back-pressure steam turbine 125. Steam Turbine Medium Pressure Condensation to Vacuum 126. Condensing Steam Turbine Surface Condenser 150.Saturator 151.Saturator water heating circuit 152. Quenching water saturator water circuit heater 153. Saturator water circuit heater during quenching oil load 154. Saturated gas feed compressor 170.Low-pressure refrigerant drum 171.Low-pressure refrigerant evaporator 172. Low-pressure to medium-pressure refrigerant compressor 173. Medium-pressure refrigerant drum 174. Medium-pressure refrigerant vaporizer 175.High-pressure refrigerant economizer 176. Medium to high pressure refrigerant compressor 177. High-pressure refrigerant desuperheater 178. High-pressure refrigerant condenser 179. High-pressure condensing refrigerant drum 180. Liquid refrigerant pressure reducing valve to medium pressure 181. Liquid refrigerant pressure reducing valve to low pressure 182. High-Pressure Refrigerant Economizer 183. Medium-pressure to high-pressure refrigerant compressor 184. High Pressure to High Pressure-High Pressure Refrigerant Compressor 185. High-Pressure Refrigerant Desuperheater 186. High-Pressure Refrigerant Condenser 187. High-pressure condensing refrigerant drum 190. Saturated Medium-Pressure Refrigerant Liquid 191.Flushing low pressure refrigerant 192.Low-pressure saturated refrigerant vapor 193. Medium-pressure slightly superheated refrigerant vapor 194. Medium-pressure saturated refrigerant vapor 195a. Medium pressure slightly superheated refrigerant vapor 195b. Medium-pressure saturated refrigerant vapor 196. Medium-pressure superheated refrigerant vapor 197. High-pressure superheated refrigerant vapor 198. High-pressure desuperheated refrigerant vapor 199. Condensed high-pressure refrigerant liquid 200. Saturated high-pressure refrigerant liquid 201. High-pressure superheated refrigerant vapor 202. High-pressure superheated refrigerant vapor 203. High-pressure-high-pressure desuperheated refrigerant vapor 204. Condensed high-pressure refrigerant liquid 205. Saturated High-Pressure Refrigerant Liquid 1000. Combustion decomposition furnace 1001. Electric Cracking Furnace Section 1010. High-pressure refrigeration circuit branch 1011. High-pressure-high-pressure refrigeration circuit branch

Claims

1. 1. An ethylene plant comprising an electrically driven pyrolysis reactor (91), the electrically driven pyrolysis reactor (91) comprising a feed inlet for a hydrocarbon feedstock-diluent mixture and an outlet for a pyrolysis reactor effluent comprising ethylene, the ethylene plant further comprising a heat exchanger (90) configured to transfer heat from the pyrolysis reactor effluent to a feed for the pyrolysis reactor, the heat exchanger (90) comprising a feed inlet and a feed outlet upstream of the pyrolysis reactor, and further comprising a pyrolysis reactor effluent inlet and a pyrolysis reactor effluent outlet, a feed passage exists between the feed outlet of the heat exchanger and the feed inlet of the pyrolysis reactor, and a feed passage exists between the reactor effluent outlet of the pyrolysis reactor and the pyrolysis reactor effluent outlet of the heat exchanger. and a cooling section located downstream of the pyrolysis reactor effluent outlet of the heat exchanger (90), the cooling section comprising a cooling system (60) selected from the group consisting of a quench water cooling system configured to further cool the reactor effluent with quench water and an air cooler configured to further cool the reactor effluent with air, and the cooling section comprising a quench oil cooling system (51) upstream of the quench water cooling system or the air cooler, the quench oil cooling system (51) configured to further cool the reactor effluent with quench oil.

2. 2. The ethylene plant of claim 1, wherein the plant comprises a humidifier (150) upstream of the feed inlet of the heat exchanger (90), the humidifier configured to humidify the hydrocarbon feedstock, thereby providing a hydrocarbon-diluent mixture, and optionally, the plant comprises a compressor configured to compress the humidified hydrocarbon feed, the compressor being in a humidified hydrocarbon feed passage between an outlet for the humidified hydrocarbon feed of the humidifier (150) and the feed inlet of the heat exchanger (90) configured to transfer heat from cracked gases from the thermal cracking reactor to the feed for the thermal cracking reactor.

3. the plant further comprises a cooling section configured to further cool the reactor effluent produced in the pyrolysis reactor to near ambient conditions without the production of high pressure steam, the cooling section being downstream of the pyrolysis reactor effluent outlet of the heat exchanger (90); the cooling section comprising a cooling system (60) selected from the group of a quench water cooling system configured to further cool the reactor effluent with quench water, and an air cooler configured to further cool the reactor effluent with air; the cooling section comprises a quench oil cooling system (51) upstream of the quench water cooling system or air cooler, the quench oil cooling system (51) being configured to further cool the reactor effluent with quench oil; the plant further comprising a heat exchanger (153) configured to transfer heat from the quench oil to water for humidifying the hydrocarbon feedstock in the humidifier (150), the heat exchanger comprising a quench oil passage and a water passage; the quench oil passage has a quench oil inlet connected to a quench oil outlet of the quench oil cooling system (51) via a passage configured to transfer quench oil from the quench oil cooling system (51) to the heat exchanger (153), and a quench oil outlet connected to the quench oil inlet of the quench oil cooling system (51) via a quench oil recycle passage; 3. The ethylene plant of claim 2, wherein the water passage of the heat exchanger has an inlet for water heated in the heat exchanger and an outlet for water connected to a water inlet of the humidifier.

4. 2. The ethylene plant of claim 1, wherein the plant comprises a dilution steam generator comprising a heat pump system configured to generate dilution steam, optionally the heat pump system having a plurality of heat sources, a plurality of sinks, or both; and further optionally, the plant comprises a heat exchanger (30, 43) for preheating the hydrocarbon feedstock upstream of the feed inlet of the heat exchanger (90) upstream of the pyrolysis reactor (91), the heat exchanger configured to receive heat from one or more of quench water, quench oil, and intermediate oil used to cool a pyrolysis reactor effluent.

5. 5. The ethylene plant of claim 4, comprising a hydrocarbon feed evaporator (46) configured to receive heat from a quench oil used in a quench oil cooling system (51) for the evaporation of the hydrocarbon feed, the quench oil cooling system being configured to further cool a pyrolysis reactor effluent with quench oil or configured to receive heat of condensation from a vapor refrigerant (48) of the heat pump for the evaporation of the hydrocarbon feed.

6. 6. The ethylene plant of claim 5, wherein the hydrocarbon feed vaporizer (44) is configured to receive at least a portion of the heat for the vaporization of the hydrocarbon feed from intermediate oil used in a quench oil cooling system (52), the intermediate oil cooling system being configured to further cool a pyrolysis reactor effluent with intermediate oil.

7. 10. The ethylene plant of claim 1, wherein the plant comprises an electrical power connection configured to supply electricity to the electrically powered pyrolysis reactor, the electrical power connection being a connection to an electrical power system for generating electrical power from renewable resources.

8. A process for producing a pyrolysis reactor effluent comprising ethylene from a hydrocarbon feed using an ethylene plant according to any one of claims 1 to 7, comprising feeding a hydrocarbon feedstock-steam mixture to an electrically powered pyrolysis reactor (91) and cracking the hydrocarbon feedstock in the presence of steam in the electrically powered pyrolysis reactor (91) of the ethylene plant to produce the pyrolysis reactor effluent comprising ethylene; 1. A process comprising: feeding the pyrolysis reactor effluent to a heat exchanger (90) configured to transfer heat from the pyrolysis reactor effluent to the hydrocarbon feedstock-vapor mixture prior to the cracking of the hydrocarbon feedstock; and transferring heat from the pyrolysis reactor effluent to the hydrocarbon feedstock-vapor mixture in the heat exchanger (90), thereby cooling the pyrolysis reactor effluent to a temperature of less than 500°C at a pyrolysis reactor effluent outlet of the heat exchanger (90).

9. 9. The process of claim 8, wherein a gaseous hydrocarbon feedstock is used as the hydrocarbon feed, and wherein said gaseous hydrocarbon feedstock is humidified in a humidifier (150) upstream of said feed inlet of said heat exchanger (90), thereby providing a hydrocarbon-diluent mixture.

10. 9. The process of claim 8, wherein a liquid hydrocarbon feedstock is used as the hydrocarbon feed, the ethylene plant comprising a refrigeration section comprising a quench water cooling system (60) with a quench water cooling circuit (65) and a primary fractionator (50), the primary fractionator comprising a quench oil cooling system (51) with a quench oil cooling circuit (55) and an intermediate oil section (52) with an intermediate oil cooling circuit (57), the refrigeration circuit being used to preheat and vaporize the liquid hydrocarbon feedstock, mix the vaporized hydrocarbon feedstock with dilution steam and feed the resulting mixture to the heat exchanger (90).

11. 9. The process of claim 8, wherein a mixture of a liquid feedstock and a gaseous hydrocarbon feedstock is used as the hydrocarbon feed.

12. feeding the hydrocarbon-vapor mixture to the heat exchanger (90) configured to transfer heat from the pyrolysis reactor effluent to the feed for the pyrolysis reactor at a temperature above the water dew point of the hydrocarbon-vapor mixture; using waste heat from the pyrolysis reactor effluent in the heat exchanger (90) to heat the hydrocarbon-vapor mixture to a suitable inlet temperature for the electrically powered pyrolysis reactor (91); and feeding the heated hydrocarbon-vapor mixture from the heat exchanger (90) to the electrically heated pyrolysis reactor (91), wherein the pyrolysis reactor further heats the heated hydrocarbon-vapor mixture to a pyrolysis reaction temperature, the pyrolysis reactor providing heat of reaction for conversion of the hydrocarbon feed to the cracked products, thereby providing the cracked products; and optionally wherein the inlet temperature of the electrically heated pyrolysis reactor (91) is in the range of 650°C to 730°C for gaseous hydrocarbon feedstocks and in the range of 570°C to 650°C for liquid hydrocarbon feedstocks.

13. 9. The process of claim 8, wherein the ethylene plant further comprises a refrigeration circuit, and wherein heat from the refrigeration circuit is used for at least one purpose selected from generating dilution steam, preheating a feedstock, and vaporizing a liquid feedstock.

Images