KR20050016718A - Process for cracking hydrocarbon feed with water substitution - Google Patents

Abstract

The present invention relates to a process for treating a hydrocarbon feedstock in a furnace, the method comprising: (a) heating a hydrocarbon feedstock, (b) adding water to the heated feedstock, (c) the heating Adding dilute steam to the prepared feedstock to form a mixture, (d) heating the resulting mixture and feeding the resulting heated mixture to a furnace, wherein the water in step (b) Water in an amount of about 1 to 100% by weight based on the weight of water and dilute steam.

Description

PROCESS FOR CRACKING HYDROCARBON FEED WITH WATER SUBSTITUTION}

The present invention relates to the decomposition of hydrocarbon feedstocks using water as supplement or replacement of dilute steam.

Steam cracking has long been used to crack various hydrocarbon feedstocks into olefins. Conventional steam cracking methods employ a pyrolysis furnace having two main zones, a convection zone and a radiation zone reaction zone. The hydrocarbon feedstock typically enters the convection zone of the furnace as liquid (except for the light feedstock supplied as steam), where it is indirect contact with hot flue gas from the radiation zone, and by mixing with water vapor Typically heated and vaporized. The vaporized feedstock and water vapor mixture is then introduced into the radiation zone where decomposition takes place. The resulting product comprising olefins is from the pyrolysis furnace for further downstream treatment (eg quenching).

As a non-limiting example, in a typical pyrolysis reactor for producing ethylene from a naphtha feedstock, the hydrocarbon feedstock is fed to the convection zone of the furnace preheated in the first heat exchanger tube by indirect contact with the furnace flue gas from the radiation zone. . The dilution steam stream enters the convection zone and is superheated in the heat exchanger tube by indirect contact with the furnace flue gas from the radiation zone. The superheated dilution steam is then mixed with the hydrocarbon feedstock to reduce the hydrocarbon partial pressure in the radiation zone reaction zone to the furnace. Reducing the hydrocarbon partial pressure in the reaction zone (1) increases reactor selectivity of the desired olefinic product, such as ethylene, and (2) reduces the rate of undesired coke formation and the rate of attachment to the inner surface of the radiation zone tube. It is known in the art. The superheated water vapor is mixed with the preheated hydrocarbon feedstock to produce a steam hydrocarbon / water vapor mixture, which is further preheated to a suitable temperature to transport the mixture to the radiation zone of the furnace. The cracking reaction to produce the desired ethylene product and other by-products takes place mainly in the radiation zone of the furnace. After exiting the radiation zone, the reactor effluent is rapidly quenched in the quench system to stop the decomposition reaction.

For the purpose of well-known energy efficiency, it is desirable to recover as much heat as possible from the flue gas exiting the radiation zone and flowing through the convection zone of the furnace to the furnace flue gas outlet. Therefore, the hydrocarbon feedstock and the dilute steam are typically heated in the convection zone by indirect contact with the flue gas from the radiation zone. Other recovery facilities may also be included in the convection zone, such as boiler feed water preheaters and / or steam superheaters used to superheat high pressure steam that may be generated in the quench system of the furnace.

In some furnace designs, boiler feed water preheaters and / or high pressure steam superheat facilities may not be able to absorb heat from the flue gas stream flowing through the convection zone. In this case, the flue gas will be released from the furnace at unacceptable high temperatures (eg, 600-700 ° F. (315-370 ° C.)). This is a substantial energy inefficiency since some designs provide flue gas emission temperatures as low as, for example, 250 to 300 ° F. (120 to 150 ° C.).

In another example, it may be desirable to provide additional dilution steam to further reduce the hydrocarbon feedstock partial pressure. However, this steam will not be available at a reasonable price.

The present invention provides the advantage of providing additional dilution steam when it is not available at a reasonable price.

The present invention also provides another advantage of improving furnace energy efficiency. These and other features and advantages of the invention will be apparent from the following description and claims.

Summary of the Invention

The present invention relates to a process for treating a hydrocarbon feedstock in a furnace, the process comprising: (a) heating a hydrocarbon feedstock, (b) adding water and dilute steam to the heated feedstock to form a mixture (C) heating the mixture, (d) feeding the heated mixture from step (c) to the furnace, wherein the water in step (b) is based on water and dilute steam weight About 1 to 100% by weight. In one embodiment, the water is added at least about 3% by weight (ie, at least about 3 to 100% by weight of water) based on the weight of water and dilute steam. In another embodiment, the water is added at least about 10% by weight based on the weight of water and dilute steam. In a further embodiment, the water is added at least about 30% by weight based on the weight of water and dilute steam. According to the invention, water can be the total substitution of the dilute steam (ie no steam added). However, it is preferred that both dilute steam and water be added to the hydrocarbon feedstock.

According to a preferred embodiment, if necessary, the water can be added prior to the addition of the dilute steam.

According to another embodiment, the ratio of water to steam added to the heated feedstock varies with the variation of one or more process variables. In one preferred embodiment said process variable is a process temperature. According to this, the process temperature may be the temperature of the flue gas discharged from the furnace, the process temperature in the convection zone of the furnace, and / or the process temperature in the radiation zone (reaction zone) of the furnace.

According to a further embodiment, the water is added to the hydrocarbon feedstock in the ejector and, if necessary, dilute steam is added to the feedstock in the other ejector. In a preferred embodiment, the first and second ejectors are part of a sparger assembly that connects the first and second ejectors to a series of fluid circulation passages.

The invention also provides a method for decomposing a hydrocarbon feedstock in a furnace comprising a radiant zone comprising a burner producing radiant heat and hot flue gas, and a convection zone comprising a heat exchanger tube. Way,

(a) preheating the hydrocarbon feedstock in a heat exchanger tube in the convection zone by indirect heat exchange with the hot flue gas from the radiation zone to provide a preheated feedstock;

(b) adding water to the preheated feedstock in the first ejector and adding diluted steam to the preheated feedstock in the second ejector to form a feedstock mixture;

(c) heating the feedstock mixture in a heat exchanger tube in the convection zone by indirect heat transfer with hot flue gas from the radiation zone to form a feedstock mixture; And

(d) feeding the heated feed mixture to a radiation zone where the hydrocarbons in the heated feedstock mixture thermally decompose to form the product, wherein the water in step (b) is the weight of water and dilute steam It is added at about 1 to 100% by weight or more based on.

In a preferred embodiment, the first ejector comprises an inner perforated conduit surrounded by an outer conduit to form an annular flow space between the inner and outer conduits. Preferably, the preheated hydrocarbon flows through the annular flow space, and the water flows through the inner conduit and is injected into the preheated hydrocarbon feedstock through the opening in the inner conduit.

In another preferred embodiment, the second ejector comprises an inner perforated conduit surrounded by an outer conduit to form an annular flow space between the inner and outer conduits. Preferably, the feedstock from the first blower flows through the annular flow space, and the diluted steam flows through the inner conduit and is injected into the first feedstock mixture through the opening in the inner conduit.

In a further preferred embodiment, the first ejector and the second ejector are part of an ejector assembly in which the first ejector and the second ejector are connected by a series of fluid circulation passages.

1 shows a schematic flow diagram of a process according to the invention using a pyrolysis furnace, in particular highlighting the convection zone of the furnace. The figure also shows a control scheme for changing the ratio of water to dilution steam according to process variables, ie the temperature of the process gas for the zone of the furnace.

FIG. 2 shows a schematic diagram of a control system used to change the ratio of water to dilution steam in relation to process parameters, in particular the temperature of the flue gases exiting the furnace.

FIG. 3 shows a schematic of the same control system as in FIG. 2, but the ratio of water to dilution steam has changed in relation to the temperature of the process gas in the convection zone of the furnace.

Unless stated otherwise, all percentages, parts, ratios, etc., are by weight. Unless stated otherwise, reference to a compound or component includes the compound or component itself, and those compounds or components (such as mixtures of compounds) mixed with other compounds or components.

In addition, when amounts, concentrations, or other values or variables are listed and listed as desired upper and preferred lower values, this means that the preferred upper and preferred lower values may be any value, whether or not these ranges are disclosed separately. It is to be understood that this disclosure specifically discloses all ranges formed from pair values.

The present invention relates to a process for treating hydrocarbon feedstock in a furnace. According to one embodiment, the process comprises (a) heating the hydrocarbon feedstock, (b) adding water and dilute steam to the heated feedstock to form the mixture, (c) heating the mixture, And (d) feeding the heated mixture to the furnace, wherein the water in (b) is added at least about 1 to 100% by weight based on the weight of the water and the dilute steam.

With particular reference to FIG. 1, (1) represents a pyrolysis furnace composed of a lower radiation zone 2, an intermediate convection zone 3 and an upper flue gas discharge zone 4. In the radiation zone, the radiant combustor provides radiant heat to the hydrocarbon feedstock to form the desired product by pyrolysis of the feedstock. The combustor generates hot gases that flow upward through the convection zone 3 and then flow out of the furnace through the flue gas discharge zone 4. As shown in FIG. 1, hydrocarbon feedstock 33 is injected into the upper portion of the preheated convection zone 3. Preheating of the hydrocarbon feedstock can occur in any form known by those skilled in the art. However, heating in the upper convection section 3 of the furnace 1 is preferred in which the feedstock comprises indirect contact with the hot flue gas from the radiant zone of the furnace. This can be achieved by way of non-limiting example, by passing the feedstock through a heat exchange tube 17 located in the convection zone 3 of the furnace 1. The preheated feedstock is about 200-600 ° F. (95-315 ° C.). Preferably, the temperature of the heated feedstock is about 300-500 ° F. (150-260 ° C.), more preferably 350-500 ° F. (175-260 ° C.).

After the preheated hydrocarbon feedstock exits the convection zone (47), water (5) and dilute steam (6) are added to form a mixture. Water is added to the preheated feedstock in an amount of about 1 to 100% by weight or more based on the combined total weight of water and dilute steam. Preferably, the water is added in an amount of at least about 3% by weight (ie, about 3 to 100% by weight of water) based on the weight of water and dilute steam. More preferably, the water is in an amount of at least about 10% by weight, most preferably at least about 30% by weight, based on the weight of water and dilute steam. According to one embodiment of the present invention, 100% of water may be added to prevent the addition of dilute steam to the hydrocarbon feedstock. The sum of the water stream and the dilute steam stream provides the amount of H ₂ O in the desired total reaction zone required to achieve the desired hydrocarbon partial pressure.

As shown in FIG. 1, prior to the addition of the dilute steam, water 5 is preferably added to the preheated feedstock 47. This order of addition will reduce undesired pressure fluctuations in the process stream resulting from the mixing of hydrocarbons, water and dilute steam. Such fluctuations are commonly referred to as water hammers or steam hammers. The addition of water and dilute steam to the preheated hydrocarbon feedstock can be accomplished using any known mixing apparatus, but it is preferred to use the ejector assembly 7 as shown in this figure. Water is preferably added in the first jet 8. As shown, the first ejector 8 comprises an inner perforated conduit 9 surrounded by an outer conduit 10 to form an annular flow space 11 between the inner and outer conduits. Preferably, the preheated hydrocarbon 41 flows through the annular flow space 11. Also preferably, water 5 flows through the inner perforated conduit 9 and can be injected into the preheated hydrocarbon feedstock through the openings (perforations) seen in the inner conduit 9.

Dilution steam 6 is preferably added to the preheated hydrocarbon feedstock in the second jet 12. As shown, the second ejector 12 includes an inner perforated conduit 13 surrounded by an outer conduit 14 to form an annular flow space 15 between the inner and outer conduits. Preferably, the preheated hydrocarbon feedstock 41 to which water is added flows through the annular flow space 15. Also preferably, dilute water vapor flows through the inner perforated conduit 13 and is injected into the preheated hydrocarbon feedstock through an opening in the inner conduit.

Preferably, the first and second ejectors are, as seen, part of an ejector assembly to which the ejectors are connected in a series of fluid circulation passages. As shown in this figure, the ejectors 8 and 12 are interconnected in a series of fluid circulation passages by a fluid circulation interconnector 16.

In addition, as shown in this figure, after exiting the ejector assembly 7, the mixture (of the hydrocarbon feedstock, water and dilute steam) is fed back into the furnace 1, where the mixture is additionally convection zone 3. In the lower part of the furnace). Further heating of the hydrocarbon feedstock can occur in any form known by those skilled in the art. However, the heating preferably comprises indirect contact between the hot flue gas from the radiation zone of the furnace 1 and the feedstock of the lower convection zone 3 of the furnace 1. This can be achieved by way of non-limiting example, by passing the feedstock through a heat exchange tube 18 located in the convection zone 3 of the furnace 1. After further heating of the mixture at (18), the resulting heated mixture exits the convection zone at (19) and then flows to the radiation zone of the furnace for thermal decomposition of hydrocarbons. The heated feedstock going to the radiation zone is preferably at a temperature between 800 and 1400 ° F. (425 to 760 ° C.). Preferably, the temperature of the heated feedstock is about 1050-1350 ° F. (560-730 ° C.).

1 additionally illustrates controlling the process temperature in the radiation zone 25 using the present invention. The process temperature is input to a regulator 26 which regulates the flow rate of water through the flow meter 28 and the control valve 29. The water then enters the jet 7. If the process temperature is too high, the regulator 26 increases the flow of water 27.

The regulator 26 sends a flow rate signal to the computer control device shown schematically at 31, which determines the dilution vapor flow rate as detailed below. The flow rate of the pre-set hydrocarbon feedstock 33 is measured by the flow rate meter 34 and input to the regulator 35, which in turn signals the feed control valve 36. Regulator 35 may also send the feed rate signal to the computer control device 37, which reserve for the feed rate and the feed rate of the non-a total H ₂ O to the radiant section is determined by multiplying the total H ₂ O is set. The total H ₂ O speed signal is input to the second input of the computer device 31. Computer device 31 subtracts the flow rate of water from the total H ₂ O speed; The difference is the set point for the dilution steam regulator 38. Flow meter 39 is also input to regulator 38 and measures the dilution steam rate. As discussed above, as the flow rate of water increases, the set point input to the dilution steam regulator 38 decreases. The regulator 38 then instructs the regulating valve 40 to reduce the dilution steam rate 32 to a new set point. When the process temperature 25 is too low, the control system instructs the control valve 29 to reduce the flow rate of water and instructs the control valve 40 to increase the steam rate, while maintaining a constant total H ₂ O speed. .

Alternatively, this control scheme operates in the same way to regulate the exhaust temperature of the flue gas 42 as shown in FIG. 2 and to adjust the process temperature in the convection zone of the furnace shown in FIG. 3. In controlling the temperature of flue gas emissions, at temperatures lower than about 650 ° F. (345 ° C.), preferably at temperatures lower than about 450 ° F. (230 ° C.), more preferably at temperatures lower than about 350 ° F. (175 ° C.). It is preferable that the flue gas is discharged.

By the process according to the invention, it is possible to maintain the desired hydrocarbon partial pressure in the radiation zone reaction zone of the furnace while increasing the heat recovery demand of the convection zone due to the heat of evaporation of the water stream. Such a system lowers flue gas emission temperatures and therefore yields a more energy efficient furnace.

Similarly, the process according to the invention makes it possible to maintain the desired reaction zone hydrocarbon partial pressure in an installation where the available supply of dilution steam is limited and / or where the operating conditions of the desired furnace are insufficient.

Claims (24)

A method of treating a hydrocarbon feedstock in a furnace, the method comprising: (a) heating a hydrocarbon feedstock to provide a heated feedstock, (b) adding water and dilute steam to the heated feedstock to form a mixture (c) heating the mixture to provide a heated mixture, and (d) feeding the heated mixture from step (c) to the furnace, wherein the water in step (b) is diluted with water A method of treating a hydrocarbon feedstock, wherein the amount is added in an amount of about 1 to 100% by weight based on the weight of water vapor. The method of claim 1, Adding water in an amount of at least about 3% by weight. The method according to claim 1 or 2, Adding water in an amount of at least about 10% by weight. The method according to claim 1, 2 or 3, Adding water in an amount of at least about 30% by weight. The method according to any one of claims 1 to 4, If necessary, water before the addition of dilute steam. The method according to any one of claims 1 to 5, A method in which the ratio of water to steam added to the heated feedstock changes with the variation of one or more process variables. The method of claim 6, The furnace comprises a flue gas zone, a convection zone and a radiation zone and the process variable is temperature. The method of claim 7, wherein The process variable is the temperature of the mixture in the flue gas zone of the furnace. The method of claim 7, wherein The process variable is the gas temperature in the convection zone of the furnace. The method of claim 7, wherein Putting the resulting heated mixture into the furnace's radiation zone and the process variable is the temperature of the resulting heated mixture prior to entering the furnace's radiation zone. The method according to any one of claims 7 to 10, A method where gases exit the flue gas section of a furnace at temperatures below 345 ° C. The method according to any one of claims 7 to 11, Wherein the gas exits the flue gas zone of the furnace at temperatures below about 230 ° C. (350 ° F.). The method according to any one of claims 7 to 12, The gas exits the flue gas section of the furnace at temperatures below about 175 ° C (350 ° F). The method according to any one of claims 1 to 13, Adding water to the jet and, if necessary, adding dilute steam to the heated feedstock of the other jet. The method according to any one of claims 1 to 14, Adding water to the first jet and, if necessary, adding dilute steam to the heated feedstock of the second jet. The method of claim 15, The first ejector and the second ejector are part of an ejector assembly that connects the first ejector and the second ejector to a series of fluid circulation passages. The method according to any one of claims 1 to 16, The furnace is a steam cracking furnace. The method of claim 1, The furnace comprises a radiant section comprising a combustor for generating radiant heat and hot flue gas, and a convection section comprising a heat exchanger tube: (a) heating the hydrocarbon feedstock in the heat exchanger tube in the convection zone by indirect heat exchange with the hot flue gas in the radiation zone to provide a heated feedstock; (b) adding water to the heated feedstock of the first ejector and diluting steam to the heated feedstock of the second ejector to form a mixture; (c) heating the mixture in a heat exchanger tube in the convection zone by indirect heat transfer with hot flue gas in the radiation zone to provide a heated mixture; And (d) supplying the heated mixture to a radiation zone of a furnace that thermally decomposes the hydrocarbon water in the heated feedstock mixture to form a product. The method of claim 18, A method of adding water to a heated feedstock prior to addition of dilute steam. The method of claim 18 or 19, And the inner perforated conduit surrounded by the outer conduit to form an annular flow space between the inner conduit and the outer conduit. The method of claim 20, Wherein the heated feedstock flows through the annular flow space, and water flows through the inner conduit and is injected into the heated feedstock through perforations in the inner conduit. The method according to any one of claims 18 to 21, And the inner perforated conduit surrounded by the outer conduit such that the second ejector forms an annular flow space between the inner and outer conduits. The method according to any one of claims 18 to 22, The feedstock from the first blower flows through the annular flow space and dilution water vapor flows through the inner conduit and is injected into the feedstock mixture through a perforation in the inner conduit. The method according to any one of claims 18 to 22, Wherein the first ejector and the second ejector are part of an ejector assembly that connects the first ejector and the second ejector to a series of fluid circulation passages.