HYBRID ETHYLENE CRACKING FURNACE

Abstract

A cracking furnace for cracking a hydrocarbon feed, the furnace including a firebox having a single radiant zone including, a first plurality of cracking coils each having a first shape arranged within the firebox. The radiant zone includes a second plurality of cracking coils each having a second shape arranged within the radiant zone. A burner section positioned below the first plurality cracking coils and below the second plurality of cracking coils. A convection section is positioned on top of the firebox configured to recover residual heat from the firebox.

Claims

1. A cracking furnace for cracking hydrocarbon feeds, the furnace comprising: a firebox including having a single radiant zone : a first plurality of cracking coils each having a first shape arranged within the firebox; a second plurality of cracking coils each having a second shape arranged within the firebox; and a burner section positioned below the first plurality cracking coils and below the second plurality of cracking coils or on side walls of the first plurality of cracking coils and the second plurality of cracking coils; and a convection section positioned on top of the firebox configured to recover residual heat from the firebox.

2. The cracking furnace of claim 1, wherein each of the coils of the first plurality of cracking coils are U-shaped coils.

3. The cracking furnace of claim 1, wherein each of the coils of the second plurality of cracking coils are M-shaped coils or W-shaped coils.

4. The cracking furnace of claim 1, wherein the burner section includes a first plurality of burners and a second plurality of burners.

5. The cracking furnace of claim 4, wherein the first plurality of burners are grouped under the first plurality of cracking coils or on side walls of the first plurality of cracking coils.

6. The cracking furnace of claim 4, wherein the second plurality of burners are grouped under the second plurality of cracking coils or on side walls of the second plurality of cracking coils.

7. The cracking furnace of claim 1, wherein each of the first plurality of coils defines a first coil inlet into the radiant zone and a first coil outlet out of the radiant zone with a first flow path defined therebetween, and wherein each of the second plurality of coils defines a second coil inlet into the radiant zone and a second coil outlet out of the radiant zone with a second flow path defined therebetween.

8. A method for cracking at least two hydrocarbon feeds comprising: feeding a first hydrocarbon feedstock into a radiant zone of a firebox; feeding a second hydrocarbon feedstock into the firebox while feeding the first hydrocarbon feedstock to the radiant zone; heating each of the feedstocks within a radiant section of the firebox to convert each of the hydrocarbon feedstocks to a unique thermally cracked product; collecting the thermally cracked products from the radiant section; cooling the thermally cracked products; and recovering at least two olefins from the thermally cracked products.

9. The method of claim 8, wherein a firebox temperature for each of the feedstocks is the same within the firebox.

10. The method of claim 8, wherein the heating temperature is dependent on outlet temperature of the first hydrocarbon feedstock.

11. The method of claim 8, wherein an outlet temperature of the second hydrocarbon feedstock is dependent on a feed rate of the second hydrocarbon feed.

12. The method of claim 8, wherein the first hydrocarbon feedstock is a liquid.

13. The method of claim 12, wherein the first hydrocarbon feedstock is vacuum gas oil or naphtha.

14. The method of claim 8, wherein the second hydrocarbon feedstock is a vapor.

15. The method of claim 14, wherein the second hydrocarbon feedstock is butane, propane or ethane.

16. The method of claim 8, wherein ethylene and propylene are recovered.

17. The method of claim 8, wherein the first hydrocarbon feedstock follows a first path within the firebox, and the second hydrocarbon feedstock follows a second path within the firebox.

18. The method of claim 17, wherein the first path is defined through a plurality of U-shaped cracking coils, and wherein the second path is defined through a plurality of M-shaped cracking coils or W-shaped cracking coils.

19. The method of claim 17, wherein the first path is shorter than the second path.

20. The method of claim 8, further comprising pre-heating the first hydrocarbon feedstock and the second hydrocarbon feedstock with residual heat from the firebox within a convection section.

21. The method of claim 8, further comprising removing a plurality of cracking coils from a second firebox and coupling the plurality of coils within the firebox in order to feed the second hydrocarbon feedstock through.

22. A method of overhauling a cracking furnace comprising: operating a liquid feed furnace including a first plurality of cracking coils having a first shape; installing a second plurality of cracking coils having a second shape;

23. A cracking furnace for cracking hydrocarbon feeds, the furnace comprising: a first plurality of cracking coils each having a first shape arranged within the first firebox; a second plurality of cracking coils each having a second shape arranged within the first firebox; and a third plurality of cracking coils each having a third shape arranged within a second firebox.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] So that those skilled in the art to which the subject invention appertains will readily understand how to make and use the devices and methods of the subject invention without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein:

[0014] FIG. 1 is a perspective view of a cracking furnace according to the disclosure;

[0015] FIG. 2 is a perspective view of an W-shaped coil of the cracking furnace of FIG. 1; and

[0016] FIG. 3 is a perspective view of u U-shaped coil of the cracking furnace of FIG. 1.

DETAILED DESCRIPTION

[0017] Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject invention. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of a cracking furnace in accordance with the invention is shown in FIG. 1 and is designated generally by reference character 100. Other embodiments of the cracking furnace in accordance with the disclosure, or aspects thereof, are provided in FIGS. 2-3, as will be described. The methods and systems of the invention can be used to process multiple types of feedstocks simultaneously.

[0018] FIG. 1 shows a cracking furnace 100 for cracking various hydrocarbon feedstocks to produce ethylene, propylene and other petrochemical products. The furnace includes a firebox 102 configured to simultaneously accept various hydrocarbon feeds. The hydrocarbon feeds differ in chemical make-up and physical state. The cracking furnace 100 also includes a convection section 104 positioned on top of the firebox 102. The convection section 104 above the firebox 102 is positioned in order to recover residual heat from the firebox and preheat the hydrocarbon feeds coming into the firebox 102.

[0019] The firebox 102 includes first plurality of cracking coils 106. Each of the cracking coils 106 of the first plurality can be configured to accept a liquid feedstock. Each of the cracking coils of the first plurality 106 have a U-shape. Each of the first plurality of coils 106 defines a first coil 106a inlet and a first coil outlet 106b with a first flow path defined therebetween. An inlet leg of the U coils can include the 25Cr35Ni alloy and the outlet leg of U coils can include the 35Cr 45Ni alloy. The cracking coils of the first plurality 106 are grouped together. There are a variety of feedstocks that can be utilized in this process, including a heavy liquid feed, such as vacuum gas oil or a light liquid feed, such as naphtha.

[0020] The furnace can be a hybrid product of an ethylene plant revamp. The furnace can be primarily designed to process fresh liquid feed in the first plurality of cracking coils. M or W shaped coils from a recycle furnace are added, and provide the ability to process gas feeds. Thus, the firebox 102 further includes a second plurality of cracking coils 108. Each of the cracking coils 108 of the second plurality are configured to accept a vapor hydrocarbon feedstock, such as butane, propane and ethane. Each of the second plurality of coils 108 defines a second coil inlet 108a and a second coil outlet 108b with a second flow path defined therebetween, Each of the cracking coils of the second plurality 108 have either an M-shape or a W-shape. An inlet leg of the M or W coils can include the 25Cr35Ni alloy and the outlet leg of W coils and of M coils can include the 35Cr 45Ni alloy. The cracking coils of the second plurality 108 are grouped together separately from the first plurality of cracking coils 106. Cracking coils 108 can have larger diameters than cracking coils 106. Further shown in FIG. 1, a burner section 110 is positioned below the cracking coils 106/108. The burner section 110 includes a first plurality of burners 110a and a second plurality of burners 110b, wherein the first plurality of burners 110a are grouped under the first plurality of cracking coils 106 and the second plurality of burners 110b are grouped under the second plurality of cracking coils 108. Typically individual burner firing duty is the same for all burners in a firebox. Different groups of burners firing rate depends on the quantity of burners in the group. In the present configuration, one firebox burner firing only has one set of fuel gas flow control valve. Hydrocarbon feed cracking severity in the firebox is controlled by its coil outlet temperature. When two types of feeds are cracked in the same firebox, to control cracking severity of the feedstocks, one feed is selected as the primary feed. The primary feed coil outlet temperature sets the individual burner firing duty. The other feed, the secondary feed, in the same firebox has the same individual burner firing duty. The secondary feed cracking severity, coil outlet temperature, has to be adjusted by the feed rate. Higher feed rate will give lower coil outlet temperature and vice versa. On the other hand, fuel gas flow rate control can be divided into different groups (zones) in the same firebox for different feeds. Then the individual burner firing rate can be different. Based on the need of different feed cracking severity, coil outlet temperature, different individual burner firing rates can be set for different groups, and then there is no need to adjust feed rate. The additional operation freedom comes from more fuel gas flow rate control valves for one firebox. However, the first approach, single fuel gas control per firebox, is the preferred typical arrangement.

[0021] The cracking furnace 100 described above is used to crack a hydrocarbon feed by feeding a first hydrocarbon feedstock into the firebox 102, feeding a second hydrocarbon feedstock into the firebox 102 while feeding the first hydrocarbon feedstock to the firebox 102, heating each of the feedstocks within a radiant section 102a of the firebox to convert each of the hydrocarbon feedstocks to a unique thermally cracked product, such as ethylene and propylene. The firing duty of the individual burner can be the same within the firebox 102. The heating temperature for both of the feedstocks is based on the outlet temperature of the first hydrocarbon feedstock. The outlet temperature of the second hydrocarbon feedstock is controlled by a feed rate of the second hydrocarbon feed. Even though both hydrocarbon feeds are cracked in the same firebox, coil outlet temperature of the primary feed can be used to control burner firing duty and the feed rate of the secondary feed can be used to control the coil outlet temperature of the secondary feed. Thus, the target cracking severity levels of both feedstocks can be achieved.

[0022] The method includes collecting the thermally cracked products from the radiant section, cooling the thermally cracked products, recovering the at least two unique olefins from the thermally cracked products. The cracking effluents needs to be quenched rapidly to preserve the olefin yields after leaving the firebox 102. The heat recovered from the cracking effluent is used to preheat hydrocarbon feed and dilution steam and generate high-pressure steam within the convection section 104. The ability to process different feedstock greatly increases operation flexibility in cracking processes. Aspects of the disclosure are also beneficial in plant revamp situations.

[0023] The methods and systems of the present disclosure, as described above and shown in the drawings, provide for a hybrid coil ethylene cracking furnace with superior properties including increased reliability and adaptability. While the apparatus and methods of the subject disclosure have been showing and described with reference to embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the spirit and score of the subject disclosure.