Method for preheating naphtha in naphtha catalytic cracking processes

Abstract

A method of converting naphtha is disclosed. The method includes heating the naphtha in stages in different heating units. The naphtha is vaporized in the first heating unit. And the vaporized naphtha undergoes the largest temperature change of the process in the second heating unit. A third heating unit can be a part of the reactor. The reactor includes a catalyst which is contacted with the pre-heated naphtha to convert it to C.sub.2 to C.sub.4 olefins.

Claims

1. A method of converting naphtha, the method comprising: evaporating the naphtha in a first heating unit, wherein the naphtha has an initial boiling point that is less than 250° C.; flowing the evaporated naphtha, at a temperature in a range of 250° C. to 300° C., from the first heating unit to a second heating unit; heating the evaporated naphtha in the second heating unit to a temperature of 550° C. to 700° C.; flowing the heated evaporated naphtha from the second heating unit to a reactor; and providing reaction conditions in the reactor sufficient to convert at least some of the heated evaporated naphtha to C.sub.2 to C.sub.4 olefins; wherein providing reaction conditions in the reactor comprises contacting the heated evaporated naphtha with a catalyst; and wherein some of the heated evaporated naphtha is converted to benzene, toluene, and xylene.

2. The method of claim 1, wherein the naphtha in the first heating unit is heated to a temperature in a range of 250° C. to 300° C. at a pressure of 5 bar to 20 bar.

3. The method of claim 2, wherein the pressure ranges from 10 bar to 20 bar.

4. The method of claim 1, wherein the reactor comprises a third heating unit.

5. The method of claim 1, wherein the naphtha is completely evaporated.

6. The method of claim 1, wherein the heated evaporated naphtha is flowed into the reactor at a temperature of 550° C. to 700° C. and at a pressure of 0.5 bar to 5 bar.

7. The method of claim 1, further comprising the steps of: flowing effluent of the first heating unit to a knockout drum; and separating the effluent of the first heating unit into a liquid stream and a stream comprising the evaporated naphtha.

8. The method of claim 1, wherein the first heating unit is an economizer, which comprises heating coils.

9. The method of claim 1, wherein the second unit is a fire box, which comprises a fired furnace.

10. The method of claim 1, wherein the reactor is a reactor box and the heated evaporated naphtha is flowed from the second heating unit to the reactor through a flexible joint, and wherein reaction conditions in reactor box are sufficient to convert the heated evaporated naphtha to the C2 to C4 olefins and also to benzene, toluene, and xylene.

11. A method of evaluating conversion of naphtha, the method comprising: evaporating the naphtha in a first heating unit, wherein the naphtha has an initial boiling point that is less than 250° C., wherein the first heating unit has an internal volume for receiving fluid in a range of 40 cm.sup.3 to 50 cm.sup.3; flowing the evaporated naphtha, at a temperature in a range of 250° C. to 300° C., from the first heating unit to a second heating unit, wherein the second heating unit has an internal volume for receiving fluid in a range of 40 cm.sup.3 to 50 cm.sub.3; heating the evaporated naphtha in the second heating unit to a temperature of 550° C. to 700° C.; flowing the heated evaporated naphtha from the second heating unit to a reactor, wherein the reactor has an internal volume for receiving fluid in a range of 55 cm.sup.3 to 65 cm.sup.3; providing reaction conditions in the reactor sufficient to convert at least some of the heated evaporated naphtha to C.sub.2 to C.sub.4 olefins; and determining a rate of conversion of the naphtha to the C.sub.2 to C.sub.4 olefins; wherein providing reaction conditions in the reactor comprises contacting the heated evaporated naphtha with a catalyst; and wherein some of the heated evaporated naphtha is converted to benzene, toluene, and xylene.

12. The method of claim 11, wherein the evaporated naphtha is flowed from the first heating unit through a flexible joint to the second heating unit.

13. The method of claim 11, wherein the naphtha in the first heating unit is heated to a temperature in a range of 250° C. to 300° C. at a pressure of 5 bar to 10 bar.

14. The method of claim 11, wherein the reactor comprises a third heating unit.

15. The method of claim 11, wherein the heated evaporated naphtha is flowed into the reactor at a temperature of 550° C. to 700° C.

16. The method of claim 11, wherein the first heating unit is an evaporator, which comprises an electrical furnace.

17. The method of claim 11, wherein the second heating unit comprises an electrical furnace.

18. The method of claim 14, wherein the third heating unit comprises an electrical furnace.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a more complete understanding, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1 shows a system for converting naphtha, according to embodiments of the invention;

(3) FIG. 2 shows a method for converting naphtha, according to embodiments of the invention;

(4) FIG. 3 shows a system for evaluating the conversion of naphtha, according to embodiments of the invention; and

(5) FIG. 4 shows a method for evaluating the conversion of naphtha, according to embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(6) Naphtha is a hydrocarbon fraction with a boiling range of 20° C. to 200° C. and with molecules of 4 to 12+ carbon atoms. A method has been discovered for converting naphtha to olefins that includes pre-heating the naphtha in stages in a plurality of heating units such that the evaporation of the naphtha and the largest temperature increase of the naphtha takes place in different heating units. Preheating in stages in a plurality of heating units can reduce coke formation and reduce maintenance costs associated with the naphtha catalytic process.

(7) FIG. 1 shows system 10 for converting naphtha, according to embodiments of the invention. FIG. 2 shows method 20 for converting naphtha, according to embodiments of the invention. Method 20 may be implemented by using system 10.

(8) Method 20, as implemented by system 10, may begin at block 200, which involves flowing naphtha feed 100 to first heating unit 101. In embodiments of the invention, first heating unit 101 comprises an economizer, which includes heating coils (heat exchanger). According to embodiments of the invention, naphtha feed 100 is a mixture of hydrocarbons that has an initial boiling point that is less than 250° C. In embodiments of the invention, first heating unit 101 comprises a heat exchanger in the top section of a fired heater “economizer.”

(9) At block 201, in embodiments of the invention, first heating unit 101 vaporizes, partially or completely, naphtha feed 100 by heating the naphtha to a temperature in a range of 250° C. to 300° C. at a pressure of 1 bar to 20 bar, so as to form effluent 106, which comprises evaporated naphtha (and liquid naphtha when there is partial vaporization). According to embodiments of the invention, a liquid film is maintained in heating unit 101, e.g., a liquid film on the economizer's coils. This has the advantage of reducing coke formation inside the coils.

(10) Method 20 may continue at block 202, which involves flowing effluent 106, at a temperature in a range of 250° C. to 300° C., from first heating unit 101 to second heating unit 102. In embodiments of invention, second heating unit 102 comprises a fire box which has a fired furnace.

(11) In embodiments of the invention, effluent 106 is flowed to knockout drum 104 at block 202a. And at block 202b, knockout drum 104 separates effluent 106 into liquid stream 107 and evaporated naphtha 108. In this way, subsequent high temperature heating units processes only gases. This has the advantage of extending the run length of the furnace and reducing the operation and maintenance cost by minimizing coke formation. At block 203, method 20 involves heating effluent 106 or evaporated naphtha 108 to a temperature of 550° C. to 700° C., in second heating unit 102 to form heated evaporated naphtha 109. According to embodiments of the invention, from knockout drum 104, vapors will flow to second heating unit 102 (e.g., a fire box (convection zone)) of the fired heater 105 to gain the biggest temperature increment of the pre-heating process. In embodiments of the invention, the heated evaporated naphtha is flowed into reactor 110 at a temperature of 550° C. to 700° C. and at a pressure of 0.5 bar to 5 bar.

(12) According to embodiments of the invention, method 20 includes, at block 204, flowing heated evaporated naphtha 109 from second heating unit 102 to naphtha catalytic cracking reactor 110. In embodiments of the invention, heated evaporated naphtha 109 passes through third heating unit 103 (e.g., superheater coils (conduction section)), where heated evaporated naphtha 109 may be heated further, at block 205, if necessary, to achieve the required feed temperature before going to naphtha catalytic cracking reactor 110.

(13) In embodiments of the invention, naphtha catalytic cracking reactor 110 comprises third heating unit 103, such as an electric furnace with superheater coils. According to embodiments of the invention, in naphtha catalytic cracking reactor 110, method 20 involves, at block 205, providing reaction conditions in naphtha catalytic cracking reactor 110 sufficient to convert at least some of the heated evaporated naphtha 109 to C.sub.2 to C.sub.4 olefins, benzene, toluene, and xylene. In embodiments of the invention, providing reaction conditions at block 206, in naphtha catalytic cracking reactor 110, includes contacting heated evaporated naphtha 109 with a catalyst.

(14) FIG. 3 shows system 30 for evaluating the conversion of naphtha, according to embodiments of the invention. System 30 may be a laboratory unit or a pilot scale unit. FIG. 4 shows method 40 for evaluating the conversion of naphtha, according to embodiments of the invention. Method 40 may be implemented by using system 30.

(15) Method 40, as implemented by system 30, may begin at block 400, which involves flowing naphtha feed 300 to first heating unit 301. The capacity (volume) of first heating unit 301 is in a range 40 cm.sup.3 to 50 cm.sup.3. In embodiments of the invention, first heating unit 301 comprises an evaporator, which comprises an electrical furnace.

(16) According to embodiments of the invention, naphtha feed 300 is a mixture of hydrocarbons that has an initial boiling point that is less than 250° C. In embodiments of the invention, first heating unit 301 comprises an evaporator. At block 401, in embodiments of the invention, first heating unit 301 vaporizes, partially or completely, naphtha feed 300 by heating the naphtha to a temperature in a range of 250° C. to 300° C. at a pressure of 1 bar to 10 bar, so as to form effluent 306, which comprises evaporated naphtha (and liquid naphtha when there is partial vaporization).

(17) Method 40 may continue at block 402, which involves flowing effluent 306, at a temperature in a range of 250° C. to 300° C., from first heating unit 301 to second heating unit 302. In embodiments of invention, second heating unit 302 comprises an electrical furnace. The capacity (volume) of second heating unit 302 is in a range 40 cm.sup.3 to 50 cm.sup.3.

(18) At block 403, method 40 involves heating effluent 306 to a temperature of 550° C. to 700° C., in second heating unit 302 to form heated evaporated naphtha 307. In some embodiments of the invention, heated evaporated naphtha 307 is flowed into reactor box 305 at a temperature of 550° C. to 700° C. and at a pressure of 0.5 bar to 5 bar. The capacity (volume) of reactor box 305 is in a range 55 cm.sup.3 to 65 cm.sup.3.

(19) According to embodiments of the invention, method 40 includes, at block 404, flowing heated evaporated naphtha 307 from second heating unit 302 through flexible joint 308 to reactor box 305. Flexible joint 308, according to embodiments of the invention, is adapted so that it is easily removable for cleaning purposes if coke or any other residue accumulates inside it. In embodiments of the invention, reactor box 305 comprises third heating unit 303, such as an electrical furnace. At block 405, third heating unit 303 is used to provide heat, if necessary, to heated evaporated naphtha 307 and thereby compensate for any heat loss that might have occurred in transit from the second heating unit to the third heating unit.

(20) According to embodiments of the invention, in reactor box 305, method 40 involves, at block 406, providing reaction conditions in reactor box 305 (at reaction section 304) sufficient to convert the heated evaporated naphtha 307 to C.sub.2 to C.sub.4 olefins, benzene, toluene, and xylene. In embodiments of the invention, providing reaction conditions at block 406, in reactor box 305, comprises contacting heated evaporated naphtha 307 with a catalyst. In embodiments of the invention, the distance between the heating units are minimized so as to avoid heat loss.

(21) At block 407, method 40, in embodiments of the invention, involves determining a rate of conversion of the naphtha to the C.sub.2 to C.sub.4 olefins. This determination may be done by various methods, for example, by calculating the average conversion of the feed components.

(22) Although embodiments of the present invention have been described with reference to blocks of FIG. 2 and FIG. 4, it should be appreciated that operation of the present invention is not limited to the particular blocks and/or the particular order of the blocks illustrated in FIG. 2 and FIG. 4. Accordingly, embodiments of the invention may provide functionality as described herein using various blocks in a sequence different than that of FIG. 2.

(23) In the context of the present invention, embodiments 1-19 are described. Embodiment 1 is a method of converting naphtha. The method includes evaporating the naphtha in a first heating unit, wherein the naphtha has an initial boiling point that is less than 250° C. and flowing the evaporated naphtha, at a temperature in a range of 250° C. to 300° C., from the first heating unit to a second heating unit. The method also includes heating the evaporated naphtha in the second heating unit to a temperature of 550° C. to 700° C., flowing the heated evaporated naphtha from the second heating unit to a reactor, and providing reaction conditions in the reactor sufficient to convert at least some of the heated evaporated naphtha to C.sub.2 to C.sub.4 olefins. Embodiment 2 is the method of embodiment 1, wherein the naphtha in the first heating unit is heated to a temperature in a range of 250° C. to 300° C. at a pressure of 1 bar to 20 bar. Embodiment 3 is the method of either of embodiments 1 and 2, wherein the reactor includes a third heating unit. Embodiment 4 is the method of any of embodiments 1 to 3, wherein providing reaction conditions in the reactor includes contacting the heated evaporated naphtha with a catalyst. Embodiment 5 is the method of any of embodiments 1 to 4, wherein some of the heated evaporated naphtha is converted to benzene, toluene, and xylene. Embodiment 6 is the method of any of embodiments 1 to 5, wherein the heated evaporated naphtha is flowed into the reactor at a temperature of 550° C. to 700° C. and at a pressure of 0.5 bar to 5 bar. Embodiment 7 is the method of any of embodiments 1 to 6 further including flowing effluent of the first heating unit to a knockout drum, and separating the effluent of the first heating unit into a liquid stream and a stream comprising the evaporated naphtha. Embodiment 8 is the method of any of embodiments 1 to 7, wherein the first heating unit is an economizer, which includes heating coils. Embodiment 9 is the method of any of embodiments 1 to 8, wherein the second unit is a fire box, which includes a fired furnace.

(24) Embodiment 10 is a method of evaluating conversion of naphtha. The method includes evaporating the naphtha in a first heating unit, wherein the naphtha has an initial boiling point that is less than 250° C., and wherein the first heating unit has an internal volume for receiving fluid in a range of 40 cm.sup.3 to 50 cm.sup.3. The method also includes flowing the evaporated naphtha, at a temperature in a range of 250° C. to 300° C., from the first heating unit to a second heating unit, wherein the second heating unit has an internal volume for receiving fluid in a range of 40 cm.sup.3 to 50 cm.sup.3. In addition, the method includes heating the evaporated naphtha in the second heating unit to a temperature of 550° C. to 700° C., flowing the heated evaporated naphtha from the second heating unit to a reactor, wherein the reactor has an internal volume for receiving fluid in a range of 55 cm.sup.3 to 65 cm.sup.3, providing reaction conditions in the reactor sufficient to convert at least some of the heated evaporated naphtha to C.sub.2 to C.sub.4 olefins, and determining a rate of conversion of the naphtha to the C.sub.2 to C.sub.4 olefins. Embodiment 11 is the method of embodiment 10, wherein the evaporated naphtha is flowed from the first heating unit through a flexible joint to the second heating unit. Embodiment 12 is the method of either of embodiments 10 and 11, wherein the naphtha in the first heating unit is heated to a temperature in a range of 250° C. to 300° C. at a pressure of 1 bar to 10 bar. Embodiment 13 is the method of any of embodiments 10 to 12, wherein the reactor includes a third heating unit. Embodiment 14 is the method of any of embodiments 10 to 13, wherein providing reaction conditions in the reactor includes contacting the heated evaporated naphtha with a catalyst. Embodiment 15 is the method of any of embodiments 10 to 14, wherein some of the heated evaporated naphtha is converted to benzene, toluene, and xylene. Embodiment 16 is the method of any of embodiments 10 to 15, wherein the heated evaporated naphtha is flowed into the reactor at a temperature of 550° C. to 700° C. Embodiment 17 is the method of any of embodiments 10 to 16, wherein the first heating unit is an evaporator, which includes an electrical furnace. Embodiment 18 is the method of any of embodiments 10 to 17, wherein the second heating unit includes an electrical furnace. Embodiment 19 is the method of any of embodiments 10 to 18, wherein the third heating unit includes an electrical furnace.

(25) Although embodiments of the present application and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the above disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.