Method and System for Directly Cracking Crude Oil to Prepare Olefin

Abstract

A method for cracking crude oil includes delivering the crude oil to a first tube group of a convection section of a cracking furnace for preheating and then performing vaporization to obtain a first gas phase and a first liquid phase; performing high-pressure extraction on the first liquid phase to obtain a non-asphalt oil and an asphalt; and mixing the first gas phase and the non-asphalt oil with water vapor respectively, or mixing the first gas phase with the non-asphalt oil prior to mixing with water vapor, then delivering the same to a second tube group of the convection section of the cracking furnace for heating, followed by delivering same to a radiation section of the cracking furnace for cracking to obtain a cracked product, and separating the cracked product to obtain low-carbon olefins.

Claims

1. Method for cracking crude oil, comprising the following steps: step 1. delivering the crude oil to a first tube group of a convection section of a cracking furnace for preheating, and then performing vaporization to obtain a first gas phase and a first liquid phase; step 2. performing high-pressure extraction on the first liquid phase to obtain a non-asphalt oil and an asphalt; step 3. mixing the first gas phase and the non-asphalt oil with water vapor respectively, or mixing the first gas phase with the non-asphalt oil prior to mixing with water vapor, then delivering the same to a second tube group of the convection section of the cracking furnace for heating to crossover temperature, followed by delivering the same to a radiation section of the cracking furnace for cracking to obtain a cracked product, and separating the cracked product to obtain low-carbon olefins.

2. The method according to claim 1, characterized in that in step 1, the vaporization is at least one of stripping, flash evaporation and cyclone separation, and cyclone separation is preferably used for the vaporization; and/or in step 2, the high-pressure extraction includes an extraction treatment, an optional sedimentation separation treatment and a solvent recovery treatment; preferably, the high-pressure extraction includes a supercritical extraction.

3. The method according to claim 1, characterized in that in step 2, the first liquid phase is subjected to the high-pressure extraction to obtain an extracted oil, a sedimented oil and the asphalt, and in step 3, the first gas phase and the extracted oil are mixed with the water vapor respectively, or the first gas phase is mixed with the extracted oil prior to being mixed with the water vapor, followed by delivery of the same to the second tube group of the convection section of the cracking furnace for heating to the crossover temperature, followed by delivery to the radiation section of the cracking furnace for cracking to obtain the cracked product, and separation of the cracked product to obtain the low-carbon olefins.

4. The method according to claim 3, characterized in that step 3 comprises the following substeps: step 3.1 mixing the first gas phase with the water vapor and then delivering the same to a first tube row of the second tube group in the convection section of the cracking furnace for heating to the crossover temperature, followed by delivery to a first radiation section of the cracking furnace for a first cracking to obtain a first cracked product; step 3.2 mixing the extracted oil with the water vapor and then delivering the same to a second tube row of the second tube group in the convection section of the cracking furnace for heating to the crossover temperature, followed by delivery to a second radiation section of the cracking furnace for a second cracking to obtain a second cracked product; step 3.3 separating the first cracked product and the second cracked product respectively or after mixing them, to obtain low-carbon olefins.

5. The method according to claim 1, characterized in that in step 1, an outflow temperature of the crude oil after preheating is 120-350° C., preferably 120-315° C., more preferably 150-300° C., and/or a liquid content in the first gas phase is lower than 10 g/m.sup.3, preferably lower than 200 mg/m.sup.3.

6. The method according to claim 3, characterized in that in step 1, the vaporization is at least one of stripping, flash evaporation and cyclone separation, and cyclone separation is preferably used for the vaporization; and/or in step 2, the high-pressure extraction includes the extraction treatment, the sedimentation separation treatment and the solvent recovery treatment, which are preferably carried out in an extraction column, a sedimentation column and a solvent recovery column, respectively; preferably, the extraction treatment is carried out in the presence of a solvent, preferably the solvent is a low-carbon hydrocarbon, more preferably, the low-carbon hydrocarbon is at least one selected from the group consisting of propane, butane, pentane, propylene and butene preferably, the high-pressure extraction includes a supercritical extraction.

7. The method according to claim 6, characterized in that the high-pressure extraction is carried out in a supercritical state, and comprises the following steps: step (I) subjecting the first liquid phase and the solvent to the extraction treatment to extract a first light phase component and the asphalt, wherein the first light phase component includes a non-asphalt portion and the solvent, and discharging the asphalt externally; preferably, in step (I), a mass ratio of the solvent to the first liquid phase is (0.1-20):1, preferably (1-10):1; step (II) subjecting the first light component to a temperature increasing treatment and then to the sedimentation separation treatment to obtain a second light phase component and the sedimented oil, wherein the second light phase component includes the solvent and the extracted oil, and discharging the sedimented oil; step (III) subjecting the second light component to the temperature increasing treatment and then to the solvent recovery treatment to obtain a recovered solvent and the extracted oil.

8. The method according to claim 7, characterized in that pressures of the extraction treatment, the sedimentation separation treatment and the solvent recovery treatment are independently 1-10 MPa, preferably 3-6 MPa; and/or a temperature of the extraction treatment is 50-200° C., preferably 80-160° C.; and/or a temperature of the sedimentation separation treatment is 1-30° C. higher, preferably 3-8° C. higher than that of the extraction treatment; and/or a temperature of the solvent recovery treatment is 1-30° C. higher, preferably 5-20° C. higher than that of the sedimentation separation treatment.

9. The method according to claim 4, characterized in that the crossover temperature in step 3.1 is 500-750° C., preferably 540-700° C.; and/or an outlet temperature of the first radiation section in step 3.1 is 780-950° C., preferably 800-900° C.; and/or a residence time of the first cracking in step 3.1 is 0.05-1 s, preferably 0.1-0.7 s; and/or a water-to-oil ratio of the first cracking in step 3.1 is (0.1-2):1, preferably (0.4-1.5):1.

10. The method according to claim 4, characterized in that the crossover temperature in step 3.2 is 520-760° C., preferably 550-710° C.; and/or an outlet temperature of the second radiation section in step 3.2 is 750-950° C., preferably 760-900° C.; and/or a residence time of the second cracking in step 3.2 is 0.05-1 s, preferably 0.1-0.7 s; and/or a water-to-oil ratio of the second cracking in step 3.2 is (0.1-2):1, preferably (0.4-1.5):1.

11. System for cracking crude oil, for carrying out the method according to claim 1, the system including a cracking furnace, a vaporization unit and a high-pressure extraction unit, wherein the cracking furnace includes a convection section and a radiation section arranged in sequence along a fluid direction, the high-pressure extraction unit includes an extraction unit, an optional sedimentation separation unit and a solvent recovery unit connected in sequence; preferably, the extraction unit, the sedimentation separation unit and the solvent recovery unit are all provided thereon with a light phase outlet and a heavy phase outlet, and the vaporization unit is provided thereon with a first gas phase outlet and a first liquid phase outlet.

12. The system according to claim 11, characterized in that the extraction unit is provided thereon with a solvent inlet and a first liquid phase inlet, the first liquid phase inlet is connected to the first liquid phase outlet of the vaporization unit, and the solvent inlet is connected to the light phase outlet of the solvent recovery unit; and/or the high-pressure extraction unit includes a sedimentation separation unit, and the light phase outlet of the extraction unit is connected to a material inlet of the sedimentation separation unit; and/or the light phase outlet of the sedimentation separation unit is connected to a material inlet of the solvent recovery unit; and/or the heavy phase outlet of the solvent recovery unit and the first gas phase outlet of the vaporization unit are connected respectively or after being combined, to a material inlet of the convection section of the cracking furnace.

13. System for cracking crude oil, for carrying out the method according to claim 3, the system including a cracking furnace, a vaporization unit and a high-pressure extraction unit, wherein the cracking furnace includes a convection section and a radiation section arranged in sequence along a fluid direction, the high-pressure extraction unit includes an extraction unit, a sedimentation separation unit and a solvent recovery unit connected in sequence; preferably, the extraction unit, the sedimentation separation unit and the solvent recovery unit are all provided thereon with a light phase outlet and a heavy phase outlet, and the vaporization unit is provided thereon with a first gas phase outlet and a first liquid phase outlet.

14. The system according to claim 13, characterized in that the extraction unit is provided thereon with a solvent inlet and a first liquid phase inlet, the first liquid phase inlet is connected to the first liquid phase outlet of the vaporization unit, and the solvent inlet is connected to the light phase outlet of the solvent recovery unit; and/or the high-pressure extraction unit includes a sedimentation separation unit, and the light phase outlet of the extraction unit is connected to a material inlet of the sedimentation separation unit; and/or the light phase outlet of the sedimentation separation unit is connected to a material inlet of the solvent recovery unit; and/or the heavy phase outlet of the solvent recovery unit and the first gas phase outlet of the vaporization unit are connected respectively or after being combined, to a material inlet of the convection section of the cracking furnace.

15. The method according to claim 3, characterized in that in step 1, the vaporization is at least one of stripping, flash evaporation and cyclone separation, and cyclone separation is preferably used for the vaporization; and/or in step 2, the high-pressure extraction includes an extraction treatment, a sedimentation separation treatment and a solvent recovery treatment; preferably, the high-pressure extraction includes a supercritical extraction.

16. The method according to claim 3, characterized in that in step 1, an outflow temperature of the crude oil after preheating is 120-350° C., preferably 120-315° C., more preferably 150-300° C., and/or a liquid content in the first gas phase is lower than 10 g/m.sup.3, preferably lower than 200 mg/m.sup.3.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0095] FIG. 1 shows a schematic structural diagram of the system of the present invention.

[0096] FIG. 2 shows a schematic structural diagram of the system of the present invention.

[0097] FIG. 3 shows a schematic structural diagram of the system adopted in Example 5.

[0098] In FIG. 1, FIG. 2 and FIG. 3 are present: 1—a cracking furnace, 2—a first tube group of a convection section, 3—a first radiation section, 4—a vaporization unit, 5—a high-pressure extraction unit, 6—an extraction unit, 7—a sedimentation separation unit, 8—a solvent recovery unit; 9—a cracked product separation unit; 10—a second tube group of the convection section; 11—a second radiation section.

[0099] In FIG. 1, crude oil is delivered to the first tube group 2 of the convection section of the cracking furnace 1 for preheating, and thereafter separated by the vaporization unit 4 to form a first gas phase and a first liquid phase; the first gas phase is delivered to the first tube row of the second tube group 10 in the convection section of the cracking furnace 1 for heating to the crossover temperature and then passed into the first radiation section 3 for a first cracking to obtain a first cracked product; the first liquid phase is delivered to the high-pressure extraction unit 5, wherein the first liquid phase is sequentially processed by the extraction unit 6, optionally the sedimentation separation unit 7 and the solvent recovery unit 8, and at the same time, a solvent is introduced to the high-pressure extraction unit 5. When a sedimentation separation treatment is not required, the first liquid phase is sequentially processed by the extraction unit 6 and the solvent recovery unit 8, but not by the sedimentation separation unit 7. An asphalt is discharged externally from the extraction unit 6, and from the solvent recovery unit 8, a gas phase solvent is withdrawn and recycled back to the extraction unit 5, and a non-asphalt oil is withdrawn and delivered to the second tube row of the second tube group 10 in the convection section of the cracking furnace 1 for heating to the crossover temperature, and then passed into the second radiation section 11 for the second cracking to obtain a second cracked product. The first cracked product and the second cracked product are processed by the cracked product separation unit 9 to obtain low-carbon olefins. When a sedimentation separation treatment is required, the first liquid phase is processed by the sedimentation separation unit 7, as shown in FIG. 2 below for details.

[0100] In FIG. 2, crude oil is delivered to the first tube group 2 of the convection section of the cracking furnace 1 for preheating, and thereafter separated by the vaporization unit 4 to form a first gas phase and a first liquid phase; the first gas phase is delivered to the first tube row of the second tube group 10 in the convection section of the cracking furnace 1 for heating to the crossover temperature and then passed into the first radiation section 3 for a first cracking to obtain a first cracked product; the first liquid phase is delivered to the high-pressure extraction unit 5, wherein the first liquid phase is sequentially processed by the extraction unit 6, the sedimentation separation unit 7 and the solvent recovery unit 8, and at the same time, a solvent is introduced to the high-pressure extraction unit 5. An asphalt is discharged externally from the extraction unit 6, a sedimented oil is discharged externally from the sedimentation separation unit 7, and from the solvent recovery unit 8, a gas phase solvent is withdrawn and recycled back to the extraction unit 5, and an extracted oil is withdrawn and delivered to the second tube row of the second tube group 10 in the convection section of the cracking furnace 1 for heating to the crossover temperature, and then passed into the second radiation section 11 for a second cracking to obtain a second cracked product. The first cracked product and the second cracked product are processed by the cracked product separation unit 9 to obtain low-carbon olefins.

[0101] In FIG. 3, crude oil is delivered to the first tube group 2 of the convection section of the cracking furnace 1 for preheating, and thereafter separated by the vaporization unit 4 to form a first gas phase and a first liquid phase; the first gas phase is delivered to the second tube group 10 in the convection section of the cracking furnace 1; the first liquid phase is delivered to the high-pressure extraction unit 5, wherein the first liquid phase is sequentially processed by the extraction unit 6, the sedimentation separation unit 7 and the solvent recovery unit 8, and at the same time, a solvent is introduced to the high-pressure extraction unit 5. An asphalt is discharged externally from the extraction unit 6, a sedimented oil is discharged from the sedimentation separation unit 7, and from the solvent recovery unit 8, a gas phase solvent is withdrawn and recycled back to the extraction unit 5, and an extracted oil is withdrawn and delivered to the second tube group 10 in the convection section of the cracking furnace 1. The first gas phase and the extracted oil are cracked in the first radiation section 3 of the cracking furnace 1 (herein the cracking furnace 1 comprises the first radiation section 3 only) to obtain a cracked product, which is processed by the cracked product separation unit 9 to obtain low-carbon olefins.

EXAMPLES

[0102] The present invention will be specifically described below in combination with specific examples. It is necessary to point out that the following examples are only used to further illustrate the present invention, and should not be construed as limitations on the protection scope of the present invention. Some non-essential improvements and adjustments made by a person skilled in the art to the present invention according to the contents of the invention still belong to the protection scope of the present invention.

[0103] In addition, it should be noted that various specific technical features described in the following specific examples may be combined in any suitable manner under the circumstance that there is no contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations.

[0104] The cracking furnace used in Examples 1-4 of the present invention is a double-radiation section cracking furnace (a double-hearth cracking furnace), specifically a CBL-VII model cracking furnace (purchased from Sinopec Group Corporation). The cracking furnace used in Example 5 of the present invention and Comparative Example is a single-radiation section cracking furnace (a single-hearth cracking furnace), specifically a CBL-III model cracking furnace (purchased from Sinopec Group Corporation).

[0105] The crude oil used in the following examples and comparative example has a relative density of 0.8724 (20° C.), a colloid content of 8.8 wt %, and an asphaltene content of 0.2 wt %, and distillation range analysis shown in Table 1, as measured according to the ASTM D5307 method.

TABLE-US-00001 TABLE 1 Distillate mass fraction/% Temperature/° C. Initial boiling point 69 10 192 20 272 30 337 40 393 50 446 60 508 70 595 75 653 80 — 90 — Final boiling point —

Example 1

[0106] The example was carried out by using the system shown in FIG. 2, wherein a guide vane type cyclone separator with internal members was used as the vaporization unit, the extraction unit 6 was an extraction column, the sedimentation separation unit 7 was a sedimentation column, and the solvent recovery unit 8 was a solvent recovery column.

[0107] (1) Dehydrated and desalted crude oil was preheated to 288° C. in the convection section 2 of the cracking furnace 1 to become a preheated crude oil with a pressure of 0.12 MPa. The preheated crude oil was delivered to the cyclone separator for vaporization to obtain a first gas phase and a first liquid phase, wherein a liquid content in the first gas phase was 270 mg/m.sup.3, a content of colloids in the first liquid phase was 11.3 wt %, and a content of asphaltenes in the first liquid phase was 0.26 wt %.

[0108] (2) The first liquid phase was delivered to the upper part of the extraction column, a solvent n-butane was passed into the lower part of the extraction column, a mass ratio of the solvent to the first liquid phase was 4:1, a pressure of the extraction column was 4 MPa, and a temperature of the extraction column was 160° C. A non-asphalt portion in the first liquid phase was extracted with the solvent and withdrawn from the top of the extraction column, and an asphalt was discharged from the bottom of the column. The solvent and the non-asphalt portion withdrawn from the top of the extraction column were subjected to temperature increase to 165° C. and then passed into the sedimentation column, the solvent and an extracted oil were withdrawn from the top of the sedimentation column, and a sedimented oil was withdrawn from the bottom of the sedimentation column. The solvent and the extracted oil withdrawn from the top of the sedimentation column were subjected to temperature increase to 180° C. and passed into the solvent recovery column, where the solvent and the extracted oil were separated, the solvent was withdrawn from the top of the column and then subjected to temperature decrease to 160° C. for recycling, and the extracted oil was withdrawn from the bottom of the column. No colloids and asphaltenes were detected in the extracted oil (by an analysis method of SY/T 7550-2000).

[0109] (3) After the first gas phase was mixed with water vapor (water-to-oil ratio of 0.7), the mixture was delivered to the first tube row of the second tube group in the convection section of the cracking furnace, heated to the crossover temperature (600° C.), and then directly delivered to the first radiation section for a first cracking to obtain a first cracked product. Operating parameters of the first radiation section 3 were a furnace tube outlet temperature of 810° C. and a residence time of 0.22 s.

[0110] (4) After the extracted oil was mixed with water vapor (water-to-oil ratio of 0.75), the mixture was delivered to the second tube row of the second tube group in the convection section of the cracking furnace, heated to the crossover temperature (575° C.), and then directly delivered to the second radiation section for a second cracking to obtain a second cracked product. Operating parameters of the second radiation section 11 were a furnace tube outlet temperature of 770° C. and a residence time of 0.21 s.

[0111] (5) The first cracked product and the second cracked product were mixed and then passed through a quenching unit and a separation unit for separating a cracked product (using a sequential separation process of LUMMUS) to be separated to obtain low-carbon olefins.

[0112] The cracked gas was separated to obtain low-carbon olefins, with the yield of ethylene being 25.07 wt %, the yield of propylene being 13.79 wt %, the yield of 1,3-butadiene being 4.66 wt %, and the yield of triene being 43.52 wt %. The operating cycle was 50 days.

Example 2

[0113] The example was carried out by using the system shown in FIG. 2, wherein a guide vane type cyclone separator with internal members was used as the vaporization unit, the extraction unit 6 was an extraction column, the sedimentation separation unit 7 was a sedimentation column, and the solvent recovery unit 8 was a solvent recovery column.

[0114] (1) Dehydrated and desalted crude oil was preheated to 230° C. in the convection section 2 of the cracking furnace 1 to become a preheated crude oil with a pressure of 0.13 MPa. The preheated crude oil was delivered to the cyclone separator for vaporization to obtain a first gas phase and a first liquid phase, wherein a liquid content in the first gas phase was 150 mg/m.sup.3, a content of colloids in the first liquid phase was 10.2 wt %, and a content of asphaltenes in the first liquid phase was 0.33 wt %.

[0115] (2) The first liquid phase was delivered to the upper part of the extraction column of the supercritical extraction unit, a solvent mixed C4 (n-butane and iso-butane of 50% for each) was passed into the lower part of the extraction column, a mass ratio of the solvent to the first liquid phase was 3:1, a pressure of the extraction column was 4 MPa, a temperature of the extraction column was 150° C. A non-asphalt portion in the first liquid phase was extracted with the solvent and withdrawn from the top of the extraction column, an asphalt was discharged from the bottom of the column. The solvent and the non-asphalt portion withdrawn from the top of the extraction column were subjected to temperature increase to 162° C. and then passed into the sedimentation column, the solvent and an extracted oil were withdrawn from the top of the sedimentation column, and a sedimented oil was withdrawn from the bottom of the sedimentation column. The solvent and the extracted oil withdrawn from the top of the sedimentation column were subjected to temperature increase to 180° C. and passed into the solvent recovery column, where the solvent and the extracted oil were separated, the solvent was withdrawn from the top of the column and then subjected to temperature decrease to 150° C. for recycling, and the extracted oil was withdrawn from the bottom of the column. No colloids and asphaltenes were detected in the extracted oil (by an analysis method of SY/T 7550-2000).

[0116] (3) After the first gas phase was mixed with water vapor (water-to-oil ratio of 0.65), the mixture was delivered to the first tube row of the second tube group in the convection section of the cracking furnace, heated to the crossover temperature (610° C.), and then directly delivered to the first radiation section for a first cracking to obtain a first cracked product. Operating parameters of the first radiation section 3 were a furnace tube outlet temperature of 815° C. and a residence time of 0.25 s.

[0117] (4) After the extracted oil was mixed with water vapor (water-to-oil ratio of 0.65), the mixture was delivered to the second tube row of the second tube group in the convection section of the cracking furnace, heated to the crossover temperature (585° C.), and then directly delivered to the second radiation section for a second cracking to obtain a second cracked product. Operating parameters of the second radiation section 11 were a furnace tube outlet temperature of 785° C. and a residence time of 0.2 s.

[0118] (5) The first cracked product and the second cracked product were mixed and then passed through a quenching unit and a separation unit for separating a cracked product (using a sequential separation process of LUMMUS) to be separated to obtain low-carbon olefins.

[0119] The cracked product was separated to obtain low-carbon olefins, with the yield of ethylene being 25.31 wt %, the yield of propylene being 13.41 wt %, the yield of 1,3-butadiene being 4.73 wt %, and the yield of triene being 43.46 wt %. The operating cycle was 52 days.

Example 3

[0120] The example was carried out by using the system shown in FIG. 2, wherein a guide vane type cyclone separator with internal members was used as the vaporization unit, the extraction unit 6 was an extraction column, the sedimentation separation unit 7 was a sedimentation column, and the solvent recovery unit 8 was a solvent recovery column.

[0121] (1) Dehydrated and desalted crude oil was preheated to 315° C. in the convection section 2 of the cracking furnace 1 to become a preheated crude oil with a pressure of 0.12 MPa. The preheated crude oil was delivered to the cyclone separator for vaporization to obtain a first gas phase and a first liquid phase, wherein a liquid content in the first gas phase was 200 mg/m.sup.3, a content of colloids in the first liquid phase was 11.9 wt %, and a content of asphaltenes in the first liquid phase was 0.27 wt %.

[0122] (2) The first liquid phase was delivered to the upper part of the extraction column, a solvent n-butane was passed into the lower part of the extraction column, a mass ratio of the solvent to the first liquid phase was 8:1, a pressure of the extraction column was 3 MPa, and a temperature of the extraction column was 140° C. A non-asphalt portion in the first liquid phase was extracted with the solvent and withdrawn from the top of the extraction column, and an asphalt was discharged from the bottom of the column. The solvent and the non-asphalt portion withdrawn from the top of the extraction column were subjected to temperature increase to 148° C. and then passed into the sedimentation column, the solvent and an extracted oil were withdrawn from the top of the sedimentation column, and a sedimented oil was withdrawn from the bottom of the sedimentation column. The solvent and the extracted oil withdrawn from the top of the sedimentation column were subjected to temperature increase to 180° C. and passed into the solvent recovery column, where the solvent and the extracted oil were separated, the solvent was withdrawn from the top of the column and then subjected to temperature decrease to 140° C. for recycling, and the extracted oil was withdrawn from the bottom of the column. No colloids and asphaltenes were detected in the extracted oil (by an analysis method of SY/T 7550-2000).

[0123] (3) After the first gas phase was mixed with water vapor (water-to-oil ratio of 0.80), the mixture was delivered to the first tube row of the second tube group in the convection section of the cracking furnace, heated to the crossover temperature (600° C.), and then directly delivered to the first radiation section for a first cracking to obtain a first cracked product. Operating parameters of the first radiation section 3 were a furnace tube outlet temperature of 800° C. and a residence time of 0.28 s.

[0124] (4) After the extracted oil was mixed with water vapor (water-to-oil ratio of 1), the mixture was delivered to the second tube row of the second tube group in the convection section of the cracking furnace, heated to the crossover temperature (570° C.), and then directly delivered to the second radiation section for a second cracking to obtain a second cracked product. Operating parameters of the second radiation section 11 were a furnace tube outlet temperature of 765° C. and a residence time of 0.15 s.

[0125] (5) The first cracked product and the second cracked product were mixed and then passed through a quenching unit and a separation unit for separating a cracked product (using a sequential separation process of LUMMUS) to be separated to obtain low-carbon olefins.

[0126] The cracked gas was separated to obtain low-carbon olefins, with the yield of ethylene being 22.85 wt %, the yield of propylene being 12.57 wt %, the yield of 1,3-butadiene being 4.27 wt %, and the yield of triene being 39.69 wt %. The operating cycle was 48 days.

Example 4

[0127] The example was carried out by using the system shown in FIG. 2, wherein a guide vane type cyclone separator with internal members was used as the vaporization unit, the extraction unit 6 was an extraction column, the sedimentation separation unit 7 was a sedimentation column, and the solvent recovery unit 8 was a solvent recovery column.

[0128] (1) Dehydrated and desalted crude oil was preheated to 200° C. in the convection section 2 of the cracking furnace 1 to become a preheated crude oil with a pressure of 0.12 MPa. The preheated crude oil was delivered to the cyclone separator for vaporization to obtain a first gas phase and a first liquid phase, wherein a liquid content in the first gas phase was 100 mg/m.sup.3, a content of colloids in the first liquid phase was 9.9 wt %, and a content of asphaltenes in the first liquid phase was 0.22 wt %.

[0129] (2) The first liquid phase was delivered to the upper part of the extraction column, a solvent n-butane was passed into the lower part of the extraction column, a mass ratio of the solvent to the first liquid phase was 10:1, a pressure of the extraction column was 18 MPa, and a temperature of the extraction column was 160° C. A non-asphalt portion in the first liquid phase was extracted with the solvent and withdrawn from the top of the extraction column, and an asphalt was discharged from the bottom of the column. The solvent and the non-asphalt portion withdrawn from the top of the extraction column were subjected to temperature increase to 170° C. and then passed into the sedimentation column, the solvent and an extracted oil were withdrawn from the top of the sedimentation column, and a sedimented oil was withdrawn from the bottom of the sedimentation column. The solvent and extracted oil withdrawn from the top of the sedimentation column were subjected to temperature increase to 180° C. and passed into the solvent recovery column, where the solvent and the extracted oil were separated, the solvent was withdrawn from the top of the column and then subjected to temperature decrease to 160° C. for recycling, and the extracted oil was withdrawn from the bottom of the column. No colloids and asphaltenes were detected in the extracted oil (by an analysis method of SY/T 7550-2000).

[0130] (3) After the first gas phase was mixed with water vapor (water-to-oil ratio of 0.6), the mixture was delivered to the first tube row of the second tube group in the convection section of the cracking furnace, heated to the crossover temperature (620° C.), and then directly delivered to the first radiation section for a first cracking to obtain a first cracked product. Operating parameters of the first radiation section 3 were a furnace tube outlet temperature of 820° C. and a residence time of 0.2 s.

[0131] (4) After the extracted oil was mixed with water vapor (water-to-oil ratio of 0.8), the mixture was delivered to the second tube row of the second tube group in the convection section of the cracking furnace, heated to the crossover temperature (590° C.), and then directly delivered to the second radiation section for a second cracking to obtain a second cracked product. Operating parameters of the second radiation section 11 were a furnace tube outlet temperature of 790° C. and a residence time of 0.21 s.

[0132] (5) The first cracked product and the second cracked product were mixed and then passed through a quenching unit and a separation unit for separating a cracked product (using a sequential separation process of LUMMUS) to be separated to obtain low-carbon olefins.

[0133] The cracked gas was separated to obtain low-carbon olefins, with the yield of ethylene being 23.51 wt %, the yield of propylene being 14.58 wt %, the yield of 1,3-butadiene being 4.35 wt %, and the yield of triene being 42.44 wt %. The operating cycle was 49 days.

Example 5

[0134] The example was carried out by using the system shown in FIG. 3, wherein a cyclone separator was used as the vaporization unit, and the cracking furnace comprised the first radiation section 3 only.

[0135] Steps (1) to (2) of Example 1 were repeated, and the difference lied in that the first gas phase and the extracted oil were cracked together, as described in details in the following step (3):

[0136] (3) The first gas phase and the extracted oil were mixed with water vapor (water-to-oil ratio of 0.7), respectively, then the mixtures were delivered to the convection section of the cracking furnace, heated to the crossover temperature (585° C.), and then directly delivered to the first radiation section 3 for cracking to obtain a cracked product. Operating parameters of the first radiation section 3 were a furnace tube outlet temperature of 780° C. and a residence time of 0.22s. The cracked product was passed through a quenching unit and a separation unit for separating a cracked product (using a sequential separation process of LUMMUS) to be separated to obtain low-carbon olefins.

[0137] The cracked gas was separated to obtain low-carbon olefins, wherein the product yield was slightly lower than that of Example 1, with the yield of ethylene being 24.25 wt %, the yield of propylene being 12.61 wt %, the yield of 1,3-butadiene being 4.51 wt %, and the yield of triene being 41.37wt %, while the operating cycle was shorter than that of Example 1, and was only 42 days.

Comparative Example 1

[0138] In this comparative example, a conventional cracking furnace was used for cracking.

[0139] Dehydrated and desalted crude oil was directly delivered to the cracking furnace, passed through the convection section to be heated to the crossover temperature (580° C.), and then directly passed into the radiation section for cracking. The cracking conditions were a water-to-oil ratio of 0.75, an outlet temperature of the radiation section of 790° C., an outlet pressure of the radiation section of 0.11 MPa, and a residence time of 0.22 s. The sequential separation process of LUMMUS was used for the cracked gas. Analysis of the steam cracking reaction product showed that the yield of ethylene was 21.49 wt %, the yield of propylene was 13.29 wt %, the yield of 1,3-butadiene was 4.03 wt %, and the yield of triene was 38.81 wt %. The operating cycle was 5 days.

[0140] From the results of the Examples and Comparative Example 1, it can be seen that using a traditional cracking apparatus, the crude oil was used to maintain only a 5-day operating cycle, while the present invention can ensure that the crude oil was normally used in the cracking apparatus, and use of the vaporization unit and the high-pressure extraction unit to treat the crude oil can effectively reduce the occurrence of coking and achieve an operating cycle of 42 days or more. Further, under the same process conditions, the examples effectively improved the yield of the low-carbon olefins as compared with the comparative example.