Patent Application
20130197285
1. Field of the Invention
The present invention relates to an integrated hydrotreating and steam pyrolysis process for direct processing of a crude oil to produce petrochemicals such as olefins and aromatics.
2. Description of Related Art
The lower olefins (i.e., ethylene, propylene, butylene and butadiene) and aromatics (i.e., benzene, toluene and xylene) are basic intermediates which are widely used in the petrochemical and chemical industries. Thermal cracking, or steam pyrolysis, is a major type of process for forming these materials, typically in the presence of steam, and in the absence of oxygen. Feedstocks for steam pyrolysis can include petroleum gases and distillates such as naphtha, kerosene and gas oil. The availability of these feedstocks is usually limited and requires costly and energy-intensive process steps in a crude oil refinery.
Studies have been conducted using heavy hydrocarbons as a feedstock for steam pyrolysis reactors. A major drawback in conventional heavy hydrocarbon pyrolysis operations is coke formation. For example, a steam cracking process for heavy liquid hydrocarbons is disclosed in U.S. Pat. No. 4,217,204 in which a mist of molten salt is introduced into a steam cracking reaction zone in an effort to minimize coke formation. In one example using Arabian light crude oil having a Conradson carbon residue of 3.1% by weight, the cracking apparatus was able to continue operating for 624 hours in the presence of molten salt. In a comparative example without the addition of molten salt, the steam cracking reactor became clogged and inoperable after just 5 hours because of the formation of coke in the reactor.
In addition, the yields and distributions of olefins and aromatics using heavy hydrocarbons as a feedstock for a steam pyrolysis reactor are different than those using light hydrocarbon feedstocks. Heavy hydrocarbons have a higher content of aromatics than light hydrocarbons, as indicated by a higher Bureau of Mines Correlation Index (BMCI). BMCI is a measurement of aromaticity of a feedstock and is calculated as follows:
BMCI=87552/VAPB+473.5*(sp. gr.)−456.8 (1)
where:
VAPB=Volume Average Boiling Point in degrees Rankine and
sp. gr.=specific gravity of the feedstock.
As the BMCI decreases, ethylene yields are expected to increase. Therefore, highly paraffinic or low aromatic feeds are usually preferred for steam pyrolysis to obtain higher yields of desired olefins and to avoid higher undesirable products and coke formation in the reactor coil section.
The absolute coke formation rates in a steam cracker have been reported by Cai et al., “Coke Formation in Steam Crackers for Ethylene Production,” Chem. Eng. & Proc., vol. 41, (2002), 199-214. In general, the absolute coke formation rates are in the ascending order of olefins>aromatics>paraffins, wherein olefins represent heavy olefins.
To be able to respond to the growing demand of these petrochemicals, other type of feeds which can be made available in larger quantities, such as raw crude oil, are attractive to producers. Using crude oil feeds will minimize or eliminate the likelihood of the refinery being a bottleneck in the production of these petrochemicals.
While the steam pyrolysis process is well developed and suitable for its intended purposes, the choice of feedstocks has been very limited.
The system and process herein provides a steam pyrolysis zone integrated with a hydroprocessing zone to permit direct processing of crude oil feedstocks to produce petrochemicals including olefins and aromatics.
An integrated hydrotreating and steam pyrolysis process for the direct processing of a crude oil is provided to produce olefinic and aromatic petrochemicals. Crude oil and hydrogen are charged to a hydroprocessing zone operating under conditions effective to produce a hydroprocessed effluent reduced having a reduced content of contaminants, an increased paraffinicity, reduced Bureau of Mines Correlation Index, and an increased American Petroleum Institute gravity. Hydroprocessed effluent is thermally cracked in the presence of steam to produce a mixed product stream, which is separated. Hydrogen from the mixed product stream is purified and recycled to the hydroprocessing zone, and olefins and aromatics are recovered from the separated mixed product stream.
As used herein, the term “crude oil” is to be understood to include whole crude oil from conventional sources, crude oil that has undergone some pre-treatment. The term crude oil will also be understood to include that which has been subjected to water-oil separation; and/or gas-oil separation; and/or desalting; and/or stabilization.
Other aspects, embodiments, and advantages of the process of the present invention are discussed in detail below. Moreover, it is to be understood that both the foregoing information and the following detailed description are merely illustrative examples of various aspects and embodiments, and are intended to provide an overview or framework for understanding the nature and character of the claimed features and embodiments. The accompanying drawings are illustrative and are provided to further the understanding of the various aspects and embodiments of the process of the invention.
The invention will be described in further detail below and with reference to the attached drawings where:
A process flow diagram including an integrated hydroprocessing and steam pyrolysis process and system is shown in
Selective hydroprocessing zone includes a hydroprocessing reaction zone 4 having an inlet for receiving a mixture of crude oil feed 1 and hydrogen 2 recycled from the steam pyrolysis product stream, and make-up hydrogen as necessary. Hydroprocessing reaction zone 4 further includes an outlet for discharging a hydroprocessed effluent 5.
Reactor effluents 5 from the hydroprocessing reactor(s) are cooled in a heat exchanger (not shown) and sent to a high pressure separator 6. The separator tops 7 are cleaned in an amine unit 12 and a resulting hydrogen rich gas stream 13 is passed to a recycling compressor 14 to be used as a recycle gas 15 in the hydroprocessing reactor. A bottoms stream 8 from the high pressure separator 6, which is in a substantially liquid phase, is cooled and introduced to a low pressure cold separator 9 in which it is separated into a gas stream and a liquid stream 10. Gases from low pressure cold separator includes hydrogen, H2S, NH3 and any light hydrocarbons such as C1-C4 hydrocarbons. Typically these gases are sent for further processing such as flare processing or fuel gas processing. According to certain embodiments herein, hydrogen is recovered by combining stream gas stream 11, which includes hydrogen, H2S, NH3 and any light hydrocarbons such as C1-C4 hydrocarbons, with steam cracker products 44. All or a portion of liquid stream 10 serves as the feed to the steam pyrolysis zone 30
In certain embodiments, an optional separation zone 20 (as indicated with dashed lines in
In additional embodiments separation zone 20 includes, or consists essentially of (i.e., operates in the absence of a flash zone), a cyclonic phase separation device, or other separation device based on physical or mechanical separation of vapors and liquids. One example of a vapor-liquid separation device is illustrated by, and with reference to,
Steam pyrolysis zone 30 generally comprises a convection section 32 and a pyrolysis section 34 that can operate based on steam pyrolysis unit operations known in the art, i.e., charging the thermal cracking feed to the convection section in the presence of steam. In addition, in certain optional embodiments as described herein (as indicated with dashed lines in
In one embodiment, a vapor-liquid separation device is illustrated by, and with reference to
A quenching zone 40 includes an inlet in fluid communication with the outlet of steam pyrolysis zone 30, an inlet for admitting a quenching solution 42, an outlet for discharging an intermediate quenched mixed product stream 44 and an outlet for discharging quenching solution 46.
In general, an intermediate quenched mixed product stream 44 is converted into intermediate product stream 65 and hydrogen 62, which is purified in the present process and used as recycle hydrogen stream 2 in the hydroprocessing reaction zone 4. Intermediate product stream 65 is generally fractioned into end-products and residue in separation zone 70, which can one or multiple separation units such as plural fractionation towers including de-ethanizer, de-propanizer and de-butanizer towers, for example as is known to one of ordinary skill in the art. For example, suitable apparatus are described in “Ethylene,” Ullmann's Encyclopedia of Industrial Chemistry, Volume 12, Pages 531-581, in particular
In general product separation zone 70 includes an inlet in fluid communication with the product stream 65 and plural product outlets 73-78, including an outlet 78 for discharging methane, an outlet 77 for discharging ethylene, an outlet 76 for discharging propylene, an outlet 75 for discharging butadiene, an outlet 74 for discharging mixed butylenes, and an outlet 73 for discharging pyrolysis gasoline. Additionally an outlet is provided for discharging pyrolysis fuel oil 71. Optionally, one or both of the heavy fraction 21 from flash zone 20 and the fuel oil portion 38 from vapor-liquid separation section 36 are combined with pyrolysis fuel oil 71 and can be withdrawn as a pyrolysis fuel oil blend 72, e.g., a low sulfur fuel oil blend to be further processed in an off-site refinery. Note that while six product outlets are shown, fewer or more can be provided depending, for instance, on the arrangement of separation units employed and the yield and distribution requirements.
In an embodiment of a process employing the arrangement shown in
Hydroprocessing reaction zone 4 operates under parameters effective to hydrodemetallize, hydrodearomatize, hydrodenitrogenate, hydrodesulfurize and/or hydrocrack the crude oil feedstock. In certain embodiments, hydroprocessing is carried out using the following conditions: operating temperature in the range of from 300° C. to 450° C.; operating pressure in the range of from 30 bars to 180 bars; and a liquid hour space velocity in the range of from 0.1 h−1 to 10 h−1. Notably, using crude oil as a feedstock in the hydroprocessing zone advantages are demonstrated, for instance, as compared to the same hydroprocessing unit operation employed for atmospheric residue. For instance, at a start or run temperature in the range of 370° C. to 375° C., the deactivation rate is around 1 T/month. In contrast, if residue were to be processed, the deactivation rate would be closer to about 3 T/month to 4 T/month. The treatment of atmospheric residue typically employs pressure of around 200 bars whereas the present process in which crude oil is treated can operate at a pressure as low as 100 bars. Additionally to achieve the high level of saturation required for the increase in the hydrogen content of the feed, this process can be operated at a high throughput when compared to atmospheric residue. The LHSV can be as high as 0.5 while that for atmospheric residue is typically 0.25. An unexpected finding is that the deactivation rate when processing crude oil is going in the inverse direction from that which is usually observed. Deactivation at low throughput (0.25 hr−1) is 4.2 T/month and deactivation at higher throughput (0.5 hr−1) is 2.0 T/month. With every feed which is considered in the industry, the opposite is observed. This can be attributed to the washing effect of the catalyst.
Reactor effluents 5 from the hydroprocessing zone 4 are cooled in an exchanger (not shown) and sent to a high pressure cold or hot separator 6. Separator tops 7 are cleaned in an amine unit 12 and the resulting hydrogen rich gas stream 13 is passed to a recycling compressor 14 to be used as a recycle gas 15 in the hydroprocessing reaction zone 4. Separator bottoms 8 from the high pressure separator 6, which are in a substantially liquid phase, are cooled and then introduced to a low pressure cold separator 9. Remaining gases, stream 11, including hydrogen, H2S, NH3 and any light hydrocarbons, which can include C1-C4 hydrocarbons, can be conventionally purged from the low pressure cold separator and sent for further processing, such as flare processing or fuel gas processing. In certain embodiments of the present process, hydrogen is recovered by combining stream 11 (as indicated by dashed lines) with the cracking gas, stream 44, from the steam cracker products. The bottoms 10 from the low pressure separator 9 are optionally sent to separation zone 20 or passed directly to steam pyrolysis zone 30.
The hydroprocessed effluent 10 contains a reduced content of contaminants (i.e., metals, sulfur and nitrogen), an increased paraffinicity, reduced BMCI, and an increased American Petroleum Institute (API) gravity. The hydroprocessed effluent 10 is optionally conveyed to separation zone 20 to remove heavy ends as bottoms stream 21 and provide the remaining lighter cut as pyrolysis feed 22. In certain embodiments in which separation zone 20 is not used hydrotreated effluent 10 serves as the pyrolysis feedstream without separation of bottoms.
The pyrolysis feedstream, e.g. having an initial boiling point corresponding to that of the feed and a final boiling point in the range of about 370° C. to about 600° C., is conveyed to the inlet of a convection section 32 in the presence of an effective amount of steam, e.g., admitted via a steam inlet. In the convection section 32 the mixture is heated to a predetermined temperature, e.g., using one or more waste heat streams or other suitable heating arrangement. The heated mixture of the pyrolysis feedstream and additional steam is passed to the pyrolysis section 34 to produce a mixed product stream 39. In certain embodiments the heated mixture of from section 32 is passed through a vapor-liquid separation section 36 in which a portion 38 is rejected as a fuel oil component suitable for blending with pyrolysis fuel oil 71.
The steam pyrolysis zone 30 operates under parameters effective to crack fraction 22 (or effluent 10 in embodiments in which separation zone 20 is not employed) into the desired products including ethylene, propylene, butadiene, mixed butenes and pyrolysis gasoline. In certain embodiments, steam cracking in the pyrolysis section is carried out using the following conditions: a temperature in the range of from 400° C. to 900° C. in the convection section and in the pyrolysis section; a steam-to-hydrocarbon ratio in the convection section in the range of from 0.3:1 to 2:1; and a residence time in the convection section and in the pyrolysis section in the range of from 0.05 seconds to 2 seconds.
In certain embodiments, the vapor-liquid separation section 36 includes one or a plurality of vapor liquid separation devices 80 as shown in
As shown in
The pre-rotational element 88 defines a curvilinear flow path, and is characterized by constant, decreasing or increasing cross-section from the inlet cross-section S1 to the outlet cross-section S2. The ratio between outlet cross-section from controlled pre-rotational element (S2) and the inlet cross-section (S1) is in certain embodiments in the range of 0.7≦S2/S1≦1.4.
The rotational velocity of the mixture is dependent on the radius of curvature (R1) of the center-line of the pre-rotational element 88 where the center-line is defined as a curvilinear line joining all the center points of successive cross-sectional surfaces of the pre-rotational element 88. In certain embodiments the radius of curvature (R1) is in the range of 2≦R1/D1≦6 with opening angle in the range of 150°≦αR1≦250°.
The cross-sectional shape at the inlet section S1, although depicted as generally square, can be a rectangle, a rounded rectangle, a circle, an oval, or other rectilinear, curvilinear or a combination of the aforementioned shapes. In certain embodiments, the shape of the cross-section along the curvilinear path of the pre-rotational element 38 through which the fluid passes progressively changes, for instance, from a generally square shape to a rectangular shape. The progressively changing cross-section of element 88 into a rectangular shape advantageously maximizes the opening area, thus allowing the gas to separate from the liquid mixture at an early stage and to attain a uniform velocity profile and minimize shear stresses in the fluid flow.
The fluid flow from the controlled pre-rotational element 88 from cross-section (S2) passes section (S3) through the connection element to the controlled cyclonic vertical section 90. The connection element includes an opening region that is open and connected to, or integral with, an inlet in the controlled cyclonic vertical section 90. The fluid flow enters the controlled cyclonic vertical section 90 at a high rotational velocity to generate the cyclonic effect. The ratio between connection element outlet cross-section (S3) and inlet cross-section (S2) in certain embodiments is in the range of 2≦S3/S1≦5.
The mixture at a high rotational velocity enters the cyclonic vertical section 90. Kinetic energy is decreased and the vapor separates from the liquid under the cyclonic effect. Cyclones form in the upper level 90a and the lower level 90b of the cyclonic vertical section 90. In the upper level 90a, the mixture is characterized by a high concentration of vapor, while in the lower level 90b the mixture is characterized by a high concentration of liquid.
In certain embodiments, the internal diameter D2 of the cyclonic vertical section 90 is within the range of 2≦D2/D1≦5 and can be constant along its height, the length (LU) of the upper portion 90a is in the range of 1.2≦LU/D2≦3, and the length (LL) of the lower portion 90b is in the range of 2≦LL/D2≦5.
The end of the cyclonic vertical section 90 proximate vapor outlet 84 is connected to a partially open release riser and connected to the pyrolysis section of the steam pyrolysis unit. The diameter (DV) of the partially open release is in certain embodiments in the range of 0.05≦DV/D2≦0.4.
Accordingly, in certain embodiments, and depending on the properties of the incoming mixture, a large volume fraction of the vapor therein exits device 80 from the outlet 84 through the partially open release pipe with a diameter DV. The liquid phase (e.g., residue) with a low or non-existent vapor concentration exits through a bottom portion of the cyclonic vertical section 90 having a cross-sectional area S4, and is collected in the liquid collector and settling pipe 92.
The connection area between the cyclonic vertical section 90 and the liquid collector and settling pipe 92 has an angle in certain embodiment of 90°. In certain embodiments the internal diameter of the liquid collector and settling pipe 92 is in the range of 2≦D3/D1≦4 and is constant across the pipe length, and the length (LH) of the liquid collector and settling pipe 92 is in the range of 1.2≦LH/D3≦5. The liquid with low vapor volume fraction is removed from the apparatus through pipe 86 having a diameter of DL, which in certain embodiments is in the range of 0.05≦DL/D3≦0.4 and located at the bottom or proximate the bottom of the settling pipe
While the various members are described separately and with separate portions, it will be understood by one of ordinary skill in the art that apparatus 80 can be formed as a monolithic structure, e.g., it can be cast or molded, or it can be assembled from separate parts, e.g., by welding or otherwise attaching separate components together which may or may not correspond precisely to the members and portions described herein.
It will be appreciated that although various dimensions are set forth as diameters, these values can also be equivalent effective diameters in embodiments in which the components parts are not cylindrical.
Mixed product stream 39 is passed to the inlet of quenching zone 40 with a quenching solution 42 (e.g., water and/or pyrolysis fuel oil) introduced via a separate inlet to produce an intermediate quenched mixed product stream 44 having a reduced temperature, e.g., of about 300° C., and spent quenching solution 46 is discharged. The gas mixture effluent 39 from the cracker is typically a mixture of hydrogen, methane, hydrocarbons, carbon dioxide and hydrogen sulfide. After cooling with water or oil quench, mixture 44 is compressed in a multi-stage compressor zone 51, typically in 4-6 stages to produce a compressed gas mixture 52. The compressed gas mixture 52 is treated in a caustic treatment unit 53 to produce a gas mixture 54 depleted of hydrogen sulfide and carbon dioxide. The gas mixture 54 is further compressed in a compressor zone 55, and the resulting cracked gas 56 typically undergoes a cryogenic treatment in unit 57 to be dehydrated, and is further dried by use of molecular sieves.
The cold cracked gas stream 58 from unit 57 is passed to a de-methanizer tower 59, from which an overhead stream 60 is produced containing hydrogen and methane from the cracked gas stream. The bottoms stream 65 from de-methanizer tower 59 is then sent for further processing in product separation zone 70, comprising fractionation towers including de-ethanizer, de-propanizer and de-butanizer towers. Process configurations with a different sequence of de-methanizer, de-ethanizer, de-propanizer and de-butanizer can also be employed.
According to the processes herein, after separation from methane at the de-methanizer tower 59 and hydrogen recovery in unit 61, hydrogen 62 having a purity of typically 80-95 vol % is obtained. Recovery methods in unit 61 include cryogenic recovery (e.g., at a temperature of about −157° C.). Hydrogen stream 62 is then passed to a hydrogen purification unit 64, such as a pressure swing adsorption (PSA) unit to obtain a hydrogen stream 2 having a purity of 99.9%+, or a membrane separation units to obtain a hydrogen stream 2 with a purity of about 95%. The purified hydrogen stream 2 is then recycled back to serve as a major portion of the requisite hydrogen for the hydroprocessing zone. In addition, a minor proportion can be utilized for the hydrogenation reactions of acetylene, methylacetylene and propadienes (not shown). In addition, according to the processes herein, methane stream 63 can optionally be recycled to the steam cracker to be used as fuel for burners and/or heaters.
The bottoms stream 65 from de-methanizer tower 59 is conveyed to the inlet of product separation zone 70 to be separated into methane, ethylene, propylene, butadiene, mixed butylenes and pyrolysis gasoline discharged via outlets 78, 77, 76, 75, 74 and 73, respectively. Pyrolysis gasoline generally includes C5-C9 hydrocarbons, and benzene, toluene and xylenes can be extracted from this cut. Optionally, one or both of the unvaporized heavy liquid fraction 21 from flash zone 20 and the rejected portion 38 from vapor-liquid separation section 36 are combined with pyrolysis fuel oil 71 (e.g., materials boiling at a temperature higher than the boiling point of the lowest boiling C10 compound, known as a “C10+” stream) and the mixed stream can be withdrawn as a pyrolysis fuel oil blend 72, e.g., a low sulfur fuel oil blend to be further processed in an off-site refinery.
In certain embodiments, selective hydroprocessing or hydrotreating processes can increase the paraffin content (or decrease the BMCI) of a feedstock by saturation followed by mild hydrocracking of aromatics, especially polyaromatics. When hydrotreating a crude oil, contaminants such as metals, sulfur and nitrogen can be removed by passing the feedstock through a series of layered catalysts that perform the catalytic functions of demetallization, desulfurization and/or denitrogenation.
In one embodiment, the sequence of catalysts to perform hydrodemetallization (HDM) and hydrodesulfurization (HDS) is as follows:
A comparative example was conducted as shown in Tables 1 and 2 below. Atmospheric residue was used as a feedstock to a hydroprocessing unit. A virgin crude oil was distillated to produce a light naphtha fraction, a heavy naphtha fraction, a kerosene fraction, a diesel fraction and an atmospheric residue fraction boiling above 370° C. The atmospheric residue fraction was hydrotreated to produce a hydrotreated effluent containing a light naphtha fraction, a heavy naphtha fraction, a kerosene fraction, a diesel fraction, an atmospheric residue fraction boiling above 370° C. and a vacuum residue fraction boiling above 540° C. The hydrotreated effluent excluding the vacuum residue fraction was passed to a steam pyrolysis reactor to produce ethylene. The ethylene yield was 6.5 wt % from the virgin crude oil, or 21.6 wt % from the feed to steam pyrolysis.
In another operation, a whole crude oil feedstock was processed according to the process described with respect to
As shown in Table 2 below, additional advantages of processing a whole crude oil instead of an atmospheric residue includes significantly reduced hydrogen consumption, higher yield of ethylene product on a feedstock basis and minimized overall processing and capital investment costs.
The method and system herein provides improvements over known steam pyrolysis cracking processes:
use of crude oil as a feedstock to produce petrochemicals such as olefins and aromatics;
the hydrogen content of the feed to the steam pyrolysis zone is enriched for high yield of olefins;
in certain embodiments coke precursors are significantly removed from the initial whole crude oil which allows a decreased coke formation in the radiant coil; and
additional impurities such as metals, sulfur and nitrogen compounds are also significantly removed from the starting feed which avoids post treatments of the final products.
In addition, hydrogen produced from the steam cracking zone is recycled to the hydroprocessing zone to minimize the demand for fresh hydrogen. In certain embodiments the integrated systems described herein only require fresh hydrogen to initiate the operation. Once the reaction reaches the equilibrium, the hydrogen purification system can provide enough high purity hydrogen to maintain the operation of the entire system.
The method and system of the present invention have been described above and in the attached drawings; however, modifications will be apparent to those of ordinary skill in the art and the scope of protection for the invention is to be defined by the claims that follow.
This application claims the benefit of U.S. Provisional Patent Application No. 61/591,811 filed Jan. 27, 2012, the disclosure of which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61591811 | Jan 2012 | US |
