Patent Application
20210189257
The present invention relates to systems using catalytic cracking units for olefins production, and more particularly relates to such systems where a light naphtha feed is produced within the system.
Fluid catalytic cracking (FCC) is an important and well-known commercial conversion process used in petroleum refineries. It is widely used to convert high-boiling, high molecular weight hydrocarbon fractions of petroleum crude oils into more valuable gasoline, olefins, and other products. Cracking of petroleum hydrocarbons is now primarily done by catalytic cracking because it produces more gasoline with a higher octane rating than thermal cracking. It also produces byproduct gases that have more carbon-carbon double bonds, that is, more olefins, and hence more economic value than those produced by thermal cracking.
The breaking of the large hydrocarbon molecules into smaller molecules is technically referred to by organic chemists as “scission” of the carbon-to-*carbon bonds. Some of the smaller alkanes are then broken and converted into even smaller alkenes and branched alkenes such as the gases ethylene (CH2═CH2 or C2=), propylene (CH3—CH═CH2 or C3=), butylenes, and isobutylenes (collectively C4=). Those olefinic gases are valuable for use as petrochemical feedstocks. The propylene, butylene and isobutylene are also valuable feedstocks for certain petroleum refining processes that can convert them into high-octane gasoline blending components. They may also be used as valuable chemical building blocks for higher molecular products such as polymers.
It is always desirable to improve catalytic cracking systems by improving reliability, controlling fractionation quality inside the battery limit, steadily producing light olefins, improving fractionation efficiency, reducing utility requirements, reducing overall energy requirements, reducing CO2/NOx emissions, reducing equipment footprint requirements, and/or improving the value of the products.
There is provided, in one non-limiting embodiment, a catalytic cracking system configured for olefins production where the system comprises a reactor/regenerator, a main fractionator, and a vapor recovery unit (VRU). The reactor/regenerator is adapted to receive a feed comprising gas oils and/or deasphalted oil (DAO) and/or atmospheric residue in a first riser and an aromatics-free C5/C6-rich light naphtha feed in a second riser, the reactor/regenerator generating a high-value product stream comprising light and heavy paraffinic, naphthenic, aromatic and olefinic hydrocarbons. The main fractionator is configured for receiving and fractionating the high-value product stream, where the main fractionator includes a fractionator vapor product stream comprising fuel gas, C3/C4, and light naphtha; a wild naphtha product stream; and fractionator liquid products stream comprising optionally heavy naphtha, light cycle oil (LCO), and slurry. The VRU includes a primary absorber, where the VRU receives the fractionator vapor and wild naphtha product streams and separates them to give an aromatics-free C5/C6-rich product stream, where the aromatics-free C5/C6-rich product stream is directed as the aromatics-free C5/C6-rich light naphtha feed back to the reactor/regenerator. The VRU further includes two embodiments. In a first non-limiting embodiment the VRU includes a combination of a debutanizer column and a naphtha splitter column, and a debutanizer bottoms product that is split between a feed to the naphtha splitter column and recycle to the primary absorber, and where the naphtha splitter column splits out the aromatics-free C5/C6-rich product stream. In a second non-limiting embodiment the VRU comprises a dividing wall column (DWC) comprising a pre-fractionator section and a main-fractionator section where the DWC comprises a side draw that is the aromatics-free C5/C6-rich product stream, and the DWC comprises a bottoms product that is split between a gasoline product and recycle to the primary absorber.
There is additionally provided method for producing olefins in a catalytic cracking system, where the method includes directing a feed to a reactor/regenerator, where the feed comprising at least one component selected from the group consisting of gas oils, deasphalted oil (DAO), atmospheric residue, and an aromatics-free C5/C6-rich light naphtha feed. The method further includes the reactor/regenerator generating a high-value product stream comprising light and heavy paraffinic hydrocarbons, naphthenic, aromatics and olefinic hydrocarbons. The method additionally includes directing the high-value product stream to a main fractionator where main fractionator fractionates the high-value product stream and generates a fractionator vapor product stream comprising fuel gas, C3/C4, and light naphtha, a wild naphtha product stream, and a fractionator liquid products stream comprising at least one component selected from the group consisting of heavy naphtha, light cycle oil (LCO), and slurry. The method also includes directing fractionator vapor and wild naphtha product streams to a vapor recovery unit (VRU) comprising a primary absorber where the VRU separates the fractionator vapor and wild naphtha product streams to give an aromatics-free C5/C6-rich product stream. The aromatics-free C5/C6-rich product stream is directed to the reactor/regenerator as an aromatics-free C5/C6-rich light naphtha feed recycle. The VRU further comprises units of either of the two embodiments described above.
Existing FCC units can be revamped or a new grassroots FCC unit can be designed with improved technology, including but not necessarily limited to MAXOFIN™ technology available from KBR to produce light olefins such as ethylene and propylene from a light naphtha stream. MAXOFIN™ technology is a process that enables refiners to maximize propylene production by 20% or more with significantly less ethylene than traditional steam cracking, and it provides the flexibility to operate as a conventional FCC system to produce gasoline depending on changing market demands.
The KBR MAXOFIN™ technology employs dual risers. The first riser processes the conventional FCC feed-stocks (gas oils, DAO and atmospheric residue) and in the second riser light paraffinic, naphthenic, or olefinic hydrocarbons are cracked to achieve the desirable high yields of the light olefins. The reactor effluent from both the risers in the MAXOFIN™ unit is fractionated in a main fractionator column.
The light naphtha feed, suitable to produce the light olefins by cracking in the second riser is conventionally imported from the outside battery limit (OSBL). It has been discovered that the light naphtha feed can be produced internally in the MAXOFIN™ unit.
A FCC unit consists of three main sections, the reactor/regenerator 10, the main fractionator 18, and the unsaturated gas plant section (also known as the vapor recovery unit (VRU) or gas concentration unit (GCU)).
A typical MAXOFIN™ unit block flow diagram when the light naphtha stream 12 is imported as a second riser feed from the outside battery limit is shown in
FCC feed (heavy atmospheric gas oils, vacuum gas oils, DAO, and/or residue) 14 is cracked into high-value products 16 in the reactor/regenerator 10 and routed to the main fractionator section 18. The liquid product 20 from the main fractionator 18 includes heavy naphtha, light cycle oil (LCO), and slurry. Only slurry is a bottoms product; the heavy naphtha and LCO are side products.
The overhead products 22 from the main fractionator 18 mainly contain fuel gas (C2- and inert), liquefied petroleum gas (LPG; C3/C4), and cat-cracked naphtha are further separated in the gas plant section (VRU). Wet gas 22 from the main fractionator 18 overhead flows to the wet gas compressor 24; this is usually a two-stage centrifugal machine. The vapors from the first stage discharge are partially condensed in an interstage cooler and flashed in an interstage drum. The vapor discharge from the second stage of the wet gas compressor 24 is combined with the liquid from the compressor interstage drum, the primary absorber bottoms liquid 62, and the stripper overhead vapors 36. This combined stream flows through the high pressure (HP) cooler into the high pressure (HP) receiver, collectively designated 26.
Vapor 32 from the HP separator drum flows to the primary absorber column 58. Hydrocarbon liquid (wild naphtha) 34 from the main fractionator 18 overhead drum is pumped to the primary absorber 58 as a lean oil. The debutanizer 40 bottoms liquid 56 is also pumped to the primary absorber 58 to increase the lean oil flow, and therefore the propylene recovery. The debutanizer bottoms liquid 56 enters the primary absorber 58 at a higher point than the wild naphtha 34. LPG (C3/C4) 62 recuperated in the primary absorber 58 bottoms is directed to the HP cooler/HP receiver 26. The primary absorber overhead gas 64 flows to the secondary or sponge absorber 66 to recover the LPG range material by absorption into a lean sponge oil 68. Rich sponge oil 70 is routed to main fractionator 18. The sponge absorber overhead 72 (C2-) flows to treating and is then routed to the refinery fuel gas system.
Liquid 28 from the HP separator drum 26 is pumped to the top of the stripper column 30. The purpose of stripper column 30 is to achieve a C2 content specification in the feed 38 to the debutanizer (stabilizer) 40. Stripped vapor 36 containing most of the C2- and some LPG leaves the top of the stripper column 30 and is returned to the HP cooler/HP receiver 26. The stripper bottoms liquid 38 is preheated by heat exchange with the debutanizer bottoms liquid and fed to the debutanizer column 40.
The debutanizer column 40 separates the feed into LPG 42 and cat-cracked naphtha (combined streams 56 and 60). The overhead product 42 from the debutanizer 40 is LPG (C3/C4). Bottoms liquid (combined streams 56 and 60) from the debutanizer 40 is cooled against the column feed and then by air and/or a water cooler (not shown). A portion of the cooled debutanizer bottoms liquid 56 is returned to the primary absorber 58 as a super lean oil and the remainder 60 is yielded as a cat-cracked naphtha gasoline blendstock. The LPG 42 from the overhead of the debutanizer after amine and mercaptan removal treatment flows to a depropanizer 44 where it is separated into C3 and C4 products. The C3 product 48 may be further separated into propylene (C3=) 54 product and propane (C3) product 52 in a propylene splitter 50 downstream of the depropanizer column 44. The C4 bottoms product 46 from depropanizer 44 is sent to OSBL.
It has been discovered that the light naphtha stream 74 can be produced inside the battery limit as the second riser feed to reactor/regenerator 10, which is a configuration that increases olefinic LPG yield.
In a different non-limiting embodiment, the VRU comprises Dividing Wall Column (DWC) technology which can be used to further improve and simplify the process flow scheme (as shown schematically in
It will be appreciated that the DWC can be a tray column, a packed column, or a combination of both.
It will also be appreciated that the systems and processes described herein will have a number of technical and commercial advantages.
For the non-limiting embodiment where two conventional columns are used for the debutanizer and naphtha splitter as schematically illustrated in
Commercial advantages for this non-limiting embodiment include, but are not necessarily limited to steady production of the light olefins.
For the non-limiting embodiment where a DWC is used as schematically illustrated in
Commercial advantages for the non-limiting embodiment where a DWC is used include, but are not necessarily limited to, the commercial advantage noted above for when two conventional columns are used, in addition to:
Stated another way, a non-limiting improvement in the
Improvements in the non-limiting embodiment of
Furthermore, there are many noticeable differences between a fractionation approach such as Honeywell UOP U.S. Patent Application Publication 2008/0081937 A1 and the proposed system described herein including, but not necessarily limited to, those listed in Table I below:
In the foregoing specification, the invention has been described with reference to specific embodiments thereof. However, the specification is to be regarded in an illustrative rather than a restrictive sense. For example, equipment, columns, DWCs, processes, reactants, olefins, products, reactors, regenerators, splitters, stabilizers, absorbers, compressors, coolers, and operating conditions falling within the claimed or disclosed parameters, but not specifically identified or tried in a particular example, are expected to be within the scope of this invention.
The present invention may be practiced in the absence of an element not disclosed. In addition, the present invention may suitably comprise, consist or consist essentially of the elements disclosed. For instance, there may be provided a catalytic cracking system configured for olefins production where the system consists essentially of or consists of a reactor/regenerator, a main fractionator, and a VRU, where the reactor/regenerator is adapted to receive a feed comprising gas oils and/or DAO and/or atmospheric residue and an aromatics-free C5/C6-rich light naphtha feed, the reactor/regenerator comprising a high-value product stream comprising light and heavy paraffinic hydrocarbons, naphthenic, aromatics and olefinic hydrocarbons; the main fractionator is configured to receive and fractionate the high-value product stream, where the main fractionator comprises a fractionator vapor product stream comprising fuel gas, C3/C4, and light naphtha, a wild naphtha stream, and a fractionator liquid products stream comprising heavy naphtha, LCO, and slurry; and the VRU comprises a primary absorber, the VRU receiving the fractionator vapor and wild naphtha product streams and separating them to give an aromatics-free C5/C6-rich product stream, where the aromatics-free C5/C6-rich product stream is directed as the aromatics-free C5/C6-rich light naphtha feed recycle to the reactor/regenerator; the VRU further comprises units selected from the group consisting of 1) a combination of a debutanizer column and a naphtha splitter column or 2) a DWC, where a debutanizer bottoms product is split between a feed to the naphtha splitter column and feed to the primary absorber, and the naphtha splitter column splits out the aromatics-free C5/C6-rich product stream; and where if the DWC is used, it comprises a pre-fractionator section and a main fractionator section where the DWC comprises a side draw that is the aromatics-free C5/C6-rich product stream and the DWC comprises a bottoms product feed to the primary absorber.
The words “comprising” and “comprises” as used throughout the claims, are to be interpreted to mean “including but not limited to” and “includes but not limited to”, respectively.
As used herein, the word “substantially” shall mean “being largely but not wholly that which is specified.”
As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.
As used herein, the term “about” in reference to a given parameter is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the given parameter).
As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
This application claims the benefit of U.S. Provisional Application Ser. No. 62/950,714 filed Dec. 19, 2019, incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62950714 | Dec 2019 | US |
