Patent Application
20230407187
This application relates to a reactor system used in a fluid catalytic cracking (FCC) system, and more particularly to methods and systems for selectively shifting the product profile from an FCC process toward more light olefin products based on the feedstock using multiple risers, each optimized based on the feedstock.
Fluid Catalytic Cracking (FCC) is a process typically used in refineries to improve yields for transportation fuels such as gasoline and distillates. The FCC process uses a reactor called a riser, essentially a pipe, in which a hydrocarbon feed is contacted with catalyst particles to effect the conversion of the feed to more valuable products. The FCC unit converts gas oil or resid feeds by “cracking” the hydrocarbons into smaller molecules. The resulting hydrocarbon gas and catalyst mixture both flow in the riser, hence the term fluid catalytic cracking.
As employed in today's refineries, the FCC unit can convert primarily heavy feeds (such as vacuum gas oils, reduced crudes, atmospheric tower bottoms, vacuum tower bottoms and the like), into transportation fuel products (such as gasoline, diesel, heating oils, and liquefied petroleum gases). There is a declining trend in global demand for transportation fuels such as diesel with a sustained growth in demand for petrochemicals. Demand reduction for transportation fuels can be attributed to increased motor vehicle fuel efficiency and use to alternative source of fuels such as hydrogen and chemically stored electricity (batteries and fuel cells). This lower demand for transportation fuels will result in its surplus availability in the marketplace. On the other hand, there will be growing demand for petrochemical products due to increasing population and consumer demand. Propylene is an important raw material in the production of polypropylene, acrylonitrile, propylene oxide, oxo-alcohols and a wide range of industrial products. Demand for propylene is increasing across all global regions, mainly driven by demand for polypropylene, which accounts for more than 60% of all propylene demand. The propylene market is forecast to grow by an average annual rate of 4% in the coming years.
In recent years, FCC has played an increasing role in the production of propylene as a valuable by-product. Hence it is envisaged to use FCC to upgrade surplus transportation fuels such as naphtha, kerosene, diesel and oxygenates, etc., into light olefins such as propylene and ethylene. However, co-processing diesel, kerosene, and/or naphtha along with vacuum gasoil (VGO) or resid in a conventional single riser FCC is challenging because the conditions required to crack lower boiling distillates to propylene and ethylene are quite different than what is required for VGO and/or resid. If diesel is co-processed with VGO or resid in a single riser, most of the diesel will convert into Light Cycle Oil (LCO), which has a lower quality than diesel, without producing appreciable amounts of propylene. Likewise, co-processing kerosene in a single riser with VGO or Resid tends to produce primarily gasoline and (LCO).
Accordingly, there is a need in the art to shift the product spectrum of FCC processes toward greater quantities of light olefins, such as propylene and ethylene.
Disclosed herein is a process for cracking hydrocarbons using a multiple riser fluid catalytic cracking (FCC) reactor, the method comprising: cracking a heavy hydrocarbon feed in a first riser using first FCC conditions to form a first effluent enriched in medium and/or light hydrocarbons, and cracking one or more light and/or medium hydrocarbon feeds in one or more risers different than the first riser under FCC conditions different than the first FCC conditions to form one or more effluents enriched in light olefins. According to some embodiments, the heavy feed comprises one or more hydrocarbons having an average carbon number of 18 or more. According to some embodiments, the heavy feed comprises one or more components selected from the group consisting of vacuum gas oil (VGO), reduced crudes, atmospheric tower bottoms, vacuum tower bottoms, resid, and de-asphalted oil (DAO). According to some embodiments, the first effluent is enriched in hydrocarbons having a carbon number of 3 to 18. According to some embodiments, the one or more light and/or medium hydrocarbon feeds comprise distillates. According to some embodiments, the one or more light and/or medium hydrocarbon feeds comprises one or more hydrocarbons having an average carbon number of 1 to 18. According to some embodiments, the one or more light and/or medium hydrocarbon feeds comprises one or more components selected from the group consisting of jet fuel, diesel, naphtha, kerosene, C4s, and oxygenates. According to some embodiments, the first FCC conditions comprise maintaining an outlet temperature of the first riser at 510° C. to 575° C. According to some embodiments, the first FCC conditions comprise mixing steam and the heavy hydrocarbon feed in the first riser a concentration of 1 wt. % to 6 wt %. According to some embodiments, the FCC conditions different than the first FCC conditions comprise maintaining an outlet temperature of the one or more risers different than the first riser at 550° C. to 675° C. According to some embodiments, the FCC conditions different than the first FCC conditions comprise mixing steam with the one or more light and/or medium hydrocarbon feeds at a concentration of 5 wt. % to 20 wt %. According to some embodiments, the process further comprises providing at least a portion of the first effluent to the one or more risers different than the first riser. According to some embodiments, providing at least a portion of the first effluent to the one or more risers different than the first riser comprises: using a fractionation system to fractionate the first effluent to yield a fractionated stream enriched in one or more of the components of the first effluent, and recycling the fractionated stream from the fractionation system to the one or more risers different than the first riser. According to some embodiments, the fractionated stream is enriched in one or more of naphtha and C4s. According to some embodiments, cracking one or more light and/or medium hydrocarbon feeds in one or more risers different than the first riser comprises: cracking a medium feed in a second riser under second FCC conditions, and cracking a light feed in a third riser under third FCC conditions different than the second FCC conditions. According to some embodiments, the medium feed comprises one or more of gasoline, kerosene, jet fuel, and diesel fuel. According to some embodiments, the second FCC conditions comprise maintaining an outlet temperature of the first riser at 550° C. to 675° C. According to some embodiments, the light feed comprises one or more of naphtha, C4s, and oxygenates. According to some embodiments, the FCC reactions in each of the risers comprise cracking using a catalyst mixture comprising a Y zeolite and a shape selective zeolite. According to some embodiments, the shape selective zeolite is ZSM-5.
Also disclosed herein is a fluid catalytic cracking (FCC) reactor, comprising: a first riser configured to crack a heavy hydrocarbon feed and using first FCC conditions to form a first effluent enriched in medium and/or light hydrocarbons, and one or more additional risers configured to crack one or more light and/or medium hydrocarbon feeds under FCC conditions different than the first FCC conditions to form one or more effluents enriched in light olefins. According to some embodiments, heavy feed comprises one or more hydrocarbons having an average carbon number of 18 or more. According to some embodiments, the heavy feed comprises one or more components selected from the group consisting of vacuum gas oil (VGO), reduced crudes, atmospheric tower bottoms, vacuum tower bottoms, resid, and de-asphalted oil (DAO). According to some embodiments, the first effluent is enriched in hydrocarbons having a carbon number of 3 to 18. According to some embodiments, the one or more light and/or medium hydrocarbon feeds comprise distillates. According to some embodiments, the one or more light and/or medium hydrocarbon feeds comprises one or more hydrocarbons having an average carbon number of 1 to 18. According to some embodiments, the one or more light and/or medium hydrocarbon feeds comprises one or more components selected from the group consisting of jet fuel, diesel, naphtha, kerosene, C4s, and oxygenates. According to some embodiments, the first FCC conditions comprise maintaining an outlet temperature of the first riser at 510° C. to 575° C. According to some embodiments, the first FCC conditions comprise mixing steam and the heavy hydrocarbon feed in the first riser a concentration of 1 wt. % to 6 wt %. According to some embodiments, the FCC conditions different than the first FCC conditions comprise maintaining an outlet temperature of the one or more risers different than the first riser at 550° C. to 675° C. According to some embodiments, the FCC conditions different than the first FCC conditions comprise mixing steam and the one or more light and/or medium hydrocarbon feeds at a concentration of 5 wt. % to 20 wt %. According to some embodiments, the reactor is configured to provide at least a portion of the first effluent to the one or more risers different than the first riser. According to some embodiments, providing at least a portion of the first effluent to the one or more risers different than the first riser comprises: using a fractionation system to fractionate the first effluent to yield a fractionated stream enriched in one or more of the components of the first effluent, and recycling the fractionated stream from the fractionation system to the one or more risers different than the first riser. According to some embodiments, the fractionated stream is enriched in one or more of naphtha and C4s. According to some embodiments, cracking one or more light and/or medium hydrocarbon feeds in one or more risers different than the first riser comprises: cracking a medium feed in a second riser under second FCC conditions, and cracking a light feed in a third riser under third FCC conditions different than the second FCC conditions. According to some embodiments, the medium feed comprises one or more of gasoline, kerosene, jet fuel, and diesel fuel. According to some embodiments, the second FCC conditions comprise maintaining an outlet temperature of the first riser at 550° C. to 675° C. According to some embodiments, the light feed comprises one or more of naphtha, C4s, and oxygenates. According to some embodiments, the FCC reactions in each of the risers comprise cracking using a catalyst mixture comprising a Y zeolite and a shape selective zeolite. According to some embodiments, the shape selective zeolite is ZSM-5.
As mentioned above, the conditions of each of the risers may be tailored based on the feedstock reacted in that riser. The conditions that may be controlled within each riser include the temperature, the residence time of the feedstock within the riser, the partial pressure of the feedstock, and the ratio of catalyst to feedstock. The partial pressure of the feedstock is controlled by controlling the amount of steam injected into the riser. Generally, lighter reactants require more steam than heavier components for cracking and paraffinic feed requires more steam than olefinic feed.
Controlling the temperature within each riser is important because the cracking reaction is endothermic, meaning that heat must be supplied to the reactor process to heat the feedstock and maintain reaction temperature. The temperature required depends on the particular feedstock, and typically lighter molecules require higher temperature to sustain the reaction than do heavier molecules. The heat for sustaining the reaction in the risers is provided by heat produced during catalyst regeneration. During the conversion process with heavy feeds, coke is formed. The coke is deposited on the catalyst and ultimately burned with an oxygen source such as air in the regenerator section 112. Burning of the coke is an exothermic process that can supply the heat needed for the cracking reaction. The resulting heat of combustion from regeneration increases the temperature of the catalyst, and the hot catalyst is recirculated for contact with the feed in the riser, thereby maintaining the overall heat balance in the system. The amount of heat provided to a riser can be controlled by adjusting the amount of catalyst provided to the riser, for example, by controlling valves (e.g., valves 116, 120, and 124,
The reactor 202 can also be configured with one or more risers configured to crack medium and/or light feeds into streams enriched with light olefins, such as ethylenes and/or propylenes. Generally, “medium feed” refers to feed materials having an average carbon number of about 8 to 18 and “light feed” refers to feed materials having an average carbon number of about 1 to 8. Examples of these medium and/or light feeds include paraffinic, cycloparaffinic, monoolefinic, diolefinic, cycloolefinic, naphthenic, and aromatic hydrocarbons, and hydrocarbon oxygenates. Further representative examples include light paraffinic naphtha; heavy paraffinic naphtha; light olefinic naphtha; heavy olefinic naphtha; mixed paraffinic C4s; mixed olefinic C4s (such as raffinates); mixed paraffinic C5s; mixed olefinic C5s (such as raffinates); mixed paraffinic and cycloparaffinic C6s; non-aromatic fractions from an aromatics extraction unit; oxygenate-containing products from a Fischer Tropsch unit; or the like; or any combination thereof. Hydrocarbon oxygenates can include alcohols having carbon numbers ranging of one to four, ethers having carbon numbers of two to eight and the like. Examples include methanol, ethanol, dimethyl ether, methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether, tertiary amyl methyl ether (TAME), tertiary amyl ethyl ether and the like
Distillates are an example of medium/light feed that may be cracked to yield light olefins in a riser of the reactor 202. As used herein, the term distillates may refer to one or more of naphtha, diesel, kerosene, and jet fuels. Distillates may be light distillates or middle distillates, as those terms are used in the art. According to some embodiments, the reactor 202 may have separate risers for different medium/light components. For example, the reactor may have a riser for diesel range material, another for jet fuel, and another for naphtha. According to some embodiments, feeds with very similar boiling points or characteristics may be provided to a common riser. Ideally, the reaction conditions in each riser can be optimized for converting its particular feedstock to light olefins. Also, the reactor 202 may comprise risers configured to handle feeds from different processes within the refinery. For example, an embodiment of a reactor 202 may have one riser configured to receive distillates from the crude distillation column, and those distillates may include straight run naphtha and/or straight run diesel as a component. The reactor may also have another riser that can receive naphtha from other processes, such as from a coker and/or from a visbreaker.
As illustrated in
Conventional FCC processes configured to produce gasoline, etc., typically use Y-zeolite catalysts, which are configured to crack larger (C9+) molecules. Other examples of catalysts useful in fluidized catalytic cracking include USY, REY, RE-USY, faujasite and other synthetic and naturally occurring zeolites and mixtures thereof. Embodiments of the disclosed dual riser processes described herein may use such catalysts combined with catalysts that are better configured for cracking light feeds to produce light olefins. Examples of light feed catalysts include shape-selective zeolites configured to crack naphtha-range molecules. Examples of suitable catalysts for use in the cracking of light feeds are exemplified by ZSM-5 and similar catalysts. Other catalysts include ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38, and ZSM-48. The proportion of Y-Zeolite catalyst and shape-selective zeolites are optimized based on the feedstock involved and product targets.
As an example of how a multi-riser FCC reactor can be used in a process for providing light olefins, consider the reactor 100 (
Although particular embodiments of the present invention have been shown and described, it should be understood that the above discussion is not intended to limit the present invention to these embodiments. It will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present invention. Thus, the present invention is intended to cover alternatives, modifications, and equivalents that may fall within the spirit and scope of the present invention as defined by the claims.
