Patent Application
20120053383
The present invention relates generally to a method for the production of olefins. More particularly, the present invention is directed to a method for producing light olefins (e.g., ethylene, and propylene) and associated byproducts from refinery saturated and unsaturated off-gases and other light hydrocarbon feedstocks.
The petroleum refining and petrochemical industries have often sought new integration opportunities for refinery products with other processes. One of the areas of interest concerns refinery off-gases that are produced as a result of various separation and conversion processes, for example, crude distillation, fluid catalytic cracking, hydrocracking, hydrotreating, delayed coking, catalytic reforming, aromatics processing and the like. Many different off-gas streams containing mixtures of hydrogen and light hydrocarbons, such as C1 to C6 hydrocarbons, are generated during oil refining and petrochemical processing steps.
While these refinery off-gas streams are a potential source of hydrogen, ethane, propane and other compounds, many refinery and petrochemical off-gas streams are not used either for their hydrogen content or to generate other valuable compounds, e.g., olefins, due to a variety of economic and practical reasons. Some of the economical and practical reasons off-gas streams are not used include: the flow is too small, the pressure is too low, the content of valuable components is too low, or the contaminant level is too high. The off-gas streams are frequently consumed as fuel within the overall refinery/petrochemical complex.
Over the years, economic pressures have driven refiners to attempt to convert even the heaviest fractions of the crude oil to gasoline components and petrochemical feedstocks. For example, hydrocracking is widely used to break down aromatic cycle oils, coker distillates and other relatively heavy feeds and reconstitute them as diesel fuels, kerosene or naphtha. Separation of the components in the raw stream leaving the reactors is typically carried out by flashing off hydrogen and other gases, followed by various stripping and fractionation steps as appropriate. During these processes, however, considerable amounts of light hydrocarbon off-gas are not recaptured.
Representative refinery treatment reactor processes carried out in refineries or petrochemical plants that can give rise to off-gas streams (useful in the practice of the present invention) include, but are not limited to, catalytic cracking, catalytic reforming, delayed coking, distillate dewaxing, aromatics production, alkylation, isomerization, hydrocracking, hydrogenation, dehydrogenation, and olefin production. Other off-gas streams also arise from unsaturated and saturated gas plants used to treat and fractionate pooled off-gases from the various refinery fractionation or conversion units.
The result is the formation of a number of diverse streams from which it may not currently be cost effective to carry out further product recovery. Thus, these off-gases are frequently used as fuel within the overall complex. Higher profits can be realized if these off-gas streams could be efficiently processed to obtain higher value products. The recovery of olefins, such as ethylene and propylene from petro-chemical plant off-gas streams, however, is economically and environmentally important, but is a highly energy intensive process. Therefore, improved processes which can achieve this goal are of great interest.
As more fully disclosed herein, the present invention provides a method for utilizing off-gases from various refinery and petrochemical fractionation and conversion processes, as feeds to economically and practically produce olefins and other valuable compounds with little, or no initial pretreatment.
The present invention provides a method for producing olefins in an integrated petrochemical facility comprised of at least one feedstock from a refinery unit, or other hydrocarbon processing unit and at least one downstream pyrolysis furnace. The method comprises: obtaining a refinery off-gas stream comprising at least one of ethane and propane from the upstream processing unit or units; combining the off-gas stream(s) with a pyrolysis furnace ethane or propane feed stream and/or any other conventional cracking furnace feedstock and saturating the combined stream with dilution steam in a feed saturator or mixing it with dilution steam. The method continues by cracking the combined stream in the downstream pyrolysis furnace to produce cracked product, and separating the cracked product into one or more of hydrogen, methane, ethylene, propylene, butenes, heavier products, a fuel gas stream and recycle streams in the unit recovery systems.
The inventive method allows the upgrade of the ethane, propane and other hydrocarbons contained in the refinery off-gas to more valuable cracking feedstock without significant investment in compression and pre-fractionation processes. The contained lighter gases, mainly hydrogen and methane, act as diluents to lower the hydrocarbon partial pressure, which improves the yield selectivity to the desired ethylene with only a slight reduction in propylene. Moreover, the benefits of the present invention can be achieved in conjunction with higher coil outlet pressures, for example, 2.4-2.8 bara (35-40 psia) and/or lower steam to hydrocarbon ratios in the range of 0.1 to 0.3 and most preferably 0.15 to 0.2, while achieving optimum yield and energy efficiency.
Further, the present invention can eliminate or significantly reduce compression, refrigeration and fractionation of the contained light gases, such as, hydrogen and methane from ethane and heavier feeds prior to cracking of said ethane, propane and heavier feeds. The contained oxygen will be converted completely to carbon monoxide, carbon dioxide and water without the need to invest in separate oxygen removal facilities.
All references cited herein are hereby incorporated by reference to the extent not inconsistent with the disclosure herewith. Although the description herein contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of the invention. Thus, the scope of the invention should be determined by the appended claims and their equivalents, rather than by the examples given.
Whenever a range is given in the specification, for example, a temperature range, a time range, a flow-rate range, or a size range, all intermediate ranges and subranges, as well as all individual values included in the ranges given are intended to be included in the disclosure.
The terms and expressions that have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims.
In general, the terms and phrases used herein have their art-recognized meaning, which can be found by reference to standard texts, journal references and contexts known to those skilled in the art. The following definitions are provided to clarify their specific use in the context of the invention.
For purposes of this invention, the phrase “refinery treatment reactor” means any one of the typical petrochemical process units in a petrochemical refinery. Examples of refinery treatment reactors include, crude distillation units (i.e., atmospheric distillation, vacuum distillation unit), naphtha hydrotreater unit, catalytic reformer unit, distillate hydrotreater unit, fluid catalytic cracker (FCC) unit, hydrocracker unit, visbreaking unit, merox unit, coking units (i.e., delayed coking, fluid coker, and flexicoker), alkylation unit, dimerization unit, isomerization unit, aromatics units, steam reforming unit, amine gas treater, and claus units.
As used herein the term “off-gas” means a refinery treatment reactor product, by-product or waste gas stream that is produced from any one of the aforementioned refinery treatment reactor processes or any other petrochemical or gas processing off-gas stream.
The present invention relates to a unique method for producing olefins in an integrated petrochemical facility from off-gas streams from refinery processing units. Olefins find widespread uses in many industries. For example, they represent the basic building blocks in such diverse uses as film and packaging, communications, construction, automotive and home appliances. These important materials are generally produced by the cracking of a hydrocarbon feedstream, which converts saturated hydrocarbons present in the feedstream into olefins, or the recovery of light olefins from unsaturated streams such as FCC off-gas.
The inventive method utilizes refinery saturated and nearly saturated off-gas streams from refinery treatment reactor(s) and, with or without further processing, directs the off-gas stream to a pyrolysis process to produce olefins and other valuable products.
The off-gas streams for the method of the present invention typically comprise, but are not limited to, hydrogen, carbon monoxide, carbon dioxide, methane, acetylene, ethylene, ethane, methyl acetylene, propadiene, propylene, propane, butadienes, butanes, butenes and heavier C5+ hydrocarbons. The off-gas streams can also include light olefin components, typically C2 to C5 olefins, although olefins with higher carbon numbers may also be used. Sources of the off-gas streams normally include: light gas streams recovered from the gas separation section of a refinery fluid catalytic cracking (FCC) process, a sweet refinery gas, coker off-gas, effluents from light paraffin (e.g. LPG) dehydrogenation zones, saturated gas separation unit or other type of off-gas containing high amounts of hydrocarbons with more than two carbon atoms.
The off-gas stream may contain oxygen, nitrogen and other contaminants such as, but not limited to hydrogen sulfide and carbon dioxide. As such, the gases from petrochemical facilities, gas separation plants, and similar facilities, which are well known in the art and produce light gases are useful as off-gas streams in the present invention.
The refinery treatment reactor off-gas stream of the presently claimed method is sent directly to at least one downstream pyrolysis cracking furnace. The inventive method eliminates or greatly reduces the need for currently practiced processes, such as, compression, refrigeration and pre-fractionation, of off-gas streams prior to downstream pyrolytic cracking. The off-gas by itself, or combined with a typical ethane or propane feed is sent to a pyrolysis system without further fractionation.
The downstream pyrolysis furnace may be any type of conventional pyrolysis furnace, especially including a tubular steam cracking furnace, designed for pyrolizing light and/or heavy feed and operated for production of lower boiling products such as olefins. Examples of pyrolysis furnaces useful in the present invention include those disclosed in the following U.S. Pat. Nos. 3,487,121 to Hallee, 3,972,682 to Stephens et al., 4,020,273 to Dix et al., 4,765,883 to Johnson et al., 5,181,990 to Arisaki et al., 5,271,827 to Woebcke and 6,419,885 to Di Nicolantonio et al. The contents of each of the above-referenced patents are incorporated herein by reference for all purposes.
The off-gas, or off-gases, are directed to the downstream pyrolysis cracking furnace(s) at any suitable conditions that provide the necessary cracking to the desired olefinic compound product(s). Accordingly, the off-gas is directed to the downstream pyrolysis cracking furnace(s) at pressures ranging from about 4 bara to about 12 bara. As such, the pressure ranges correspond to a furnace coil outlet pressure that will typically be in the range of about 1.2 bara to about 2.8 bara but could also be as high as about 5 bara or as low as about 1 bara to produce primarily light olefins, e.g., ethylene and propylene.
The pyrolysis furnace feed includes dilution steam, which is generated separately and added to the refinery treatment reactor(s) off-gas, ethane, propane, and other selected furnace feeds. Likewise, the refinery treatment reactor(s) off-gas can be humidified in a saturator system. Dilution steam systems and saturator systems for cracking hydrocarbons are well known in the art. For example, U.S. Pat. Nos. 3,487,121 to Hallee and 4,940,828 to Pettersen et al. disclose dilution steam for cracking hydrocarbons, the entire contents of which are incorporated herein by reference. The cracking will occur in the presence of dilution steam typically in the range of about 0.1 to about 0.4 on a steam to feed weight basis, however, the steam to feed weight basis can be as low as 0 or as high as about 0.7.
Once the off-gas stream is introduced into the downstream pyrolysis cracking furnace, the cracking reactions can take place at any suitable conditions that provide the necessary cracking to the desired olefinic compound product(s). Generally, the cracking temperature of the furnace can be in a range of from about 1000° F. to about 2000° F., preferably about 1100° F. to about 1850° F., and most preferably 1250° F. to 1650° F. The residence time of the hydrocarbon fluid, based on the conditions described above, is generally in the range of from about 0.02 second to about 0.5 second, more preferably from about 0.02 to about 0.2 seconds.
The time required for converting a saturated hydrocarbon to an olefinic compound can vary widely depending on the hydrocarbon used in the process, the olefinic compound(s) desired, and the rate of the introduction of off-gas stream. Generally, the flow rate of the off-gas stream is in the range of from about 6,000 to about 20,000 pounds per hour per cracking coil depending on the capacity of the cracking furnace.
Also, useful in the method of the present invention are pyrolysis furnace feeds following limited pre-fractionation such as, but not limited to, deethanization (e.g., in a deethanization column as known in the art) to allow separate cracking of the ethane-rich gas, propane and heavier components of the feed to achieve optimum olefin yield. Optionally, the method provides limited contaminant removal from the pyrolysis furnace feed. A non-limiting example of contaminant removal would include amine treatment to remove acid gas, such as hydrogen sulfide and carbon dioxide. Most significant of the inventive method is that oxygen contained in the furnace feed is completely converted to carbon monoxide, carbon dioxide and water, thus elimination the need for the deoxygenation reactor system.
Once the off-gas stream has been subjected to downstream pyrolysis, known and conventional processes are used to separate the mainly C1 to C3 gaseous mixtures containing large amounts of ethene (ethylene), ethane, propylene, propane and methane are performed. In addition contained C4+ components are also fractionated. Significant amounts of hydrogen usually accompany cracked hydrocarbon gas, along with minor amounts of acetylene. The acetylene component may be removed before or after cryogenic operations (see, e.g., U.S. Pat. No. 5,414,170 to McCue et al.). The cracked off-gas stream typically is compressed at ambient temperature or below and at process pressure of at least about 2500 kPa (350 psig), preferably about 3700 kPa (37.1 kgf/cm2, 520 psig), then separated in a chilling train under cryogenic conditions into several liquid streams and gaseous methane/hydrogen streams. The more valuable olefin streams are decontaminated prior to recovery.
While the specification concludes with claims distinctly pointing at the subject matter that applicants regards as their invention, it is believed that the invention will be better understood when taken in connection with the accompanying
In
Unsaturated refinery gas, from, for example, FCC gas, in stream 105 is directed to amine absorber 05, which is also operatively connected to an amine regenerator 09, via 109a (i.e., rich amine from unsaturated gas absorber to amine regenerator) and 109c (i.e., lean amine from amine regenerator to unsaturated gas amine absorber). The effluent from the amine absorber 05 in a line 106 is directed to a selective deoxygenation reactor 06 for conversion of oxygen to water and nitrogen oxide to ammonia and water.
In the embodiment of prior art in
In the embodiment of prior art in
In an embodiment of the claimed method of
In the embodiment of prior art in
In a specific embodiment of the claimed method of
As such, the inventive method eliminates the prior art steps of compression 02, deoxygenation 03 and the remaining contaminant removal 04 as presented in
In known and conventional manner as depicted in both
In known and conventional manner as depicted in both
While the present invention has been described with reference to a preferred embodiment, as will occur to those skilled in the art, numerous changes, additions and omissions may be made without departing from the spirit and scope of the present invention.
A material balance for the method presented in
TABLE 1: Presents an exemplary overall material balance feed useful in the method of the present invention.
TABLE 2: Presents Prophetic Examples of upstream off-gas feeds from refinery treatment reactors useful in the present method of producing olefins as an ethane rich feed.
TABLE 3: Presents Prophetic Examples of off-gas feeds from ‘fresh’ refinery propane, propane rich stream from a saturated refinery gas, and refinery recycled propane, all of which are useful in the present method for producing olefins.
TABLE 4: Presents Prophetic Examples of the present method effluent and recovered products.
While certain preferred and alternative embodiments of the invention have been set forth for purposes of disclosing the invention, modifications to the disclosed embodiments may occur to those who are skilled in the art. Accordingly, the appended claims are intended to cover all embodiments of the invention and modifications thereof which do not depart from the spirit and scope of the invention.
This application claims priority to U.S. Provisional Patent Application No. 61/376,755 which was filed on Aug. 25, 2010 and is incorporated by reference as if fully set forth herein.
| Number | Date | Country | |
|---|---|---|---|
| 61376755 | Aug 2010 | US |
