Patent Application
20180245002
Not applicable.
The present invention relates to a system and method for Fischer-Tropsch gas to liquid hydrocarbon production. Specifically, the present invention relates to a system and method for using carbon dioxide in a Fischer-Tropsch system.
The Fischer-Tropsch (or “Fischer Tropsch” or “FT”) process (or synthesis) involves a set of chemical reactions that convert a mixture of carbon monoxide and hydrogen (known as reformed gas or synthesis gas, or ‘syngas’) into liquid hydrocarbons. The FT process was first developed by German chemists Franz Fischer and Hans Tropsch in the 1920's. The FT conversion is a catalytic and exothermic process. The FT process is utilized to produce petroleum substitutes, typically from carbon-containing energy sources such as coal, natural gas, biomass, or carbonaceous waste streams (such as municipal solid waste) that are suitable for use as synthetic fuels, waxes and/or lubrication oils. The carbon-containing energy source is first converted into a reformed gas (or synthetic gas or syngas), using a syngas preparation unit in what may be called a syngas conversion. Depending on the physical form of the carbon-containing energy source, syngas preparation may involve technologies such as steam methane reforming, gasification, carbon monoxide shift conversion, acid gas removal gas cleaning and conditioning. These steps convert the carbon source to simple molecules, predominantly carbon monoxide and hydrogen, which are the active ingredients of synthesis gas but inevitably also containing carbon dioxide, water vapor, methane, nitrogen. Impurities deleterious to catalyst operation such as sulfur and nitrogen compounds are often present in significant or trace amounts and are removed to very low concentrations as part of synthesis gas conditioning.
Turning to the syngas production step, to create the syngas from natural gas, for example, methane in the natural gas reacts with steam and/or oxygen in a syngas preparation unit to create syngas. This syngas comprises principally carbon monoxide, hydrogen, carbon dioxide, water vapor and unconverted methane. When partial oxidation is used to produce the synthesis gas, typically it contains more carbon monoxide and less hydrogen than is optimal and consequently, the steam is added to the react with some of the carbon monoxide in a water-gas shift reaction. The water gas shift reaction can be described as:
CO+H2O⇄H2+CO2 (1)
Thermodynamically, there is an equilibrium between the forward and the backward reactions. That equilibrium is determined by the concentration of the gases present and temperature.
Once the syngas is created and conditioned, the syngas is used as an input to an FT reactor having an FT catalyst to make the liquid FT hydrocarbons in a Fischer-Tropsch synthesis (or FT synthesis or FT conversion). Depending on the type of FT reactor, the FT conversion of the syngas to liquid FT hydrocarbons takes place under appropriate operating conditions. The Fischer-Tropsch (FT) reactions may be simplistically expressed as:
(2n+1)H2+n CO→CnH2n+2+n H2O, (2)
where ‘n’ is a positive integer, preferably greater than 1.
As mentioned above, the FT reaction is performed in the presence of a catalyst, called a Fischer-Tropsch catalyst (“FT catalyst”). Unlike a reagent, a catalyst accelerates the chemical reaction and is not consumed by the reaction itself. In addition, a catalyst may participate in multiple chemical transformations. The activity level of an FT catalyst may decrease over time with use.
In addition to liquid hydrocarbons, Fischer-Tropsch synthesis also commonly produces gases (“Fischer-Tropsch tail gases” or “FT tail gases”) and water (“FT water”). The FT tail gases typically contain CO (carbon monoxide), CO2 (carbon dioxide), H2 (hydrogen), light hydrocarbon molecules, both saturated and unsaturated, typically ranging from C1 to C4, and a small amount of light oxygenated hydrocarbon molecules such as methanol. Typically, FT tail gases are mixed in a facility's fuel gas system for use as fuel. The FT water may contain contaminants, such as dissolved hydrocarbons, oxygenates (alcohols, ketones, aldehydes and carboxylic acids) and other organic FT products. Typically, FT water is treated in various ways to remove the contaminants and is properly disposed of.
Carbon dioxide emissions from use of fossil fuels are becoming increasingly problematic. The lifetime of carbon dioxide as a pollutant is poorly defined because the gas is may move among different parts of the ocean-atmosphere-land system. Some of the excess carbon dioxide will be absorbed quickly (e.g. by the ocean surface, forests, etc.), but some will remain in the atmosphere for thousands of years, due in part to the very slow process by which carbon is transferred to ocean sediments. As carbon dioxide is a component of FT tail gas, some operators recover the carbon dioxide from the FT tail gas for sequestration or other disposal.
Many Fischer Tropsch catalysts have been tested since 1920's. What is commonly understood is that iron-based FT catalysts have water gas shift properties, while cobalt-based FT catalysts do not. These conclusions were made under conditions involving using syngas having low H2/CO ratios in a Fischer Tropsch reactor using either an iron-based FT catalyst or a cobalt-based FT catalyst. By a “low H2/CO ratio,” a ratio lower than the approximately 2:1 stoichiometric ratio of a Fischer Tropsch reaction is meant. A ratio of 2.15:1 is typical. See also, for example, “Comparative study of Fischer-Tropsch synthesis with H2/CO and H2/CO2 syngas using Fe- and Co-based catalysts,” T. Riedel, M. Claeys, H. Schulz, G. Schaub, S. Nam, K. Jun, M. Choi, G. Kishan, K. Lee, in A
Consideration of the H2/CO ratio that will be present in the syngas is important when selecting the combination of syngas production technology (i.e. how the syngas is created, also called the “reforming process”) and the Fischer Tropsch synthesis technology (i.e. how the syngas is used in an FT reactor with an FT catalyst to create the liquid hydrocarbons). For example, using coal to produce the syngas results in a syngas having a relatively low H2/CO ratio. With a syngas having a relatively low H2/CO ratio, operators have typically selected an iron-based catalyst for the Fischer Tropsch catalyst because iron has a strong water-gas shift activity. The strong water-gas shift activity promotes the production of additional hydrogen for use in the FT reaction. In effect, the selection of an iron-based FT catalyst to be used with syngas from coal balances the relatively low H2/CO ratio in the syngas. Thus, many iron-based catalysts are able to reach thermodynamic equilibrium while performing as a Fischer Tropsch catalyst. This is not the case of cobalt-based FT catalysts, which have been considered to have a very low water gas shift activity. Most of the reported cobalt-based FT catalysts have less than 1% CO2 selectivity.
A syngas feed for an FT process typically contains less than 1.62 volume % carbon dioxide. See, for example, K. A. Petersen, T. S. Christensen, I. Dybkjaer, J. Sehested, M. Ostberg, R. M. Coertzen, M. J. Keyser, A. P. Steynberg., Chapter 4, “Synthesis Gas Production for FT Synthesis,” in F
For many years, CO2 has been considered either to be inert or detrimental to cobalt-based FT catalysts. See, for example, “Development of a CO2 Tolerant Fischer Tropsch Catalyst: From Laboratory to Commercial Scale Demonstration in Alaska”, J. J. H. M. Font Freide, T. D. Gamlin, J. R. Hensman, B. Nay, C. Sharp, Journal of Natural Gas Chemistry 13 (2004), pp 1-9. When testing 100% CO2 hydrogenation for very low concentrations of CO2 (<6.1%), researchers have found that some portion of the CO2 that reaches the FT reactor actually helps make the liquid hydrocarbons. However, those researchers concluded that CO2 hydrogenation to Fischer Tropsch products was not a commercial alternative. See “CO and CO2 Hydrogenation Study on Supported Cobalt Fischer Tropsch Synthesis Catalyst,” Y. Zhang, G. Jacobs, D. Sparks, M. E. Dry, B. H. Davis, Catalysis Today 71, (2002), pp. 411-418.
U.S. Pat. No. 8,168,684 to Hildebrandt, et al. (the “Hildebrandt patent”), incorporated in its entirety herein by reference for purposes not contrary to this disclosure, discloses a Fischer Tropsch process with a “CO2 rich syngas.” The Hildebrandt patent defines a “CO2 rich syngas” as “a gas mixture in which there is CO2, H2 and CO. The CO2 composition in this mixture is in excess of the CO2 which would usually occur in conventional syngas.” (Column 2, lines 17-20.) The example described therein used coal as a feedstock. (See the Hildebrandt patent at Col. 4, line 32 “The feed considered was coal.”) The patent also mentions the use of feedstocks comprising methane from natural gas (the Hildebrandt patent at Col. 3, lines 36-40 and Col. 5, lines 23-25) and gas “generated by fermentation of natural waste dumps” (the Hildebrandt patent at Col. 5, lines 23-25). The Hildebrandt patent at Col. 2, lines 20-21 states: “The CO2 is utilized as a reactant and is converted into the desired product.” The Hildebrandt patent also notes, “Unreacted carbon dioxide, carbon monoxide and hydrogen may be recirculated from the Fischer Tropsch synthesis section (5) into the gasifier/reforming process stage (3) via a conduit (7) or back to the Fischer Tropsch synthesis section.” (The Hildebrandt patent at Col. 3, lines 28-31.)
Claim 1 of the Hildebrandt patent recites in part the production of “hydrocarbons according to the overall process mass balance:
CO2+3H2⇄CH2+2H2O,″ (3)
an reaction which is known to work with iron-based FT catalysts, but not known to work with cobalt-based FT catalysts. (See Riedel et al, which at page 212 concluded, “Fischer-Tropsch CO2 hydrogenation would be possible even in a commercial process with iron, however, not with cobalt catalysts.”) The Hildebrandt patent does not, however, disclose the FT catalyst or the type of FT catalyst used in the FT process(es) described.
U.S. Pat. No. 8,461,219 to Steiner et al. (the Steiner Patent) discloses preparation of synthesis gas used as an input to an FT process with the “introduction of carbon dioxide recirculated from” the output of the FT reactor “into the synthesis gas during or after the preparation of synthesis gas,” wherein the synthesis gas used as an input to the FT reactor has “a hydrogen to carbon ratio of [less than or equal to] 1.2:1.” (The Steiner Patent at Col. 2, lines 12-30.) The specified H2:CO ratio of 1.2:1 may be considered quite low. While the Steiner Patent asserts that “iron- or cobalt-comprising heterogeneous catalyst can preferably be used in step c) [the FT conversion step],” (the Steiner Patent at Col. 3, lines 8-10), the Steiner Patent further states, “A Fischer-Tropsch catalyst which is a carbonyl iron powder catalyst having spherical primary particles is particularly preferred in step c).” (The Steiner Patent at Col. 3, lines 11-13.) It appears that such an iron-based catalyst was used in each of the examples described in the Steiner Patent: (1) for Example 1, “a carbonyl iron powder catalyst having spherical primary particles was produced . . . ” (the Steiner Patent at Col. 4, lines 64-Col. 5, line 1) and used with synthesis gas mixture having a H2 to CO ratio of 1:1; (2) for Example 2, the “trial was carried out by a method analogous to example 1, with the ratio of hydrogen to carbon monoxide in the synthesis gas being 0.9:1” (the Steiner Patent at Col. 5, lines 17-19); and (3) for Example 3, a “Comparative Example” which was conducted at a much higher H2:CO ratio, outside of that recited in the claims, the “process was operated under reaction conditions analogous to example 1, with the ratio of hydrogen to carbon monoxide in the synthesis gas being set to 2:1” (the Steiner Patent at Col. 5, lines 33-35).
A publication entitled, “Effect of Recycle Gas on Activity and Selectivity of CO—Ru/Al2O3 Catalyst in Fischer-Tropsch Synthesis,” A. A. Rohani, B. Hatami, L. Jokar, F. Khorasheh, A. A. Safekordi, World Academy of Science, Engineering and Technology, Vol. 3, Jan. 21, 2009 (pp. 549-553) (“Rohani, et al.”) reports experiments in carbon dioxide recycling in an FT system with cobalt FT catalysts with combination ruthenium and lanthanum promoters on an Al2O3 support. Rohani et al., conducted experiments using the Co—Ru—La catalysts in a micro reactor with a fixed bed column and a ratio of H2 to CO of 2. (Rohani et al., page 550, left column). Reactions were performed at three temperatures and at atmospheric pressure. Ibid.
Rohani et al., disclose that while adding “small amounts of CO2 to the feed stream did not change the CO conversion significantly,” with an “injection of about 10 vol. % and more [of CO2 in the feed], however, the CO conversion would decrease.” (Rohani et al., page 551, right column). The reduction in CO conversion was more significant at lower temperatures. (Rohani et al., page 552, left column). Similarly, “adding small amounts of CO2 (less than 10 vol. %) would not significantly affect the product selectivity. Further increases in the amount of CO2 in the feed, however, would decrease the selectivity for CH4 and other volatile hydrocarbons and increase those for the heavy components (C5+).” (Rohani et al., page 552, left column). “If there was no CO2 in the feed, the relative activity of the catalyst would decrease 21.8% in the first 15 hours but with 20% CO2 in the feed, the reduction of the relative activity was 39.8% over the same time period. The reduction of activity was only significant in the first 15 hours.” (Rohani et al., page 553, bottom of left column to top of right column).
Many operators use a cleaning step for the syngas to reduce the level of carbon dioxide. For example, some use a costly acid gas removal process, in which both CO2 and H25 are removed. The H2S is considered a poison for the FT catalyst, while the CO2 is considered inert; simultaneous removal has been commonly practiced. When natural gas is the feedstock used to create the syngas, the removal of sulfur and sulfur compounds can be done prior to the reforming step. If natural gas is the feedstock and if the sulfur and sulfur compounds are removed prior to reforming the natural gas into syngas, an acid gas cleaning step performed after the reforming would be solely for the removal of CO2.
Accordingly, there are needs in the art for novel systems and methods for using a syngas containing higher levels of carbon dioxide than are normally recommended in an FT process, to avoid the costs involved in reducing the carbon dioxide down to the recommended levels. Desirably, such systems and methods would enable an recycling as much of the carbon dioxide in the process as possible. Desirably, such systems and methods would have no deleterious effects on the FT process and in one or more embodiment would improve performance of the FT reactor.
These and other embodiments, features and advantages will be apparent in the following detailed description and drawings.
The present disclosure includes a method of producing Fischer-Tropsch (“FT”) hydrocarbons via FT synthesis in an FT reactor. The method includes producing a liquid FT hydrocarbon stream, an FT tail gas stream and an FT water stream using an FT reactor feed in the FT reactor under low temperature, high pressure FT operating conditions using a cobalt-based, alumina-supported FT catalyst. The FT reactor feed includes a mixture of carbon dioxide and syngas, the syngas having a low H2:CO ratio in the range of approximately 1.4:1 to approximately 1.8:1, and, the FT reactor feed having a level of carbon dioxide at least as high as about 10 volume percent. The syngas may be produced by a syngas preparation unit. The syngas preparation unit may be a steam methane reformer and the method may include a step of treating the syngas produced by the syngas preparation unit to achieve the low H2:CO ratio.
The present disclosure includes a system for producing Fischer Tropsch (“FT”) hydrocarbons. The system includes a syngas preparation unit for using a sweet natural gas, a stream of steam and a stream of carbon dioxide gas as inputs to produce a mixture of carbon dioxide and a syngas, the syngas comprising hydrogen and carbon monoxide, having an initial H2:CO ratio. The system includes a LTHP FT reactor, fluidly connected to the syngas preparation unit. The LTHP FT reactor includes an FT synthesis catalyst comprising a cobalt-based, alumina-supported FT catalyst. The LTHP FT reactor is configured to use a mixture of syngas that has a low H2:CO ratio ratio in the range of approximately 1.4:1 to approximately 1.8:1, and carbon dioxide as an FT reactor feed to make, under FT operating conditions, liquid FT hydrocarbons. The FT reactor feed has a carbon dioxide level of at least about 10 volume percent. The system may include a carbon dioxide recovery unit to recover a carbon dioxide stream from a portion of the FT tail gas.
The present disclosure includes an apparatus for producing Fischer Tropsch (“FT”) hydrocarbons. The apparatus includes a LTHP FT reactor having an FT synthesis catalyst comprising a cobalt-based, alumina-supported FT catalyst. The LTHP FT reactor is configured to use a FT reactor feed of a conditioned mixture including syngas having a low H2:CO ratio in the range of approximately 1.4:1 to approximately 1.8:1, and carbon dioxide to make, under FT operating conditions liquid FT hydrocarbons, FT tail gas and FT water. The FT reactor feed has a carbon dioxide level of at least about 12 volume percent. Some of the carbon dioxide in the FT reactor feed may be carbon dioxide recovered from the FT tail gas and recycled upstream of the FT reactor.
For a more detailed description of the present invention, reference will now be made to the accompanying drawings, wherein:
As used herein, the abbreviation “FT” and/or “F-T” stand for Fischer Tropsch (which may be written “Fischer-Tropsch”). A Fisher-Tropsch reactor, for example, may also be referred to as a “FT synthesis reactor” or “FT reactor” herein.
As used herein, the term “FT purge stream” means excess FT tail gas removed from the primary FT tail gas stream. The FT purge stream has the same composition as the FT tail gas.
As used herein, the term “FT tail gas” means gas produced from an FT reactor. The FT tail gas may typically contain unreacted hydrogen and carbon monoxide, as well as carbon dioxide, some light hydrocarbons, and other light reaction byproducts.
As used herein, the term “FT water” means water produced by an FT reaction. The water will typically include dissolved oxygenated species, such as alcohols, and light hydrocarbons.
As used herein, the term “liquid FT hydrocarbon products” means liquid hydrocarbons produced by an FT reactor.
As used herein, the phrase a “low H2/CO ratio” as used herein means a H2/CO ratio lower than the 2:1 stoichiometric ratio of a Fischer Tropsch reaction. The phrase a “low H2:CO ratio” as used herein means a H2/CO ratio higher than 1.2:1, lower than 2:1, preferably in a range of 1.4:1 to approximately 1.8 to 1 and more preferably about 1.6:1.
As used herein, the terms “reformed gas” or “synthesis gas” or “syngas” means the effluent from a syngas preparation unit, such as (without limitation) a steam methane reformer, autothermal reformer, hybrid reformer, or partial oxidation reactor. Steam methane reformers do not use oxygen as part of the process; autothermal reformers do. Both use reformer catalysts. Hybrid reformers are a combination of steam methane reforming, as a first step, and an autothermal reforming with oxidation as a second step. Partial oxidation reactors are similar to autothermal reformers, but do not include the use of a reformer catalyst.
As used herein, the term “sweet natural gas” means natural gas from which any excess sulfur or sulfur compounds such as H2S has been previously removed.
As used herein, the term “tubular reactor” refers to Fischer-Tropsch reactors containing one or more tubes containing FT catalyst, wherein the inner diameter or average width of the one or more tubes is typically greater than about 0.5 inches. Use of the term “tubular” is not meant to be limiting to a specific cross sectional shape. For example, tubes may have a cross-sectional shape that is not circular. Accordingly, the tubes of a tubular reactor may, in one or more embodiments, have a circular, elliptical, rectangular, and/or other cross sectional shape(s).
As used herein and as mentioned above, the abbreviation “WGSR” stands for water-gas-shift reaction, while “WGS” stands for water-gas-shift.
In one or more embodiments of the embodiments of the disclosure, recycling CO2 recovered from production of an FT reactor appears to have no deleterious effects on the FT process. If a steam methane reformer (“SMR”) is used to produce the syngas, it would ordinarily produce a higher ratio of hydrogen with respect to carbon monoxide than needed in the feed for the FT reactor. In one or more embodiments of the embodiments of the disclosure, a portion of the CO2 recycled to the SMR is converted to carbon monoxide, mitigating the need to adjust the hydrogen level. While the phenomena of conversion of carbon dioxide to carbon monoxide has been used with methanol plants, it is not believed to have been implemented in an FT process in conjunction with recycling recovered CO2. In addition, it appears that having a higher ratio of CO2 in the syngas mixture used as a feed to the FT reactor improves the heat transfer properties of the feed gas and thus the performance of the FT reactor.
Laboratory test results made with respect to an FT system in accordance with the present disclosure indicate that carbon dioxide in the feed gas to the FT reactor at levels around 12-25% or more may improve performance of the FT reactor, using a LTHP (low temperature, high pressure) FT reactor having a cobalt-based, alumina-supported FT catalyst, such as TL8™ or TL8H™ available from Emerging Fuels Technologies, Inc. (“EFT”) or FT Co Premier™ available from Cosmas Inc. Pilot plant operations have confirmed that an advantage to the presence of carbon dioxide at levels around 12-25% or more in the synthesis gas feed to the FT Reactor. From pilot plant tests, it does not appear that any noticeable amount of CO2 acts as a reactant in the FT reactor. Instead, while not being bound by theory, it is surmised that the high carbon dioxide concentration significantly improves the heat transfer properties of the syngas in the FT reactor. Preferably, the feedstock for a syngas preparation unit to make syngas comprises natural gas, although other carbonaceous feedstocks may also be used. The feed gas to the FT reactor would comprise carbon dioxide and syngas, with the syngas preferably having a low H2:CO ratio, such as in a range of 1.4:1 to 1.8:1 and preferably approximately 1.6:1.
When steam methane reforming is used to produce syngas from natural gas for FT synthesis, CO2 will typically be present in the raw syngas in concentrations up to 10 vol. % on a dry basis. A smaller volume of CO2 may also be captured from an FT tail gas and/or an FT purge stream taken from an FT tail gas by one or more means, such as an amine CO2 removal system or similar absorbent. Alternatively, carbon dioxide may be supplied from outside the FT plant.
CO2+H2⇄CO+H2O. (4)
Carbon dioxide combines with hydrogen in the steam methane reformer, converting to carbon monoxide and water, thus resulting in a lower ratio of hydrogen to carbon monoxide in the resulting syngas than would be produced without the additional carbon dioxide. Accordingly, provision of additional CO2 to a steam methane reformer, for example through recycling of CO2, may be beneficial to the overall FT process, as more carbon monoxide is produced and less hydrogen has to be removed. In addition or in the alternative, carbon dioxide from other sources (not depicted in
In
Continuing to refer to
The FT reactor 170 is preferably a low temperature, low pressure fixed bed, tubular FT reactor and may comprise two or more reactor vessels operating in parallel. The tube velocity used in the FT reactor is in a range of approximately 0.3 ft/sec to 1.5 ft/sec and preferably approximately 0.5 ft/sec. In other embodiments, the FT reactor may be a slurry FT reactor or a bubble-column FT reactor or a compact FT reactor.
Although not depicted in
Referring again to
In the embodiments of
A flue gas and a syngas exit the syngas preparation unit 230 via a flue gas flowline 232 and a first syngas flowline 234, respectively. A first stream of process condensate exits the syngas preparation unit 230 via a first process condensate flowline 233. Unlike a steam methane reformer, an ATR does not produce syngas with a high hydrogen to carbon monoxide ratio, so there may be little if any excess hydrogen to be removed. However, if an adjustment of the hydrogen to carbon monoxide ratio is to be made, the syngas passes via the first syngas flowline 234 to a syngas conditioning unit 260. In the embodiments depicted in
Referring again to
The FT reactor 270 is preferably a low temperature, high pressure, fixed bed, tubular FT reactor and may comprise two or more reactor vessels operating in parallel. The tube velocity used in the FT reactor is in a range of approximately 0.3 ft/sec to 1.5 ft/sec and preferably approximately 0.5 ft/sec. In other embodiments, the FT reactor 270 may comprise a slurry FT reactor or a bubble-column FT reactor or a compact FT reactor.
Although not depicted in
Continuing to refer to
The syngas preparation unit 330, preferably a steam methane reformer, converts the carbonaceous source into a syngas, which is a component of a gas mixture, which also contains CO2. A flue gas exits the syngas preparation unit 330 via a flue gas flowline 332. The produced gas mixture exits the syngas preparation unit 330 via a first mixed flowline 334. A first stream of process condensate 333 exits the syngas preparation unit 330 via a first process condensate flowline. The gas mixture passes to a syngas conditioning unit 360. The syngas conditioning unit 360 removes from the syngas a second stream of process condensate, which exits the syngas conditioning unit 360 via a second process condensate flowline 362. The syngas conditioning unit 360 adjusts the hydrogen and carbon monoxide ratios in the syngas of the gas mixture to pre-determined levels, if needed, to form a conditioned gas mixture. Excess hydrogen may be carried from the syngas conditioning unit 360 in hydrogen flowline 363. Preferably, the H2:CO ratio of the conditioned syngas is sub-stoichiometric, that is below 2 to 1, preferably in the range of approximately 1.4:1 to approximately 1.8:1 and more preferably approximately 1.6 to 1.
The conditioned gas mixture is sent via a third flowline 365 to an FT reactor 370 as a feed. A second portion of the carbon dioxide recycle stream is optionally added to the conditioned gas mixture upstream of the FT reactor 370, as part of the FT reactor feed. The FT reactor 370 preferably uses a cobalt-based, alumina-supported catalyst, such a TL8™ or TL8H™, both available from Emerging Fuels Technologies, Inc. (“EFT”) or FT Co Premier available from Cosmas, as the FT catalyst. In accordance with the present disclosure, the FT reactor feed to the FT reactor 370 may contain substantial amounts of carbon dioxide, such as 12-25% or greater. In embodiments, the FT reactor feed contains about at least 10 vol % of carbon dioxide. In embodiments, the FT reactor feed contains about at least 12 vol % of carbon dioxide. In embodiments, the FT reactor feed contains about at least 15 vol % of carbon dioxide. In embodiments, the FT reactor feed contains about at least 20 vol % of carbon dioxide. In embodiments, FT reactor feed contains about at least 25 vol % of carbon dioxide.
The FT reactor 370 is preferably a low temperature, high pressure, fixed bed, tubular FT reactor and may comprise two or more reactor vessels operating in parallel. The tube velocity used in the FT reactor 370 is in a range of approximately 0.3 ft/sec to 1.5 ft/sec and preferably approximately 0.5 ft/sec. In other embodiments, the FT reactor 370 may comprise a slurry FT reactor or a bubble-column FT reactor or a compact FT reactor. Although not depicted in
The inlet pressure of the FT reactor 370 may be in the range of approximately 400 psia to approximately 500 psia. In embodiments, the inlet pressure of the FT reactor 370 may be in the range of approximately 420 psia to approximately 480 psia. In embodiments, the inlet pressure of the FT reactor 370 may be in the range of approximately 440 psia to approximately 460 psia.
Fluids produced by the FT reactor 370 include an FT tail gas stream, an FT water stream, and liquid FT hydrocarbon stream. The FT tail gas exits the FT reactor 370 via a first FT tail gas flowline 371. The liquid FT hydrocarbon stream exits the FT reactor 370 via an FT products flowline 379, to storage and/or additional processing. The FT water stream exits the FT reactor 370 via an FT water flowline 374. As described in co-pending PCT Patent Application No. PCT/US2015/033233, optionally, a first portion of the FT tail gas is recycled as a feed to the syngas preparation unit 330 via a second FT tail gas flowline 372.
A second portion of the FT tail gas is sent via a third FT tail gas flowline 373 to a carbon dioxide removal unit 390, which removes carbon dioxide from the second portion of the FT tail gas. The removed carbon dioxide forms a carbon dioxide recycle stream, which exits the carbon dioxide removal unit 390 via a first carbon dioxide recycle line 392. The carbon dioxide removal unit 390 also produces a treated purge steam gas. The treated purge steam gas may contain hydrogen. The treated purge steam gas exits the carbon dioxide removal unit 390 via a treated purge gas line 394 and may be used for fuel for the syngas preparation unit 330 or for other plant purposes.
In accordance with the present disclosure, as depicted in
Continuing to refer to
While some preferred embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments described herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations. The use of the term “optionally” with respect to any element of a claim is intended to mean that the subject element is required, or alternatively, is not required. Both alternatives are intended to be within the scope of the claim. Use of broader terms such as comprises, includes, having, etc. should be understood to provide support for narrower terms such as consisting of, consisting essentially of, comprised substantially of, and the like.
Accordingly, the scope of protection is not limited by the description set out above but is only limited by the claims that follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated into the specification as an embodiment of the present invention. Thus, the claims are a further description and are an addition to the preferred embodiments of the present invention. The inclusion or discussion of a reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated by reference, to the extent that they provide background knowledge; or exemplary, procedural or other details supplementary to those set forth herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2016/000830 | 5/31/2016 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62168743 | May 2015 | US |
