The present invention relates generally to the recovery of valuable by-products from refinery gas streams, such as hydrogen.
The petroleum industry has often sought new integration opportunities for its refinery products with other processes. One of the areas of interest concerns refinery gases that are currently used as a fuel. In addition, refineries are processing heavier crude oils and sulfur specifications for both diesel and gasoline products are becoming more stringent. Hydrogen can be used within hydrotreaters to remove sulfur, oxygen, and nitrogen and also within hydrocrackers to produce lighter and more paraffinic oils. Consequently, refineries are looking for low cost sources of hydrogen.
While the refinery gases are a potential source of hydrogen, many refinery gas streams are not used either for their hydrogen content or to generate hydrogen through known reforming techniques due to a variety of economic and practical reasons. For instance, the economics for separating hydrogen from refinery gases that contain less than about 30% hydrogen are generally unfavorable. Generally, the hydrogen concentration within such refinery off-gases is too low for the hydrogen to be economically recovered using current available separation technologies.
Several processes are known in the art for the separation and recovery of hydrogen from hydrogen-hydrocarbon feed gas streams. Among these are the following:
U.S. Pat. No. 3,838,553 (Doherty) describes a combination pressure swing adsorption (PSA) and cryogenic process to recover a light gas, especially hydrogen or helium, at high purity and at high recovery from a multicomponent gaseous mixture. The process described by Doherty utilizes both a low temperature separator unit (LTU) and a pressure swing adsorber with recompression of the regeneration stream from the latter and recycle of the recompressed stream to the LTU. However, Doherty requires upgrading the hydrogen stream to at least 95% hydrogen prior to PSA purification. Also, Doherty teaches the recycling of the PSA tailgas, which is uneconomical for PSAs with reasonable recovery (e.g., higher than 80%) due to high compression costs. Furthermore, Doherty does not consider the recovery of heavy hydrocarbons (ethane and heavier).
U.S. Pat. No. 3,691,779 (Meisler et al.) describes a process consisting of a low temperature refrigeration unit and a PSA for producing a high purity, 97 to 99.9% hydrogen. The hydrogen-rich feed, containing methane, nitrogen, carbon monoxide and traces of argon, oxygen, carbon dioxide and light hydrocarbons, passes through a series of cooling and condensation stages having successively lower temperatures, the lowest being −340° F. (120° R). Hydrogen containing vapors and condensate are separated between cooling stages. The hydrogen-enriched gas is sent for further upgrading to an adsorption system operating between −260 to −320° F. (200 to 140° R). A portion of the upgraded stream is expanded, passed through at least one refrigeration stage to provide refrigeration, and then used for regeneration in the PSA system. Most of the refrigeration is provided by Joule-Thomson expansion of the condensates. Meisler et al. teach the use of a capital intensive system, due to the multiple steps required for refrigeration in order to upgrade the feed to approximately 97% hydrogen before sending to PSA. Meisler et al. also teach very low temperature levels in the cold box, driven mostly by the amount of non-condensable compounds present in the feed and the high purity required for the hydrogen stream.
U.S. Pat. No. 7,041,271 (Drnevich et al.) discloses an integrated method for olefins recovery and hydrogen production from a refinery off-gas. After conventional pretreatment, the refinery gas is separated to obtain a light ends stream containing hydrogen, nitrogen and methane, and a heavy ends stream containing olefins. The light ends stream is mixed with natural gas and subjected to reforming and water gas shift reactions for hydrogen production. The heavy ends can be further processed for olefin recovery, such as ethylene and propylene. Drnevich et al. teach the recovery one light end stream from the refinery off-gas. Also, the present invention does not consider the further processing of C2+hydrocarbon stream for olefin/liquefied petroleum gas (LPG) recovery. Furthermore, Drnevich et al. teach the use of low temperature distillation, membrane, PSA and adsorption-desorption processes as means for light end separation, but partial condensation is not discussed.
U.S. Pat. No. 4,749,393 (Rowles et al.) describes a hybrid gas separation process which recovers both heavy hydrocarbon (C2+, C3+ or C4+) and high purity hydrogen products from a gas containing a relatively low concentration of hydrogen (<40%). The process comprises a warm heat exchanger where the feed (together with recycle from the hydrogen purifier) is cooled to an intermediate temperature to allow the recovery of heavy hydrocarbons, a separator coupled with a dephlegmator (reflux condenser) for enriching the heavy hydrocarbons condensate, and a cold heat exchanger followed by a separator, from which an enriched hydrogen gas is obtained and, after warming to recover the refrigeration, is sent to the hydrogen purifier (e.g., PSA, membrane). An optional turboexpander or compressor (depending on the hydrogen purifier requirements) can be added on the hydrogen-enriched stream. The condensate from the cold end separator, rich in methane (80-85%) is used to generate the refrigeration through Joule-Thomson expansion and then is sent to fuel. Additional refrigeration is generated by Joule-Thomson expansion of the condensate from the warm end separator/dephlegmator. The tailgas from the hydrogen purifier (PSA) is recycled to the feed, which can be uneconomical due to recompression requirements. In addition, the use of the dephlegmator for enriching the hydrocarbon condensate can be expensive.
As will be discussed, the present invention provides a process for recovering valuable products, especially hydrogen, from refinery fuel gases in order to economically and practically produce such products and increase efficiency and lower costs.
The present invention relates to a process and system for recovering high purity hydrogen and optionally one or more hydrocarbon-rich products from a feed gas containing less than 50 mole % hydrogen via partial condensation in an auto-refrigeration cold box and PSA. The process can be used stand-alone, only for hydrogen recovery, or can be modified to allow the recovery of other valuable by-products such as methane-rich gas and raw LPG (methane depleted gas containing ethane and heavier hydrocarbons, usually used as feedstock for LPG recovery). In the stand-alone process, the feed is compressed, treated for water and impurities removal, cooled in a cold box and then sent to a separator. The separator liquid is used to provide refrigeration through Joule-Thomson expansion and, after warming in the heat exchanger against the incoming feed, is sent to fuel. The high pressure vapor from the separator, containing at least 60% hydrogen, is warmed against the incoming feed and sent to PSA for purification. The PSA tailgas is sent to fuel after recompression.
In another embodiment of the invention, the feed, after compression and treatment, is cooled in two stages. After the first cooling stage (warm end heat exchanger) the feed is separated at high pressure and a temperature chosen such as to maximize the recovery of the C2+ hydrocarbons in the liquid phase. The gas phase is sent to a second cooling stage (cold end heat exchanger), and then separated into a hydrogen-rich stream containing at least 60% hydrogen and a liquid containing at least 70% methane. The condensate, after Joule-Thomson expansion to provide refrigeration and warming in the cold end heat exchanger, is used as stripping gas in a low pressure wash column, to enhance hydrocarbon recovery in the condensate. The hydrogen-rich vapor is warmed against incoming feed in both cold end and warm end heat exchangers and then sent to PSA for purification. The PSA tailgas is sent, after recompression, to fuel. Wash column vapor product is, after warming against incoming feed, sent to fuel or, after further compression and cooling, sent as SMR feed. The liquid product from the wash column is, after warming against incoming feed, sent to further processing for LPG recovery.
Compared to the prior art, the present invention is more efficient. For example, Doherty teaches that the hydrogen stream must be at 95% prior to PSA purification, whereas the present invention requires only around 60% hydrogen. The present invention also uses a wash column for recovering C2+ hydrocarbons from the gaseous phase. Using the wash column arrangement, a simpler configuration is used to obtain basically the same quality products, leading to lower capital costs. As compared to the invention of Drnevich et al., the present invention separates two light end streams, a low pressure methane-rich stream, which is blended with natural gas and sent as feed to a steam methane reformer (SMR) and a hydrogen-rich stream at high pressure, which can be fed directly to the PSA. This allows for more flexibility in blending in order to meet certain requirements for SMR feed. For example, the hydrogen needs for the hydrotreating step can be satisfied by mixing a part of the hydrogen-rich stream with the SMR feed.
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 drawings:
The present invention relates to a process and system for recovering high purity hydrogen and optionally one or more hydrocarbon-rich product from a feed gas containing less than 50 mole % hydrogen via partial condensation in an auto-refrigeration cold box and PSA. The process can be used stand-alone, only for hydrogen recovery, or can be modified to allow the recovery of other valuable by-products such as methane-rich gas and raw LPG (methane depleted gases containing ethane and heavier hydrocarbons, usually used as feedstock for LPG recovery). As used herein, the percentage of hydrogen or other components may be expressed as “%” or “mole %”. In the stand-alone process (
In another embodiment of the invention (
One embodiment of the present invention is a process for recovering high purity hydrogen and optionally one or more hydrocarbon-rich products from a feed gas containing less than 50 mole % hydrogen, as represented by
Another embodiment of the present invention is a process for recovering high purity hydrogen and optionally one or more hydrocarbon-rich products from a feed gas containing less than 50 mole % hydrogen, as represented by
A third embodiment of the present invention is represented by
Process 1: Hydrogen Only (
Referring to
Process scheme shown in
Process 2: Hydrogen, Raw LPG and Methane-Rich Gas (
The partial condensation arrangement in
The process scheme shown in
Process 3: Hydrogen, Raw LPG and SMR Feed (
The methane-rich gas obtained as vapor product from the wash column can be used either as fuel (as in embodiment in
Process scheme shown in
Although the invention has been described in detail with reference to certain preferred embodiments, those skilled in the art will recognize that there are other embodiments within the spirit and the scope of the claims.
This application claims the benefit of U.S. Provisional Application Ser. No. 60/872,919, filed Dec. 5, 2006, which is incorporated herein by reference.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US2007/086488 | 12/5/2007 | WO | 00 | 1/12/2010 |
Publishing Document | Publishing Date | Country | Kind |
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WO2008/070714 | 6/12/2008 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
3223745 | Davison | Dec 1965 | A |
3359744 | Bolez et al. | Dec 1967 | A |
3628340 | Meisler et al. | Dec 1971 | A |
3691779 | Meisler et al. | Sep 1972 | A |
3796059 | Banikiotes et al. | Mar 1974 | A |
3838553 | Doherty | Oct 1974 | A |
4043770 | Jakob | Aug 1977 | A |
4242875 | Schaefer | Jan 1981 | A |
4443238 | Beddone et al. | Apr 1984 | A |
4482369 | Carson et al. | Nov 1984 | A |
4547205 | Steacy | Oct 1985 | A |
4617039 | Buck | Oct 1986 | A |
4732596 | Nicholas et al. | Mar 1988 | A |
4749393 | Rowles et al. | Jun 1988 | A |
4756730 | Stupin | Jul 1988 | A |
6159272 | Baker et al. | Dec 2000 | A |
6560989 | Roberts et al. | May 2003 | B1 |
6931889 | Foglietta et al. | Aug 2005 | B1 |
7402287 | Wheat et al. | Jul 2008 | B2 |
Number | Date | Country |
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WO 03051482 | Jun 2003 | WO |
Number | Date | Country | |
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20100107685 A1 | May 2010 | US |
Number | Date | Country | |
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60872919 | Dec 2006 | US |