This invention relates generally to the field of heat exchanger operations. Our immediate interest is in preventing stoppage of operations of a cryogenic heat exchange process due to fouling.
Heat exchange is a fundamental unit operation in nearly all chemical processes, from simple in-home heaters to extraordinarily complex industrial furnaces. The art of cryogenic heat exchange is a less mature branch of industrial heat exchange. Cryogenic heat exchange adds a new problem to heat exchange. Whereas traditional heat exchangers are typically blocked by scale formation or deposition of entrained solids, cryogenic heat exchangers can also be blocked by constituents in the process fluid condensing out of the process fluid and depositing onto the walls of the heat exchanger. These deposits can not only exacerbate deposition of entrained solids, but can block the heat exchanger independently.
Fouling removal methods are common and can include techniques ranging from the complexity of dismantling the system to manually remove scale to the simplicity of banging on the exchanger with a hammer. However, removal of cryogenic deposits is not addressed well by these techniques as continuous operations are very important at these low temperatures.
Further, heat exchangers are not inexpensive pieces of equipment. While the standard in heavy industry is to have spare, in-line equipment for some operations, such as pumps, larger capital equipment is often too expensive to keep one spare and one standby. Even when there are spare heat exchangers, switching between these exchangers often results in significant downtime. Cryogenics, being a relatively young industry, requires better methods for maintaining continuous or semi-continuous operations.
With the need for cryogenic heat exchange on the rise, new methods are needed to address any limitations that exist.
United States patent publication number 2006/0156744 to Cusiter teaches a liquefied natural gas floating storage regasification unit. This disclosure is pertinent and may benefit from semi-continuous heat exchanger methods disclosed herein and is hereby incorporated for reference in its entirety for all that it teaches.
United States patent publication number 2008/0073063 to Clavenna et al. teaches a method for reduction of fouling in heat exchangers. This disclosure is pertinent and may benefit from semi-continuous heat exchanger methods disclosed herein and is hereby incorporated for reference in its entirety for all that it teaches.
A method for semi-continuous operation of a heat exchange process that alternates between a first heat exchanger and a second heat exchanger is disclosed. The method comprises, first, providing a contact liquid to a first heat exchanger to cool via heat exchange with a coolant while the second heat exchanger is on standby. The contact liquid contains a dissolved gas, an entrained gas, or residual small particles that foul the first heat exchanger by condensing or depositing as a foulant onto at least a portion of the interior walls of the first heat exchanger, restricting free flow of the contact liquid. Second, detecting a pressure drop across the first heat exchanger, the first heat exchanger operating while the second heat exchanger is on standby. Third, stopping flow of the coolant to the first heat exchanger, beginning flow of the contact liquid to the second heat exchanger, stopping flow of the contact liquid to the first heat exchanger, and beginning flow of the coolant to the second heat exchanger. Fourth, removing the foulant from the now standby first heat exchanger by providing heat to the portion of the interior walls of the heat exchanger where the foulant is condensed, passing a non-reactive gas across the portion of the interior walls of the heat exchanger where the foulant is condensed, or a combination thereof. At this point, the first heat exchanger and the second heat exchanger switch roles from standby to operating, and steps i to iv repeated with reversed roles, as necessary. In this manner, the heat exchange process operates semi-continuously.
In some embodiments of the present invention, the foulant comprises carbon dioxide, nitrogen oxide, sulfur dioxide, nitrogen dioxide, sulfur trioxide, hydrogen sulfide, mercury, entrained particulate, hydrogen cyanide, impurities of burned fuel, byproducts of burned fuel, or a combination thereof.
In some embodiments of the present invention, the contact liquid comprises 1,1,3-trimethylcyclopentane, 1,4-pentadiene, 1,5-hexadiene, 1-butene, 1-methyl-1-ethylcyclopentane, 1-pentene, 2,3,3,3-tetrafluoropropene, 2,3-dimethyl-1-butene, 2-chloro-1,1,1,2-tetrafluoroethane, 2-methylpentane, 3-methyl-1,4-pentadiene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-methylpentane, 4-methyl-1-hexene, 4-methyl-1-pentene, 4-methylcyclopentene, 4-methyl-trans-2-pentene, bromochlorodifluoromethane, bromodifluoromethane, bromotrifluoroethylene, chlorotrifluoroethylene, cis 2-hexene, cis-1,3-pentadiene, cis-2-hexene, cis-2-pentene, dichlorodifluoromethane, difluoromethyl ether, trifluoromethyl ether, dimethyl ether, ethyl fluoride, ethyl mercaptan, hexafluoropropylene, isobutane, isobutene, isobutyl mercaptan, isopentane, isoprene, methyl isopropyl ether, methylcyclohexane, methylcyclopentane, methylcyclopropane, n,n-diethylmethylamine, octafluoropropane, pentafluoroethyl trifluorovinyl ether, propane, sec-butyl mercaptan, trans-2-pentene, trifluoromethyl trifluorovinyl ether, vinyl chloride, bromotrifluoromethane, chlorodifluoromethane, dimethyl silane, ketene, methyl silane, perchloryl fluoride, propylene, vinyl fluoride, or combinations thereof.
In some embodiments of the present invention, the heat exchanger comprises a brazed plate, aluminum plate, shell and tube, plate, plate and frame, plate and shell, or plate fin style heat exchanger.
In some embodiments of the present invention, the non-reactive gas comprises nitrogen, methane, argon, or combinations thereof.
In some embodiments of the present invention, the non-reactive gas is pre-heated and moisture removed by passing the non-reactive gas across a desiccant.
In some embodiments of the present invention, the heat provided to the interior walls of the fouled heat exchanger is provided by heating elements attached to the heat exchanger. These heating elements can be attached to an exterior wall of the heat exchanger. The contact liquid can travel through the exterior elements of the heat exchanger. In other embodiments, the contact liquid travels through interior elements of the heat exchanger. In this latter case, the heating elements can be attached to the outside of the interior elements.
In some embodiments of the present invention, the heating elements are comprised of piezoelectric heaters, heat trace tape, heat trace sheets, band heaters, or combinations thereof.
In some embodiments of the present invention, the heating elements are located at the inlet and outlet of the interior elements to the heat exchanger. In this instance, the heating elements warm only the portion of the interior elements that extend out of the heat exchanger, and heat is conducted along the interior elements.
In one embodiment of the present invention, the heat exchangers are shell and tube style heat exchangers, as in
In some embodiments of the present invention, the contact liquid travels through interior elements of the heat exchanger and the heat provided to the interior walls of the heat exchanger is provided by passing a warm fluid through the outer elements of the heat exchanger. The warm fluid can be air, nitrogen, carbon dioxide, argon, or combinations thereof. The warm fluid may also be a liquid such as water or one of the contact liquids mentioned above.
In some embodiments of the present invention, the heating elements are attached to the inside of the interior elements. The heating elements are comprised of piezoelectric heaters, heat trace tape, heat trace sheets, or combinations thereof.
In one embodiment of the present invention, after shutdown of the restricted heat exchanger, the connections to the interior elements by external piping are disconnected and the heating elements are inserted into the inside of the interior elements.
In order that the advantages of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through use of the accompanying drawings, in which:
It will be readily understood that the components of the present invention, as generally described and illustrated in the Figures herein, may be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the invention, as represented in the Figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of certain examples of presently contemplated embodiments in accordance with the invention.
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In some embodiments, coolants 112, 212, 312, and 412 comprise liquid nitrogen, ethane, methane, propane, refrigerants, or combinations thereof.
In some embodiments, the heat exchangers comprise brazed plate, aluminum plate, shell and tube, plate, plate and frame, plate and shell, or plate fin style heat exchangers.
In some embodiments, the non-reactive gas comprises nitrogen, methane, argon, or combinations thereof.
In some embodiments, the foulant comprises carbon dioxide, nitrogen oxide, sulfur dioxide, nitrogen dioxide, sulfur trioxide, hydrogen sulfide, mercury, entrained particulate, hydrogen cyanide, impurities of burned fuel, byproducts of burned fuel, or a combination thereof.
In some embodiments, contact liquids 102, 202, and 302 would comprise 1,1,3-trimethylcyclopentane, 1,4-pentadiene, 1,5-hexadiene, 1-butene, 1-methyl-1-ethylcyclopentane, 1-pentene, 2,3,3,3-tetrafluoropropene, 2,3-dimethyl-1-butene, 2-chloro-1,1,1,2-tetrafluoroethane, 2-methylpentane, 3-methyl-1,4-pentadiene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-methylpentane, 4-methyl-1-hexene, 4-methyl-1-pentene, 4-methylcyclopentene, 4-methyl-trans-2-pentene, bromochlorodifluoromethane, bromodifluoromethane, bromotrifluoroethylene, chlorotrifluoroethylene, cis 2-hexene, cis-1,3-pentadiene, cis-2-hexene, cis-2-pentene, dichlorodifluoromethane, difluoromethyl ether, trifluoromethyl ether, dimethyl ether, ethyl fluoride, ethyl mercaptan, hexafluoropropylene, isobutane, isobutene, isobutyl mercaptan, isopentane, isoprene, methyl isopropyl ether, methylcyclohexane, methylcyclopentane, methylcyclopropane, n,n-diethylmethylamine, octafluoropropane, pentafluoroethyl trifluorovinyl ether, propane, sec-butyl mercaptan, trans-2-pentene, trifluoromethyl trifluorovinyl ether, vinyl chloride, bromotrifluoromethane, chlorodifluoromethane, dimethyl silane, ketene, methyl silane, perchloryl fluoride, propylene, vinyl fluoride, or combinations thereof.
In some embodiments, the non-reactive gas is pre-heated and moisture removed by passing the non-reactive gas across a desiccant.
In some embodiments, warm fluid 314 would comprise water, 1,1,3-trimethylcyclopentane, 1,4-pentadiene, 1,5-hexadiene, 1-butene, 1-methyl-1-ethylcyclopentane, 1-pentene, 2,3,3,3-tetrafluoropropene, 2,3-dimethyl-1-butene, 2-chloro-1,1,1,2-tetrafluoroethane, 2-methylpentane, 3-methyl-1,4-pentadiene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-methylpentane, 4-methyl-1-hexene, 4-methyl-1-pentene, 4-methylcyclopentene, 4-methyl-trans-2-pentene, bromochlorodifluoromethane, bromodifluoromethane, bromotrifluoroethylene, chlorotrifluoroethylene, cis 2-hexene, cis-1,3-pentadiene, cis-2-hexene, cis-2-pentene, dichlorodifluoromethane, difluoromethyl ether, trifluoromethyl ether, dimethyl ether, ethyl fluoride, ethyl mercaptan, hexafluoropropylene, isobutane, isobutene, isobutyl mercaptan, isopentane, isoprene, methyl isopropyl ether, methylcyclohexane, methylcyclopentane, methylcyclopropane, n,n-diethylmethylamine, octafluoropropane, pentafluoroethyl trifluorovinyl ether, propane, sec-butyl mercaptan, trans-2-pentene, trifluoromethyl trifluorovinyl ether, vinyl chloride, bromotrifluoromethane, chlorodifluoromethane, dimethyl silane, ketene, methyl silane, perchloryl fluoride, propylene, vinyl fluoride, or combinations thereof.
This invention was made with government support under DE-FE0028697 awarded by. The Department of Energy. The government has certain rights in the invention.
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Number | Date | Country | |
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20180224225 A1 | Aug 2018 | US |