FIELD OF THE INVENTION
This invention relates generally to operation of heat exchangers. More particularly, we are interested in continuous operations of heat exchangers for use in foulant removal.
BACKGROUND
The art of removing condensable vapors from gases, such as carbon dioxide from combustion flue gas, is a new and growing field. One of the greatest challenges in the field is heat exchange in indirect-contact heat exchangers. Cooling of liquids containing condensable gases can lead to desublimation of gases directly onto the outside surface of the cooling section of the exchanger, fouling and eventually blocking the process fluid flow. Shut down, drainage, and removal can be a significant cost, both from downtime of the equipment and from startup costs inherent in cryogenic exchange. The ability to remove foulants and prevent blockage without shutdown or significant re-cooling costs is required.
United States patent publication number 8715401, to Baxter teaches methods and systems for separating condensable vapors from gases. Condensable vapors, such as carbon dioxide, are separated from light gases using heat exchangers. The present disclosure differs from this disclosure in that the only strategy for preventing fouling of the heat exchanger surface is to provide a bed of particles on which the vapors can desublimate, minimizing the amount of desublimation that can occur on the heat exchanger surface. This disclosure is pertinent and may benefit from the devices disclosed herein and is hereby incorporated for reference in its entirety for all that it teaches.
U.S. patent application Ser. No. 15/425,276, to Baxter, et al., teaches a method for semi-continuous heat exchange operations by alternating between heat exchangers. Condensable vapors, such as carbon dioxide, desublimate onto exchanger surfaces, causing fouling. The method consists of switching heat exchangers when fouling occurs in one, allowing the first to have fluids removed and foulant to melt. The present disclosure differs from this disclosure in that the procedure requires two heat exchangers and shuts down the fouled heat exchanger entirely. This disclosure is pertinent and may benefit from the devices disclosed herein and is hereby incorporated for reference in its entirety for all that it teaches.
SUMMARY
A method for removing a foulant from a heat exchanger is disclosed. The heat exchanger, comprising a process side and a coolant side, is provided. A process fluid, comprising a process liquid and a fouling component, are provided to the process side. A flow of a coolant to the coolant side is provided by opening an inlet to the coolant side. The process fluid is cooled, a portion of the fouling component desublimating, crystallizing, freezing, condensing coupled with solidifying, or a combination thereof as a first portion of the foulant onto an outer surface of the coolant side. The inlet to the coolant side is periodically closed such that the flow of the coolant slows or stops, warming the process side, and causing the first portion of the foulant to sublimate, melt, absorb, or a combination thereof off the outer surface of the coolant side. The process then returns to the providing the flow of the coolant step. In this manner, the foulant is removed from the heat exchanger.
Cooling the process fluid may further crystallize, freeze, solidify, or a combination thereof a portion of the process liquid onto the outer surface of the coolant side such that the portion of the process liquid forms a second portion of the foulant. The heat exchanger may further comprise a shell and tube style exchanger, plate style exchanger, plate and frame style exchanger, plate and shell style exchanger, spiral style exchanger, plate fin style exchanger, or combinations thereof. The inlet to the coolant side may comprise a valve or a pump. The coolant may be removed from the coolant side through an outlet from the coolant side when the inlet to the coolant side is closed. The coolant may be removed by pumping the coolant as a liquid from the heat exchanger or by boiling the coolant out of the heat exchanger. Vacuum may be provided to the outlet of the coolant side to increase the rate of removal of the coolant. The heat exchanger may comprise instruments, the instruments comprising a flow meter on an inlet of the process side, a temperature sensor on the process side, a pressure sensor on the process side, or a combination thereof. A controller that receives signals from the instruments may be provided. The controller may use the signals to control the inlet of the coolant side. A change in pressure on the process side indicates a change in the amount of the foulant. An increase in the pressure above a threshold may trigger the controller to completely close the inlet to the coolant side, and the pressure returning below the threshold may trigger the controller to completely open the inlet to the coolant side. The increase in the pressure above the threshold may trigger the controller to close the inlet to the coolant side in proportion to how far above the threshold the pressure climbs. with the inlet to the coolant side fully open with the pressure below the first threshold, and the inlet to the coolant side fully closed above a high pressure limit.
The fouling component may comprise carbon dioxide, nitrogen oxide, sulfur dioxide, nitrogen dioxide, sulfur trioxide, hydrogen sulfide, hydrogen cyanide, water, condensed hydrocarbons, or combinations thereof. The fouling component may further comprise a solid portion comprising particulates, mercury, other heavy metals, condensed organics, soot, inorganic ash components, biomass, salts, water ice, other impurities common to a vitiated flow, producer gases, or other industrial flows, or combinations thereof.
The process liquid may comprise any compound or mixture of compounds with a freezing point below the temperature at which the fouling component solidifies. The contact liquid stream may comprise water, brine, hydrocarbons, liquid ammonia, liquid carbon dioxide, other cryogenic liquids, and combinations thereof. The contact liquid stream may comprise 1,1,3-trimethylcyclopentane, 1,4-pentadiene, 1,5-hexadiene, 1-butene, 1-methyl-1-ethylcyclopentane, 1-pentene, 3,3,3,3-tetrafluoropropene, 3,3-dimethyl-1-butene, 3-chloro-1,1,1,2-tetrafluoroethane, 3-methylpentane, 3-methyl-1,4-pentadiene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-methylpentane, 5-methyl-1-hexene, 5-methyl-1-pentene, 5-methylcyclopentene, 5-methyl-trans-2-pentene, bromochlorodifluoromethane, bromodifluoromethane, bromotrifluoroethylene, chlorotrifluoroethylene, cis 3-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.
The coolant may comprise liquid nitrogen, ethane, methane, propane, or other refrigerants.
BRIEF DESCRIPTION OF THE DRAWINGS
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:
FIG. 1 shows a method for removing a foulant from a heat exchanger.
FIG. 2 shows a method for removing a foulant from a heat exchanger.
FIGS. 3A-B show a method for removing foulant from a heat exchanger with reference to an isometric view of a plate and frame heat exchanger and a side view cross section of plates.
FIG. 4 shows a method for removing foulant from a heat exchanger is shown with reference to an isometric view of the internal components of a plate and tube heat exchanger.
FIG. 5 shows a method for removing foulant from a heat exchanger is shown with reference to an isometric exploded view of a plate and shell heat exchanger.
FIG. 6 shows a method for removing foulant from a heat exchanger is shown with reference to a cross-sectional view of a shell and tube heat exchanger.
FIG. 7 shows a method for removing foulant from a heat exchanger is shown with reference to a cross-sectional view of a u-tube bundle style shell and tube heat exchanger.
FIG. 8 shows a method for removing foulant from a heat exchanger is shown with reference to a cutaway isometric view of a spiral heat exchanger.
DETAILED DESCRIPTION
It will be readily understood that the components of the present invention, as generally described and illustrated in the Figures herein, could 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.
Referring to FIG. 1, a method for removing a foulant from a heat exchanger is shown at 100, as per one embodiment of the present invention. A heat exchanger comprising a process side and a coolant side is provided 101. A process fluid, comprising a process liquid and a fouling component, are provided to the process side 102. A flow of a coolant is provided to the coolant side 103. The process fluid is cooled, a portion of the fouling component desublimating, crystallizing, freezing, condensing coupled with solidifying, or a combination thereof as the foulant onto an outer surface of the coolant side 104. The inlet to the coolant side is periodically closed such that the flow of the coolant slows or stops, warming the process side, and causing the foulant to sublimate, melt, absorb, or a combination thereof off the outer surface of the coolant side 105. The process is then repeated starting at the coolant step 103.
Referring to FIG. 2, a method for removing a foulant from a heat exchanger is shown at 200, as per one embodiment of the present invention. A heat exchanger comprising a process side and a coolant side is provided 201. The heat exchanger further comprises a flow meter on an inlet of the process side, a temperature sensor on an outlet of the process side, and a pressure sensor on the process side 202. A process fluid, comprising isopentane and carbon dioxide, are provided to the process side 203. A flow of liquid nitrogen is provided to the coolant side through a control valve 204. The process fluid is cooled, a portion of the carbon dioxide desublimating, crystallizing, freezing, condensing coupled with solidifying, or a combination thereof as the foulant onto an outer surface of the coolant side 205. The flow, temperature, and pressure sensors provide signals indicating flow, temperature, and pressure, respectively 206. An increase in the pressure, a decrease in the flow, or an increase in the temperature indicate an increase in the amount of the foulant. The inlet to the coolant side is periodically closed such that the flow of the liquid nitrogen slows or stops 207. An outlet of the coolant side is provided with vacuum such that the liquid nitrogen boils from the coolant side and is removed 208. The process side is warmed, causing the foulant to sublimate, melt, absorb, or a combination thereof off the outer surface of the coolant side 208. The process is then repeated starting at the coolant step 204.
Referring to FIGS. 3A-B, a method for removing foulant from a heat exchanger is shown with reference to an isometric view of a plate and frame heat exchanger (PFHE) at 300 and a side view cross section of plates at 301, as per one embodiment of the present invention. The PFHE comprises frame 302 holding together plates 304 with process inlet 308, process outlet 310, coolant inlet 312, coolant outlet 314, and coolant inlet control valve 320. The spaces between the plates comprise process side 316 and coolant side 318. Process fluid 330, comprising a process liquid and a fouling component, is provided to process inlet 308 and passes through process side 316, where it is cooled against coolant 334. Coolant 334 is passed through coolant inlet control valve 320 and coolant inlet 312 into coolant side 318 where it cools process fluid 330. A portion of the fouling component and a portion of the process liquid desublimates, crystallizes, freezes, condenses coupled with solidifying, or a combination thereof as a foulant onto process side surfaces 322. Periodically, coolant inlet control valve 320 is closed. Coolant 334 drains out of coolant outlet 314, leaving plates 304 to warm due to process fluid 330. This warming causes the foulant to sublimate, melt, absorb, or a combination thereof off process side surfaces 322. At this point, coolant inlet valve 320 is re-opened, starting the cycle again. In some embodiments, coolant inlet control valve 320 is replaced by a pump. In some embodiments, the flow direction of coolant 334 is reversed and coolant inlet control valve 320 is attached to coolant outlet 314, now coolant inlet 314. In this embodiment, coolant 334 cannot drain, so vacuum is supplied to the now coolant outlet 312, boiling off the coolant.
Referring to FIG. 4, a method for removing foulant from a heat exchanger is shown with reference to an isometric view of the internal components of a plate and tube heat exchanger (PTHE) at 400, as per one embodiment of the present invention. The PTHE comprises coolant side 418 and process side 416. Coolant 434 is provided to coolant side 418, between plates 404 while process fluid 430, comprising a process liquid and a fouling component, is provided to process side 416, inside tubes 402. Coolant 434 cools process fluid 430 through tubes 402. A portion of the fouling component and a portion of the process liquid desublimates, crystallizes, freezes, condenses coupled with solidifying, or a combination thereof as a foulant onto inside surfaces 422 of tubes 402. Periodically, the coolant feed pump (not shown) is stopped. Coolant 334 drains and evaporates out of coolant side 418, leaving tubes 402 to warm due to process fluid 430. This warming causes the foulant to sublimate, melt, absorb, or a combination thereof off inside surfaces 422. At this point, the inlet pump is restarted, starting the cycle again. In some embodiments, the pump comprises a variable frequency drive, and rather than stopping the coolant feed pump, the coolant feed rate is lowered until the process fluid 430 can counter the cold from coolant 434, allowing the foulant to be removed.
Referring to FIG. 5, a method for removing foulant from a heat exchanger is shown with reference to an isometric exploded view of a plate and shell heat exchanger (PSHE) at 500 as per one embodiment of the present invention. The PSHC comprises shell 502 holding together plates 504 with process inlet 508, process inlet control valve 524, process outlet 510, coolant inlet 512, coolant outlet 514, and coolant inlet control valve 520. The spaces between the plates comprise process side 516 and coolant side 518. Process fluid 530, comprising a process liquid and a fouling component, is passed through process control valve 524, inlet 508, process side 516, where it is cooled against coolant 534. Coolant 534 is passed through coolant inlet control valve 520 and coolant inlet 512 into coolant side 518 where it cools process fluid 530. A portion of the fouling component and a portion of the process liquid desublimates, crystallizes, freezes, condenses coupled with solidifying, or a combination thereof as a foulant onto process side surfaces 522. Periodically, coolant inlet control valve 520 is closed and process inlet control valve 524 is fully opened. Vacuum is applied to coolant outlet 514 and coolant 534 evaporates out of coolant outlet 514. Process fluid 530 is provided by a process pump (not shown) which is ramped up to provide a higher flow rate of process fluid 530. The combination of no coolant 534 and faster flow of process fluid 530 results in warming of plates 504. This warming causes the foulant to sublimate, melt, absorb, or a combination thereof off process side surfaces 522. At this point, coolant inlet valve 520 is re-opened and vacuum is stopped, the process pump is returned to ramped down, and process control inlet valve is returned to its partially closed state, starting the cycle again.
Referring to FIG. 6, a method for removing foulant from a heat exchanger is shown with reference to a cross-sectional view of a shell and tube heat exchanger (STHE) at 600, as per one embodiment of the present invention. The STHE comprises shell 602 and tubes 604 with process inlet 608, process outlet 610, coolant inlet 612, coolant outlet 614, and coolant inlet control valve 620. The space inside tubes 604 comprises process side 616 and the space outside of tubes 604 comprises coolant side 618. Process fluid 630, comprising a process liquid and a fouling component, is provided to process inlet 608 and passes through process side 616, where it is cooled against coolant 634. Coolant 634 is passed through coolant inlet control valve 620 and coolant inlet 612 into coolant side 618 where it cools process fluid 630. A portion of the fouling component and a portion of the process liquid desublimates, crystallizes, freezes, condenses coupled with solidifying, or a combination thereof as a foulant onto the inside of tubes 604. Periodically, coolant inlet control valve 620 is closed. Vacuum is provided to coolant outlet 614 and coolant 634 evaporates out of coolant outlet 614, leaving tubes 604 to warm due to process fluid 630. This warming causes the foulant to sublimate, melt, absorb, or a combination thereof off the inside of tubes 604. At this point, coolant inlet valve 620 is re-opened and vacuum is stopped, starting the cycle again.
Referring to FIG. 7, a method for removing foulant from a heat exchanger is shown with reference to a cross-sectional view of a u-tube bundle style shell and tube heat exchanger (STHE) at 700 and a side view cross section of plates at 701, as per one embodiment of the present invention. The STHE comprises shell 702 and tubes 704 with process inlet 708, process outlet 710, coolant inlet 712, coolant outlet 714, and coolant inlet control valve 720. The space inside tubes 704 comprises process side 716 and the space outside of tubes 704 comprises coolant side 718. Process fluid 730, comprising a process liquid and a fouling component, is provided to process inlet 708 and passes through process side 716, where it is cooled against coolant 734. Coolant 734, supplied by a coolant pump (not shown), is passed through coolant inlet 712 into coolant side 718 where it cools process fluid 730. A portion of the fouling component and a portion of the process liquid desublimates, crystallizes, freezes, condenses coupled with solidifying, or a combination thereof as a foulant onto the inside of tubes 704. A flow sensor (not shown) and a pressure sensor (not shown) are provided on the pipe feeding process inlet 730. A temperature sensor (not shown) is provided on the pipe that receives cooled process fluid 732 out of process outlet 710. These sensors provide signals indicating flow, pressure, and temperature, respectively. An increase in the pressure, a decrease in the flow, or an increase in the temperature indicate an increase in the amount of the foulant. The coolant pump is periodically stopped and coolant flows back through the coolant pump such that coolant 734 is removed. Process side 716 is warmed, causing the foulant to sublimate, melt, absorb, or a combination thereof off the inside surface of tubes 704. Coolant 734 is then started again, restarting the cycle.
Referring to FIG. 8, a method for removing foulant from a heat exchanger is shown with reference to a cutaway isometric view of a spiral heat exchanger (SHE) at 800 and a side view cross section of plates at 801, as per one embodiment of the present invention. The SHE comprises spiraling plates 804 with process inlet 808 and coolant inlet 812. The space between spiraling plates 804 comprises process side 816 and coolant side 818, alternating. Process fluid 830, comprising a process liquid and a fouling component, is provided to process inlet 808 and passes through process side 816, where it is cooled against coolant 834. Coolant 834, supplied by a coolant pump (not shown), is passed through coolant inlet 812 into coolant side 818 where it cools process fluid 830. A portion of the fouling component and a portion of the process liquid desublimates, crystallizes, freezes, condenses coupled with solidifying, or a combination thereof as a foulant onto process side surface 822 of spiraling plates 804. A flow sensor (not shown) and a pressure sensor (not shown) are provided on the pipe feeding process inlet 830. A temperature sensor (not shown) is provided on the pipe that receives a cooled process fluid out of the process outlet. These sensors provide signals indicating flow, pressure, and temperature, respectively. An increase in the pressure, a decrease in the flow, or an increase in the temperature indicate an increase in the amount of the foulant. The coolant pump is periodically stopped and coolant flows back through the coolant pump such that coolant 834 is partially removed. Process side 816 is warmed, causing the foulant to sublimate, melt, absorb, or a combination thereof off the inside surface of tubes 804. Coolant 834 is then started again, restarting the cycle. In some embodiments, vacuum is supplied to the coolant outlet while the pump is shut down and coolant 834 is boiled off.
In some embodiments, the heat exchanger further comprises a shell and tube style exchanger, plate style exchanger, plate and frame style exchanger, plate and shell style exchanger, spiral style exchanger, plate fin style exchanger, or combinations thereof. In some embodiments, the removing the coolant step is accomplished by pumping the coolant as a liquid from the heat exchanger. In some embodiments, a controller is provided that receives signals from the instruments and uses the signals to control the inlet of the coolant side.
In some embodiments, a change in pressure on the process side indicates a change in the amount of the foulant, an increase in the pressure above a threshold triggers the controller to completely close the inlet to the coolant side, and the pressure returning below the threshold triggers the controller to completely open the inlet to the coolant side. In other embodiments, an increase in the pressure above a threshold triggers the controller to close the inlet to the coolant side in proportion to how far above the threshold the pressure climbs, with the inlet to the coolant side fully open with the pressure below the first threshold, and the inlet to the coolant side fully closed above a high pressure limit.
In some embodiments, the fouling component comprises carbon dioxide, nitrogen oxide, sulfur dioxide, nitrogen dioxide, sulfur trioxide, hydrogen sulfide, hydrogen cyanide, water, condensed hydrocarbons, or combinations thereof. In some embodiments, the fouling component further comprises a solid portion comprising particulates, mercury, other heavy metals, condensed organics, soot, inorganic ash components, biomass, salts, water ice, other impurities common to a vitiated flow, producer gases, or other industrial flows, or combinations thereof.
In some embodiments, the process liquid comprises any compound or mixture of compounds with a freezing point below the temperature at which the fouling component solidifies. In some embodiments, the contact liquid stream comprises water, brine, hydrocarbons, liquid ammonia, liquid carbon dioxide, other cryogenic liquids, and combinations thereof. In some embodiments, the contact liquid stream comprises 1,1,3-trimethylcyclopentane, 1,4-pentadiene, 1,5-hexadiene, 1-butene, 1-methyl-1-ethylcyclopentane, 1-pentene, 3,3,3,3-tetrafluoropropene, 3,3-dimethyl-1-butene, 3-chloro-1,1,1,2-tetrafluoroethane, 3-methylpentane, 3-methyl-1,4-pentadiene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-methylpentane, 5-methyl-1-hexene, 5-methyl-1-pentene, 5-methylcyclopentene, 5-methyl-trans-2-pentene, bromochlorodifluoromethane, bromodifluoromethane, bromotrifluoroethylene, chlorotrifluoroethylene, cis 3-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 coolant comprises liquid nitrogen, ethane, methane, propane, or other refrigerants.
Patent Application
20180328661
