COMBINED CONDENSER-EVAPORATOR

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 (a) and (b) to Chinese patent application No. CN2025/10037796.6, filed Jan. 9, 2025, which is herein incorporated by reference in its entirety.

[0002] The present invention relates to a condenser-evaporator, and particularly to a combined condenser-evaporator that simultaneously evaporates multiple liquids through indirect heat exchange with the same gas being condensed.

[0003] A condenser-evaporator, as a type of heat exchange equipment, has a wide range of applications in various process flows. For example, in cryogenic air separation, a condenser-evaporator is used to generate reflux liquid and/or rising gas for a distillation column, and to obtain corresponding gas products. Condenser-evaporators include different types such as bath-type, falling-film-type, etc., and the specific designs of their heat exchange components include plate-fin type, shell-and-tube type, plate-and-tube type, and so on.

[0004] As the condenser-evaporator is a key component in a distillation column system that occupies a large space, has a high manufacturing cost, and significantly impacts energy consumption, relevant technical personnel in the industry have carried out continuous research and optimization over the years.

[0005] CN106662395B discloses a multi-stage liquid-retaining condenser-evaporator, which has a heat exchanger core composed of a heat exchange section and a liquid communication section. The heat exchange section is formed by adjacent lamination of condensation channels and evaporation channels constructed from plates and fins. The condensation channels are in communication vertically, but the evaporation channels are divided into multiple segments, each segment corresponding to a liquid communication section comprising a liquid storage part and a liquid communication channel. This design reduces the liquid head of liquefied oxygen in each segment of the evaporation channel, resulting in higher heat exchange efficiency; additionally, the integrated manufacturing of the heat exchanger core also reduces costs. However, this condenser-evaporator only allows indirect heat exchange between two fluids.

[0006] U.S. Pat. No. 11,933,540B2 discloses an integrated condenser-evaporator. This condenser-evaporator is a “once-through” type heat exchange device placed in a gas-liquid separator, comprising one set of condensation channels and two sets of evaporation channels. The condenser-evaporator is divided into a top zone, a middle zone, and a bottom zone. The gas to be condensed enters from the top zone and leaves from the bottom zone after condensation. A first condensing medium enters from the bottom zone, and after partial evaporation, flows from the top zone into the gas-liquid separator, where it is separated into a liquid phase and a gas phase. The liquid phase, as a second condensing medium, enters the condenser-evaporator from the middle zone, leaves from the top after partial evaporation, and is then sent back to the distillation column system. In this configuration, both the first condensing medium and the second condensing medium flow from bottom to top in the evaporation channels in a “once-through” manner, and flammable impurities mixed therein may deposit in the evaporation channels, causing a safety hazard.

[0007] In view of this, how to design a combined condenser-evaporator that allows one gas to exchange heat with multiple liquids simultaneously, thereby making the equipment more compact, lowering manufacturing costs, and increasing the safety factor, is a pressing issue to be solved by relevant technical personnel in the industry.

[0008] An object of the present invention is to provide a combined condenser-evaporator with a simple structure and convenient manufacturing, which allows one gas to perform indirect heat exchange with multiple liquids simultaneously, while ensuring safety and heat exchange performance.

[0009] In one aspect, the present invention provides a combined condenser-evaporator, comprising: a condensation channel, a gas flowing over a condensation surface of the condensation channel to condense; a first evaporation channel, a first liquid flowing over a first evaporation surface of the first evaporation channel and performing indirect heat exchange with the gas to at least partially evaporate; and a second evaporation channel, a second liquid flowing over a second evaporation surface of the second evaporation channel and performing indirect heat exchange with the gas to at least partially evaporate. It further comprises a heat exchanger core submerged in a bottom liquid. The heat exchanger core is formed by stacking the condensation channel and the first evaporation channel and the second evaporation channel, which are spaced apart. It further comprises a dividing plate, which separates the heat exchanger core into a closed section and a semi-open section. The closed section comprises the condensation channel and the first evaporation channel, which are spaced apart, and both are not in communication with the bottom liquid. The semi-open section comprises the condensation channel and the second evaporation channel, which are spaced apart, wherein the condensation channel therein is not in communication with the bottom liquid, but the second evaporation channel is in communication with the bottom liquid, and the bottom liquid undergoes circulating evaporation in the second evaporation channel; wherein the first liquid and the second liquid are different, and an oxygen content of the second liquid is greater than that of the first liquid.

[0010] Further, a flow direction of the gas in the condensation channel, and flow directions of the liquids in the first evaporation channel and the second evaporation channel are all substantially perpendicular to a horizontal plane.

[0011] Still further, a stacking direction of the condensation channel and the first evaporation channel and the second evaporation channel is substantially orthogonal to the condensation surface, the first evaporation surface, and the second evaporation surface.

[0012] In addition, the dividing plate is substantially parallel to the condensation surface.

[0013] In another aspect, the condensation channel, the first evaporation channel, and the second evaporation channel all comprise a plate-fin structure.

[0014] Furthermore, an upper part of the side of the heat exchanger core has a gas distribution header, and a lower part of the side of the heat exchanger core has a post-condensation liquid discharge manifold.

[0015] In addition, a top of the closed section of the heat exchanger core has a first liquid distribution header and a first liquid inlet, a bottom of the closed section of the heat exchanger core has a first gas-liquid mixed flow discharge manifold and a first gas-liquid mixed flow outlet, and the flow directions of the gas and the first liquid are the same.

[0016] Alternatively, a bottom of the closed section of the heat exchanger core has a first liquid distribution header and a first liquid inlet, a top of the closed section of the heat exchanger core has a first gas-liquid mixed flow discharge manifold and a first gas-liquid mixed flow outlet, and the flow directions of the gas and the first liquid are opposite.

[0017] In yet another aspect, the present invention provides a distillation column system comprising the combined condenser-evaporator described above, further comprising an optional first gas-liquid separator, a second gas-liquid separator, and a second pressure-reducing device. The first liquid inlet of the closed section of the heat exchanger core is connected to a first liquid outlet of the first gas-liquid separator, and the first gas-liquid mixed flow outlet of the closed section of the heat exchanger core is connected to a middle part of the second gas-liquid separator, and a liquid phase outlet of the second gas-liquid separator is connected to a middle part of the combined condenser-evaporator after passing through the second pressure-reducing device.

[0018] Further, it also comprises a first pressure-reducing device. A rich liquid generated by the distillation column system enters the first gas-liquid separator after being depressurized by the first pressure-reducing device.

[0019] Still further, gas phase products generated by the first gas-liquid separator and the second gas-liquid separator are mixed and then returned to the distillation column system.

[0020] Compared with the prior art, the technical solution provided by the present invention has the following advantages:

• • [0021] 1. The structure is simple and easy to manufacture;
  • [0022] 2. The gas distribution header and the post-condensation liquid discharge manifold in the closed section and the semi-open section are integrated, producing a synergistic effect;
  • [0023] 3. The semi-open section submerged in the bottom liquid is equivalent to a bath-type heat exchanger. Using it to evaporate the second liquid with a higher oxygen content improves the safety factor.

[0033] To make the objects, technical solutions, and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below with reference to the drawings. Obviously, the described embodiments are a part, not all of the embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0034] In the description of the present invention, it should be noted that unless otherwise expressly specified and defined, the terms “assemble” and “connect” refer to forming two or more parts into a component that is sealed against fluids such as liquids and gases. The methods of assembly and connection include welded connection, flange connection, bolted connection, adhesion, or integral molding, etc. The terms “connected” and “in communication” refer to a state formed between two or more parts that allows fluids such as liquids and gases to flow. The terms “downstream” and “upstream” are relative to the flow direction of a liquid or gas. The process of a liquid or gas flowing from an inlet to an outlet is the process of flowing from upstream to downstream. Terms indicating orientation, such as “below”, “above”, “parallel to a horizontal plane”, and “perpendicular to a horizontal plane”, all correspond to the orientation of the combined condenser-evaporator of the present invention in a normal use scenario. In addition, qualifiers similar to “a” or “an” appearing herein do not refer to a limitation of quantity, but rather describe a technical feature that has not appeared previously in the preceding text. Similarly, unless a noun is modified by a specific numerical quantifier, it should be regarded herein as including both the singular form and the plural form; that is, the technical solution may include a single one of the technical feature, or multiple ones of the technical feature.

[0035] It should be understood that in the present invention, “at least one (item)” means one or more, and “multiple” means two or more. “and/or” is used to describe the association relationship of associated objects, indicating that three relationships can exist. For example, “A and/or B” can represent: only A exists, only B exists, and both A and B exist, where A and B can be singular or plural. The character “/” generally indicates that the associated objects before and after it have an “or” relationship. “at least one of (the following)” or similar expressions refer to any combination of these items, including any combination of a single item (or items) or plural items (or items). For example, at least one of a, b, or c can represent: a, b, c, “a and b”, “a and c”, “b and c”, or “a, b, and c”, where a, b, and c can be single or multiple.

[0036] The combined condenser-evaporator in the present invention comprises a heat exchanger core, which is placed in a liquid storage container enclosed by a shell. The shell includes a shell side wall, an top head, and a bottom head. During use, the interior of the liquid storage container is filled with a bottom liquid, and the heat exchanger core is placed in the bottom liquid. Preferably, the semi-open section of the heat exchanger core is submerged in the bottom liquid.

[0037] Embodiment 1 is a heat exchanger core according to one embodiment of the present invention. FIG. 1 shows a 3D external view of the heat exchanger core of the combined condenser-evaporator according to Embodiment 1. The heat exchanger core 100 comprises a closed section 5 and a semi-open section 6, which are completely isolated from each other by a dividing plate 4. As can be seen from FIG. 2, both the closed section 5 and the semi-open section 6 are formed by stacking multiple channels. In the closed section 5, these channels are the gas condensation channels 1 and the first evaporation channels 2 for partially evaporating the first liquid, which are spaced apart; in the semi-open section 6, these channels are the gas condensation channels 1 and the second evaporation channels 3 for partially evaporating the second liquid, which are spaced apart.

[0038] The characteristic of the closed section 5 is that its interior is completely not in communication with the bottom liquid in the liquid storage container. This sealing can be achieved either by a complete continuous shell or by a combination of a shell and sealing strips. The top and bottom of the closed section 5 have components for distributing or collecting the first liquid and its partially evaporated products. In FIG. 1, the top of the closed section 5 is provided with a first liquid inlet 13 and a first liquid distribution header 11, and the bottom of the closed section 5 is provided with a first gas-liquid mixed flow outlet 14 and a first gas-liquid mixed flow discharge manifold 12. Alternatively, the first liquid inlet 13 and the first liquid distribution header 11 may be provided at the bottom of the closed section 5, and the first gas-liquid mixed flow outlet 14 and the first gas-liquid mixed flow discharge manifold 12 may be placed at the top of the closed section 5.

[0039] The characteristic of the semi-open section 6 is that the condensation channels therein are completely not in communication with the bottom liquid in the liquid storage container, while the second evaporation channels therein are completely in communication with the bottom liquid in the liquid storage container at the top and bottom. The sealing of the condensation channels can be achieved by adding the gas distribution header and the post-condensation liquid discharge manifold at the top and bottom, and applying sealing strips on the sides; whereas the second evaporation channels only have sealing strips applied on the sides. Such a design makes the closed section 5 equivalent to a “once-through” heat exchanger, and the semi-open section 6 equivalent to a bath-type heat exchanger. Therefore, the advantages of two different heat exchange methods are integrated in one combined heat exchanger.

[0040] On a side surface of the heat exchanger core (mainly referring to the fluid inlet and outlet locations), preferably, but not necessarily on the same surface, spanning the closed section 5 and the semi-open section 6, a gas distribution header 7 and a post-condensation liquid discharge manifold 8 are provided. Wherein, the gas distribution header 7 and a gas inlet 9 are provided at an upper edge of the side surface, and the post-condensation liquid discharge manifold 8 and a post-condensation liquid outlet 10 are provided at a lower edge of the side surface, and a radius of the gas inlet 9 is larger than a radius of the post-condensation liquid outlet 10. Since the gas to be condensed in the closed section 5 and the semi-open section 6 is the same, the two can share one gas distribution header and one post-condensation liquid discharge manifold, which reduces manufacturing difficulty and cost, reflecting the synergistic advantage of combining different types of condenser-evaporator equipment.

[0041] FIG. 2 is a side cross-sectional view of the combined condenser-evaporator heat exchanger core according to Embodiment 1. The heat exchanger core 100 preferably adopts a plate-fin structure. The plate-fin structure has the advantages of a compact structure, a large heat exchange area, and a small pressure drop. It consists of a set of parallel plates, and intermediate elements such as corrugated or wavy structures can be inserted between the plates to form a fin-like heat exchange structure. A stack of planar channels is formed between the stacked plates for different fluids to enter into a heat exchange relationship. During the manufacturing process, plates, fin partitions, and other exchanger components are first stacked and pressed together, and then brazed together in a vacuum furnace at a temperature of 550° C. to 900° C.

[0042] The channel through which the gas to be condensed flows is the condensation channel 1. In the closed section 5, the condensation channels 1 are distributed spaced apart and substantially parallel to the first evaporation channels 2 for partially evaporating the first liquid; in the semi-open section 6, the condensation channels 1 are distributed spaced apart and substantially parallel to the second evaporation channels 3 for partially evaporating the second liquid. In the condensation channel 1, the surface that contacts the evaporation channel for heat exchange is called a condensation surface 1a, and at least one condensation surface is provided with a condensation fin 1b. Correspondingly, in the first and second evaporation channels, the surfaces that contact the condensation channel 1 for heat exchange are called a first evaporation surface 2a and a second evaporation surface 3a, respectively, on which a first evaporation fin 2b and a second evaporation fin 3b are respectively provided. The stacking direction of the plates (y-direction in FIG. 1) is perpendicular to the extension direction of the condensation surface, the first evaporation surface, and the second evaporation surface (x-direction in FIG. 1). FIG. 2 is a side cross-sectional view taken along the stacking direction y of the plates.

[0043] In FIG. 2, the gas to be condensed enters from the gas inlet 9 provided on the upper side of the heat exchanger core, is uniformly distributed to each condensation channel 1 in the gas distribution header 7, and flows from top to bottom along the condensation channel 1 in a direction substantially perpendicular to a horizontal plane (z-direction in FIG. 1). During this process, the gas is condensed. In the semi-open section 6, the bottom liquid, i.e., the second liquid, enters from below the second evaporation channel. The second liquid is at least partially evaporated during the process of indirect heat exchange with the gas, and is discharged from above the evaporation channel. Due to the thermosiphon effect, the bottom liquid, i.e., the second liquid, continuously circulates in the second evaporation channel 3.

[0044] In FIG. 2, the first liquid enters the first liquid distribution header 11 via the first liquid inlet 13 provided at the top of the closed section 5, is distributed therein to each first evaporation channel 2, and then flows from top to bottom along the first evaporation channel 2 in a direction substantially perpendicular to a horizontal plane. The partially evaporated first liquid gathers in the first gas-liquid mixed flow discharge manifold 12 located at the bottom of the closed section 5, and then leaves via the first gas-liquid mixed flow outlet 14. The top-to-bottom flow of the first liquid in the channel is equivalent to falling-film heat exchange, which has the advantages of a small temperature difference and high heat exchange efficiency. At the same time, the gas-liquid mixed flow stream after heat exchange completely flows out of the heat exchange channel under the action of gravity, avoiding the deposition of impurities such as hydrocarbons contained in the flow stream in the evaporation channel, thus improving the safety of the equipment.

[0045] FIG. 3 shows a top view of the heat exchanger core of the combined condenser-evaporator according to Embodiment 1. The dividing plate 4 separates the heat exchanger core into the closed section 5 and the semi-open section 6. The top of the closed section 5 is the first liquid inlet 13. The same side of the closed section 5 and the semi-open section 6 shares the same gas distribution header 7 and gas inlet 9. At the top of the semi-open section 6, the condensation channels 1 sealed by sealing strips and the second evaporation channels 3 opening to the top are visible. Wherein, the dividing plate 4 is parallel to the condensation channel 1. The dividing plate 4 can also be set perpendicular to the condensation channel 1 (not shown in the figure), but the parallel arrangement is a more preferred solution because the gas or liquid distribution parts can be combined.

[0046] FIG. 4 is a cross-sectional view of the semi-open section 6, taken along the condensation surface of the condensation channel. In the condensation surface 1a, the condensation fins 1b are distributed longitudinally.

[0047] FIG. 5 is a cross-sectional view of the closed section 5, taken along the evaporation surface of the first evaporation channel. In the first evaporation surface 2a, the first evaporation fins 2b are distributed longitudinally.

[0048] FIG. 6 is a cross-sectional view of the semi-open section 6, taken along the evaporation surface of the second evaporation channel. In the second evaporation surface 3a, the second evaporation fins 3b are distributed longitudinally.

[0049] Embodiment 2 is a schematic flow diagram of the combined condenser-evaporator of the present invention applied in cryogenic air separation. Taking CN 1136426C as an example, it discloses a method and apparatus for producing high-purity nitrogen gas using a single column and two bath-type condenser-evaporators. After a feed gas is distilled in the single column, nitrogen-rich vapor is generated at the top of the column, and oxygen-rich liquid is obtained at the bottom. In a first condenser, the nitrogen-rich vapor and a portion of the oxygen-rich liquid undergo indirect heat exchange, causing the nitrogen-rich vapor to condense to form a nitrogen-rich condensate; the oxygen-rich liquid is at least partially vaporized, generating an oxygen-rich liquid and a second nitrogen-rich vapor. In a second condenser, the nitrogen-rich vapor and the oxygen-rich liquid from the first condenser undergo indirect heat exchange, causing the nitrogen-rich vapor to condense to form a nitrogen-rich condensate; the oxygen-rich liquid is at least partially vaporized, generating a waste stream.

[0050] FIG. 7 discloses a schematic flow diagram of applying the combined condenser-evaporator of the present invention to the aforementioned patented method. In the figure, the closed section 5 implements the function of the first condenser, and the open section 6 implements the function of the second condenser. At the same time, two gas-liquid separators are added to further optimize the process.

[0051] In FIG. 7, a rich liquid 52 from the bottom of the column is depressurized by a first pressure-reducing device 18, forming a gas-liquid mixed flow due to flash evaporation. This flow stream is separated in a first gas-liquid separator 20 to obtain a first liquid 53. The first liquid 53 enters the top of the closed section 5 of the heat exchanger core 100 via the first liquid inlet 13. The first gas-liquid separator 20 is not necessary, but it can completely remove gas phase components from the first liquid 53. Without the interference of bubbles, the purely liquid first liquid 53 is more uniformly distributed to each first evaporation channel in the first liquid distribution header 11, improving the performance of the heat exchanger.

[0052] This first liquid undergoes indirect heat exchange with nitrogen vapor 50 from the distillation column in the first evaporation channel, and a first gas-liquid mixed flow 59 obtained after partial evaporation is sent to a second gas-liquid separator 21. A liquid phase 55 of the second gas-liquid separator obtained by separation here is depressurized by a second pressure-reducing device 19 and then sent into the shell of the combined condenser-evaporator to supplement the bottom liquid 25. A gas phase 54 from the first gas-liquid separator and a gas phase 56 from the second gas-liquid separator are combined and can be returned to the distillation column as a circulating flow stream (not shown).

[0053] The semi-open section 6 is completely submerged in the bottom liquid 25. The bottom liquid 25 (i.e., the second liquid) enters from an inlet of the second evaporation channel at the bottom of the semi-open section 6, and undergoes indirect heat exchange therein with the nitrogen vapor 50 from the distillation column. The partially evaporated bottom liquid 25 (second liquid) is discharged from the top of the second evaporation channel, forming an oxygen-rich gas 57 at the top of the condenser-evaporator. After this oxygen-rich gas 57 is discharged, it can be reheated in a main heat exchanger. The semi-open section 6 can be regarded as a bath-type condenser-evaporator that circulates heat exchange through the thermosiphon effect.

[0054] The nitrogen vapor 50 simultaneously participates in indirect heat exchange with the first liquid and the second liquid in the condensation channel, and liquid nitrogen 51 is obtained after condensation. To prevent the accumulation of flammable impurities in the bottom liquid, the condenser-evaporator of the present invention also periodically produces a liquid discharge 58.

[0055] In the above embodiment, oxygen is gradually enriched during the evaporation process, and its concentration gradually increases. For example, the oxygen content in each flow stream is about 40% in the rich liquid 52, about 45% in the first liquid 53, about 50%~55% in the first gas-liquid mixed flow 59, about 55% in the liquid phase 55 of the second gas-liquid separator, and about 75%~80% in the bottom liquid 25. The higher the oxygen concentration, the higher the concentration of impurities contained therein, which greatly increases the risk of explosion. ¹⁷⁴Therefore, evaporating the bottom liquid in a closed channel will pose a great safety hazard. The present invention uses the semi-open section to circulate and evaporate the bottom liquid, which greatly increases the safety of the equipment.

[0056] In practice, the combined condenser-evaporator can be arranged separately outside the distillation column, or arranged inside the distillation column. For example, the column wall of the distillation column can be used as the shell side wall of the combined condenser-evaporator, and an top head 60 and a bottom head 61 are provided, thereby forming a closed liquid storage container.

[0057] What is described in this specification is only preferred specific embodiments of the present invention, and the above embodiments are only used to illustrate the technical solutions of the present invention, not to limit the present invention. Unless clearly indicated otherwise, each aspect or embodiment defined herein may be combined with any other one or more aspects or one or more embodiments. In particular, any feature indicated as preferred or advantageous may be combined with any other feature indicated as preferred or advantageous. Any technical solution obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation shall fall within the scope of the present invention.

[0058] In the drawings: 100—heat exchanger core; 1—condensation channel; 1a—condensation surface; 1b—condensation fin; 2—first evaporation channel; 2a—first evaporation surface; 2b—first evaporation fin; 3—second evaporation channel; 3a—second evaporation surface; 3b—second evaporation fin; 4—dividing plate; 5—closed section; 6—semi-open section; 7—gas distribution header; 8—post-condensation liquid discharge manifold; 9—gas inlet; 10—post-condensation liquid outlet; 11—first liquid distribution header; 12—first gas-liquid mixed flow discharge manifold; 13—first liquid inlet; 14—first gas-liquid mixed flow outlet; 18—first pressure-reducing device; 19—second pressure-reducing device; 20—first gas-liquid separator; 21—second gas-liquid separator; 25—bottom liquid; 30—shell side wall; 50—nitrogen vapor; 51—liquid nitrogen; 52—rich liquid; 53—first liquid; 54—gas phase of first gas-liquid separator; 55—liquid phase of second gas-liquid separator; 56—gas phase of second gas-liquid separator; 57—oxygen-rich gas; 58—liquid discharge; 59—first gas-liquid mixed flow; 60—top head; 61 bottom head.

[0059] While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

[0060] The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

[0061] “Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein.

[0062] “Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

[0063] Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.