Systems and methods for cryogenic gasification using a recirculating cooling loop

Abstract

A cryogenic gasification system and method are provided. A first heat exchanger (202) heats a liquid refrigerant via indirect heat exchange to output a cryogenic vapor at a first temperature. A second heat exchanger (204) receives the cryogenic vapor at the first temperature. The second heat exchanger heats the cryogenic vapor to a second temperature via indirect heat exchange. The cryogenic vapor at the second temperature is recirculated to the first heat exchanger to heat the liquid refrigerant and cool the recirculated cryogenic vapor to a third temperature. A third heat exchanger (206) receives the cryogenic vapor at the third temperature. The third heat exchanger heats the cryogenic vapor to a fourth temperature. The third heat exchanger outputs the cryogenic vapor at the fourth temperature.

Description

Technical Field

[0001] This disclosure generally relates to cryogenic vaporization systems, and more specifically to a system for cryogenic vaporization using recycled cryogenic steam and an existing equipment cooling loop for indirect heat exchange. Background Technology

[0002] like Figure 1 As shown, a conventional cryogenic regasification system includes a liquid cryogenic storage tank 102 that supplies liquid refrigerant to a control valve 104. The control valve 104 controls the flow of liquid refrigerant to a heat exchanger (or vaporizer) 106. The heat exchanger 106 vaporizes the liquid refrigerant into superheated vapor at approximately ambient temperature or higher. The superheated vapor is supplied to the end user via piping. The classification of the heat exchanger 106 depends on the heating medium used for vaporization. For example, ambient air is used as the heating medium for an ambient air vaporizer (AAV), while a water-based solution is used as the heating medium for a water bath vaporizer (WBV).

[0003] If a regasification system is used continuously to supply vaporized gas to the end user, it is called a continuous supply system. If the regasification system is only used when the air separator is shut down, it is called a standby system. Standby systems can also be used for "peak shaving," supplying vaporized gas to the end user for a period of time when the end user's demand exceeds the air separator's capacity. Piping within a regasification system is typically made of stainless steel or another suitable material for low temperatures. However, piping to the end user is usually made of carbon steel, which can become brittle at lower temperatures. Therefore, typical piping standards specify a minimum design temperature for carbon steel.

[0004] An AAV (Atmospheric Vaporizer) system comprises one or more vertically positioned tubes or modules, or a row of AAV units. The exterior of the tubes is exposed to the ambient atmosphere and has extended heat transfer surfaces. Liquid refrigerant flows inside the tubes and is vaporized and subsequently superheated, sometimes to near ambient atmospheric temperature.

[0005] AAV units offer significant advantages over other heat exchangers, including, for example, low equipment cost, simple and reliable operation, low maintenance, and low operating costs. However, AAV units have several drawbacks, including, for example, large size and footprint due to low heat transfer performance, and performance degradation due to icing on tube surfaces. AAV units can also be extremely sensitive to environmental conditions. For example, in relatively cold climates, more units need to be connected in parallel to achieve the same production. This may be necessary even if an additional electrically balanced heater is installed after the AAV unit. AAV units can also pose certain safety hazards, such as ice shedding and fogging when a "ground air layer" forms under cooler, heavier air and moister, warmer air. During long operating cycles, the accumulation of cold air around the vaporizer can significantly degrade performance to unacceptable levels.

[0006] Attempts to address these problems have been complex, expensive, and impractical. Furthermore, the effectiveness of such attempts remains uncertain. The aforementioned drawbacks of AAV units sometimes necessitate the use of alternative heat exchangers, such as natural gas (combustion) or steam-heated WBVs.

[0007] WBV is a vaporizer system comprising a water tank or bath in which vaporization coils or tube bundles are immersed to transfer heat from the hot water bath to the liquid refrigerant flowing through the tubular coils or tube bundles. Due to the low temperature range, the coils or tube bundles are typically made of austenitic stainless steel. Energy input maintains the water temperature above a certain level to prevent icing on the tube surfaces. This energy can be generated by a combustion process within the coils heated by flue gas submerged at the bottom of the tank, or by hot steam injected directly into the tank via steam nozzles. All such energy generation systems require an additional combustion process to generate heat.

[0008] WBVs are more expensive due to the cost of the fuels they require. Their increased complexity and greater environmental impact due to combustion also significantly limit their geographical applicability.

[0009] Heat exchangers can also utilize intermediate fluid types, which are more commonly used for liquefied natural gas (LNG) regasification compared to air separation equipment. Instead of vaporizing the liquid refrigerant by directly heating it with hot water or ambient air, a refrigerant with a low freezing point (e.g., propane or fluorinated hydrocarbons) is used. First, the refrigerant is heated with hot water or steam in a separate loop. Then, the superheated refrigerant is used to vaporize the liquid refrigerant, causing it to cool and condense.

[0010] Refrigerants can effectively eliminate icing and fogging problems in AAV units and also allow for a compact footprint. However, using intermediate fluid types requires heating devices for producing hot water or steam, and operating costs are higher due to fuel consumption. Summary of the Invention

[0011] According to one embodiment, a method for cryogenic vaporization is provided. A first heat exchanger heats a liquid refrigerant via indirect heat exchange to output cryogenic vapor at a first temperature. A second heat exchanger receives the cryogenic vapor at the first temperature. The second heat exchanger heats the cryogenic vapor to a second temperature via indirect heat exchange. The cryogenic vapor at the second temperature is recirculated back to the first heat exchanger to heat the liquid refrigerant and cool the recirculated cryogenic vapor to a third temperature. A third heat exchanger receives the cryogenic vapor at the third temperature. The third heat exchanger heats the cryogenic vapor to a fourth temperature. The third heat exchanger outputs cryogenic vapor at the fourth temperature.

[0012] According to one embodiment, a cryogenic vaporization system is provided. The system includes a first heat exchanger configured to receive a liquid refrigerant, heat the liquid refrigerant via indirect heat exchange with cryogenic vapor at a first temperature, and output cryogenic vapor at a second temperature. The cryogenic vapor at the first temperature is cooled and output as cryogenic vapor at a third temperature. The system also includes a second heat exchanger configured to receive the cryogenic vapor at the second temperature, heat the cryogenic vapor to the first temperature via indirect heat exchange, and recycle the cryogenic vapor at the first temperature back to the first heat exchanger to heat the liquid refrigerant. The system further includes a third heat exchanger configured to receive the cryogenic vapor at the third temperature, heat the cryogenic vapor to a fourth temperature via indirect heat exchange, and output cryogenic vapor at the fourth temperature. Attached Figure Description

[0013] The above and other aspects, features and advantages of certain embodiments of the present disclosure will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, in which:

[0014] Figure 1 This is a diagram showing a low-temperature regasification system;

[0015] Figure 2 This is a diagram illustrating the gasification process and system according to an embodiment of this disclosure;

[0016] Figure 3 It is a graph showing the temperature profiles in the superheater or reheater of a gasification system according to an embodiment of the present disclosure;

[0017] Figure 4This diagram illustrates the integration of the gasification system as a backup system with the air separation infrastructure according to an embodiment of this disclosure; and

[0018] Figure 5 This is a flowchart illustrating a method for regasifying a refrigerant according to an embodiment of the present disclosure. Detailed Implementation

[0019] The embodiments of this disclosure will now be described in detail with reference to the accompanying drawings. It should be noted that the same elements will be represented by the same reference numerals, even though they are shown in different drawings. In the following description, specific details such as detailed configurations and components are provided merely to aid in the overall understanding of the embodiments of this disclosure. Therefore, it will be apparent to those skilled in the art that various changes and modifications can be made to the embodiments described herein without departing from the scope of this disclosure. Furthermore, for clarity and brevity, descriptions of well-known functions and constructions have been omitted. The terminology described below is defined in consideration of the functions in this disclosure and may vary depending on the user, the user's intent, or custom. Therefore, the definition of the terminology should be determined based on the entirety of this specification.

[0020] This disclosure can have various modifications and embodiments, which are described in detail below with reference to the accompanying drawings. However, it should be understood that this disclosure is not limited to these embodiments, but includes all modifications, equivalents, and alternatives within the scope of this disclosure.

[0021] Although terms including ordinal numbers such as first, second, etc., are used to describe various elements, structural elements are not limited by these terms. These terms are used only to distinguish one element from another. For example, a first structural element may be referred to as a second structural element without departing from the scope of this disclosure. Similarly, a second structural element may also be referred to as a first structural element. As used herein, the term "and / or" includes any and all combinations of one or more related items.

[0022] The terminology used herein is for the purpose of describing various embodiments of this disclosure only and is not intended to limit this disclosure. The singular form is intended to include the plural form unless the context clearly indicates otherwise. In this disclosure, it should be understood that the terms “comprising” or “having” indicate the presence of a feature, quantity, step, operation, structural element, component, or combination thereof, and do not preclude the possibility of the presence or addition of one or more other features, quantities, steps, operations, structural elements, components, or combinations thereof.

[0023] Unless otherwise defined, all terms used herein have the same meaning as understood by one of ordinary skill in the art to which this disclosure pertains. Terms such as those defined in commonly used dictionaries are to be interpreted as having the same meaning as in the context of the relevant technical field and are not to be interpreted as having an ideal or overly formal meaning unless clearly defined in this disclosure.

[0024] According to the implementation plan, during the cryogenic vaporization process, a cooling circuit already available in the air separation infrastructure is used to superheat and reheat the cryogenic vapor, and the superheated cryogenic vapor is used to vaporize the liquid refrigerant. The cooling circuit can be an open water circuit in a relatively warm climate or a closed water-glycol circuit in a relatively cold climate.

[0025] refer to Figure 2 The figure illustrates a vaporization process and system according to an embodiment of the present disclosure. Subcooled liquid refrigerant is first pumped to a high pressure and then supplied to a first heat exchanger 202. The first heat exchanger 202 can be implemented as a reboiler with an ice-free shell, which heats the liquid refrigerant via indirect heat exchange. A thermal storage unit 208 can be disposed upstream of the first heat exchanger 202. The thermal storage unit 208 comprises a loosely packed material with a high specific heat capacity, such as rock or phase change material (PCM) with a suitable phase change temperature, which initiates the heating process of the subcooled liquid refrigerant via direct heat exchange. The thermal storage unit 208 supplies liquid refrigerant to the first heat exchanger 202 at a temperature generally ranging from -200°C to -150°C (e.g., -190°C). In order to enable rapid system capacity increases, or if ballast time is required, the thermal storage unit 208 is configured to provide additional heating to the liquid refrigerant to compensate for the reduced heating capacity at the first heat exchanger 202, which may result in severe icing in the second heat exchanger 204.

[0026] Using recirculated cryogenic vapor as a heat source, subcooled liquid refrigerant is boiled into saturated cryogenic vapor. This low-temperature, saturated cryogenic vapor is output from the first heat exchanger 202 to the second heat exchanger 204, with a general temperature range of -200°C to -120°C (e.g., -140°C). The second heat exchanger 204 can be implemented as a superheater, which uses circulating water or a water-glycol solution to superheat the low-temperature vapor to approximately ambient temperature. Accordingly, the second heat exchanger operates as a forced-flow (circulating) water-based heat exchanger.

[0027] A water-based solution is supplied from the existing cooling water circuit of the compression unit used for the foundation equipment to the second heat exchanger 204. The water-based solution is pumped into the second heat exchanger 204 at a temperature generally ranging from 10°C to 50°C (e.g., 25°C). See below for reference. Figure 4 The integration with the existing cooling water circuit is described in more detail.

[0028] Although the cryogenic vapor enters the second heat exchanger 204 at a low temperature (e.g., approximately -140°C), the risk of icing on the water-based solution side of the internal piping can be avoided using appropriate process conditions and heat exchanger design. Cryogenic vapor has a significantly lower heat transfer coefficient and energy density (i.e., specific heat and density) compared to liquid refrigerants. Furthermore, the forced flow of the water-based solution maintains a very high heat transfer coefficient (e.g., a value of 3000 W / m²-K or higher). Therefore, assuming the heat transfer resistance between the cryogenic vapor and the water-based solution can be controlled to above 15:1, the pipe wall temperature can be effectively raised above the freezing point of the water-based solution. Additionally, a hydrophobic coating can be applied to the outer surface of the pipe to prevent any formed ice particles from adhering to the pipe surface. Moreover, the velocity of the water-based solution can carry away any formed ice particles.

[0029] When output from the second heat exchanger 204, the superheated cryogenic vapor is approximately at ambient temperature, with a general temperature range of -5°C to 40°C (e.g., 0°C). The water-based solution is cooled to a general temperature range of 5°C to 40°C (e.g., 10°C). The water-based solution is returned to the existing cooling water loop, and the superheated cryogenic vapor is recirculated to the first heat exchanger 202 to serve as a heat source for indirect heat exchange with the liquid refrigerant.

[0030] When used as a vaporization heat source in the first heat exchanger 202, the superheated warm steam is cooled back to a lower temperature low-temperature steam, which is then output from the first heat exchanger 202 to the third heat exchanger 206. The approximate temperature range of this lower temperature low-temperature steam can be from -200°C to -120°C (e.g., -140°C).

[0031] The third heat exchanger 206 utilizes the same heating medium as the second heat exchanger 204 and also operates as a forced-flow (circulating) water-based heat exchanger. Specifically, a water-based solution is supplied to the third heat exchanger 206 from an existing cooling water circuit. The water-based solution is pumped into the third heat exchanger 206 at a temperature generally ranging from 10°C to 50°C (e.g., 25°C). See below for reference. Figure 4 The integration with the existing cooling water circuit is described in more detail.

[0032] At the third heat exchanger 206, the water-based solution is cooled to a general temperature range of 5°C to 40°C (e.g., 10°C). The water-based solution is returned to the existing cooling water loop. Using the water-based solution, the third heat exchanger 206 heats the low-temperature steam back to a general ambient temperature, which can be in the range of -5°C to 40°C (e.g., 0°C). This reheated warm steam is output from the third heat exchanger 206 to the end user as the final gaseous product.

[0033] In an alternative implementation, the second heat exchanger 204 and the third heat exchanger 206 may be integrated into a single heat exchanger with a common heating channel.

[0034] Now for reference Figure 3 The graph shows the temperature profile along the length of the tube according to an embodiment of this disclosure. Figure 3 The pipe involves Figure 2 The second heat exchanger 204 or the third heat exchanger 206 uses, for example, a hairpin-type exchanger to reduce size and achieve compactness. In this embodiment, the heat exchanger housing containing the tube bundle for indirectly heating the cryogenic steam can have an outer diameter of approximately 6 inches to 24 inches and an overall length of approximately 10 feet to 40 feet. Alternative embodiments can combine different tube sizes while achieving similar results as described below.

[0035] like Figure 3 As shown, at the inlet of the heat exchanger, the temperature of the cryogenic steam is approximately -140°C, the temperature of the water-based solution is approximately 25°C, and the temperature of the heat exchanger tube wall is approximately 10°C, which is significantly higher than the freezing point of water. The heat transfer coefficient on the water-based solution side of the tube wall is approximately 10-15 times that on the cryogenic steam side. This difference maintains the tube wall temperature at approximately 10°C, which is roughly the temperature at which the water-based solution decreases along the tube length with increasing distance from the inlet. Therefore, the tube wall temperature remains above the freezing point of water. Simultaneously, the temperature of the cryogenic steam inside the tube rises to ambient temperature (approximately 0°C).

[0036] This feature is achieved by separating liquid vaporization and steam superheating into two different sections or two different heat exchange devices. Specifically, in Figure 2 Liquid vaporization occurs at the first heat exchanger 202, while... Figure 2 Steam superheating occurs at the second heat exchanger 204 and the third heat exchanger 206.

[0037] Figure 4 This diagram illustrates the integration of a vaporization system as a backup system with an air separation base according to an embodiment of this disclosure. In the air separation base, a cooling tower 402 is required to provide a cooling water-based solution to the compression unit (e.g., the main air compressor). The vaporizer system utilizes existing cooling water circuits and cooling water pumps for cryogenic vaporization without adding equipment or cost.

[0038] When the base unit is operating and the standby vaporizer system is functioning as a "peak shaving" unit, a cooling water-based solution (stream 1) at approximately 10°C to 25°C is output from cooling tower 402 and supplied to base unit 404 for interstage cooling of the compressor. This typically causes the solution temperature to rise to approximately 35°C to 50°C (stream 2). A portion of the heated solution (stream 2) is supplied to the standby vaporizer system 406 to act as a cooling source for the compressor stages. Figure 2 The indirect heating source for the low-temperature steam in the second heat exchanger 204 and the third heat exchanger 206 is as described above. The solution leaves the standby vaporizer system 406 (stream 3) at a reduced temperature of approximately 25°C to 40°C and mixes with the remainder of the heated solution (stream 2) from the base unit 404. The mixed solution (stream 4) is then supplied back to the common cooling tower 402.

[0039] According to this implementation, the gasification process provides additional cooling to the water-based solution and helps reduce the workload of cooling tower 402. This thermal integration provides additional energy savings to the base equipment cooling system. When the base equipment is shut down and the standby gasifier supplies all cryogenic steam to the end user, the cooling water-based solution can be directly supplied to the gasification system, and cooling tower 402 functions as a heating tower to dissipate cold energy into the ambient air. Typically, the size of cooling tower 402 is determined by the cooling requirements of the base equipment, which are approximately 4-6 times the heating load of the standby gasification process. Therefore, the performance of cooling tower 402 is sufficient to provide the water flow for the standby gasification process.

[0040] The embodiments disclosed herein reduce the risks of icing and fogging, while also significantly reducing the space required for the gasification system due to its high heat transfer performance (up to 90% less than conventional AAV-based systems). No additional heating is required (e.g., natural gas combustion or steam-based WBV systems). The embodiments disclosed utilize cooling loops and fluids from the underlying equipment process, thus eliminating the need for intermediate fluid loops. These advantages can result in potential cost savings of approximately 10%–30%.

[0041] Now for reference Figure 5The flowchart illustrates a method for cryogenic vaporization according to an embodiment of this disclosure. At 502, a liquid refrigerant is pumped to a high pressure and then supplied to a first heat exchanger at a temperature of approximately -200°C to -150°C. Cryogenic liquid can be supplied to the first heat exchanger from a thermal storage unit having a loosely packed material with high specific heat capacity or high latent heat, such as rock or another PCM with a suitable phase change temperature, which initiates the heating process of the subcooled liquid refrigerant via direct heat exchange. At 504, the first heat exchanger heats the liquid refrigerant via indirect heat exchange using recirculated cryogenic vapor as a heat source. The first heat exchanger outputs cryogenic vapor at a first temperature of approximately -200°C to -120°C.

[0042] At 506, the second heat exchanger receives cryogenic vapor at a first temperature of approximately -200°C to -120°C. At 508, the second heat exchanger receives a water-based solution from the base equipment at a temperature of approximately 10°C to 50°C. The water-based solution can be circulating water or a water-glycol solution. At 510, the second heat exchanger uses the water-based solution to heat the cryogenic vapor to a second temperature of approximately -5°C to 40°C via indirect heat exchange, while simultaneously cooling the water-based solution to a temperature of approximately 5°C to 40°C. The second temperature is approximately ambient temperature. At 512, the second heat exchanger outputs the cooled water-based solution to the base equipment. At 514, the second heat exchanger outputs cryogenic vapor at the second temperature. The cryogenic vapor is recirculated to the first heat exchanger to heat the liquid refrigerant via indirect heat exchange, while the recirculated cryogenic vapor is cooled to a third temperature of approximately -200°C to -120°C.

[0043] At point 516, the third heat exchanger receives cryogenic steam at a third temperature of approximately -200°C to -120°C. At point 518, the third heat exchanger receives a water-based solution from the base equipment at a temperature of approximately 10°C to 50°C. The water-based solution can be circulating water or a water-glycol solution. At point 520, the third heat exchanger uses the water-based solution to heat the cryogenic steam to a fourth temperature of approximately -5°C to 40°C via indirect heat exchange, while simultaneously cooling the water-based solution to 5°C to 40°C. The fourth temperature is approximately ambient temperature. At point 522, the third heat exchanger outputs the cooled water-based solution to the base equipment. At point 524, the third heat exchanger outputs cryogenic steam at the fourth temperature for supply to the end user.

[0044] Although certain embodiments of this disclosure have been described in detail herein, this disclosure may be modified in various forms without departing from its scope. Therefore, the scope of this disclosure should not be determined solely based on the described embodiments, but rather on the appended claims and their equivalents.

Claims

1. A method for low-temperature vaporization, the method comprising the following steps: Receives subcooled liquid refrigerant; In the thermal storage unit, subcooled liquid refrigerant is heated by direct heat exchange to produce liquid refrigerant; The liquid refrigerant is received in the first heat exchanger; In the first heat exchanger, the liquid refrigerant is vaporized via indirect heat exchange with superheated cryogenic vapor to output cryogenic vapor at a first temperature. The low-temperature steam at the first temperature is received in the second heat exchanger; The low-temperature steam at the first temperature is heated in the second heat exchanger via indirect heat exchange to generate superheated low-temperature steam at the second temperature; The superheated low-temperature steam at the second temperature is recirculated to the first heat exchanger; The superheated cryogenic steam at the second temperature is cooled in the first heat exchanger to produce cryogenic steam at the third temperature, which is colder than the superheated cryogenic steam at the second temperature. The low-temperature steam at the third temperature is received in the third heat exchanger; The low-temperature steam at the third temperature is heated in the third heat exchanger via indirect heat exchange to generate low-temperature steam at the fourth temperature; as well as The low-temperature steam at the fourth temperature is output from the third heat exchanger to the end user; The second heat exchanger is virtually ice-free.

2. The method according to claim 1, further comprising the steps of pumping the liquid refrigerant to generate pumped liquid refrigerant and delivering the pumped liquid refrigerant to the first heat exchanger.

3. The method according to claim 1, wherein the superheated cryogenic steam at the second temperature is between -5°C and 40°C.

4. The method of claim 1, wherein the second heat exchanger and the third heat exchanger are forced flow water-based heat exchangers, and the step of heating the cryogenic steam at the first temperature in the second heat exchanger via indirect heat exchange further includes heating the cryogenic steam at the first temperature via indirect heat exchange with a water-based solution, and the step of heating the cryogenic steam at the third temperature in the third heat exchanger via indirect heat exchange further includes heating the cryogenic steam at the third temperature via indirect heat exchange with a water-based solution.

5. The method according to claim 4, wherein the water-based solution comprises a water-ethylene glycol solution.

Images