Apparatus and method for forming semi-cage hydrates

Abstract

An apparatus and method for forming semi-cage hydrates. An apparatus for forming a semi-cage hydrate (SCH) is provided. The apparatus may include a first tank, a heat exchanger in fluid connection with the first tank, a cooling unit connected to the heat exchanger, and a second tank for collecting and / or storing the formed SCH. Also provided is a method of forming a half-cage hydrate, the method comprising feeding a half-cage hydrate-based solution into a heat exchanger, cooling the heat exchanger to form the half-cage hydrate-based solution into an SCH.

Description

Technical Field

[0001] The present invention relates to an apparatus for forming semi-cage hydrates (SCH) and a method for forming SCH. Background Technology

[0002] The demand for cooling is growing rapidly, in areas such as space cooling, industrial process cooling, food preservation, and cold chain transportation. Cooling is a major contributor to electricity consumption, especially in tropical regions. There is a need to improve the efficiency of cooling systems to save energy and reduce carbon emissions. Currently, the common practice is to use chilled water to deliver cooling energy from the source to the user. However, due to the limited cooling capacity of water, large amounts of chilled water may be required to supply specific cooling loads, resulting in high pumping energy consumption.

[0003] Compared to the sensible heat of single-phase materials, solid-liquid phase changes possess a higher latent heat of phase change, thus phase change materials (PCMs) have been considered as heat carriers to replace chilled water in cooling systems. Ice slurries, microencapsulated PCM slurries, and semi-cage hydrates are some examples considered advantageous for cooling applications. However, their use has many limitations. For example, semi-cage hydrates have not been widely used in commercial cooling systems due to the lack of efficient preparation methods and their poor rheological properties.

[0004] Therefore, there is a need for an improved cooling system that is more energy-efficient and scalable for a variety of applications. Summary of the Invention

[0005] This invention seeks to address these problems and / or provide an improved method for forming semi-cage hydrates (SCH). An apparatus for forming semi-cage hydrates is also provided.

[0006] According to a first aspect, an apparatus for forming a SCH is provided, the apparatus comprising:

[0007] The first storage tank is used to store solutions based on semi-cage hydrates;

[0008] A heat exchanger, which is fluidly connected to the first storage tank, is used to form a semi-cage hydrate (SCH) based solution, wherein the inner surface of the heat exchanger is coated with a hydrophobic coating.

[0009] A cooling unit, connected to the heat exchanger, for providing cooling to the heat exchanger; and

[0010] The second storage tank is used to collect and / or store the formed SCH.

[0011] This device can be connected to a system used to transport the formed SCH as a heat carrier.

[0012] According to one particular aspect, the hydrophobic coating comprises a polymer. The polymer can be any suitable polymer. For example, the coating may comprise a polymer including, but not limited to, perfluoroalkoxy (PFA), polytetrafluoroethylene (PTFE), polydimethylsiloxane (PDMS), or combinations thereof.

[0013] The coating can have a suitable thickness. For example, the coating can have a thickness of 10-80 μm.

[0014] The heat exchanger can be any suitable heat exchanger. For example, the heat exchanger can be, but is not limited to, a shell-and-tube heat exchanger, a plate heat exchanger, a coaxial heat exchanger, or a combination thereof.

[0015] According to one particular aspect, the device may further include a resistivity sensor fluidly connected to the heat exchanger for measuring the resistivity of the slurry contained in the heat exchanger.

[0016] According to the second aspect, a method for forming a semi-cage hydrate (SCH) is provided, the method comprising:

[0017] A solution based on a semi-cage hydrate is fed into a heat exchanger, wherein the inner surface of the heat exchanger is coated with a hydrophobic coating; and

[0018] The heat exchanger is cooled to allow the semi-cage hydrate-based solution to form SCH.

[0019] According to one particular aspect, the hydrophobic coating can be any suitable coating. For example, the hydrophobic coating can include a polymer. The polymer can be any suitable polymer. For example, the polymer includes, but is not limited to, perfluoroalkoxy (PFA), polytetrafluoroethylene (PTFE), polydimethylsiloxane (PDMS), or combinations thereof.

[0020] The hydrophobic coating can have a suitable thickness. For example, the hydrophobic coating can have a thickness of 10-80 μm.

[0021] The heat exchanger can be any suitable heat exchanger. For example, the heat exchanger can be, but is not limited to, a shell-and-tube heat exchanger, a plate heat exchanger, a coaxial heat exchanger, or a combination thereof.

[0022] According to one specific aspect, the solution based on semi-cage hydrates may contain additives used to increase the kinetics of SCH formation and reduce viscosity. For example, the additives may include, but are not limited to: semi-cage hydrate seed crystals, amino acids, anti-coagulation agents (AA), or combinations thereof.

[0023] The method may further include measuring the resistivity of the slurry contained in the heat exchanger during the SCH formation process, so as to be able to measure the weight fraction of SCH in the slurry.

[0024] According to one particular aspect, the method may further include adding a pre-formed SCH as a seed crystal to a slurry containing SCH formed after cooling.

[0025] According to one particular aspect, the method may further include conveying the formed SCH for use as a heat carrier. Specifically, the method may include adding a viscosity-reducing additive to the formed SCH prior to conveying. The viscosity-reducing additive may be any suitable viscosity-reducing additive. For example, the viscosity-reducing additive may include, but is not limited to, amino acids, anti-coagulation agents (AA), or combinations thereof. Attached Figure Description

[0026] In order to fully understand the invention and readily put it into practice, the invention will now be described by way of non-limiting exemplary embodiments, with reference to the accompanying illustrative drawings. In the drawings:

[0027] Figure 1 A schematic diagram of an apparatus for forming a SCH according to one embodiment is shown;

[0028] Figure 2 A schematic diagram of an apparatus for forming a SCH according to one embodiment is shown;

[0029] Figure 3 A schematic diagram of an apparatus for forming a SCH according to one embodiment is shown;

[0030] Figure 4 The changes in temperature and resistivity during the formation of SCH are shown;

[0031] Figure 5 The cooling performance of different cooling media is shown;

[0032] Figure 6 The results show the SCH slurry with a content of 0.32 formed from tetrabutylammonium bromide (TBAB) at 8°C, and the cooling capacity of chilled water at 8°C to hot air at 35°C.

[0033] Figure 7 The hydrate fraction is shown according to one embodiment, determined by lever rule and resistivity-based method;

[0034] Figure 8 The resistivity and hydrate fraction of SCH at 3°C ​​are shown according to one embodiment;

[0035] Figure 9 The dynamics of SCH formation according to one embodiment are shown; and

[0036] Figure 10 The final hydrate fraction formed according to one embodiment is shown. Detailed Implementation

[0037] As mentioned above, there is a need for an improved cooling system, particularly one that uses semi-cage hydrate (SCH) as a heat transfer medium.

[0038] In general, this invention provides an apparatus for generating SCH and subsequently transporting it to end users via pipeline. The apparatus may include a coated heat exchanger for efficient SCH generation. A method for forming SCH is also provided, particularly by using cold energy from a suitable source, such as LNG regasification. Specifically, the integration of cold energy eliminates the need for traditional refrigeration cooling loops utilizing coolers and cooling towers. This saves significant energy and space. The method may also employ seed-induced generation to enhance SCH formation kinetics while reducing the viscosity of the formed SCH, thereby reducing the pumping power required to transport the SCH via pipeline.

[0039] Specifically, SCH is made from water and quaternary ammonium salts. The SCH exhibits a high enthalpy of dissociation (~200 kJ / kg) due to its extensive ice-like hydrogen-bonded structure. Its advantages include: a phase transition temperature (0-27°C) suitable for cooling applications, higher thermal density compared to chilled water, highly controllable solid-phase content in the slurry, and excellent stability during cyclic operation.

[0040] According to a first aspect, an apparatus for forming a SCH is provided, the apparatus comprising:

[0041] The first storage tank is used to store solutions based on semi-cage hydrates;

[0042] A heat exchanger, which is fluidly connected to the first storage tank, is used to form SCH from the semi-cage hydrate-based solution, wherein the inner surface of the heat exchanger is coated with a hydrophobic coating.

[0043] A cooling unit, connected to the heat exchanger, for providing cooling to the heat exchanger; and

[0044] The second storage tank is used to collect and / or store the formed SCH.

[0045] This device can be connected to a system used to transport the formed SCH as a heat carrier.

[0046] The hydrophobic coating may have a suitable thickness. According to one particular aspect, the hydrophobic coating may be any suitable coating. For example, the hydrophobic coating may include a polymer. The polymer may be any suitable polymer. For example, the polymer includes, but is not limited to, perfluoroalkoxy (PFA), polytetrafluoroethylene (PTFE), polydimethylsiloxane (PDMS), or combinations thereof.

[0047] The hydrophobic coating can have a suitable thickness. For example, the hydrophobic coating can have a thickness of 10-80 μm. In particular, the thickness can be 15-75 μm, 20-70 μm, 25-65 μm, 30-60 μm, 35-55 μm, 40-50 μm, or 45-47 μm. Even more specifically, the thickness can be 35-45 μm, preferably about 40 μm.

[0048] The heat exchanger can be any suitable heat exchanger. For example, the heat exchanger can be, but is not limited to, a shell-and-tube heat exchanger, a plate heat exchanger, a coaxial heat exchanger, or a combination thereof.

[0049] According to one particular aspect, the device may further include a resistivity sensor fluidly connected to the heat exchanger for measuring the resistivity of the slurry contained in the heat exchanger.

[0050] The apparatus has now been generally described, and it will be more readily understood by referring to the following embodiments, which are provided by way of illustration and not limitation.

[0051] Devices including continuous plate heat exchangers

[0052] A schematic diagram of an embodiment of an apparatus including a continuous plate heat exchanger is shown below. Figure 1 As shown. The device includes a plate heat exchanger, a pump, solution and slurry storage tanks, a cooler, a resistivity sensor, a fan coil unit or air handling unit, and pressure and temperature sensors.

[0053] The plate heat exchanger (PHE) is coated with a hydrophobic material to prevent the formation of hydrate crystals from adhering to or depositing on the heat exchanger walls. A cooler can be connected to the PHE to provide necessary cooling. The cooler can be replaced with cold energy from waste LNG from LNG regasification. A resistivity sensor can be placed between the PHE and the hydrate slurry storage tank to measure the resistivity of the hydrate slurry. The weight fraction of hydrate in the slurry can be determined from the measured resistivity, as detailed below in the second aspect.

[0054] The semi-cage-based hydrate solution from the solution storage tank can be pumped to the PHE using pump P2 to cool to the desired temperature. When the solution cools to below the semi-cage-based hydrate phase equilibrium temperature, SCH crystals begin to form. To accelerate and ensure consistent hydrate slurry formation, a trace amount of pre-prepared crystals can be injected as a nucleating agent (seed) into the supercooled solution using an injection pump. This seed can be injected after the supercooled solution has left the PHE.

[0055] The resistivity of the solution / slurry can be measured to check if the desired hydrate fraction has been reached. If the desired hydrate fraction is not reached, a three-way valve can be used to circulate the cooled solution / slurry through a PHE loop to achieve the desired hydrate fraction. Once the desired hydrate fraction is reached, the slurry can be collected in a slurry storage tank. This process can constitute a generation cycle. The slurry can be pumped to a fan coil unit (FCU) or air handling unit (AHU) using pump P1. In the FCU or AHU, the SCH in the slurry is heated and melted by the incoming air. The incoming air is cooled due to the melting of the SCH, as melting is an endothermic process. A PID controller is used to control the slurry flow rate to achieve the desired air temperature. The solution from the AHU or FCU is returned to the solution storage tank. This process can constitute a generation cycle. By optimizing the solution / slurry flow rate, this process can be operated in continuous mode.

[0056] Devices including shell and tube heat exchangers

[0057] A schematic diagram of an embodiment of a device including a shell-and-tube heat exchanger is shown below. Figure 2 As shown. The device includes a cooler, two semi-cage-shaped hydrate slurry / solution tanks, a shell-and-tube heat exchanger, a pump, a resistivity sensor, an AHU or FCU, and pressure and temperature sensors.

[0058] In this embodiment, the shell-and-tube heat exchanger has a shell and multiple tubes. However, the heat exchanger can be any suitable shell-and-tube heat exchanger. A tank containing a semi-cage hydrate solution acts as the shell. These tubes deliver the coolant needed to cool the semi-cage hydrate solution in the tank. The outer layer of the tubes can be coated with a hydrophobic coating as described above to prevent SCH crystal deposition. Vibrators can be incorporated into the tubes, which also helps prevent SCH deposition. A resistivity sensor can measure the resistivity of the solution / slurry to determine the weight fraction of hydrate in the slurry.

[0059] The prototype device operates as follows: The semi-cage-shaped hydrate solution in tank 1 can be cooled to a predetermined temperature to obtain the desired hydrate weight fraction. In the initial stage, a trace amount of hydrate seed crystals can be injected into tank 1 to prepare a hydrate slurry. Once the desired weight fraction is reached, the slurry from tank 1 can be pumped to an AHU or FCU to cool the incoming air. The solution from the AHU or FCU can be collected in tank 2. Simultaneously, the flow of coolant is transferred to cool the solution in tank 2, thereby producing a hydrate slurry in tank 2. The tanks are operated in series and parallel to ensure continuous slurry production. A PID controller and control valves (such as...) can be used. Figure 2 The flow of slurry and coolant to different tanks is achieved by using V1 to V4 as shown.

[0060] Devices including plate heat exchangers

[0061] A schematic diagram of an embodiment of a device including a plate heat exchanger is shown below. Figure 3 As shown. Figure 3 The apparatus shown integrates hydrate generation and utilization. It utilizes a highly efficient hydrate generation method and an environmentally friendly promoter. The generation section of the apparatus may include a temperature control system, a plate heat exchanger, a centrifugal pump (pump 1), and three tanks. During the semi-cage hydrate slurry generation process, a warm liquid TBAB solution can be pumped from tank 1, passed through the plate heat exchanger, and returned to tank 1. The other side of the heat exchanger can be cooled by a stream of cold glycol simulating a cold energy source. Once all the TBAB solution in tank 1 has cooled to a suitable temperature, semi-cage hydrates are generated.

[0062] The utilization section consists of a slurry pump (pump 2), a blower, a heater, and an air handling unit (AHU). TBAB semi-cage hydrate slurry can be pumped from tank 1 into the AHU to deliver cold energy. Meanwhile, hot air can be circulated by the blower and cooled by the AHU heat exchanger. The heater can generate heat at a heating load of up to 10 kW, simulating the heat source on a data rack. After the hot air is cooled, the TBAB semi-cage hydrate slurry can melt and become a liquid solution again, which can be collected in tank 2. During the utilization cycle of the semi-cage hydrate slurry in tank 1, tank 3 can undergo a generation cycle, making the entire generation and utilization process continuous.

[0063] The control and data acquisition program can optionally be used to control the temperature control system settings to simulate various conditions on the cooling energy side. The flow rates of pumps 1 and 2, as well as the fan speed, can be controlled manually or via proportional-integral-derivative (PID) control. The opening and closing of 14 digital control valves can be controlled via the interface. A total of 15 temperature measurement points, 7 pressure measurement points, 4 conductivity measurement points, 3 liquid level measurement points, 3 flow rate measurement points, and 1 airflow velocity measurement point can be recorded simultaneously. However, those skilled in the art will understand that this solution can be modified in various ways.

[0064] Figure 3 The practicality of the illustrated device has been verified. Specifically, using Figure 3 The apparatus forms a semi-cage hydrate slurry of TBAB from 500 kg of a 20 wt% TBAB solution.

[0065] Figure 4 Temperature and resistivity curves are shown during one generation cycle run at approximately 8 °C. Cooling the TBAB solution from 20 °C to 8 °C took approximately 60 min. Subsequently, approximately 40 mL of TBAB SCH seed crystals were injected into the solution, after which a temperature peak was observed, indicating hydrate nucleation. Simultaneously, the resistivity increased due to the temperature decrease in the first hour and the formation of non-conductive hydrates after one hour. At the end of the generation cycle (approximately 280 min), it was estimated that 32% of the solution had been converted to SCH. The substantial production of SCH was confirmed by visual observation.

[0066] Once a sufficient amount of SCH is produced, the slurry is pumped into the AHU at different flow rates to test its performance in cooling 35°C hot air with the heater off. Figure 5 This study compares the cooling performance of TBAB semi-cage hydrate slurry and TBAB aqueous solution at 8°C. Figure 5 As can be seen, at the same flow rate, the TBAB semi-cage hydrate slurry can cool hot air from 35°C to below 20°C at a much faster rate. The cooling rate of the TBAB hydrate slurry is more than twice that of the TBAB solution. Furthermore, even when the flow rate of the TBAB solution increases from 400 kg / h to 800 kg / h, its cooling performance is still significantly worse than that of the TBAB semi-cage hydrate slurry at 400 kg / h.

[0067] The cooling performance of TBAB semi-cage hydrate slurry was also compared with that of cooling water, such as... Figure 6As shown. In this case, both cold energy carriers were pumped into the AHU to cool 35°C hot air with the heater on, and the maximum cooling capacity achievable by each energy carrier at a specific flow rate was measured. The cooling capacity of TBAB hydrate slurry was higher than that of chilled water, and the advantage was more pronounced at high flow rates; for example, at 400 kg / h, the cooling capacity of TBAB hydrate slurry was more than 60% higher than that of chilled water.

[0068] According to the second aspect, a method for forming a semi-cage hydrate (SCH) is provided, the method comprising:

[0069] A solution based on a semi-cage hydrate is fed into a heat exchanger, wherein the inner surface of the heat exchanger is coated with a hydrophobic coating; and

[0070] The heat exchanger is cooled to allow the semi-cage hydrate-based solution to form SCH.

[0071] The hydrophobic coating may have a suitable thickness. According to one particular aspect, the hydrophobic coating may be any suitable coating. For example, the hydrophobic coating may include a polymer. The polymer may be any suitable polymer. For example, the polymer includes, but is not limited to, perfluoroalkoxy (PFA), polytetrafluoroethylene (PTFE), polydimethylsiloxane (PDMS), or combinations thereof.

[0072] The hydrophobic coating can have a suitable thickness. For example, the hydrophobic coating can have a thickness of 10-80 μm. In particular, the thickness can be 15-75 μm, 20-70 μm, 25-65 μm, 30-60 μm, 35-55 μm, 40-50 μm, or 45-47 μm. Even more specifically, the thickness can be 35-45 μm, preferably about 40 μm.

[0073] The heat exchanger can be any suitable heat exchanger. For example, the heat exchanger can be, but is not limited to, a shell-and-tube heat exchanger, a plate heat exchanger, a coaxial heat exchanger, or a combination thereof.

[0074] The solution based on semi-cage hydrates can be any suitable solution. According to one aspect, the solution based on semi-cage hydrates may contain additives for increasing the kinetics of SCH formation and reducing viscosity. According to one aspect, the additives may include, but are not limited to: semi-cage hydrate seed crystals, amino acids, anti-coagulation agents (AA), or combinations thereof.

[0075] The solution based on semi-cage hydrates may contain an appropriate amount of a semi-cage hydrate forming agent. Specifically, the amount of the semi-cage hydrate forming agent contained in the solution may be 10-60 wt%, preferably 10-40 wt%. In particular, based on the total mass of the solution, the solution may contain 15-35 wt%, 20-30 wt%, or 25-27 wt% of the semi-cage hydrate forming agent.

[0076] The semi-cage hydrate forming agent can be any suitable semi-cage hydrate forming agent. For example, the semi-cage hydrate forming agent may include, but is not limited to, tetra-n-butylammonium bromide (TBAB), tetra-n-butylammonium fluoride (TBAF), tetra-n-butylammonium chloride (TBAC), tetra-n-butylammonium acetate (TBAAce), tetra-n-butylammonium acrylate (TBAAcr), tetra-n-butylammonium propionate (TBAPro), tetra-n-butylammonium butyrate (TBABut), tetra-n-butyl-2-hydroxybutyrate (TBA2HB), tetra-n-butyl-3-hydroxybutyrate (TBA3HB), tetra-n-butylammonium 2-ethylbutyrate (TBA2EB), tetra-n-butylammonium lactate (TBALac), tetra-n-butylphosphine bromide (TBPB), tetra-n-butylphosphine chloride (TBPC), tetra-n-butylphosphine acetate (TBPAce), tetra-n-butylphosphine acrylate (TBPAcr), tetra-n-butylphosphine propionate (TBPPro), tetra-n-butylphosphine butyrate (TBPBut), tetra-n-butylphosphine lactate (TBPLac), or combinations thereof.

[0077] During the generation cycle, the fraction of solid semi-cage hydrate formed in the resulting SCH slurry can depend on the required cooling load. For the purposes of this application, "slurry" refers to a mixture of the formed SCH in a semi-cage hydrate-based solution. For example, based on the total weight of the semi-cage hydrate-based solution, the formed SCH slurry may contain 5-60 wt% solid SCH. This means that 5-60 wt% of the semi-cage hydrate-based solution may be converted into SCH. Specifically, based on the total weight of the semi-cage hydrate-based solution, the formed SCH slurry may contain 10-55 wt%, 15-50 wt%, 20-45 wt%, 25-40 wt%, and 30-35 wt% SCH. According to one specific embodiment, for a 10 kW cooling load, the feed may contain 40 wt% Type B semi-cage hydrate slurry, prepared from an initial 40 wt% TBAB solution, at a feed flow rate of 340.38 kg / h.

[0078] According to one specific aspect, the method may further include adding a pre-formed SCH as a seed crystal to a slurry containing SCH formed after cooling. As described above, the slurry contains a mixture of SCH formed after cooling in the solution based on the semi-cage hydrate. The pre-formed SCH as the seed crystal may contain any suitable SCH. In particular, the pre-formed SCH may include, but is not limited to, tetra-n-butylammonium bromide (TBAB) hydrate, tetra-n-butylammonium fluoride (TBAF) hydrate, tetra-n-butylammonium chloride (TBAC) hydrate, tetra-n-butylammonium acetate (TBAAce) hydrate, tetra-n-butylammonium acrylate (TBAAcr) hydrate, tetra-n-butylammonium propionate (TBAPro) hydrate, tetra-n-butylammonium butyrate (TBABut) hydrate, tetra-n-butyl 2-hydroxybutyrate (TBA2HB) hydrate, and tetra-n-butyl 3-hydroxybutyrate (T... Tetra-n-butylammonium 2-ethylbutyrate (TBA2EB) hydrate, tetra-n-butylammonium lactate (TBALac) hydrate, tetra-n-butylphosphine bromide (TBPB) hydrate, tetra-n-butylphosphine chloride (TBPC) hydrate, tetra-n-butylphosphine acetate (TBPAce) hydrate, tetra-n-butylphosphine acrylate (TBPAcr) hydrate, tetra-n-butylphosphine propionate (TBPPro) hydrate, tetra-n-butylphosphine butyrate (TBPBut) hydrate, tetra-n-butylphosphine lactate (TBPLac) hydrate, or combinations thereof.

[0079] The amino acids that can be added as additives can be any suitable amino acid. For example, the amino acids may include, but are not limited to, alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, valine, or combinations thereof.

[0080] The anticoagulant (AA) can be any suitable AA. For example, the AA includes, but is not limited to, cyclodextrin, rhamnolipid, sorbitan fatty acid ester, amine oxide, or combinations thereof.

[0081] The method may further include measuring the resistivity of the slurry contained in the heat exchanger during the formation of the SCH, in order to measure the weight fraction of the SCH in the slurry. The polymer can be any suitable polymer. For example, the method includes, but is not limited to, using an LCR meter with two or four probes, or an integrated resistivity or conductivity sensor.

[0082] According to one specific aspect, the method may further include transporting the formed SCH for use as a heat carrier. Specifically, the method may include adding a viscosity-reducing additive to the formed SCH prior to transport. The viscosity-reducing additive may be any suitable viscosity-reducing additive. For example, the viscosity-reducing additive may include, but is not limited to, amino acids, anti-coagulation agents (AA), or combinations thereof. Each of the amino acids and AA may be as described above.

[0083] The method has now been generally described, and it will be easier to understand by referring to the following embodiments, which are provided by way of illustration and not limitation.

[0084] Hydrate fraction monitoring system using resistivity

[0085] The mass fraction of hydrates in a hydrate slurry, referred to as the hydrate fraction, is likely a key factor determining the cooling capacity and flow properties of the SCH slurry. Currently available methods estimate the hydrate fraction at equilibrium based solely on the equilibrium temperature, salt concentration in the liquid solution, and the hydrate phase. However, this approach only determines the hydrate fraction at equilibrium, not at non-equilibrium levels. Therefore, due to the lack of suitable methods, most kinetic experiments on semi-cage hydrates have failed to reveal the trend of hydrate fraction variation (non-equilibrium state).

[0086] For typical gas hydrate systems, hydrate growth kinetics (including non-equilibrium states) can be reliably assessed by the pressure drop in the gas phase within the system. On the other hand, for systems containing SCH, since no gas is involved, it is difficult to determine detailed kinetic data during hydrate formation. Therefore, there is no reliable and direct method to quantitatively observe hydrate formation kinetics. Based on the method of this invention, an accurate and direct method for quantifying the SCH fraction in a slurry is provided based on in-situ resistivity measurements.

[0087] This study first verified whether the resistivity method can be used to predict the hydrate fraction in semi-cage hydrate slurry under equilibrium conditions by comparing the results of the lever rule (i.e., the commonly used method currently used under equilibrium conditions, as mentioned above). Figure 7 As shown, the hydrate fractions calculated using the lever rule and the resistivity method are in good agreement.

[0088] Research has found that when a conductive electrolyte solution is converted into a non-conductive gas hydrate, the resistivity of the hydrate slurry changes with the amount of hydrate formed (e.g., the hydrate fraction in the slurry). This characteristic can be used to analyze the kinetics of hydrate formation. Figure 8The resistivity and estimated hydrate fraction in TBAB SCH slurry during hydrate formation (non-equilibrium state), as measured by the method of the present invention, are shown. The resistivity of the hydrate slurry increases with hydrate formation and growth.

[0089] Interestingly, in the case of TBAB hydrate formation in a 20 wt% TBAB solution, the resistivity showed a two-step change, indicating that hydrate growth has two stages (see...). Figure 8 This may be related to the formation of two types of TBAB hydrates, namely type A and type B, with different hydration numbers and crystal structures. The hydration values ​​of type A and type B TBAB hydrates are 26 and 38, respectively, meaning that at the same temperature, the hydration fraction of type B is generally higher than that of type A. The first growth stage indicates the formation of type A hydrate, and the second growth stage indicates the transformation of type A hydrate into type B hydrate, leading to an increase in the hydration fraction.

[0090] Methods for forming SCH

[0091] Key challenges in SCH formation include the high supercooling and long induction time required for nucleation. Lower formation temperatures (i.e., high supercooling) are typically employed to shorten induction time and improve hydrate formation kinetics. However, lower formation temperatures may require more energy and produce larger solid fractions, leading to poorer flowability.

[0092] like Figure 8 As shown, type A TBAB hydrate is first formed, and then it transforms into type B hydrate. However, the transformation from type A to type B is unpredictable, which presents another challenge for the practical application of SCH in the cooling process.

[0093] Therefore, one embodiment of the method employs two pre-prepared seed crystals, type A and type B. It is important to note that each type of pre-prepared seed crystal can be prepared at stoichiometric concentrations (e.g., 40.8 wt% for type A and 32.0 wt% for type B) in a flowable slurry state near equilibrium temperature, for example, 11.5°C for type A and 9.5°C for type B. It was observed that SCH was generated immediately within minutes after adding a small amount of seed crystals (less than 0.1 wt% in the total solution) to an ultracooled TBAB solution.

[0094] Figure 9The kinetics of TBAB hydrate formation with and without pre-prepared seed crystals are shown. Interestingly, the initial hydrate formation type depends on the type of pre-prepared seed crystals provided. For example, pre-prepared type A seed crystals induce the formation of needle-like type A TBAB hydrates, and no phase transition was observed within 12 hours, a characteristic consistent with hydrates formed without seed crystals. On the other hand, the addition of type B seed crystals directly forms type B TBAB hydrates with irregular morphology, and the final hydrate proportion is higher than that of type A seed crystals. Figure 10 It is worth noting that this method is very simple and can quickly generate hydrates without adding any additional compounds.

[0095] While exemplary embodiments have been described in the foregoing description, those skilled in the art will understand that many modifications can be made without departing from the invention.

[0096] In summary, the apparatus and method of this invention provide a simple and scalable solution for the formation of semi-cage hydrates (SCHs). The resulting semi-cage hydrates are applicable to various applications, particularly in the cooling field. Compared to current methods using chilled water, using SCHs in cooling applications offers a more efficient cooling method.

Claims

1. An apparatus for forming a semi-cage hydrate (SCH), the apparatus comprising: The first storage tank is used to store solutions based on semi-cage hydrates; A heat exchanger, which is fluidly connected to the first storage tank, is used to enable the solution based on semi-cage hydrate to form SCH, wherein the inner surface of the heat exchanger is coated with a hydrophobic coating. A cooling unit, connected to the heat exchanger, for supplying cooling to the heat exchanger; and, The second storage tank is used to collect and / or store the formed SCH.

2. The apparatus of claim 1, wherein the hydrophobic coating comprises a polymer.

3. The apparatus according to claim 1 or 2, wherein the hydrophobic coating comprises: Perfluoroalkoxy (PFA), polytetrafluoroethylene (PTFE), polydimethylsiloxane (PDMS), or combinations thereof.

4. The apparatus according to any one of the preceding claims, wherein the thickness of the hydrophobic coating is 10-80 μm.

5. The apparatus according to any one of the preceding claims, wherein the heat exchanger is a shell-and-tube heat exchanger, a plate heat exchanger, a coaxial heat exchanger, or a combination thereof.

6. The apparatus according to any one of the preceding claims, wherein the apparatus further comprises a resistivity sensor fluidly connected to the heat exchanger for measuring the resistivity of the slurry contained in the heat exchanger.

7. The apparatus according to any one of the preceding claims, wherein the apparatus is connected to a system for conveying the formed SCH as a heat carrier.

8. A method for forming a semi-cage hydrate (SCH), the method comprising: A solution based on a semi-cage hydrate is fed into a heat exchanger whose inner surface is coated with a hydrophobic coating. and, The heat exchanger is cooled to allow the semi-cage hydrate-based solution to form SCH.

9. The method of claim 8, wherein the hydrophobic coating comprises a polymer.

10. The method according to claim 8 or 9, wherein the hydrophobic coating comprises: Perfluoroalkoxy (PFA), polytetrafluoroethylene (PTFE), polydimethylsiloxane (PDMS), or combinations thereof.

11. The method according to any one of claims 8 to 10, wherein the thickness of the hydrophobic coating is 10-80 μm.

12. The method according to any one of claims 8 to 11, wherein the heat exchanger is a shell-and-tube heat exchanger, a plate heat exchanger, a coaxial heat exchanger, or a combination thereof.

13. The method according to any one of claims 8 to 12, wherein the method may further include measuring the resistivity of the slurry contained in the heat exchanger during the SCH formation process, so as to be able to measure the weight fraction of SCH in the slurry.

14. The method according to any one of claims 8 to 13, wherein the method further comprises adding a pre-formed SCH as a seed crystal to a slurry containing SCH formed after cooling.

15. The method according to any one of claims 8 to 14, wherein the solution based on semi-cage hydrate comprises an additive for increasing the kinetics of SCH formation and reducing viscosity.

16. The method of claim 15, wherein the additive comprises: Semi-cage-shaped hydrate seed crystals, amino acids, anti-coagulant (AA), or combinations thereof.

17. The method according to any one of claims 8 to 16, wherein the method further comprises delivering the formed SCH for use as a heat carrier.

18. The method of claim 17, wherein the method further comprises adding a viscosity-reducing additive to the formed SCH prior to delivery.

19. The method of claim 18, wherein the viscosity-reducing additive comprises: Amino acids, anticoagulants (AA), or combinations thereof.

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