A method for determining the structural stability of a solid gas hydrate under storage conditions

Abstract

The application relates to the technical field of natural gas safe storage and transportation, and discloses a method for determining the structural stability of solid-state gas hydrate in a storage state. The method comprises the following steps: (1) setting the temperature of a reaction kettle as T0, contacting a gas with water in the reaction kettle to generate solid-state gas hydrate, recording the system pressure P0 at t0, the system pressure P1 and the system temperature T1 at t1, the system pressure P2 and the system temperature T2 at t2, the decomposition pressure P3 to be measured, and the system pressure P4 at t4, and calculating the structural stability parameter SS of the solid-state gas hydrate in the storage state through a formula. The method for determining the structural stability of solid-state gas hydrate in a storage state has the advantages of high calculation precision and wide application range.

Description

Technical Field

[0001] This invention relates to the field of natural gas safe storage and transportation technology, and more specifically, to a method for determining the structural stability of solid gas hydrates under storage conditions. Background Technology

[0002] Solid gas hydrates are crystalline cage-like structures formed by small gas molecules (methane, carbon dioxide, etc.) and water molecules under low temperature and high pressure conditions. Theoretically, 1m 3 Hydropower storage capacity: 150-180m³ 3 Methane gas.

[0003] Compared with conventional gas recovery and storage technologies (such as compressed natural gas, liquefied natural gas, adsorbed natural gas, etc.), it has the following advantages: (1) The hydrate preparation process is environmentally friendly, requiring only some water and low-concentration promoters (ppm level); (2) The conditions for hydrate formation and decomposition are relatively mild, usually forming at 1-5℃ and pressure above 5.0MPa; (3) The hydrate storage form and storage conditions are stable, with gas molecules reacting with the water phase to exist in a solid state, and its self-protection effect can be used to achieve low-pressure or normal-pressure storage at low temperatures; (4) Its non-explosive characteristics make the storage process safe and reliable.

[0004] Therefore, the solid-state gas hydrate method, as a novel technology for natural gas recovery and storage, has received great attention from academia and industry in recent years.

[0005] Solid-state gas hydrate storage technology can be divided into three stages according to the process: rapid preparation of hydrates, safe transfer and storage, and efficient decomposition and recovery. Among them, rapid preparation of hydrates is the prerequisite for the industrial application of this technology, because the reaction of small gas molecules with the water phase to form hydrates is a typical phase transformation reaction.

[0006] Conventional enhancement methods include mechanical and chemical methods. Mechanical methods primarily enhance mass and heat transfer through mechanical means, such as stirring, bubbling, and spraying, to increase the gas-liquid contact area and thus improve the nucleation and growth rate of hydrates. However, this method has drawbacks such as high energy consumption, limited promotion effect, and high cost of corresponding enhancement equipment. Chemical methods mainly use additives to reduce the surface tension between gas and liquid, increase the gas-liquid contact area, thereby increasing the solubility of the gas phase in the liquid phase and promoting the rapid nucleation and growth of hydrates. Therefore, from the perspective of hydrate reaction, chemical methods are a suitable enhancement method.

[0007] The safe storage and transportation of solid hydrates is also of great significance to the development of hydrate-based gas storage technology. Although hydrates have a significant self-protection effect between -5 and -35°C, forming a certain thickness of ice layer on the surface of the hydrate to inhibit the diffusion of decomposition gases, thus sealing the solid hydrate within the ice layer, resulting in a low decomposition rate of the hydrate in this temperature range, thereby achieving the purpose of safe storage and transportation.

[0008] However, there are relatively few studies on how to effectively characterize and accurately calculate the actual decomposition rate of hydrates under storage conditions.

[0009] CN110564472A discloses a method for inhibiting hydrate decomposition and a method for storing and transporting hydrates, including the following steps: after hydrates form, a hydrate promoter is added to the surface of the hydrates, wherein the hydrate promoter includes at least one of tetrahydrofuran or cyclohexane, which reduces the pressure during the hydrate-based gas storage process, thereby further improving the safety of the gas storage process. However, this prior art only uses the pressure changes during storage and decomposition to simply describe the structural stability of the hydrates, without calculating the actual gas storage capacity.

[0010] CN109321215A discloses a hydrate decomposition inhibitor suitable for drilling in natural gas hydrate formations, comprising the following raw materials by mass percentage: poly(3-methylene-2-pyrrolidone) 0-100%, lecithin 0-100%, and poly(N-vinylpyrrolidone) 0-100%. However, the hydrate decomposition rate method used in this prior art is also a simple description of pressure changes, without considering the influence of factors such as volume changes during the actual hydrate phase transition process.

[0011] CN113189279A discloses an experimental apparatus for analyzing hydrate formation and stability, including a circulating cold bath cabinet. A data acquisition instrument is fixedly connected to one side of the circulating cold bath cabinet, and a computer is fixedly connected to the side of the circulating cold bath cabinet near the data acquisition instrument. A reaction vessel is installed inside the circulating cold bath cabinet, and sensors are installed on the outer surface of the reaction vessel. The reaction vessel is connected to a transformer via a pipeline, and the transformer is connected to a gas dioxide cylinder via a pipeline. The transformer is connected to a gas precooling tank via a pipeline and a four-way valve. The gas precooling tank is connected to a refrigeration device via a pipeline and a vacuum pump via a pipeline. The two reaction vessels are connected by a dual pipeline, which improves working efficiency and saves energy and space. However, this prior art does not specify a concrete method for calculating the structural stability of hydrates. Summary of the Invention

[0012] The purpose of this invention is to overcome the shortcomings of existing methods for describing the stability of solid gas hydrates, which have large errors and cannot accurately and effectively describe the structural stability of solid gas hydrates in the storage state.

[0013] To achieve the above objectives, the present invention provides a method for determining the structural stability of solid gas hydrates in a storage state, the method comprising:

[0014] (1) Set the temperature of the reactor to T0, and carry out a contact reaction between the gas and the water phase in the reactor to generate solid gas hydrate. Record the system pressure P0 at the time t0 when the solid gas hydrate particles first appear in the reactor.

[0015] And the system pressure P1 and system temperature T1 at the time t1 when the pressure change in the reactor is less than 20 kPa per unit time.

[0016] Then, the actual gas molar amount Δn1 used to generate a portion of the solid gas hydrate during the time interval from t0 to t1 is calculated using formulas (I), (I1), (I2), and (I3).

[0017] Δn 11 =(P0V0÷Z0RT0)-(P1V) 11 ÷Z1RT1) formula (I1),

[0018] V0 = V 11 =VV L Equation (I2),

[0019] V1=V-(n W -5.8Δn 11 V W -Δn 11 ×1.2V W Formula (I3),

[0020] Δn1=(P0V0÷Z0RT0)-(P1V1÷Z1RT1) Formula (I);

[0021] (2) Cool the reactor in step (1) to the storage temperature T2, and record the system pressure P2 and system temperature T2 at the time t2 when the temperature change in the reactor per unit time is less than 0.2K and the pressure change per unit time is less than 20kPa.

[0022] Then, the actual gas molar amount Δn2 used to generate another part of the solid gas hydrate during the time interval from t1 to t2 is calculated using formulas (II), (II1), and (II2).

[0023] (P1V1÷Z1RT1)=(P2V2÷Z2RT2) Formula (II1),

[0024] V2 = Vn W ×1.2V W Formula (II2),

[0025] Δn2=(P2V2-P 21 Formula (II) is derived from V2)÷Z2RT2.

[0026] (3) Reduce the pressure of the reactor in step (2) to the decomposition pressure P3 to be measured, and record the system pressure P4 at time t4 when the solid gas hydrate decomposes.

[0027] Then, the molar amount Δn3 of gas generated by the decomposition of the solid gas hydrate during the time interval from t3 to t4 is calculated using formula (III).

[0028] Δn3=(P4V2÷Z4RT2)-(P3V2÷Z3RT2) Formula (III);

[0029] (4) The structural stability parameter SS of the solid gas hydrate in the storage state is calculated using formula (IV). The structural stability parameter SS can be used to determine the structural stability of the solid gas hydrate in the storage state.

[0030] SS%=[1-Δn3÷(Δn1+Δn2)]×100% Formula (IV);

[0031] In formula (I),

[0032] P0 represents the system pressure at time t0, in kPa.

[0033] P1 represents the system pressure at time t1, in kPa.

[0034] V0 represents the gas phase volume at time t0, in L.

[0035] V1 represents the actual gas phase space volume at time t1, in L.

[0036] T0 represents the system temperature at time t0, in Kelvin (K).

[0037] T1 represents the system temperature at time t1, in Kelvin (K).

[0038] Z0 represents the compression factor at time t0.

[0039] Z1 represents the compression factor at time t1.

[0040] R represents Avogadro's constant;

[0041] In formula (I1),

[0042] Δn 11 This represents the theoretical molar amount of gas used to generate a portion of the solid gas hydrate during the time interval from t0 to t1, expressed in mol.

[0043] V 11 This represents the theoretical gas phase space volume at time t1, in L.

[0044] The definitions of P0, P1, V0, T0, T1, Z0, Z1 and R are the same as those in formula (I);

[0045] In formula (I2),

[0046] V represents the total volume of the reactor, in liters (L).

[0047] V L This indicates the total volume of the aqueous phase added to the reactor, in liters (L).

[0048] The definitions of V0 and V1 are the same as those in formula (I);

[0049] In formula (I3),

[0050] n W This indicates the total molar amount of the aqueous phase added to the reactor, expressed in mol.

[0051] V W This indicates the total molar volume of the aqueous phase added to the reactor, expressed in L / mol.

[0052] V1 and Δn 11 The definition and formula (I1) of V1 and Δn 11 The definitions correspond to the same,

[0053] The definition of V is the same as the definition of V in formula (I2);

[0054] In formula (II),

[0055] P2 represents the theoretical system pressure at time t2, in kPa.

[0056] P 21 This represents the actual system pressure at time t2, in kPa.

[0057] V2 represents the gas phase volume at time t2, in L / mol.

[0058] T2 represents the system temperature at time t2, in Kelvin (K).

[0059] Z2 represents the compression factor at time t2.

[0060] The definition of R is the same as the definition of R in formula (I);

[0061] In formula (II1),

[0062] The definitions of P1, V1, T1, Z1, and R are the same as those in formula (I).

[0063] The definitions of P2, V2, T2, and Z2 are the same as those in formula (II);

[0064] In formula (II2),

[0065] V、n W and V W The definition of V and n in formula (II2) W and V W The definitions are the same;

[0066] In formula (III),

[0067] P3 represents the system pressure at time t3, in kPa.

[0068] P4 represents the system pressure at time t4, in kPa.

[0069] Z3 represents the compression factor at time t3.

[0070] Z4 represents the compression factor at time t4.

[0071] The definitions of V2, T2, and R are the same as those in formula (II).

[0072] The method for determining the structural stability of solid gas hydrates under storage conditions provided by this invention systematically considers the volume expansion ratio during the solid gas hydrate formation process and the influence of secondary formation of solid gas hydrates during cooling to the storage temperature. It also inversely calculates the molar decomposition amount of solid gas hydrates through pressure changes during the storage stage. Finally, it accurately characterizes the structural stability of solid gas hydrates under storage conditions through solid gas hydrate structural stability parameters. It has the advantages of high calculation accuracy and wide applicability. Attached Figure Description

[0073] Figure 1 This is a schematic diagram of pressure changes during a preferred method for determining the structural stability of solid gas hydrates in storage conditions, provided by the present invention.

[0074] Figure 2 This is a schematic diagram of a preferred device for determining the structural stability of solid gas hydrates under storage conditions, provided by the present invention.

[0075] Explanation of reference numerals in the attached figures

[0076] 1-Gas cylinder 2-Stop valve 3-Stop valve 4-High and low temperature test chamber 5-Buffer vessel

[0077] 6-Stop valve 7-Three-way valve 8-Stop valve 9-Exhaust port 10-Fixing bolt

[0078] 11-Fixing rod; 12-High-pressure sapphire reactor; 13-Magnet; 14-Magnetic ring; 15-Gas-liquid mixture

[0079] 16-Stop valve; 17-High and low temperature test chamber; 18-Automatic data acquisition system

[0080] DPT - High-precision pressure sensor; RTD - Temperature sensor Detailed Implementation

[0081] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0082] It should be noted that in this invention, some of the solid gas hydrates and some of the solid gas hydrates have similar compositions, and the only difference between them is the time period in which they are generated.

[0083] As previously described, a first aspect of the present invention provides a method for determining the structural stability of solid gas hydrates in a storage state, the method comprising:

[0084] (1) Set the temperature of the reactor to T0, and carry out a contact reaction between the gas and the water phase in the reactor to generate solid gas hydrate. Record the system pressure P0 at the time t0 when the solid gas hydrate particles first appear in the reactor.

[0085] And the system pressure P1 and system temperature T1 at the time t1 when the pressure change in the reactor is less than 20 kPa per unit time.

[0086] Then, the actual gas molar amount Δn1 used to generate a portion of the solid gas hydrate during the time interval from t0 to t1 is calculated using formulas (I), (I1), (I2), and (I3).

[0087] Δn 11 =(P0V0÷Z0RT0)-(P1V) 11 ÷Z1RT1) formula (I1),

[0088] V0 = V 11=VV L Equation (I2),

[0089] V1=V-(n W -5.8Δn 11 V W -Δn 11 ×1.2V W Formula (I3),

[0090] Δn1=(P0V0÷Z0RT0)-(P1V1÷Z1RT1) Formula (I);

[0091] (2) Cool the reactor in step (1) to the storage temperature T2, and record the system pressure P2 and system temperature T2 at the time t2 when the temperature change in the reactor per unit time is less than 0.2K and the pressure change per unit time is less than 20kPa.

[0092] Then, the actual gas molar amount Δn2 used to generate another part of the solid gas hydrate during the time interval from t1 to t2 is calculated using formulas (II), (II1), and (II2).

[0093] (P1V1÷Z1RT1)=(P2V2÷Z2RT2) Formula (II1),

[0094] V2 = Vn W ×1.2V W Formula (II2),

[0095] Δn2=(P2V2-P 21 Formula (II) is derived from V2)÷Z2RT2.

[0096] (3) Reduce the pressure of the reactor in step (2) to the decomposition pressure P3 to be measured, and record the system pressure P4 at time t4 when the solid gas hydrate decomposes.

[0097] Then, the molar amount Δn3 of gas generated by the decomposition of the solid gas hydrate during the time interval from t3 to t4 is calculated using formula (III).

[0098] Δn3=(P4V2÷Z4RT2)-(P3V2÷Z3RT2) Formula (III);

[0099] (4) The structural stability parameter SS of the solid gas hydrate in the storage state is calculated using formula (IV). The structural stability parameter SS can be used to determine the structural stability of the solid gas hydrate in the storage state.

[0100] SS%=[1-Δn3÷(Δn1+Δn2)]×100% Formula (IV);

[0101] In formula (I),

[0102] P0 represents the system pressure at time t0, in kPa.

[0103] P1 represents the system pressure at time t1, in kPa.

[0104] V0 represents the gas phase volume at time t0, in L.

[0105] V1 represents the actual gas phase space volume at time t1, in L.

[0106] T0 represents the system temperature at time t0, in Kelvin (K).

[0107] T1 represents the system temperature at time t1, in Kelvin (K).

[0108] Z0 represents the compression factor at time t0.

[0109] Z1 represents the compression factor at time t1.

[0110] R represents Avogadro's constant;

[0111] In formula (I1),

[0112] Δn 11 This represents the theoretical molar amount of gas used to generate a portion of the solid gas hydrate during the time interval from t0 to t1, expressed in mol.

[0113] V 11 This represents the theoretical gas phase space volume at time t1, in L.

[0114] The definitions of P0, P1, V0, T0, T1, Z0, Z1 and R are the same as those in formula (I);

[0115] In formula (I2),

[0116] V represents the total volume of the reactor, in liters (L).

[0117] V L This indicates the total volume of the aqueous phase added to the reactor, in liters (L).

[0118] The definitions of V0 and V1 are the same as those in formula (I);

[0119] In formula (I3),

[0120] n W This indicates the total molar amount of the aqueous phase added to the reactor, expressed in mol.

[0121] V W This indicates the total molar volume of the aqueous phase added to the reactor, expressed in L / mol.

[0122] V1 and Δn 11 The definition and formula (I1) of V1 and Δn 11 The definitions correspond to the same,

[0123] The definition of V is the same as the definition of V in formula (I2);

[0124] In formula (II),

[0125] P2 represents the theoretical system pressure at time t2, in kPa.

[0126] P 21 This represents the actual system pressure at time t2, in kPa.

[0127] V2 represents the gas phase volume at time t2, in L / mol.

[0128] T2 represents the system temperature at time t2, in Kelvin (K).

[0129] Z2 represents the compression factor at time t2.

[0130] The definition of R is the same as the definition of R in formula (I);

[0131] In formula (II1),

[0132] The definitions of P1, V1, T1, Z1, and R are the same as those in formula (I).

[0133] The definitions of P2, V2, T2, and Z2 are the same as those in formula (II);

[0134] In formula (II2),

[0135] V、n W and V W The definition of V and n in formula (II2) W and V W The definitions are the same;

[0136] In formula (III),

[0137] P3 represents the system pressure at time t3, in kPa.

[0138] P4 represents the system pressure at time t4, in kPa.

[0139] Z3 represents the compression factor at time t3.

[0140] Z4 represents the compression factor at time t4.

[0141] The definitions of V2, T2, and R are the same as those in formula (II).

[0142] According to a preferred embodiment, the method further includes: obtaining Z0, Z1, Z2, Z3, and Z4 using formula (V).

[0143] Z-(1-B)Z 2 +(A-2B-3B 2 )Z-(AB-B 2 -B 3 Formula (V) = 0;

[0144] In formula (V),

[0145] A = 0.45724(T) c / T)×[1+k(1-(T / T c ) 0.5 )] 2 ×(P / P c Meanwhile, k = 0.3746 + 1.54226ω - 0.26992ω 2 ,

[0146] B = 0.0778(T) c / T)×(P / P c ),

[0147] Furthermore, when Z is Z0, T is T0 and P is P0;

[0148] When Z is Z1, T is T1 and P is P1;

[0149] When Z is Z2, T is T2, and P is P2;

[0150] When Z is Z3, T is T2 and P is P3;

[0151] When Z is Z4, T is T2 and P is P4;

[0152] T c The critical temperature of a gas is indicated by the unit K.

[0153] P c This represents the critical pressure of a gas, expressed in kPa.

[0154] ω represents the gas eccentricity factor.

[0155] Preferably, in steps (1) and (2), the unit time is 1 hour.

[0156] In a preferred embodiment, in step (1), the gas is selected from at least one of methane, ethane, n-propane, isopropane, n-butane, isobutane, tert-butane, and carbon dioxide.

[0157] Preferably, in step (1), the aqueous phase is selected from pure water or an aqueous solution containing a hydrate promoter.

[0158] More preferably, the hydrate promoter is selected from at least one of amino acid compounds and sodium dodecyl sulfonate (SDS).

[0159] In a preferred embodiment, the amino acid compound is selected from at least one of leucine, valine, histidine, and alanine.

[0160] According to another preferred embodiment, in step (1), the conditions for the contact reaction are at least: carried out under stirring conditions, with a stirring speed of 60-200 rpm, a temperature greater than 273 K, a pressure greater than 3000 kPa, and a time of 60-120 min.

[0161] Preferably, in step (2), the cooling rate is 0.2-0.5 K / min.

[0162] Preferably, in step (2), the storage temperature is 243-268K.

[0163] In a preferred embodiment, in step (3), the depressurization operation includes: depressurizing at 1000-2000 kPa / min to 500-1000 kPa above the thermodynamic phase equilibrium pressure of the solid gas hydrate corresponding to the storage temperature T2, and then depressurizing at 100-500 kPa / s to the decomposition pressure to be measured.

[0164] Figure 1 This is a schematic diagram illustrating pressure changes during a preferred method for determining the structural stability of solid gas hydrates under storage conditions, provided by the present invention. The stages t0 to t1 represent the period from the initial formation of solid gas hydrates to their stable formation; t1 to t2 represent the period after the solid gas hydrates have stabilized and are stored; t2 to t3 represent the period after storage when the solid gas hydrates begin to decompose; and t3 to t4 represent the period of continuous decomposition of the solid gas hydrates.

[0165] Figure 2 This is a schematic diagram of a preferred device for determining the structural stability of solid gas hydrates under storage conditions, provided by the present invention.

[0166] The following combination Figure 2 The present invention will be described by way of example.

[0167] (1) Add pure water to the high-pressure sapphire reactor 12, and perform vacuum treatment on the buffer reactor 5 and the high-pressure sapphire reactor 12 and methane gas replacement treatment, then close the shut-off valve 6, the three-way valve 7 and the shut-off valve 16.

[0168] Set the temperature of the high-pressure sapphire reactor 12 to T0, open the shut-off valve 2 of the gas cylinder 1, introduce methane gas into the buffer vessel 5, and then close the shut-off valve 3; after the temperature inside the high-pressure sapphire reactor 12 reaches the set value and remains stable for a certain period of time, open the shut-off valve 3, shut-off valve 6 and three-way valve 7, introduce the methane gas from the buffer vessel 5 into the high-pressure sapphire reactor 12, and after it reaches a dissolution equilibrium with pure water (the pressure of the introduced methane gas is less than the equilibrium pressure of the solid gas hydrate corresponding to the T0 temperature), pressurize it to P0 at a certain pressurization rate, then close the shut-off valve 3, shut-off valve 6 and three-way valve 7, and turn on the magnetic stirring system, so that the magnet 13 controls the magnetic ring 14 to make the methane gas and pure water react at a certain stirring speed;

[0169] The macroscopic morphological evolution of the gas-liquid mixture 15 inside the high-pressure sapphire reactor 12 is observed in real time. When solid gas hydrate particles first appear inside the high-pressure sapphire reactor 12, the system pressure P0 inside the high-pressure sapphire reactor 12 at this moment t0 is recorded.

[0170] When the gas and pure water continue to react until the system pressure decreases by less than 20 kPa per unit time, and the system pressure P1 in the high-pressure sapphire reactor 12 at this moment t1;

[0171] (2) Cool the aforementioned high-pressure sapphire reactor 12 to the storage temperature T2 at a certain cooling rate. When the temperature change value in the high-pressure sapphire reactor 12 is less than 0.2K per unit time and the pressure change value is less than 20kPa per unit time, record the system pressure P2 and system temperature T2 at this moment t2.

[0172] (3) Open the three-way valve 7 and the shut-off valve 8, and reduce the pressure inside the high-pressure sapphire reactor 12 to a certain pressure through the exhaust port 9 at a certain pressure reduction rate. Then reduce the pressure to the decomposition pressure to be measured as P3 at a certain pressure reduction rate and close the three-way valve 7 and the shut-off valve 8. Record the system pressure P4 at t4 after a certain time to obtain the structural stability parameter SS of the solid gas hydrate in the storage state.

[0173] In the following examples, unless otherwise specified, all raw materials used were commercially purchased.

[0174] Example 1

[0175] (1) Add 10 mL of pure water (V LAdd it to the high-pressure sapphire reactor 12, and after vacuuming the buffer reactor 5 and the high-pressure sapphire reactor 12 and replacing them with methane gas, close the shut-off valve 6, the three-way valve 7 and the shut-off valve 16.

[0176] The temperature of the high-pressure sapphire reactor 12 is set to 274.15K (T0). The shut-off valve 2 of the gas cylinder 1 is opened, and methane gas is introduced into the buffer vessel 5. Then the shut-off valve 3 is closed. After the temperature inside the high-pressure sapphire reactor 12 reaches the set value and remains stable for 2 hours, the shut-off valves 3, 6, and 7 are opened to introduce the methane gas from the buffer vessel 5 into the high-pressure sapphire reactor 12. After the methane gas reaches a dissolution equilibrium with pure water (the pressure of the introduced methane gas is less than the equilibrium pressure of the solid gas hydrate at 274.15K, which is 2820 kPa), the pressure is increased to 6598 kPa (P0) at a rate of 10000 kPa / min. Then the shut-off valves 3, 6, and 7 are closed, and the magnetic stirring system is turned on. The magnet 13 controls the magnetic ring 14 to stir at a speed of 60 rpm to allow the methane gas to contact and react with the pure water.

[0177] The macroscopic morphological evolution of the gas-liquid mixture 15 inside the high-pressure sapphire reactor 12 is observed in real time. When solid gas hydrate particles first appear inside the high-pressure sapphire reactor 12, the system pressure (P0) inside the high-pressure sapphire reactor 12 at this moment (t0) is recorded.

[0178] Wait until the gas and pure water continue to react until the system pressure decreases by less than 20 kPa within 1 hour, and at this moment (t1), the system pressure (P1) inside the high-pressure sapphire reactor 12 is measured.

[0179] (2) Cool the aforementioned high-pressure sapphire reactor 12 to a storage temperature of 263.15K (T2) at a rate of 0.5K / min. When the temperature change in the high-pressure sapphire reactor 12 within 1 hour is less than 0.2K and the pressure change within 1 hour is less than 18kPa, record the system pressure P2 and system temperature T2 at this moment (t2).

[0180] (3) Open the three-way valve 7 and the shut-off valve 8, and reduce the pressure inside the high-pressure sapphire reactor 12 to 950 kPa at a rate of 1500 kPa / min through the exhaust port 9 (at this time, the thermodynamic phase equilibrium pressure of the solid gas hydrate under 263.15 K conditions is 450 kPa). Then, reduce the pressure to the decomposition pressure to be measured at a rate of 200 kPa / s to 100 kPa (P3), and then close the three-way valve 7 and the shut-off valve 8. Record the system pressure P4 at this moment (t4) 2 hours later to obtain the structural stability parameter SS of the solid gas hydrate in the storage state.

[0181] Example 2

[0182] This embodiment uses a method similar to that of Embodiment 1, except that:

[0183] The conditions were T0 = 274.15 K, P0 = 6552 kPa, and the aqueous phase was 10 mL of 0.02 wt% SDS aqueous solution. All other conditions were the same as in Example 1. The specific results are shown in Table 1.

[0184] Example 3

[0185] This embodiment uses a method similar to that of Embodiment 1, except that:

[0186] The conditions were T0 = 274.15 K, P0 = 6523 kPa, and the aqueous phase was 10 mL of 0.1 wt% leucine aqueous solution. All other conditions were the same as in Example 1. The specific results are shown in Table 1.

[0187] Example 4

[0188] This embodiment uses a method similar to that of Embodiment 1, except that:

[0189] The conditions were T0 = 274.15 K, P0 = 6594 kPa, and the aqueous phase was 10 mL of 0.1 wt% valine aqueous solution. All other conditions were the same as in Example 1. The specific results are shown in Table 1.

[0190] Example 5

[0191] This embodiment uses a method similar to that of Embodiment 1, except that:

[0192] The conditions were T0 = 274.15 K, P0 = 6673 kPa, and the aqueous phase was 10 mL of 0.1 wt% alanine aqueous solution. All other conditions were the same as in Example 1. The specific results are shown in Table 1.

[0193] Example 6

[0194] This embodiment uses a method similar to that of Embodiment 1, except that:

[0195] The conditions were T0 = 274.15 K, P0 = 6273 kPa, and the aqueous phase was 10 mL of 0.1 wt% histidine aqueous solution. All other conditions were the same as in Example 1. The specific results are shown in Table 1.

[0196] Example 7

[0197] This embodiment uses a method similar to that of Embodiment 1, except that:

[0198] The conditions were T0 = 274.15 K, P0 = 6577 kPa, T2 = 272.15 K, and the aqueous phase was 10 mL of 0.1 wt% leucine aqueous solution. All other conditions were the same as in Example 1. The specific results are shown in Table 1.

[0199] Example 8

[0200] This embodiment uses a method similar to that of Embodiment 1, except that:

[0201] The conditions were T0 = 274.15 K, P0 = 6597 kPa, T2 = 268.15 K, and the aqueous phase was 10 mL of 0.1 wt% leucine aqueous solution. All other conditions were the same as in Example 1. The specific results are shown in Table 1.

[0202] Example 9

[0203] This embodiment uses a method similar to that of Embodiment 1, except that:

[0204] The conditions were: T0 = 274.15 K, P0 = 6405 kPa, T2 = 272.15 K, P3 = 500 kPa, and the aqueous phase was 10 mL of 0.1 wt% leucine aqueous solution. All other conditions were the same as in Example 1. The specific results are shown in Table 1.

[0205] Example 10

[0206] This embodiment uses a method similar to that of Embodiment 1, except that:

[0207] The conditions were: T0 = 274.15 K, P0 = 6543 kPa, T2 = 272.15 K, P3 = 1000 kPa, and the aqueous phase was 10 mL of 0.1 wt% leucine aqueous solution. All other conditions were the same as in Example 1. The specific results are shown in Table 1.

[0208] Note: The volume V of the high-pressure sapphire reactor in this invention is 59 mL.

[0209] Table 1

[0210]

[0211] Note: SS (%) * This represents the structural stability parameters of solid gas hydrates obtained using existing methods.

[0212] The aforementioned existing methods for determining the structural stability parameters of solid gas hydrates are as follows:

[0213] (I) Record the system pressure P0 at the initial storage time of the solid gas hydrate and the system pressure P after a certain storage time. d The system was then heated to completely decompose the solid gas hydrate within it, and the system pressure P at the moment of complete decomposition was recorded. e ;

[0214] (II) The structural stability parameter SS of solid gas hydrate is calculated using the formula shown in Equation (1). The structural stability parameter SS can evaluate the structural stability of solid gas hydrate under storage conditions.

[0215]

[0216] As can be seen from Table 1, the method for determining the structural stability of solid gas hydrates under storage conditions provided by this invention can effectively calculate the actual structural stability parameters of solid gas hydrates, which is of great significance for improving the theory of safe storage and transportation of solid gas hydrates and promoting the development of solid gas hydrate technology.

[0217] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for determining the structural stability of solid gas hydrates under storage conditions, characterized in that, The method includes: (1) Set the temperature of the reactor to be T 0. The gas and water phase are reacted in a reactor to generate solid gas hydrate. The moment when solid gas hydrate particles first appear in the reactor is recorded. t 0 system pressure P 0, and the time when the pressure change in the reactor is less than 20 kPa per unit time. t 1 system pressure P 1 and system temperature T 1, Then, the results are obtained through formulas (I), (I1), (I2), and (I3). t 0 to t The actual molar amount Δ of gas used to generate a portion of the solid gas hydrate within time 1. n 1, Δ n 11 =( P 0 V 0÷ Z 0 RT 0)-( P 1 V 11 ÷ Z 1 RT 1) Formula (I1), V 0= V 11 = V - V L Equation (I2), V 1= V -( n W -5.8Δ n 11 ) V W -Δ n 11 ×1.2 V W Formula (I3), Δ n 1 = ( P 0 V 0÷ Z 0 RT 0)-( P 1 V 1÷ Z 1 RT 1) Formula (I); (2) Cool the reactor in step (1) to the storage temperature. T 2. Record the times when the temperature change in the reactor is less than 0.2 K per unit time and the pressure change is less than 20 kPa per unit time. t 2 system pressure P 2 and system temperature T 2, Then, the results are obtained by formula (II), formula (II1), and formula (II2). t 1 to t The actual molar amount Δ of gas used to generate another portion of the solid gas hydrate within time 2. n 2, ( P 1 V 1÷ Z 1 RT 1)=( P 2 V 2÷ Z 2 RT 2) formula (II1), V 2 = V - n W ×1.2 V W Formula (II2), Δ n 2 = ( P 2 V 2 - P 21 V 2) ÷ Z 2 RT 2 formula (II); (3) Reduce the pressure of the reactor in step (2) to the decomposition pressure to be measured. P 3, and record the decomposition of the solid gas hydrate to t System pressure at 4 o'clock P 4, Then, the result is obtained by formula (III). t 3 to t The amount of gas molarity Δ generated by the decomposition of the solid gas hydrate within time 4. n 3, Δ n 3 = ([[]] P 4 V 2 ÷ Z 4 RT 2) - ([[]] P 3 V 2 ÷ Z 3 RT 2) Formula (III); (4) The structural stability parameters of the solid gas hydrate under storage conditions are calculated using formula (IV). SS The structural stability parameters SS It can be used to determine the structural stability of solid-state gas hydrates in their storage state. SS % = [1 - Δ n 3 ÷ (Δ n 1 + Δ n 2)] × 100% Formula (IV); In formula (I), P 0 represents t The system pressure at time 0, in kPa. P 1 represents t The system pressure at time 1, in kPa. V 0 represents t The volume of the gas phase space at time 0, in liters (L). V 1 represents t The actual gas phase volume at time 1, in liters (L). T 0 represents t The system temperature at time 0, in Kelvin. T 1 represents t The system temperature at time 1, in Kelvin. Z 0 represents t Compression factor at time 0 Z 1 represents t Compression factor at time 1 R Represents Avogadro's constant; In formula (I1), Δ n 11 express t 0 to t The theoretical molar amount of gas required to generate a portion of the solid gas hydrate within a given time period is expressed in mol. V 11 express t The theoretical gas phase volume at time 1, in liters (L). P 0 、P 1 、V 0 、T 0 、T 1 、Z 0 、Z 1 and R In the definition and formula (I) P 0 、P 1 、V 0 、T 0 、T 1 、Z 0 、Z 1 and R The definitions correspond to the same; In formula (I2) V This indicates the total volume of the reactor, expressed in liters (L). V L This indicates the total volume of the aqueous phase added to the reactor, in liters (L). V 0 and V The definition and formula (I) of 1 V 0 and V The definition of 1 corresponds to the same; In formula (I3), n W This indicates the total molar amount of the aqueous phase added to the reactor, expressed in mol. V W This indicates the total molar volume of the aqueous phase added to the reactor, expressed in L / mol. V 1 and Δ n 11 The definition and formula (I1) V 1 and Δ n 11 The definitions correspond to the same, V The definition and formula (I2) V The definitions are the same; In formula (II), P 2 indicates t The theoretical system pressure at time 2, in kPa. P 21 express t The actual system pressure at time 2, in kPa. V 2 indicates t The volume of the gas phase space at time 2, in L / mol. T 2 indicates t The system temperature at time 2, in K. Z 2 indicates t The compression factor at time 2, R In the definition and formula (I) R The definitions are the same; In formula (II1), P 1 、V 1 、T 1 、Z 1 and R In the definition and formula (I) P 1 、V 1 、T 1 、Z 1 and R The definitions correspond to the same, P 2 、V 2 、T 2 and Z 2. Definition and Formula (II) P 2 、V 2 、T 2 and Z The definition of 2 corresponds to the same; In formula (II2), V、n W as well as V W The definition and formula (II2) V、n W as well as V W The definitions are the same; In formula (III), P 3 indicates t The system pressure at time 3, in kPa. P 4 represents t The system pressure at time 4, in kPa. Z 3 indicates t Compression factor at time 3 Z 4 represents t Compression factor at time 4 V 2 、T 2 and R Definition and Formula (II) V 2 、T 2 and R The definitions correspond to the same.

2. The method according to claim 1, wherein, The method also includes: obtaining using formula (V) Z 0 、Z 1 、Z 2 、Z 3. Z 4, Z -(1- B ) Z 2 +( A -2 B -3 B 2 ) Z -( AB - B 2 - B 3 Formula (V) = 0; In formula (V), A =0.45724 ( T c / T )×[1+ k (1-( T / T c ) 0.5 )] 2 ×( P / P c ),at the same time, k =0.3746+1.54226 ω -0.26992 ω 2 , B =0.0778（ T c / T ）×（ P / P c ）， And, when Z for Z At 0 o'clock, T for T 0, P for P 0; when Z for Z At 1 o'clock, T for T 1, P for P 1; when Z for Z At 2 o'clock, T for T 2, P for P 2; when Z for Z At 3 o'clock, T for T 2, P for P 3; when Z for Z At 4 o'clock, T for T 2, P for P 4; T c The critical temperature of a gas is indicated by the unit K. P c This represents the critical pressure of a gas, expressed in kPa. ω The eccentricity factor represents the gas.

3. The method according to claim 1 or 2, wherein, In steps (1) and (2), the unit time is 1 hour.

4. The method according to any one of claim 1 or 2, wherein, In step (1), the gas is selected from at least one of methane, ethane, n-propane, isopropane, n-butane, isobutane, tert-butane, and carbon dioxide.

5. The method according to any one of claims 1 or 2, wherein, In step (1), the aqueous phase is selected from pure water or an aqueous solution containing a hydrate promoter.

6. The method according to claim 5, wherein, The hydrate promoter is selected from at least one of amino acid compounds and sodium dodecyl sulfonate.

7. The method according to any one of claims 1 or 2, wherein, In step (1), the conditions for the contact reaction must at least be met: the reaction is carried out under stirring conditions, with a stirring speed of 60-200 rpm, a temperature greater than 273 K, a pressure greater than 3000 kPa, and a time of 60-120 min.

8. The method according to any one of claims 1 or 2, wherein, In step (2), the cooling rate is 0.2-0.5 K / min.

9. The method according to any one of claims 1 or 2, wherein, In step (2), the storage temperature is 243-268K.

10. The method according to any one of claims 1 or 2, wherein, In step (3), the pressure reduction operation includes: reducing the pressure to the storage temperature at a rate of 1000-2000 kPa / min. T The pressure is 500-1000 kPa above the thermodynamic phase equilibrium pressure of the corresponding solid gas hydrate, and then reduced to the decomposition pressure to be measured at 100-500 kPa / s.

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