Screening method of sulfur hexafluoride substitute gas

Abstract

The invention discloses a method for screening sulfur hexafluoride substitute gas, and relates to the technical field of electric appliance insulation. The substitute gas comprises perfluorodimethyl sulfide, the other components are screened from the existing components, the insulating gas with the insulating strength higher than that of sulfur hexafluoride and perfluorodimethyl sulfide, low liquefaction temperature and weak flammability is screened, and the insulating gas with the macroscopic property similar to that of a single substance can be obtained by mixing the two gases; and the insulating gas with high insulating strength, low liquefaction temperature, low toxicity and low GWP is obtained through screening.

Description

Technical Field

[0001] The invention relates to the technical field of electrical insulation, and in particular to a method for screening sulfur hexafluoride alternative gas. Background Art

[0002] The insulation strength of perfluoromethyl sulfide gas is about 1.7 times that of sulfur hexafluoride, its boiling point is -22°C, the insulation strength is 1.73 times that of sulfur hexafluoride, and its GWP is estimated to be only 2.8 times that of carbon dioxide. Compared with SF6, fluoromethyl sulfide has a lower boiling point and GWP, and low toxicity, which is significantly better than most existing sulfur hexafluoride alternative gases. Perfluoromethyl sulfide or its azeotropic gas can be used as an insulating gas to replace sulfur hexafluoride, meeting the requirements of low boiling point, high insulation strength, low toxicity, and low GWP.

[0003] The group contribution model is the main way to predict azeotropic gases. The group contribution model assumes that the molecules in the solution are composed of multiple groups, and the interactions between molecules are derived from the interactions between the groups. If the group parameters of the molecules and the interaction parameters between the groups are known, the azeotropic gases can be accurately predicted without experimental data. However, since perfluoromethyl sulfide is a new gas, the existing UNIFAC and PPR7 group contribution models lack the parameters for predicting the groups and interaction parameters between perfluoromethyl sulfide, and it is impossible to screen azeotropic gases containing perfluoromethyl sulfide. Summary of the invention

[0004] In view of the defects or shortcomings of the prior art, the present invention provides a method for screening sulfur hexafluoride alternative gas.

[0005] The sulfur hexafluoride substitute gas of the present invention comprises component i and component j, wherein component i is perfluoromethyl sulfide, and component j is screened and determined by the following steps:

[0006] S1, select the insulating gas with a liquefaction temperature range of -40 to 20°C under standard atmospheric pressure as the initial component j;

[0007] S2, find at least one set of T, x that satisfies the following formulas (1) to (16) under the given equilibrium pressure P, when the mixed gas of component i and initial component j is in gas-liquid equilibrium i ,y i 、x j and j ; Where: the given equilibrium pressure P is the working pressure of SF6 gas, the unit of P is: MPa; T is the gas-liquid equilibrium temperature, the unit is ℃; x i is the molar percentage of gas component i in the liquid phase of the mixed gas; i is the molar percentage of gas component i in the gas phase of the mixed gas; x jis the molar percentage of gas component j in the liquid phase of the mixed gas; j is the molar percentage of gas component j in the gas phase of the mixed gas; -40℃≤T≤20℃, 0<x i <1,0<y i <1,0<x j <1,0<y j <1, and x i +x j =1,y i +y j =1;

[0008]

[0009]

[0010]

[0011] 0.30000≤β2≤0.40000,

[0012] 1.50000≤β3≤1.60000,

[0013] 0.20000≤β4≤0.30000 (12)

[0014]

[0015] 0.40000≤β6≤0.50000,

[0016] 0.30000≤β7≤0.40000,

[0017] 1.50000≤β8≤1.60000,

[0018] 0.20000≤β9≤0.30000

[0019] In formulas (1)-(16):

[0020] is the gas phase fugacity of gas component i in the mixed gas, is the liquid phase fugacity of gas component i in the mixed gas, is the gas phase fugacity of gas component j in the mixed gas;

[0021] is the liquid phase fugacity of gas component j in the mixed gas;

[0022] R is the gas constant;

[0023] Z Lis the gas phase compressibility factor of the mixed gas, Z V is the liquid phase compressibility factor of the mixed gas, V L is the molar volume of the liquid phase of the mixed gas under the conditions of P and T, in m 3 / mol; V V is the gas phase molar volume of the mixed gas under P and T conditions, in m 3 / mol; V is the volume of the mixed gas under the conditions of P and T, in m 3 ;

[0024] N i is the molar amount of gas component i in the mixed gas, in mol;

[0025] N j is the molar amount of gas component j in the mixed gas, in mol;

[0026] N is the total molar amount of the mixed gas, in mol;

[0027] a and b are the state equation parameters of the mixed gas;

[0028] a i is the molecular energy constant of gas component i, ranging from 12000 to 3845000; b i is the volume correction constant of gas component i, ranging from 12.85 to 140.68;

[0029] is the free energy of the gas mixture;

[0030] k ij is the binary interaction parameter, 0<k ij <5;

[0031] C is a constant, ranging from 24.68500 to 24.68600;

[0032] ω i is the eccentricity factor of gas component i, which is taken as 0.335;

[0033] ω j is the eccentricity factor of gas component j;

[0034] T ri is the relative state temperature of gas component i; the value range is 0.5~1;

[0035] T ci is the critical temperature of gas component i; the unit is K, and it is 376.75K;

[0036] T cjis the critical temperature of gas component j; unit: K;

[0037] p ci is the critical pressure of gas component i, in MPa; take 3.843MPa; p cj is the critical pressure of gas component j, in MPa;

[0038] is the saturated vapor pressure of gas component i at temperature T, in MPa; is the saturated vapor pressure of gas component j at temperature T, in MPa;

[0039] is the liquid volume of gas component i under conditions of P and T, in m 3 ;

[0040] is the liquid volume of gas component j under conditions P and T, in m 3 ;

[0041] T / K is the temperature after the equilibrium temperature T is converted into Kelvin;

[0042] N gi All the groups decomposed from the molecules of gas component i, CF3SCF3 as the whole group; N gi The value is 1.

[0043] N gj All the groups decomposed by the molecules of gas component j;

[0044] k represents the molecular group CF3SCF3 of gas component i;

[0045] l represents any group among the groups decomposed by the molecules of gas component j;

[0046] α ik is the relative molar fraction of the group CF3SCF3, which is the value of the number of groups CF3SCF3 divided by the total number of groups in the gas component i molecule, and is 1;

[0047] α jk is the relative molar fraction of the group CF3SCF3 of the gas component j, which is the value of the number of groups CF3SCF3 divided by the total number of groups in the gas component j molecule;

[0048] α il is the relative molar fraction of group l of gas component i, which is the number of groups l divided by the total number of groups in the molecules of gas component i;

[0049] α jlis the relative molar fraction of group l of gas component j, which is the number of groups l divided by the total number of groups in the gas component j molecule;

[0050] A kl With B kl are the group parameters of the group CF3SCF3 and the group l;

[0051]

[0052] In the formula, A wk _CH2 is the interaction parameter between the ethylene group and the group 1; A wk _CH2 is the interaction parameter between the ethylene group and the group 1; N l is the number of positively charged atoms in group l;

[0053] S3, based on the screening results of S2, further screen the existence of x under the given equilibrium pressure P. i =y i Under the condition, the equilibrium temperature T is the minimum equilibrium temperature, and the minimum equilibrium temperature is less than the liquefaction temperature of each gas component in the mixed gas.

[0054] Further, the method of the present invention also includes:

[0055] S4, further screen the insulation strength Er_ based on the gas component j screened in S3 混合气体 Mixed gas that satisfies the relationship shown in formula (17):

[0056] Er_ 混合气体 > Er_ i × x i + Er_ j × x j (17)

[0057] In the formula, Er_ i is the dielectric strength of perfluoromethyl sulfide relative to SF6; Er_ j is the insulation strength of gas component j relative to SF6; x1 is the mass percentage of gas component i in the mixed gas; x2 is the mass percentage of gas component j in the mixed gas; the mixed gas is a mixed gas composed of gas component i and gas component j.

[0058] Optionally, the initial component j is selected from hydrofluoroolefins, hydrofluorocarbons, alkanes or hydrofluoronitriles.

[0059] The method for screening sulfur hexafluoride alternative gases provided by the present invention can screen out insulating gases with higher insulation strength than sulfur hexafluoride and perfluoromethyl sulfide, lower liquefaction temperature and weak flammability from existing components, and by mixing and screening the two gases 1 and gas 2, an insulating gas similar to a single substance in macroscopic properties can be obtained, and an insulating gas with high insulation strength, low liquefaction temperature, low toxicity and low GWP can be obtained by screening.

[0060] The insulating mixed gas of the present invention has good environmental performance, an ODP value of 0, and a GWP value significantly lower than that of sulfur hexafluoride; and, compared with perfluoroisoamyl ketone (C5F 10 O), perfluoroisobutyronitrile and other G3 gas alternatives also have characteristics similar to those of insulating gases of a single substance, with better overall effects. DETAILED DESCRIPTION

[0061] Unless otherwise specified, the scientific and technical terms in this document are understood according to the knowledge of ordinary technicians in the relevant fields. The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0062] Embodiment 1:

[0063] The screening objects of component j in this embodiment are: perfluoromethyl sulfide (A), trifluoroiodomethane (B), cis-1,3,3,3-tetrafluoropropylene (C), 1,1-difluoroethane (D), 3,3,3-trifluoropropylene (E), 1,1,2,2-tetrafluoroethane (F), 2,3,3,3-tetrafluoropropylene (G), and heptafluoroisobutyronitrile (H), a total of 8 gases, as shown in Table 1.

[0064] Table 1 Step S1 Gas Combination Screening Results

[0065] gas serial number Liquid temperature / ℃ Perfluoromethyl sulfide A -22 Trifluoroiodomethane B -25 cis-1,3,3,3-tetrafluoropropene C 9 1,1-Difluoroethane D -52 3,3,3-Trifluoropropene E -28 1,1,2,2-Tetrafluoroethane F -23 2,3,3,3-Tetrafluoropropene G 9 Heptafluoroisobutyronitrile H -7

[0066] According to the condition of S1, 7 gases are used as initial component j; further based on MATLAB software, the method screening calculation of the above steps S2 and S3 is performed, and P is taken as p=0.1MPa in the process (in other specific schemes, P can be taken according to the working pressure of the insulating gas, and 0.1MPa is selected as an example here to explain the present invention in detail; the common working pressure of the insulating mixed gas described in the present invention is 0.1MPa~0.5MPa); the screening results are shown in Table 2;

[0067] The results screened by the conditions of steps S2 and S3 are: perfluoromethyl sulfide+1,1-difluoroethane, perfluoromethyl sulfide+1,1,2,2-tetrafluoroethane, perfluoromethyl sulfide+2,3,3,3-tetrafluoropropylene, a total of 3 mixed gases.

[0068] During the screening process, the value of C was 24.68544; Take 1.1001; Take 1.3741; a i Take 1645070; b i Take 40.78; T ri Take 0.8; β1=-0.62323, β2=0.37464, β3=1.54226, β4=0.26992, β5=0.07780, β6=0.45724, β7=0.37464, β8=1.54226, β9=0.26992;

[0069] Table 2 Calculation results of the screening gas combinations in steps S2 and S3 at 0.1 MPa

[0070]

[0071]

[0072] In order to meet the use scenarios with higher insulation strength, a further preferred solution is to use formula (17) to screen the mixed gas with synergistic effect characteristics of insulation strength.

[0073] The following examples prepare mixed gases of perfluoromethyl sulfide+1,1,2,2-tetrafluoroethane, perfluoromethyl sulfide+2,3,3,3-tetrafluoropropylene, and perfluoromethyl sulfide+1,1-difluoroethane in different ratios, and conduct insulation strength experimental measurements.

[0074] Embodiment 2:

[0075] Under a temperature condition of -40°C, 45.5% by mass of perfluoromethyl sulfide and 54.5% by mass of 1,1-difluoroethane are physically mixed under liquid phase conditions and completely gasified to obtain a mixed insulating gas.

[0076] Embodiment 3:

[0077] Under a temperature condition of -40°C, 45.5% by mass of perfluoromethyl sulfide and 54.5% by mass of perfluoromethyl sulfide + 1,1,2,2-tetrafluoroethane are physically mixed under liquid phase conditions and completely gasified to obtain a mixed insulating gas.

[0078] Embodiment 4:

[0079] Under a temperature condition of -40°C, 48.5% by mass of perfluoromethyl sulfide and 61.9% by mass of perfluoromethyl sulfide + 1,1,2,2-tetrafluoroethane are physically mixed under liquid phase conditions and completely gasified to obtain a mixed insulating gas.

[0080] Embodiment 5:

[0081] Under a temperature condition of -40°C, 55.5% by mass of perfluoromethyl sulfide and 44.5% by mass of 2,3,3,3-tetrafluoropropylene are physically mixed under liquid phase conditions and completely gasified to obtain a mixed insulating gas.

[0082] Embodiment 6:

[0083] Under the temperature condition of -40°C, 63.5% by mass of perfluoromethyl sulfide and 36.5% by mass of 2,3,3,3-tetrafluoropropylene are physically mixed under liquid phase conditions and completely gasified to obtain a mixed insulating gas.

[0084] Embodiment 7:

[0085] Under a temperature condition of -40°C, 70.5% by mass of perfluoromethyl sulfide and 29.5% by mass of 2,3,3,3-tetrafluoropropylene are physically mixed under liquid phase conditions and completely gasified to obtain a mixed insulating gas.

[0086] Embodiment 8:

[0087] Under a temperature condition of -40°C, 75.5% by mass of perfluoromethyl sulfide and 24.5% by mass of 2,3,3,3-tetrafluoropropylene are physically mixed under liquid phase conditions and completely gasified to obtain a mixed insulating gas.

[0088] Comparative Example 1:

[0089] Perfluoromethyl sulfide with a mass percentage of 100% was used as the insulating gas.

[0090] Comparative Example 2:

[0091] 1,1-difluoroethane with a mass percentage of 100% was used as the insulating gas.

[0092] Comparative Example 3:

[0093] 1,1,2,2-tetrafluoroethane with a mass percentage of 100% was used as the insulating gas.

[0094] Comparative Example 4:

[0095] 100% by mass of 2,3,3,3-tetrafluoropropylene was used as the insulating gas.

[0096] After the temperature of the liquid mixture of the above embodiment rises to room temperature and is completely gasified, the insulation strength of the gas in the above embodiment and each comparative example relative to SF6 gas is tested under the condition of an inter-electrode spacing of 0.1 inches. The results are shown in Table 3; wherein the GWP value is based on CO2 as a reference value of 1.0 (100 years), and the insulation strength is based on sulfur hexafluoride as a reference value.

[0097] A flammability determination experimental device was built according to EU standard EN14756 [European standard. Determination of the limiting oxygen concentration (LOC) for gases and vapours: EN 14756-2007 [S]. Berlin: European committee for standardization, 2006.].

[0098] The liquefaction temperatures of the embodiments and comparative examples were measured by observation method. The results are shown in Table 3. The present invention has a lower liquefaction temperature.

[0099] Table 3 Comparison of environmental performance and insulation strength

[0100] Insulating gas <![CDATA[Insulation strength relative to SF6]]> GWP Liquid temperature / ℃ Example 2 1.83 538 -54 Example 3 1.80 907 -27 Example 4 1.84 870 -27 Example 5 1.71 3 -26 Example 6 1.85 1 -27 Example 7 1.98 1 -32 Example 8 2.07 1 -31 Comparative Example 1 1.70 8 -22 Comparative Example 2 0.65 675 -52 Comparative Example 3 0.72 1360 -26 Comparative Example 4 0.66 4 -28 <![CDATA[SF6]]> 1 23900 -62℃

[0101] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. It is particularly pointed out that for those skilled in the art, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for screening sulfur hexafluoride alternative gas, characterized in that: The sulfur hexafluoride substitute gas includes component i and component j, wherein component i is perfluoromethyl sulfide, and component j is screened and determined by the following steps: Step S1, selecting an insulating gas at a standard atmospheric pressure and a liquefaction temperature range of -40 to 20° C. as an initial component j; Step S2, obtaining at least one set of T, x that satisfies the following formulas (1) to (16) under a given equilibrium pressure P, when the mixed gas of component i and initial component j is in a gas-liquid equilibrium state: i ,y i 、x j and j ; Where: the given equilibrium pressure P is the working pressure of SF6 gas, the unit of P is: MPa; T is the gas-liquid equilibrium temperature, the unit is ℃; x i is the molar percentage of gas component i in the liquid phase of the mixed gas; i is the molar percentage of gas component i in the gas phase of the mixed gas; x j is the molar percentage of gas component j in the liquid phase of the mixed gas; j is the molar percentage of gas component j in the gas phase of the mixed gas; -40℃≤T≤20℃, 0<x i <1,0<y i <1,0<x j <1,0<y j <1, and x i +x j =1,y i +y j =1; 0.40000≤β6≤0.50000， 0.30000≤β7≤0.40000， 1.50000≤β8≤1.60000， 0.20000≤β9≤0.30000 In formulas (1)-(16): is the gas phase fugacity of gas component i in the mixed gas, is the liquid phase fugacity of gas component i in the mixed gas, is the gas phase fugacity of gas component j in the mixed gas; is the liquid phase fugacity of gas component j in the mixed gas; R is the gas constant; Z L is the gas phase compressibility factor of the mixed gas, Z V is the liquid phase compressibility factor of the mixed gas, V L is the molar volume of the liquid phase of the mixed gas under the conditions of P and T, in m 3 / mol; V V is the gas phase molar volume of the mixed gas under P and T conditions, in m 3 / mol; V is the volume of the mixed gas under the conditions of P and T, in m 3 ; N i is the molar amount of gas component i in the mixed gas, in mol; N j is the molar amount of gas component j in the mixed gas, in mol; N is the total molar amount of the mixed gas, in mol; a and b are the state equation parameters of the mixed gas; a i is the molecular energy constant of gas component i, ranging from 12000 to 3845000; b i is the volume correction constant of gas component i, ranging from 12.85 to 140.68; is the free energy of the gas mixture; k ij is the binary interaction parameter, 0<k ij <5; C is a constant, ranging from 24.68500 to 24.68600; ω i is the eccentricity factor of gas component i, which is taken as 0.335; ω j is the eccentricity factor of gas component j; T ri is the relative state temperature of gas component i; the value range is 0.5~1; T ci is the critical temperature of gas component i; the unit is K, and it is 376.75K; T cj is the critical temperature of gas component j; unit: K; p ci is the critical pressure of gas component i, in MPa; take 3.843MPa; p cj is the critical pressure of gas component j, in MPa; P i sat is the saturated vapor pressure of gas component i at temperature T, in MPa; is the saturated vapor pressure of gas component j at temperature T, in MPa; V i L is the liquid volume of gas component i under conditions of P and T, in m 3 ; is the liquid volume of gas component j under conditions P and T, in m 3 ; T / K is the temperature after the equilibrium temperature T is converted into Kelvin; N gi All the groups decomposed from the molecules of gas component i, CF3SCF3 as the whole group; N gi The value is 1. N gj All the groups decomposed by the molecules of gas component j; k represents the molecular group CF3SCF3 of gas component i; l represents any group among the groups decomposed by the molecules of gas component j; α ik is the relative molar fraction of the group CF3SCF3, which is the value of the number of groups CF3SCF3 divided by the total number of groups in the gas component i molecule, and is 1; α jk is the relative molar fraction of the group CF3SCF3 of the gas component j, which is the value of the number of groups CF3SCF3 divided by the total number of groups in the gas component j molecule; α il is the relative molar fraction of group l of gas component i, which is the number of groups l divided by the total number of groups in the molecules of gas component i; α jl is the relative molar fraction of group l of gas component j, which is the number of groups l divided by the total number of groups in the gas component j molecule; A kl With B kl are the group parameters of the group CF3SCF3 and the group l; In the formula, A wk _CH2 is the interaction parameter between the ethylene group and the group 1; A wk _CH2 is the interaction parameter between the ethylene group and the group 1; N l is the number of positively charged atoms in group l; Step S3, based on the screening results of S2, further screening for the existence of x under a given equilibrium pressure P. i =y i Under the condition, the equilibrium temperature T is the minimum equilibrium temperature, and the minimum equilibrium temperature is less than the liquefaction temperature of each gas component in the mixed gas.

2. The method for screening sulfur hexafluoride alternative gas according to claim 1, characterized in that: The method also includes: Step S4, further screening the dielectric strength Er_ based on the gas component j screened in S3 混合气体 Mixed gas that satisfies the relationship shown in formula (17): Is_ 混合气体 > Is_ i × x i + Is_ j × x j (17) In the formula, Er_ i is the dielectric strength of perfluoromethyl sulfide relative to SF6; Er_ j is the insulation strength of gas component j relative to SF6; x1 is the mass percentage of gas component i in the mixed gas; x2 is the mass percentage of gas component j in the mixed gas; the mixed gas is a mixed gas composed of gas component i and gas component j.

3. The method for screening sulfur hexafluoride alternative gas according to claim 1 or 2, characterized in that: The initial component j is selected from hydrofluoroolefins, hydrofluorocarbons, alkanes or hydrofluoronitrile.

Images