High-pressure mixed gas preparation method considering temperature and pressure influence

Abstract

The invention provides a high-pressure mixed gas preparation method considering temperature and pressure influences, and relates to the technical field of unconventional natural gas extraction. Comprising the following nine steps: determining constant parameters, determining proportioning concentration, initializing a pressure value, calculating the partial pressure of each component of mixed gas, vacuumizing a device, filling a component I gas, vacuumizing a pipeline, filling a component I gas and analyzing the components of the gas. According to the method, the partial pressure of each component gas is accurately calculated in combination with the compression factor, so that high-precision and flexible preparation of the mixed gas components can be realized, high cost caused by frequent purchase of prefabricated gas is avoided, trace gas can be accurately prepared according to actual requirements, and gas consumption and cost are greatly reduced. And meanwhile, the repeatability and the reliability of the gas preparation process are improved, and the device is particularly suitable for experiment conditions of high pressure and various gas components.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of unconventional natural gas exploitation, and particularly relates to a high-pressure mixed gas preparation method considering the influence of temperature and pressure. BACKGROUND

[0002] The efficient development and utilization of unconventional natural gas resources such as coalbed methane, and the feasibility evaluation of carbon dioxide enhanced coalbed methane recovery and storage (CO2-ECBM) technology, are highly dependent on the in-depth study of the gas adsorption characteristics of coal. CO2-ECBM technology is to inject CO2 into deep unrecoverable coal seams, and its essence is the competitive adsorption process of different gas components (mainly CO2 and CH4) on the surface of coal matrix, which uses the competitive adsorption mechanism to replace and drive the gas (mainly CH4) in the coal seam, thereby improving the gas recovery rate. Since the study of competitive adsorption of gases in coal is mainly carried out in the laboratory, it is of great theoretical and engineering significance to accurately prepare high-pressure mixed gas, simulate the temperature and pressure conditions of the reservoir, and deeply study the competitive adsorption mechanism of multi-component gas in coal.

[0003] The commonly used methods for preparing mixed gas include partial pressure method, static volume method, flow method, permeation method and weighing method, etc. Among them, the partial pressure method is simple to operate and low in cost, but requires accurate pressure measurement equipment; the static volume method has simple equipment structure and low cost, but has low preparation accuracy; the flow method has high preparation accuracy, but its instrument and equipment are complex and expensive, and need to be calibrated and maintained regularly, and it is not suitable for preparing high-concentration gas, and is usually used for preparing special mixed gas (polar gas, etc.); the permeation method can prepare ppm-level or even ppb-level ultra-low concentration mixed gas, but requires a precise temperature control system and a permeation device, and is suitable for limited gases; the weighing method controls the molar mass fraction of each component gas by controlling the mass of each component, which has high requirements for equipment and operation, and is suitable for preparing a small amount of mixed gas with high accuracy. In the study of the competitive adsorption mechanism of gases in coal, the component ratio of the mixed gas required by the experiment often changes, and the use of industrial pre-prepared mixed gas often cannot meet the experimental gas conditions that need to be frequently adjusted, and the pre-prepared mixed gas purchased will have gas stratification phenomenon after long-term storage, resulting in changes in the component ratio of the pre-prepared gas. In addition, the experimental cost of purchasing a large number of pre-prepared mixed gas components is high, therefore, the present application proposes a high-pressure mixed gas preparation method considering the influence of temperature and pressure to solve the problems in the prior art. SUMMARY

[0004] In view of the above problems, the present application aims to provide a high-pressure mixed gas preparation method considering the influence of temperature and pressure, which can correct the pressure of each component of the mixed gas according to the ratio of each component in the target mixed gas combined with the collected temperature data, thereby providing a reliable gas source for the study of the competitive adsorption mechanism of multi-component gas in coal and rock.

[0005] To achieve the objectives of this invention, the invention is implemented through the following technical solution: a method for preparing high-pressure mixed gases considering the effects of temperature and pressure, comprising the following steps:

[0006] Step S101: Determine constant parameters

[0007] Based on the actual needs of the experiment, the experimental temperature T, the fixed container volume V, and the target total pressure P for the preparation of the mixed gas were determined. m The number of components in the mixed gas N, the input iteration step size k1, and the output iteration accuracy k2;

[0008] Step S102: Determine the concentration ratio

[0009] Based on the actual needs of the experiment, determine the required concentration ratio C of the different component gases for preparing the mixed gas. i ;

[0010] Step S103: Initialize pressure value

[0011] The initial pressure value P is calculated using the first gas state equation. j The first gas law is as follows:

[0012] PV = nRT;

[0013] Step S104: Calculation of partial pressures of each component in the mixed gas

[0014] Using the compressibility factor Z, the partial pressure P of each component gas is calculated using the second gas law combined with the volume fraction calculation method. i Then, the total output pressure P is adjusted through iterative calculations until the result meets the set accuracy requirements. The second gas state equation is as follows:

[0015] PV = nZRT;

[0016] Step S105: Vacuuming the apparatus

[0017] A gas distribution device is set up, which includes a gas cylinder, an exhaust valve, a pressure reducing valve, a constant temperature water tank, an inlet valve, a sampling valve, a fixed container, a vacuum valve, a vacuum pump, and pipelines. The experimental temperature is set through the constant temperature water tank. After the temperature stabilizes, the vacuum pump, vacuum valve, and inlet valve are opened in sequence, and then the vacuuming operation is performed.

[0018] Step S106: Introduce component one gas

[0019] Open the inlet valve, use the pressure reducing valve to adjust and control the output pressure of the gas in the cylinder, inject the low-pressure gas in the mixed gas into the fixed container, close the inlet valve, and wait for the gas pressure to reach equilibrium before closing the pressure reducing valve.

[0020] Step S107, vacuumizing the pipeline

[0021] The exhaust valve is opened again, the high-pressure gas in the pipeline is exhausted, and then the vacuum pump and the vacuum valve are opened in sequence, and the vacuumizing operation is performed.

[0022] Step S108, filling component i gas

[0023] The inlet valve is opened, the output pressure of the gas in the cylinder is adjusted and controlled by the pressure reducing valve, the component i gas in the mixed gas is filled in the fixed container in which the low-pressure gas has been injected, the target pressure is reached, the inlet valve is closed, and the pressure reducing valve is closed after the gas pressure is balanced again.

[0024] Step S109, gas component analysis

[0025] The sampling valve is opened, the sampling bag is used for sampling, the sampling valve is closed after the sampling is completed, and the gas components are analyzed by using the gas chromatograph.

[0026] Further improvement lies in that in the S101, the value range of the iteration step length k1 and the output iteration precision k2 is 0.0001-0.001.

[0027] Further improvement lies in that in the S104, the calculation formula of the partial pressure P i of each component gas is:

[0028]

[0029] In the formula, Z i is the compression factor of component i, and the final output total pressure P=P N .

[0030] Further improvement lies in that in the S104, the precision requirement is:

[0031] If P m -k2<P<P m +k2, the partial pressure of each component gas of the mixed gas is output; if the condition is not met, the iteration needs to be performed again.

[0032] Further improvement lies in that the specific rule of the iteration is:

[0033] If P m -k2, P1=P1+(N-1)k1, and P i =P i -k1(i=1) are adjusted.

[0034] If P>P m +k2, P1=P1-(N-1)k1, and P i =Pi +k1(i≠1).

[0035] Further improvement lies in that in the step S105, the gas cylinders are provided in groups, and the output ends of the gas cylinders are connected with pipelines through pressure reducing valves, one end of the pipeline is provided with an exhaust valve, and the other end is connected with a vacuum pump through a vacuum valve, a fixed container is arranged in the constant-temperature water tank, a sampling pipe is arranged on the fixed container, and the sampling pipe is connected with the pipeline through an air inlet valve, and a sampling valve is arranged on the sampling pipe.

[0036] Further improvement lies in that in the step S106 and the step S108, the balanced state is that the pressure fluctuation is less than or equal to 0.001 MPa / h.

[0037] Further improvement lies in that in the step S109, the gas chromatograph is used to verify the deviation between the measured component concentration and the proportioning concentration.

[0038] The beneficial effects of the present application are that: the present application can realize high-precision and flexible preparation of mixed gas components by accurately calculating the partial pressure of each component gas by combining the compression factor, not only avoids the high cost caused by frequent purchase of prefabricated gas, but also can accurately prepare trace gas according to actual demand, thereby greatly reducing gas consumption and cost. At the same time, the present application improves the repeatability and reliability of the gas preparation process, and is especially suitable for experimental conditions with high pressure and diverse gas components. In addition, the present application provides stable and reliable gas source support for competitive adsorption experiments in the fields of coalbed methane exploitation and CO2 sequestration. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 is a step flow schematic diagram of the present application.

[0040] Figure 2 is a mixed gas component gas partial pressure calculation flow schematic diagram of the present application.

[0041] Figure 3 is a gas preparation device structure schematic diagram of the present application.

[0042] Figure 4 is a concentration change schematic diagram of the present application.

[0043] Figure 5 is a chromatographic peak value schematic diagram of the present application. DETAILED DESCRIPTION

[0044] In order to deepen the understanding of the present application, the present application will be further described in combination with the embodiments below, and the present embodiments are only used to explain the present application and do not constitute a limitation on the protection scope of the present application.

[0045] According to Figures 1-3As shown, this embodiment proposes a method for preparing high-pressure mixed gases that takes into account the effects of temperature and pressure, including the following steps:

[0046] Step S101: Determine constant parameters

[0047] Based on the actual needs of the experiment, the experimental temperature T, the fixed container volume V, and the target total pressure P for the preparation of the mixed gas were determined. m The parameters are: the number of components in the mixed gas N, the input iteration step size k1, and the output iteration accuracy k2, where the values ​​of the iteration step size k1 and the output iteration accuracy k2 range from 0.0001 to 0.001.

[0048] Step S102: Determine the concentration ratio

[0049] Based on the actual needs of the experiment, determine the physical property parameters (critical pressure P) of the different component gases required for preparing the mixed gas. c Critical temperature T c ), calculate the corresponding comparison temperature T r Comparison of pressure P r Determine the concentration C i ;

[0050] Step S103: Initialize pressure value

[0051] The initial pressure value P is calculated using the first gas state equation. j The first gas law is as follows:

[0052] PV = nRT;

[0053] Step S104: Calculation of partial pressures of each component in the mixed gas

[0054] Using the compressibility factor Z, the partial pressure P of each component gas is calculated using the second gas law combined with the volume fraction calculation method. i Then, the total output pressure P is adjusted through iterative calculations until the result meets the set accuracy requirements. The second gas state equation is as follows:

[0055] PV = nZRT;

[0056] Step S105: Vacuuming the apparatus

[0057] A gas distribution device is set up, which includes a gas cylinder 1, an exhaust valve 2, a pressure reducing valve 3, a constant temperature water tank 4, an inlet valve 5, a sampling valve 6, a fixed container 7, a vacuum valve 8, a vacuum pump 9, and pipelines. The experimental temperature is set through the constant temperature water tank 4. After the temperature stabilizes, the vacuum pump 9, vacuum valve 8, and inlet valve 5 are opened sequentially to evacuate the device. Figure 3As shown in the figure, one end of the pipeline is provided with an exhaust valve 2, the other end is connected with a vacuum pump 9 through a vacuum valve 8, a constant temperature water tank 4 is provided with a fixed container 7, a sampling tube is arranged on the fixed container 7, the sampling tube is connected with the pipeline through an air inlet valve 5, and a sampling valve 6 is arranged on the sampling tube;

[0058] Step S106, filling component i gas

[0059] The air inlet valve 5 is opened, the output pressure of the gas in the gas cylinder 1 is adjusted and controlled by using the pressure reducing valve 3, according to the principle that high-pressure gas flows to low-pressure gas, the low-pressure gas in the mixed gas is injected into the fixed container 7, then the air inlet valve 5 is closed, and the pressure reducing valve 3 is closed after the gas pressure reaches balance (pressure fluctuation ≤0.001 MPa / h);

[0060] Step S107, pipeline vacuumizing

[0061] The exhaust valve 2 is opened again, the high-pressure gas in the pipeline is exhausted, then the vacuumizing operation is performed;

[0062] Step S108, filling component i gas

[0063] The air inlet valve 5 is opened, the output pressure of the gas in the gas cylinder 1 is adjusted and controlled by using the pressure reducing valve 3, the component i gas in the mixed gas is filled into the fixed container 7 which has been injected with the low-pressure gas, to reach the predetermined target pressure, then the air inlet valve 5 is closed, and the pressure reducing valve 3 is closed after the gas pressure reaches balance again (pressure fluctuation ≤0.001 MPa / h);

[0064] Step S109, gas component analysis

[0065] The sampling valve 6 is opened, sampling is performed by using a sampling bag, after the sampling is completed, the sampling valve 6 is closed, gas component analysis is performed by using a gas chromatograph, and the gas chromatograph analysis is used to verify the deviation between the measured component concentration and the proportioning concentration.

[0066] Further, for the step S104, the specific steps are as follows:

[0067] S202, calculating the compression factor Z, the steps are as follows:

[0068] Firstly, the Lee-Kesler equation is selected as the state equation, the compression factor Z of each component gas in the high-pressure mixed gas is calculated, and the expression is as follows:

[0069]

[0070] In the formula, Z is the fluid compression factor; Z 0 is the compression factor of a simple fluid component (ω=0); Z R is the compression factor of n-octane component (ω R= 0.3978) of the compressibility factor; ω is the eccentric factor of the simple fluid component; ω R is the eccentric factor of the n-octane component.

[0071] V is calculated by the following formula r 0 :

[0072]

[0073] In the formula, P r is the fluid contrast pressure, P r = P / P c ; P is the absolute pressure of the fluid in the actual state, in MPa; P c is the critical pressure, in MPa, P c = 4.60 MPa for methane; T r is the contrast temperature, T r = T / T c ; T is the absolute temperature of the fluid in the actual state, in K; T c is the critical temperature, in K, T c = 190.55 K for methane.

[0074] Z is calculated by the following formula 0 :

[0075]

[0076] Substitute the same P r , T r into the formula to obtain V r R .

[0077] Z is calculated by the following formula R :

[0078]

[0079] According to the expression formula of the compressibility factor Z, the value of Z at a certain temperature T and pressure P is calculated.

[0080] The compressibility factor Z is introduced, and according to the modified mixed gas calculation method, the actual gas state equation (i.e. the second gas state equation) is selected to calculate the partial pressure of each component of the mixed gas. The specific steps are as follows:

[0081] PV = nZRT

[0082] In the formula, P is the gas pressure, in MPa; V is the container volume, in L; n is the amount of substance of the gas, in mol; Z is the compressibility factor of the gas; R is the ideal gas constant, 8.314 J / (mol·K); T is the temperature, in K.

[0083] V is calculated by the following formula m :

[0084]

[0085] In the formula, V m is the molar volume, unit L / mol; V is the gas volume, unit L.

[0086] The concentration C is calculated by the following formula i :

[0087]

[0088] In the formula, C i is the concentration of gas component i in the mixed gas, unit %; P i is the filling pressure of gas component i in the mixed gas, unit MPa; n i is the amount of substance of gas component i in the mixed gas, unit mol.

[0089] S203, calculate the partial pressure P of each component gas i :

[0090]

[0091] S204, calculate the output total pressure P:

[0092] P=P N

[0093] S205, adjust the output total pressure P by iteration until the result meets the set accuracy requirement:

[0094] If P meets the condition P m -k2<P<P m +k2, output the partial pressure of each component gas of the mixed gas; if it does not meet the condition, iteration needs to be performed again.

[0095] The specific rules of iteration are:

[0096] If P m -k2, adjust P1=P1+(N-1)k1, P i =P i -k1(i=1);

[0097] If P m +k2, adjust P1=P1-(N-1)k1, P i =P i +k1(i≠1).

[0098] S206, output the partial pressure of each component gas of the mixed gas: through iteration, the partial pressure of each component gas of the mixed gas is calculated.

[0099] According to Figure 4 and Figure 5 As shown in the present embodiment, the component gas one is methane (CH4), and the component gas two is carbon dioxide (CO2), and the mixed gas preparation operation process according to the present method realizes high-precision proportioning of 25% concentration CH4 and 75% concentration CO2 mixed gas, and according to the determination result of the gas chromatograph, the chromatographic peaks of the prepared mixed gas are basically overlapped, which proves that the mixed gas prepared by the method has good repeatability and reliability. The method comprehensively considers the influence of temperature and pressure, can accurately control the proportion and pressure of CH4, CO2 and other mixed gas components, realizes flexible preparation of high-precision mixed gas under laboratory conditions, and can provide reliable gas source support for competitive adsorption experimental research in the fields of coalbed methane and CO2 storage.

[0100] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above-mentioned embodiments, and the above-mentioned embodiments and descriptions in the specification are only to illustrate the principles of the present application, and various changes and improvements can be made to the present application without departing from the framework and scope of application of the present application, and these changes and improvements all fall within the scope of the present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing high-pressure mixed gases considering the effects of temperature and pressure, characterized in that: Includes the following steps: Step S101: Determine constant parameters Based on the actual needs of the experiment, the experimental temperature T, the fixed container volume V, and the target total pressure P for the preparation of the mixed gas were determined. m The number of components in the mixed gas N, the input iteration step size k1, and the output iteration accuracy k2; Step S102: Determine the concentration ratio Based on the actual needs of the experiment, determine the required concentration ratio C of the different component gases for preparing the mixed gas. i ; Step S103: Initialize pressure value The initial pressure value P is calculated using the first gas state equation. j The first gas law is as follows: PV = nRT; Step S104: Calculation of partial pressures of each component in the mixed gas Using the compressibility factor Z, the partial pressure P of each component gas is calculated using the second gas law combined with the volume fraction calculation method. i Then, the total output pressure P is adjusted through iterative calculations until the result meets the set accuracy requirements. The second gas state equation is as follows: PV = nZRT; Step S105: Vacuuming the apparatus The gas distribution device is set up, which includes a gas cylinder (1), an exhaust valve (2), a pressure reducing valve (3), a constant temperature water tank (4), an air inlet valve (5), a sampling valve (6), a fixed container (7), a vacuum valve (8), a vacuum pump (9), and pipelines. The experimental temperature is set through the constant temperature water tank (4). After the temperature stabilizes, the vacuum pump (9), the vacuum valve (8), and the air inlet valve (5) are opened in sequence, and then the vacuuming operation is performed. Step S106: Introduce component one gas Open the inlet valve (5), use the pressure reducing valve (3) to adjust and control the output pressure of the gas in the gas cylinder (1), inject the low-pressure gas in the mixed gas into the fixed container (7), close the inlet valve (5), and wait for the gas pressure to reach equilibrium before closing the pressure reducing valve (3). Step S107: Vacuuming the pipeline Open the exhaust valve (2) again to vent the high-pressure gas in the pipeline and then close it. Open the vacuum pump (9) and vacuum valve (8) in sequence and then perform the vacuuming operation. Step S108: Introduce component i gas Open the inlet valve (5), use the pressure reducing valve (3) to adjust and control the output pressure of the gas in the gas cylinder (1), fill the fixed container (7) with low-pressure gas, fill the mixed gas component i gas, reach the predetermined target pressure, close the inlet valve (5), and wait for the gas pressure to balance again before closing the pressure reducing valve (3). Step S109, Gas Component Analysis Open the sampling valve (6), take a sample using a sampling bag, and close the sampling valve (6) after sampling is completed. Analyze the gas components using a gas chromatograph.

2. The method for preparing high-pressure mixed gas considering the effects of temperature and pressure according to claim 1, characterized in that: In S101, the iteration step size k1 and the output iteration precision k2 range from 0.0001 to 0.

001.

3. The method for preparing high-pressure mixed gas considering the effects of temperature and pressure according to claim 1, characterized in that: In S104, the partial pressure P of each component gas i The calculation formula is: In the formula, Z i Let P be the compressibility factor of component i, and the final output total pressure P = P N .

4. The method for preparing high-pressure mixed gas considering the effects of temperature and pressure according to claim 1, characterized in that: In S104, the accuracy requirement is: If P satisfies condition P m -k2 <P<P m If +k2 is applied, the partial pressures of each component gas in the mixture will be output; if the condition is not met, the iteration needs to be repeated.

5. The method for preparing high-pressure mixed gas considering the effects of temperature and pressure according to claim 4, characterized in that: The specific rules for the iteration are as follows: If P <P m -k2, then adjust P1=P1+(N-1)k1, P i =P i -k1(i=1); If P>P m +k2, then adjust P1=P1-(N-1)k1, P i =P i +k1(i≠1).

6. The method for preparing high-pressure mixed gas considering the effects of temperature and pressure according to claim 1, characterized in that: In step S105, the gas cylinder (1) is provided in several groups, and the output end of the gas cylinder (1) is connected to the pipeline through the pressure reducing valve (3). One end of the pipeline is equipped with an exhaust valve (2), and the other end is connected to the vacuum pump (9) through the vacuum valve (8). The constant temperature water tank (4) is equipped with a fixed container (7), and a sampling tube is installed on the fixed container (7). The sampling tube is connected to the pipeline through the air inlet valve (5), and a sampling valve (6) is installed on the sampling tube.

7. The method for preparing high-pressure mixed gas considering the effects of temperature and pressure according to claim 1, characterized in that: In steps S106 and S108, the equilibrium state is that the pressure fluctuation is ≤0.001MPa / h.

8. The method for preparing high-pressure mixed gas considering the effects of temperature and pressure according to claim 1, characterized in that: In step S109, gas chromatography analysis is used to verify the deviation between the measured component concentration and the ratio concentration.

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