JP2014048186A - Gas analysis method using gas chromatograph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an error in implementing sum correction and improve performance of measurement of a heat release value of a natural gas.SOLUTION: A sample gas of the time when concentration of measured gas components becomes stabilized is set as a reference gas, the reference gas is mixed with a carrier gas to produce a reference analysis gas, and component reference gas concentration of this reference analysis gas at a first analysis and at a second analysis is measured (S101). The sample gas is mixed with the carrier gas to produce an analysis gas, and component concentration before sum correction of the analysis gas at the first analysis and at the second analysis is measured (S102). A correction coefficient is obtained from a sum of the component reference gas concentrations at the first analysis and at the second analysis, and a sum of the component concentrations before the sum correction at the first analysis and at the second analysis and, with the use of the obtained correction coefficient, the component concentrations in the sample gas before the sum correction at the first analysis and at the second analysis respectively are corrected and made into component concentrations after the sum correction (S103).

Description

  The present invention relates to a gas analysis method using a gas chromatograph in which a sample gas and a carrier gas are mixed, a gas component to be measured contained in the mixed gas is separated, and a concentration of the separated gas component to be measured is measured.

  Conventionally, gas chromatographs have been used to measure the calorific value of natural gas. When measuring the calorific value of natural gas using a gas chromatograph, a small sample of natural gas is collected and taken into an analyzer, and the mixture contained in the natural gas is separated into 11 components by a column, and the separated 11 The concentration value of the component is measured, and the calorific value value of natural gas is calculated from the measured concentration value.

  The applicant has reduced the size of the natural gas calorific value measurement device (calorimeter) using a gas chromatograph by using a single valve for multiple normally required devices such as gas flow path switching valves and sample introduction valves. Realized. However, in this measuring apparatus, it is necessary to perform sampling twice (first analysis and second analysis) for each calorific value output as a disadvantage.

  That is, the sample gas and the carrier gas are mixed to obtain an analysis gas, and the analysis gas is separated into seven components in the first analysis and the remaining four components in the second analysis as gas components to be measured, and the concentration is calculated. Therefore, it is necessary to collect the sample gas twice in order to measure the concentration of these 11 components. The same technique is also adopted in the fuel gas analyzer disclosed in Patent Document 1.

JP 2000-32260 A

  As described above, the applicant employs a method of collecting the sample gas twice in order to measure the concentration of the 11 components. In this case, it is ideal that the sampling amount of the two times is exactly the same. It is. However, in reality, there is a slight difference in the sampling amount, which becomes an error when performing the total correction, and adversely affects the repeatability of the calorific value.

  FIG. 5 shows an image of the current sum correction. In this example, before the sum correction, the sum of the concentrations of the seven components measured in the first analysis is 9%, and the sum of the concentrations of the four components measured in the second analysis is 90%. In this case, adjustment is performed by multiplying the value before correction by the correction coefficient so that the total density becomes 100%. In this example, since the sum before correction is 99%, the correction coefficient α is obtained with α = 100 / 99≈1.01, and α = 1 is added to 9% of the concentration of the seven components measured in the first analysis. Is multiplied by .01 to obtain 9.09%, and the sum of the concentrations of the four components measured in the second analysis is multiplied by α = 1.01 to obtain 90.91%. To be 100%.

  This can be expressed by the following equation (1), where the density before each component sum correction is xi, the density after each component sum correction is yi, and i is the number assigned to each component.

  In this total correction, since the same correction coefficient α is multiplied in both the first analysis and the second analysis, this becomes an error when performing the total correction, and adversely affects the repeatability of the calorific value. The measurement performance of the calorific value of natural gas is generally defined by repeatability, and the smaller the repeatability, the better the measurement performance. When measuring the calorific value of this natural gas, the error during the sum correction increases the repeatability of the calorific value and degrades the calorific value measurement performance.

  The present invention has been made in order to solve such problems, and the object of the present invention is to reduce errors during the sum correction and improve the measurement performance of the calorific value of natural gas. Another object of the present invention is to provide a gas analysis method using a gas chromatograph.

  In order to achieve such an object, according to the present invention, a sample gas and a carrier gas are mixed to make an analysis gas, and the types determined for each of the first to N-th (N ≧ 2) analyzes of the analysis gas. In a gas analysis method using a gas chromatograph in which different measured gas components are separated and the concentration of each separated measured gas component is measured as the concentration of each component in the first to N-th analysis, the sample gas when stabilized And the carrier gas are mixed to obtain a reference analysis gas, and the measurement gas components having different types determined for each of the first to Nth analyzes are separated from the reference analysis gas, and each of the separated measurement gas components is separated. The first step of measuring the concentration as each component reference gas concentration in the first to Nth analyzes, the first to Nth analysis sample gases and the carrier gas are mixed to make an analysis gas, and this analysis gas In The gas components to be measured which are different for each of the first to Nth analyzes are separated, and the concentrations of the separated gas components to be measured are the concentrations before each component sum correction in the first to Nth analyses. And the sum of the component reference gas concentrations obtained in the first step and the sum of the concentration before each component sum obtained in the second step for each of the first to Nth analyzes. And a third step of obtaining a correction coefficient, and correcting each component sum before density correction obtained in the second step using the correction coefficient to obtain a density after each component sum correction.

  For example, in the present invention, in the third step, for each of the first to Nth analyses, each component reference gas concentration obtained in the first step is ci, and each component total concentration before correction is obtained in the second step. xi, i is the number assigned to each component in the analysis, n is the number of each component in the analysis, and each component total corrected concentration yi is obtained by the following equation (2).

  In this case, in each analysis, the correction coefficient αi is different, and the summation correction is performed step by step, so that the error at the time of summation correction is reduced. Thereby, when measuring the calorific value of natural gas, the repeatability of the calorific value is reduced, and the measurement performance of the calorific value is improved.

  According to the present invention, the sample gas and the carrier gas at the time of stabilization are mixed to obtain the reference analysis gas, and the measured gas components having different types determined for each of the first to N-th analyzes of the reference analysis gas are obtained. The concentration of each of the gas components to be measured is measured as each component reference gas concentration in the first to Nth analysis, and the first to Nth analysis sample gases and the carrier gas are mixed. The analysis gas is separated, and the measurement gas components having different types determined for each of the first to N-th analyzes are separated from the analysis gas, and the concentrations of the separated measurement gas components are classified into the first to N-th analysis. In each of the first to Nth analyses, a correction coefficient is obtained from the sum of each component reference gas concentration and the sum of each component sum before correction, and this correction coefficient is used. The density before each component sum correction was corrected. In case of measuring the calorific value of natural gas by reducing the error at the time of performing the sum correction and reducing the error when performing the total correction, the repeatability of the calorific value is reduced. The measurement performance of the calorific value can be improved.

It is a schematic block diagram which shows the basic composition of the gas chromatograph used for implementation of this invention. It is a flowchart which shows the characteristic processing operation which CPU performs in this gas chromatograph. It is an image figure of total correction implemented in this gas chromatograph. It is a figure which illustrates the measurement result of the calorific value. It is an image figure of the present sum total correction | amendment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic block diagram showing the basic configuration of a gas chromatograph used in the practice of the present invention.

  In FIG. 1, 1 is an analyzer body that forms a thermostat and is maintained at a predetermined temperature, 2 is a sample valve disposed in the analyzer body 1, 3-1 is a first column, and 3-2 is a second column. A column, 4 is a detector, 5 is a metering tube, 6 is a pressure reducing valve for reducing the carrier gas (such as helium gas) CG to a predetermined pressure, 7 is a CPU, and 8 is a memory.

  In this gas chromatograph, by periodically switching the flow path of the sample valve 2, the sample gas SG to be measured separated by the measuring tube 5 is mixed with the carrier gas CG to be placed in the columns 3-1 and 3-2. The first analysis gas G1 and the second analysis gas G2 are alternately sent to the detector 4 while separating the predetermined seven gas components contained in the first analysis gas G1 in the column 3-1. Then, the gas components are fed to the detector 4 while separating the predetermined four gas components contained in the second analysis gas G2 in the column 3-2, and the thermal conductivity of the gas components is detected by the detector 4. And the concentration of each gas component in the first analysis and the second analysis is measured based on the measured thermal conductivity. This concentration measurement is executed by the processing operation of the CPU 7 in accordance with a program stored in the memory 8.

  The characteristic processing operation performed by the CPU 7 in the gas chromatograph of the present embodiment will be described below with reference to the flowchart shown in FIG.

  In starting the concentration measurement of each gas component to be measured as described above, first, the reference gas PG obtained by separating the stable sample gas SG by the measuring tube 5 is mixed with the carrier gas CG, and the first reference analysis gas G1 is first prepared. To the column 3-1 and then to the column 3-2 as the second reference analysis gas G2, and the predetermined seven component gas components contained in the first reference analysis gas G1 in the column 3-1. The gas is fed to the detector 4 while being separated, and is fed to the detector 4 while separating each of the predetermined four gas components contained in the second reference analysis gas G2 in the column 3-2. 4, the thermal conductivity of each gas component is measured, and based on the measured thermal conductivity, the concentration of each gas component is measured as the component reference gas concentration in the first analysis and the second analysis (step S101).

  Next, the sample gas SG is sent to the sample valve 2, the sample gas SG collected by the measuring tube 5 is mixed with the carrier gas CG, and first sent to the column 3-1 as the first analysis gas G1, and then the second 2 is sent to the column 3-2 as the analysis gas G2, and is fed to the detector 4 while separating each of the seven predetermined gas components contained in the first analysis gas G1 in the column 3-1. -2 is supplied to the detector 4 while separating each of the predetermined four gas components contained in the second analysis gas G2, and the thermal conductivity of each gas component is measured by the detector 4, Based on the measured thermal conductivity, the concentration of each gas component is measured as the concentration before each component sum correction in the first analysis and the second analysis (step S102).

  Next, for each of the first analysis and the second analysis, the CPU 7 obtains a correction coefficient from the sum of each component reference gas concentration obtained in step S101 and the sum of each component sum total concentration obtained in step S102. Then, the density before each component sum correction obtained in step S102 is corrected using this correction coefficient, and the corrected density before each component sum correction is used as the density after each component sum correction (step S103).

  The CPU 7 performs the sum correction in step S103 as follows. That is, each component reference gas concentration in the first analysis obtained in step S101 is ci, each component total concentration before correction in the first analysis obtained in step S102 is xi, and i is each component in the analysis. The assigned number, n, is the number of each component in the analysis, and each component total corrected concentration yi in the first analysis is obtained by the following equation (3). In this case, since the number of each component in the first analysis is 7, n = 7.

  Also, each component reference gas concentration in the second analysis obtained in step S101 is cj, each component total concentration before correction in the second analysis obtained in step S102 is xj, and j is each component in the analysis. The assigned number, m, is the number of each component in the analysis, and each component total corrected concentration yj in the second analysis is obtained by the following equation (4). In this case, since the number of each component in the second analysis is 4, m = 4.

  FIG. 3 shows an image diagram of total correction in the present embodiment. In this example, before the sum correction, the sum of the concentrations of the seven components measured in the first analysis is 9%, and the sum of the concentrations of the four components measured in the second analysis is 90%. In this case, according to the sum correction of the present embodiment, for the first analysis, the correction coefficient α1 expressed as the ratio of the sum of ci and the sum of xi in the above equation (3) is multiplied by the value before correction. For the second analysis, the value before correction is multiplied by a correction coefficient α2 expressed as a ratio of the sum of cj and the sum of xj in the above equation (4).

  In this example, α1≈1.019 is obtained, α2≈1.0093 is obtained, and the sum of the concentrations of the seven components measured in the first analysis is multiplied by α1 = 1.019 to obtain 9.17%. The sum of 90% of the concentrations of the four components measured in the second analysis is multiplied by α2 = 1.0092 to obtain 90.83%, and after the sum correction, the total concentration is 100%. Is done.

  As described above, in the present embodiment, the correction coefficients α1 and α2 are different between the first analysis and the second analysis, and the total correction is performed in two stages. The error becomes smaller. The CPU 7 repeats the measurement of the density before each component total correction in step S102 and the calculation of the density after each component total correction in step 103 (two-stage total correction). Thereby, when measuring the calorific value of natural gas, the repeatability of the calorific value is reduced, and the measurement performance of the calorific value is improved.

  FIG. 4 illustrates the measurement result of the calorific value. In the figure, the horizontal axis is the number of measurements, the vertical axis is the measured calorific value, and the measurement result I is the current result when the total correction (two-stage total correction) of this embodiment is used. This is a case where summation correction is used. In the current sum correction, there is a point where the calorific value is greatly different during measurement (a point surrounded by a one-dot chain line), but such an abnormal point does not exist in the two-step sum correction of the present embodiment. I understand that. From this, it can be estimated that the repeatability is improved.

  In the above-described embodiment, the concentration measurement is performed separately for the first analysis and the second analysis. However, for example, the concentration is divided for the first analysis, the second analysis, and the third analysis. Measurement may be performed. Each component reference gas concentration obtained in the third analysis is ck, each component sum total concentration obtained in the third analysis is xk, k is a number assigned to each component in the analysis, and p is in the analysis. In the third analysis, the concentration yk after each component sum correction in the third analysis can be obtained by the following equation (5).

  As can be seen from the above equations (3) to (5), when the number of analyzes is divided into N times (N ≧ 2) in the present embodiment, each component reference gas concentration is set to ci in each analysis. , Where xi is the concentration before each component sum correction, i is the number assigned to each component under analysis, and n is the number of each component under analysis, the concentration y i after each component sum correction is (6 ).

[Extension of the embodiment]
The present invention has been described above with reference to the embodiment. However, the present invention is not limited to the above embodiment. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the technical idea of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Analyzer main body, 2 ... Sample valve, 3-1 ... 1st column, 3-2 ... 2nd column, 4 ... Detector, 5 ... Metering tube, 6 ... Pressure reducing valve, 7 ... CPU, 8 ... Memory .

Claims (2)

A sample gas and a carrier gas are mixed to obtain an analysis gas, and the gas components to be measured that are different for each of the first to N-th (N ≧ 2) analyzes are separated for the analysis gas, and the separated gas components In a gas analysis method using a gas chromatograph that measures the concentration of a gas component to be measured as the concentration of each component in the first to Nth analyzes,
When the concentration of the gas component to be measured is stabilized, the sample gas and the carrier gas are mixed to obtain a reference analysis gas, and the types determined for each of the first to Nth analyzes of the reference analysis gas are different. A first step of separating the gas component to be measured, and measuring the concentration of each separated gas component to be measured as each component reference gas concentration in the first to N-th analysis;
The first to N-th sample gases for analysis and the carrier gas are mixed to obtain an analysis gas, and the measured gas components having different types determined for each of the first to N-th analysis are analyzed for the analysis gas. A second step of separating and measuring the concentration of each measured gas component as the concentration before each component sum correction in the first to Nth analyzes;
For each of the first to Nth analyses, a correction coefficient is obtained from the sum of the component reference gas concentrations obtained in the first step and the sum of the concentration before each component sum obtained in the second step. A gas analysis method using a gas chromatograph, comprising: a third step of correcting the concentration before each component sum correction obtained in the second step using the correction coefficient to obtain the concentration after each component sum correction. In the gas analysis method by the gas chromatograph according to claim 1,
The third step includes
For each of the first to Nth analyses, each component reference gas concentration obtained in the first step is ci, each component total concentration before correction obtained in the second step is xi, and i is being analyzed. A gas analysis method using a gas chromatograph, wherein the number y given to each component, n is the number of each component in the analysis, and the concentration yi after each component sum correction is obtained by the following equation (1).

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