JP2007218873A - Instrument for measuring volatile organic compound - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent dew condensation after hydrogen flame is ignited to shorten a stabilization time, in an instrument for measuring a volatile organic compound using a hydrogen flame ionization detector (FID). <P>SOLUTION: One or more of set values out of a flow rate set value of hydrogen, a flow rate set value of a combustion improver and a temperature set value of the FID, are controlled to a set value larger than a set value in a usual measuring time, during a tentative time before and after the hydrogen flame is ignited, and the tentative set values are returned to the set value in the usual measuring time, based on an output signal level or by a preset time program, after ignited. Relative humidity is reduced in an inside of the FID after the ignition, by this constitution, the dew is thereby prevented from being generated just after the ignition, and the stabilization time for the instrument is also shortened. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a volatile organic compound measuring apparatus that measures the concentration of an organic compound in a sample gas using a flame ionization detector.

For example, a volatile organic compound measuring device using a hydrogen flame ionization detector (hereinafter referred to as FID) is used as a device for measuring the concentration of organic solvent vapor or the like contained in exhaust from a painting booth (for example, FID) Non-Patent Document 1).
FID is an ion generated by passing sample gas through a flame in which hydrogen gas burns in the presence of an auxiliary gas, and carbon atoms (organic carbon) constituting the organic substance in the sample gas are ionized in the hydrogen flame. It measures current and is well known as a detector for gas chromatography. Since the output of FID is almost proportional to the number of atoms of organic carbon, the total organic compound concentration is measured as the concentration of organic carbon by passing the sample gas as it is without separating the organic compound into individual components. can do. This is the principle of organic compound concentration measurement using FID. In this case, since the sample is a gas, the organic compound contained therein is limited to volatile, so a volatile total organic compounds measurement device. Also called (hereinafter referred to as TVOC measuring device).

FIG. 3 shows an example of the configuration of a conventional TVOC measurement apparatus.
In the figure, reference numeral 1 denotes an FID, in which a nozzle 11 and a collector electrode 12 are provided, a sample gas flow path 14, a hydrogen gas flow path 15 and an auxiliary combustion gas flow path 16 are connected to the lower part, and the top is an atmosphere. An exhaust port 13 communicating with is established. Reference numeral 2 denotes a thermostatic chamber that accommodates the FID 1 and keeps it at a predetermined temperature. Reference numeral 3 denotes an amplifier that amplifies an ionic current flowing through the collector electrode 12 to generate an output signal. 4 is a pump for taking in sample gas, 5 and 6 are flow control devices for controlling the flow rates of hydrogen gas and auxiliary combustion gas, and 7 is a temperature control device for controlling the temperature of the thermostatic chamber 2.

Next, the operation of the conventional TVOC measuring apparatus shown in FIG. 3 will be described.
The flow rate of the hydrogen gas is controlled by the flow rate control device 5, and the hydrogen gas is ejected from the nozzle 11 through the hydrogen gas flow path 15 and burned to form a hydrogen flame 17. Similarly, the auxiliary combustion gas (air from which organic substances and moisture have been removed) is controlled by the flow rate control device 6 and sent into the FID 1 through the auxiliary combustion gas passage 16 to supply oxygen necessary for combustion to the hydrogen flame 17. The sample gas is fed by the pump 4 through the sample gas flow path 14 into the hydrogen flame 17 where the carbon atoms constituting the organic compound in the sample are ionized. An electric field is formed around the hydrogen flame 17 by voltage application means (not shown), and the generated ions are guided to this electric field and reach the collector electrode 12 to be detected as a current. This is amplified by the amplifier 3 to be an output signal of FID1.
When igniting hydrogen gas, it is ignited electrically by a filament (not shown) or a discharge igniter.

Catalog C180-0155 “FID VOC Analyzer VMS-1000F” Shimadzu Corporation, December 2005

In the TVOC measuring apparatus configured as described above, the temperature of the thermostatic chamber, that is, the temperature of the FID does not need to be kept particularly high because the measurement object is limited to a gas such as air. ˜60 ° C.). Therefore, when the hydrogen flame is ignited, dew condensation may occur on the surface of the collector electrode inside the FID or the insulator supporting the FID due to water vapor generated by hydrogen combustion. In particular, when ignition is performed immediately after the apparatus is turned on and the temperature of the thermostatic chamber is not sufficiently increased, dew condensation is likely to occur. When dew condensation occurs, the output signal of the FID greatly fluctuates beyond the normal measurement range and is in a so-called “shattered” state. Condensation gradually evaporates and disappears due to the heat of the thermostatic chamber and the heat generated from the hydrogen flame, so the output signal gradually returns to the normal level, but the time until it becomes measurable (stabilization time) is 1. It may take some time.
The present invention has been made in view of such circumstances, and an object of the present invention is to prevent the occurrence of dew condensation after hydrogen flame ignition and shorten the stabilization time in a TVOC measuring apparatus using an FID.

  In order to solve the above-described problem, the present invention provides one or more of the hydrogen gas flow rate setting value, the auxiliary combustion gas flow rate setting value, and the FID temperature setting value before and after igniting the hydrogen flame. It is configured to control to a set value larger than the set value during normal measurement only during the provisional period, and the set value is returned to the set value during normal measurement based on the output signal level after ignition or by a preset time program. Configure.

  Since the present invention is configured as described above, the occurrence of dew condensation immediately after ignition is prevented, and the stabilization time of the apparatus can be shortened.

The TVOC measurement apparatus provided by the present invention has the following characteristics. That is, the first feature is that one or more of the hydrogen gas flow rate setting value, the auxiliary combustion gas flow rate setting value, and the FID temperature setting value is measured normally during a provisional period before and after the hydrogen flame is ignited. The second feature is that, after ignition, for example, the set value is returned to the set value during normal measurement based on the output signal level. It is.
Therefore, the basic configuration of the best mode is a TVOC measuring device having the above two features.

FIG. 1 shows the configuration of an embodiment of the present invention. In the figure, since the components denoted by the same reference numerals as those in the conventional example shown in FIG. 3 are the same as those in FIG. The difference between this embodiment and the conventional example is that a set value switching means 8 is provided.
As described above, the temperatures of the hydrogen gas, auxiliary combustion gas, and FID1 are controlled by the flow rate control devices 5, 6 and the temperature control device 7, respectively. The set values (normal set values) at the time of these normal measurements are examples. The hydrogen gas is 40-50 ml / min, the auxiliary combustion gas is 100 ml / min, and the temperature of FID1 is about 40-60 ° C. The set value switching means 8 temporarily switches any one or a plurality of set values to a value larger than the above normal set value only during a period before and after igniting the hydrogen flame 17 (provisional period). . Since each of the control devices 5, 6, and 7 is configured electronically, it can be set by an electrical input signal, and the set value switching means 8 transmits such setting signals a, b, and c. It is an electronic functional block and is configured as a part of a computer that controls the entire TVOC measuring apparatus.

In the present embodiment, the set value switching means 8 changes the hydrogen gas flow rate set value by the signal a only during the period before and after ignition. That is, the hydrogen gas flow rate setting is changed to about 1.5 times the normal set value, that is, 60 to 70 ml / min, just before the ignition of the hydrogen flame 17 or almost simultaneously with the ignition. As a result, the hydrogen flame 17 becomes larger than usual and the amount of heat generation also increases, so the temperature of the nozzle 11 and the collector electrode 12 around the hydrogen flame 17 rises, and condensation is unlikely to occur. After ignition, the output signal level of FID1 fluctuates greatly temporarily, but gradually returns to the normal level. The set value switching means 8 includes a comparator that compares the output signal level with the reference value, and returns the set value of the hydrogen gas flow rate to the normal set value when the output signal level drops to the reference value. Thereby, the stabilization time until the start of measurement can be shortened.
FIG. 2 is a graph showing the change in the hydrogen flow rate setting described above (solid line in the figure). In this example, it returns to the normal setting value 15 minutes after ignition, and further requires some stabilization time. About 30 minutes after ignition, the state is measurable.

As another example, the auxiliary combustion gas flow rate setting value may be increased during the provisional period after the ignition of the hydrogen flame 17 in the configuration of FIG. The set value switching means 8 switches the auxiliary combustion gas flow rate setting value so that, for example, the normal setting value of 100 ml / min is increased to about 200 to 300 ml / min. As a result, water vapor generated by the combustion of hydrogen is diluted and the relative humidity inside the FID 1 is lowered, so that condensation is unlikely to occur.
Thereafter, the output signal level of FID1 is determined by the set value switching means 8 and returned to the normal set value as in the case of the first embodiment.

As another embodiment, in the configuration of FIG. 1, the set value of the temperature control device 7 is switched by the signal c from the set value switching means 8 prior to ignition, and the temperature of the thermostatic chamber 2 during the temporary period is set to the normal set value. It is also possible to set a higher value. That is, as described above, the normal setting value of the temperature of the thermostat 2 is, for example, 40 to 60 ° C. and 100 to 150 ° C. Since the inside of FID1 communicates with the atmosphere through the exhaust port 13, the internal atmospheric pressure is 1 atm, and if the temperature is 100 ° C. or higher, dew condensation cannot occur theoretically. In this state, the hydrogen flame 17 is ignited, and then the output signal level of FID1 is determined by the set value switching means 8 to return the temperature of the thermostatic chamber 2 to the normal set value as in the case of the first or second embodiment. It is.
The change of the temperature set value in this case is shown by a dotted line in FIG.
It is effective to set the temperature of the thermostat 2 to 100 ° C. or more at all times to prevent dew condensation, but on the other hand, an increase in power consumption or an electron placed in the vicinity of the thermostat 2 This is not preferable because problems such as thermal protection measures for the device occur.

Each of the above embodiments is an example in which only one of a plurality of condition set values is changed to a period before and after ignition. However, by changing two or more set values in combination, It is also possible to enhance the effect. Further, as an example of determining the timing for returning to the normal setting, the above example has been described based on the output signal level. However, the timing may be switched by a preset time program.
In the above description, the TVOC measuring apparatus for measuring the total amount of volatile organic compounds in the sample gas has been described. However, for example, a chromatographic separation means is provided in the previous stage to separate and measure the organic compound into each component. The present invention can also be applied to the volatile organic compound measuring apparatus.

  The present invention can be used for a volatile organic compound measuring device that measures the concentration of organic solvent vapor or the like contained in, for example, exhaust from a painting booth.

It is a figure which shows one Example of this invention. It is a figure explaining operation | movement of this invention. It is a figure which shows the conventional structure.

Explanation of symbols

1 FID
2 Thermostatic chamber 3 Amplifier 4 Pump 5 Flow rate control device 6 Flow rate control device 7 Temperature control device 8 Set value switching means 11 Nozzle 12 Collector electrode 13 Exhaust port 14 Sample gas flow path 15 Hydrogen gas flow path 16 Auxiliary gas flow path 17 Hydrogen flame

Claims (3)

A hydrogen flame ionization detector that measures an ionic current generated by ionizing organic carbon in the sample gas in a hydrogen flame in which hydrogen gas burns in the presence of the auxiliary combustion gas, and a flow rate of the hydrogen gas and the auxiliary combustion gas. In the volatile organic compound measuring device configured to include a flow rate control device to be controlled and a temperature control device to control the temperature of the flame ionization detector, the flow rate setting value of the hydrogen gas and the flow rate setting of the auxiliary combustion gas A setting value for switching one or a plurality of setting values among the value and the temperature setting value of the hydrogen flame ionization detector to a setting value larger than the setting value at the time of normal measurement only for a provisional period before and after the ignition of the hydrogen flame A volatile organic compound measuring device comprising switching means. The volatile organic compound measuring apparatus according to claim 1, wherein the end of the provisional period before and after the ignition of the flame is determined based on an output signal of the flame ionization detector. 2. The volatile organic compound measuring apparatus according to claim 1, wherein a provisional period before and after the hydrogen flame ignition is determined by a time program.

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