JPH0580010A - Method for measuring concentration of carbon dioxide gas within gas - Google Patents

Abstract

PURPOSE:To enable concentration of carbon dioxide gas within a gas to be measured continuously, accurately, and with a high measurement sensitivity. CONSTITUTION:A channel of a gas-separation device 1 is isolated by a gas- transmission film 1A, a gas 3 mixed with carbon dioxide gas which is sandwiched by an acid solution 4 is allowed to flow to one channel 1B of the gas-separation device 1, and then an alkali solution 5 is circulated at the other channel 1C for reaction with carbon dioxide gas within the gas 3 which is transmitted through the gas-transmission film 1A of the gas-separation device 1. Conductivity of the alkali solution 5 which reacted with carbon dioxide gas at a downstream of the other channel 1C is measured, thus enabling the carbon dioxide concentration within the specimen gas 3 to be measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon dioxide concentration measuring method for continuously measuring the concentration of carbon dioxide in a gas such as air.

[0002]

2. Description of the Related Art Conventionally, there have been various CO ₂ concentration meters in gas. For example, a CO ₂ concentration meter based on the principle of selective absorption of an absorbing solution measures the CO ₂ concentration by absorbing CO _{2 in} an alkaline solution and measuring the absorption loss.

CO which utilizes selective absorption of infrared rays
_{The 2} densitometer has the structure shown in FIG. 4, in which the sample gas 12 is continuously flown into the cell 11 having a predetermined length according to the concentration,
Of the infrared passing through the cell 11, the intensity of the infrared ray (specific wavelengths) of varying absorption with the amount of CO ₂ changes in the quantity of electricity to measure the CO ₂ concentration.

A CO ₂ concentration meter utilizing the thermal conductivity of gas has a structure as shown in FIG. 5, and attention has been paid to the fact that CO ₂ gas has a lower thermal conductivity than other gases. CO ₂
This is a densitometer that measures the concentration. By incorporating the thin heating wire 15 stretched between the measurement chamber 13 and the comparison chamber 14 into the Wheatstone bridge, the gas composition changes from air to N ₂ + O ₂ + CO ₂ + (H ₂ O). Designed with a constant compositional change, the thermal conductivity of the produced gas (sample) decreases with the increase of CO ₂ .
This relationship is detected as an increase in the temperature of the heating wire, that is, an increase in electrical resistance.

Further, the density comparison type CO ₂ concentration meter is C
In the densitometer focusing on the large density of O ₂ , two passive impellers 17 and 18 facing each other are connected by a link mechanism 19 as shown in FIG. Since the rotational torque in the opposite direction is transmitted by the fluid coupling action, it is designed to equilibrate at different positions depending on the property change [density + (viscosity)] of the sample gas 22, and the change in sample density based on air (In other words, increase / decrease in CO ₂ ) can be detected.

[0006]

[Problems to be Solved by the Invention]
Among the conventional densitometers, CO based on the principle of selective absorption of absorbing liquid
₂The densitometer has the problem that continuous measurement is not possible.
It was In addition, CO that utilizes selective absorption of infrared rays₂Densitometer
Has the problem of being affected by the interference of water in the sample.
there were. Furthermore, CO that utilizes the thermal conductivity of gas₂concentration
CO and density comparison type CO₂Concentration meter, selection of gas components
There is a problem that it is not stable and is affected by the coexisting gas.
It was

The present invention has been made in order to solve such a conventional problem, and provides a carbon dioxide concentration measuring method for continuously and accurately measuring the concentration of carbon dioxide in a gas with high measurement sensitivity. It is intended to be provided.

[0008]

In the method for measuring the concentration of carbon dioxide gas in a gas according to the present invention, the flow path of a gas separation device is separated by a gas permeable membrane, and carbon dioxide gas is mixed in one flow path of this gas separation device. A gas is flown, an alkali solution is circulated in the other channel to react with carbon dioxide in the gas that has permeated the gas permeable membrane of the gas separation device, and the conductivity of the alkali solution reacted with carbon dioxide in the downstream of the other channel. The carbon dioxide concentration in the gas is measured by measuring the rate.

Further, the method for measuring the concentration of carbon dioxide in a gas according to the present invention is to measure the concentration of carbon dioxide in a gas by sandwiching a gas mixed with carbon dioxide with an acidic solution and flowing it into one flow path of a gas separation device. taking measurement.

[0010]

In the above structure, a gas containing carbon dioxide gas is caused to flow through one flow path of the gas separation device, and the carbon dioxide gas contained in the gas reacts with the alkali solution flowing through the gas permeable membrane and the other flow path. Then, the conductivity of the alkaline solution is changed.
The amount of change in conductivity is determined by the amount of carbonate ions generated when carbon dioxide gas reacts with the alkaline solution. Therefore,
The carbon dioxide concentration in the gas can be measured by measuring the change in conductivity of the alkaline solution with a conductivity meter.

Further, by flowing the gas sandwiched by the acidic solution through one flow path of the gas separation device, the permeability of carbon dioxide gas that permeates the gas permeable membrane of the gas separation device is improved, and the measurement accuracy is improved. ..

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view of the case where the carbon dioxide concentration in the gas is continuously measured in the first embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a gas separator, which is an air pump 2A from an upstream side of one flow path 1B of a pair of flow paths separated by a gas permeable membrane tube 1A.
The gas 3 (for example, air) and the acid solution 4 are sent in a sandwich state by the first liquid feed pump 2B, and the other flow path
The alkaline solution 5 is fed from the upstream side of 1C by the second liquid feeding pump 2C. Gas 3 and acidic solution 4 in one channel 1B
Is discharged from the downstream side, and the alkaline solution 5 in the other channel 1C
Flows into the conductivity meter 6, the conductivity is measured, and then discharged as drainage.

The gas separation device 1 is a long cylinder,
A gas permeable membrane tube 1A made of Teflon that permeates carbon dioxide in the central longitudinal direction is arranged so that carbon dioxide permeates from one flow passage 1B side to the other flow passage 1C side. Teflon is a material that is efficient in performing gas-liquid separation, but the material of the gas permeable membrane tube 1A is not limited to Teflon and may be polyethylene, polystyrene, or the like.

Next, a method for measuring the carbon dioxide concentration in the gas 3 will be described. The air pump 2A is driven to send the gas 3 and the first liquid sending pump 2B is driven to pass the acidic solution 4, and the both are mixed and sent to one flow passage 1B of the gas separation device 1. As the acidic solution 4, sulfuric acid (H ₂ SO ₄ ), perchloric acid (HCIO ₄ ), nitric acid (HNO ₃ ), hydrochloric acid (HCI) and the like are used.

The gas sent into one of the flow paths 1B is as shown in FIG.
As shown in, the gas is sandwiched by the acidic solution and flows from the upstream side to the downstream side of the one channel 1B. In the gas 3 flowing through one of the flow paths 1B, carbon dioxide gas (CO
₂ ) is included, this carbon dioxide gas permeates only the carbon dioxide gas through the gas permeable membrane tube 1A while flowing from the upstream side to the downstream side of one flow path 1B of the gas separation device 1 and the other side. Flows into the flow channel 1C of.

In the other flow path 1C, the second liquid feed pump 2C is driven to flow the alkaline solution 5. This alkaline solution 5
Is sodium hydroxide (NaOH), sodium carbonate (Na ₂ CO ₃ ), sodium acetate (CH ₃ CO ₂ N
By using a) or the like and varying the concentration of the alkaline solution 5, it is possible to measure a wide range of carbonic acid concentration in the gas 3.

The carbon dioxide gas that has permeated the gas permeable membrane tube 1A as described above is treated with the alkaline solution 5 in the other channel 1C.
Reacts with to form carbonate. For example, when carbon dioxide gas reacts with sodium hydroxide, the reaction formula is as follows.

2NaOH + CO ₂ → Na ₂ CO ₃ + H ₂ O The carbon dioxide gas reacts with the sodium hydroxide solution to change the conductivity of the solution. The amount of change in conductivity changes depending on the amount of sodium hydroxide (NaOH) reduced and sodium carbonate (Na ₂ CO ₃ ) generated corresponding to the amount of carbon dioxide gas. Therefore, the conductivity meter 6 installed downstream of the other flow path 1C should measure the amount of change in conductivity of the alkaline solution 5 (2 [OH ⁻ ] − [CO ₃ ²⁻ ]) with the conductivity meter 6. The carbon dioxide concentration in the gas 3 can be measured by.

FIG. 3 is a schematic diagram for continuously measuring the carbon dioxide concentration in the gas in the second embodiment of the present invention. The second embodiment is different from the first embodiment in that a mechanism for feeding the acidic solution 4 is not provided, and the gas 3 flows as it is from the upstream side to the downstream side of the one flow path 1B. It is configured. Carbon dioxide contained in the gas 3 permeates the permeable membrane tube 1A, reacts with the alkaline solution 5 in the other channel 1C to generate a carbonate, and the carbonate ion of this carbonate is measured. The measurement of the carbon dioxide concentration in the gas is the same as in the first embodiment.

In the above embodiment, the gas 3 and the acidic solution 4 are sent from the upstream side of the one flow path 1B, and the alkaline solution 5 is sent from the upstream side of the other flow path 1C. The flow paths for flowing the mixed solution of the solution 4 and the alkaline solution 5 may be reversed.

In each of the above embodiments, the gas-liquid flowing through the gas separation device 1 is configured to flow in the same direction from the upstream side to the downstream side, but the gas-liquid flows are opposed to each other. Thus, for example, one flow channel 1B may flow from upstream to the downstream side, and the other flow channel 1C may flow from the downstream side to the upstream side. In this way, by making the gas-liquid flow direction reverse, the carbon dioxide gas that has permeated the gas permeable membrane reacts well with the alkaline solution 5 to improve the measurement accuracy.

[0023]

As described above, according to the present invention, carbon dioxide gas in a gas is reacted with an alkaline solution for measurement, so that the measurement accuracy and measurement sensitivity of carbon dioxide gas are improved. Furthermore, by changing the concentration of the alkaline solution flowing through one of the flow paths, it is possible to measure the carbon dioxide concentration in a wide range in the gas.

Further, the gas mixed with carbon dioxide gas is sandwiched with the acidic solution and allowed to flow through one flow path of the gas separation device, so that the permeability of carbon dioxide gas passing through the gas permeable membrane is improved and the measurement accuracy is improved. To do.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a method for measuring a carbon dioxide concentration in a gas according to a first embodiment of the present invention.

FIG. 2 is a partially enlarged view of a flow path of the gas separation device according to the first embodiment.

FIG. 3 is a schematic diagram of a method for measuring a carbon dioxide concentration in a gas according to a second embodiment of the present invention.

FIG. 4 CO ₂ utilizing selective absorption of infrared rays in a conventional example
It is the schematic of a densitometer.

FIG. 5 is a schematic diagram of a CO ₂ concentration meter that utilizes the thermal conductivity of gas in a conventional example.

FIG. 6 is a schematic diagram of a density comparison type CO ₂ concentration meter of a conventional example.

[Explanation of symbols]

 1 Gas Separator 1A Gas Permeable Membrane Tube 1B One Channel 1C The Other Channel 3 Gas 4 Acidic Solution 5 Alkaline Solution 6 Conductivity Meter

Claims (2)

[Claims] 1. A gas separation device, wherein a flow path of a gas separation device is separated by a gas permeable membrane, a gas mixed with carbon dioxide gas is caused to flow through one flow path of the gas separation device, and an alkaline solution is caused to flow through the other flow path. It is possible to measure the carbon dioxide concentration in the gas by reacting with the carbon dioxide in the gas that has permeated the gas permeable membrane of the device and measuring the conductivity of the alkaline solution that has reacted with the carbon dioxide downstream of the other channel. Characteristic method for measuring carbon dioxide concentration in gas. 2. The method for measuring a carbon dioxide concentration in a gas according to claim 1, wherein the gas mixed with carbon dioxide is sandwiched with an acidic solution and allowed to flow through one flow path of the gas separation device.