CN217385309U - VOCs on-line measuring device - Google Patents

Abstract

The utility model discloses a VOCs online detection device, which comprises an insulation can, a preheating device, a catalytic oxidation sensor, a flowmeter, an air extractor, an electric signal measurer and a processor; the catalytic oxidation sensor is arranged in the heat preservation box and is used for catalytically oxidizing VOCs; the preheating device is arranged at the upstream of the catalytic oxidation sensor and is used for preheating sample gas, zero air or standard gas introduced into the catalytic oxidation sensor; the flowmeter and the air extractor are sequentially arranged at the downstream of the catalytic oxidation sensor; the electric signal measurer is electrically connected with the catalytic oxidation sensor and is used for collecting resistance changes at two ends of the catalytic oxidation sensor to obtain a voltage-time curve; the processor is electrically connected with the electric signal measurer and used for calculating the concentration of NMHC in the VOCs. The utility model discloses the resistance value that utilizes catalyst active oxygen's change to produce changes, can directly survey the NMHC concentration in the VOCs, principle, simple structure, operation maintenance convenient operation, sexual valence relative altitude.

Description

VOCs on-line measuring device

Technical Field

The utility model relates to a gas monitoring technology field, concretely relates to VOCs on-line measuring device.

Background

VOCs (volatile organic compounds) can participate in atmospheric photochemical reaction, are important pollutants for forming ozone and PM 2.5, and pollution control of VOCs is one of the strongest contents of the current standard-reaching management requirements. VOCs themselves contain a wide variety of substances and are heterogeneous in nature, mainly including alkanes, aromatics, olefins, halocarbons, esters, aldehydes, ketones, and other organic compounds. At present, monitoring aiming at VOCs is divided into two types of total amount monitoring and component monitoring, the index aiming at the total amount monitoring is NMHC (non-methane total hydrocarbon), the current mainstream test methods are a gas chromatography + FID (hydrogen flame ion detection) method and a catalytic oxidation + FID method, and the methods have the advantages and the disadvantages:

(1) gas chromatography + FID method:

the advantages are that: the sensitivity is high, the test repeatability is good, and the stability is high;

the disadvantages are as follows:

an injection valve, a chromatographic column, an FID and a signal amplification system are integrated in the equipment, so that the equipment cost is high;

the separation of methane and VOCs is required, so the test period is long, and generally 2 min/time is required;

the structure is complex, and the maintenance amount is large;

for different types of organic matters, the FID response is different, and the response of oxygen-containing organic matters is smaller;

hydrogen is needed as combustion gas, so that investment and safety risks are increased;

(2) catalytic oxidation + FID process:

the advantages are that: the sensitivity is high, the analysis period is short, and the response is fast;

the disadvantages are as follows:

the FID response is greatly influenced by the sample injection flow, and the stability is poor;

a catalytic oxidation component, a methane deduction mechanism, an FID (flame ionization detector), a signal amplification system and the like are integrated inside, so that the relative equipment cost is high;

for different types of organic matters, the FID response is different, and the response of oxygen-containing organic matters is smaller;

hydrogen is required as a combustion gas, increasing input and safety risks.

SUMMERY OF THE UTILITY MODEL

To the not enough of above-mentioned prior art, the utility model provides a VOCs on-line measuring device can directly survey NMHC, does not need the separation or deduct methane and VOCs, simple structure, and the cost drops into low, and sensitivity is high, and the oxygen-containing organic substance response is high.

In order to realize the above purpose, the utility model adopts the technical scheme that:

a VOCs online detection device comprises a heat preservation box, a preheating device, a catalytic oxidation sensor, a flow meter, an air extraction device, an electric signal measurer and a processor;

the catalytic oxidation sensor is arranged in the heat preservation box and used for catalytically oxidizing VOCs, and the resistance at two ends of the catalytic oxidation sensor changes along with the change of active oxygen on the surface of the catalyst;

the preheating device is arranged at the upstream of the catalytic oxidation sensor and is used for preheating sample gas, zero air or standard gas introduced into the catalytic oxidation sensor;

the flowmeter and the air extractor are sequentially arranged at the downstream of the catalytic oxidation sensor and are used for quantitatively introducing sample gas, zero air or standard gas;

the electric signal measurer is electrically connected with the catalytic oxidation sensor and is used for collecting resistance changes at two ends of the catalytic oxidation sensor to obtain a voltage-time curve;

the processor is electrically connected with the electric signal measurer and used for calculating the response area of the voltage-time curve and calculating the NMHC concentration in the VOCs according to the corresponding relation between the response area and the NMHC concentration.

As an improvement of the utility model, the device also comprises a dust removal filter which is arranged at the upstream of the preheating device and used for pretreating the introduced sample gas.

Compared with the prior art, the beneficial effects of the utility model reside in that:

1. the utility model discloses utilize the change of the catalyst active oxygen of sensor, the resistance value of production changes, can directly survey the NMHC concentration in the VOCs, whole device simple structure, and the hardware drops into fewly, and the device is with low costs, the sexual valence relative altitude.

2. The utility model discloses utilize the method of intermittent type nature ventilation, resume the active oxygen of catalyst, can reduce NMHC's detection limit, improve the repeatability, and can record the NMHC concentration in the oxygen deficiency sample gas.

3. The utility model discloses need not dispose the hydrogen, reduce safe risk, do not need the separation or deduct methane, the operation maintenance operation is more convenient.

4. The utility model discloses respond well to the oxygen-containing organic matter, to the gas that oxygen-containing organic matter content is high, more can truly reflect VOCs's organic carbon content.

Drawings

FIG. 1 is a schematic structural diagram of the online VOCs detection device of the present invention;

FIG. 2 is a cross-sectional view of a catalytic oxidation sensor of the present invention;

fig. 3 is a schematic diagram of a voltage-time curve of the present invention;

fig. 4 is a linear plot of the response area versus NMHC concentration of table 1;

FIG. 5 is a graph of zero air standard gas voltage versus time;

FIG. 6 is a plot of methane standard gas voltage versus time;

description of reference numerals: 1-insulation box; 2-a preheating device; 3-a catalytic oxidation sensor; 4-a dust removal filter; 5, a first flowmeter; 6-an air extracting device; 7-an electrical signal measurer; 8-a processor; 9-a second flowmeter; 10-electrode probe; 11-a conductive crosslinking agent; 12-catalytic oxidation supporter.

Detailed Description

In order to make the above objects, features and advantages of the present invention more comprehensible, the present invention is described in detail with reference to the accompanying drawings and the detailed description.

Examples

As shown in figure 1, the VOCs on-line detection device mainly comprises an insulation can 1, a preheating device 2, a catalytic oxidation sensor 3, a dust removal filter 4, a first flowmeter 5, an air extraction device 6, an electric signal measurer 7, a processor 8 and a second flowmeter 9.

The sample gas is connected with the preheating device 2 through the electromagnetic valve and the dust removal filter 4, and the zero air and the standard gas are respectively connected with the preheating device 2 through the electromagnetic valve and the flow meter II 9. Thus, the sample gas, the zero air and the standard gas can be respectively introduced into the preheating device 2 according to the requirement. Wherein, the sample gas is the gas of the VOCs to be detected, and the standard gas is the gas of the VOCs with known concentration, such as propane, butanone, ethyl acetate, triphenyl standard gas, and the like.

The preheating device 2, the catalytic oxidation sensor 3, the first flowmeter 5 and the air extracting device 6 are connected in sequence to form a gas flow path. The preheating device 2 can be arranged in the heat insulation box 1 and used for preheating the sample gas, the zero air and the standard gas. The gas extraction device 6 provides power for the gas flow and the flow meter one 5 is used to accurately meter the amount of gas flowing through the catalytic oxidation sensor 3. The preheating device 2 preheats the sample gas, the zero air and the standard gas to the reaction temperature, then the sample gas, the zero air and the standard gas enter the catalytic oxidation sensor 3 under the suction force of the air exhaust device 6, and the sample gas, the zero air and the standard gas are discharged through the flowmeter 5 and the air exhaust device 6 after the reaction.

Catalytic oxidation sensor 3 is commercially available, is disposed in thermal container 1, and is capable of catalytically oxidizing VOCs, but not methane, at operating temperatures. For the sake of understanding, this embodiment shows an exemplary configuration, as shown in fig. 2, the catalytic oxidation sensor 3 is a horizontally placed cylindrical structure, and is composed of transition metal oxides such as Mn, Co, Cu, Ni, Ce, etc. and electrodes, the main body is a catalytic oxidation support 12 with a built-in gas flow channel, and the electrode probe 10 is fixed on the cylindrical surface of the catalytic oxidation support 12 through a conductive cross-linking agent 11.

When the catalytic oxidation sensor is used, when the sample gas and the standard gas are introduced into the catalytic oxidation sensor 3, the NMHC in the sample gas and the standard gas can consume active oxygen on the surface of the catalyst, so that the resistance at two ends of the catalytic oxidation sensor 3 is increased. When zero air is introduced into the catalytic oxidation sensor 3, active oxygen on the surface of the catalyst is repaired, so that the resistance at two ends of the catalytic oxidation sensor 3 is reduced. Wherein methane does not consume active oxygen on the surface of the catalyst, so that the increase of the resistance across the catalytic oxidation sensor 3 is not caused.

The electric signal measurer 7 is electrically connected with the catalytic oxidation sensor 3 and is used for collecting resistance changes at two ends of the catalytic oxidation sensor 3 and obtaining a voltage-time curve through simple conversion. Specifically, the electrical signal measuring device 7 can measure the resistance change at two ends of the sensor by using a wheatstone bridge, so as to obtain a voltage-time curve.

The processor 8 can be a conventional computer or a singlechip, is electrically connected with the electric signal measurer 7 and is used for calculating the response area of a voltage-time curve and calculating the NMHC concentration of the sample gas according to the corresponding relation between the response area and the NMHC concentration.

An exemplary voltage-time curve is given in fig. 3, where the sample gas passage time is 30s and the zero air passage time is 60 s. The response area of the voltage-time curve is represented by the area formed by the connection line of the curve and the curve end point (because the voltage measurement parameter has delay, the response area is generally delayed for several seconds when the response area is calculated, and the stable part of the curve data is intercepted). The application adopts the response area, and can better reflect the linear relation with the NMHC concentration relative to the signal height of a curve.

Fig. 5 is a zero air standard gas voltage-time curve, fig. 6 is a methane standard gas voltage-time curve, and the corresponding area is calculated, and as shown in table 1, it can be seen that the methane response of 121mg/m3 is almost the same as that of zero gas, which indicates that methane hardly consumes active oxygen on the surface of the catalyst, does not cause an increase in resistance at both ends of the catalytic oxidation sensor 3, and cannot be catalyzed by the catalytic oxidation sensor 3.

TABLE 1

The calculation of the response area of the voltage-time curve as a function of the NMHC concentration is described below using propane standard gas:

as shown in Table 2, the concentration of the propane standard gas was increased from 0 to 128.55mg/m ³ The concentration of each stage is repeated for 3 times, the signal value in the table refers to the calculated response area,the specific data are as follows:

TABLE 2

A linear equation of the response area and the gas concentration can be obtained through linear fitting, as shown in FIG. 4, the fitting degree of the linear equation reaches 0.9953, and the test requirement can be met.

The following combines foretell VOCs on-line measuring device, is right the utility model discloses a VOCs on-line measuring method carries out the exemplary explanation:

under the suction of the air extractor 6, the sample gas passes through the dust removal filter 4, enters the preheating device 2 in the insulation can 1 for preheating, enters the catalytic oxidation sensor 3 after being preheated, NMHC in the sample gas consumes active oxygen on the surface of the catalyst, so that the resistance at two ends of the catalytic oxidation sensor 3 is increased, the voltage values at two ends of the circuit are also changed, the change condition of the voltage values is measured by the electric signal measurer 7 in real time, and the sample gas is continuously introduced for 30 s.

And when the voltage value changes, the zero air is continuously introduced for 60s, so that the resistors at the two ends of the catalytic oxidation sensor 3 can be ensured to return to the initial value.

The processor 8 draws a voltage-time curve according to the measurement result, calculates the response area, calls a corresponding linear equation, and obtains the NMHC concentration of the sample gas and displays the NMHC concentration in real time.

The built-in linear equation can be established by the following method:

preparing standard gas with known concentration, which can be propane, butanone, ethyl acetate, triphenyl and other standard gas;

opening a corresponding electromagnetic valve, introducing standard gas, entering a preheating device 2 in the heat insulation box 1 for preheating under the suction force of an air extractor 6, entering a catalytic oxidation sensor 3 after preheating, wherein NMHC in the standard gas consumes active oxygen on the surface of a catalyst, so that the resistance at two ends of the catalytic oxidation sensor 3 is increased, the voltage value at two ends of a circuit is also changed, the change condition of the voltage value is measured by an electric signal measurer 7 in real time, and the standard gas is continuously introduced for 30 s;

when the voltage of the catalytic oxidation sensor is 30 seconds, the electromagnetic valve is switched, zero air is introduced, the zero air enters the preheating device 2 in the heat preservation box 1 under the action of negative pressure of the air extractor 6 to be preheated, the preheated zero air enters the catalytic oxidation sensor 3, active oxygen on the surface of a catalyst is repaired, the resistance at two ends of the catalytic oxidation sensor 3 is reduced, the change condition of the voltage value is measured by the signal measurer, the zero air is continuously introduced for 60 seconds, the resistance at two ends of the catalytic oxidation sensor 3 can return to the initial value, and meanwhile, the processor 8 draws a voltage-time curve according to the measurement result;

the steps are repeated, the response area of the voltage-time curve under different concentrations can be obtained, and a linear equation of the response area and the gas concentration can be obtained through linear fitting.

It should be noted that the above-mentioned introduction time of the sample gas and the standard gas is 30s, and the introduction time of the zero air is 60s, which is a preferred embodiment, and the specific introduction time can be flexibly determined according to the principle of taking efficiency and precision into consideration.

The utility model is further explained by the following specific experimental data:

by using the detection device and the detection method, the flow of the first flow meter 5 is adjusted to be 2L/min, the flow of the second flow meter 9 is adjusted to be 2L/min, and the temperature of the heat preservation box 1 is 300 degrees.

1) Respectively introducing low-concentration isopropanol standard gas and ethylene standard gas, and after 7 continuous tests, calculating the detection limit through a formula:

wherein n is the number of times of test, X _i For the concentration value measured at the i-th time,

to measure the average of the concentrations, the results are shown in table 2:

TABLE 2

It can be seen that the detection limit meets the requirement of the standard HJ1013-2018 on the detection limit of less than or equal to 0.8mg/m 3.

2) After standard gases of propane, butanone, ethyl acetate and triphenyl are respectively introduced, and each standard gas is tested for 6 rounds, the results are shown in the following table 3:

TABLE 3

Compared with the carbon response of propane, the device and the method have the advantages that the device and the method for testing butanone, ethyl acetate and triphenyl substances by using oxygen-containing organic substances have good repeatability, and meet the daily stable detection requirement; and the C response of butanone and ethyl acetate is close to 1, which shows that the device and the method of the invention have good response performance to oxygen-containing organic matters. Compare in the response of FID to the oxygen-containing organic matter, the utility model discloses the device response is closer to 1.

The above embodiments are only for illustrating the technical concept and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and to implement the present invention, which cannot limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered by the protection scope of the present invention.

Claims (2)

1. The utility model provides a VOCs on-line measuring device which characterized in that: comprises a heat preservation box, a preheating device, a catalytic oxidation sensor, a flowmeter, an air extractor, an electric signal measurer and a processor;

the catalytic oxidation sensor is arranged in the heat preservation box and used for catalytically oxidizing VOCs, and the resistance at two ends of the catalytic oxidation sensor changes along with the change of active oxygen on the surface of the catalyst;

the preheating device is arranged at the upstream of the catalytic oxidation sensor and is used for preheating sample gas, zero air or standard gas introduced into the catalytic oxidation sensor;

the flowmeter and the air extractor are sequentially arranged at the downstream of the catalytic oxidation sensor and are used for quantitatively introducing sample gas, zero air or standard gas;

the electric signal measurer is electrically connected with the catalytic oxidation sensor and is used for collecting resistance changes at two ends of the catalytic oxidation sensor to obtain a voltage-time curve;

the processor is electrically connected with the electric signal measurer.

2. The online detection device for VOCs according to claim 1, wherein: the device also comprises a dust removal filter which is arranged at the upstream of the preheating device and is used for pretreating the introduced sample gas.

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