System and method for measuring gas humidity by using dew-point meter through flue gas dilution method

Abstract

The invention belongs to the technical field of flue gas humidity detection. A system for measuring gas humidity through a flue gas dilution method dew-point instrument comprises a dryer, a third three-way valve, a dilution probe, a first three-way valve, a first dew-point instrument, a needle valve, a second dew-point instrument, a second three-way valve and an MCU. According to the scheme, the zero-point air background value problem can be processed in real time in a differential mode, the zero-point problem can be processed in real time, and no redundant time is needed for zero-point calibration, namely zero-time zero-point calibration; and a zero time difference zero point calibration function is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of smoke humidity detection. Background Art

[0002] Dew point meter: A dew point meter is an instrument that can directly measure the dew point temperature. A mirror is cooled in the sample wet air until dew drops (or ice crystals) appear on the mirror surface. The average temperature of the mirror surface is measured, which is the dew point (frost) temperature. Dew point meters can be divided into capacitance method or resistance capacitance method dew point meters according to different principles. The measurement accuracy is average; the cold mirror dew point meter has high measurement accuracy and is usually a laboratory traceability method.

[0003] In the process of existing pollution source flue gas monitoring, several humidity measurement methods are commonly used. One is the direct measurement method, which usually puts the probe in direct contact with the flue gas for measurement, usually the capacitance method or dry and wet oxygen measurement. This method is affected by the working conditions and has poor measurement accuracy. The other method is used in the dilution sampling system. The humidity of the diluted flue gas is usually at the ppm concentration level. At this time, a dew point meter is used to measure it. The dew point meter is divided into two categories according to accuracy and price. One is a conventional dew point meter, which is usually based on the capacitance method or resistance-capacitance method. It is cheap, but the disadvantage is that the accuracy is slightly poor. The other is a chilled mirror dew point meter, which is more expensive and has high measurement accuracy. It can be traced back to the laboratory method and is currently an internationally recognized high-precision measurement method.

[0004] The existing method for calibrating the zero point of the dew point meter is to connect a three-way solenoid valve to the zero point air end, control the solenoid valve to switch the air path into the dew point meter, and perform regular dew point measurement on the collar air to obtain the collar air dew point value, thereby achieving the purpose of calibrating the zero point.

[0005] The humidity content of compressed air on site will change with time, ambient temperature and equipment aging. Similarly, after passing through the dryer, the background dew point humidity value will change. The dilution method measurement process usually uses a dilution multiple of about 100 times. The humidity deviation of 100ppm concentration is calculated by multiplying it by 100. The smoke humidity deviation can reach 10000ppm, that is, 1%. Therefore, it is particularly important to ensure the accuracy of the zero-point air dew point humidity.

[0006] The gas after the instrument air passes through the dryer is the zero gas driving gas for the dilution probe. There is a three-way solenoid valve between the dryer and the probe to control the switching state of the solenoid valve, which can realize two directions. One way goes to the dilution probe to sample the flue gas, and the diluted flue gas enters the dew point meter for mixed gas dew point measurement; the other way is through the dryer zero gas, switched by the three-way valve, and the needle valve adjusts the flow rate to enter the dew point meter for zero air dew point measurement.

[0007] Since the dew point temperature of zero air is very low, usually -30 to -40 degrees or even lower, the corresponding humidity is usually less than 100ppm. During the measurement of flue gas humidity, the dew point temperature is usually around 0 degrees, corresponding to a humidity of about 3000ppm. During zero point calibration, after the solenoid valve is switched, the original humidity in the pipeline and dew point meter cavity is replaced very slowly and takes a long time, usually more than 30 minutes to reach a stable state. The environmental protection standard clearly requires that the amount of effective data for online measurement should not be less than 95%. If the zero point calibration time is too long, it will inevitably affect the data efficiency. Failure to calibrate will also affect the measurement accuracy. Summary of the invention

[0008] In view of this, the present invention provides a system for measuring gas humidity by a flue gas dilution method dew point meter, comprising: a dryer, a third three-way valve, a dilution probe, a first three-way valve, a first dew point meter, a needle valve, a second dew point meter, a second three-way valve and an MCU; the first port of the third three-way valve is connected to the zero gas inlet gas pipeline of the dilution probe; the second port of the third three-way valve is connected to the inlet gas pipeline of the needle valve; the third port of the third three-way valve is connected to the outlet gas pipeline of the dryer; the first port of the first three-way valve is connected to the gas inlet gas pipeline of the first dew point meter The second port of the first three-way valve is connected with the exhaust air pipeline; the third port of the first three-way valve is connected with the smoke outlet gas pipeline of the dilution probe; the gas inlet of the second dew point meter is connected with the outlet gas pipeline of the needle valve; the gas outlet of the second dew point meter is connected with the third port gas pipeline of the second three-way valve; the first port of the second three-way valve is connected with the zero gas inlet gas pipeline of the first dew point meter; the MCU is respectively connected with the signal circuits of the first dew point meter, the second dew point meter, the first three-way valve, the second three-way valve and the third three-way valve.

[0009] Furthermore, the dew point meter is a capacitance method dew point meter, a resistance-capacitance method dew point meter, or a cold mirror dew point meter.

[0010] The present invention also provides a method for measuring gas humidity by a flue gas dilution method dew point meter, comprising the following steps: after the zero gas passes through a dryer and enters a third three-way valve, the gas path is divided into two parallel gas paths: a detection gas path and a calibration gas path; the zero gas in the detection gas path enters a dilution probe and mixes with the flue gas to form a mixed gas to be measured; after the mixed gas to be measured passes through a first three-way valve, the gas is divided into two gas paths: a measurement gas and an exhaust gas; the measurement gas enters a first dew point meter for dew point measurement to obtain a humidity value of the mixed gas to be measured; the zero gas in the calibration gas path enters a second dew point meter after flow adjustment by a needle valve to measure the dew point of the zero gas; the humidity value of the zero gas is obtained; and the humidity value of the flue gas is calculated based on the humidity value of the mixed gas to be measured and the humidity value of the zero gas.

[0011] Furthermore, the exhaust gas is directly exhausted through the first three-way valve and the exhaust pipeline.

[0012] The solution of the present invention can process the zero-point air background value problem in real-time differential processing, and can process the zero-point problem in real-time without extra time for zero-point calibration, that is, 0-time zero-point calibration; and realize the zero-time difference zero-point calibration function. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a system diagram of the flue gas dilution method dew point meter for measuring gas humidity. DETAILED DESCRIPTION

[0014] Example

[0015] The technical problem to be solved by the present invention is that during the process of measuring the humidity of the dew point by sampling using the flue gas dilution method, during the process of measuring and calibrating the zero-point gas of the dew point meter, the response time is long, which affects the online measurement data rate.

[0016] The present invention provides a system for measuring humidity by a flue gas dilution method dew point meter, comprising: a dryer 1, a third three-way valve, a dilution probe 2, a first three-way valve 3, a first dew point meter 4, a needle valve 5, a second dew point meter 6, a second three-way valve 7 and an MCU 8;

[0017] The first port of the third three-way valve is connected to the zero gas inlet pipeline of the dilution probe; the second port of the third three-way valve is connected to the inlet pipeline of the needle valve; the third port of the third three-way valve is connected to the outlet pipeline of the dryer;

[0018] The first port of the first three-way valve is connected to the gas inlet pipeline of the first dew point meter; the second port of the first three-way valve is connected to the exhaust air pipeline; the third port of the first three-way valve is connected to the flue gas outlet pipeline of the dilution probe;

[0019] The gas inlet of the second dew point meter is connected to the outlet gas pipeline of the needle valve; the gas outlet of the second dew point meter is connected to the third port gas pipeline of the second three-way valve;

[0020] The first port of the second three-way valve is connected to the zero gas inlet gas pipeline of the first dew point meter;

[0021] The MCU is respectively connected to the first dew point meter, the second dew point meter, the first three-way valve, the second three-way valve and the third three-way valve signal lines;

[0022] The dew point meter is a capacitance method dew point meter or a resistance-capacitance method dew point meter or a cold mirror dew point meter.

[0023] The method for measuring gas humidity by a flue gas dilution method dew point instrument comprises the following steps:

[0024] After the zero gas passes through the dryer and enters the third three-way valve, the gas path is divided into two parallel gas paths: the detection gas path and the calibration gas path;

[0025] The zero gas in the test gas path enters the dilution probe and mixes with the flue gas to form a mixed gas to be tested;

[0026] After the mixed gas to be tested passes through the first three-way valve, the gas is divided into two gas paths: measuring gas and exhaust gas;

[0027] The measured gas enters the first dew point meter for dew point measurement to obtain the humidity value of the mixed measured gas;

[0028] The exhaust gas is directly exhausted through the first three-way valve and the exhaust pipeline;

[0029] The zero gas of the calibration gas path enters the second dew point meter after the flow rate is adjusted by the needle valve, and the zero gas dew point is measured to obtain the humidity value of the zero gas;

[0030] The humidity value of the flue gas is calculated based on the humidity value of the mixed gas to be tested and the humidity value of the zero gas.

[0031] The solution of the present invention can process the zero-point air background value problem in real-time differential processing, and can process the zero-point problem in real-time without extra time for zero-point calibration, that is, 0-time zero-point calibration; and realize the zero-time difference zero-point calibration function.

Claims

1. The system for measuring gas humidity by the flue gas dilution method dew point meter is characterized by: include: Dryer, third three-way valve, dilution probe, first three-way valve, first dew point meter, needle valve, second dew point meter, second three-way valve and MCU; The first port of the third three-way valve is connected to the zero gas inlet pipeline of the dilution probe; the second port of the third three-way valve is connected to the inlet pipeline of the needle valve; the third port of the third three-way valve is connected to the outlet pipeline of the dryer; The first port of the first three-way valve is connected to the gas inlet pipeline of the first dew point meter; the second port of the first three-way valve is connected to the exhaust air pipeline; the third port of the first three-way valve is connected to the flue gas outlet pipeline of the dilution probe; The gas inlet of the second dew point meter is connected to the outlet gas pipeline of the needle valve; the gas outlet of the second dew point meter is connected to the third port gas pipeline of the second three-way valve; The first port of the second three-way valve is connected to the zero gas inlet gas pipeline of the first dew point meter; The MCU is respectively connected with the first dew point meter, the second dew point meter, the first three-way valve, the second three-way valve and the third three-way valve signal lines.

2. The system for measuring gas humidity by a flue gas dilution method dew point meter according to claim 1 is characterized in that: The dew point meter is a capacitance method dew point meter or a resistance-capacitance method dew point meter or a cold mirror dew point meter.

3. The method of measuring gas humidity by using a flue gas dilution method dew point meter is characterized by: The steps include: After the zero gas passes through the dryer and enters the third three-way valve, the gas path is divided into two parallel gas paths: the detection gas path and the calibration gas path; The zero gas in the test gas path enters the dilution probe and mixes with the flue gas to form a mixed gas to be tested; After the mixed gas to be tested passes through the first three-way valve, the gas is divided into two gas paths: measuring gas and exhaust gas; The measured gas enters the first dew point meter for dew point measurement to obtain the humidity value of the mixed measured gas; The zero gas of the calibration gas circuit enters the second dew point meter after the flow rate is adjusted by the needle valve to measure the zero gas dew point; Get the humidity value of zero air; The humidity value of the flue gas is calculated based on the humidity value of the mixed gas to be tested and the humidity value of the zero gas.

4. The method for measuring gas humidity by a flue gas dilution method dew point instrument according to claim 3, characterized in that: The exhaust gas is directly exhausted through the first three-way valve and the exhaust pipeline.

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