In the monitoring of air and waste gas, we often use the solution absorption method to collect gaseous pollutant samples. This method uses different sizes and shapes of absorption bottles / tubes to concentrate gaseous pollutants such as sulfur dioxide, carbon monoxide, and formaldehyde in the absorption bottle. In the absorption solution, the collected samples are analyzed and processed in the laboratory with analytical instruments, and finally the pollutant concentration value is obtained. In the quality control process of monitoring the whole process, the error of the test results caused by the on-site sampling link is much larger than the error brought by the laboratory analysis, and the quality of the absorption bottle directly affects the sampling quality. Because the foaming element-glass plate of the absorption bottle is easy to be damaged during the manufacturing and using process, the foaming is not uniform and the absorption efficiency is reduced. According to the requirements of environmental monitoring quality control, in order to ensure the sampling and absorption efficiency, there is a clear requirement for the resistance of the absorption bottle: fill in the same volume of distilled water as the absorption liquid and pump the air according to the actual sampling flow, the resistance should be 4.7 ± 0.6KPa ～ 6.0 ± 0.6 Kpa, those who do not meet the requirements can not use [1]. The resistance of the newly purchased absorption bottle must be tested during acceptance. In daily use, the resistance of the absorption bottle should be measured once a month. When the difference between the measured value and the previous measurement result is greater than 0.3kPa, the absorption efficiency test should be performed. The absorption efficiency should be greater than 95% [2]. For the resistance test of the absorption bottle, there is no shaped equipment on the market so far. Generally, the U-shaped water column pressure difference method is used to determine the resistance of the absorption bottle, which is inconvenient to operate, low in efficiency, and large reading error. If there is an absorption bottle resistance test device that conforms to the standard and is convenient and fast to use, it must be required by the monitoring personnel.
2 Overall thinking and working principle
The absorption bottle resistance tester simulates the actual on-site sampling conditions [3], connects the negative pressure gauge and the absorption bottle in parallel in the working gas path, and reads the resistance value of the absorption bottle in real time. The technical route is shown in Figure 1: Start the pumping during the measurement Air pump, air passes through the absorption bottle, water filter trap and flow meter, and finally is discharged through the vacuum pump. Since the negative pressure gauge is connected to the connection pipe between the water filter trap and the absorption bottle, during the pumping process, the specified flow rate Below, the reading of the negative pressure gauge is the resistance value of the absorption bottle.
3 prototype and practical application
3.1 The prototype of the resistance tester is shown in Figure 21. Power switch; 2. Absorption bottle; 3. Negative pressure meter; 4. Flow meter
3.2 Main technical parameters 1. Resistance test range: 0 ～ 10Kpa2, flow adjustment range: 0 ～ 2.0L / min3, working voltage: AC 220V; power 50W4, working environment temperature -10 ～ 40 ℃; relative humidity <85% 5, Dimensions: 246 * 124 * 200 (length * width * height)
3.3 The whole structure of the absorption bottle resistance tester is mainly composed of a negative pressure meter, a water filter trap, a dryer, a flow meter and an air pump. The above components are connected through a connecting pipe, and the other port of the water filter trap is connected to an absorption bottle, negative pressure The meter is connected to the connecting pipe between the water trap and the absorption bottle through a tee. The measuring instrument includes a supporting frame for supporting the absorption bottle to be measured, and the supporting frame is arranged on the left side of the cabinet. A dryer is provided between the water filtering well and the flow meter, and the dryer is respectively connected with the water filtering trap and the flow meter through a connecting pipe. With this structure, the dryer can not only prevent water vapor in the air from entering the flow meter and cause flow errors, but also prevent water vapor from entering the vacuum pump and damaging the vacuum pump. A negative pressure gauge with a range of 0 to 10Kpa and a glass rotor flowmeter with a range of 0 to 2.0L / min are selected. The resistance range value and sampling working flow of a qualified absorption bottle are near the half-range of the pressure gauge and the flowmeter respectively. The most accurate position of the reading device. The pressure gauge and flow meter are qualified by the measurement department before assembly and commissioning. The whole resistance measuring instrument can also be sent to the measurement department for pressure and flow calibration.
3.4 Main features The whole machine is small and light, with reasonable structure, convenient and fast operation, stable performance, and meets the actual work requirements.
4 Applicability analysis
After being used by monitoring personnel, the resistance tester is very convenient to use: the instrument starts after the instrument switch is turned on, connect the absorption bottle that needs resistance measurement, adjust the flow meter to the corresponding position, the pressure gauge reading will be stable within half a minute, and the reading value is The resistance value of the absorption bottle. Continuous measurement of the same type of absorption bottle, the analyzer can always be turned on, there is no need to adjust the flow every time, the test time of a single absorption bottle does not exceed 1 minute. If the U-shaped water column pressure difference method is used for the resistance test of the absorption bottle, the U-shaped liquid pressure gauge used is relatively high: according to the pressure range of the absorption bottle, the height of the U-shaped tube needs to be at least 700mm, and the operation count is not convenient. The resistance of the absorption bottle exceeds the upper limit of the normal pressure, and the working fluid may also rush out of the glass tube mouth; when it is used, it must be hung vertically on the wall or the support, and a slight tilt will cause test errors. At the same time, it is easy to cause damage due to the connection between the glassware through pipes.
5 Conclusion
In summary, the developed absorption bottle resistance tester is much better than the U-shaped water column pressure difference method in terms of appearance volume, ease of operation and working efficiency. It is easy to detect unqualified absorption bottles to ensure gaseous pollution sampling Auxiliary instruments of important quality are suitable for resistance testing of various types of absorption bottles in the fields of environmental monitoring, health and epidemic prevention, environmental scientific research, and enterprises.
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