Current situation and development trend of gas leakage detection technology

First, natural gas leak detection technology

The chemical properties of natural gas are flammable and explosive gases, and the boiling point is low and the relative density of gas is smaller than that of air. Natural gas is mainly composed of organic compounds such as methane CH4. Therefore, the detection of natural gas leakage can be divided into two categories according to the principle: the first type of methane gas detection. The second category is the detection of natural gas pipelines. At present, the main methods for detecting methane are optical fiber absorption method and optical interference method. Natural gas pipeline detection methods mainly include acoustic detection methods, intelligent detection methods and so on.

(1) Optical interference method

The optical interference sensor is prepared according to the measurement principle of equal thickness method.

In 1930, Japanese scientists developed the world's first detection instrument, which is based on the principle that light is closely related to gas density through the change of refractive index of the gas medium, and the air chamber and methane chamber are filled with the same amount of fresh air to produce different stripes, according to this standard, once the natural gas pipeline leakage accident, the methane content in the air rises. The change in the density of the air in turn affects the change in the refractive index, and the end result is a change in the stripes, which can be seen through the eyepiece. With the progress of science and technology, intelligent detection instruments can achieve goals through the sensor incoming channel signal processing module and replace the more backward detection methods. The advantages of this detection method include long service life and high detection accuracy, while the disadvantages include complex operation and narrow application surface, which are easy to cause errors to the measurement results according to the field environment.

(2) Optical fiber absorption method

Compared with the developed countries in the world, China lags behind in the research and application of optical fiber absorption method. Among these detection methods, the optical fiber absorption methane detector is the most used and the most common detection instrument. This instrument utilizes Beer-

The Lambert principle allows precise detection of methane. Long distance optical fiber detection of air pollution proposed in 1979, for online detection of methane, the lower limit of the detected methane volume fraction is 25% of the lower explosive limit of methane. In 2000, T.Nakaya et al. used a laser with a wavelength of 1.66×10-12m as a light source to detect the volume fraction of methane in air more comprehensively and accurately.

(3) New gas pipeline leakage detection technology

The above two methods are more traditional, simple operation and low cost, but with the progress of science and technology, pipeline design is more complex, and people are more stringent on detection requirements.

Acoustic detection method. When the natural gas pipeline leakage occurs, the pipeline vibration frequency is 20Hz, and the frequency detector is generally used for detection. First, the natural gas leakage point is accurately located through professional. One of the detection technologies is called negative pressure method, which uses the pressure sensor in the equipment to detect the frequency of pipeline vibration when the natural gas pipeline leaks to determine whether there is a leak. If the sound wave is detected as abnormal, the detection instrument will give an alarm.

Intelligent detection method in tube. Intelligent pig began to be used in real-time detection of gas pipeline internal conditions, through the use of acoustic radiation and pressure differential method to detect pipeline leakage. This detection method can realize the accurate location of the leak point, and the application range is quite wide, and the application prospect is broad. The measurement results can provide important input for pipeline inspection and operational maintenance planning. In particular, the measurement results can provide a database of the pipeline's health and over-capacity, which will help technicians determine when more expensive and expert inspections are needed.

(4) Other methods for methane detection

1. Volumetric methane measurement

This detection method is based on the main principle, the methane is burned on the catalytic element, and then the volume fraction of methane is detected by the change of the combustion chamber volume. The results of volumetric methane measurement are scientifically based, and the results are very authoritative. Small error, accurate results. However, in the specific needs, the operation time is very long, and the internal structure is more responsible. This determines its operation trouble, these shortcomings are obvious.

2. Pressure methanometry

The volume fraction of methane is measured by the change of combustion chamber pressure caused by the combustion of methane on the catalytic element. Compared with the volumetric methanometry, the pressure methanometer itself has very distinct characteristics. The most remarkable is that the structure is very simple and easy to operate. However, in the specific measurement process, the error is large, and the low accuracy of the measuring machine also makes its shortcomings exposed very obvious.

3, methane detection lamp method

This test is mainly based on the length of the methane burning flame to measure. The advantage is that the methane volume fraction can be measured in the absence of oxygen, and the structure of this type of instrument is relatively simple. However, the error is large and the measurement results are not accurate enough. Can not measure the high volume fraction of methane, and its safety performance is not very good, the staff in the specific operation process a little careless Ozhe improper operation will cause an explosion, which can be seen that its safety performance is more worrying.

4, density difference methane measurement method

This method uses the change in the angular velocity of the rotor resulting from the density difference between methane and air (in this paper, the Angle at which methane gas is swept by the radius of rotation per second) to measure the methane volume fraction. This method has the advantages of simple structure and firmness. High safety performance, but its volume is too large, not easy to place and slack, at the same time, its detection accuracy error is also its more obvious shortcomings.

5, thermal conductivity measurement method

The principle of this method is to determine the methane volume fraction by using the change of the relative air thermal conductivity caused by the change of methane volume fraction. However, this method has low accuracy when detecting methane with low volume fraction, and is more susceptible to the influence of gas purity when detecting.

Second, development trend

Using intelligent detection to visually display whether there is leakage in the pipe segment is the focus of global technical research. Through ultrasonic technology using frequency detector detection, can quickly meet the requirements. The use of magnetic flux leakage technology is more difficult to achieve than ultrasonic technology, which is determined by the principle of magnetic flux leakage detection technology.

Optical fiber absorption method and optical interference method are generally used in large natural gas storage devices to detect whether there is leakage due to the instability of the external environment, and the future development prospects of magnetic flux leakage detector mainly have two aspects: first, the probe in the probe to control the accuracy of the probe and the number of probes, in order to ensure the accuracy of the data collection.

The second is to improve the level of automation based on accurate analysis with data, which can paint a picture of the true condition of the pipeline. One of the most important is the need to make continuous efforts in the study of the mathematical model of the corresponding relationship between magnetic leakage and defects.

Iii. Summary

The timely development and application of natural gas leakage detection play an important role in the safe use of natural gas in our country. Among the methane detection technologies, due to the influence of the external environment, it has a very large instability, and its main means are relatively simple. With the use of intelligent detectors, especially the rapid development of internal detection technology, the construction and use in China have been widely used.