A Study On Fiber-optic F-P Acoustic Sensor Used In Hydraulic Decoking On-line Monitoring

The delayed coking unit is a large chemical machinery equipment which is lack of effective means of sensing monitoring. In order to remove more than a thousand tons of coke up to fifty meters in the seal pot shaped coking unit whose diameter is three meters, workers usually finish the hydraulic decoking task relied on their working experience at present, which may lead to high energy consumption of production, low worker productivity, as well as high risk of personal security. Aiming at solving those problem, a study on optical fiber F-P acoustic sensor used in high temperature environment is being carried out in this paper to apply the sensor to the online real-time monitoring of hydraulic decoking. What the research have done can make a contribution to the improvement of productivity as well as safety in current delayed coking, which has great theoretical value and application prospect. This paper has done some work as follows:1. Summarized the condition of the research on the monitoring of hydraulic decoking at home and abroad, and gave a introduction of the application of the optical fiber acoustic sensor. Then, made a decision that applying the fiber-optic F-P acoustic sensor to the monitoring of hydraulic decoking system and analyzed the basic principle of F-P optical fiber acoustic emission sensor.2. Designed the general structure of heat dissipation component of the sensor used to required temperature according to the theory of heat conduction as well as the principle of F-P fiber sensing theory and the actual processing situation. On the basis of the principle of F-P optical fiber sensing and theory of the mechanics of elasticity calculated and simulated the relationship between the sensor frequency response and the effective radius as well as the thickness of the elastic diaphragm, so did the relationship between the sensitivity of sensor and the effective radius as well as the thickness of the elastic diaphragm. Additionally, made a simulation of the relationship between cavity length and the output light intensity contrast for the optical fiber F-P cavity. Finally, obtained the optimal size of optical fiber F-P cavity.3. Developed the process of the sensor fabrication and aging of the optical fiber F-P cavity with self temperature compensation structure and finished the fabrication, aging and package of the F-P cavity based on the known size.4. Conducted a temperature stability test of F-P sensing probe to make sure that the sensing probe has a good temperature stability by the analysis of result, so that the F-P sensing probe can be used under the expected temperature. Besides, carried out experiments to test the performance of the F-P sensing probe for acoustic signal detection. Finally, got a conclusion that our F-P sensing probe can be used to detect the acoustic signal from 1000 Hz to 5000 Hz with high performance, which presented a larger range of acoustic signal detection than the actual signal in hydraulic decoking process.5. Installed the F-P sensor acoustic we have made on the delayed coking unit for detecting the acoustic signal in hydraulic decoking process. The preliminary results shown that the cleanliness and the thickness changes of the coke in the hydraulic decoking process can be detected by the sensor, verifying the possibility of the optical fiber F-P acoustic sensor’s application to the hydraulic decoking online monitoring system.