(237g) Gas Phase Composition Measurements Using Ultrasonics

Currently commonly used techniques for gas (vapour) composition measurement are unable to satisfy all the requirements of industrial and laboratorial applications. These techniques include IR, NIR and GC can be both expensive to implement, require calibration and in some cases are not suitable for rapid on-line measurements. Speed of sound (SoS) is a fundamental property of a gas (vapour) system and has been demonstrated to be functionally dependent on gas phase composition. This project has deployed a novel speed of sound sensor which can be directly applied in real industrial problems for online composition measurement of binary gas mixtures (e.g. CO₂-N₂) and quasi-binary gas (vapour) mixtures (e.g. dry air-octane). Argon is used to calibrate the cellâ??s pathlength as its SOS data are well published and not frequency dependent. This presentation will discuss the fundamentals of the instrumentation design, data analysis and the performance of the sensor systems using a series of model gas mixtures.

Considering all of the factors which could cause inaccuracy, the standard uncertainty of this SOS measurement is estimated in this instrument to be < ±0.01 m/s. A temperature-speed of sound-composition database has been constructed for 20 industrially important air-vapour and several binary gas systems over a temperature range from 5 to 55 °C. The SOS across the temperature range of 5 to 55 °C and the gas composition has also been independently determined using a highly accurate gas buoyancy method. The average deviation in accuracy between the predicted and the measured composition for 15-55 °C is typically < 0.5%, and for specific test temperatures can be <0.1%. Typical precision is 1: 300000. In comparison with traditional measurement techniques, this technique is not only robust but also has the potential to be faster, simpler, more cost-effective, more precise and more accurate.