Low-pressure gap discharge ultrasonic gas flowmeter

摘要

Low-pressure gas measurements are of increasing interest in the process industry for both control purposes and emission measurements. Industrial measurement environments include some very challenging components, such as: 1. Dust, particles, vapor, water droplets, etc.; 2. Temperatures up to 1200 deg C; 3. Pipe diameters of 1 to 10 m. Ultrasound flow measurement techniques have many advantages for such industrial measurement problems. Currently, a major problem is the lack of transducer technology that is sufficiently robust to operate in the presence of the above given industrial components. For the purpose of producing more robust technology, a gap discharge sound transmitter has been developed [1, 2]. Theoretical and experimental studies of the gap discharge transmitter indicate that flow measurement performances in the range of 1-2percent of the actual flow is achievable [3]. Based on this gap discharge transmitter, an experimental ultrasound gas flowmeter was designed. The design features a gap discharge transmitter and piezo-based receivers. The design was tested in a real industrial environment. The test environment included heavy dust and water vapor in an exhaust pipe at a pelletization plant at LKAB, Kiruna, Sweden. The pipe diameter is 3 m, the pressure is ambient, and the gas flow speed is in the range of 5-20 m/s. The flow conditions were highly turbulent, using a straight pipe length ten times the pipe diameter in front of the experimental flowmeter. This paper presents the experimental gap discharge ultrasonic flowmeter design, the experimental setup and some measurement data. These data indicate that the gap discharge transmitter is feasible for operation in an industrial environment. Further preliminary flow measurement data demonstrate the feasibility of using a gap discharge transmitter as the sound-emitting source in an ultrasonic gas flowmeter.