Discussion on using vortex flowmeter to replace orifice flowmeter

1. Current technical level of vortex flowmeter and orifice flowmeter

The basic structure of vortex flowmeter consists of vortex generator, detection element, and signal processing amplifier circuit. At present, the research on vortex generator has reached a fairly complete level, with triangular generator as the best type. The detection elements include thermistor, strain gauge, piezoelectric crystal, differential capacitor, ultrasonic wave, etc. Many signal processing parts have been microcomputerized. Vortex flowmeter is easy to install (can be installed directly on the pipeline), small in size, strong in interchangeability, and high in long-term operation accuracy. It can be applied to most liquid, gas and steam measurements. At present, the sales volume of vortex flowmeter in the world market increases by about 30% every year.

At present, the technical development level of orifice flowmeter is still based on the determined empirical formula. In 1980, the International Organization for Standardization merged the two standards R541 and R781 into the standard ISO5167 (1980).

The orifice throttling device is suitable for almost all medium measurements due to its simple structure, low cost, and reliability. The differential pressure transmitter matched with it has developed rapidly, making up for its own shortcomings.

2. Comprehensive performance evaluation of vortex flowmeter and orifice flowmeter

The orifice flowmeter (orifice for short) consists of a throttling device, a pressure taking device and a differential pressure transmitter. The pressure pipe needs to have heating measures for places prone to freezing. There are about 20 static sealing points in a flow measurement loop. The following problems exist in use:

easy to freeze, easy to block, easy to leak, heating easily causes aging of differential pressure transmitter components, and in some occasions, the pressure pipe needs to be added with isolation liquid. Due to heating or unstable process operation, the positive and negative pressure pipe isolation liquid lines are often not equal, resulting in liquid column difference, making the flow indication inaccurate.

All of the above will cause the flow coefficient to change, the measurement accuracy to decrease, and the differential pressure transmitter is directly installed on the pipeline by shortening the pressure pipe, but there is still a dead zone for flow.

The vortex flowmeter (vortex for short) has only 3 static sealing points, is not easy to leak, has no dead zone for flow, does not require heating and insulation, is not affected by fluid weight, temperature, pressure, and viscosity, and the flow coefficient remains unchanged for a long time.

However, when the vortex is used in a vibrating environment, the flow measurement will be inaccurate. At present, vibration-resistant vortex flowmeters have been launched on the market to overcome the impact of vibration on inaccurate flow measurement. (end)