Application of Vortex Flow Meter in Steam Measurement

Steam is the most widely used heat transfer medium and an important secondary energy source. It is widely used in fields such as electricity, smelting, steel, automobiles, textile printing and dyeing, chemical fibers, food, and medicine. As an important energy source in various industries, accurate measurement of steam flow is of great significance in saving energy and improving the economic efficiency of enterprises.
Steam is divided into saturated steam and superheated steam, which are affected by temperature and pressure changes. The measurement of its flow rate is greatly affected by steam density, so temperature and pressure compensation is required when measuring steam flow rate (saturated steam can provide single compensation for temperature or pressure).
At present, the flow instruments used for steam flow measurement mainly include vortex flowmeters and differential pressure flowmeters. Due to the high pressure loss, large maintenance requirements, and low accuracy level of differential pressure flow meters, they are gradually being phased out by users. Compared to other methods, using vortex flow meters to measure steam flow has obvious advantages.

Saturated steam metering system

Untreated steam is called saturated steam. It is a colorless, odorless, non combustible, and non corrosive gas. The content of droplets or mist in saturated steam reflects the quality of the steam, which is generally represented by the parameter of dryness. The dryness of steam refers to the percentage of dry steam in a unit volume of saturated steam.
The saturated steam metering system has the following characteristics ：

① The temperature and pressure of saturated steam correspond one-to-one, with only one independent variable between the two.
② Saturated steam is prone to condensation, and if there is heat loss during transmission, it can lead to a decrease in temperature and pressure. Strictly speaking, saturated vapor is a two-phase fluid that contains droplets or mist to varying degrees, so the same gas state equation cannot be used to describe different states.
③ Accurately measuring the flow rate of saturated steam is difficult because the dryness of saturated steam is difficult to guarantee. Generally, flow meters cannot accurately detect the flow rate of two-phase fluids, and fluctuations in steam pressure will cause changes in steam density, resulting in additional errors in flow meter readings. Therefore, in steam measurement, it is necessary to maintain the dryness of the steam at the measurement point to meet the requirements, and if necessary, compensation measures should be taken to achieve accurate measurement.

Overheated steam metering system

Superheated steam is a relatively special medium, and generally refers to superheated steam. Overheated steam is a common source of power, often used to drive the rotation of a steam turbine, which in turn drives the operation of a generator or centrifugal compressor. Superheated steam is obtained by heating saturated steam, which contains no liquid droplets or mist and is a real gas. The temperature and pressure parameters of superheated steam are two independent parameters, and their density should be determined by these two parameters. It can be checked from the superheated steam density table. Overheated steam, after long-distance transportation, varies with the working conditions(Such as temperature, pressure, etc)The change, especially in the case of low superheat, will cause the temperature to decrease due to heat loss, leading it from a superheated state to a saturated or supersaturated state, transforming into saturated steam or supersaturated steam with water droplets. When saturated steam suddenly experiences significant pressure reduction and the liquid undergoes adiabatic expansion, it will also transform into superheated steam, thus forming a gas-liquid two-phase flow medium.