Vortex flowmeter for steam metering precautions
PTFE Coated Fiberglass Fabrics Black Teflon Coated Fiberglass Fabric,Teflon Coated Fiberglass Fabric,Ptfe Glass Coated Fabric Dongjian Hi-Tech Materials Co., Ltd. , http://www.js-ptfefabric.com
1. Superheated steam can calculate the mass flow according to the temperature and pressure of the superheated steam in the flow rate calculator. However, when the superheated steam is transported over a long distance, or because the pipeline insulation measures are improper, the heat loss temperature often occurs. Reducing it from the superheated state to the critical saturation state, even part of the steam condensation changes into a water droplet, which becomes wet saturated steam (saturated steam).
The output of the vortex flowmeter is only proportional to the flow velocity of the fluid flowing through the measuring tube. When the saturated steam is measured, the influence of the water drop on the output of the vortex flowmeter is negligible. Therefore, it can be considered that the output of the vortex flowmeter is completely controlled by the It is caused by the saturation of the dry (saturated) portion of the steam, and the density of the dry portion can be accurately detected based on pressure compensation or temperature compensation. If the two parties agreed to settle the cost of the dry part of the steam and the condensate does not charge for steam metering, the effect of the phase change on the measurement is negligible and can be ignored. If the condensate is also charged in the same way as steam, the vortex flowmeter has a low measurement result.
2. Wet saturated steam When the vortex flowmeter is installed in the pressure reducing valve, the wet saturated steam suddenly decompresses, the fluid undergoes adiabatic expansion, the water droplets partially evaporate, and the vaporization heat is absorbed from the liquid phase and the vapor phase. The temperature of the liquid phase decreases. If the temperature is reduced a little or the humidity before the evaporation is high, the temperature will rapidly decrease to the saturation temperature corresponding to the new pressure and a new equilibrium will be established. At this time, the steam will still be saturated steam if the pressure is reduced. If there is a lot or the humidity is low before evaporation, the steam will turn into superheated steam because the water droplets evaporate and the temperature is still lower than the saturation temperature corresponding to the new pressure.
After the above evaporation occurs, the former has no effect on the compensation. Only the dry part in the steam increases, and the dryness increases accordingly. The latter case is when the wet saturated steam becomes superheated steam. The effect on the flowmeter is as follows: three conditions:
(1) The steam has been considered to be in an overheated state during design, or it is difficult to determine in which state, or sometimes it is in an overheated state or sometimes in a saturated state. Therefore, if the temperature and pressure compensation is adopted, the above phase change has no effect on the measurement result.
(2) Considering saturated steam design and using pressure compensation, the phase change mentioned above will bring about a small error, namely the compensation error due to the density difference corresponding to the difference between the superheated steam temperature and the saturated steam temperature.
(3) Saturated steam is considered in design, but using temperature compensation, that is, using superheated steam temperature as the saturation temperature to check the density meter will generally cause relatively large errors.
There are three ways to solve the above problems:
(1) Before installing the total steam flow meter in the pressure reducing valve, since the above steam is not decompressed, there is no phase change problem. Therefore, before installing the flow meter in the pressure reducing valve, it is processed by the saturated steam compensation method to ensure the measurement. Accuracy.
(2) If the flow meter can only be installed behind the pressure reducing valve, an additional pressure transmitter can be added for temperature and pressure compensation.
(3) If the stability of the pressure reducing valve is better, the upstream pressure value of the flow meter can be set as a constant value in the display instrument to perform temperature and pressure compensation.